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

Cyclic voltammetry (CV) measurements on (eta(2)-C(60))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 pi-backbonding may explain the observed positive shifts. Lewis bases (L = piperidine and triphenyl phosphine) displace 60]fullerene from (eta(2)-C(60))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.