New 1,2,3-triazole ligands through click reactions and their palladium and platinum complexes

Article abstract of DOI:10.1039/b910660j

The new ligands, 1-(4-isopropyl phenyl)-4-(2-pyridyl)-1,2,3-triazole, 1 and 1-(mesityl)-4-(2-pyridyl)-1,2,3-triazole, 2 were prepared by the reactions of the respective azides with 2-ethynylpyridine following the "click method". These ligands together with the reported ligands 1-(phenyl)-4-(2-pyridyl)-1,2,3-triazole, 3 and 1-(benzyl)-4-(2-pyridyl)-1,2,3- triazole, 4 were reacted with palladium and platinum precursors to give mononuclear cis-dichloropalladium and platinum complexes containing the triazole ligands. Structural characterisation of the free ligand 3 shows that the central N-N bond in the triazole ring has double bond character and hence is best described as an "azo-like" N-N double bond. The pyridine ring in 3 has an almost "anti" conformation with respect to the central triazole ring. The metal centers bind to the ligands through the pyridine N and a triazole N atom. The metal-N(triazole) distances are shorter than the metal-N(pyridine) distances. Cyclic voltammograms of the ligands show reduction processes that appear at extreme negative potentials. Coordination of metal centers induces huge anodic shifts of the reduction potentials due to σ-polarisation by the metal centers. UV/Vis spectra of the ligands and complexes are also discussed. The properties of such chelating triazole ligands towards palladium and platinum centers is being compared and contrasted to the widely used 2,2′-bipyridine ligand.

Full text of DOI:10.1039/b910660j

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PAPER
www.rsc.org/dalton | Dalton Transactions
New 1,2,3-triazole ligands through click reactions and their palladium
and platinum complexes†
David Schweinfurth,a Roberto Pattacini,b Sabine Strobela and Biprajit Sarkar*a
Received 1st June 2009, Accepted 18th August 2009
First published as an Advance Article on the web 11th September 2009
DOI: 10.1039/b910660j
The new ligands, 1-(4-isopropyl phenyl)-4-(2-pyridyl)-1,2,3-triazole, 1 and 1-(mesityl)-4-(2-pyridyl)-
1,2,3-triazole, 2 were prepared by the reactions of the respective azides with 2-ethynylpyridine following
the “click method”. These ligands together with the reported ligands 1-(phenyl)-4-(2-pyridyl)-
1,2,3-triazole, 3 and 1-(benzyl)-4-(2-pyridyl)-1,2,3-triazole, 4 were reacted with palladium and platinum
precursors to give mononuclear cis-dichloropalladium and platinum complexes containing the triazole
ligands. Structural characterisation of the free ligand 3 shows that the central N–N bond in the triazole
ring has double bond character and hence is best described as an “azo-like” N–N double bond. The
pyridine ring in 3 has an almost “anti” conformation with respect to the central triazole ring. The metal
centers bind to the ligands through the pyridine N and a triazole N atom. The metal–N(triazole)
distances are shorter than the metal–N(pyridine) distances. Cyclic voltammograms of the ligands show
reduction processes that appear at extreme negative potentials. Coordination of metal centers induces
huge anodic shifts of the reduction potentials due to s-polarisation by the metal centers. UV/Vis
spectra of the ligands and complexes are also discussed. The properties of such chelating triazole
ligands towards palladium and platinum centers is being compared and contrasted to the widely
used 2,2¢-bipyridine ligand.
substituents on the triazole ring are aliphatic.19,20 Complexes of
cis-dichloroplatinum with nitrogen co-ligands are interesting for
Introduction
a variety of reasons such as tumor therapy,21 luminescence in
solid state and solution22 and as catalysts and pre-catalysts for
C–H bond activation.23,24 In recent years cis-dichloropalladium
complexes have found extensive use as catalysts and pre-catalysts
in various organic transformations.25 2,2¢-Bipyridine is the proto-
typical nitrogen ligand that has been extensively used for many of
the research fields mentioned above. The click method provides
an extremely convenient route for the synthesis of (2-pyridyl)-
substituted 1,2,3-triazoles which could potentially be used as
“2,2¢-bipyridine analogues”.15 In comparison to 2,2¢-bipyridine
it is relatively easy to vary the steric and electronic properties of
such triazole ligands. In addition platinum complexes of “non-
click” 1,2,3-triazoles have been studied for a variety of purposes.26
With this background in mind, we prepared two new substi-
tuted triazoles 1-(4-isopropyl phenyl)-4-(2-pyridyl)-1,2,3-triazole,
1 and 1-(mesityl)-4-(2-pyridyl)-1,2,3-triazole, 2 (Scheme 1 and 2).
