Ligand Basicity and Chelate Effects on Sulfur Insertion vs. Sulfur Reduction by Zinc Thiolate Complexes.

4- and 5-coordinate zinc thiolate complexes supported either by bis(carboxamide)pyridine frameworks or by substituted tris(pyrazolyl)borate ligands react with elemental sulfur (S) following two distinct pathways. Some zinc thiolate moieties insert sulfur atoms to form zinc polysulfanide complexes, while others reduce sulfur and oxidize the thiolate. Here, we compare the effects of ligand electronics, strain, and sterics for selecting the respective reaction pathway.

Sulfane Decreases the Nucleophilic Reactivity of Zinc Thiolates: Implications for Biological Reactive Sulfur Species.

A zinc dithiolate complex supported by a [NS] ligand was studied as a model for zinc-mediated thiolate-disulfide exchange, enabling isolation of a zinc-bound mixed-disulfide intermediate. Solution-phase characterization of this zinc-disulfide complex indicates an interaction between the zinc center and the disulfide moiety that results in activation of the S-S bond for subsequent reactions. Comparison of this reaction with disulfide exchange by a previously prepared zinc tetrasulfanido complex demonstrates that sulfane sulfur (S) acts as an efficient thiolate trapping agent, that is, polysulfanide anions are much less basic than thiolates.

Reactivity of Zinc Thiolate Bonds: Oxidative Organopolysulfide Formation and S Insertion.

Zinc thiolate bonds are intriguing targets of study because of their redox noninnocence and prevalence in bioinorganic sites. A five-coordinate zinc dithiolate complex [EtN][LZn] (HL = ,'-di(2-sulfhydrylphenyl)-pyridine-2,6-dicarboxamide) was synthesized to study the oxidative reactivity of zinc thiolate bonds. Multiple chemically reversible reactions of the zinc thiolate bonds were identified.