Synthesis, crystal structure and protonation of the asymmetric iron-only hydrogenase model [Fe2(CO)3(μ-pdt){μ,η2-Ph2PCH2CH2P(Ph)CH2CH2PPh2}] (pdt = SCH2CH2CH2S)

Heating [Fe2(CO)6(μ-pdt)] (pdt = SCH2CH2CH2S) and bis(2-diphenylphosphinoethyl) phenylphosphine (triphos) in toluene gives [Fe2(CO)3(μ-pdt){μ,η2-Ph2PCH2CH2P(Ph)CH2CH2PPh2}], the major form of which has been characterised crystallographically. The complex is highly asymmetric; while one iron centre has the expected square-based pyramidal coordination environment, the second is nearer a trigonal bipyramid. In solution at room temperature, four isomers of the major form interconvert via two processes which can be frozen out at low temperature, while protonation affords a bridging hydride complex which appears to be static at all temperatures.