Electrocatalytic Hydrogen Production by a Nickel(II) Complex with a Phosphinopyridyl Ligand

Abstract

A novel nickel(II) complex [Ni(L)2Cl]Cl with a bidentate phosphinopyridyl ligand 6-((diphenylphosphino)methyl)pyridin-2-amine (L) was synthesized as a metal-complex catalyst for hydrogen production from protons. The ligand can stabilize a low Nioxidation state and has an amine base as a proton transfer site. The X-ray structure analysis revealed a distorted square-pyramidal NiIIcomplex with two bidentate L ligands in a transarrangement in the equatorial plane and a chloride anion at the apex. Electrochemical measurements with the NiII complex in MeCN indicate a higher rate of hydrogen production under weak acid conditions using acetic acid as the proton source. The catalytic current increases with the stepwise addition of protons, and the turnover frequency is 8400s-1 in 0.1 m [NBu4][ClO4]/MeCN in the presence of acetic acid (290equiv) at an overpotential of circa 590mV. A nickel(II) complex [Ni(L)2Cl]Cl (L= 6-((diphenylphosphino)methyl)pyridin-2-amine), having an amine base as a proton-transfer site, was synthesized and used as a hydrogen-production catalyst. Electrochemical measurements with the complex show that a higher rate of H2 production (turnover frequency=8400s-1) can be achieved under weak acid conditions using acetic acid as a proton source.