Tetracarboxylatodirhenium complexes linked by axial cyano bridges to metalpentacarbonyl ligands - Synthesis and characterization

Reaction of Re₂{μ-O₂CC(CH₃)₃}₄Cl₂ with [(CO)₅M-CN]Na (M = Cr, Mo, W) leads to tetranuclear complexes of formula Re₂{μ- O₂CC(CH₃)₃}₄[-NC-M(CO)₅]₂ (M = Cr, Mo, W). These complexes were characterized by ¹H-, ¹³C-, and ⁹⁵Mo-NMR, IR and Raman spectroscopy, elemental analysis and examined by cyclic voltammetry. The applied methods show the donor capabilities of the [(CO)₅M-CN]^- ligands which shift electron density towards the Re centers weakening the Re-Re quadruple bond. The Re-Re bond lengths and the v(Re-Re) force constants are estimated based on the FT-IR and Raman examinations. Photochemical examinations and TG/MS experiments have also been conducted. The latter method shows that the product complexes decompose around 100 °C, by first loosing their carbonyl substituents; as do the Cr, Mo, W precursor compounds. The dirhenium tetrapivalate unit decomposes only at higher temperatures in a distinct second step.