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

Abstract

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(AlAr^iPr4-4-SiMe₃)₂ (3) (Ar^iPr4-4-SiMe₃ = 2,6-(2,6-ⁱPr₂C₆H₃)₂-4-SiMe₃C₆H₂) with either the diiodide Al(Et₂O)I₂Ar^iPr4-4-SiMe₃ (1) or the 1,2-diiododialane 4-SiMe₃Ar^iPr4(I)Al–Al(I)Ar^iPr4-4-SiMe₃ (2). This cleanly generates the dialuminene 4-SiMe₃Ar^iPr4AlAlAr^iPr4-4-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.