Reduction of oxygen catalyzed by nickel diphosphine complexes with positioned pendant amines

Nickel(II) bis(diphosphine) complexes that contain positioned bases in the second coordination sphere have been found to catalyze the reduction of O-2 with H-2 to selectively form water. The complexes also serve as electrocatalysts for the reduction of O-2 with the addition of a weak acid. In contrast, a closely related nickel diphosphine complex without the positioned bases is catalytically inactive for O-2 reduction. These results indicate that pendant bases in synthetic catalysts for O-2 reduction can play a similar role to proton relays in enzymes, and that such relays should be considered in the design of catalysts for multi-electron and multi-proton reactions.