Electroactive tetrathiafulvalenyl-1,2,3-triazoles by click chemistry: Cu- versus Ru-catalyzed azide-alkyne cycloaddition isomers

Article abstract of DOI:10.1002/chem.201201905

Two series of 4- and 5-tetrathiafulvalenyl-1,2,3-triazoles, as multifunctional ligands and precursors for molecular materials, have been synthesized by copper- or ruthenium-based "click" chemistry. The solid-state structures of three ligands and two Cu

Full text of DOI:10.1002/chem.201201905

FULL PAPER
DOI: 10.1002/chem.201201905
Electroactive Tetrathiafulvalenyl-1,2,3-triazoles by Click Chemistry:
Cu- versus Ru-Catalyzed Azide–Alkyne Cycloaddition Isomers
Thomas Biet, Thomas Cauchy, and Narcis Avarvari*[a]
Abstract: Two series of 4- and 5-tetrathiafulvalenyl-1,2,3-triazoles, as multifunc-
tional ligands and precursors for molecular materials, have been synthesized by
Keywords: click chemistry · coordi-
copper- or ruthenium-based “click” chemistry. The solid-state structures of three li-
nation chemistry · crystal structures ·
gands and two CuII complexes were determined. Large differences in the electron-
nitrogen heterocycles
fulvalene
· tetrathia-
donating properties between the 1,4- and 1,5-isomers were evidenced by cyclic vol-
tammetry. Theoretical calculations support this observation and allow the assign-
ment of the electronic transitions observed in UV/Vis spectra of the ligands.
Introduction
been prepared (1,4-isomers) by using Cu-catalyzed azide–
alkyne cycloaddition (CuAAC).[10] Although the main goal
of these studies was to connect the TTF unit to other moie-
Attachment of tetrathiafulvalene (TTF) units, well-known
electroactive compounds extensively used in diverse fields
of applications,[1] to various ligands constitutes one of the
privileged strategies to access valuable precursors for molec-
ular materials.[2] Indeed, the preparation of functional mate-
rials, in which combination of properties, such as conductivi-
ty, magnetism, luminescence, chirality, sensing, and so forth,
has been achieved[3] by starting from TTF-based ligands and
-derived metal complexes, represents one of the major re-
search direction in TTF field within the last decade.[2] Al-
though six-membered-ring nitrogen heterocycles, for exam-
ple, pyridines, bipyridines, pyrimidines, and so forth, have
been widely employed in such electroactive ligands and
complexes,[2,4] five-membered rings have been comparatively
much less investigated,[2] and especially those containing at
least two nitrogen atoms. For example, two series of TTF–
pyrazoles with ReI[5] and FeII[6] complexes, respectively, have
been recently described, and also two families of TTF–im-
AHCTUNGTRENNUNG
ties through the triazole linker,[11] its propensity as a ligand
has not yet been exploited. On the other hand, the comple-
mentary strategy, that is, Ru-catalyzed azide–alkyne cycload-
dition (RuAAC),[12] which gives rise to 1,5-isomers, has
never been reported so far in the case of TTF–triazole de-
rivatives. It is worth noting that 1,2,3-triazole heterocycles,
besides their well-known chemical stability, aromatic charac-
ter, large dipole moment (4.8–5.6 Debye), and hydrogen-
bond accepting ability,[13] proved to be not only efficient li-
gands for spin-crossover FeII complexes[14] and other transi-
tion metals,[15] although their coordination chemistry is rela-
tively unexplored especially for the monotriazoles, but also
offer an useful structural motif in peptidomimetic re-
search[16] and for the structure of chemical sensors.[17] We
therefore decided to directly attach a 1,2,3-triazole motif to
a TTF unit to take advantage of their individual features
into a multifunctional precursor for organic conductors and
electroactive metal complexes. We report herein the click
synthesis, solid-state structures, and properties of an unpre-
cedented family of TTF–1,2,3-triazoles containing both 1,4-
and 1,5-isomers together with CuII complexes of the latter.
ACHTUNGTRENNUNG
idazoles, used either in conducting charge-transfer salts[7] or
as donor/acceptor compounds with tunable intramolecular
charge transfer.[8] Note that in all but one case,[7] the TTF
unit and the ligands were spaced by variable lengths linkers,
and thus were not directly attached.
