Hydroesterification of cyclohexene using the complex Pd(PPh3)2(TsO)2 as catalyst precursor. Effect of a hydrogen source (TsOH, H2O) on the TOF and a kinetic study (TsOH: p-toluensulfonic acid)

The hydroesterification of cyclohexene is catalyzed by a preformed Pd(PPh3)2(TsO)2 complex I in methanol as solvent. The effect of PPh3, TsOH, and water on the TOF has been evaluated. The system I/PPh3/TsOH=1/6/8, in the presence of 800 ppm of H2O, at 373 K and under 2.0 MPa of CO leads to a TOF as high as 850 h−1. The increase of TOF observed adding a hydride source such as TsOH and H2O suggests that Pd-hydride species plays a key role in the first step of the catalytic cycle. The initial reaction rate increases linearly with the concentration of cyclohexene and of MeOH and passes through a maximum with increasing the pressure of CO. The rate equation r0=k1PCO (1+k2PCO+k3PCO2)−1 fits well the experimental data. The values of k1, k2, and k3 have been evaluated at different temperatures. From the plot ln k versus 1/T, E1=19.4 kcal/mol, E2=20.6 kcal/mol and E3=6.5 kcal/mol have been evaluated. On the basis of experimental evidences and of the kinetic study, a catalytic cycle mechanism has been proposed.