[Ni(P^Me₂N^Ph₂)₂](BF₄)₂ as an Electrocatalyst for H₂ Production

Abstract

A nickel(II) bis(diphosphine) complex, [Ni(PMe2NPh2)2](BF4)2 (PMe2NPh2 = 1,5-diphenyl-3,7-dimethyl-1,5-diaza-3,7-diphosphacyclooctane), has been synthesized and characterized. This complex, which contains pendant amines in the diphosphine ligand, is an electrocatalyst for hydrogen production by proton reduction. Using [(DMF)H]OTf as the acid, a turnover frequency of 1,540 s–1 was obtained with no added water, and a turnover frequency of 6,700 s–1 was found with 1.0 M water added. Thermochemical studies show that the hydride donor ability of [HNi(PMe2NPh2)2](BF4) is ΔG°H– = 54.0 kcal/mol, and we estimate a driving force for H2 elimination of 13.8 kcal/mol. [Ni(PMe2NPh2)2](BF4)2 is the fastest H2 production catalyst in the [Ni(PR2NR′2)2](BF4)2 family of complexes.