Valorization of a CO₂‐Derived Lactone by Acyclic Diene Metathesis Polymerization

Abstract

The exploitation of carbon dioxide (CO2) as a feedstock for the chemical processes has been an evasive venture due to its thermodynamic stability. The synthesis of highly functionalized metastable δ‐lactone (3‐ethylidene‐6‐vinyltetrahydro‐2H‐pyran‐2‐one) was reported in 1970s which is formed by the condensation of CO2 and 1,3‐butadiene in the presence of palladium catalyst. Several attempts have been made to utilize the intermediate for the polymerization processes, however, only a few have been successful. Here, we report a novel mechanism of metathesis polymerization of the metastable monomer by the action of a transition metal carbene complex (Hoveyda Grubb's II generation catalyst) to yield a new class of materials. The reaction mechanism for the polymerization has been proposed and substantiated by nuclear magnetic spectroscopic analysis. The obtained polymeric species consist of a complex unit structure where the cyclic lactone groups are connected by the olefin groups in different combinations.

The Divergent Reactivity of Lactones Derived from Butadiene and Carbon Dioxide in Macromolecular Synthesis

“…Although the trisubstituted tiglate moiety exhibits low reactivity in metathesis, the removal of ethylene from the reaction afforded higher oligomers, which interestingly depolymerized to afford monomer 1 when quenching the reaction with vinyl ether. [ 34 ]…”

“…Kimura and Katiyar reported that the olefin moieties of 1 are reactive in ADMET reactions (Figure 12). [34] The use of Hoveyda-Grubb's II catalyst (26) led to the formation of oligomeric species (27)(28)(29)(30) as a mixture of regioisomers (e.g., head-to-head ratios). As would be expected for Ru-catalyzed metathesis catalysts, the monosubstituted vinyl lactone is more reactive, so dimers of the type 27 and 28 form as the major products.…”