Redox Transformations of Sulfane Sulfur at Zinc Thiolate Complexes and Other Metal Cations

This dissertation details investigations into the reactivity between Zn-S bonds in molecular zinc thiolate complexes and elemental sulfur. With spectroscopic, voltammetric, and crystallographic evidence, changes in both metal cation with benzenethiolate anion and the ligand environment of zinc thiolate complexes were observed to influence whether sulfur was inserted, resulting in zinc polysulfanide products, or reduced via thiolate oxidation. Chapter 2 describes the comparison of nucleophilic reactivity between synthetic zinc dithiolate and zinc tetrasulfanide complexes. Comparing rates of catalytic thiolate-disulfide exchange as well as alkylation kinetics demonstrates that sulfane sulfur decreases the nucleophilic reactivity of the less basic tetrasulfanide moiety when compared to that of the zinc thiolate. Chapter 3 describes the study of the shifts induced by redox-inert metal cations in the equilibria that results from reaction between thiolate anion and elemental sulfur, forming distributions of polysulfanide anions, polysulfide anions, and organic disulfide species. Spectroscopic characterization was used to track solution-phase speciation of reduced sulfur species and thiolate oxidation to organic disulfide. Electrochemical analysis reveals changes in equilibria in the presence of metal cations results from metal-sulfur interactions which shift the sulfur reduction and thiolate oxidation half-reaction potentials. Together with computational studies, the stability of strong, covalent metal polysulfide interactions of more highly-charged cations over those of metal thiolates or metal polysulfanides is shown to promote sulfur reduction and thiolate oxidation pathways over sulfur catenation at thiolate. Chapter 4 describes the effects of ligand environment in zinc thiolate complexes on their reactivity with sulfur. Modulation of thiolate-containing ligand across a series of 4- and 5-coordinate platforms suggests a dissociative mechanism of thiolate nucleophilicity dependent on ligand electronics and chelation. More electron-rich and monodentate thiolate donors were observed to favor sulfur reduction and thiolate oxidation while electron-poor, chelating thiolate moieties selectively insert sulfur to form zinc polysulfanide complexes.