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Palladium and Platinum Complexes for the Oxidation of Small Molecules

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Palladium and Platinum Complexes for the Oxidation of Small Molecules PALLADIUM AND PLATINUM COMPLEXES FOR THE OXIDATION OF SMALL MOLECULES A DISSERTATION SUBMITTED TO THE DEPARTMENT OF CHEMISTRY AND THE COMMITTEE ON GRADUATE STUDIES OF STANFORD UNIVERSITY IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY David M. Pearson October 2010 © 2011 by David Michael Pearson. All Rights Reserved. Re-distributed by Stanford University under license with the author. This work is licensed under a Creative Commons Attribution- Noncommercial 3.0 United States License. http://creativecommons.org/licenses/by-nc/3.0/us/ This dissertation is online at: http://purl.stanford.edu/zn293zr6223 ii I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy. Robert Waymouth, Primary Adviser I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy. Eric Kool I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy. Barry Trost Approved for the Stanford University Committee on Graduate Studies. Patricia J. Gumport, Vice Provost Graduate Education This signature page was generated electronically upon submission of this dissertation in electronic format. An original signed hard copy of the signature page is on file in University Archives. iii Abstract Palladium is a versatile metal used prominently in synthesis. The rapid growth of palladium oxidation chemistry in the past decade has spurred a number of new processes that allow for the selective oxidation of substrates under mild conditions. This growth, specifically in the field of aerobic alcohol oxidation, attracted our attention, with the hope that it would provide new catalysts for use in direct methanol fuel cells. Toward that goal we developed a new cationic palladium complex, [(neocuproine)Pd(OAc)]2[OTf]2, which shows unprecedented initial turnover frequencies for aerobic alcohol oxidation at room temperature. However, catalyst lifetimes are limited due to the generation of reactive partially reduced oxygen species that promote oxidation of the ligand and deactivation of the catalyst. The use of milder oxidant like benzoquinone extended catalyst lifetimes prompting a further exploration of the substrate scope. Oxidation of glycerol proceeds exclusively at the secondary alcohol to yield dihydroxyacetone. Other 1,2-diols also favors oxidation of the secondary alcohol. Methanol oxidation proceeds at a much slower rate, but yields methyl formate with selectivities greater than 90 %. The mechanism for this process was probed through the use of model studies and isotopic labels suggesting the transient generation and oxidation of methyl hemiformal. In a parallel effort toward the extension of catalyst lifetimes, a number of new oxidatively resistant ligands were synthesized and used toward the formation of palladium catalysts that exhibit extended catalyst lifetimes. Additional efforts have focused on the use of similar catalyst for the oxidative carbonylation of 1,2- and 1,3-diols to yield iv 5-membered and 6-membered cyclic carbonates in the presence of N- chlorosuccinimide, iodosylbenzene, or dichloroisocyanuric acid. Finally, a new platinum dimer containing a trimethylplatinum unit and bridging amides was synthesized and characterized. Its reactivity toward the reductive elimination of ethane of methanol derivatives was explored. Additional work with known platinum dimers suggests these species, upon addition of silver triflate, facilitates the C-H activation of a number of unactivated arenes and promotes the C-H functionalization of propargyl aryl ethers. v Acknowledgements First and foremost, I want to thank my parents, Michael and Patricia. They have shaped my very being, and have supported me through this process one calls life. They’ve taught me much of what I know outside of chemistry and I don’t think I could have gotten through graduate school without them. They have always been available to listen and to offer advice on many problems that have arisen; giving me a different and often times wiser prospective. So many have inspired me to pursue chemistry. My first chemistry teacher Mr. Lawson would talk frequently about his many exploits in the field before he settled down to teach. The life he lived seemed so foreign and exciting that I couldn’t help but be intrigued. The trail continued through AP chemistry where I first began to realize that the field came naturally to me eventually landing me in Professor Robert Sheridan’s Organic Chemistry Lecture at which time I made the decision to pursue a Bachelor’s Degree in Chemistry at the University of Nevada, Reno (UNR). I