The Monoanionic π-Radical Redox State of α-Iminoketones in Bis(ligand)metal Complexes of Nickel and Cobalt

The electronic structures of nickel and cobalt centers coordinated by two α-iminoketone ligands have been elucidated
using density functional theory calculations and a host of physical methods such as X-ray crystallography, cyclic
voltammetry, UV−vis spectroscopy, electron paramagnetic resonance spectroscopy, and magnetic susceptibility
measurements. In principle, α-iminoketone ligands can exist in three oxidation levels:  the closed-shell neutral form
(L)0, the closed-shell dianion (Lred)2-, and the open-shell monoanion (L•)-. Herein, the monoanionic π-radical form
(L•)- of α-iminoketones is characterized in the compounds [(L•)2Ni] (1) and [(L•)2Co] (3), where (L•)- is the one-electron-reduced form of the neutral ligand (t-Bu)NCHC(Ph)O. The metal centers in 1 and 3 are divalent,
high-spin, and coupled antiferromagnetically to two ligand π radicals. These bis(ligand)metal complexes can be
chemically oxidized by two electrons to give the dications [trans-(L)2Ni(CH3CN)2](PF6)2 (2) and [trans-(L)2Co(CH3CN)2](PF6)2 (4), wherein the ligands are in the neutral form.