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Secondary Coordination Sphere Contributions to Primary Sphere Structure, Bonding and Reactivity

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Secondary Coordination Sphere Contributions to Primary Sphere Structure, Bonding and Reactivity Secondary coordination sphere contributions to primary sphere structure, bonding and reactivity by Cameron M. Moore A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Chemistry) in The University of Michigan 2015 Doctoral Committee: Assistant Professor Nathaniel K. Szymczak, chair Professor Vincent L. Pecoraro Professor Stephen W. Ragsdale Professor Melanie S. Sanford © Cameron M. Moore 2015 Dedication For my family ii Acknowledgments I would first like to thank Professor Nate Szymczak for mentoring me over the past five years. I feel fortunate to have been one of the first students in his group and help build the lab from the ground up. Nate has given me tremendous amounts of freedom during my graduate career to explore concepts and pursue wild ideas. He has also always had an open door while I’ve been in the group. I wouldn’t be able to count the number of times I’ve come to his office in a panic and he’s been there to help me keep my cool. I’ve learned how to write, think critically and practice good science from Nate, and for that I am very thankful. I’d like to thank the members of my dissertation committee, both past and present: Prof. Melanie Sanford, Prof. Steve Ragsdale, Prof. Vince Pecoraro and Prof. Mi Hee Lim. During our meetings, I have very much appreciated your input and advice. I have valued the different perspectives you have all provided during these times and thank you for helping me to understand science in a more broad sense. I would be remiss if I didn’t thank Prof. Bart Bartlett. When I first arrived at Michigan, Bart was kind enough to lend me a hood to work in before our lab space was ready. Bart took me in as part of his lab for the summer and has had a much larger impact on my life and career than he may imagine. He’s also been someone who was willing to lend an ear whenever I was in need of advice or had a naïve question. Some of the chemistry presented in this thesis would not have been possible without valuable discussions from Prof. Nicolai Lehnert and Prof. Pavel Nagorny. I’m sure I’ve been quite the pest for Nicolai over the past few years with all of my questions, but I thank him very much for iii his willingness to offer technical advice on copper chemistry, spectroscopy and computational chemistry. I gratefully thank Prof. Nagorny for some key suggestions in helping to synthesize some of the ligands presented in this thesis; I don’t think I would have gotten there if not for his advice. None of the crystallography would have been possible without the aid of Dr. Jeff Kampf. I’ve had a blast learning how to solve crystal structures from Jeff and I’ve accumulated a tremendous amount of knowledge from him over the past five years. Jeff’s lab was also a great place to hide now and then when I needed a break and I thank him for being so willing to help me learn (and vent) about crystallography. The Szymczak lab has been a great place to earn my degree thanks to a fun group of coworkers. I’d like to thank all members of the group, past and present, for always being there for helpful science discussions, advice and fun. I’d also like to thank the Chemistry Department and Rackham Graduate School for funding the first and final years of my graduate studies. I’ve also been fortunate to have been supported by the National Science Foundation Graduate Research Fellowship Program, and I’d like to thank them for their support. Of course I’d like to thank my family for all of their love. I’d like to thank my parents, Mike Moore and Coral Holman, for supporting me every step of the way through my education. They have always encouraged me to pursue anything and everything I possibly can and I couldn’t ask for more. I’d like to thank my sister Jen for always being available when I could use a phone call, and Kellan for giving me so many smiles over the last few months. Last not but not least, thank you Tanya for every moment of help, encouragement and love you have given me over the past five years. Much of my success has been due to you and I can’t wait to see where our next adventure in life takes us. iv Table of Contents Dedication ....................................................................................................................................... ii Acknowledgments ......................................................................................................................... iii List of Figures ................................................................................................................................ ix Abstract ...................................................................................................................................... xviii Chapter 1 Introduction .................................................................................................................... 1 1.1 [Fe]-hydrogenase and synthetic 2-hydroxypyridine catalysis .............................................. 1 1.1.1 Reductive chemistry promoted by 2-hydroxypyridine catalysts ................................... 6 1.1.2 Oxidative chemistry promoted by 2-hydroxypyridine catalysts .................................. 11 1.1.3 H2 storage schemes enabled by 2-hydroxypyridine catalysts ...................................... 12 1.1.4 Water oxidation promoted by 2-hydroxypyridine catalysts ......................................... 15 1.1.5 Outlook for 2-hydroxypyridine catalysis ..................................................................... 17 1.2 Appended functionality in synthetic pincer systems .......................................................... 18 1.2.1 Design criteria .............................................................................................................. 19 1.2.2 Motivations .................................................................................................................. 19 1.2.3 Appended functionality co-planar with the pincer chelate .......................................... 23 1.2.4 Appended functionality not co-planar to the pincer chelate ........................................ 30 v 1.2.5 Outlook for multifunctional pincer complexes ............................................................ 37 1.3 Outline and scope of this thesis .......................................................................................... 38 1.4 References ........................................................................................................................... 39 Chapter 2 Hydrogen bonding interactions far removed from the metal center ............................ 47 2.1 Motivation and design criteria for the TQA’ ligand ........................................................... 47 2.2 Hydrogen bonding interactions with a non-classical donor ................................................ 49 2.2.1 Solid- and solution-state structures of copper(II)-TQA’ adducts ................................ 50 2.2.2 Confirmation of CHO hydrogen bonding in solution ................................................ 54 2.3 Lewis acid encapsulation within the secondary coordination sphere ................................. 57 2.4 Reactivity toward hydrogen peroxide ................................................................................. 60 2.5 Urea coordination and hydrogen bonding interactions ....................................................... 63 2.6 Experimental section for Chapter 2 .................................................................................... 68 2.7 Notes and References .......................................................................................................... 76 Chapter 3 Tautomerizable ligands in 3-fold symmetry ................................................................ 80 3.1 Constraining the 2-hydroxypyridine motif within a tripodal framework ........................... 80 3.1.1 Motivation and ligand design....................................................................................... 80 3.1.2 Ligand synthesis and solution/solid state speciation ................................................... 82 3.1.3 Coordination to copper(I) chloride .............................................................................. 84 3.1.4 Oxidation to copper(II) ................................................................................................ 85 3.1.5 Quantifying hydrogen bonding interactions ................................................................ 88 vi 3.2 Stabilization of copper fluoride adducts via hydrogen bonding ......................................... 89 3.2.1 Synthesis and characterization of a copper(II) fluoride ............................................... 90 3.2.2 Isolation of a copper(I) fluoride complex .................................................................... 92 3.3 Reactivity toward nitrite ..................................................................................................... 98 3.3.1 Motivation from Nature: Nitrite reductase .................................................................. 98 3.3.2 Reactivity toward silyl-nitrite .................................................................................... 100 3.3.3 Characterization of copper-containing product upon nitrite reduction ...................... 103 3.3.4 Confirmation of NO formation and control experiments .......................................... 104 3.3.5 Possible reaction pathway for nitrite reduction ......................................................... 106 3.4
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