Bimetallic Cooperativity in Proton Reduction with an Amido-Bridged Cobalt Catalyst.

The bimetallic catalyst [Co (L )(bpy) ]ClO (1), in which L is an [NN' O ] fused ligand, efficiently reduced H to H in CH CN in the presence of 100 equiv of HOAc with a turnover number of 18 and a Faradaic efficiency of 94 % after 3 h of bulk electrolysis at -1.6 V (vs. Ag/AgCl). This observation allowed the proposal that this bimetallic cooperativity is associated with distance, angle, and orbital alignment of the two Co centers, as promoted by the unique Co-N -Co environment offered by L . Experimental results revealed that the parent [Co Co ] complex undergoes two successive metal-based 1 e reductions to generate the catalytically active species [Co Co ], and DFT calculations suggested that addition of a proton to one Co triggers a cooperative 1 e transfer by each of these Co centers. This 2 e transfer is an alternative route to generate a more reactive [Co (Co -H )] hydride, thus avoiding the Co -H required in monometallic species. This [Co (Co -H )] species then accepts another H to release H .