Nickel-Molybdenum and Nickel-Tungsten Dithiolates: Hybrid Models for Hydrogenases and Hydrodesulfurization

The heterobimetallic complexes [(dppe)Ni(pdt)Mo(CO)₄], [(dcpe)Ni(pdt)Mo(CO)₄], [(dppe)Ni(pdt)W(CO)₄] and [(dcpe)Ni(pdt)W(CO)₄] {dppe = Ph₂P(CH₂)₂PPh₂; dcpe = Cy₂P(CH₂)₂PCy₂; pdt^2- = ^-S(CH₂)₃S^-} have been prepared and structurally characterized. The internuclear separation in these Ni^IIM⁰ species is highly sensitive to diphosphine basicity and is smallest in the dppe complexes wherein the planar Ni centres are electron-poor and require interaction with the group 6 metal. The Ni^IIW⁰ species [(dppe)Ni(pdt)W(CO)₄] was converted into its stable conjugate acid [(dppe)Ni(pdt)HW(CO)₄]⁺, a rare example of a nickel-tungsten hydride. This Ni^IIHW^II complex is an electrocatalyst for H⁺ reduction and is relevant to both biological and synthetic H₂-processing catalysts.