With the emergence and rapid widespread synthetic use
of click-chemistry methods in the last decade,[9] a few exam-
ples of TTF derivatives containing 1,2,3-triazole units have
Results and Discussion
Synthesis and solid-state structures of the TTF–triazoles:
For the click reactions, TTF- or ortho-dimethyl-TTF-trime-
thylsilylethynyl derivatives 1a and 1b, prepared according
to standard procedures (1b was not previously described),
were first deprotected and then engaged in metal-catalyzed
dipolar cycloaddition reactions to give 4-TTF–1,2,3-triazoles
2a,b and 5-TTF–triazoles 3a,b (Scheme 1). The conditions
chosen for the CuAAC reaction used CuI as the CuI
source[18] because the use of the classic CuSO4/ascorbate
system proved to promote the oxidation of TTF, whereas
[a] T. Biet, Dr. T. Cauchy, Dr. N. Avarvari
LUNAM Universitꢀ
Universitꢀ dꢁAngers, CNRS UMR 6200
Laboratoire MOLTECH-Anjou
2 bd Lavoisier, 49045 Angers (France)
Fax : (+33)02-41-73-54-05
E-mail: narcis.avarvari@univ-angers.fr
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201201905.
Chem. Eur. J. 2012, 18, 16097 – 16103
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Scheme 1. Synthesis of 4-TTF–1,2,3-triazoles 2 and 5-TTF–1,2,3-triazoles
3. Reaction conditions: i) (nBu)4NF, THF/MeOH (1:1); ii) CuI, PhCH2N3,
CHCl3/DIPEA (1:1), 708C; iii) [RuCp*Cl
Cp*=1,2,3,4,5-pentamethylcyclopentadienyl, DIPEA=N,N-diisopropyl-
ACHTUNGTRENNUNGethylamine.
ACHTNUGTNERN(NUG PPh3)2], PhCH2N3, THF, 658C.
Figure 1. Molecular structures of 2a (top) and 3a (bottom) with the num-
bering scheme.
the standard catalyst [RuCp*ClACHTNUGTRNEUNG(PPh3)2] gave satisfactory re-
sults for the preparation of 3a,b.[19]
The four ligands were isolated in moderate (2a,b) and
good (3a,b) yields as air-stable yellow–orange solids after
chromatographic workup, although solutions of 2a,b proved
to be more air sensitive than those of 3a,b. Accordingly, the
comparatively lower yields obtained for the 1,4-isomers can
be explained by the partial oxidation of 2a,b during purifi-
cation. Besides the usual spectroscopic characterization,
suitable single crystals for X-ray analysis were obtained for
2a, 3a, and 3b, whereas the crystals of 2b were of poorer
quality. Compounds 2a and 3b crystallize in the triclinic
space group P-1, whereas 3a crystallizes in the orthorhom-
bic space group Pcab, all of them with one independent
molecule in the asymmetric unit. It is worth noting the qua-
siplanarity between the triazole cycle and the TTF unit, with
dihedral angles of 4.3 and 4.48 for 2a and 3a, respectively
(Figure 1), thus suggesting some conjugation between the
two moieties.
Figure 2. Molecular structure of 3b with the numbering scheme.
The bond lengths and angles for 2a and 3a are in the
usual range for neutral TTF compounds, as shown by the
values of the central C3=C4 bonds of 1.335(3) and
1.338(4) ꢃ for 2a and 3a, respectively, and also by the aver-
ꢀ
ages of the internal C S bonds of 1.760 and 1.757 ꢃ for 2a
and 3a, respectively. In the case of the dimethyl-TTF deriva-
tive 3b, the dihedral angle TTF···triazole amounts to 6.08,
whereas the lengths of the central C3=C4 double bond
(1.350(5) ꢃ) is in the normal range for neutral TTF com-
pounds (Figure 2).
At the supramolecular level, several short S···S intermo-
lecular contacts are established especially in the packing of
2a, in which the formation of head-to-tail dimers occurs in
the bc plane (see Figure 3 and the Supporting Information).
These dimers interact laterally along the a direction through
S···S contacts of 3.69 and 3.73 ꢃ. In the packing of 3a (see
the Supporting Information), the shortest S···S intermolecu-
lar contacts range between 3.84 and 3.93 ꢃ, whereas the
Figure 3. Packing diagram for 2a. Intermolecular S···S contacts [ꢃ]: S3-
S4: 3.69, S3-S2: 3.92, S3-S1: 3.88, S1-S2 3.73, S1-S4: 3.94. Highlighted:
S3-S4 and S1-S2.
donors 3b form also centrosymmetric dimers, as do 2a, and
establish short lateral S···S contacts of 3.75 ꢃ (see the Sup-
porting Information).
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Preparation of Electroactive “Click” Ligands
FULL PAPER
Electrochemistry and UV/Vis spectroscopy: Cyclic vol-
tammetry (CV) measurements show reversible two one-
electron oxidation processes for the four ligands, which cor-
respond to the generation of radical cations, and then di-
TTF character, with the participation of the triazole ring
being more important for the 1,5-isomers (around 35%)
than for the 1,4-isomers (28 and 19% for 2a and 2b, respec-
tively; see Figure 4 and Tables S7 and S8 in the Supporting
Information).
