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.