2-(1H-1,2,3-triazol-4-yl)-pyridine ligands as alternatives to 2,2′-bipyridines in ruthenium(II) complexes

Article abstract of DOI:10.1002/asia.200800297

The synthesis of a variety of 2-(1H-1,2,3-triazol-4-yl)-pyridines by click chemistry is demonstrated to provide straightforward access to mono-functionalized ligands. The ring-opening polymerization of e-caprolactone initiated by such a mono-functionalize

Full text of DOI:10.1002/asia.200800297

FULL PAPERS
DOI: 10.1002/asia.200800297
2-(1H-1,2,3-Triazol-4-yl)-Pyridine Ligands as Alternatives to 2,2’-Bipyridines
in Ruthenium(II) Complexes
Bobby Happ,[a, b] Christian Friebe,[a, b] Andreas Winter,[b] Martin D. Hager,[b]
Richard Hoogenboom,[b] and Ulrich S. Schubert*[a, b]
Abstract: The synthesis of a variety of 2-(1H-1,2,3-triazol-4-yl)-pyridines by click
chemistry is demonstrated to provide straightforward access to mono-functional-
ized ligands. The ring-opening polymerization of e-caprolactone initiated by such a
mono-functionalized ligand highlights the synthetic potential of this class of bi-
Keywords: click chemistry · coordi-
nation chemistry · ruthenium · UV/
Vis spectroscopy · supramolecular
chemistry
ACHTUNGTRENNUNGdentate ligands with respect to polymer chemistry or the attachment onto surfaces
and nanoparticles. The coordination to RuII ions results in homoleptic and hetero-
leptic complexes with the resultant photophysical and electrochemical properties
strongly dependent on the number of these ligands attached to the RuII core.
Introduction
conformations, that is, facial (fac) and meridional (mer) ste-
reoisomers, which is difficult to control.[5] In addition, the
synthesis of functionalized ligands and complexes is of
utmost importance. Incorporation of these ligands and com-
plexes into polymers or the attachment onto surfaces as well
as to nanoparticles can be realized through such functionali-
ties. The covalent linking of metal complexes to a polymer
backbone results in materials that combine the photophysi-
cal and electrochemical properties of the complex with the
good mechanical properties of the polymer, while at the
same time reducing aggregation of the complexes. Addition-
ally, the processing features of the materials, for example, by
spin coating or inkjet printing, are enhanced.[6]
Therefore, the development of new synthetic strategies
for an easy and broad access to functionalized bipyridine-
type ligands is a general target of current research. The
modern synthetic methodologies to obtain functionalized
2,2’-bipyridines have been reviewed recently[1,7] and clearly
reveal that the selective and easy synthesis of mono-func-
tionalized ligands in high yields still remains a significant
synthetic challenge.
The development of novel functional materials with interest-
ing photophysical and electrochemical properties, for exam-
ple, for applications in solar cells, sensors, or organic light-
emitting diodes (OLEDs), represents a major challenge in
current material science.[1] Transition-metal complexes, in
particular the d6 species such as ruthenium(II) and iridium-
ACHTUNGTRENNUNG(III) with chelating ligands, have been intensively investigat-
ed to extend the application possibilities in modern device
technology. In this respect, particularly the RuII complexes
of bipyridine-type ligands are highly interesting owing to
their predictable photophysical and electrochemical proper-
ties.[2] As kinetically stable bonds with bipyridines are
formed, the selective synthesis of homoleptic and heterolep-
tic complexes is possible.[3,4] However, the coordination of
three unsymmetrical ligands can give rise to two different
[a] B. Happ, C. Friebe, Prof. Dr. U. S. Schubert
Laboratory of Organic and Macromolecular Chemistry
Friedrich-Schiller-University Jena
Flood and co-workers have shown that the 1H-1,2,3-tri-
Humboldtstrasse 10, 07743 Jena (Germany)
AHCTUNGTREGaNNNU zole moiety can be used as an alternative for pyridine in
[b] B. Happ, C. Friebe, Dr. A. Winter, Dr. M. D. Hager,
Dr. R. Hoogenboom, Prof. Dr. U. S. Schubert
Laboratory of Macromolecular Chemistry and Nanoscience
Eindhoven University of Technology
oligopyridine ligands.[8] They have synthesized a set of 2,6-
bis(1H-1,2,3-triazol-4-yl)-pyridines that utilize the Huisgen
1,3-dipolar cycloaddition,[9] the so-called click reaction. As a
comparable structure to 2,2’:6’,2’’-terpyridines, these exam-
ples have demonstrated the versatility of this approach to
substitute pyridine rings of the oligopyridine ligands by
functionalized 1H-1,2,3-triazoles while still maintaining
P. O. Box 513, 5600 MB Eindhoven (The Netherlands)
Fax : (+31)40-2474186
E-mail: u.s.schubert@tue.nl
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.200800297.
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Chem. Asian J. 2009, 4, 154 – 163

metal-complexation properties.[8] Since the early reports on
the preparation of simple mono-(1H-1,2,3-triazole)-pyri-
dines,[10] various synthetic strategies based on click-type re-
actions as well as pharmaceutical or biomedical applications
have been reported for this class of substances.[11] Their po-
tential usage as fluorescence sensors for transition-metal
ions has very recently been introduced by Bunz and co-
workers.[12]
Scheme 1. Schematic representation of the synthesis of the bidentate
(1H-1,2,3-triazole)-pyridine ligands
1 and 2 by click reactions (see
Table 1 for details).
The proper combination of chelating ligands with the
wide scope[13] of the click reaction opens new avenues to-
wards novel functional materials.[14] To explore the applica-
bility of this approach and to carefully investigate the prop-
erties of such functionalized (1H-1,2,3-triazole)-bipyridine
bidentate ligands, we have synthesized a library of pyridin-
2-yl substituted 1H-1,2,3-triazole systems L. Subsequently,
the selective coordination of these ligands with rutheni-
products 1 have been isolated in moderate to good overall
yields (Table 1). For the synthesis of the aromatic deriva-
tives 2, a modified procedure for the one-pot click reaction
Table 1. Synthesized (1H-1,2,3-triazole)-pyridine ligands 1 and 2.
ACHTUNGTRENNUNG
Entry
R
Yield[a] Entry
R
Yield[a]
naphthalen-1-yl 64%
p-MeO-C6H4 44%
p-HOCH2-C6H4 20%
A
ACHTUNGTRENNUNG
1a
1b
1c
1d
1e
1 f
n-C10H21
79%
66%
76%
21%
2a
2b
2c
methyl-2,2’-bipyridine) with their photophysical and electro-
chemical properties strongly dependant on the number of
complexed triazole-based ligands L. The general click proto-
col is also suited for the straightforward synthesis of func-
tionalized ligands (e.g., the hydroxyl derivative 1b) for fur-
ther applications in the fields of polymer chemistry or
n-C11H22OH
2-(C2H5)C6H12
n-C11H22COOH
CH2(p-tBu-C6H4) 66%
AHCTNUGTERNG(NNU CH2CH2O)4H 22%
[a] Yield of the isolated product after flash column chromatography (neu-
tral Al2O3) and/or recrystallization (See the Supporting Information for
details). TBA=tetrabutylammonium.
nanotechnoACHTUNGTRENNUNGlogy.
Results and Discussion
of boronic acids has been used.[17] The aromatic azides have
been generated in situ and subsequently reacted with 2-ethy-
nylpyridine to give the desired N1-aryl-substituted 1H-1,2,3-
triazoles 2 in moderate yields (Scheme 1, Table 1). The
purity of all of the ligands 1 and 2 has been confirmed by
NMR spectroscopy, mass spectrometry, and elemental analy-
sis. As was also concluded from the spectroscopic data, the
cycloaddition has in all cases resulted in the selective forma-
tion of the 1,4-disubstituted 1H-1,2,3-triazoles.[12] Notably,
the mild click reaction protocol is very compatible with
additional reactive functional groups (e.g., hydroxyl deriva-
tives 1b and 2c). Hence, a subsequent incorporation of the
synthesized ligands through these functionalities into poly-
mers or the covalent attachment to surfaces is enabled in a
straightforward manner.
