Organoaluminium complexes with sterically demanding oximato ligands: does a bulky and rigid ligand backbone change the aggregation motif?

The four organoaluminium ketoximates [(2,4-dimethylpentane-3-one oximato)AlMe(2)](2) (1), (meso)-[(norcamphor oximato)AlMe(2)](2) (2), {[(R,R)-camphor oximato]AlMe(2)}(3) (3) and {[(R,S)-fenchone oximato]AlMe(2)}(2) (4) have been prepared by the reactions of the corresponding oximes with trimethylaluminium. All compounds have been fully characterized by means of IR, mass and multi-nuclear NMR spectroscopy ((1)H, (13)C, (27)Al) and by elemental analyses. The crystal structures of three of these compounds (2, 3 and 4) were determined, revealing the aggregation motif of organometallic group 13 oximates to vary from the hitherto predominant six-membered dimeric M(2)N(2)O(2) array to others (six-membered M(3)O(3) core ring in the case of the camphor derivative; five-membered M(2)NO(2) core ring in the case of the fenchone derivative) so far only found e.g. in hydroxylamino complexes of group 13 metals. Furthermore, complexes 3 and 4 exhibit an unusual behaviour in solution, as indicated by upfield-shifted additional signals in their (27)Al NMR spectra, pointing at aluminium atoms in penta- or hexacoordination, respectively.