Ring-opening metathesis polymerization by monoalkoxide pyrrolide (MAP) initiators of Mo and W produces both cis,syndiotactic and trans,isotactic polymer sequences from enantiomerically pure monomers.  Cis,syndiotactic and trans,isotactic structures for (+)-DCMNBE (2,3-dicarbomethoxynorbornene) made with Mo(NAd)(CHCMe2Ph)(pyr)(HMTO) (1a ) as the initiator (Ad = 1-adamantyl, HMTO = 2,6-dimesitylphenoxide, Pyr- = NC4H4-) arise from two mechanisms.  Formation of trans,isotactic-poly[(+)-DCMNBE] can best be rationalized by invoking a fluxional process in the five-coordinate intermediate metallacyclobutane that consists of a turnstile pseudorotation in which the configuration at the metal center is retained.  In other circumstances pseudorotation exchanges aryloxide and pyrrolide ligands and accounts for formation of cis,syndiotactic structures with inversion at the metal center.

Stereoselective ROMP by Mo and W monoalkoxide pyrrolide (MAP) initiators

244th National Meeting (2012)

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