C-H activation at a bidentate ligand coordinated to palladium(II) - An electrophilic attack supported by an external base

Article abstract of DOI:10.1002/ejic.201402149

2-(2-Phenylaminopyrimidin-4-yl)pyridines undergo C-H activation at the phenyl ring in the ortho position to the amine nitrogen atom when reacted with (PhCN)₂PdCl₂ and finally form N,N,C-coordinated palladium(II) complexes in high yields. Five differently substituted complexes were synthesized and characterized by spectroscopy and X-ray structure analysis. The reaction mechanism for the formation of these complexes was elucidated by kinetic experiments, which allowed the calculation of the activation parameters of the complex formation.

Full text of DOI:10.1002/ejic.201402149

FULL PAPER
DOI:10.1002/ejic.201402149
C–H Activation at a Bidentate Ligand Coordinated to
Palladium(II) – an Electrophilic Attack Supported by an
External Base
Merve Cayir,[a] Leila Taghizadeh Ghoochany,[a] Adam Walli,[b]
Mark Busch,[c] Yu Sun,[a] Franc Meyer,[b] Stefan Bräse,[c] and
Werner R. Thiel*[a]
Keywords: C–H activation / Palladium / Reaction mechanisms / Kinetics / Nitrogen heterocycles
2-(2-Phenylaminopyrimidin-4-yl)pyridines undergo C–H ac-
tivation at the phenyl ring in the ortho position to the amine
nitrogen atom when reacted with (PhCN)2PdCl2 and finally
form N,N,C-coordinated palladium(II) complexes in high
yields. Five differently substituted complexes were synthe-
sized and characterized by spectroscopy and X-ray structure
analysis. The reaction mechanism for the formation of these
complexes was elucidated by kinetic experiments, which al-
lowed the calculation of the activation parameters of the
complex formation.
quantum chemical calculations, we proved that such ligands
can undergo intramolecular C–H activation at the 5-posi-
tion of the 2-aminopyrimidin-4-yl site and that this process
is the crucial step for the formation of the active species.
For this to happen, a tertiary 2-amino group is required. In
this manuscript, we report on the ortho C–H activation of
phenyl groups attached to the amino moiety of 2-(2-amino-
pyrimidin-4-yl)pyridine ligands that occurs spontaneously
after the formation of N,NЈ-coordinated palladium(II) com-
plexes. The palladium-centered C–H activation was investi-
gated by a kinetic study that allowed the elucidation of the
kinetic parameters of this reaction. Similar C–H activation
processes have been reported as primary steps in a series of
palladium-catalyzed and pyridine-directed reactions,
namely, for carbazole[6] and indole[7] syntheses as well as
arene–alkyne[8] and arene–allene[9] couplings.
Introduction
The discovery of palladium-catalyzed C–C cross-cou-
pling reactions has given a further dynamic impulse to the
development of palladium chemistry.[1] Most of these reac-
tions are nowadays well-established as tools in organic syn-
thesis and follow a sequence wherein an aryl or alkyl halide
undergoes an oxidative addition to the catalytically active
palladium(0) species to generate a palladium(II) intermedi-
ate of the type RPdIIX(L)n, which allows the transfer of the
R group to the substrate. However, during the last decade,
palladium-mediated C–H activation came into the focus of
research to generate the palladium(II) intermediate
RPdIIX(L)n from nonfunctionalized starting materials.[2]
This type of substrate activation often occurs with high effi-
ciency as soon as cyclic products are formed.[3] Although
cyclopalladation reactions have been studied extensively,
only some of the proposed mechanisms have been sup-
ported by kinetic measurements.[4]
Results and Discussion
Recently, we reported the synthesis and application of 2-
(2-aminopyrimidin-4-yl)pyridines as ligands for a base-free
hydrogen transfer reaction catalyzed by ruthenium com-
plexes.[5] By spectroscopic investigations supported by
Complex Synthesis and Characterization
A multitude of different routes to functionalized pyr-
imidines have been reported.[10] For the synthesis of the 2-
(2-arylaminopyrimidin-4-yl)pyridines 2a–2e, the condensa-
tion of the appropriate arylated guanidinium salt 1a–1e
[a] Fachbereich Chemie, Technische Universität Kaiserslautern,
Erwin-Schrödinger-Str. 54, 67663 Kaiserslautern, Germany
E-mail: thiel@chemie.uni-kl.de
with
(E)-3-(dimethylamino)-1-(pyridin-2-yl)prop-2-en-1-
one in the presence of base proceeded best and provided
moderate-to-good yields (45–70%) of the desired products
(Scheme 1).[11] The corresponding phenylguanidinium salts
1a–1e can be prepared from substituted anilines and cyan-
amide in the presence of nitric acid.[12] By following this
strategy, five 2-(2-phenylaminopyrimidin-4-yl)pyridines 2a–
2e were obtained. Ligands 2a–2e bear different functional
http://www.chemie.uni-kl.de/index.php?id=378
[b] Institut für Anorganische Chemie, Georg-August-Universität
Göttingen,
Tammannstr. 4, 37077 Göttingen, Germany
[c] Institute of Organic Chemistry, Karlsruhe Institute of
Technology,
Fritz-Haber-Weg 6, 76131 Karlsruhe, Germany
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201402149.
