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-toluene sulphonic 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. (C) 2004 Elsevier B.V. All rights reserved.