ACHTUNGTRENNUNGcations. The main peculiarity of the CV measurements of
these ligands is the more facile oxidation of the 1,4- isomers
2a,b with respect to the 1,5-isomers 3a,b, as shown by
DE11/2 =0.1 V between 2a and 3a and DE11/2 =0.13 V be-
tween 2b and 3b (Table 1). This feature suggests that the
Table 1. Redox potentials (V vs SCE) of compounds 2–4 in CH2Cl2/
CH3CN.
ox1
ox2
Compound
E1/2
E1/2
2a
2b
3a
3b
4a
4b
0.39
0.31
0.49
0.44
0.28
0.23
0.83
0.74
0.90
0.85
0.68
0.63
Figure 4. HOMO (left) and LUMO (right) for 2a with an isovalue of
0.05.
An interesting feature concerns the relative positions of
the HOMOs, that is, ꢀ4.89, ꢀ4.77, ꢀ5.13, and ꢀ5.01 eV for
2a,b and 3a,b, respectively, thus clearly indicating that the
1,4-isomers 2a,b are more electron donating than the 1,5-
isomers 3a,b, which supports the electrochemical data (see
above). This difference is likely related to the position of
the sp3 N p donor atom (N1 and N3 for 2a and 3a, respec-
HOMO of the 1,4-isomers is comparatively higher in energy
than that of the 1,5-isomers (see the theoretical calcula-
tions). Moreover, the attachment of the triazole ring on
TTF as a 1,4-isomer seems to provide a slight electron-densi-
ty enrichment of TTF, very likely thanks to the possible con-
jugation with the sp3 N atom of the triazole ring. Note also
that the dimethyl-TTF derivatives 2b and 3b, which are
more electron rich due to the lateral methyl groups, oxidize
at lower potentials than their TTF counterparts 2a and 3a,
respectively.
Another interesting feature of this family of compounds
concerns the possible charge transfer from the TTF unit to
the triazole cycle. The UV/Vis spectroscopic study of the li-
gands shows, in all the cases, the existence of relatively large
absorption bands centered at lmax =388–394 nm, with extinc-
tion coefficients between e=2870 and 1760mꢀ1 cmꢀ1 for 2a
and 3b, respectively (see the Supporting Information). Fur-
thermore, the absorption bands that appear at higher energy
(lmax =250–350 nm), with e values on the order of 1.4ꢄ103–
1.7ꢄ104 mꢀ1 cmꢀ1 can be ascribed to the TTF unit[20] and p–
p* transitions of the triazole ring.
Theoretical calculations: To assign the corresponding
transitions, and also to understand the better electron-donat-
ing properties of the 1,4-isomers relative to the 1,5-isomers
and thus the higher stability of the latter, theoretical calcula-
tions at the DFT level were performed on the four ligands.
The optimized geometries were in good agreement with
those determined by X-ray diffraction studies (see Table S6
in the Supporting Information), with the exception of the di-
hedral angle TTF···triazole in 3a,b, which converged to a
value of around 328 to accommodate an intramolecular
(CH)TTF···Ph interaction, thus suggesting that the experimen-
tal value is determined by the solid-state packing. The anal-
ysis of the frontier orbitals shows that both the HOMO and
LUMO are of the p-type, with the HOMO based exclusively
on the TTF unit, whereas the LUMO has a mixed triazole/
ꢀ
tively; Figure 1) within the 1,3-diene system (C=C)TTF C=
C)triazole, that is, in the terminal position for the 1,4-isomers,
which thus has an electron-enriching effect on the (C=C)TTF
group due to conjugation. However, in the 1,5-isomers this
N atom is bound to the internal sp2 C atom of the diene
system, hence the donating effect is mainly felt by the (C=
C)triazole group. Note however that, very likely, a part of the
p electron density of the sp3 N atom is also delocalized over
the neighboring N=N unit. Furthermore, time-dependent
DFT (TD DFT) calculations, performed on the optimized
geometries with the same functional, allow the assignment
of the UV/Vis absorption bands (see Tables S9–12 in the
Supporting Information). Accordingly, the low-energy bands
calculated at lmax =412, 410, 432, and 434 nm for 2a,b and
3a,b, respectively, in agreement with the experimental
values (see Figure 5 and the Supporting Information), corre-
spond mainly to HOMO!LUMO transitions and thus can
be partially regarded as charge transfer from TTF to tria-
zole, when considering the nature of the frontier orbitals.
Also, the computed relative intensities for these low-
energy bands, deduced from the oscillator strength values,
well reproduce the experimental ones and show that the
charge transfer is slightly more favorable for the 1,4-isomers
2a,b, probably because of the better conjugation.
Copper (II) complexes 4a,b: As mentioned above, the co-
ordination chemistry of 1,2,3-triazoles as monodentate li-
gands is relatively underexplored and restrained to only a
few metal centers, such as PdII, PtII, and AgI.[15] Moderate
heating of solutions of ligands 3a,b in hexane/CH2Cl2 and
the CuII precursor [Cu
ACTHNUTRGEN(UNG hfac)2]·xH2O (hfac=hexafluoroace-
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N. Avarvari et al.
two units can adopt a coplanar arrangement, in which estab-
lishment of intramolecular hydrogen bonding might occur,
especially of the CH(triazole)···O(hfac) type, with regard to the
proximity of the triazole and hfac groups.
