Iminophenolate based titanium and hafnium compounds for ROCOP of epoxides with anhydrides and epoxides with CO 2 Sriparna Sarkar and Debashis Chakraborty * Department of Chemistry, Indian Institute of Technology Madras, India * dchakraborty@iitm.ac.in The increase in global demand for plastics has led researchers to find alternatives for synthetic plastics derived from non-renewable petrochemical feedstock. In addition, these plastics are a severe threat to the environment as they do not degrade easily and thus add to landfill waste. The ring-opening copolymerization (ROCOP) of CO 2 or anhydrides with epoxides that form polycarbonates and polyesters is one of the efficient ways to overcome the environmental challenges that arise from petroleum-based polymers, as these polymers are biodegradable. 1 The field of homogeneous catalysis for ROCOP studies has been dominated by divalent or trivalent metal compounds such as Mg, Al, Zn, Cr, and Co. 2 The tetravalent Group 4 metal compounds are seldom explored in the literature for ROCOP studies though Group 4 metal compounds have been widely used for ring-opening polymerization (ROP) reactions. 3 The ROP and ROCOP operate through different mechanistic pathways, but the coordination of monomer to the Lewis acidic metal center at the initiation step is similar for both reactions. The similarities in the catalytic cycle for ROP and ROCOP, oxophilicity of tetravalent Group 4 metal compounds and low toxicity associate with them invoked us to explore the catalytic activity of titanium and hafnium compounds for ROCOP studies. In this study, we investigated the catalytic activities of Ti(IV) and Hf(IV) compounds supported by iminophenolate ligands containing a heterocycle ring attached to the imine sidearm and different substituents present at the phenolate core. The hafnium compounds showed superior catalytic activities in comparison to the titanium analogues for the ROCOP studies. The hafnium compounds gave polymers that were exclusively alternating in nature, while the titanium compounds showed significant polyether linkages in the polymer chain. The studies have been well correlated to the steric and electronic environment of the ligand backbone. The systematic studies have been performed by varying the epoxide and anhydride used for the copolymerization reaction. References 1. Song, B.;Qin, A.;Tang, B. Z.Syntheses, Properties, and Applications of CO 2 -based Functional Polymers. Cell Rep. Phys. Sci. 2022 , 3 ,100719. 2. Fazekas, E.; Lowy, P. A.; Rahman, M. A.; Lykkeberg, A.; Zhou, Y.; Chambenahalli, R.; Garden, J. A. Main group metal polymerisation catalysts. Chem. Soc. Rev. 2022 , 51 , 8793. 3. Laia, F. J.;Huang, T. W.;Chang, Y. L.;Chang, H. Y.;Lu, W. Y.;Ding, S.;Chen, H. Y.;Chiu, C. C.;Wu, K. H.Titanium complexes bearing 2,6-Bis(o-hydroxyalkyl)pyridine ligands in the ring-opening polymerization of L -Lactide and ε -caprolactone. Polymer 2020 , 204 ,122860.
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