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由于其强给电子能力、结构易修饰性和拓扑学特性,N-杂环卡宾成为继有机膦配体之后又一类重要的配体。其金属络合物在均相及不对称催化领域的催化性能是近期研究的热点,已有许多成功的结果。本文综述了近年来N-杂环卡宾及其金属络合物以及N-杂环卡宾的重要前体咪唑盐的合成方法。金属-N-杂环卡宾络合物的合成方法包括:(a)游离卡宾与金属化合物直接络合;(b)咪唑盐与金属化合物在强碱作用下络合;(c)利用Ag-NHC通过卡宾配体转移方法制备新的金属络合物。关于N-杂环卡宾前体的合成途径主要有:(a)乙二醛、伯胺和多聚甲醛的缩合反应;(b)卤代烷与咪唑或取代咪唑的烷基化反应;(c)原甲酸酯与1,2-二胺的成环反应;(d)肼或酰胺与酸酐的环化反应;(e)用Na/K对环硫脲化合物的还原反应。
Due to their strong electron-donating ability, structurally easy modification and topological properties, N-heterocyclic carbenes have become another important class of ligands following the organophosphine ligands. The catalytic properties of its metal complexes in the field of homogeneous and asymmetric catalysis have been the focus of recent research and many successful results have been obtained. This review summarizes the recent progress in the synthesis of N-heterocyclic carbenes and their metal complexes as well as the important precursors of imidazole salts of N-heterocyclic carbenes. The method for synthesizing a metal-N-heterocyclic carbene complex comprises: (a) direct coupling of a free carbene with a metal compound; (b) complexation of an imidazole salt with a metal compound under the action of a strong base; (c) A new metal complex was prepared by carbene ligand transfer method. The synthetic routes to N-heterocyclic carbene precursors are mainly: (a) condensation of glyoxal, primary amine and paraformaldehyde; (b) alkylation of alkyl halides with imidazole or substituted imidazole; (c) A cyclization reaction of a formic acid ester with 1,2-diamine; (d) a cyclization reaction of a hydrazine or an amide with an acid anhydride; and (e) a reduction reaction of a cyclic thiourea compound with Na / K.