Carbonyl insertion at [PtX(Ph)(CO)L]: the effects of varying the anionic ligand X and the neutral ligand L

Abstract

From the reaction of HgPh₂ with cis-[PtCl₂(CO)L], the benzoyl complexes [Pt₂(µ-Cl)₂(COPh)₂L₂] can be isolated when L = PEt₃, PMe₂Ph, PMePh₂, PPh₃, or P(C₆H₁₁)₃, but when L = P(C₆H₄Me-o)₃, AsMePh₂, or AsPh₃ only the [PtCl(Ph)(CO)L] complexes are formed. Metathetical replacements of the chloride ions in [Pt₂(µ-Cl)₂(COPh)₂-(PMePh₂)₂] lead to the corresponding bromide or iodide complexes. Low-temperature n.m.r. studies show that the reaction between HgPh₂ and cis-[PtCl₂(CO)L] gives first the carbonyl derivative [PtCl(Ph)(CO)L], from which CO insertion proceeds. The equilibrium positions in solution between [PtX(Ph)(CO)L](each with Ph trans to L) and the binuclear benzoyl complexes are reported. The effect of X on the equilibrium position depends on the bridging ability of that group in the benzoyl dimers, stronger bridges favouring the insertion product. The neutral ligands L exert an effect by both electronic and steric factors. The magnitude of the trans influence of L directly affects the tendency of the trans phenyl group to migrate to CO, unless a critical size of L is exceeded. In these cases, the steric bulk of L favours the mononuclear carbonyl derivative.