Co-complexation Syntheses, Structural Characterization, and DFT Studies of a Novel Series of Polymeric Alkali-Metal Tetraorganogallates

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• 作者：David R. Armstrong ; Elanor Brammer ; Thomas Cadenbach ; Eva Hevia ; Alan R. Kennedy
• 刊名：Organometallics
• 出版年：2013
• 出版时间：January 28, 2013
• 年：2013
• 卷：32
• 期：2
• 页码：480-489
• 全文大小：444K
• 年卷期：v.32,no.2(January 28, 2013)
• ISSN：1520-6041

文摘

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}_{鈭?/sub>] (M = Li, 1; Na, 2) and related benzene adduct [{(C6H6)2KGa(CH2SiMe3)4}鈭?/sub>] (3). By combining X-ray crystallography, NMR spectroscopy, and DFT calculations, this study sheds new light on the constitution of these mixed-metal species. X-ray 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鈥揅 and Ga鈥揅 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路路路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鈥?b>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 蟺-electrostatic interactions, appears to be the major contributor to its overall stability.}