Synthesis and Characterization
Substituted (1H-1,2,3-triazole)-pyridine ligands: The synthe-
sis of the N1-alkyl-substituted ligands 1 has been performed
under microwave-assisted click conditions,[15] starting from
2-ethynylpyridine and the corresponding aliphatic azide
compounds, which utilize copper(II) sulfate in the presence
of sodium ascorbate as the catalytic system (Scheme 1).[9a,16]
The azide compounds have been prepared from the respec-
tive alkyl bromides in a microwave-assisted nucleophilic
substitution reaction by using an excess of NaN3, and have
been used without any purification or isolation. The final
Abstract in German: Die Click-Reaktion ermçglicht die
Synthese von chelatisierenden, unsymmetrischen 2-(1H-
1,2,3-Triazol-4-yl)-pyridin-Liganden, die als Strukturanaloga
zu 2,2’-Bipyridinen dienen. Das große Synthesepotential
dieser zweizꢁhnigen Liganden hinsichtlich mçglicher An-
wendungen in den Bereichen der Polymerchemie oder der
Nanowissenschaft wird am Beispiel der Ringçffnungspoly-
merisation von e-Caprolacton, initiiert durch einen derarti-
gen, monofunktionalisierten Liganden, aufgezeigt. Homo-
leptische und heteroleptische Komplexe sind durch gezielte
Koordinierung an RuII-Zentren zugꢁnglich. Die photophysi-
kalischen und elektrochemischen Eigenschaften der Kom-
plexe weisen eine starke Abhꢁngigkeit von der Anzahl der
koordinierten neuen Liganden auf.
Poly(e-caprolactone)-containing macroligand: In recent
years, various synthetic strategies to incorporate chelating li-
gands into polymers have been reported in the literature.[18]
In prior work, for example, we have successfully introduced
polystyrene, polyACTHNUTRGNE(NUG ester)s, and poly(ethylene oxide) into such
materials.[1] Among other techniques, the ring-opening poly-
merization (ROP) of cyclic esters, such as e-caprolactone,
with a hydroxy-functionalized initiator, is a suitable and effi-
cient technique to synthesize functionalized polymers and
complex polymeric architectures.[19] With the appropriate
catalyst and reaction conditions, the ROP of cyclic esters
proceeds in a controlled manner. Well-defined polymers
with low polydispersity indices (PDIs) and tunable molar
masses are accessible by control of the reaction stoichiome-
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155

U. S. Schubert et al.
FULL PAPERS
try. Tin(II) 2-ethylhexanoate has been found to be a highly
active catalyst for this kind of polymerization reaction. As a
general proof of concept that the ligands can be easily intro-
duced into polymers, we have chosen this approach to syn-
thesize the poly(e-caprolactone)-containing macroligand
pCL-1b as summarized in Scheme 2.
traces have been recorded with N,N-dimethylformamide
(DMF; containing 5 mmol NH4PF6) as the eluent and indi-
cated the purity of the polymeric systems with a mono-
modal distribution. The molar mass has been calculated by
using a linear poly(ethylene oxide) calibration to be compa-
1
rable with the values derived from the H NMR spectrum
(Mn =3,600 gmolÀ1, PDI 1.29).
The high similarity of the GPC traces (refractive index
(RI) and UV detector), together with the absorption data of
1b and pCL-1b, led us to conclude that the fully ligand-
functionalized material has been synthesized. However, the
rather broad PDI value around 1.3 indicates that the poly-
merization has not proceeded in a fully controlled fashion.
This observation might be explained by the limited solubility
of ligand 1b in the bulk monomer, and the increasing viscos-
ity during the reaction resulting in hindered diffusion. The
matrix-assisted laser desorption-ionization time-of-flight
(MALDI-TOF) mass spectrum has additionally confirmed
the incorporation of 1b into the polymer (Figure 2). The ob-
served molar mass distribution is in very good agreement
with the theoretical value for the Na+ ion adduct. The dis-
tance between two peaks is, in all cases, 114 Da, which fits
exactly with the repeating unit of the pCL.
Scheme 2. Schematic representation of the synthesis of the macroligand
pCL-1b by ring-opening polymerization of e-caprolactone.
The reaction has been performed in bulk monomer, using
the OH-functionalized ligand 1b as the initiator (I; M/I
ratio=25:1) and tin(II) 2-ethylhexanoate as the catalyst.
Precipitation in methanol from dichloromethane has result-
ed in the desired macroligand pCL-1b in high yield (89%;
the yield of the macroligand has been calculated on the
1
basis of the initiator). The H NMR spectrum of the purified
polymer has confirmed the successful incorporation of the
(1H-1,2,3-triazole)-pyridine moiety into the polymeric struc-
ture. The molar mass of the polymer (Mn =3,500 gmolÀ1)
1
has been calculated from the H NMR spectra by comparing
the integrals of the main-chain methylene groups to the res-
onances in the aromatic region (Figure 1). A slightly higher
molar mass than the theoretical values (Mn =3,100 gmolÀ1
;
predetermined from the monomer-to-initiator ratio) has
been obtained. The gel-permeation chromatography (GPC)
Figure 2. MALDI-TOF MS of pCL-1b (dithranol as the matrix).
Ruthenium(II) complexes: As already pointed out, ruthe-
nium(II) complexes of bipyridine-type ligands are highly in-
teresting owing to their predictable photophysical and elec-
trochemical properties.[2] Upon complexation, kinetically
stable bonds with the ligands are formed, making the selec-
tive synthesis of homoleptic and heteroleptic complexes pos-
sible.[3,4]
To study the influence of the (macro)ligands L described
herein on the corresponding RuII complexes with respect to
their photophysical and electrochemical properties, a series
of complexes of the general formula [Ru
(PF6)2 has been synthesized (Scheme 3). Therefore, we have
optimized a procedure known from literature to prepare the
ACHTUGNERTN(NUNG dmbpy)3Àn(L)n]
AHCTUNGTRENNUNG
[20]
Figure 1. 1H NMR spectrum of pCL-1b (400 MHz, CD2Cl2, RT); the aro-
reference complex [Ru
N
ACHTUGNTRENUN(GN PF6)2 as well as the ho-
matic region is highlighted as an inset.
moleptic complexes [Ru(L)3]ACHTUNGTRENNUNG
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Chem. Asian J. 2009, 4, 154 – 163

Alternatives to 2,2’-Bipyridines in Ruthenium(II) Complexes
As generally outlined in Scheme 3, the selective synthesis
of the two different types of heteroleptic complexes involves
a stepwise procedure. Therefore, [Ru
cyclooctadiene) has been converted to the precursor com-
plexes [Ru(L)2]Cl2 and [Ru(dmbpy)2]Cl2, by reaction with
ACHTUNGRTEN(UNGN cod)Cl2]n (cod=1,5-
AHCTUNGTRENNUNG
the appropriate ligands in DMF under microwave irradia-
tion. Subsequently, by microwave-assisted coordination of
the respective other ligand, the heteroleptic complexes [Ru-
AHCUTNGRETNN(GNU dmbpy)2(L)]ACHTUTNGRENNUG(PF6)2 and [RuACHTNUEGTRG(NNNU dmbpy)(L)2]ACHTUNGTRENUN(NG PF6)2 have been
synthesized in good yields (>80%). In this context, it is
noteworthy that a complex mixture of all possible isomers,
which could not previously be separated through chroma-
tography, has been obtained for the system [Ru
(PF6)2.
