Reduction by alkoxyaluminium hydrides is thought in most cases to proceed by a polar mechanism. Hydride transfer to the organic substrate generates an organic anion, which is neutralized either by protic solvent or upon acidic workup.
Reductions of α,β-unsaturated carbonyl compounds may occur in a 1,2 sense (direct addition) or a 1,4 sense (conjugate addition). The tendency to add in a 1,4 sense is correlated with the softness of the hydride reagent according to Pearson's hard-soft acid-base theory. Experimental results agree with the theory—softer hydride reagents afford higher yields of the conjugate reduction product.
A few substrates, including diaryl ketones, diarylalkenes, and anthracene, are known to undergo reduction by single-electron transfer pathways with lithium aluminium hydride.
Metal alkoxylaluminium hydride reagents are well characterized in a limited number of cases. Precise characterization is complicated in some cases by disproportionation, which converts alkyoxyaluminium hydrides into alkoxyaluminates and metal aluminium hydride:<br>