Domyati Doaa, Hope Sydney L, Latifi Reza, Hearns Micah D, Tahsini Laleh
Department of Chemistry, Oklahoma State University , Stillwater, Oklahoma 74078, United States.
Inorg Chem. 2016 Nov 21;55(22):11685-11693. doi: 10.1021/acs.inorgchem.6b01646. Epub 2016 Nov 3.
Six new Cu(I) complexes with pincer N-heterocyclic carbene (NHC) ligands of the type 2,6-bis(3-alkylimidazol-2-ylidene)pyridine, I(R), and 2,6-bis(3-alkylimidazol-2-ylidene)methylpyridine, I(R), where R = Me, Et, and Pr have been synthesized using Cu precursors and bis(imidazolium) salts. All of these compounds, namely, Cu(IMe), 1; Cu(IEt), 2; Cu(IPr), 3; Cu(IMe), 4; Cu(IEt), 5; and Cu(IPr), 6, have been characterized by H and C NMR spectroscopies, elemental analysis, solution conductivity, and electrochemical studies. Single crystal X-ray structures were obtained for all complexes except 1. The crystallographic data reveal a binuclear structure containing two Cu atoms at a close distance, 2.622-2.811 Å for all the complexes except 5, which shows a unique mononuclear structure. Spatial syn arrangement of ethyl groups and extensive π-π stacking in the solid state accounts for the mononuclear structure of complex 5. A pseudolinear coordination geometry about metal centers consisting of two Cu-carbene bonds, as well as weak Cu-pyridine interactions, exist among all the complexes independent of their ligand. Solution-state conductivity data reveal a dominant 1:2 electrolyte behavior for 1-3 but 1:1 electrolyte for 4-6, consistent with the sustainable binuclear structure in solutions of Cu(I)-I(R) complexes. Cyclic voltammetry and differential pulse voltammetry studies reveal an irreversible and two quasi-reversible peaks for the one-electron oxidation of solvent-bound and solvent-free binuclear and mononuclear Cu-NHC species in complexes 1-3. In contrast, the reversible Cu(II)/Cu(I) couples of 4-6 at potentials close to that of complexes with tripodal polydentate NHC scaffolds indicate the electronic and structural flexibility of I(R) ligands to accommodate both Cu(I) and Cu(II) ions.
利用铜前驱体和双（咪唑鎓）盐合成了六种新型的含钳形 N - 杂环卡宾（NHC）配体的 Cu(I) 配合物，配体类型为 2,6 - 双（3 - 烷基咪唑 - 2 - 亚基）吡啶，记为 I(R)，以及 2,6 - 双（3 - 烷基咪唑 - 2 - 亚基）甲基吡啶，记为 I(R)，其中 R = 甲基、乙基和丙基。所有这些化合物，即 Cu(IMe)，1；Cu(IEt)，2；Cu(IPr)，3；Cu(IMe)，4；Cu(IEt)，5；和 Cu(IPr)，6，均通过氢谱和碳谱核磁共振光谱、元素分析、溶液电导率和电化学研究进行了表征。除 1 外，所有配合物均获得了单晶 X 射线结构。晶体学数据表明，除 5 外，所有配合物均含有两个近距离的 Cu 原子的双核结构，5 显示出独特的单核结构。固态中乙基的空间顺式排列和广泛的 π - π 堆积导致了配合物 5 的单核结构。所有配合物中，无论其配体如何，金属中心周围均存在由两个 Cu - 卡宾键组成的准线性配位几何结构以及弱的 Cu - 吡啶相互作用。溶液态电导率数据表明，1 - 3 呈现主要的 1:2 电解质行为，而 4 - 6 为 1:1 电解质行为，这与 Cu(I) - I(R) 配合物溶液中可持续的双核结构一致。循环伏安法和差分脉冲伏安法研究表明，配合物 1 - 3 中与溶剂结合和无溶剂的双核及单核 Cu - NHC 物种的单电子氧化呈现一个不可逆峰和两个准可逆峰。相比之下，4 - 6 在接近具有三脚架多齿 NHC 支架的配合物的电位处的可逆 Cu(II)/Cu(I) 偶合表明 I(R) 配体在容纳 Cu(I) 和 Cu(II) 离子方面具有电子和结构灵活性。