All synthesized homoleptic and heteroleptic complexes
ACHTUNGTRENN(UNG dmbpy)(L)2]
AHCTUNGTRENNUNG
shown have been fully characterized by NMR spectroscopy,
mass spectrometry, and elemental analysis. In general, all
complexes have exhibited well-resolved 1H NMR spectra
with a number of characteristic features. A significant down-
field shift (0.5–0.75 ppm) of the signal for the triazole-H
(H5’) has been observed in all cases. The same stands for the
H3, H4, and H5 resonances of the pyridine rings of L, though
it is less pronounced. These effects have been attributed to
the induced charges, together with the p-cloud perturbance
and conformational changes that occur as a consequence of
the coordination of the ligand to the RuII moiety.[8a]
Scheme 3. Schematic representation of the syntheses of the homoleptic
and heteroleptic complexes [Ru
to 3).
ACHTUGTNRNENUG(dmbpy)3Àn(L)n]ACHTUGNTRENN(UGN PF6)2 (L=1 and 2, n=0
high yields by using microwave irradiation (>90%;
Scheme 3). Generally speaking, the coordination of three
unsymmetrical ligands will give rise to two different prod-
ucts, that is, facial (fac) and meridional (mer) conformers,
the formation of which is difficult to control.[5] As expected,
the homoleptic tris-(1H-1,2,3-triazole)-pyridine complexes
have been isolated as statistic mixtures of their two re-
gioisomers (fac and mer). Only in the case of the bulky
naphthalene-substituted ligand 2a have we been able to sep-
arate the fac- and the mer-isomer by chromatography (SiO2,
saturated NH4Cl in DMF/EtOH (4:1 ratio)),[21] and the re-
sulting NMR spectra (Figure 3) could be fully assigned by
using 1D and 2D NMR techniques. Owing to the loss of
symmetry, three different signals for the proton of the tri-
Furthermore, we have successfully applied the complexa-
tion protocol for the synthesis of the heteroleptic RuII sys-
tems for the coordination of the macroligand pCL-1b. The
microwave-assisted reaction has been carried out in ethanol
yielding the polymer-containing complex [Ru
ACHUTGTNRNE(NUG dmbpy)2ACHTUNGTRENNUNG(pCL-
1b)]
AHCTUNGTRENNUNG
show no fragmentation on GPC columns by using optimized
conditions, the macroligand complex has been investigated
by this technique. A significant shift towards higher Mn has
been obtained compared with the uncomplexed macroligand
(Figure 4, top). For both compounds, mono-modal distribu-
tions have been observed. The incorporation of the RuII
core into the polymer has been confirmed by applying GPC
coupled with a photodiode array (PDA) detector (Figure 4,
bottom). The characteristic metal-to-ligand charge-transfer
(MLCT) band for such RuII complexes has been observed at
around 450 nm.
ACHTUNGTRENNUNG
azole-ring (H5’) have been observed for the mer-isomer.
The purity of the metal-containing polymer has addition-
1
ally been confirmed by H NMR spectroscopy. The well-re-
solved signals within the aromatic region (Figure 5) have
been fully assigned by comparison with the related complex
[Ru
ACHTUNGTERNNU(GN dmbpy)2ACHTNURTGEGN(NUN 1b)]ACTHUNGTRENNUNG
maining precursor complex [Ru
AHCTUNGTRENNUNG
plexed macroligand have been detected. The molar mass as
1
calculated from the H NMR spectrum (Mn =4,100 gmolÀ1,
27 CL-repeating units) is in good agreement with the data
obtained for the macroligand (28 repeating units).
Figure 3. 1H NMR spectra (400 MHz, CD2Cl2, aromatic region) of the ho-
moleptic complexes mer-[Ru(2a)3](PF6)2 and fac-[Ru(2a)3](PF6)2.
A
E
N
ACHTUNGTRENNUNG
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U. S. Schubert et al.
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Photophysical and Electrochemical Properties
The influence of the synthesized ligands on the photophysi-
cal and electrochemical properties of the derived RuII com-
plexes has been investigated by UV/Vis and emission spec-
troscopy, as well as cyclic voltammetry. As a chromato-
graphic separation of the configurational isomers could not,
in general, be achieved, the properties are discussed for the
isomeric mixtures of the respective complexes.
The UV/Vis behavior of the complexes is, in general,
characterized by two strong absorption bands attributed to
ligand-centered (LC, 280–300 nm) and MLCT (380–460 nm)
transitions. The absorption spectra of the [Ru
(1a)n](PF6)2 series in CH2Cl2 is depicted in Figure 6 (top).
The homoleptic complex [Ru(1a)3](PF6)2 shows the most
ACHTUNGTRNE(NUNG dmbpy)3Àn
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
pronounced blue-shift of approximately 10 nm of the LC
band compared with free ligand 1a. The same effect can be
observed in the case of the MLCT bands. A distinct blue-
Figure 4. Top: GPC elution chromatograms of pCL-1b (a) and [Ru-
A
R
ACHTUNGTRENNUNG
A
U
Figure 6. Top: UV/Vis absorption spectra of the [Ru
ACHTUNGTREN(NUG dmbpy)3ÀnACHTUNGTRENNUNG(1a)n]-
AHCTUNGTRENNUNG
UV/Vis absorption spectra of [RuACHTUNRGTENNUG(2a)3]ACHTUNGTREN(NNGU PF6)2 (fac-isomer: c, mer-
Figure 5. 1H NMR spectrum (aromatic region) of [Ru
G
G
isomer: c). For all spectra: 10À6 m of the respective complex in CH2Cl2
1b)]
G
was used.
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Alternatives to 2,2’-Bipyridines in Ruthenium(II) Complexes
shift of this band, compared with the reference complex
(n=0),[22] is observed with an increasing number of (1H-
1,2,3-triazole)-based ligands. The large relative difference of
the MLCT energies for the two heteroleptic complexes can
be explained by the evident transition from a dmbpy-domi-
nated system to a more triazole-rich system (Figure 6).
As a consequence of the chromatographic separation, we
have been able to determine the energetic differences of the
two isomers of [RuACHTUNGTRNENUG(2a)3]AHCTUNGTRNE(NUGN PF6)2 independently (Figure 6,
bottom). The MLCT band of the mer-isomer is blue shifted
(fac: labs,max =381 nm, mer: labs,max =367 nm) and exhibits a
slightly increased optical band gap (~0.04 eV).[23] Obviously,
the homoleptic complexes shown here are more sensitive to
their coordination geometry compared with complexes
based exclusively on unsymmetrical bipyridine ligands in
which negligible differences between the two isomers have
been reported.[21]
Subsequently, the influence of various aliphatic and aro-
matic substituents on the (1H-1,2,3-triazole)-ring on the ab-
sorption properties of the complexes [RuACHTNUTRGENNUG(dmbpy)2(L)]ACHUTGNTREN(NUNG PF6)2
has been investigated (see the Supporting Information for
details). The LC and MLCT absorption bands exhibit only
small shifts upon changing the substituent on the N1 position
of the triazole moiety. Obviously, such an exchange does
neither affect the pmetal (t2g) highest occupied molecular orbi-
tal (HOMO) nor the p*-ligands lowest unoccupied molecu-
lar orbital (LUMO). This leads to the general assumption
that the p* LUMO of these complexes is mainly located on
the dmbpy ligand, and that the nature of the N1 substituent
will not have a great influence on the energy of the frontier
orbitals.[24]
The photoluminescence (PL) spectra as recorded in n-bu-
tyronitrile glass at 77 K have revealed strong orange emis-
sion for the heteroleptic complexes [Ru
and [Ru(dmbpy)(1a)2](PF6)2 with a blue-shift of 17 nm and
29 nm, respectively, compared with the homoleptic reference
complex [Ru(dmbpy)3](PF6)2 (lPL,max =592 nm, Figure 7
ACHTUNGTNERU(NGN dmbpy)2ACHTNUTRGEG(NNUN 1a)]ACTHNUGTREN(NUNG PF6)2
Figure 7. Top: PL spectra at 77 K of the [Ru
(n=2: g, n=1: a, n=0: c). Bottom: PL spectra of [Ru
(1a)]
(PF6)2 at various temperatures. For all spectra, 10À6 m of the respec-
ACHTUGNERTN(UNGN dmbpy)3ÀnACHNUTRTGEGN(NUN 1a)n]ACTHUNGTRENNUNG
G
U
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
tive complex in n-butyronitrile was used.
