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)