Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India.
Dalton Trans. 2010 Mar 14;39(10):2515-24. doi: 10.1039/b917892a. Epub 2010 Jan 21.
A comparison is drawn between the nickel and palladium precatalysts of 1,2,4-triazole based N-heterocyclic carbenes in the hydroamination of activated olefins. Though all of the newly designed nickel and palladium precatalysts, trans-1-i-propyl-4-R-1,2,4-triazol-5-ylideneMBr(2) [R = Et, M = Ni (1b); R = Et, M = Pd (1c); R = CH(2)CH=CH(2), M = Ni (2b) and R = CH(2)CH=CH(2), M = Pd (2c)], are moderately active for hydroamination reaction of a variety of secondary amines viz. morpholine, piperidine, pyrrolidine and diethylamine with activated olefins like, acrylonitrile, methyl acrylate, ethyl acrylate and t-butyl acrylate at room temperature in 1 hour, the nickel complexes (1b and 2b) exhibited superior activity compared to its palladium counterparts (1c and 2c). The better performance of the nickel complexes has been correlated to the more electron deficient metal center in the nickel 1b and 2b complexes than in the palladium 1c and 2c analogs based on the density functional theory studies. The 1b-c and 2b-c complexes were synthesized by the reaction of 1-i-propyl-4-R-1,2,4-triazolium bromide [R = Et (1a) and R = CH(2)CH=CH(2) (2a)] with MCl(2) [M = Ni, Pd] in presence of NEt(3) as a base.
将 1,2,4-三唑基 N-杂环卡宾的镍和钯前催化剂在活性烯烃的氢胺化反应中进行了比较。虽然所有新设计的镍和钯前催化剂，反式-1-异丙基-4-R-1,2,4-三唑-5-亚基MBr(2)[R=Et，M=Ni(1b)；R=Et，M=Pd(1c)；R=CH(2)CH=CH(2)，M=Ni(2b)和 R=CH(2)CH=CH(2)，M=Pd(2c)]，在室温下对各种仲胺如吗啉、哌啶、吡咯烷和二乙胺与丙烯腈、甲基丙烯酸甲酯、丙烯酸乙酯和叔丁基丙烯酸酯的氢胺化反应具有中等活性，但镍配合物(1b 和 2b)的活性优于其钯对应物(1c 和 2c)。基于密度泛函理论研究，镍配合物(1b 和 2b)中的金属中心电子缺失程度比钯配合物(1c 和 2c)更高，这与镍配合物的更好性能有关。1b-c 和 2b-c 配合物是通过 1-异丙基-4-R-1,2,4-三唑𬭩溴化物[R=Et(1a)和 R=CH(2)CH=CH(2)(2a)]与 MCl(2)[M=Ni，Pd]在 NEt(3)作为碱的存在下反应合成的。
