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

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