Dearomatized 1,4-dihydropyridyl motifs are significant in both chemistry and biology for their potential abilities to deliver the stored hydride, driven by rearomatization. Biological cofactors like nicotinamide adenine dinucleotide (NADH) and organic 'hydride sources' like Hantzsch esters are prime examples. An organoaluminum chemistry on a 2-anilidomethylpyridine framework is reported, where such hydride storage and transfer abilities are displayed by the ligand's pyridyl unit. The pyridylmethylaniline proligand (NN LH) is simultaneously deprotonated and 1,4-hydroaluminated by AlH3 (NMe2 Et) to [(NN Lde )AlH(NMe2 Et)] (1; NN Lde =hydride-inserted dearomatized version of NN L). A hydride abstraction by B(C6 F5 )3 rearomatizes the pyridyl moiety to give the cationic aluminum hydride [(NN L)AlH(NMe2 Et)][HB(C6 F5 )3 ] (6). Notably, such chemical non-innocence is priorly unseen in this established ligand class. The hydroalumination mechanism is investigated by isolating the intermediate [(NN L)AlH2 ] (2) and by control experiments, and is also analyzed by DFT calculation. The results advocate an intriguing 'self-promoting' pathway, which underlines alane's Lewis acid/Brønsted base duality. NMe2 Et carrying the alane also plays a crucial role. In contrast, the chemistry between NN LH and AlMe3 is much different, giving only [(NN L)AlMe2 ] (4) from the adduct [(NN LH)AlMe3 ] (3) by deprotonation but not a subsequent pyridyl dearomatization in the presence or absence of NMe2 Et. This divergence is also justified by DFT analyses.
Keywords: 1,4-dihydropyridyl; acid-base duality; alane; hydride storage; hydroalumination.
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