Redox Reactions of Nickel, Copper, and Cobalt Complexes with “Noninnocent” Dithiolate Ligands: Combined in Situ Spectroelectrochemical and Theoretical Study

The redox properties of copper, nickel, and cobalt complexes (MePh3P)­[M­(bdt)2] with the ligand benzene-1,2-dithiolate (bdt) and synthesized complexes (MePh3P)­[M­(bdtCl2)2] with the ligand 3,6-dichlorobenzene-1,2-dithiolate (bdtCl2) have been studied by cyclic voltammetry and in situ EPR–UV/vis/NIR spectroelectrochemistry. The addition of chlorine substituents to the 3- and 6-positions of the benzene ring not only facilitates the reduction of [M­(bdtCl2)2]− complexes but also leads to the remarkable stabilization of [M­(bdtCl2)2]2– dianions in solution. In contrast to the EPR-silent copper complexes, the solutions of nickel samples exhibit a broad singlet EPR signal at room temperature which becomes anisotropic at 100 K with a characteristic rhombic pattern. Cathodic reduction of copper and cobalt complexes leads to paramagnetic species having an EPR signal with splitting from 63,65Cu for copper and from 59Co for cobalt samples, confirming a strong contribution of the central atom with substantial delocalization of the unpaired spin onto the central atom. B3LYP/6-311g*/pcm calculations of the monoanions as well as of their oxidized and reduced forms were performed. The spin density of all open-shell ground states calculated for the investigated complexes in different redox states corresponds well to the experimental spectroelectrochemical data.