Synthesis and characterization of a monocyanide-bridged bimetallic iron(II) and copper(I) complex

The experiments reported here describe the interaction of the cyanide ligand in the neutral CpFe(CO)₂CN derivative with copper(I) in both acetonitrile and methylene chloride solutions. In acetonitrile solution, acetonitrile competes with the Fe-CN moiety for binding to copper(I), where an equilibrium is established with K_cq = 4.3 x 10³ ?? 25 °C. On the other hand, in methylene chloride, complete adduct formation is observed. Adduct formation in solution is based on shifts of the v_co and V_CN vibrations to higher frequencies, as compared to the corresponding values in CpFe(CO)₂CN, with v_cN being more significantly affected by complex formation. Upon adding 2 equiv of PCy₃ to a methylene chloride solution of CpFe(CO)₂CN and Cu(CH₃CN)₄⁺, the complex cation CpFe(CO)₂(μ-CN)Cu(PCy₃)₂⁺ is formed and isolated as its BF₄^- salt in crystalline form. X-ray crystallography has shown that the interatomic distances and angles in the parent complex CpFe(CO)₂CN and its copper(I) adduct are quite similar. Further, the Fe-CN-Cu bridge is nonlinear, displaying a C-N-Cu angle of 161.3(5)°.