Diamond-shaped heterometallic complexes of Iron(II) and copper(I) bridged by cyanide groups containing monodentate or bidentate phosphanes bound to copper(I), including an alternative structure based on the nature of the bidentate phosphane ligand

The diamond-shaped heterometallic cyanide-bridged complex of iron(II) and c opper(l), [CpFe(CO)(mu -CN)(2)Cu(CH3CN)(2)](2) (1), has been synthesized fr om the reaction of K[CpFe(CO)(CN)(2)] and [Cu(CH3CN)(4)][BF4] in acetonitri le. Upon the addition of 2-4 equivalents of phosphane ligands to complex 1, the coordination geometry of the copper centers can be varied from trigona l planar as in [CpFe(CO)(mu -CN)(2)Cu(PCy3)](2) (2), to tetrahedral as foun d in [CpFe(CO)(mu -CN)(2)Cu(PCy3)(2)](2) (3), Analogous derivatives contain ing other phosphane ligands, namely PMe3, P(p-to-lyl)(3), PMe2Ph, and PPh2M e have been synthesized as well. Prolonged exposure of complex 3 in CH2Cl2 to excess PCy3 has provided the bimetallic complex [CpFe(PCy3)(CN)(mu -CN)C u(PCy3)(2)] (4), where the metal aggregate is disrupted and PCy3 has displa ced CO at the iron center. Bidentate phosphane analogs of complex 3 have be en prepared by adding two equivalents of dcpp [bis(dicyclohexylphosphanyl)- ethane] or dcpp [bis(dicyclohexylphosphanyl)propane] to complex 1. The soli d-state structures of several of these diamond-shaped derivatives, in addit ion to complex 4, have been determined by X-ray crystallography. The overla pping diamond-shaped [Fe-2(CN)(4)Cu-2] cores, which form channels within th e solids, are blocked by bulky, copper-bound phosphane ligands such as PCy3 . However, in the case of the small phosphane PMe3, or the chelating phosph anes dcpe and dcpp, these channels are not blocked by the phosphane ligands ; solvent molecules occupy the channels created by the overlapping metal co res instead. Alternatively, the complex [CpFe(CO)(CN)(mu -CN)Cu(dcpm)](2) ( 13), derived from bis(dicyclohexylphosphanyl)methane(dcpm), possesses two c opper(l) centers, each in a distorted trigonal coordination geometry, bridg ed by two dcpm ligands to form an eight-membered metallacycle with a short (CuCu1)-Cu-1... separation of 2.844 Angstrom The third ligand completing ea ch copper's coordination sphere is a nitrogen-bound bridging cyanide group from a CpFe(CO)(CN)(2)(-) anion.