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A new generation of giant analogs of tetrathiafulvalene (TTF): Bis-and tetrakis-(1,4-dithiafulvalenyl)-TTF
Synthetic Metals, 41-43 (1991) 2575-2578
2575
A NEW GENERATION OF GIANT ANALOGS OF TETRATHIAFULVALENE (TIT): BIS-
AND TETRAKIS-(1.4-Drlq-IIAFULVALENYL)-'ITF.
M. SALLE, A. GORGUES,* M. JUBAULT and Y. GOURIOU. Laboratoire de Synth~se Organique et d'Electrochimie (LSOE), Universit'6 d'Angers, 2 Bd Lavoisier, 49045 Angers Crdex, France.
ABSTRACT The synthesis of new highly extended sulfur enriched derivatives of TIT is reported and their remarquably ~-donating ability is demonstrated by cyclic voltammetry.
INTRODUCTION l~w-dimensional organic metals of the "Iq'F series often sustain metal-insulator instabilities at low temperature. These instabilities can be suppressed by chemical modifications of the TIT framework in order to increase the dimensionality of molecular conductors. Thus, the replacement of the sulfur atoms of ~ with bigger chalcogens such as selenium successfully led to the first organic superconductor [(TMTSF)2PF6] [1] which is quasi two-dimensional due to interstacks Se..Se contacts. Another way is a subtle functionalization of the TIT framework with outer thio substituents
in order to multiply the
S..S
intermolecular interactions,
as in
bis(ethylenedithio)tetrathiafulvalene(ET), which holds the Tc record of organic superconductors in the corresponding ET2Cu(NCS)2 salt [2]. Relative to this point, we now describe the synthesis of new highly extended, sulfur enriched ~-donors (1-3). RESULTS Our synthetic strategy to reach (1-3) (Scheme 1) involves a Wittig reaction in the last step, with the phosphoranes (W) and the corresponding polyaldehydes (9.11). The synthesis of the attractive tetraformyltetrathiafulvalene (TFVI'F) (9) starting from acetylene dicarbaldehyde mono-(diEt)acetal (4) [3] has previously been depicted by us [4]. The reaction of (4) with ethylenetrithio0379-6779/91/$3.50
© Elsevier Sequoia/Printed in The Netherlands
2576
carbonate affords the key intermediate (5); the new acetal-aldehydes (7-8) are prepared by a cross coupling of (5) with 1,3-dithiole-2-thione and ethylenetrithiocarbonate respectively, using octacarbonyldicobalt as coupling agent [5]. Subsequent acetals hydrolysis allows to reach the desired polyaldehydes (9-11). Twice and fourfold Wittig reactions with adequatly substituted (W) then produce the bis- and tetrakis- (1,4-dithiafulvalenyl)-TIT (1-3), as deeply coloured powders ( yields given in Table 1). The oxydation potentials of (1-3) obtained by cyclic voltammetry (except for (lc) which is ¢irtually insoluble in common organic solvents) are summarized in Table 2.
Yield (%) (la) (lb) (le) (2a) (3a)
70 65 73 82 70
Table 1.Yields of Wittig reactions.
(la) (lb) (2a) (3a) (TTF)
Elox/V
E2oxN
0.19 0.34 0.22 0.22 0.38
0.34 0.65 0.30 0.30 0.74
Solvent A B A A A
Table 2: Cyclic voltammetric data: Bu4nC104 (0.1M) 20°C, v s S.C.E., Pt electrode, scan rate 100 mV/sec Solvent A: N,N-Dimethylformamide B: 1,1,2-Trichloroethane
The new electron donors (1-3) exhibit two reversible oxidation reduction processes in the indicated solvents [6]. Their strong K-donor ability is beared out by remarquably low values of oxidation potentials relative to TTF ones, which can be explained by the extension of the x-system with the electron rich dithiole rings. Another important feature is the low value observed for the difference between ionization potentials, especially in the case of (2a) and (3a) (AEox=0,08V); these compounds have identical electrochemical behaviours, which may suggest that charges in oxydized states, are localized in the two common conjugated external 1,3-dithiole tings rather than on the central framework which differs from (2a) to (3a); thus the low value of AEox should be due to a stabilization of the dicationic state by a decreasing of the on-site coulombic repulsions, owing to existence of four sp2 carbon atoms between the two external dithiole rings. Compounds (1-3) react instantaneously with tetracyanoquinodirnethane in boiling solutions, to form black conducting powders of complexes [7]. We are now investigating the preparation of electrogenerated radical cation salts of (1-3). ACKNOWLEDGEMENTS We thank the ANVAR and the CNET de Lannion B for financial supports; M. S. is indebted to the CNRS and to the R6gion des Pays de la Loire for a grant.
