分子内C—H键胺化反应机理的DFT研究

Mechanism of intramolecular C—H amination investigated by DFT method

采用密度泛函理论研究了溴化亚铁催化芳基叠氮化物C—H键胺化生成苯并咪唑的反应机理.研究结果表明,溴化亚铁催化剂使反应由协同机理转变为分步机理,反应活化能降低了大约167kJ/mol.催化反应由氮气消去、C—N形成和2H-苯并咪唑异构化3个基元步骤组成.其中金属亚胺/金属氮烯FeNR PhNCPh进攻C形成C—N键是无能垒过程,且与金属氮烯中氮的电荷密切相关.氮气消去与2H-苯并咪唑异构化反应的能垒均在41~54kJ/mol之间.

The mechanism of iron（Ⅱ）bromide-catalyzed intramolecular C—H amination with aryl azides as the substrates to produce benzimidazoles was investigated by DFT calculations.The results show that Iron catalyst can change the reaction from concerted to stepwise which are N（2）eilimination,C—N bond formation and isomeration,and thus the activation energy is reduced by about 167kJ/mol.The C—N formation process involves metal imido complex/metal-nitrene Fe NR PhN CPh attacking electrophilic C to form C—N bond barrierlessly,which is markedly impacted by the negative charge of the metal-nitrene N.The activation energies of N2 elimination are about 41-54kJ/mol,similar to that of the isomerization reactions.