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 ( 2 -C 60 )W(CO) 5 to produce the complexes ( 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 ( 2 -C 60 )W(CO) 5 . The reactions in various solvents were first order with respect to ( 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] 0. Under conditions where 0 [C 60 ]/[L] 1, 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 ( 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 ( 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.