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Synthesis 2009(6): 1000-1006  
DOI: 10.1055/s-0028-1087974
PAPER
© Georg Thieme Verlag Stuttgart ˙ New York

Light-Induced Synthesis of π-Extended Tetrathiafulvalenes Incorporating Ferrocenes: An Efficient Route for the Synthesis of Electron-Donor Materials

Abdelwareth A. O. Sarhan*a,b, Carsten Bolma
a Institute of Organic Chemistry, RWTH Aachen University, 52056 Aachen, Germany
b Chemistry Department, Faculty of Science, Assiut University, Assiut 71516, Egypt
e-Mail: elwareth@aun.edu.eg; e-Mail: Carsten.Bolm@RWTH-Aachen.de;

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Publication History

Received 6 October 2008
Publication Date:
24 February 2009 (online)

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Abstract

A new method for the synthesis of π-extended tetrathia­fulvalenes was developed. The protocol is based on the exposure of 1,4-dithiafulvenes to sunlight or UV light at ambient temperature. In the resulting chalcogenofulvalenes the 1,3-dithiole ring systems are separated by conjugated spacers. Extended TTF analogues are obtained by insertion of linear π-conjugated spacers (C=C-C=C) of increasing dimensions between the two 1,4-dithiafulvenyl moieties.

Key words

Wittig-Horner reaction - 1,4-dithiafulvenes - ferrocene - oxidative dimerization - sunlight - π-extended tetrathiafulvalenes - organic conductors - electrochemical properties - charge-transfer complex

After the discovery that tetrathiafulvalene (TTF, 1a) can act as a molecular conductor, [¹] modifications of TTF involving the replacement of the four hydrogen atoms at positions 4,5 and 4′,5′ have been extensively studied (Figure  [¹] ). [²] With the finding of the metallic behavior of the TTF-TCNQ complex, synthetic approaches towards tetrathiafulvalenes and tetraselenafulvalenes gained significant attention and various electrically (super)conducting salts and charge-transfer (CT) complexes were prepared. Furthermore, the charge-transfer process from tetrathiafulvalene to tetracyanoquinodimethane (TCNQ) between adjacent stacks has been extensively investigated. [³]

Figure 1 Tetrathiafulvalenes [for 1a (TTF), X = S and R¹-R4 = H] and tetraselenafulvalenes (1b, X = Se)

Various TTF derivatives can be prepared in a single step in low to moderate yields. [4] The replacement of the central ethylenic linkage (C=C) by larger conjugated spacers (C=C-C=C)n leads to extended TTFs such as ETTH (2) with enhanced intra- and interchain contacts (Figure  [²] ), due to the lowering of their charge density and increased π-interactions. [5] Also from these extended derivatives, conducting salts have been prepared. [6] Studies of their properties revealed that the extended tetrathiafulvalenes are strong electron donors, which exhibit small on-site Coulomb repulsion owing to the extended π-conjugation. [7] Furthermore, vinylogous TTFs with bulky groups at the vinylic positions afforded conductors with uncommon multidimensional structures and, due to the Coulomb repulsion in the dicationic states as a result of the extended π-conjugation, stable dication salts with unusual crystal structures were obtained. [8]

Ueno and co-workers synthesized the first ferrocene-containing­ tetrathiafulvalene and its vinylogues 3. [9] Their charge-transfer complexes with TCNQ and DDQ were also described. Since then a few more reports have appeared, which deal with the electrochemical properties and charge-transfer complexes of tetrathiafulvalenes bearing ferrocene moieties. [¹0]

Figure 2 π-Extended tetrathiafulvalenes

Here, we describe an environmentally benign approach towards the synthesis of new electron-donor tetrathiafulvalene vinylogues using 1,4-dithiafulvenes as building blocks.

Starting point for the synthesis of the tetrachalcogenofulvalene derivatives was a Wittig-Horner reaction with dimethyl 1,3-benzodithiol-2-ylphosphonate (4), which was prepared following the previously reported method. [¹¹] After deprotonation of 4 with butyllithium at -78 ˚C in anhydrous tetrahydrofuran under argon, the resulting anion was allowed to react with aldehydes 5a-e to give the corresponding 1,4-dithiafulvenes 6a-e (Scheme  [¹] ). [¹²]

Scheme 1 Synthesis of thiafulvenes 6a-e

Attempts to synthesize extended TTFs 7 from 6a-e using either electrochemical oxidation or treatment with hydrogen chloride and/or hydrogen bromide in an organic solvent followed by reduction with zinc to dimerize the intermediately formed radical cation of 6 led to low yields of 7 and decomposition of the 1,4-dithiafulvenes. [¹¹d] Unexpected nitrofulvene 8 was obtained (as yellow crystals) in considerable amounts when the oxidation was tried with a mixture of acetic acid and nitric acid (Figure  [³] ). The molecular ion peak in the mass spectra of 8 ([M - 1], 286) confirmed its structures. Refluxing 6a in acetic acid in the presence of concentrated sulfuric acid gave no product and only the starting material was recovered.

