Achieving
multielectron activity at first-row transition-metal
complexes has important implications for homogeneous catalysis using
earth-abundant metals. Here, we report a family of cobalt–phenylenediamide
complexes that undergo reversible 2e– oxidation
regardless of the ligand substituents, enabling unprecedented multielectron
redox tuning over 0.5 V and, in each case, affording the dicationic
Co(III)-benzoquinonediimine species. The neutral complexes are best
described as delocalized systems with π-bonding in the metallocycle,
consistent with a closed-shell singlet ground state predicted by density
functional theory (DFT) calculations. Our DFT results also predict
an ECE pathway for 2e– oxidation (ECE = electrochemical
step, chemical step, electrochemical step), where the first 1e– step involves redox-induced electron transfer to yield
a Co(II) intermediate. Disruption of the metallocycle bonding in this
state enables a change in the coordination geometry through association
of an addition ligand, which is critical for accessing the potential
inversion. The electronic properties of the phenylenediamide ligand
govern whether the second electron is lost from the ligand or metal,
providing a remarkable example of tunable 2e– behavior
at first-row systems.