Effect of organic groups on the carbonyl-insertion reaction of platinum(II)

Abstract

The equilibria between the isomers of [PtCl(R)(CO)(PMePh₂)] which undergo CO insertion and their halidebridged insertion products [Pt₂Cl₂(COR)₂(PMePh₂)₂] have been examined for 12 ortho-, meta-, and para-substituted aryl groups, R. Values of the equilibrium constants, enthalpy, and entropy of the reactions are presented. The electronic effects of the aryl groups on this R migration reaction are found to be at least as critical as any previously reported factors influencing this process. Electron-donating substituents in meta- or para-positions promote the insertions, whereas electron-withdrawing groups inhibit them. A correlation with Hammett σ values is found. Ortho-substituents tend to prevent the reaction for steric reasons. Enthalpies of the reactions become less negative with electron-withdrawing groups, and this may reflect strengthening Pt–aryl bonds.