These ligands together with the reported ligands 1-(phenyl)-4-
(2-pyridyl)-1,2,3-triazole, 315 and 1-(benzyl)-4-(2-pyridyl)-1,2,3-
triazole, 418 (Scheme 1) were reacted with Pd(COD)Cl2 (COD =
1,5-cyclooctadiene) and Pt(dmso)2Cl2 respectively to give the
complexes 1a–4a and 1b–4b (Scheme 3). Herein we present
the detailed synthesis and characterisation of the ligands and
complexes together with the crystal structures of 3, 1a and 3b. The
electrochemical as well as the UV/Vis spectroscopic results of all
the compounds are also reported and discussed. These studies are
presented to compare the properties of the metal complexes of
such triazole ligands with their known 2,2¢-bipyridine analogues.
In addition, electrochemical and spectroscopic studies on these
complexes also help in probing the effects of substituents and of
metal complexation on various properties of such ligands.
The 1,3-dipolar cycloaddition reaction between azides and ter-
minal alkynes was first systematically studied by Huisgen sev-
eral decades ago.1,2 The copper catalysed form of this reaction
has been renamed as the “click reaction”.3,4 These reactions
demonstrate high regioselectivity to give the 1,4-linked triazoles
in excellent yields. Since the discovery of the click reaction, this
method has found use in diverse areas of chemistry such as
dendrimers and polymers,5-7 drug discovery,8 material science9
and bioconjugation,10 to name but a few. The same reaction has
also been used to generate metal responsive fluorophores.11 Even
though substituted 1,2,3-triazoles should be good candidates for
acting as ligands in coordination chemistry, their use as ligands has
been much less explored in comparison to their 1,2,4-counterparts.
There have been some recent reports on the use of such ligands as
“analogues of terpyridine and bipyridine”.12-15 Copper complexes
have been reported with potentially tetradentate 1,2,3-triazole
ligands where the question of the mechanism of the click reaction
was also addressed.16 Additionally, rhenium complexes of such
ligands have been studied in the therapeutic and photophysical
context.17,18 To the best of our knowledge the only report of
platinum complexes with such 1,2,3-triazole ligands are the ones
where such ligands act in a monodentate fashion or the donor
aInstitut fu¨r Anorganische Chemie, Universita¨t Stuttgart, Pfaffenwaldring
55, D-70550 Stuttgart, Germany. E-mail: sarkar@iac.uni-stuttgart.de
bLaboratoire de Chemie de Coordination, UMR CNRS 7513, Universite´ de
Strasbourg, 4 rue Blaise Pascal, F-67070 Strasbourg Ce´dex, France
† Electronic supplementary information (ESI) available: 1H NMR and 13
C
NMR spectra of 2; UV/vis spectra of 1a–4a. CCDC reference numbers
733411–733413. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/b910660j
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©

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regioselective towards the 4-(2-pyridyl) isomer as has previously
been observed with such click reactions.14,15,18 The regioselectivity
was also unambiguously determined through the crystal structure
of ligand 3 (vide infra), the synthesis of which was previously
reported.15 The ligands were characterised by 1H- and 13C NMR
spectroscopy, mass spectroscopy and by elemental analysis. In the
1H NMR, the C–H proton of the triazole ring is characteristic
and appears relatively downfield as a singlet (see experimental)
for all the ligands. Thus this method provides a facile route to
the synthesis of a variety of pyridyl substituted triazole ligands
with the substituents on the triazole ring being limited only by the
availability of the corresponding azide compound.
Complexes 1a–4a were synthesised by the reactions of
[Pd(COD)Cl2] with the respective ligands in CH2Cl2 at room tem-
perature. The yields were almost quantitative. For the complexes
1b–4b the precursor [Pt(dmso)2Cl2] was used and the reactions
were carried out under reflux in nitromethane (Scheme 3). Much
higher reaction times and temperature were necessary for the
synthesis of the platinum complexes as compared to the palladium
complexes. Although the triazole ligands can in principle bind to
a metal center through either the N2 or N3 atoms of the triazole
ring, substitution of a 2-pyridyl group at the 4-position of the
triazole ring results in preferential binding to the N3 atom with
the formation of a five membered chelate ring. The complexes were
Scheme 1 Triazole ligands used in this work.
