Abstract: The new reaction mechanism of Pd (OAc)₂ with dppm or dppe in different chlorom ethane solvent was studied by EPR-ST method. The used capturer were PBN and POBN. The obtained experimental spectra were simulated. The free radicals·PPh₂ and containing carbon free radicals were trapped in these experiments. The reaction mechanism was given and discussed. A new ligand PPh₂CHClPPh₂ was formed after the homolysis, the deprivation of chlorine and the deprivation of hydrogen. Then the substituted and complex reaction occurred between new ligand and Pd(OAc)₂ to form a new complex PdCl₂[PPh₂CHClPPh₂]. Some influence factors on the reaction were tentatively discussed. Solvent effects play an important role on the free radical reaction because CH₂Cl₂ or CHCl₃ is both reactant and solvent. Its polarity largely acts on the transitional state 1 or 2 and determines the occurance of reaction. Pd(OAc)₂ is both reactant and initiator. It affects the reaction by its molecular induction.

Key words: Pd(OAc)₂, ERR-ST, Free radical, Chloromethane, Phosphine