Kinetics and mechanisms of ligand exchange reactions on (dihapto-buckminsterfullerene) pentacarbonyl tungsten(0)

The Lewis bases triphenyl phosphine and triethyl phosphite (L) displace C-60 from (eta(2) -C-60)W(CO)(5) to produce the complexes (eta(1)-L)W(CO)(5) . These displacement reactions were studied under conditions where the concentrations of C-60 and L were at least 50 times the concentration of (eta(2) -C (60))W(CO)(5) . The reactions in various solvents were first order with respect to (eta(2) -C-60)W(CO)(5) . The pseudo first order rate constant values were independent of the concentration and of the nature of L but dependent on the coordinating ability of the solvent under conditions where [C-60]/[L]approximate to0. Under conditions where 0less than or equal to[C-60]/[L]less than or equal to1, the pseudo first order rate constant values decrease as the values of [C-60]/[L] increase. Two limiting cases of an interchange displacement of C-60 from (eta(2) -C-60)W(CO)(5) , whose relative contributions to the overall mechanism depend on the nature of the solvent, are proposed to be a solvent-assisted C-60-W(CO)(5) bond displacement and a dissociative displacement. The first step of the associative displacement pathway is a solvent-assisted dissociation of C 60 from (eta(2)-C-60)W(CO)(5) producing the intermediate species (solv)W(CO)(5) , (solv=solvent), whereas the 16 electron unsaturated species W(CO)(5) is produced in the dissociative displacement pathway.