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groups at the para position of the phenyl group and, there-
fore, allow the elucidation of their electronic influence on
the C–H activation step.
Scheme 1. Synthesis of the ligands 2a–2e.
Although the chemical shift of the pyridine protons is
hardly affected by the substitution pattern of the phenyl Figure 1. Solid-state molecular structures of the palladium com-
1
plexes 3a (top) and 3d (bottom). Characteristic bond lengths [Å]
ring, the H NMR resonances of the pyrimidine protons
and angles [°]: 3a: Pd1–Cl1 2.3192(7), Pd1–N1 2.111(2), Pd1–N2
reflect the influence of the different substituents. As ex-
2.015(2), Pd1–C15 1.990(3), S1–O1 1.496(2), Cl1–Pd1–N1 92.03(7),
Cl1–Pd1–N2 169.37(7), Cl1–Pd1–C15 94.75(7), N1–Pd1–N2
80.28(9), N1–Pd1–C15 172.29(10), N2–Pd1–C15 93.45(9), N4–O1
pected, the electron-donating methoxy group (2d) leads to
a shift of the pyrimidine 1H NMR resonances to higher
0.85(3), H4N···O1 2.09(3), N4···O1 2.931(3), N4–H4N···O1 168(3);
3d: Pd1–Cl1 2.3226(5), Pd1–N1 2.1163(19), Pd1–N2 2.0068(18),
Pd1–C15 1.993(3), S1–O2 1.511(2), Cl1–Pd1–N1 92.71(5), Cl1–
Pd1–N2 168.76(6), Cl1–Pd1–C15 94.84(6), N1–Pd1–N2 79.97(7),
N1–Pd1–C15 171.25(8), N2–Pd1–C15 93.20(8), N4–H4N 0.85(2),
field and the electron-withdrawing cyanide group (2e)
causes a shift to lower field. This effect is even more pro-
nounced for the NH resonances [δ = 9.76 (2a), 9.79 (2b),
9.92 (2c), 9.56 (2d), and 10.34 (2e) ppm].
The reactions of 2a–2e with (PhCN)2PdCl2 in dichloro- H4N···O2 2.00(2), N4···O2 2.848(3), N4–H4N··· O2 175(3).
methane at room temperature furnished the tetracoordinate
palladium complexes 3a–3e with a chelating N,N,C ligand
in almost quantitative yields (Scheme 2).
The X-ray structure analyses proves that the C–H acti-
vation occurs at the phenyl ring and proceeds here without
the addition of any external base or the use of basic ligands
(e.g., CH3COO–) coordinated to the palladium center. Both
complexes show the typical distorted square-planar geome-
try of palladium(II) compounds. The palladium center is
coordinated by a chlorido ligand and a tridentate NNC-
type ligand through the nitrogen atom of the pyridine moi-
ety, the nitrogen atom at the 3-position of the pyrimidine
ring, and one of the ortho carbon atoms of the phenyl
group. The distances Pd–N1 (3a: 2.111; 3d: 2.116 Å), Pd–
N2 (3a: 2.015; 3d: 2.007 Å), Pd–C15 (3a: 1.990; 3d:
1.993 Å), and Pd–Cl1 (3a: 2.319; 3d: 2.323 Å) are similar to
Scheme 2. Synthesis of the palladium complexes 3a–3e.
Complexes 3a–3e precipitated from the reaction mixture those of related structures.[5,13] Owing to steric restrictions
as yellow to deep orange solids. Optimized yields were ob- caused by the tridentate coordination mode, the Pd–N2
tained by adding a large excess of diethyl ether to the reac- bond is considerably shorter than the Pd–N1 bond, and the
tion mixture. For further purification, 3a–3e were redis- aromatic rings are not completely coplanar. In both struc-
solved in dimethyl sulfoxide (DMSO) and a very small tures, an additional molecule of DMSO forms a hydrogen
amount of ethanol and subsequently reprecipitated by the bond with the N–H moiety of the C–H-activated 2-(2-phen-
addition of diethyl ether.
ylaminopyrimidin-4-yl)pyridine ligand.