Figure 3 π-Extended tetrathiafulvalenes and nitrofulvene 8

Consequently, the strategy for the preparation of extended tetrathiafulvalenes had to be changed. Formylation of dithiafulvenes 6a-e according to the reported procedure [¹³] using oxalyl chloride in anhydrous N,N-dimethylform­amide at 0 ˚C and subsequent alkaline hydrolysis afforded the corresponding products 9a-e in high yields. Wittig-Horner-type reactions of 9a-e with phosphonate ester 4 gave the extended tetrathiafulvalene 10a-e in excellent yields (Scheme  [²] ).

Scheme 2 Synthesis of extended tetrathiafulvalenes 10a-e

Upon standing a darkening of the red color of 1,4-dithia­fulvene 6c was noticed and ¹H NMR spectroscopy revealed that the ethylenic CH proton disappeared with time. To our delight, mass spectrometry and ¹³C NMR spectroscopy showed that 6c had unexpectedly dimerized to form the extended tetrathiafulvalene 7c. Encouraged by this result the behavior of the other 1,4-dithiafulvenes was studied (Table  [¹] ). As noticed also by Bryce and co-workers, [¹²] only the ferrocenyl-substituted substrates underwent rapid dimerization, and thus, 7c (50%) and 7d (23%) were obtained in conversions of 6c and 6d, respectively. Oxidation of 6d with iodine in dichloromethane [¹³] followed by the reduction of the resulting dication with sodium thiosulfate (Na2S2O4) afforded 7d in 60% yield. The aryl-substituted dithiafulvenes 6a, 6b, and 6e were more stable. Thus, neither stirring them in chloroform or dichloromethane solutions in a reactor under UV light at room temperature for 4-12 hours nor treating them with hydrogen chloride (as oxidizing agent) in anhydrous diethyl ether [¹²a] or using the iodine/dichloromethane method [¹³] led to significant amounts of the corresponding dimers. At best, only traces of 7b could be identified by mass spectrometry {[M]+ 542 (12%)} upon boiling 1,4-dithiafulvene 6b in an iodine/dichloromethane mixture.

Table 1 Syntheses of π-Extended Tetrathiafulvalenes 7 by Induced Dimerizations

Product Ara Yield (%) Methodb
7a Ph - a-d
7b 4-MeOC6H4 trace a, c
7c Fc 50 a
7d 4-(Fc)C6H4 23/60 a/c
7e 4-BrC6H4 - a, c
a Fc = ferrocenyl.
b Method a: sunlight; b: UV light; c: I2, CH2Cl2; d: HCl, Et2O.

Following the same strategy established for the dimerizations of 1,4-dithiafulvenes 6a-e, the conversions of tetrathiafulvalenes 10a-e were attempted. Those compounds possessed highly active CH protons on the conjugated system [>C=C(Ar)-CH=C<], and their dimer formation was expected to lead to chalcogenofulvalenes 11a-e (Table  [²] ). Confirming this hypothesis, dimers 11b-d were formed upon exposure to sunlight albeit the yields remained moderate ranging from 37% to 45%. Use of UV light led to substrate decomposition and from the complex product mixtures none of the targeted compounds could be isolated. Oxidative dimerization of 10d using iodine/dichloromethane gave 11d in 28% yield.

Table 2 Syntheses of π-Extended Tetrathiafulvalenes 11 by Induced Dimerizations

Product Ara Yield (%) Methodb
11a Ph trace a-d
11b 4-MeOC6H4 39 a
11c Fc 37 a
11d 4-(Fc)C6H4 45/0/28/0 a/b/c/d
11e 4-BrC6H4 trace a, c
a Fc = ferrocenyl.
b Method a: sunlight; b: UV light; c: I2, CH2Cl2; d: HCl, Et2O.

In conclusion, we prepared various ferrocene-containing π-extended tetrathiafulvalenes by dimerization of thiafulvenes using a simple protocol involving sunlight. The electrochemical properties and conductivity measurements are now being investigated and those results will be published in due course.

All Wittig-Horner reactions were carried out under argon using standard Schlenk techniques. THF was distilled from Na/benzophenone ketyl radical. Hexane, CH2Cl2, and CHCl3 for column chromatography were distilled before use. ¹H and ¹³C NMR spectra were recorded on a Varian Gemini 300 spectrometer (300 MHz and 75 MHz respectively) and on a Varian Inova 400 spectrometer (400 MHz and 100 MHz respectively); TMS was used as an internal standard. Phosphonate ester 4 was prepared according to the method previously reported in literature. [¹¹] Except 4-(ferrocenyl)benzaldehyde, which was synthesized following a previously reported method, [¹4] all aldehydes were commercially available and used without further purification. The analytical data for compounds 6a and 6b were in agreement with those previously reported. [¹¹]

1,4-Dithiafulvenes 6a-e; General Procedure

A sample of the 1,3-benzdithiol-2-ylphosphonate 4 (0.786 g, 3 mmol) was stirred in anhyd THF (50 mL) under a stream of argon at -78 ˚C. A soln 1.6 M of BuLi (2.3 mL) was added portionwise and the mixture was stirred for 15 min. A soln of the aldehyde 5 (3 mmol) in anhyd THF (50 mL) was added portionwise over 15 min. The temperature of the reaction was raised to r.t., and the mixture was stirred overnight. Then the solvent was removed under vacuum and the residue washed with H2O and extracted with CHCl3. The extracts were dried (MgSO4) and the crude product was chromatographed (silica gel, CHCl3-hexane, 1:2) to give the corresponding product 6a-e in high yields. The analytical data for compounds 6a and 6b were in satisfactory agreement with those reported in the literature. [¹¹d]

2-(Ferrocenylmethylene)-1,3-benzodithiole (6c)

Orange red crystals; yield: 71%; mp 154-155 ˚C.

