title: Molecular saddles. 7. New 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene cyclophanes: synthesis, redox properties, and x-ray crystal structures of neutral species and a dication salt.
abstract: We report the synthesis of cyclophanes 18-20 by ester-forming macrocyclization reactions of diols 15 and 16 with 1,4-benzenedicarbonyl chloride. Compounds 18 and 19 display a two-electron, quasireversible oxidation wave in the cyclic voltammogram to yield the dication species at E(ox)(pa) 0.52 and 0.47 V, respectively (vs Ag/AgCl in acetonitrile), whereas the 2 + 2 product 20 undergoes a single four-electron oxidation process at E(o)(x)(pa) 0.51 V. X-ray crystal structures are reported for compounds 18-20 and the dication salt 18(2+)(I(3)(-))(2).(I(2))(0.5). For comparative purposes, the structures are also reported for the precursor diol 15 and its dication salt 15(2+)(ClO(4)(-))(2), which was obtained by electrocrystallization. In the neutral cyclophanes 18-20, the 9,10-bis(1,3-dithiol-2-ylidene)-9, 10-dihydroanthracene moieties adopt a saddle-shaped conformation. The overall measure of folding, the dihedral angle (theta) between the S(1)C(16)C(17)S(2) and S(5)C(21)C(22)S(6) planes, is similar in 15 and 18 (87.6 degrees and 83.7 degrees, respectively) whereas this angle is significantly narrower in 19 (61.1 degrees ), illustrating the flexibility of the saddle conformation and its dependence on the packing. Dimeric molecule 20 contains two saddle moieties with very similar conformations, theta = 73.4 degrees and 73.1 degrees. The structures of dication salts 15(2+)(ClO(4)(-))(2) and 18(2+)(I(3)(-))(2).(I(2))(0.5) reveal that a dramatic conformational change accompanies oxidation of the donor with the dithiolium rings planar and nearly perpendicular to the mean plane of the anthracene moieties. A notable feature of 18(2+) is that the bridge enforces a fold of 22 degrees along the C(9).C(10) vector of the anthracene unit. In 15(2+) there is no fold about this axis, instead the anthracene moiety is slightly twisted with the two (planar) outer rings forming an angle of 7 degrees.
authors.affiliation: Department of Chemistry, University of Durham, Durham DH1 3LE, UK.
authors.forename: C A
authors.initials: CA
authors.lastname: Christensen
authors.forename: A S
authors.initials: AS
authors.lastname: Batsanov
authors.forename: M R
authors.initials: MR
authors.lastname: Bryce
authors.forename: J A
authors.initials: JA
authors.lastname: Howard