摘要/Abstract

研究了氮上取代基为1-金刚烷基的苯基硼桥联三氮杂环卡宾配体在铁促进的氮气活化转化反应中的应用.通过苯基硼桥联三氮杂环卡宾亚铁氯化物[PhB（AdIm）₃FeCl]（1）在氮气氛下与KC₈反应合成了一价铁分子氮配合物[PhB（AdIm）₃Fe（N₂）]（2）.进一步通过2与KC₈和18-C-6的反应合成了零价铁分子氮配合物[K（18-C-6）（THF）]-[PhB（AdIm）₃Fe（N₂）]（4）.这些配合物均通过核磁共振、紫外吸收光谱、红外光谱、元素分析等表征，其中配合物2和4的结构经单晶X射线衍射表征确定.配合物2和4的N—N伸缩振动频率分别为1928和1807 cm^－1，均为同价态铁末端分子氮配合物最低值.在过量KC₈和Me₃SiCl存在下，配合物1，2和4均可催化N₂的还原硅基化反应，生成N（SiMe₃）₃.催化体系的TON可达87.
关键词: 氮杂环卡宾, 铁, 分子氮配合物, 氮气活化, 氮气硅基化
The use of the N-adamantyl-substituted tris(NHC)borate ligand phenyltris(3-(1-adamantylimidazol-2-ylidene))borate (PhB(AdIm)₃^-) has enabled the preparation of the high-spin tetrahedral iron(I)-and iron(0)-N₂ complexes[PhB(AdIm)₃Fe(N₂)] (2) and[K(18-C-6)(THF)] [PhB(AdIm)₃Fe(N₂)] (4), from the reduction of the ferrous precursor[PhB(AdIm)₃FeCl] (1) and the iron(I) complex 2 with KC₈ under N₂, respectively. Single-crystal X-ray diffraction studies revealed a distorted tetrahedral coordination geometry for the iron centers in 2 and 4 with the terminally bonded N₂ ligand sitting in the cavity composed by the three adamantyl groups of the borate ligand. The frequencies of the N-N stretching resonance (1928 and 1807 cm^-1) of 2 and 4 are the lowest among the reported terminal N₂complexes of iron(I) and iron(0), respectively. ⁵⁷Fe Mössbauer spectrum (δ=0.59 mms^-1; ΔE_Q=1.31 mms^-1) and solution magnetic susceptibility measurement (μ_eff=5.2(1) μ_B) of 2 supported its high-spin iron(I) nature. The cyclic voltammogram of 2 measured in THF shows a quasi-reversible redox waves with E_1/2=-2.11 V (vs SCE), which is assignable to the corresponding redox process of[PhB(AdIm)₃Fe(N₂)]^1-/0. In addition, the reaction of 2 with an excess amount of CO led to the formation of the bis(carbonyl)iron(I) complex,[PhB(AdIm)₃Fe(CO)₂] (3), that was characterized by IR spectrum, solution magnetic susceptibility measurement, ¹H NMR, as well as elemental analysis. The protonation of 2 and 4 with HCl or HOTf at -78℃ only led to the formation of NH₂NH₂ and NH₃ in low yields[less than 9(3)% and 5(3)% (per mol Fe), respectively]. However, 1, 2, and 4 proved effective catalysts for the reductive silylation of N₂by KC₈ and Me₃SiCl to afford N(SiMe₃)₃ with comparable catalytic activity. The TON of these catalytic systems could reach 87 using 0.005 mmol of the catalyst, 2000 equiv. of KC₈, and 2000 equiv. of Me₃SiCl in 10 mL Et₂O at room temperature after 24 h.
Key words: N-heterocyclic carbene, iron, dinitrogencomplex, N₂ activation, reductive silylation of N₂


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