IR (KBr): 3091 (m), 2994 (w), 1589 (s), 1448 (s), 1430 (s), 1407 (s), 1292 (m), 1259 (m), 1124 (m), 1101 (m), 1049 (m), 1029 (m), 998 (s), 809 (s), 744 cm-¹ (s).

¹H NMR (CDCl3): δ = 7.24 (m, 1 Harom), 7.17 (m, 1 Harom), 7.08 (m, 2 Harom), 6.16 (s, 1 H, CH=C), 4.42 (t, J = 2 Hz, 2 Hferrocene), 4.23 (t, J = 2 Hz, 2 Hferrocene), 4.17 (s, 5 Hferrocene).

¹³C NMR (CDCl3): δ = 137.6, 136.2, 128.3, 126.4, 126.1, 122.3, 121.6 (Carom, CHarom, thiafulvalene-C=CH), 112.7 (thiafulvalene-C=CH), 83.4 (Cferrocene), 69.8, 69.0, 68.1 (CHferrocene).

MS (FAB): m/z (%) = 350 ([M]+, 90).

Anal. Calcd for C18H14FeS2 (350.2756): C, 61.72; H, 4.03; S, 18.31. Found: C, 61.51; H, 4.22; S, 18.61.

2-[4-(Ferrocenyl)benzylidene]-1,3-benzodithiole (6d)

Orange crystals; yield: 85%; mp (dec).

IR (KBr): 3093 (m), 3050 (w), 2987 (w), 1604 (m), 1575 (s), 1546 (s), 1521 (s), 1448 (s), 1284 (s), 1083 (s), 1033 (s), 1002 (m), 935 (s), 887 (s), 844 (s), 819 (s), 744 cm-¹ (s).

¹H NMR (CDCl3): δ = 7.48 (d, J = 8.5 Hz, 2 Harom), 7.26 (d, J = 8.5 Hz, 4 Harom), 7.12-7.10 (m, 2 Harom), 6.54 (s, 1 H, CH=C), 4.65 (t, J = 2 Hz, 2 Hferrocene), 4.32 (t, J = 2 Hz, 2 Hferrocene), 4.04 (s, 5 Hferrocene­).

¹³C NMR (CDCl3): δ = 137.1, 136.5, 134.8, 134.2, 131.3, 127.0, 126.1, 126.0, 125.6, 121.7, 120.9, 114.7, 114.7 (Carom, CHarom, thiafulvalene­-C=CH), 85.0 (Cferrocene), 69.6, 69.0, 66.4 (CHferrocene).

MS (EI): m/z (%) = 425 ([M - 1], 100), 426 ([M]+, 41).

Anal. Calcd for C24H18FeS2 (426.2756): C, 67.61; H, 4.26. Found: C, 67.49; H, 4.15.

2-(4-Bromobenzylidene)-1,3-benzodithiole (6e)

Colorless crystals (EtOH); yield: 70%; mp 189.5-190 ˚C.

IR (KBr): 3050 (m), 2982 (w), 2918 (w), 1643 (s), 1549 (s), 1478 (s), 1431 (s), 1387 (s), 1332 (w), 1260 (w), 1187 (m), 1117 (s), 1068 (m), 931 (m), 831 (s), 738 (s), 670 cm-¹ (m).

¹H NMR (CDCl3): δ = 7.47 (d, J = 8.5 Hz, 2 Harom), 7.27-7.18 (m, 4 Harom), 7.13-7.11 (m, 2 Harom), 6.48 (s, 1 H, CH=C).

¹³C NMR (CDCl3): δ = 135.4, 131.5, 128.4, 126.1, 125.7, 121.7, 121.0, 119.4, 113.2 (Carom, CHarom, thiafulvalene-C=CH).

MS (EI): m/z (%) = 321 ([M]+, 100).

Anal. Calcd for C14H9BrS2 (321.2553): C, 52.34; H, 2.82. Found: C, 52.06; H, 2.85.

2-[Nitro(phenyl)methylene]-1,3-benzodithiole (8)

To a sample of dithiafulvene 6a (60 mg, 0.25 mmol) in stirred hot AcOH (10 mL), concd HNO3 (32 mg, 0.5 mmol) was added, and the mixture kept at ca. 100 ˚C for 5-10 min. The color turned to orange red and the mixture was stirred for an additional 10 min at r.t. and monitored (TLC). After 10 min no starting material was left in the mixture. H2O (25 mL) was added, and the yellow precipitate thus formed was collected by filtration and chromatographed (CH2Cl2) to give the product as yellow crystals; yield: 35%.

¹H NMR (CDCl3): δ = 7.68-7.65 (m, 1 Harom), 7.58-7.50 (m, 4 Harom), 7.45-7.30 (m, 4 Harom).

