Unexpected Formation of a Cobalt(III) Phenoxazinylate Electron Reservoir

The redox-active ligand N,N′-bis(3,5-di-tert-butyl-2-hydroxyphenyl)-1,2-phenylenediamine (H4L), known for supporting catalytic processes with both late and early transition metals, unexpectedly undergoes an unusual and thus far unobserved cyclization. Upon equimolar treatment of a cobalt(II) salt in the presence of Et3N under aerobic conditions, a ligand rearrangement occurs to afford an unprecedented phenoxazinyl radical moiety (L′). The resulting bisligated Co complex, thoroughly characterized structurally and electronically and analyzed by multiple experimental and computational approaches, is presented. It is shown to traverse oxidation states from 2+ to 3–, spanning a thermodynamic window of approximately 2 V.