Metal-metal interaction in polynuclear complexes with cyanide bridges: Synthesis, characterisation, and theoretical studies

The reaction of the cyanide anion [M(CO)₅CN]^- (M=Cr or Mo) with metallocenes of Groups 4 and 6 produced polynuclear complexes of the type [CpCp′M(CO){-NC-M′(CO)₅}]BF₄ (M=Mo, W; M′=Mo, Cr; Cp′=Cp, Ind), Cp₂TiCl{-NC-Mo(CO)₅} and Cp₂Ti{-NC-Mo(CO)₅}₂. These complexes were characterised by ¹H-, ¹³C- and ⁹⁵Mo-NMR, IR and UV-vis spectroscopies, elemental analysis and examined by cyclic voltammetry. These methods show that the [M(CO)₅CN]^- ligands shift the electron density towards the metallocene centres. The complex [Cp₂W(CO){-NC-Mo(CO)₅}]⁺ is additionally examined by single crystal X-ray structure determination. The Density Functional Theory (DFT) calculations with the ADF program were performed on selected compounds to understand the nature of the redox processes taking place. Compared with a nitrile, the coordination of a [M(CO)₅CN]^- fragment to the metallocene moiety does not significantly change the geometrical features, but leads to the stabilisation of the HOMO of the latter, with all the oxidation processes occurring in the pentacarbonyl moiety of the binuclear species. Time-dependent DFT calculations were used to identify the band appearing in the visible spectrum of Cp₂TiCl{-NC-Mo(CO)₅} as a Mo to Ti charge transfer.