¹³C NMR (CDCl3): δ = 130.4 (thiafulvalene, >C=C), 130.3, 129.6 (Carom), 128.8, 127.2, 127.1, 123.1 (CHarom), 121.9 (>C=CNO2).

MS (EI): m/z (%) = 286 ([M - 1], 87), 288 ([M + 1], 14), 240 (M - NO2], 100).

Anal. Calcd for C14H9NO2S2 (287.3568): C, 58.52; H, 3.16; N, 4.87. Found: C, 59.06; H, 3.67, N; 4.02.

2-Aryl-2-(1,3-benzodithiol-2-ylidene)acetaldehydes 9a-e; General Procedure

To anhyd DMF (25 mL) under stream of argon at 0 ˚C was added dropwise oxalyl chloride (0.3 mL, 3.45 mmol) and the mixture stirred for 15 min. After this time, 6 (2.28 mmol) was added and the mixture warmed to 20 ˚C and stirred overnight. The mixture was quenched with aq 1 M NaOH (75 mL), precipitating a deep yellow to red solid. This product was collected by filtration and washed with H2O (50 mL). The solid product was dissolved in CH2Cl2, washed with H2O; the organic phase was separated, dried (MgSO4), and evaporated under reduced pressure. The residue was chromatographed (silica gel, CH2Cl2) to afford products 9a-e.

2-(1,3-Benzodithiol-2-ylidene)-2-phenylacetaldehyde (9a)

Yellow crystals (EtOH); yield: 76%; mp 97-98 ˚C.

IR (KBr): 3058 (s), 2928 (s), 2830 (s), 1695 (s), 1627 (s), 1558 (s), 1499 (s), 1459 (s), 1424 (s), 1382 (s), 1251 (s), 1096 (s), 926 (m), 854 (m), 745 (s), 701 cm-¹ (s).

¹H NMR (CDCl3): δ = 9.45 (s, 1 H, CHO), 7.61-7.60 (m, 1 Harom), 7.58-7.56 (m, 1 Harom), 7.52-7.38 (m, 5 Harom), 7.33-7.24 (m, 2 Harom).

¹³C NMR (CDCl3): δ = 184.7 (CHO), 159.3, 138.3, 137.4 (C=CS2), 132.4, 129.3, 128.8, 128.4, 126.6, 126.5, 122.9, 122.8, 121.6 (Carom, CH).

MS (EI): m/z (%) = 269 ([M - 1], 100), 271 ([M + 1], 23).

Anal. Calcd for C15H10OS2 (270.3693): C, 66.63; H, 3.73. Found: C, 66.43; H, 4.09.

2-(1,3-Benzodithiol-2-ylidene)-2-(4-methoxyphenyl)acetaldehyde (9b)

Yellow crystals; yield: 91%; mp 123.5-124.5 ˚C.

IR (KBr): 3093 (m), 2848 (m), 1635 (s), 1562 (s), 1492 (s), 1452 (s), 1427 (s), 1376 (s), 1265 (s), 1114 (s), 1047 (s), 1002 (s), 831 (s), 802 (s), 736 cm-¹ (s).

¹H NMR (CDCl3): δ = 9.43 (s, 1 H, CHO), 7.58 (dd, J = 3, 8 Hz, 1 Harom), 7.43-7.41 (m, 1 Harom), 7.37-7.34 (m, 2 Harom), 7.32-7.27 (m, 2 Harom), 7.03-7.01 (m, 2 Harom), 3.86 (s, 3 H, OCH3).

¹³C NMR (CDCl3): δ = 184.9 (CHO), 159.6, 158.9, 136.4, 132.4, 130.2 (Carom, C=CS2), 129.7, 126.6, 126.5, 122.8, 122.6, 121.6, 114.7 (Carom), 55.4 (OCH3).

MS: m/z (%) = 300 (M+, 100).

Anal. Calcd for C16H12O2S2 (300.3953): C, 63.97; H, 4.03. Found: C, 63.38; H, 4.12.

2-(1,3-Benzodithiol-2-ylidene)-2-(ferrocenyl)acetaldehyde (9c)

Red crystals; yield: 71%; mp 147-148 ˚C.

IR (KBr): 3094 (m), 3010 (s), 2920 (s), 2847 (m), 1632 (s), 1493 (s), 1426 (s), 1378 (s), 1272 (s), 1213 (s), 1164 (w), 1112 (s), 1048 (s), 999 (m), 931 (m), 824 (s), 752 (s), 665 cm-¹ (m).

¹H NMR (CDCl3): δ = 9.96 (s, 1 H, CHO), 7.58-7.57 (m, 1 Harom), 7.51-7.49 (m, 1 Harom), 7.31-7.28 (m, 2 Harom), 4.55 (t, J = 1.5 Hz, 2 Hferrocene), 4.36 (t, J = 1.5 Hz, 2 Hferrocene), 4.21 (s, 5 Hferrocene).

¹³C NMR (CDCl3): δ = 186.3 (CHO), 154.8, 138.5 (C=CS2), 132.9, 126.5, 126.4, 122.6, 121.6, 118.0 (Carom, CH), 84.2 (Cferrocene), 69.3, 68.3, 67.6 (CHferrocene).

