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m-Terphenylaluminum and -gallium Compounds: Synthesis and Conversion into Low-Coordinate Organogallium Cations



The reaction of two or 3 equiv. of m-terphenyllithium with MCl3 or AlH3·NMe3 (M = Al, Ga) affords the bis(terphenyl)aluminum and -gallium chloride compounds [{2,6-(4-tBuC6H4)2C6H3}2GaCl] (1), [{2,6-(3,5-Me2C6H3)2C6H3}2GaCl] (2), [{2,6-(4-tBuC6H4)2C6H3}3Ga] (3), [(2,6-Mes2C6H3)2AlCl] (5), and [(2,6-Mes2C6H3)2AlH] (7; Mes = 2,4,6-Me3C6H2). While the gallium compounds can be obtained at room temperature, heating is required for the aluminum derivatives. The dibutyl compounds [(2,6-Mes2C6H3)GaBu2] (8) and[(2,6-Dipp2C6H3)GaBu2] (9; Dipp = 2,6-iPr2C6H3) have also been synthesized by the reaction of m-terphenyllithium with ClGaBu2. A metathesis reaction of 2 with Li[Al{OCH(CF3)2}4] gives the ionic species [(2,6-Mes2C6H3)2Ga]+[Li{Al[OCH(CF3)2]4}2] (11). The cationic butyl(terphenyl)gallium compounds [(2,6-Mes2C6H3)GaBu]+ ([13]+) and [(2,6-Dipp2C6H3)GaBu]+ ([14]+) have been prepared by butanide abstraction with the trityl salts of the weakly coordinating anions [B(C6F5)4], [CHB11Br6Me5], and [CHB11Cl11]. These ionic species are stable at room temperature for days or weeks, although their combinations with the borate anion [B(C6F5)4] suffer from C6F5 migration, which is slow at room temperature and faster at elevated temperatures. The compound [14]+[CHB11Cl11] is stable at 70 °C for at least 23 h. Addition of 1-octene to a solution of [14]+[CHB11Cl11] in C6D6 results in olefin exchange and formation of the octyl species [(2,6-Dipp2C6H3)Ga(octyl)]+ ([17]+), and a slow alkylation of the solvent to afford various octylbenzenes. Hydrolysis of 8 and [13]+[CHB11Br6Me5] gives the compounds [{(2,6-Mes2C6H3)GaBu(μ-OH)}2] (10) and [(BuGa)4(μ-OH)6]2+[CHB11Br6Me5]2 (16). All compounds have been characterized by 1H and 13C{1H} NMR spectroscopy and mass spectrometry, and compounds 3, 5, 7, 10, and 16·4.5C6H6 have also been characterized by single-crystal X-ray crystallography. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

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