Drei- oder Vierfach-Koordination des Aluminiums in Alkylaluminiumphenoxiden und deren Unterscheidung durch 27Al-NMR-Spektroskopie

Abstract

The 27Al NMR spectra for a series of aryloxyaluminium compounds [R n Al(OAr) 3− n ] m (R  methyl, isobutyl; n  0–2; m  1, 2, 3) with various alkyl substituents in the 2 and 6 positions of the phenoxy rings have been measured. The δ( 27Al) resonances give an indication of the number of aryloxy ligands and the coordination number of each Al atom. Monomeric R 2AlOAr compounds have δ( 27Al) resonances around 190 ppm whereas dimeric analogues give signals at 167 ppm. The 27Al NMR resonances for monomeric RAl(OAr) 2 are found at ca. 100 ppm while those for [Al(OAr) 3] 2, where the aluminium atoms are solely bonded to aryloxy groups, lie at ca. 50 ppm. Characteristic shifts of the resonances were also observed for complexes of these compounds with THF, whereby it was found that the resulting change Δδ( 27Al) decreases with increasing number of aryloxy ligands. The crystal structures of three selected compounds, 3, 8 and 11, were determined by X-ray crystallography.