Kinetics and mechanism of ligand substitution in [Cr(π-ligand)(CO)3] complexes (ligand = naphthalene, pyrene, thiophene, 2,6-dimethylpyridine, or cycloheptatriene) and of fac/mer isomerization in [M(CO)3L3](M = Cr, Mo or W; L = phosphite, phosphine or isocyanide)

Abstract

Kinetic studies of the reaction [Cr(π-ligand)(CO)₃]+ 3L →[Cr(CO)₃L₃]+π-ligand revealed a second-order rate law with the π-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 < PBu₃. 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}(PR₃)_x] complexes (x= 1–3, R = H or Me).