The polymerization processes of isoprene (IP) based on (CF3CO2)2LnCl·EtOH一(i-Bu)2AlH homogeneous catalysts were traced out by 13C-NMR. First，IP coordina-ted to rare earth to become

n4-IP rare earth complexes trans and cis)．Then C-3 and C-4 of

n4-IP inserted into Ln-H bond to form n3-allyl rare earth complexes (syn and anti)．13C chemical shifts and 1JcH coupling constants of n4-IP indicated that C一1 and C-2 of n4-IP coordinated to rare earth with π coordination bond，while the double bond between C-3 and C-4 transformed to σ bond to form a metal cyclopropane structure with rare earth，i.e. a activated structure．2D 13C-NMR exchange spectra showed that the slow exchange (tautomcrism) reaction between every pair of n4-IP and

n3-allyl isomers could take place at ambient temperature．These reactions underwent the processes of bond breaking and reformi-ng

which enable insert reaction to take place at room temperature．The suggested polymerization mechanism is IP—n4-trans—IP→n4-cis-IP一n3-syn-allyl→n3一anti-allyl—trans一1，4一IP／cis—1，4一IP(C-1 insert) or 3

4-IP(C-3 insert)unit．