Tetrathiafulvalene-acetylene scaffolding: New π-electron systems for advanced materials

Article abstract of DOI:10.1039/b105749a

Novel extended tetrathiafulvalenes (TTFs) with hexa-2,4-diyne-1,6-diylidene spacers between the two 1,3-dithiole rings and laterally appended alkynyl moieties for one- and two-dimensional scaffolding were synthesised and investigated for their electronic

Full text of DOI:10.1039/b105749a

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Tetrathiafulvalene–acetylene scaffolding: new p-electron systems for
advanced materials
Mogens Brøndsted Nielsen,a Nicolle N. P. Moonen,a Corinne Boudon,b Jean-Paul Gisselbrecht,b
Paul Seiler,a Maurice Grossb and François Diederich*a
a Laboratorium für Organische Chemie, ETH-Zentrum, Universitätstrasse 16, CH-8092 Zürich,
Switzerland. E-mail: diederich@org.chem.ethz.ch
b Laboratoire d’Electrochimie et de Chimie Physique du Corps Solide, UMR 7512, C.N.R.S, Université
Louis Pasteur, 4, rue Blaise Pascal, F-67000 Strasbourg, France
Received (in Cambridge, UK) 2nd July 2001, Accepted 7th August 2001
First published as an Advance Article on the web 5th September 2001
Novel extended tetrathiafulvalenes (TTFs) with hexa-
2,4-diyne-1,6-diylidene spacers between the two 1,3-dithiole
rings and laterally appended alkynyl moieties for one- and
two-dimensional scaffolding were synthesised and investi-
gated for their electronic properties.
appended alkynyl moieties for introduction into larger one- and
two-dimensional scaffolds.
The first target compound 6a† was obtained by deprotection
of the silylated alkyne 5a using K2CO3 in MeOH–THF (Scheme
1), followed by oxidative coupling under Hay conditions7
(CuCl, TMEDA, O2). Precursor 5a was prepared by a Wittig
reaction between phosphonium salt 38 and aldehyde 4a.9
Wittig reaction of 3 with ketones 4bc9 gave the dialkynylated
dithiafulvenes 5bc. After selective removal of the SiMe3 group
in 5b, Hay coupling provided the extended TTF 6b† as an
orange solid, whereas cross-coupling with 4-(N,N-didodecyl-
amino)phenylacetylene (4.5 equiv.) afforded compound 7b.
Alkyne deprotection followed by oxidative coupling provided
the extended TTF 8 with two laterally appended electron-
donating anilino groups.
The X-ray crystal structure of 6a (Fig. 1)‡ reveals that the two
fulvene double bonds adopt the s-trans conformation with
respect to the connecting buta-1,3-diynediyl moiety. The two
dithiafulvene units are rotated about the central diacetylene core
with a torsional angle C1–C14–C19–C20 of 2138.6°.
Proceeding from the dithiafulvene monomers 5abc and 7b to
the extended TTFs 6ab and 8 results in significant bath-
ochromic shifts of the longest wavelength absorption maxima
(Table 1). The origin of this transition was elucidated by a
computational study employing the GAUSSIAN 98 program
package10 at the HF/3-21G level of theory. It transpires that the
HOMO of 6a is distributed over the four sulfur atoms and the
connecting spacer unit (Fig. 2), whereas the LUMO is located at
the two peripheral ethylene biscarbonyl units; both HOMO and
Tetrathiafulvalene (TTF) is a reversible, two-electron donor
which has found wide applications in both materials and
supramolecular chemistry.1 The on-going quest for TFF-based
organic conductors has stimulated much structural variation, in
particular the insertion of p-conjugated spacers between the two
1,3-dithiole units.2 Indeed, a considerable number of olefinic
and aromatic spacers have been introduced with the aim to tune
the redox properties of the p-electron system.3 In contrast, only
two examples of acetylenic spacers have been reported.4,5 Thus,
Gorgues and co-workers4 reported the synthesis of substituted
1,4-bis(1,3-dithiol-2-ylidene)but-2-ynes, such as 2. We decided
to expand the family of acetylenic TTFs6 by members
containing a hexa-2,4-diyne-1,6-diylidene spacer between the
two dithiole rings while at the same time featuring laterally
Scheme 1 Reagents and conditions: i, n-BuLi, THF, 278 °C; ii, K2CO3, THF, MeOH, 20 °C; iii, CuCl, TMEDA, CH2Cl2, O2, 20 °C. iv, Bu4NF, THF, H2O,
20 °C.
1848
Chem. Commun., 2001, 1848–1849
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b105749a

