Thiết kế và tổng hợp polymer nhánh cho xúc tác - Luận án tiến sĩ Brett Helms

Design and Synthesis of Branched Polymer Architectures for Catalysis By Brett Anthony Helms B. (Harvey Mudd College) 2000 A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Chemistry in the GRADUATE DIVISION of the UNIVERSITY of CALIFORNIA at BERKELEY Committee in charge: Professor Jean M. Fréchet Professor Dirk Trauner Professor David Schaffer Spring 2006 UMI Number: 3228353 Copyright 2006 by Helms, Brett Anthony All rights reserved. INFORMATION TO USERS The quality of this reproduction is dependent upon the quality of the copy submitted.

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All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest Information and Learning Company 300 North Zeeb Road P. Box 1346 Ann Arbor, MI 48106-1346 Design and Synthesis of Branched Polymer Architectures for Catalysis Copyright 2006 By Brett Anthony Helms Abstract Design and Synthesis of Branched Polymer Architectures for Catalysis By Brett Anthony Helms Doctor of Philosophy in Chemistry University of California, Berkeley Professor Jean M.

Fréchet, Chair Polymers have been broadly applied in synthesis applications for decades in part due to their macromolecular nature, which facilitates product recovery, and their multivalency, which enables high loading. Both heterogeneous and homogeneous polymer supported reagents, catalysts, scavengers, etc. are known and have widespread use in industry for the production of fine chemicals. It was clear, however, from the onset of their implementation in chemical synthesis that functional polymers displayed unique behavior in solution that was not observed for their small molecule counterparts.

In fact, the reactivity of moieties bound to the support was regulated by steric accessibility, mircoenvironment, proximal confinement and other properties that were associated with the polymer. As these effects became enumerated, it was thought that they could be controlled through more precisely constructed materials. However, only recently have such methods for controlled polymer synthesis become available. Particularly useful have been the families of branched polymers: for example, dendrimers, dendronized polymers, star polymers, hyperbranched polymers, and shell crosslinked nanoparticles.

These macromolecules have proven effectiveness in advanced applications, including light harvesting, vaccine and drug delivery, bioimaging, molecular transport, etc. In the realm of catalysis, they offer unprecedented opportunity for further development. Their globular nature is reminiscent of enzymes, whose function and efficiency are only now being approached by these systems. In Chapter 1, the “dendritic effect” as it applies to catalysis applications is addressed.

The benefits of catalyst placement throughout this perfectly branched polymer architecture are outlined. In Chapter 2, a series of porphyrin- cored poly(benzyl ethers) is described. The light harvesting efficiency of the polymers is evaluated as a function of polymer topology (i. linear or branched).

Chapter 3 presents the synthesis and application of the first organocatalytic dendronized polymer. This molecule acts as a molecular concentrator for substrates undergoing chemical transformation. This phenomenon is revisited in Chapter 4 with a related pair of dendrimer catalysts, which differ in either architecture or catalyst nanoenvironment. Their impact on the catalytic properties of the material is described.

In Chapter 5, a one-pot reaction cascade employing acid- and amine-containing star polymers is presented. Through precise chemical synthesis, these otherwise opposing reagents are confined to the sterically restricted cores of the macromoecules and are thus _ spatially segregated in solution, thereby preventing their mutual deactivation. Finally, a facile method for the preparation of dendronized polymers via “click chemistry” is described in Chapter 6. approved: a Chair TJanuayy 22,200¢ Date Table of Contents ACKNOWIECGEMENL.

ce en ELE EEE Eee EEE EEE EEE Kế nà nà kết iii Chapter 1. The Dendrimer Effect in CatalySiS. eee renee nhu ho 1 lntroducfiOn.----- Een nh hà bà kh kh 2 Commonly Used Dendrimer Platforms for Macromolecular Catalysts. 4 Core-Functionalized Dendrimers in Cafalysis.

