Halogenated Olefins as Chain Transfer Agents in the Synthesis of Telechelic Polynorbornenes Using Ruthenium Alkylidene Catalysts. Computational and Experimental Studies

Ring-opening metathesis polymerization (ROMP) of norbornene (NB) and its derivatives N-adamantyl-exo- endo-norbornene-5,6-dicarboximide (AdNDI) and N-cyclohexyl-exo-endo-norbornene-5,6-dicarboximide (CyNDI) in the presence of cis-1,4-dichloro-2-butene (2a) and cis-1,2-dichloro-ethylene (2b) as chain transfer agents (CTAs) using a (1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazolilydene) (PCy3)Cl2Ru=CHPh (I) has been studied. � Halogenated ole- fin 2b shows no activity as a CTA whenhalogenated olefin 2a is readily cross-metathesized with NB and norbornene dicarboximides. The chain transfer reaction pathways during the ROMP of NB to 2b using a (1,3-diphenyl-4,5- dihydroimidazol-2-ylidene) (PCy3)Cl2Ru=CHPh (1) have been studied at B3LYP/LACVP* level of theory. The calcula- tions show that 2b is a poor substrate for the metathesis reaction due to the steric effect produced by chlorine atoms di- rectly linked to the double bond. The calculated Gibbs free activation energy of a chain transfer reaction from ring-opened NB to 2b was 25.1 kcal/mol.