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喹喔啉并(咪唑基)二烯:一种电子可配体双(N-杂环卡宾)及其双金属配合物的合成与研究。

Quinobis(imidazolylidene): synthesis and study of an electron-configurable bis(N-heterocyclic carbene) and its bimetallic complexes.

机构信息

Department of Chemistry & Biochemistry, The University of Texas at Austin, Austin, TX 78712, USA.

出版信息

Chemistry. 2010 Jan 4;16(1):304-15. doi: 10.1002/chem.200901883.

Abstract

Reaction of bromanil with N,N'-dimesitylformamidine followed by deprotonation with NaN(SiMe(3))(2) afforded 1,1',3,3'-tetramesitylquinobis(imidazolylidene) (1), a bis(N-heterocyclic carbene) (NHC) with two NHC moieties connected by a redox active p-quinone residue, in 72 % yield of isolated compound. Bimetallic complexes of 1 were prepared by coupling to FcN(3) (2) or FcNCS (3; Fc=ferrocenyl) or coordination to [M(cod)Cl] (4 a or 4 b, where M=Rh or Ir, respectively; cod=1,5-cyclooctadiene). Treatment of 4 a and 4 b with excess CO(g) afforded the corresponding [M(CO)(2)Cl] complexes 5 a and 5 b, respectively. Analysis of 2-5 by NMR spectroscopy and X-ray diffraction indicated that the electron-deficient quinone did not significantly affect the inherent spectral properties or coordination chemistry of the flanking imidazolylidene units, as compared to analogous NHCs. Infrared spectroscopy and cyclic voltammetry revealed that decreasing the electron density at ML(n) afforded an increase in the stretching energy and a decrease in the reduction potential of the quinone, indicative of metal-quinone electronic interaction. Differential pulse voltammetry and chronoamperometry of the metal-centered oxidations in 2-4 revealed two single, one-electron peaks. Thus, the metal atoms bound to 1 are oxidized at indistinguishable potentials and do not appear electronically coupled. However, the metal-quinone interaction was used to increase the electron density at coordinated metal atoms. Infrared spectroelectrochemistry revealed that the average nu(CO) values for 5 a and 5 b decreased by 14 and 15 cm(-1), respectively, upon reduction of the quinone embedded within 1. These shifts correspond to 10 and 12 cm(-1) decreases in the Tolman electronic parameter of this ditopic ligand.

摘要

溴代苯胺与 N,N'-二甲基甲脒反应,然后用 NaN(SiMe(3))(2)脱质子化,得到 1,1',3,3'-四甲基喹二亚胺基双(咪唑啉基)(1),这是一种双(N-杂环卡宾)(NHC),两个 NHC 部分通过氧化还原活性的对醌残基连接,产率为分离化合物的 72%。通过与 FcN(3)(2)或 FcNCS(3;Fc=二茂铁基)偶联或与 [M(cod)Cl](4 a 或 4 b,其中 M=Rh 或 Ir,分别;cod=1,5-环辛二烯)配位,制备了 1 的双金属配合物。用过量的 CO(g)处理 4 a 和 4 b 分别得到相应的 [M(CO)(2)Cl] 配合物 5 a 和 5 b。通过 NMR 光谱和 X 射线衍射分析 2-5 表明,与类似的 NHC 相比,缺电子的醌并没有显著影响侧翼咪唑啉基单元的固有光谱性质或配位化学。红外光谱和循环伏安法表明,降低 ML(n)的电子密度会增加醌的伸缩能,并降低醌的还原电位,表明金属-醌的电子相互作用。2-4 中金属中心氧化的差分脉冲伏安法和计时安培法显示出两个单电子、一电子峰。因此,与 1 结合的金属原子在可区分的电位下被氧化,并且似乎没有电子偶联。然而,金属-醌相互作用被用来增加配位金属原子的电子密度。红外光谱电化学表明,嵌入在 1 中的醌还原后,5 a 和 5 b 的平均 nu(CO)值分别降低了 14 和 15 cm(-1)。这些位移对应于这个双齿配体的 Tolman 电子参数降低了 10 和 12 cm(-1)。

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