基于非血红素铁模型配合物FeⅣ(O)(N4Py)2+的新型N杂环卡宾配合物的理论设计

摘要

基于四价非血红素铁模型配合物[FeⅣ(O) (N4Py)]2+[N4Py=N,N-bis (2-pyridylmethyl) -N-bis (2-pyridylmethylamine)],通过理论计算设计出一种新型N杂环卡宾配合物[FeⅣ(O) (NHC)4]2+.采用密度泛函理论B3 LYP方法,计算了[FeⅣ(O) (NHC)4]2+的几何结构和电子结构,并研究了[FeⅣ(O) (NHC)4]2+使环己烷C-H键羟基化的反应机理.结果表明,[FeⅣ(O) (NHC)4]2+的五重态能量比基态三重态能量高约5.7kJ/mol,故五重态几乎不能参与反应.赤道方向的配位基N杂环卡宾(NHC)对FeO单元的σ-贡献要大于N4Py的贡献,而它的空间位阻效应也大于N4Py,因此[FeⅣ(O)·(NHC)4]2+的稳定性强于[FeⅣ(O)(N4Py)]2+.[FeⅣ(O) (NHC)4]2+的三重态的反应能垒比[FeⅣ(O)·(N4Py)]2+的三重态反应能垒高2.0kJ/mol,且为单态反应,所以[FeⅣ(O) (N4Py)]2+的反应活性要高于[FeⅣ(O) (NHC)4]2+.%Based on non-heme iron complex [FeⅣ(O) (N4Py) ]2+[N4Py = N,N-bis(2-pyridylmethyl)-N-bis (2-pyridylmethylamine) ] , a new designed iron-carbene complex [FeIV(O) (NHC)4]2+ was theoretically designed. The geometric and electronic structures of [ FeⅣ(0)·(NHC)4]2+ were studied via density functional theory and B3LYP method, and the [ FeⅣ(0) (NHC)4]2+catalytic properties versus cyclohexane were investigated. The calculation results show that the energy of the quintet spin state of [FeⅣCO) (NHC)4]2+ is ca. 4. 8 kJ/mol higher than that of the triplet ground state, suggesting that the quintet spin state can hardly participate in the reaction. The N-heterocyclic carbene (NHC) equatorial ligand was found to have stronger cr-dona-ting and greater steric hindrance than N4Py ligand, indicating that the complex [FeⅣ(O)(NHC)4]2+ is more stable than [ FeⅣ(0) ( N4Py)]2+ complex. Moreover, on the triplet spin surface, the energy barrier of [FeIV(O)(NHC)4]2+ has higher activation energy than that of [Few(0) (N4Py) ]2+ by 2.0 kj/mol via a single-state reactivity pattern, implying that [ FeⅣ(0) (N4Py)]24 complex is more reactive than [FeIV(O)(NHC)4]2t complex.