Azido- and ethynyl-substituted 2,2′:6′,2″-terpyridines as suitable substrates for click reactions

Article abstract of DOI:10.1055/s-0028-1088159

The click reaction of azido- and ethynyl-functionalized terpyridines has been exploited to obtain a series of 1H-1,2,3-triazole-substituted terpyridines. This protocol was extended towards the synthesis of terpyridine-based macroligands via end group modi

Full text of DOI:10.1055/s-0028-1088159

1506
PAPER
Azido- and Ethynyl-Substituted 2,2¢:6¢,2¢¢-Terpyridines as Suitable Substrates
for Click Reactions
Clicking with
T
erp
n
yridine
s
dreas Winter,a Andreas Wild,b Richard Hoogenboom,a Martin W. M. Fijten,a Martin D. Hager,b
Reza-Ali Fallahpour,c Ulrich S. Schubert*a,b
a
Laboratory of Macromolecular Chemistry and Nanoscience, Eindhoven University of Technology, P. O. Box 513, 5600 MB Eindhoven,
The Netherlands
Fax +31(40)2474186; E-mail: u.s.schubert@tue.nl
Laboratory of Organic and Macromolecular Chemistry, Friedrich-Schiller-University Jena, Humboldtstr. 10, 07743 Jena, Germany
HetCat, Gundeldingerstr. 174, 4053 Basel, Switzerland
b
c
Received 27 September 2008; revised 13 January 2009
properties arising from the polymer backbone, as well as
Abstract: The click reaction of azido- and ethynyl-functionalized
the reversible self-assembly properties of the supramolec-
terpyridines has been exploited to obtain a series of 1H-1,2,3-triaz-
ole-substituted terpyridines. This protocol was extended towards
the synthesis of terpyridine-based macroligands via end group mod-
ular moieties attached to the polymeric structure.1b,c We
have introduced a range of polymeric materials into such
ification of ethynyl-functionalized polymers. Finally, the combina- assemblies by this approach.6 For this purpose, a variety
tion of two orthogonal terpyridines within one click reaction
of modified chelating ligands have been used successfully
as initiators, monomers, or terminating agents.1a Further-
highlights the potential of this approach with respect to the prepara-
tion of new building blocks for supramolecular assemblies and
more, the complexes have been utilized as supramolecular
functional materials.
linkers between two polymeric chains to obtain well-de-
Key words: click reaction, complexes, cycloaddition, ligands,
terpyridines
fined homo and block copolymers, as well as chain-ex-
tended polymers.1a
The Huisgen 1,3-dipolar cycloaddition, the so-called
‘click’ reaction,7 has been used in the field of polymer
Supramolecular chemistry has evolved into one of the
chemistry for the covalent linkage of suitable functional-
most active research areas in modern chemistry with the
ized polymers as well as for end group modification reac-
design and preparation of new functional ligands and their
tions.8 Additionally, the click reaction has been
incorporation into supramolecular assemblies by transi-
tion metal complexation, p–p stacking, or hydrogen bond-
introduced as a versatile tool for the attachment of organic
substrates to surfaces and nanoparticles.9 In continuation
ing as cornerstones of this field.1 In general,
of previous work we have now combined the wide scope10
supramolecular interactions are weaker than covalent
of the click reaction with the chemistry of functionalized
bonds, and therefore they can be easily affected by exter-
2,2¢:6¢,2¢¢-terpyridines to open new avenues towards new
nal parameters (e.g., pH, temperature, solvent, redox pro-
cesses, and shear forces) allowing the design of
functional supramolecular materials.
In order to explore the applicability of this approach and
to investigate the properties of such 1,2,3-triazol-1-yl-
substituted terpyridines, we have synthesized a set of
model compounds 2 starting from 4¢-azido-2,2¢:6¢,2¢¢-
terpyridine (1)11 and the corresponding ethynyl com-
pounds (Scheme 1). As expected, a large range of func-
tional groups can be easily clicked to the terpyridine
moiety revealing the broad scope of this mild protocol. All
synthesized 4¢-substituted terpyridine derivatives 2 have
been obtained in good yields (>65%) and the purity has
been proven by NMR spectroscopy (Figure 1), mass spec-
trometry, and elemental analyses.
responsive and ‘smart’ materials with potential self-heal-
ing properties.2
The remarkably high binding affinity towards most tran-
sition metal ions, together with their chelating properties,
make terpyridines attractive building blocks for the con-
struction of supramolecular assemblies.3 Recently, oli-
gopyridyl ligands and, in particular, their transition metal
complexes have found applications as luminescent sen-
sors in molecular biology and medical diagnostics, in pho-
tocatalysis, as active materials in self-assembled
molecular devices, and as photoactive molecular wires
and they have been used for storage applications in molec-
ular electronics and photonics.4,5
An excess of copper(I) iodide had to be used in all cases
to avoid the deactivation of the catalyst by coordination to
the chelating terpyridine moiety. During the workup pro-
cedure, the remaining copper ions were removed by re-
peated extraction with aqueous sodium hydroxy-
ethylenediaminetriacetate (HEDTA) solution.
