TY - JOUR

T1 - Ring-Opening Polymerization of rac-Lactide Catalyzed by Octahedral Nickel Carboxylate Complexes

AU - Nikiforov, Alexey

AU - Panina, Natalia

AU - Blinou, Daniil

AU - Gurzhiy, Vladislav

AU - Nashchekina, Juliya

AU - Korzhikova-vlakh, Evgenia

AU - Eremin, Alexey

AU - Stepanova, Mariia

PY - 2023/1/29

Y1 - 2023/1/29

N2 - 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 in demand in biomedicine and industry. In this study, carboxylate complexes of nickel(II) containing various N-donor ligands with different nuclearity, metal core rigidity and nature of carboxylate ligands were synthesized and studied by infrared spectroscopy, X-ray diffraction, elemental and thermogravimetric analyses. The obtained complexes were examined in the ROP of the rac-lactide in bulk and in toluene solution with and without the addition of a benzyl alcohol initiator. In the series of complexes studied, the complex [Ni(DBED)2(O2CC(CH3)3)2]·(CH3)3CCO2H (DBED is N,N′-dibenzylethylenediamine) was a syndioselective catalyst and showed the highest catalytic ability in the polymerization without the addition of benzyl alcohol. For this complex, according to 1D DOSY 1H NMR spectroscopy and mass spectrometry with electrospray ionization, polymerization is initiated by a free secondary amine, DBED, leaving the metal’s inner coordination sphere. Based on the experimental data obtained, a comprehensive density functional theory (DFT) study of the ROP pathways including the initiation and first chain growth cycle steps with a detailed description of the intermediates and evaluation of the energy barriers of the steps was carried out. It was shown that one of the key roles in the reaction process is played by carboxylate ligands, which act as proton carriers from the initiator molecule and have a significant influence on the reactivity of the catalytic metal complexes.

AB - 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 in demand in biomedicine and industry. In this study, carboxylate complexes of nickel(II) containing various N-donor ligands with different nuclearity, metal core rigidity and nature of carboxylate ligands were synthesized and studied by infrared spectroscopy, X-ray diffraction, elemental and thermogravimetric analyses. The obtained complexes were examined in the ROP of the rac-lactide in bulk and in toluene solution with and without the addition of a benzyl alcohol initiator. In the series of complexes studied, the complex [Ni(DBED)2(O2CC(CH3)3)2]·(CH3)3CCO2H (DBED is N,N′-dibenzylethylenediamine) was a syndioselective catalyst and showed the highest catalytic ability in the polymerization without the addition of benzyl alcohol. For this complex, according to 1D DOSY 1H NMR spectroscopy and mass spectrometry with electrospray ionization, polymerization is initiated by a free secondary amine, DBED, leaving the metal’s inner coordination sphere. Based on the experimental data obtained, a comprehensive density functional theory (DFT) study of the ROP pathways including the initiation and first chain growth cycle steps with a detailed description of the intermediates and evaluation of the energy barriers of the steps was carried out. It was shown that one of the key roles in the reaction process is played by carboxylate ligands, which act as proton carriers from the initiator molecule and have a significant influence on the reactivity of the catalytic metal complexes.

KW - DFT quantum-chemical modeling

KW - carboxylate ligands

KW - homogeneous catalysis

KW - lactide

KW - mass spectrometry

KW - molecular structures

KW - nickel

KW - polylactide

KW - ring-opening polymerization

UR - https://www.mendeley.com/catalogue/0471e91d-441f-302f-b094-fdad7ad91c4b/

U2 - 10.3390/catal13020304

DO - 10.3390/catal13020304

M3 - Article

VL - 13

JO - Catalysts

JF - Catalysts

SN - 2073-4344

IS - 2

M1 - 304

ER -