2577
S
R
W, :
R
Wb R= C02Me W, R-R=(CH--CH)2J
Ra~ P
O-t0 I m
C
I
S....../CH(OEt)2 +
~
S
S
S
¢ y s , co~(co)~
(EtO)2CyScI.C / ~S~$~syCH(OEt)2"(3-10
, Co2(C0)8 ~-S
OH0\~ S
S ~ J CH(OEt)2
S..~/CHO
s,~s
~.~s
~s
~. s
s~=
1 a:R=H
b : R=CO2Me c : R-R=(CH=CI-~,
Scheme 1
< S ~ s ~ - S S~ .,CH(OEt)2
\
2 a : R=H
sy..
x
,/ 3 a : R=H
2578 REFERENCES I D. Jerome, A. Mazaud, M. Ribault and K. Bechgaard, L , ~ % ~ . . ~ ( 1 9 8 0 ) 95. 2 (a) H. Urayama, H. Yamochi, G. Saito, K. Nozawa, T. Sugano, M. Kinoshim, S. Sato, K. Oshima, A. Kawamoto and J. Tanaka, Chem. Lett..(1988) 55; (b) H. Urayama, H. Yamochi, G. S~dto, S. Sato, A. Kawamoto, J. Tanaka, T. Moil, Y. Maruy~na and H. Inokuchi, idem. 463. 3 A. Gorgues, D. Stephan, A. Belyasm/ne, A. Khanous and A. Le Coq, Te~'ahedron.46 (1990) 2817. 4 A. Gorgues, P. Ba~l and A. Le Coq, ~. Chem. Sot.. Chem. Commun.. (1983) 405. 5 G. Le Coustumer and Y. Mollier, idem, (1980) 38. 6 Although two reversible redox couples are observed for (lb) in 1,1,2-trichloroethane as solvent, the redox system is much more complicated when N,N-dimethylformamide is used. 7 Complexes conductivities have not been measured yet.
2575
A NEW GENERATION OF GIANT ANALOGS OF TETRATHIAFULVALENE (TIT): BIS-
AND TETRAKIS-(1.4-Drlq-IIAFULVALENYL)-'ITF.
M. SALLE, A. GORGUES,* M. JUBAULT and Y. GOURIOU. Laboratoire de Synth~se Organique et d'Electrochimie (LSOE), Universit'6 d'Angers, 2 Bd Lavoisier, 49045 Angers Crdex, France.
ABSTRACT The synthesis of new highly extended sulfur enriched derivatives of TIT is reported and their remarquably ~-donating ability is demonstrated by cyclic voltammetry.
INTRODUCTION l~w-dimensional organic metals of the "Iq'F series often sustain metal-insulator instabilities at low temperature. These instabilities can be suppressed by chemical modifications of the TIT framework in order to increase the dimensionality of molecular conductors. Thus, the replacement of the sulfur atoms of ~ with bigger chalcogens such as selenium successfully led to the first organic superconductor [(TMTSF)2PF6] [1] which is quasi two-dimensional due to interstacks Se..Se contacts. Another way is a subtle functionalization of the TIT framework with outer thio substituents
in order to multiply the
S..S
intermolecular interactions,
as in
bis(ethylenedithio)tetrathiafulvalene(ET), which holds the Tc record of organic superconductors in the corresponding ET2Cu(NCS)2 salt [2]. Relative to this point, we now describe the synthesis of new highly extended, sulfur enriched ~-donors (1-3). RESULTS Our synthetic strategy to reach (1-3) (Scheme 1) involves a Wittig reaction in the last step, with the phosphoranes (W) and the corresponding polyaldehydes (9.11). The synthesis of the attractive tetraformyltetrathiafulvalene (TFVI'F) (9) starting from acetylene dicarbaldehyde mono-(diEt)acetal (4) [3] has previously been depicted by us [4]. The reaction of (4) with ethylenetrithio0379-6779/91/$3.50
© Elsevier Sequoia/Printed in The Netherlands
2576
carbonate affords the key intermediate (5); the new acetal-aldehydes (7-8) are prepared by a cross coupling of (5) with 1,3-dithiole-2-thione and ethylenetrithiocarbonate respectively, using octacarbonyldicobalt as coupling agent [5]. Subsequent acetals hydrolysis allows to reach the desired polyaldehydes (9-11). Twice and fourfold Wittig reactions with adequatly substituted (W) then produce the bis- and tetrakis- (1,4-dithiafulvalenyl)-TIT (1-3), as deeply coloured powders ( yields given in Table 1). The oxydation potentials of (1-3) obtained by cyclic voltammetry (except for (lc) which is ¢irtually insoluble in common organic solvents) are summarized in Table 2.