The basic principles and binding moieties known from su-
pramolecular chemistry have successfully been intro-
duced in the field of polymer chemistry, bringing together
the characteristics from both fields: the intrinsic material
The application of the click reaction in the field of poly-
mer chemistry has recently gained much attention, since
the end group modification of functionalized polymers as
SYNTHESIS 2009, No. 9, pp 1506–1512
Advanced online publication: 25.03.2009
DOI: 10.1055/s-0028-1088159; Art ID: T16708SS
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x
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x
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© Georg Thieme Verlag Stuttgart · New York

PAPER
Clicking with Terpyridines
1507
N
N
N
N3
R
CuI (1.1 equiv),
EtOH–H2O (7:3),
r.t., 12 h
N
N
+
R
N
N
N
N
1
2a: R = CH2OH (85%)
2b: R = Ph (73%)
2c: R = 4-OHC-C6H4 (69%)
Scheme 1 Schematic representation of the synthesis of 4¢-(1,2,3-triazol-1-yl)-2,2¢:6¢,2¢¢-terpyridines 2 by click chemistry
N
CuI (1.1 equiv),
EtOH–H2O (7:3),
r.t., 12 h
N3
OH
N
n
N
+
O
1
3
N
O
N
N
N
N
OH
n
N
N
4
N
Scheme 2 Schematic representation of the click reaction of ethynyl-
functionalized poly(2-ethyl-2-oxazoline) 3
Figure 1 1H NMR spectrum (400 MHz, CDCl3, r.t., aromatic
region) of 2c
Figure 2 (top), no signal for the ethynyl-functionalized
poly(2-ethyl-2-oxazoline) 3 were detected with a UV de-
tector. The high similarity of the two size exclusion chro-
matography traces obtained for 4 (RI and UV detector)
lets us to conclude that a fully terpyridine-functionalized
material has been synthesized. Since size exclusion chro-
matography alone is not a proof of quantitative attachment
of the aromatic groups, MALDI-TOF mass spectrometry
(Figure 2, bottom) was also performed. For both polymers
3 and 4 only one distribution was observed in the spectra,
with the spacing between the peaks corresponding to one
monomer unit (2-ethyl-2-oxazoline, M = 99.13 g/mol).
The end group analysis of 4 revealed that the peak molar
masses correspond exactly to the expected structure of the
terpyridine-functionalized polymer with a sodium ion,
since sodium iodide was used as an additive for the MAL-
well as the coupling of different polymer chains can be
performed in high yields and under mild conditions.8 2-
Oxazolines are known as versatile monomers in living
cationic ring-opening polymerizations (CROP).12 The re-
sulting poly(2-oxazoline)s consist of a poly(ethylene-
imine) chain with narrow molecular weight distributions
(PDI £ 1.20), bearing the 2-substituent of the starting ox-
azoline monomer as amidic side chains. Overall, the prop-
erties of the polymers are strongly dependent on the 2-
substituent and can therefore, be easily tuned.13 Due to
their manifold properties, (co)poly(2-oxazoline)s are cur-
rently of significant interest in chemical and medicinal re-
search.14
We recently reported the cationic ring-opening polymer- DI-TOF MS measurements.
ization of 2-ethyl-2-oxazoline in acetonitrile at 140 °C
The fluorescent Kröhnke-type derivative 517 was used as
with propargyl tosylate as initiator (monomer to initiator
ratio 20:1) using microwave irradiation15 yielding the de-
sired ethynyl-functionalized poly(2-ethyl-2-oxazoline)
3.16 Subsequently, the click reaction of polymer 3 with 4¢-
azido-2,2¢:6¢,2¢¢-terpyridine (1) afforded the new terpy-
ridyl-functionalized macroligand 4 (Scheme 2).
an example for ethynyl-functionalized terpyridines and,
therefore, as a substrate for click reactions with organic
azide compounds. A modified procedure for the one-pot
click reaction of aromatic boronic acids was used for the
synthesis of the 1,2,3-triazol-4-yl-substituted terpyridine
derivatives 6 (Scheme 3).18 The selective in situ formation
Size exclusion chromatography (SEC) was carried out of the azide in the presence of other functional groups
with chloroform–triethylamine–propan-2-ol (94:4:2) as highlights the feasibility of modifications of the products
eluent and indicated the purity of the polymeric systems 3 after the click reaction, e.g. by palladium(0)-catalyzed
and 4 with monomodal distributions. As illustrated in cross-coupling reactions.
