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)(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(II) complex [PPN][(CN)(CO)(2)Fe(mu-SEt)(3)Fe(CO)(2)(CN)] (2) with the torsion angle of two CN- groups (C(5)N(2) and C(3)N(1)) being 126.9degrees. The extrusion of two sigma-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) Angstrom for complexes 1 and 2, respectively) do not change significantly, but the Fe-II-Fe-II distance contracts from 3.505 Angstrom in complex 1 to 3.073 Angstrom in complex 2. The considerably longer Fe-II-Fe-II distance of 3.073 Angstrom in complex 2, compared to the reported Fe-Fe distances of 2.6/2.62 Angstrom in DdHase and CpHase, was attributed to the presence of the third bridging ethylthiolate, instead of pi-accepting CO-bridged ligand as observed in [Fe] hydrogenases. Additionally, in a compound of unusual composition {[Na-5/2H(2)O][(CN)(CO)(2)Fe(mu-SEt)(3)Fe(CO)(2)(CN)]}(n){1/2O(Et)(2)}(n) (3), the Na+ cations and H2O molecules combining with dinuclear [(CN)(CO)(2)Fe(mu-SEt)(3)Fe(CO)(2)(CN)](-) anions create a polymeric framework wherein two CN- ligands are coordinated via CN--Na+/CN--(Na+)(2) linkages, respectively.