Bioinspired Cobalt Amino Acid Complexes for Synthesis of Polyester Polyols from Epoxide and Cyclic Anhydride

Cobalt(III) complexes with a variety of amino acid ligands prove active in the ROCOP reaction of epoxide and cyclic anhydride. The copolymerization reaction shows high selectivity of over 99% toward polyester formation. Bias toward bimodal molar mass distribution shifted to a monomodal weight distribution with a chain transfer agent.

The design of bioinspired catalysts offers a promising route to sustainable polyester synthesis. Herein, a series of chiral cobalt(III) amino acid complexes are introduced as highly efficient catalysts for epoxide/cyclic anhydride ring-opening copolymerization (ROCOP). Structure–activity studies reveal that complex 2, featuring a polar organosoluble side chain, exhibits exceptional catalytic performance, achieving turnover frequency (TOF) = 1151 h⁻¹ in CHO/PA ROCOP at 100 °C with DMAP-comparable to state-of-the-art Cr(III)-salen catalysts. Furthermore, complex 3, which features a lysine-derived ligand, shows improved reactivity at elevated anhydride ratios, indicating an influence from the outer coordination sphere on catalysis. Mechanistic analysis reveals a zero-order dependence on anhydride concentration, confirming that the propagation step saturates the catalyst. Further, complex 2 maintains high TOF (1164 h⁻¹) even in the presence of a chain transfer agent, enabling precise molecular weight control. This work illustrates tuning by an amino acid ligand as a powerful strategy for developing efficient, selective, and sustainable ROCOP catalysts, bridging the gap between bioinspired design and high-performance polymerization.

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