8 Peripherally Modified Dendrimers in CatalysSis. 34 Conclusions and OuflOOK.c ST eee eee nh be Đà bà kho 50 REFEFENCES 0. EEE ern rene etter ites 52 Chapter 2. The Effect of Macromolecular Architecture in Nanomaterials: A Comparison of Site Isolation in Porphyrin Core Dendrimers and Their Ilsomeric Linear AnaloQU€S.

EE nà ĐK EEE Ere Enea Ki cà 59 0wss00ei 0 eee eeeeenenn nee EEE EEE ene Ete neta ret bettas 60 EXperimental. cece cece ee ee cece eens ee ee TT TK Km ng net 61 Results and DiscUssion. ST «BE BE Bề kh ta 80 ConcluSÌOn.-c c nnnn nen KĐT ki Ki kh 102 Acknowledgemerl. nnn n nh HH 103 Ref©r©enC©S.

ere EEE ELLE LEELA kh gi hà cà eS 103 Chapter 3. Dendronized Cyclocopolymers with a Radial Gradient of Polarity and Their Use as Catalysts in a Difficult Esterification .cccScnnnnnnnề nhe hao 111 INTPOGUCTION. UE EOE EOE EEE net kh 112 ExperimenfalL.‹ re SE nà nh TK EEE EE EEE 113 Results and DisCUSSỈOn.-c ee enn ene kh ch 118 Acknowledgemen.c SH Ene ern EE nh ke tee 121 Supporting lnforrmafiOn. HT eee HT nh kh ru 121 R€Í©r©nC6S.cQQQQnnnnnnnn Đn BE BE ĐK HT hit kt 127 Chapter 4.

Effects of Polymer Architecture and Nanoenvironment in Acylation Reactions Employing Dendritic 4-(Dialkylamino)pyridine Catalysts. 130 Talixe\e [0 (e; ((0)q enc 131 EXperimentl. 0c cece cece eter e tenner rte enn EEE EEE EEE eae Ett ng 134 Results and Discussion. nh nh nh ko bà Hy 142 ConclUSỈOn.-- SH nền TT nh nà ch nh kh kg 145 Acknowledgement.ccQnnnnnn Tnhh nh nh kh ch 146 Supporting lInformatfion.--c nền nh nh nh nà nas 146 Ref©erenC©S.

ch nen Ki BE nh nh kh EES 162 Chapter 5. One-Pot Reaction Cascades Using Star Polymers with Core-Confined Catalytic GFOUDS.- cence SH TT nh nh Km kh Thì in ee een etes 166 JaixeeI9ie:|eaEưdddiiiiiiad(dÁđú. TS nn nn nh nh nh nh ni bon ki kinh ng 169 Results and DisCuSSỈOn. rr nh nh bờ 175 ® si Iei).-- ee entree nà kh kh 178 B201,.

EEL EEE EEE et eter teen nan EteE 182 Chapter 6. Dendronized Linear Polymers via “Click Chemisftry”. 185 INTPODUCTION 0 ee rE UC Kế Đà ky 186 Results and DiscusSiOn. rE En kh He 189 CONCIUSION.

en nner n EERE TEE nen nh bà bà kh EES 193 Acknowledgemenl. HT En een ee tea kh kh HH 193 Supporting Information.-- LH nà ke re 194 R€fer©nC©S. EEE nh TK BC EEE EEE EER ch Bà Yến 199 il Acknowledgements The experience I’ve gained here at Berkeley is in no small part due to the generosity and guidance of Professor Jean. His leadership, depth and drive are a constant source of inspiration for me.

| have learned from him that a successful yet aggressive approach to innovation and creative expression is a delicate balance between individuality and humility. For this, | will always be grateful. To my colleagues who helped make this all possible, | would like to extend my many thanks: Prof. Craig Hawker, Scoobie Mynar, Amanda Murphy, Cathy Liang, Yu Xie, Steve Guillaudeu, Zack Fresco, Claire Pitois, Lisa Marcaurelle, John Klopp, Shawn Burdette, Ray Thibault, Jeff Pyun, Cameron Lee, Sarah Goh, Stephanie Standley, Kevin Sivula, Christine Luscombe, Will Dichtel, Stefan Hecht, and countless others.

