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.