N -Heterocyclic donor- and acceptor-type ligands based on 2-(1 H -[1,2,3]Triazol-4-yl)pyridines and their ruthenium(II) complexes

Article abstract of DOI:10.1021/jo100286r

New 2-(1H-[1,2,3]triazol-4-yl)pyridine bidentate ligands were synthesized as bipyridine analogs, whereas different phenylacetylene moieties of donor and acceptor nature were attached at the 5-position of the pyridine unit. The latter moieties featured a crucial influence on the electronic properties of those ligands. The N-heterocyclic ligands were coordinated to ruthenium(II) metal ions by using a bis(4,4′-dimethyl-2,2′-bipyridine)ruthenium(II) precursor. The donor or acceptor capability of the 2-(1H-[1,2,3]triazol-4-yl) pyridine ligands determined the quantum yield of the resulting ruthenium(II) complexes remarkably. Separately, 2-([1,2,3]triazol-4-yl)pyridine ligands are known to be potential quenchers, but using these new ligand systems led to room temperature emission of the corresponding ruthenium(II) complexes. The compounds have been fully characterized by elemental analysis, high-resolution ESI mass spectrometry, ¹H and ¹³C NMR spectroscopy, and X-ray crystallography. Theoretical calculations for two ruthenium(II) complexes bearing a donor and acceptor unit, respectively, were performed to gain a deeper understanding of the photophysical behavior.

Full text of DOI:10.1021/jo100286r

pubs.acs.org/joc
N-Heterocyclic Donor- and Acceptor-Type Ligands Based on
2-(1H-[1,2,3]Triazol-4-yl)pyridines and Their Ruthenium(II) Complexes
Bobby Happ,†,‡ Daniel Escudero,§ Martin D. Hager,†,‡ Christian Friebe,†
z
†
,§
Andreas Winter,†,‡,^ Helmar Gorls, Esra Altuntas-, Leticia Gonzalez,* and
€
ꢀ
Ulrich S. Schubert*,†,‡,^
†Laboratory of Organic and Macromolecular Chemistry, Friedrich-Schiller-University Jena, Humboldtstrasse
10, 07743 Jena, Germany, ‡Dutch Polymer Institute (DPI), P.O. Box 902, 5600 AX Eindhoven,
The Netherlands, §Laboratory of Physical Chemistry, Friedrich-Schiller-University Jena, Helmholtzweg 4,
07743 Jena, Germany, ^Laboratory of Macromolecular Chemistry and Nanoscience, Eindhoven University of
Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands, and zLaboratory of Inorganic and
Analytical Chemistry, Friedrich-Schiller-University Jena, Lessingstrasse 8, 07743 Jena, Germany
*To whom correspondence should be addressed. L.G.: fax þ49 (0)3641 948302 and e-mail leticia.
gonzalez@uni-jena.de. U.S.S.: fax: þ49 (0)3641 948202, e-mail ulrich.schubert@uni-jena.de, and internet
www.schubert-group.com.
Received February 19, 2010
New 2-(1H-[1,2,3]triazol-4-yl)pyridine bidentate ligands were synthesized as bipyridine analogs,
whereas different phenylacetylene moieties of donor and acceptor nature were attached at the
5-position of the pyridine unit. The latter moieties featured a crucial influence on the electronic
properties ofthose ligands. The N-heterocyclicligands were coordinated toruthenium(II) metal ions by
using a bis(4,40-dimethyl-2,20-bipyridine)ruthenium(II) precursor. The donor or acceptor capability of
the 2-(1H-[1,2,3]triazol-4-yl)pyridine ligands determined the quantum yield of the resulting ruthenium(II)
complexes remarkably. Separately, 2-([1,2,3]triazol-4-yl)pyridine ligands are known to be potential
quenchers, but using these new ligand systems led to room temperature emission of the corresponding
ruthenium(II) complexes. The compounds have been fully characterized by elemental analysis, high-
resolution ESI mass spectrometry, 1H and 13C NMR spectroscopy, and X-ray crystallography. Theo-
retical calculations for two ruthenium(II) complexes bearing a donor and acceptor unit, respectively,
were performed to gain a deeper understanding of the photophysical behavior.
Introduction
photophysical and electrochemical properties that can result
from their corresponding metal complexes. Such distinctiveness
can be utilized for supramolecular self-assembly, molecular
electronics, and catalysis applications.1 Because functionalization
The well-known N-heterocycles 2,20-bipyridine (bpy) and
2,20:60,200-terpyridine (tpy) have been widely studied owing to
their predictable coordination behavior and the interesting
DOI: 10.1021/jo100286r
r
Published on Web 05/24/2010
J. Org. Chem. 2010, 75, 4025–4038 4025
2010 American Chemical Society

Happ et al.
JOCArticle
Our interest was to tune in particular the electronic
properties of the bidentate 2-(1H-[1,2,3]triazol-4-yl)pyridine
ligands. This was accomplished by introducing electron-
donating and electron-withdrawing units on the 5-position
of the pyridine ring with a 2-(1H-[1,2,3]triazol-4-yl)pyridine
system (trzpy) as central structural motive (Scheme 1). In the
present study the synthesis and the characterization of new
2-(1H-[1,2,3]triazol-4-yl)pyridine ligand systems with donor
and acceptor nature are described by using the efficient
Sonogashira coupling and the versatile copper(I)-catalyzed
azide-alkyne 1,3-cycloaddition intended for the ligand
synthesis as well as the subsequent coordination onto a bis-
(4,40-dimethyl-2,20-bipyridine)ruthenium(II) precursor com-
plex. The photophysical properties were studied by UV-vis
and emission spectroscopy, cyclic voltammetry and analyzed
in detail by theoretical calculations.
The coordination to the ruthenium(II) metal ion by using
bis(4,40-dimethyl-2,20-bipyridine) as ancillary ligand reve-
aled two interesting features. First, 2-(1H-[1,2,3]triazol-4-yl)-
pyridine systems are known to be potential luminescence
quenchers at room temperature as soon as they are attached
to a ruthenium(II) metal ion8 and, unexpectedly, the here-
in described heteroleptic ruthenium(II) complexes bearing a
2-(1H-[1,2,3]triazol-4-yl)pyridine ligand furnished with an
acceptor unit overcame this luminescence quenching and
yielded in room temperature emission. Second, by replacing
the latter acceptor system with a donor structure the lumine-
scence at room temperature decreased considerably. There-
fore, time-dependent density functional theory calculations
(TD-DFT) were done to gain a deeper insight into the
photophysical processes.
FIGURE 1. Schematic representation of 1H-[1,2,3]triazole-containing
ligand architectures.
of polypyridine-based chelators can be synthetically trouble-
some,2 it remains important to search for new approaches in
the preparation of analogous bidentate chelating ligands
that also possess well-defined coordination properties and
can be prepared and modified with high effectiveness. In this
respect the CuI-catalyzed 1,3-cycloaddition of organic azides
with terminal alkynes (the CuAAC reaction) has a great
potential due to its mild reaction conditions and wide range
of usable substrates.3 The latter features have directed its
application in the synthesis of functional molecules for
biological and material sciences.4 Furthermore, the develop-
ment of the CuAAC reaction resulted in an increased interest
toward the coordination chemistry of 1,4-functionalized
1H-[1,2,3]triazoles due to their potential as N-donor ligands.
A variety of new bi-,5,6 tri-,7 and polydentate6 1H-[1,2,3]-
triazole-containing ligands have been synthesized and their
coordination properties were investigated (Figure 1).
Results and Discussion
Synthesis. The general procedure for the synthesis of donor-
type 2-(1H-[1,2,3]triazol-4-yl)pyridine 5 is outlined in Scheme 2.
The Sonogashira cross-coupling9 and the CuAAC3b,c reaction
were the key reaction types for the construction of the targeted
ligand. Consecutive Sonogashira reactions with 2 mol % of Pd0
catalyst were carried out to synthesize intermediate 3. Subse-
quently, deprotection of the trimethylsilyl group (TMS) utilizing
fluoride ions afforded 4 in good yield (75%). The subsequent
CuAAC reaction provided the final product 5 (67% yield) by
using 5 mol % CuSO4 and 25 mol % sodium ascorbate as the
catalytic system. The purity of 5 was proven by NMR spectro-
scopy, mass spectrometry, and elemental analysis.
The synthesis of the acceptor systems 10a-dalso involved the
Sonogashira cross-coupling and the CuAAC reaction as syn-
thetic tools; however, a different synthetic approach had to be
used. The synthesis of a precursor compound similar to 3 with
electron-withdrawing substituents could not be performed. As a
result, two alternative routes were applied to synthesize pre-
cursor compound 9(Scheme 3). Though the first route consisted
of one step less, both routes gave comparable overall yields
(route 1: 61%; route 2: 51%). The reason for this observation
might be the efficient cleavage of the TMS group10 affording 6
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SCHEME 1. Schematic Representation of the Synthesis of the N-Heterocyclic Ligands and Their Corresponding Heteroleptic
Ruthenium(II) Complexes
in quantitative yield. Subsequently, the ligands 10a-d were
obtained in good to high yields (70-93%) utilizing the straight-
forward Sonogashira cross-coupling with 2-4 mol % of the
palladium(0) catalyst. All final products were purified by col-
umn chromatography on silica and the purity was confirmed by
elemental analysis, high-resolution mass spectrometry (HR-
ESI-MS), as well as 1H and 13C NMR spectroscopy.
The second route turned out to be also a versatile way to
introduce an aromatic substituent in the N1-position of the
triazole as an alternative to the decyl-moiety in 10 (Scheme 4).
Substitution of the flexible alkyl-chain by a more rigid phenyl
ring should enhance the growth of single crystals, in particular of
the targeted heteroleptic RuII complexes.Forthispurpose,6was
allowed to react with phenylazide8 using the CuAAC reaction
yielding compound 11 (45%) after cleavage of the isopropanol
protection group (Scheme 4). Finally, the N1-phenyl-substituted
compound 12 was obtained by Sonogashira cross-coupling
reaction in good yield (77%).
