Comparison of Cobalt and Nickel Complexes with Sterically Demanding Cyclic Diphosphine Ligands: Electrocatalytic H2Production by [Co(PtBu2NPh2)(CH3CN)3](BF4)2

The cyclic diphosphine ligands P t Bu 2 N Ph 2 and P t Bu 2 N Bz 2 have been synthesized and used to prepare new complexes of Co(II) and Ni(II) with the formula [M(P t Bu 2 N R 2 )(CH 3 CN) n ](BF 4 ) 2 ( n = 2, 3). The products have been characterized by variable-temperature NMR data, X-ray diffraction studies, and cyclic voltammetry, and properties of the new complexes have been compared with those of previously studied complexes containing P Ph 2 N R 2 ligands. The variation of either phosphorus or nitrogen substituents in these ligands can result in significant differences in the structure, electrochemistry, and reactivity of the metal complexes. [Co(P t Bu 2 N Ph 2 )(CH 3 CN) 3 ](BF 4 ) 2 is found to be an effective electrocatalyst for the formation of hydrogen using bromoanilinium tetrafluoroborate as the acid, with a turnover frequency of 160 s −1 and an overpotential of 160 mV. These cobalt derivatives are a promising class of catalysts for further study and optimization.