Thiolate-Bridged Nickel–Iron and Nickel–Ruthenium Complexes Relevant to the CO-Inhibited State of [NiFe]-Hydrogenase

By employing S­(CH₂CH₂S^–)₂ (tpdt) and O­(CH₂CH₂S^–)₂ (opdt) as bridging ligands, two nickel–iron and two nickel–ruthenium heterodimetallic complexes, [Cp*M­(μ-1κ³SSS′:2κ²SS-tpdt)­Ni­(dppe)]­[PF₆] (1, M = Fe; 3, M = Ru) and [Cp*M­(μ-1κ³SSO:2κ²SS-opdt)­Ni­(dppe)]­[PF₆] (2, M = Fe; 4, M = Ru) (Cp* = η⁵-C₅Me₅; dppe = Ph₂P­(CH₂)₂PPh₂), were obtained by a one-pot synthetic method and were identified by spectroscopy and X-ray crystallography. At 1 atm of CO, the pendant oxygen atom dissociated from the iron or ruthenium center and rapidly transferred to the nickel center when a CO molecule attacked the iron or ruthenium center in 2 and 4. However, there was no similar reaction occurring in 1 and 3 with the pendant sulfur atom. We confirmed the solid-state structure of the CO complex [Cp*Fe­(t-CO)­(μ-1κ²SS:2κ³SSO-opdt)­Ni­(dppe)]­[PF₆] (5), which represents a possible configuration in the CO-inhibited state of [NiFe]-hydrogenase and exhibits no catalytic activity in electrochemical proton reduction.