Modulating the Frontier Orbitals of an Aluminylene for Facile Dearomatization of Inert Arenes.

Lewis bases are well known to stabilize electron-deficient species. We demonstrate herein that the redox property of a monocoordinated aluminylene 1 featuring only four valence electrons for the shell of Al can be boosted by a Lewis base. The coordination of 1 with an N-heterocyclic carbene (NHC) effectively shrinks the HOMO-LUMO gap, thereby enhancing the reactivity of the ensuing acyclic mono-NHC-stabilized aluminylene 2, which is isoelectronic with singlet carbenes. Moreover, such base coordination completely reverses the predominant chemical reactivity (i.e. electrophilicity/nucleophilicity) of aluminylenes. In marked contrast to 1, 2 readily undergoes a [4+1] cycloaddition reaction with naphthalene and biphenylene at room temperature. Strikingly, the enhanced ambiphilic nature of Al in 2 also enables facile cleavage of aromatic C-C bonds of inert arenes in both intra- and intermolecular fashion affording 3 and 5. The formation of 5 represents the first example of the cleavage of an aromatic C(3)-C(4) bond in biphenylene by a single-atom center.