MS (DIP): m/z (%) = 378 ([M]+, 100).

Anal. Calcd for C19H14FeOS2 (378.2889): C, 60.33; H, 3.73. Found: C, 60.44; H, 3.89.

2-(1,3-Benzodithiol-2-ylidene)-2-[4-(ferrocenyl)phenyl]acetaldehyde (9d)

Red crystals; yield: 51%; mp 188.5-189 ˚C.

IR (KBr): 3057 (w), 2925 (m), 2815 (m), 1526 (s), 1458 (s), 1382 (s), 1264 (s), 1101 (s), 937 (m), 819 (s), 738 cm-¹ (s).

¹H NMR (CDCl3): δ = 9.5 (d, J = 3 Hz, 1 H, CHO), 7.61-7.60 (dd, J = 3, 5.5 Hz, 1 Harom), 7.55-7.54 (d, J = 7.5 Hz, 2 Harom), 7.46-7.45 (d, J = 7.5 Hz, 1 Harom), 7.36-7.25 (m, 4 Harom), 4.75 (s, 2 Hferrocene), 4.42 (s, 2 Hferrocene), 4.14 (s, 5 Hferrocene).

¹³C NMR (CDCl3): δ = 184.8 (CHO), 158.9, 139.7 (C=CS2), 138.4, 134.9, 132.5 (Carom), 128.7, 126.9, 126.7, 126.5, 122.8, 122.8, 121.6 (CHarom), 78.8 (Cferrocene), 70.3, 69.9, 67.0 (CHferrocene).

MS (EI): m/z (%) = 454 ([M]+, 100).

Anal. Calcd for C25H18FeOS2 (454.3848): C, 66.08; H, 3.99. Found: C, 65.23; H, 4.01.

2-(1,3-Benzodithiol-2-ylidene)-2-(4-bromophenyl)acetaldehyde (9e)

Dark yellow crystals; yield: 97%; mp 173-173.5 ˚C.

IR (KBr): 3055 (m), 2920 (m), 2808 (s), 1694 (s), 1638 (s), 1556 (s), 1495 (s), 1438 (s), 1380 (s), 1268 (s), 1176 (m), 1074 (s), 1008 (m), 934 (m), 869 (s), 816 (s), 741 (s), 670 cm-¹ (s).

¹H NMR (CDCl3): δ = 9.42 (s, 1 H, CHO), 7.65-7.60 (m, 3 Harom), 7.47-7.44 (m, 1 Harom), 7.36-7.27 (m, 4 Harom).

¹³C NMR (CDCl3): δ = 184.1 (CO), 138.2, 136.2 (C=CS2), 132.5, 130.5, 126.8 (Carom), 126.7, 122.9, 122.4, 121.7.

MS (EI): m/z (%) = 349 ([M]+, 100).

Anal. Calcd for C15H9BrOS2 (349.2654): C, 51.58; H, 2.60. Found: C, 51.36; H, 2.70.

π-Extended Tetrathiafulvalenes 10a-e; General Procedure

To a stirred soln of the Wittig-Horner reagent 4 (1.0 mmol) in anhyd THF (50 mL) under argon atmosphere 1.6 M BuLi in hexane was added at -78 ˚C and the reaction allowed to stir at this temperature for 30 min. A soln of aldehyde 9 (1.0 mmol) in anhyd THF was then added dropwise and the reaction allowed to warm to 20 ˚C and stirred overnight. The solvent was evaporated under vacuum and the residue was washed with H2O, extracted with CH2Cl2, and the organic phase was separated, washed with H2O, dried (MgSO4), and evaporated. The solid residue was chromatographed (silica gel, CH2Cl2-hexane, 1:3) to give the targeted π-extended tetrathiafulvalenes 10a-e.

2,2′-(1-Phenylethane-1,2-diylidene)bis(1,3-benzodithiole) (10a)

Yellow crystals; yield: 68%; mp 185.5-186 ˚C.

IR (KBr): 3104 (m), 3051 (w), 2961 (w), 2924 (m), 2842 (w), 1641 (s), 1558 (s), 1505 (s), 1432 (s), 1383 (s), 1320 (s), 1253 (s), 1154 (s), 1112 (s), 1062 (s), 926 (s), 807 (s), 739 (s), 691 cm-¹ (s).

¹H NMR (CDCl3): δ = 7.47-7.35 (m, 4 Harom), 7.23 (m, 1 Harom), 7.22-7.19 (m, 4 Harom), 7.13-6.89 (m, 4 Harom), 6.21 (s, 1 H, CH=C).

¹³C NMR (CDCl3): δ = 137.6, 137.6 (C2, C2′, C=CS2), 136.4, 136.0, 134.6, 132.7, 131.3, 125.3 (Carom, C=CH), 129.9, 129.1, 128.3, 125.7, 125.5, 124.7, 121.5, 121.4, 121.4, 120.8 (CHarom, CH=C), 112.5 (CH).

MS (EI): m/z (%) = 406 ([M]+, 100).

Anal. Calcd for C22H14S4 (406.6066): C, 64.99; H, 3.47. Found: C, 64.64; H, 3.52.

