From CO2 to CS2: Mechanistic mapping of cooperative (CS2/CO2)/epoxide ring-opening copolymerisation catalysis

The placement of main group functionalities within the polymer main chain represents a strategy to access a wide catalogue of materials but is limited by poor understanding of the catalyst selection criteria and polymerisation mechanism when moving down the periodic table. Here we study a series of new heterobimetallic CO2 and CS2/epoxide copolymerisation catalysts which allow for a comparative mechanistic understanding of two ROCOP processes. We reveal that the distinct roles each metal plays are preserved from CO2 to CS2 maintaining activity and selectivity across copolymerisations. Experimental and computational studies show that CS2/epoxide copolymerisation can be understood as a series of structurally related insertion events which are interlinked by a central O/S scrambling reaction at the propagating chain end. This facilitates the synthesis of new CO2/CS2/epoxide derived terpolymers with improved degradability over the parent CO2/epoxide copolymers at low levels of sulfur incorporation.