Synthesis of bis(ethylenedithio)tetrathiafulvalene derivatives with metal ion ligating centres

Article abstract of DOI:10.1016/S0040-4039(03)00539-2

The syntheses of eight derivatives of BEDT-TTF (ET) containing pyridine, 2,2′-bipyridine or 2,4′-pyridylpyrimidine binding sites on a side chain are reported, for use in the preparation of organic/inorganic hybrid materials. The intermediate hydroxyethyl derivative of BEDT-TTF is prepared in an efficient five-step procedure.

Full text of DOI:10.1016/S0040-4039(03)00539-2

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 44 (2003) 3127–3131
Synthesis of bis(ethylenedithio)tetrathiafulvalene derivatives with
metal ion ligating centres
Jon-Paul Griffiths,a R. James Brown,a Peter Day,b Craig J. Matthews,a Bertrand Vitala and
John D. Wallisa,*
aDepartment of Chemistry and Physics, The Nottingham Trent University, Clifton Lane, Nottingham NG11 8NS, UK
bThe Royal Institution of Great Britain, 21 Albemarle Street, London W1S 4BS, UK
Received 20 December 2002; revised 13 February 2003; accepted 21 February 2003
Abstract—The syntheses of eight derivatives of BEDT-TTF (ET) containing pyridine, 2,2%-bipyridine or 2,4%-pyridylpyrimidine
binding sites on a side chain are reported, for use in the preparation of organic/inorganic hybrid materials. The intermediate
hydroxyethyl derivative of BEDT-TTF is prepared in an efficient five-step procedure. © 2003 Elsevier Science Ltd. All rights
reserved.
Bis(ethylenedithio)tetrathiafulvalene, BEDT-TTF or
ET, 1, a readily oxidisable organosulfur donor, has
played a major role in the field of organic conductors
over the last ten years.1 Of particular importance is the
observation of superconductivity at low temperatures in
radical cation salts such as ET2[Cu(N(CN)2)Br].2 How-
ever, only a few substituted derivatives of ET have been
prepared, e.g. the tetramethyl3 and tetraethyl4 deriva-
tives. Charge transfer salts of the latter are under
investigation as ‘molecular rulers’ in nanotechnology.
Keywords: organic conductors; BEDT-TTF; organosulfur donors.
* Corresponding author.
0040-4039/03/$ - see front matter © 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4039(03)00539-2

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J.-P. Griffiths et al. / Tetrahedron Letters 44 (2003) 3127–3131
Formigue has prepared poly-chloro and -fluoro ana-
logues as isomeric mixtures,5 and we have prepared
both racemic and enantiopure versions of the hydroxy-
methyl derivative HMET 2,6 polysubstituted materials
such as 3 and hydroxy derivatives with expanded outer
rings such as 47 which all have the potential for attach-
ment to other molecular systems.
Coronado reported a material with independent electri-
cal conductivity and ferromagnetism containing ET and
a mixed metal oxalate network.9 Interplay of magnetic
and electrical effects was demonstrated in k-
(BETS)2FeBr4 and l-(BETS)2FeCl4 which changed
from an insulator to a metal and then to a supercon-
ductor by increasing the external magnetic field.10
Recently, Day has reported radical cation salts of metal
complex anions containing a heterocyclic ligand, e.g.
(ET)2Fe(phen)(NCS)4 which is a paramagnetic semi-
conductor, and (ET)2Cr(isoquin)2(NCS)4 which is a fer-
romagnetic semiconductor.11 The organosulfur donor
and the complex anion are separate species in these
systems. In order to gain some control over the relative
There is increasing interest in bifunctional materials
which combine the electrical conducting properties of
organosulfur donors with the magnetic effects of transi-
tion metal ions, and in which these properties may
interact in novel ways. Day prepared a paramagnetic
superconductor from ET and Fe(III) oxalates,8 and
Scheme 1. Reagents and conditions: (a) allyl alcohol, toluene, reflux; (b) 2 equiv. tosyl chloride, pyridine, rt; (c) pyridyl-2-thiolate−
Na+, THF or DMF; (d) mercuric acetate, acetic acid, chloroform; (e) 2 equiv. 12, triethyl phosphite, 80°C, 5 h.