Besides the systems featuring donor or acceptor units att-
ached to the pyridine ring (5, 10, and 12), also derivatives with
similar substituents in the N1-position of the 1H-[1,2,3]tri-
azole subunit were in the focus (Scheme 5). For this purpose,
(1-azidophenyl)boronic acid8 and 2-ethynylpyridine were con-
jugated by using the CuAAC reaction yielding 13. The purifica-
tion steps, i.e. simple filtration and recrystallization from
ethanol, fully met the criteria of a “click reaction” as defi-
ned by Sharpless et al.3a Following two times the standard
protocol for the Sonogashira cross-coupling reaction, the final
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SCHEME 2. Schematic Representation of the Synthesis of the Donor-Type Ligand 5
SCHEME 3. Schematic Representation of the Synthesis of the Acceptor-Type Ligands 10
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SCHEME 4. Schematic Representation of the Synthesis of the Acceptor-Type Ligand 12 Bearing an Aromatic Moiety
SCHEME 5. Schematic Representation of the Synthesis of a 2-(1H-[1,2,3]Triazol-4-yl)pyridyl Ligand with an Acceptor-Unit Attached
on the Triazole Ring
acceptor-functionalized compound 15 was synthesized in mode-
rate yield (50%). However, the implementation of the O-alkyl
donor system in analogy to 5 was not yet successful.
Crystallographic Analysis. For the heteroleptic RuII com-
plex 17 single crystals suitable for X-ray crystallographic
analysis were obtained by slow diethyl ether diffusion reveal-
ing the coordination of the two 4,40-dimethyl-2,20-bipyridine
and the 2-(1H-[1,2,3]triazol-4-yl)pyridine ligand 12 to the
RuII core. The molecule crystallizes in a triclinic system with
P1 symmetry (for ORTEP see the Supporting Information).
The structural parameters observed from 17 were compared
to the corresponding structurally related homoleptic com-
plex [Ru(bpy)3](PF6)212 (Figure 2).
It is noteworthy that the interligand angle of the nitrogen
atoms in the square plane were similar for both complexes
(17: 170.40ꢀ and 174.40ꢀ; [Ru(bpy)3](PF6)2: 172.3ꢀ; see
Figure 2) resulting in a comparable distortion of the ideal
octahedral geometry. The bond length from ruthenium
to the coordinating nitrogen atom of the triazole ring
(N0: 2.028(2), Figure 2) was shortened significantly compared
The heteroleptic ruthenium(II) complexes 16 to 18 of the
general structure [(dmbpy)2RuL](PF6)2 (dmbpy =4,40-di-
methyl-2,20-bipyridine) were synthesized by heating Ru-
8,11
(dmbpy)2Cl2
and the appropriate ligands (L = 5, 10,
12, 15) under microwave irradiation (Table 1). After 2 h the
reactions were completed and a 10-fold excess of NH4PF6
was added to precipitate the products. In most cases, pre-
cipitation occurred after 15 min and the pure complex was
isolated after washing with ethanol and diethyl ether in
moderate to very good yields (Table 1). Only 16c and 17
had to be recrystallized from ethanol/water. The latter fact
may explain the moderate yields obtained for these com-
plexes. The verification of the structures of 16-18 was
1
carried out by H and 13C NMR spectroscopy as well as
HR-ESI mass spectrometry.
(12) Biner, M.; Buergi, H. B.; Ludi, A.; Roehr, C. J. Am. Chem. Soc. 1992,
114, 5197–5203.
€
(13) Egbe, D. A. M.; Bader, C.; Nowotny, J.; Gunther, W.; Klemm, E.
Macromolecules 2003, 36, 5459–5469.
€
€
(11) Rau, S.; Ruben, M.; Buttner, T.; Temme, C.; Dautz, S.; Gorls, H.;
Rudolph, M.; Walther, D.; Vos, J. G. J. Chem. Soc., Dalton Trans. 2000,
3649–3657.
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TABLE 1. Synthesis of the Heteroleptic Ruthenium(II) Complexes
FIGURE 2. A comparison of bond angles and bond lengths derived
from the crystallographic analysis. Left: RuII complex 17. Right:
Ru(bpy)3(PF6)2.12
FIGURE 3. Cyclic voltammograms of ruthenium(II) complexes
16a to 16e (10-4 M, CH3CN containing 0.1 M TBAPF6).
electrochemical properties are presented in Table 2 and
Figure 3.
In all cases a first reversible oxidation wave occurred at
around 0.85 V (vs Fc/Fcþ) that can be assigned to a RuII/RuIII
oxidation process. Furthermore, compound 16a showed a
second oxidation process at 1.28 V, probably originating from
an oxidation process of the triazole ligand. Due to the absence
of electron-donating substituents at the triazole ligand, the
respective ligand-centered π-orbitals are more stabilized for
complexes 16b-e and, therefore, no such oxidation processes
were visible in the CV spectrum.
In contrast to the other systems, the nitro-containing
complexes 16b and 16d featured a single reversible reduction
wave at around -1.35 V vs Fc/Fcþ that could be assigned to
a triazole ligand-based reduction process. Both complexes
provided a strongly electron-withdrawing substituent caus-
ing a stabilization of the triazole-ligand-located antibonding
to that of the adjacent coordinating nitrogen atom of the
bipyridine ring (N: 2.052(1), Figure 2). In contrast, the bond
length of the opposed coordinating nitrogen to the triazole
nitrogen was not reduced but comparable to that of bipyridine.
This observation could be rationalized by the expected higher
π-acceptor strength of the triazole ring and, consequently, the
increased π-back-bonding resulting in a reduced bond length.
Additionally, the distance between the ruthenium center and
the nitrogen atom of the pyridine moiety of 12 was elongated
considerably (N: 2.102(1), Figure 2). This fact derives from a
reduction of electron density of this bond in concert with an
increased π-back-bonding toward the triazole ring.
Electrochemical Properties. The complexes 16a-e were
subsequently characterized by cyclic voltammetry (CV). The
TABLE 2. Electrochemical Data of Selected RuII Complexes
complex
E1/2,ox [V]a
E1/2,red [V]a
Egopt [eV]b
EHOMO [eV]c
ELUMO [eV]c
16a
16b
16c
16d
16e
0.82, 1.28
0.88
0.84
0.88
0.84
-1.85, -2.06, -2.23
-1.34, -1.97, -2.18
-1.89, -2.13
-1.36, -1.98, -2.11
-1.85, -2.03, -2.18
2.48
2.43
2.44
2.43
2.49
-5.62
-5.67
-5.69
-5.64
-5.64
-3.18
-3.70
-3.21
-3.62
-3.17
aMeasurements were performed in CH3CN containing 0.1 M TBAPF6. The potentials are given vs ferrocene/ferricinium (Fc/Fcþ) couple. bEstimated
from the UV-vis spectra at 10% of the maximum of the longest-wavelength absorption band on the low-energy side. cDetermined using EHOMO
-[(Eonset,ox - Eonset,Fc/Fcþ) - 4.8]eV and ELUMO = -[(Eonset,red - Eonset,Fc/Fcþ) - 4.8]eV, respectively.13
=
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TABLE 3. Photophysical Data of the Donor- and Acceptor-Type
Ligands
transition. More bands were present below 280 nm that arose
from further MLCT, ligand-to-ligand charge transfer (LLCT)
and metal-centered (MC) d-d transitions, respectively.
compound
λ
abs [nm] (ε [103 L mol-1 cm-1])a
λ
em [nm]a
3
3
The observed emission energies (Table 4) showed a clear
dependency on the used substituent. Starting at 602 nm in the
case of the alkoxy-containing system, the emission was
strongly red-shifted to 621 nm for the unsubstituted triazole
ligand and to 640 and even 674 nm in the case of the com-
plexes possessing an o- and p-nitrophenyl moiety, respec-
tively. This trend was most likely caused by the stabilization
of the π*-orbitals located at the triazole ligand via introduc-
tion of electron-withdrawing groups. These orbitals are, at
least in case of electron-acceptor substituents, supposed to be
involved in the emissive 3MLCT state, so that a lower energy
level led to decreased emission energy.
Also depicted in Table 4 are the photoluminescence quan-
tum yields (ΦPL) of the ruthenium(II) systems. At least in
aerated acetonitrile, the ΦPL values were rather low (around
0.1% for 16a-e, nearly no emission in the case of phenyl-
substituted 17 and about 0.3% for the “inverse” system 18).
When changing to dichloromethane as solvent, the emission
efficiencies rose and a significant difference between the
donor- (16a) and the acceptor-substituted complex (16b)
became obvious (0.5% and 2.2%, respectively).
DFT Calculations. To gain a more detailed insight into the
photophysical properties of the acceptor- and donor-based
complexes, density functional theory (DFT) and time-depended
(TD) DFT (B3LYP/6-31G*) calculations were performed.
DFT/TD-DFT studies on Ru(II) polypyridyl complexes have
been successfully used to understand and rationalize the experi-
mental photophysical features of these complexes.15 Figure 4
shows the obtained Kohn-Sham frontier orbitals and energy
level schemes of the ground state optimized geometries of
complexes 16a and 16b. In complex 16b the highest occupied
molecular orbitals (HOMOs) were the set t2g of the central RuII
atom. A π-orbital localized in the 2-(1H-[1,2,3]triazol-4-yl)-
pyridine ligand (πL) was lower in energy corresponding to
the HOMO-3. These orbitals were in different order in the
complex 16a: The πL corresponded to the HOMO orbital and
the set t2g of orbitals was found lower in energy. Both com-
plexes 16a and 16b also differed in the order of the lowest
unoccupied molecular orbitals (LUMO). In the case of the
acceptor-type compound the LUMO orbital corresponded to a
π-antibonding orbital located in the 2-(1H-[1,2,3]triazol-4-yl)-
pyridine ligand (π*L), while this orbital was shifted to the
LUMOþ2 in complex 16a. In 16a the LUMO possessed
π-antibonding character and was located on the dmbpy ligand
(π*dmbpy). Substitution of the 2-(1H-[1,2,3]triazol-4-yl)pyridine
ligand with an electron-donating or -withdrawing group,
5
250 (2), 323 (32), 338 (30)
273 (26), 343 (47)
271 (30), 315 (33), 338 (21)
297 (24), 315 (32), 329 (26)
297 (24), 315 (29), 329 (25)
270 (18), 342 (25)
378
-
b
10a
10b
10c
10d
12
b
-
363
358
b
-
aFor all measurements: 10-6 M solution (CH2Cl2). For emission
measurements: excitation at longest absorption wavelength. bNo emis-
sion detectable at room temperature.
π*-orbitals (q.v. results of the DFT calculations). Starting at
-1.8 V all five complexes showed additional reduction waves
deriving from ligand-based (dmbpy and triazole ligand)
π*-orbitals.
