[(CH 3 )Al(CH 2 )] 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 [Ga 8 (CH 2 ) 12 ] and AlMe 3 . The existence of cage-like methylaluminomethylene moieties was initially suggested by the reaction of rare-earth-metallocene complex [Cp* 2 Lu{(μ-Me) 2 AlMe 2 }] with excess AlMe 3 affording the deca-aluminium cluster [Cp* 4 Lu 2 (μ 3 -CH 2 ) 12 Al 10 (CH 3 ) 8 ] in low yield (Cp*=C 5 Me 5 ). Treatment of [Ga 8 (CH 2 ) 12 ] with excess AlMe 3 reproducibly gave the crystalline dodeca-aluminium complex [(CH 3 ) 12 Al 12 (μ 3 -CH 2 ) 12 ] (MAM-12). Revisiting a previous approach to "poly(aluminium-methyl-methylene" by using a (C 5 H 5 ) 2 TiCl 2 /AlMe 3 (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.