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Syntheses and Applications of Soluble Polyisobutylene

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Syntheses and Applications of Soluble Polyisobutylene SYNTHESES AND APPLICATIONS OF SOLUBLE POLYISOBUTYLENE (PIB)-SUPPORTED TRANSITION METAL CATALYSTS A Dissertation by JIANHUA TIAN Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY December 2008 Major Subject: Chemistry SYNTHESES AND APPLICATIONS OF SOLUBLE POLYISOBUTYLENE (PIB)-SUPPORTED TRANSITION METAL CATALYSTS A Dissertation by JIANHUA TIAN Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Approved by: Chair of Committee, David E. Bergbreiter Committee Members, Daniel A. Singleton Marcetta Y. Darensbourg Daniel Shantz Head of Department, David H. Russell December 2008 Major Subject: Chemistry iii ABSTRACT Syntheses and Applications of Soluble Polyisobutylene (PIB)-supported Transition Metal Catalysts. (December 2008) Jianhua Tian, B.S., Liaoning Normal University, China; M.S., Dalian University of Technology, China Chair of Advisory Committee: Dr. David E. Bergbreiter Soluble polymer supports facilitate the recovery and recycling of expensive transition metal complexes. Recently, polyisobutylene (PIB) oligomers have been found to be suitable polymer supports for the recovery of a variety of transition metal catalysts using liquid/liquid biphasic separations after a homogeneous reaction. Our work has shown that PIB-supported Ni(II) and Co(II) β-diketonates prepared from commercially available vinyl terminated PIB oligomers possess catalytic activity like that of their low molecular weight analogs in Mukaiyama epoxidation of olefins. Carboxylic acid terminated PIB derivatives can act as carboxylate ligands for Rh(II) cyclopropanation catalysts. An achiral PIB-supported Rh(II) carboxylate catalyst showed good activity in cyclopropanation of styrene in hydrocarbon solvents, and could be easily recycled nine times by a post reaction extraction. Further application of PIB supports in asymmetric cyclopropanation reactions were investigated using PIB- supported arenesulfonyl Rh(II) prolinates derived from L-proline as examples. The PIB- supported chiral Rh carboxylates demonstrated moderate activity and were recovered iv and reused for four to five cycles. The prolinate catalyst prepared from PIB-anisole also showed encouraging enantioselectivity and about 8% ee and 13% ee were observed on trans- and cis-cyclopropanation product respectively. Finally, PIB oligomers can be modified in a multi step sequence to prepare PIB- supported chiral bisoxazolines that can in turn be used to prepare active, recyclable PIB- supported Cu(I) bisoxazoline complexes for olefin cyclopropanation. These chiral copper catalysts showed moderate catalytic activity and good stereoselectivity in cyclopropanation of styrene. A chiral ligand prepared from D-phenylglycinol provided the most effective stereo control and gave the trans- and cis-cyclopropanation product in 94% ee and 68% ee respectively. All three PIB-supported chiral bisoxazoline-Cu(I) catalysts could be reused five to six times. v DEDICATION To my parents and my wife, for supporting me all the way. vi ACKNOWLEDGEMENTS First of all, I would like to give my most sincere thanks to my advisor, Prof. David E. Bergbreiter, for giving me the opportunity to join his research group, for his guidance and support throughout the course of my research and for his big help in deciding the next step in my life. I would also like to thank my committee members, Prof. Daniel A. Singleton, Prof. Marcetta Y. Darensbourg, and Prof. Daniel Shantz, for their useful advice for my research and their strong support during the course of my application for postdoctoral positions. I also want to extend my thanks to Prof. Gyula Vigh, for helping me with analysis of chiral cyclopropanation products. Thanks also go to the Bergbreiter’s group, especially to Jun, Shayna, Patric, Denisse, Film, Shawn, Hui, Haw-Lih, Criss, and Scott for helping me with my research. vii TABLE OF CONTENTS Page ABSTRACT .......................................................................................................... iii DEDICATION ...................................................................................................... v ACKNOWLEDGEMENTS ................................................................................... vi TABLE OF CONTENTS....................................................................................... vii LIST OF FIGURES ............................................................................................... ix LIST OF TABLES................................................................................................. x CHAPTER I INTRODUCTION............................................................................. 