2,2′-[1-(4-Methoxyphenyl)ethane-1,2-diylidene]bis(1,3-benzodithiole) (10b)

Yellow crystals; yield: 89%; mp 187-187.5 ˚C.

IR (KBr): 3047 (m), 2947 (m), 2828 (m), 1603 (s), 1565 (s), 1513 (s), 1440 (s), 1383 (s), 1320 (s), 1293 (s), 1246 (s), 1171 (s), 1115 (s), 1027 (s), 927 (s), 828 (s), 739 (s), 674 (s), 606 cm-¹ (s).

¹H NMR (CDCl3): δ = 7.33-7.23 (m, 4 Harom), 7.23-7.06 (m, 4 Harom), 7.05-6.96 (m, 4 Harom), 6.23 (s, 1 H, CH=C), 3.90 (s, 3 H, OCH3).

¹³C NMR (CDCl3): δ = 159.65 (Carom-O), 137.9, 136.6, 136.3, 134.7, 131.5, 125.9, 125.7 (C2, C2′, C=CS2, Carom), 125.6, 125.5, 121.6, 121.5, 121.0, 114.6 (CHarom, CH=C), 55.5 (OCH3).

MS (EI): m/z (%) = 406 (M+, 100).

Anal. Calcd for C23H16OS4 (436.6325): C, 63.27; H, 3.69. Found: C, 63.20; H, 3.73.

2,2′-[1-(Ferrocenyl)ethane-1,2-diylidene]bis(1,3-benzodithiole) (10c)

Red crystals; yield: 61%; mp 94-95 ˚C.

IR (KBr): 3056 (s), 2923 (s), 2851 (m), 1642 (s), 1539 (s), 1441 (s), 1383 (s), 1262 (s), 1187 (m), 116 (s), 1031 (s), 997 (s), 814 (s), 738 (s), 675 cm-¹ (s).

¹H NMR (CDCl3): δ = 7.30-7.28 (m, 1 Harom), 7.24-7.20 (m, 2 Harom), 7.15-7.13 (m, 1 Harom), 7.10-7.03 (m, 4 Harom), 6.18 (s, 1 H, CH=C), 4.56 (t, J = 2 Hz, 2 Hferrocene), 4.27 (t, J = 2 Hz, 2 Hferrocene), 4.23 (s, 5 Hferrocene).

¹³C NMR (CDCl3): δ = 137.2, 136.8, 136.2, 136.3, 135.5, 128.5, 125.5 (C2, C2′, C=CS2, Carom), 125.5, 125.5, 125.3, 121.7, 121.5, 121.3, 121.2, 119.5, 114.7 (CHarom, CH=C), 83.8 (Cferrocene), 69.2, 68.3, 67.4 (CHferrocene).

MS (EI): m/z (%) = 513 ([M - 1], 100), 514 ([M]+, 49).

Anal. Calcd for C26H18FeS4 (514.5261): C, 60.69; H, 3.53. Found: C, 60.46; H, 3.70.

2,2′-{1-[4-(Ferrocenyl)phenyl]ethane-1,2-diylidene}bis(1,3-benzodithiole) (10d)

Orange crystals; yield: 96%; mp (dec).

IR (KBr): 3052 (s), 2926 (m), 2859 (m), 1633 (s), 1566 (s), 1522 (s), 1441 (s), 1383 (s), 1278 (s), 1159 (s), 1113 (s), 1060 (s), 1007 (s), 925 (s), 881 (m), 815 (s), 739 (s), 676 (m), 608 cm-¹ (s).

¹H NMR (CDCl3): δ = 7.57-7.54 (m, 2 Harom), 7.30-7.24 (m, 4 Harom), 7.15-7.10 (m, 4 Harom), 7.09-6.89 (m, 2 Harom), 6.25 (s, 1 H, CH=C), 4.75 (t, J = 2 Hz, 2 Hferrocene), 4.37 (t, J = 2 Hz, 2 Hferrocene), 4.04 (s, 5 Hferrocene).

¹³C NMR (CDCl3): δ = 139.5, 137.7, 136.6, 136.1, 134.8, 134.6, 132.5, 130.5, 130.1 (C2, C2′, C=CS2, Carom), 126.3, 125.7, 125.5, 125.4, 124.7, 122.8, 121.5, 121.4, 121.3, 120.8, 112.5 (CHarom, CH=C), 84.1 (Cferrocene), 70.0, 69.4, 66.4 (CHferrocene).

MS (EI): m/z (%) = 590 ([M]+, 100).

Anal. Calcd for C32H22FeS4 (590.6221): C, 65.07; H, 3.75. Found: C, 64.97; H, 3.96.

2,2′-[1-(4-Bromophenyl)ethane-1,2-diylidene]bis(1,3-benzodithiole) (10e)

Yellow crystals; yield: 66%; mp 206.5-207.5 ˚C.

IR (KBr): 3058 (s), 2928 (s), 2804 (m), 1652 (s), 1557 (s), 1507 (s), 1472 (s), 1433 (s), 1387 (s), 1258 (m), 1161 (m), 1116 (s), 1063 (s), 1009 (s), 927 (s), 819 (s), 740 (s), 675 (m), 603 cm-¹ (s).

