Ring opening metathesis polymerization with binaphtholate or biphenolate complexes of molybdenum

Several racemic or enantiomerically pure complexes of the general type Mo(CHR)(NR')-(O(2)R'') that contain binaphtholate or biphenolate (O(2)R'') ligands have been prepared and employed to ring open several achiral, racemic, or enantiomerically pure norbornenes and norbornadienes. A bimodal molecular weight distribution sometimes results from polymerization of an enantiomerically pure monomer with a racemic initiator as a consequence of a different rate of chain growth from enantiomeric metal centers. The analogous polymerization of an enantiomerically pure monomer with an enantiomerically pure initiator yields only a single polymer chain, as expected. Evaluation of the cis content of the resulting polymers suggests that cis polymer results from polymerization via syn alkylidene propagating species and that accessibility of the anti rotamer on the polymerization time scale is determined by a subtle combination of steric bulk in the biphenoxide and imido ligands. All cis polymers were found to be highly isotactic. The X-ray structures of two catalytically active species are also described. One is a THF adduct of 3,3'-diphenyl-2,2'-diolate-1,1'-dinaphthyl (anti rotamer) while the other is a base-free syn species that contains the 6,6'-dimethyl-3,3',5,5'-tetra-tert-butyl-1,1'-biphenyl-2,2'-diolate ligand.