Dinuclear Iron(II)−Cyanocarbonyl Complexes Linked by Two/Three Bridging Ethylthiolates: Relevance to the Active Site of [Fe] Hydrogenases

Dinuclear iron(II)−cyanocarbonyl complex [PPN]2[Fe(CN)2(CO)2(μ-SEt)]2 (1) was prepared by the reaction of [PPN][FeBr(CN)2(CO)3] and [Na][SEt] in THF at ambient temperature. Reaction of complex 1 with [PPN][SEt] produced
the triply thiolate-bridged dinuclear Fe(II) complex [PPN][(CN)(CO)2Fe(μ-SEt)3Fe(CO)2(CN)] (2) with the torsion
angle of two CN- groups (C(5)N(2) and C(3)N(1)) being 126.9°. The extrusion of two σ-donor CN- ligands from
Fe(II)Fe(II) centers of complex 1 as a result of the reaction of complex 1 and [PPN][SEt] reflects the electron-rich
character of the dinuclear iron(II) when ligated by the third bridging ethylthiolate. The Fe−S distances (2.338(2)
and 2.320(3) Å for complexes 1 and 2, respectively) do not change significantly, but the FeII−FeII distance contracts
from 3.505 Å in complex 1 to 3.073 Å in complex 2. The considerably longer FeII−FeII distance of 3.073 Å in
complex 2, compared to the reported Fe−Fe distances of 2.6/2.62 Å in DdHase and CpHase, was attributed to the
presence of the third bridging ethylthiolate, instead of π-accepting CO-bridged ligand as observed in [Fe]
hydrogenases. Additionally, in a compound of unusual composition {[Na·5/2H2O][(CN)(CO)2Fe(μ-SEt)3Fe(CO)2(CN)]}n{1/2O(Et)2}n (3), the Na+ cations and H2O molecules combining with dinuclear [(CN)(CO)2Fe(μ-SEt)3Fe(CO)2(CN)]- anions create a polymeric framework wherein two CN- ligands are coordinated via CN-−Na+/CN-−(Na+)2 linkages, respectively.