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Synthesis and electrochemical properties of bis(3,4-furyldimethylthio)tetrathiafulvalene and other tetrathiafulvalene donors with eight-membered heterocycles
S " nTIHTilIE I I T ILS ELSEVIER
Synthetic Metals 96 (1998) 205-207
Synthesis and electrochemical properties of bis(3,4-furyldimethylthio) tetrathiafulvalene and other tetrathiafulvalene donors with eight-membered heterocycles Ronald L. Meline, In Tae Kim, Sanjay Basak, Ronald L. Elsenbaumer * Department of Chemistry and Biochemistry, The University of Texas at Arlington, Arlington, TX 76019, USA Received 27 January 1998; accepted 18 May 1998
Abstract
Bis(3,4-furyldimethytthio)tetrathiafulvalene, bis(but-2-ene-l,4-dithio)tetrathiafulvalene and bis(2,3-dimethylbut-2-ene-l,4-dithio)tetrathiafulvalene are synthesized in high yield from tetrakis(cyanoethylthio)tetrathiafulvalene and primary alkyl halides. Electrochemical properties are compared and the new donors are related to analogous quasi-one-dimensionalorganic metals. © 1998 Elsevier Science S.A. All rights reserved. Ke3words: Tetrathiafulvalene; Synthesis; Electrochemical properties
1. Introduction
Organic metals based on radical cation salts of tetrathiafulvalene (TrF, 1) and its derivatives have received much attention in the past two decades [ 1]. Although highly conductive, radical cation salts of TTF are nearly one dimensional in character, and do not exhibit superconductive properties owing to a phase transition (Peierls distortion) upon cooling which converts the metallic state to an insulating one [2]. The synthesis of quasi-two-dimensional systems based on TrF, in particular bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF, 2) permitted great progress to be made in the design of organic metals able to suppress a low temperature metal-insulator transition and thereby exhibit superconductivity [ 3 ]. BEDT-TTF has eight highly polarizable chalcogen atoms on its periphery. Such systems in the crystalline solid state are characterized by short S-S intermolecular contacts within the stacks and also short distances between neighboring stacks. Along these lines, more recently, even higher dimensional analogues of dibenzotetrathiafulvalene (DBTrF, 3, the first known tetrathiafulvalene) have been synthesized and characterized; for example, bis (oxylylphenyldithio)tetrathiafulvalene(4) [4,5] (Scheme 1). An alternative to extended donors such as 2 and 4 with eight chalcogen atoms has been the annelation of TIT with * Corresponding author. Tel.: + 1 817 272 3809; fax: + i 817 272 3808;
e-mai~:elsen®meead.uta.edu
S I S~
3 S
4 S
~
~S
5a, G=S fib, G=O 5c, G=Se 5d, G=NH
S
S
S'-'-
641,G=S Cob,G=O 6¢, G=Se Cod,G=NH
Scheme 1.
five-membered chalcogen heterocycles first demonstrated by Cowan and co-workers [6] with the synthesis of thiopheneannelated TTF (5a). This system is characterized by having six chalcogen atoms on its periphery, thereby increasing the conduction dimensionality of TIT, although it does exhibit a higher electrochemical oxidation potential than TTF. Aside from thiophene (Sa) [6-8], selenophene (Se) [9], pyrrole (5d) [ 10] and most recently furan-annelated donors (DFTTF, 5b) [ 11] have been prepared. Among these, only pyrrole annelated to TIT plays a role in improving the donor properties of the parent TTF. 5a, 5b, 5c, and 5d have not formed superconductive charge transfer complexes. A conceivable next step in this study would be to synthesize and compare heterocycle functionalized bis(dithio)TIT donors (6a, 6b, 6c). Such donors would contain ten chalcogen atoms
0379-6779/98/$ - see front matter © 1998 Elsevier Science S.A. All rights reserved.
