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Synlett 2005(7): 1117-1120  
DOI: 10.1055/s-2005-865204
LETTER
© Georg Thieme Verlag Stuttgart · New York

Chemical and Electrochemical Investigations on the Powerful π-Electron Donor Dithiadiazafulvalene: Isolation, Spectroscopic Characterization and Charge-Transfer Complexation

Georges Morel*, Grégory Gachot, Dominique Lorcy
Synthèse et Electrosynthèse Organiques, UMR 6510, Université de Rennes I, Campus de Beaulieu, 35042 Rennes Cedex, France
Fax: +33(223)236738; e-Mail: Georges.Morel@univ-rennes1.fr;
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Publication History

Received 18 January 2005
Publication Date:
14 April 2005 (online)

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Abstract

A representative of the title system has been accessible by three methods, namely the electrochemical reduction of the corresponding 2-(phenylthio)thiazolium salt, the chemical coupling of the thiazoline-2-selone in the presence of triethyl phosphite and a basic treatment of the 2-unsubstituted thiazolium salt. The last two procedures allow the isolation in a preparative scale of nearly pure dithiadiazafulvalene, which can be characterized by cyclic voltammetry and usual spectroscopic methods. The crystal structure of a 1:2 charge-transfer complex between this excellent π-donor molecule and tetracyanoquinodimethane as acceptor establishes that the dithiadiazafulvalene is in the dicationic state in the complex.

Key words

thiazolium salts - heterogeneous deprotonation - heterocycle - oxidation - complex

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The reduction of compound 1 on a platinium electrode at -1.3 V vs. SCE was performed in a degassed CH2Cl2 solution containing Bu4NPF6 as the conducting salt (1 M). On the first cathodic scan, an intense reduction peak was found at -1.13 V. On the reverse scan, two oxidation peaks were measured at -0.34 V and -0.23 V vs. SCE.

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Experimental Procedure.
NaBH4 (0.29 g, 7.6 mmol) was added portionwise over 10 min to a suspension of black selenium powder (0.45 g, 5.6 mmol) in degassed (N2) EtOH (25 mL). The colorless solution of NaHSe thus obtained was maintained under inert atmosphere during the addition of salt 1 (1.15 g, 2.5 mmol), which had been previously dissolved in degassed CH2Cl2 (10 mL). After 45 min at r.t., the mixture was poured into 60 mL of H2O and extracted with CH2Cl2 (2 × 10 mL). The combined CH2Cl2 layers were dried over Na2SO4 and concentrated in vacuo to give a yellowish solid which was recrystallized from EtOH (4, 0.60 g, 80%); mp 125 °C. 1H NMR (200 MHz, CDCl3): δ = 2.28 (s, 3 H), 3.57 (s, 3 H), 7.30 (m, 2 H), 7.57 (m, 3 H). 13C NMR (50.5 MHz): δ = 20.8 (q, 1 J = 141 Hz), 39.9 (q, 1 J = 143 Hz), 123.5 (q, 3 J = 5.5 Hz), 129.6, 129.9, 130.4, 130.8 (arom. C), 147.4 (m), 181.8 (q, 3 J = 5 Hz). Anal. Calcd for C11H11NS2Se: C, 43.85; H, 3.65; N, 4.65. Found C, 43.73; H, 3.59; N, 4.62.

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Procedure for Preparation of DTDAF 3 from Selone 4.
A solution of selone (0.17 g, 0.56 mmol) in freshly distilled toluene (15 mL) was degassed with nitrogen and heated to reflux for 5-6 min. After addition of P(OEt)3 (0.11 g, 0.65 mmol), the solution was stirred 10 min under N2 in boiling toluene and the mixture was cooled to r.t. and concentrated under reduced pressure. Trituration of the residue with anhyd Et2O produced an orange-colored solid, which was washed several times with Et2O, absolute EtOH and then dried in a vacuum desiccator. This crude material was used for cyclic voltammetry and spectroscopic experiments without further purification (0.10 g, about 80% yield). 1H NMR analysis (500 MHz, degassed CDCl3) confirmed that the fulvalene 3 was the major isolated product along with oxidation derivatives 5, 6 (£10%). The system showed a ten proton multiplet centered at δ = 7.41 ppm and four broad singlets, indicating a mixture of syn/anti isomers and the spectrum close to coalescence at r.t. (rel. int. 1:4, twelve protons on the totality); major isomer: δ = 2.22, 2.81; minor isomer: δ = 2.24, 2.84. The assignments of the 13C NMR signals (125.8 MHz, degassed CDCl3) were made under proton decoupling and HMBC; major isomer: δ = 20.3 (CH3S), 38.6 (CH3N), 108.3 (C5), 119.7 (C2), 128.3, 128.8, 129.9, 131.3 (arom. C), 145.7 (C4); minor isomer: δ = 20.0, 36.6, 109.8, 117.3, 128.3, 129.6, 129.9, 131.5, 146.2. MS (EI): m/z calcd for C22H22N2S4: 442.06659 [M]+; found: 442.06454. Cyclic voltammetry [MeCN, Bu4NPF6 (1 M)]: one oxidation peak at -0.31 V vs. SCE.