Single crystals of 3a and 3d suitable for X-ray diffraction
The NMR spectra of 3a–3e further confirm that the C–
studies were obtained by slow diffusion of diethyl ether into H activation occurs at the phenyl ring. All resonances of
DMSO solutions. The solid-state molecular structures of 3a the N–H protons are shifted to lower field; however, the
and 3d and characteristic structural parameters are pre- clear correlation for the free ligands between the electronic
sented in Figure 1.
impact of the substituent at the para position and the chem-
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ical shift is lost [δ = 11.10 (3a), 11.03 (3b), 11.19 (3c), 11.02 second-order reaction rate constants k increase as the elec-
(3d), and 11.51 (3e) ppm]. The 1H and 13C NMR reso- tron donor ability of the meta substituent of the ligands
nances of the phenyl moieties now show the typical patterns increases. This is a clear indication that the reaction builds
of 1,2- (3a) or 1,2,4-substituted phenyl groups (3b–3e). The a positive charge during the rate-determining step and of
13C NMR chemical shift of the quaternary, palladium- the electrophilic nature of the intermediate. Further support
bound carbon atom C-11 that possesses anionic character for this conclusion came from the Hammett analysis [plot
is typical for all complexes [δ =125.0 (3a), 126.5 (3b), 126.4 of log(k/kH) vs. Hammett constants σmeta] shown in Fig-
(3c), and 125.8 (3d) ppm]. As expected, the influence of the ure 3.[14] A good linear correlation (R2 = 0.982) was ob-
substituent at the meta position to this site on the chemical tained with a Hammett parameter ρ of –1.21Ϯ0.09 for the
shift of C-11 is small. Compound 3e was not soluble reactions at 25 °C. The investigation of the reaction rates at
enough to allow measurement of a 13C NMR spectrum.
different temperatures gave ρ constants of ca. –1 over the
investigated temperature range.[15] Thus, an electrophilic
aromatic substitution mechanism such as that depicted in
Scheme 3 can be assumed. In that scenario, the palladium
center serves as the electrophile and a proton is liberated
from the ligand precursor; a chloride anion probably acts as
the base. Second-order kinetics indicate an intermolecular
reaction during proton abstraction. The alternative scenario
of a σ-bond metathesis reaction is usually characterized by
a positive value for the Hammett parameter ρ and can, thus,
be excluded in the present case.[16]
Kinetic Studies
The kinetics of the formation of the cyclometalated
(NNC)PdCl complexes in a CH2Cl2/DMSO (1:1) solution
were followed by monitoring the spectral changes by UV/
Vis spectroscopy (Figure 2). Although 3a–3e were synthe-
sized in neat CH2Cl2, DMSO was added for the kinetic
studies to assure the complete solubility of even the rather
poorly soluble, cyano-functionalized complex 3e. Some
changes of the UV/Vis spectrum with isosbestic points at
383 and 345 nm occur within the first 60 s after the addition
of equimolar amounts of the NNC ligand precursor to a
0.66 mm solution of (PhCN)2PdCl2 in CH2Cl2/DMSO (1:1)
at 40 °C (see Figure S1). This is followed by a much slower
second phase of the reaction, which is characterized by
isosbestic points at 433 and 355 nm (Figure 2; first spec-
trum 90 s after mixing). We attribute the fast initial phase
to the binding of the bidentate pyrimidinylpyridine part of
the ligand to the palladium center; the subsequent cyclo-
metalation occurs in a slower second step.
Figure 3. Hammett plot for the formation of the cyclopalladated
complexes 3a–3e at 25 °C based on rate constants taken from linear
fits as exemplarily shown in Figure 2. The linear regression gives
the Hammett parameter ρ = –1.21Ϯ0.09. The grey dot for X =
OMe represents the average of four measurements. This value was
not included in the fit owing to the large deviations between the
different measurements.
Scheme 3. Proposed mechanism for the formation of the cyclomet-
alated complexes 3a–3e.
In addition to the Hammett analysis, a full kinetic inves-
tigation was performed in the temperature range –10 to
+45 °C. The activation parameters for the rate-limiting step
were determined from the temperature dependence of the
respective rate constants (Eyring plots shown in Figure 4)
and are compiled in Table 1.
Figure 2. Absorption spectral changes for the reaction of
(PhCN)2PdCl2 (0.66 mm) with 2a (X = H) in CH2Cl2/DMSO (1:1)
at 40 °C. Curves: bold grey, t = 0 min (90 s after mixing); bold
black, t = 40 min; 15 s steps. Inset: kinetic trace at 490 nm (black
line) with second-order fit (grey line). The isosbestic points are at
433 and 355 nm.