PIIS0379-6779(98)00089-7
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206
R.L. Meline et at./Synthetic Metals 96 (1998) 205-207
on their periphery and may improve the redox properties and/ or dimensionality of the TTF donor.
N C"--~S,,,~. s
S.....~/Sf--~qN
7
2. Results and discussion
Building on this concept, we have synthesized bis(3,4furytdimethylthio)tetrathiafulvalene (6b) from tetrakis(cyanoethylthio)tetrathiafulvalene (7) and 3,4-bis(chloromethyt)furan (8). Compound 4, bis(but-2-ene-l,4dithio)tetrathiafulvalene (10) and bis(2,3-dimethylbut-2ene- 1,4-dithio) tetrathiafulvalene (11) were also prepared for electrochemical comparisons using the same method (Scheme 2). Alternatively, 6b can be made from standard coupling methods (trialkylphosphite/heat) of thioketone 9, albeit in far lower yield (Scheme 2). Compound 9 is useful for characterization purposes due its solubility as compared to 6b. Likewise 10 and 11 are available from thioketones 12 and 13, respectively (Scheme 3). It is noted that 6b, 10 and 11 (like 4) are substituted T I T donors containing eightmembered dithiane heterocycles. Six-membered dithiane heterocyles without methyl spacers would be expected to have a greater effect on the redox properties of the donors, but bis (phenyldithio) tetrathiafulvalene [ 12] has redox properties similar to 4. A comparison between 3 and 4 and between 5b and 6b is valid and invariably informative. As expected, the cyclic voltammograms of the new donors 6b, 10 and 11, as well as the known donor 4, exhibit two fully reversible one-electron oxidation waves corresponding to the generation of radical cation and dication states as summarized in Table 1. A comparison of oxidation potentials shows that the nature of the substituent eight-membered heterocycle does not seem to affect the redox properties of his (dithio) tetrathiafulvalenes. In addition, it is noted that 6b may provide a precursor to other donors due to the rich chemistry afforded by the functionalization of the furan groups [ll].
-s o 1) 8 NaOEt 2) " ' - ~ x 2 RflJ~X
As
-
10 R : H 11 R=CHs S
1) 8 NaOEt 2
S
s
S
6b
a
8
Scheme 2. o
sNZsp S
.S~Ph
14
14
14
O
1) 2 NaOEt
2) {'~.,---~,
v
~-s
s
s
1) 2 NaOEt K,]~ s-"~s ~=s 12 R=H
2) R ~ x
HEAT
P,O-,3( FI~ 10, 11 HEAT
13 R = CHa
1) 2 NaOEt 14
2)
~SNIs. ~ ~---s
,.
o
o/'~'TA~t
s
s"~=
P(OR)3 6b HEAT
g
8
Scheme 3. Table i Oxidation peak potentials (V) a
3. Experimental
Donor
First
Second
cis-l,4-Dichloro-2-butene [13], (Z)-l,4-dibromo-2,3dimethyl-2-butene [ 14,15 ], 3,4-bis (chloromethyl) furan (8) [16], dibenzoyl dimercaptoisotrithione (dibenzoyl-DMIT, 14) [ 17] and tetrakis(cyanoethylthio)tetrathiafulvalene (7) [ 18 ] were prepared by published methods. THF was distilled over Na/benzophenone prior to use. Uncorrected melting points were obtained from Mel-Temp 2 apparatus. NMR spectra were recorded with a Bruker MSL 300 and mass spectra were obtained from a Finnegan Mat TSQ 70. Elemental analyses were determined directly for each element.
2 4 6b 10 11
0.55 0.60 0.60 0.59 0.57
0.87 0.94 0.92 0.93 0.92
3.1.4,5-(2,3-Dimethyl-2-butenedithio)-l,3-dithiole-2-thione (13) Sodium (0.5 g, 21.7 retool) was suspended in 30 ml of dry methanol in a 100 ml round-bottomed flask under N2.
