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Synthesis and properties of the ttf donors with a five-membered cyclic o,o-, s,s-, or o, s-acetal
ELSEVIER
Synthetic Metals 102 (1999) 1701-1702
Synthesis and properties of the TTF donors with a five-membered cyclic O,O-, S,S-, or O,S-acetal J. Yamada’,* R. Okat, H. Anzai’, H. Nishikawa*, I. Ikemoto*, and K. Kikuchi* ‘Department of Material Science, Faculty of Science, Himeji Institute of Technology, 147.5-2 Kanaji, Kamigori-cho, Ako-gun, Hyogo 678-1297, Japan ‘Department of Chemistry, Faculty of Science, Tokyo Metropolitan University, Hachioji. Tokyo 192-0397, Japan Abstract Synthesis of the TIP (tetrathiafulvalene) donors with a 1,3-dioxolane, 1,3-dithiolane, or 1,3-oxathiolane ring (l-3) has been accomplished via (MeO)JP-promoted cross-coupling reaction of the corresponding new ketones (6-S) and thiones (9a-c). Although an X-ray diffraction analysis of the neutral 2a revealed that its molecular structure is nonplanar, its radical-cation salts with AuIi, BF4-, and AsFe- exhibited metallic conducting behavior. Keywords: 1.
Heterocycle
synthesis; Coupling
reactions; Organic conductors
Introduction
In the course of our search for the development of new molecular-based organic metals composed of the extended lTF donors by addition of heterocycles [l], we have found that the 1,3-dioxolane derivative of MET [methylenedithio(ethylenedithio)tetrathiafulvalene] (la) produces a metallic TCNQ (tetracyanoquinodimethane) complex even though the dioxolane ring is attached perpendicularly to the MET framework [lc]. Although this donor could be synthesized via the MesAl-mediated rearrangement reaction, its yield was relatively low [lc,d]. In addition, the replacement of the outer ring oxygen atom(s) in such a donor with the larger and more polarizable sulfur atom(s) might result in an enhancement of intermolecular SS interactions in the CT (charge-transfer)state. However, for example, the dithiolane analogue of la (2a) could not be obtained by the MesAl-promoted reaction of the corresponding tin-masked dithiolate with an ester since the analogous rearrangement as can be found in the synthesis of la did not take place [la,d]. In this paper, synthesis of the dioxolane derivatives la-d by employing a different synthetic route, and a synthetic approach to the construction of their dithiolane analogues 2a-d and the oxathiolane derivative of
la R-R = S(CH,),S 1 b R-R = SCH,S lcR=R=C02Me ldR=R=H
Ndp4
based on radical cation and/or anion salts
MET (3) are described. We also disclose the electrochemical properties of new compounds (lb, Za,b,d, and 3). the molecular structure of 2a by X-ray diffraction, and the conducting behavior of the 2a-based CT complex and salts. 2.