The CuII center lies in a slightly distorted-octahedral coor-
dination geometry, as shown by the angles about the metal
ꢀ
center, which are close to 908, whereas the Cu O1 bonds
ꢀ
(2.298(3) ꢃ) are significantly longer than the Cu O2 and
ꢀ
Cu N3 bonds (1.977(2) and 2.013(3) ꢃ, respectively). The
central C3=C4 bond length (1.339(5) ꢃ) clearly indicates
that the TTF unit is neutral. At the supramolecular level,
the formation of dimers in the bc plane through the estab-
lishment of S···S intermolecular contacts of 3.87–3.89 ꢃ is
observed (Figure 7), whereas the shortest Cu···Cu distance
amounts to 7.25 ꢃ. Note that shorter lateral S2···S2 contacts
of 3.54 ꢃ are established between the dimers along the a di-
rection.
Figure 5. Experimental (dashed lines) and theoretical (solid lines) absorp-
tion spectra of 2a (black) and 3a (red).
tylacetonate) in a 2:1 ratio, followed by the slow evapora-
tion of the solvents, affords complexes 4a,b, formulated as
[CuACHTUNGTRENNUNG(hfac)2(3)2], as yellow crystalline solids. Complex 4b (the
overall quality of the structure of 4b is superior to that of
4a; see the Supporting Information) crystallizes in the tri-
clinic system and space group P-1, with one independent
half molecule in the asymmetric unit and the metal ion lo-
cated on an inversion center. As generally observed in other
complexes, it is the N3 atom that acts as the ligand (N1 in
Figure 6). The triazole rings are now twisted by 468 with re-
Figure 7. Packing diagram for 4b in the bc plane. Intermolecular dis-
AHCTUNGTERGtNNUN ances [ꢃ]: S2-S2: 3.5, S2-S3: 3.89, S2-S1: 3.87, Cu-Cu: 7.25. Highlighted:
S2-S3 and S2-S1.
Complex 4a also crystallizes in the triclinic system, space
group P-1, and presents identical structural characteristics as
4b, which includes moderate twists of 38 and 438 between
the TTF and triazole units (see Figures S7–9 in the Support-
ing Information), intermolecular CHTTF···Ohfac and intramo-
lecular CHtriazole)···O(hfac) contacts. Note that complexes 4a,b
represent, to the best of our knowledge, the first structurally
characterized CuII complexes with monodentate 1,2,3-tria-
zole ligands. Interestingly, CV measurements show, besides
the typical pair of reversible oxidation processes, that the
TTF units in 4a,b oxidize at much lower potentials than in
the free ligands 3a,b, according to the E11/2 = +0.28 and
+0.23 V, respectively, relative to E11/2 = +0.49 and +0.44 V
in 3a,b, which represents an important cathodic shift. The
same trend is observed for the second oxidation process.
This feature is in sharp contrast with the classical behavior
of other TTF-based ligands, for which anodic shifts or un-
changed potentials are observed for the TTF units upon
complexation to a metal center.[2] The unusual low-oxidation
values observed here can be tentatively attributed to a more
Figure 6. Molecular structure of 4b with the numbering scheme. Hydro-
gen atoms have been omitted.
