Incorporating Trimethylaluminium into the Structures of Alkali Metal (Li, Na, K, Cs) dihydropyridines

Co-complexation of equimolar amounts of 1-alkali-metal-2tertbutyldihydropyridines with AlMe3 in the presence of a polydentate N-donor ligand has delivered four crystallographically verified alkali-metal aluminates [donor center dot AM(mu tBuDHP)AlMe3](n) (1, AM= Li, donor= TMEDA, n= 1; 2, AM= Na, donor= PMDETA, n= 1; 3, AM= K, donor= PMDETA, n= 2; 4, AM= Cs, donor= PMDETA, n=infinity; TMEDA= N,N,N',N'-tetramethylethylenediamine; PMDETA= N,N,N',N'',N''-pentamethyldiethylenetriamine). While the monomeric complexes (1, 2) and the polymeric complex (4) are thermally stable, the dimeric complex (3) undergoes a disproportionation process yielding the known ion-separated homoanionic complex [K center dot(PMDETA)(2)](+) [AlMe4](-) (3a). Utilizing TMEDA as the N-donor resulted in the same disproportionation, but gave rise to two distinct solid-state aggregated forms of aluminate [K center dot(TMEDA)(2)](+) [AlMe4](-), namely monomeric (3b) and polymeric (3b') polymorphs, in which the anionic moiety acts as a bidentate chelator or monodentate bridge respectively to the potassium cationic moieties.