N
ACHTUNGTRENNUNG
(top)). Owing to the experimental setup, PL quantum yields
(FPL) could not be determined. For the homoleptic complex
[RuACHTUNGTRENNUNG(1a)3]ACHTUNGTRENNUNG(PF6)2, no emission has been observed.
Table 2. Electrochemical properties of the complexes
[Ru
G
N
As depicted in Figure 7 (bottom), the PL spectra shows a
strong temperature dependence. A drastic decrease in the
emission intensity could be observed between 150 K and
200 K, which can be attributed to the melting of the solvent
matrix resulting in an increased feasibility of radiationless
[a]
[a]
Entry
Eox
Ered
HOMO[b] LUMO[c] Eg
[Ru
[Ru
[Ru
[Ru
fac-[Ru
mer-[RuACTHUNGTRENNNUG
[Ru
[Ru
[Ru
N
1.15 V À1.48 V À5.52 eV À2.99 eV 2.53 eV
(1a)]2+ 1.16 V À1.55 V À5.55 eV À2.93 eV 2.62 eV
ACHTUNGTRENNUNG
1.26 V
1.44 V
1.46 V
–
–
–
À5.60 eV
À5.77 eV
À5.77 eV
–
–
–
–
–
–
relaxation. In contrast with [RuACHTNUGTRENN(UG dmbpy)3]HCAUTGNTERNN(GNU PF6)2 (lmax,PL =
ACHTUNGTRENNUNG
609 nm, FPL =0.13), there was no observed PL in the de-
gassed CH2Cl2 solution for all of the described complexes at
room temperature.
It is thought that for all dmbpy-containing heteroleptic
complexes, the p* LUMO is mainly located on the dmbpy
ligand and the low-temperature PL spectra are comparable
with those from bipyridine-based RuII complexes. In the
(1b)]2+ 1.20 V À1.50 V À5.54 eV À2.95 eV 2.59 eV
(2a)]2+ 1.24 V À1.48 V À5.64 eV À2.95 eV 2.69 eV
(2b)]2+ 1.23 V À1.49 V À5.61 eV À2.93 eV 2.69 eV
[a] Measured in degassed CH2Cl2 (containing 1 mm TBAPF6) at a scan
rate of 100 mVsÀ1 vs Ag/AgCl. [b] Calculated from the measured oxida-
tion potential. [c] Calculated from the measured reduction potential.
case of the homoleptic complexes, [Ru(L)3]ACTHNUTRGNE(NUG PF6)2, the
HOMO–LUMO transition, and thus the emission, is located
on the pmetal (t2g) HOMO and p*L LUMO, respectively. With
an increasing number of ligands L in the complex, the emis-
sion energy increases and in particular, the relative PL in-
tensity at comparable concentrations decreases.
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U. S. Schubert et al.
FULL PAPERS
the complexes are strongly influenced by the (1H-1,2,3-tri-
AHCTUNGTREGaNNUN zole)-pyridine ligands that exhibit a significantly lower
energy of the HOMO compared with analogous bipyridine-
based complexes.
The photophysical and electrochemical properties of the
macroligand complex [Ru
been found to be in very good agreement with its small mol-
ecule analogue [Ru(dmbpy)2A(1a)](PF6)2 (see the Supporting
ACHTUNGTRENNU(NG dmbpy)2ACHTUNRTGE(NGNUN pCL-1b)]ACHTUNGTREN(NUGN PF6)2 have
A
N
ACHTUNGTRENNUNG
Information). Therefore, the covalent linking of the RuII
complexes to the polymer backbone results in a material
that now combines the photophysical and electrochemical
properties of the complex with the properties of the poly-
mer. In contrast with examples in which complexes are
blended into polymer matrices, aggregation of the com-
plexes is generally reduced. Additionally, the processing fea-
tures of the materials, for example, by spin coating or inkjet
printing, as well as the film-forming abilities should be
strongly enhanced.
Figure 8. Cyclic voltammogram of [RuCATHUNGTRENNN(UG dmbpy)3ÀnAHCTUNRTGE(GUNNN 1a)n]ACHTNGURTEN(NUNG PF6)2 (n=3:
c, n=2: g, n=1: a, n=0: c). For all measurements, approxi-
mately 1 mm of the respective complex in CH2Cl and 0.1 mm TBAPF6 at
100 mVsÀ1 was employed. Yield of the isolated product after flash
column chromatography (neutral Al2O3) and/or recrystallization (See the
Supporting Information for details). TBA=tetrabutylammonium.
Conclusions
In conclusion, we were able to achieve the synthesis of vari-
ous substituted (1H-1,2,3-triazole)-pyridines by a general
click chemistry approach. The mild protocol is compatible
with terminal functional groups that pave the way to the tar-
geted unsymmetrical, mono-functionalized ligands, which
can furthermore be easily introduced into polymers or at-
tached to surfaces. To generally prove this concept, the in-
corporation of such a mono-functionalized ligand into a po-
lymer was carried out through the ring-opening polymeri-
zation of e-caprolactone. A full series of homoleptic and
heteroleptic RuII complexes was derived from the bidentate
ligands. In this case, the chromatographic separation of the
fac and mer isomer of a homoleptic RuII complex was ach-
ieved in the case of bulky naphthalene substituents.
As seen for the photophysical properties, the electro-
chemical behavior of the complexes is also strongly influ-
enced by the number of triazole-containing ligands L
(Table 2). A single metal-based reversible oxidation step has
been observed in the cyclic voltammograms (CV) for all
RuII complexes (Figure 8). With an increasing number of
(1H-1,2,3-triazole)-pyridine ligands L, the energy band gap
Eg of the complexes increases significantly as the pmetal (t2g)
HOMO is slightly stabilized and the ligand-based p*
LUMO is significantly destabilized. As a result, no reduc-
tion peaks could be determined for the homoleptic com-
plexes [Ru(L)3]ACHTUNGTRENNUNG(PF6)2 (L=1 or 2) within the solvent
window.
The question, if (1H-1,2,3-triazol-4-yl)-pyridines can be
effectively used as alternative ligands to 2,2’-bipyridines in
RuII complexes, was answered by investigating the photo-
physical and electrochemical properties of the synthesized
complexes. A strong dependency on the number of coordi-
nated (1H-1,2,3-triazole)-pyridine ligands was revealed.
Overall, the synthesized ligands were found to stabilize the
HOMO of the derived complexes leading to a significant in-
crease of the energy-band gap. Together with the reversible
redox properties, the complexes mainly resemble their bi-
pyridine-based counterparts, but with distinctive differences.
The complexes containing the (1H-1,2,3-triazole)-pyridine
and bearing at least one bipyridine ligand exhibited a strong
orange emission at low temperatures. In contrast with con-
ventional RuII tris-bipyridine complexes, this photolumines-
cence is fully quenched at room temperature.
The assumption that the p* LUMO is mainly located on
the dmbpy ligand is supported by the fact that no significant
changes of the LUMO energies have been observed within
the series of complexes of the general type [Ru-
ACHTUNGTRENNUNG(dmbpy)2(L)]ACHTUNGTRENNUNG(PF6)2 (Table 2). On the other hand, the energy
of the pmetal (t2g) HOMO is significantly decreased (~0.1 eV)
and Eg is increased to the same extent when aromatic sub-
stituents are introduced (L=2a/b).