spect to the TTF units and coordinate the metal center trans
to each other. The observed twist between the TTF and tria-
zoles is very likely due to the establishment of unconven-
tional intermolecular CH(TTF)···O(hfac) hydrogen bonds (see
Figure S10 in the Supporting Information) as attested by the
short distance H5···O1(1+x, y, z) of 2.68 ꢃ. Moreover, an in-
tramolecular CH(triazole)···O(hfac) interaction can be disclosed,
when considering the short distance H8···O2 of 2.69 ꢃ. Note
that, when relative to the structures of the ligands, the
mutual conformation between the TTF and triazole units is
now s-cis, when considering the relative orientation of the
double bonds C5=C6 and C7=C8 with respect to the single
ꢀ
bond C6 C7. However, in solution it is conceivable that the
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Preparation of Electroactive “Click” Ligands
FULL PAPER
efficient conjugation of the sp3 N atom with the unsaturated
Experimental Section
ꢀ
system, as suggested by the comparatively shorter N3 C7,
ꢀ
ꢀ
General: Dry THF and diethyl ether were obtained from a solvent purifi-
cation system (LC Technology Solutions Inc.). NMR spectra were record-
ed on a Bruker Advance DRX 300 spectrometer operating at 300 and
N3 N2, and N1 C8 bond lengths in 4a,b relative to 3a,b,
which pushes some of the p electron density toward the
TTF unit. Thus, it seems that the attachment of the
75 MHz for H and 13C, respectively. The chemical shifts are expressed in
1
{CuACHTUNGTRENNUNG(hfac)2} fragment on the triazole induces an electron en-
parts per million (ppm, d) downfield from external TMS. The following
abbreviations are used: s=singlet, d=doublet, t=triplet, and m=multip-
let. MALDI-TOF MS spectra were recorded on a Bruker Biflex-IIITM
apparatus equipped with a N2 laser at d=337 nm. Elemental analyses
were recorded using Flash 2000 Fisher Scientific Thermo Electron ana-
lyzer. IR spectra were recorded on Bruker FTIR Vertex 70 spectrometer
equipped with a platinum–diamond ATR accessory. 2-Trimethylsilylethy-
nyltetrathiafulvalene (1a) was prepared by using a reported procedure.[23]
richment of the TTF unit when compared to the ligand
alone. It should be pointed out that, although in the solid
state the TTF and triazole units are mutually twisted, which
is the consequence of intermolecular hydrogen bonding (see
above) that should not be operative in solution, and thus a
coplanar arrangement might become the most stable confor-
mation in the absence of packing forces and intermolecular
interactions. To explain this unusual cathodic shift, one
might also consider the involvement of the HTTF or Htriazole
atoms (the distance H8···O2 is only 2.69 ꢃ in 4b and on the
same order of magnitude in 4a) in intramolecular hydrogen
bonding with the strongly negative fluorine or oxygen atoms
of the hfac ligands, in line with the intermolecular H5···O1
and intramolecular H8···O2 interactions observed in the
solid state. However, it seems more likely, with regard to
the closer proximity of the triazole and hfac groups than
TTF and hfac, that the main interaction should be
CH(triazole)···O(hfac) as already observed in the solid state. Such
2-Ethynyl-tetrathiafulvalene 1a: Tetrabutylammonium fluoride (1.4 mL,
1.40 mmol; 1m solution in THF) was added to a degassed solution of 1a
(350 mg, 1.17 mmol) in THF/methanol (30 mL, 1:1 v/v). The reaction
mixture was stirred at room temperature for 45 min and then the solvents
were removed under vacuum. The crude product was purified by flash
chromatography over neutral alumina (CH2Cl2 as the eluent) to yield 1a
as an orange–brown oil (189 mg, 71%), which was directly engaged in
the next step because of fast degradation. 1H NMR (CDCl3, 300 MHz):
d=6.61 (s, 1H), 6.44 (s, 2H), 3.27 ppm (s, 1H).
1-Benzyl-4-tetrathiafulvalenyl-1,2,3-triazole (2a): In a Schlenk tube, 1a
(150 mg, 0.66 mmol), benzyl azide (131 mg, 0.99 mmol), and CuI (7.5 mg,
6 mol%) were dissolved in CHCl3 (5 mL) and N,N-diisopropylethylamine
(3 mL). The reaction mixture was heated at 658C overnight and concen-
trated under vacuum. The crude product was purified by chromatography
over SiO2 (CH2Cl2/AcOEt (3:1) with and a few drops of NEt3 as the
eluent; Rf =0.3) to yield 2a as an orange–yellow solid (87 mg; 37%).
Suitable single crystals for X-ray analysis were grown by vapor diffusion
d+
an interaction, thus leading to a Cdꢀ
polarization,
ꢀ
H
would produce an increase of electron density on the tria-
zole ring and provide a partial triazolyl anion character,
which is also supported by the shorter bond lengths within
the ring in 4a, b relative to the corresponding ligands 3a,b
(see above). Thus, the electron-enriched triazole ring would
act as an electron-donating group toward TTF, and hence
easier oxidation for the latter. In the UV/Vis spectrum of 4a
and 4b the charge-transfer bands appear at lmax =403 and
394 nm, respectively, with an intensity that is comparatively
higher per TTF–triazole unit by a factor of 1.3, as indicated
by e=2010, 5220, 1760, and 4750mꢀ1 cmꢀ1 for 3a, 4a, 3b,
and 4b, respectively.
of pentane onto
a
solution of 2a in CH2Cl2. 1H NMR (CD2Cl2,
300 MHz): d=7.57 (s, 1H), 7.47–7.41 (m, 3H), 7.37–7.32 (m, 2H), 6.78 (s,
1H), 6.41 (s, 2H), 5.58 ppm (s, 2H); {1H} 13C NMR (CD2Cl2, 75 MHz):
d=140.8, 134.6, 129.1, 128.8, 128.2, 125.0, 120.1, 119.2, 119.1, 115.0,
54.3 ppm; MS (MALDI-TOF): m/z 361.0 [M+]; elemental analysis (%)
for C15H11N3S4: C 49.83, H 3.07, N 11.62, S 35.48; found: C 49.60, H 3.06,
N 11.24, S 35.02.
