The Design of New Ligands and Transition Metal Compounds
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THE DESIGN OF NEW LIGANDS AND TRANSITION METAL COMPOUNDS FOR THE OXIDATION OF ORGANIC COMPOUNDS A Dissertation by JOSEPH MICHAEL GRILL 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 August 2006 Major Subject: Chemistry THE DESIGN OF NEW LIGANDS AND TRANSITION METAL COMPOUNDS FOR THE OXIDATION OF ORGANIC COMPOUNDS A Dissertation by JOSEPH MICHAEL GRILL 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, Stephen A. Miller Committee Members, David E. Bergbreiter Marcetta Y. Darensbourg Dragomir B. Bukur Head of the Department, Emile A. Schweikert August 2006 Major Subject: Chemistry iii ABSTRACT The Design of New Ligands and Transition Metal Compounds for the Oxidation of Organic Compounds. (August 2006) Joseph Michael Grill, B.S., University of Illinois at Urbana-Champaign Chair of Advisory Committee: Dr. Stephen A. Miller A review of metal-mediated epoxidation is given. Jacobsen’s catalyst and the Sharpless asymmetric epoxidation catalyst are discussed. The origins of enantio- selectivity are explained using stereochemical models. Several new salen-type ligands were synthesized based on biphenol and binaphthol. The synthesis of these ligands and their subsequent coordination to transition metals were described. The transition metal complexes were structurally characterized by X-ray diffraction of single crystals. The manganese (III) complexes were evaluated for catalytic activity in epoxidation reactions. Despite the fact that these many of these complexes were optically active, little asymmetric induction was observed in any of the epoxidation reactions. The investigation of a soluble nickel salen complex for the epoxidation of olefins led to the discovery of a new heterogeneous catalyst for the epoxidation of α,β- unsaturated carboxylic acids. Nickel salen complexes, upon reaction with commercial bleach, yield a fine black powder, which we identified as nickel oxide hydroxide—a known but poorly characterized nickel peroxide containing species. The reaction of an iv aqueous nickel (II) source with commercial bleach also yields nickel oxide hydroxide. This material was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). Extremely broad peaks in the X-ray diffraction pattern suggested that this material consisted of particles with a very small diameter and this was confirmed by TEM. This insoluble material was found to function as a heterogeneous catalyst for the epoxidation of α,β-unsaturated carboxylic acids in the presence of sodium hypochlorite. The high activity of this catalyst in the epoxidation of certain olefins is due in part to its small particle size, which increases the overall surface area of this heterogeneous catalyst. Large particles of nickel oxide hydroxide were prepared and the catalytic activity was comparatively less. The oxidation of several other organic substrates was also explored using this catalyst. Both primary and secondary alcohols can be oxidized with our nickel-based system. Primary alcohols go through an aldehyde intermediate which is then in turn oxidized to the carboxylic acid. v For Sue Krystof who taught my first chemistry class and to whom I am greatly indebted for the knowledge she bestowed. vi ACKNOWLEDGMENTS I would like to express my sincere thanks to my advisor, Dr. Stephen A. Miller, for allowing me the freedom to determine the creative course of my research. I would also like to thank the entire Miller group for their assistance and support. I am grateful to Dr. Joy Heising for many insightful conversations about solid state analytical techniques. I am also indebted to Dr. Joseph H. Reibenspies for solving all of the X-ray structures contained within this document, Dr. Zhiping Luo in the Microscopy & Imaging Center at Texas A&M for taking all of my TEM images, Dr. Nattamai Bhuvanesh for taking the XRD data and the entire mass spectroscopy lab for taking all of the mass spectra contained within this document. I would also like to express my gratitude to the Welch Foundation for funding this research as well as to the Texas A&M University College of Science. vii TABLE OF CONTENTS Page ABSTRACT .............................................................................................. iii DEDICATION........................................................................................... v ACKNOWLEDGMENTS.......................................................................... vi TABLE OF CONTENTS........................................................................... vii LIST OF SCHEMES.................................................................................. ix LIST OF FIGURES ................................................................................... xi LIST OF TABLES..................................................................................... xii CHAPTER I INTRODUCTION: AN OVERVIEW OF METAL MEDIATED EPOXIDATION CHEMISTRY..................... 1 II NEW SALEN LIGANDS BASED ON 2,2’-BIPHENOL AND BINAPHTHOL ......................................................... 16 Synopsis.................................................................. 16 Introduction............................................................. 16 Results and discussion............................................. 18 Conclusions............................................................. 35 Experimental........................................................... 36 III EPOXIDATIONS USING NICKEL OXIDE HYDROXIDE 48 Synopsis.................................................................. 48 Introduction............................................................. 48 Results and discussion............................................. 50 Conclusions............................................................. 63 viii CHAPTER Page Experimental........................................................... 63 IV OTHER OXIDATIONS USING NICKEL OXIDE HYDROXIDE .................................................................... 73 Synopsis.................................................................. 73 Introduction............................................................. 73 Results and discussion............................................. 75 Conclusions............................................................. 87 Experimental........................................................... 87 V CONCLUSIONS ................................................................ 101 REFERENCES .......................................................................................... 103 APPENDIX A ........................................................................................... 108 APPENDIX B............................................................................................ 215 APPENDIX C............................................................................................ 225 VITA......................................................................................................... 241 ix LIST OF SCHEMES SCHEME Page 1.1 Olefin epoxidation.......................................................................... 2 1.2 Reaction of olefins with oxygen and silver ..................................... 2 1.3 Epoxidation of α,β-unsaturated carboxylic acids with catalytic sodium tungstate and hydrogen peroxide ........................................ 3 1.4 The Sharpless asymmetric epoxidation reaction.............................. 4 1.5 Salen ligands .................................................................................. 6 1.6 Jacobsen’s epoxidation catalyst, 1-3 ............................................... 7 1.7 Gilheany's epoxidation catalyst....................................................... 10 1.8 Radical epoxidation mechanism using manganese.......................... 13 1.9 Mechanism of the Sharpless asymmetric epoxidation ..................... 14 2.1 Synthesis of a new salen-type ligand and its coordination to metals............................................................................................. 20 2.2 Synthesis of an expanded chiral salen-type ligand (2-7a, salbinH2; 2-7b, salbin(t-Bu)4H2) and its coordination to metals...................... 25 2.3 Catalytic epoxidation of olefins with [Mn] = 4-Mn, 8-Mn, or 9- Mn................................................................................................. 30 2.4 Synthesis of an unsymmetrical ligand derived from binaphthol ...... 34 3.1 Synthesis of 3-1-Ni and catalytic epoxidation................................. 51 3.2 Epoxidation of methacrylic acid ..................................................... 53 3.3 Proposed mechanism for epoxidation ............................................. 62 x SCHEME Page 4.1 Oxidation of 3-butenoic acid to fumaric acid .................................. 85 4.2 Oxidation of acrylic acid ................................................................ 86 xi LIST OF FIGURES FIGURE Page 2.1 X-ray structures of 2-4-Mn, 2-4-Co, 2-4-Ni, and 2-4-Cu with 50% probability ellipsoids and hydrogen atoms omitted for clarity. 21 2.2 X-ray structures of 2-8-Co and 2-8-Cu with 50% probability ellipsoids and hydrogen atoms omitted for clarity........................... 26 2.3 Coordination sphere of 2-4-Co and 2-8-Co with 50%