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

Abstract

Treatment of the tetraalkyldigallium(4) compound R 2 Ga−GaR 2 [1; R = CH(SiMe 3 ) 2 ] with the highly functionalized acids 3-and 4-carboxyphenylthiourea, 7azaindole-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 CH 2 (SiMe 3 ) 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.

A Dimeric Gallium Hydrazide as an Active Lewis Pair – Complexation and Activation of Me2GaH and Various Heterocumulenes

“…230 pm) . A similar effect influences the structures of dicarboxylate digallium compounds, in which the unusual bridging of the Ga–Ga bonds by the carboxylate ligands (five‐membered GaOCOGa heterocycles) is preferred over the terminal coordination of the Ga atoms (four‐membered GaO 2 C heterocycles). Replacing the O atoms by the less electronegative N and/or S atoms reduces the partial charges on the C and metal atoms and increases their transannular distances to 250 to 260 pm ( 8 , 9 ) as a result of longer C–S and M –S bonds.…”

Ga–Ga Bonds as Key Building Blocks for the Formation of Supramolecular Entities – Unusual Macrocyclic Tetra‐ and Octagallium Compounds

“…The Ga-Ga bond lengths deviate only slightly from the average value of 238 pm for the standard bond lengths in comparable compounds. [7][8][9][10][11][12][13][14] They are significantly shorter than those observed in the starting compound 1 [254.1(1) pm] [3] and the OH-bridged compounds 3a-c (244 pm on average). [14] The short bonds in 2a-c and the unusual perpendicular arrangement of the chelating ligands are both caused by the relatively small bite of the chelating CO 2 group (distance between the coordinating O atoms: 225 pm) which forces a short distance between the Ga atoms.…”

“…The general trends in both types of compounds are comparable to those of related macrocycles. [8][9][10][11][12][13][14] Despite the similarity of angles and distances to those of previously published compounds, 2 and 3 show unprecedented molecular structures. In 2a the carboxylate groups are in the 1,2-positions of the phenylene ring.…”

“…Nitrogen‐ or hydroxy‐functionalised carboxylic acids yielded three‐dimensional cages with three to six digallium groups in a single molecule . These compounds show supramolecular chemistry with the formation of carcerands,, the coordination of molecules by hydrogen bonding, orthogonal dipolar interactions and sulfur–sulfur closed‐shell interactions . Hydroxido–carboxylato‐bridged digallium compounds (molecular boxes) were obtained by the reaction of 1 with oligofunctional carboxylic acids in the presence of water .…”

Treatment of the Digallium Compound R2Ga–GaR2 [R = CH(SiMe3)2] with Functionalized Dicarboxylic Acids: Macrocycles, Hydrogen Bonding, and Sulfur–Sulfur Closed‐Shell Interactions

“…Tetranuclear compounds with two intact Ga–Ga bonds were obtained with relatively flexible organic backbones,8 whereas octanuclear heterocycles (four Ga–Ga bonds) resulted in rigid spacers between both acidic groups (Scheme , middle) 9. Further functionalization of the acids by thiourea, hydroxy, or amino groups afforded unique supramolecular entities with ring10 or cage structures (Scheme , bottom) and up to six Ga–Ga bonds in a single molecule. Solvent molecules and other suitable substrates were irreversibly encapsulated in the cavities of the large cages11 (carcerands)12 or coordinated to their surface by hydrogen bonding 13.…”