The metathesis reaction of cycloolefins and heterocyclic olefins: Thermodynamics and mechanistic aspects

Abstract

The metathesis reaction of cycloolefins results in polymers consisting of open chain molecules showing a most probable molecular weight distribution. Beside the polymer residual monomer and/or a homologous series of cyclic oligomers are formed by a "back-biting" reaction. The relation between acyclic polymer and cyclic oligomers can be aiscussed in terms of a ring chain equilibrium. The equilibrium, however, is not established instantaneously: the reaction may be kinetically hindered. The oligoner concentration in the kinetically controlled regime is proportional to Gvhen the thermodynamic equilibrium is established the oligomer distribution is determined by a ring chain equilibrium. From the Jacobson-Stockmayer plots a characteristic ratio of 5,8 is derived for polyoctenylene and of 13,9 for polynorbornene.The Casey carbene (CO)5W=C(QHg)2 is more active as catalyst than carbenes of the Fischer type such as (CG)5W=C(OCH3)CgH5; Fischer carbenes are only active with respect to strained olefins. Consequently, in the presence of the latter carbene only polymers are observed; the "back-biting" reaction to yield the cyclic oligomers does not occur.The corresponding chromium carbenes (C0)5Cr=C(R)C6H promote the metathesis reaction of vinylethers. Cyclic vinylethers, e.g. 2,3-aihyarofuran and 2,3,4,5-tetrahydrooxepin-2-y1 acetate are polymerized in a fully head-to-tail fashion.

Olefin Metathesis Reaction in Rubber Chemistry and Industry and Beyond

“…In the ROMP system, cyclic oligomers are usually formed by a "backbiting" reaction, thermodynamically controlled by the ring−chain equilibrium. 76,77 Chen et al developed a computational method to accurately predict the critical concentration and equilibrium ring−chain distribution in the ROMP of cycloolefins, based on the JS-RIS model and a Monte Carlo configurational search with the ring strain as an enthalpic term. 78 The calculation results were in good agreement with experiment, so the product distribution could be completely predicted under a certain ROMP condition.…”