ALUMATRANE, AL(OCH2CH2)3N - A REINVESTIGATION OF ITS OLIGOMERIC BEHAVIOR

In various literature reports the behavior of the title compound 1 has been described as dimeric in the gas phase; monomeric, hexameric, and octameric in solution; and tetrameric (by X-ray crystallography) in the solid state. Herein we present mass spectral evidence for the presence of both 1(2) and 1(4) in the gas phase. Al-27 NMR evidence is put forth for the tetramer 1(4) as the only detectable oligomer in solution, wherein 1(4) contains one hexacoordinate and three pentacoordinate aluminums. H-1, H-1 DQF COSY experiments confirm the presence Of 1(4) in solution and VT C-13 NMR spectral studies reveal the occurrence of an interesting dynamic behavior of 1(4) in which the three pentacoordinate alumatranes rotate around their pseudo-3-fold axes while remaining fluxionally oxygen-bridged to the central cage containing the hexacoordinated aluminum. Solid-state Al-27 and C-13 NMR and Al-2p, N1a, and O1a XPS evidence has also been gathered that is consistent with the tetrameric structure of solid alumatrane.