Photophysical Properties. The UV-vis absorption and
emission data of the donor- and acceptor-type systems are
depicted in Table 3. As expected, ligand 10a (nitro-moiety in
the para-position) revealed the largest bathochromic shift in
the absorption spectrum, but did not show fluorescence at
room temperature. In contrast to 10a, the donor-system 5 as
well as the acceptor ligands without nitro groups (10c/d)
revealed room temperature emission. Compound 5 showed
the largest Stokes shift of 3130 cm-1 whereas 10c and 10d
featured remarkably small Stokes shifts (10c: 1220 cm-1
;
10d: 1240 cm-1). The reason for the large Stokes shift of 5
was probably caused by the charge transfer nature of the
electronic transition.
The optical properties of the heteroleptic ruthenium(II)
complexes are summarized in Table 4. A common feature of
all complexes was a broad absorption band at around 400 to
500 nm, which could be assigned mainly to various metal-to-
ligand charge-transfer (MLCT) transitions between the ruthe-
nium metal center and either the 4,40-dimethyl-2,20-bipyridine
or the triazole ligand (see DFT calculations). All complexes
possessed extinction coefficients of about 20 000 M-1 cm-1
,
whereas the alkoxy and the unsubstituted systems showed
3
slightly higher values (24 000 and 21 000 M-1 cm-1) than
3
their trifluoromethyl (18 000 M-1 cm-1) or even nitro coun-
3
3
terparts (12 000 and 13 000 M-1 cm-1). Between 300 and
400 nm, the complexes investigated herein exhibited different
absorption behavior concerning their wavelength maxima and
band shape. Therefore, this region seemed to be dominated by
intraligand (IL) transitions, namely located at the triazole ligand.
A comparison with the respective absorption spectra of triazole
ligands (Table 3) supported this assumption. At 286 nm a strong
absorption (65 000 to 135 000 M-1 cm-1) could be observed for
all complexes, most likely originating from a dmbpy-located IL
3
TABLE 4. Photophysical Data Recorded for the RuII Complexes
abs [nm] (ε [103 L mol-1 cm-1])a,b
λ
em [nm]a
ΦPL
a,c
complex
λ
3
3
16a
16b
16c
16d
16e
17
206 (145.6), 286 (133.1), 333 (59.8), 435 (23.6)
209 (58.4), 286 (63.4), 328 (38.6), 441 (11.6)
209 (88.1), 286 (103.9), 312s (51.6), 440 (18.3)
208 (66.6), 286 (74.7), 341s (22.6), 442 (12.4)
205 (131.1), 286 (125.6), 315s (60.9), 438 (20.6)
206 (83.7), 286 (76.9), 326 (52.5), 440 (12.8)
195 (102.9), 286 (83.1), 316s (40.5), 442s (12.5)
602
674
620
640
621
642
610
0.001 [0.005d]
0.001 [0.022d]
0.002
0.001
0.001
<0.001
0.003
18
aFor all measurements: 10-6 M solution in aerated CH3CN at room temperature. For emission measurements: excitation at longest absorption
wavelength. b“s” signifies absorption shoulder. cPhotoluminescence quantum yields determined with [Ru(bpy)3](PF6)2 (ΦPL = 0.062) as standard.14
dMeasured in aerated CH2Cl2 solution at room temperature (10-6 M).
J. Org. Chem. Vol. 75, No. 12, 2010 4031

Happ et al.
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FIGURE 4. Energy level scheme for the Kohn-Sham orbitals of complexes 16a and 16b, including the most relevant Kohn-Sham orbitals
and the HOMO-LUMO gaps calculated with B3LYP/6-31G*.
respectively, had therefore an important influence on the
energy level and ordering of the molecular orbitals.
hybrid functional and the consideration of solvent effects on
the electronic excitations seemed to be a reasonable app-
roach to reproduce the photophysical properties of the
ruthenium(II) complexes (with errors amounting to approxi-
mately 0.3 eV). The main features of the experimental spectra
were reproduced. Three main bands were obtained for both
complexes 16a and 16b. As seen in Figure 5, no absorption
for both compounds was theoretically predicted beyond
470 nm. Experimentally, absorption was recorded up to
500 nm. The tail between 470 and 520 nm, where singlet-
singlet excitations are dark or do not exist, should then be
attributed to singlet-triplet excitations (due to non-negligi-
ble spin-orbit coupling for the ruthenium atom).
The effect of substitution with an acceptor or a donor unit
attached in the 5-position of the pyridine ring had a signi-
ficant influence on the nature as well as on the position of the
UV-vis bands. Thus, in the case of 16a, the low-energy
broad band centered around 440 nm could be assigned to
different singlet-singlet electronic excitations of MLCT
character (see S4, S8, and S9 in Table 5) as well as LLCT
character (see S3 and S7 in Table 5). Although a very similar
broad band was obtained in the case of compound 16b, the
character of the underlying transitions was different. In
complex 16b this band was mainly composed of MLCT
states (see S4, S5, S6, and S8 in Table 5).
The set eg of RuII orbitals was, as shown in Figure 4,
strongly destabilized. Thus, the dz2 and dx2-y2 orbitals corre-
sponded to LUMOþ10 and LUMOþ11 in complex 16a,
respectively, while in complex 16b they related to the orbitals
LUMOþ12 and LUMOþ14. The energetic gaps between the
HOMO and LUMO levels are also shown in Figure 4. We
obtained theoretical HOMO-LUMO gaps of 3.10 and 3.22
eV for 16a and 16b, respectively.
Figure 5 shows the theoretical UV-vis spectra of com-
plexes 16a and 16b vs the experimental ones. Table 5 collects
the main TD-DFT electronic excitations recorded in the
presence of solvent (i.e., CH2Cl2). A fairly good agreement
between experiment and theory was observed, notwithstand-
ing that TD-DFT generally tends to underestimate the
energy of the charge-transfer states,16 even if it is well-
established that hybrid functionals, such as B3LYP, are less
affected by this problem.17 However, the combination of a
(14) (a) Demas, J. N.; Crosby, G. A. J. Phys. Chem. 1971, 75, 991–1024.
(b) Juris, A.; Balzani, V.; Barigelletti, F.; Campagna, S.; Belser, B.; von
Zelewsky, A. Coord. Chem. Rev. 1988, 84, 85–277.
(15) (a) Vlcek, A., Jr.; Zalis, S. Coord. Chem. Rev. 2007, 251, 258–287.
(b) Charlot, M.-F.; Aukauloo, A. J. Phys. Chem. A 2007, 111, 11661–11672.
€
(c) Abbotto, A.; Barolo, C.; Bellotto, L.; De Angelis, F.; Gratzel, M.;
The explanation of the different character of the low-
energy bands of 16a and 16b could be found by analyzing
the orbitals involved in these transitions. For instance, the
LLCT states (S3 and S7) of compound 16b, which involved
Manfredi, N.; Marinzi, C.; Fantacci, S.; Yum, J.-H.; Nazeeruddin, M. K.
Chem. Commun. 2008, 5318–5320.
(16) Dreuw, A.; Head-Gordon, M. Chem. Rev. 2005, 105, 4009–4037.
(17) Dreuw, A.; Weisman, J. L.; Head-Gordon, M. J. Chem. Phys. 2003,
119, 2943–2946.
4032 J. Org. Chem. Vol. 75, No. 12, 2010

Happ et al.
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TABLE 5. Main Theoretical Electronic Transition Energies (ΔE) with Corresponding Oscillator Strengths (f) and Assignment for Complexes 16a and 16b
16a 16b
state
ΔE (nm)
f
assignment
state
ΔE (nm)
f
assignment
S1
S2
S3
S4
S7
S8
477
462
453
441
430
425
0.003
0.003
0.056
0.162
0.180
0.191
dxy f π*dmbpy (0.53) MLCT
dxy f π*dmbpy (0.59) MLCT
S1
S2
S4
S5
S6
S8
479
466
448
439
433
414
0.010
0.011
0.023
0.065
0.030
0.136
dxy f π*L (0.66) MLCT
dxy f π*dmbpy (0.65) MLCT
dxz f π*L (0.66) MLCT
π
L f π*dmbpy (0.53) LLCT
dxy f π*L (0.51) MLCT
L f π*dmbpy (0.54) LLCT
dxy f π*dmbpy (-0.35) MLCT
L f π*L (0.35) IL
dyz f π*L (0.54) MLCT
π
dxz f π* dmbpy (0.49) MLCT
dyz f π* dmbpy (0.40) MLCT
dxz f π* dmbpy (0.43) MLCT
dxz f π* dmbpy (0.54) MLCT
πL f π*L (0.63) IL
dyz f π* L (0.54) MLCT
dyz f π* dmbpy (-0.29) MLCT
dxz f π* dmbpy (0.30) MLCT
dyz f π* dmbpy (0.32) MLCT
dyz f π* dmbpy (0.44) MLCT
dxy f π* dmbpy (-0.38) MLCT
dyz f π*L (0.47) MLCT
π
S9
420
407
401
360
0.313
0.104
0.243
0.192
dxz f π*dmbpy (0.44) MLCT
dxz f π*L (0.63) MLCT
dxz f π*dmbpy (0.45) MLCT
S9
395
371
348
312
0.124
1.262
0.039
0.071
S10
S11
S13
S11
S13
S27
π
L f π*L (0.61) IL
S30
307
0.094
dyz f π*dmbpy (0.51) MLCT
dxy f π*dmbpy (0.37) MLCT
S32
305
0.116
S32
S47
S52
S54
306
282
276
273
0.034
0.234
0.177
0.286
S42
S49
S50
S51
294
276
274
273
0.066
0.284
0.419
0.286
π
π
π
L f π*L (0.52) IL
πdmbpy f π* dmbpy (0.41) IL
πdmbpy f π* dmbpy (0.33) IL
πdmbpy f π* dmbpy (0.23) IL
πdmbpy f π*dmbpy (-0.22) IL
πL f π*L (0.54) IL
dmbpy f π*L (0.54) LLCT
dmbpy f π*dmbpy (0.25) LLCT
dxz f dx2-y2 (0.24) MC
S55
273
0.509
π
π
π
dmbpy f π* L (0.27) LLCT
dmbpy f π* dmbpy (-0.23) IL
dmbpy f π* dmbpy (0.23) IL
S54
265
0.146
second band, located experimentally around 360 and 340 nm
in complexes 16a and 16b, respectively, was characterized by
the same electronic excitations (S13 and S11 for compounds
16a and 16b, respectively). These corresponded to intra-
ligand (IL) states, which involved local πL f π*L electronic
excitations within the 2-(1H-[1,2,3]triazol-4-yl)pyridine liga-
nd. Finally, the most intense peak centered at 286 nm in both
complexes was mainly due to IL states in 16b and states of IL
and LLCT character in the case of 16a (see Table 5). In the
case of 16a, one of these states (S54) was mixed with a MC
transition, involving an electronic excitation from the dxz
orbital to the unoccupied dx2-y2 orbital.
