Synthesis of Novel Chelating Benzimidazole-Based Carbenes and Their Nickel(II) Complexes: Activity in the Kumada Coupling Reaction

Nickel(II) halide complexes of novel chelating bidentate benzimidazole-based N-heterocyclic carbenes have been prepared from Ni(OAc)2 and bisbenzimidazolium salts. Single-crystal X-ray structure determination on four complexes revealed a cis-geometry on a square-planar nickel center. The complexes are active catalysts for the Kumada coupling of 4-chloroanisole and 4-bromoanisole with phenylmagnesium chloride. The most active catalyst gives a complete conversion of 4-bromoanisole within 75 min with a selectivity to 4-methoxybiphenyl of 82% and a complete conversion of 4-chloroanisole in less than 14 h with a selectivity to 4-methoxybiphenyl of 99%.

本研究以乙酸镍(II)（Ni(OAc)₂）与双苯并咪唑鎓盐为起始原料，合成了一类新型的基于苯并咪唑的双齿螯合氮杂环卡宾卤化镍(II)配合物。通过单晶X射线衍射对其中4个配合物的结构进行解析，结果表明其镍中心均呈现平面正方形配位构型，且为顺式几何结构。该系列配合物可作为高效催化剂应用于4-氯苯甲醚、4-溴苯甲醚与氯化苯基镁的熊田（Kumada）交叉偶联反应。其中催化活性最优的催化剂可在75分钟内完全转化4-溴苯甲醚，对4-甲氧基联苯的选择性达82%；并可在14小时内完全转化4-氯苯甲醚，对4-甲氧基联苯的选择性高达99%。