The slopes of the linear fits in the Eyring plots are
roughly equal and give enthalpies of activation ΔH‡ in the
The spectral changes during the slow cyclometalation narrow range 12.5–15.3 kcalmol–1. The entropies of acti-
step follow second-order kinetics (see inset of Figure 2; a vation ΔS‡ are quite small (3.4 to –8.0 calK–1 mol–1). Al-
linearized form of the kinetic trace is shown in Figure S2). though ΔH‡ shows only a minor trend towards smaller val-
For the differently substituted ligand precursors 2a–2e, the ues with the more-electron-withdrawing substituents, such
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vents for the syntheses of the palladium complexes and for the
kinetic experiments were dried by standard methods prior to use.
The elemental analyses were performed at the Fachbereich Chemie
of the TU Kaiserslautern. Infrared spectra with a resolution of
Ϯ2 cm–1 were recorded with a PerkinElmer FT-ATR IR 1000 spec-
trometer equipped with a diamond-coated ZnSe window. 1H and
13C NMR spectra were recorded with a Bruker Spectrospin device
with resonance frequencies of 400.1 and 100.6 MHz for the 1H and
13C nuclei, respectively. The NMR resonances of the ligands 2a–2e
and of the palladium complexes 3a–3e are assigned according to
Scheme 4.
Figure 4. Eyring plots, ln(kT–1) vs. T–1, of the second-order rate
constants k for the formation of cyclopalladated complexes 3a–3e
with linear regressions (see Table 1 for kinetic parameters).
Scheme 4. Assignment of the NMR resonances (14 and 15 are only
relevant for the palladium complexes).
Table 1. Activation parameters for the reaction of Pd(PhCN)2Cl2
with the ligands 2a–2e.
[a]
2
¯
R
X
k298
[m–1 min–1]
ΔH‡
ΔS‡
ΔG‡
298
Kinetic Measurements: The reactions were followed by UV/Vis
spectroscopy, and measurements of the reaction solutions were per-
formed directly with an all-quartz immersion probe in a custom-
made reaction tube (transmission measurement with 1 mm optical
path, Hellma Analytics). Time-dependent UV/Vis spectra were re-
corded approximately every 15 s with a Cary 50 Bio spectrometer
through the use of a fiber-optical connection. Temperature control
of the solutions was accomplished with a Lauda ECO RE 630 cryo-
stat. CH2Cl2/DMSO (1:1, 0.66 mm) solutions were prepared, and
five different temperatures were applied, depending on the ligand.
Single-wavelength kinetic traces were then obtained from the spec-
tra and fitted by applying second-order kinetics with Cary Win UV
and OriginLab OriginPro 8.5.1 software. All measurements yielded
consistent results. However, in the case of experiments with ligand
X = OMe, the determined rate constants were barely reproducible
and showed only a weak linear temperature-dependent correlation.
Therefore, only the rate constants obtained at 25 °C have been con-
sidered in the further evaluation.
[kcalmol–1] [calK–1 mol–1][kcalmol–1]
OMe[b] 335.4[c]
–
–
–
–
H
F
Cl
CN
197.5
88.1
75.7
40.5
0.993 15.32Ϯ0.65 3Ϯ2
0.993 13.76Ϯ0.60 –4Ϯ2
0.993 12.48Ϯ0.65 –8Ϯ2
0.995 13.64Ϯ0.49 –5Ϯ2
14.31Ϯ0.93
14.79Ϯ0.84
14.88Ϯ0.91
15.25Ϯ0.69
[a] Rate constants at 25 °C from the linear regressions in the Eyring
plots in Figure 4. [b] No determination of activation parameters
for X = OMe, see the Exp. Section for details. [c] Average of four
measurements at 25 °C.
a trend is more obvious for ΔS‡. Regarding the Eyring plot,
the almost parallel linear fits decrease to lower values with
more-electron-withdrawing substituents. This results in
more-negative entropies, which render the reactions less en-
tropically favored, and more-ordered transition states are
indicated. Entropies around zero are difficult to inter-
pret;[17] however, as the entropies are mostly negative, an
associative mechanism in the rate-determining step is likely,
in accordance with the mechanism outlined above.
General Procedure for the Synthesis of the Guanidinium Salts 1a–
1e:[7] Concentrated nitric acid was added to a solution of the appro-
priate arylamine in ethanol followed by a 50% aqueous solution of
cyanamide (1.5 equiv.). The reaction mixture was heated under re-
flux for 16 h and then cooled to 0 °C, diethyl ether was then added.
