UNIVERSITY OF CALIFORNIA, IRVINE Synthesis, Characterization, and Electronic Structure of Heteromultimetallic Complexes Incorporating a Redox-Active Metalloligand DISSERTATION submitted in partial satisfaction of the requirements for the degree of DOCTOR OF PHILOSOPHY in Chemistry by Michael Kenneth Wojnar Dissertation Committee: Professor Alan F. Heyduk, Chair Professor Andrew S. Borovik Professor William J. Evans 2019 Portions of Chapter 2 © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim All other material © 2019 Michael Kenneth Wojnar DEDICATION To My family, my friends, and Ryan ii TABLE OF CONTENTS Page LIST OF FIGURES iv LIST OF TABLES viii LIST OF SCHEMES x ACKNOWLEDGEMENTS xi CURRICULUM VITAE xiii ABSTRACT OF THE DISSERTATION xvi CHAPTER 1: Introduction 1 CHAPTER 2: Heterobimetallic and Heterotrimetallic Clusters Containing a Redox–Active Metalloligand 19 CHAPTER 3: Ancillary Ligand Effects on Heterobimetallic Mo[SNS]2CuL2 Complexes 46 CHAPTER 4: Interrogation of Late First-Row Transition Metals Bridged by a Redox-Active Mo[SNS]2 Metalloligand 69 CHAPTER 5: Synthesis and Characterization of a Library of M[SNS]2 Metalloligands Incorporating Group IV, V, VI Metals 96 CHAPTER 6: Mixed Valency in Heterotrimetallic V[SNS]2{Ni(dppe)}2 124 iii LIST OF FIGURES Page Figure 1.1. Resonance structures of Ni(dtb)2 (dtb = dithiobenzil) (top); normal vs. inverted bonding scheme invoked in bis dithiolene chemistry, adapted from reference 9. 3 Figure 1.2. Two-state electron transfer model of Hush and Marcus. 4 Figure 1.3. Three-state model in a general system (left) and the three-state model of the Creutz-Taube ion (right). 6 Figure 1.4. Examples of metal–ligand–metal (left), ligand–metal–ligand (middle), and ligand–ligand– ligand mixed–valent architectures. 6 Figure 1.5. Examples of mixed-valent systems involving different bonding "metal–ligand–metal" mo- tifs: coordinate covalent bonds in Prussian Blue (left) and non-covalent hydrogen bonding in rutheni- um dimers (right). 7 Figure 1.6. Valence trapping vs. detrapping in monocation (left) and monoanionic (right) complexes of the Group 10 bis(iminosemiquinone) due to metal contributions to the molecular orbital of interest. 8 Figure 1.7. The Busch-Jicha complex (left) and the active site of acetyl-coenzyme A synthase (ACS). 11 Figure 1.8. Variation in vanadium–metal bond order as a function of metal identity and d electron i count (L = Pr2), adapted from reference 49. 12 Figure 1.9. "Metal–Metal–Metal" mixed valency motif incorporating metal-metal bonds. 13 Figure 1.10. Previous work with six-coordinate metalloligands: ferromagnetic coupling in Fe2[ONO]3 in the absence of direct Fe–Fe bonds (top) and an S=0 W[SNS]2Ni(dppe) with a formal W–Ni bond (bottom). 15 Figure 1.11. "Metal–Metal–Metal" architecture in M[SNS]2{M(dppe)}2 heteromultimetallic systems. 16 Figure 2.1. Active site of acetyl co-A synthase (middle) and M(N2S2) metalloligand (left) used to mimic this site synthetically. In comparison, M[SNS]2 (right) allows for the bridging of two metal centers and metal-metal interactions. 21 Figure 2.2. ORTEP diagram of Mo[SNS]2 (1), Mo[SNS]2Ni(dppe) (2), Mo[SNS]2{Ni(dppe)}2 (3). Ellipsoids are shown at 50% probability. Hydrogen atoms (and a pentane solvent molecule in 3) have been omitted for clarity. 23 1 Figure 2.3. H VT NMR spectra in tetrachloroethane-d2 (left) and Eyring plot (right) for Mo[SNS]2Ni(dppe) (2). 27 Figure 2.4. Cyclic voltammograms of (a) Mo[SNS]2 (1), (b) Mo[SNS]2Ni(dppe) (2),and (c) Mo[SNS]2{Ni(dppe)}2 (3) dissolved in THF. Measurements were made under N2 using a scan rate of –1 200 mV sec on 1.0 mM analyte solutions containing 0.10 M [Bu4N][PF6] as the supporting iv +/0 electrolyte. Potentials were referenced to [Cp2Fe] using an internal standard. The asterisk (arrowhead) denotes the open circuit potential. Voltammetric data were collected using three electrodes: glassy carbon working, platinum counter, and silver wire pseudo-reference. 28 Figure 2.5. General molecular orbital diagram (top) and frontier molecular orbital diagram with Kohn-Sham molecular orbitals for 3 (bottom). Orbital rendering was performed using VMD. 31 Figure 2.6. Metal-metal σ bond between molybdenum and nickel for Mo[SNS]2Ni(dppe) (2). 31 Figure 2.7. Three-center four-electron metal-metal bond between molybdenum and nickel ions for Mo[SNS]2{Ni(dppe)}2 (3). 32 Figure 2.8. General molecular orbital diagram (top) and frontier molecular orbital diagram with Kohn-Sham molecular orbitals for 3 (bottom). Orbital rendering was performed using VMD. 33 Figure 3.1. ORTEP diagrams of MoCu(dppe) (top left), MoCu(bpytBu2) (top right), and [K(THF)][Mo[SNS]2] (bottom). Ellipsoids are shown at 50% probability. Hydrogen atoms were omitted for clarity. 