Electrochemistry and [60]fullerene displacement reactions of (dihapto-[60]fullerene) pentacarbonyl metal(0) (M = Cr, Mo, W)

Abstract

Cyclic voltammetry (CV) measurements on (η²-C₆₀)M(CO)₅ complexes (M = Cr, Mo, W) in dichloromethane show three [60]fullerene-centered and reversible reduction/oxidation waves. The E_1/2 values of these waves are shifted to positive values relative to the corresponding values of the uncoordinated [60]fullerene in the same solvent. A Jahn–Teller type distortion of the spherical surface of [60]fullerene promoted by [60]fullerene–metal π-backbonding may explain the observed positive shifts. Lewis bases (L = piperidine and triphenyl phosphine) displace [60]fullerene from (η²-C₆₀)M(CO)₅ complexes. Analysis of the activation parameters for the metal–[60]fullerene dissociation, the metal–[60]fullerene bond enthalpies (from DFT computations), and metal–solvent (benzene) bond enthalpies (from DFT computations) suggests appreciable solvent contribution to the transition state leading to formation of the intermediate species solvent–M(CO)₅. Appreciable transition state stabilization due to solvation of the intermediate species is inferred for M = Mo and W. For M = Cr, stabilization of the intermediate species due to solvation is not accompanied by the corresponding transition state stabilization.