Synthesis 2008(5): 696-698  
DOI: 10.1055/s-2008-1032167
SHORTPAPER
© Georg Thieme Verlag Stuttgart · New York

Synthesis of Bis(ethylenedithio)dithiadiazafulvalenes (BEDT-DTDAF) and Generation of Charge-Transfer Complexes with Tetracyanoquinodimethane

Sławomir Makowiec*, Wioletta Koczan, Janusz Rachoń
Department of Organic Chemistry, Faculty of Chemistry, Gdansk University of Technology, Narutowicza 11/12, 80-952 Gdansk, Poland
Fax: +48(58)3472694; e-Mail: [email protected];

Further Information

Publication History

Received 25 October 2007
Publication Date:
08 February 2008 (online)

Abstract

The synthesis of bis(ethylenedithio)dithiadiazafulvalenes (BEDT-DTDAFs), in four steps via 4,5-(ethylenedithio)thiazole and 3-alkyl-4,5-(ethylenedithio)thiazolium salts, and the generation of conducting charge-transfer complexes from a new type of dithiadiazafulvalene and tetracyanoquinodimethane are reported.

Tetraheterafulvalenes, such as TTF, TSeF, TTeF, and DTDAF­, are widely used for the preparation of organic metals and organic superconductors. [1-8] So far, many modified variants to the four parent compounds have been synthesized. One of the most noteworthy modifications of the tetrathiafulvalene (TTF) core is bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF, Figure [1] ), in which two-dimensional conductivity was observed. [9] Moreover, organic superconductors are most commonly prepared from BEDT-TTF.

Dithiadiazafulvalenes (DTDAFs, Figure [1] ), which contain two nitrogen atoms in the tetraheterafulvalene core, are especially good electron donors (E HOMO = -3.916 eV). [10] Despite this fact DTDAFs are among the less explored tetraheterafulvalenes due to their oxygen sensitivity, [11] which makes synthesis of many of them very challenging.

To the best of our knowledge, DTDAF with four sulfur or selenium atoms at the ends of the π-system, i.e. the diaza-BEDT-TTF analogue, has not been previously synthesized and its electric properties have not been explored.

Figure 1

In this paper we wish to report the first synthesis of bis(ethylenedithio)dithiadiazafulvalenes (BEDT-DTDAFs­). The reaction of thiazolium salts with base is one of the most commonly used methods for the preparation of dithiadiazafulvalenes, [8] hence the key intermediates for the preparation of BEDT-DTDAFs are the respective thiazolium salts 3a-d.

Scheme 1

We applied a modified Hantzsch synthesis to the preparation of 5,6-dihydro[1,4]dithiino[2,3-d]thiazole (2). 3-Chloro-1,4-dithian-2-one (1) was prepared according to a procedure described by Larsen and Lenoir. [12] Reaction of 1 with freshly prepared thioformamide affords 2 in moderate yields (Scheme [1] ). Of course, Hantzsch’s synthesis has been applied to the preparation of thiazoles from α-halocarbonyl compounds and thioamides, and it is well known that reaction of α-halo esters with thioamides leads to thiazol-4(5H)-ones rather than to thiazoles. [13] Fortunately in our case the dehydration process was faster than 1,4-dithiane ring opening.

In the next step we alkylated 2 with alkyl bromides, followed by treatment with tetrafluoroboric acid, or trimethyloxonium tetrafluoroborate to give thiazolium tetrafluoroborate salts 3a-d. The thiazolium salts could also be synthesized in one step by reaction of 1 with substituted thioformamides; we obtained thiazolium salts in this manner only in the case of 3-benzyl-5,6-dihydro[1,4]dithiino[2,3-d]thiazol-3-ium tetrafluoroborate (3b), but the yield did not exceed 12%. Phenylthioform­amide in reaction with 1 did not give a thiazolium salt. The attempts to improve this reaction by facilitating the process with dehydrating agents, like thionyl chloride, 4-toluenesulfonic acid, or magnesium sulfate, according to a procedure similar to that of Salmond and Reid [14] failed.

