Unlike previously reported dianionic dialanes, this compound features an Al–Al bond that is part of a three-membered ring (pictured). Prepared in two steps from the corresponding dialane complex by reduction with potassium graphite followed by reaction with stoichiometric amounts of triethylphosphine oxide, it is stable at room temperature but sensitive to moisture and oxygen. Its solid-state structure reveals a highly distorted tetrahedral geometry for each aluminium centre and a shorter Al–Al bond (2.490(1) Å) than found in other dianionic dialanes. Moreover, computational studies indicate that the Al–Al σ-bond is highly strained.
Koshino and Kinjo show that this aluminium oxirane analogue reacts with a variety of organic molecules under mild conditions. The Al–Al σ-bond is cleaved and aluminium-containing heterocycles are obtained through addition, C–C coupling or arene ring C–C bond-activation reactions. For example, the reaction with tert-butyl isocyanide gives a four-membered dialuminyl imine heterocycle. Five-membered rings can be formed by the insertion of ethylene or benzophenone, resulting in aluminium analogues of furan and dioxolane derivatives, respectively. A seven-membered heterocycle is obtained from the reductive coupling of two benzonitrile molecules and cleavage of the Al−Al σ-bond. Finally, reaction with biphenylene affords a dialuminium-substituted benzo[8]annulene derivative, featuring a nine-membered ring; unusually the C–C cleavage occurs chemoselectively between two adjacent carbon atoms in one of the phenyl rings of biphenylene rather than the more commonly reported central C–C σ-bond cleavage.
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