Role of Solvent Coordination in the Multi-electron Redox Cycle of Nickel Diethyldithiocarbamate.

Nickel(II) diethyldithiocarbamate, Ni II (dtc) 2 , is known to undergo a 2e - ligand-coupled electron transfer (LCET) oxidation to form [Ni IV (dtc) 3 ] + . However, the thermodynamics and kinetics of this 2e - process can be greatly affected by solvent coordination. For low coordinating solvents like acetonitrile and acetone, 2e - oxidation is observed via cyclic voltammetry (CV) at a single potential while stronger coordinating solvents like methanol, N , N -dimethylformamide, dimethyl sulfoxide, and pyridine exhibit a 1e - oxidation wave by formation of [Ni III (dtc) 2 (sol) x ] + intermediates. The decay of these complexes to eventually yield [Ni IV (dtc) 3 ] + was monitored as a function of CV scan rate and temperature to extract rate constants and activation parameters. A thorough analysis of activation parameters revealed that Δ H app ⧧ generally increased with solvent coordination ability, suggesting solvent dissociation was a key factor in the rate limiting step. However, Δ S app ⧧ was found to be negative for all solvents, suggesting an associative mechanism in line with dimer formation with Ni II (dtc) 2 to facilitate ligand exchange. Density function theory calculations supported the competitive nature of dissociative and associative steps. Using these calculations, we propose two paths for decay of [Ni III (dtc) 2 (sol) x ] + species based on the coordination strength of the solvent. These studies point to the ability of solvents to either aid or hinder multielectron LCET reactions.