In the case of the fac- and mer-isomer of [RuACTHUNRGTENNG(U 2a)3]ACHTUNTGERN(NUGN PF6)2,
small differences for the oxidation potential (approximately
0.02 V, see the Supporting Information) but similar HOMO
levels have been obtained. However, compared with the ho-
moleptic complexes bearing N1-alkyl substituents (L=1a), a
remarkable decrease in the HOMO energy of 0.17 eV has
been obtained. This lets us conclude that, in accordance
with the [Ru
(dmbpy)2(L)]
E
The combination of functionalized (1H-1,2,3-triazol-4-yl)-
pyridines with ruthenium(II) ions opens new avenues for
the design of new supramolecular architectures. Their ap-
plicability as functional materials, for example, photovoltaic
devices, needs to be the focus of further investigation.
electrochemical properties can be influenced significantly by
aryl substituents in the N1 position (L=2). Overall, the CV
data are consistent with the previously discussed absorption/
emission behavior and clearly show that the properties of
160
www.chemasianj.org
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2009, 4, 154 – 163

Alternatives to 2,2’-Bipyridines in Ruthenium(II) Complexes
further purified by gel filtration (Al2O3, CH2Cl2 as the eluent), followed
by precipitation from CH2Cl2 into n-pentane. For full characterization of
1a–f and variational experimental details, see the Supporting Informa-
tion.
2: N1-aryl-substituted 1H-1,2,3-triazoles. Sodium azide (6 mmol) and an-
hydrous CuSO4 (62 mg, 0.4 mmol) were dissolved in absolute methanol
Experimental Section
General Methods
All reagents were purchased from commercial sources and used without
further purification unless specified. The solvents were received from
Biosolve and were dried and distilled according to standard procedures.
(15 mL) in
a 20-mL microwave vial. The aromatic boronic acid
The syntheses of the ruthenium(II) complexes [Ru
(dmbpy)2]Cl2 and [Ru(dmbpy)3]
ACHTUNGTRENNUNG
(3.84 mmol) was added to the brown solution and the mixture was stirred
for 17 h at room temperature. The conversion of the reaction was moni-
tored by TLC (SiO2, CHCl3 as eluent). Then CuSO4·5H2O (30 mg,
0.2 mmol), sodium ascorbate (384 mg, 1.95 mmol), 2-ethynylpyridine
(4.2 mmol), and water (5 mL) were added. The reaction mixture was
heated under microwave irradiation at 1008C for 1 h. Water (30 mL) was
added and the product was extracted with toluene (3ꢂ15 mL). After
drying (MgSO4) and evaporation of the solvent, the crude product was
purified by column chromatography (Al2O3, CH2Cl2/EtOAc (1:1 ratio) as
eluent). For full characterization of 2a–c and variational experimental
details, see the Supporting Information.
A
A
ACHTUNGTRENNUNG
literature.[20, 25] Chromatographic separations were performed on alumi-
num oxide (neutral, Macherey & Nagel, 0.063–0.200 mm). Preparative
layer chromatography (PLC) was performed on silica gel (SiO2 60 on
20ꢂ20 cm2 glass plates, 1-mm layer thickness, Merck).
Instrumentation
The 1D (1H and 13C) and 2D NMR (gCOSY) spectra were recorded in
deuterated solvents (Cambridge Isotope Laboratories Inc.) at 258C on a
Varian Mercury 400 MHz instrument and reported in ppm relative to
TMS as reference. Matrix-assisted laser desorption-ionization time-of-
flight mass spectrometry (MALDI-TOF MS) was performed on a Voyag-
er-DE PRO biospectrometry workstation (Applied Biosystems) time-of-
flight mass spectrometer reflector, with dithranol as a matrix. High-reso-
lution electrospray ionization mass spectrometry (HR-ESI MS) was car-
ried out on a Finnigan MAT 95XL machine. Elemental analyses were ob-
tained on a EuroVector EuroEA3000 elemental analyzer for CHNS-O.
Gel permeation chromatograms were obtained using a Waters GPC
equipped with an isocratic pump, a solvent degasser, a column oven, a
2996 photodiode array (PDA) detector, a 2414 refractive index detector,
a 717plus autosampler, and a styragel HT4 GPC column with a pre-
column installed (DMF, 5 mmol NH4PF6, 508C, flow rate of
0.5 mLminÀ1, poly(ethylene oxide) calibration). UV/Vis spectra were
measured on a Perkin–Elmer Lambda-19 spectrometer, room tempera-
Macroligand pCL-1b by ring-opening polymerization of e-caprolactone:
A degassed solution of 1b (30 mg, 0.095 mmol) in bulk e-caprolactone
(freshly distilled, 0.251 mL, 2.37 mmol, 25 equiv) in a sealed 5-mL micro-
wave vial was heated to 1208C. A catalytic amount of tin(II) 2-ethylhexa-
noate (2 drops) was added by using a syringe and stirring was continued
at 1208C for 2 h. The crude polymer was dissolved in CH2Cl2 (5 mL)
after cooling to room temperature. Precipitation into methanol yielded
1
the desired polymer pCL-1b as a white powder (276 mg, 89%). H NMR
(400 MHz, CD2Cl2): d=1.25–1.41 (m, polymer backbone), 1.55–1.66 (m,
polymer backbone), 2.25–2.33 (m; polymer backbone), 3.95–4.09 (m; po-
3
lymer backbone), 4.41 (t, 3JH,H =7.2 Hz, 2H; Ha), 7.23 (ddd, JH,H
=
7.5 Hz, JH,H =4.9 Hz, JH,H =1.2 Hz, 1H; H5), 7.78 (mc, 1H; H4), 8.13 (mc,
3
4
1H; H3), 8.15 (s, 1H; H5’), 8.56 ppm (ddd, 3JH,H =4.9 Hz, 4JH,H =1.8 Hz,
5JH,H =1.0 Hz, 1H; H6); MS (MALDI-TOF): M
Mn =3,600 gmolÀ1 (PDI=1.29).
maxACHTUNGTREN(NUNG m/z)=2,849. GPC:
ture photoluminescence spectra were recorded on
a Perkin–Elmer
LS50B luminescence spectrometer. Absolute quantum yields were evalu-
ated on a Hamamatsu Photonic Multi-Channel Analyzer C10027. For
these three techniques, a concentration of 10À6 m in degassed CH2Cl2
(1 cm cuvette) at 258C was used. Low-temperature emission measure-
ments were performed on an Edinburgh Instruments FS 920 Fluores-
cence Spectrometer. Therefore, solutions were prepared in non-degassed
n-butyronitrile. The experimental set-up allowed the measurement of PL
spectra at arbitrary temperatures between 77 K and room temperature.
Electrochemical experiments were carried out by using an Autolab
PGSTAT30 potentiostat at a scan rate of 100 mVs.À1 For this, a standard
three-electrode configuration was used with a platinum disk working
electrode, a platinum-rod auxiliary electrode, and an Ag/AgCl reference
electrode. Ferrocene was added at the end of each experiment as an in-
ternal standard. The potentials are quoted vs. the Fc/Fc+ couple. The sol-
vent was CH2Cl2, containing tetra-n-butylammonium hexafluorophos-
phate (nBu4NPF6, 0.1m).
[RuACHTUNTRGENN(UG 1a)2]Cl2: [RuACHUTNTGERN(NUGN cod)Cl2]n (140 mg, 0.5 mmol) and 1a (280 mg,
0.98 mmol) were suspended in dry and degassed DMF (20 mL). The sus-
pension was refluxed at 1508C for 48 h. After cooling to room tempera-
ture, the precipitate was filtered off and washed with acetone (2ꢂ10 mL)
and diethyl ether (2ꢂ10 mL). [RuACHTNUGTRENUNG(1a)2]Cl2 was obtained as a dark-green
powder (204 mg, 56%). 1H NMR and 13C NMR spectra: Owing to the
very low solubility in most organic solvents, no NMR spectra could be
obtained. MS (MALDI-TOF): m/z: 674.02 [MÀ2Cl]+, 708.96 [MÀCl]+,
898.95 [MÀ2Cl+dithranol]+; elemental analysis: calcd (%) for
C34H52Cl2N8Ru: C 54.83, H 7.04, N 15.04; found: C 54.93, H 7.31, N 15.02.
