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

We report the synthesis of cyclophanes 18-20 by ester-forming macrocyclizat ion reactions of diols 15 and 16 with 1,4-benzenedicarbonyl chloride. Compo unds 18 and 19 display a two-electron, quasireversible oxidation wave in th e cyclic voltammogram to yield the dication species at E-pa(ox) 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-pa(ox) 0.51 V. X -ray crystal structures are reported for compounds 18-20 and the dication s alt 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+)(C lO4-)(2), which was obtained by electrocrystallization. In the neutral cycl ophanes 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, res pectively) whereas this angle is significantly narrower in 16 (61.1 degrees ), illustrating the flexibility of the saddle conformation and its dependen ce on the packing. Dimeric molecule 20 contains two saddle moieties with ve ry similar conformations, theta = 73.4 degrees and 73.1 degrees; The struct ures of dication salts 15(2+)(ClO4-)(2) and 18(2+)(I-3(-))(2). (I-2)(0.5) r eveal that a dramatic conformational change accompanies oxidation of the do nor with the dithiolium rings:planar and nearly perpendicular to the mean p lane of the anthracene moieties. A notable feature of 182+ is that the brid ge enforces a fold of 22 degrees along the C(9)...C(10) vector of the anthr acene unit. In 15(2+) there is no fold about this axis, instead the anthrac ene moiety is slightly twisted with the two (planar) outer rings forming an angle of 7 degrees.