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Gallium–Gallium Bonds As Effective Templates for the Generation of Macrocycles and Supramolecular Entities

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posted on 08.10.2012, 00:00 by Werner Uhl, Christina Stefaniak, Matthias Voß, Jutta Kösters, Friedhelm Rogel
Treatment of the tetraalkyldigallium(4) compound R2Ga–GaR2 [1; R = CH­(SiMe3)2] with the highly functionalized acids 3- and 4-carboxyphenylthiourea, 7-azaindole-3-carboxylic acid, and 6-aminonicotinic acid afforded macrocyclic compounds in which two or four Ga–Ga bonds are bridged by the respective number of organic spacer ligands. In each reaction two equivalents of CH2(SiMe3)2 per formula unit of 1 were released. The Ga–Ga bonds of the products 2 to 5 are bridged by a carboxylato group and a chelating ligand containing two nitrogen donor atoms or the sulfur and nitrogen atoms of a thiourea group. The thiourea derivatives afforded different species with four or eight gallium atoms in the heterocycles (2 and 3) depending on their substitution patterns (1,3- versus 1,4-positions at the benzene rings). Supramolecular aggregates resulted that had up to 12 THF molecules encapsulated in the heterocycles or bonded to the surface of the molecules via hydrogen bonding or orthogonal dipolar interactions.