Synthesis
Our strategy for synthesizing l-3 was based on the (MeO)BP-promoted cross-coupling reaction, and to this end, the development of a synthetic method for preparation of new derivatives of 1,3-dithiol-2-one utilized for this reaction was necessitated. Exposure of the dioxane-fused ketone 5, prepared from tin dithiolate 4 and 2,3-dichloro-I ,4-dioxane in the presence of 2 equiv of BF3*OEt2 [la,d], to an excess of BF3*OEt2 (10 equiv) in CHCl3 at room temperature for one day induced isomerization of the bis-fused six-membered heterocycle to the five-membered biheterocycle, affording the dioxolane-appended ketone 6 in 80% yield together with trace amounts of 5. The ratio of 65 determined by ‘H-NMR was 46:l. Pure ketone 6 was obtainable by recrystallization from CH2C12-EtOH. Similarly, the use of 10 equiv of BF3*OEt2 in the reaction of 4 with dichlorodioxane under the same conditions as used for the isomerization of 5 furnished an 8:l
2a R-R = S(CH,),S 2b R-R = SCH2S
2cR=R=COzMe SdR=R=H
s==(I Sx
S 5
0379-6779/99/$ - see front matter 0 1999 Elsevier Science S.A. All rights resewed. PII: SO379-6779(98)00623-7
6X=Y=O 7X=Y=S 8X=O,Y=S
9a R-R = S(CH&S 9b R-R = SCH,S 9cR=R=C02Me
1702
J. Yamadu
et ul. I Synthetic
mixture of 6 and 5 in 89% yield. Further, the addition of l,2ethanedithiol in this isomerization reaction followed by stirring for two days enable us to obtain the dithiolane-added ketone 7 in 95% yield. While conversion of 5 into the oxathiolane-appended ketone 8 could not be effected by the BFJ-promoted reaction of 5 with 2-mercaptoethanol even under prolonged reaction time, the analogous reaction of 6 in CH2Cl2 for two days provided the desired product 8 in 40% yield. Cross-coupling synthesis of la-c, 2a-c, and 3 was carried out by reaction of the resulting ketones 6-8 with 2 equiv of thiones 9a-c using (Me0)3P as a phosphite reagent in toluene at 110 “C for 2 h (la, 80% yield; lb, 52% yield; lc, 96% yield; 2a, 94% yield; 2b, 66% yield; 2c, 72% yield; 3, 83% yield). Demethoxycarbonylation of lc and 2c was performed by heating with LiBr*HzO (IO equiv) in HMPA at 90 “C for I h, and then at 130 “C for 1 h, furnishing the dioxolane derivative of MDT-TI’F (methylenedithiotetrathiafulvalene) (ld) and its dithiolane analogue (2d) in 46% and 63% yields, respectively. 3.
Electrochemical
properties
Oxidation potentials of new compounds lb, Za,b,d and 3 were measured by the use of cyclic voltammetry, and the results are summarized in Table 1. The dithiolane derivatives Za,b,d and the oxathiolane derivative 3 exhibited three pairs of reversible redox waves, whereas the dioxolane derivative of BMDT-TTF [bis(methylenedithio)tetrathiafulvalene) (ld) showed three pairs of reversible redox waves and one irreversible oxidation wave. The El-E3 values of 3 are very similar to those of 2a rather than those of la (El = +0.57 V, Ez = +0.84 V, E3 = +I 58 V) [lc,d]. Table 1 Oxidation
potentials
Compound lb 2a 2b 2d 3 %
vs. saturated
El
E2
0.53 0.55 0.55 0.48 0.55
0.76 0.83 0.77 0.80 0.83
calomel
electrode, at room blrreversible wave.
4.
Molecular
of lb, ta,b,d,
and 3.a
E3
1.38 1.63 1.57 1.67 1.64
electrode
(SCE),
temperature,
under
E4
.a?
1.56b
0.1 M (a-Bu)qNCl04 nitrogen.
scan rate
6%EI)
0.23 0.28 0.22 0.32 0.28
Metals
102 (1999)
Fig. I. Molecular 5.
structure of 2a: (a) top view; (b) side view.
Conducting
behavior
Small amount of the TCNQ complexes with 2a could be prepared by reaction with TCNQ (1 equiv) in TCE (l,l,2trichloroethane) at 80 ‘C for 2 h, though no complex was formed when the same reaction was carried out at room temperature overnight. In contrast to a metallic TCNQ complex of la, the room temperature conductivity for a single crystal of this complex, prepared by recrystallization from TCE with slow cooling, was rather low ((J, < 10e7 S cm-t). On the other hand, the Za-based CT salts listed in Table 2 were accessible by the controlled-current electrocrystallization method [2] in TCE containing the corresponding tetrabutylammonium salts, and their room temperature conductivities were lo‘*-10’ S cm-t. While a compressed pellet of the I3 or C104 salt showed semiconducting behavior with small or relatively small activation energy, single crystals of the At&, BF4, and AsFs salts were all metallic, which underwent metalto-semiconductor (or insulator) transitions. Further investigation on the growth of good single crystals suitable for X-ray diffraction and the development of other organic metals derived from the dichalcogenolane-added TTF donors, described herein, is currently in progress. Table 2 Electrical
in PhCN. Pt 50 mV s -I
Anion I,-
Structure
The molecular structure of the neutral 2a was determined by X-ray diffraction analysis of its single crystal obtained by recrystallization from CS2 [CtzH loSlo, M = 474.00, monoclinic, space group P2,/u, a = 18.75(l) A, b = 9.791(5) A, c = 10.165(7) A, /I = 103.73(5)‘, V= 1812.43 A3,Z=4, D, = 1.737 g cme3, R = 0.058 (R, = 0.092) for 3997 observed reflections]. As shown in Figure 1, compound 2a has a distorted structure, wherein the plane formed by two sulfur atoms and one carbon atom linking them in the 1,3-dithiolane ring is roughly parallel to the central tetrathioethylene medium plane of the MET molecule. On comparing the molecular structure of 2a with that of its dioxolane analogue la [lc,d], it is noted that the conformation of the dithiolane ring in the former evidently makes it less bulky than the latter. Nevertheless, that molecule is far from being planar.