50 Figure 3.2. X-band EPR spectra, at 298 K (left column) and 77 K (right column) in THF, of Mo[SNS]2Cu(bpytBu2) (top row), Mo[SNS]2Cu(dppe) (middle row), [K(THF)][Mo[SNS]2] (bottom row). 55 Figure 3.3. Electronic absorption spectra of Mo[SNS]2Cu(dppe) (blue), Mo[SNS]2Cu(bpytBu2) (red), and [K][Mo[SNS]2] (black). 57 Figure 3.4. Spin density plots for Mo[SNS]2Cu(dppe) (left) Mo[SNS]2Cu(bpytBu2) (middle), and [K][Mo[SNS]2] (right) with the contribution of Mo in bold (isovalue = 0.00186). 58 Figure 3.5. Frontier molecular orbital picture of Mo[SNS]2Cu(dppe) (left) and Mo[SNS]2Cu(bpytBu2) (right). 58 Figure 3.6. Time-dependent density functional theory (TD-DFT) calculations demonstrating the main electronic transition (denoted by *) in Mo[SNS]2Cu(dppe). 59 Figure 4.1. Heterometallic ligand platforms used to investigate metal-metal interactions (left) and metalloligand platform used to bridge two metal centers and study metal-metal bonds in linear trimetallic systems. 71 Figure 4.2. ORTEP diagram for Mo[SNS]2{Co(dppe)}2 (left) and Mo[SNS]2{Cu(dppe)}2 (right) with thermal ellipsoids shown at 50% probability. Hydrogen atoms and solvent molecules (THF) have been omitted for clarity. 73 Figure 4.3. Isolation of the Mo[SNS]2 metalloligand in Mo[SNS]2{Cu(dppe)}2 (top) and Mo[SNS]2{Co(dppe)}2 demonstrating the Bailar twist and coordination geometry around the Mo ion. (M(dppe) and aryl rings of [SNS] ligand removed for clarity). 75 Figure 4.4. Overlay of the solid-state structure of Mo[SNS]2{Co(dppe)}2 (blue) with Mo[SNS]2{Cu(dppe)}2 (red) (left) and Mo[SNS]2{Co(dppe)}2 (blue) with Mo[SNS]2{Ni(dppe)}2 (green) (right). The phenyl substituents on the bidentate phosphine ligands have been omitted for clar- ity. 78 v Figure 4.5. Electronic absorption spectra of [Mo[SNS]2{M(dppe)}2] obtained in THF (M = Co (light brown), M = Cu (red), and M = Ni (green). 79 Figure 4.6. Cyclic voltammograms of [Mo[SNS]2{Co(dppe)}2] (top, brown), Mo[SNS]2{Cu(dppe)}2 (middle, red), and Mo[SNS]2{Ni(dppe)}2 (bottom, green) dissolved in THF. –1 Measurements were made under N2 using a scan rate of 200 mV sec on 1.0 mM analyte solutions +/ containing 0.10 M [Bu4N][PF6] as the supporting electrolyte. Potentials were referenced to [Cp2Fe] 0 using an internal standard. The asterisk (arrowhead) denotes the open circuit potential. Voltammetric data were collected using three electrodes: glassy carbon working, platinum counter, and silver wire pseudo-reference. 81 Figure 4.7. Spin density plot of Mo[SNS]2{Co(dppe)}2 (top) and metal-metal bonding Kohn-Sham molecular orbital (bottom). 82 Figure 4.8. Highest occupied molecular orbital (HOMO) in Mo[SNS]2{Cu(dppe)}2 (left) and time- dependent density functional theory (TD-DFT) calculation of the dominant transition in Mo[SNS]2{Cu(dppe)}2 (right). 83 Figure 4.9. General molecular orbital diagram for Mo[SNS]2{Ni(dppe)}2, illustrating the three-center bonding scheme found in these Mo[SNS]2{M(dppe)}2 heterotrimetallic systems. 84 Figure 4.10. Three-center metal-metal bonding scheme for Mo[SNS]2{M(dppe}2 (M = Co (light purple), Ni (green), Cu (red). 90 Figure 5.1. Active site of acetyl-coenzyme A synthetase (ACS) upon reduction (left) and M(N2S2)Fe hemilability (right). 97 – Figure 5.2. X-ray Crystal Structures of [M[SNS]2] (M = V, Nb, Ta) with thermal ellipsoids shown at 50% probability. Hydrogen atoms have been removed for clarity. 101 Figure 5.3. Bailar twist (θ) demonstrating the geometric constraints of a trigonal prism and trigonal antiprism (left) and definition of the two trigonal faces in M[SNS]2 metalloligands, denoted by red and blue colors (right). 101 Figure 5.4. Electronic absorption spectra of Kx[M[SNS]2] metalloligands in THF (M = Hf (yellow); Zr (orange); Ta (red); Nb (green); W (brown); Mo (purple) (Inset contains absorption spectra of K2[Ti[SNS]2] (maroon) and K[V[SNS]2] (blue)). 104 Figure 5.5. Differential pulse voltamograms of Kx[M[SNS]2] metalloligands (M (top to bottom) = Ti (maroon); Ta (red); Nb (green); V (blue); W (brown); Mo (purple)). 106 Figure 5.6. HOMO-LUMO gap energies for the Group IV (left) and Group V (right) metalloligands, calculated with the TPSS functional at the TZVP level of theory. 108 Figure 5.7. Time-dependent density functional theory (TD-DFT) calculations performed for K[Nb[SNS]2] (left) and W[SNS]2 (right), calculated with the TPSS functional at the TZVP level of theory. 109 Figure 5.8. Electronic structure of M[SNS]2 metalloligands. 111 Figure 5.9.