-' 4
~Pt electrodes,PhNOff0.1M n-Bu4NCLO4vs. Ag/AgCI (KC1),scanrate 100 mV/s. After all the sodium had reacted, dibenzoyl-DMIT [15] (3.25 g, 8 mmol) was added at once giving a purple solution of disodium DMIT. After 30 min, cis-1,4-dichloro-2-butene (2 g, 8.26 mmol) was slowly syringed into the flask forming a yellow precipitate. The precipitate was collected on a glasssintered funnel and washed with water, methanol and then air dried to give 1.94 g (87%) of a yellow powder; m.p. 110115°C (dec.). IH NMR (CDC13): 1,78(s), 3.79(s). 13C
R.L. Meline et at. / Synthetic Metals 96 (1998) 205-207
NMR (CDC13): 19.8, 39.9, 128.9, 138.5, 212.3. M/z 278 (M+). Anal. Calc.: C, 38.81; H, 3.62; S, 57.57. Found: C, 38.97; H, 3.63; S, 57.41%.
3.2. 4,5-(3,4-Dimethylfi¢randithio)-l,3-dithiole-2-thione (9) Disodium DMIT was prepared exactly as for 13, then 8 [ 16] ( 1.37 g, 8.3 mmol) was dissolved in 10 ml of Tt-IF and slowly syringed into the reaction flask forming a yellow precipitate. The precipitate was collected on a glass-sintered funnel and washed with water, methanol and finally ether to give 2.11 g (91%) of a yellow powder; m.p. 177-180°C. ~H NMR (CDC13): 4.16(s), 7.35(s). 13C NMR (C6DsNO2/ Cr(acac)3): 30.0, 118.5, 119.5, 141.7, 211.6. M/z 290 (M+). Anal. Calc.: C, 37.21; H, 2.08; O, 5.51; S, 55.20. Found: C, 37.29; H, 2.06; O, 5.65; S, 55.31%. 3.3. B is( 2,3-dimethy lbut- 2-ene- l ,4-dithio )tetrathiafulvaIene
(10) Sodium (0.26 g, 11.3 mmol) was added to 30 ml of dry methanol in a 100 ml round-bottomed flask under Na. After all the sodium had reacted, 7 (0.75 g, 1.38 mmol) was introduced into the flask at once. After 8 h, all of 7 had converted into tetrathiafulvalene tetrathiole sodium salt (TTFTr) as monitored by TLC. cis-l,4-Dichloro-2-butene (0.37 g, 2.96 mmol) was slowly added to the flask. An orange precipitate soon formed, and was collected on a glass-sintered funnel and washed with water, methanol and ether to give 0.56 g (93%) of a burnt orange powder; m.p. 167-170°C. 1H NMR (CDC13) : 3.85(s), 5.87(s). M / z 4 3 6 (M+). Anal. Calc.: C, 38.50; H, 2.77; S, 58.73. Found: C, 38.48; H, 2.83; S, 58.55%. 3.4. Bis( 2,3-dimethylbut-2-ene- l ,4-dithio )tetrathiafidvalene
(11) Trb-TI' was prepared exactly as for 10, then (Z)-I,4dibromo-2,3-dimethyl-2-butene [13] (0.73 g, 3.02 mmol) was slowly added to the reaction flask. An orange precipitate soon formed, and was purified in the same manner as 10 to give 0.62 g (91%) of a bright orange powder; m.p. 195200°C (dec.). ~H NMR (CDCl3): 1.83(s), 3.68(s). M / z 492 (M + ). Anal. Calc.: C, 43.86; H, 4.09; S, 52.05. Found: C, 43.77; H, 4.09; S, 52.11%.
