A Cobalt–Dithiolene Complex for the Photocatalytic and Electrocatalytic Reduction of Protons

Abstract

The complex [Co(bdt)(2)](-) (where bdt = 1,2-benzenedithiolate) is an active catalyst for the visible light driven reduction of protons from water when employed with Ru(bpy)(3)(2+) as the photosensitizer and ascorbic acid as the sacrificial electron donor. At pH 4.0, the system exhibits very high activity, achieving >2700 turnovers with respect to catalyst and an initial turnover rate of 880 mol H(2)/mol catalyst/h. The same complex is also an active electrocatalyst for proton reduction in 1:1 CH(3)CN/H(2)O in the presence of weak acids, with the onset of a catalytic wave at the reversible redox couple of -1.01 V vs Fc(+)/Fc. The cobalt-dithiolene complex [Co(bdt)(2)](-) thus represents a highly active catalyst for both the electrocatalytic and photocatalytic reduction of protons in aqueous solutions.

Cobalt-dithiolene complexes for the photocatalytic and electrocatalytic reduction of protons in aqueous solutions

“…The CoðmntÞ − 2 catalyst 4 achieves the highest activity of the dithiolene complexes, achieving a total TON of approximately 9,000 (measured with respect to cobalt), with an initial turnover frequency up to 3450 h −1 . This level of activity places 4 among the most active H 2 generating catalysts reported (26,30,31). The systems remain active for 6-10 h before decomposition of catalyst and chromophore contribute to a gradual decrease in hydrogen evolution.…”

“…1,2-Benzenedithiol, 3,6-dichlorobenzenedithiol, sodium maleonitriledithiolate, toluenedithiol, cobalt(II) tetrafluoroborate hexahydrate, ½RuðbpyÞ 3 Cl 2 , potassium tert-butoxide, and tetrabutylammonium bromide were purchased from Aldrich and used without further purification. Catalyst 1 was synthesized according to a literature procedure (30).…”

“…We have previously noted that 1 does indeed quench *RuðbpyÞ 2þ 3 following good Stern-Volmer behavior with a quenching rate constant near the diffusion limit of i pc value was taken at top of catalytic wave. 4 × 10 10 M −1 s −1 (30). We find that complexes 2-4 also quench *RuðbpyÞ 2þ 3 following good Stern-Volmer behavior with quenching rate constants that are near the diffusion limit, ranging from…”

“…Based on these properties, we commenced an examination of dithiolene complexes of the 3d transition elements to determine if they would be active as catalysts for the reductive side of water splitting. In an initial disclosure, we reported that (Bu 4 NÞ½CoðbdtÞ 2 (1, where bdt ¼ 1; 2-benzenedithiolate) is an active electrocatalyst and photocatalyst for proton reduction in aqueous/organic media (30). Complex 1 exhibited high activity (>2; 700 TONs with respect to catalyst and an initial turnover frequency of >800∕h) when paired with RuðbpyÞ 3 2þ as the chromophore and ascorbic acid as the sacrificial electron donor under moderately acidic conditions.…”

Homogeneous ligand-centered hydrogen evolution and hydrogen oxidation : exploiting redox non-innocence to drive catalysis.

“…Dithiolenes are well-known to exhibit noninnocent redox behavior, affording ligand-centered reductions and oxidations. 11,12,143,153,161 This ligand non-innocence offers extremely reactive thiyl radicals. As detailed in ( Figure 9A) the facial arrangement of the PS chelates in [ReL 3 ] n enforces a symmetry preferred interligand addition route.…”