Mechanisms of organometallic reactions. Part I. Kinetics of the reaction of acetonitrile with tricarbonyl(tropylium) cations of metals in Group VI

Abstract

The kinetics of removal of the tropylium ligand from the complexes [(C₇H₇)M(CO)₃]BF₄(M = Cr, Mo, or W) have been studied using acetonitrile as nucleophile. A rate law of the form Rate =k[Complex][MeCN] is obeyed suggesting an S_N2 displacement mechanism. The ease of displacement of the tropylium ligand decreases markedly in the order Mo > W Cr, the relative rates being largely enthalpy controlled (ΔH^‡= 10·5, 15·0, and 24·2 kcal mol^–1 for M = Mo, W, and Cr respectively).