Synthesis of cis,syndiotactic-A-alt-B Copolymers from Enantiomerically Pure Endo-2-Substituted-5,6-Norbornenes.

Cis,syndiotactic A-alt-B copolymers, where A and B are two enantiomerically pure endo-2-substituted-5,6-norbornenes with "opposite" chiralities of the endo-2-substituted-5,6-norbornene skeleton, can be prepared using Mo(N-2,6-Me2C6H3)(CHCMe2Ph)(OHMT)(pyrrolide) (1) as the initiator (OHMT = O-2,6-Mesityl2C6H3). Formation of a high percentage of A-alt-B dyads is proposed to rely on an inversion of chirality at the metal with each propagating step and a kinetically preferred diastereomeric relationship between a given chirality at the metal in propagating species and the chirality of the endo-2-substituted-5,6-norbornene skeleton. We also demonstrate that A-alt-B copolymers can be modified to give new variations which may not be accessible through direct copolymerization.