Six complexes of two series were studied as the catalyst precursors for CO/ethylene copolymerization by using catalytic evaluation method and EXAFS technique.The first series of the complexes has general formular (L)Pd(OCOCF3)2 in which L is DPPPr,DPPBu or DPPEt.The second series of the complexes has general formular (DPPPr)Pd(A)2 in which A-is CF3COO-,P-CH3PhSO3-,Cl-or CH3COO-.The results showed that suitable ligands have relatively strong coordination ability to palladium(Ⅱ) center.Suitable anoins belonging to strong acids,have excellent stability on cationic palladium(Ⅱ),and easy to leave away to give coordination vacant to comonomers.
With high presure in situ 1H NMR technique,the alternative copolymerization of CO with ethylene catalyzed by Pd(Ⅱ) DPPPr CF 3COOH catalyst were studied under 2.0MPa CO/ethylene(1:1 ,molar ratio) using CD 3OD and CD 3COCD 3 as solvents.The 1H NMR signals of coordinated ethylene and methylene linked to Pd(Ⅱ) were observed,which showed that ethylene was activated by coordination with Pd(Ⅱ) during the copolymerization before it’s insertion into Pd—C bond to achieve the chain propagation.But the signal of Pd—H bond was not observed in all the in situ 1H NMR experiments,which indicated that the copolymerization initiation was not caused by Pd—H bond,or Pd—H initiation was very few in alcoholic solvent.
