Gallium–gallium bonds as efficient templates for the generation of a large cage containing twelve gallium atoms

Abstract

Treatment of the digallium compound R(2)Ga-GaR(2) [R = CH(SiMe(3))(2)] with benzotriazol-5-carboxylic acid afforded a large cage-like compound in which six Ga-Ga bonds are bridged by six trifunctional ligands. The central cavity encapsulated a THF molecule which cannot be removed in vacuo and does not show exchange with a large excess of the solvent.

Supramolecular Chemistry Based on Gallium–Gallium Single Bonds – Formation of Large Heterocycles and Cages with up to Twelve Gallium Atoms

“…Compared to 9·THF and 9·dioxane the molecules of 10·THF are relatively flat. In these three compounds two triangles of Ga-Ga bonds form a trigonal antiprism and the distances between the triangles are 565 and 566 pm in the structures of 9, but only 346 pm in 10·THF (average planes calculated with all six gallium atoms; 386 pm in the only other known compound of this type based on benzotriazol-5-carboxylic acid [10] ). This observation reflects an inverse correlation between the lengths of the spacer and the intertriangular distances.…”

“…One terminal CH(SiMe 3 ) 2 group of each gallium atom was replaced by a second metal atom to generate a cage compound, in which Only two carboxylatedigallium compounds with a three-dimensional arrangement of four or six Ga-Ga bonds have been reported in the literature. [9,10] They have spacer ligands with a Y-shaped arrangement of the donor atoms, which may be an important prerequisite for the formation of such cages. The acids 4 and 5 (Scheme 1) fit reasonably well into this scheme, and their treatment with 1 afforded in surprisingly selective transformations two new cage compounds with six Ga-Ga bonds (9·THF and 10·THF, yields ca.…”

“…We calculated the sizes of the cavities with the program PLATON [16] by consideration of the inner van der Waals surfaces and obtained a volume of 131 ϫ 10 6 pm 3 for 9·THF. A comparable value of 138 ϫ 10 6 pm 3 was calculated for the related dodecagallium triazol derivative, which has been published previously [10] and encapsulated also a THF molecule. Interestingly the cavity of 10·THF is relatively open and part of a three-dimensional porous network.…”

“…[8] This surprising observation allowed the selective synthesis of unprecedented heterocycles or cages. Particularly interesting were reactions with trifunctional acids such as citracinic acid or benzotriazol-5-carboxylic acid which gave compounds with four [9] or six Ga-Ga bonds [10] in single molecules. The first compound had a highly functional surface, which allowed the coordination of bases such as desazapurine by hydrogen bonding, the latter had a large central cavity and irreversibly encapsulated a THF molecule which showed unusual chemical shifts in the 1 H NMR spectrum (δ = -1.2 to -3.6) caused by the vicinity of its hydrogen atoms to aromatic rings of the spacer ligands.…”

Anorganische Chemie 2010

“…Außergewöhnlich ist hier die Templatwirkung der Ga‐Ga‐Bindung unter Bildung eines organometallischen Gerüsts. Dieses enthält in seinem Hohlraum ein fest eingekapseltes THF‐Molekül 1_14. Dieses Konzept der Ga‐Ga‐Bindung als Templat lässt sich erfolgreich auf weitere funktionalisierte Carboxylatoliganden übertragen 1_15.…”