This solution was kept in the refrigerator for 12 h. The resulting
solids were collected by filtration to afford the products in good
yield.
Conclusions
We have presented the synthesis and characterization of
new palladium complexes with N,N,C coordination, which
were obtained by C–H activation at the phenyl group of a
2-(2-phenylaminopyrimidin-4-yl)pyridine ligand. The reac-
tion was investigated by kinetic methods, which clearly sug-
gested that it follows a mechanism similar to an electro-
philic aromatic substitution at the aniline site with the pal-
ladium center as the electrophile.
Phenylguanidinium Sulfate (1a): This compound was prepared ac-
cording to a previously published procedure (yield 35%).[18]
C14H20N6O4S (368.41): calcd. C 45.64, H 5.47, N 22.81, S 8.70;
found C 45.06, H 5.36, N 23.02, S 8.66. 1H NMR (400 MHz, D2O):
3
δ = 7.49–7.46 (t, JH,H = 7.5 Hz, 2 H, m-H), 7.40–7.37 (t, 1 H, p-
H), 7.29 (d, 2 H, o-H) ppm. 13C NMR (100.6 MHz, D2O): δ =
156.3 (CN3), 134.1 (C-i), 129.9 (C-m), 128.0 (C-p), 125.8 (C-o) ppm.
(4-Fluorophenyl)guanidinium Nitrate (1b): Prepared from 4-fluoro-
aniline according to the general procedure (yield 63%).
C7H9FN4O3 (216.17): calcd. C 38.89, H 4.20, N 25.92; found C
39.04, H 4.49, N 26.02. 1H NMR (400 MHz, D2O): δ = ppm 7.35–
7.29 (m, 2 H, o-H), 7.25–7.16 (m, 2 H, m-H) ppm. 13C NMR
Experimental Section
General Information: All chemicals for the syntheses of the ligands
were purchased from Sigma–Aldrich or Acros Organics;
(PhCN)2PdCl2 was obtained from STREM Chemicals. Solvents for
the ligand syntheses were used without further purification; sol-
1
(100.6 MHz, D2O): δ = 161.8 (d, JF,C = 245.5 Hz, C-p), 156.6
3
2
(CN3), 130.0 (C-i), 128.5 (d, JF,C = 9.1 Hz, C-o), 116.7 (d, JF,C
23.2 Hz, C-p) ppm.
=
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3
3
(4-Chlorophenyl)guanidinium Nitrate (1c): Prepared from 4-chloro-
aniline according to the general procedure (yield 58%).
NH), 8.75 (d, JH,H = 3.9 Hz, 1 H, 1-H), 8.66 (d, JH,H = 4.7 Hz,
3
3
1 H, 8-H), 8.40 (d, JH,H = 7.8 Hz, 1 H, 4-H), 8.04 (t, JH,H =
C7H9ClN4O3 (232.62): calcd. C 36.14, H 3.90, N 24.08; found C 7.8 Hz, 1 H, 3-H), 7.89 (d, JH,H = 8.0 Hz, 2 H, 12-H), 7.75 (d, 1
3
36.05, H 3.96, N 24.04. 1H NMR (400 MHz, D2O): δ = 7.48 (d,
3JH,H = 8.6 Hz, 2 H, m-H), 7.28 (d, 2 H, o-H) ppm. 13C NMR
(100.6 MHz, D2O): δ = 156.3 (CN3), 133.0, 132.9 (C-i, C-p), 129.9
(C-m), 127.4 (C-o) ppm.
H, 7-H), 7.58–7.55 (m, 1 H, 2-H), 7.39 (d, 3JH,H = 8.0 Hz, 2 H, 11-
H) ppm. 13C NMR (100.6 MHz, [D6]DMSO): δ = 162.9 (C-9),
159.8 (C-6), 159.6 (C-8), 153.5 (C-5), 149.6 (C-1), 139.5 (C-10),
137.6 (C-3), 128.4 (C-11), 125.8 (C-2), 124.9 (C-13), 121.1 (C-4),
120.3 (C-12) 108.3 (C-7) ppm.
(4-Methoxyphenyl)guanidinium Nitrate (1d): Prepared from para-
anisidine according to the general procedure (yield 82%).
C8H12N4O4 (228.21): calcd. C 42.11, H 5.30, N 24.55; found C
2-(N-4-Methoxyphenylamino)-4-(pyridine-2-yl)pyrimidine
(2d):
From 1d according to the general procedure (yield 70%).
