Aluminium isopropoxide tetrameric

The structure of the tetrameric molecule of aluminium isopropoxide containing the metal atoms with 2 types of coordination — octahedral and tetrahedral — has been predicted by Bradley and then confirmed by the NMR data The X-ray single crystal study has shown that the central and the three peripheric aluminium atoms are situated in the same plane perpendicular to the main trigonal axis, which goes through the central atom. The 3 [A1202] 4-member cycles are situated in the mutually perpendicular planes [1642, 574] (Fig. 4.8 b). 

H, 13C, and 27Al FT n.m.r. spectra of tetrameric aluminium isopropoxide are consistent with the structure (69 R = CHMe2).402... 

Similar to the alcoholysis reaction of tetrameric aluminium isopropoxide with tert-butyl alcohol, the alcoholysis reaction of dimeric aluminium tris(dimethyl amide) with rert-butyl alcohol is also slow owing to steric factors. However, the amide route affords finally the tris product [Al(OBu )3], (Eq. 2.108) instead of the mixed product of the type Al2(OBu )5(OPr ) which was finally obtained in the reaction of [Al(OIV)3]4 with an excess of Bu OH. 

The Al NMR spectrum of the tetrameric aluminium isopropoxide investigated by Kleinschmidt showed a broad and a sharper peak in the ratio 3 1, in agreement with the proposed structure (2-IX). 

Akitt and Duncan have provided further Al NMR evidence for the structure of the tetramer in solution. The spectrum consisted of a very broad peak due to tetrahedral aluminium and a sharper peak due to the central octahedral aluminium in the required 3 1 ratio of intensities. Owing to the quadrupole moment of the Al nucleus, the line width of the NMR signal depends on the symmetry of the electric field and gives independent evidence of the coordination of the aluminium. Furthermore, the structures of a number of other aluminium alkoxides were elucidated in 1984 by Al NMR spectroscopy, which supported the earlier proposed structures of a dimer (2-VII) and linear trimer (2-XI). It may be mentioned that a tetrameric structure for aluminium isopropoxide [Al(OPr )3]4 ° and a dimeric structure for aluminium f-butoxide [Al(OBu )3]2 have been confirmed by X-ray crystallography. 

The chemistry of heterometallic alkoxides involving a common chelating ligand, Al(OPr )4 finds a close parallelism in an early suggestion by Bradley that tetrameric aluminium isopropoxide Al(OPr )3 4 may be represented by Al (/r-OPr )2Al(OPr )2 3 in which the central aluminium is hexacoordinated by being ligated with three bidentate Al(OPr )4 figands. This unusual structure of... 

The spectrum of scandium alumoisopropoxide displays 3 doublets with the relative intensity 1 1 3. The identity of this spectrum with the spectrum of tetrameric aluminium isopropoxide confirms the shown above structure of similar associates. The structure with the central 6-coordinated REM atom is supposed for zirconoalkoxides as well [54]. The Li and Na derivatives obviously have an analogous structure, however, the coordinating number of the REM atom in these complexes decreases to 4. 

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