Synthesis 2009, No. 9, 1506–1512 © Thieme Stuttgart · New York

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A. Winter et al.
PAPER
1. MeOH, cat. N-ethyl-morpholine,
reflux, 8 h
6a: 37%
6b: 41%
RuCl3⋅H2O
[Ru(6)2](PF6)2
+
6
2. NH4PF6
Scheme 4 Schematic representation of the synthesis of homoleptic
ruthenium(II)–bis(terpyridine) complexes [Ru(6)2](PF6)2
The shift of the signals in the 1H NMR spectra compared
to the uncomplexed ligands revealed the coordination of
the chelating ligand 6 to the ruthenium(II) core. In partic-
ular the protons in 6/6¢¢-position, directed towards the
shielding region of the central pyridine ring of the orthog-
onal second ligand, experience a considerable upfield
shift of about 1.5 ppm (see Figure 3 for 6a).
The [M – PF6]+ and [M – 2 PF6]+ peaks were detected by
MALDI-TOF mass spectrometry.19 No dissociation of the
complex occurred during the laser desorption/ionization
process, indicating the high stability of these complexes.
However, for all herein described terpyridine ligands as
well as ruthenium(II) complexes a characteristic fragmen-
tation of the triazole moiety was observed. Obviously,
such 1,4-diaryl-substituted 1H-1,2,3-triazole derivatives
tend to eliminate nitrogen under the conditions of
MALDI-TOF mass spectrometry. This effect has previ-
ously been described only for a variety of benzotriazole
derivatives.20
Figure 2 Top: Normalized size exclusion chromatograms (SEC,
CHCl3–Et3N–i-PrOH, 94:4:2) of the starting polymer 3 and the
macroligand 4. Bottom: MALDI-TOF mass spectra of the starting po-
lymer 3 (gray curve) and the macroligand 4 (black curve)
N
1. CuSO4, NaN3,
MeOH, r.t. 20 h
N
+
R
B(OH)2
2. CuI, Na-ascorbate,
MeOH, MW 1 h, 80 °C
5
N
N
N
N
N
N
N
R
6
4
Scheme 3 Schematic representation of the one-pot click reaction
with 4¢-(4-ethynylphenyl)-2,2¢,6¢,2¢¢-terpyridine (5)
Figure 3 Aromatic region of the 1H NMR spectra of terpyridine 6a
(bottom, THF-d8) and the corresponding ruthenium(II) complex
[Ru(6a)2](PF6)2 (top, CD3CN); for both spectra: 400 MHz, r.t.
The subsequent coordination of 6 to ruthenium (II) ions
afforded the desired homoleptic complexes of the general
formula [Ru(6)2](PF6)2 in moderate yields (Scheme 4).1b
The UV/Vis absorption spectra (MLCT band at ~500 nm,
Figure 4) additionally proved the formation of rutheni-
Synthesis 2009, No. 9, 1506–1512 © Thieme Stuttgart · New York

PAPER
Clicking with Terpyridines
1509
um(II)–bis(terpyridine) complexes. Since in the present
cases this band appears to be indifferent from the nature
of the lateral aromatic substituent, we could assume that
p-conjugation is interrupted by the triazole moiety21 and
thus, the ruthenium–terpyridine unit and the aryl substitu-
ent might have to be considered as ‘isolated’ chromo-
phores.22 The complexes showed only very weak emis-
sion at room temperature, since, in contrast to analogue
bipyridine-based complexes, the photoluminescence is
strongly quenched by the transition metal ion.
N3
N
CuI (1.1 equiv),
EtOH–H2O (7:3),
r.t., 12 h
N
+
N
N
N
1
5
N
N
N
N
N
N
N
N
7
N
N
Scheme 5 Schematic representation of the click reaction of the two
orthogonal terpyridyl derivatives 1 and 5
1
The H and 13C NMR spectra were recorded at 25 °C on a Varian
Mercury 400 MHz instrument with TMS as standard. Matrix-assist-
ed laser desorption-ionization time-of-flight mass spectrometry
(MALDI-TOF MS) was performed on a Voyager-DE PRO biospec-
trometry workstation (Applied Biosystems) time-of-flight mass
spectrometer, with dithranol as matrix. Elemental analyses were
obtained on a EuroVector EuroEA3000 elemental analyzer for
CHNS-O. UV/Vis absorption and photoluminescence spectra were
recorded at r.t. at concentrations of 10–6 M on an Analytik Jena
SPECORD 250 and Jasco FP-6500 spectrophotometer, respective-
ly. Size exclusion chromatography (SEC) was measured on a
Shimadzu system equipped with a SCL-A10 system controller, a
LC-10AD pump, a RID-10A refractive index detector, a SPD-10A
UV-detector at 254 nm and a PLgel 5 mm Mixed-D column at 50
°C utilizing a CHCl3–Et3N–i-PrOH (94:4:2) mixture as eluent at a
flow rate of 1 mL/min. The molar masses were calculated against
polystyrene standards.
