Co-complexation syntheses, structural characterization, and DFT studies of a novel series of polymeric alkali-metal tetraorganogallates

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Armstrong, David R. and Brammer, Elanor and Cadenbach, Thomas and Hevia, Eva and Kennedy, Alan R. (2013) Co-complexation syntheses, structural characterization, and DFT studies of a novel series of polymeric alkali-metal tetraorganogallates. Organometallics, 32 (2). pp. 480-489. ISSN 0276-7333 (https://doi.org/10.1021/om3009469)

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Abstract

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.

ORCID iDs

Armstrong, David R., Brammer, Elanor ORCID logoORCID: https://orcid.org/0000-0002-9350-7761, Cadenbach, Thomas, Hevia, Eva ORCID logoORCID: https://orcid.org/0000-0002-3998-7506 and Kennedy, Alan R. ORCID logoORCID: https://orcid.org/0000-0003-3652-6015;
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