C16H14N4O (278.31): calcd. C 69.05, H 5.07, N 20.13; found C
69.36, H 4.81, N 19.70. 1H NMR (400.1 MHz, [D6]DMSO): δ =
1
42.05, H 5.31, N 24.43. H NMR (400 MHz, DMSO): δ = 9.40 (s,
3
1 H, NH), 7.23 (br, 4 H, NH), 7.18 (d, JH,H = 8.8 Hz, 2 H, o-H),
3
7.00 (d, 2 H, m-H), 3.77 (s, 3 H, OCH3) ppm. 13C NMR
(100.6 MHz, DMSO): δ = 158.2 (C-p), 156.3 (CN3), 127.5 (C-i),
127.3 (C-o), 114.9 (C-m), 55.4 (OCH3) ppm.
9.56 (br, 1 H, NH), 8.74 (d, JH,H = 4.3 Hz, 1 H, 1-H), 8.59 (d,
3JH,H = 4.7 Hz, 1 H, 8-H), 8.37 (d, 3JH,H = 7.8 Hz, 1 H, 4-H), 8.03
3
3
(t, JH,H = 7.8 Hz, 1 H, 3-H), 7.73 (d, JH,H = 8.0 Hz, 2 H, 12-H),
7.66 (d, 1 H, 7-H), 7.57–7.54 (m, 1 H, 2-H), 6.94 (d, 2 H, 11-H),
3.74 (s, 3 H, OCH3) ppm. 13C NMR (100.6 MHz, [D6]DMSO): δ
= 162.7 (C-9), 160.2 (C-6), 159.5 (C-8), 154.3 (C-5), 153.8 (C-13),
149.6 (C-1), 137.5 (C-3), 133.6 (C-10), 125.6 (C-2), 121.0 (C-4),
120.7 (C-11), 113.8 (C-12) 107.4 (C-7), 55.2 (OCH3) ppm.
(4-Cyanophenyl)guanidinium Nitrate (1e): Prepared from 4-amino-
benzonitrile according to the general procedure (yield 33%).
C8H9N5O3 (223.19): calcd. C 43.05, H 4.06, N 31.38; found C
43.07, H 3.75, N 30.92. 1H NMR (400 MHz, DMSO): δ = 10.04
3
(s, 1 H, NH), 7.88 (d, JH,H = 8.6 Hz, 2 H, m-H), 7.66 (br, 4 H,
NH), 7.40 (d, 2 H, o-H) ppm. 13C NMR (100.6 MHz, DMSO): δ
= 155.3 (CN3), 140.7 (CN), 133.9 (C-m), 123.4 (C-o), 118.6 (C-i),
107.5 (CN) ppm.
2-(N-4-Cyanophenylamino)-4-(pyridine-2-yl)pyrimidine (2e): From
1e according to the general procedure (yield 47%). C16H11N5·
(H2O)0.2 (276.90): calcd. C 69.40, H 4.15, N 25.29; found C 69.70,
H 4.14, N 25.01. 1H NMR (400.1 MHz, [D6]DMSO): δ = 10.34
General Procedure for the Synthesis of Ligands 2a–2e: Sodium
(0.5 g, 22 mmol) was dissolved in a solution of the appropriate
guanidinium salt 1a–e (11 mmol) in dry EtOH (50 mL) under an
atmosphere of dinitrogen. As soon as the evolution of dihydrogen
3
3
(br, 1 H, NH), 8.77 (d, JH,H = 4.7 Hz, 1 H, 1-H), 8.74 (d, JH,H
=
3
4.7 Hz, 1 H, 8-H), 8.42 (d, JH,H = 7.8 Hz, 1 H, 4-H), 8.06–8.04
(m, 3 H, 3-H, 12-H), 7.85 (d, 1 H, 7-H), 7.8 (d, JH,H = 8.6 Hz, 2
3
H, 11-H), 7.61–7.58 (m, 1 H, 2-H) ppm. 13C NMR (100.6 MHz,
[D6]DMSO): δ = 163.1 (C-9), 159.9 (C-6), 159.5 (C-8), 153.3 (C-5),
149.7 (C-1), 144.9 (C-10), 137.7 (C-3), 133.1 (C-11), 126.0 (C-2),
121.2 (C-4), 119.6 (C-13), 118.4 (C-12), 109.4 (C-7), 102.5 (CN)
ppm.
ceased,
(E)-3-(dimethylamino)-1-(pyridin-2-yl)prop-2-en-1-one
(1.80 g, 10 mmol) was added, and the mixture was heated to reflux
for 24 h. The solution was cooled to 0 °C, and the precipitated solid
was collected by filtration; unreacted salt and the excess base were
washed out with water, and the product was dried in vacuo.
