Bicyclic guanidines are a potent class of organocatalysts that mediate ring-opening polymerization (ROP) of lactide and other lactone monomers. TBD (1,5,7-triazabicyclo[4.4.0]dec-5-ene) is a bicyclic guanidine that mediates ROP of lactide at room temperature and can complete polymerization in a matter of seconds (Scheme 1). However, the relative rate of transesterification can compete with the rate of polymerization, broadening molecular weight distributions of the formed polymers. A related bicyclic guanidine, TBO, has been compared with TBD in ester aminolysis and ROP reactions and shown to require higher temperatures and longer reaction times to reach complete monomer conversion. The aim of this study is to synthesize a homologous series of bicyclic guanidines in which the ring size is systematically varied. It is hypothesized that the active site geometry of TBD explains its high reactivity, and one-carbon deletion in the ring structure of the related guanidine TBN will result in diminished catalytic rates. Polymerization data for these catalysts are presented, in addition to screening data for various lactone monomers

Bicyclic guanidine organocatalysts: A comparison of three structural analogs

2019 Spring National Meeting

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