Concerning the emission behavior, the trzpy-type ligand
systems are known to be potential luminescence quenchers and
the ruthenium(II) complexes reported previously did not show
any luminescence at room temperature.7e,8 Also the complexes
presented in this contribution showed only very weak emission
intensities (see Table 4). For excited RuII polypyridyl complexes
it is well-known that the triplet excited states are populated
rapidly via efficient intersystem crossings (ISC) from the singlet
photoexcited states18 (due to the strong spin-orbit coupling of
the ruthenium center). Afterward, relaxation to the lowest triplet
excited state (T1) follows. Obviously, the nature of the low-lying
singlets and triplets excited states should determine the effective-
ness of the ISC. As revealed, different singlet excited states were
obtained for complexes 16a and 16b and, consequently, a
different emission behavior was expected. We are currently
developing a methodology to estimate the phosphorescence rates
and the quantum yields, based on accurate estimation of the
spin-orbit couplings between the singlet and triplet manifolds
which, in turn, determine the ISC rates.
FIGURE 5. Experimental spectra of complexes 16a (top) and 16b
(bottom) in solid lines superimposed to the TD-DFT (B3LYP/
6-31G* in CH2Cl2) vertical excitations. The main electronic states
are highlighted (see Table 5 for assignments).
electronic transitions from the same π-orbital localized in
the 2-(1H-[1,2,3]triazol-4-yl)pyridine ligand (πL) to different
π-antibonding orbitals located on the dmbpy ligands
(π*dmbpy), appeared lower in energy in 16a. This fact was
due to the destabilization of the πL orbital in the donor-based
compound as compared to the same orbital in the acceptor-
based compound (recall that the πL orbital is the HOMO in
compound 16a but the HOMO-3 in 16b, see Figure 4). The
Conclusions
New 2-(1H-[1,2,3]triazol-4-yl)pyridine bidentate ligands
were synthesized as bipyridine analogs, whereas different
(18) Bhasikuttan, A. C.; Suzuki, M.; Nakashima, S.; Okada, T. J. Am.
Chem. Soc. 2002, 124, 8398–8345.
J. Org. Chem. Vol. 75, No. 12, 2010 4033

Happ et al.
JOCArticle
phenylacetylene moieties of donor and acceptor nature,
respectively, were attached at the 5-position of the pyridine
unit. The moieties featured a crucial influence on the
electronic properties of these ligands. In addition, the N-
heterocyclic ligands were coordinated to the ruthenium(II)
metal ion by using the bis(4,40-dimethyl-2,20-bipyridine-
)ruthenium(II) precursor. The RuII complex with elec-
tron-donor nature revealed considerable weaker lumin-
escence intensity at room temperature in contrast to the
one with acceptor capability revealing remarkable lumines-
cence at room temperature in CH2Cl2. Furthermore,
2-(1H-[1,2,3]triazol-4-yl)pyridine systems are known to be
potential luminescence quenchers at room temperature as
soon as they are attached to a ruthenium(II) metal ion. All
herein described heteroleptic ruthenium(II) complexes over-
came this luminescence quenching and led to room tempera-
ture emission in acetonitrile. The highest quantum yield
could be found for the RuII complex 16b (Φ = 0.02) bearing
a nitro group in the para-position of the phenylacetylene
subunit.
model,22,23 (ε = 8.93). All the calculations were performed with
the Gaussian03 program package.24
1-Ethynyl-4-(hexyloxy)benzene (1).25 1-Iodo-4-(hexyloxy)-
benzene (1.5 g, 4.93 mmol), tetrakis(triphenylphosphine)-
palladium(0) (114 mg, 0.1 mmol), and CuI (20 mg, 0.1 mmol)
were dissolved ina degassed NEt3/THF mixture (3:7 ratio, 35 mL)
at room temperature. After trimethylsilylacetylene (0.7 mL, 4.93
mmol) was added quickly through a syringe, the solution was
stirred for 24 h at room temperature. The salts formed were
filtered off, and the solution was evaporated under reduced
pressure. The yellow oil was purified by a chromatographic fil-
tration over a silica gel pad (toluene as eluent) yielding pure
1-(trimethylsilyl)ethynyl-4-(hexyloxy)benzene. Subsequently, the
silylated compound was dissolved in a mixture of THF and
methanol and aq NaOH (5 M, 1 mL) was added. The reaction
mixture was stirred overnight at room temperature and then
extracted with dichloromethane after adding brine (50 mL). The
organic extract was dried over anhydrous MgSO4 and subsequent
gel filtration (silica, toluene) afforded the pure, colorless product
(0.91 g, 91%).
5-Bromo-2-((trimethylsilyl)ethynyl)pyridine (2).26 2,5-Dibro-
mopyridine (3.5 g, 14.8 mmol), tetrakis(triphenylphosphine)-
palladium(0) (347 mg, 0.3 mmol), and CuI (57 mg, 0.3 mmol)
were dissolved in a degassed NEt3/THF mixture (3:7 ratio,
50 mL) at 0 ꢀC. After trimethylsilylacetylene (2.09 mL,
14.8 mmol) was added quickly through a syringe, the solution
was stirred for 2 h at 0 ꢀC and was then allowed to stir at room
temperature overnight. The salts formed were filtered off, and
the solution was evaporated under reduced pressure. The dark
orange oil was purified by a chromatographic filtration over a
silica gel pad (toluene as eluent) providing the product as yellow
oil, which solidifies upon standing at room temperature after
one week. Finally, purification by gentle sublimation (3.3ꢀ10-2
mbar, 60 ꢀC) afforded the pure product as a white powder (3.25
g, 86%).
2-Ethynyl-5-((4-(hexyloxy)phenyl)ethynyl)pyridine (4). 5-Bromo-
2-((trimethylsilyl)ethynyl)pyridine (2, 1.0 g, 4 mmol), 1-ethynyl-
4-(hexyloxy)benzene (1, 0.8 g, 4 mmol), tetrakis(triphenyl-
phosphine)palladium(0) (90 mg, 0.08 mmol), and CuI (16 mg,
0.08 mmol) were dissolved in a degassed NEt3/THF mixture
(3:7 ratio, 35 mL) at room temperature and the solution
was stirred for 48 h at room temperature. The salts formed
were filtered off, and the solution was evaporated under redu-
ced pressure. The dark red oil was purified by a gel filtration
over silica (toluene as eluent). The obtained 2-(trimethylsilyl)-
ethynyl-5-((4-(hexyloxy)phenyl)ethynyl)pyridine was desilylated
by dissolving in THF/MeOH (1:2 ratio, 30 mL) and treating
with an equimolar amount of potassium fluoride. The red solu-
tion was stirred overnight under an argon atmosphere. After
that the reaction mixture was concentrated under vacuum and
Experimental Section
Materials and Instrumentation. Unless noted otherwise, all
reagents were acquired from commercial sources and used
without further purification. Solvents were dried and distilled
according to standard procedures and stored under argon. If not
specified otherwise solvents were degassed by bubbling with
argon 1 h before use. All reactions were performed in air-dried
flasks under an argon atmosphere unless stated otherwise.
Purification of reaction products was carried out by column
chromatography with 40-63 μm silica gel. Analytical thin layer
chromatography (TLC) was performed on silica sheets pre-
coated with silica gel 60 F254 and visualization was accom-
plished with UV light (254 nm). The heteroleptic ruthenium(II)
complexes were synthesized by microwave-assisted reactions,
using a Biotage Initiator ExpEU (maximum power: 400 W;
working frequency: 2450 MHz) with closed reaction vials.
During the experiments the temperature and the pressure pro-
files were detected. 1D-(1H and 13C) and 2D-(1H-1H gCOSY)
nuclear magnetic resonance spectra were recorded at 298 K.
Chemical shifts are reported in parts per million (ppm, δ scale)
relative to the signal of the applied solvent. Coupling constants
are given in hertz. Data are reported as follows: multiplicity
(ap=apparent, br = broad, s = singlet, d = doublet, t =triplet,
q = quartet, m = multiplet).
Computational Details. The geometries of 16a and 16b were
optimized in the electronic singlet ground state using density
functional theory (DFT) with the hybrid functional B3LYP19,20
and the 6-31G* basis set for all atoms. Relativistic effects were
included in the Ru atom, using the ECP-28-mwb Stuttgart/
Dresden pseudopotential.21 For computational ease the struc-
tures were reduced by substitution of the decyl chain attached to
the triazole ring by a methyl group and in the case of compound
16b, additionally the hexyloxy group of 16a was replaced by a
methoxy group. The lowest-lying 55 vertical singlet electronic
excitation energies were obtained by using TD-DFT at the S0
optimized geometries. This calculation was performed in solu-
tion with CH2Cl2 as solvent with the polarization continuum
(24) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.;
Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci,
B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada,
M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian,
H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski,
J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J.
J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.;
Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.;
Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.;
Al-Laham, M. A.;Peng, C. Y.; Nanayakkara, A.; Challacombe, M.;Gill, P. M.
W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian-
03, Revision C.02; Gaussian, Inc., Wallingford, CT, 2004.
(19) Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652.
(20) Lee, C. T.; Yang, W. T.; Parr, R. G. Phys. Rev. B 1988, 37, 785–789.
(21) Andrae, D.; Hausermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor.
Chim. Acta 1990, 77, 123–141.
(22) Cossi, M.; Barone, V.; Menucci, B.; Tomasi, J. Chem. Phys. Lett.
1998, 286, 253–260.
(23) Menucci, B.; Tomasi, J. J. Chem. Phys. 1997, 106, 5151–5158.
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(25) Chang, J. Y.; Yeon, J. R.; Shru, Y. S.; Han, M. J.; Hong, S.-K.
Chem. Mater. 2000, 12, 1076–1082.
