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New routes to synthetically useful, sterically encumbered arylaluminum halides and hydride halides

The synthesis and structural characterization of the compounds Mes*AlCl2(THF) (1), Mes*AlCl2 (2), Mes*Al(H)Cl(THF) (3a), Mes*Al(H)Cl (4a), and (Mes*AlH2): (5) (Mes* = 2,4,6-t-Bu3C6H2-) are described as well as those for two compounds 3b and 4b that are analogs of 3a and 4a but have H:Cl ratios that are less than 1:1. All compounds were characterized by 1H, 13C NMR, and IR spectroscopy, and 1, 2, 3a, and 4b were additionally characterized by X-ray crystallography. Compound 1 is best synthesized by the reaction of [(THF)2LiH3AlMes*]2 (6) with 6 equiv of Me3SiCl. A more conventional route involving the addition of (THF)2LiMes* to 2 equiv of AlCl3 in toluene usually affords a mixture of 1 and AlCl3·THF. Recrystallization of 1 from n-hexane results in a species that has less than 1 equiv of THF per Mes* AlCl2 The THF free complex 2 may be obtained in quantitative yield by heating 1 for 20 min at 90 °C under reduced pressure. Compound 3a may be obtained by treating a 1:1 mixture of Mes*Li(THF)2 and LiAlH4 with 2 equiv of Me30SiCl or by the addition of slightly less than 4 equiv of Me3SiCl to 6. The THF can be removed from 3a by sublimation to give 4a. The related compounds 3b and 4b, which display an aluminum-bound H:Cl ratio that is deficient in H, can be obtained by reactions with slightly more than 2 equiv of Me3SiCl. Crystal data at 130 K with Cu Kα (λ = 1.541 78 A?) radiation: 1, C22H37AlCl2O, a = 11.889(3) A?, b = 9.992(3) A? , c = 19.704(5) A?, orthorhombic, space group Pca21, Z = 4, R = 0.068 for 1556 (I > 2σ(I)) data; 2, C18H29AlCl2, a = 12.147(5) A?, b = 18.042(6) A?, c = 17.771(7) A?, β= 95.77(3)°, monoclinic, space group P21/n, Z = 8, R = 0.032 for 4610 (I > 2σa(I)} data; 3a, C22H38AlClO, a = 16.887(7) A?, b = 16.333(6) A?, c = 8.739(3) A?, β= 101.41(3)°, monoclinic, space group P21/c, Z = 4, R = 0.073 for 2752 (I > 2σ(I)) data; 4b, C18H29.64AlCl1.36, a = 12.077(3) A?, b = 17.920(3) A?, c = 17.634(5) A? ; β = 95.21(2) A?, monoclinic, space group P21/n, Z = 8, R = 0.070 for 4261 (I > 2σ(I)) data.