And to the little bulls, Andrew Cramer and Canadian Dan. You all contribute more than what is asked to our community, and we are better for it. To my family, | thank you for your patience, love and support for all my endeavors, fruitful or otherwise. We will grow old together and it will be grand.

Finally, | would like to thank my extended family: those who have dared tread the same path as | these last 5 years (or longer). Houston and Taylor deserve merit badges for their stamina in this respect. Glendon and Jeremy, for taking me down new paths. Patrick and Tony for always leading me down the wrong one.

And the Claremont kids for returning me down old ones: Sage, Elise, Dallas, Vida, Addy, Minna, Annie, Brett, Sara, Govil, Yumé, Yumi, Leika, Cho, Heidi, Ju Young, Pete, Kimmy, Mikel, Andy. You all have my respect, admiration and love. This thesis is dedicated to my Great Grandfather Joseph Manuel Gomes Jr. on the occasion of his 90" birthday.

After you have exhausted what there is in business, politics, conviviality, and so on - have found that none of these finally satisfy, or permanently wear - what remains? Nature remains. Walt Whitman | took a deep breath and listened to the old bray of my heart. Sylvia Plath iv Chapter 1. The Dendrimer Effect in Catalysis.

Abstract The immobilization of catalytic groups at the core of dendrimers or at their periphery gives rise to unique properties that affect rates of reaction, substrate activation or selectivity, etc. When advantageous, these properties can be classified as a positive dendritic effect. Positive dendritic effects can arise from site isolation, transition state stabilization and/or dielectric effects in the case of core-modified dendrimers, while peripherally modified dendrimers usually benefit from steric crowding or cooperativity for catalytic residues at the polymers surface. In this review, the appearance of positive dendritic effects from the literature will be highlighted as well as prospects for future work in the field.

Introduction In the interest of “green chemistry” and atom economy, molecular catalysis remains an active area of research in both academia and industry, primarily for the production of fine chemicals used in agribusiness, drug manufacture, organic electronics, etc.” Solution-based methodologies rely not only on the discovery and optimization of small molecule catalysts for a given transformation, but also on efficient means to separate the desired product(s) from the catalyst and any byproducts in the reaction mixture. While this process can be facilitated by using heterogeneous catalysts, i. catalysts immobilized onto organic or inorganic solid supports such as silica or crosslinked polymeric beads, there are several drawbacks to this approach that generally limit their widespread application to batch processes. These drawbacks include nonuniformity in catalyst structure and microenvironment once it is immobilized onto the support material, slow diffusion of substrates therein, catalyst leaching, and lower overall activities than the homogeneous system.Š Solid polymeric supports also exhibit limited swelling ability in certain solvents.

Efforts to overcome these disadvantages have primarily been directed at using soluble polymers for catalyst immobilization.* In this manner, the desirable features of homogeneous catalysis, such as comparable reaction kinetics and mass transfer, can be maintained while the macromolecular nature of the material provides a convenient means of purification and, in some cases, recyclability (vida infra). Both linear polymers and various families of branched polymers have been used as soluble macromolecular supports for reagents and catalysts. While the former are, in general, more readily available, they can suffer from poor loading capacity. It is common for only one catalyst moiety to be appended to the end of a linear polymer, such as monomethoxy-poly(ethylene glycol) (MeO-PEG).

For example, MeO-PEGzooo-catalyst conjugates carry a loading of only 0.2 mmol catalyst per gram of polymer while branched polymers typically carries between 5 to 25 mmol g1 when the degree of branching is greater than 50%.° In the case of dendrimers, where the degree of branching is 100%, the highest possible loading can be achieved. Certainly, in the literature, there has been extensive work to optimize the catalytic activity of functional dendrimers so as best represent that for the small molecule, but with the inherent retention ability that accompanies immobilization on macromolecular supports. There are both covalent®’ and noncovalent®"° approaches described in the literature and many have been used in continuous flow membrane reactors (CFMRs) with high efficacy.2""'? The dendrimers in these studies showed a high degree of independence and stability for the catalytic groups at the polymer surface even at high loadings for the larger dendrimers.