The effects of stereochemistry at platinum and the nature of the organic group on carbonyl insertion at [PtCl(R)(CO)(PMePh2)]

Abstract

The three geometric isomers of [PtCl(Ph)(CO)(PMePh₂)] have been prepared. Only the isomer with Ph trans to PmePh₂ readily undergoes carbonyl insertion, and produces the halide-bridged acyl complex [Pt₂(µ-Cl)₂(COPh)₂(PMePh₂)₂], with which it equilibrates in solution. The other isomers are reluctant to undergo CO insertion, and attempts to promote this lead to elimination of carbon monoxide. Replacing the phenyl group by other R groups has a critical effect on the equilibrium position between the acyl and carbonyl complexes, the tendency towards the acyl decreasing in the order R = Et > Ph > Me > CH₂Ph (≃0). These observations are compatible with R migration to CO as the mechanism of acyl formation at platinum(II).