Investigating the effects of bulky allylic substituents on the regioregularity and thermodynamics of ROMP on cyclopentene

Abstract

The interplay between equilibrium ROMP thermodynamics and the regioregular insertion of allylic trialkylsiloxy-substituted cyclopentenes during propagation with Hoveyda-Grubbs 2nd generation catalyst at varying temperatures is investigated. In general, bulkier substituents reduce monomer conversion and increase regioregular insertion. However, polymerization entropy (ΔSp) also appears to play an important role on ROMP thermodynamics when compared to ring strain (ΔHp) which is typically the parameter of focus for the efficacy of low-strain monomer conversion. This analysis has allowed for the determination of a “Goldilocks” monomer (i.e. one that provides the best compromise of monomer conversion (56% conversion at −10 °C) and regioregularity (97% HT insertion) to be 3-(tert-butyldimethylsiloxy)cyclopentene which has never before been explored or reported. Due to this study, this monomer has now been identified as the ideal choice for isotactic polypentenamer studies moving forward.