1
characterised by H NMR spectroscopy and elemental analyses.
1
In the H NMR spectra of the complexes 1b–4b, 195Pt satellites
were observed for the 5-triazoleH and 6-pyridylH protons (see
experimental). This unambiguously proves the binding of the
platinum centers to the ligands.
Scheme 2 Synthesis of triazole ligands.
The molecular structure of ligand 3 was determined by single
crystals X-ray diffraction (Fig. 1). Crystallographic data are
presented in Table 1 and selected bond lengths are reported in
Table 2.
Fig. 1 ORTEP of the molecular structure of 3. Ellipsoids include 30% of
electron density.
Scheme 3 Synthesis of metal complexes.
In the structure of 3, the pyridine ring has an almost “anti”
conformation with respect to the triazole ring (Fig. 1). The angle
between the least square planes of the triazole and pyridine rings
is 17.8(1)◦. This value is comparable to what has been previously
observed for other such 1,2,3-triazole ligands.18 The twisting of the
phenyl ring with respect to the triazole ring is about 27.8(1)◦. As
has been observed previously,18 the N2–N3 distance of the 1,2,3-
Results and discussion
Synthesis and structures
Ligands 1 and 2 were prepared by the Cu(I) catalysed 1,3-
dipolar cycloaddition (“click method”) from the reactions of
the respective azide derivatives with 2-ethynylpyridine. Thus the
reactions of 4-isopropyl-phenylazide or mesitylazide, respectively,
with2-ethynylpyridine in the presence of CuSO4, sodium ascorbate
and TBTA (tris[(1-benzyl-1H-1,2,3-triazole-4-yl)methyl]amine) in
a mixture of CH2Cl2–H2O–t-BuOH at room temperature gave 1
and 2 in excellent yields (Scheme 2). These reactions are highly
˚
triazole at 1.309(2) A is shorter than the N2–C6 and N3–N4 bonds
˚
(1.366(1) and 1.356(1) A respectively). For the corresponding
1,2,4-triazoles, the N2–N3 bonds are longer than those of the
adjacent two bonds. This suggests that the 1,2,3-triazoles have an
azo character while 1,2,4-triazoles have an azine character as has
been observed by Obata et al. for ligand 4 (Scheme 4).18
9292 | Dalton Trans., 2009, 9291–9297
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Table 1 Crystallographic details
Table 3 Selected bond angles (◦)
3
1a
3b
1a
3b
Chemical formula C13H10N4
C16H16Cl2N4Pd C13H10Cl2N4Pt
441.63 488.24
Orthorhombic Monoclinic
N1–M–N2
N1–M–Cl2
N2–M–Cl1
Cl1–M–Cl2
80.6(2)
94.4(1)
94.0(1)
91.01(5)
52.3(2)
80.0(3)
94.8(2)
94.7(2)
90.8(1)
32.2(3)
Mr
222.25
Cell setting
Space group
Temperature/K
Monoclinic
P21/n
100(2)
5.7757(2)
19.3231(6)
9.7917(2)
99.295(2)
1078.45(6)
4
Pbca
173(2)
P21/c
173(2)
a
w
˚
a/A
6.8228(2)
18.1883(6)
27.2193(9)
90.00
3377.78(19)
8
7.5513(3)
19.237(1)
9.6692(7)
102.301(4)
1372.34(13)
4
a Dihedral angle between the triazole ring and the free substituent (angle
between the mean planes defined by the atoms of (a) the phenyl and
(b) the triazole ring).
˚
b/A
˚
c/A
b/◦
3
˚
V/A
Z
Dx/Mg m-3
1.369
Mo Ka
0.087
1.737
Mo Ka
1.418
2.363
Mo Ka
10.607
Radiation type
m/mm-1
Crystal size/mm
0.3 ¥ 0.1 ¥ 0.05 0.1 ¥ 0.02 ¥ 0.02 0.14 ¥ 0.08 ¥ 0.08
7108, 3868, 2522 4587, 2773, 2104
Meas., indep. and 5135, 2660,
obsvd refl.
R[F2 > 2s(F2)]
wR(F2)
2095
0.038
0.093
1.02
0.043
0.127
1.07
0.035
0.098
1.08
S
No. of parameters 195
210
181
Rint
0.023
28.3
0.27, -0.21
0.057
27.5
0.67, -1.31
0.039
26.4
1.43, -1.47
◦
qmax
/
-3
˚
Drmax, Drmin/e A
Fig. 2 ORTEP of the molecular structure of 1a. Ellipsoids include 30%
of electron density.
