According to an X-ray structure analysis, the annulenone 4 is not planar in the crystal; the 'H-NMR spectra of 4 reveal an averaged planarity with respect to the NMR timescale. The McMurry reaction of4 yields fulvalene 3 in 43 YO yield as the most expanded fulvalene hithertoo known. The X-ray structure analyses of 3 surprising establishes a 'syn'-orientation of the two rings with respect to the central C=C bond, thus forming a basket-like molecule. The 'H-NMR spectrum confirms the averaged planarity of both macrocycles in 3. CV and spectroelectrochemical measurements of 3 suggest a reversible two-electron reduction producing dianion 15 with two aromatic, anionic 5a,l5a-didehydro-1OH-21,22,23,24-tetraoxa-5a,l5a-dihomocorrole (= tetraoxa[22]porphyrin(2.1.2.0)) ring systems containing 2271 electrons each. The formation of 15 can also be achieved chemically by reaction of 3 with metallic potassium. The dication 16 of 3 may be antiaromatic, but the exact electronic structure is dubious. ESR and ENDOR investigations on the radical cation and the radical anion of 3 indicate that the free electron is delocalized in the entire molecule.
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