1701-1702
Au12 BF4c104AsF(,-
conductivities 2a:Aniona 3:l 5:3 2:l -f 3:l
of radical-cation
salts based on 2a.
0, IS cm-’ b 3.2 x IO-tc (E = 15 meV) ,3d(T~f=&) 7.0d (TM, = 110 K) 9.5 x 10m2c(E, = 58 meV) 1gd (TM, = ,60 K)
aDetermined by elemental analysis. bRoom temperature conductivity measured by a four-probe technique. %kasured on a compressed pellet. dMeasured on a single crystal. vemperature of metal-to-semiconductor (or insulator) transition. fNot determined because this complex may explode during analysis.
References [I] [2]
J. Yamada, S. Tanaka, J. Segawa, M. Hamasaki, K. Hagiya, H. Anzai, H. Nishikawa, 1. Ikemoto, K. Kikuchi, J. Org. Chem. 63 (1998) 3952. H. Anzai, J.M. Delrieu, S. Takasaki, S. Nakatsuji, J. Yamada, J. Crystal Growth I54 (1995) 145.
Synthetic Metals 102 (1999) 1701-1702
Synthesis and properties of the TTF donors with a five-membered cyclic O,O-, S,S-, or O,S-acetal J. Yamada’,* R. Okat, H. Anzai’, H. Nishikawa*, I. Ikemoto*, and K. Kikuchi* ‘Department of Material Science, Faculty of Science, Himeji Institute of Technology, 147.5-2 Kanaji, Kamigori-cho, Ako-gun, Hyogo 678-1297, Japan ‘Department of Chemistry, Faculty of Science, Tokyo Metropolitan University, Hachioji. Tokyo 192-0397, Japan Abstract Synthesis of the TIP (tetrathiafulvalene) donors with a 1,3-dioxolane, 1,3-dithiolane, or 1,3-oxathiolane ring (l-3) has been accomplished via (MeO)JP-promoted cross-coupling reaction of the corresponding new ketones (6-S) and thiones (9a-c). Although an X-ray diffraction analysis of the neutral 2a revealed that its molecular structure is nonplanar, its radical-cation salts with AuIi, BF4-, and AsFe- exhibited metallic conducting behavior. Keywords: 1.
Heterocycle
synthesis; Coupling
reactions; Organic conductors
Introduction
In the course of our search for the development of new molecular-based organic metals composed of the extended lTF donors by addition of heterocycles [l], we have found that the 1,3-dioxolane derivative of MET [methylenedithio(ethylenedithio)tetrathiafulvalene] (la) produces a metallic TCNQ (tetracyanoquinodimethane) complex even though the dioxolane ring is attached perpendicularly to the MET framework [lc]. Although this donor could be synthesized via the MesAl-mediated rearrangement reaction, its yield was relatively low [lc,d]. In addition, the replacement of the outer ring oxygen atom(s) in such a donor with the larger and more polarizable sulfur atom(s) might result in an enhancement of intermolecular SS interactions in the CT (charge-transfer)state. However, for example, the dithiolane analogue of la (2a) could not be obtained by the MesAl-promoted reaction of the corresponding tin-masked dithiolate with an ester since the analogous rearrangement as can be found in the synthesis of la did not take place [la,d]. In this paper, synthesis of the dioxolane derivatives la-d by employing a different synthetic route, and a synthetic approach to the construction of their dithiolane analogues 2a-d and the oxathiolane derivative of
la R-R = S(CH,),S 1 b R-R = SCH,S lcR=R=C02Me ldR=R=H
Ndp4
based on radical cation and/or anion salts
MET (3) are described. We also disclose the electrochemical properties of new compounds (lb, Za,b,d, and 3). the molecular structure of 2a by X-ray diffraction, and the conducting behavior of the 2a-based CT complex and salts. 2.