˚
Table 2 Selected bond lengths in A
3
1a
3b
N2–N3
N3–N4
N4–C7
N2–C6
C6–C7
C5–C6
M–N1
M–N2
M–Cl1
M–Cl2
1.309(1)
1.356(1)
1.354(1)
1.366(1)
1.373(2)
1.470(2)
1.312(6)
1.33(1)
1.349(5)
1.343(6)
1.364(6)
1.359(7)
1.464(7)
2.055(4)
2.007(4)
2.264(1)
2.285(1)
1.344(9)
1.36(1)
1.35(1)
1.36(1)
1.48(1)
2.044(7)
1.987(7)
2.283(2)
2.291(2)
Fig. 3 ORTEP of the molecular structure of 3b. Ellipsoids include 30%
of electron density.
structures, the slightly distorted square planar coordination is
completed by two chlorides. The chelating N1–M–N2 bite angles
(80.6(2) and 80.0(3)◦ respectively for 1a and 3b) are slightly shorter
in both complexes compared to the other angles around the metal
centers. The M–N(triazole) distances are shorter than the M–
N(pyridine) distances. This is due to the strong electron-donating
properties of the 1,2,3-triazole ring in comparison to the pyridine
ring. Similar trends are known for metal complexes of other azole
ligands containing a 2-pyridyl substituent.18,28 Consistently with
the enhanced trans influence of N2 with respect to N1, the M–Cl2
distances are slightly longer than the M–Cl1 distances. The N2–N3
bond distance inside the 1,2,3-triazole ring is slightly longer in the
metal complexes (particularly 3b) compared to the free ligand. This
is possibly due to p back donation from the metal centers into the
triazole ring. Such elongation of the N–N double bond has been
previously observed for metal complexes containing substituted
“azo” ligands.29 While the pyridyl–MCl2–triazole parts in 1a and
3b are almost co-planar, the angle between the phenyls mean
Scheme 4 Differences in bonding pattern in isomeric triazole compounds.
For bond lengths of the azine-like structure see Cingi et al.27
The molecular structures of complexes 1a and 3b were also
determined (Fig. 2 and 3). Crystal data and details of the structure
determination are listed in Table 1. Selected bond lengths and
angles are given in Table 2 and 3. The coordination mode of
the metal centers to the substituted 1,2,3-triazole ligands is very
similar to that of the 2,2¢-bipyridine derivative. The platinum and
palladium centers bind to the 1,2,3-triazole ligands through the
pyridine-N atom and the N2 atom of the triazole ring. In both
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Table 4 Electrochemical and UV/vis spectroscopic data
coordination induced anodic shifts compared to the free ligands
(Table 4). This is because of the excellent s-acceptor capacity of
the [PdCl2] fragment. The platinum complexes 1b–4b show an
irreversible reduction process at around -2.1 V in CH2Cl2/0.1 M
Bu4NPF6 vs. ferrocene/ferrocenium (Fig 5 and Table 4). Just like
for the palladium complexes the reversibility did not improve upon
changing the temperature or scan rates. The reduction potentials
for the platinum complexes are also anodically shifted compared
to those of the free ligands. However, the anodic shift in this case is
much smaller than that of the palladium complexes. This has to do
with the much better s-acceptor capacity of the [PdCl2] fragment
compared to the [PtCl2] fragment in such complexes. The influence
of the substituents on the triazole ring on the reduction potentials
of both the palladium as well as platinum complexes is negligible.
a
b
Compound
Epc
l
1
-2.80c
-2.83c
-2.86c
-2.78c
-1.25
-1.23
-1.17
-1.28
-2.11
-2.16
-2.13
-2.15
-1.06
-0.54
288
281
287
281
273, 379
275, 381
269, 380
280, 373
266, 337
266, 337
264, 335
261, 335
312, 324, 389
395, 516
2
3
4
1a
2a
3a
4a
1b
2b
3b
4b
d
Pt(bpy)Cl2
Pt(abpy)Cl2
e
a Cathodic peak potential in V for irreversible reduction in CH2Cl2/0.1
M Bu4NPF6. The ferrocene/ferrocenium couple was used as internal
standard. b Wavelength in nm. Measurements in CH2Cl2. c Measurements
in DMF. d Half wave potential for reversible reduction. Measurements in
DMF. Ref. 31. e Half wave potential for reversible reduction at -50 ◦C. Ref.