3.5. Bis(3,4-fivyldimethylthio)tetrathiafulvalene (6b ) TITTT was prepared exactly as for 10, then 3,4bis(chloromethyl)furan (0.50 g, 3.03 mmol) was dissolved
207
in 10 ml of THF and then slowly syringed into the reaction flask. A bright red precipitate soon formed, and was purified in the same manner as 10 to give 0.67 g (94%) of a bright red-orange powder; m.p. 185-188°C (dec.). IH NMR (CDC13) : 4.04(s), 7.33 (s). M/z 516 (M + ). Anal. Calc.: C, 41.83; H, 2.34; O, 6.19; S, 49.64. Found: C, 41.76; H, 2.44; O, 6.18; S, 49.57%.
Acknowledgements The authors would like to acknowledge AFOSR for financial support under Grant F49620-92-J-0516.
References [ 1 ] J.M. Williams, J.R. Ferraro, R.J. Thorn, K.D. Carlson, U. Geiser, H.H. Wang, A.M. Kini, H. Whangbo, Organic Superconductors, PrenticeHall, Englewood Cliffs, NJ, 1992. [2] M. Adam, K. MtiIlen, Adv. Mater. 6 (1994) 439. [3] M. Mizuno, A.F. Garito, M.P. Cava, J. Chem. Soc., Chem Commun. (1978) 18. [4] L.M. Goldenberg, R.N. Lyubovskaya, K/aim. Geterositd. Soedin. 6 (1986) 855. [5] J. RtShrieh, K. Mtillen, J. Org. Chem. 57 (1992) 2374. [6] P. Shu, L. Chiang, T. Emge, D. Holt, T, Kistenmacher, M. Lee, J. Stokes, T. Poehler, A. Bloch, D. Cowan, J. Chem. Soc., Chem. Commun. (i981) 920. [7] L.-Y. Chiang, P. Shu, D. Holt, D. Cowan, J. Org. Chem, 48 (1983) 4713. [8] N. Santalo, J. Veciana, C. Rovira, K. Molins, C. Miravitlles, J. Claret, Synth. Met. 4i--43 (1991) 2205. [9] R. Ketcham, A.-B. H~Srnfeldt,S. Gronowitz, J. Org. Chem. 49 (1984) 1117. [ I0] W. Chen, M.P. Cava, M.A. Takassi, R.M. Metzger, J. Am. Chem. Soc. 110 (1988) 7903. [ I 1] Y. Siquot, P. Frtre, T. Nozdryn, J. Cousseau, M. Sall6, M. Jubault, J. Orduna, J. Gaffn, A. Gorgues, Tetrahedron Lett. 38 (1997) 1919. [ I2] H. Mtilter, H.P. Fritz, R. Nemetshek, R. Hacld, W. Biberacher, C.-P. Heidmann, Z. Naturforsch., Teil B 47 (1992) 718. [ 13] J.M. Bobbitt, L.H. Amundsen, R.T. Steiner, J. Org. Chem. 25 (1960) 2230. [14] N. Frederikson, R.B. Jensen, S.E. JOrgensen, J.U.R. Nielsen, L. NOrskov, G. Schroll, Acta Claim. Scan&, Ser. B 31 (1977) 694. [ 15] P. MtilIer, D. Rodriquez, Hetv. Chem. Acta 68 (1985) 975. [ 16] D.I. Rawson, B.K. Carpenter, H.M.R. Hoffmann, J. Am. Chem. Soc. 101 (1979) 1786. [ 17] N. Svenstrup, J. Becher, Synthesis (1995) 215. [18] N. Svenstrnp, K.M. Rasmussen, T.K. Hansen, J. Becher, Synthesis (1994) 809.
