Bioinspired Tungsten Dithiolene Catalysts for Hydrogen Evolution: A Combined Electrochemical, Photochemical, and Computational Study

Bis­(dithiolene)­tungsten complexes, W^VIO₂ (L = dithiolene)₂ and W^IVO (L = dithiolene)₂, which mimic the active site of formate dehydrogenases, have been characterized by cyclic voltammetry and controlled potential electrolysis in acetonitrile. They are shown to be able to catalyze the electroreduction of protons into hydrogen in acidic organic media, with good Faradaic yields (75–95%) and good activity (rate constants of 100 s^–1), with relatively high overpotentials (700 mV). They also catalyze proton reduction into hydrogen upon visible light irradiation, in combination with [Ru­(bipyridine)₃]²⁺ as a photosensitizer and ascorbic acid as a sacrificial electron donor. On the basis of detailed DFT calculations, a reaction mechanism is proposed in which the starting W^VIO₂ (L = dithiolene)₂ complex acts as a precatalyst and hydrogen is further formed from a key reduced W–hydroxo–hydride intermediate

A Bioinspired Nickel(bis-dithiolene) Complex as a Homogeneous Catalyst for Carbon Dioxide Electroreduction

Inspired by the metal active sites of formate dehydrogenase and CO-dehydrogenase, a nickel complex containing a NiS₄ motif with two dithiolene ligands mimicking molybdopterin has been prepared and structurally characterized. During electroreduction, it converts to a good catalyst for the reduction of CO₂ into formate as the major product, together with minor amounts of carbon monoxide and hydrogen, with reasonable overpotential requirement, good faradaic yield, and notable stability. Catalysis operates on a mercury electrode and dramatically less on a carbon electrode, as observed in the case of [Ni­(cyclam)]²⁺ complexes. Density functional theory (DFT) computations indicate the key role of a Ni­(III)-hydride intermediate and provide insights into the different reaction pathways leading to HCOOH, CO, and H₂. This study opens the route toward a new, yet unexplored, class of mononuclear sulfur-coordinated Ni catalysts for CO₂ reduction