Thesis for the degree Doctor of Philosophy Submitted to the Scientific Council of the Weizmann Institute of Science Rehovot, Israel עבודת גמר )תזה( לת

תמליל

1 Thesis for the degree Doctor of ilosophy Submitted to the Scientific Council of the Weizmann Institute of Science Rehovot, Israel עבודת גמר )תזה( לתואר דוקטור לפילוסופיה מוגשת למועצה המדעית של מכון ויצמן למדע רחובות, ישראל By oam Levi מאת נעם לוי אנאלוגים של פוליאתילן-אימינים לקטליזה סטראוסלקטיבית בתמיסות מימיות ובי- פאזיות ודפולימריזציה של צלולוז במים Polyethyleneimine Analogs for Stereoselective Aqueous Biphasic Catalysis and Depolymerization of Cellulose in Water Advisor: Prof. Ronny eumann מנחה: פרופ' רוני נוימן February 2012 שבט-אדר התשע"ב 1

2 This work was carried under the supervision of Professor Ronny eumann Department of rganic Chemistry Weizmann Institute of Science 2

3 Acknowledgments I wish to express my deep gratitude to my.d supervisor Prof. Ronny eumann for his guidance, support, engorgement and understanding through the curse of the thesis. I'm grateful for the opportunity he gave me and his comforting patience through it all. I would like to express my gratitude to Dr. Alex Khenkin for his help and advice when ever needed during the work in the lab. I would like to extend my gratitude to Prof. Mordechai Sheves and Prof. Michael Bendikov, who served in my.d advisory committee, for their challenging questions and suggestions. I would like to thank my colleagues in Prof. eumann research group, for their friendship, deep support and encouragement. Thanks to Dr. Jessica Ettedgui, Dr. ila Goldberg, Dr. Anat Milo, Delina Damatov, Sasha Laskovy, aviv Ben-David, Amir Rubinstein and Eynat aviv. To the former group members which whom I had the privilege to work with and get to know, I wish to thank, Dr. Itzik Bar-ahum and Dr. Adina aimov. Special thanks to my dear friend Dr. Mirit Cohen-hana for her friendship, encouragement and good words when needed throughout the course of the.d. Last, but surely not least, I would like to thank my dear family, my mother Tsippora Levi and my sister Michal Shapiro for their unconditional love, and their close and warm support however far away. To the memory of my beloved father the Late aim Levi (Sevi). 3

4 תקציר המחקר המוצג עוסק בכימיה של פוליאתילן-אימינים )PEIs( והיכולת לעשות מודיפיקציות כימיות עליהם לצורך השראת סלקטיביות, ולשמש כמערכות להעברת מסה במערכות מימיות ובי-פאזיות. הפרוייקט מתחלק לשני חלקים, כאשר המרכזי שבהם )I( עוסק בסינתזה של אנאלוגיים כיראליים לפוליאתילן- אימינים ובניית מערכות כיראליות לצורך השראה כיראלית על קטליזטוריים א-כיראליים סטריאוסלקטיביות שונות בסביבה מימית ובי-פאזית. והחלק )II( השני.I פוליאתילן-אימינים עם חומצה פניל-בורונית לצורך פירוק צלולוז במים בסביבה נטרלית. הוכנו מגוון פוליאתילן-אימינים כיראליים אשר עברו הצלבה )crosslinked( לתגובות עוסק במודיפיקציות על בתוכם מגוון ומכילים קטליזרטורים, כגון פוליאוקסומתכות, קומפלקסים של מתכות-מעבר וננו-חלקיקים בעלי יכולות קטליטיות. כמו כן, פותחה שיטה קשרים אימינים. מגוון השיטות אימיניות, מאפשר סינתטית חדשה להכנת מערכות פוליאתילן-אמיניות מפולמרים ע"י העומדות לרשותינו עתה לתכנון וסינתזה של מערכות פוליאתילן- לנו את הגמישות לעבוד ולשנות מערכות אלו בדרכים שונות, מערכות קטליטיות שונות בסביבות מימיות ביפאזיות, ואורגניות. לכמ יס ה ולאפשר בחינה של המערכות הפוליאתילן-אימיניות המוצלבות על בסיס אפיכלורוהידרין )epichlorohydrin( נבדקו )encapsulation( של קומפלקים אורגאנו-מתכתיים א-כיראליים לשתי תגובות עיקריות: )1( אפוקסידציה של אולפינים על ידי שימוש בקומפלקסים מנגן-סיילנים,)Mn(III)Salen( ו )2( הידרוגניציה של קטונים על ידי קומפלקסיים מבוססי רותניום.)Ru(II)( בשני המקרים המערכות השרו כיראליות על הקטליזטורים, בצורה לא קוולנטית, לתת עודף אננטיומרי נמוך ee( - 17% 3%(. לפיכך, הראנו שמערכות פוליאתילן-אמיניות כיראליות מוצלבות הן כלליות די לביצוע שתי ראקציות שונות לגמרי מבחינה קטליטית, הן במחינת סוג התגובה עצמה והן בסוג הקטליזטורים, ולהשרות סטריאוסלקטיביות. המערכות האימיניות המוצלבות )מוארכות( ע"י קשרים אימינים )שחוזרו לאמינים( הראו הצלחה רבה בייצוב ננו-חלקיים של מתכות אצילות:,Pd, Pt, Ru ו-.Rh כאן מוצגת בעיקר מערכת ננו-חלקיקים של פלאדיום )Pd(0)( להידרוגנציה של אסימטריה בהידרוגנציה של ו- אל קנים אלק נים לאלקאנים ואימינים לאמינים. המערכת הראתה לא משופעלים בעלי שתים ושלוש התמרות. במערכות אלו נשאר עדיין קביעת האננטיטסלקטיביות. שיטות הפרדה כיראליות המבוססות על האתגר העיקרי PLC GC לא הניבו הצלחה, אך מדידות פולרימטיות היו אפשריות, והראו סיבוב אופטי עבור תוצרי ההידרוגנציה האלקאנים. כמו כן, המערכת הראתה סטראוסלקטיביות עבור הידרוגנציה של אימין כיראלי לתת את התוצר האמיני בדיאסטריוסלקטיביות טובה. במקרה זה האתגר והקושי התבטאו בעיקר בסינתזה של סובסטרטים אימינים לא יציבים, והאנליזה של אותם אמינים כיראליות פאזה-נורמלית ב - PLC ו.GC על ידי שימוש בשיטות.II סונתזו מספר תרכובות המכילות חומצה פניל-בורונית, על בסיס פוליאתילן-אימין מסועף מסחרי )06,666 - w M(, הנבדלות על ידי דרגת התמרה שונה של חומצה פניל-בורונית. פוליאתילן-אמין עם התמרה של 06% חומצה פניל-בורונית על האמינים הראשונים,,PEI-50%B() 2 נבחר לפירוק של צלולוז במים בסביבה נטרלית ב C החלק האמיני של הפוליאתילן-אימין מאפשר את שבירת מארג קשרי 4

5 המימן שבין שרשראות הפוליגלוקוז בצלולוז, בעוד שהחומצה הפניל-בורונית אחראית להידרוליזה של שיחרור אותם מקטעים נותר העיקרי האתגר הקשרים הבטא-גליקוזידים בשרשראות הפוליגלוקוז. אוליגוסכרידים שנוצרו. 5

6 Abstract This research dealt with the chemistry of polyethylenimine and the ability to chemically modify them to yield derivatives that would lead to induction of stereoselectivity, and allow improved mass transfer in water-based reactions. The project was divided into two parts, where the main part (I) was the synthesis of chiral catalytic assemblies based on polyethyleneimine derivatives in order to provide a chiral environment to achiral catalysts towards stereoselective transformations in aqueous and biphasic media; and (II) the modification of polyethylenimine with phenylboronic acid in order to depolymerize cellulose in water towards high yield glucose formation at neutral p. I. We prepared chiral polyethylenimine derivatives that were crosslinked and intercalated catalysts such as polyoxometalates, transition metal complexes, and catalytically active nanoparticles. We also developed a new synthetic method for the preparation of imine crosslinked polyethylenimine assemblies. The variety of methods available to us now for the design and synthesis of chiral polyethylenimine derivatives gave us the flexibility to alter the polyethylenimine-based assemblies in various ways and allowed the examination of several catalytic systems in aqueous biphasic and organic reaction media. Chiral crosslinked polyethylenimine derivatives using epichlorohydrin-based crosslinkers were examined for the encapsulation of achiral organometallic complexes for two main transformations: (1) the epoxidation of olefins using Mn(III)Salen complexes, and (2) ketone hydrogenation using Ru(II)complexes. In both cases the catalytic assemblies imparted chirality to yield reaction products with low enantiomeric excesses by non-covalent stereoselective induction. Thus, we were able to show that a chiral crosslinked polyethylenimine-based scaffold was general enough to be used on two completely different catalytic systems for two different transformations to lead to asymmetric transformations. The imine crosslinked chiral polyethylenimine derivatives were used to stabilize Pd, Pt, Ru and Rh noble metal nanoparticles. ere, we mainly focused on Pd nanoparticles stabilized by a crosslinked chiral polyethylenimine for the hydrogenation of prochiral alkenes to alkanes and prochiral and chiral imines to amines. The assemblies catalyzed the asymmetric hydrogenation of unfunctionalized disubstituted and trisubstituted alkenes. A main uncompleted challenge remains to determine the enantioselectivity of the reactions since the use of known chiral PLC or GC methods were unsuccessful and polarimetery showed optical rotation in a non-quantitative manner. Such a crosslinked chiral Pd/polyethyleniminebased assembly was used for the hydrogenation of chiral imine to afford an amine with high 6

7 diastereomeric excess. ere, a remaining challenge is the difficult synthesis of unstable imine substrates and the analysis of the corresponding amine products by normal phase chiral PLC methods. II. We synthesized several phenylboronic acid modified derivatives of commercial polyethylenimine (M w - 60,000) that are differentiated by the degree of phenylboronic acid substitution Polyethylenimine modified at 50 % of the primary amine sites, PEI- 50%B() 2, was used for the depolymerization of cellulose in water at 150 C and neutral p in water. The polyamine backbone allowed the breaking of the intermolecular hydrogen bonds between the polyglucose chains and the phenylboronic acid moieties led to the hydrolysis of the -glycoside bonds within the polyglucose chains. The remaining challenge remains the liberation of the short chain oligosaccharides formed 7

8 Abbreviations A aq. Aqueous amu atomic mass unit (in MS) atm atmosphere (pressure) Ar aryl group B BIAP 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl Bu butyl Bu; n-bu normal butanol C calc. calculated conc. concentrated CD circular dichroism CLS crosslinked system/s Cryo-TEM cryogenic transmission electron microscopy D D, d dexter (Latin: on the right) - enantiomer configuration DCM dichloromethane DDW double distilled water DW distilled water de diastereomeric excess DMF,-dimethylformamide DMS dimethylsulfoxide DS 3,5-dinitrosalicylic acid DRA direct reductive amination E eq equivalent ES(+/-) electron spray (MS) Et ethyl Et 2 diethyl ether; ether EtAC ethyl acetate ee enantiomeric excess G g gram Gx glucose oxidase enzyme h hour ep normal heptane z hertz 8

9 I ICP-MS Inductively coupled plasma mass spectrometry IPA isopropyl alcohol (2-propanol) L L, l laevus (Latin: on the left) - enantiomer configuration LDA lithium diisopropylamide Leu leucine amino-acid M M molar Me methyl Me methanol mg milligram min minutes ml milliliter L microliter mmol millimoles MS mass spectrometry MALDI Matrix-assisted laser desorption/ionization (MS) normal CA -carboxy anhydride M -methylmorpholine oxide MR nuclear magnetic resonance ESY nuclear over-house effect spectroscopy P phenyl e phenylalanine amino-acid PM polyoxometalate PEI polyethyleneimine R R Rectus (Latin: right) - enantiomer configuration R f RT retention factor room temperature S S Sinister (Latin: left) - enantiomer configuration sat. saturated T tbu, tert-butyl tbu, tert-butyl alcohol TFA trifluoroacetic acid TF tetrahydrofurane 9

10 TLC thin layer chromatography TMS tetramethyl silane TF time of flight (in MS) T turnover number TEM Transmission electron microscopy U UV ultra violet (spectroscopy) V vis visible Vol./v volume W wt weight 10

11 Table of contents 1. Introduction: General background, basic concepts, known literature and research objective General aspects of green chemistry Aqueous biphasic catalysis Basic concepts ydroformylation as practice aqueous biphasic catalytic process Chirality and optical activity Catalysis and asymmetric catalysis: Basic concepts omogeneous and heterogeneous catalysis Mechanistic understanding of catalysis anoparticles: Catalytic activity and enantioselectivity Polyethylenimine Polyethylenimine and Synzyme Properties Polyethylenimines and catalysts Chiral polyethylenimine derivatives Immobilizations of catalysts, encapsulation and enantioselectivity Cellulose and sugars Cellulose as a renewable source of fuel and materials Boronic acid as receptor, sensor and reagent for saccharides Main goals and research objectives Materials and methods DS test Glucose oxidase assay (Gx) Cellulases: Endo, exo and -glucosidase Results Synthesis of chiral polyethylenimine derivatives Crosslinked PEI with MnSalen complexes for asymmetric biphasic epoxidation Crosslinked chiral polyethylenimine derivatives with Ru(II) complexes for asymmetric hydrogenation Asymmetric hydrogenation of prochiral olefins and imines using Pd(0) nanoparticles stabilized with chiral polyethylenimine derivatives Synthesis Alkene ydrogenation: Reactivity and selectivity ydrogenation of prochiral imines with Pd nanoparticles stabilized by chiral polyethylenimine derivatives: Reactivity and selectivity

12 3.5. Modified polyethylenimine for the solubilization and depolymerization of Cellulose Synthesis of PEI-phenylboronic acid polymers Cellulose Solubilization and Degradation with PEI-B() 2 Systems Discussion and summary Leu/e-Crosslinked systems: MnSalen and Ru(II) catalysts Pd(0) nanoparticle stabilized by chiral crosslinked polyethylenimine derivatives for asymmetric hydrogenations Alkene hydrogenation catalyzed by Pd(0) nanoparticles stabilized by chiral crosslinked polyethylenimine derivatives Imine hydrogenation with chiral Pd(0) nanoparticles system PEI-boronic acid polymers for the solubilization and degradation of cellulose Summary of goals Experimental References

13 1. Introduction: General background, basic concepts, known literature and research objective 1.1. General aspects of green chemistry Environmentally benign and sustainable transformations in organic chemistry are now considered to be a basic goals and requirements in the development of modern organic synthesis. There are twelve basic tenants of green chemistry" 1 relating to various topics such as biodegradable products and energy economy. owever, the two important topics that are at the focus of this.d. thesis are (1) reaction efficiency and (2) use of benign and environmentally favored solvents. In the first case the objective is that reactions should have a high atom economy and/or be free of the formation of dangerous waste. In this context, the use of catalytic transformations can obviate stoichiometric reactions thereby increasing atom efficiency and reducing waste formation. For example, in oxidation chemistry, benign oxidants such as molecular oxygen or hydrogen peroxide can be used instead of toxic reagents such as chromium oxide. In reduction reactions catalytic hydrogenation is to be preferred over stoichiometric use of reagents such as those based on boron hydrides. Towards the reduction of the use of problematic organic solvents, new reaction media, such as ionic liquids 2-4, fluorous solvents 5-7, supercritical liquids (especially C 2 ) 4, 8, 9 and, of course, water as a cheap, nontoxic, safe and highly abundant solvent are being proposed as alternative reaction media. These use of catalysis for the preparation of organic compounds has led to the introduction of mainly homogeneous liquid phase catalysis to the field of organic chemistry. A combination of catalysis and the use of water have led to the introduction of aqueous biphasic catalysis Aqueous biphasic catalysis Basic concepts Aqueous biphasic catalysis can be defined as a system wherein an aqueous phase containing a catalyst leads to reaction with an immiscible organic substrate. This method uses a homogeneous catalyst, dissolved in water (mobile phase/support), and by simple separation methods the catalyst and the reactants/reaction products are separated. In relation to the reaction products the catalyst is "immobilized" and "heterogenized", but not anchored, on "liquid support". In this way the advantages of homogenous catalysis are supplemented by the argument that the catalyst and the reaction products can be separated immediately after 13

14 the reaction without any chemical stress (distillation, decomposition, transformation, rectification). Furthermore, thermal separation processes seldom ensure quantitative recovery of the catalyst, which consequently causes loss of productivity. The most basic and strict definitions of biphasic systems are systems which: (1) use no additional measures, except moderate temperature gradients, to ensure phase separation, and (2) make it possible to immediately start a new catalytic cycle in the same phase and without any additional steps. Two factors have considerably limited the application of aqueous biphasic catalysis. The first factor has been the availability of suitable water-soluble catalysts. The second factor, and the one principally addressed in this research program, is the slow mass transfer of the substrate to the catalytic site. The aqueous biphasic processes require a minimum solubility of the reactants in the catalyst phase. This can be improved by (1) addition of solvents and/or cosolvents 15, 16, and (2) variation of the water-soluble ligands by means of surfactant or solubilizing properties. In the past, mass transfer limitations have been tempered by use of surfactants in emulsion, microemulsion and micellular systems, Figure owever, these methods suffer severely from difficult separation of the products, very significant difficulty in recovering and recycling the catalytic aqueous phase, and low volume yields of products. Figure 1.1. Cartoon representation of a micelle Aqueous homogenous catalysts depend on the developments of polar (water soluble) ligands and their incorporation into organometallic complexes. The solubility of the ligands usually achieved by introduction of highly water-soluble substituents such as S 3, -C, - or 2, and their salts into phosphine ligands, Figure By variation of the nature and number of substituents coupled by the choice of the aqueous phase conditions, almost any desired ratio of hydrophilic and hydrophobic properties may be obtained. For example, sulfophenylphosphines dissolve in aqueous media at any p, but carboxy or amino substituted phosphines dissolve in basic or acidic solutions, respectively. The water solubility of the ligands may be imparted to the metal complex catalysts via incorporation in complexes. The thermodynamics or complex formation and the different ability of the 14

15 transition metal ions to bind different ligands forming "in-situ catalysts" have been investigated carefully 28-31, and the synthesis of the water-soluble ligands have been reviewed by errmann and Kohlpainther. 24 Such ligands and complexes may catalyzed reactions under aqueous mild conditions for bioorganic substrates, such as the hydrogenation of a wide range 24, 25, 32, 33 of lipids. C S 3 a P P TPPMS C 2 CC 3 P C 2 CC 3 S 3 a S 3 a P (C 2 ) n C P P TPPDS S 3 a amphos a 3 S S 3 a C 2 P 2 C P C 2 TPPTS Figure 1.2. Water-soluble ligands for oxo homogeneous catalysis Product separation is easier in biphasic systems, especially with aqueous biphasic and watersoluble catalysts. The basic concept of aqueous biphasic catalysis is represented in Figure 1.3, where the hydrophilic organometallic coordination complex catalyst (and as such, is well defined like conventional homogenous catalyst), is insoluble in the organic product phase. The reaction occurs in the aqueous phase or at the phase boundary, and the desired product separated at the end from the reaction by simple separation. Because of the high polarity of the water-soluble catalyst, and its insolubility in the organic phase, the loss rate is often below detection limits. In this respect, the biphasic "heterogenized" catalyst show no leaching, which is a typical problem in other heterogenized and anchored catalysts systems (see also section 1.7). Characteristic data for metal removal from biphasic hydroformylations have been given for Ruhrchemie-Rhône-Poulenc's oxo process

16 A-B Catalyst A-B Catalyst A B A B Catalyst Catalyst Figure 1.3. General principle of biphasic catalysis in water. Reaction example of propene and syngas (A-B) to product, which can be separated from the catalyst by phase separation. Reaction rates achievable with biphasic systems are strongly dependent on the polarity of the reacting substrates. In the Rh catalyzed hydroformylation of propene, for example, using water-soluble catalyst Rh(C)(TTPTS) 3 (TTPTS = triphenylphosphine trisulfonate, Figure 1.2), the reaction take place with the apparent activation energy as in homogenous reaction, whereas with 1-hexene the rate determining step appears to be the mass transfer ydroformylation as practice aqueous biphasic catalytic process The most important industrial homogeneous catalyzed biphasic C-C coupling reaction is hydroformylation. 36 following the recommendation of Manassen 37 the history of hydroformylation began with various water-soluble ligands, Figure 1.2. Kuntz expressed the basic idea of a new generation of water-soluble oxo catalysts with tri-phenylphosphine trisulfonate (the a salt of TPPTS) as ligands for Rh-based oxo process, 38 mainly for the hydroformylation of lower olefins such as propene, Scheme C + 2 Rh TPPTS C + C propene syngas n- isobutyraldehyde Scheme 1.1. ydroformylation of propene More ligands for oxo processes have been developed improving the activity and selectivity. 24, 35, 39, 40 A novel group of ligands for biphasic reactions, especially hydroformylations, was discovered by errmann using carbene complexes, Figure In this case, the bond between the carbon and the Rh is extremely stable allowing mono- or biphasic 16

