Living Ring-Opening Metathesis Polymerization Catalyzed by Well-CharacterizedTransition Metal Alkylidene Complexes

摘要

2,3-distributed norbornadienes can be polymerized by Mo(CH-t-Bu)(NAr)(O-t-Bu)2 ina well-behaved living manner to give essentially monodisperse homopolymers. In some cases the polymers are highly trans, and are believed to be tactic. An X-ray structure of a 'first insertion product' shows it to be a pseudo-tetrahedral species containing a syn alkylidene ligand (substituent pointing toward the imido nitrogen atom), one face of which is blocked by the isopropylidene group and the other face of which is blocked by a carbomethoxy group. An x-ray structure of a tungstacycle made from 2,3-bis(trifluoromethyl)norbornadiene is also reported. Keywords: Metathesis polymerization, Molybdenum, Biochemistry, Tungsten, Alkylidene. Reprints. (jes)