General Procedure for the Synthesis of the Palladium Complexes 3a–
3e: A solution of the appropriate ligand 2a–2e (0.50 mmol) in
CH2Cl2 (10 mL) was added dropwise to a solution of [(PhCN)2-
PdCl2] (192 mg, 0.50 mmol) in CH2Cl2 (10 mL). The reaction mix-
ture was stirred at room temperature for 16 h. The precipitated
products were collected by filtration and washed with CH2Cl2. The
complexes can be recrystallized from DMSO.
2-(N-Phenylamino)-4-(pyridine-2-yl)pyrimidine (2a): From 1a ac-
cording to the general procedure (yield 50%). C15H12N4 (248.29):
calcd. C 72.56, H 4.87, N 22.57; found C 72.35, H 5.21, N 22.47.
1H NMR (400.1 MHz, [D6]DMSO): δ = 9.76 (br, 1 H, NH), 8.75
3
3
(d, JH,H = 4.3 Hz, 1 H, 1-H), 8.65 (d, JH,H = 5.1 Hz, 1 H, 8-H),
3
3
8.41 (d, JH,H = 7.8 Hz, 1 H, 4-H), 8.05 (t, JH,H = 7.8 Hz, 1 H, 3-
3
H), 7.85 (d, JH,H = 7.8 Hz, 2 H, 11-H), 7.73 (d, 1 H, 7-H), 7.57
(dd, 1 H, 2-H), 7.33 (t, JH,H = 7.8 Hz, 2 H, 12-H), 6.98 (t, 1 H,
3a: From 2a according to the general procedure (yield 93%).
C15H11ClN4Pd·(CH2Cl2)0.25 (410.36): calcd. C 44.64, H 2.82, N
13.65; found C 44.58, H 2.90, N 13.73. 1H NMR (400.1 MHz, [D6]-
3
13-H) ppm. 13C NMR (100.6 MHz, [D6]DMSO): δ = 162.8 (C-9),
160.1 (C-6), 159.5 (C-8), 153.7 (C-5), 149.6 (C-1), 140.5 (C-10),
137.6 (C-3), 128.6 (C-12), 125.7 (C-2), 121.5 (C-4), 121.0 (C-13),
119.0 (C-11) 108.0 (C-7) ppm.
3
DMSO): δ = 11.10 (br, 1 H, NH), 9.33 (d, JH,H = 4.7 Hz, 1 H, 1-
H), 9.00 (d, 3JH,H = 4.7 Hz, 1 H, 8-H), 8.67 (d, 3JH,H = 7.8 Hz, 1 H,
4-H), 8.37 (d, 3JH,H = 8.2 Hz, 1 H, 12-H), 8.28 (t, 3JH,H = 7.0 Hz, 1
3
2-(N-4-Fluorophenylamino)-4-(pyridine-2-yl)pyrimidine (2b): From
1b according to the general procedure (yield 53%). C15H11FN4
(266.28): calcd. C 67.66, H 4.16, N 21.04; found C 67.49, H 4.28,
N 20.90. 1H NMR (400.1 MHz, [D6]DMSO): δ = 9.79 (br, 1 H,
H, 3-H), 7.99 (d, JH,H = 4.7 Hz, 1 H, 7-H), 7.89–7.86 (m, 1 H, 2-
3
H), 7.19 (d, JH,H = 7.4 Hz, 1 H, 15-H), 7.04 (t, JH,H = 7.0 Hz, 1
3
H, 14-H), 6.71 (t, JH,H = 7.0 Hz, 1 H, 13-H) ppm. 13C NMR
(100.6 MHz, [D6]DMSO): δ = 162.1 (C-6), 161.1 (C-8), 152.5 (C-
5), 150.0 (C-9), 149.2 (C-1), 140.3 (C-10), 139.8 (C-3), 136.6 (C-
11), 128.0 (C-2), 125.0, 124.5 (C-12, C-14), 123.9 (C-4), 120.6 (C-
13), 116.2 (C-15), 108.8 (C-7) ppm.
3
3
NH), 8.74 (d, JH,H = 4.3 Hz, 1 H, 1-H), 8.63 (d, JH,H = 4.7 Hz,
3
3
1 H, 8-H), 8.39 (d, JH,H = 7.8 Hz, 1 H, 4-H), 8.03 (t, JH,H
=
7.8 Hz, 1 H, 3-H), 7.85–7.81 (m, 2 H, 12-H), 7.81 (d, 1 H, 7-H),
4
7.58 (dd, 1 H, 2-H), 7.17 (t, JF,H
=
3JH,H = 8.0 Hz, 2 H, 11-H)
3b: From 2b according to the general procedure (yield 94%).