17 hydroformylations without any excess of ligands, and may be anchored to a polymer support without leaching. R' C R'' Figure 1.4. An example of Rh-carbene complex for C-C coupling Rh C C 1.3. Chirality and optical activity ne of the major topics in this research dealt with chirality and asymmetry. A basic definition of chirality is: an object and its mirror image that cannot be made to coincide in space. In other words, the objects are not superimposable even though they are identical in almost all other aspects in an achiral environment. The most used and popular example to emphasize this point are the left and right hands, which are identical mirror images of one another (for our purpose at least), but cannot be superimposed, Figure 1.5. This handedness is chirality, as it originated form the Greek word "chiral" which means "hand", and two compounds that differ in handedness in this aspect are called "enantiomers". Figure 1.5. Part of Michelangelo's fresco "Creation of Adam", with a nice touch to the importance of chirality in life (which was yet to be discovered in the time of Michelangelo). It was Louis Pasteur, in 1848 that noticed that crystals of sodium ammonium tartrate are enantiomorphous, and that all of the crystals show chirality in the same sense, Figure 1.6. From additional 19 observations of different tartrate salts he postulated that there is a relationship between the chirality of the each crystal and the fact that its salt rotate polarized light in solutions. 42 It was Mitscherlich who reported previously that isolate crystals of the sodium ammonium tartrate and those of the racemic form are identical in all respects, but he did not realized that only the racemic form was optically inactive in solution. 43, 44 Pasteur 17

18 concluded that the racemic crystals formed are not all chiral in the same sense. As he put it: "the hemihedral faces which in the tartrate are all turned one way are in the racemate inclined sometimes to the right and sometimes to the left". 42 Since he found that racemate salts afforded a mixture of non-superimposable crystals of right and left, which he separated simply by using a pair of tweezers, he performed the first chiral resolution and found, in his great excitement that one solution rotated the light dextrorotatory (to the right) and the other levorotatory (to the left). This excitement, I believe, is now shared by all chemists who strive to achieve enantiomeric excesses in their asymmetric catalytic or synthetic research. Pasteur's research paved the way for an understanding of stereoisomerism. C C C C C C C C (+)-(R,R)-tartaric acid C Figure 1.6. Tartaric acid isomers C (-)-(S,S)-tartaric acid C C meso-tartaric acid Enantiomers have identical physical and chemical properties except in two important aspects: 1. As we have seen above, they rotate the plan of polarized light in opposite directions and to equal degrees. The enantiomer that rotates the plane to the right (clockwise) is called dextro isomer and is assigned (+). The enantiomer that rotates the plan to the left (counterclockwise) is called levo isomer and is assigned (-). 2. They react at different rates with other chiral compounds. In practice, these rates may be so close together that no distinction is possible, or on the other hand, they can be so far apart that one enantiomer undergoes that reaction at a convenient rate and the other does not react at all. In essence, this is the basic mechanism of asymmetric induction, as we try to obtain the chiral environment that will afford the highest discrimination of one enantiomer from the other, to afford the highest enantioselectivity (see section 1.4). Furthermore, enantiomers may react with different rates with achiral molecules if an optically active catalyst is present; they may give different solubilities in chiral solvent, and different indexes of refraction or absorption spectra when examined with circularly polarized light. In most cases these differences are often too small to be measured. As was presented above in the case of tartaric acid, the properties of racemic mixtures of enantiomers are not always the same as of the individual enantiomer. In the gaseous or liquid state, or in solution they are usually the same, since the mixture is nearly ideal, but properties 18

19 involving the solid state, such as melting point, solubility and heats of fusion are often different. Thus, a racemic mixture of tartaric acid has melting point of ~205 C, and solubility in water at 20 C of 206 g/l, while the enantiomer (either (+) or (-)) has the corresponding melting point of 170 C, and solubility of 1390 g/l. ne more important remark regarding optical activity and racemates is the fact that the presence of optical activity always proves that a given compound is chiral, but the absence of optical activity does not, since a compound that is optically inactive may be either achiral or a racemic mixture Catalysis and asymmetric catalysis: Basic concepts Much information about mechanism of a reaction can be obtained from a knowledge of which substances catalyze the reaction, which inhibit the reaction, and which do neither. The study of reaction mechanism was beyond the scope of this thesis, but in general terms catalysts preform their action by providing an alternate pathways for the reaction in which the free energy of the transition state, G, is less of what it would be without the catalyst. This also means that catalysts do not change the free energy, G r, of the reaction itself. The changes or alternative pathways of a reaction can lead to selectivity as is presented in Figure 1.7 left, where one catalyst will lower the activation energy of a pathway to afford P 1 rather than P 2. As related to enantioselectivity, the objective is to find the pathway that will afford enantiomeric excess, the formation of one enantiomer in preference for the other. By using a chiral catalyst, enantiomeric transition states will be diastereomeric to one another, and will have different free energies of activation that if are large enough, will discriminate one pathway from the other and afford a product with enantiomeric excess, Figure 1.7 right. G Selectivity Enantioselectivity R Cat. 2 Cat.1 R-Cat.- S* = RS R-Cat.- R* = RR G1 G2 R GRR GRS P 2 P* Figure 1.7. Schematic representations of selective and enantioselective catalytic pathways; for a chiral R catalyst the transition states will be the diastereomers RR or RS. reaction coordinate The difference in the free energy of the transition states (G ) for each of the enantiomeric pathways, can be calculated by the Arrhenius or Eyring equations and its proportionality to 19

20 the enantiomeric excess is schematically presented in Figure 1.8. A difference of 3 kcal/mol will afford 98% ee, while 100% ee is asymptotically infinite in free energy by definition. G 3 Kcal/mol %ee Figure 1.8. ot to scale representation of the G transition states energy difference of the two diastereomeric pathways to a chiral product 1.5. omogeneous and heterogeneous catalysis Practically catalysis can be divided into three main sub-categories: (1) Biocatalysis; (2) omogeneous catalysis and (3) eterogeneous catalysis. This historic distinction results from the different techniques and research methodologies applied in the corresponding disciplines. In the classic sense one could define homogenous catalysis when the catalyst is soluble in the liquid phase where the reaction takes place, whereas in heterogeneous catalysis the catalyst is not soluble and the reaction occurs on the solid. owever the distinction between colloidal and true homogeneous catalysis is often very difficult and these simple definitions are not comprehensive enough when dealing with systems, such as catalytic metal nanoparticles, which forms, what at least appears to be, homogenous solution, but in fact mechanistically falls into the definition of heterogeneous catalysis. 45 omogenous catalysts often have the advantages of better catalyst reproducibility and better selectivity. They are also less susceptible to catalyst poisoning, where heterogeneous catalysts are often poisoned, for example by small amounts of compounds containing sulfur, such as thiols and sulfides that are often found in rubber stoppers and other equipment. n the other hand, heterogeneous catalysts are usually easier to separate from the reaction mixture, and thus are much more appealing for large volume processes Mechanistic understanding of catalysis In contrast to heterogeneous catalysis, homogeneous catalysis is typically based on welldefined organometallic species that can be investigated in detail with the spectroscopic techniques of molecular chemistry. In many cases, we have at least a good working 20

21 hypothesis for the catalytic cycle and catalyst development can be achieved by systematic and, in favorable cases, even rational modification of the molecular structure. This largely true also in understanding the pathways of asymmetric induction of the catalyst on given substrate, as illustrated and elaborated in the next section (1.4.3) for a variety of catalysts related to the reactions addressed in this thesis. n the other hand, owing to the solid nature of the catalyst in heterogeneous catalysis, our understanding of the transformations on a molecular level lags far behind their applications. Therefore, heterogeneous catalyst development is still very much dependent on trial and error with high-throughput techniques that have increased in importance in recent times. 46 ere we will demonstrate the mechanism of heterogeneous catalytic hydrogenation of double bonds that is related to the nanoparticle hydrogenation system, which is a part of this research thesis, and by extension to several aspects connected to the crosslinked encapsulated systems as a biphasic (and tri-phasic) catalytic systems (see also sections 1.6 and 1.7). The mechanism of the heterogeneous catalytic hydrogenation of double bonds is still not thoroughly understood. It is very difficult reaction to study, because of the difficulty in interpreting the kinetic data, and due to hydrogen exchange reactions. The currently accepted mechanism for the common two phase reaction was originally proposed by oriuti and Polanyi in For steric reasons, it is apparent that the adsorption of the alkene takes place on the less hindered side attached to the catalyst surface, most probably as shown as 2 - complex, Figure 1.9a. Furthermore, the fact that the hydrogen addition is generally also from the less hindered side indicates that the hydrogen is probably adsorbed on the catalyst surface prior to its reaction with the alkene. C C C C C C 2 C C (a) (b) Figure 1.9. Schematic representation of heterogeneous hydrogenation of alkene. a. 2 -coplex; b. 1 -coplex. The nature of the adsorption of the substrate on the surface of the catalyst (Figure 1.9a) could basically be one of two types: (1) ysical adsorption, which suggests weak interactions between the catalyst and the substrate, and capable in creating multilayers; (2) chemical adsorption (chemisorbtion), which suggests strong bonding interactions between the catalyst and the substrate (> 3 kcal/mol) and can be regarded as oxidative addition. These kinds of 21

22 interactions will generally form a monolayer. It is likely that as molecular hydrogen is adsorbed on the metal catalyst, it cleaved to afford a 1 coordinated hydrogen atom. In effect, an alkyl radical is formed by reaction of a hydrogen atom and the adsorbed alkene, probably bound to the catalyst through a 1 coordination (Figure 1.9b). The transfer of the hydrogen atom to the carbon atom opens a coordination site on the metal catalyst for additional hydrogen atoms. Finally, another hydrogen atom combines with the bound alkyl radical to give the reaction product, which then desorbs from the catalyst surface and the metal site is then available again for coordination. The described mechanistic pathway is illustrated for a general reaction coordinate as presented in Figure 1.10, including also diffusion of substrates and products to and from the reactive sites of the heterogeneous surface. G R P R Edif E act Eads R* P* Edif Edes reaction coordinate Figure General energy reaction scheme from R (reactant/s) to P (product/s) on a heterogeneous catalytic surface. E = energy; dif = diffusion; ads = adsorption; act = activation (of the reaction) des = desorption; P There are a few drawbacks in this model, as it suggests only a single type of a metal site for coordination of the alkene and the hydrogen atoms, while they could be coordinated to different metal sites as well. Furthermore, this mechanistic suggestion does not address the nature of the bonding on the surface, the differences arising from them, or does it consider the structure of the surface of the metal catalyst itself. The surface of the catalyst in heterogeneous catalysis is not homogeneous and contains different types of metal sites. Maier suggested the presence of terrace-, step- and kink- types atoms, which refers to different atom types characterized by the number of nearest neighbors, and correspond to different transition metal fragments, as well as to different coordination states of the metal, as illustrated in Figure

23 Figure Similar surface atom types on flat surfaces and particles of FCC metals. Atom types are characterized by the numbers of nearest neighbors in parentheses. A = on (111) or (100) terraces; B = on steps or edges; C = on kinks or corners. The terrace-type atom has 8 or 9 neighbors and corresponds to geometry ML 5 (A in Figure 1.11). The step-type atom usually has 7 neighbors and can be correlated with geometry ML 4 (B in Figure 1.11), and the kink-type atom has 6 neighbors and correspond to geometry ML 3 (C in Figure 1.11). In general, as the particle size increase, the relative concentration of terrace-type atoms will increase, whereas small particle sizes, as in nanoparticles, favors the kink-type of surface atoms. This and many more complex parameters relating to the surface of the catalyst may have an impact on the reactivity and the selectivity of the catalyst anoparticles: Catalytic activity and enantioselectivity The use of well-defined metal nanoparticles for catalytic transformations of organic substrates is an exciting and rapidly growing area. The development of uniform nanometer size particles has been intensively pursued because of their technological and fundamental scientific interest. They have a characteristic high surface-to-volume ratio, and consequently a large fraction of the metal atoms are at the surface and hence are available for catalysis. Many colloidal transition metal nanoparticles, especially noble metals, have been applied as efficient and selective catalysts for reactions which are also catalyzed by molecular complexes such as Sonogashira coupling with i nanoparticles, 49 Pauson-Khand reaction with Co nanoparticles, 50, 51 and the reduction of nitroarenes to the corresponding amines with Fe nanoparticles, 52 as well as for reactions which are not or poorly catalyzed by molecular species such as hydrogenation of aromatic hydrocarbons. ne of the early works on heterogeneous asymmetric catalysis was published by S. Akabori in 1956 on PdCl 2 adsorbed on silk, as a chiral platform, for the asymmetric hydrogenations of oximes and oxazolone. 53 Recently, some research has been published with promising approaches for nanoparticle stabilization and asymmetric hydrogenation mostly reporting low enantiomeric excesses (up to 6%), 54 in C-C bond formation, 55 56, 57 hydrogenation of ketones, 23

24 and other transformations owever, only few colloidal catalysts has been shown to yield high enantioselectivity. otable are the use of Pt(Pd)/cinchonidine for the hydrogenation of ethyl pyruvate with reported ee s of 76%, 61, 62 and in 2004, Bruno et al. published the highly enantioselective (97% ee) allylic alkylation catalyzed by palladium nanoparticles stabilized by chiral xylofuranoside diphosphite. 63 Asymmetric hydrogenation of alkenes is one of the most useful reactions for the synthesis of optically active compounds. owever, the application of a wide range of both homogenous and heterogeneous catalysts is usually limited to alkenes with coordinating functional groups and utilization of a template effect. There are only a few literature examples on the hydrogenation of unfunctionalized alkenes (mostly trisubstituted double bonds) Chiral metal organic catalysis and asymmetric induction omogeneous catalysis Asymmetric metal catalysis is a powerful tool for the synthesis of optically active products. 67, 68 With regard to oxidation chemistry, various enantioselective catalysis have been introduced 69 and their applicability in larger scale processes has been demonstrated In this respect, epoxidation reactions are a very important method for the formation of carbonoxygen bonds. ne of the most known examples is the titanium catalyzed Sharpless Asymmetric Epoxidation (SAE) of allylic alcohols 74, 75 and the osmium catalyzed Sharpless Asymmetric Dihydroxylation (AD) The SAE reaction is specific for allylic alcohols and is carried out with titanium tetra-isopropoxide (Ti(iPr) 4 ) and tert-butylhydroperoxide (TBP) which is a mono oxygen donor (D) in the presence of chiral additive diethyl tartarate ((-) or (+)-DET). The product is an epoxy alcohol, where the transition state is presumably bi-titanic complex with a face constricted area by the chiral DET complex directing the double bond approach towards the peroxide species, Scheme 1.2. Since both enantiomers of the tartaric ester are commercially available, SAE can be used to prepare either one of the enantiomers of the desired product. 24

25 t-c 4 9 (i-c 3 7 )Ti (+)-DET 97% ee C25C CC25 (+)-DET t-c 4 9 (i-c 3 7 )Ti (-)-DET 97% ee C25C CC25 (-)-DET putative transition state Scheme 1.2. Sharpless asymmetric epoxidation (SAE). ne of the most known asymmetric epoxidation reactions of nonfunctionalized alkenes and one directly related to this research, is the Jacobsen-Katsuki epoxidation, using manganese(iii)salen (MnSalen) complexes It was found that the use of chiral Salen 85, 86 ligand complexes, in such transformations and others can excesses, Scheme 1.3A. yield high enantiomeric A R 1 R 1 (III) Mn L Mn(III)Salen [] R 1 Mn L Mn(V)Salen oxo R 1 R 3 R 5 R 4 R 6 - Mn(III)Salen R 3 R 4 R5 R 6 B Scheme 1.3. Schematic mechanistic representation of Jacobsen-Katsuki MnSalen reaction. L = counter anion or amine -oxide ligand; A. examples of known chiral MnSalen complexes; B. preferred directions of attack of cis alkenes on chiral MnSalen complex: path a. according to Jacobsen, path b. according to Katsuki. A variety of oxidants (D) can be used, such as iodosobenzene (I), sodium hypochlorite (acl) and m-chloroperbnzoic acid (mcpba), usually with combination of amine -oxide additives such as -methylmorpholine oxide (M) as axial coligands (L in Scheme 1.3), 25

26 which stabilize the manganese(v) oxo complex formed in the transition state, and has an effect on the yield and enantiomeric excess of the epoxide formed, Scheme 1.3. The enantioselectivity originates from the di-imine bridge (R 1 and R 2, Scheme 1.3A) lying in the same plane of the aromatic system. The directionality of the incoming alkene to the metal center is governed by the enantio-steric effects, and a side on approach of the double bond parallel to the salen ligand is generally accepted (Scheme 1.3B). Jacobsen proposed an attack of a cis-alkene from the direction of the di-imine bridge (Scheme 1.3B. path a) such as the smaller substituent R s is on the same side as the axial hydrogen of the chiral center. Katsuki favors path b (Scheme 1.3B) due to - interactions. Additionally, it was found by Jacobsen that electronic effects also play a role, especially electron donation substituents on R 2, Scheme 1.3A. This is thought to stabilize the reactive Mn(V)-oxo species and to decrease the rate of the oxygen transfer. Thus, according to ammond postulate, implies a late transition state in which the interaction between the alkene and the chiral salen ligand is more important. Regarding hydrogenations, most catalytic reductions of double or triple bonds, either homogenous or heterogeneous, have been shown to be syn, with the hydrogen entering from the less-hindered side of the molecule (see also section 1.4.1). 87 Asymmetric hydrogenation of prochiral ketones is a major route to chiral alcohols that are especially important in the synthesis of biologically active compounds. ne of the most known asymmetric hydrogenation reactions of ketones and imines is the oyori asymmetric hydrogenation, using Ru(II)-BIAP complexes, Figure P Ru(Et 3 ) 2 P Figure oyori Ru(II) type catalyst with BIAP ligand. It was found that the use of such catalysts, in such transformations yielded secondary alcohols in high enantiomeric excess. Usually a base is needed in order to activate the catalyst for the uptake of hydrogen. Mechanistic insight is presented in Figure 1.13 for the hydrogenation of a ketone. A more detailed mechanism is presented in the literature

27 Figure Mechanistic suggestion of ketone hydrogenation by Ru(II) complex. The base is required to form the starting active structure (on the left). This mechanism, involving both the ligand as well as the metal center, is general enough to explain the hydrogenation imines to amines as well. 95 The enantioselectivity is governed by enantio-sterics to yield the more favorable transition state as presented in Figure Favored Unfavored Figure Favored and unfavored transition states of oyori Ru(II) catalyst and acetophenone; to the right: Ru(R-binap)() 2 (temp) 3D representation Polyethylenimine Polyethylenimine (PEI) is a polymer that has been known for a long time and which, for example, has been widely used in processes involving paper production, water purification, and shampoos manufacturing. PEI is also being used as DA transfection agent due to its ability to complex DA, pass through cell walls, and as an efficient gene delivery vehicle. 96 This polymer is available in two main forms: linear and branched, Figure m Linear PEI 2 Branched PEI 2 Figure Linear and Branched Polyethylenimine. 27

28 The most important feature of PEI is its high cationic charge density, since every third atom can potentially be protonated. Commercial PEI used here is highly branched, has a molecular weight of about 60,000, and contains about 1400 monomer residues. About 25% of the amino groups in PEI are primary, about 50% secondary and the remaining 25% are tertiary Polyethylenimine and Synzyme Properties Koltz showed that PEI modified by alkylation or acylation of their amine groups can act as enzyme-like acid catalysts, "synzyme" (Synzyme - synthetic enzyme) with substantial rate acceleration of order of , 98 These modified PEI synzymes structurally resemble micelles, but offer a higher degree of structural organization and chemical diversity. They exhibit significant rate accelerations of the Kemp elimination (Scheme 1.4) as well as for many other reactions. Tawfik and coworkers investigated the "tuning" of the microenvironment of these amine bases systematically to optimize the specific transition state (TS) stabilization in the Kemp elimination B 2 TS B 2 B + C Scheme 1.4. Kemp elimination Polyethylenimine alkylated with various combination of dodecyl iodide, benzyl bromide and methyl iodide are thought to generate catalytic enzymatic like sites in a range of hydrophobic cavities or regions. This drives the substrate binding: (i) in close proximity to a range of amine gropes which serve as catalytic bases, (ii) to be embedded in a positively charge polymer framework, and (iii) expected to stabilize the delocalized negatively charge transition state. Breslow and Liu further reported the use of modified PEI to examine transamination between an amino acid and the keto acid, which is the most important form of nitrogen transfer in diverse biological systems, Scheme 1.5. Since modified PEI were already shown to be effective hydrolysis catalysts, the additional coupling of a pyridoxamine moiety led to a modified PEI that catalyzed conversion of pyruvic acid to the corresponding D,Lalanine amino acid with a remarkable acceleration factor of The long alkyl chains create a cavity in which the transformation reaction can take place in a less than fully aqueous environment. 28

29 R C R C R C R C 2 Me X R C Pyruvic acid 2 Me X Me X Me X Me X R C 2 R C + X ydrolysis X Me Me Scheme 1.5. Amino acid Keto acid transformation Polyethylenimines and catalysts In order to overcome the obstacle of the lack of availability of the hydrophobic substrate (see section 1.2) to the catalytic site and to allow aqueous biphasic oxidation of hydrophobic alkenes with 2 2 catalyzed by polyoxometalates, the idea that an alkylated polyethylenimine could be considered a very primitive enzyme or synzyme having a 97, hydrophobic core and a hydrophilic surface was utilized in Ronny eumann's group. Alkylation of polyethylenimine led to an amorphous structure, soluble in water that retained hydrophobic cores that intercalated polyoxometalate catalysts and permitted solubilization of the hydrophobic substrates in the alkylated polyethylenimine-catalyst construct. 10 allowed for the efficient aqueous biphasic oxidation of even very hydrophobic substrates such as methyloleate with hydrogen peroxide. The recovery and recycle of the aqueous catalyst phase was simple and efficient. The concept is pictured in the Figure This ydrophobic substrates xidaized product Figure Alk-PEI/PM synzyme oxidative catalysis The concept of alkylated polyethylenimine to facilitate aqueous biphasic catalysis was extended in two directions: First, alkylated polyethylenimine stabilized palladium nanoparticles in water allowed aqueous biphasic catalytic hydrogenation of alkenes, Figure 29