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In summary, we have developed a new family of dithia-
fulvene–acetylene hybrid chromophores. We are currently
investigating the possibility of employing these versatile
building blocks for the construction of expanded radialene-
type15 acetylenic macrocycles containing peripheral dithiole
groups.
Support by the ETH Research Council is gratefully acknow-
ledged. We thank Drs Arno Blok (University of Nijmegen) for
assistance with the calculations.
Fig. 1 ORTEP plot of 6a. Atomic displacement parameters obtained at 248
K are drawn at the 30% probability level. Hydrogen atoms are omitted for
clarity. Selected bond lengths (Å) and bond angles (°): C1–S2 1.739(6), C1–
S5 1.755(6), S2–C3 1.739(6), C3–C4 1.346(8), C4–S5 1.739(6), C1–C14
1.367(9), C14–C15 1.408(9), C15–C16 1.197(9), C16–C17 1.357(10); C1–
C14-C15 122.6(6), C14–C15–C16 175.8(7), C15–C16–C17 175.0(8).
Notes and references
† All new compounds were characterised by IR, UV-Vis, 1H and 13C-NMR,
elemental analysis or HR-MS. Selected data: for 6a: dH (200 MHz, CDCl3)
3.84 (6 H, s), 3.85 (6 H, s), 5.53 (2 H, s); dC (50 MHz, CDCl3) 53.4, 82.9,
84.0, 91.9, 131.1, 131.6, 149.5, 159.3, 159.5; m/z (HR-MALDI-MS
2,5-dihydroxybenzoic acid (DHB)) 509.9559 (M+, calcd. 509.9572).
‡ X-Ray crystal structure of 6a: preliminary measurements indicated that
crystals of 6a exhibit a phase transition below ca. 230 K. Because of bad
crystal quality (large mosaic spread up to 2.8°), the low-temperature phase
was not investigated any further. For the present structure, a crystal with
linear dimensions of ca. 0.28 3 0.22 3 0.10 mm was measured at 248 K.
Crystal data for C20H14O8S4 [Mr = 510.55]: monoclinic, space group P21/c
(no. 14), Dc = 1.572 g cm23, Z = 4, a = 25.782(8), b = 4.107(1), c =
Table 1 Longest wavelength absorption maxima lmax/nm and molar
extinction coefficients (e/M21 cm21) in CHCl3
lmax/nm
(e/M21 cm21
lmax/nm
(e/M21 cm21
lmax/nm
(e/M21 cm21
)
)
)
5aa 348b (6100)
6a 429 (25400)
5ba 372 (15000)
6b 441b (18600)
7b 422 (25300)
8
460b (33300)
a Compounds 5a and 5b experience ‘tail’ absorptions at lmax 405 nm (e
21.947(5) Å, b
= 111.87(2)°, V =
2156.6(10) Å3. Nonius-CAD4
1600) and 410 nm (e 1440), respectively. b Shoulder.
diffractometer, CuKa radiation, l = 1.5418 Å. The structure was solved by
direct methods and refined by full-matrix least-squares analysis (SHELXL-
97). Static disorder occurs within the sub-unit C20–S21 until C32, and thus
the corresponding geometry is somewhat unreliable. Preliminary refine-
ments show that the disorder can be resolved, in principle for C22 and C23,
while the corresponding refinements of the ethoxy groups (including
restraints) are not satisfactory. All heavy atoms were refined anisotropically
(H-atoms of the ordered sub-unit isotropically, whereby H-positions are
based on stereochemical considerations). Final R(F) = 0.093, wR(F2) =
0.255 for 295 parameters and 2512 reflections with I > 2s(I) and 3.69 < q
< 60.0° (the corresponding R-values based on all 3163 reflections are 0.110
and 0.280, respectively). CCDC 164802. See http://www.rsc.org/suppdata/
cc/b1/b105749a for crystallographic files in .cif or other electronic
format.
Fig. 2 HF/3-21G-calculated HOMO and LUMO of 6a.
LUMO are of pure p-nature. A similar intramolecular charge-
transfer transition was observed for parent, CO2Me-substituted
