Synthesis and properties of new π-conjugated pyridine ligands with tetrathiafulvalene derivatives and the rhenium(I) tricarbonyl complexes

Article abstract of DOI:10.1016/j.tetlet.2010.11.129

Three new π-conjugated pyridine ligands with redox-active tetrathiafulvalene (TTF) derivatives, L₁-L₃, have been synthesized and characterized. The Diels-Alder reaction is the key step for this multistep synthetic strategy. The crystal structures of L₁ and L₃ have been studied. The electrochemical and spectroscopic properties of these new ligands, as well as the corresponding tricarbonyl rhenium(I) complexes (ReL₁(CO)₃X, X = Cl, 5; X = Br, 6) have also been investigated.

Full text of DOI:10.1016/j.tetlet.2010.11.129

Tetrahedron Letters 52 (2011) 675–678
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Synthesis and properties of new
p-conjugated pyridine ligands with
tetrathiafulvalene derivatives and the rhenium(I) tricarbonyl complexes
⇑
Gao-Nan Li, Di Wen, Tao Jin, Ya Liao, Jing-Lin Zuo , Xiao-Zeng You
State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing National Laboratory of Microstructures,
Nanjing University, Nanjing 210093, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
Three new
p-conjugated pyridine ligands with redox-active tetrathiafulvalene (TTF) derivatives, L1–L3,
Received 17 October 2010
Revised 18 November 2010
Accepted 26 November 2010
Available online 9 December 2010
have been synthesized and characterized. The Diels–Alder reaction is the key step for this multistep syn-
thetic strategy. The crystal structures of L1 and L3 have been studied. The electrochemical and spectro-
scopic properties of these new ligands, as well as the corresponding tricarbonyl rhenium(I) complexes
(ReL1(CO)3X, X = Cl, 5; X = Br, 6) have also been investigated.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Tetrathiafulvalene
Diels–Alder reaction
New pyridine ligands
Rhenium complexes
The synthesis and coordination chemistry of tetrathiafulvalene
(TTF) and its derivatives have been intensively studied during the
past two decades, because of their unique p-electron donor prop-
exhibited a lower polarity than the compound II and was easily
decomposed in air. The ligand L1 was obtained from the classical
coupling reaction in P(OEt)3 with the yield of 24% after column
chromatography (PE/EA = 1:1).10 The synthetic details are provided
in Supplementary data.
The reactions of the ligand L1 and Re(CO)5Cl or Re(CO)5Br in tol-
uene afforded the corresponding tricarbonyl rhenium(I) com-
plexes, ReL1(CO)3X (X = Cl, 5; X = Br, 6) in high yield (70% and
77%), respectively. The metal complexes were characterized by IR
spectra, UV–vis and mass spectrometry. In IR spectra, typical three
CO stretching vibrations for ReI complexes 5 and 6 were observed,
indicating the facial arrangement of three coordinated C„O
ligands.5
The orange crystals of L1 and L3 suitable for X-ray structural
analysis were obtained by slow evaporation of a mixture solution
of CH2Cl2 and MeOH.11 For the ligand L1,12 except for the terminal
methyl groups trans to the molecule mean plane, the TTF moiety
and bipyridine moiety of the ligand are almost coplanar with the
average deviation from a least-squares plane of 0.0965 Å (Fig. 1).
It is noteworthy that the nitrogen atoms of bipyridyl moiety lie
in the anti position.13,14 For the ligand L3,15 the skeleton of the
erties and serving as useful building blocks for new advanced
materials.1,2 A variety of mono- or polydentate coordinating func-
tional groups have been attached to the TTF moiety, and the corre-
sponding metal complexes have been reported.3–5 For instance, the
pyridine unit has been grafted on the TTF core through various
conjugated linkers, such as the ethylenic/acetylenic spacer group6
or the imino bridge.7 In order to investigate the electronic commu-
nication between the TTF moiety and pyridine or bipyridine units,
in this Letter, three new TTF ligands with the phenyl bridge as
conjugated linker have been synthesized by a multistep synthetic
approach. The key step is the efficient [4+2] Diels–Alder cycloaddi-
tion reaction. The synthetic approach presented herein expands
the further studies on
p-conjugated pyridine ligands with TTF
derivatives, which is beneficial to intramolecular electron transfer
and communications.
