Anion controlled selectivity in oxygen reduction catalysed by a dinuclear cobalt N,O-Schiff base complex.

A new dinuclear cobalt complex selectively catalyses 4e- reduction of O2 to water in methanol containing acetic acid. Its TOF of 0.031 s-1 and overpotential of 690 mV outperform the few previous Co N,O-chelate based catalysts for the 4e- ORR. Replacing acetic acid with NH4PF6 as proton source induces a complete and unprecedented switch to the H2O2 producing 2e- pathway. Mechanistic studies suggest a peroxo intermediate for both pathways, with acetate coordination/decoordination determining the destination of a key electron transfer.