Co(II) Complex with a Covalently Attached Pendent Quinol Selectively Reduces O 2 to H 2 O.

A Co(II) complex with the polydentate quinol-containing ligand H 2 qp1 acts as an efficient electrocatalyst for oxygen reduction. Without any additional electron-proton transfer mediators, the electrocatalysis is selective for H 2 O; a related complex that substitutes a phenol for the quinol, conversely, instead produces mostly H 2 O 2 under the same conditions. We propose that the ability of the redox-active quinol to donate two electrons impacts the product-determining step.