Preparative and structural studies on iron(ii)–thiolate cyanocarbonyls

A number of thermally stable iron(ii)–thiolate cyanocarbonyl complexes, cis, cis-[Fe(CN)2(CO)2(CS3-S, S)]2− (1), mer-[Fe(CO)2(CN)3(NCCH3)]− (2) mer-[Fe(CO)3(CN)(CS3-S, S)]− (3), cis-[Fe(CO)2(CN)(S(CH2)2S(CH2)2S-S, S, S)]− (4), [Fe(CO)2(CN)3Br]2− (5), mer-[Fe(CO)2(CN)3(m-SC6H4Br)]2− (6) and mer-[Fe(CO)2(CN)3(SPh)]2− (7) were isolated and characterized by IR and X-ray diffraction analysis. The extrusion of one strong σ-donor CN− ligand instead of CO from the iron(ii) center of the thermally stable complexes [FeII(CO)2(CN)3Br]2− (5) containing less electron-donating bromide reflects the electron-rich character of the mononuclear [FeII(CN)2(CO)2(CS3-S, S)]2− (1) when ligated by by the bidentate thiolate, and the combination of one cyanide, two carbonyls and a tridentate thiolate provides the stable complex 4 as a result of the reaction of complex 5 and chelating ligand [S(CH2)2S(CH2)2S]2−. The preference of the sixth ligand coordinated to the unsaturated [FeII(CO)(CN)2(CS3-S, S)]2− Fe(ii) center, the iron-site architecture of the bimetallic Ni–Fe active-site of [NiFe] hydrogenases, is a strong π-acceptor CO group. Scrutiny of the coordination chemistry of iron(ii)–thiolate cyanocarbonyl species [FeII(CO)x(CN)y(SR)z ]n− reveals that certain combinations of thiolate, cyanide and carbonyl ligands (3 ≤ y + z ≤ 4) bound to Fe(ii) are stable and this could point the way to understand the reasons for Nature’s choice of combinations of these ligands in hydrogenases.