The Chemoselective C–C σ-Bond Activation of the Arene Ring of Biphenylene

The chemoselective cleavage of an arene ring in biphenylene is reported using an aluminium(I) complex. The reaction proceeds with complete integrity of the central 4-membered ring despite this ring containing the weakest C–C σ-bond in the hydrocarbon scaffold. A reaction intermediate derived from the (4+1) cycloaddition of the aluminium(I) complex to the p-system of biphenylene was isolated. Further experiments and DFT calculations suggest that this intermediate is involved in breaking of the C–C σ-bond. Activation strain analysis was used to understand the origins of the remarkable chemoselectivity of this system. Both the symmetry and diffuseness of the frontier molecular orbitals of the aluminium(I) fragment are implicated in its unusual reactivity with biphenylene.