Bioinspired Tungsten Dithiolene Catalysts for Hydrogen
Evolution: A Combined Electrochemical, Photochemical, and Computational
Study
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Abstract
Bis(dithiolene)tungsten
complexes, W<sup>VI</sup>O<sub>2</sub> (L
= dithiolene)<sub>2</sub> and W<sup>IV</sup>O (L = dithiolene)<sub>2</sub>, 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<sup>–1</sup>), with relatively high overpotentials
(700 mV). They also catalyze proton reduction into hydrogen upon visible
light irradiation, in combination with [Ru(bipyridine)<sub>3</sub>]<sup>2+</sup> 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<sup>VI</sup>O<sub>2</sub> (L = dithiolene)<sub>2</sub> complex acts as a precatalyst and hydrogen
is further formed from a key reduced W–hydroxo–hydride
intermediate