Compounds I and II were prepared in the five-step and four-
step synthetic procedures similar to the literature methods,
respectively.8,9 As shown in Scheme 1, compound 1 was prepared
through Wittig reaction in the presence of n-BuLi at 0 °C. After
the reaction of NaI and compound II in DMF, the formed interme-
diate diene III was further undertaken the Diels–Alder cycloaddi-
p-conjugated molecule is nearly planar and exhibits only a slight
undulation. The average deviation from a least-squares plane
through all atoms, excluding the methyl groups, is 0.1338 Å. For
the TTF core alone, it amounts to 0.0560 Å, reflecting its almost
coplanar conformation.12 In L1 and L3, the pyridine and bipyridine
rings linked by phenyl are almost coplanar to the plane of TTF,
which may optimize the communication between the D and A
units.
tion reaction with compound
1 (Scheme 2). The diene III
⇑
Corresponding author. Fax: +86 25 83314502.
E-mail address: zuojl@nju.edu.cn (J.-L. Zuo).
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.11.129

676
G.-N. Li et al. / Tetrahedron Letters 52 (2011) 675–678
S
S
O
O
[PPh3Me]Br
II
N
N
n-BuLi, THF
82%
NaI, DMF
43%
N
N
N
N
I
1
2
N
S
S
N
S
S
S
S
S
Re(CO)5X
S
S
S
S
Re(CO)3(L1)X
P(OEt)3
2
5
6
X=Cl,
X=Br,
L1
N
N
S
S
S
S
S
S
S
S
S
S
S
S
L2
L3
Scheme 1. Synthesis of L1–L3, 5, and 6.
Br
Br
S
S
Br
Br
R
R
S
NaI
S
S
Br
Br
-HBr
R
S
S
O
O
O
O
S
Br
Br
II
III
[4+2] cycladdition
N
N
N
S
S
S
N
S
O
O
O
S
S
4
3
2
Scheme 2. Synthetic applications of tetrabromomethyl group in Diels–Alder cycloaddition reaction.
Table 1
Redox potentials of ligands (L1–L3) and rhenium(I) complexes (5 and 6)
Eopx (Re2+/+) (V)
E11=2 (V)
E21=2 (V)
Compounds
L1
L2
L3
5
0.42
0.42
0.43
0.44
0.46
0.72
0.71
0.73
0.73
0.73
—
—
—
1.29
1.31
6
CH3CN/CH2Cl2 (1:1) solution. All compounds exhibited two revers-
ible one-electron redox couples at about 0.40 and 0.70 V (Table 1),
which were associated with the successive oxidation of the TTF
unit to TTF+ and TTF2+ (Fig. 2 and Fig. S15). In addition, the cyclic
voltammograms of complexes 5 and 6 exhibited the irreversible
anodic waves at 1.29 and 1.31 V, which could be assigned to
Re(I)-based oxidation process (Re+?Re2+). The result was consis-
tent with the redox behavior of other TTF-based Re(I) diimine com-
plexes reported in the literature.16
Figure 1. Crystal structures of L1 (top) and L3 (bottom).
The absorption and emission spectra of compounds L1, 5, and 6 in
CH2Cl2 solution are shown in Figure 3, and the absorption and emis-
sion data are summarized in Table 2. For the ligand L1, the dominant
absorption peaks at 306 and 384 nm were assigned to an admixture
The electrochemical properties of the ligands L1–L3 and com-
plexes (5 and 6) were studied by cyclic voltammetry (CV) in

G.-N. Li et al. / Tetrahedron Letters 52 (2011) 675–678
677
15
10
8
L1
5
10
5
6
4
2
0
0
-2
-4
-5
6
4
4
L2
L3
2
0
2
0
-2
-4
-2
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0 -1.0
-0.5
0.0
0.5
1.0
1.5
2.0
E / V (vs Ag/AgNO3)
E / V (vs Ag/AgNO3)
Figure 2. Cyclic voltammograms of L1, L2, L3, and 5 measured in CH3CN/CH2Cl2 (1:1) solution containing n-Bu4NClO4 (0.1 M). The scan rate was 100 mV/s.
