The Dialuminene Ar^iPr8AlAlAr^iPr8 (Ar^iPr8=C₆H‐2,6‐(C₆H₂‐2,4,6‐ⁱPr₃)₂‐3,5‐ⁱPr₂)

Abstract Careful analysis of the crystals formed in the reduction of Ar iPr8 AlI 2 (Ar iPr8 =C 6 H‐2,6‐(C 6 H 2 ‐2,4,6‐ i Pr 3 ) 2 ‐3,5‐ i Pr 2 ) with sodium on sodium chloride showed them to contain the long sought‐after dialuminene Ar iPr8 AlAlAr iPr8 ( 1 ) that forms alongside the previously characterized alanediyl :AlAr iPr8 . The single crystal X‐ray structure of 1 revealed a nearly planar, trans ‐bent C(ipso)AlAlC(ipso) core with an Al−Al distance of 2.648(2) Å. The molecular and electronic structure of 1 are consistent with an Al−Al double dative interaction augmented with diradical character and stabilized by dispersion interactions. Density functional theory calculations showed that the reactivity of :AlAr iPr8 with dihydrogen involves 1 , not :AlAr iPr8 , as the reactive species. In contrast, the reaction of :AlAr iPr8 with ethylene gave two products, the 1,4‐dialuminacyclohexane Ar iPr8 Al(C 2 H 4 ) 2 AlAr iPr8 ( 2 ) and the aluminacyclopentane Ar iPr8 Al(C 4 H 8 ) ( 3 ), that can both form from the aluminacyclopropane intermediate Ar iPr8 Al(C 2 H 4 ). Although the [2+2+2] cycloaddition of 1 with two equivalents of ethylene was also calculated to be exergonic, it is likely to be kinetically blocked by the numerous isopropyl substituents surrounding the Al−Al bond. Attempts to fine‐tune the steric bulk of the terphenyl ligand to allow stronger Al−Al bonding were unsuccessful, leading to the isolation of the sodium salt of a cyclotrialuminene, Na 2 [AlAr iPr6 ] 3 ( 4 ), instead of Ar iPr6 AlAlAr iPr6 .