Due to the sensitivity of dithiadiazafulvalenes to oxygen [11] all reactions of thiazolium tetrafluoroborate salts 3 with triethylamine were performed under argon in degassed solvents. We did not try to isolate the BEDT-DTDAFs as free compounds; tetracyanoquinodimethane (TCNQ) was immediately added to the mixture of the prepared BEDT-DTDAF in order to trap them as complexes 4a-g (Table [1] ).

The position of νCN in the FTIR spectra of charge-transfer complexes of TCNQ can reflect the charge of TCNQ; [15] for the prepared complexes we usually observed two bands: a weak one in the region 2201-2189 and a strong one in the region 2165-2150, which would suggest the existence of TCNQ with a charge of up to 1.75, but such a charge value is obviously incorrect due to solid state environmental interaction that can considerably shift νCN. [16]

The electrochemical properties of BEDT-DTDAFs as well as superconductivity of the prepared complexes are currently being examined.

Table 1 BEDT-DTDAF·TCNQ Complexes 4a-g Prepared
Compd R TCNQ (equiv) Stoichiometry of complexes
Yielda (%) Elemental analysisa IRb νCN (cm-1) Conductivityc (mS·cm-1)
BEDT-DTDAF TCNQ MeCN
4a Me 2 3 8 1 37 C134H77N39S18 2194, 2160 3.23
4b Me 4 3 16 1 64 C230H109N71S18 2176, 2153 3.54
4c Et 2 3 10 2 29 C166H100N48S18 2194, 2165 8.06
4d Et 4 3 16 0 48 C234H118N70S18 2200, 2153 7.23
4e allyl 4 1 10 2 31 C140H64N44S6 2201, 2150 1.40
4f Bn 2 3 16 2 29 C268H136N72S18 2196, 2154 2.56
4g Bn 6 3 19 1 55 C302H145N83S18 2194, 2153 2.44

a All products had analysis C ±0.14, H ±0.40; N ±0.49; S ±0.22; except 4e: C +0.66, H +1.07; N -1.14; S -1.14; 4f: C -0.3, H +0.71; N -0.69; S -0.61.
b KBr.
c Conductivity for two-probe method, r.t., compaction.

IR spectra were recorded from KBr pellets on a Bruker IFS66 infrared spectrometer. 1H and 13C NMR spectra were recorded on a Varian­ Unity Plus 500 MHz spectrometer using TMS as a reference. Elemental analyses were recorded on an Eager 200 instrument. Melting points are uncorrected. THF was distilled from potassium/benzophenone ketyl. CCl4 and CH2Cl2 were dried with CaCl2 and distilled. MeCN was dried with molecular sieves 4A, and four times frozen in a dry ice/acetone bath and degassed under vacuum (oil pump). All other commercially available reagents were used as received.

5,6-Dihydro[1,4]dithiino[2,3- d ]thiazole (2)

NCS (8.01 g, 60 mmol) was added to a cooled soln of 1,4-dithian-2-one (5.36 g, 40 mmol) [12] in CCl4 (150 mL) at 0 °C; the soln was stirred for 2 h. After filtration the solvent was removed at reduced pressure and the resulting oil was dissolved in anhyd THF (100 mL). The filtered soln was ice-cooled and a soln of HC(S)NH2 in THF (200 mL) [freshly prepared from HC(O)NH2 (9 g, 200 mmol) and P2S5 (8.88 g, 40 mmol)] was added dropwise; when the addition was complete (0.5 h) the mixture was stirred for 48 h. The solvent was removed under reduced pressure and the residue was made alkaline (to pH 10) with 2 M NaOH and extracted with EtOAc (5 × 50 mL). The combined organic phases were dried (MgSO4), and the solvent was removed under reduced pressure. The crude product was purified by chromatography (silica gel, CH2Cl2-hexane, 1:1); yield: 3.08 g (44%).

1H NMR (500 MHz, CDCl3): δ = 8.56 (s, 1 H, CH), 3.41 (m, 2 H, CH2), 3.27 (m, 2 H, CH2).

