- Facile high-yield synthesis of pure, crystalline Mg(BH4) 2
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Magnesium borohydride, Mg(BH4)2, a long-sought candidate for efficient hydrogen storage chemisorption technology, has been obtained in a pure and crystalline form by two new synthetic routes in a hydrocarbon solvent. A first synthetic approach involves a metathetical reaction between organometallic magnesium compounds; a second route consists of an insertion reaction of BH3 species, released from BH 3·S(CH3)2, into the Mg-C bonds of MgR2, with complete replacement of R groups with BH4 groups. Both methods, based on commercially available reagents, afford identical, pure, polycrystalline materials, identified by X-ray diffraction as the so-called low-temperature hexagonal form of Mg(BH4)2, stable below 180°C, recently shown to possess a complex, unpredictable, crystal structure.
- Zanella, Pierino,Crociani, Laura,Masciocchi, Norberto,Giunchi, Giovanni
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- Discrete Organofluoroaluminate Anions: Synthetic, Structural, and Spectroscopic Aspects
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The reaction of alkylaluminum compounds (AlR3, R = Me, n-Bu) with the series of imidazolium-based fluorinating reagents [IPrH][F], [IPrH][(HF)F] and [IPrH][(HF)2F] led to the isolation of salts containing discrete triorganofluoroaluminate ([R3AlF]-), diorganodifluoroaluminate ([R2AlF2]-), and organotrifluoroaluminate ([RAlF3]-) anions, respectively. The formation of [R2AlF2]- and [RAlF3]- anions was accompanied by the release of RH. The syntheses are effective, selective, and straightforward. The related reactions of an arylaluminum compound (AlPh3) resulted in a mixture of different phenylfluoroaluminate anions. All of the obtained products were characterized by NMR and Raman spectroscopy. Structural features of [IPrH][Me2AlF2] (2), [IPrH][MeAlF3] (3), [IPr][AlF4] (4), [IPrH][n-Bu3AlF] (5), [IPrH][n-Bu2AlF2] (6), [IPrH][n-BuAlF3] (7), [IPrH][Ph3AlF] (8), and [IPrH][PhAlF3] (10) were determined by single-crystal X-ray diffraction and compared with DFT calculations of structurally optimized salts.
- Gruden, Evelin,Tav?ar, Ga?per,Tram?ek, Melita
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- General copper-catalyzed coupling of alkyl-, aryl-, and alkynylaluminum reagents with organohalides
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We report the first example of a very general Cu-catalyzed cross-coupling of organoaluminum reagents with organohalides. The reactions proceed for the couplings of alkyl-, aryl-, and alkynylaluminum reagents with aryl and heteroaryl halides and vinyl bromides, affording the cross-coupled products in good to excellent yields. Both primary and secondary alkylaluminum reagents can be utilized as organometallic coupling partners. These reactions are not complicated by β-hydride elimination, and as a result rearranged products are not observed with secondary alkylaluminum reagents even for couplings with heteroaryl halides under "ligand-free" conditions. Radical clock experiment with a radical probe and relative reactivity study of Ph3Al with two haloarenes, 1-bromonaphthalene and 4-chlorobenzonitrile, having two different redox potentials indicates that the reaction does not involve free aryl radicals and radical anions as intermediates. These results combined with the result of the Hammett plot obtained by reacting Ph3Al with iodoarenes containing p-H, p-Me, p-F, and p-CF3 substituents, which shows a linear curve (R2 = 0.99) with a ρ value of +1.06, suggest that the current transformation follows an oxidative addition-reductive elimination pathway.
- Shrestha, Bijay,Thapa, Surendra,Gurung, Santosh K.,Pike, Ryan A. S.,Giri, Ramesh
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p. 787 - 802
(2016/02/18)
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