Investigations into the Reactivity of Transition Metal Complexes with Redox-Active Ligands for Proton Coupled Electron Transfer and Nitrene Transfer
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Investigations into the Reactivity of Transition Metal Complexes with Redox-Active Ligands for Proton Coupled Electron Transfer and Nitrene Transfer

  • Author(s): Charette, Bronte Joan
  • Advisor(s): Heyduk, Alan F
  • et al.

The theme of this dissertation centers around understanding the propensity of transitionmetal complexes with redox and proton non-innocent ligands to serve as proton and electron transfer agents either in proton-coupled electron transfer or group transfer reactivity. Chapter 2 describes kinetic and thermodynamics investigations into ligand-centered hydrogen-atom transfer (HAT) reactivity for a family of Group 10 metal complexes containing a tridentate pincer ligand derived from bis(2-mercapto-p-tolyl)amine, [SNS]H3. Six new metal complexes of palladium and platinum were synthesized with the [SNS] ligand platform in different redox and protonation states to complete the Group 10 series previously reported with nickel. Hydrogen-atom transfer (HAT) reactivity was examined for this family of nickel, palladium, and platinum complexes to determine the impact of metal ion on the ligand-centered reactivity. Chapter 3 discusses the preparation of a pseudo-tetrahedral cobalt (II) complex bearing the redox and proton non-innocent ligand, [SN(H)S]2–. The [SN(H)S]Co(DMAP)2 complex was subject reactivity studies with p-tolylazide to reveal its transformation into p-toluidine through two H-atom transfers. To elucidate the electronic structure of the cobalt by-product, reactivity studies with TEMPO•, DFT studies and kinetic analysis were conducted and indicated a resulting four coordinate square planar [SNS]Co(DMAP) as a result electron transfer from the metal and ligand deprotonation through a binuclear mechanism. Chapter 4 examines a new nickel(II) complex, [ON(H)O]Ni(PPh3) ([ON(H)O]2– = bis(3,5-di-tert-butyl-2-phenoxy)amine), bearing a protonated redox-active ligand, for its ability to serve as a hydrogen-atom (H●) and hydride (H–) donor. Bond dissociation free energy (BDFE) and hydricity (ΔG˚H–) measurements benchmark the thermodynamic propensity of this complex to participate in ligand-centered H● and H– transfer reactions. The products of both (H●) and hydride (H–) reveal interesting nickel products with unusual geometries. Chapter 5 investigates ligand displacement and nitrene transfer reactivity for the anionic {[ONOcat]Ni(L)}1– complex where L = PPh3 and pyridine. Here the redox-active ligand undergoes a single electron transfer to a nitrene substrate while the metal remains in the same oxidation date through a binuclear pathway. While the nickel imido complex was unable to be isolated and fully characterized, the identification of a two-electron nitrene transfer product, carbodiimide, suggests a transient nickel imido complex. Appendix A examines the potential diverted pathways and side-products formed during the unsuccessful catalytic reactivity and attempts to isolate the nickel imido discussed in Chapter 5.

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