LiAlH disproportionation with

The disproportionation of tertiary and primary alkoxy species 4 has been reported. The NMR spectrum of an equivalent molar mixture of LiAlH3(OBu ) and LiAlH(OBu )3 was the same as that of LiAlH2(OBu )2, suggesting disproportionation of the nonsymmetrical compounds (37). Kinetics of the reduction of several aromatic ketones in ether with reagents formed by the reaction of LAH with Bu OH were consistent with partial disproportionation of species 4 (38) ... 

LiAlH(OBu )3 does not undergo disproportionation to the tetraalkoxy species. Reduction of the aromatic ketones studied involved either monomeric LAH or both this species and the monoalkoxy species, depending on the steric hindrance of the substrate. In a similar study of the reduction of camphor in THF (39), the kinetic results were also consistent with disproportionation of r-butoxy species (eqs. [6] and [7]), active reducing species being LAH and LiAl(OBu )H3. In the reduction of camphor with a series of reagents prepared by the reaction of LAH... 

The slow disproportionation of LiAlH(OMe)3 in THF was also observed by Ashby and co-workers (40). It should be noted that Brown and Shoaf had earlier (34) found that the reaction of LAH with EtOH did not lead to simple, unique reaction products. 

Although these reactions proceed rapidly, LiZnjMe,H reacts with LiAlH, slowly, requiring five days. The reaction involves a slow exchange of a methyl group from LiZnjMe,H to yield the intermediate LiZn MejHj which then disproportionates ... 

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