Exploring Enantiopure Zinc-Scorpionates as Catalysts for the Preparation of Polylactides, Cyclic Carbonates, and Polycarbonates

DFT studies were carried out to rationalize the different complexation ability of these pro-ligands. These complexes have proved to act as highly efficient catalysts for a variety of sustainable bioresourced processes industrially attractive, with wide substrate scope. Thus, complex 7 behaves as a highly efficient initiator for the well-behaved living ring-opening polymerization (ROP) of rac-lactide under very mild conditions.

The PLA materials produced exhibited enhanced levels of isoselectivity, comparable to the highest value reported so far for zinc-based catalysts (Pi = 0.88). In addition, the combination of 7 with onium halide salts functioned as a very active and selective catalyst for CO2 fixation into five‐membered cyclic carbonates through the cycloaddition of CO2 into epoxides under very mild and solvent-free conditions, reaching very good to excellent conversions (TOF = 227 h−1).

Furthermore, these bicomponent system displays a broad substrate scope and functional group tolerance, including mono- and di-substituted epoxides, as well as the very challenging bio-renewable tri-substituted terpene-derived cis/trans-limonene oxide, whose reaction proceeds with high stereoselectivity. Finally, complex 7 also achieved high activity and selectivity as one-component initiator for the synthesis of poly(cyclohexene carbonate) via ring-opening copolymerization (ROCOP) of cyclohexene oxide and CO2 under very soft conditions, affording materials with narrow dispersity values.