30 1.17. Surprisingly the hydrogenation was highly chemoselective for hydrogenation of the less hindered alkene; for example 3-methylcyclohexene was reduced selectively in the presence of 1-methylcyclohexene. 12 Figure Cartoon representation of palladium nanoparticles stabilized by alkylated polyethylenimine and dispersed in water Secondly, the preparation of a crosslinked polyethylenimine assembly that encapsulated a polyoxometalate catalyst resulted in the lipophiloselective oxidation of secondary alcohols, Figure Thus, even though reactions were carried out in water, competitive oxidation of a more hydrophobic alcohol in the presence of a hydrophilic alcohol significantly favored the former. The lipophiloselectivity was proportional to the relative partition coefficient of the substrates. Figure Simplified 2D representation and polyethylenimine is shown as a linear polymer although it is branched, and oxidation of secondary alcohols Chiral polyethylenimine derivatives Some work regarding chiral polyamines had been done by Breslow et al. who synthesized 107, 108 chiral polyamines from the corresponding amino acid by oxazoline polymerization. Most of the research reported, describes the organic catalytic chiral induction on the 30

31 formation of an amino acid, such as valine, from the corresponding ketoacid. Low conversions (5-7%) and enantioselectivity ranging from 16% to 66% ee were disclosed. 108 In other examples transition metal salts were combined with chiral polyamines probably forming coordinative bonds with the polymer frameworks, but no clearly defined organometallic catalyst were described. 107 Chiral polyamines in the presence of CuS 4 were used to synthesize phenylalanine with ee s ranging from 0% to 53% ee, and Michael addition reactions of dimethylmalonate to azachalcone were performed upon addition of is 4 or Zn(Ac) 2 yielding the corresponding product with reported ees in the range of 0.3% to 46% ee Immobilizations of catalysts, encapsulation and enantioselectivity In recent years, supported catalysts have become valuable tools for the simplified separation and recovery of catalysts from reaction mixtures. Usually, the catalysts are attached by covalent bonding to a solid support, but in many cases the covalent attachment leads to partial loss of efficacy due to the decrease in mobility. Alternatively, catalysts can be immobilized by non-covalent bonding through hydrogen bridges, ionic, hydrophobic, fluorous and - interactions. Compared to covalent attachments, such non-covalent interactions increase the flexibility in choices of support materials, reaction conditions and work up methods. Furthermore, in the ideal case in the non-covalently bound immobilization strategy the catalyst itself is basically not changed by these types of interactions, making it one of the most favorable ways for the immobilization of chiral catalysts. 109 Despite this, in almost all cases, immobilization of chiral catalysts is accompanied with loss of enantioselectivity compared to the homogenous catalysts. 110 In that respect, encapsulation is the only catalyst immobilization process, which, in theory, does not require any interaction between the catalyst and the support. ence it is the only method which attempts to mimic the homogeneously catalyzed reaction process. The supported catalyst can be prepared by either assembling the catalyst within the pores of the support or assembling the support around the catalyst, mostly through silica based support or polydimethylsiloxane. 110 These advantages have led us in this research to develop and implement ways to encapsulate catalysts in a chiral organic framework, with the notion that the non-covalently immobilized or embedded achiral catalyst will increase enantioselectivity through weak interaction in aqueous or biphasic systems. 31

32 Two important boundary conditions have to be considered in the design and development of multiphase systems for organometallic catalysis: (1) As was pointed above (section 1.2), mass transfer between the various phases must be high enough to allow for sufficiently high reaction rates, and (2) in order to achieve an efficient separation and immobilization, crosscontamination between the catalyst phase and the continuous substrate/product phase must be kept to a minimum to avoid catalyst leaching and impurities in the products. bviously, these two constraints are contradicting and need to be compromised in real systems. evertheless, it can be addressed by controlling the solubility of the catalyst, for example, encapsulating in a hydrophobic catalyst in a hydrophobic space and the dispersing the latter assembly in an aqueous media Cellulose and sugars Cellulose is probably the single most abundant organic compound on the planet. It makes up most of the biomass, and is the chief structural component of plant cells, where it comprises 10-20% the weight of dry leaves, about 50% of the weight of tree wood and bark, and around 90% of the weight of cotton fibers, from which pure cellulose is most easily obtained. Cellulose is a water insoluble polymer of D-glucose with a C- binding through -1,4- glycosidic bond (from the anomeric carbon of one unit to the C-4 hydroxy of the next unit), whereas the corresponding -1,4-glycosidic binding forms amylose, Figure Cellulose n Amylose n Figure Structure of cellulose and amylose Regarding its polymer characteristics, cellulose is a polysaccharide containing 3000 units per chain on average, with a molecular weight of about 500,000 (some degradation occurs during isolation and actually, as it exist in plants, it may contain as many as 10,000-15,000 glucose units with the corresponding molecular weight of million). The strength of the wood derives principally from the hydrogen bonds of the hydroxy groups between the chains. This contrastive configuration of the glycosidic bond in the polymeric chain is one of the main reasons for the stability of cellulose towards hydrolysis and biodegradation, compared to amylose. Partial hydrolysis, which can be brought about by enzymatic methods, yields the disaccharide cellobiose. 32

33 Cellulose as a renewable source of fuel and materials Catalytic conversion of biomass, mainly cellulose, to fuels and chemicals has attracted a great deal of attention as one of the future technologies for reducing global warming and for renewable fuel production. Much research and many approaches have been reported describing attempts to utilize cellulose and biomass as an efficient energy source and chemical resource to meaningful products In the past strong acids such as 3 P 4, 2 S 4 and Cl were used at high temperatures to hydrolyze cellulose to glucose with low selectivity, due to numerous further transformations that glucose undergoes in a noncontrolled manner. 112 Therefore, the challenge is to find moderate conditions for hydrolysis of cellulose. The first attempts to dissolved cellulose or cellulose containing material such as cotton, were described about 150 years ago. 119 Some cellulose solvents have been developed usually involving derivitization of cellulose, for example, as nitrates, xanthates, or acetates or by non-derivatizing solvents such as ionic liquids, which are expensive, demand high purity and sometimes even water exclusion. 120 Therefore, the search for water compatible cellulose manipulation is highly important in order to achieve an industrial process to utilize cellulose for energy and as a material source. For the water solvation of cellulose, there is still no consensus on the mechanisms or reactions needed to disrupt the intermolecular hydrogen bonds of cellulose to initiate the solvation of cellulose chains Boronic acid as receptor, sensor and reagent for saccharides Boric acid and its derivatives, and phenylboronic acid and its derivatives are known to react with sugars. Stable phenylboronic acid based receptors offer the possibility for saccharide sensors 121 that can be selective and sensitive for any chosen saccharide, primarily by interactions that involve the reversible formation of a pair of covalent bonds. Despite the long history, the structure of the phenylboronic acid-saccharide complexes in aqueous solution continues to be discussed, 122, 123 but it is agreed that phenylboronic acids covalently react with 1,2 or 1,3 diols to form five or six membered cyclic esters. The adjacent rigid cis-diols of saccharides form stronger cyclic esters than the simple acyclic diols. The equilibria for the binding of diols are presented in Figure

34 Figure enylboronic acid equilibria in aqueous solution enylboronic acid reacts with water to form the boronate anion and hydrated proton (K a ) with rapid water exchange. In all the equilibria the tetrahedral complex (K tet ) is greater (more stable) than the trigonal complex (K trig ), ence at higher p the tetrahedral complex is formed. 124 In order to form a saccharide complex at neutral p, it is necessary that the pk a of phenylboronic acid itself will be 7, since the ester is more acidic that the phenylboronic acid itself. The pk a of the ester is 1-2 units lower than that of the phenylboronic acid, pk a = 8.8. ence phenylboronic acid will form strong complexes in basic aqueous conditions. There are two approaches to lower the p for phenylboronic acid, either by electron withdrawing groups on the aromatic ring or employing aminomethyl substituent as pioneered by Wulf, Figure The pk a of the second protonation of these orthoaminomethylboronic acid is 5.3. Figure pk a of ortho-aminomethylboronic acid Studies have been conducted on the interactions of boric acids and boronic acids as reagents on cellulose activation, but scarcely applied because of unpredictable reactions. 126 The most reactive site of cellulose towards boronation is the trans-1,2-diol system in position 2 and 3. Model studies carried out with phenylboronic acid on methyl--d-glucopyranoside (Me-- D-glcp) showed six membered ring borate ester through the hydroxyls in position 4 and 6, as shown in Figure 1.22A, and a seven membered ring with two boron atoms with trans-1,2-diol moiety in position 2 and 3, Figure 1.19B. 120 The product of fission I (Figure 1.22A) has only a diol structure at positions 2 and 3, making it a reasonable model for the conversion of oligo- 34

35 or polyglucans. Furthermore, it was observed that treatment with water resulted in complete removal of the boronates, offering the possibility of the trans-1,2-diol structure to lead to forms of activation, or as a system for solubilizing cellulose as boronation intermediate. B B I I II B B Me Me Me- 4,6 (B)--D-glcp, A Me- 2,3 (B) 2-4,6 (B)--D-glcp, B Figure Boronate structures and the expected fission processes in MS studies. Recently, Yinghuai et al. published a new approach by introducing a phenylboronic acid moiety to an ionic liquid structure, and was able to stabilized Ru nanoparticles for the conversion of cellulose to hexitols, by what was suggested as a reversible binding. 111 owever, they did not show glucose, or any other sugar formation, as the simple hydrolysis product of cellulose. 35

36 1.9. Main goals and research objectives I. Most asymmetric transformations in synthetic organic chemistry are based on the concept of a chiral ligand complexes to a catalytic center by strong interactions such as covalent or coordination bonds. In such a way, asymmetric transformations are induced by using stereo controlled access to the active site often augmented by template effects. There are a few reported examples on the use of chiral ionic liquids as solvents for asymmetric catalysis, which show low to moderate enantiomeric excess (ee) in a variety of transformations that are likely due to strong ionic or electrostatic interactions of the catalysts with the solvent. 127 Three previous findings in our laboratory, as discussed in section 1.6.2, provided us a proof of principle that indeed derivatives of polyethylenimine significantly facilitated mass transfer in aqueous biphasic media and also imparted very significant reaction selectivity when catalysts were incorporated within the polyethylenimine-based medium Therefore, based on previously developed concepts, in this.d research, we examined the ability of novel chiral polyethyleneimine analogs to induce stereoselectivity, typically enantioselectivity to a variety of chemical transformations such as alcohol oxidation, epoxidation, reduction and hydrogenation by combining chiral polyethylenimine derivatives with known achiral catalysts. The research is motivated by the idea that we can induce stereoselectivity to an achiral catalytic center by weak interactions such as van der Waals, hydrogen bonding, and stacking interactions in confined space by using chiral polyethylenimine derivatives. A secondary goal is to implement these achiral catalysts/chiral PEI scaffolds in aqueous or aqueous biphasic systems. II. ydrolysis of cellulose requires harsh conditions using strong acids and high temperatures, which affords low selectivity in the formation of monosaccarides. Milder conditions and high monosaccaride yields are a major goal towards use of cellulose as a renewable resource. Since cellulose is highly water insoluble, complex solvents such as expensive ionic liquids are required for cellulose dissolution and hydrolysis. Therefore another aspect addressed in this.d. research is related to the hydrolysis of cellulose. Since polyethylenimine is a highly water soluble polymer that can be modified chemically and can carry a high cationic charge, these properties make polyethylenimine derivatives suitable candidates for the design of a water soluble system for cellulose hydrolysis. The research is motivated by the notion that we can use the well-known chemistry of phenylboronic acid, which was used by previous workers for cellulose hydrogenation in ionic liquid systems

37 and in the field of sugar recognition in biology, and combine it with polyethylenimine to induce better cellulose solubility, hydrolysis and other transformations in water. 37

38 2. Materials and methods Starting materials were obtained from commercial suppliers and were used without further purification. Solvents were dried over molecular sieves (3Å and 4Å), and TF was refluxed over sodium/benzophenone ketyl and distilled under argon atmosphere for dryness. Freshly deionized 17.3 MΩcm water (DDW) from a Millipore (Millipore Corp., Danvers, MA) water purification system was used for catalytic experiments. Cellulose was pretreated and mostly used as such (for pretreatment see experimental). Solution state MR spectra were recorded at 20 C on Bruker Avance spectrometers: 1 and 13 C at 250, 300, 400 & 500 Mz. MR chemical shifts are reported in parts per million (ppm) downfield from tetramethylsilane (TMS) (δ scale). 1 and 13 C{ 1 } MR chemical shifts were referenced to the residual signal of chloroform-d and acetone-d 6. For basic conditions, chloroform-d was run through basic alumina. Coupling constants (J) are reported in ertz (z), and splitting patterns are designated as s (singlet), d (doublet), t (triplet), q (quartet), m (multiplet), b (broad), and the corresponding combinations: bs (broad singlet), dd (doublet of doublet), etc. IR spectra were recorded on a icolet 6400 FT-IR spectrophotometer with the samples loaded into KBr pellets or dried on a disk for highly viscous materials. UV-vis spectra were measured on a P 8452A diode array UV-vis spectrometer. Matrix-assisted laser desorption/ionization (MALDI) mass-spectrometry was performed on Bruker Reflex III reflector time-of-flight instrument with Scout multiprobe (384) inlet and gridless delayed extraction ion source. Electrospray ionization (ESI) massspectrometry was measured on a Micromass Platform LCZ 4000 (Manchester, UK) utilizing the electron spray ionization method. ptical rotation measurements were conducted on a Perkin Elmer model 341 polarimeter, using a standard cell, l = 1 decimeter. Circular dichroism (CD) measurements were conducted on Applied otonics Chirascan Instrument ("Applied otophysics" Ltd. UK), using quartz quvette, l = 1 cm. Transmission Electron Microscopy (TEM) was carried out with a FEI (ilips) CM-120 ST transmission electron microscope, operating at 120 kv. Cryo-TEM images were obtained on a FEI (ilips) T12 - Tecnai transmission electron microscope, operating at 120 kv. Samples were maintained under cryogenic temperature with a Gatan 626D cryo holder. Elemental analyses were performed on FlashEA 1112 C Elemental Analyzer using Eager 300 software. Products were quantified using GLC (P-6890 gas chromatograph) with a flame ionization detector and a 30 m 0.32 mm 5% phenylmethylsilicone (0.25 μm coating) capillary column 38

39 and helium carrier gas. The products were identified using a gas chromatograph equipped with a mass selective detector (GC-MS P 5973) equipped with the same column. Chiral GC was carried out using a Lipodex C column- heptakis-(2,3,6)-tri--phentyl)--cyclodextrin stationary phase. PLC was carried out on Agilent 1100 series chromotgraph, using Daicel normal phase chiral columns (D-, AD-, IC). PLC grade 2-propanol (IPA) and heptane (ep) were used as mobile phase. TLC plates -"Merck" silica gel 60 F 254 aluminum sheets or glass. For column chromatography "Merck" silica gel 60 ( mm) was used. Reactions (up to 4 atm) were carried out in ml glass pressure tubes. For higher pressure autoclave was used DS test 128 A DS test is often used for the detection of free sugars. The reductive ends of sugars, also called reducing sugars, (aldehydes and ketones) are oxidized to the corresponding carboxylic acids. 3,5-dinitrosalicylic acid (DS) is reduced to form 3-amino-5-nitrosalicylic acid, which absorbs light strongly at 540 nm and can be calibrated to afford quantitative measurement, Scheme 2.1. The main drawbacks of this method are its low specificity and many side reactions such as sugar decomposition. In addition, different reducing sugars afford different color intensities. C 2 a 2 2 C 2 DS-3,5-dinitrosalicylic acid Scheme 2.1. DS test amino-5-nitrosalicylic acid 2.2. Glucose oxidase assay (Gx) The assay was conducted using a Sigma-Aldrich Glucose (G) Assay Kit, Cat. o. GAG20. This is a specific test used to quantify glucose concentration. Glucose is oxidized to the corresponding gloconic acid and hydrogen peroxide, which in turn oxidizes the reduced form of ortho-dianisidine, which is brown. Quenching the reaction with sulfuric acid yields a pink colored solution, which is measured at wavelength = 540 nm, and calibrated according to standard solution, Scheme

40 Glucose oxidase D-glucose C D-gluconic acid 2 Peroxidase reduced o-diansidine (colorless) oxidaized o-diansidine (brown) oxidaized o-diansidine (brown) 2S 4 oxidaized o-diansidine (pink) Scheme 2.2. Glucose oxidase assay, reaction cascade 2.3. Cellulases: Endo, exo and -glucosidase Endo and exo cellulases were supplied as a cocktail mixture solution from ovozyme Cat. o , and -glucosidase in a separate solution from ovozymes Cat. o In the proposed mechanism of action, endo cellulases are responsible for the breaking of the internal bonds of the crystalline structure of cellulose, while the exo cellulases cleaves 2-4 units from the end of the corresponding exposed chain affording tetra-saccharides or di-saccharides (cellobiose). -glucosidase (cellobiase) hydrolyzes the exo-cellulases products into monosaccharides. The process is illustrated in Figure 2.1. Figure 2.1. Cellulose degradation and hydrolysis by cellulases 40

41 3. Results 3.1. Synthesis of chiral polyethylenimine derivatives We have developed a new method to synthesize chiral polyethylenimine derivatives, based on amino acids with nonpolar side chains, that can be extended or crosslinked using imine linkers. In the design of an imine crosslinked system we had a few points to consider: 1. In order to achieve a crosslinked system we have to have at least two primary amino groups. 2. The nucleophilic amine (which starts the polymerization of the -carboxyanhydride (CA), Scheme 2.1) must have either one protected amine or a precursor of a primary amino group. 3. A priori, one could assume that the crosslinked systems with the most rigidity would be the most likely to impart stereoselectivity to the catalytic reaction. In order to achieve a more rigid crosslinked system we sought for 6 repeating units of amino acids as precursors for the corresponding chiral polyethylenimine derivative. 4. The crosslinker preferably should possess dialdehyde functional groups. The synthesis of the chiral Leu-PEI3 was carried out as illustrated in Scheme C L-leucine Cl 3C Cl TF, 50 C, Charcoal L-CA 1 CC 2 2 TF CA : Amine 6 : 1 B 3*TF C C reflux, 3 days 2 n n = 4-8 Cyanomethyl amine-l-polyleucine 2 2 n n = 4-8 Ethylamine-L-Leu-PEI Leu-PEI3 Scheme 3.1. Synthesis of Leu-PEI3 CA 1 was reacted with 2-aminoacetonitrile in a 6 to 1 ratio to afford cyanomethyl amine-lpolyleucine 2, with an average of 6 repeating units of leucine. MALDI-TF-MS showed a normal chain length distribution of 2 around 4 to 8 repeating units of leucine. Reduction of 2 with borane-tf gave Leu-PEI3, with no starting material observed by MR and ESI-MS measurements. The MS spectrum of Leu-PEI3 is easy to decipher with molecular peaks at m/z = 458, 557, 656, 755 and 854 amu for 4 to 8 repeating units. Fragments for the molecular peak minus the i-butyl side chain are also identified at m/z = 500, and 797 amu, Figure

42 2 n Figure 3.1. ESI-MS of compound Leu-PEI3 In principle different amines can be used as initiators for the CA polymerization, and indeed in different cases octyldecylamine and aniline were used in different ratios with CA 1. ctyldecylamine, with ratio of 10:1 CA:amine respectively, afforded distribution of chain lengths between 5 to 12 repeating units as observed by MALDI. With aniline, ratio of 6:1 CA:amine respectively afforded the peptide with the corresponding 5 repeating units on average as observed by MALDI. The first attempts to crosslink Leu-PEI3 were made using glutaraldehyde. This choice of dialdehyde as an imine crosslinker turned out to give low yields likely because, aliphatic imines are significantly less stable than those conjugated to unsaturated aliphatic or aromatic groups; the use of an aromatic dialdehyde will be favorable and so we decided to use the aromatic dialdehyde, terephthalaldehyde 4, as a crosslinker, Scheme 3.2. Leu-PEI3 + n n = Dry Et, reflux Trimethyl-o-formate Imine crosslinked L-Leu-PEI Leu-PEI5 m ab 4 Dry Et Crosslinked L-Leu-PEI Leu-PEI6 Scheme 3.2. Imine crosslinked synthesis of Leu-PEI6 m 42

43 Therefore, crosslinking Leu-PEI3 with terephthalaldehyde 4 afforded the imine crosslinked Leu-PEI5. The crosslinked PEI can be either entangled or cyclic. Reduction of the imine Leu-PEI5 using ab 4 in ethanol gave the amine crosslinked Leu-PEI6. The formation of the imine bond in Leu-PEI5 (~161 ppm), the aromatic region (~129 ppm), and the corresponding reduction of the imine bond (hence its disappearance) to afford Leu-PEI6 is observable in the 13 C MR of both compounds, Figure 3.2. C C C C m 2 C C 2 2 C C 2 m Figure 3.2. a) top: 13 C-MR of compound Lue-PEI5; b) bottom: 13 C-MR of compound Lue-PEI6 (both in CDCl 3 ) The synthesis of the corresponding L-phenylalanine-polyethyleneimine imine crosslinked polymer was done in a similar manner, Schemes 3.3 and 3.4. The main reason to synthesize a chiral polyethylenimine derivative with aromatic moieties was to introduce another set of interactions to the system, mainly - stacking interactions that might improve the interactions between the substrate and the chiral polyethylenimine derivative. It was thought that this would lead to better enantioselectivity, or to form more complex 3D chiral structures. 43

