Methoxycarbonylation of Styrene to Methyl Arylpropanoates Catalyzed by Palladium(II) Precursors with 1,1 -Bis(diphenylphosphino)metallocenes

Palladium(II) complexes with 1,1-bis(diphenylphosphino)ferrocene (dppf), 1,1-bis(diphenylphosphino)octamethylferrocene (dppomf), 1,1-bis(diphenylphosphino)ruthenocene (dppr) and 1,1-bis(diphenylphosphino)osmocene (dppo) have been synthesized and used to catalyze the methoxycarbonylation of styrene. Irrespective of the precursor, all the reactions gave methyl phenylpropanoates with prevalence of the linear isomer methyl 3-phenylpropanoate (up to 85% regioselectivity). The highest turnover frequency was obtained with the dppr precursor in the presence of p-toluenesulphonic acid co-catalyst (334 mol of styrene converted (mol of catalyst h)-1). A reaction mechanism accounting for both activity and selectivity has been proposed on the basis of operando high-pressure NMR experiments and reactions with model compounds.