新型卡宾前体1,3-二取代-2-羧基咪唑(啉)的合成及表征

Synthesis and characterization of 1,3-disubstituted imidazol(in)ium-2-carboxylates

性质稳定的1,3-二取代-2-羧基咪唑(啉)(NHC-CO2)是一类重要的卡宾前体,以3条路线合成了一系列含有不同取代基结构的NHC—CO2。通过核磁共振(1HNMR)、元素分析以及红外光谱(IR)对产物进行了结构表征。利用热重/微商热重分析(TG/DTG)对产物的热脱羧性能进行了研究。结果表明:随着温度升高,NHC—CO22-位羧基脱除,得到游离卡宾;芳基取代的NHC—CO2在50～350℃间有脱羧和降解两个阶段,并且拥有相同芳香取代基的2-羧基咪唑和2-羧基咪唑啉具有相似的脱羧性能;烷基取代的NHC—CO2较芳香基取代的NHC—CO2初始脱羧温度低,且不存在降解阶段。

The air-and water-stable 1,3-disubstituted imidazol（in）ium-2-carboxylates（NHC—CO2） as important precursors of N-heterocyclic carbenes were prepared by three routes.Nine kinds of NHC—CO2 with different groups on nitrogen atoms were obtained.The structure was characterized by 1H NMR,elemental analysis and IR.Thermogravimetric analysis（TG/DTG） provided the evidence for decarboxylation in NHC—CO2.The results show that CO2 escapes from the molecule in the process of elevating temperature and free carbenes are released.Two processes（decarboxylation and decomposition） occur when the substituents on the nitrogen atoms are aryl group,and the imidazolium-2-carboxylates and the imidazolinium-2-carboxylates show similar performance of decarboxylation.The initial temperatures of mass loss are lower when the substituents on the nitrogen atoms are alkyl group,and no decomposition occurs.