Reactivity of a Dithiocarbamate-Ligated [W VI ≡S] Complex with Hydride Donors: Toward a Synthetic Mimic of Formate Dehydrogenase.

Formate dehydrogenase (FDH) enzymes catalyze redox interconversion of CO 2 and HCO 2 - , with a key mechanistic step being the transfer of H - from HCO 2 - to an oxidized active site featuring a [M VI ≡S] group in a sulfur-rich environment (M = Mo or W). Here, we report reactivity studies with HCO 2 - and other reducing agents of a synthetic [W VI ≡S] model complex ligated by dithiocarbamate (dtc) ligands. Reactions of [W VI S(dtc) 3 ][BF 4 ] ( 1 ) conducted in MeOH solvent generated [W VI S(S 2 )(dtc) 2 ] ( 2 ) and [W V S(μ-S)(dtc)] 2 ( 3 ) products by a solvolysis pathway that was accelerated by the presence of [Me 4 N][HCO 2 ] but did not require it. Under MeOH-free conditions, the reaction of 1 with [Et 4 N][HCO 2 ] produced some [W IV (μ-S)(μ-dtc)(dtc)] 2 ( 4 ), but predominantly [W V (dtc) 4 ] + ( 5 ), along with stoichiometric CO 2 detected by headspace gas chromatography (GC) analysis. Stronger hydride sources such as K-selectride generated the more reduced analogue, 4 , exclusively. The reaction of 1 with the electron donor, CoCp 2 , also produced 4 and 5 in varying amounts depending on reaction conditions. These results indicate that formates and borohydrides act as electron donors rather than hydride donors toward 1 , an outcome that diverges from the behavior of FDHs. The difference is ascribed to the more oxidizing potential of [W VI ≡S] complex 1 when supported by monoanionic dtc ligands that allows electron transfer to outcompete hydride transfer, as compared to the more reduced [M VI ≡S] active sites supported by dianionic pyranopterindithiolate ligands in FDHs.