27.
planes and the triazole ones are 52.3(2) and 32.2(3)◦, respectively,
for 1a and 3b. The 4-isopropylphenyl or the phenyl substituents in
1a and 3b twist apparently in order to minimise the steric repulsion
between the C–H bonds of the C7 and C9 atoms.
Fig. 5 Cyclic voltammogram of 4b in CH2Cl2/0.1 M Bu4PF6 at 295 K.
On comparing the reduction potentials of complexes 1b–4b with
Cyclic voltammetry
33
29
Cyclic voltammetry was employed in order to probe the redox
properties of the ligands and the metal complexes. The lig-
ands had to be measured in DMF because of their extremely
negative reduction potentials. For instance ligand 3 shows an
irreversible reduction at -2.86 V in DMF/0.1 M Bu4NPF6 vs.
ferrocene/ferrocenium (Table 4). The effect of the substituents on
the phenyl rings of the triazole ligands on the redox potentials
is negligible and all the ligands 1–4 show very similar reduction
potentials. Such high reduction potentials for 1,2,3-triazole ligands
have been observed previously.12
those of Pt(bpy)Cl2 and Pt(abpy)Cl2 (bpy = 2,2¢-bipyridine,
abpy = 2,2¢-azobispyridine, Table 4) one sees that the reduction
potentials for the present triazole containing complexes are more
negative than those of Pt(bpy)Cl2 and Pt(abpy)Cl2 with the
complex Pt(abpy)Cl2 being the easiest to reduce (least negative
reduction potential). These results point to the fact that the p*
LUMO for complexes 1b–4b are energetically higher than the
LUMOs of Pt(bpy)Cl2 and Pt(abpy)Cl2.
UV/Vis spectroscopy
The palladium complexes 1a–4a show an irreversible reduc-
tion process at around -1.2 V in CH2Cl2/0.1 M Bu4NPF6 vs.
ferrocene/ferrocenium (Fig 4 and Table 4). The reversibility of
this process did not improve on lowering the temperature or
varying the scan rates. Metal–halide bonds are known to be labile
on reduction30 and such reduction induced bond activation can
sometimes be useful for certain kinds of catalytic activation.31,32
The reduction potential for complexes 1a–4a show huge metal-
Ligands 1–4 show a p–p* transition between 281–288 nm (Fig. S3†
and Table 4). The strongly shifted reduction potentials evidenced
for the metal complexes would point to a relatively low lying p*
orbital. Despite this fact, the absorption bands for the complexes
appear at quite high energies. This is probably due to the strong
stabilisation of the predominantly [MCl2] centered HOMOs in
these complexes. Such effects have been observed previously for the
corresponding metal complexes with the bpy and abpy ligands.29,33
All the complexes show two main features in their absorption
spectrum (Fig. 6 and S4† and Table 4). The long wavelength band
(e.g. 379 nm for 1a) is tentatively assigned to a mixture of metal-
to-ligand charge transfer (MLCT) with some contribution from
halide-to-ligand (XLCT) charge transfer. The next highest energy
transition (e.g. 273 nm for 1a) is most likely a p → p* transition
centered on the triazole ligand. The transitions for the palladium
complexes 1a–4a are shifted to lower energies compared to those
of the corresponding platinum complexes 1b–4b (Fig. 6 and
Table 4). This is in keeping with the lower lying LUMO for the
palladium complexes as compared to the platinum complexes.
The long wavelength bands for the Pt(bpy)Cl2 and Pt(abpy)Cl2
Fig. 4 Cyclic voltammogram of 4a in CH2Cl2/0.1 M Bu4PF6 at 295 K.
9294 | Dalton Trans., 2009, 9291–9297
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and the solution was stirred for 2 d at room temperature. The
reaction mixture was poured into water (50 mL) and was extracted
with CH2Cl2 (3 ¥ 20 mL). The combined organic layers were
washed with water (20 mL), dried over Na2SO4 and the solvent
was evaporated. The compound was dried in vacuo to give the
desired product as a yellow oil. Yield: 500 mg (95%). Found C,
72.97; H, 6.37; N, 20.45% C16H16N4 requires C, 72.70; H, 6.10; N,
21.20%; 1H NMR (250 MHz, CDCl3): d/ppm 1.27 (d, 3J = 6.9 Hz,
6H, –CH3, isopropyl), 2.97 (sept., 1H, –CH, isopropyl), 7.23 (t,
3J = 6.1 Hz, 1H), 7.37 (d, 3J = 8.5 Hz, 2H), 7.70 (d, 3J = 8.5 Hz,
2H), 7.78 (t, 3J = 7.8 Hz, 1H), 8.23 (d, 3J = 7.9 Hz, 1H), 8.55 (s,
Fig. 6 UV/Vis spectra of 1b–4b in CH2Cl2.
