Co-complexation Syntheses, Structural Characterization, and DFT Studies of a Novel Series of Polymeric Alkali-Metal Tetraorganogallates
Co-complexation Syntheses, Structural Characterization, and DFT Studies of a Novel Series of Polymeric Alkali-Metal Tetraorganogallates
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DOI：
10.1021/om3009469
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发表时间：
2013-01-28
期刊：
影响因子：
2.8
通讯作者：
Kennedy, Alan R.
中科院分区：
文献类型：
--
作者：
Armstrong, David R.;Brammer, Elanor;Kennedy, Alan R.
利用芳烃/己烷溶剂混合物探索烷基镓Ga(CH2SiMe3)(3)与碱金属烷基MCH2SiMe3 （M = Li， Na或K）之间的共络合反应，分离出无溶剂的碱金属四有机没食子酸盐[{MGa(CH2SiMe3)(4)}（无穷）]（M = Li, 1; Na, 2）和相关的苯加合物[{(C6H6)(2)KGa-(CH2SiMe3)(4))（无穷）](3)。通过结合x射线晶体学，核磁共振波谱学和DFT计算，本研究揭示了这些混合金属物种的组成。x射线晶体学研究表明，所有没食子酸酯都表现出新的聚合物排列，其中1和2具有相同的线性链结构，完全由M-C和Ga-C键组成，而3显示出更开放的结构基序。其中K原子和Ga原子由单个烷基桥连接，通过较弱的K中心点中心点中心点Me进行传播，来自烷基配体的SiMe3基团的甲基与来自相邻单体单元的钾的静电相互作用。多核核磁共振光谱研究表明，在氘化苯溶液中，1-3以离散的溶剂分离离子对形式存在，其中碱金属被芳烃溶剂溶解。DFT计算表明，虽然这些聚合物结构的无限聚集是热力学上有利于形成1和2的关键，但在3的情况下，通过pi-静电相互作用，两个苯分子对不饱和钾的溶剂化似乎是其整体稳定性的主要因素。
Exploring the co-complexation reactions between the gallium alkyl Ga(CH2SiMe3)(3) and alkali-metal alkyl MCH2SiMe3 (M = Li, Na, or K) using an arene/hexane solvent mixture has allowed the isolation of solvent-free alkali-metal tetraorganogallates [{MGa(CH2SiMe3)(4)}(infinity)] (M = Li, 1; Na, 2) and related benzene adduct [{(C6H6)(2)KGa-(CH2SiMe3)(4))(infinity)] (3). By combining X-ray crystallography, NMR spectroscopy, and DFT calculations, this study sheds new light on the constitution of these mixed-metal species. Xray crystallographic studies reveal that all gallates exhibit novel polymeric arrangements, with 1 and 2 sharing the same linear chain structure, made up exclusively of M-C and Ga-C bonds, whereas 3 displays a significantly more open structural motif, where the K and Ga atoms are connected by a single alkyl bridge and propagation occurs via weaker K center dot center dot center dot Me electrostatic interactions of a methyl from a SiMe3 group of an alkyl ligand from one monomer to the potassium from a neighboring monomeric unit. Multinuclear NMR spectroscopic studies suggest that in deuterated benzene solutions 1-3 exist as discrete solvent-separated ion-pair species where the alkali-metal is solvated by the arene solvent. DFT calculations show that while the infinite aggregation of these polymeric structures is key for thermodynamically favoring the formation of 1 and 2, in the case of 3 the solvation of unsaturated potassium by two molecules of benzene, via pi-electrostatic interactions, appears to be the major contributor to its overall stability.