Synthesis and properties of tetrathiafulvalenes bearing 6-aryl-1,4-dithiafulvenes

Novel multistage redox tetrathiafulvalenes (TTFs) bearing 6-aryl-1,4-dithiafulvene moieties were synthesized by palladium-catalyzed direct C–H arylation. In the presence of a catalytic amount of Pd(OAc)2, P(t-Bu3)·HBF4, and an excess of Cs2CO3, the C–H arylation of TTF with several aryl bromides bearing 1,3-dithiol-2-ylidenes took place efficiently to produce the corresponding π-conjugated molecules. We also succeeded in the estimation of the oxidation potentials and number of electrons involved in each oxidation step of the obtained compounds by digital simulations.


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Synthesis of 10: To a mixture of 9 (300.8 mg) in DMF (10 mL) and distilled water (10 mL) PTSA·H2O (244.0 mg, 0.602 mmol) was added at room temperature, and the mixture was stirred for 1 h. The organic compounds were extracted with dichloromethane three times. The combined organic layer was washed with H2O, sat. NaHCO3 aq., and brine, dried over anhydrous Na2SO4, and concentrated in vacuo. The obtained solid was washed with methanol and hexane to yield 10 as black solid. Being identified by 1 H NMR, this compound was used for the next step without further purification.

Compound 12 was synthesized as outlined below
Synthesis of 12: Compound 21 (196.1 mg, 0.501 mmol), 11 (456.0 mg, 2.01 mmol), dry toluene (2.4 mL), and P(OEt)3 (2.4 mL) were placed in a 50-mL reaction flask under an argon atmosphere. The mixture was heated at reflux for 4 h. After removal of the solvent and excess P(OEt)3 in vacuo, the residue was precipitated from dichrolomethane/hexane and washed with methanol to give 12 in 80% yield.

Synthesis of 13:
To a mixture of 1a (33.0 mg, 0.025 mmol) in DMF (10 mL) POCl3 (74 L, 0.79 mmol) was added at 0 °C, and the mixture was warmed to room temperature and stirred for 2 h. Afterwards, 1 M NaOH aq. (1.2 mL) was added at 0 °C and the mixture was warmed to room temperature and stirred for 30 min. The mixture was extracted with dichloromethane. The combined organic layers were washed with H2O and brine three times, dried over anhydrous Na2SO4, and concentrated in vacuo. The product was obtained by suction filtration with dichloromethane and hexane in 44% yield from 1a. Being identified by 1 H NMR, this compound was used for the next step without further purification.

Synthesis of 21:
To compound 6a (1.150 g, 3.16 mmol) in DMF (20 mL) POCl3 (1.2 mL, 12.7 mmol) was added at 0 °C and the mixture was warmed to room temperature and stirred for 2 h. After the reaction, 1 M NaOH aq. (38 mL) was added at 0 °C and the mixture was warmed to room temperature, and stirred for 30 min. The mixture was extracted with dichlorometane. The combined organic layers were washed with H2O and brine three times, S7 dried over anhydrous Na2SO4, and concentrated in vacuo. The product was obtained by suction filtration with dichlorometane and hexane in 77% yield.

Theoretical calculations
The theoretical calculations of the compounds 1a, 3a, and 4, and their pristine compounds were carried out based on density functional theory (DFT) using the spin-restricted B3LYP/6-