13C NMR (125 MHz, CDCl3): δ = 149.05, 139.51, 117.24, 29.42, 28.80.

3-Methyl-5,6-dihydro[1,4]dithiino[2,3- d ]thiazol-3-ium Tetra­fluoroborate (3a)

To a soln of 2 (1.75 g, 10 mmol) in anhyd CH2Cl2 was added tri­methyloxonium tetrafluoroborate (2.07 g, 14 mmol); the soln was stirred and heated to reflux for 24 h. The solvent was removed under reduced pressure and the residue was recrystallized twice (CH2Cl2-Et2O); yield: 1.94 g (69%); mp 160-161 °C.

1H NMR (500 MHz, acetone-d 6): δ = 10.09 (s, 1 H, CH), 4.23 (s, 3 H, NCH3), 3.72 (m, 2 H, CH2), 3.64 (m, 2 H, CH2).

13C NMR (125 MHz, acetone-d 6): δ = 155.31, 135.60, 126.88, 40.27, 28.39, 28.11.

3-Benzyl-5,6-dihydro[1,4]dithiino[2,3- d ]thiazol-3-ium Tetra­fluoroborate (3b)

To a soln of 2 (2.62 g, 15 mmol) in i-PrOH (50 mL) was added every 48 h at total of BnBr (20.52 g, 120 mmol) in 5 portions. The soln was stirred and heated to reflux for 10 d. The solvent was removed under reduced pressure and the residue was dissolved in CH2Cl2 and washed with H2O (5 × 30 mL). The aqueous layer was concentrated to 50 mL under reduced pressure and 50% HBF4 (50 mL) was added. The precipitated crude salt 3b was filtered and dried in vacuum; the product was recrystallized (CH2Cl2-Et2O); yield: 3.20 g (60%); mp 137-139 °C.

1H NMR (500 MHz, acetone-d 6): δ = 10.16 (s, 1 H, CH), 7.48 (m, 5 H, Ph), 5.82 (s, 2 H, NCH2), 3.66 (m, 2 H, CH2), 3.62 (m, 2 H, CH2).

13C NMR (125 MHz, acetone-d 6): δ = 155.22, 135.33, 132.09, 129.72, 129.53, 129.09, 128.77, 57.23, 28.65, 28.49.

3-Allyl-5,6-dihydro[1,4]dithiino[2,3- d ]thiazol-3-ium Tetrafluoroborate (3c)

Compound 2 (1.05 g, 6 mmol) was dissolved in allyl bromide (3 g, 24 mmol) and then sealed in a glass ampoule and heated to 62 °C for 48 h. The solvent was removed under reduced pressure and the residue was crystallized (MeOH-Et2O). The crude thiazolium bromide (1.36 g, 4.6 mmol) was dissolved in CH2Cl2 and HBF4·OEt2 (0.626 mL, 4.6 mmol) was added. Solvent was removed under reduced pressure and a new portion of CH2Cl2 was added and evaporation was repeated (5 ×). The crude product was recrystallized (acetone-Et2O); yield: 1.36 g (75%); mp 78-80 °C.

1H NMR (500 MHz, acetone-d 6): δ = 10.12 (s, 1 H, CH), 6.07-6.23 (m, J = 5.8, 10, 18 Hz, 1 H, CH2=CH), 5.55 (dd, J = 10, 18, 2 H, CH 2=CH), 5.32 (d, J = 5.8 Hz, 2 H, NCH2), 3.61-3.74 (m, 4 H, CH2CH2).

13C NMR (125 MHz, acetone-d 6): δ = 154.98, 135.27, 129.45, 128.42, 122.81, 55.95, 28.83, 28.56.