[RuACTHNURTGENNU(G 1a)3]ACHTUNGTREN(NUGN PF6)2: A solution of RuCl3·H2O (10 mg, 0.038 mmol) and 1a
(33 mg, 0.115 mmol) in degassed ethylene glycol (6 mL) was irradiated
under microwave conditions at 2208C for 30 min. The yellow solution
was treated with NH4PF6 (10-fold excess). The precipitate was isolated
by filtration, washed with water (5 mL) and diethyl ether (10 mL) yield-
ing the homoleptic complex [RuACTHNUTRGENNUG(1a)3]ACHTUNGTREN(NUNG PF6)2 as a yellow solid (97%,
46 mg, mixture of the facial and meridional isomer). A chromatographic
Safety Comment
separation of the isomers could not be achieved. UV/Vis (CH2Cl2): l(e)=
385 (15,590), 270 nm (61,200). H NMR (400 MHz, CD2Cl2): d=0.89 (mc,
Sodium azide is very toxic; personal protection precautions should be
taken. As low-molecular-weight organic azides are potential 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 num-
bers of nitrogen atoms (nN) by a ratio of three, that is, (nC+nO)/nN ꢀ3,
the compound is considered as an explosive hazard. Therefore, the com-
pounds were prepared prior to use and used immediately.
1
12H; Hj), 1.21–1.36 (m, 42H; Hc–i), 1.90 (mc, 6H; Hb), 4.39 (mc, 6H; Ha),
7.25 and 7.34 (2 mc, 3H; Hpyridine), 7.71 and 7.78 (2 mc, 3H; Hpyridine), 7.93
and 8.00 (2 mc, 3H; Hpyridine), 8.13 (mc, 4H; Hpyridine), 8.50, 8.56, 8.62 and
8.67 ppm (4 s, 3H; H5’); 13C NMR (CD2Cl2, 100 MHz): d=13.8, 22.6,
26.0, 26.1, 26.3, 28.8, 28.9, 29.3, 29.4, 29.5, 29.6, 29.7, 31.9, 52.4, 52.5, 52.6,
52.67, 52.9, 121.7, 122.0, 122.4, 122.7, 123.7, 124.1, 124.6, 124.9, 125.0,
125.8, 125.9, 137.6, 138.0, 138.1, 147.7, 148.1, 148.2, 151.3, 151.4, 151.5,
151.7, 151.8, 152.3 ppm; MS (MALDI-TOF MS): m/z=674.20
[MÀ1aÀ2PF6]+, 898.22 [MÀ1aÀ2PF6+matrix]+, 1105.32 [MÀPF6]+; ele-
mental analysis: calcd (%) for C51H78F12N6P2Ru: C 48.99, H 6.29,
N 13.44; found: C 49.29, H 6.44, N 13.26.
Synthesis
1: N1-alkyl-substituted 1H-1,2,3-triazoles. Sodium azide (1.2 equiv), 1-
bromoalkane (2 mmol; the resulting azides are potentially explosive in
the cases of (nC+nO)/nN ꢀ3) and 2-ethynylpyridine (1 equiv) were sus-
pended in EtOH/water (8 mL, 7:3 ratio) in a 20 mL microwave vial. Sub-
sequently, CuSO4 ꢂ5H2O (23 mg, 5 mol%) and sodium ascorbate (90 mg,
25 mol%) were added. The reaction mixture was heated under micro-
wave irradiation at 1258C for 20 min. After cooling to room temperature,
water (15 mL) was added to the brownish suspension. The precipitate
was filtered off and washed with water (3ꢂ5 mL). The crude product was
[RuACTHNURTGENNU(G 2a)3]ACHTUNGTREN(NUGN PF6)2: A solution of RuCl3·H2O (20 mg, 0.076 mmol) and 2a
(62 mg, 0.230 mmol) in degassed ethylene glycol (12 mL) was irradiated
under microwave conditions at 2208C for 15 min. The yellow solution
was treated with NH4PF6 (10-fold excess). After 1 h of stirring at room
temperature, the precipitate was isolated by filtration and washed with
Chem. Asian J. 2009, 4, 154 – 163
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
161

U. S. Schubert et al.
FULL PAPERS
water (5 mL) and diethyl ether (10 mL) to yield the homoleptic complex
150.8, 150.9, 151.0, 151.1, 156.3, 156.7, 156.8, 156.9, 157.1 ppm; MS
[Ru
G
N
(MALDI-TOF):
m/z=602.17
[MÀ2PF6Àdmbpy+H]+,
695.04
meridional isomer). Chromatographic separation of the isomers was per-
formed by PLC (SiO2, saturated NH4Cl in DMF/EtOH (4:1 ratio) as the
eluent). The pure isomers (fac: Rf =0.2, 45 mg, 56%; mer: Rf =0.5,
36 mg, 44%) were isolated by extraction with a solution of NH4PF6
(10 mol%) in acetone for 2 h, followed by precipitation in diethyl ether.
[MÀ2PF6Àtripy+matrix]+, 786.18 [MÀ2PF6]+, 931.12 [MÀPF6]+; ele-
mental analysis: calcd (%) for C42H52F12N8OP2Ru: C 46.89, H 4.87, N
10.41; found: C 47.09, H 5.17, N 10.06.
[RuACTHNUGTNER(NNUG dmpby)2ACHTNURTGEN(GNNU 2a)]ACHTNUGTRENNGUN(PF6)2: Yield: 79%; UV/Vis (CH2Cl2) l(e)=430
(10,610), 286 (60,230), 260 nm (19,420); 1H NMR (400 MHz, CD3CN):
d=2.44 (s, 3H; Hmethyl), 2.58 (s, 3H; Hmethyl), 2.60 (s, 3H; Hmethyl), 2.61 (s,
3H; Hmethyl), 7.12 (mc, 2H), 7.29–7.38 (m, 4H), 7.53 (mc, 1H), 7.58 (d,
3JH,H =5.8 Hz, 1H), 7.66–7.78 (m, 6H), 7.96 (d, 3JH,H =5.8 Hz, 1H), 8.05
fac-[RuACHTUNGTRENNUNG(2a)3]ACHTUNGTRENNUNG(PF6)2: UV/Vis (CH2Cl2) l(e)=385 (14,400), 272 (56,200);
3
295 nm (35,250); 1H NMR (400 MHz, CD2Cl2): d=6.07 (ddd, JH,H
=
8.3 Hz, 3JH,H =6.9 Hz, 4JH,H =1.2 Hz, 1H; H5), 7.13 (dd, 3JH,H =8.5 Hz,
4
4JH,H =0.7 Hz, 1H; H6), 7.34 (ddd, 3JH,H =8.1 Hz, 3JH,H =6.9 Hz, JH,H
=
3
(mc, 1H), 8.09 (d, JH,H =8.3 Hz, 1H), 8.20 (mc, 2H), 8.25 (s, 1H), 8.37 (s,
1.0 Hz, 1H; H4), 7.61 (mc, 3H; Hnaph), 7.96 (d, 3JH,H =8.3 Hz, 1H; H3),
8.14 (mc, 2H; Hnaph), 8.25 (mc, 2H; Hnaph), 8.75 ppm (s, 1H; H5’);
13C NMR (100 MHz, CD2Cl2): d=121.1, 123.0, 123.9, 124.9, 126.6, 126.7,
127.2, 128.2, 128.3, 128.5, 131.9, 132.3, 134.0, 138.6, 148.4, 151.3,
1H), 8.41 (s, 2H), 9.08 ppm (s, 1H, H5’); 13C NMR (100 MHz, CD3CN):
d=20.1, 20.2, 20.3, 20.4, 121.1, 122.8, 124.1, 124.3, 124.5, 124.8, 124.9,
125.0, 125.3, 126.1, 127.4, 127.5, 127.6, 127.9, 128.1, 128.2, 128.3, 128.4,
128.6, 131.7, 132.3, 134.1, 138.0, 148.1, 150.0, 150.2, 150.3, 150.4, 150.9,
151.1, 151.2, 151.6, 151.8, 156.5, 156.9, 156.9, 157.2 ppm; MS (MALDI-
TOF): m/z=695.17 [MÀ2aÀ2PF6+matrix]+, 742.22 [MÀ2PF6+Na]+,
887.19 [MÀPF6]+; elemental analysis: calcd (%) for C41H36F12N8P2Ru:
C 47.53, H 3.52, N 10.86; found: C 47.38, H 3.86, N 11.02.