44 2 C Cl 3C Cl TF, 50 C, Charcoal CC 2 2 TF CA : Amine 6 : 1 C C 2 n n = 5 average B 3*TF reflux, 3 days 2 n m = 5 average L-enylalanine L-CA 7 Cyanomethyl amine-l-polyphenylalanine 8 Ethylamine-L-e-PEI e-pei9 Scheme 3.3. Synthesis of e-pei9 Thus, CA 7 was reacted with 2-aminoacetonitrile in 6 to 1 ratio, respectively, to afford cyanomethyl amine-l-polyphenylalanine 8. Compound 8 turned out to be completely insoluble, thus no MR or even a clear MALDI-MS could be obtained. The following reduction of compound 8 with borane-tf gave e-pei9 and was confirmed by MR and ESI-MS measurements. In this case, 5 repeating units of phenylalanine on average were obtained, Figure 3.3. The MS spectrum of e-pei9 shows considerable fragmentation in comparison to Leu-PEI3. Molecular peaks were observed at 726 and 859 amu for 5 and 6 repeating units. Fragments of the molecular peaks minus the benzyl side chain where observed at 635 and 768 amu, and fragments for the molecular peaks minus the chain terminator, 2 C 2 C 2 were obtained at 684 and 817 amu. ther fragments including molecular peaks plus a + are also observed. It would appear from the ESI-MS that Leu-PEI3 has a broader range of molecular weights (n = 4-8) relative to e-pei9 where mostly polymers of 5 and 6 repeating units were obtained. This may be explained by the relative higher solubility of peptide 2 in TF, while the peptide of 5-6 e repeating units is insoluble and leads to its precipitation. 2 n Figure 3.3. ESI-MS spectrum of e-pei9 44

45 Crosslinking e-pei9 with 4 afforded the imine crosslinked e-pei10, Scheme n n = 5 average e-pei9 4 + Dry Et, reflux Triethyl-o-formate Imine crosslinked L-e-PEI e-pei10 ab 4 Dry Et m Imine crosslinked L-Leu-PEI e-pei11 m Scheme 3.4. Imine crosslinked synthesis of e-pei11 The crosslinked polyethylenimine derivative can be, as in the case of Leu-PEI5, either entangled or cyclic. Reduction of the imine e-pei10 using ab 4 in ethanol gave the corresponding amine e-pei11. As before, the formation of the imine bond in e-pei10 (~161 ppm) and its reduction and hence its disappearance to afford e-pei11 is easily observed presents in the 13 C MR of both compounds, Figure 3.4. C C C C n TEF TEF Figure 3.4. a) left: 13 C-MR of compound e-pei10; b) right: 13 C-MR of compound e-pei11 (both in CDCl 3 ); TEF = triethyl-ortho-foramte residual peaks. 45

46 3.2. Crosslinked PEI with MnSalen complexes for asymmetric biphasic epoxidation Chiral polyethylenimine derivatives with achiral MnSalen complexes were prepared for enantioselective epoxidation. Two achiral MnSalen complexes, MnSalen13 and MnSalen15, were synthesized, Scheme C + Et, Ref lux 4 h Trimethyl-o-formate Mn(Ac) LiCl Mn Et, reflux, 3 h Et, ref lux, 2 h Cl air C + Et, Ref lux 4 h Trimethyl-o-formate Mn(Ac) Et, reflux, 3 h air LiCl Et, ref lux, 2 h Mn Cl Scheme 3.5. MnSalen synthesis The simple mixture of the imine crosslinked L-leucine based polyethylenimine with the MnSalen complex was tested first. In order to increase the solubility of Leu-PEI6 in water, which is not highly water soluble, hydroxyl groups were introduced by reaction of the Leu- PEI6 with an excess of 2-bromoethanol to afford Leu-PEI16, Scheme 3.6. Leu-PEI6 n Br Et, reflux Leu-PEI16 n Scheme 3.6. ydroxylated Leu-PEI16 Both the MR and the elemental analysis are in good agreement that most of the nitrogen atoms in the polymeric framework reacted with bromoethanol. Since the Leu-PEI16 has both hydrophilic and hydrophobic parts, it was assumed that it might form an enzyme like configuration with a hydrophilic surface and hydrophobic core (synzyme) in aqueous phases. This synzyme configuration was confirmed by cryo-tem of Leu-PEI16 in aqueous solution, Figure 3.5. Indeed it would appear that the polymer shows a disperse structure (suspension) in solution which, however, is not micellar. 46

47 60 nm 50 nm Figure 3.5. Cryo-TEM images of Leu-PEI16 in 4.85% tbu/ddw The resulting hydroxylated PEI analog, Leu-PEI16, was solubilized in 4.85% tbu in water and water soluble MnSalen complex Mnsalen13 was dissolved in the Leu-PEI16 suspension (with gentle heating, 60 0 C for 1 h, for full homogeneity). A buffered solution of acl (bleach) with a 2 P 4 (p = 11.4) was used as the oxidant. Several reactions on different styrene derivatives showed nearly quantitative conversions, but epoxide yields were lower and no enantiomeric excess was detected, Table 3.1. Table 3.1. Epoxidation of aromatic alkenes catalyzed by Mnsalen13/Leu-PEI16. Conversion xide yield Substrate xide product Temp' [%] [%] RT RT RT C Reaction conditions: Leu-PEI16 (10 mg) in water (9.8 ml) and tbu (0.5 ml)) stock; MnSalen13 or 15 (8 mg, mmol/1 ml of the above stock suspension) was heated at ~ 75 C for 1 h and cooled to RT, M (27 mg, 0.23 mmol, 0.5 eq), olefin (0.46 mmol, 1 eq), cooled (ice-water), acl (2 ml, ~ 0.5M, a2p4 buffer, p = 11.4). The reaction was stirred at 3 C (or RT) for 60 h. Furthermore, the UV-vis spectra of the Lue-PEI16, MnSalen13, and Lue-PEI16 with MnSalen13 showed no significant differences. ence it was concluded that there are no significant interactions, if any, between the polyethylenimine derivative and MnSalen13, and therefore no stereoselctive induction on the catalyst. Even with the hydrophobic MnSalen15, 47

48 which presumably will have higher affinity to the hydrophobic core of the system, in a fully hydrated system (no co-solvent) no enantioselectivity was observed in the epoxidation of 1,2- dihydronaphthalene. In order to improve the stereoselective induction, it was surmised that the catalyst should be in a more confined space. Thus, we turned to the method of crosslinking the polymer and the catalyst together with epichlorohydrin-based crosslinker, Schemes 3.7 and eq Cl TF reflux, 2 h Cl Cl Aminoethanol Epichlorohydrine 17 Scheme 3.7. Aminoethanol epichlorohydrin crosslinker 17 Epichlorohydrin was reacted with 2-aminoethanol to afford the corresponding crosslinker Aminoethanol was chosen since it is water-soluble and should increase the hydrophlicity of the crosslinked system. The first crosslinked system, Leu-CLS18, was synthesized from Leu- PEI3 and MnSalen15 complex, Scheme 3.8. The drawing of the crosslinked system (Leu- CLS18) is a simplified representation of the corresponding 3D structure formed. The crosslinking can occur on both primary and secondary amines. This is true for all the epichlorohydrin based crosslinked system shown from hereon. 2 Mn + Cl Cl + t t dioxane/water Bu Cl Bu n 80 C, 5h t Bu reflux, 2.5 h Leu-PEI3 17 MnSalen15 Mn Cl Leu-CLS18 Scheme 3.8. Synthesis of Leu-CLS18 The system was tested for the asymmetric epoxidation of 1,2-dihydronaphthalene. The t-butyl analog of the MnSalen ligand was chosen since it has much lower solubility in water and hence will have much less leakage into the aqueous phase. The reaction afforded the corresponding epoxide with 8% ee, and 45% yield (Table 3.2, entry 1). Even though the enantiomeric excess is not high, it shows that there is stereoselctive induction on the catalyst. Different systems were synthesized in a similar manner from e-pei9 with the notion that the phenyl moiety will induce better interaction between the substrate, the catalyst and the 48

49 chiral parts of the system, and will improve the ee s, Scheme 3.9. Crosslinked system e- CLS21 was synthesized with the notion that if the crosslinker itself will be chiral, and thus the chiral mass of the system will be higher, it might result in better enantiomeric excesses. The synthesis of the chiral crosslinker began with the amino acid L-phenylalanine which was reduced to the corresponding amino alcohol 22 using ab 4 and iodine, Scheme 3.9. Amino alcohol 22 was reacted with epichlorohydrin to afford crosslinker 23, which was reacted with e-pei9 and MnSalen13 to afford the crosslinked system e-cls21. The screening results of the crosslinked systems for the epoxidation of 1,2-dihydronaphthalene are summarized in Table e-pei9 m Cl Cl 17 Mn Cl MnSalen13 water/dioxane C, 3.5 h reflux, 2.5 h Mn Cl t B u MnSalen15 water/dioxane C, 5 h reflux, 2 h P h t Bu Mn Cl Mn Cl e-cls19 P h e-cls20 water/dioxane, C, 5 h, reflux, 2 h Cl Cl + 23 Mn Cl MnSalen13 Mn Cl e-cls21 2 C L-phenylalanine ab 4, I 2 TF, reflux, 18 h 2 Cl Cl Cl 2eq, C Scheme 3.9. Synthesis of e-cls19, e-cls 20 and e-cls21 with chiral crosslinker 23 49

50 Table 3.2 Asymmetric epoxidation of 1,2-dihydronaphthalene with different crosslinked assemblies Catalyst embedded Crosslinked system o. Product Yields [%] ee a [%] Comments Mn 1 Leu-CLS in water Cl Mn 2 e-cls in water Cl 3 Mn e-cls in water Cl 4 Mn e-cls impregnation b Cl 5 Mn e-cls Cl biphasic with DCM 6 Mn e-cls Cl in water 7 Mn e-cls impregnation b Cl 8 Mn e-cls Cl 20% TF in water Reaction conditions: PEI crosslinked system (32.8 mg/1 mmol of substrate), M (0.5 eq), substrate (1,2- dihydronaphthalene, 1 eq) in 1 ml DDW (or the stated solution), 0.55M acl (a 2 P 4 buffered solution, p = 11.4) (1.4 ml/1 eq of substrate). Stirred at 3 C for h; a determined by PLC (see experimental); b Dissolved with the catalyst in DCM, evaporated and dried under high vacuum. The best enantiomeric excesses were obtained with Leu-PEI18 in aqueous phase and with system e-pei19 under biphasic conditions with dichloromethane (DCM), (entries 1 and 5). The phenyl system, e-cls19, gave lower enantioselectivity compared to isopropyl in Leu-PEI18 (entries 1 and 2), but it did improve, to some extent, by using impregnation methods (compare entry 4 to entry 3). Crosslinked system e-cls21 did improve the enantioselectivity, but less than expected (entries 6 and 7). The fact that the DCM biphasic conditions (entry 5) gave the best enantiomeric excess with the phenylalanine system, and not 50

51 much improvement was found with the chiral crosslinker, may indicate that the reactions occur on the surface of the crosslinked system, where the chirality will be at minimum. ence it was needed to allow the substrate to penetrate more deeply into the crosslinked system. ne way of doing that is by using TF, which will make the system more soluble and more flexible. e-cls19 was reacted in 20% TF in water, and, indeed, it raised the ee from 3.5% to 7% (entry 8 compared to entry 3). Leu-CLS18 was chosen for examining the epoxidation of additional alkenes due to its higher reactivity and enantioselectivity, driven by the motivation to conduct the catalysis in aqueous biphasic media. The results are summarized in Table 3.3 (For full catalytic conditions see experimental). Substrate Table 3.3. Epoxidations catalyzed by Leu-CLS18 in water. xide product Conversions [%] Yield [%] Selectivity [%] ee [%] Racemic Racemic impregnation * Reaction conditions: Leu-CLS18 (5 mg/0.5 ml DDW), M (9 mg, mmol, 0.5 eq/1 eq of olefin) in DDW (0.5 ml), at 3 C olefin (0.154 mmol, 1 eq), acl (0.57 ml, ~ 0.5M, a 2 P 4 buffer, p = 11.4), stirred for 3 days at 3 C; * Dissolved with the catalyst in DCM, evaporated and dried under high vacuum. The system was successful in imparting some chirality on different alkenes affording enantiomeric excesses. The epoxidation of styrene and -methyl styrene afforded moderate to high conversions, but in both cases did not afford any enantiomeric excess (entry 4 and 5). It seems that a disubstituted double bond is essential to achieve enantioselectivity in this system, and indeed the -substituted position of the double bond afforded ee s (entries 1-3). Furthermore, it seems that the more heavily substituted the double bond the higher the ee, but with loss of reactivity (entry 6). 51

52 In order to get a better understanding of this system, and to gain insight on the arrangement of the catalyst in this amorphic system, circular dichroism (CD) measurements of the system was conducted in different solvents coupled with UV-vis spectra, Figures 3.6 and 3.7 respectively. Figure 3.6. CD plots of Leu-CLS18 in different solvents at 25 C. c = 0.2 mm (calculated for 40% TF) Figure 3.7. U.V spectra of Leu-CLS18 in different solvents; the molar absorptivities are: log 232 = 4.01; log 260 = 3.82; log 331 = 3.35 (for 40% TF/water). The CD plots show chiral arrangement around the absorbance bands of the catalyst. The solubility of the system is higher in TF than in water, thus the intensity of the peaks is higher. In both 10% and 20% TF solutions the plots are similar showing a Cotton effect, 52

53 however, in 40% TF the plot is not the same indicating different chiral arrangement. The UV-vis spectrum shows some minor shifts of the catalyst in the crosslinked system in different solvents versus the free catalyst, which indicates weak interactions between the catalyst and the crosslinked system, but with no real catalyst change. Both the CD plots and the UV-vis spectrum are in good agreement with a catalyst encapsulated in chiral environment of the polymeric framework. evertheless, the degree of chirality shown in the CD plots is not necessarily correlated to the enantiomeric excess achieved in the catalytic reactions. Many factors have to be taken under consideration in the catalytic system such as substrate, products, concentrations, oxidant, temperature, etc. where each and every one can significantly change the dynamic chiral arraignment. This can be seen by the simple time and temperature change example presented in Figure 3.8. Furthermore, the epoxidation of 1,2- dihydronaphthalene with Leu-PEI18 in 20% TF in water showed a slight decrease in ee from 8% (in water, Table 3.3 entry 1) to 7.2%, with no major change in conversion and selectivity. This is in contrast to the improvement in the ee from 3.4% to 7.1%, with e- PEI19 in 20% TF in water (Table 3.2 entry 8 compared to 3). Figure 3.8. ne week old sample of Leu-PEI18 in 20% TF (Figure 3.6 as fresh sample) at different temperatures (same sample and concentration) In order to examine the possibility of synergistic effect between the crosslinked system and chiral MnSalen complex, four of crosslinked systems containing the chiral Jacobsen catalyst were synthesized as in the same manner as before. Two systems were synthesized with both enantiomers of the Jacobsen catalyst (RR and SS) with the chiral PEI framework, and two were synthesized using the achiral linear PEI as the polymeric framework, Scheme All 53

54 these systems were tested in the catalytic epoxidation of 1,2-dihydronapthalene under the same conditions as before and the comparisons are presented in Table 3.4. R R Mn t Cl Bu RR-Jacobsen catalyst R R Mn Cl 2 e-pei3 m Cl 17 water/dioxane C, 5 h reflux, 2.5 h Cl RRMnSalen-Leu-PEI24 SS-Jacobsen catalyst S S Mn Cl Mn Cl S S SSMnSalen-Lue-PEI25 R R Mn Cl RR-Jacobsen catalyst R R Mn Cl n 2 Linear PEI n Cl Cl 17 water/dioxane C, 5 h reflux, 2.5 h RRMnSalen- PEI26 n n SS-Jacobsen catalyst S S Mn Cl Scheme Synthesis of crosslinked systems RRMnsalen-Leu-PEI24, SSMnsalen-Leu-PEI25, RRMnsalen-PEI26 and SSMnsalen-PEI27 54 S Mn Cl S SSMnSalen-PEI27 n

55 Table 3.4. Epoxidation results forjacobsen catalyst crosslinked systems for the epoxidation of 1,2- dihydronaphthalene. Conversions Yields Selectivity ee CLS Product Confign * [%] [%] [%] [%] 1 Lue-PEI R,2S-(+) 2 RRMnsalen- PEI R,2S-(+) 3 SSMnsalen- PEI R,2S-(+) 4 RRMnsalen- Leu-PEI R,2S-(+) 5 SSMnsalen- Leu-PEI S,2R-(-) Reaction conditions: PEI-CLS (5 mg/0.5 ml DDW), M (9 mg, mmol, 0.5 eq/1 eq of olefin) in DDW (0.5 ml), at 3 C olefin (0.154 mmol, 1 eq), acl (0.57 ml, ~ 0.5M, a 2 P 4 buffer, p = 11.4), stirred for 3 days at 3 C; * Dissolved with the catalyst in DCM, evaporated and dried under high vacuum; * Determined from literature 80 Interestingly, we found that RRMnSalen-PEI26 and SSMnSalen-PEI27, embedded within achiral crosslinked polyethylenimine yielded epoxide products with only low enantioselectivity, 4% ee, entries 2 and 3. This trend is similar to the enantioselectivity observed for achiral MnSalen catalyst within Leu-PEI18 (8% ee, entry 1). Thus, the Jacobsen catalysts are surprisingly ineffective in these aqueous biphasic media. n the other hand when RR-Jacobsen catalyst was embedded within the chiral Leu-PEI based framework, RRMnsalen-Leu-PEI24, there was a synergistic effect between the chiral catalyst and the chiral environment and a 41% ee of the (1R,2S+) epoxide was obtained (entry 4). owever, when SSMnSalen-Leu-PEI25 was used a lower 27% ee of the opposite (1S,2R-) enantiomer was obtained (entry 5), indicating interaction between that chiral polymeric framework and the chiral catalyst, but not enough to effect the handedness determined by the catalyst itself. e-cls19 under biphasic conditions with DCM showed less reactivity regarding the conversions and yields, Table 3.5. The decrease in reactivity probably arises from the solubility of the substrate and the crosslinked system in the organic phase decreasing the mass transfer efficiency. Also one can regard the system as tri-phasic system between the crosslinked system, the organic phase and the aqueous phase. There is small extant of improvement in the enantioselectivity of several substrates, especially -methyl styrene 55

56 (entry 2) compering to the more reactive aqueous system with Leu-PEI18 (Table 3.3 entry 4). Table 3.5. Epoxidations catalyzed by e-cls19 using DCM as co-solvent Conversion Yields Selectivity ee Substrate Product [%] [%] [%] [%] * Racemic Reaction conditions: e-cls19 (3 mg/0.3 ml DCM), M (5.4 mg, mmol, 0.5 eq/1 eq of olefin) in DCM (0.3 ml), at 3 C olefin (0.09 mmol, 1 eq), 0.5M acl(sol.) (0.3 ml, ~ 2 eq, buffered with a 2 P 4, p=11.4) were added. Stirred at 3 C for ~3 days; * Could not be determined exactly. ere too the enantioselectivity was obtained only with substitution on the double bond with higher effect on the -position (entries 1 and 3 compared to 2). The CD and UV spectra the of e-cls19 (Figure 3.9) is more complex than that of the Leu-CLS18 due to the additional absorbance bands of the phenyl groups of e-pei9 framework at 385 and 230 nm. The CD plots in DCM (as in the biphasic catalytic conditions) show chiral arrangement around the catalysts especially around 314 nm which corresponds to the absorbance band of the catalyst. Figure 3.9. CD and UV spectra of e-cls19, free Mnsalen13 and e-cls(no catalyst) in DCM; c e-cls19 = mg/ml (for CD), c e-cls(no catalyst) = mg/ml (for CD) 56

57 3.3. Crosslinked chiral polyethylenimine derivatives with Ru(II) complexes for asymmetric hydrogenation We wanted to explore the possibility of a general trend in enantioselective induction using the crosslinking method of described above on different kind of catalysts and transformations. In order to examine this idea we chose a series of achiral commercially available Ru(II) catalysts for the oyori type of hydrogenation of ketones. Three types of crosslinked systems were prepared as shown in Scheme 3.11, using the same synthetic method presented for the MnSalen encapsulation shown in schemes 3.8 and n e-pei9 + Cl 17 Cl + P Cl Ru Cl P water/dioxane C, 3.5 h reflux, ~3 h Ar P Cl P Ru Cl e-cls28 2 n e-pei9 + Cl Cl + 17 P Cl Ru Cl P water/dioxane C, 3.5 h reflux, ~3 h Ar hp ph hp ph P Cl Ru P Cl e-cls29 2 n Leu-PEI3 + Cl Cl + 17 P Cl Ru Cl P water/dioxane C, ~4 h reflux, ~3.5 h Ar hp ph hp ph P Cl Ru P Cl Leu-CLS30 Scheme Synthesis of Ru(II) catalyst encapsulated crosslinked systems e-cls28, e-cls29 and Leu-CLS30 In all cases the synthesis was conducted under gentle flow of argon in order to prevent the possibility of ruthenium oxidation, and assumed that all of the catalyst was quantitatively incorporated in the crosslinked system. In e-cls29 the phenyl-ru catalyst was chosen with the thought of affording better -interactions with the phenyl moieties of PEI, and thus inducing better enantioselectivity. 57