(26) Bianchini, C.; Giambastiani, G.; Rios, I. G.; Meli, A.; Oberhauser,
W.; Sorace, L.; Toti, A. Organometallics 2007, 26, 5066–5078.
4034 J. Org. Chem. Vol. 75, No. 12, 2010

Happ et al.
JOCArticle
purified by means of gel filtration on silica gel yielding the
desired product as a slight yellow powder (1.06 g, 87%). H
methanol (80 mL) and treated with aq NaOH (5 M, 12 mL).
The yellow solution was stirred overnight, whereupon the solution
turned black. Subsequent gel filtration on silica (CHCl3) yielded
the product as white powder (3.79 g, 69%).
1
NMR (CDCl3, 300 MHz) δ 8.62 (d, J = 1.3 Hz, 1H), 7.73 (dd,
J = 8.1 Hz, J = 2.1 Hz, 1H), 7.49-7.42 (m, 3H), 6.91-6.85 (m,
2H), 3.97 (t, 3J = 6.6 Hz, 2H), 3.25 (s, 1H), 1.79-1.74 (m, 2H),
1.49-1.30 (m, 6H), 0.91 (t, J = 6.8 Hz, 3H). 13C NMR (CDCl3,
75 MHz) δ 159.8, 152.2, 140.3, 138.1, 133.2, 126.71, 120.7, 114.7,
114.0, 94.9, 84.5, 82.6, 78.6, 68.1, 31.5, 29.1, 25.7, 22.6, 14.0.
Anal. Calcd for C21H21NO: C 83.13, H 6.98, N 4.62. Found: C
82.78, H 7.08, N 4.92.
5-Bromo-2-(1-decyl-1H-[1,2,3]triazol-4-yl)pyridine (8). 5-Bromo-
2-ethynylpyridine (7, 1.04 g, 5.45 mmol) and 1-azidodecane
(see synthesis of 5, 1.0 g, 5.45 mmol) were dissolved in an
ethanol/water mixture (7:1 ratio, 70 mL), using a round-
bottomed flask (100 mL). Then copper(II) sulfate (80 mg, 0.5 mmol,
dissolved in 3 mL of water) and sodium ascorbate (490 mg,
2.5 mmol, dissolved in 4 mL of water) were added. The reaction
mixture turned yellow after a while and was stirred for 72 h at
25 ꢀC. The yellow precipitate was filtered and washed with
ethanol. After recrystallization from ethanol the pure product
was obtained as colorless crystals (1.35 g, 67%). 1H NMR
(CDCl3, 300 MHz) δ 8.61 (s, 1H), 8.09-8.07 (m, 2H),
7.89-7.86 (m, 1H), 4.40 (t, J = 7.2 Hz, 2H), 1.94-1.89 (m,
2H), 1.34-1.24 (m, 14H), 0.87-0.81 (m, 3H). 13C NMR
(CDCl3, 75 MHz) δ 150.3, 148.9, 147.4, 139.4, 121.9, 121.3,
119.3, 50.5, 31.8, 30.2, 29.4, 29.3, 29.2, 28.9, 26.4, 22.6, 14.0.
Anal. Calcd for C17H25BrN4: C 55.89, H 6.90, N 15.34. Found:
C 56.22, H 7.23, N 14.98.
2-(1-Decyl-1H-[1,2,3]triazol-4-yl)-5-ethynylpyridine (9, Route 1).
4-(6-Ethynylpyridin-3-yl)-2-methylbut-3-yn-2-ol (6, 300 mg, 1.58
mmol) and 1-azidodecane (see synthesis of 5, 275 mg, 1.5 mmol)
were dissolved in an ethanol/water mixture (7:3 ratio, 30 mL), using
a round-bottomed flask (100 mL). Then copper(II) sulfate (24 mg,
0.15 mmol, dissolved in 1 mL of water) and sodium ascorbate
(150 mg, 0.75 mmol, dissolved in 1 mL of water) were added. The
reaction mixture turned green after a while and was stirred for 72 h
at 50 ꢀC. Subsequently, an excess of water was poured into the
reaction mixture (100 mL) and the crude product precipitated and
was filtered off. Gel filtration on silica (CHCl3/EtOAc 1:1) provided
4-(6-(1-decyl-1H-[1,2,3]triazole-4-yl)pyridin-3-yl)-2-methylbut-
3-yn-2-ol as white powder (490 mg, 85%). This intermediate was
dissolved in dry toluene (30 mL). After adding ground NaOH
(200 mg, 5 mmol) and KOH (150 mg, 2.6 mmol) the reaction
mixture was refluxed for 5 h. Subsequent column chromatography
on silica (CHCl3/EtOAc 2:1 ratio) yielded 2-(1-decyl-1H-[1,2,3]-
triazole-4-yl)-5-ethynylpyridine as transparent crystals (303 mg,
74%). 1H NMR (CDCl3, 300 MHz) δ 8.67 (d, J = 1.6 Hz, 1H),
8.20-8.14 (m, 2H), 7.89-7.83 (m, 1H), 4.41 (t, J = 7.2 Hz, 2H),
3.25 (s, 1H), 1.95-1.89 (m, 2H), 1.34-1.25 (m, 14H), 0.87 (t, J =
6.5 Hz, 3H). 13C NMR (CDCl3, 75 MHz) δ 152.4, 149.7, 147.7,
139.9, 122.2, 119.3, 118.0, 80.8, 80.5, 50.5, 31.8, 30.2, 29.4, 29.3,
29.2, 28.9, 26.4, 22.6, 14.0. Anal. Calcd for C19H26N4: C 73.51, H
8.44, N 18.05. Found: C 73.50, H 8.24, N 18.38.
2-(1-Decyl-1H-[1,2,3]triazol-4-yl)-5-ethynylpyridine (9, Route
2). To a solution of 5-bromo-2-(1-decyl-1H-[1,2,3]triazol-4-yl)-
pyridine (8, 1.0 g, 2.74 mmol), CuI (13 mg, 0.07 mmol), and
Pd(PPh3)4 (80 mg, 0.07 mmol) in degassed NEt3/CH2Cl2 (3:1
ratio, 500 mL) was added trimethylsilylacetylene (280 mg, 2.8
mmol). The mixture was stirred 48 h at room temperature under
argon atmosphere. After removal of the solvent under reduced
pressure, the residue was purified by gel filtration on silica
(chloroform). Afterward, the trimethylsilyl-protected product
was dissolved in methanol (40 mL) and treated with aq NaOH
(5 M, 1 mL). After 5 h the solvent was removed and the crude
product was finally purified by gradient column chromatogra-
phy on silica (CHCl3, CHCl3/EtOAc 3:1 ratio) yielding the
product as white powder (470 mg, 55%).
General Procedure of the Sonogashira Reaction. 2-(1-Decyl-
1H-[1,2,3]triazol-4-yl)-5-ethynylpyridine (0.32 mmol), nitro-
substituted 1-iodobenzene (0.32 mmol), tetrakis(triphenylphos-
phine)palladium(0) (16 mg, 0.012 mmol), and CuI (8 mg, 0.012
mmol) were dissolved in a degassed NEt3/THF mixture (1:1,
10 mL). The solution was stirred for 48 h at 40 ꢀC under argon
atmosphere. The salts formed were filtered off, and the solution
2-(1-Decyl-1H-[1,2,3]triazol-4-yl)-5-((4-(hexyloxy)phenyl)-
ethynyl)pyridine (5). A sealed microwave vial with 1-bromode-
cane (91 mg, 0.41 mmol) and 1.5 equiv of sodium azide (40 mg)
in DMSO (5 mL) was heated under microwave irradiation for
1 h at 100 ꢀC. Water was then added to quench the reaction and
the product was extracted into diethyl ether, washed with brine,
and dried over Na2SO4. The solution was subsequently reduced
in vacuo to yield 1-azidodecane (95%). The organic azide,
2-ethynyl-5-((4-(hexyloxy)phenyl)ethynyl)pyridine (4, 127 mg,
0.42 mmol), CuSO4 (7 mg, 0.042 mmol, dissolved in 0.5 mL
water), and sodium ascorbate (42 mg, 0.21 mmol, dissolved in
1 mL water) were dissolved in THF (15 mL) and the reaction
mixture was stirred for 24 h at room temperature. Subsequently,
ethylenediaminetetraacetic acid-containing water (60 mL) was
added to the reaction mixture and the product was extracted
with CH2Cl2. Gel filtration on silica (CHCl3/EtOAc 1:1 ratio)
and subsequent column chromatography (silica, CHCl3/EtOAc
20:1 ratio) provided the pure product as white powder (134 mg,
1
67%). H NMR (CDCl3, 300 MHz) δ 8.68 (s, 1H), 8.13-8.11
(m, 2H), 7.86 (dd, J = 8.2 Hz, J = 2.1 Hz, 1H), 7.46-7.42 (m,
2H), 6.86-6.82 (m, 2H), 4.4 (t, J = 7.2 Hz, 2H), 3.97 (t, J = 6.5
Hz, 2H), 1.94-1.88 (m, 2H), 1.79-1.76 (m, 2H), 1.48-1.22 (m,
20H), 0.87-0.81 (m, 6H). 13C NMR (CDCl3, 75 MHz) δ 159.5,
151.6, 148.7, 147.8, 139.0, 133.0, 122.0, 119.6, 119.3, 114.5,
114.3, 93.1, 84.8, 68.0, 50.4, 31.7, 31.5, 30.1, 29.3, 29.2, 29.1,
29.0, 28.9, 26.3, 25.6, 22.5, 22.5, 14.0, 13.9. Anal. Calcd for
C31H42N4O: C 76.50, H 8.70, N 11.51. Found: C 76.52, H 8.79,
N 11.71.
4-(6-Ethynylpyridin-3-yl)-2-methylbut-3-yn-2-ol (6).27 To a
degassed solution of 5-bromo-2-[(trimethylsilyl)ethynyl]pyridine
(2, 1.5 g, 5.9 mmol), CuI (23 mg, 0.12 mmol), and Pd(PPh3)4 (140
mg, 0.12 mmol) in triethylamine (50 mL) was added 2-methyl-3-
butyn-2-ol (0.58 mL, 5.9 mmol) and the reaction mixture was
stirred for 24 h at 55 ꢀC. The mixture was diluted with diethyl
ether, washed once with brine, and dried over MgSO4. Concen-
tration in vacuo yielded the crude product, which was purified
by chromatography on silica gel (chloroform/ethyl acetate 4:1)
to afford 5-(3-hydroxy-3-methyl-1-butynyl)-2-[(triisopropylsilyl)-
ethynyl]pyridine. To a stirred solution of the latter product in
methanol (50 mL) was added solid potassium fluoride (1.5 equiv),
and the mixture was stirred at room temperature overnight under
an argon atmosphere. Subsequently, the reaction mixture was
filtered by means of gel filtration on silica gel (chloroform/ethyl
acetate 4:1) and concentrated in vacuo yielding the desired
product as an orange powder (670 mg, 61%).