Figure 4 UV/Vis absorption spectra of terpyridines 6 (THF) and
their corresponding homoleptic ruthenium(II) complexes
[Ru(6)2](PF6)2 (MeCN); for all spectra: 10–6 M, r.t.
The combination of the two orthogonally substituted sub-
strates 1 and 5 within one click reaction yielded directly
the new 1,4¢-(triazol-4-yl-phenyl)-bridged bis(terpyri-
dine) derivative 7 (Scheme 5). Due to the highly rigid
structure and the absence of any solubilizing side chains,
only very low solubility of the bis(terpyridine) 7 in com-
mon organic solvents was observed.23 Nonetheless, this
example shows that the click chemistry approach is also
suited for the straightforward construction of p-conjugat-
ed rigid-linear terpyridyl derivatives with potential in the
design of new functional materials by transition metal ion
complexation.
Unless stated otherwise, all reagents were purchased from commer-
cial sources and used without further purification. The solvents
were received from Biosolve and were dried and distilled according
to standard procedures. All reactions were performed under an at-
mosphere of argon unless specified. Column chromatographic sep-
arations were performed on alumina (neutral, Macherey & Nagel,
0.063–0.200 mm). Preparative size exclusion chromatography was
carried out using BioBeads SX-5, swollen with CH2Cl2. The terpy-
ridines 111 and 517d as well as the poly(2-ethyl-2-oxazoline) 316 were
synthesized following previously published methods.
In conclusion, the azide–alkyne click reaction has been
applied for the synthesis of a series of 1H-1,2,3-triazole-
substituted terpyridines. Two independent approaches
have been carried out to obtain a diverse set of functional-
ized terpyridine derivatives, including end group modi-
fied polymers, in good yields. Furthermore, ruthenium(II)
model complexes have been synthesized to highlight the
potential of the herein described terpyridines as chelating
ligands for the coordination of transition metal ions. In ad-
dition, the combination of the building blocks within one
click reaction has enabled the realization of a new type of
Safety comment: NaN3 is very toxic, personal protection precautions
should be taken. As low molecular weight organic azides are poten-
tial explosives, care must be taken during their handling. Generally,
when the total number of carbon (NC) plus oxygen (NO) atoms is less
than the total numbers of nitrogen atoms (NN) by a ratio of three, i.e.
(NC + NO)/NN £ 3, the compound is considered as an explosive haz-
ard. Therefore, the compounds were prepared prior to use and used
immediately.
Click Reactions Involving 4¢-Azido-2,2¢:6¢,2¢¢-terpyridine (1);
General Procedure
To a suspension of 4¢-azido-2,2¢:6¢,2¢¢-terpyridine (1, 50 mg, 0.18
bridged bis(terpyridine)s that represent potentially inter- mmol) and an alkyne derivative (0.25 mmol) in EtOH–H2O (7:3, 10
mL) was added CuI (37.7 mg, 0.20 mmol). The mixture was stirred
esting substrates for the design of supramolecular assem-
at r.t. for 15 h. The brown precipitate was filtered off, washed with
blies, including block copolymers or chain-extended
H2O (10 mL) and vigorously stirred with aq HEDTA (20 mL) for 2
polymers, by metal complexation.
h. The product was extracted into CHCl3 (3 × 20 mL). The com-
Synthesis 2009, No. 9, 1506–1512 © Thieme Stuttgart · New York

1510
A. Winter et al.
PAPER
bined organic phases were washed with H2O (3 × 20 mL) and dried
(MgSO4). The solvent was evaporated and the crude product 2 was
purified by column chromatography (neutral alumina, CH2Cl2–
MeOH, 98:2).
the terpyridine-functionalized polymer 4 was collected by precipi-
tation into Et2O.