Synthetic Metals 96 (1998) 205-207
Synthesis and electrochemical properties of bis(3,4-furyldimethylthio) tetrathiafulvalene and other tetrathiafulvalene donors with eight-membered heterocycles Ronald L. Meline, In Tae Kim, Sanjay Basak, Ronald L. Elsenbaumer * Department of Chemistry and Biochemistry, The University of Texas at Arlington, Arlington, TX 76019, USA Received 27 January 1998; accepted 18 May 1998
Abstract
Bis(3,4-furyldimethytthio)tetrathiafulvalene, bis(but-2-ene-l,4-dithio)tetrathiafulvalene and bis(2,3-dimethylbut-2-ene-l,4-dithio)tetrathiafulvalene are synthesized in high yield from tetrakis(cyanoethylthio)tetrathiafulvalene and primary alkyl halides. Electrochemical properties are compared and the new donors are related to analogous quasi-one-dimensionalorganic metals. © 1998 Elsevier Science S.A. All rights reserved. Ke3words: Tetrathiafulvalene; Synthesis; Electrochemical properties
1. Introduction
Organic metals based on radical cation salts of tetrathiafulvalene (TrF, 1) and its derivatives have received much attention in the past two decades [ 1]. Although highly conductive, radical cation salts of TTF are nearly one dimensional in character, and do not exhibit superconductive properties owing to a phase transition (Peierls distortion) upon cooling which converts the metallic state to an insulating one [2]. The synthesis of quasi-two-dimensional systems based on TrF, in particular bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF, 2) permitted great progress to be made in the design of organic metals able to suppress a low temperature metal-insulator transition and thereby exhibit superconductivity [ 3 ]. BEDT-TTF has eight highly polarizable chalcogen atoms on its periphery. Such systems in the crystalline solid state are characterized by short S-S intermolecular contacts within the stacks and also short distances between neighboring stacks. Along these lines, more recently, even higher dimensional analogues of dibenzotetrathiafulvalene (DBTrF, 3, the first known tetrathiafulvalene) have been synthesized and characterized; for example, bis (oxylylphenyldithio)tetrathiafulvalene(4) [4,5] (Scheme 1). An alternative to extended donors such as 2 and 4 with eight chalcogen atoms has been the annelation of TIT with * Corresponding author. Tel.: + 1 817 272 3809; fax: + i 817 272 3808;
e-mai~:elsen®meead.uta.edu
S I S~
3 S
4 S
~
~S
5a, G=S fib, G=O 5c, G=Se 5d, G=NH
S
S
S'-'-
641,G=S Cob,G=O 6¢, G=Se Cod,G=NH
Scheme 1.
five-membered chalcogen heterocycles first demonstrated by Cowan and co-workers [6] with the synthesis of thiopheneannelated TTF (5a). This system is characterized by having six chalcogen atoms on its periphery, thereby increasing the conduction dimensionality of TIT, although it does exhibit a higher electrochemical oxidation potential than TTF. Aside from thiophene (Sa) [6-8], selenophene (Se) [9], pyrrole (5d) [ 10] and most recently furan-annelated donors (DFTTF, 5b) [ 11] have been prepared. Among these, only pyrrole annelated to TIT plays a role in improving the donor properties of the parent TTF. 5a, 5b, 5c, and 5d have not formed superconductive charge transfer complexes. A conceivable next step in this study would be to synthesize and compare heterocycle functionalized bis(dithio)TIT donors (6a, 6b, 6c). Such donors would contain ten chalcogen atoms
0379-6779/98/$ - see front matter © 1998 Elsevier Science S.A. All rights reserved.
PIIS0379-6779(98)00089-7
2
206
R.L. Meline et at./Synthetic Metals 96 (1998) 205-207
on their periphery and may improve the redox properties and/ or dimensionality of the TTF donor.