5-Bromo-2-ethynylpyridine (7).28 To a solution of 2,5-dibromo-
pyridine (7 g, 30 mmol), CuI (70 mg, 0.37 mmol), and Pd-
(PPh3)4 (260 mg, 0.37 mmol) in degassed NEt3/THF (1:1 ratio,
100 mL) was added trimethylsilylacetylene (4.2 mL, 30 mmol).
The mixture was stirred at room temperature overnight under
argon atmosphere. After removal of the solvent under reduced
pressure, the residue was purified by gel filtration (CHCl3) to yield
2-(trimethylsilyl)ethynyl-5-bromopyridine as off-white powder
(6.95 g, 92%). Subsequently, the compound was dissolved in
(27) Nakano, Y.; Ishizuka, K.; Muraoka, K.; Ohtani, H.; Takayama, Y.;
Sato, F. Org. Lett. 2004, 6, 2373–2376.
(28) Tilley, J. W.; Zawoiski, S. J. Org. Chem. 1988, 53, 386–390.
J. Org. Chem. Vol. 75, No. 12, 2010 4035

Happ et al.
JOCArticle
was evaporated under reduced pressure. The pure product was
isolated by column chromatography over silica.
(1.5 equiv). The toluene solution was washed with water and
subsequent gel filtration on silica provided the pure desired product
(360 mg, 45%). 1H NMR (CDCl3, 300 MHz) δ 8.71 (s, 1H), 8.61 (s,
1H), 8.23 (d, J= 8.2 Hz, 1H), 7.90 (dd, J=8.2Hz, J=2.0Hz,1H),
7.83-7.80 (m, 2H), 7.59-7.44 (m, 3H), 3.28 (s, 1H, CH). 13C NMR
(CDCl3, 75 MHz) δ 152.5, 149.2, 148.3, 140.0, 136.8, 129.9, 128.9,
120.4, 119.6, 118.3, 81.0, 80.5. Anal. Calcd for C15H10N4: C 73.16, H
4.09, N 22.75. Found: C 73.49, H 3.78, N 22.50.
2-(1-Decyl-1H-[1,2,3]triazol-4-yl)-5-((4-nitrophenyl)ethynyl)-
pyridine (10a). According to the general procedure the product
was synthesized and purified by column chromatography over
silica (CHCl3, Rf 0.6) yielding 10a as a slight yellow powder (128
mg, 93%). 1H NMR (CDCl3, 300 MHz) δ 8.76 (s, 1H), 8.26-8.16
(m, 4H), 7.94-7.90 (m, 1H), 7.71-7.68 (m, 2H), 4.4 (t, J = 7.2 Hz,
2H), 1.99-1.91 (m, 2H), 1.35-1.25 (m, 14H), 0.87-0.81 (m, 3H).
13C NMR (CDCl3, 75 MHz) δ 152.1, 150.0, 147.6, 147.3, 139.5,
132.4, 129.5, 123.7, 122.4, 119.6, 118.1, 91.3, 90.9, 50.6, 31.8, 30.2,
29.4, 29.3, 29.2, 29.0, 26.5, 22.6, 14.1. ESI-TOF MS: m/z 432.24
([M þ H]þ). Anal. Calcd for C25H29N5O2: C 69.58, H 6.77, N
16.23. Found: C 69.21, H 6.72, N 16.58.
2-(1-Decyl-1H-[1,2,3]triazol-4-yl)-5-((2-nitrophenyl)ethynyl)-
pyridine (10b). According to the general procedure the product
was synthesized and purified by column chromatography over
silica (CHCl3/EtOAc, 5:1 ratio) yielding 10b as off-white powder
(63 mg, 69%). 1H NMR (CDCl3, 300 MHz) δ 8.76 (s, 1H),
8.21-8.10 (m, 3H), 7.97-7.91 (m, 1H), 7.73-7.69 (m, 1H),
7.63-7.60 (m, 1H), 7.53-7.49 (m, 1H), 4.42 (t, J = 7.2 Hz,
2H), 1.99-1.91 (m, 2H), 1.34-1.24 (m, 14H), 0.88 (t, J = 6.7 Hz,
3H). 13C NMR (CDCl3, 75 MHz) δ 152.2, 150.0, 149.5, 147.7,
139.7, 134.6, 132.9, 129.0, 124.8, 122.4, 119.5, 118.1, 93.8, 88.2,
50.6, 31.8, 30.2, 29.4, 29.3, 29.2, 29.0, 26.4, 22.6, 14.1. ESI-HRMS
calcd for C25H30N5O2 ([M þ H]þ) 432.2394, found 432.2390.
2-(1-Decyl-1H-[1,2,3]triazol-4-yl)-5-((4-(trifluoromethyl)phe-
nyl)ethynyl)pyridine (10c). According to the general procedure,
the product was synthesized and purified by column chromato-
graphy over silica (CHCl3, Rf 0.5) yielding 10d as white powder
(81 mg, 94%). 1H NMR (CDCl3, 300 MHz) δ 8.72 (s, 1H),
8.21-8.17 (m, 2H), 7.92-7.88 (m, 1H), 7.68-7.61 (m, 4H), 4.42
(t, J = 7.2 Hz, 2H), 1.96-1.90 (m, 2H), 1.34-1.24 (m, 14H),
0.88 (t, J = 6.7 Hz, 3H). 13C NMR (CDCl3, 75 MHz) δ 152.0,
139.5, 131.9, 126.4, 125.6, 125.5, 125.4, 125.4, 125.3, 122.4,
119.5, 118.5, 91.4, 88.5, 50.6, 31.8, 30.2, 29.5, 29.4, 29.2, 29.0,
26.5, 22.7, 14.1. ESI-HRMS calcd for C26H30F3N4 ([M þ H]þ)
455.2417, found 455.2408.
5-((4-Phenyl)ethynyl)-2-(1-phenyl-1H-[1,2,3]triazol-4-yl)pyr-
idine (10d). According to the general procedure the product was
synthesized and purified by column chromatography over silica
(CHCl3/EtOAc, 5:1 ratio) yielding 10d as off-white powder
(44 mg, 61%). 1H NMR (CDCl3, 300 MHz) δ 8.74 (s, 1H), 8.16-
8.11 (m, 2H), 7.90-7.84 (m, 1H), 7.58-7.54 (m, 2H), 7.39-7.35
(m, 3H), 4.42 (t, J = 7.2 Hz, 2H), 1.96-1.89 (m, 2H), 1.34-1.24
(m, 14H), 0.88 (t, J = 6.7 Hz, 3H). 13C NMR (CDCl3, 75 MHz)
δ 151.8, 139.3, 131.7, 128.8, 128.4, 122.6, 122.2, 119.5, 119.4,
93.1, 86.1, 50.6, 31.8, 30.2, 29.4, 29.3, 29.2, 29.0, 26.4, 22.6, 14.1.
ESI-HRMS calcd for C25H30N4Na ([M þ Na]þ) 409.2363,
found 409.2334.
5-Ethynyl-2-(1-phenyl-1H-[1,2,3]triazol-4-yl)pyridine (11).Sodium
azide (330 mg, 5.1 mmol) and anhydrous CuSO4 (54 mg,
0.34 mmol) were dissolved in abs methanol (30 mL). Phenylboronic
acid (414 mg, 3.4 mmol) was added to the brown solution and the
reaction mixture was stirred for 48 h at room temperature. The
conversion was controlled by TLC on silica (CHCl3). The slightly
green solution was concentrated to 10 mL in vacuum and, subse-
quently, THF (20 mL), sodium ascorbate (336 mg, 1.7 mmol, in
1 mL of water), 4-(6-ethynylpyridin-3-yl)-2-methylbut-3-yn-2-ol
(600 mg, 3.24 mmol), and water (4 mL) were added. The reaction
wasstirredfor72hat50ꢀC. After that, an excess of water was added
to the reaction mixture and the precipitate was filtered off. The
filtrate was cautiously extracted with CHCl3 and the organic extract
was combined with the precipitate. The CHCl3 solution was dried
over NaSO4 and filtered. Column chromatography on silica
(CHCl3/EtOAc, 2:1 ratio) provided the (2-methylbut-3-yn-2-ol)-
protected product as a white powder. The deprotection was accom-
plished by refluxing overnight in toluene with ground NaOH
5-((4-Nitrophenyl)ethynyl)-2-(1-phenyl-1H-[1,2,3]triazol-4-yl)-
pyridine (12). 5-Ethynyl-2-(1-phenyl-1H-[1,2,3]triazol-4-yl)pyr-
idine (11, 75 mg, 0.3 mmol), 1-iodo-4-nitrobenzene (76 mg, 0.3
mmol), tetrakis(triphenylphosphine)palladium(0) (8 mg, 0.006
mmol), and CuI (2 mg, 0.006 mmol) were dissolved in a degassed
NEt3/THF mixture (3:1 ratio, 10 mL) and the solution was
stirred for 48 h at 40 ꢀC under argon atmosphere. The solvent
was evaporated under reduced pressure. The pure product was
isolated by column chromatography over silica (CHCl3) as
1
slightly yellow powder (85 mg, 77%). H NMR (CDCl3, 300
MHz) δ 8.80 (s, 1H), 8.65 (s, 1H), 8.32-8.25 (m, 3H), 7.98-7.96.
(m, 1H), 7.85-7.82 (m, 2H), 7.74-7.71 (m, 2H), 7.61-7.47 (m,
3H). 13C NMR (CDCl3, 75 MHz) δ 147.3, 143.3, 139.6, 136.9,
132.4, 129.9, 129.1, 123.7, 120.5, 91.2, 91.1 (some carbon signals
are missing due to the low solubility of the compound). ESI-
HRMS calcd for C21H13N5O2Na ([M þ Na]þ) 390.0961, found
390.0940.
