Use of polymer matrices to activate palladium(0) catalysts and reduce catalyst agglomeration

The dimerization–alkylation of butadiene to 1-methoxy-3,7-octadiene and 3-methoxy-1,7-octadiene has been studied in benzene at 100°C using both homogeneous and resin-attached palladium(0) catalysts. Pd(PPh3)4 was used as the homogeneous catalyst. Styrene-divinylbenzene (1% crosslinked) resins, functionalized with diphenylphosphine groups, were treated with Pd(PPh3)4 to give the resin-bound catalysts by ligand exchange. The rates of the homogeneously catalyzed reactions reach a limiting value as the catalyst concentration reaches 4 X 10−3 to 6 X 10−3 M due to equilibrium processes which limit the concentration of active species. The concentration of palladium in the resins is far higher (0.5 X 10−1 to 7 X 10−1 M), yet at similar P/Pd ratios the rates are greater per Pd using the resins. Furthermore, much larger catalyst charges may be employed, with the resin catalysts, without reaching limiting rates. Apparently, the resin retards the ability polymer-attached phosphines to highly coordinate (i.e., 3 or 4) palladium(0) relative to the corresponding situation in homogeneous solution. The resin matrix appears to retard the tendency, exhibited in the homogeneous reactions, for the catalyst to agglomerate and precipitate from solution as an inactive material.