J.-P. Griffiths et al. / Tetrahedron Letters 44 (2003) 3127–3131
3129
Scheme 2. Reagents and conditions: (a) but-3-en-1-ol, toluene, reflux; (b) acetic anhydride, pyridine, rt; (c) mercuric acetate, acetic
acid, chloroform; (d) 2 equiv. 12, triethyl phosphite, 90°C, 5 h; (e) 2 M HCl, THF; (f) picolinoyl chloride hydrochloride, THF,
Et3N; (g) nicotinoyl chloride hydrochloride, THF, Et3N; (h) isonicotinoyl chloride hydrochloride, THF, Et3N; (i) 2,6-pyridine
dicarbonyl dichloride, THF, Et3N.
orientations of these moieties we set out to attach the
metal binding ligand to the ET system. Here we report
efficient syntheses of systems 13–15, 20–23 and 25 in
which the ET group is covalently bound to pyridine,
2,2%-bipyridine or 2,4%-pyridylpyrimidine ligands for use
in the construction of new organic/inorganic hybrid
materials. This approach contrasts with the recent
report of the conducting paramagnetic molecule 5 in
which the organosulfur donor itself coordinates the
metal.12
thione 7 in 71% yield from reaction of 6 with allyl
alcohol using refluxing toluene as the solvent. The
alcohol 7 was converted to the corresponding tosylate 8
in 94% yield. This material slowly eliminates tosic acid
to give alkene 9, but nevertheless can be used when
freshly prepared or, if stored, it can be purified by
chromatography before use. The tosylate can be readily
displaced by pyridine-2-thiolate to give thione 10 in 78%
yield (Scheme 1). The synthesis is completed by stan-
dard procedures: conversion of the thione to oxo com-
pound 11, and then cross coupling with excess of thione
12 in triethyl phosphite gives the pyridine substituted
ET derivative 13 in an overall yield of 35% from 8. In
an analogous way tosylate 8 can be substituted with
2,2%-bipyridine-6-thiolate14 or 2,4%-pyridylpyrimidine-2%-
The trithione 6, an oligomeric material in the solid state,
undergoes Diels–Alder reactions with a variety of func-
tionalised alkenes, though the reported yields are vari-
able (10–70%).13 However, we were able to obtain