Synthesis
Our strategy for synthesizing l-3 was based on the (MeO)BP-promoted cross-coupling reaction, and to this end, the development of a synthetic method for preparation of new derivatives of 1,3-dithiol-2-one utilized for this reaction was necessitated. Exposure of the dioxane-fused ketone 5, prepared from tin dithiolate 4 and 2,3-dichloro-I ,4-dioxane in the presence of 2 equiv of BF3*OEt2 [la,d], to an excess of BF3*OEt2 (10 equiv) in CHCl3 at room temperature for one day induced isomerization of the bis-fused six-membered heterocycle to the five-membered biheterocycle, affording the dioxolane-appended ketone 6 in 80% yield together with trace amounts of 5. The ratio of 65 determined by ‘H-NMR was 46:l. Pure ketone 6 was obtainable by recrystallization from CH2C12-EtOH. Similarly, the use of 10 equiv of BF3*OEt2 in the reaction of 4 with dichlorodioxane under the same conditions as used for the isomerization of 5 furnished an 8:l
2a R-R = S(CH,),S 2b R-R = SCH2S
2cR=R=COzMe SdR=R=H
s==(I Sx
S 5
0379-6779/99/$ - see front matter 0 1999 Elsevier Science S.A. All rights resewed. PII: SO379-6779(98)00623-7
6X=Y=O 7X=Y=S 8X=O,Y=S
9a R-R = S(CH&S 9b R-R = SCH,S 9cR=R=C02Me
1702
J. Yamadu
et ul. I Synthetic
mixture of 6 and 5 in 89% yield. Further, the addition of l,2ethanedithiol in this isomerization reaction followed by stirring for two days enable us to obtain the dithiolane-added ketone 7 in 95% yield. While conversion of 5 into the oxathiolane-appended ketone 8 could not be effected by the BFJ-promoted reaction of 5 with 2-mercaptoethanol even under prolonged reaction time, the analogous reaction of 6 in CH2Cl2 for two days provided the desired product 8 in 40% yield. Cross-coupling synthesis of la-c, 2a-c, and 3 was carried out by reaction of the resulting ketones 6-8 with 2 equiv of thiones 9a-c using (Me0)3P as a phosphite reagent in toluene at 110 “C for 2 h (la, 80% yield; lb, 52% yield; lc, 96% yield; 2a, 94% yield; 2b, 66% yield; 2c, 72% yield; 3, 83% yield). Demethoxycarbonylation of lc and 2c was performed by heating with LiBr*HzO (IO equiv) in HMPA at 90 “C for I h, and then at 130 “C for 1 h, furnishing the dioxolane derivative of MDT-TI’F (methylenedithiotetrathiafulvalene) (ld) and its dithiolane analogue (2d) in 46% and 63% yields, respectively. 3.
Electrochemical
properties
Oxidation potentials of new compounds lb, Za,b,d and 3 were measured by the use of cyclic voltammetry, and the results are summarized in Table 1. The dithiolane derivatives Za,b,d and the oxathiolane derivative 3 exhibited three pairs of reversible redox waves, whereas the dioxolane derivative of BMDT-TTF [bis(methylenedithio)tetrathiafulvalene) (ld) showed three pairs of reversible redox waves and one irreversible oxidation wave. The El-E3 values of 3 are very similar to those of 2a rather than those of la (El = +0.57 V, Ez = +0.84 V, E3 = +I 58 V) [lc,d]. Table 1 Oxidation
potentials
Compound lb 2a 2b 2d 3 %
vs. saturated
El
E2
0.53 0.55 0.55 0.48 0.55
0.76 0.83 0.77 0.80 0.83
calomel
electrode, at room blrreversible wave.