152.0 ppm; MS (MALDI-TOF): m/z=435.86 [MÀLÀ2PF6+matrix]2+
,
645.91 [MÀLÀ2PF6+H]+, 870.88 [MÀLÀ2PF6+matrix]+, 1062.86
[MÀPF6]+; MS (HR-ESI) m/z calcd for C51H36P96RuF6N12 [MÀPF6]:
1057.1907; found: 1057.1911.
mer-[RuACHTUNGTRENNUNG(2a)3]ACHTUNGTRENNUNG(PF6)2: UV/Vis (CH2Cl2) l (e)=368 (16,190), 272 (59,270),
[RuACTHNUGTNER(NNUG dmpby)2ACHTNURTGEN(GNNU 2b)]ACHTNUGTRENNGUN(PF6)2: Yield: 90%; UV/Vis (CH2Cl2) l(e)=417
1
(10,370), 285 (80,440), 260 nm (30,100); 1H NMR (400 MHz, CD3CN):
d=2.54 (s, 3H; Hmethyl), 2.55 (s, 3H; Hmethyl), 2.57 (s, 3H; Hmethyl), 2.58 (s,
3H; Hmethyl), 3.85 (s, 3H; Hmethoxy), 7.09 (d, 3JH,H =8.5 Hz, 2H, Hb), 7.20
295 nm (38,800); H NMR (400 MHz, CD2Cl2): d=6.80 (mc, 1H), 7.21 (d,
3JH,H =9.5 Hz, 1H), 7.37 (mc, 2H), 7.47 (mc, 2H), 7.55–7.75 (m, 10H),
7.86 (d, 3JH,H =8.2 Hz, 2H), 7.92–8.02 (m, 4H), 8.05–8.21 (m, 10H), 8.36
(d, 3JH,H =8.1 Hz, 1H), 8.78 (s, 1H; H5’), 9.01 (s, 1H; H5’), 9.05 ppm (s,
1H; H5’); 13C NMR (100 MHz, CD2Cl2): d=120.8, 120.9, 122.4, 122.7,
123.6, 124.1, 124.3, 124.5, 124.9, 125.2, 125.8, 125.9, 126.4, 126.8, 127.0,
127.3, 127.4, 127.5, 127.6, 128.1, 128.2, 128.4, 128.6, 128.7, 128.8, 131.9,
132.0, 132.2, 132.3, 134.0, 134.2, 134.3, 138.1, 138.3, 138.6, 148.4, 148.8,
150.9, 151.2, 152.1, 152.4, 152.6 ppm; MS (MALDI-TOF): m/z=435.86
3
4
3
(dd, JH,H =5.8 Hz, JH,H =1.1 Hz, 1H; Hdmbpy), 7.29 (d, JH,H =5.8 Hz, 3H;
Hdmbpy), 7.33 (mc, 1H; H4), 7.61–7.67 (m, 5H; H3, Ha, Hdmbpy), 7.71 (d,
3JH,H =5.8 Hz, 1H; Hdmbpy), 7.83 (d, 3JH,H =5.8 Hz, 1H; Hdmbpy), 8.03 (dd,
3JH,H =7.8 Hz, 4JH,H =1.4 Hz, 1H; H5), 8.30 (d, 3JH,H =7.8 Hz, 1H; H6),
8.34 (s, 1H; Hdmbpy), 8.37 (s, 1H; Hdmbpy), 8.41 (s, 1H; Hdmbpy), 8.42 (s, 1H;
Hdmbpy) 9.51 ppm (s, 1H; H5’); 13C NMR (100 MHz, CD3CN): d=20.3,
55.5, 114.9, 122.4, 122.6, 123.9, 124.2, 124.6, 124.8, 124.9, 125.9, 127.4,
128.1, 128.3, 129.5, 137.9, 148.3, 149.9, 150.1, 150.2, 150.9, 151.0, 151.1,
151.2, 151.4, 151.6, 156.5, 156.9, 156.9, 157.2, 160.8 ppm; MS (MALDI-
TOF): m/z=469.91 [MÀ2PF6À2b]+, 537.89 [MÀ2PF6Àdmbpy]+, 694.89
[MÀ2PF6À2b+matrix]+, 721.93 [MÀ2PF6]+, 866.83 [MÀPF6]+; elemen-
tal analysis: calcd (%) for C38H36F12N8OP2Ru: C 45.11, H 3.59, N 11.08;
found C 44.85, H 3.84, N 10.72.
[MÀ2aÀ2PF6+matrix]2+
,
645.91
[MÀLÀ2PF6+H]+,
870.88
[MÀLÀ2PF6+matrix]+, 1062.86 [MÀPF6]+; MS (HR-ESI) m/z calcd for
C51H36P96RuF6N12 [MÀPF6]: 1057.1907; found: 1057.1911.
General procedure for [Ru
ACHUTNGTERN(NGU dmbpy)2(L)]AHCTUNGTREN(NUGN PF6)2: A suspension of [Ru-
ACHTUNGTRENNUNG
in degassed ethanol (8 mL) was heated at 1258C under microwave irradi-
ation for 1 h. The clear red solution was treated with a 10-fold excess of
NH4PF6 and stirred for 2 h until precipitation occurred. The precipitate
was filtered off and washed with ethanol (2ꢂ5 mL) and diethyl ether (2ꢂ
10 mL), followed by recrystallization from acetonitrile/diethyl ether (3:1),
[Ru
(dmpby)
N
U
A
suspension of [RuACHTUGNTERNNU(G 1a)2]Cl2 (30 mg,
0.04 mmol) and dmbpy (8 mg, 0.042 mmol) in degassed ethanol (6 mL)
was heated under microwave irradiation at 1258C for 4 h. The red solu-
tion was filtered through a pipette filled with a cotton pad. The clear fil-
trate was treated with NH4PF6 (10-fold excess) to give a precipitate,
which was purified by column chromatography (Al2O3, CH3CN as
eluent). Precipitation from the concentrated acetonitrile solution in di-
to yield the heteroleptic complex [Ru
ACHTUTGNRNENUG(dmbpy)2(L)]ACHUTNTGREN(NUGN PF6)2.
