Reactivity and Derivatization of Five-Coordinate, Chelated Aluminum

The convenient five-coordinate starting materials, Salen(^tBu)AlCl (Salen(^tBu) = N,N‘-alkylene (or arylene) bis (3,5-di-tert-butyl-2-hydroxybenzylideneamine) (1−4) can be used in a wide range of reactions to form five-coordinate aluminum compounds. Herein, these reagents were used to produce new five-coordinate azides, LAlN₃ (L = Salen(^tBu) (5), Salpen(^tBu) (6), and Salomphen(^tBu) (7)) through trimethylsilylhalide elimination. The decomposition of the azides produce first hydroxide (LAlOH (L = Salen(^tBu) (8)) and, subsequently in the presence of chlorotrimethylsilane, the siloxide compounds, LAlOSiMe₃ (L = Salen(^tBu) (9), Salpen(^tBu) (10), and Salomphen(^tBu) (11)). Alkane elimination reactions may also be used to access this type of compound as evidenced by the formation of Salomphen(^tBu)AlOSiPh₃ (12). Additionally, the first structurally characterized five-coordinate monomeric amide, Salcen(^tBu)AlN(SiMe₃)₂ (13), can prepared by a salt elimination utilizing Salcen(^tBu)AlCl (4). The compounds were characterized by spectroscopic methods (¹H and ²⁷Al NMR, MS, and IR) and, in the case of 2 (Salpen(^tBu)AlCl), 3 (Salomphen(^tBu)AlCl) 9, 11, 12, and 13, by X-ray analysis. Several of the compounds were explored as potential catalysts for the living polymerization of propylene oxide.