1600
L1
0.8
0.6
0.4
0.2
0.0
1400
1200
1000
800
600
400
200
0
5
6
300
400
500
600
700
800
Wavelength / nm
Figure 3. Electronic absorption (left) and emission spectra (right) of L1, 5, and 6 in CH2Cl2 at room temperature.
of intraligand (
p
–
p⁄) transitions of the TTF moiety and the bipyri-
the absorption spectra of the Re(I) complexes in Figure 3, the weaker
broad band at 400–520 nm was attributed to a metal-to-ligand
dine moiety. Similarly, complexes 5 and 6 displayed absorption
bands at 259–327 nm in CH2Cl2, which could also be assigned to
spin-allowed intraligand (
band of complexes 5 and 6 were both red-shifted compared to the
absorption peak at 306 nm for the free ligand L1 in CH2Cl2, because
the energy of the LUMO localized on the bipyridine unit was low-
ered upon coordination to the rhenium(I) ion.17 With reference to
charge transfer (MLCT, dp
(Re)?p⁄(L)) transition.
p–
p⁄) transitions. The ILCT absorption
At room temperature, the emission spectra of all complexes
exhibited rather a weak photoluminescence in CH2Cl2 solution.
Upon excitation at k 6 400 nm, complexes 5 and 6 exhibited two
emission bands, a low-energy emission band at ca. 610 nm and
three high-energy emission peaks at ca. 430 nm. The high energy

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G.-N. Li et al. / Tetrahedron Letters 52 (2011) 675–678
Table 2
References and notes
Absorption and emission data of compounds L1, 5, and 6
1. (a) Bendikov, M.; Wudl, F.; Perepichka, D. F. Chem. Rev. 2004, 104, 4891; (b)
Compounds
Absorption
kabs/nm (
/MÀ1 cmÀ1
Luminescence (nm)
Segura, J. L.; MartOn, N. Angew. Chem. 2001, 113, 1416; (c) Coronado, E.; Day, P.
Chem. Rev. 2004, 104, 5419.
e
)
kex
kem
2. (a) Dumur, F.; Gautier, N.; Gallego-Planas, N.; Sahin, Y.; Levillain, E.; Mercier,
N.; Hudhomme, P.; Masino, M.; Girlando, A.; Lloveras, V.; Vidal-Gancedo, J.;
Veciana, J.; Rovira, C. J. Org. Chem. 2004, 69, 2164; (b) Li, H.-C.; Jeppesen, J. O.;
Levillain, E.; Becher, J. Chem. Commun. 2003, 846; (c) Feng, Y.-L.; Zhang, Q.; Tan,
W.-J.; Zhang, D.-Q.; Tu, Y.-Q.; Agren, H.; Tian, H. Chem. Phys. Lett. 2008, 455(4–
6), 256.
L1
5
235 (4107), 306 (7266),
384sh (7648)
259 (5325), 327 (6019),
450 (681)
259 (3668), 326 (4206),
449 (463)
348
383
383
440
407, 430,
453, 611
409, 432,
455, 612
6
3. Iwahori, F.; Golhen, S.; Ouahab, L.; Carlier, R.; Sutter, J.-P. Inorg. Chem. 2001, 40,
6541.
4. Liu, S.-X.; Dolder, S.; Franz, P.; Neels, A.; Stoeckli-Evans, H.; Decurtins, S. Inorg.
Chem. 2003, 42, 4801.
