新型卡宾前体1, 3-二取代-2-羧基咪唑(啉）

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（¹H NMR）、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-

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

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.