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, <b>1</b>^<b>2-</b>, and its corresponding one-electron oxidized forms <b>2</b>^<b>-</b>, <b>3,</b> and <b>4</b>^<b>+</b> are discussed herein. <b>1</b>^<b>2-</b> undergoes aerobic oxidation to form <b>2</b>^<b>-</b>, a square planar <i>S</i> = 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 <b>2</b>^<b>-</b> also reveals that further oxidations are possible at mild potentials. Indeed, the stoichiometric addition of a suitable chemical oxidant yields a ligand-oxidized <i>S</i> = 1/2 Co^III complex, <b>3</b>, while the addition of a further equivalent of the oxidant putatively yields <b>4</b>^<b>+</b>. The formation of the ligand oxidized species <b>3</b> suggests that bis(amidateanilido) ligation can further behave as a redox-active ligand upon additional oxidation.