Amine-alane adduct

Dissociation Enthalpies De [kcal/mol] of Selected Borane- and Alane-Amine Adducts... 

In the proposed scheme depicted by reaction (9.5) Li3AlH6 will precipitate in solution to be filtered out and the alane vhll be recovered from the alane amine adduct by heating under vacuum. 

Two of the mechanisms for aluminum amide formation assume the formation of an alane-amine adduct and, from a structural point of view, such Lewis pairs have been extensively studied. For instance, the treatment of AIMe3 with Ph(tBuCH2)NH in hexane at room temperature yielded a monomeric adduct Ph(rBuCH2)NH(AlMe3)... 

Tertiary amine adducts of alane show a diverse range of stmctures based on four and five coordinate species, hydride-bridging dimeric and polymeric species, and ionic species. 

A further interesting category of aluminium compounds are the aluminium tetrahydroborates for which mixed species of the type A1(BH4) R3 (n = 1,2 R = alkyl) have been reported. (161) While in the parent compound A1(BH4)3 the Al resonance is found at 97 ppm (162) the mixed forms lead to resonances between this and those of the alanes. Like the parent compound the mixed species show a tendency towards adduct formation. The ether and amine adduct exhibits Al resonances in the region 100-150 ppm with excessively broad lines ( 2kHz). (161)... 

Adenosine triphosphate alkali metal complexes, 34 vanadyl complexes, 568 Alane, 123 amine adducts, 107 phosphine adducts, 111 Alane, alkoxy-, 124 Alane, amino-, 109 Alane, imino-, 109 Alkali metal complexes, 1-70 acid anions, 30 acid salts, 30 bipyridyl, 13 crown ethers cavity size, 38 cryptates... 

The reaction between a Lewis acid R3M and a Lewis base ER3, usually resulting in the formation of a Lewis acid-base adduct R3M—ER3, is of fundamental interest in main group chemistry. Numerous experiments, in particular reactions of alane and gallane MH3 with amines and phosphines ER3, have been performed [14]. Several general coordination modes, as summarized in Fig. 2, have been identified by X-ray diffraction. 

Steric interactions between bulky substituents such as t-Bu, leading to larger C-E-C bond angles, obviously affect the Lewis basicity caused by the increased -character of the electron lone pair. However, the strength of the Lewis acid-base interaction within an adduct as expressed by its dissociation enthalpy does not necessarily reflect the Lewis acidity and basicity of the pure fragments, because steric (repulsive) interactions between the substituents bound to both central elements may play a contradictory role. In particular, adducts containing small group 13/15 elements are very sensitive to such interactions as was shown for amine-borane and -alane adducts... 

H3A1 NMe3,53 whose structure has been determined by X-ray diffraction.54 Since these initial studies, comparable reactions were observed for alanes, gallanes and indanes R3M (M = Al, Ga, In R = H, halogen) with amines and phosphines, yielding bis-amine, bis-phosphine and mixed amine/ phosphine adducts. Figure 13 presents the different coordination modes that have been observed so far. 

In 1981 the first attempt for the asymmetric hydroalumination with a chiral alane reagent took place. The reaction of a chiral amine-trialkylaluminum complex, Al((-Bu)3-[(-)-DMMA] (172), with 1,1-dialkylethylenes (excess) catalyzed by Ni(Il)rMesal]2 (173) (2 mol%) without solvent, followed by exposure of the resulting adduct to the oxygen atmosphere gave the corresponding alcohols with low enantiopurity, for example, the reaction of 2-tm-butylpropene with 172 in the presence of 173 gave 144 with 27% ee (R) (Scheme 2.19) [98],... 

Gallane-tertiary amine or -tertiary phosphine adducts 106, L-GaH3 (L = Me3N, quinuclidine, ( -G6Hn)3P), reduce a carbonyl group and other unsaturated functional groups. The selectivities are different to those observed for similar alane... 

The most studied adducts are the trialkylamine alanes. Trimethylamine reacts to give both 1 1 and 2 1 adducts with AIH3, but the latter is stable only in the presence of an excess of amine. The monoamine has a tetrahedral structure (4) and is a white, volatile crystalline solid (mp 75 °C) that is readily hydrolyzed by water. Like the etherate, it slowly decomposes to (A1H3) . The bisamine has a trigonal bipyramidal stmcture with the amines in the axial positions (5). This was the first compound in which aluminum was demonstrated to adopt a five-coordinate stmcture. Tetrahydrofiuan also gives 1 1 and 1 2 complexes but diethyl ether only gives the 1 1 complex. 

Ruff et al. in a series of publications described the synthesis of amine complexes of aluminum hydride [32, 33]. Their study investigated the reaction of these materials with typical Lewis bases in order to define the conditions for the stability of aluminum hydride derivatives in which the aluminum atom exhibits a coordination number of five. They first described methods for making tertiary alkyl amine complexes of aluminum hydride utilizing lithium aluminum hydride and an amine hydrochloride. A finely ground lithium aluminum hydride was placed together with trimethylammonium chloride (ratio 1 2). They prepared other trialkylamine alanes and the N-dialkylaminoalanes, in a similar fashion. These adducts of alane were found to sublime readily at temperatures up to 40 °C except for the tri-n-propylamine alane, which sublimed very slowly and could also be recrystallized from hexane at — 80 °C. 

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