Comproportionation of a dialuminyne with alane or dialane dihalides as a clean route to dialuminenes.

Dialuminenes RAlAlR (R = m-terphenyl or bulky aryl) react with the aromatic solvents (e.g. benzene or toluene) in which they dissolve. We synthesized -SiMe3 substituted derivatives of known terphenyl ligands to increase their solubility in alkanes which have lower reactivity than arenes. The new dialuminene was synthesized via the comproportionation reaction of Na2(AlAriPr4-4-SiMe3)2 (3) (AriPr4-4-SiMe3 = 2,6-(2,6-iPr2C6H3)2-4-SiMe3C6H2) with either the diiodide Al(Et2O)I2AriPr4-4-SiMe3 (1) or the 1,2-diiododialane 4-SiMe3AriPr4(I)Al-Al(I)AriPr4-4-SiMe3 (2). This cleanly generates the dialuminene 4-SiMe3AriPr4AlAlAriPr4-4-SiMe3 which was trapped as its cycloaddition product (4) with benzene. Even in non-aromatic, essentially inert, solvents red 4 decomposes to colorless solutions. This indicates that the instability of the free dialuminene is an inherent property rather than arising from of the method of synthesis, solvent employed, or the presence of impurities.