1H NMR (400 MHz, CDCl3): d = 8.90 (br, 2 H, H3¢,5¢-tpy), 8.73–8.59
(br, 4 H, H6¢6¢¢-tpy, H3,3¢¢-tpy), 8.04–7.84 (br, 3 H, Htriaz, H4,4¢¢-tpy), 7.47–
7.35 (br, 2 H, H5,5¢¢-tpy), 4.68 (br, 2 H, Ha), 3.64–3.18 (br, 80 H, Hb,
Hc), 2.53–2.08 (br, 40 H, Hd), 1.35–0.90 (br, 60 H, He).
[1-(2,2¢:6¢,2¢¢-Terpyridin-4¢-yl)-1H-1,2,3-triazol-4-yl]methanol
(2a)
According to the general protocol for the click reaction, 1 (50 mg,
0.18 mmol), propargyl alcohol (2 mL, excess), and CuI (37.7 mg,
0.20 mmol) were reacted to yield 2a (51 mg, 85%) as a white solid.
MS (MALDI-TOF, dithranol): m/z = Mn = 3,050 g/mol; Mw = 3,250
g/mol; PDI = 1.07.
GPC (CHCl3–Et3N–i-PrOH): Mn = 2,300 g/mol; Mw = 2,480 g/mol;
1H NMR (400 MHz, CDCl3): d = 8.90 (s, 2 H, H3¢,5¢-tpy), 8.73 (d,
3J = 4.1 Hz, 2 H, H6¢6¢¢-tpy), 8.65 (d, 3J = 7.5 Hz, 2 H, H3,3¢¢-tpy), 8.15
(s, 1 H, Htriaz), 7.89 (mc, 2 H, H4,4¢¢-tpy), 7.39 (mc, 2 H, H5,5¢¢-tpy), 4.33
(s, 2 H, HCH2), 2.46 (br s, 1 H, HOH).
PDI = 1.08.
Click Reaction of Aromatic Boronic Acids; General Procedure
NaN3 (78 mg, 1.2 mmol) and anhyd CuSO4 (80 mg, 0.5 mmol) were
placed in an oven-dried round-bottomed flask. Subsequently, anhyd
MeOH (3 mL) and the aromatic boronic acid (1.0 mmol) were add-
ed. The mixture was stirred vigorously at r.t. till full conversion of
the boronic acid (TLC monitoring). Then H2O (0.3 mL), sodium
ascorbate (5 mol%), CuI (10 mol%), and 4¢-(4-ethynylphenyl)-
2,2¢:6¢,2¢¢-terpyridine (5, 333 mg, 1 mmol) were added. The result-
ing mixture was heated under microwave irradiation at 80 °C for 1
h. Subsequently H2O (15 mL) was added and the formed precipitate
was collected by filtration. The precipitate was washed with dil aq
NH3 soln (15 mL), extracted with toluene (2 × 20 mL), and purified
by precipitation into MeOH, followed by recrystallization and/or
preparative size exclusion chromatography.
13C NMR (100 MHz, CDCl3): d = 155.9, 155.5, 149.1, 141.3, 137.2,
136.0, 123.8, 121.2, 118.5, 117.9, 52.9.
MS (MALDI-TOF, dithranol): m/z = 302.34 ([M – N2]+), 331.29
([M + H]+).
Anal. Calcd for C18H14N6O: C, 65.44; H, 4.27; N, 25.44. Found: C,
65.22; H, 3.98; N, 25.51.
4¢-(4-Phenyl-1H-1,2,3-triazol-1-yl)-2,2¢:6¢,2¢¢-terpyridine (2b)
According to the general protocol for the click reaction, 1 (50 mg,
0.18 mmol), phenylacetylene (25.5 mg, 0.25 mmol), and CuI (37.7
mg, 0.20 mmol) were reacted to yield 2b (49.5 mg, 73%) as an off-
white solid.
4¢-{4-[1-(4-Bromophenyl)-1H-1,2,3-triazol-4-yl]phenyl}-
2,2¢:6¢,2¢¢-terpyridine (6a)
According to the general protocol for the click reaction, NaN3 (78
mg, 1.2 mmol), 4-bromophenylboronic acid (200 mg, 1 mmol), and
5 (333 mg, 1 mmol) were reacted to yield 6a (329 mg, 62%) as an
off-white solid.
1H NMR (400 MHz, THF-d8): d = 8.96 (s, 1 H, Htriaz), 8.94 (s, 2 H,
H3¢,5¢-tpy), 8.75 (d, 3J = 8.0 Hz, 2 H, H6,6¢¢-tpy), 8.73 (d, 3J = 5.4 Hz, 2
H, H3,3¢¢-tpy), 8.19 (d, 2 H, Haryl), 8.07 (d, 2 H, Haryl), 7.93 (t, 3J = 8.2
Hz, 2 H, H4,4¢¢-tpy), 7.94 (d, 2 H, Haryl), 7.78 (d, 2 H, Haryl) 7.34 (t,
3J = 6.2 Hz, 2 H, H5,5¢¢-tpy).