¹H NMR (CDCl3): δ = 7.59-7.55 (m, 2 Harom), 7.29-7.21 (m, 3 Harom), 7.16-6.97 (m, 7 Harom), 6.17 (s, 1 H, CH=C).

¹³C NMR (CDCl3): δ = 136.5, 136.2, 134.6, 133.3 (C2, C2′, C=CS2, Carom), 132.3, 131.6 (CHarom), 127.7, 125.9, 125.7, 125.6, 125.4, 122.3, 121.6, 120.9, 112.1 (CHarom, CH=C).

MS (EI): m/z (%) = 485 ([M]+, 100).

Anal. Calcd for C22H13BrS4 (485.5026): C, 54.43; H, 2.70. Found: C, 54.14; H, 2.76%

1,2-Diaryl-1,2-bis(1,3-benzodithiol-2-ylidene)ethanes 7c,d and 2,2′,2′′,2′′′-(1,4-diarylbutane-1,2,3,4-tetraylidene)tetrakis(1,3-benzodithioles) 11b-d; General Procedures

Method a: A sample of the dithiafulvene 6 (0.1 mmol) in CHCl3 (20 mL) was stirred at r.t. under sunlight for 3-18 h. The soln was concentrated under vacuum and the residue was chromatographed (silica gel, hexane-CH2Cl2) to give the corresponding π-extended tetrathiafulvalenes (Tables  [¹] and  [²] ).

Method b: A sample of the dithiafulvene 6 or 10 (0.1 mmol) in CH2Cl2 (20 mL) was stirred in a UV reactor at r.t. under UV irradiation for 3-18 h. The soln was concentrated under vacuum and the residue was chromatographed (silica gel, hexane-CH2Cl2) to afford the corresponding π-extended tetrathiafulvalenes (Tables  [¹] and  [²] ).

Method c: To a soln of the dithiafulvene 6a,b,d,e, 10a,d,e (100 mg) in CH2Cl2 (20 mL) under a stream of argon, I2 (3 mmol) was added and the mixture was heated to reflux for 8 h. Then, excess Na2S2O4 (0.5 g) was added. The mixture was refluxed overnight and allowed to reach r.t. After filtration of the suspension, the filtrate was washed with H2O (2 × 50 mL) and dried (MgSO4); the solvent was removed under vacuum and the extended TTFs 7b,d and 11a,d,e were purified by column chromatography (silica gel, hexane-CH2Cl2).

Method d: To a stirred soln of the dithiafulvene (0.10 mmol) in anhyd Et2O (25 mL) under argon at r.t. was added anhyd HCl (0.1 mL in anhyd Et2O) and the mixture was stirred for 24 h. The solvent was evaporated and the residue chromatographed (silica gel, hexane-CH2Cl2) to afford the corresponding chalcogenofulvalenes 7 and 11 (Tables  [¹] and  [²] ).

1,2-Bis(1,3-benzodithiol-2-ylidene)-1,2-bis(ferrocenyl)ethane (7c)

Dark red crystals; yield: 50% (method a); mp (dec).

IR (KBr): 3055 (w), 2968 (w), 2814 (w), 1636 (s), 1534 (s), 1440 (s), 1383 (s), 1253 (s), 1159 (m), 1108 (s), 1043 (m), 999 (m), 924 (s), 821 (s), 734 (s), 676 cm-¹ (m).

¹H NMR (CDCl3): δ = 7.34 (m, 2 Harom), 7.22-7.20 (m, 2 Harom), 7.13-7.09 (m, 4 Harom), 4.55 (m, 2 Hferrocene), 4.45 (m, 2 Hferrocene), 4.28 (s, 10 Hferrocene), 4.21 (m, 4 Hferrocene).

¹³C NMR (CDCl3): δ = 137.5, 136.4, 130.7, 123.6 (C1, C2, 2 C=CS2, Carom), 125.5, 125.1, 122.5, 121.2 (CHarom), 83.9 (Cferrocene), 69.4, 68.0, 67.9, 67.7, 65.9 (CHferrocene).

MS (EI): m/z (%) = 698 ([M]+, 100).

MS (FAB): m/z (%) = 698 ([M]+, 100).

Anal. Calcd for C36H26Fe2S4 (698.5314): C, 61.90; H, 3.75. Found: C, 62.60; H, 4.60%

1,2-Bis(1,3-benzodithiol-2-ylidene)-1,2-bis[4-(ferrocenyl)phenyl)]ethane (7d)

Chromatography (silica gel, hexane-CHCl3, 1:1) gave orange crystals; yield: 23% (method a), 60% (method c).

IR (CHCl3): 3091 (m), 3013 (m), 2924 (m), 2854 (m), 1603 (w), 1571 (m), 1528 (s), 1441 (s), 1383 (m), 1281w (s), 1215 (s), 1107 (s), 1073 (s), 927 (w), 887 (w), 823 (s), 756 cm-¹ (s).

¹H NMR (CDCl3): δ = 7.49 (m, 8 Harom), 7.24-7.17 (m, 4 Harom), 7.12-7.06 (m, 4 Harom), 4.61 (s, 4 Hferrocene), 4.30 (s, 4 Hferrocene), 4.05 (s, 10 Hferrocene).