Yield (%) (la) (lb) (le) (2a) (3a)
70 65 73 82 70
Table 1.Yields of Wittig reactions.
(la) (lb) (2a) (3a) (TTF)
Elox/V
E2oxN
0.19 0.34 0.22 0.22 0.38
0.34 0.65 0.30 0.30 0.74
Solvent A B A A A
Table 2: Cyclic voltammetric data: Bu4nC104 (0.1M) 20°C, v s S.C.E., Pt electrode, scan rate 100 mV/sec Solvent A: N,N-Dimethylformamide B: 1,1,2-Trichloroethane
The new electron donors (1-3) exhibit two reversible oxidation reduction processes in the indicated solvents [6]. Their strong K-donor ability is beared out by remarquably low values of oxidation potentials relative to TTF ones, which can be explained by the extension of the x-system with the electron rich dithiole rings. Another important feature is the low value observed for the difference between ionization potentials, especially in the case of (2a) and (3a) (AEox=0,08V); these compounds have identical electrochemical behaviours, which may suggest that charges in oxydized states, are localized in the two common conjugated external 1,3-dithiole tings rather than on the central framework which differs from (2a) to (3a); thus the low value of AEox should be due to a stabilization of the dicationic state by a decreasing of the on-site coulombic repulsions, owing to existence of four sp2 carbon atoms between the two external dithiole rings. Compounds (1-3) react instantaneously with tetracyanoquinodirnethane in boiling solutions, to form black conducting powders of complexes [7]. We are now investigating the preparation of electrogenerated radical cation salts of (1-3). ACKNOWLEDGEMENTS We thank the ANVAR and the CNET de Lannion B for financial supports; M. S. is indebted to the CNRS and to the R6gion des Pays de la Loire for a grant.
2577
S
R
W, :
R
Wb R= C02Me W, R-R=(CH--CH)2J
Ra~ P
O-t0 I m
C
I
S....../CH(OEt)2 +
~
S
S
S
¢ y s , co~(co)~
(EtO)2CyScI.C / ~S~$~syCH(OEt)2"(3-10
, Co2(C0)8 ~-S
OH0\~ S
S ~ J CH(OEt)2
S..~/CHO
s,~s
~.~s
~s
~. s
s~=
1 a:R=H
b : R=CO2Me c : R-R=(CH=CI-~,
Scheme 1
< S ~ s ~ - S S~ .,CH(OEt)2
\
2 a : R=H
sy..
x
,/ 3 a : R=H
2578 REFERENCES I D. Jerome, A. Mazaud, M. Ribault and K. Bechgaard, L , ~ % ~ . . ~ ( 1 9 8 0 ) 95. 2 (a) H. Urayama, H. Yamochi, G. Saito, K. Nozawa, T. Sugano, M. Kinoshim, S. Sato, K. Oshima, A. Kawamoto and J. Tanaka, Chem. Lett..(1988) 55; (b) H. Urayama, H. Yamochi, G. S~dto, S. Sato, A. Kawamoto, J. Tanaka, T. Moil, Y. Maruy~na and H. Inokuchi, idem. 463. 3 A. Gorgues, D. Stephan, A. Belyasm/ne, A. Khanous and A. Le Coq, Te~'ahedron.46 (1990) 2817. 4 A. Gorgues, P. Ba~l and A. Le Coq, ~. Chem. Sot.. Chem. Commun.. (1983) 405. 5 G. Le Coustumer and Y. Mollier, idem, (1980) 38. 6 Although two reversible redox couples are observed for (lb) in 1,1,2-trichloroethane as solvent, the redox system is much more complicated when N,N-dimethylformamide is used. 7 Complexes conductivities have not been measured yet.