1-Benzyl-5-tetrathiafulvalenyl-1,2,3-triazole (3a): In a Schlenk tube, 1a
(150 mg, 0.66 mmol), benzyl azide (131 mg, 0.99 mmol), and [RuCp*Cl-
AHCTUNTGRENNG(UN PPh3)2] (31 mg, 6 mol%) were dissolved in dry THF (8 mL). The reac-
tion mixture was heated at 658C overnight and concentrated under
vacuum. The crude product was purified by chromatography over SiO2
(CH2Cl2/AcOEt (3:1) with a few drops of NEt3 as the eluent; Rf =0.3) to
yield 3a as a dark-yellow oil, which rapidly solidifies (164 mg; 70%).
Suitable single crystals for X-ray analysis were obtained by slow evapora-
tion of solvent from
a
solution of 3a in hexane/CH2Cl2. 1H NMR
Conclusion
(CD2Cl2, 300 MHz): d=7.77 (s, 1H), 7.44–7.35 (m, 3H), 7.24–7.18 (m,
2H), 6.42 (s, 2H), 6.30 (s, 1H), 5.69 ppm (s, 2H); {1H} 13C NMR (CD2Cl2,
75 MHz): d=135.1, 134.4, 129.5, 129.0, 128.4, 127.1, 121.6, 119.4, 119.3,
119.2, 52.4 ppm; MS (MALDI-TOF): m/z 360.6 [M+]; elemental analysis
(%) for C15H11N3S4: C 49.83, H 3.07, N 11.62, S 35.48; found: C 49.67, H
3.11, N 11.05, S 34.78.
We have synthesized two unprecedented families of mono-
dentate TTF–1,2,3-triazole ligands as 1,4- and 1,5-isomers by
using CuAAC and RuAAC click strategies, with a direct
connection between the TTF unit and triazole ring. Their
electrochemical and spectroscopic properties have been de-
termined, compared, and supported by DFT calculations.
Both series of compounds are excellent electron donors.
The charge transfer from the TTF to the triazole unit can be
possibly modulated by reaction with electrophiles, thus pro-
viding triazolium salts.[21] The 1,5-isomers have been used to
synthesize CuII complexes, which were structurally charac-
terized and shown to be valuable precursors for paramag-
netic molecular conductors. These two synthetic strategies
can be extended to the preparation of TTF-based chelating
pyridine–triazole ligands by the appropriate choice of the
starting azide.[22]
2-Iodo-6,7-dimethyl-tetrathiafulvalene (o-DMTTF-I): In a Schlenk tube,
6,7-dimethyl-tetrathiafulvalene (o-DMTTF; 800 mg, 3.44 mmol), was dis-
solved in dry diethyl ether (100 mL) under argon at ꢀ788C. Diisopropy-
lethylamine (532 mL, 3.79 mmol) followed by butyllithium (2.37 mL,
3.79 mmol; 1.6m solution in hexane) were added to the reaction mixture,
which was stirred at ꢀ788C for 1 h and then a yellow precipitate ap-
peared. Perfluorohexyl iodide (893 mL, 4.13 mmol) was added to the re-
action mixture, which was allowed to warm slowly to room temperature
and stirred overnight. After evaporation of the solvent, the crude product
was purified by chromatography over SiO2 (cyclohexane/CS2 (1:1) as the
eluent; Rf =0.8) to yield o-DMTTF-I as a light-orange solid (790 mg,
64%). 1H NMR (CDCl3 +NEt3, 300 MHz): d=6.43 (s, 1H), 1.98 ppm (s,
6H); {1H} 13C NMR (CDCl3 +NEt3, 75 MHz): d=124.4, 122.9, 111.5,
110.1, 77.3, 13.8 ppm; MS (MALDI-TOF): m/z 357.6 [M+]; elemental
Chem. Eur. J. 2012, 18, 16097 – 16103
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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16101

N. Avarvari et al.
analysis (%) for C8H7IS4: C 26.82, H 1.97, S 35.90; found: C 27.15, H
2.04, S 36.44.
Table 2. Crystal data and structure refinement for the ligands 2a, 3a, and
3b.
