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-)]center dot 4THF, as confirmed by single-crystal X-ray diffraction. The product consists of a dimeric sigma-bonded dianion (C-C, 1.568(7) angstrom) having two endo-eta(6) coordinated {Rb+(18-crown-6)} moieties (Rb-C, 3.272(4)-3.561(4) angstrom). The (C26H12-C26H12)(2-) dimer represents the first crystallographically confirmed example of spontaneous coupling for indenocorannulene monoanion radicals, C26H12 center dot-. Comprehensive theoretical investigation of the new dimer confirms the single s-bond character of the linker and reveals a significant increase of both thermodynamic and kinetic stability of [sigma-(C26H12)(2)](2-) in comparison with analogues formed by such pi-bowls as corannulene and its dibenzoderivative. 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 pi-radicals.