4.
Molecular
of lb, ta,b,d,
and 3.a
E3
1.38 1.63 1.57 1.67 1.64
electrode
(SCE),
temperature,
under
E4
.a?
1.56b
0.1 M (a-Bu)qNCl04 nitrogen.
scan rate
6%EI)
0.23 0.28 0.22 0.32 0.28
Metals
102 (1999)
Fig. I. Molecular 5.
structure of 2a: (a) top view; (b) side view.
Conducting
behavior
Small amount of the TCNQ complexes with 2a could be prepared by reaction with TCNQ (1 equiv) in TCE (l,l,2trichloroethane) at 80 ‘C for 2 h, though no complex was formed when the same reaction was carried out at room temperature overnight. In contrast to a metallic TCNQ complex of la, the room temperature conductivity for a single crystal of this complex, prepared by recrystallization from TCE with slow cooling, was rather low ((J, < 10e7 S cm-t). On the other hand, the Za-based CT salts listed in Table 2 were accessible by the controlled-current electrocrystallization method [2] in TCE containing the corresponding tetrabutylammonium salts, and their room temperature conductivities were lo‘*-10’ S cm-t. While a compressed pellet of the I3 or C104 salt showed semiconducting behavior with small or relatively small activation energy, single crystals of the At&, BF4, and AsFs salts were all metallic, which underwent metalto-semiconductor (or insulator) transitions. Further investigation on the growth of good single crystals suitable for X-ray diffraction and the development of other organic metals derived from the dichalcogenolane-added TTF donors, described herein, is currently in progress. Table 2 Electrical
in PhCN. Pt 50 mV s -I
Anion I,-
Structure
The molecular structure of the neutral 2a was determined by X-ray diffraction analysis of its single crystal obtained by recrystallization from CS2 [CtzH loSlo, M = 474.00, monoclinic, space group P2,/u, a = 18.75(l) A, b = 9.791(5) A, c = 10.165(7) A, /I = 103.73(5)‘, V= 1812.43 A3,Z=4, D, = 1.737 g cme3, R = 0.058 (R, = 0.092) for 3997 observed reflections]. As shown in Figure 1, compound 2a has a distorted structure, wherein the plane formed by two sulfur atoms and one carbon atom linking them in the 1,3-dithiolane ring is roughly parallel to the central tetrathioethylene medium plane of the MET molecule. On comparing the molecular structure of 2a with that of its dioxolane analogue la [lc,d], it is noted that the conformation of the dithiolane ring in the former evidently makes it less bulky than the latter. Nevertheless, that molecule is far from being planar.
1701-1702
Au12 BF4c104AsF(,-
conductivities 2a:Aniona 3:l 5:3 2:l -f 3:l
of radical-cation
salts based on 2a.
0, IS cm-’ b 3.2 x IO-tc (E = 15 meV) ,3d(T~f=&) 7.0d (TM, = 110 K) 9.5 x 10m2c(E, = 58 meV) 1gd (TM, = ,60 K)
aDetermined by elemental analysis. bRoom temperature conductivity measured by a four-probe technique. %kasured on a compressed pellet. dMeasured on a single crystal. vemperature of metal-to-semiconductor (or insulator) transition. fNot determined because this complex may explode during analysis.
References [I] [2]
J. Yamada, S. Tanaka, J. Segawa, M. Hamasaki, K. Hagiya, H. Anzai, H. Nishikawa, 1. Ikemoto, K. Kikuchi, J. Org. Chem. 63 (1998) 3952. H. Anzai, J.M. Delrieu, S. Takasaki, S. Nakatsuji, J. Yamada, J. Crystal Growth I54 (1995) 145.