2-Trimethylsilylethynyl-6,7-dimethyltetrathiafulvalene (1b): In a Schlenk
tube, o-DMTTF-I (600 mg, 1.68 mmol), [PdACHTNUTRGNE(UNG PPh3)4] (97 mg, 5 mol%),
2a
3a
3b
Empirical formula C15H11N3S4
C15H11N3S4
361.51
293(2)
orthorhombic
Pcab
7.7058 (6)
19.852 (3)
20.971 (3)
90.00
90.00
90.00
3208.0 (7)
8
1.497
C17H15N3S4
389.58
293(2)
triclinic
P-1
6.655 (3)
9.5467 (17)
14.134 (3)
84.081 (15)
84.93 (2)
78.43 (3)
872.9 (5)
2
and CuI (32 mg, 10 mol%) were dissolved in dry THF (15 mL). Diisopro-
pylamine (1 mL, 7.12 mmol) and trimethylsilylacetylene (477 mL,
3.35 mmol) were added to the reaction mixture, which was heated at
608C overnight under argon. After evaporation of the solvent, the crude
product was purified by chromatography over SiO2 (cyclohexane as the
eluent; Rf =0.8) to yield 1b as an orange solid (510 mg, 92%). 1H NMR
(CDCl3 +NEt3, 300 MHz): d=6.52 (s, 1H), 1.97 (s, 6H), 0.23 ppm (s,
9H); {1H} 13C NMR (CDCl3 +NEt3, 75 MHz): d=125.8, 123.0, 122.6,
116.0, 111.6, 107.1, 99.7, 95.2, 13.8, ꢀ0.3 ppm; MS (MALDI-TOF):
m/z 327.7 [M+]; elemental analysis (%) for C13H14S4Si: C 47.51, H 4.91, S
39.03 found: C 47.59, H 5.07, S 40.23.
FW
T [K]
Crystal system
Space group
a [ꢃ]
b [ꢃ]
c [ꢃ]
a [8]
b [8]
361.51
293(2)
triclinic
P-1
6.2917 (2)
11.3734 (5)
11.4902 (8)
98.724 (5)
96.622 (4)
101.683 (3)
786.76 (7)
2
g [8]
V [ꢃ3]
Z
2-Ethynyl-6,7-dimethyltetrathiafulvalene (1b): Tetrabutylammonium flu-
oride (1.1 mL, 1.11 mmol; 1m solution in THF) was added to a degassed
solution of 1b (300 mg, 0.91 mmol) in THF/methanol (30 mL, 1:1 v/v).
The reaction mixture was stirred at room temperature for 45 min and the
solvents were removed under vacuum. The crude product was purified by
flash chromatography over neutral alumina (CH2Cl2 as the eluent) to
yield 1b as an orange–brown solid (178 mg, 78%), which was directly en-
Dc [gcmꢀ3
]
1.526
1.482
0.548
Absorption coeffi- 0.601
0.590
cient [mmꢀ1
]
GOF on F 2
1.023
1.114
1.047
Final R indices
[I>2s(I)]
R indices (all
data)
R1=0.0438,
wR2=0.0757
R1=0.0924,
wR2=0.0898
R1=0.0523,
wR2=0.0767
R1=0.1190,
wR2=0.0929
R1=0.0494,
wR2=0.1108
R1=0.0925,
wR2=0.1303
1
gaged in the next step. H NMR (CDCl3, 300 MHz): d=6.59 (s, 1H), 3.24
(s, 1H), 1.97 ppm (s, 6H).
1-Benzyl-4-(6’,7’-dimethyltetrathiafulvalenyl)-1,2,3-triazole (2b): In
a
Schlenk tube, 1b (150 mg, 0.59 mmol), benzyl azide (117 mg, 0.88 mmol),
and CuI (6.7 mg, 6 mol%) were dissolved in CHCl3 (5 mL) and N,N-dii-
sopropylethylamine (3 mL). The reaction mixture was heated at 658C
overnight and concentrated under vacuum. The crude product was puri-
fied by chromatography over SiO2 (CH2Cl2/AcOEt (3:1) with a few
drops of NEt3 as the eluent; Rf =0.3) to yield 2b as a dark-yellow solid
(102 mg, 45%). 1H NMR (CDCl3 +NEt3, 300 MHz): d=7.44–7.39 (m,
4H), 7.32–7.29 (m, 2H), 6.81 (s, 1H), 5.55 (s, 2H), 1.98 ppm (s, 6H);
{1H} 13C NMR (CDCl3 +NEt3, 75 MHz): d=141.3, 134.2, 129.3, 129.0,
128.2, 124.5, 122.9, 122.8, 119.9, 115.5, 54.6, 13.8 ppm; MS (MALDI-
TOF): m/z 389.1 [M+]; elemental analysis (%) for C17H15N3S4: C 52.41,
H 3.88, N 10.79, S 32.92; found: C 52.82, H 3.80, N 10.55, S 33.31.
Table 3. Crystal data and structure refinement for the complexes 4a and
4b.
