Tetracarboxylatodirhenium Complexes Linked by Axial Cyano Bridges to Metalpentacarbonyl Ligands – Synthesis and Characterization

Abstract

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 ν(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.