Stereospecific polymerization of donor-acceptor cyclopropanes with C(sp3)–H bond as the dormant species

Abstract

Chiral polymers have long attracted interest in polymer chemistry; however, accessing those with unique C3 repeating units remains a significant challenge. Here, we report a stereospecific ring-opening polymerization (ROP) of enantiopure donor–acceptor cyclopropanes (DACs), enabled by MgBr₂/DBU cooperative catalysis and a C–H bond-mediated reversible-deactivation equilibrium, yielding a range of chiral homopolymers and stereo-block copolymers. Stoichiometric reactions of distinct DACs revealed an unprecedented structure–stereospecificity relationship. DFT calculations provide mechanistic insights, indicating that a phenyl substituent on the cyclopropane favors a stereoinvertive SN2 pathway, whereas a vinyl group largely stabilizes the α-carbocation, thus promoting a mixed SN1/SN2 mechanism that leads to atactic polymer formation.