Department of Chemistry, University of Texas at El Paso , El Paso, Texas 79968, United States.
Computational OrganoMetallic and Inorganic Chemistry Group, Eenheid Algemene Chemie, Vrije Universiteit Brussel , Pleinlaan 2, Brussels 1050, Belgium.
J Am Chem Soc. 2017 Nov 8;139(44):15691-15700. doi: 10.1021/jacs.7b06919. Epub 2017 Oct 19.
Utilizing the bulky guanidinate ligand [L] (L = (ArN)C(R), Ar = 2,6-bis(diphenylmethyl)-4-tert-butylphenyl, R = NCBu) for kinetic stabilization, the synthesis of a rare terminal Fe(IV) nitride complex is reported. UV irradiation of a pyridine solution of the Fe(II) azide [L]FeN(py) (3-py) at 0 °C cleanly generates the Fe(IV) nitride [L]FeN(py) (1). The N NMR spectrum of the 1 (50% Fe≡N) isotopomer shows a resonance at 1016 ppm (vs externally referenced CHNO at 380 ppm), comparable to that known for other terminal iron nitrides. Notably, the computed structure of 1 reveals an iron center with distorted tetrahedral geometry, τ = 0.72, featuring a short Fe≡N bond (1.52 Å). Inspection of the frontier orbital ordering of 1 shows a relatively small HOMO/LUMO gap with the LUMO comprised by Fe(d)N(p) π*-orbitals, a splitting that is manifested in the electronic absorption spectrum of 1 (λ = 610 nm, ε = 1375 L·mol·cm; λ = 613 nm (calcd)). Complex 1 persists in low-temperature solutions of pyridine but becomes unstable at room temperature, gradually converting to the Fe(II) hydrazide product [κ-(BuCN)C(η-NAr*)(N-NAr*)]Fe (4) upon standing via intramolecular N-atom insertion. This reactivity of the Fe≡N moiety was assessed through molecular orbital analysis, which suggests electrophilic character at the nitride functionality. Accordingly, treatment of 1 with the nucleophiles PMePh and Ar-N≡C (Ar = 2,6-dimethylphenyl) leads to partial N-atom transfer and formation of the Fe(II) addition products [L]Fe(N═PMePh)(py) (5) and [L]Fe(N═C═NAr)(py) (6). Similarly, 1 reacts with PhSiH to give [L]FeN(H)(SiHPh) (7) which Fukui analysis shows to proceed via electrophilic insertion of the nitride into the Si-H bond.
利用庞大的胍基配体 [L]（L = (ArN)C(R)，Ar = 2,6-双（二苯基甲基）-4-叔丁基苯基，R = NCBu）进行动力学稳定，报告了一种罕见的末端 Fe(IV)氮化物配合物的合成。在 0°C 下，将 Fe(II)叠氮化物[L]FeN(py)(3-py)的吡啶溶液用紫外线照射，可干净地生成 Fe(IV)氮化物[L]FeN(py)(1)。1 的 15N NMR 谱（50% Fe≡N）在 1016 ppm 处出现共振（相对于外部参考 CHNO 在 380 ppm），与其他末端铁氮化物相似。值得注意的是，计算出的 1 的结构显示出一个具有扭曲四面体几何形状的铁中心，τ = 0.72，具有短的 Fe≡N 键（1.52 Å）。检查 1 的前线轨道排序表明，HOMO/LUMO 间隙较小，LUMO 由 Fe(d)N(p)π*-轨道组成，这种分裂在 1 的电子吸收光谱中表现出来（λ = 610 nm，ε = 1375 L·mol·cm；λ = 613 nm（计算））。配合物 1 在吡啶的低温溶液中稳定存在，但在室温下不稳定，静置时通过分子内 N 原子插入逐渐转化为 Fe(II)腙产物[κ-(BuCN)C(η-NAr*)(N-NAr*)]Fe(4)。通过分子轨道分析评估了 Fe≡N 部分的反应性，这表明氮化物官能团具有亲电性。因此，用亲核试剂 PMePh 和 Ar-N≡C（Ar = 2,6-二甲基苯基）处理 1 会导致部分 N 原子转移，并形成 Fe(II)加成产物[L]Fe(N═PMePh)(py)(5)和[L]Fe(N═C═NAr)(py)(6)。同样，1 与 PhSiH 反应生成[L]FeN(H)(SiHPh)(7)，福井分析表明该反应通过氮化物对 Si-H 键的亲电插入进行。