Empirical formula
C40H26Cu1F12N6O4S8
C44H34Cu1F12N6O4S8
FW
T [K]
1200.72
293(2)
1256.78
293(2)
Crystal system
Space group
a [ꢃ]
b [ꢃ]
c [ꢃ]
triclinic
P-1
triclinic
P-1
12.6740 (9)
15.2920 (13)
15.5360 (11)
110.600 (7)
100.420 (6)
111.11 (6)
2460.9 (3)
2
7.2569 (6)
12.2100 (18)
15.479 (3)
103.560 (12)
90.642 (7)
98.604 (11)
1316.8 (3)
1
1-Benzyl-5-(6’,7’-dimethyl-tetrathiafulvalenyl)-1,2,3-triazole (3b): In
Schlenk tube, 1b (150 mg, 0.59 mmol), benzyl azide (117 mg, 0.88 mmol),
and [RuCp*Cl(PPh3)2] (28 mg, 6 mol%) were dissolved in dry THF
a
a [8]
b [8]
ACHTUNGTRENNUNG
g [8]
(8 mL). The reaction mixture was heated at 658C overnight and concen-
trated under vacuum. The crude product was purified by chromatography
over SiO2 (CH2Cl2/AcOEt (3:1) as the eluent; Rf =0.3) to yield 3b as an
orange–red solid (164 mg; 72%). Suitable single crystals for X-ray analy-
sis were obtained by slow evaporation of solvent from a solution of 3b in
CH2Cl2. 1H NMR (CDCl3 +NEt3, 300 MHz): d=7.76 (s, 1H), 7.38–7.35
(m, 3H), 7.21–7.18 (m, 2H), 6.17 (s, 1H), 5.67 (s, 2H), 2.00 ppm (s, 6H);
{1H} 13C NMR (CDCl3 +NEt3, 75 MHz): d=134.8, 134.6, 129.6, 129.1,
128.5, 127.1, 123.0, 122.9, 121.6, 119.4, 52.5, 13.8 ppm; MS (MALDI-
TOF): m/z 388.8 [M+]; elemental analysis (%) for C17H15N3S4: C 52.41,
H 3.88, N 10.79, S 32.92; found: C 52.39, H 3.92, N 9.84, S 33.02.
V [ꢃ3]
Z
Dc [gcmꢀ3
]
1.620
1.585
Absorption coefficient
[mmꢀ1
GOF on F 2
0.876
0.822
]
1.004
1.058
Final R indices [I>2s(I)] R1=0.0711,
wR2=0.1327
R1=0.0461,
wR2=0.0888
R1=0.0831,
wR2=0.1030
R indices (all data)
R1=0.2118,
wR2=0.1740
4a: In a Schlenk tube, 3a (14.5 mg, 0.04 mmol) and [CuACHTNUTRGNEUNG(hfac)2]·xH2O
(9.58 mg, 0.02 mmol) were stirred at 608C in hexane/dichloromethane
(8 mL, 1:1) over 1 h. The solution was allowed to return to room temper-
ature, and dark-yellow crystals of 4a were obtained after slow evapora-
tion of the solvents (23 mg, 96%). MS (ES): m/z 994.77 [Mꢀhfac+]; ele-
mental analysis (%) for C40H26CuF12N6O4S8: C 39.95, H 2.18, N 6.99, S
21.33; found: C 39.77, H 2.24, N 6.62, S 21.58.
with a MoKa (l=0.71073 ꢃ) X-ray tube with a graphite monochromator.
The structures were solved (SHELXS-97) by direct methods and refined
(SHELXL-97) by full-matrix least-square procedures on F2. All non-hy-
drogen atoms were refined anisotropically. Hydrogen atoms were intro-
duced at calculated positions (riding model), included in structure-factor
calculations but not refined.
4b: In a Schlenk tube, 3b (15.7 mg, 0.04 mmol) and [CuACHTNUTRGNEUNG(hfac)2]·xH2O
CCDC 875364 (2a), CCDC 875365 (3a), CCDC 875366 (3b),
CCDC 894407 (4a), and CCDC 875367 (4b) contain the supplementary
crystallographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Center via
www.ccdc.cam.ac.uk/data_request/cif.
(10 mg, 0.02 mmol) were stirred at 608C in hexane/dichloromethane
(8 mL, 1:1) over 1 h. The solution was allowed to return to room temper-
ature, and dark-yellow crystals of 4b were obtained after slow evapora-
tion of the solvents (25 mg, 98%). MS (ES): m/z 1050.87 [Mꢀhfac+]; ele-
mental analysis (%) for C44H34CuF12N6O4S8: C 41.98, H 2.72, N 6.68, S
20.38; found: C 41.87, H 2.75, N 6.44, S 20.82.
Electrochemical studies: CV measurements were performed by means of
a three-electrode cell equipped with a platinum millielectrode with a sur-
face area of 0.126 cm2, an Ag/Ag+ pseudoreference, and a platinum-wire
counterelectrode. The potential values were readjusted with respect to
X-ray structure determinations: Details about data collection and solu-
tion refinement are given in Tables 2 and 3. X-ray diffraction measure-
ments were performed on a Bruker Kappa CCD diffractometer operating
16102
www.chemeurj.org
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 16097 – 16103

Preparation of Electroactive “Click” Ligands
FULL PAPER
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a
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Received: May 30, 2012
Revised: August 29, 2012
Published online: October 18, 2012
Chem. Eur. J. 2012, 18, 16097 – 16103
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
16103