1
1H, 5-triazoleH), 8.59 (d, 3J = 4.4 Hz, 1H); 13C{ H} NMR (62.5
complexes appear at lower energies compared to the present
complexes with triazole ligands.29,33 This can be rationalised by
the lower energy p* LUMO for the Pt(bpy)Cl2 and Pt(abpy)Cl2
complexes compared to the complexes 1b–4b.
MHz, CDCl3): d/ppm 23.8, 33.8, 119.8, 120.3, 120.4, 122.9, 127.7,
134.9, 136.8, 148.7, 149.4, 149.8, 150.1; HRMS (ESI): Calcd for
C16H15N4Na ([M + Na]+): 287.1267; Found 287.1267.
2. Ligand 2 was synthesised by using a procedure identical
to 1 using mesitylazide instead of 4-isopropyl-phenylazide. Yield:
500 mg (95%). Found C, 71.08; H, 6.00; N, 20.87% C16H16N4
requires C, 72.70; H, 6.10; N, 21.20%; 1H NMR (250 MHz,
CDCl3): d/ppm 2.02 (s, 6H, o-CH3 groups, mesityl), 2.37 (s, 3H,
p-CH3 group, mesityl), 7.01 (s, 2H, phenylH, mesityl), 7.25 (t, 3J =
6.0 Hz, 1H), 7.82 (t, 3J = 7.8 Hz, 1H), 8.20 (s, 1H, 5-triazoleH),
Conclusions
Using theincreasingly popular “click method”we have synthesised
two new 1,2,3-triazole containing ligands. Reactions of these
and other previously reported ligands with the appropriate metal
precursors gave the palladium complexes 1a–4a and the platinum
complexes 1b–4b. Structural characterisation of some of the
complexes show that the bond between the metal centers and the
triazole-N is shorter compared to that between the metal centers
and the pyridine-N. The reduction processes for the free ligands as
well as the metal complexes are irreversible. However, large metal
coordination induced anodic shifts were observed for the reduction
of the metal complexes as compared to those of the free ligands.
The present studies show the utility of such substituted 1,2,3-
triazole compounds, obtained through the “click method”, as
excellent ligands in coordination chemistry. Future efforts will be
dedicated to tuning the properties of such ligands and their metal
complexes by varying the electronic properties of such ligands.
3
3
1
8.28 (d, J = 7.9 Hz, 1H), 8.61 (d, J = 4.0 Hz, 1H); 13C{ H}
NMR (62.5 MHz, CDCl3): d/ppm 17.3, 21.1, 120.4, 122.9, 124.0,
129.1, 133.5, 135.0, 136.9, 140.1, 148.2, 149.4, 150.3; HRMS (ESI):
Calcd for C16H15N4Na ([M + Na]+): 287.1267; Found 287.1274.
Despite repeated attempts at purification the value of carbon in
elemental analyses did not improve. The purity of this substance
1
was ascertained by H and 13C NMR spectroscopy (see Fig. S1
and S2†).
1a. Under an argon atmosphere 1 (26.4 mg, 0.10 mmol) and
Pd(COD)Cl2 (28.4 mg, 0.10 mmol) were dissolved in CH2Cl2
(10 mL). The mixture was stirred at room temperature for 1 h and
the formed precipitate was collected by filtration. After washing
with n-hexane (10 mL) the compound was dried in vacuo to give
the desired product. Yield: 40 mg (90%). Found C, 43.32; H, 3.95;
N, 12.52% C16H16N4Cl2Pd requires C, 43.51; H, 3.65; N, 12.69%;
Experimental
General
3
1H NMR (250 MHz, CDCl3): d/ppm 1.25 (d, J = 6.8 Hz, 6H,
All solvents were dried and distilled using common techniques
unless otherwise mentioned. 1H and 13C NMR spectra were
recorded at 250.13 and 62.90 MHz respectively on a Brucker
AC250 instrument. UV/Vis absorption spectra were recorded on
a J&M JIDAS spectrometer. Cyclic voltammetry was carried out
in 0.1 M Bu4NPF6 solution using a three-electrode configuration
(glassy carbon working electrode, Pt counter electrode, Ag wire
as pseudo reference) and a PAR 273 potentiostat and function
generator. The ferrocene/ferrocenium (Fc/Fc+) couple served as
an internal reference. Elemental analysis was performed on a
Perkin Elmer Analyser 240. Ligands 315 and 418 were prepared
according to reported procedures.
