Water-soluble palladium(II) catalysts for the alternating co- and terpolymerization of CO and olefins in aqueous phase

The water-soluble diphosphine (NaO3S(C6H4)CH2)(2)C(CH2PPh2)(2) (Na2DPPPDS) was employed to prepare the bis-trifluoroacetate Pd(II) complex Pd(Na2DPPPD S)(CO2CF3)(2). 2THF (1). The catalytic performance of 1 in the co- and terp olymerization of CO and ethene and propene in water has been studied in dif ferent experimental conditions. In combination with both a protic acid, com monly p-toluenesulfonic acid, and an organic oxidant such as 1,4-benzoquino ne, 1 forms the most efficient catalyst systems ever reported for the copol ymerization of CO and ethene in water. Under comparable conditions, the act ivity of 1 is similar to that of the industrial Pd(II) 1,3-bis(diphenylphos phino)propane catalysts in MeOH. Unlike the latter which yield a mixture of copolymers bearing diketone, keto-ester, or diester end groups, the copoly mers and terpolymers produced with the Na2DPPPDS-based catalysts have exclu sively ketonic end groups for average molecular weights ranging from 10 to 30 kg mol(-1) depending on the reaction conditions. In situ high-pressure N MR (HPNMR) studies have been performed in actual copolymerization condition s using D2O as solvent. The only palladium complex visible on the NMR time scale contains the diphosphine ligand and TsO- or water groups. It is sugge sted that this palladium complex acts as a reservoir of "(diphosphine)Pd(II )" moieties which are delivered into the catalysis cycle as Pd-H species by reaction with water and/or H+. A catalysis cycle is proposed on the basis of HPNMR experiments, the structure of the copolymers, and the occurrence o f the water-gas-shift reaction.