5. (a) Liu, W.; Wang, R.; Zhou, X.-H.; Zuo, J.-L.; You, X.-Z. Organometallics 2008, 27,
126; (b) Liu, W.; Xiong, J.; Wang, Y.; Zhou, X.-H.; Wang, R.; Zuo, J.-L.; You, X.-Z.
Organometallics 2009, 28, 755.
6. (a) Andreu, R.; Malfant, I.; Lacroix, P.; Cassoux, P. Eur. J. Org. Chem. 2000, 3, 737;
(b) Xue, H.; Tang, X.-J.; Wu, L.-Z.; Zhang, L.-P.; Tung, C.-H. J. Org. Chem. 2005, 70,
9727; (c) Zhao, Y.-P.; Wu, L.-Z.; Si, G.; Liu, Y.; Xue, H.; Zhang, L.-P.; Tung, C.-H. J.
Org. Chem. 2007, 72, 3632.
7. (a) Chahma, M.; Hassan, N.; Alberola, A.; Stoeckli-Evans, H.; Pilkington, M.
Inorg. Chem. 2007, 46, 3807; (b) Cosquer, G.; Pointillard, F.; Le Gal, Y.; Golhen,
S.; Cador, O.; Ouahab, L. Dalton Trans. 2009, 3495.
emission bands at ca. 430 nm could be resulted from p–
p⁄ ligand-
centered (LC) transitions. Similar to other reported Re(I) com-
plexes,18,19 the low-energy emission band was attributed to 3MLCT
transition. Moreover, both complexes 5 and 6 displayed well-re-
solved vibronically structured emissions at 407–453 and 409–
455 nm, respectively, corresponding to the C@N and C@C stretches
of the aromatic diimine ligand in the excited state.20–23
The absorption spectral changes of complexes 5 and 6 upon
addition of 7,7,8,8-tetracyanoquinodimethane (TCNQ) were inves-
tigated (Figs. S16 and S17). After adding the TCNQ to the solution
of 5 in CH2Cl2, a new absorption peak appeared at around
400 nm. With the enhancement of the amount of TCNQ, the inten-
sity of absorption peak was increasing. The results were consistent
with the formation of charge-transfer complexes between the
compounds containing electron-donor TTF unit and the classical
electron-acceptor TCNQ during the titration of compounds 5 and
6.16,24
8. Crivillers, N.; Oxtoby, N. S.; Mas-Torrent, M.; Veciana, J.; Rovira, C. Synthesis
2007, 1621.
9. Renner, R. M.; Burns, G. R. Tetrahedron Lett. 1994, 35, 269.
10. Characterization data of compound L1: 1H NMR (500 MHz, CDCl3): d 8.87 (s, 1H),
8.72 (s, 1H), 8.47–8.54 (m, 2H), 7.99 (dd, J12 = 1.5 Hz, J13 = 8.0 Hz, 1H), 7.88 (t,
J = 7.5 Hz, 1H), 7.51 (s, 1H), 7.35–7.41 (m, 3H), 2.45 (s, 6H); 13C NMR (500 MHz,
CDCl3): d 155.7, 155.3, 149.3, 147.4, 138.2, 137.2, 137.1, 136.0, 135.3, 135.1,
127.7, 127.6, 125.0, 124.0, 122.4, 121.3, 120.2, 111.1, 111.0, 19.3; MS (MALDI-
TOF): m/z 500.04 (M+1).
11. The X-ray crystallographic data for L1 and L3 have been deposited, as
supplementary publication numbers CCDC 796819 and CCDC 796820,
respectively at the Cambridge Crystallographic Data. Copies of the data can
be obtained free of charge from the CCDC, 12 Union Road, Cambridge CB2 1EZ,
In conclusion, three new
p-conjugated pyridine ligands with
UK; e-mail: deposit@ccdc.cam.ac.uk.
12. Crystal data for L1: C22H16N2S6, M = 500.73 g molÀ1
;
triclinic, P1,
ꢀ
tetrathiafulvalenes derivatives have been successfully prepared.