–CH3, isopropyl), 2.96 (sept., 1H, –CH, isopropyl), 7.20 (t, 3J =
6.3 Hz, 1H), 7.42 (d, 3J = 8.3 Hz, 2H), 7.75 (d, 3J = 8.5 Hz, 2H),
7.82 (t, 3J = 7.7 Hz, 1H), 8.35 (d, 3J = 7.8 Hz, 1H), 8.75 (s, 1H,
5-triazoleH), 9.02 (d, 3J = 4.6 Hz, 1H, 6-pyridylH).
2a. Similar to 1a by using 2 and Pd(COD)Cl2. Yield: 40 mg
(90%). Found C, 43.42; H, 3.93; N, 12.57% C16H16N4Cl2Pd requires
C, 43.51; H, 3.65; N, 12.69%; 1H NMR (250 MHz, CDCl3): d/ppm
2.02 (s, 6H, o-CH3 groups, mesityl), 2.34 (s, 3H, p-CH3 group,
mesityl), 6.99 (s, 2H, phenylH, mesityl), 7.52 (t, 3J = 6.5 Hz, 1H),
3
3
7.79 (d, J = 7.7 Hz, 1H), 8.07 (t, J = 6.5 Hz, 1H),8.21 (s, 1H,
5-triazoleH), 9.37 (d, 3J = 4.6 Hz, 1H, 6-pyridylH).
Synthesis
3a. Similar to 1a by using 3 and Pd(COD)Cl2. Yield: 38 mg
1. 4-Isopropyl-phenylazide (322 mg, 2.00 mmol) and 2-
ethynylpyridine (206 mg, 2.00 mmol) were dissolved in CH2Cl2–
tert-butanol–H2O (2.5 : 5 : 2.5 mL). CuSO4·5H2O (25.0 mg,
0.10 mmol), sodium ascorbate (79.0 mg, 0.40 mmol) and tris-
(benzyltriazolylmethyl)amine (11.0 mg, 0.02 mmol) were added
(95%). Found C, 38.92; H, 2.63; N, 14.27% C13H10N4Cl2Pd requires
1
C, 39.08; H, 2.52; N, 14.02%; H NMR (250 MHz, dmso-d6):
3
d/ppm 7.59–7.65 (m, 5H, phenylH), 7.87 (d, J = 6.5 Hz, 1H),
8.19 (d, 3J = 7.6 Hz, 1H), 8.43 (t, 3J = 7.7 Hz, 1H), 9.38 (d, 3J =
5.4 Hz, 1H, 6-pyridylH), 9.90 (s, 1H, 5-triazoleH).
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Dalton Trans., 2009, 9291–9297 | 9295
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4a. Similar to 1a by using 4 and Pd(COD)Cl2. Yield: 40 mg
97) and refined by full-matrix least-squares procedures (based on
F2, SHELXL-97)35 with anisotropic thermal parameters for all the
non-hydrogen atoms. The hydrogen atoms were introduced into
the geometrically calculated positions (SHELXS-97 procedures)
and refined riding on the corresponding parent atoms, with the
exception of those of 3, which were found in the DF2 maps an
refined isotropically. A MULTISCAN absorption correction was
applied for 3b.36
(90%). Found C, 39.89; H, 3.33; N, 12.87% C14H12N4Cl2Pd requires
1
C, 40.66; H, 2.92; N, 13.55%; H NMR (250 MHz, dmso-d6):
