Electrocatalytic Hydrogen Evolution and Hydrogen Oxidation with a Ni(PS)2 Complex

Tetra‐coordinate Ni II and Zn II complexes employing the PS chelates 2‐(diphenylphosphanyl)benzenethiol (HL 1 ) and 2‐(diisopropylphosphanyl)benzenethiol (HL 2 ) have been synthesized and characterized by spectroscopic, structural, and electrochemical methods. All complexes were screened for electrocatalytic activity for hydrogen evolution with acetic acid and hydrochloric acid and hydrogen oxidation in the presence of triethylamine. The nickel complex Ni(L 1 ) 2 ( 1 ) was found to reduce protons from external acids to generate hydrogen with a turnover frequency of 140 s –1 at an overpotential of 1.1 V and cleave dihydrogen using redox active base triethylamine (Et 3 N) with a turnover frequency of 23 s –1 at an overpotential of 0.33 V. Ni(L 2 ) 2 ( 3 ) was also found to be an active catalyst for dihydrogen oxidation, but inefficient for proton reduction due to inaccessible Ni (II/I) reduction in the potential window. Zn(L 1 ) 2 ( 2 ) and Zn(L 2 ) 2 ( 4 ) complexes were found to be inadequate for their electrocatalytic behaviour towards both the reactions.