2-(1-(4-Bromophenyl)-1H-[1,2,3]triazol-4-yl)pyridine (13). Sodi-
um azide (480 mg, 7.5 mmol) and anhydrous CuSO4 (80 mg,
0.5 mmol) were dissolved in abs methanol (40 mL). (4-Bromo-
phenyl)boronic acid (1 g, 5 mmol) was added to the brown
solution and the reaction mixture was stirred for 48 h at room
temperature. The conversion was controlled by TLC on silica
(ethyl acetate). Sodium ascorbate (400 mg, 2 mmol, in 1 mL of
water), 2-ethynylpyridine (515 mg, 5 mmol), and water (5 mL)
were added. The reaction was stirred for 5 days at 40 ꢀC. After that,
an excess of water was added to the reaction mixture and the
precipitate was filtered off. The filtrate was cautiously extracted
with CHCl3 and the organic extract was combined with the
precipitate. The CHCl3 solution was dried over NaSO4 and filtered
and the solvent was evaporated. Subsequent recrystallization from
ethanol provided the pure product as colorless crystalls (905 mg,
61%). 1H NMR (CDCl3, 300 MHz) δ 8.62-8.60 (m, 1H), 8.59 (s,
1H), 8.24-8.21 (m, 1H), 7.83-7.80 (m, 1H), 7.75-7.67 (m, 4H),
7.29-7.26 (m, 1H). 13C NMR (CDCl3, 75 MHz) δ 149.5, 137.0,
133.0, 123.2, 121.8, 120.5, 119.8. Anal. Calcd for C13H9BrN4: C
51.85, H 3.01, N 18.60. Found: C 51.76, H 3.09, N 18.69.
2-(1-(4-Ethynylphenyl)-1H-[1,2,3]triazol-4-yl)pyridine (14).
2-(1-(4-Bromophenyl)-1H-[1,2,3]triazol-4-yl)pyridine (13, 600 mg,
2 mmol), trimethylsilylacetylene (0.3 mL, 2.05 mmol), tetrakis-
(triphenylphosphine)palladium(0) (95 mg, 0.08 mmol) and CuI
(18 mg, 0.08 mmol) were dissolved in a degassed NEt3/THF
mixture (2:1 ratio, 10 mL) and the reaction mixture was stirred
for 24 h at 40 ꢀC under argon atmosphere. The solution was
evaporated under reduced pressure. The trimethylsilyl-protected
product was isolated by column chromatography over silica
(CHCl3). The product was dissolved in a MeOH/THF solvent
mixture (2:1 ratio, 30 mL) and treated with aq NaOH (200 mg of
NaOH in 3 mL of water). After stirring overnight under an argon
atmosphere the final product was purified by column chromato-
graphy over silica (CHCl3) and obtained as white powder (340 mg,
69%). 1H NMR (CDCl3, 300 MHz) δ 8.63-8.60 (m, 2H),
8.23-8.20 (m, 1H), 7.84-7.78 (m, 3H), 7.67-7.63 (m, 2H),
7.26-7.21 (m, 1H), 3.19 (s, 1H). 13C NMR (CDCl3, 75 MHz) δ
149.7, 149.5, 136.9, 133.5, 123.1, 122.8, 120.4, 120.0, 119.6, 82.2,
79.0. Anal. Calcd for C15H10N4: C 73.16, H 4.09, N 22.75. Found:
C 73.34, H 4.12, N 23.04.
2-(1-(4-((4-Nitrophenyl)ethynyl)phenyl)-1H-[1,2,3]triazol-4-
yl)pyridine (15). 2-(1-(4-Ethynylphenyl)-1H-[1,2,3]triazol-4-yl)-
pyridine (14, 65 mg, 0.26 mmol), 1-iodo-4-nitrobenzene (68 mg,
4036 J. Org. Chem. Vol. 75, No. 12, 2010

Happ et al.
JOCArticle
0.27 mmol), tetrakis(triphenylphosphine)palladium(0) (16 mg,
0.006 mmol), and CuI (3 mg, 0.006 mmol) were dissolved in a
degassed NEt3/THF mixture (10:1 ratio, 25 mL) and the solu-
tion was stirred for 24 h at 50 ꢀC under argon atmosphere. The
solvents were evaporated under reduced pressure and the pure
product was obtained by crystallization from chloroform at 5 ꢀC
Bis(4,40-dimethyl-2,20-bipyridine)-{2-(1-decyl-1H-[1,2,3]tri-
azol-4-yl)-5-((4-(trifluoromethyl)phenyl)ethynyl)pyridine}ruthenium-
(II) Hexafluorophosphate (16c). According to the above standing
general procedure cis-dichlorobis(4,40-dimethyl-2,20-bipyridine)-
ruthenium(II) (30 mg, 0.056 mmol) and 2-(1-decyl-1H-[1,2,3]tri-
azol-4-yl)-5-((4-(trifluoromethyl)phenyl)ethynyl)pyridine (10c, 25
mg, 0.056 mmol) were reacted to yield the pure complex as red
powder after recrystallization from ethanol (32 mg, 48%). 1H NMR
(CD3CN, 300 MHz) δ 8.71 (s, 1H), 8.38 (s, 2H), 8.31-8.27 (m, 2H),
8.11-8.08 (m, 2H), 7.79-7.60 (m, 8H), 7.49-7.46 (m, 1H),
7.28-7.23 (m, 3H), 7.18-7.16 (m, 1H), 4.35 (t, J = 7.0 Hz, 2H),
2.56-2.51 (m, 12H), 1.80-1.72 (m, 2H), 1.37-1.07 (m, 14H), 0.89
(t, J = 6.7 Hz, 3H). 13C NMR (CD3CN, 75 MHz) δ 157.2, 156.9,
156.7, 156.6, 153.4, 151.3, 151.2, 151.1, 151.0, 150.7, 150.3, 150.3,
150.2, 150.0, 147.1, 140.1, 132.2, 128.2, 128.0, 127.5, 126.0, 125.7,
125.6, 125.0, 124.9, 124.5, 124.1, 122.1, 121.3, 93.2, 86.1, 52.1, 31.6,
29.2, 29.2, 29.1, 29.0, 28.4, 25.6, 22.4, 20.4, 20.3, 20.2, 13.4. ESI-
TOF MS m/z 1069.30 ([M - PF6]þ), 462.17 ([M - 2PF6]2þ). ESI-
HRMS calcd for C50H53F9N8PRu ([M - PF6]þ) 1069.3025, found
1069.2993.
1
(48 mg, 50%). H NMR (CDCl3, 300 MHz) δ 8.66-8.62 (m,
2H), 8.25-8.22 (m, 3H), 7.88-7.70 (m, 7H), 7.30-7.26 (m, 1H).
13C NMR (CDCl3, 75 MHz) δ 147.3, 133.4, 132.4, 129.6, 123.7,
122.8, 120.2, 119.6, 93.1 (some carbon signals are missing due to
the low solubility of the compound). ESI-TOF MS: m/z 368.12
([M þ H]þ). Anal. Calcd for C21H13N5O2: C 68.66, H 3.57, N
19.06. Found: C 68.32, H 3.74, N 19.31.
General Procedure for Complexing the (1H-1,2,3-Triazole)-
pyridine Ligand to Ru(dmbpy)2Cl2. cis-Dichlorobis(4,40-dimethyl-
2,20-bipyridine)ruthenium(II)11 (43 mg, 0.08 mmol) and the
respective 1H-[1,2,3]triazole ligand (0.08 mmol) were suspended
in degassed ethanol (8 mL). After heating under microwave
irradiation at 125 ꢀC for 2 h, the red solution was treated with a
10-fold excess of NH4PF6 and subsequently stirred until pre-
cipitation occurred (10 min to 2 h). The colored precipitate was
filtered off and purified by washing twice with ethanol and
diethyl ether providing the pure product. In the cases where the
1H NMR spectrum indicated any impurities, the compound was
further purified by recrystallization from ethanol.
Bis(4,40-dimethyl-2,20-bipyridine)-{2-(1-decyl-1H-[1,2,3]tri-
azol-4-yl)-5-((2-nitrophenyl)ethynyl)pyridine}ruthenium(II) Hexa-
fluorophosphate (16d). According to the above standing general
procedure cis-dichlorobis(4,40-dimethyl-2,20-bipyridine)ruthenium-
(II) (30 mg, 0.056 mmol) and 2-(1-decyl-1H-[1,2,3]triazol-4-yl)-
5-((2-nitrophenyl)ethynyl)pyridine (10b, 24 mg, 0.056 mmol) were
reacted to yield the pure complex as red powder after washing twice
with ethanol and diethyl ether (59 mg, 90%). 1H NMR (CD3CN,
300 MHz) δ 8.71 (s, 1H), 8.38-8.29 (m, 4H), 8.13-8.09 (m, 3H),
7.74-7.53 (m, 8H), 7.27-7.23 (m, 3H), 7.17-7.15 (m, 1H), 4.35
(t, J = 7.0 Hz, 2H), 2.58-2.52 (m, 12H), 1.80-1.72 (m, 2H),
1.37-1.07 (m, 14H), 0.89 (t, J = 6.7 Hz, 3H). 13C NMR (CD3-
CN, 75 MHz) δ 158.1, 157.8, 157.7, 157.5, 154.5, 152.2, 152.2, 152.0,
151.8, 151.6, 151.3, 151.2, 150.9, 147.9, 140.5, 135.5, 134.6, 131.5,
129.2, 129.0, 128.4, 127.0, 126.0, 125.9, 125.8, 125.4, 125.1, 123.0,
122.1, 91.4, 91.2, 53.1, 32.6, 30.1, 30.1, 30.0, 29.9, 29.3, 26.6, 23.3,
21.3, 21.2, 21.1, 14.3. ESI-TOF MS m/z 1046.30 ([M - PF6]þ),
450.67 ([M - 2PF6]2þ). ESI-HRMS calcd for C49H53F6N9O2PRu
([M - PF6]þ) 1046.3002, found 1046.2997.
