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首页> 外文期刊>RSC Advances >Zwitterionic niobium and tantalum complexes with bidentate aminophenol scaffolds: synthesis, structural characterization and use in the ring opening polymerization of lactides
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Zwitterionic niobium and tantalum complexes with bidentate aminophenol scaffolds: synthesis, structural characterization and use in the ring opening polymerization of lactides

机译：双层铌和钽络合物，具有二齿氨基苯酚支架：合成，结构表征和在丙酸酯的开环聚合中使用

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摘要

The stoichiometric reaction of the aminophenol ligands L1–L3 with NbCl _(5) or TaCl _(5) afforded a series of metal chloride complexes 1–6 . These were characterized by ~(1) H, ~(13) C NMR, mass spectroscopy and elemental analysis. Complex 2 crystallized as ethoxy substituted complex 2a upon attempting crystallization from a solvent mixture of chloroform and ethanol. The molecular structure confirms the zwitterionic nature of the complex where the protonated nitrogen atom of the ligand backbone is neutralised by a negative charge on the metal center. Moderate electrostatic hydrogen bonding interactions between the NH ~(+) donor moieties and acceptor chlorine atoms stabilise these complexes. The complexes show moderate activities towards the ring opening polymerization (ROP) of lactides ( rac -LA, L -LA) with good control over the polymerization parameters. All the complexes produced heterotactic enriched poly(lactic acid) (PLA). Low molecular weight oligomers prepared and analysed by MALDI-TOF mass and ~(1) H NMR spectroscopy revealed that the ligand initiates the ROP. The complexes were optimized at the B3LYP/LANL2DZ level and the frontier orbitals were studied in order to calculate the trend in reactivity order theoretically.
机译：氨基苯酚配体L1-L3与NbCl _（5）或TaCl _（5）的化学计量反应得到一系列金属氯化物络合物1-6。这些以〜（1）H，〜（13）C NMR，质谱和元素分析为特征。在尝试从氯仿和乙醇的溶剂混合物结晶时作为乙氧基取代的复合物2a结晶，复合物2结晶。分子结构证实了复合物的两性离子性质，其中通过金属中心上的负电荷中和配体骨架的质子化氮原子。 NH〜（+）供体部分与受体氯原子之间的中等静电氢键相互作用稳定这些配合物。该配合物显示出促进丙酸盐的开环聚合（ROP）的适度活动（RAC -LA，L-LA），良好地对聚合参数进行控制。所有复合物都产生了异诊富含聚（乳酸）（PLA）。由MALDI-TOF质量制备和分析的低分子量低聚物和〜（1）H NMR光谱显示，配体引发ROP。在B3LYP / LANL2DZ水平上进行优化复合物，研究了前轨道以理论上计算反应性顺序的趋势。

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