13C NMR (100 MHz, THF-d8): d = 156.1, 156.0, 149.2, 149.0,
147.5, 138.1, 136.5, 132.7, 131.7, 127.4, 126.1, 123.7, 121.5, 121.5,
121.4, 120.7, 118.3, 118.0.
1H NMR (400 MHz, CDCl3): d = 8.91 (s, 2 H, H3¢,5¢-tpy), 8.76
3
(d, 3J = 3.4 Hz, 2 H, H6¢,6¢¢-tpy), 8.67 (d, J = 7.8 Hz, 2 H, H3,3¢¢-tpy),
8.55 (s, 1 H, Htriaz), 7.96 (d, 3J = 7.4 Hz, 2 H, Ho-aryl), 7.91 (mc, 2 H,
H4,4¢¢-tpy), 7.49 (mc, 3 H, Hm,p-aryl), 7.40 (mc, 2 H, H5,5¢¢-tpy).
13C NMR (100 MHz, CDCl3): d = 156.1, 155.7, 149.2, 146.5, 137.0,
134.8, 130.1, 129.2, 128.5, 127.4, 123.6, 122.6, 120.9, 118.9.
MS (MALDI-TOF, dithranol): m/z = 349.07 (M – N2]+), 377.04
([M + H]+), 412.98 ([M + K]+).
Anal. Calcd for C23H16N6: C, 73.39; H, 4.28; N, 22.33. Found: C,
73.17; H, 4.37; N, 22.54.
4-[1-(2,2¢:6¢,2¢¢-Terpyridin-4¢-yl)-1H-1,2,3-triazol-4-yl]benzal-
dehyde (2c)
According to the general protocol for the click reaction, 1 (50 mg,
0.18 mmol), 4-ethynylbenzaldehyde (32.5 mg, 0.25 mmol), and CuI
(37.7 mg, 0.20 mmol) were reacted to yield 2c (50.3 mg, 69%) as an
off-white solid.
MS (MALDI-TOF, dithranol): m/z = 530.89 ([M + H]+).
Anal. Calcd for C29H19BrN6: C, 65.55; H, 3.60; N, 15.81. Found: C,
65.67; H, 3.69; N. 15.62.
1H NMR (400 MHz, CDCl3): d = 10.01 (s, 1 H, HCHO), 8.98 (s, 2 H,
H3¢,5¢-tpy), 8.76 (mc, 2 H, H6,6¢¢-tpy), 8.69 (d, 3J = 7.9 Hz, 2 H, H3,3¢¢-tpy),
8.69 (s, 1 H, Htriaz), 8.16 (d, 3J = 8.2 Hz, 2 H, Haryl), 8.02 (d, 3J = 8.2
Hz, 2 H, Haryl), 7.93 (mc, 2 H, H4,4¢¢-tpy), 7.42 (mc, 2 H, H5,5¢¢-tpy).
13C NMR (100 MHz, CDCl3): d = 155.9, 155.3, 189.9, 149.3, 146.1,
137.3, 136.8, 136.2, 135.9, 130.1, 128.2, 123.5, 122.5, 121.2, 118.9.
4¢-{4-[1-(10-Bromoanthracen-9-yl)-1H-1,2,3-triazol-4-yl]phe-
nyl}-2,2¢:6¢,2¢¢-terpyridine (6b)
According to the general protocol for the click reaction, NaN3 (78
mg, 1.2 mmol), (10-bromoanthracen-9-yl)boronic acid (301 mg, 1
mmol), and 5 (333 mg, 1 mmol) were reacted to yield 6b (360 mg,
57%) as an off-white solid.
1H NMR (400 MHz, CDCl3): d = 8.84 (s, 2 H, H3¢,5¢-tpy), 8.77 (d,
3J = 4.4 Hz, 2 H, H6,6¢¢-tpy), 8.71–8.67 (m, 4 H, H3,3¢¢-tpy, Hanthracene),
8.30 (s, 1 H, Htriaz), 8.19 (d, 2 H, Haryl), 8.09 (d, 2 H, Haryl), 7.91 (dt,
3J = 7.8 Hz, 4J = 1.8 Hz, 2 H, H4,4¢¢-tpy), 7.70 (dt, 3J = 7.8 Hz,
4J = 1.2 Hz, 2 H, Hanthracene), 7.59 (dt, 3J = 7.7 Hz, 4J = 1.2 Hz, 2 H,
Hanthracene), 7.42 (d, 3J = 8.7 Hz, 2 H, Hanthracene), 7.38 (mc, 2 H, H5,5¢¢-tpy).
