Cobalt(II) complexes supported by iminomethylpyridine derived ligands: Synthesis, characterization and catalytic application towards methyl methacrylate and rac-lactide polymerisations

초록

A series of cobalt(II) complexes, [LnCoCl2] (L-n = L-A - L-F), supported by iminomethylpyridine derivatives have been synthesized. The crystal structures of [LACoCl2], [LDCoCl2] and [LECoCl2] were identified by X-ray diffraction studies and they showed five-coordinated distorted square pyramidal geometries. All the complexes synthesized were evaluated as potential mediators for the coordination polymerisation of methyl methacrylate (MMA), in the presence of modified methylaluminoxane (MMAO). The Co(II) complex with the ligand (E)-N-1,N-1-dimethyl-N-3-(pyridin-2-ylmethylene)propane-1,3-diamine displayed the highest catalytic activity (4.48 x 10(4) g PMMA / mol Co h) for MMA polymerisation. Regardless of the ligand architecture, syndio-enriched poly(methyl methacrylate) (PMMAs) with high molecular weights (11.1 x 10(5) g/mol) have been furnished. Additionally, the in situ generated dimethyl Co(II) complexes polymerized racemic-lactide (rac-LA), yielding hetero-enriched polylactide (PLA). Importantly, the stereoselectivities of the Co(II) complexes towards PLA have been found to be influenced by the steric and electronic properties of the amine substituents. (C) 2020 Published by Elsevier Ltd.

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