The Real Role of N-Heterocyclic Carbene in Reductive Functionalization of CO2: An Alternative Understanding from Density Functional Theory Study

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	The Real Role of N-Heterocyclic Carbene in Reductive Functionalization of CO2: An Alternative Understanding from Density Functional Theory Study
	Zhou QH(周庆海); Li YX(李玉学)
刊名	J. Am. Chem. Soc.
	2015
卷号	137 期号:32 页码:10182-10189
其他题名	氮杂环卡宾(NHC)在CO2还原官能团化中真实角色的理论研究
通讯作者	李玉学
英文摘要	The mechanisms of reductive functionalization of CO2 to formamide catalyzed by N-heterocyclic carbene (NHC) were comprehensively studied with DFT calculations. New activation mode with much lower energy barrier than those proposed before was discovered. In this reaction, NHC acts as neither a CO2, nor a silane activator, but as a precursor of the real catalyst, i.e., the in situ formed ionic liquid [NHCH](+)[Carbamate](-). In this loose contact ion pair, the negatively charged O atom of the carbamate anion becomes the new active site and is free to do nucleophilic attack. When amine is absent, CO2 will be converted into methanol. In this case, the NHC-CO2 adduct is the real catalytic species; the active site shifted from the carbene C atom to the negatively charged O atom. These new activation modes follow a pattern of "S(N)2@Si-Acceptor", in which the Si-H bond is activated via concerted backside S(N)2 nucleophilic attack by the negatively charged O atom, and the leaving hydride is directly accepted by a free CO2 molecule. The advantages of these new activation modes originate from the following points: (1) The ionic liquid [NHCH](+)[Carbamate](-) and NHC-CO2 adduct are thermodynamically more stable than NHC. (2) The active site of the NHC catalyst is extended outside a lot. Consequently, the large steric effect between the NHC arms and the substrates in transition state can be avoided to some extent. (3) The O atom has good silicon affinity. In addition, a free CO2 molecule, whose carbon atom is more electrophilic than those of the CO2 moieties in NHC-CO2 adduct and carbamate, acts as an efficient hydride acceptor.
学科主题	金属有机化学
收录类别	SCI
原文出处	http://dx.doi.org/10.1021/jacs.5b03651
语种	英语
WOS记录号	WOS:000359962000037
内容类型	期刊论文
源URL	[http://ir.sioc.ac.cn/handle/331003/39634]
专题	上海有机化学研究所_金属有机化学国家重点实验室
作者单位	中科院上海有机化学研究所, 金属有机化学国家重点实验室
推荐引用方式 GB/T 7714	Zhou QH,Li YX. The Real Role of N-Heterocyclic Carbene in Reductive Functionalization of CO2: An Alternative Understanding from Density Functional Theory Study[J]. J. Am. Chem. Soc.,2015,137(32):10182-10189.
APA	周庆海,&李玉学.(2015).The Real Role of N-Heterocyclic Carbene in Reductive Functionalization of CO2: An Alternative Understanding from Density Functional Theory Study.J. Am. Chem. Soc.,137(32),10182-10189.
MLA	周庆海,et al."The Real Role of N-Heterocyclic Carbene in Reductive Functionalization of CO2: An Alternative Understanding from Density Functional Theory Study".J. Am. Chem. Soc. 137.32(2015):10182-10189.