Directing Group Strategy for the Isolation of Organoselenium(VI) Benzoselenonates: Metal-Free Catalysts for Hydrogen Evolution Reaction

The exploration of fourth-period
organoelements, particularly
organoseleniums
in their highest VI oxidation state, is limited owing to their stability
and synthesis. Herein, the isolation of a new class of quinolinyl-embedded,
hexavalent selenium(VI) benzoselenonates has been discussed and further
evaluated for a metal-free electrocatalytic hydrogen evolution reaction
(HER). The Se(VI) benzoselenonates exhibited high Faradaic efficiency
(F.E.) of metal-free H2 gas production up to 86% with a
very good turnover number (TON) up to 43 and moderate overpotential
(η) of 500 mV; in the presence of mild acetic acid source in
a less deprotonating DMF solvent. Taken together with various (NMR,
UV–vis, and EPR) spectroscopic and DFT computation studies,
a plausible HER pathway is proposed, which suggests that the electrochemical
reduction of quinolinyl ring is the initiation step and Se(VI) acts
as the reaction site by involving a hydridic type of intermediate
for the electrochemical H2 gas generation.