N C"--~S,,,~. s
S.....~/Sf--~qN
7
2. Results and discussion
Building on this concept, we have synthesized bis(3,4furytdimethylthio)tetrathiafulvalene (6b) from tetrakis(cyanoethylthio)tetrathiafulvalene (7) and 3,4-bis(chloromethyt)furan (8). Compound 4, bis(but-2-ene-l,4dithio)tetrathiafulvalene (10) and bis(2,3-dimethylbut-2ene- 1,4-dithio) tetrathiafulvalene (11) were also prepared for electrochemical comparisons using the same method (Scheme 2). Alternatively, 6b can be made from standard coupling methods (trialkylphosphite/heat) of thioketone 9, albeit in far lower yield (Scheme 2). Compound 9 is useful for characterization purposes due its solubility as compared to 6b. Likewise 10 and 11 are available from thioketones 12 and 13, respectively (Scheme 3). It is noted that 6b, 10 and 11 (like 4) are substituted T I T donors containing eightmembered dithiane heterocycles. Six-membered dithiane heterocyles without methyl spacers would be expected to have a greater effect on the redox properties of the donors, but bis (phenyldithio) tetrathiafulvalene [ 12] has redox properties similar to 4. A comparison between 3 and 4 and between 5b and 6b is valid and invariably informative. As expected, the cyclic voltammograms of the new donors 6b, 10 and 11, as well as the known donor 4, exhibit two fully reversible one-electron oxidation waves corresponding to the generation of radical cation and dication states as summarized in Table 1. A comparison of oxidation potentials shows that the nature of the substituent eight-membered heterocycle does not seem to affect the redox properties of his (dithio) tetrathiafulvalenes. In addition, it is noted that 6b may provide a precursor to other donors due to the rich chemistry afforded by the functionalization of the furan groups [ll].
-s o 1) 8 NaOEt 2) " ' - ~ x 2 RflJ~X
As
-
10 R : H 11 R=CHs S
1) 8 NaOEt 2
S
s
S
6b
a
8
Scheme 2. o
sNZsp S
.S~Ph
14
14
14
O
1) 2 NaOEt
2) {'~.,---~,
v
~-s
s
s
1) 2 NaOEt K,]~ s-"~s ~=s 12 R=H
2) R ~ x
HEAT
P,O-,3( FI~ 10, 11 HEAT
13 R = CHa
1) 2 NaOEt 14
2)
~SNIs. ~ ~---s
,.
o
o/'~'TA~t
s
s"~=
P(OR)3 6b HEAT
g
8
Scheme 3. Table i Oxidation peak potentials (V) a
3. Experimental
Donor
First
Second
cis-l,4-Dichloro-2-butene [13], (Z)-l,4-dibromo-2,3dimethyl-2-butene [ 14,15 ], 3,4-bis (chloromethyl) furan (8) [16], dibenzoyl dimercaptoisotrithione (dibenzoyl-DMIT, 14) [ 17] and tetrakis(cyanoethylthio)tetrathiafulvalene (7) [ 18 ] were prepared by published methods. THF was distilled over Na/benzophenone prior to use. Uncorrected melting points were obtained from Mel-Temp 2 apparatus. NMR spectra were recorded with a Bruker MSL 300 and mass spectra were obtained from a Finnegan Mat TSQ 70. Elemental analyses were determined directly for each element.
2 4 6b 10 11
0.55 0.60 0.60 0.59 0.57
0.87 0.94 0.92 0.93 0.92
3.1.4,5-(2,3-Dimethyl-2-butenedithio)-l,3-dithiole-2-thione (13) Sodium (0.5 g, 21.7 retool) was suspended in 30 ml of dry methanol in a 100 ml round-bottomed flask under N2.
-' 4
~Pt electrodes,PhNOff0.1M n-Bu4NCLO4vs. Ag/AgCI (KC1),scanrate 100 mV/s. After all the sodium had reacted, dibenzoyl-DMIT [15] (3.25 g, 8 mmol) was added at once giving a purple solution of disodium DMIT. After 30 min, cis-1,4-dichloro-2-butene (2 g, 8.26 mmol) was slowly syringed into the flask forming a yellow precipitate. The precipitate was collected on a glasssintered funnel and washed with water, methanol and then air dried to give 1.94 g (87%) of a yellow powder; m.p. 110115°C (dec.). IH NMR (CDC13): 1,78(s), 3.79(s). 13C
R.L. Meline et at. / Synthetic Metals 96 (1998) 205-207
NMR (CDC13): 19.8, 39.9, 128.9, 138.5, 212.3. M/z 278 (M+). Anal. Calc.: C, 38.81; H, 3.62; S, 57.57. Found: C, 38.97; H, 3.63; S, 57.41%.