look back with fondness on my days spent in Professor David A. Lightner’s classes on Spectroscopy and Structure Determination. They were no less than extraordinary. It was at UNR that I was introduced to inorganic and organometallic chemistry thanks to the wonderful classes taught by Professor Brain J. Frost and Professor Jason Shearer. Finally, it was through the guidance of Professor Benjamin T. King that I first experienced chemical research in a laboratory setting. Being away from home, the King lab soon became my second family and I have met many lifelong friends there. vi I’d like to acknowledge my fellow labmates who showed me the joys of experimental chemistry; Cameron Hilton, Jason Ormsby, Charlie Robertson, Justin Korinek, Jeremy Crowfoot, Pawel Rempala, and Lisa Gotari. When I first came to Stanford I couldn’t help but feel that I was coming home in a sense. My grandparents once had a fruit orchard off Maude and Highway 237 in Mountain View and my grandmother still lives nearby. We visited the area with some frequency as I grew up and while we had toured Stanford in the past, I never really expected to be here. The five years I have spent here have been better than I could have imagined. I have learned so much from my teachers here at Stanford. The lectures taught by Professor Dimitry Yandalov, Professor Bernhard Breit, Professor Barry Trost, Professor Paul Wender, Professor Robert Waymouth, and Dr. Stephen Lynch have provided me with a comprehensive background in organic and organometallic chemistry for which I am in their debt. I would like to thank all my former and current labmates. Darcy Culkin, Yasu, Stefan Benson, Bridgett Payne, Nahrain Kamber, Wonhee Jeong, Marc Scholton, Nicole Kirn, Sang-Jin Jeon, Binia and Jorge, Nick Conley, Soren Randall, Karen Son, Elizabeth Kiesewetter, Matt Kiesewetter, Ron Painter, Eun-Ji Shin, Kristen Brownell, Justin “Junior” Edward, Hayley Brown, Anthony De Crisci, and Jeff Simon. It’s been a pleasure working with all of you. I’ve had the pleasure of collaborating with many people through my graduate school career. I’d like to thank Nicholas Conley, Charles McCrory, Karen Son, Sang- Jin Jeon, Anando Devadoss, Anthony De Crisci, and Ali Hosseini. While not all of vii these collaborations have been successful, they have all been stimulating and informative. Most importantly, they have all been fun. I have made many wonderful friends here at Stanford; DJ Kleinbaum, Douglas Cordeau, Patrick Morris, Nate Cardin, Scott Tabakman, Charles McCrory, Anando Devadoss, Jonathan Prange, Ali Hosseini, John Parkhill, Michelle Bond, Phillip Walls, Ashley, Matt Cordeau, Jill Porter, Josh Rosenberg, the Wetter’s of Kiese, and many more. The chemistry department here at Stanford has a wonderful support staff. I want to thank our CAS representative Dewi Fernandez. She’s been crucial in all the Waymouth lab’s contact with the outside world; from sample analysis to ordering and without her, nothing would get done. Steven Lynch has been a good friend, teacher, and last but not least a great NMR laboratory manager. Alice Chen has done a great job with the mass spec facility, and has always been helpful in establishing new analysis methods and getting results. Brian Palermo has made dealing with our computers and networks painless, which is a tremendous feat. Lastly I’d like to thank Todd Eberspacher. All the things that I can’t fathom can be done, he does! I’m still in amazement. I would like to thank my advisor, Professor Robert M. Waymouth. Throughout my five years here I think Bob has given me a great appreciation for establishing research programs that are meaningful. The GCEP collaboration between the Stack, Chidsey, and Waymouth labs is nothing short of ambitious. I’m proud to have been a part of the collaboration, and fortunate that we’ve found a few nice stories along the viii path to better understanding the problems and challenges of electrocatalysis. He’s been a great advisor and friend. Lastly, I would like to thank my wife, Amanda. I don’t think either of us could have imagined we’d be here after we first met in an art supply store, shopping for the introductory painting class for which we’d both registered. We’ve had a wonderful seven years together. She has been my foundation throughout these years. She has been incredibly patient, understanding, and supportive. There have been many evenings working late, missing dinners or weekend activities. I hope that all those sacrifices will prove worthwhile as we proceed into the next stage of our lives together. ix Preface “I do not write books, I write pages.” -Dan Fante x Table of Contents Abstract iv Acknowledgements vi Preface x Table of Contents
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