Nickel(ii) PE1CE2P pincer complexes (E = O, S) for electrocatalytic proton reduction.

Nickel(ii) chloride and thiolate complexes with iPrPE1CE2PiPr (E = O, S) pincer ligands were investigated as electrocatalysts for the hydrogen evolution reaction in CH3CN in the presence of acetic acid and trifluoroacetic acid. The bis(thiophosphinite) (S,S) chloride complex reduced protons at the lowest overpotential in comparison with the bis(phosphinite) (O,O) and mixed phosphinite-thiophosphinite (O,S) complexes. A combination of electrochemical, NMR and UV-vis spectroscopic and mass spectrometric experiments provides mechanistic insights into the catalytic cycle for proton reduction to dihydrogen.