Synthesis and Characterization of Co Complexes Coordinated by a Tetraanionic Bis(amidateanilido) Ligand

The synthesis and characterization of a square planar Co^II complex coordinated by the tetraanionic bis(amidateanilido) L^4- ligand, 1, and its corresponding one-electron oxidized forms 2, 3, and 4 are discussed herein. 1 undergoes aerobic oxidation to form 2, a square planar S = 1 Co^III complex. This aerobic reactivity is attributed to a remarkably negative Co^II/Co^III potential, as observed in its cyclic voltammogram, which is among the most negative Co^II/Co^III couples reported. This supports the conclusion that the L^4- ligation is strongly stabilizing to the oxidized Co^III center. The cyclic voltammogram of 2 also reveals that further oxidations are possible at mild potentials. Indeed, the stoichiometric addition of a suitable chemical oxidant yields a ligand-oxidized S = 1/2 Co^III complex, 3, while the addition of a further equivalent of the oxidant putatively yields 4. The formation of the ligand oxidized species 3 suggests that bis(amidateanilido) ligation can further behave as a redox-active ligand upon additional oxidation.