58 The systems were tested under different hydrogenation conditions of acetophenone to the corresponding 1-phenylethanol. The results are summarized in Table 3.6, and the main experimental studies are presented in scheme CLS CLS28 CLS28 CLS28 CLS28 CLS28 CLS28 CLS28 CLS29 CLS29 CLS29 CLS28 CLS30 CLS30 e- e- e- e- e- e- e- e- e- e- e- Leu- Leu- Leu- CLS30 Table 3.6. Asymmetric hydrogenation of acetophenone with different Ru-crosslinked systems. Substrate Substrate/CLS (ratio v/wt) acetophenone 100/3 acetophenone 100/3 acetophenone 100/3 acetophenone 100/3 acetophenone 100/3 acetophenone 100/3 acetophenone 100/3 acetophenone 100/3 acetophenone 1/1 acetophenone 1/1 acetophenone 1/1 acetophenone 10/3 acetophenone 10/3 acetophenone 10/6 Conditions Base Solvent Yields [%] T a ee [%] 4 atm 2, RT, 22 h K water 1 30 racemic 3 atm 2, RT, 20 h 3 atm 2, RT, 20 h 3 atm 2, RT, 22 h 3 atm 2, 3 C, 20 h tbuk, 3 mg tbuk, 30 mg tbuk, 120 mg tbuk, 120 mg IPA 3 atm 2, RT, 20 h a 3 P 4 IPA 3 atm 2, RT, 20 h K no Solvent traces (< 1) < 30 D b IPA IPA IPA no reaction traces (< 1) < atm 2, RT, 20 h K water ±2 10 atm 2, RT, 48 h K no Solvent racemic 3 atm 2, RT, 22 h K no Solvent no reaction 10 atm 2, RT, 26 h K no Solvent atm 2, RT, 25 h K no Solvent traces (< 1) < 31 (17) c 3 atm 2, RT, 19 h K water atm 2, RT, 23 h K no Solvent racemic Reaction conditions: In Water Ru-CLS (3 mg/1 ml DDW + 2M K 1 ml), in IPA Ru-CLS (3 mg/0.5 ml IPA) tbuk (3 mg/1.5 ml IPA), no solvent Ru-CLS (3 mg/1 ml IPA + 2M K, dried by lyophilization), acetophenone (in L, according to the ratios mentioned with the Ru-CLS, 100:3 or 10:10 = 1:1, etc.), 2 (3 or 10 atm), stirred at RT for h. a T approximation was calculated according to the mol % of the catalyst in the total mass of the crosslinked system synthesized; b D: Could ot Be Determined; c ot conclusive (PLC). 58

59 Yields: < 1% ee: 17% no solvent, K 3 atm 2 RT P Cl P Ru Cl IPA, 3 atm 2 tbuk - 30 mg RT Yields: 1.1% ee: 10% IPA, 3 atm 2 tbuk mg RT Yields: 4% ee: 4.5% Yields: 3% ee: 8.5% no solvent, K 10 atm 2 RT e-cls28 IPA, 3 atm 2 tbuk - 120mg 3 C Yields: 1.6% ee: 10% Yields: 100% ee: Racemic water, 10 atm 2 K RT hp ph hp ph P Cl P Ru Cl water, 3 atm 2 K RT Yields: 1% ee: ~ 8% e-cls29 Yields: 100% ee: Racemic no solvent, 10 atm 2 K RT hp ph hp ph P Cl P Ru Cl water, 3 atm 2 K RT Yields: 1% ee: 3% L eu-cls30 Scheme 3.12 Main results of the reaction studies of Ru crosslinked systems Initially we found that base played an important role in both the reactivity of the systems (conversions and yields) and the enantioselectivity. When a weak base was used there was no reaction (entry 6), and relatively strong bases are needed. The conversion, and hence the corresponding yields, of the cross linked systems turn to be surprisingly low at moderate pressure, and very much depended on the basicity of the system with the trend that the more basic the conditions, the higher the conversions (entries 2-5). The yields were calculated with high accuracy by GC-MS, even when low conversions were observed (0.2% - 1%). In most cases, the PLC used for chiral resolution is more sensitive than the GC-MS itself and enantiomeric excess could be determined with good repeatability. The best enantioselectivity was achieved with e-cls28 with no solvent at 3 atm affording 17% ee (entry 7). e- CLS29 in water afforded around 8% ee (entry 8), but with very low conversions and yields in both cases. In order to increase the conversion of the systems higher hydrogen pressure was applied. The crosslinked systems with the more reactive catalyst Ru-phenyl, in e-cls29 and Leu-CLS30, afforded at 10 atm full conversions but with the total loss of enantioselectivity (entries 9 and 14). owever, with the less reactive Ru-alkyl catalyst, in e-cls28, we were able to increase the yields to 3% with decrease of ee from 17% to 8.5% (entries 7 and 11). Leu-CLS30 was less enantioselective than the previous systems probably 59

60 due to the reactivity of the Ru-phenyl catalyst and the lack of -interactions with the chiral crosslinked polyethylenimine derivatives (entries 12-14). A solvent effect was also prominent. IPA gave the best conversions with e-cls28 under moderate pressure and relatively good enantioselectivity even at 3 C (entries 3-5). Under aqueous conditions the conversion dropped in comparison to IPA, but the enantioselectivity seemed to be very much effected by the concentration of water in the system. When the reaction was conducted in water no enantiomeric excess was observed (entry 1) but with no solvent and with the 15 wt % structural water in K (dried by lyophilization), the enantiomeric excess increased to 17% (entry 7). The reactivity of the free Ru catalysts was examined, under the reaction conditions that afforded the best ee results in the crosslinked systems, in order to gain some insight on the reactivity of the free catalysts in comparison to those in the crosslinked systems. The results are presented in Table 3.7. Under the reaction conditions the catalysts have very poor reactivity. The Ru-phenyl catalyst is three time more reactive that the Ru alkyl catalyst (entries 1 compared to 2), as was also observed in e-cls28 and e-cls29 (Table 3.6 entries 7 compared to 8). From this we can conclude that the low reactivity is not the product of the crosslinked system, but rather of the catalyst itself under the reaction conditions. Despite the low reactivity, the Ru crosslinked systems showed some induction of enantioselectivity and additional substrates can be considered for hydrogenation, including imines. Table 3.7. ydrogenation of acetophenone with free Ru(II) catalysts Catalyst Substrate Product Solvent Pressure [ 2 ] Yield [%] T 1 P Cl Ru P Cl "Ru(iPr)" no solvent 3 atm water 3 atm "Ru()" Reaction conditions: Ru(iPr) (0.17 mg/1 ml IPA), 2M K (1 ml), dried by lyophilization, acetophenone (100 L), 3 atm 2, stirred at RT for 22 h; Ru() (0.17 mg), K (120 mg/1 ml DDW), 3 atm 2, stirred at RT for 24 h. 60

61 3.4. Asymmetric hydrogenation of prochiral olefins and imines using Pd(0) nanoparticles stabilized with chiral polyethylenimine derivatives Synthesis We succeeded in creating and stabilizing palladium nanoparticles, by reducing Pd(DMS) 2 Cl 2 in a Lue-PEI6 methanol solution with ab 4, Scheme 3.13 and Figure The clear black solution that was formed appears to be stable for weeks standing on the bench without apparent precipitation. TEM imaging showed spherical Pd nanoparticle with the average diameter of 4 nm, and also crystalline patterns of the nanoparticles can be observed, Figure Lue-PEI6 + Pd(DMS) 2 Cl 2 + ab 4 Me RT Pd(0) Leu-Pd31 n Scheme Palladium nanoparticle assembly Leu-Pd31 5 nm Figure TEM image of Leu-PEI6 stabilized Pd nanoparticles Alkene ydrogenation: Reactivity and selectivity With the notion that one of the most common uses of Pd(0) catalysts in organic synthesis is the hydrogenation of double bonds, we set out to investigate the reactivity of our Pd nanoparticle system towards the hydrogenation of simple prochiral alkenes to yield chiral alkanes. Firstly, we examined the reactivity of the Leu-Pd31 system for the catalytic hydrogenation of simple unfunctionalized alkenes, Table 3.8. The system showed remarkable activity towards the hydrogenation of aromatic alkenes (styrene derivatives), with 100% selectivity towards styrene (entry 1) and 85% selectivity towards 1-phenyl-cyclohexene, partly due to a competing transfer hydrogenation reaction, which formed 1,1'-biphenyl (entry 61

62 2). For the non-aromatic alkene, 1-methyl-1-cyclohexane, the conversion was lower than observed in aromatic olefins, and the selectivity dropped due to hydration byproduct and isomerization of the double bond (entry 3). Table 3.8. ydrogenation of unfunctionalized alkenes catalyzed by Leu-Pd31 Conversions * Products identified * Substrate Conditions [%] [%] 1 4 atm 2, RT, 18 h 100 Ethylbenzene atm 2, RT, 18 h 100 enylcyclohexane 85 1,1 -Biphenyl atm 2, RT, 18 h 90 Methylcyclohexane - 30 isomers-methylcyclohexene Methylcyclohexanol - 4 Reaction conditions: Lue-Pd31 (0.5 ml), olefin (30 L), 4 atm 2, stirred at RT for 18 h; * Determined by GC- MS The next challenge was to find a prochiral unfunctionalized olefin for asymmetric hydrogenation that would both be readily hydrogenated with our system, and would allow relatively easy determination of enantioselectivity. As a model of such an alkene the unfunctionalized disubstituted olefin, 1-cyclopentyl-1-phenylethene, was chosen and tested for asymmetric hydrogenation under different conditions. The results are summarized in Table 3.9. In all cases, the hydrogenation of 1-cyclopentyl-1-phenylethene afforded high conversions, and 100% selectivity, even at C (entry 3). We could not find suitable methods for the determination of ee, either with chiral PLC or with chiral GC. evertheless, since the yields of the hydrogenation are high, and no byproducts are present, we could use polarimetric measurements on isolated product. In water we did not observed any optical rotation of the product (entry 1), probably since the catalytic system Leu-Pd31 is not water soluble. owever, when methanol was used as solvent a small but constant optical rotation was observed indicating that a preferred enantiomer is present in the product (entry 2). This was also confirmed by the control experiment (with no substrate), which proved that the chirality is not from the chiral framework of the nanoparticle system (entry 4). At C, however, no optical rotation was observed (entry 3). Since we do not have the specific rotation () of the pure enantiomer, we have not determined the degree of 62

63 enantioselectivity. Even though it seems that the degree of enantioselectivity is low, it is a very interesting and promising result especially for a disubstituted unfunctionalized alkene. The hydrogenation of the trisubstituted trans--methylstilbene was highly efficient and selective (entry 5) and also showed an enantiomeric excess by the specific optical rotation measured. Table 3.9. ydrogenation of 1-cyclopentyl-1-phenylethene catalyzed by Leu-Pd31. Conversion Selectivity bserved Substrate Conditions Solvent [%] [%] rotation Specific rotation * 1 3 atm 2, RT, 22 h water atm 2, RT, 24 h 3 atm 2, C, 62 h 3 atm 2, RT, 21 h o Substrate 3 atm 2, RT, 23 h Me Me Me Me (EtAc) (CCl 3 ) ** ** Reaction conditions: Lue-Pd31 (2 ml), olefin (25 L), 3 atm 2 ; for entry 5 - Lue-Pd31 (0.5 ml), olefin (20 mg), 3 atm 2, time and temp' are mentioned in the table; * [] D, 20 C, c ~ g/ml, solvent: EtAc (entries 1-4); ** [] D, 20 C, c ~ g/ml Additional disubstituted prochiral alkenes with no templating functional groups were synthesized according to a known procedure, Scheme The results of their hydrogenation are summarized in Table TFA, DCM 30 0 C 32 + TFA, DCM 30 0 C Scheme Disubstituted arylalkene synthesis 33 63

64 Table ydrogenation results of arylalkenes with the Pd-chiral PEI nanoparticle system. Conversion Selectivity Substrate Conditions Solvent [%] [%] 1 3 atm 2, RT, 5 days (3 atm 2, RT, 23 h) * Me (28) * 100 * atm 2, RT, 4 days Me Reaction conditions: entry 1 - Lue-Pd31 (4 ml), olefin (25 L), 3 atm 2 ; entry 2 - Lue-Pd31 (2 ml), olefin (30 mg), 3 atm 2 time and temp' are mentioned in the table; * In brackets: An old sample of chiral Pd nanoparticle system, Leu-PEI31 (~ 1 month old). The mesitylene arylalkene substrate afforded, with an old batch of chiral Pd nanoparticle system, 28% conversion upon hydrogenation and 100% selectivity (entry 1, in brackets). When a fresh batch of the Pd nanoparticle was used the conversion dropped to 4.6% over 5 days, without loss in selectivity (entry 1). That might suggest that there is an aging effect on the Pd nanoparticle system possibly connected to the size and distribution of the nanoparticles. With tetramethylbenzyl arylalkene the conversion dropped to 0.5% with 100% selectivity using the fresh batch of Pd nanoparticle system (entry 2). In all cases, it turned out that the system was much less reactive towards hydrogenation for these arylalkenes, probably due to the increased stability conjugated double bond with the aromatic system coupled with higher steric hindrance. Under these conditions of low conversions we could not determine the angle of rotation. Also, chiral separation was not successful using the chiral GC column. Different substrates are been examining that will afford high conversion and selectivity, and that could be resolved by means of chiral PLC or GC ydrogenation of prochiral imines with Pd nanoparticles stabilized by chiral polyethylenimine derivatives: Reactivity and selectivity The Pd nanoparticle system, Leu-Pd31, was examined for the hydrogenation of prochiral imines. indered imines derived from ketones are difficult to prepare and reported synthetic methods employ harsh conditions that include the use of strong Lewis acids 127 or strong dehydrating agents, dissolving the starting materials in benzene, toluene or xylene and refluxing the mixture for prolonged time (hours) with azeotropic removal of water through a 64

65 Dean-Stark apparatus. 127 hydrogenated with Leu-Pd31, Scheme evertheless, some prochiral imines were synthesized and F F F 2 F CF Et F F Et F CF 3 F Lue-PEI31 4 atm 2 Lue-PEI31 4 atm 2 o reaction (Pd deposits) C no ee 3 0 C no ee rt no ee Scheme Synthesis and hydrogenation of prochiral imines o hydrogenation occurred in the case of strong electron withdrawing groups on imine 34. Furthermore, it turned out that with imine 34 the system was not stable and the formation of Pd black was observed. Compound 35 was quantitatively hydrogenated to the corresponding amine 36. The reaction was conducted under several conditions: at room temperature (RT), 3 C and -20 C, and in all cases no enantiomeric excess was observed. Since there was no enantiomeric excess we examined the hydrogenation of chiral imines for the possibility of a diastereoselective reaction. R-(+)-methylbenzyl amine was reacted with acetophenone to afford imine 37 in a relative easy manner, Scheme The hydrogenation of 37 with Leu- Pd31 afforded amine 38 in 93% de (determined by non-chiral GC-MS) and around 60% yield with some decomposition of the imine to the starting materials. Direct reductive amination (DRA) to the corresponding amine 38 was successful using the Leu-PEI31 system at 3 atm hydrogen yielding 86% de with 20% conversions and 12% yield. Amine 38* was synthesized by the same direct reductive amination conditions as the above, using the corresponding S-(- )-methylbenzyl amine enantiomer, yielding 89% de, 16% conversion and 10% yield, Scheme R + Et Leu-PEI31 R 4 atm 2 Yield: 60% de: 93% S + DRA Leu-PEI31 3 atm 2 DRA Conversion: 20% Yield: 12% de: 86% 38* S Conversion: 16% Yield: 10% de: 89% Scheme Chiral imine synthesis, hydrogenation and DRA 65

66 Very low yields As it turns out, the separation conditions of amine 38 were very difficult to reproduce using our chiral PLC separation methods due to its high lipophilicity and afforded poor chiral resolution of only 58% de. Even the corresponding salts of amine 38 (d-mandelic acid and TFA) did not afford clear separations on either chiral PLC and GC methods or 1 -MR (for the mandelic acid salt). Several different chiral imines were synthesized (Scheme 3.17) in order to address this problem and introduce functional groups that might afford better resolution on PLC, but since the reactions were not selective and with low yield, and due to decomposition of the imines upon workup and purification, no good results were obtained by chiral PLC methods. 2 + Et, MS + 2 TiCl4, toluene Cl + 2 Et, MS Cl Cl + 2 S 3 to luen e, re flu x Cl X 2 + Et, MS + 2 S 3 tolue ne, reflux X Scheme Some examples of the synthesized imines Due to the difficult in the synthesis and the analysis of these hindered imines, we turned to the synthesis of more stable prochiral imines. It is known that 2'-hydroxy acetophenones form stable hindered imines, in high yields and simple workups. 130 We have prepared imines 39 and 40, from the corresponding 2'-hydroxy acetophenone and 2'-hydroxy propiophenone, respectively, Scheme RT, 1 d 39 Pd nano, 2 reduction X + 2 RT, 1 d Scheme Synthesis of 2-imidoylphenol and hydrogenation 40 Pd nano, 2 reduction X Unfortunately, these imines turned out to be too stable and did not hydrogenated with nanoparticle system Leu-PEI31 even when harsher conditions were employed. 131 ere too 66

67 the challenge was to find good separation methods on chiral PLC columns. Better hydrogenation conditions and additional reactions are now being explored. 67

68 3.5. Modified polyethylenimine for the solubilization and depolymerization of Cellulose Synthesis of PEI-phenylboronic acid polymers Three PEI-phenylboronic acid compounds were synthesized, in order to examine the effect of boronic acid coupled with PEI (branched form) on the solubility and hydrolysis of cellulose. The degree of phenylboronic acid substitution was relative to the number of primary amino groups present in branched form of PEI (25% of the total amines). The synthesis was designed to be a one pot reaction with two sequential steps, Scheme In first step dry branched PEI (M w ~ 60,000) was refluxed with 2-formylphenylboronic acid, 41, in Et forming the imine bond in a ratio determined in advance, followed by reduction of the imine groups using ab 4 at RT, affording the clean PEI-B() 2 in the desired ratio (after dialysis). The ratios were calculated and confirmed by 1 MR relative integration between the aromatic region of the phenyl boronic acid (~ ppm) and the methylene region of the polyethyleneimine framework ( ppm). We chose to use 10%, 50% and 100% phenylboronic acid substitution, and, in principle, any degree of substitution can be achieved applying this method. The benzylic amine moiety formed in the product was designed with the notion that it will act as an anchor to bind the cellulose, allowing close proximity to the phenylboronic acid for hydrolysis and to allow better binding to diols at neutral p (see introduction, section ). The p of the resulting polymeric product, in all cases, was above 10, and the solution was acidified to p = B 1. Et, reflux 2. ab 4 B m Branched PEI 41 m PEI-10%B() 2-10% boronic acid over 1 0 amines PEI-50%B() 2-50% boronic acid over 1 0 amines PEI-100%B() 2-100% boronic acid over 1 0 amines Scheme Synthesis of phenylboronic acid substituted PEI Cellulose Solubilization and Degradation with PEI-B() 2 Systems The PEI-B() 2 systems were first screened and examined for the solubility of microcrystalline cellulose in water under neutral p conditions. The results are summarized in Table The best results for solubilization of cellulose under these mild conditions were 68

69 achieved with PEI-50%B() 2 (entry 2). PEI-100%B() 2 turned out to be much less water soluble compared to the other systems, mainly due to the high aromatic content, and more water was needed to solubilize it (entry 3). In addition to the higher cellulose solubility observed by PEI-50%B() 2, it might perform better regarding cellulose hydrolysis on account of the increased amount of phenylboronic acid compared to PEI-10%B() 2 (entry 1). Furthermore, in all the cases no real difference was observed in using microcrystalline cellulose or the pretreated form prepared by a known literature procedure (see experimental). This is also with good agreement with what is known in the literature for an ethylenediamine solvent system. 132 Table Water solubility of cellulose with PEI-B()2 systems PEI Degree of Substitution [%] p a Temp. [ 0 C] Time PEI- B() 2 [mg] Water [ml] Cellulose [mg] Cellulose Recovered [mg] 1 PEI-10%B() days PEI-50%B() days PEI-100%B() days PEI-50%B() days b 67 Reaction conditions: PEI-B() 2 (100 mg), water (2-3 ml), 2 S 4 to p = 7, Cellulose microcrystalline (20 mg), stirred for 3 days at 100 C; entry 4 - PEI-50%B() 2 (500 mg), water (3 ml), 2 S 4 to p = 7, pretreated cellulose (100 mg), stirred at 150 C for 3 days in an autoclave; a Adjusted with 2 S 4 ; b Pretreated cellulose; In order to increase the solubility and hydrolytic potential of PEI-50%B() 2 we increased temperature to 150 C at p = 7 as before, using pretreated cellulose (entry 4). Under these conditions the cellulose solubilization capacity of 500 mg PEI-50%B() 2 is around 33 mg. The 1 MR of the solubilized cellulose (washed clean with Et) did not show free glucose, but was in good agreement with formation of oligosaccharide bound to the PEI- B() 2 framework as was observed in the regions of 7.4 ppm (aryl boronic acid region), ppm (benzylic amine region), ppm (cellulosic region and PEI region), and especially at ppm corresponding to the anomeric hydrogen atoms shifts (Figure 2.11b). This was also indicated by TLC, DS (Dinitrosalicilic acid) and glucose oxidase assays (using endo/exo cellulases and -glucosidase), Figure The DS test did not afford a clear brown solution that can be spectroscopically calibrated, but rather brown precipitates that confirmed only qualitatively that there are free reducing end of sugars that are probably attached to the polymer. The glucose oxidase assay did afford qualitative results. 69

