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

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 Ni oxidation state and has an amine base as a proton transfer site. The X‐ray structure analysis revealed a distorted square‐pyramidal NiII complex with two bidentate L ligands in a trans arrangement 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 8400 s−1 in 0.1 m [NBu4][ClO4]/MeCN in the presence of acetic acid (290 equiv) at an overpotential of circa 590 mV. Der Nickel(II)‐Komplex [Ni(L)2Cl]Cl (L=6‐((Diphenylphosphanyl)methyl)pyridin‐2‐amin) mit einer basischen Aminposition für den Protonentransfer wurde synthetisiert und als Katalysator in der Wasserstofferzeugung erprobt. Elektrochemische Messungen zeigen, dass die H2‐Erzeugung mit Essigsäure als Protonenquelle unter schwach sauren Bedingungen beschleunigt werden kann (Umsatzfrequenz 8400 s−1).