Kinetics and mechanism of ligand substitution in [Cr(pi-ligand)(CO)(3)] complexes (ligand equals naphthalene, pyrene, thiophene, 2,6-dimethylpyridine, or cycloheptatriene) and of fac/mer isomerization in [M(CO)(3)L(3)] (M=Cr, Mo or W; L equals phosphite, phosphine or isocyanide)

Kinetic studies of the reaction [Cr(pi-ligand)(CO)(3)] + 3L --> [Cr(CO)(3)L(3)] + pi-ligand revealed a second-order rate law with the pi-ligand lability decreasing in the order naphthalene > thiophene > cycloheptatriene > 2,5-dimethylpyridine. In terms of the entering ligand, the rates increased in the order PrCN < P(OMe)(3) < PBu(3). Rates of intramolecular exchange in the [M(CO)(6-x){P(OMe)(3)}(x)] series increased in the order x = 3 < 1 < 2 and M = Mo < W < Cr. These results are consistent with molecular modelling of the trigonal twist pathway for [Cr(CO)(6-x)(PR(3))(x)] complexes (x = 1-3, R = H or Me).