Radikalionen von überbrückten [14] Annulenen. Untersuchungen zum Frontorbitaleinfluss auf Reaktivität und Bindungszustand

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Abstract
Radical Ions of Bridged [14] Annulenes. Investigations on the Influence of Frontier Orbitals on Reactivity and BondingThe radical anions and the radical cations derived from trans‐15, 16‐dimethyl‐1, 4:8,11‐ethandiyliden[14]annulene (6), trans‐15‐methyl‐1,4:8,11‐ethandiyliden[14]annulene (7) and cis‐15, 16‐propano‐1,4:8,11‐ethandiyliden[14]annulene (8) are described. The hyperfine data of the radical anions 6, 7 and 8 resemble those of the structurally related radical anions of trans‐10b, 10c‐dimethyldihydropyrene (4) and trans‐10b, 10c‐dihydropyrene (5). This finding leads to the conclusion, that the change in the relative arragement of the saturated bridge within the fourteen‐membered π‐perimeter by passing from 4 (5) to 6 (7, 8) does not in fluence the energetic sequence of the lowest unoccupied molecular orbitals. The behavior of 6 and 7 towards oxidation parallels the photochemical reactivity of 4. The hyperfine coupling constants of the radical cations derived from 6 and 7 indicate that the removal of an electron is accompanied by an isomerization of the molecular framework. The investigation of the electron transfer process gby cyclic voltammetry supports these findings. The radical cations prefer the cyclophane‐like structures 6a and 7a, in which the central σ‐bond (C(15)–C(16) bond) is broken.

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