TTFs,11 but with a much smaller extinction coefficient: eCT(1)
= 1930 M21 cm21 at lmax 445 nm.12
The electrochemical data for the new extended TTFs are
collected in Table 2. TTF 6b was oxidised in two reversible one-
electron steps in CH2Cl2, with a separation of only 120 mV,
indicating a lower coulombic repulsion between the two charges
1 Recent reviews: M. B. Nielsen, C. Lomholt and J. Becher, Chem. Soc.,
Rev., 2000, 29, 153; M. R. Bryce, J. Mater. Chem., 2000, 10, 589; J. L.
Segura and N. Martín, Angew. Chem., Int. Ed., 2001, 40, 1372.
2 For a review on linearly p-extended TTFs, see: J. Roncali, J. Mater.
Chem., 1997, 7, 2307.
3 Some recent examples: S.-G. Liu, I. Pérez, N. Martín and L. Echegoyen,
J. Org. Chem., 2000, 65, 9092; M. R. Bryce, M. A. Coffin, P. J. Skabara,
A. J. Moore, A. S. Batsanov and J. A. K. Howard, Chem. Eur. J., 2000,
6, 1955.
4 A. Khanous, A. Gorgues and F. Texier, Tetrahedron Lett., 1990, 31,
7307; A. Khanous, A. Gorgues and M. Jubault, Tetrahedron Lett., 1990,
31, 7311.
5 H. Awaji, T. Sugimoto and Z. Yoshida, J. Phys. Org. Chem., 1988, 1,
47.
ox
ox
in the dication as compared to that of 1 (E2 2 E1 = 320 mV
in MeCN)13 and 2 (E2 2 E1 = 380 mV in MeCN).4 TTF 6a
was oxidised in an irreversible two-electron step in CH2Cl2.
Also, 8 experienced irreversible oxidation steps, with the first
oxidation occurring at the anilino donors. Thus, structural
changes in the acetylenic spacer unit as well as solvent polarity
are influencing the oxidation behavior, as was likewise
recognised for a series of TTF vinylogues.14 Interestingly, it
was also possible to reduce the acetylenic TTFs.
ox
ox
6 TTFs with alkynyl substituents at the peripheral 2,3,6,7-positions
represent another class: D. Solooki, T. C. Parker, S. I. Khan and Y.
Rubin, Tetrahedron Lett., 1998, 39, 1327.
7 A. S. Hay, J. Org. Chem., 1962, 27, 3320.
8 M. Sato, N. C. Gonnella and M. P. Cava, J. Org. Chem., 1979, 44,
Table 2 Cyclic voltammetry data in CH2Cl2 (+0.1 M n-Bu4NPF6);
potentials vs. Fc/Fc+. Working electrode: glassy carbon electrode; counter
electrode: Pt; reference electrode: Ag/AgCl. Scan rate: 0.1 V s21
930.
9 J. Anthony, A. M. Boldi, Y. Rubin, M. Hobi, V. Gramlich, C. B.
Knobler, P. Seiler and F. Diederich, Helv. Chim. Acta., 1995, 78, 13.
10 M. J. Frisch et al., SGI-G98, Rev. A.5, Gaussian, Inc., Pittsburg, PA,
1998.
E°/Va
Ep/Vb
E°/Va
Ep/Vb
11 A. S. Batsanov, M. R. Bryce, J. N. Heaton, A. J. Moore, P. J. Skabara,
J. A. K. Howard, E. Ortí, P. M. Viruela and R. Viruela, J. Mater. Chem.,
1995, 5, 1689.
12 H. D. Hartzler, J. Am. Chem. Soc., 1973, 95, 4379.
13 S.-G. Liu, M. Cariou and A. Gorgues, Tetrahedron Lett., 1998, 39,
8663.
14 N. Bellec, K. Boubekeur, R. Carlier, P. Hapiot, D. Lorcy and A. Tallec,
J. Phys. Chem. A, 2000, 104, 9750.
15 M. B. Nielsen, M. Schreiber, Y. G. Baek, P. Seiler, S. Lecomte, C.
Boudon, R. R. Tykwinski, J.-P. Gisselbrecht, V. Gramlich, P. J. Skinner,
C. Bosshard, P. Günter, M. Gross and F. Diederich, Chem. Eur. J., 2001,
7, 3263.
6a
0.58 (2e)
21.81 (2e)
0.70 (2e)
7b
8
0.42 (1e)
0.67 (1e)
6bc
6b
21.70 (1e)
21.81 (1e)
0.43 (2e)
0.87 (1e)
1.12 (1e)
21.75 (2e)
0.64 (1e)
0.76 (1e)
21.86 (2e)
21.70 (2e)
a E° = (Epc + Epa)/2, where Epc and Epa = cathodic and anodic peak
potentials. b Ep = irreversible peak potential. c Solvent: MeCN.
Chem. Commun., 2001, 1848–1849
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