Bis(4,40-dimethyl-2,20-bipyridine)-{2-(1-decyl-1H-[1,2,3]tri-
azol-4-yl)-5-((4(hexyloxy)phenyl)ethynyl)pyridine}ruthenium(II)
Hexafluorophosphate (16a). According to the above standing
general procedure cis-dichlorobis(4,40-dimethyl-2,20-bipyridine)-
ruthenium(II) (30 mg, 0.056 mmol) and 2-(1-decyl-1H-[1,2,3]-
triazol-4-yl)-5-((4-(hexyloxy)phenyl)ethynyl)pyridine (5, 27 mg,
0.056 mmol) were reacted to yield the complex as an orange
powder after washing twice with ethanol and diethyl ether
1
(55 mg, 81%). H NMR (CD3CN, 300 MHz) δ 8.68 (s, 1H),
8.38 (s, 2H), 8.31 (s, 1H), 8.28 (s, 1H), 8.10-8.0 (m, 2H),
7.73-7.61 (m, 4H), 7.50 (d, J = 5.8 Hz, 1H), 7.43-7.38 (m,
2H), 7.28-7.22 (m, 3H), 7.17-7.14 (m, 1H), 6.94-6.87 (m, 2H),
4.34 (t, J = 7.0 Hz, 2H), 4.0 (t, J = 6.5 Hz, 2H), 2.56-2.52 (m,
12H), 1.95-1.92 (m, 4H), 1.83-1.69 (m, 4H), 1.47-1.08 (m,
20H), 0.93-0.86 (m, 6H). 13C NMR (CD3CN, 75 MHz) δ 161.3,
158.1, 157.8, 157.7, 157.5, 153.8, 152.2, 152.1, 152.0, 151.9,
151.21, 151.2, 151.1, 150.9, 150.6, 148.1, 140.5, 134.2, 129.2,
129.0, 128.4, 126.6, 125.9, 125.8, 125.4, 125.0, 123.3, 122.9,
115.8, 113.9, 96.6, 83.8, 69.1, 53.0, 32.6, 32.2, 30.1, 30.0, 29.9,
29.7, 29.3, 26.6, 26.3, 23.3, 23.2, 21.22, 21.2, 21.1, 14.3, 14.2. ESI-
TOF MS m/z 1101.40 ([M - PF6]þ), 478.22 ([M - 2PF6]2þ).
ESI-HRMS calcd for C55H66N8ORu [M - 2PF6]2þ 478.2203,
found 478.2199.
Bis(4,40-dimethyl-2,20-bipyridine)-{5-((4-phenyl)ethynyl)-2-(1-
phenyl-1H-[1,2,3]triazol-4-yl)pyridine}ruthenium(II) Hexafluoro-
phosphate (16e). According to the above-mentioned general pro-
cedure cis-dichlorobis(4,40-dimethyl-2,20-bipyridine)ruthenium(II)
(30 mg, 0.056 mmol) and 5-((4-phenyl)ethynyl)-2-(1-phenyl-
1H-[1,2,3]triazol-4-yl)pyridine (10d, 23 mg, 0.056 mmol) were
reacted to yield the pure complex as red powder after washing
1
twice with ethanol and diethyl ether (48 mg, 75%). H NMR
(CD3CN, 300 MHz) δ 8.69 (s, 1H), 8.37-8.27 (m, 4H), 8.11-8.05
(m, 2H), 7.75-7.72 (m, 2H), 7.66-7.62 (m, 2H), 7.50-7.39 (m,
6H), 7.27-7.24 (m, 3H), 7.18-7.16 (m, 1H), 4.34 (t, J = 7.0 Hz,
2H), 2.56-2.51 (m, 12H), 1.79-1.71 (m, 2H), 1.37-1.06 (m, 14H),
0.89 (t, J = 6.7 Hz, 3H). 13C NMR (CD3CN, 75 MHz) δ 157.2,
156.9, 156.7, 156.6, 153.2, 151.3, 151.2, 151.1, 151.0, 150.3, 150.3,
150.2, 150.2, 150.0, 147.1, 139.9, 131.6, 129.7, 128.8, 128.2, 128.0,
127.5, 125.8, 125.0, 124.9, 124.5, 124.1, 122.0, 121.9, 121.4, 95.0,
83.9, 52.1, 31.6, 29.2, 29.1, 29.0, 28.4, 25.6, 22.4, 20.3, 20.2, 13.4.
ESI-TOF MS m/z 1001.32 ([M - PF6]þ), 428.18 ([M - 2PF6]2þ).
ESI-HRMS calcd for C49H54F6N8PRu [M - PF6]þ 1001.3151,
found 1001.3168.
Bis(4,40-dimethyl-2,20-bipyridine)-{5-((4-nitrophenyl)ethynyl)-
2-(1-phenyl-1H-[1,2,3]triazol-4-yl)pyridine}ruthenium(II) Hexa-
fluorophosphate (17). According to the above standing general
procedure Ru(dmbpy)2Cl2 (35 mg, 0.065 mmol) and 5-((4-
nitrophenyl)ethynyl)-2-(1-phenyl-1H-[1,2,3]triazol-4-yl)pyridine
(12, 24mg, 0.065 mmol) were reacted to yield the pure complex as
red powder after washing twice with ethanol and diethyl ether
(45 mg, 63%). 1H NMR (CD3CN, 300 MHz) δ 9.24 (s, 1H), 8.39
(s, 2H), 8.33-8.18 (m, 6H), 7.86 (s, 1H), 7.79-7.76 (m, 2H),
Bis(4,40-dimethyl-2,20-bipyridine)-{2-(1-decyl-1H-[1,2,3]triazol-
4-yl)-5-((4-nitrophenyl)ethynyl)pyridine}ruthenium(II) Hexa-
fluorophosphate (16b). According to the above standing general
procedure cis-dichlorobis(4,40-dimethyl-2,20-bipyridine)ruthe-
nium(II) (35 mg, 0.065 mmol) and 2-(1-decyl-1H-[1,2,3]triazol-
4-yl)-5-((4-nitrophenyl)ethynyl)pyridine (10a, 28 mg, 0.065 mmol)
were reacted to yield the pure complex as an orange powder
after washing twice with ethanol and diethyl ether (68 mg,
1
88%). H NMR ((CD3)2CO, 300 MHz) δ 9.23 (s, 1H), 8.67-
8.60 (m, 4H), 8.42-8.39 (m, 1H), 8.30-8.25 (m, 3H), 8.12-
8.08 (m, 2H), 7.96 (d, 1H), 7.87 (d, 1H), 7.78-7.70 (m, 3H),
7.44-7.32 (m, 4H), 4.52 (t, J = 7.1 Hz, 2H), 2.58-2.52 (m,
12H), 2.05-2.01 (m, 2H), 1.89-1.79 (m, 2H), 1.25-1.07 (m,
12H), 0.87-0.81 (m, 3H). 13C NMR ((CD3)2CO, 75 MHz) δ
158.1, 158.0, 157.8, 154.5, 152.4, 152.21, 152.2, 151.2, 151.1,
148.9, 148.2, 141.4, 133.6, 129.4, 129.0, 128.7, 126.0, 125.5,
125.2, 124.7, 123.1, 121.9, 95.6, 89.3, 52.1, 32.6, 26.7, 23.3,
21.2, 14.3. ESI-TOF MS m/z 1046.3 ([M - PF6]þ), 450.67
([M - 2PF6]2þ). ESI-HRMS calcd for C49H53N9O2Ru ([M -
2PF6]2þ): 450.6684, found 450.6685.
J. Org. Chem. Vol. 75, No. 12, 2010 4037

Happ et al.
JOCArticle
7.71-7.53 (m, 9H), 7.29-7.25 (m, 3H), 7.17 (m, 1H), 2.56-2.53
(m, 12H). 13C NMR (CD3CN, 75 MHz) δ 157.1, 156.8, 156.7,
156.5, 153.7, 151.5, 151.4, 151.0, 150.9, 150.5, 150.5, 150.4, 150.4,
150.2, 148.0, 140.4, 136.1, 132.7, 130.3, 130.1, 128.3, 128.2, 128.0,
127.5, 125.0, 124.9, 124.6, 124.2, 123.9, 122.2, 121.4, 120.7,
92.9, 88.2, 20.3, 20.3, 20.2. ESI-TOF MS m/z 982.17 ([M -
PF6]þ). ESI-HRMS calcd for C45H37F6N9O2PRu ([M - PF6]þ)
982.1750, found 982.1776.
Bis(4,40-dimethyl-2,20-bipyridine)-{2-(1-(4-((4-nitrophenyl)-
ethynyl)phenyl)-1H-[1,2,3]triazol-4-yl)pyridine}ruthenium(II) Hexa-
fluorophosphate (18). According to the above standing general
procedure Ru(dmbpy)2Cl2 (25 mg, 0.046 mmol) and 2-(1-(4-((4-
nitrophenyl)ethynyl)phenyl)-1H-[1,2,3]triazol-4-yl)pyridine (15, 17
mg, 0.046 mmol) were reacted 2.5 h to yield the pure complex as red
powder after washing twice with ethanol and diethyl ether (40 mg,
77%). 1H NMR (CD3CN, 300 MHz) δ 9.25 (s, 1H), 8.38-8.32 (m,
4H), 8.25-8.21 (m, 2H), 8.17-8.15 (m, 1H), 8.03-8.0 (m, 1H),
7.83-7.73 (m, 7H), 7.71-7.58 (m, 4H), 7.36-7.19 (m, 5H),
2.55-2.51 (m, 12H). 13C NMR (CD3CN, 75 MHz) δ 157.2,
156.8, 156.8, 156.5, 151.7, 151.3, 151.1, 151.1, 150.8, 150.6, 150.4,
150.3, 150.1, 148.7, 147.6, 138.1, 136.1, 133.4, 132.5, 129.0, 128.3,
128.2, 127.5, 126.2, 124.9, 124.8, 124.6, 124.2, 123.9, 123.8, 123.4,
122.7, 120.8, 92.1, 89.4, 20.3, 20.3. ESI-TOF MS m/z 982.17 ([M -
PF6]þ). ESI-HRMS calcd for C45H37F6N9O2PRu ([M - PF6]þ)
982.1750, found 982.1759.
Acknowledgment. Financial support of this work by the
Dutch Polymer Institute (DPI), the Nederlandse Organisatie
voor Wetenschappelijk Onderzoek (NWO, VICI award
to U.S.S.), the Fonds der Chemischen Industrie (C.F.), and
the Carl-Zeiss Stiftung (D.E.) is kindly acknowledged.
Supporting Information Available: UV-vis absorption and
emission spectra for the ligands and corresponding ruthenium
complexes, crystallographic data for 17, computational details
of 16a and 16b (Cartesian coordinates and total energies),
and 1H and 13C NMR spectra of all new compounds. This
material is available free of charge via the Internet at http://
pubs.acs.org.
4038 J. Org. Chem. Vol. 75, No. 12, 2010