Dimerization of indenocorannulene radicals: imposing stability through increasing strain and curvature

One-electron reduction of bowl-shaped indenocorannulene, C26H12, with Rb metal in THF affords [{Rb+(18-crown-6)}2(C26H12–C26H12)2−]·4THF, as confirmed by single-crystal X-ray diffraction. The product consists of a dimeric σ-bonded dianion (C–C, 1.568(7) A) having two endo-η6 coordinated {Rb+(18-crown-6)} moieties (Rb–C, 3.272(4)–3.561(4) A). The (C26H12–C26H12)2− dimer represents the first crystallographically confirmed example of spontaneous coupling for indenocorannulene monoanion radicals, C26H12˙−. Comprehensive theoretical investigation of the new dimer confirms the single σ-bond character of the linker and reveals a significant increase of both thermodynamic and kinetic stability of [σ-(C26H12)2]2− in comparison with analogues formed by such π-bowls as corannulene and its dibenzo-derivative. The in-depth computational analysis and direct comparison of the series demonstrates the effect of curvature on radical coupling processes, allowing control over stability and reactivity of bowl-shaped π-radicals.