Conversion of methyl carbonyl complexes of platinum(II) into acetyl derivatives: a kinetic study

Abstract

Study of the reactions [Pt(CO)(PPh₃)(I)Me]+ L′→[Pt(PPh₃)(L′)I(COMe)][L′= AsPh₃,As(p- MeC₆H₄)3,AsMe(o-MeC₆H₄)₂, and SbPh₃] indicates that the first, and largely rate-controlling, step involves neither the incoming ligand nor the solvent, in sharp contrast to related reactions of alkyl carbonyl complexes of other metals and to the normal pattern of ligand-substitution reactions of platinum(II) complexes. This step is thought to involve formation of the intermediate [Pt(PPh₃)I(COMe)], which then reacts rapidly with the ligand L′. The apparent change in kinetic behaviour when one or more phenyl groups in the phosphine ligand of the starting material are replaced by o-tolyl groups is believed to be due to a large drop in the rate constant for reaction of the intermediate with ligand L′, arising from crowding caused by the o-tolyl substituents.