Search Results (3)

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. Full article

Two copper coordination compounds bearing an N,N’-dibenzylethylenediamine ligand, namely [Cu₃L(CH₃COO)₆]_n (1) and [(CuCl₄)∙(C₆H₅CH₂NH₂CH₂)₂] (2) (L = N,N’-dibenzylethylenediamine) were synthesized by the ethanol refluxing method. Powder X-ray diffraction (PXRD), infrared spectra (IR), elemental analyses, and single crystal X-ray diffraction were used to characterize and verify their structures. Structural analyses showed that the asymmetric unit of compound (1), composed of two Cu(II) cations, three acetate anions, and half of the ligand, was bridged by one acetate to obtain an infinite 1D chain structure. The analyses further showed that the asymmetric unit of compound (2), composed of two crystallographically independent [C₆H₅CH₂NH₂CH₂]⁺ units, four chloride anions, and one central Cu(II) cation is connected into an infinite 2D network structure by the hydrogen bonding interactions. The copper compounds were used to catalyze the decomposition of H₂O_2, and the results showed that both of the compounds exhibited excellent catalytic activities under optimized conditions. Full article