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Stabilizing Metal-Alanes and Metal-Metal Multiple Bonds to Effect Small Molecule

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Stabilizing Metal-Alanes and Metal-Metal Multiple Bonds to Effect Small Molecule Stabilizing Metal-Alanes and Metal-Metal Multiple Bonds to Effect Small Molecule Transformations A Thesis SUBMITTED TO THE FACULTY OF UNIVERSITY OF MINNESOTA BY Paul Alexander Rudd IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Professor Connie C. Lu October, 2018 © Paul Alexander Rudd, 2018 Acknowledgements I have enjoyed my time in Minnesota, thanks in large part to my friends here. As an early member of a new group, I’m forever indebted to the people who helped guide me through my early years in the lab: the ladies of the McNeil group, Kristen, Elodie, and Emily; Keying, our sagacious postdoc; and, Kit, Deanna, and Aubrey, the first students to trek into the unknown. Of course, I’ve made many other friends along the way. Thanks to the rest of the Lu group, the Tolman, Que, and Ellis groups, who always made themselves available when we needed help. I would also like to acknowledge my friends in the Joint Safety Team, which was worth it just to get to know the three Katies, Ian, Brian, Nick, Kelly, Anna, and everyone else. I would also like to acknowledge the mentorship I have received, which has substantially influenced the course of my career. Professors Cora MacBeth and Justin Gallivan at Emory University (Atlanta, GA) played an instrumental role in my genesis as an inorganic chemist, even though Justin was ostensibly teaching a class on bio-organic chemistry. At Minnesota, I have to thank Prof. John Ellis—John has always been a good sport no matter what esoteric topic I’ve dropped by to bother him about, and his generous donation of 2,2,2-crypt (1 g) made a large part of chapters 4 and 5 possible. Additionally, much to the annoyance of my labmates, I’ve picked up John’s love of pKa values. Professor Larry Que taught me to think more analytically, especially regarding what your experiments do not tell you. We will also never forget that “phosphines are not biologically relevant!” (It also turns out, however, this is an insufficient reason not to give an MPIG seminar.) Lastly, I would like to thank Professor Connie Lu, who has taught me innumerable lessons both inside and outside of the lab. Her willingness to let us follow our own interesting projects was extremely liberating, and her patience when we got stuck was gratifying. Looking back, I don’t think I could have picked a better advisor, which I believe that is the highest praise I can give. i Table of Contents Acknowledgements .............................................................................................................. i List of Tables ...................................................................................................................... v List of Figures .................................................................................................................... vi Introduction ......................................................................................................................... 1 1.1 Bio-inspired Strategies for Small Molecule Activation ................................................ 2 1.3 Multiple bonds between two transition metals ........................................................... 24 1.4 Scope of Thesis ........................................................................................................... 35 Metal-Alane Adducts with Zero-Valent Nickel, Cobalt, and Iron .................................... 36 2.1 Overview ..................................................................................................................... 37 2.2 Introduction ................................................................................................................. 38 2.3 Results and Discussion ............................................................................................... 43 2.3.1 Nuclear Magnetic Resonance Studies .............................................................................. 46 2.3.2 Single Crystal X-ray Diffraction and Infrared Spectroscopy Studies .............................. 52 2.3.3 Cyclic Voltammetry Studies ............................................................................................. 59 2.3.4 UV-vis-NIR Spectroscopy and Density Functional Theory Calculations ........................ 63 2.4 Conclusions ................................................................................................................. 68 2.5 Experimental ............................................................................................................... 69 Dinitrogen Activation at Cobalt and Iron Metallalumatranes ........................................... 78 ii 3.1 Overview ..................................................................................................................... 79 3.2 Introduction ................................................................................................................. 81 3.3 Results and Discussion ............................................................................................... 86 3.3.1 Nuclear Magnetic Resonance Studies .............................................................................. 87 3.3.2 Single Crystal X-ray Diffraction Studies ......................................................................... 99 3.3.3 Mössbauer and Electron Paramagnetic Resonance Spectroscopy Studies ..................... 106 3.3.4 Density Functional Theory Calculations ........................................................................ 110 3.3.5 Preliminary Results with Iron Bimetallics of Ga3+, In3+, and Sc3+ ................................. 112 3.3.6 Preliminary Results with Cobalt Bimetallics of Ga3+, In3+, and Sc3+ ............................. 120 3.4 Conclusions ............................................................................................................... 124 3.5 Experimental ............................................................................................................. 125 Multiple Metal-Metal Bonds in Iron-Chromium Complexes ......................................... 137 4.1 Overview ................................................................................................................... 138 4.2 Introduction ............................................................................................................... 139 4.3 Results and Discussion ............................................................................................. 146 4.3.1 Nuclear Magnetic Resonance Studies ............................................................................ 146 4.3.2 Cyclic Voltammetry Studies ........................................................................................... 150 4.3.3 Electron Paramagnetic Resonance Spectroscopy, Mössbauer Spectroscopy, and SQUID Magnetometry Studies ............................................................................................................. 152 4.3.5 Single Crystal X-ray Diffraction Studies ....................................................................... 158 4.3.6 Computational Studies .................................................................................................... 160 4.5 Experimental ............................................................................................................. 164 iii A Comparison of Isoelectronic Multiple Bonds in Chromium-M (M = Cr, Mn, Fe) Complexes ....................................................................................................................... 172 5.1 Overview ................................................................................................................... 173 5.2 Introduction ............................................................................................................... 174 5.3 Results and Discussion ............................................................................................. 177 5.3.1 Synthesis and Cyclic Voltammetry ................................................................................ 177 5.3.2 Nuclear Magnetic Resonance and Electron Paramagnetic Resonance Studies .............. 179 5.3.3 Single Crystal X-ray Diffraction Studies ....................................................................... 185 5.3.4 Evaluation of the Diamagnetic Anisotropy of Metal-Metal Bonds ................................ 189 5.3.5 Theoretical Calculations ................................................................................................. 192 5.3.6 UV-vis-NIR and resonance Raman (rR) Spectroscopy .................................................. 198 5.3.7 Mössbauer spectroscopy ................................................................................................. 203 5.4 Conclusions ............................................................................................................... 208 5.5 Experimental ............................................................................................................. 209 References ....................................................................................................................... 218 iv List of Tables Table 1.1 Comparison of quadruply bonded Group 6 homo- and heterobimetallic species ........................................................................................................................................... 32 Table 1.2 Comparison of structurally characterized heterobimetallic phorphyrin complexes ........................................................................................................................
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