Formation of ring-opened syndiotactic and atactic polynorbornenes using metathesis catalysts; evidence for retention and loss of configuration of the intermediate metallocarbene

Abstract

All-cis ring-opened polymer made from (+)-exo-5-methylbicyclo[2.2.1]hept-2-ene (1) has a totally syndiotactic ring sequence whereas 11/89 cis/trans polymer is essentially atactic and 74/26 cis/trans polymer has mainly syndiotactic cis junctions and isotactic trans junctions; these results give information concerning the configurations of the propagating metallocarbenes in different catalyst systems.