Dinuclear lron(ll)-Cyanocarbonyl Complexes Linked by Two/Three Bridging Ethylthioiates: Relevance to the Active Site of [Fe] Hydrogenases

Dinuclear iron(ll)-cyanocarbonyl complex [PPN]2[Fe(CN)2(CO)2(mu-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(ll) complex [PPN][(CN)(CO)2Fe(mu-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 twoalphaa-donor CN~ ligands from Fe(ll)Fe(ll) 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(ll) when ligated by the third bridging ethylthiolate. The Fe-S distances (2.338(2) and 2.320(3) A for complexes 1 and 2, respectively) do not change significantly, but the Fell-Fell distance contracts from 3.505 A in complex 1 to 3.073 A in complex 2. The considerably longer Fe"-Fe" distance of 3.073 A in complex 2, compared to the reported Fe-Fe distances of 2.6/2.62 A in DdHase and CpHase, was attributed to the presence of the third bridging ethylthiolate, instead of Ji-accepting CO-bridged ligand as observed in [Fe] hydrogenases. Additionally, in a compound of unusual composition {[Na.5/2H2O][(CN)(CO)2Fe(mu-SEt)3Fe(CO)2(CN)]}n{1/2O(Et)2}n (3), the Na^+ cations and H2O molecules combining with dinuclear [(CN)(C2)2Fe(mu-SEt)3Fe(CO)2(CN)]- anions create a polymeric framework wherein two CN~ ligands are coordinated via CN--Na^+/CN(Na^+)2 linkages, respectively.