Trimethylaluminium: Bindungsverhältnisse nach Ladungs- und Stromtopologie

[(CH3 )Al(CH2 )]12 : Methylaluminomethylene (MAM-12)

The molecular structure of enigmatic "poly(aluminium-methyl-methylene)" (first reported in 1968) has been unraveled in a transmetalation reaction with gallium methylene [Ga8 (CH2 )12 ] and AlMe3 . The existence of cage-like methylaluminomethylene moieties was initially suggested by the reaction of rare-earth-metallocene complex [Cp*2 Lu{(μ-Me)2 AlMe2 }] with excess AlMe3 affording the deca-aluminium cluster [Cp*4 Lu2 (μ3 -CH2 )12 Al10 (CH3 )8 ] in low yield (Cp*=C5 Me5 ). Treatment of [Ga8 (CH2 )12 ] with excess AlMe3 reproducibly gave the crystalline dodeca-aluminium complex [(CH3 )12 Al12 (μ3 -CH2 )12 ] (MAM-12). Revisiting a previous approach to "poly(aluminium-methyl-methylene" by using a (C5 H5 )2 TiCl2 /AlMe3 (1 : 100) mixture led to amorphous solids displaying solubility behavior and spectroscopic features similar to those of crystalline MAM-12. The gallium methylene-derived MAM-12 was used as an efficient methylene transfer reagent for ketones.