Functionalised oligoenes with unusual topologies: Synthesis, electrochemistry and structural studies on redox-active [3]- and [4]-dendralenes

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Bryce, M.R. and Coffin, M.A. and Skabara, P.J. and Moore, A.J. and Batsanov, A.S. and Howard, J.A.K. (2000) Functionalised oligoenes with unusual topologies: Synthesis, electrochemistry and structural studies on redox-active [3]- and [4]-dendralenes. Chemistry - A European Journal, 6 (11). pp. 1955-1962. ISSN 1521-3765 (http://dx.doi.org/10.1002/1521-3765(20000602)6:11<...)

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Abstract

New [3]- and [4]-dendralenes bearing electron-donor 1,3-dithiole and ferrocene substituents have been synthesised. Compounds 8, 15 and 17 have been characterised by single-crystal X-ray diffraction. Two of the dithiole rings of 8 are conjugated (dihedral angle 9 degrees), while the third dithiole ring is almost orthogonal to this plane, and hence its pi-electron system is isolated. For the dendralene precursor molecule 15, the substituted cyclopentadienyl ring, two C=C bonds and fused dithiole and dithiine rings comprise an extended pi-conjugated system. In molecule 17 the potential conjugation path C(6)C(3) C(4)C(5)-C5H5 is distorted by an 8 degrees twist around the C(3)-C(4) bond and a 7 degrees twist around the C(5)-C(21) bond, and the delocalisation along the chain is insignificant. Solution electrochemical data demonstrate that the dendralenes are strong pi-electron donors, which give rise to dication, radical trication or tetracation species. Spectroelectrochemical studies on compounds 7 and 10 suggest that the radical species are situated within the linear 1,2-ethylenediylidene moieties and that a conformational change may occur at the dication redox stage. UV/Vis spectroscopic data are consistent with poor cross-conjugation in these systems.

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