70 B m 50% substituted over 1 o Figure a) left: 1 -MR of PEI-50%B() 2 in D 2 ; b) right: 1 -MR of the combined PEI- 50%B() 2 with cellulose in D 2 (entry 4, Table 2.11) control no enzymes test colored precipitation test control o enzymes blank standard test PEI- glucose cellulose (entry 4) 50%B()2 (not soluble) Figure a) left: DS test the control without hydrolytic enzymes; b) middle: Glucose oxidase assay control without hydrolytic enzyme, blank water. Calibrated on standard solution of glucose, = 540 nm; c) right: comparative TLC of the combined cellulose-pei-50%b() 2, free PEI-50%B() 2, glucose and cellulose (not soluble), R f = 0.32 (middle of circle), Me:DCM: 2 5:4.5:0.5 (respectively), developed with yellow spray (ammonium molibdate solution) Several attempts were made to separate the cellulose fragments from the PEI-B() 2 system using acidic and basic hydrolysis conditions, but with no success. It seems that the binding of the solubilized cellulose to the PEI-B() 2 is much too strong and probably is based on combinations of hydrogen bonding and some covalent bonding with the amines of the polymers (imine, aminal or hemiaminal). Using endo/exo celluloses and - glucosidaseenzyme cocktail (p = 5, 50 C) prior to the glucose oxidase assay we could quantify liberation of 3.6 mg of glucose out of the total ~ 33 mg of cellulose solubilized in the system. The rest of the oligosaccharide probably could not be hydrolyzed under these enzymatic conditions. Using only -glucosidase with our solubilized cellulose system also 70

71 gave a positive result in the DS assay indicating free sugars (free reductive end), which is a good indication to the presence of short length cellulose fragments in the system. This led us to examine PEI-50%B() 2 in combination with cellulose hydrolytic enzymes in order to liberate the oligosaccharide from PEI-B() 2 framework under enzymatic conditions. PEI-50%B() 2 was mixed with -glucosidase and endo/exo cellulases separately and tested on pretreated cellulose. The results are summarized in Table Table Combined PEI-50%B() 2 system with enzymes for cellulose hydrolysis. Combined System PEI-50%B() 2 + -Glucosidase PEI-50%B() 2 (o -Glucosidase) -Glucosidase, (o PEI- 50%B() 2 ) PEI-50%B()2 + Exo/Endo Celluloses Exo/Endo Celluloses, (o PEI-50%B() 2 ) Conditions p = 5 (Acetate buffer( 50 0 C, 72 h p = 5 (Acetate buffer( 50 0 C, 72 h p = 5 (Acetate buffer( 50 0 C, 68 h p = 5 (Acetate buffer( 50 0 C, 72 h p = 5 (Acetate buffer( 50 0 C, 72 h Cellulose * [mg] Cellulose Consumed [mg] Comments o Free glucose/oligosaccharide on MR o Free glucose/oligosaccharide on MR o Free glucose/oligosaccharide on MR Free glucose/cellubiose on MR Free glucose/cellubiose on Reaction conditions: ~ 143 mg PEI-50%B() 2, water (2 ml), 20 L solution of the corresponding enzymes, "ovozyme": -glucosidase Cat. o , endo/exo celluloses Cat. o , p Adjusted to p=5 by 2 S 4 and then acetate buffer, pretreated cellulose (200 mg), stirred at 50 C for 72h; * Pretreated cellulose MR Unfortunately, no free glucose or oligosaccharide was detected upon addition of - glucosidase (entry 1), but a favorable synergism was observed with this combined system in comparison to the controls regarding cellulose consumption (entries 2 and 3). owever, it seems that the PEI-50%B() 2 has a mild inhibiting effect on the endo/exo celluloses regarding cellulose consumption (entries 4 and 5). In order to examine the effect of the phenylboronic acid on the solubilization and hydrolysis of cellulose, we conducted a control experiment with normal branched PEI, Table From both the control experiment with PEI (entry 2) and PEI-50%B() 2 (entry 1), it appears that 71

72 the solubility of cellulose has much to do with the PEI itself rather than the presence of the phenylboronic acid. Thus we can conclude that the solubility of cellulose is based on the interactions (covalent or hydrogen bonds) with the free amines of the polymer. owever, the glucose oxidase assay shows conclusively that more glucose is liberated from the PEI- 50%B() 2 system than from PEI itself (entries 1 and 2). It seems that in the PEI- 50%B() 2 case the cellulose is solubilized into the system and fragmented to shorter oligosaccharides, and thus is more easily hydrolyzed by the hydrolytic enzymes, whereas in the PEI case the cellulose is mainly solubilized and bound to the polymer with no major fragmentation and thus less susceptible to enzymatic hydrolytic conditions. When both the PEI-50%B() 2 and the PEI were tested on free D-glucose (25 mg each), under the amounts and conditions above, no free glucose was detected, by TLC or MR. The glucose oxidase assay showed only 4% - 8% of the quantitative amounts of glucose initially solubilized in the systems. 1 2 PEI System PEI-50%B() mg PEI 60, mg Table PEI-50%B() 2 Vs. PEI cellulose consumption Conditions p = 7, C, 70 h, water p = 7, C, 72 h, water Cellulose * [mg] Cellulose Consumed [mg] Total amount of glucose (Glucose xidase Assay) [mg] Reaction conditions: polymer (500 mg), water (3 ml), 2 S 4 to p = 7, pretreated cellulose (100 mg), stirred at 150 C for h in an autoclave; * Pretreated cellulose The main problem of releasing the oligosaccharide from the polymeric system has not yet been solved, even using different hydrolytic conditions as mentioned above. It seems that it is too strongly bound to be released in a one pot reaction and an additional process is required. In previous studies conducted in this project we learned that the combination of PEI or PEI- 50%B() 2 with an acidic polyoxometalate produced an insoluble precipitate. We set out to examine if the acidic conditions of the polyoxometalate coupled with the ability to precipitate PEI can present a convenient method to release and separate the oligosaccharide from the PEI by means of simple filtration. The polyoxometalate chosen was polysilicotungstic acid, 4 SiW 12 40, and a solution of the PEI-50%B() 2 solubilized cellulose was added a solution of the corresponding polyoxometalate, keeping the p at the acidic range to prevent decomposition of the polyoxometalate. Several experiments have been conducted with no major success. evertheless, it seems that the quantity of the PEI in the system was reduced, 72

73 but not completely, and we are looking for better isolation conditions. Furthermore, different polymeric systems are also under consideration that will overcome the problem of multiple amine interactions in the system. 73

74 4. Discussion and summary In this research we have prepared chiral polyethylenimine derivatives that can be crosslinked and intercalate a variety of catalysts such as polyoxometalates, transition metal complexes, and catalytically active nanoparticles, for several of catalytic transformations. We also have developed a new synthetic method for the preparation of imine crosslinked polyethylenimine assemblies which allow us to enlarge the polyethylenimine-based polymer and in principle to introduce many options of new chiral copolymers. The variety of methods available to us now for the design and synthesis of chiral polyethylenimine derivatives have given us the flexibility to work and alter the polyethylenimine-based systems in various ways so different catalytic systems can be examined in different reaction media (aqueous, biphasic and organic). It is already known that peptides 133 and even amino acids themselves such as proline 134, can be used as organic catalyst for asymmetric catalysis. The main mechanism usually involves a defined configuration of the catalyst with the substrate using hydrogen bonding with the carbonyl and amine groups of the amino acids. evertheless, chemically speaking, peptides, especially short ones, are not stable and suspect to hydrolysis and degradation. Furthermore, the advantage of specificity (as in enzymes) is in many cases its drawback due to the inability to form a more general system to include a variety of substrates and transformations. This difficulty to predict a good catalyst for a substrate, without using the trial and error approach, is true for many asymmetric transformations, even though efforts are being made to overcome this difficulty. The chiral polyethylenimine approach, as presented in this research, in many ways address most of these challenges in great deal of success, in terms of chemical stability (amines are much more stable than amides, especially under hydrolytic conditions), diversity (the ability to use amines as functional groups for modifications) and other chemical and physical properties, such as solubility. It is predictable that the loss of the amide groups and hence orderly structures (as secondary and tertiary configurations) will express itself in the degrees of enantiospecificity, especially with amorphous systems such as the crosslinked polyethylenimine derivatives. owever, conceptually, wherever even low enantiomeric excess was present the potential for improvement and increasing the enantiomeric excess is valid, especially through further understanding of mechanism. 74

75 In this research we present a preliminary proof of concept demonstrating a general system that can be "suited" to a variety of achiral catalysts for a variety of transformations and induce stereoselectivity by non-covalent interactions. The building blocks of the chiral polyethylenimine-based framework were chosen to be the natural amino-acids L-leucine and L-phenylalanine, both possessing a non-functionalized lipophilic side residue, which meet two important criteria: (1) chemically inactive groups under the synthetic conditions of the CA polymerization, crosslinking methodology and reductive conditions (for the nanoparticles synthesis for example) which simplify the synthesis, and introduce weak bonding interactions (Van-der-Waals and -interactions in the case of phenylalanine side residue); (2) coincide with our synzyme approach of assembly in aqueous media as globules with hydrophilic surface and hydrophobic cores with chiral domains. erein we present and describe the achievements in building assemblies with chiral polyethylenimine-based frameworks for different catalytic entities and for asymmetric catalysis: 1. Design and synthesis of chiral crosslinked polyethylenimine derivatives based on an epichlorohydrin crosslinker that encapsulate achiral Mnsalen catalysts for asymmetric epoxidation of olefins in aqueous and biphasic systems. We were also able to show the general application of the crosslinking methodology to a totally different transformation using Ru(II) achiral oyori type of complexes for the asymmetric hydrogenation of acetophenone. 2. Imine crosslinked chiral PEIs (both the leucine and the phenylalanine based PEI) were successfully used in stabilizing Pd, Pt, Ru and Rh noble metal nanoparticles. ere we mainly focused on the Pd(0) nanoparticle/chiral polyethylenimine assembly for the hydrogenation of alkenes to alkanes and imines to amines Leu/e-Crosslinked systems: MnSalen and Ru(II) catalysts As we were driven by a bottom-up approach for the preparation of an enzyme mimic with a metal-based active site, our first step was to introduce hydrophilic hydroxyl groups to the lipophilic Leu-PEI6, in order to induce a globular like structure in aqueous solutions. This is thought to form lipophilic chiral cavities or sites in which the catalyst would be positioned. Indeed this structure was verified by cryo-tem imaging (Figure 3.5), but unfortunately, while the MnSalen catalyst under catalytic conditions was active towards epoxidation of 75

76 alkenes in the presence of Leu-PEI6, no enantioselectivity was observed. The working hypothesis for asymmetric induction is that there must be sufficient interaction between the chiral framework of the polymeric system and the catalyst. This turned out not to be the case with the system above by the simple mixture of the components, and was also evident by UV-vis spectrometry where no significant shifts in the absorption bands of the catalyst were observed. In order to achieve higher degree of interactions (or reduce the degrees of freedom) we confined the catalyst inside the system in a more rigid manner by the crosslinking methodology, which was used previously in Ronny eumann's group. 11 In this way four chiral crosslinked systems were designed and synthesized (and of course many more are optional), which afforded low enantiomeric excess in the epoxidation of 1,2- dihydronaphthalene, Table 3.2. There were only small differences between the crosslinked systems with the benzylic versus i-propyl side chain regarding enantiomeric excess, and crosslinked system Leu-CLS18, which gave the best results, both in conversions and enantioselectivity in aqueous phase, was chosen for further epoxidations. Epoxidation of additional substrates showed that under the same conditions with Leu-CLS18 the enantioselectivity (in brackets) increased in the following order: styrene (0) < trans-methylstyrene (7) < 1,2-dihydronaphthalene (8) < cis--methylstyrene (12) < -methyl-transstilbene (17), indicating that the more sterically inhibited alkenes yielded higher %ee. - methyl styrene did show very high reactivity (100% conversion) and selectivity (95%) towards epoxidation with the Leu-CLS18 system, but with total loss of enantioselectivity. The increased %ee seems to be inversely proportional to the total epoxide yield, or in other words, the less reactive the system toward a substrate the higher its enantioselectivity. Furthermore, it seems that the substitution on the double bond is essential in order to achieve enantiomeric excess, which was also observed in the different catalytic system of e- CLS19 under biphasic conditions with DCM. There styrene did not afford any ee but the - methyl styrene did afford around 7% ee, and 17% yields. The apparent low enantiomeric excess are reasonable relative to several other systems published in the literature, which report low to moderate enantioselectivities when trying to mimic weak or distant enantioinductive interactions on a catalyst. Some examples include the enantiopure dendritic polyoxometalates reported by Bonchio and late. affording low to moderate enantioselectivities (4-14% ee) in the oxidation of thioanisole to the corresponding sulfoxide, and various transformations with chiral ionic liquids to afford low to moderate enantiomeric excess, mostly between 1% to 40% ee

77 Constructs such as Leu-CLS18 containing 6.8 wt% MnSalen (by ICP-MS) are not freely soluble in water, but form a rather well dispersed hydrogel especially if gently heated to C and then cooled. This was expected due to their crosslinked nature as was reported previously for another epichlorohydrin crosslinked polyethylenimine construct. 11 The addition of a water soluble co-solvent, such as TF does yield a clear solution that enabled better measurements of circular dichroism (CD) spectrum of Leu-CLS18 compared to water. Since the Leu-CLS18 polymeric organic framework does not absorb above 230 nm, the CD spectrum at longer wavelengths ( > 230 nm) can only be attributed to the interaction of MnSalen with the chiral environment of the crosslinked Leu-PEI framework. Indeed the strong Cotton effects at 260 and 330 nm clearly coincide with the absorption maximum of the MnSalen moiety (Figures 3.6 and 3.7), as can be seen very well for the 10% and 20% TF/water solution, Figure 3.6. Furthermore, the UV spectra show small shifts of the MnSalen complex in Leu-CLS18 in different solvents. These results are in good agreement with a catalyst encapsulated in a chiral environment induced by the polymeric framework. Chiral induction and interactions with the catalyst was also observed for e-cls19, Figure 3.9. An asymmetric induction of the chiral polyethyleneimine environment unto an achiral MnSalen catalyst was clearly observed, however, the absolute %ee obtained in the reactions was low despite what may have been expected from the interaction of the achiral catalyst with the chiral framework observed in the CD spectrum. In order to further understand the effect of the chiral polyethyleneimine scaffold on the degree of enantioselectivity obtained in the epoxidation reaction, the R,R- and S,S-Jacobsen s catalysts were incorporated into the Leu-PEI crosslinked framework (RRMnSalen-Leu24 and SSMnSalen-Leu25) and into an achiral cross-linked polyethylenimine framework using linear PEI to yield RRMnSalen26 and SSMnSalen27. Interestingly, we found that chiral Jacobsen catalysts embedded within achiral cross-linked polyethylenimine yielded epoxide products with only low enantioselectivity (4% ee), which was relatively similar to the enantioselectivity observed for achiral MnSalen within crosslinked Leu-CLS18 (8% ee) showing that the Jacobsen catalysts are surprisingly ineffective as embedded catalysts in these aqueous biphasic media. owever, when RRMnSalen was embedded within the Leu-PEI crosslinked framework, RRMnSalen- Leu24, there was a synergistic effect between the chiral catalyst and the chiral environment and 41% ee of the (1R,2S+) epoxide was obtained. n the other hand when SSMnSalen- Leu-25 was used a lower 27% ee of the opposite (1S,2R-) enantiomer was obtained. From 77

78 here was concluded that the handedness of the Jacobsen catalyst determines the enantiomer formed and the chiral cross-linked polyethylenimine very significantly increased the enantiomeric excesses relative to those obtained in achiral cross-linked polyethylenimine. In principle, the approach of the crosslinked systems should be general enough to incorporate different catalysts for different transformations. In order to examine this possibility we turned to the achiral Ru(II) oyori type catalyst. We have prepared, using the same synthetic methodology as in the MnSalen crosslinked systems, three types of Ru crosslinked systems (e-pei28, e-pei29 and Leu-PEI30). These systems did show enantioselectivity upon hydrogenation of acetophenone under basic conditions with a variety of solvents (IPA and water) and also under dry conditions (no solvent). The major difficulty was the low reactivity of the RuCLS in aqueous and dry conditions, which was found to arise from the inherent lack of activity of the free Ru catalysts under the corresponding catalytic conditions (4-12 T). evertheless, the RuCLS did seem to be more active in organic solvent (IPA) and afford higher yields, but with a decrease in enantiomeric excess. ere once again, the inverse relation between reactivity and enantioselectivity is observed. Efforts to increase the reactivity of the RuCLS were made by oxygen exclusion from the reaction prior to the hydrogenation. owever, degasing and pretreatment activation of the encapsulated catalyst under basic hydrogenation conditions, did not improve by much the reactivity (from 12 to 18 T for e-pei29). Even though the Ru crosslinked systems appear to be not reactive towards the hydrogenation of acetophenone, we were able to show enantioselective induction (up to 17% ee with e-pei28) and gain general insights on the reactivity of the systems. Different ketones need to be considered along with different compounds like imines, which could be promising candidates for these Ru crosslinked systems. Several conclusions can be drawn from this research on the catalyst encapsulated (embedded) crosslinked systems: (1) Easy to synthesize cross-linked chiral polyethyleneimines can be used as a convenient aqueous biphasic reaction media for inducing enantioselectivity with an achiral catalyst. The method is a general one, and therefore, one can consider a multitude of catalysts and transformations that may be applicable. The present MnSalen crosslinked system showed a close interaction between the achiral catalysts and the cross-linked chiral polyethylenimine framework, but elicited only low %ee in a benchmark epoxidation reaction; others may be more effective. (2) The significant synergistic effect obtained when using a chiral catalyst and a cross-linked chiral polyethylenimine has the potential for increasing 78

79 enantioselectivities obtained in transformations with well-known chiral catalysts, provided they work well in these media, without the need for extensive and work-intensive ligand synthesis and optimization Pd(0) nanoparticle stabilized by chiral crosslinked polyethylenimine derivatives for asymmetric hydrogenations There are several significant advantages in using heterogeneous hydrogenation catalysts. 81 Most of them are safe and easy to handle and can be readily separated from the reaction mixture by simple filtration, allowing convenient work-up and isolation of the desired product. A stable nanoparticle system event though one might not regard it as a classical heterogeneous system, does possess the apparent important advantages of heterogeneous system. The imine crosslinked chiral polyethylenimine derivatives (both the leucine and the phenylalanine based compounds) was successfully used to stabilize various noble metal nanoparticles (Pd, Pt, Ru and Rh) using the same methodology with ab 4, for the asymmetric hydrogenation of a variety of substrates, such as ketones (acetophenone), functionalized ketones (ethyl pyruvate), etc. ere we mainly focused on the Pd(0) nanoparticle/chiral polyethylenimine-based systems for the hydrogenation of alkenes to alkanes and imines to amines Alkene hydrogenation catalyzed by Pd(0) nanoparticles stabilized by chiral crosslinked polyethylenimine derivatives As was mentioned in the introduction (section 1.5.2), asymmetric hydrogenation of alkene is one of the most useful reactions in the synthesis of optically active compounds. This has giving us a great motivation trying our system towards asymmetric hydrogenation on unfunctionalized prochiral alkenes. Based on our experience we know that Lue-PEI31 has high reactivity and selectivity towards the hydrogenation of alkenes especially aromatic alkenes such as styrene derivatives, coupled with the inherent advantages of using a heterogeneous nanoparticle system. The system showed remarkable reactivity towards the hydrogenation of 1-cyclopentyl-1-phenylethene under moderate conditions in Me with high reactivity (97% conversions) and selectivity (100%), but because of the high lipophilic nature of the product and the lack of any functional group, chiral resolution was not possible using either PLC or GC methods. Since the reaction yielded a very clean single product (by GC-MS), polarimetery measurements were possible, and indeed a small but constant specific rotation of +0.8 was observed (Table 3.9, entry 2). Since we do not have the literature data 79

80 for the specific rotation of the pure enantiomer, we could not determine the ee. Even though the rotation seems small it is definitely an important result as enantioselective hydrogenation of a non-functional alkene in the absence of template binding is difficult. Solvent had a major effect on the steroselectivity of the system, and in water, even though the system exhibited the same reactivity and selectivity as in Me, there enantioselectivity observed. Additionally, the way the polymer interacts and arranges around the nanoparticles may have an impact on the enantioselectivity, which probably has something to do with the surprising loss of enantioselectivity in Me at -20 C (Table 3.6, entry 3). Size and shape of the nanoparticles themselves also need to be considered, as it may change the reactivity as well. Very importantly, the control experiment was conclusive enough to show that the chirality observed did not arise from the polymeric stabilizing framework. Unfortunately the system seems to be less active on the more promising arylalkene, probably, as was mentioned before, due to the increased stability conjugated double bond with the aromatic system coupled with higher steric hindrance. evertheless, the Lue-PEI31 system showed remarkable reactivity (100% conversion) and selectivity (100%) towards the hydrogenation of the trisubstituted olefin, trans--methylstilbene yielding a specific rotation of in CCl 3 (Table 3.9, entry 5) Imine hydrogenation with chiral Pd(0) nanoparticles system Reduction of imines is one of the most fundamental reactions in organic chemistry because of 135, 136 their versatility as intermediates for synthesis of pharmaceuticals and agrochemicals. There is a constant interest for more efficient and practical methods. The classic and conventional reagents for this kind of transformation are ab 4 and its derivatives (ab 3 C, ab(ac) 3, etc.). owever, in some cases, such as using TF and toluene as solvents, these reagents are less effective due to solubility problems. Most of the imine reduction reactions are homogeneous, but there is some literature on heterogeneous imine hydrogenation using Pd/C. 81, 137 Since there is almost no record of asymmetric heterogeneous imine hydrogenation in the literature (most of them deal with immobilization of homogeneous catalysts) 81 we turned to test the option of using our chiral PEI to stabilize Pd nanoparticles system, Lue-PEI31, for the asymmetric hydrogenation of prochiral imines. This project turned to be the most challenging regarding substrate preparation and product analysis. The Pd nanoparticle system turned out to have high reactivity towards highly lipophilic and non-functionalized imines but was totally unreactive toward imines with strong electron withdrawing groups (in which the system itself was not stable and Pd deposits were 80