1 Water/Organic Biphasic Systems.................................................. 4 Organic/Organic Biphasic Systems ............................................... 17 Polymer Stabilized Nanoparticles ................................................. 34 Catalyst Recovery in Self-Separating Systems .............................. 39 Fluorous/Organic Biphasic Catalysis............................................. 41 Polymer-Supported Catalysts in Ionic Liquids .............................. 43 II POLYISOBUTYLENE-SUPPORTED NICKEL(II) AND COBALT(II) β-DIKETONATES FOR OLEFINS MUKAIYAMA EPOXIDATION...................................................... 45 Introduction................................................................................. 45 Results and Discussion................................................................. 51 Conclusions.................................................................................. 60 III POLYISOBUTYLENE-SUPPORTED RHODIUM(II) AND COPPER(II) COMPLEXES FOR OLEFIN CYCLOPROPANATION ................................................................. 62 Introduction................................................................................. 62 viii CHAPTER Page Results and Discussion ................................................................. 88 Conclusions.................................................................................. 120 IV EXPERIMENTAL ............................................................................ 123 V SUMMARY ...................................................................................... 158 REFERENCES...................................................................................................... 159 VITA..................................................................................................................... 172 ix LIST OF FIGURES FIGURE Page 1 1H NMR spectrum of PIB-alkene............................................................. 53 2 1H NMR spectrum of PIB-β-diketone 62 ................................................. 56 3 Possible stereo isomers of rhodium(II) carboxamidate.............................. 77 4 Preferred spatial orientation in the transition state of cyclopropanation using rhodium(II) carboxamidate............................................................. 79 5 1H NMR spectrum of PIB-supported bisoxazoline ligand 158b ................ 117 x LIST OF TABLES TABLE Page 1 Phase selective solubility of dye labeled PIB in heptane/polar solvent biphasic system ....................................................................................... 53 2 Recycling of PIB-supported Ni and Co catalysts in Mukaiyama epoxidation of α-pinene........................................................................... 59 3 Cyclopropanation of octene with Rh catalyst 117..................................... 91 4 Cyclopropanation of styrene with Rh catalyst 117.................................... 94 5 Cyclopropanation of styrene with Rh catalyst 131.................................... 103 6 Cyclopropanation of styrene with Rh catalyst 135.................................... 105 7 Asymmetric cyclopropanation of styrene with PIB-supported bisoxazoline ligated copper triflates ......................................................... 118 1 CHAPTER I INTRODUCTION Liquid/liquid separations are ubiquitous in chemistry. Indeed most organic reactions involve a gravity separation of two phases of different density and polarity in the work-up steps. This same concept of separations also has precedent in homogeneous catalysis for separation of catalysts and products too.1 Processes like the SHOP process and later processes like the Ruhrchemie/Rhone–Poulenc (RCH/RP) oxo process commercialized in 1980s,1,2 advantageously immobilize a catalyst in one of the two liquid phases to facilitate catalyst recovery and reuse. More recent biphasic systems that use organic solvents,3,4 fluorous solvents,5 ionic liquids6 and supercritical fluids7 have been developed and used in a variety of catalytic transformations over the past two decades. The use of soluble polymer supports to bind a catalyst and ensure high levels of catalyst and ligand recovery in liquid/liquid separations in biphasic liquid/liquid systems is a more recent concept. When a liquid/liquid separation is used, the polymeric catalysts are isolated as a solution at the separation stage. As was true for solid/liquid separation strategies that used soluble polymer facilitated catalysis, catalytic reactions prior to the separation process often involve single phase conditions. However, sometimes reactions are carried out under biphasic conditions. In some of those cases, partial misciblization occurs or the polymeric catalyst’s
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