Ring-Opening Polymerization of rac-Lactide Catalyzed by Octahedral Nickel Carboxylate Complexes

To date, nickel(II) complexes have not been practically investigated as catalysts in ring-opening polymerization (ROP) of lactide to produce biodegradable poly(lactic acid), which is demand biomedicine and industry. In this study, carboxylate containing various N-donor ligands with different nuclearity, metal core rigidity nature were synthesized studied by infrared spectroscopy, X-ray diffraction, elemental thermogravimetric analyses. The obtained examined the ROP rac-lactide bulk toluene solution without addition a benzyl alcohol initiator. series studied, complex [Ni(DBED)2(O2CC(CH3)3)2]·(CH3)3CCO2H (DBED N,N?-dibenzylethylenediamine) was syndioselective catalyst showed highest catalytic ability alcohol. For complex, according 1D DOSY 1H NMR spectroscopy mass spectrometry electrospray ionization, initiated free secondary amine, DBED, leaving metal’s inner coordination sphere. Based on experimental data obtained, comprehensive density functional theory (DFT) study pathways including initiation first chain growth cycle steps detailed description intermediates evaluation energy barriers carried out. It shown that one key roles reaction process played ligands, act proton carriers from initiator molecule significant influence reactivity complexes.