81 observed. This has left us with very problematic highly lipophilic compounds such as 35 and 37 and there corresponding lipophilic product 36 and 38 (respectively), Schemes 3.15 and Even though no ee was observed for amine 36, we did get one very encouraging result of de (58%) upon the hydrogenation of chiral imine 37 to the corresponding amine 38. Even though chiral PLC resolution was not sufficient, we did manage to find the correct separation conditions for the diastereomers of amine 38, on a non-chiral GC column, yielding 93% de. Thus we could advance and explore direct reductive amination (DRA) reactions with Leu-PEI31 system, yielding amine 38 and its corresponding enantiomer amine 38* with 86% and 89% de (respectively), Scheme We are now encouraged to continue and find different analogs of such amines for asymmetric direct reductive amination. Several conclusions could be made regarding the Pd nanoparticle/iminepei system, Leu- PEI31: (1) imine crosslinked polyethylenimine derivatives have been able to stabilize a variety of metal nanoparticle for catalysis. (2) Pd nanoparticle system has shown a remarkable reactivity towards hydrogenations of aromatic styrene derivatives with promising enantio-resolution considering the nature of these unfunctionalized alkenes. (3) It has shown a promising result in the diastereoselective hydrogenation of imine, which yet needs to be expanded to additional substrates and reactions. The results shown regarding the nanoparticle system indicate a promising, easy to synthetized and stable system for the asymmetric hydrogenations of a variety of different substrates PEI-boronic acid polymers for the solubilization and degradation of cellulose Even though this project is not a direct continuation of the previous ones, and does not involve asymmetric catalysis, it does utilize two of the very important properties of PEI: water solubility and the ability to be chemically modified as was in the case of chiral polyethylenimine derivatives. We have developed a highly efficient, simple and convenient method for the synthesis of highly water soluble boronic acid substituted, commercially available, branched PEI (60,000). The motivation to solubilize and hydrolyze cellulose in water under mild conditions for a variety of transformation and formation of simple sugars, such as glucose, is very high. This is mostly due to the fact that cellulose is highly water insoluble, and in fact solubilized mostly in costly solvents such as ionic liquids, or hydrolyzed non-selectively to sugars in very strong acids (see introduction section 1.8.1). Three types of modified PEIs were synthesized with different amounts of a phenylboronic acid moiety (PEI-10%B() 2, PEI-50%B() 2 and PEI-100%B() 2 ), as was 81

82 calculated and determined by the degree of substitution on the primary amines in branched PEI (25% of the amines). In all of the cases the PEI-B() 2 showed consumption of cellulose under mild conditions (p = 7, 100 C), however PEI-50% B() 2 was the most potent and was chosen for additional work. At higher temperature (150 C) PEI- 50%B() 2 showed a remarkable consumption of 33 mg (out of 100 mg) of cellulose. This was also confirmed by MR and TLC, to what seems to be oligosaccharide bound to the PEI-B() 2 framework, indicating that cellulose was not only solubilized in the system by "simple binding" but also cleaved to form oligosaccharides. owever, no free sugars were observed by either MR or TLC. This was also confirmed by the DS and glucose oxidase (Gx) assays, but when hydrolytic enzymes were applied on the PEI-50%B() 2 /cellulose solubilized system both DS and Gx assays were positive. The DS test gave only qualitative results due to precipitation formation, but quantification was possible with Gx assay to afford 3.6 mg of glucose. We do not know if the Gx assay is the best choice for this system, in the aspect of chemical compatibility between the different components in the assay and the polymeric system, but it did produce a positive result compared to the control, and no major incompatibilities, such as precipitation or color differences, were observed. o doubt that the interactions of the system with enzymes are complex and difficult to predict. These interactions were observed by different experiments conducted with the PEI-50%B() 2 system, where a favorable synergism was observed, regarding cellulose consumption, with - glucosidase, but a mild inhibiting effect with the exo/endo cellulases, Table Mechanistic insight on the system was gained from the control experiment with the nonmodified branched PEI (60,000), indicating that the PEI part in the PEI-50%B() 2 system is mostly responsible for the solubilization of cellulose, involving strong interaction probably based on considerable hydrogen bonding coupled with covalent bonding forming aminal, hemiaminal, and so forth whereas the phenylboronic moieties are probably responsible for the cleaving of cellulose to form shorter oligosaccharides. arsh hydrolytic conditions (acidic, basic, the use of acidic PM for precipitation and separation) were applied in order to liberate the bound sugars with little or no success. It seems that the large percentage of amines in the polymeric system is the major problem, with what otherwise looks as a working cleaving system of cellulose. This challenge in now being addressed in different ways. Several conclusions can be drawn from this project: (1) we have managed to develop an easy general method for the synthesis of a variety of water soluble phenylboronic acid modified 82

83 PEIs. (2) The system is effective in solubilizing and cleaving cellulose under mild aqueous conditions (150 C, p = 7). (3) The PEI framework is not suitable for the liberation of the fragmented cellulose in one simple step process Summary of goals Modified polyethyleneimines can exhibit variety of properties. In this we demonstrated the ability to impart chirality and stereoselectivity on achiral organo metallic catalysts and active nanoparticles for several transformations using chiral analogs of polyethyleneimine. We have presented a simple and versatile method for the synthesis of such chiral polyethyleneimine analogs based on the amino acids L-leucine and L-phenylalanine, coupled with a new imine crosslinking methodology that enables enlargement of the polymers. Crosslinked structures were synthesized encapsulating achiral organometallic catalysts for the asymmetric epoxidation of alkenes and hydrogenation of acetophenone under biphasic aqueous conditions. anoparticle systems were stabilized by the imine enlarge chiral polyethyleneimines affording stereoselective hydrogenation of alkenes and imines. Furthermore, phenylboronic acid modified polyethyleneimines exhibited depolymerization of cellulose to shorter oligosaccharides in water under mild conditions and neutral p, providing a big step forward in utilizing cellulose as a source of fuel and materials. 83

84 5. Experimental Synthesis and catalysis The numbering of compounds is as presented as in the result and discussion sections. The numbering on the chemical structure is for spectral analysis only, and is based on chemical analysis and predictions. The ICP-MS (Mn) results were varied and may change between measurements, and in some cases could not be determined accurately. General procedure for amino acid based CA: L-amino acid (30.5 mmol) and charcoal (80 mg) were predried under vacuum, and were added to flame dried tri--necked flask under argon. TF (80 ml) was added, followed by trichloromethyl chloroformate (23 mmol). The reaction mixture was stirred at ~ 55 C for 1.5 h under argon. After cooling to RT, the reaction mixture was filtered through a bed of silica on top of celite, and the silica/celite was washed with Et 2 (400 ml). The filtrate was dried over a 2 S 4 and evaporated to dryness (S)-4-isobutyloxazolidine-2,5-dione, (L-Leu-CA), 1: Crystallization from Et 2 :exane afforded white crystals (4.6 g, 96% yield). 1 -MR (250 Mz, CDCl 3 ): ppm 7.30 (bs, 1, ), 4.36 (bs, 1, -1), 1.79 (bm, 3, ), 0.98 (s, 6, -4). 13 C-MR (250 Mz, CDCl 3 ): ppm (1C, -5), (1C, C-6), (1C, C-1), (1C, C-2), (1C, C-3), (2C, C-4). MS-ES(-): [M] calc. = ; found [M-1] = (S)-4-benzyloxazolidine-2,5-dione, (L-phe-CA), 7: White solid (5.84 g, quantitative yield). The product was used without further purification. 1 -MR (300 Mz, CDCl 3 ): ppm (5, Ar), 4.54 (bs, 1, -1), (bdd, 2, -4). 13 C-MR (300 Mz, CDCl 3 ): ppm (1C, C-2 (, )1C, C-3 (, (5C, Ar(, )1C, C-1 (, )1C, C-4). MS-ES(-): [M] calc. = ; found [M-1] =

85 General procedure for methylcyanide-l-polyamino-acids (compounds 2 and 8): To a solution of L-amino acid-ca, (6 mmol) in TF (2 ml/1mmol), under argon, was added a solution of aminoacetonitrile (1 mmol) in TF (5 ml/1 mmol). The mixture was stirred at RT for 3.5 days.the suspension was vacuum filtered, washed with TF and dried. C 2 Cyanomethyl amine-l-polyleucine 2, (Methylcyanide-L-polyleucine) (average 4-8 units of Leu): Cream color solid (88% yield by weight). MALDI-TF (major peaks): [6 units of Leu, M] calc. = , found [M + a + ] = , [5 units of Leu + a + ] = , [4 units of Leu + a + ] = C 2 Cyanomethyl amine-l-polyphenylalanine 8, (Methylcyanide-L-polyphenylalanine) (average 5 units of e): Pale-brown insoluble solid (quntitative yields by weight). MALDI- TF: [5 units of e, M] calc. = , found [M + + ] = , [M - 40 (cyanomethyl fragment)] ~ , [6 units of e, M] calc. = , found [M - 40 (cyanomethyl fragment)] ~ , found [M - 40 (cyanomethyl fragment) + a + ] ~ Leu-PEI3, (Ethylamine-L-Leu-PEI): Methylcyanide-L-polyleucine, 2 (7 g, 9.5 mmol, calc. for 6 units of Leu) was dissolved in 1M B 3. TF solution (293 ml, 293 mmol), under argon. The mixture was stirred under gentle reflux and flow of argon for 3 days. The solution was cooled to RT and reduced under vacuum. The residue was dissolved in Me (180 ml) and refluxed for 4 h. After the solution was cooled to RT the solvent was evaporated. The oily residue was dissolved in DCM and 2M K (aq.) under vigorous stirring over 20 min. The organic phase was separated and the aqueous phase was extracted with DCM (X3). The

86 organic phases were combined, washed with brine (X2), dried over a 2 S 4 and evaporated. The oily residue was suspended/dissolved in dry EtAc (30 ml), added to a freshly prepared dry solution of 4 Cl/EtAc (100 ml, see procedure below) and stirred at RT for 4 h. The solvent was evaporated and the powder was mixed with DCM/Et 2 and precipitated overnight in the fridge. The precipitate was filtered under vacuum and washed with Et 2 and dried. The powder was stirred in DCM/2M K (aq.) for 4 h. The organic phase was separated and the aqueous phase was extracted with DCM (X2). The organic phases were combined, washed with brine (X1), dried over a 2 S 4 and evaporated to afford clear sticky oil (5.4 g). 1 -MR (400 Mz, CDCl 3 ): ppm (bm, ), (bm, ), (bm, ), (bs, ). 13 C-MR )400 Mz, CDCl 3 (: ppm (C-4 + C-8), (C-1 + C-2 + C-3 + C-12), C-6 + C-7 + C-10 + C-11). MS- ES(+): [4 units of reduced Leu, M] calc. = , found [M + +, 46%] = , [5 units of reduced Leu, M] calc. = , found ]M + +, 100%] = , [6 units of reduced Leu, M] calc. = , found ] M + +, 86%] = , [7 units of reduced Leu, M] calc. = , found [M + +, 44%] = , [7 units of reduced e, M] calc. = , found [M + +, 40%] = e-pei9, (Ethylamine-L-e-PEI): Methylcyanide-L-polyphenylalanine. 8 (4 g, 4.26 mmol, calc. for 6 units of e) was dissolved in 1M B. 3 TF solution (133 ml, 133 mmol), under argon. The mixture was stirred under gentle reflux and flow of argon for 3 days. The solution was cooled to RT and reduced under vacuum. The residue was dissolved in Me (72 ml) and refluxed for 4 h. After the solution was cooled to RT the solvent was evaporated.the residue was dissolved in DCM and the precipitate was separated from the solvent by centrifuge. The DCM phase was washed with brine (X2), dried over a 2 S 4 and evaporated to afford brown oil (4.6 g). Further purification was done by dissolving the oil in 1,4-dioxane (5 ml) and adding a freshly prepared dry solution of 4 Cl/EtAc (40 ml, see procedure below). The mixture was stirred for 30 min at RT and the solvent was evaporated to dryness. The solid residue was washed with Et 2 (X2) and dried in vacuum. The white solid obtained was dissolved in DCM/2M K (aq.) mixture and stirred for 15 min. The 86

87 organic phase was separated and the aqueous phase was extracted with DCM (X2). The organic phases were combined and washed with water and brine (X1), dried over a 2 S 4 and evaporated. Further basifying was obtained by dissolving the product in DCM (50 ml) and stirring with K 2 C 3 at RT for 3 days, centrifuge, filtering and drying. The residue was again dissolved in DCM and washed with brine until no emulsion appeared in the organic phase. The organic phase was dried over a 2 S 4 and evaporated to afford brown sticky oil as the product (2.8 g). 1 -MR (500 Mz, CDCl 3 ): ppm (bm, Ar), (bm, ). 13 C-MR )500 Mz, CDCl 3 (: ppm (Ar(, (C-4 + C-7), (C-1 + C-2 + C-3 + C-5 + C-6 + C-8). MS-ES(+): [3 units of reduced e, M] calc. = , found [M + +, 8%] = , [4 units of reduced e, M] calc. = , found ]M + +, 44%] = , [5 units of reduced e, M] calc. = , found ] M + +, 100%] = , [6 units of reduced e, M] calc. = , found [M + +, 44%] = , [7 units of reduced e, M] calc. = , found [M + +, 25%] = Cl/EtAc dry solution (100 ml): Into 250 ml dry flask equipped with drying tube (CaCl 2 ) were added dry EtAc (20 ml) and dry Et (23.5 ml). The solution was cooled in an ice-water bath and acetyl chloride (28.5 ml) was added gently dropwise. After the reaction ceased (no vigorous Cl release) EtAc (28 ml) was added and the mixture was allowed to warm to RT and stirred for additional 30 min. General Procedure: PEI-imine polymerization (compounds Leu-PEI5 and e-pei10). A. Imine bond formation. In a flame dried reflux system under argon, ethylamine-l-amino-acid-pei (1 mol. Eq, calculated for the average repeating units of the amino acid distribution in the PEI) was dissolved in dry Et (~66 ml/1 mmol) and trimethyl-ortho-formate (7% Vol). Terephthalaldehyde (1 eq) was added and the reaction brought to reflux for 7 h. the reaction was cooled, evaporated and dried. 87

88 Leu-PEI5, (Imine polymerized Ethylamine-L-Leu-PEI): Glass like yellow solid. Used without further purification for the next step. 1 -MR (400 Mz, CDCl 3 ): ppm (m, ), (m, Ar), (small m, ), (bm), (bm), 0.9 (s, ). 13 C-MR )400 Mz, CDCl 3 (: ppm (C-1 + C-2 + C C-16), (Ar), (multiple broad peaks, C-3 + C-4 + C-5 + C-6 + C-7 + C-8 + C-9 + C-10 + C-11 + C-12 + C C-14) n e-pei10, (Imine polymerized Ethylamine-L-e-PEI): Brown-orange sticky oil. Used without further purification for the next step. 1 -MR (300 Mz, CDCl 3 ): ppm (m, ), (bm, Ar), (bm, ), (bm, ). 13 C-MR )300 Mz, CDCl 3 (: ppm (C-1 + C-2 + C-11 + C-12), (=C-C Ar-quaternary ), (Ar), (multiple broad peaks) n Procedures: PEI-imine polymerization (compounds Leu-PEI6 and e-pei11). B. Imine bond reduction Leu-PEI6, (Reduce polymerized Ethylamine-L-Leu-PEI): To a cooled solution (ice-water bath) of Imine polymerized Ethylamine-L-Leu-PEI, Leu-PEI5 (2.17 g, 1.44 mmol, calc. for M.W ) in dry Et (80 ml) was added ab 4 (435.9 mg, 11.5 mmol) under argon. The reaction was allowed to warm to RT over 1 h and stirred for 2-3 days. The solvent was evaporated and the residue dissolved in CCl 3 /a (aq.) (3.5 g/20 ml water). The organic phase was separated and the aqueous phase was extracted with CCl 3 (X2). The organic n

89 phases were combined, washed with brine (X2), dried over a 2 S 4 and evaporated. The solids were dissolved in dry EtAc (20 ml), treated with freshly prepared solution of 4 Cl/EtAc (see procedure above) and stirred for 1.5 h. The solvent was decanted, the solid washed with Et 2 (X2) and dried. The residue was dissolved in 2M K (aq.) /DCM and stirred for 4 h. The organic phase was separated and the aqueous phase extracted with DCM (X2). The organic phases were combined and washed with brine (X1), dried over a 2 S 4, evaporated and dried to afford a yellow solid (~ 2 g). 1 -MR (300 Mz, CDCl 3 ): ppm 7.30 (bs, Ar), (bm, ), (bm, ), (bs, ), (two bs, ), 0.89 (bs, ). 13 C-MR )400 Mz, CDCl 3 (: ppm (quaternary Ar), (C-2 + C-3 + C-4 + C-5 + C-6 + C-10 + C-11+ C-15), (C-7 + C-12), (C-8 + C-9 + C-13 + C-14). C Elemental Analysis. calc. [for structure Leu-PEI6] = C, 72.75%;, 11.53%;, 15.71%; found = C, 71.48%;, 11.64%;, 13.02% e-pei11, (Reduce polymerized Ethylamine-L-e-PEI): To a cooled solution (icewater bath) of Imine polymerized Ethylamine-L-e-PEI, e-pei10 (1.7 g, 1.03 mmol, calc. for M.W ) in dry Et (100 ml) was added ab 4 (312.6 mg, 8.26 mmol) under argon. After 15 min the reaction was allowed to warm to RT and stirred for 3 days. The solvent was decanted and evaporated. The residue dissolved in DCM/K (aq.) (5 g/20 ml water). The organic phase was separated and the aqueous phase was extracted with DCM (X2). The organic phases were combined, washed with brine (X1), dried over a 2 S 4, evaporated and dried to afford the product as yellow solid (890 mg). 1 -MR (300 Mz, CDCl 3 ): ppm (bm, Ar), (bm, ), (bm, ). 13 C-MR )300 Mz, CDCl 3 (: ppm (quaternary Ar), (Ar), (m, C-1 + C-2 + C-3 + C-4 + C-5 + C-6 + C-7 + C-8 + C-9 + C-10 + C-11 + C-12) n 89

90 n Leu-PEI16, (ydroxylated reduce polymerized Ethylamine-L-Leu-PEI): To a solution of reduce polymerized Ethylamine-L-Leu-PEI, Leu-PEI6, (52 mg, mmol, calc. for M.W ) in dry Et (5 ml) under argon were added bromoethanol (390 L, 5.5 mmol) and a 2 C 3 (2.95 g). The mixture was refluxed for 20 h, cooled to RT and the solvent was separated by centrifugation and evaporated. The residue was dissolved in DCM filtered and evaporated to afford yellow glassy oil. 1 -MR (400 Mz, CDCl 3 ): ppm 7.26 (bs, Ar), (bm, ), (bs, ), (bm, ), 0.90 (bs, ). 13 C-MR )400 Mz, CDCl 3 (: ppm (Ar), (C-18 + C-19), (C-1 + C-2 + C-3 + C-4 + C-5 + C-6 + C-7 + C-10 + C-11 + C-12 + C-15 + C-16 + C-17 + C-19), (C-8 + C-9 + C-13 + C-14). C Elemental Analysis. calc. [for structure Leu- PEI16] = C, 66.73%;, 10.75%;, 10.52%; found = C, 65.45%;, 10.73%;, 10.35% Salen 12, (2,2'-(1E,1'E)-(ethane-1,2-diylbis(azan-1-yl-1-ylidene))bis(methan-1-yl-1- ylidene)diphenol): To a solution of ethylene diamine (175 ml, 2.62 mmol) and trimethyl orthoformate )1.5 ml) in dry Et (20 ml), under argon, was added salicylaldehyde (559 ml, 5.24 mmol). The mixture was refluxed for 4 h and then cooled to RT for crystallization, and then in the fridge.the solids were separated by vacuum filtration and rinsed with cold ether to afford a yellow solid as the product (500 mg, 71% yield). 1 -MR (250 Mz, Acetone-d 6 ): ppm 8.54 (s, 2, -7), 7.33)dd, J = 26.76, 1.75 z, 2, -5 (, )m, 2, -3), 6.88 )m, 4, (, 3.98 )s, 4, -8). 13 C-MR )250 Mz, Acetoned 6 ): ppm (2C, C-7), (2C, C-1), (4C, C-3 + C-5), (2C, C-6), (4C, C-2 + C-4), (2C, C-8). MS-ES(+): [M[ calc. = , found ]M + + ] = , [M + a + ] = , [M + K + ] =

91 General procedure for Mn(III)Salen complexes (compounds MnSalen13 and MnSalen15): Salen ligand (1 eq) was dissolved in Et under reflux open to air. Mn(Ac) (2.5 eq) was added in one portion. The mixture was refluxed for 3 h, then LiCl (3 eq) was added, and the mixture was refluxed for additional 2 h. The mixture was cooled to RT and put in ice. The precipitation was filtered under vacuum and dried. Mn Cl MnSalen13, Salen 14, (6,6'-((1E,1'E)-(ethane-1,2-diylbis(azanylylidene))bis(methanylylidene)) bis(2,4-di-tert-butylphenol): To a refluxed solution of ethylene diamine (0.43 ml, 6.4 mmol) in dry Et (34 ml), under argon, was added dropwise a solution of di-tert-butyl-2- hydroxy benzaldehyde (3 g, 12.8 mmol, in 14 ml Et). The reaction was refluxed for 2 h, cooled and refrigerated. The precipitation was filtered and dried to afford the product as a yellow solid (2.9 g, 92% yield). 1 -MR (300 Mz, CDCl 3 ): ppm 8.41(s, 2, -7), (d, 4, J = 2.4 z, ), 3.93 (s, 4, -8), (two s, , ). 13 C MR (300 Mz, CDCl 3 ): ppm (2C, C-7), (2C, C-1), (4C, C-2 + C-4), (4C, C-3 + C-5), (2C, C-6), (2C, C-8), (4C, C-9 + C-11), (12C, C-10 + C-12). MS-ES(+): [M[ calc. = , found ]M + + ] = , [M + a + ] = (2,2'-(1E,1'E)-(ethane-1,2-diylbis(azan-1-yl-1-ylidene))bis(methan-1-yl-1- ylidene)diphenol Mn(III) chloride): The solids were rinsed with small amount of cold Et and dried in high vacuum to afford the product as brown solid (79% yield). MS-ES(+): [M] clac. = , found [M] = Mn Cl MnSalen15, 6,6'-((1E,1'E)-(ethane-1,2-diylbis(azanylylidene))bis(methanylylidene))bis (2,4-di-tert-butylphenol) Mn(III) chloride: Light brownish solid (30% yield). MS-ES(+): [M] clac. = , found [M - Cl] =