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J.-P. Griffiths et al. / Tetrahedron Letters 44 (2003) 3127–3131
Scheme 3. Reagents and conditions: (a) 4 equiv. tosyl chloride, pyridine; (b) pyridyl-4-thiolate−Na+, THF/DMF (1:2).
thiolate14 and the products converted to ET derivatives
14 and 15 which bear bidentate metal ion binding groups
in overall yields of 30 and 35%, respectively, from 8.
This compound was expected to be a mixture of racemic
and meso compounds, though unsurprisingly there is no
1
difference discernable in the H and 13C NMR spectra.
Finally, the hydroxy derivative HEET was also con-
verted to its tosylate 24, which was substituted with the
sodium salt of pyridine-4-thiolate to give the donor 25
(Scheme 3). All the donors reported here are racemic,
but access to enantiopure HMET 26 and ET-
CH2CO2Me,15 a precursor to enantiopure HEET, means
that in principle single enantiomers can be obtained.
The second series of ET derivatives 20–23 was prepared
by an alternative route in which the metal binding group
is installed at the end of the synthesis (Scheme 2).
Hydroxyethyl-ET, HEET, 19, was prepared in a very
convenient fashion starting from trithione 6 and but-3-
en-1-ol. The latter two substances react in refluxing
toluene to give thione 16 in a yield of 83%. Protection
of the hydroxyl function as an acetate, followed by the
standard procedure for exchange of thione sulfur for
oxygen using mercuric acetate gave the oxo compound
17 in 87% yield from the thione 16. Cross coupling with
the unsubstituted thione 12 in triethyl phosphite gave the
protected ET derivative 18 in 60% yield after chromatog-
raphy to separate from homocoupled material. Finally,
HEET, 19 was generated by hydrolysis with 2 M HCl in
THF. By this route a functionalised ET, which will
facilitate the attachment of the ET grouping to many
other molecular systems via ester, ether and other link-
ages, was accessed in 43% overall yield from trithione 6.
The cyclic voltammetry data for seven of the new donors
show the expected two reversible oxidations with almost
no variation in the potentials (ꢀ0.50 and ꢀ0.90 V) at
which they occur (Table 1). In contrast, compound 23
which bears two ET moieties shows two reversible half
wave potentials at 0.43 and 0.55 V, which together
correspond to loss of two electrons, and a further
irreversible oxidation process at 0.82 V (Fig. 1). Since the
molecular structure allows the two ET moieties to lie
close to one another, the first two oxidations are
+
assigned to conversion of (-ET)2 to (-ET)2 and then to
(-ET+)2, and interestingly the first of these takes place at
a lower potential than for oxidation of ET itself. We
speculate that the irreversibility of the oxidation at 0.82
V may be due an intramolecular reaction between the
further oxidised ET moieties. This is under further
investigation.
HEET 19 reacted smoothly with a variety of pyridine
acid chlorides to provide compounds 20–23 in moderate
to high yields (50–90%). Of particular interest was 23
where two ET moieties were linked in the same molecule.
Figure 1. Cyclic voltammogram of 23 in CH2Cl2 containing 0.1 M n-Bu4NPF6, scan rate of 100 mV s−1, E (V) relative to
Ag/AgCl.

J.-P. Griffiths et al. / Tetrahedron Letters 44 (2003) 3127–3131
3131
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Table 1. Oxidation potentials (V, relative to the AgCl/Ag
electrode) measured by cyclic voltammetrya for oxidation
of ET and novel derivatives
E1 (V)
E2 (V)
1
0.48
0.48
0.49
0.50
0.49
0.50
0.50
0.43, 0.55
0.50
0.87
0.89
0.90
0.91
0.90
0.90
0.90
0.82b
0.89
13
14
15
20
21
22
23
25
a Measured in dichloromethane containing 0.1 M tetrabutylammo-
nium hexafluorophosphate with a scan rate of 100 mV s−1 relative
to Ag/AgCl using a m-Autolab type II apparatus.
b Irreversible.
Thus, we have demonstrated simple preparative routes
to ET derivatives containing metal binding groups,
which should be applicable not only to the installation
of the many alternative metal ligating groups but also
to other functionalities to provide novel materials and
building blocks in supramolecular chemistry. The coor-
dination chemistry and electrocrystallisation of the
molecules reported in this work are under current
study. Other workers16 have reported the synthesis of
related pyrid-2-yl and pyrid-4-yl derivatives of ET, 26
and 27, though these were only obtained in low yields,
and the general approach is less flexible requiring vinyl
derivatives of the pyridines. Ouahab et al. have
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Acknowledgements
We would like to thank the EPSRC Mass Spectrometry
Service for data, and EPSRC and The Nottingham
Trent University for studentships (R.J.B. and J.P.G.).
We thank The Royal Society for support for electro-
chemical equipment (C.J.M.). We thank Mr. G.
Appleby for help in some of the synthetic work.
13. Neilands, O. Y.; Katsens, Y. Y.; Kreitsberga, Y. N. Zh.
Org. Khim. 1989, 25, 658–660.
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15. Brown, R. J.; Wallis, J. D., unpublished work.
16. Xu, W.; Zhang, D.; Li, H.; Zhu, D. J. Mater. Chem. 1999,
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