Substituent Effects upon Dissociation and Migration Reactions of Five-Coordinate Platinum( 11) Carbonyl Complexes

A series of five iodobis(triphenylphosphine)arylplatinum(II) complexes was prepared and rates of carbonylation in the presence and absence of excess triphenylphosphine were measured. Four related palladium(I1) complexes were compared with the platinum complexes. The results are interpreted in terms of a five-coordinated carbonyl intermediate which forms the acylmetal product by two reaction paths-a migratory route and a dissociative route. The migratory reaction is much more sensitive to changes in the electronic character of the migrating group than the dissociative reaction is. The results show that carbon monoxide insertion is not rate limiting in the catalytic carbonylation of aryl halides.