化学
催化作用
还原消去
氧化加成
镍
芳基
催化循环
配体(生物化学)
药物化学
杂原子
组合化学
吲哚试验
反应机理
卡宾
立体化学
均相催化
有机化学
戒指(化学)
受体
生物化学
烷基
作者
Silvia G. Rull,Ignacio Funes‐Ardoiz,Celia Maya,Feliu Maseras,Manuel R. Fructos,Tomás R. Belderraín,M. Carmen Nicasio
标识
DOI:10.1021/acscatal.8b00856
摘要
Nickel catalysis is gaining in popularity in recent years, mostly within the area of cross-coupling. However, unlike Pd, the mechanisms of Ni-catalyzed C–C and C–heteroatom bond forming reactions have been much less studied, in particular when N-heterocyclic carbenes are used as ligands. Here, we present a thorough study of the mechanism of C–N cross-coupling reactions catalyzed by an NHC-Ni complex. Focusing on the coupling of 2-chloropyridines with indole catalyzed by [(IPrNi(styrene)2] (IPr = N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), we have examined each of the elementary steps: i.e., oxidative addition, ligand substitution, and reductive elimination. All relevant catalytic intermediates have been isolated and structurally characterized by both spectroscopic and crystallographic methods. Kinetic studies have revealed that the reductive elimination is the rate-limiting step. Catalyst deactivation is related to the formation of unproductive dinuclear pyridyl-bridged NHC-NiII species, which can be prevented by increasing the size of the heteroaryl chloride. These investigations support a neutral Ni(0)/Ni(II) catalytic cycle. Calculations corroborate the experimental evidence and confirm the influence exerted by the ligands in each of the elementary steps.
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