¹³C NMR (CDCl3): δ = 139.6, 138.1, 136.7, 136.3, 126.3 (C1, C2, 2 C=CS2, Carom), 128.3, 126.9, 125.7, 125.5, 121.6, 121.2 (CHarom), 85.3 (Cferrocene), 69.7, 69.0, 66.5 (CHferrocene).

MS (FAB): m/z (%) = 850 ([M]+, 8).

Anal. Calcd for C48H34Fe2S4 (850.7336): C, 67.77; H, 4.03. Found: C, 66.98; H, 4.12.

2,2′,2′′,2′′′-[1,4-Bis(4-methoxyphenyl)butane-1,2,3,4-tetraylid­ene]tetrakis(1,3-benzodithiole) (11b)

Chromatography (silica gel, hexane-CH2Cl2, 1:1); yellow crystals; yield: 40% (method a); mp >300 ˚C.

IR (KBr): 3051 (m), 2923 (m), 2838 (w), 1602 (s), 1566 (m), 1506 (s), 1453 (s), 1385 (s), 1297 (m), 1245 (s), 1175 (s), 1118, 1026 (s), 908 (s), 826 (s), 734 (s), 676 cm-¹ (m).

¹H NMR (CDCl3): δ = 7.35 (m, 4 Harom), 7.25 (m, 8 Harom), 7.10 (m, 8 Harom), 6.78 (m, 4 Harom), 3.79 (s, 6 H, OCH3).

¹³C NMR (CDCl3): δ = 137.7, 128.7, 125.8, 125.7, 121.8, 121.3, 120.8, 114.4, 114.1 (C1, C2, 2 C=CS2, Carom, CHarom), 55.4 (OCH3).

MS (EI): m/z (%) = 870 ([M]+, dec.).

MS (FAB): m/z (%) = 870 ([M]+, 12).

Anal. Calcd for C46H30O2S8 (871.2492): C, 63.41; H, 3.47. Found: C, 63.22; H, 3.99.

2,2′,2′′,2′′′-[1,4-Bis(ferrocenyl)butane-1,2,3,4-tetraylidene]tetrakis(1,3-benzodithiole) (11c)

Chromatography (silica gel, hexane-CHCl3, 2:1); dark red crystals; yield: 37% (method a); mp (dec).

IR (CHCl3): 3021 (m), 2922 (m), 2854 (w), 1542 (m), 1437 (s), 1384 (s), 1262 (w), 1215 (s), 1091 (s), 923 (w), 756 (s), 670 cm-¹ (s).

¹H NMR (CDCl3): δ = 7.61-7.56 (m, 4 Harom), 7.36-7.30 (m, 4 Harom), 7.24 (m, 4 Harom), 7.04 (m, 4 Harom), 4.89 (m, 2 Hferrocene), 4.77 (m, 4 Hferrocene), 4.50 (t, 2 Hferrocene), 4.26 (s, 10 Hferrocene).

MS (ESI): m/z (%) = 1094 ([M + 67], 6), 566 ([M - 461], 100).

Anal. Calcd for C52H34Fe2S8 (1027.0364): C, 60.81; H, 3.34. Found: C, 60.46; H, 3.52.

2,2′,2′′,2′′′-{1,4-Bis[4-(ferrocenyl)phenyl]butane-1,2,3,4-tetra­ylidene}tetrakis(1,3-benzodithiole) (11d)

Chromatography (silica gel, hexane-CH2Cl2, 3:1); dark red crystals; yield: 45% (method a), 0% (method b); 28% (method c); mp 164-165 ˚C.

IR (KBr): 3060 (m), 3011 (s), 2997 (s), 2858 (s), 1670 (s), 1574 (m), 1527 (m), 1444 (s), 1381 (m), 1262 (m), 1215 (s), 1116 (s), 1013 (s), 925 (m), 872 (s), 823 (s), 755 (s), 670 cm-¹ (m).

¹H NMR (CDCl3): δ = 7.55 (m, 4 Harom), 7.30 (m, 8 Harom), 7.20-6.9 (m, 12 Harom), 4.74 (t, J = 3 Hz, 4 Hferrocene), 4.39 (t, J = 3 Hz, 4 Hferrocene­), 4.06 (s, 10 Hferrocene).

MS (EI): m/z (%) = 648 ([M - 530], 28), 590 ([M - 589], 100).

Anal. Calcd for C64H42Fe2S8 (1179.2283): C, 65.19; H, 3.59. Found: C, 65.35; H, 3.27.

Acknowledgment

We thank the Fonds der Chemischen Industrie and gratefully acknowledge­ the Alexander von Humboldt Stiftung for supporting this work by a Georg-Forster fellowship for A.A.O.S.

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Figure 1 Tetrathiafulvalenes [for 1a (TTF), X = S and R¹-R4 = H] and tetraselenafulvalenes (1b, X = Se)

Figure 2 π-Extended tetrathiafulvalenes

Scheme 1 Synthesis of thiafulvenes 6a-e

Figure 3 π-Extended tetrathiafulvalenes and nitrofulvene 8

Scheme 2 Synthesis of extended tetrathiafulvalenes 10a-e