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

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.