Dinucleating ligand platforms supporting zinc and indium catalysts for stereoselective lactide polymerization

With the recent advances in cyclic ester polymerization to access biodegradable and bio-based plastic, an increasing number of metal-based initiators have been reported to mediate ring opening polymerization with high yield and stereoselectivity. However, the origin of the stereoselectivity and the factors affecting it are yet little understood. The role of the metal nuclearity for the polymerization of lactide has especially been subject to various speculations. In our group, we developed unique asymmetrically bridged indium initiators, explored their ring opening polymerization mechanism and found evidence for a type of tandem catalysis. In order to have a better understanding of the role of the two indium metal centres during polymerization, we aimed to synthesize dinucleating analogues. The syntheses of the first alkoxide bridged indium complex supported by a chiral dinucleating ligand platform, along with its zinc analogue, are reported. Both complexes were synthesized in a one pot reaction starting from a chiral dinucleating bis(diamino)phenolate ligand platform, NaOEt, and respective metal salts. The dinucleating indium species bearing an achiral ligand backbone previously synthesized in our group was also further investigated. Both indium complexes catalyze the ring opening polymerization of racemic lactide to afford highly heterotactic PLA (Pr > 0.85). The indium complex bearing the achiral ligand backbone affords atactic PLA (Pr = 0.46) from meso-LA. The role of the dinucleating ligand structure in catalyst synthesis and polymerization activity is discussed.Science, Faculty ofChemistry, Department ofGraduat