ARTICLE DOI: 10.1002/zaac.201100252 Reactions of the Tetraalkyldigallium Compound R 2 Ga–GaR 2 [R = CH(SiMe 3 ) 2 ] with Acidic Reagents, Retention vs. Cleavage of the Ga–Ga Bond and Formation of Supramolecular Aggregates via Hydrogen Bonding Werner Uhl,* [a] Matthias Voß, [a] and Alexander Hepp [a] In Memory of Professor Kurt Dehnicke Keywords: Gallium; Hydrazides; Phosphinic acid; Subvalent compounds; Hydrogen bonding Abstract. Treatment of the tetraalkyldigallium compound R 2 Ga–GaR 2 [1, R = CH(SiMe 3 ) 2 ] with two equivalents of carboxylic acid hydra- zides (4-trifluormethylbenzhydrazide, 2-fuoric acid hydrazide and 2- chlor-6-hydrazineisonicotinic acid hydrazide) afforded new digallium species by the release of CH 2 (SiMe 3 ) 2 . The intact Ga–Ga bonds of the products (2 to 4) are terminally coordinated by two chelating hydrazide ligands via NH 2 groups and the carbonyl oxygen atoms. Interesting supramolecular aggregates are formed in the solid state, which contain dimeric formula units of the digallium species connected via a complex Introduction The tetraalkyldigallium compound R 2 Ga–GaR 2 [1, R = CH(SiMe 3 ) 2 ] is accessible on a facile route by the treatment of the digallium subhalide Ga 2 Br 4 ·2dioxane with four equiva- lents of bis(trimethylsilyl)methyllithium. [1] It shows a fascinat- ing and unique chemical reactivity which afforded a broad variety of different secondary products by electron transfer, insertion, adduct formation, deprotonation or metathesis. [2] One of the most exciting secondary reactions comprises the treatment of 1 with carboxylic acids [3–5] or other acidic sub- strates [6] having chelating residues. Unexpectedly the Ga–Ga bonds are retained in most cases, and two alkyl groups of 1 are replaced by two chelating ligands in very selective trans- formations. Different reaction courses were observed for the corresponding dialuminium or diindium derivatives, [7] which gave oxidation of the metal atoms and the quantitative cleav- age of the metal–metal bonds under similar conditions. [8] The dicarboxylatedigallium compounds have the chelating ligands in bridging positions across the Ga–Ga bonds and in an almost ideal perpendicular arrangement. With this unusual configura- tion these compounds are perfectly preorganized to form macrocycles or cages upon treatment of 1 with bifunctional dicarboxylic acids. Indeed we isolated large squaric molecules * Prof. Dr. W. Uhl Fax: +49-251-8336660 E-Mail: uhlw@uni-muenster.de [a] Institut für Anorganische und Analytische Chemie Universität Münster Corrensstraße 30 48149 Münster, Germany Z. Anorg. Allg. Chem. 2011, 637, 1845–1852 © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1845 system of hydrogen bonds. Two ether molecules are additionally coor- dinated to terminal N–H functions. Phenylphosphinic acid and 1 gave the analogous substituent replacement reaction with the formation of a dimeric tetragallium compound (5). Its two Ga–Ga bonds are in a perpendicular arrangement with four phosphinate ligands in the bridg- ing positions. Oxidation of the gallium atoms and insertion of an N=N double bond into the Ga–Ga bond was observed upon treatment of 1 with azodicarbonamide. with an inner diameter of up to 1.9 nm in which four Ga– Ga bonds are bridged by four spacer ligands. [9] However, the distortion of the angles at the gallium atoms (O–Ga–O ≈ 90°, C–Ga–Ga ≈ 155°) and relatively short Ga–Ga distances verify a considerable strain in the resulting molecules. Donor func- tionalized acids gave large cages with up to six Ga–Ga bonds, which encapsulated solvent molecules very effectively [10] or formed supramolecular aggregates by hydrogen bonding. [11] Further acidic components may be suitable to replace alkyl groups of 1 and may help to increase the variability of access- ible structural motifs and functionalities of the digallium com- pounds. Reactions with acid hydrazides, phenylphosphinic acid and a diaza compound are reported here. Results and Discussion Reactions of the Digallium Compound 1 with Carboxyhydrazides Following a standard procedure the digallium compound 1 and two equivalents of acid hydrazides (4-trifluormethylbenz- hydrazide, 2-fuoric acid hydrazide and 2-chlor-6-hydrazineiso- nicotinic acid hydrazide) were dissolved in THF and stirred for different reaction times between 12 h and 3 d at room temperature [Equation (1)]. H 2 C(SiMe 3 ) 2 was identified as a by-product by its characteristic singlet signals in the 1 H NMR spectra. The reaction mixtures were concentrated and cooled to yield the colorless, solid products in yields of 62 (2), 83 (3) and 65% (4). Single crystals were obtained from diethyl ether