Thiolated π-Extended Tetrathiafulvalenes: Versatile Multifunctional π-Systems

Derivatives of 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene (ex-TTF) have been synthesized
by a new synthetic methodology, viz., direct phosphite-mediated cross-couplings of anthraquinone with
1,3-dithiole-2-thione derivatives. These ex-TTFs bear one, two, or four cyanoethyl-protected thiol groups
on the dithiole rings. Deprotection (NaOMe, MeOH, DMF, 20 °C) and trapping of the transient thiolates
with electrophiles have afforded the new ex-TTF trimer 19, dimeric cyclophanes 22 and 25, the tetrakis(hydroxyethylthio) derivative 23, and the strained cyclophane 24. Solution redox properties have been
studied by cyclic voltammetry. For compounds 19, 22, and 25 each ex-TTF unit behaves as an independent
2-electron redox system giving rise to a single, quasi-reversible 6-, 4-, and 4-electron wave, respectively.
The Eox value for 24 (0 → 2+ wave) is positively shifted by 290 mV compared to that of its precursor
15 due to the short bridge in 24 obstructing the conformational change which accompanies oxidation.
X-ray crystal structures of 23·2.5MeOH, 23·1.5MeCN, 24·CH2Cl2, and 24·1.5CH2Cl2 show the saddle-shape folding (typical of ex-TTF derivatives), which in 24 is enhanced by the pentamethylene chain
bridging the dithiole units. Both solvates of 23 show an unprecedented crystal packing motif due to
hydrogen bonding.