[Ru(dmpby)2A(1a)](PF6)2: Yield: 72%; UV/Vis (CH2Cl2) l(e)=451
A
E
ACHTUNGTRENNUNG
1
(12,530), 413 (11,900), 286 (71,500), 260 nm (27,750); H NMR (400 MHz,
CD2Cl2): d=0.89 (t, JH,H =6.9 Hz, 3H; Hj), 1.15–1.31 (m, 14H; Hc–i), 1.86
3
(mc, 2H; Hb), 2.56 and 2.59 (2 s, 12H; Hmethyl), 4.38 (t, JH,H =7.4 Hz, 2H,
3
ethyl ether afforded [RuACTHUNGTRENN(UNG dmbpy)ACHUTNRGTEG(NNUN 1a)2]ACHTNGURTEN(NUGN PF6)2 (mixture of isomers, 36 mg,
Ha), 7.15 (dd, 3JH,H =5.8 Hz, 4JH,H =0.8 Hz, 1H; Hdmbpy), 7.23–7.31 (m,
78%). UV/Vis (CH2Cl2) l(e)=393 (13,700), 361 (10,000) 286 (47,300),
273 (65,400), 240 nm (34,900); 1H NMR (400 MHz, CD2Cl2): d=0.89 (t,
3JH,H =6.9 Hz, 6H; Hj), 1.16–1.36 (m, 28H; Hc–i), 1.82–1.95 (m, 4H; Hb),
2.57–2.61 (m, 6H; Hmethyl), 4.40 (mc, 4H; Ha), 7.15–7.35 (m, 4H), 7.57–
7.73 (m, 4H), 7.87–7.99 (m, 2H), 8.04–8.23 (m, 4H), 8.59 (s, 1H), 8.62 (s,
1H), 8.67 (s, 1H), 8.70 ppm (s, 1H); 13C NMR (100 MHz, CD2Cl2): d=
13.8, 21.1, 22.6, 26.2, 28.7, 29.2, 29.3, 29.4, 29.5, 29.6, 31.8, 52.6, 122.1,
122.3, 122.4, 122.7, 122.8, 123.6, 123.89, 124.3, 124.5, 124.7, 124.9, 125.1,
125.2, 125.8, 125.9, 127.5, 127.7, 128.4, 137.6, 138.0, 147.4, 147.7, 147.8,
149.7, 149.8, 150.3, 150.4, 150.8, 151.0, 151.1, 151.2, 151.4, 151.5, 151.6,
151.7, 156.7, 157.1, 157.2 ppm; MS (MALDI-TOF): m/z=572.21
[MÀ2PF6À1a+H]+, 797.22 [MÀ2PF6À1a+matrix]+, 1003.32 [MÀPF6]+;
elemental analysis: calcd (%) for C46H64F12N10P2Ru: C 48.12, H 5.62,
N 12.02; found: C 48.29, H 5.42, N 11.97.
4H; H4, Hdmbpy), 7.52 (d, 3JH,H =5.8 Hz, 1H; Hdmbpy), 7.56 (d, JH,H
=
3
5.5 Hz, 1H; H3), 7.56–7.62 (m, 3H; Hdmbpy), 7.95 (mc, 1H; H5), 8.13 (mc,
1H; H4), 8.14 (s, 1H; Hdmbpy), 8.18 (s, 1H; Hdmbpy), 8.23 (s, 2H; Hdmbpy),
8.65 ppm (s, 1H; H5’); 13C NMR (100 MHz, CD2Cl2): d=13.8, 21.0, 21.1,
22.6, 26.2, 28.7, 29.2, 29.3, 29.4, 29.5, 31.8, 52.5, 122.7, 124.0, 124.3, 124.6,
124.7, 125.1, 125.9, 127.6, 128.4, 128.4, 128.5, 128.7, 137.9, 147.4, 149.7,
150.3, 150.3, 150.4, 150.6, 150.8, 150.9, 151.1, 156.2, 156.3, 156.7, 156.8,
156.9 ppm; MS (HR-ESI) m/z calcd for C41H50P96RuF6N8 [MÀPF6]:
895.2876; found: 895.2833; elemental analysis: calcd (%) for
C41H50F12N8P2Ru: C 47.08, H 4.78, N 10.71; found: C 47.23, H 4.78,
N 10.69.
[RuACHTUNGTRENNUNG(dmpby)2ACHTUNGTRENNUNG(1b)]ACHTUNGTRENNUNG(PF6)2: Yield: 90%; UV/Vis (CH2Cl2) l(e)=418
(10,200), 380 (7,500), 286 (70,600), 261 (32,400) 249 nm (28,720);
1H NMR (400 MHz, CD2Cl2): d=1.18–1.30 (m, 12H; Hc–h), 1.52 (m, 4H;
[RuCATHNUGTRENU(NGN dmbpy)2ACHTUNGTERN(GUN pCL-1b)]AHCTNUEGRTG(NNNU PF6)2: A suspension of [RuACHTNGURTEN(NUNG dmbpy)2]Cl2 (26 mg,
Hb, Hi), 1.86 (mc, 2H; Hb), 2.56, 2.58, 2.59 (3 s, 12H; Hmethyl), 3.59 (t,
0.046 mmol) and pCL-1b (80 mg, 0.02 mmol) in degassed ethanol (6 mL)
was heated under microwave irradiation at 1258C for 8 h. The reaction
mixture was filtered through a pad of glass wool. An excess of NH4PF6
(10 equiv) was then added and after 2 h the precipitation was completed
by adding water. The red precipitate was filtered off and dissolved in ace-
tone. The solution was concentrated and precipitated in cold methanol to
3
3JH,H =6.6 Hz, 2H; Hj), 4.38 (t, 3JH,H =7.4 Hz, 2H; Ha), 7.15 (dd, JH,H
=
5.8 Hz, JH,H =0.8 Hz, 1H; Hdmbpy), 7.23–7.31 (m, 4H; H4, Hdmpby), 7.52 (d,
3JH,H =5.8 Hz, 1H; Hdmbpy), 7.56–7.62 (m, 4H; H3, Hdmbpy), 7.94 (dd,
3JH,H =7.8 Hz, 4JH,H =1.4 Hz 1H; H5), 8.13 (d, 3JH,H =7.8 Hz, 1H; H4),
8.16 & 8.20 & 8.24 & 8.26 (4 brs, 4H; Hdmbpy), 8.67 ppm (s, 1H; H5’);
13C NMR (100 MHz, CD2Cl2): d=18.2, 20.9, 21.0, 21.1, 25.7, 26.1, 28.7,
29.2, 29.3, 29.4, 29.5, 32.8, 52.5, 62.7, 122.7, 124.0, 124.3, 124.7, 124.8,
125.1, 125.9, 127.6, 128.4, 128.5, 128.6, 137.9, 149.8, 150.3, 150.4, 150.5,
4
(PF6)2 (45 mg, 48%). 1H NMR
yield pure [RuCATHGNUTREN(NNUG dmbpy)2AHCTUNRTGENN(GUN pCL-1b)]ACHTGUNTRENNUGN
(400 MHz, [D6]acetone): d=1.33–1.42 (m; polymer backbone), 1.55–1.63
(m; polymer backbone), 2.26–2.35 (m; polymer backbone), 2.57 (mc,
162
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ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2009, 4, 154 – 163

Alternatives to 2,2’-Bipyridines in Ruthenium(II) Complexes
12H; Hmethyl), 4.05 (mc; polymer backbone), 4.52 (t, 3JH,H =7.1 Hz, 2H;
Ha), 7.33–7.45 (m, 5H; Hdmbpy, H4), 7.82 (d, 3JH,H =5.8 Hz, 1H; Hdmbpy),
7.87–7.94 (m, 4H; Hdmbpy, H3), 8.11 (dt, 3JH,H =7.9 Hz, 4JH,H =1.4 Hz 1H;
H5), 8.33 (d, 3JH,H =7.9 Hz, 1H; H4), 8.60 (s, 1H; Hdmbpy), 8.64 (s, 1H;
Hdmbpy), 8.67 (s, 1H; Hdmbpy), 8.68 (s, 1H; Hdmbpy), 9.19 ppm (s, 1H; H5’);
Am. Chem. Soc. 2005, 127, 15521–15527; g) J. Li, M. Zheng, W.
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MS (MALDI-TOF): M
maxACHTUNGTRENN(UNG m/z)=3014.
Acknowledgements
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The authors acknowledge financial support from the Nederlandse Organ-
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Received: August 1, 2008
Published online: November 17, 2008
Chem. Asian J. 2009, 4, 154 – 163
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www.chemasianj.org
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