Palladium-phosphine catalyst with different DPPP/Pd(OAc)2 ratio has been studied with in situ ^3^1P NMR spectroscopy under reaction conditions (C2H4/CO 1:1, 2.0MPA). The results showed that the reaction of DPPP with Pd(OAc)2 produced a stable six-membered ring complex which had efficient catalytic activity. When the reaction temperature was above 100℃, the complex began to decompose. When the reaction temperature was above 260℃, th complex decomposed completely. No free DPPP was found in the experiment. The active complex (DPPP)Pd(OCOCF3)2 was formed when DPPP/Pd=1. The unactive complex (DPPP)2Pd(OCOCF3)2 was formed when DPPP/Pd>=2.

Key words: REACTION MECHANISM, COPOLYMERIZATION, ETHYLENE, CARBON MONOXIDE, PHOSPHINE, PALLADIUM, PHOSPHORUS 31 MAGNETIC RESONANCE SPECTROMETRY