3-Ethyl-5,6-dihydro[1,4]dithiino[2,3- d ]thiazol-3-ium Tetrafluoroborate (3d)

Compound 2 (1.22 g, 7 mmol) was dissolved in EtBr (10.68 g, 98 mmol) and then sealed in a glass ampoule and heated to 62 °C for 21 d. The solvent was removed under reduced pressure and the residue was crystallized (MeOH-Et2O). The crude thiazolium bromide (1.0 g, 3.52 mmol) was dissolved in CH2Cl2 and HBF4·OEt2 (0.48 mL, 3.52 mmol) was added. Solvent was removed under reduced pressure and new portion of CH2Cl2 was added and evaporation was repeated (5 ×). The crude product was recrystallized (CH2Cl2-Et2O); yield: 0.69 g (34%); mp 107-108 °C.

1H NMR (500 MHz, acetone-d 6): δ = 10.11 (s, 1 H, CH), 4.62 (q, J = 7.3 Hz, 2 H, CH 2CH3), 3.76 (m, 2 H, CH2), 3.65 (m, 2 H, CH2), 1.66 (t, J = 7.3 Hz, 3 H, CH2CH 3).

13C NMR (125 MHz, acetone-d 6): δ = 154.40, 134.66, 127.78, 49.80, 29.62, 29.46, 13.95.

Tetracyanoquinodimethane Charge Transfer Complexes of 3,3′-Dialkyl-5,5′,6,6′-tetrahydro-3 H ,3H -[2,2′]bi[1,4]dithi­ino[2,3- d ]thiazoles 4a-g; General Procedure

Compound 3 (0.5 mmol) was dissolved under argon in thoroughly degassed MeCN (10 mL). Et3N (51 mg, 0.5 mmol) was added to a stirred soln, a deep red color appeared immediately. After 10 min a soln of TCNQ (102 mg, 0.5 mmol, or 204 mg, 1 mmol, or 306 mg, 1.5 mmol) in MeCN (20, 40, or 60 mL) was added. After 3 h the soln was concentrated to one fifth of its volume and refrigerated for 24 h. The precipitate was filtered, washed with MeCN (1 mL) and Et2O (2 mL), and dried in a vacuum desiccator to yield 4a-g (Table [1] ).

    References

  • 1 Ferraris J. Cowan DO. Walatka V. Perlstein JH. J. Am. Chem. Soc.  1973,  95:  948 
  • 2 Geiser U. Schlueter JA. Chem. Rev.  2004,  104:  5203 
  • 3 Shibaeva RP. Yagubskii EB. Chem. Rev.  2004,  104:  5347 
  • 4 Kobayashi A. Fujiwara E. Kobayashi H. Chem. Rev.  2004,  104:  5243 
  • 5 Kobayashi H. Cui H. Chem. Rev.  2004,  104:  5265 
  • 6 Kobayashi A. Tanaka H. Kobayashi H. J. Mater. Chem.  2001,  11:  2078 
  • 7 Cowan DO. McCullough R. Bailey A. Lerstrup K. Talham D. Herr D. Mays M. Phosphorus, Sulfur Silicon Relat. Elem.  1992,  67; 277 
  • 8 Lorcy D. Bellec N. Chem. Rev.  2004,  104:  5185 
  • 9a Saito G. Phosphorus, Sulfur Silicon Relat. Elem.  1992,  67:  354 
  • 9b Kurmoo M. Graham AW. Day P. Coles SJ. Hursthouse MB. Caulfield JL. Singleton S. Pratt FL. Hayes W. Ducasse L. Guionneaul P. J. Am. Chem. Soc.  1995,  117:  12209 
  • 9c Yamochi H. Komatsu T. Matsukawa N. Saito G. Mori T. Kusunoki M. Sakaguchi K. J. Am. Chem. Soc.  1993,  115:  11319 
  • 9d Geiser U. Schlueter JA. Wang HH. Kini AM. Williams JM. Sche PP. Zakowicz HI. VanZile ML. Dudek JD. J. Am. Chem. Soc.  1996,  118:  9996 
  • 10 Eid S. Guerro M. Roisnel T. Lorcy D. Org. Lett.  2006,  8:  2377 
  • 11a Bssaibis M. Robert A. Lemagueres P. Ouahab L. Carliere R. Tallec A. J. Chem. Soc., Chem. Commun.  1993,  601 
  • 11b Tonnos GV. Baker MG. Wang P. Lakshmikantham MV. Cava MP. Metzger RM. J. Am. Chem. Soc.  1995,  117:  8528 
  • 12 Larsen J. Lenoir Ch. Synthesis  1989,  134 
  • 13 Metzger JV. Katritzky AR. Comprehensive Heterocyclic Chemistry   Chap. 4.19, Part 4B, Vol. 6:  Katritzky AR. Rees CW. Pergamon; Oxford: 1983.  p.235-333  
  • 14 Reid DH. Salmond WG. J. Chem. Soc. C  1966,  686 
  • 15 Chappel JS. Bloch AN. Bryden WA. Maxfield M. Poehler TO. Cowan DO. J. Am. Chem. Soc.  1981,  103:  2442 
  • 16 Meneghetti M. Pecile C. J. Chem. Phys.  1986,  84:  4149 