13C NMR (100 MHz, CDCl3): d = 156.2, 156.1, 149.6, 149.2, 147.5,
138.6, 136.9, 130.8, 130.3, 129.0, 128.7, 128.4, 128.2, 128.0, 127.8,
126.5, 126.5, 124.5, 123.9, 122.6, 121.4, 118.7.
MS (MALDI-TOF, dithranol): m/z = 404.14.
Anal. Calcd for C24H16N6O: C, 71.28; H, 3.99; N, 20.78. Found: C,
70.93; H, 4.21; N, 21.01.
4¢-[4-Poly(2-ethyloxazoline)-1H-1,2,3-triazol-1-yl]-2,2¢:6¢,2¢¢-
terpyridine (4)
A soln of 1 (20 mg, 75 mmol), acetylene-functionalized poly(2-eth-
yl-2-oxazoline) (2,16 100 mg, 44 mmol, Mn = 2,300 g/mol,
PDI = 1.08) and CuI (23 mg, 121 mmol) in a mixture of EtOH (3
mL) and H2O (1 mL) was stirred at r.t. for 24 h. After evaporation
of the solvent and redissolution in CHCl3 (2 mL), the crude mixture
was precipitated into Et2O (20 mL). The resulting green powder was
redissolved in CHCl3 (20 mL) and washed with aq HEDTA (10
mL). The resulting colorless organic phase was concentrated and
MS (MALDI-TOF, dithranol): m/z = 630.97 ([M + H]+).
Anal. Calcd for C37H23N6Br: C, 70.37; H, 3.67; N, 13.31. Found: C,
70.56; H, 3.77; N, 13.22.
Synthesis 2009, No. 9, 1506–1512 © Thieme Stuttgart · New York

PAPER
Clicking with Terpyridines
1511
4¢-{4-[1-(2,2¢:6¢,2¢¢-Terpyridin-4¢-yl)-1H-1,2,3-triazol-4-yl]phe-
nyl}-2,2¢:6¢,2¢¢-terpyridine (7)
Acknowledgment
To a suspension of 4¢-azido-2,2¢:6¢,2¢¢-terpyridine (1,11 50 mg, 0.18
mmol) and 4¢-(4-ethynylphenyl)-2,2¢:6¢,2¢¢-terpyridine (5,17d 67 mg,
0.20 mmol) in EtOH–H2O (7:3, 10 mL) was added CuI (94.3 mg,
0.50 mmol). The mixture was stirred at r.t. for 15 h. The brown pre-
cipitate was filtered off, washed with H2O (10 mL) and vigorously
stirred with aq HEDTA (20 mL) at 40 °C for 2 h. The product was
extracted into CHCl3 (3 × 20 mL). The combined organic phases
were washed with H2O (3 × 20 mL) and dried (MgSO4). The solvent
was evaporated and the crude product was purified by column chro-
matography (neutral alumina, CH2Cl2–MeOH, 98:2) to yield 7 (52
mg, 47%) as a pale brown solid.
Financial support of this work by the Nederlandse Organisatie voor
Wetenschappelijk Onderzoek (VICI award for U. S. Schubert), and
the Fonds der Chemischen Industrie is kindly acknowledged. The
authors would also like to thank T. Erdmenger, N. Herzer, A. Baum-
gärtl and R. Eckardt for the help with MALDI-TOF MS measure-
ments and elemental analyses.
References
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1H NMR (400 MHz, CDCl3): d = 8.91 (s, 2 H, Htpy), 8.83 (s, 2 H,
H3¢,5¢-tpy), 8.75 (mc, 4 H, Htpy), 8.72 (mc, 2 H, Htpy), 8.64 (d, 3J = 7.5
Hz, 2 H, Htpy), 8.40 (s, 1 H, Htriaz), 8.17 (d, 2 H, Haryl), 8.04–7.93 (d,
4 H, Htpy, Haryl), 7.88 (mc, 2 H, H4,4¢¢-tpy), 7.36 (mc, 4 H, Htpy).
13C NMR spectroscopy could not be performed due to the low sol-
ubility.
MS (MALDI-TOF, dithranol): m/z = 594.22 [M – N2 + H]+), 608.17
([M + H]+).
Anal. Calcd for C38H25N9: C, 75.11; H, 4.15; N, 20.75. Found: C,
75.39; H, 4.37; N, 21.01.