3.2. 4,5-(3,4-Dimethylfi¢randithio)-l,3-dithiole-2-thione (9) Disodium DMIT was prepared exactly as for 13, then 8 [ 16] ( 1.37 g, 8.3 mmol) was dissolved in 10 ml of Tt-IF and slowly syringed into the reaction flask forming a yellow precipitate. The precipitate was collected on a glass-sintered funnel and washed with water, methanol and finally ether to give 2.11 g (91%) of a yellow powder; m.p. 177-180°C. ~H NMR (CDC13): 4.16(s), 7.35(s). 13C NMR (C6DsNO2/ Cr(acac)3): 30.0, 118.5, 119.5, 141.7, 211.6. M/z 290 (M+). Anal. Calc.: C, 37.21; H, 2.08; O, 5.51; S, 55.20. Found: C, 37.29; H, 2.06; O, 5.65; S, 55.31%. 3.3. B is( 2,3-dimethy lbut- 2-ene- l ,4-dithio )tetrathiafulvaIene
(10) Sodium (0.26 g, 11.3 mmol) was added to 30 ml of dry methanol in a 100 ml round-bottomed flask under Na. After all the sodium had reacted, 7 (0.75 g, 1.38 mmol) was introduced into the flask at once. After 8 h, all of 7 had converted into tetrathiafulvalene tetrathiole sodium salt (TTFTr) as monitored by TLC. cis-l,4-Dichloro-2-butene (0.37 g, 2.96 mmol) was slowly added to the flask. An orange precipitate soon formed, and was collected on a glass-sintered funnel and washed with water, methanol and ether to give 0.56 g (93%) of a burnt orange powder; m.p. 167-170°C. 1H NMR (CDC13) : 3.85(s), 5.87(s). M / z 4 3 6 (M+). Anal. Calc.: C, 38.50; H, 2.77; S, 58.73. Found: C, 38.48; H, 2.83; S, 58.55%. 3.4. Bis( 2,3-dimethylbut-2-ene- l ,4-dithio )tetrathiafidvalene
(11) Trb-TI' was prepared exactly as for 10, then (Z)-I,4dibromo-2,3-dimethyl-2-butene [13] (0.73 g, 3.02 mmol) was slowly added to the reaction flask. An orange precipitate soon formed, and was purified in the same manner as 10 to give 0.62 g (91%) of a bright orange powder; m.p. 195200°C (dec.). ~H NMR (CDCl3): 1.83(s), 3.68(s). M / z 492 (M + ). Anal. Calc.: C, 43.86; H, 4.09; S, 52.05. Found: C, 43.77; H, 4.09; S, 52.11%.
3.5. Bis(3,4-fivyldimethylthio)tetrathiafulvalene (6b ) TITTT was prepared exactly as for 10, then 3,4bis(chloromethyl)furan (0.50 g, 3.03 mmol) was dissolved
207
in 10 ml of THF and then slowly syringed into the reaction flask. A bright red precipitate soon formed, and was purified in the same manner as 10 to give 0.67 g (94%) of a bright red-orange powder; m.p. 185-188°C (dec.). IH NMR (CDC13) : 4.04(s), 7.33 (s). M/z 516 (M + ). Anal. Calc.: C, 41.83; H, 2.34; O, 6.19; S, 49.64. Found: C, 41.76; H, 2.44; O, 6.18; S, 49.57%.
Acknowledgements The authors would like to acknowledge AFOSR for financial support under Grant F49620-92-J-0516.
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