The preparation of low-coordinate cationic organoaluminum compounds as reactive alternatives to transitionmetal catalysts for the polymerization of olefins or cyclic ethers has been reported by several groups in recent years. [1][2][3][4] Stable weakly coordinating anions such as [B(C 6 F 5 ) 4 ]were essential for the synthesis of these compounds. The stabilization of the more reactive alkylsubstituted cationic species required the employment of the more robust carborane ligands, as has been shown by Reed and co-workers for [Et 2 Al] + [CB 11 H 6 X 6 ] -(X ) Cl, Br). 5 The Lewis acidity of the cationic aluminum center is sufficiently high, even in these compounds, that there were relatively close Al‚‚‚X contacts leading to an essentially four-coordinate aluminum center and C-Al-C angles of 136.6 and 130.0°. These close contacts significantly decreased the reactivity of these species. As an alternative strategy to prepare and stabilize twocoordinate cationic aluminum compounds and at the same time minimize cation‚‚‚anion contacts, we have

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)

The title compound [2,6-Mes(2)C(2)H(3)](2)Ga(+)Li[Al(OCH(CF(3))(2))(4)](2)(-), 1, containing a linear two-coordinate gallium cation, has been obtained by metathesis reaction of [2,6-Mes(2)C(2)H(3)](2)GaCl with 2 equiv of Li[Al(OCH(CF(3))(2))(4)] in C(6)H(5)Cl solution at room temperature. Compound 1 has been characterized by (1)H, (13)C((1)H), (19)F, and (27)Al NMR spectroscopy and X-ray crystallography. Compound 1 consists of isolated [2,6-Mes(2)C(6)H(3)](2)Ga(+) cations and Li[Al(OCH(CF(3))(2))(4)](2)(-) anions. The C-Ga-C angle is 175.69(7) degrees, and the Ga-C distances are 1.9130(14) and 1.9145(16) A. The title compound is remarkably stable, is only a weak Lewis acid, and polymerizes cyclohexene oxide.

Unsymmetrical 9-chloro-9-phosphafluorenes (dibenzophospholes) and 9-chloro-9-arsafluorenes (dibenzoarsoles) have been obtained by simple thermolysis of m-terphenyldichlorophosphines and -arsines in close to quantitative yields. The reaction temperatures are about 200 degrees C for the phosphines and 140 degrees C for the arsine, and the reactions are complete within 5 min. Alternatively, these compounds can be synthesized through an AlCl3-catalyzed Friedel-Crafts type ring-closure reaction at low temperatures, but this method suffers from difficult workup procedures. The P(As)-Cl functionality is readily alkylated. Methylation of m-xylyl derivative 4 afforded 1-(3,5-dimethylphenyl)-6,8,9-trimethyl-9-phosphafluorene, 11. The latter compound formed the complexes 11 x Fe(CO)4, 12, and 11 x RuCl2(eta(6)-p-cymene), 13, indicating its good donor properties. The new compounds have been characterized by 1H, 13C{1H}, and 31P{1H} NMR spectroscopy; mass spectrometry; and single-crystal X-ray crystallography in the case of 11, 12, and 13.