Synthesis of Ru(II)–Bis(terpyridine) Complexes; General Pro-
cedure
A suspension of 6 (0.07 mmol) and RuCl3·H2O (0.1 mmol) in
MeOH (3 mL) was refluxed for 4 h and filtered.23 The residue was
washed with MeOH (2 mL) and H2O (2 mL) and subsequently sus-
pended with 6 (0.05 mmol) in MeOH (5 mL) containing N-ethyl-
morpholine (1 drop). After 8 h at reflux, the soln was filtered and
the complex precipitated using methanolic NH4PF6 soln. The pre-
cipitate was filtered off and washed with H2O (5 mL) and MeOH (5
mL). Purification was carried out by precipitation of the crude prod-
uct ( MeCN soln into Et2O) and/or recrystallization (MeCN) to yield
the desired complex [Ru(6)2](PF6)2.
[Ru(6a)2](PF6)2
According to the general protocol for the complexation reaction, 6a
(74 mg, 1.40 mmol) and RuCl3·H2O (25 mg, 0.10 mmol) were re-
acted to yield [Ru(6a)2](PF6)2 (38 mg, 37%) as a red solid.
1H NMR (400 MHz, CD3CN): d = 9.10 (s, 4 H, H3¢,5¢-tpy), 8.91 (s, 2
H, Htriaz), 8.70 (d, 3J = 8.0 Hz, 4 H, H3,3¢¢-tpy), 8.34 (mc, 8 H, Haryl),
3
7.97 (t, J = 7.9 Hz, 4 H, H4,4¢¢-tpy), 7.86 (mc, 8 H, Haryl), 7.46 (d,
3J = 5.6 Hz, 4 H, H6,6¢¢-tpy), 7.20 (t, 3J = 6.2 Hz, 4 H, H5,5¢¢-tpy).
MS (MALDI-TOF, dithranol): m/z = 1307.78 ([M – PF6]+), 1164.01
(f) Benniston, A.; Harriman, A.; Li, P.; Patel, P. V.; Sams,
C. A. J. Org. Chem. 2006, 71, 3481.
([M – 2 PF6]+), 1114.33 ([M – 2PF6 – 2 N2]+).
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J. Polym. Sci., Part A: Polym. Chem. 2004, 42, 4016.
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Hofmeier, H.; Schubert, U. S. Macromolecules 2003, 36,
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U. S. Macromol. Rapid Commun. 2003, 24, 852. (f)Winter,
A.; Schubert, U. S. Macromol. Chem. Phys. 2007, 208, 1956.
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K. B. Angew. Chem. Int. Ed. 2002, 41, 2596. (b) Chan,
T. R.; Hilgraf, R.; Sharpless, K. B.; Fokin, V. V. Org. Lett.
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Anal. Calcd for C58H38Br2F12N12P2Ru: C, 47.92; H, 2.63; N, 11.56.
Found: C, 48.28; H, 2.90; N, 11.86.
[Ru(6b)2](PF6)2
According to the general protocol for the complexation reaction, 6b
(88 mg, 1.40 mmol) and RuCl3·H2O (25 mg, 0.10 mmol) were re-
acted to yield [Ru(6b)2](PF6)2 (47 mg, 41%) as a red solid.
1H NMR (400 MHz, CD3CN): d = 9.12 (s, 4 H, H3¢,5¢-tpy), 8.82 (s, 2
H, Htriaz), 8.77–8.70 (m, 8 H, H3,3¢¢-tpy, Hanthracene), 8.19 (mc, 8 H,
Haryl), 7.99 (t, 3J = 8.4 Hz, 4 H, H4,4¢¢-tpy), 7.84 (t, 3J = 6.8 Hz, 4 H,
Hanthracene), 7.70 (t, 3J = 8.0 Hz, 4 H, Hanthracene), 7.50–7.46 (m, 8 H,
H6,6¢¢-tpy, Hanthracene), 7.23 (t, 3J = 6.3 Hz, 4 H, H5,5¢¢-tpy).
MS (MALDI-TOF, dithranol): m/z = 1362.03 ([M – 2 PF6]+),
1338.22 ([M – 2 PF6 – N2]+), 1314.15 ([M – 2 PF6 – 2 N2]+).
Anal. Calcd for C74H46Br2F12N12P2Ru: C, 53.73; H, 2.80; N, 10.16.
Found: C, 54.02; H, 3.17; N, 10.42.
Synthesis 2009, No. 9, 1506–1512 © Thieme Stuttgart · New York

1512
A. Winter et al.
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Synthesis 2009, No. 9, 1506–1512 © Thieme Stuttgart · New York