Bimetallic Manganese Catalysts: A Route to Controlled and Switchable Polymerization of Lactones

Abstract

AbstractThe sustainable solution to the environmental problem of polymeric materials calls for efficient and well‐controlled ring‐opening polymerization catalytic systems. Inspired by the highly reactive and stereospecific bimetallic catalysts, three kinds of bimetallic Salen‐Mn catalysts supported by biaryl linking moieties are synthesized and applied to polymerization catalysis of lactide (LA) and ϵ‐caprolactone (ϵ‐CL) in this work. The polymerization is initiated in situ by the ring‐opening of epoxide compounds, in which the ionic cocatalyst could accelerate the reaction process. The Mn−Mn coordination effect contributes to the higher activity and iso‐selectivity towards LA compared to the mononuclear Salen‐Mn catalyst. The reactivity and stereoselectivity are determined by the conformation of catalysts, specifically the Mn−Mn separation and dihedral angle. Finally, the CO2‐controlled switchable polymerizations are carried out with LA and ϵ‐CL. The reversibility of the on‐off switching operation is influenced by the combination between CO2 molecules and active species. The success in binuclear Salen‐Mn catalysts not only expands the range of bimetallic catalyst analogues but also claims the promising potential of Mn‐based catalysts in practical and theoretical research.