Four new Rh(I) complexes bearing chelating imine-functionalized N-heterocyclic carbene ligands have been synthesized and characterized. The catalytic activity of these new Rh(I) complexes has been tested in the cyclopropanation reaction between ethyl diazoacetate and styrene. One of the new complexes, having ethyl groups on the ligand N-aryl ring, exhibited a reactivity and a cis-diastereoselectivity that were comparable to our previously reported Rh(I) cyclopropanation catalyst of this type, and a higher yield and cis-diastereoselectivity were obtained at lower catalyst loadings and higher temperatures. The other new Rh(I) complexes were found to be inferior to the previously reported Rh(I) cyclopropanation catalyst. The catalytic study gave important information about the effect that changing the steric requirements of the substituents at the ligand system has on the efficiency and cis-diastereoselectivity of the complexes as cyclopropanation catalysts.
合成了四种新型Rh(I)配合物,它们带有螯合
亚胺功能化的N-杂环卡宾
配体,并对这些配合物进行了表征。测试了这些新型Rh(I)配合物在二氮
乙酸乙酯和
苯乙烯的
环丙烷化反应中的催化活性。其中一种新型配合物在
配体N-芳基环上具有乙基,其反应活性和顺式立体选择性与先前报道的该类型Rh(I)
环丙烷化催化剂相当,并在较低催化剂用量和较高温度下获得了更高的产率和顺式立体选择性。其他新型Rh(I)配合物的性能则不如先前报道的Rh(I)
环丙烷化催化剂。这项催化研究提供了重要信息,即改变
配体系统上取代基的立体要求对配合物作为
环丙烷化催化剂的效率和顺式立体选择性的影响。