The Diels–Alder reaction is the key step for this multistep synthetic
strategy. The UV absorption and fluorescence studies on complexes
5 and 6 indicate that the TTF unit interacts with the electron
accepting group, thus leading to the intramolecular charge transfer
a = 5.0132(17) Å,
b = 95.707(3)°,
k(Mo ) = 0.71073 Å, 5655 reflections (1.61 < h < 26°) were collected at
291 K, 4092 unique reflections and 3157 reflections with I > 2 (I) used in
b = 13.1559(14) Å,
c = 17.038(2) Å,
a
= 102.8340(10)°,
c
= 97.260(2)°, V = 1077.3(4) Å3, Z = 2,
q ,
calcd = 1.544 g cmÀ3
K
a
r
refinements, 259 parameters, R1 = 0.0522, wR2 = 0.1284, GOF = 1.073.
13. Wu, J.-C.; Dupont, N.; Liu, S.-X.; Neels, A.; Hauser, A.; Decurtins, S. Chem. Asian J.
2009, 4, 392.
(ILCT) and metal-to-ligand (MLCT) transitions. These new p-conju-
gated pyridine ligands with tetrathiafulvalenes derivatives are ver-
satile electro-active ligands and more works on other metal
complexes based on these new ligands are underway in our
laboratory.
14. Devic, T.; Avarvari, N.; Batail, P. Chem. Eur. J. 2004, 10, 3697.
15. Crystal data for L3: C17H13NS6, M = 423.64 g molÀ1
;
monoclinic, P21/n,
= 90°, b = 91.511(4)°,
k(Mo ) = 0.71073 Å,
8868 reflections (1.85 < h < 25°) were collected at 291 K, 3191 unique
reflections and 1611 reflections with I > 2 (I) used in refinements, 219
a = 4.8958(10) Å, b = 11.718(2) Å, c = 31.761(6) Å,
a
c
= 90°, V = 1821.4(6) Å3, Z = 4, calcd = 1.545 g cmÀ3
q
,
Ka
r
parameters, R1 = 0.0655, wR2 = 0.1291, GOF = 0.923.
16. Chen, Y.; Liu, W.; Jin, J.-S.; Liu, B.; Zou, Z.-G.; Zuo, J.-L.; You, X.-Z. J. Organomet.
Chem. 2009, 694, 763.
Acknowledgment
17. Wang, K.-Z.; Huang, L.; Gao, L.-H.; Jin, L.-P.; Huang, C.-H. Inorg. Chem. 2002, 41,
3353.
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(b) Striplin, D. R.; Crosby, G. A. Chem. Phys. Lett. 1994, 221, 426; (c) Worl, L. A.;
Duesing, R.; Chen, P.; Ciana, L. D.; Meyer, T. J. J. Chem. Soc., Dalton Trans. 1991,
849.
This work was supported by the Major State Basic
Research Development Program (Grants 2007CB925103 and
2011CB808704), the National Science Fund for Distinguished
Young Scholars of China (Grant 20725104), and Academician Work
Station of Changzhou Trina Solar Energy Co., Ltd.
19. Li, M.-J.; Kwok, W.-M.; Lam, W. H.; Tao, C.-H.; Yam, V. W.-W.; Phillips, D. Lee
Organometallics 2009, 28, 1620.
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K. I. Organometallics 2008, 27, 1427.
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Valore, A. Inorg. Chem. 2007, 46, 8533; (b) Colombo, M. G.; Hauser, A.; Güdel, H.
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Supplementary data
Supplementary data (the experimental procedure and addi-
tional characterization data for all compounds along with their
1H NMR and 13C NMR spectra, absorption and fluorescence spectra,
cyclic voltammogram) associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2010.11.129.
24. Morita, Y.; Maki, S.; Ohmoto, M.; Kitagawa, H.; Okubo, T.; Mitani, T.; Nakasuji,
K. Org. Lett. 2002, 4, 2158.