Comparing the Ligand Behavior of N-Heterocyclic Phosphenium and Nitrosyl Units in Iron and Chromium Complexes
Comparing the Ligand Behavior of N-Heterocyclic Phosphenium and Nitrosyl Units in Iron and Chromium Complexes
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DOI：
10.1021/acs.inorgchem.9b00737
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发表时间：
2019-05-06
影响因子：
4.6
通讯作者：
Gudat, Dietrich
中科院分区：
文献类型：
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作者：
Feil, Christoph M.;Hettich, Thomas D.;Gudat, Dietrich
N-杂环膦（NHP）和亚硝基（NO+）配体通常被视为等瓣类似物，它们具有在不同电荷状态之间切换的能力，从而显示氧化还原“非无辜”行为。我们在这里报告的混合配合物[（NHP）M（CO）（n）（NO）]（M = Fe，Cr; n = 2，3），它允许评估两种类型的配体和它们的相互作用在一个单一的配合物的供体/受体的性质。通过N-杂环三氟甲磺酸磷鎓盐分别与PPN[Fe（CO）（3）（NO）]或PPN[Cr（CO）（4）-（NO）]反应，得到了晶体目标化合物，并对其进行了全面表征（PPN =氮-双三苯基膦阳离子）。的结构和光谱（IR，UV-vis）数据支持存在的卡宾类似物NHP配体与整体正电荷状态和π-受体字符。即使M-NO单元的结构特征，但在所有的产品模糊的结晶CO/NO障碍，光谱研究和结构数据的剩余化合物表明，NO单元表现出氮氧（NO-）的字符。计算结果表明，铁NHP/ NO复合物的电子结构与Hieber阴离子[Fe（CO）（3）（NO）]（-）非常相似。NHP单元的亲电特性进一步反映在混合配合物的化学行为中。循环伏安法和红外光谱研究表明，配合物[（NHP）Fe（CO）（2）（NO）]（4）发生了化学可逆的单电子还原反应。计算研究表明，在所得产物中的NHP单元具有显著的自由基特征，因此还原可以被分类为主要以配体为中心。4与叠氮化钠的反应同样在磷的亲核攻击和解络合下进行，而超氢化物和甲基锂通过将氢化物或甲基阴离子转移到NHP单元与所有铬和铁络合物反应，得到阴离子膦络合物。这些物种中的一些在阳离子交换后被分离或用亲电试剂（H+，SnPh 3（+））捕获，以提供代表原始M=P双键的形式氢化或氢化锡烷基化的产物的中性络合物。
N-Heterocyclic phosphenium (NHP) and nitro-sonium (NO+) ligands are often viewed as isolobal analogues that share the capability to switch between different charge states and thus display redox "noninnocent" behavior. We report here on mixed complexes [(NHP)M(CO)(n)(NO)] (M = Fe, Cr; n = 2, 3), which permit evaluating the donor/acceptor properties of both types of ligands and their interplay in a single complex. The crystalline target compounds were obtained from reactions of N-heterocyclic phosphenium triflates with PPN[Fe(CO)(3)(NO)] or PPN[Cr(CO)(4)-(NO)], respectively, and fully characterized (PPN = nitride-bistriphenylphosphonium cation). The structural and spectroscopic (IR, UV-vis) data support the presence of carbene-analogue NHP ligands with an overall positive charge state and pi-acceptor character. Even if the structural features of the M-NO unit were in all but one product blurred by crystallographic CO/NO disorder, spectroscopic studies and the structural data of the remaining compound suggest that the NO units exhibit nitroxide (NO-) character. This assignment was validated by computational studies, which reveal also that the electronic structure of iron NHP/ NO complexes is closely akin to that of the Hieber anion, [Fe(CO)(3)(NO)](-). The electrophilic character of the NHP units is further reflected in the chemical behavior of the mixed complexes. Cyclic voltammetry and IR-SEC studies revealed that complex [(NHP)Fe(CO)(2) (NO)] (4) undergoes chemically reversible one-electron reduction. Computational studies indicate that the NHP unit in the resulting product carries significant radical character, and the reduction may thus be classified as predominantly ligand-centered. Reaction of 4 with sodium azide proceeded likewise under nucleophilic attack at phosphorus and decomplexation, while super hydride and methyl lithium reacted with all chromium and iron complexes via transfer of a hydride or methyl anion to the NHP unit to afford anionic phosphine complexes. Some of these species were isolated after cation exchange or trapped with electrophiles (H+, SnPh3(+)) to afford neutral complexes representing the products of a formal hydrogenation or hydrostannylation of the original M=P double bond.