Electrocatalytic proton reduction by an air-stable nickel(II)-thiolato PNN pincer complex

We report an air-stable nickel(II)-thiolato PNN pincer complex [(PNN)NiII(SC6H4Me)]+[MeC6H4SO3]− (PNN = 2-((di-tert-butylphosphinomethyl-6-diethylaminomethyl)pyridine)) which is capable of reducing protons at an overpotential of 0.54 V at low acid concentrations. The proton reduction can be catalysed using weak or strong acids such as acetic acid and trifluoroacetic acid respectively. In contrast, the chloro and nitrate derivatives of the nickel pincer complex behave as poorer catalysts. A mechanism accounting for the role of the ligand in proton reduction is also briefly outlined.