    References

  • 1 Ferraris J. Cowan DO. Walatka V. Perlstein JH. J. Am. Chem. Soc.  1973,  95:  948 
  • 2 Geiser U. Schlueter JA. Chem. Rev.  2004,  104:  5203 
  • 3 Shibaeva RP. Yagubskii EB. Chem. Rev.  2004,  104:  5347 
  • 4 Kobayashi A. Fujiwara E. Kobayashi H. Chem. Rev.  2004,  104:  5243 
  • 5 Kobayashi H. Cui H. Chem. Rev.  2004,  104:  5265 
  • 6 Kobayashi A. Tanaka H. Kobayashi H. J. Mater. Chem.  2001,  11:  2078 
  • 7 Cowan DO. McCullough R. Bailey A. Lerstrup K. Talham D. Herr D. Mays M. Phosphorus, Sulfur Silicon Relat. Elem.  1992,  67; 277 
  • 8 Lorcy D. Bellec N. Chem. Rev.  2004,  104:  5185 
  • 9a Saito G. Phosphorus, Sulfur Silicon Relat. Elem.  1992,  67:  354 
  • 9b Kurmoo M. Graham AW. Day P. Coles SJ. Hursthouse MB. Caulfield JL. Singleton S. Pratt FL. Hayes W. Ducasse L. Guionneaul P. J. Am. Chem. Soc.  1995,  117:  12209 
  • 9c Yamochi H. Komatsu T. Matsukawa N. Saito G. Mori T. Kusunoki M. Sakaguchi K. J. Am. Chem. Soc.  1993,  115:  11319 
  • 9d Geiser U. Schlueter JA. Wang HH. Kini AM. Williams JM. Sche PP. Zakowicz HI. VanZile ML. Dudek JD. J. Am. Chem. Soc.  1996,  118:  9996 
  • 10 Eid S. Guerro M. Roisnel T. Lorcy D. Org. Lett.  2006,  8:  2377 
  • 11a Bssaibis M. Robert A. Lemagueres P. Ouahab L. Carliere R. Tallec A. J. Chem. Soc., Chem. Commun.  1993,  601 
  • 11b Tonnos GV. Baker MG. Wang P. Lakshmikantham MV. Cava MP. Metzger RM. J. Am. Chem. Soc.  1995,  117:  8528 
  • 12 Larsen J. Lenoir Ch. Synthesis  1989,  134 
  • 13 Metzger JV. Katritzky AR. Comprehensive Heterocyclic Chemistry   Chap. 4.19, Part 4B, Vol. 6:  Katritzky AR. Rees CW. Pergamon; Oxford: 1983.  p.235-333  
  • 14 Reid DH. Salmond WG. J. Chem. Soc. C  1966,  686 
  • 15 Chappel JS. Bloch AN. Bryden WA. Maxfield M. Poehler TO. Cowan DO. J. Am. Chem. Soc.  1981,  103:  2442 
  • 16 Meneghetti M. Pecile C. J. Chem. Phys.  1986,  84:  4149 

Figure 1

Scheme 1