offer the possibility to study bicentric metal-centered reactions between chiral complexes and chiral or prochiral substrates in order to achieve asymmetric syntheses.Formation of [Fe2(CO)(NO)(p-"S4n)2]PF, (3) from 2 and NOPF,.proves the accessibility of coordination sites at the iron centers in 2. Surprisingly, only one of the two CO ligands in 2 can be substituted by NO' . This indicates an interaction of the iron centers via thiolato bridges such that the C O / N O + substitution at one iron center reduces the electron densitv at the second [Fe("S2")2]22-(6). The results show that mononuclear iron carbonyl complexes with multidentate thioether thiolato ligands can be used as synthons for the synthesis of binuclear and possibly even polynuclear complexes. The binuclear complexes described here have model character for several iron oxidoreductases with respect to their structure, e g , coordination sphere of sulfur and chirotopicity of metal centers, as well as to their reactivity shown by the coordination of "soft" u-A ligands CO and NO to the iron centers.Acknowledgment. These investigations were supported by the Deutsche Forschungsgemeinschaft and by the Fonds der Chemischen Industrie. W e gratefully acknowledge this support. iron center in the molecule, preventing the subskution of the second CO ligand. Interaction between the iron centers is also revealed by IR and Mossbauer spectra of 2 and 3.The iron centers of 2 are 18-electron confieurated. Substitution of the 2-electron donor CO by the 3-electr;n donor NO leads to metal centers exceeding the noble gas configuration. As a conthe Fe-S(thiolato) bridges are cleaved, and mononuclear(4) forms in which the Supplementary Material Available: Listings of crystallographic data and data collection procedures, anisotropic thermal parameters, complete bond distances and bond angles, and fractional coordinates of atoms and isotropic thermal parameters (1 5 pages); listings of Fo and Fc values (24 pages). Ordering information is given on any current masthead page.Eggenstein-Leopoldshafen 2, FRG, and can be obtained by quoting the deposition number (CSD-320152 (2), CSD-320153 (l)), the authors' names, and the reference. ligand acts as tridentate ligand only' Drastic conditions are Further details ofthe X-ray structure analysis have &en deposited with the Fachinformationszentrum Energie, Physik, Mathematik, D-75 14 required for the reactions Of with PMe3 and MeLi, They lead also to cleavage of 2 into mononuclear entities and formation of [Fe(CO)(PMe3)("S4")I (5) in the case of PMe3. With MeLi, the final reaction product is the binuclear anion Contribution from the A series of seven high-spin ferrous complexes of 2,2'-biimidazole and 2,2'-bibenzimidazole ligands have been prepared and studied with IR and Miissbauer spectroscopy and variable-temperature magnetic susceptibility. The crystal and molecular structures of [ Fe(bb~imH~)~](ClO~)~"~O (1) and [Fe(bb~imH,)~]Cl~.MeOH.4.33H~O (2) have been determined. 1 crystallizes in the monoclinic system, space group P2.,/c, with...