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Procedure for Preparation of DTDAF 3 from Thiazolium Iodide 2.
To a suspension of salt 2 (0.35 g, 1 mmol), Na2SO4 (0.4 g) and CH2Cl2 (10 mL) was added finely ground KOH (0.45 g as a commercial product containing about 15% H2O). After shaking at r.t. for 6 min, the mixture was rapidly filtered and the filtrate was concentrated in vacuo. The crude 3 (0.35 g) was isolated in the way described in ref.16; analysis by 1H NMR spectroscopy allowed assessment of the efficiency of the method (the 3, 5, 6 distribution was estimated at roughly 85:10:5). For 1H NMR and 13 C NMR see ref.16. Cyclic voltammetry [CH2Cl2, Bu4NPF6 (1 M)]: -0.34 and -0.19 V vs. SCE.

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Compound 5: pale yellow needles from EtOH, mp 154 °C. 1H NMR (300 MHz, CDCl3): δ = 2.18 (s, 6 H), 2.95 (s, 6 H), 7.40 (m, 6 H), 7.80 (m, 4 H). 13C NMR (75.5 MHz): δ = 18.7, 34.4 (2 × q, 1 J = 141 Hz), 128.6, 129.7, 130.5, 134.6 (arom. C), 134.9 (q, 3 J = 4.4 Hz), 145.6 (m), 165.1 (q, 3 J = 3 Hz). MS (EI): m/z calcd for C22H22N2O2S4: 474.0564 [M]+; found: 474.0578. MS: m/z = 265, 237, 222, 165, 162, 118. Anal. Calcd: C, 55.67; H, 4.67; N, 5.90. Found: C, 55.56; H, 4.60; N, 5.87.
Compound 6: colorless solid from petroleum ether-Et2O, mp 98 °C. 1H NMR (300 MHz, CDCl3): δ = 2.22 (s, 3 H), 3.10 (s, 3 H), 7.31 (m, 2 H), 7.49 (m, 3 H). 13C NMR (75.5 MHz): δ = 20.7 (q, 1 J = 141 Hz), 32.0 (q, 1 J = 142 Hz), 107.9 (q, 3 J = 5.3 Hz), 128.7, 129.6, 129.8, 129.9 (arom. C), 140.8 (m), 171.9 (q, 3 J = 3.3 Hz). MS (EI): m/z calcd for C11H11NOS2: 237.02821 [M]+; found: 237.02820.

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Compound 7, main isomer: 1H NMR (300 MHz, CDCl3): δ = 2.66 (s, 6 H), 2.87 (s, 6 H), 6.74 (s, 2 H), 7.26 (s, 4 H), 7.37 (s, 6 H). 13C NMR (75.5 MHz): δ = 19.8 (q, 1 J = 142 Hz), 33.4 (qd, 1 J = 140 Hz, 3 J = 3.5 Hz), 71.7 (br d, 1 J = 142 Hz), 128.8, 130.1, 130.2, 135.0 (arom. C), 165.2 (m), 234.7 (m). MS (EI, oily mixture): m/z calcd for C20H21N2O2S2: 385.10445 [M - CS2CH3]+; found: 385.10460.

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Thiazolium salt 8: 1H NMR (300 MHz, CDCl3): δ = 2.26 (s, 3 H), 2.49 (s, 3 H), 3.04 (s, 3 H), 3.99 (s, 3 H), 7.03 (s, 1 H), 7.26-7.67 (m, 10 H). The assignments of 13C NMR signals (75.5 MHz, see numbering in Scheme [2] ) were made after proton decoupling, HMBC and HMQC: δ = 19.6, 20.8 (CH3S), 40.3, 41.0 (CH3N), 68.5 (C2′-sp3), 108.6 (C5′), 126.0, 130.2 (quat. arom. C), 135.3 (C5), 144.5 (C4′), 150.7 (C4), 178.9 (C2-sp2).

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Formamide 9 (two isomers): 1H NMR (300 MHz, CDCl3): δ = 2.67, 2.72, 2.85, 2.88 (4 s), 5.85, 6.65 (2 s), 7.35-7.80 (m), 8.23 (s). 13C NMR (75.5 MHz): δ = 19.8, 20.0, 30.4, 33.1, 70.1, 77.0, 163.2, 163.9, 233.9, 234.1 and eight aromatic carbons.

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A sat. MeCN solution of TCNQ was added to a degassed CH2Cl2 solution of DTDAF 3 (crude solid, 0.05 g). The mixture immediately turned from orange to black. After a couple of days at r.t. with protection from light, black shiny single crystals produced were filtered and washed with Et2O: mp 226 °C. FTIR (KBr diffuse reflectance spectra): νCN = 2180 cm-1.

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Full details of the X-ray structure determination have been deposited at the Cambridge Crystallographic Data Centre (deposition number CCDC 259963). The crystallographic data can be obtained free of charge from the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK; e-mail: deposit@ccdc.cam.ac.uk.