Synthesis of Pyridine/Pyrrolimidine Cobalt/Nickel Complexes and Methyl Methacrylate Polymerization Catalyzed by Them
A series of ligands L1-L4 were synthesized by Schiff base condensation reaction of 2-acetylpyridine/pyrrole with p-phenylenediamine and carbazide catalyzed by glacial acetic acid/microwave radiation.Complexes 1-8 were further synthesized by reaction with cobalt/nickel chloride in methanol/tetrahydrofuran.The comprehensive structural characterization of the product was carried out using elemental analysis,nuclear magnetic resonance spectroscopy,infrared spectroscopy,ultraviolet spectroscopy,and X-ray single-crystal diffraction.It was found that the ligands L1-L3 has a diamine bridged double imine pyridine/pyrrole structure,L4 has a single imine pyrrole structure,and complexes 1-6 are all binuclear complexes,while complexes 7 and 8 are mononuclear.In the ligand synthesis experiment,it was found that the yield of L1 was the highest,reaching 89.8％,indicating that aniline has stronger nucleophilicity compared to linear amines and is more conducive to the generation of products.Through a systematic study of the relationship between the catalytic behavior of complexes 1-8 for the polymerization of methyl methacrylate(MMA)and the catalyst structure and polymerization reaction conditions,it was found that when the polymerization time was 6 h,the temperature was 90 ℃,the ratio of monomer to catalyst n(M)/n(Ni)was 3000∶1,and the ratio of main catalyst to initiator n(Ni)/n(AIBN)was 2∶1,the catalytic activity of the double imine ligand Ni(Ⅱ)complex formed by the condensation of 2-acetylpyridine and p-phenylenediamine was the highest,reaching 4.3281 × 104 g·mol-1·h-1.
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