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

Abstract

Nickel(II) chloride and thiolate complexes with ^iPrPE¹CE²P^iPr (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.