d/ppm 5.78 (s, 2H, –CH2–, benzyl), 7.30–7.48 (m, 5H, phenylH,
3
4
3
benzyl), 7.62 (dt, J = 6.6 Hz, J = 1.5 Hz, 1H), 8.22 (d, J =
7.7 Hz, 1H), 8.33 (dt, 3J = 7.6 Hz, 4J = 1.4 Hz, 1H), 9.18 (d, 3J =
5.3 Hz, 1H, 6-pyridylH), 9.28 (s, 1H, 5-triazoleH).
1b. Ligand 1 (50 mg, 0.19 mmol) and Pt(dmso)2Cl2 (80.0 mg,
0.19 mmol) were dissolved in nitromethane and refluxed for 5
h. After removing the solvent diethylether was added and the
precipitate was filtered. The compound was washed with acetone
(10 mL) and was dried in vacuo to give the desired product. Yield:
80 mg (80%). Found C, 36.03; H, 3.28; N, 9.93% C16H16N4Cl2Pt
requires C, 36.24; H, 3.04; N, 10.56%; 1H NMR (250 MHz,
CDCl3): d/ppm 1.26 (d, 3J = 6.6 Hz, 6H, –CH3, isopropyl), 2.97
(sept., 1H, –CH, isopropyl), 7.22 (t, 3J = 6.3 Hz, 1H), 7.40 (d, 3J =
8.5 Hz, 2H), 7.70 (d, 3J = 8.3 Hz, 2H), 7.78 (t, 3J = 7.4 Hz, 1H),
8.30 (d, 3J = 7.5 Hz, 1H), 8.78 (s, 1H, 4JPt–H = 11 Hz, 5-triazoleH),
9.12 (d, 3J = 4.5 Hz, 3JPt–H = 32 Hz, 1H, 6-pyridylH).
Acknowledgements
B. S. is indebted to the LANDESSTIFTUNG Baden-
Wuerttemberg for the financial support of this research project
through the Eliteprogramme for Postdocs. Prof. P. Braunstein
is kindly acknowledged for access to the X-ray facilities of the
Universite´ de Strasbourg.
References
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2b. Similar to 1b by using 2 and Pt(dmso)2Cl2. Yield: 75 mg
(75%). Found C, 36.66; H, 3.42; N, 10.96% C16H16N4Cl2Pt requires
C, 36.24; H, 3.04; N, 10.56%; 1H NMR (250 MHz, CDCl3): d/ppm
2.01 (s, 6H, o-CH3 groups, mesityl), 2.33 (s, 3H, p-CH3 group,
mesityl), 6.92 (s, 2H, phenylH, mesityl), 7.49 (t, 3J = 6.6 Hz, 1H),
3
3
7.82 (d, J = 7.6 Hz, 1H), 8.12 (t, J = 6.4 Hz, 1H),8.20 (s, 1H,
4JPt–H = 10 Hz, 5-triazoleH), 9.42 (d, 3J = 4.8 Hz, 3JPt–H = 32 Hz,
1H, 6-pyridylH).
3b. Similar to 1b by using 3 and Pt(dmso)2Cl2. Yield: 83.5
mg (90%). Found C, 31.66; H, 1.86; N, 11.75% C13H10N4Cl2Pt
requires C, 31.98; H, 2.06; N, 11.48%; 1H NMR (250 MHz, dmso-
d6): d/ppm 7.63–7.78 (m, 5H, phenylH), 7.91 (d, 3J = 6.6 Hz, 1H),
8.17 (d, 3J = 7.7 Hz, 1H), 8.40 (t, 3J = 7.8 Hz, 1H), 9.36 (d, 3J =
5.1 Hz, 3JPt–H = 32 Hz, 1H, 6-pyridylH), 9.87 (s, 1H, 5-triazoleH).
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4b. Similar to 1b by using 4 and Pt(dmso)2Cl2. Yield: 67 mg
(70%). Found C, 32.81; H, 2.48; N, 10.95% C14H12N4Cl2Pt requires
1
C, 33.48; H, 2.41; N, 11.16%; H NMR (250 MHz, dmso-d6):
d/ppm 5.82 (s, 2H, –CH2–, benzyl), 7.34–7.53 (m, 5H, phenylH,
3
4
3
benzyl), 7.68 (dt, J = 6.8 Hz, J = 1.6 Hz, 1H), 8.19 (d, J =
7.5 Hz, 1H), 8.31 (dt, 3J = 7.8 Hz, 4J = 1.3 Hz, 1H), 9.20 (s, 1H,
4JPt–H = 12 Hz, 5-triazoleH), 9.32 (d, 3J = 5.4 Hz, 3JPt–H = 33 Hz,
1H, 6-pyridylH).
Crystallographic details†
X-Ray data collection, structure solution and refinement for all
compounds
Ligand
3
was crystallised by slow evaporation of
a
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˚
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9296 | Dalton Trans., 2009, 9291–9297
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©

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This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 9291–9297 | 9297
©