Effect of molecular hydrogen on the highly regioselective hydrocarboxylation of propene promoted by dichlorobis(triphenyl phosphine)palladium-triphenyl phosphine as catalytic precursor

The hydrocarboxylation of propene with MeOH or BuOH promoted by [PdCl2(PPh3)2] as catalyst precursor in combination with added PPh3 occurs with high selectivity towards the linear ester, particularly at low Pco. The yield is almost independent of Pco (in the range experienced, 13-95 atm) when using MeOH and decreases on decreasing Pco with BuOH. With this alc. the yield can be increased in the presence of mol. H, while maintaining the selectivity and without aldehyde formation; this H effect is odsd. also with MeOH when using toluene as solvent. When using BuOH, the complex trans-[Pd(COPr)Cl(PPh3)2] (A) can be isolated; when using MeOH a mixt. of A and trans-[Pd(COOMe)Cl(PPh3)2] (B) is isolated; with both alcs. and toluene as solvent the starting complex is isolated. Both complexes A and B are intermediate in the hydrocarboxylation reaction. These facts suggest that when using BuOH the reaction occurs via olefin insertion into Pd-H bond, while in the other base the olefin may insert into a Pd-H bond as well as a Pd-COOM bond.