Chemoselective C-C σ-Bond Activation of the Most Stable Ring in Biphenylene**

The chemoselective cleavage of a six-membered aromatic ring in biphenylene is reported using an aluminum(I) complex. This type of selectivity is unprecedented. In every example of transition metal mediated C-C sigma-bond activation reported to date, the reaction occurs at the central four-membered ring of biphenylene. Insight into the origin of chemoselectivity was obtained through a detailed mechanistic analysis (isolation of an intermediate, DFT studies, activation strain analysis). In conclusion, the divergent reactivity can be attributed to differences in both the symmetry and radial extension of the frontier molecular orbitals of the aluminum(I) fragment compared to that of common transition metal fragments.

Automated summary

This study reports the chemoselective cleavage of a six-membered aromatic ring in biphenylene using an aluminum(I) complex, which is unprecedented. Insight into the origin of the chemoselectivity was obtained through a detailed mechanistic analysis, revealing that differences in the symmetry and radial extension of the frontier molecular orbitals of the aluminum(I) fragment compared to common transition metal fragments contribute to the divergent reactivity observed.