92 Cl Cl 3,3'-(2-hydroxyethylazanediyl)bis(1-chloropropan-2-ol), 17: Epichlorohydrin (2 ml, mmol) was dissolved in TF (30 ml), and to the solution was added ethanolamine (0.77 ml, mmol). The solution was stirred at RT for 15 min and then refluxed for 2 h. the solvent was allowed to cool, evaporated and dried in high vacuum to afford the product as pink-orange oil (2.12 g, 67% yield). The product was used without further purification. MS- ES(+): [M] calc. = , found [M] = , [M + a + ] = , [M + aminoethanol adduct] = , [M - C 2 C()C 2 Cl] = , [M - C 2 C()C 2 Cl + a + ] = amino-3-phenylpropan-1-ol, 22: A reflux system under argon was charged with ab 4 (2.75 g, mmol) and dry TF (140 ml). L-phenylalanine (5 g, mmol) was added and the mixture was cooled in an ice bath. A solution of iodine (7.68 g, mmol, in 20 ml TF) was added dropwise over 25 min. After gas evolution was ceased the ice bath was removed, and the mixture stirred at RT for 10 min, then refluxed for 18 h. The reaction was cooled to RT and methanol was cautiously added until the mixture turned clear, and stirred additional 30 min. The solvent was evaporated and the residue was dissolved in 20% K (aq.) (110 ml) and stirred for 4 h. Extraction with DCM (X3), the organic phase dried over a 2 S 4 and evaporated. Crystallization from EtAc and washed with hexane to afford colorless needles (2.8 g, 61% yield). 1 -MR (300 Mz, CDCl 3 ): ppm (m, 5, ), 3.62 (dd, J = 10.5, 3.6 z, 1, -9), 3.39 (bdd, 1, -9), 3.11 (bm, 1, -8), 2.75 (bdd, 1, -7), 2.68 (bs), 2.50 (bdd, 1, -7). 3 C MR (300 Mz, CDCl 3 ): ppm (1C, C-1), (5C, C-2 + C-3 + C-4 + C-5 + C-6), (1C, C-9), (1C, C-8), (1C, C-7). MS-ES(+): [M] clac. = , found [M + + ] = Cl Cl * 3,3'-((1-hydroxy-3-phenylpropan-2-yl)azanediyl)bis(1-chloropropan-2-ol), 23: 2-amino- 3-phenylpropan-1-ol hydrochloric salt, 22 (200 mg, 1.32 mmol) was dissolved in epichlorohydrin (0.21 ml, 2.65 mmol) under heating, and stirred at ~ 65 C for 2.5 h. The 92

93 sticky oil was high vacuumed and dried to afford the product (386.2 mg). MS-ES(+): [M] calc. = , found [M + a + ] = Mn Cl Leu-CLS18: To a solution of 3,3'-(2-hydroxyethylazanediyl)bis(1-chloropropan-2-ol), 17, (291.2 mg/0.8 ml DDW ml dioxane) was added a combined solution of Lue-PEI3 (78.8 mg/0.8 ml dioxane) and 6,6'-((1E,1'E)-(ethane-1,2-diylbis(azanylylidene)) bis(methanylylidene))bis(2,4-di-tert-butylphenol) Mn(III) chloride, MnSalen15 (106 mg/0.8 ml dioxane). The combined solutions were heated to 85 C for 5 h, and then refluxed for 2.5 h. The reaction was cooled to RT and the solvent was evaporated. The residue was first washed with DDW and lyophilized to afford a brown powder (70 mg). ICP-MS [Mn] = 6.8%. Cat. Load [Catalyst/CLS] = 1.24X10-3 mmol/mg. C Elemental Analysis. C, 58.14%;, 9.30%;, 9.30% P h Mn Cl e-cls19: To a stirred solution of e-pei9, (100.4 mg/ 10 ml dioxane) were added a solution of 2,2'-(1E,1'E)-(ethane-1,2-diylbis(azan-1-yl-1-ylidene))bis(methan-1-yl-1- ylidene)diphenol Mn(III) chloride, MnSalen13, (82 mg/10 ml DDW) and a solution of 3,3'- (2-hydroxyethylazanediyl)bis(1-chloropropan-2-ol), 17, (305.4 mg/2 ml DDW). The combined solutions were heated to 85 C for 3.5 h, and then refluxed for 2.5 h. The reaction was cooled to RT and the solvent was evaporated. The residue was first washed with DDW and then sonicated in DDW. The fine brown-yellow powder was washed with DDW and centrifuged until the aqueous phase became clear. The brown- yellow powder was P h 93

94 lyophilized to afford the product (60 mg). ICP-MS [Mn] = 3.3%. Cat. Load [Catalyst/CLS] = 6X10-4 mmol/mg. C Elemental Analysis. C, 71.94%;, 7.10%;, 8.80%. e-cls20: To a stirred solution of e-pei9, (100.4 mg/ 2 ml dioxane) were added a solution of 6,6'-((1E,1'E)-(ethane-1,2-diylbis(azanylylidene)) bis(methanylylidene))bis(2,4- di-tert-butylphenol) Mn(III) chloride, MnSalen15 (100 mg/6 ml dioxane) and a solution of 3,3'-(2-hydroxyethylazanediyl)bis(1-chloropropan-2-ol), 17 (120.9 mg/2.5 ml DDW). The combined solution was heated to 85 C for 5 h, and then refluxed for 2 h. The reaction was cooled to RT and the solvent was evaporated. The residue was first washed with DDW and then sonicated in DDW. The fine brown-yellow powder was washed with DDW and centrifuged until the aqueous phase became clear. The brown powder was lyophilized to afford the product (71 mg). Calc. Cat. Load [Mn] = 3% wt., [Catalyst/CLS] = 5.36X10-4 mmol/mg. C Elemental Analysis. C, 70.34%;, 7.67%;, 8.30%. t Bu Mn Cl e-cls21: To a stirred solution of e-pei9, (92 mg/4 ml dioxane) were added a solution of 2,2'-(1E,1'E)-(ethane-1,2-diylbis(azan-1-yl-1-ylidene))bis(methan-1-yl-1-ylidene)diphenol Mn(III) chloride, MnSalen13, (75.2/4 ml DDW) and a solution of 3,3'-((1-hydroxy-3- phenylpropan-2-yl)azanediyl)bis(1-chloropropan-2-ol), 23 (382.8 mg/3 ml dioxane) in DDW (2 ml). The combined solutions were heated to 85 C for 5 h, and then refluxed for 2 h. The reaction was cooled to RT and the solvent was evaporated. The residue was washed with DDW and then sonicated in DDW. The residue was washed again with DDW and centrifuged until the aqueous phase became clear to afford a brown-yellow powder (285.9 mg). ICP-MS 94 Mn Cl

95 [Mn] = 3.1%. Cat. Load [Catalyst/CLS] = 5.64X10-4 mmol/mg. C Elemental Analysis. C, 61.65%;, 7.44%;, 6.47%. R R Mn Cl RRMnSalen-Leu24: To a solution of 3,3'-(2-hydroxyethylazanediyl)bis(1-chloropropan-2- ol), 17, (312.6 mg/4.2 ml DDW ml dioxane) was added a combined solution Leu- PEI3 (84.6 mg/0.86 ml dioxane) and,'-bis(3,5-di-tert-butylsalicylidene)-1r,2rcyclohexanediaminomanganese(iii) chloride (122.8 mg/3 ml dioxane). The combined solutions were heated to 85 C for 5 h, and then refluxed for 2.5 h. The reaction was cooled to RT and the solvent was evaporated. The residue was washed with DDW and lyophilized to afford a brown powder (49.3 mg). ICP-MS [Mn] = 7.3%. Cat. Load [Catalyst/CLS] = 1.33X10-3 mmol/mg. C Elemental Analysis. C, 67.89%;, 9.80%;, 6.99%. S S Mn Cl SSMnSalen-Leu25: To a solution of 3,3'-(2-hydroxyethylazanediyl)bis(1-chloropropan-2- ol), 17, (72.3 mg/0.97 ml DDW ml dioxane) was added a combined solution of Leu- PEI3 (19.5 mg/0.2 ml dioxane) and,'-bis(3,5-di-tert-butylsalicylidene)-1s,2scyclohexanediaminomanganese(iii) chloride (28.3 mg/1 ml dioxane). The combined solutions were heated to 85 C for 5 h, and then refluxed for 2.5 h. The reaction was cooled to RT and the solvent was evaporated. The residue was washed with DDW and lyophilized to 95

96 afford a brown powder (28.7 mg). ICP-MS [Mn] = 7.8%. Cat. Load [Catalyst/CLS] = 1.42X10-3 mmol/mg. C Elemental Analysis. C, 66.96%;, 8.81%;, 5.32%. General procedure for linear PEI encapsulated chiral Jacobsen catalysts (compounds RRMnSalen26 and SSMnSalen27): To a solution of linear PEI (376 mg/2 ml DDW, Aldrich Cat.o , Mn: 423 g/mol) were added 3,3'-(2-hydroxyethylazanediyl)bis(1-chloropropan-2-ol), 17 (50.6 mg/2 ml DDW) and,'-bis(3,5-di-tert-butylsalicylidene)-1(r or S),2(R or S)-cyclohexane diaminomanganese(iii) chloride (19.6 mg/2.4 ml dioxane). The combined solutions were heated to 85 C for 5 h, and then refluxed for 2.5 h. The reaction was cooled to RT and the solvent was evaporated. The residue was washed with DDW and lyophilized. n R R Mn Cl RRMnSalen26: Yellow solid (16.5 mg). ICP-MS [Mn] = 0.34%. Cat. Load [Catalyst/CLS] = 6.19X10-5 mmol/mg. C Elemental Analysis. C, 72.31%;, 9.80%;, 8.79%. n n S S Mn Cl SSMnSalen27: Yellow solid (18.5 mg). ICP-MS [Mn] = 0.54%. Cat. Load [Catalyst/CLS] = 9.83X10-5 mmol/mg. C Elemental Analysis. C, 73.16%;, 10.18%;, 9.48%. n 96

97 e-cls(no catalyst): To a solution of e-pei9, (100.5 mg/10 ml dioxane) was added a solution of 3,3'-(2-hydroxyethylazanediyl)bis(1-chloropropan-2-ol), 17 (305.5 mg/2 ml DDW). The combined solution was heated to 85 C for 3.5 h, and then refluxed for h. The reaction was cooled to RT and the solvent was evaporated. The residue was washed with DDW, centrifuged and lyophilized to afford a creamy yellowish solid (17 mg). 1 -MR (300 Mz, CDCl 3 ): ppm 7.22 (bs, Ar), 5.02 (small s, C-), 4.1 (bs, C 2 -), 3.63 (bs), (bs), 1.43 (s), 1.25 (s). 13 C-MR (500 Mz, CDCl 3 ): ppm (quaternary C Ar), (Ar), (b), (b), (b), (b), (b), 30.50, General procedure: Epoxidation of with Leu-PEI16 in aqueous: System preparation: Leu-PEI16 (10 mg) was dissolved water (9.8 ml) and tbu (0.5 ml) upon heating and sonication. A solution of MnSalen13 (8 mg, mmol) in 1 ml of the above suspension was heated at ~ 75 C for 1 h and cooled to RT. M (27 mg, 0.23 mmol, 0.5 eq) and olefin (0.46 mmol, 1 eq) were added. The mixture was cooled by means of ice-water bath and acl (2 ml, ~ 0.5M, a 2 P 4 buffer, p = 11.4) was added and the reaction was stirred at 3 C (or RT) for 60 h. The aqueous phase was extracted with DCM (X3). The organic phases were combined and washed with brine (X1), dried over a 2 S 4 and evaporated. General procedure: Epoxidations with Leu-CLS18 in water: Leu-CLS18 (5 mg) was suspended in boiling DDW (0.5 ml) for 5 min. The mixture was cooled to RT and a solution of M (9 mg, mmol, 0.5 eq/1 eq of olefin) in DDW (0.5 ml) was added. The mixture was cooled to 3 C, olefin (0.154 mmol) and a solution of acl (0.57 ml, ~ 0.5M, a 2 P 4 buffer, p = 11.4) were added. The reaction was stirred for 3 days at 3 C and extracted with hexane (X4, 3 C). The organic phase was washed with brine (X1, RT), dried over a 2 S 4 and evaporated. 97

98 General procedure: Epoxidations with e-cls19 in biphasic system with DCM: To a solution of e-cls19 (3 mg) in DCM (0.3 ml) was added a solution of M (5.4 mg, mmol, 0.5 eq/1 eq of olefin) in DCM (0.3 ml). The solution was cooled to 3 C and olefin (0.09 mmol, 1 eq) and 0.5M acl (sol.) (0.3 ml, ~ 2 eq, buffered with a 2 P 4, p=11.4) were added. The mixture was stirred at 3 C for ~3 days. The mixture was filtered through celite (exane eluent, 3 C). The filtrate was washed with brine (X1, RT), dried over a 2 S 4, and evaporated. The residue was dissolved in exane, filtered and evaporated. e-cls28: To a stirred solution of e-pei9, (100.3 mg/ 3 ml dioxane) under gentle flow of argon was added a solution of Dichlorobis[2-(di-phenylphosphino) ethylamine] ruthenium(ii) (20.1 mg/3 ml dioxane) and to the overall volume was added 4 ml dioxane. A solution of 3,3'-(2-hydroxyethylazanediyl)bis(1-chloropropan-2-ol), 17, (305.4 mg/2 ml DDW) was added and the total mixture was sttired at RT for 30 min, heated to 85 C for 3.5 h, and then refluxed for 2.5 h. The reaction was cooled to RT and the solvent was evaporated. The residue was washed and sonicated with DDW, and centrifuged (X2) and washed again with DDW. The solids were dried by lyophization to afford powder (20 mg). Calc. Cat. Load [Ru] = 1% wt., [Catalyst/CLS] = 9.6X10-5 mmol/mg. C Elemental Analysis. C, 48.84%;, 8.27%;, 6.37%. P Cl P Ru Cl 98

99 hp ph hp ph P Cl Ru P Cl e-cls29: To a stirred solution of e-pei9, (100 mg/ 3 ml dioxane) under gentle flow of argon was added a solution of Dichlorobis[2-(di-phenylphosphino) ethylamine] ruthenium(ii) (25.7 mg/7 ml dioxane). A solution of 3,3'-(2-hydroxyethylazanediyl)bis(1-chloropropan-2- ol), 17, (305.4 mg/2 ml DDW) was added and the total mixture was sttired at RT for 30 min, heated to 85 C for 3.5 h, and then refluxed for 2.5 h. The reaction was cooled to RT and the solvent was evaporated. The residue was washed and sonicated with DDW, and centrifuged. The solid were washed with DDW until the solution became clear. The solids were dried by lyophization to afford powder (24 mg). Calc. Cat. Load [Ru] = 1% wt, [Catalyst/CLS] = 9.5X10-5 mmol/mg. C Elemental Analysis. C, 62.89%;, 7.04%;, 6.36%. hp ph hp ph P Cl Ru P Cl Leu-CLS30: To a stirred solution of Leu-PEI3, (100 mg/ 5 ml dioxane) under gentle flow of argon was added a solution of Dichlorobis[2-(di-i-propylphosphino) ethylamine] ruthenium(ii) (25 mg/2 ml dioxane) and to the overall volume was added 3 ml dioxane. A solution of 3,3'-(2-hydroxyethylazanediyl)bis(1-chloropropan-2-ol), 17, (305.4 mg/2 ml DDW) was added and the total mixture was sttired at RT for 30 min, heated to 85 C for 4 h, and then refluxed for 3.5 h. The reaction was cooled to RT and the solvent was evaporated. The residue was washed and sonicated with DDW, and centrifuged (X2). The solids were dried by lyophilization to afford powder (39 mg). Calc. Cat. Load [Ru] = 1% wt, [Catalyst/CLS] = 9.2X10-5 mmol/mg. C Elemental Analysis. C, 56.57%;, 8.20%;, 7.76%. 99

100 General procedure: Catalytic hydrogenation of acetophenone with Ru(II)CLS. A. Without solvent: Ru(II)CLS (3 mg) was in IPA (1 ml) and 2M K (1 ml) in a pressure tube equipped with a magnetic stirring bar. The solvent was lyophilized and to the solids was added acetophenone (100 L). The tube was washed twice and filled with 3 atm 2 and stirred at RT for 22 h. The tube was vented and the residue extracted with hexane (X3), filtered and evaporated. B. In water: Ru(II)CLS (3 mg) was treated with a solution of K (120 mg/1 ml DDW) with vigorous stirring in a pressure tube, and acetophenone (100 L) was added. The tube was washed twice and filled with 3 atm 2 and stirred at RT for 22 h. The tube was vented and the residue extracted with hexane (X3), dried over a 2 S 4 and evaporated. C. In IPA (example): Ru(II)CLS (3 mg) was dissolved in IPA (0.5 ml) and a solution of tbuk (3 mg/1.5 ml IPA) and acetophenone (100 L) were added. The tube was washed twice and filled with 3 atm 2 and stirred at RT for 20 h. The tube was vented and the solvent evaporated. The residue was washed with hexane, filtered and washed with brine (X1). The brine was extracted with hexane (X3), and all of the organic phases were combined, dried over a 2 S 4 and evaporated. Alkene and imine synthesis for catalytic hydrogenation: Arylalkenes 32 and 33 are known compounds and were synthesized according to literature procedure. 129 Imine 35: Into a pressure tube were added benzylamine (1020 L, 9.33 mmol), Et (1.5 ml) and acetophenone (1090 L, 9.33 mmol). The tube was wash with argon and stirred at 90 C for 3 days. The reaction was cooled to RT, evaporated and high vacuumed (49% yield by GC). 100

101 Imine 37: To a flame dried flask under argon were to dry Et (20 ml) R-(+)- methylbenzylamine ( L, 8.25 mmol), acetophenone (964 L, 8.25 mmol) and trimethyl-o-formate (1.5 ml). The reaction was refluxed under argon for 48 h. the mixture was cooled, evaporated and high vacuumed overnight to afford the product as yellow oil (560 mg, 30% yield, 99% purity by GC-MS) Imines 39 and 40 are known compounds and were synthesized according to literature procedure. 130 Pd(DMS) 2 Cl 2 :To Pd(II)Cl 2 (250 mg, 1.41 mmol) was added DMS (5 ml) and the mixture was stirred at 60 C for 30 min. and left at 60 C for 3 days. The mixture was cooled to RT and the solvent decantated from the precipitation. The solid was washed with Et 2 (X3) and dried to afford the product as a yellow powder (417 mg, 89% yield). Pd nanoparticles stabilized by imine crosslinked Leu-PEI, Leu-PEI31: In a 20 ml vial Leu-PEI6 (10.8 mg) was dissolved in dry Me (10 ml). To the solution was added Pd(DMS) 2 Cl 2 (30 mg, 0.09 mmol) and the mixture was stirred for 10 min. Freshly prepared solution of ab 4 (3.8 mg/1 ml Me) was added under vigorous stirring. The solution turned black immediately and stirred for 2.5 h. The system was left to rest over-night before use. 101

102 TEM images of stabilized Pd nanoparticles, ~ 4 nm General procedure for olefin hydrogenation with Leu-PEI31 (example): In a pressure tube olefin (25 L) was dissolved in Leu-PEI31 (2 ml of stock solution). The tube was washed twice and filled with 3 atm 2. The reaction was stirred at RT for ~24 h. the tube was vented and the solvent evaporated. The residue was treated with hexane and filtered. The organic phase was washed with brine (X1). The brine was extracted with hexane (X1), and all of the organic phases were combined, dried over a 2 S 4 and evaporated. General procedure for imine hydrogenation with Leu-PEI31 (example): In a pressure tube imine (25 L) was dissolved in Leu-PEI31 (0.5 ml of stock solution). The tube was washed twice and filled with 4 atm 2. The reaction was stirred at RT for 20 h. the tube was vented and the mixture filtered over celite and evaporated. PEI-boronic acid synthesis, reactions and assays: General Procedure for PEI-B() 2 : Branched PEI 60,000 (Aldrich Cat. o. P % (w/v) in 2 ) was dried by azeotrope distillation with absolute Et using evaporator under high vacuum (at least 3 times) and lyophilized until no further weight loss was observed. Dry PEI 60,000 (1 g, mmol of 1, 1 eq) was dissolved in dry Et (13.5 ml/1 g PEI) and was added to a flame dry reflux system under argon. To the solution was added 2- formyl benzene boronic acid (the corresponding mmol eq for the desired 10%, 50% or 100% 1 substitution) with additional wash of dry Et (~ 3.8 ml/g). The solution was refluxed for 5.5 h and cooled to RT. ab 4 (4 mmol eq of the 2-formyl benzene boronic acid) was added and the reaction was stirred over-night at RT. Additional batch of ab 4 (~ 25 mg/1 102