C15H10ClFN4Pd·DMSO (485.25): calcd. C 42.08, H 3.32, N 11.55;
found C 41.80, H 3.42, N 11.46. 1H NMR (400.1 MHz, [D6]-
ppm. 13C NMR (100.6 MHz, [D6]DMSO): δ = 162.8 (C-9), 160.0
1
(C-6), 159.5 (C-8), 158.4 (d, JC,F = 237.7 Hz, C-13), 153.6 (C-5),
149.6 (C-1), 137.6 (C-3), 136.9 (4JC,F = 2.8 Hz, C-10), 125.7 (C-2),
3
DMSO): δ = 11.07 (br, 1 H, NH), 9.21 (d, JH,H = 5.0 Hz, 1 H, 1-
3
2
121.1 (C-4), 120.7 (d, JC,F = 7.4 Hz, C-11), 115.2 (d, JC,F
=
3
3
H), 8.93 (d, JH,H = 4.7 Hz, 1 H, 8-H), 8.59 (d, JH,H = 8.2 Hz, 1
22.2 Hz, C-12), 108.0 (C-7) ppm.
3
3
H, 4-H), 8.23 (t, JH,H = 8.2 Hz, 1 H, 3-H), 8.07 (dd, JF,H
2-(N-4-Chlorophenylamino)-4-(pyridine-2-yl)pyrimidine (2c): From 11.4 Hz, JH,H = 2.9 Hz, 1 H, 12-H), 7.91 (d, 1 H, 7-H), 7.82 (dd,
=
5
4
1c according to the general procedure (yield 45%). C15H11ClN4
(282.73): calcd. C 63.72, H 3.92, N 19.82; found C 63.46, H 4.10,
N 19.75. 1H NMR (400.1 MHz, [D6]DMSO): δ = 9.93 (br, 1 H,
1 H, 2-H), 7.15 (dd, JF,H = 5.5 Hz, 1 H, 15-H), 6.86 (m, 1 H, 14-
H) ppm. 13C NMR (100.6 MHz, [D6]DMSO): δ = 162.0 (C-6),
1
161.2 (C-8), 156.2 (d, JF,C = 240 Hz, C-13), 152.6 (C-5), 150.0 (C-
Eur. J. Inorg. Chem. 2014, 2618–2624
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FULL PAPER
9), 149.2 (C-1), 139.8 (C-3), 133.5 (C-10), 128.0 (C-2), 126.5 (d,
Table 2. Summary of the crystallographic data and details of data
2
3JC,F = 5.0 Hz, C-11), 124.9 (d, JC,F = 20.6 Hz, C-12), 123.9 (C- collection and refinement.
3
2
4), 116.8 (d, JC,F = 7.7 Hz, C-15), 112.0 (d, JC,F = 23.4 Hz, C-
3a
3d
14), 108.7 (C-7) ppm.
Empirical formula
Formula weight
Crystal size /mm
T /K
C17H17ClN4OPdS
467.26
0.32ϫ0.15ϫ0.14
150(2)
C18H19ClN4O2PdS
497.28
0.26ϫ0.07ϫ0.06
150(2)
3c: From 2c according to the general procedure (yield 88%).
C15H10Cl2N4Pd·(CH2Cl2)0.30 (449.06): calcd. C 40.92, H 2.38, N
12.48; found C 40.95, H 2.41, N 12.70. 1H NMR (400.1 MHz, [D6]-
λ /Å
1.54184
1.54184
3
DMSO): δ = 11.19 (br, 1 H, NH), 9.27 (d, JH,H = 5.1 Hz, 1 H, 1-
Crystal system
Space group
a /Å
b /Å
c /Å
monoclinic
P21/c
11.3161(2)
20.3112(4)
7.6539(1)
90
monoclinic
P21/n
9.0633(2)
16.6341(3)
13.2038(3)
90
3
3
H), 9.00 (d, JH,H = 4.7 Hz, 1 H, 8-H), 8.66 (d, JH,H = 8.2 Hz, 1
3
H, 4-H), 8.32 (s, 1 H, 12-H), 8.28 (dd, JH,H = 8.2 Hz, 1 H, 3-H),
7.99 (d, JH,H = 4.70 Hz, 1 H, 7-H), 7.88 (dd, 1 H, 2-H), 7.16 (d,
3
3JH,H = 8.0 Hz, 1 H, 15-H), 7.07 (d, 1 H, 14-H) ppm. 13C NMR
(100.6 MHz, [D6]DMSO): δ = 162.1 (C-6), 161.3 (C-8), 152.6 (C-
5), 150.1 (C-9), 149.3 (C-1), 139.9 (C-3), 138.6 (C-13), 135.9 (C-
10), 128.0 (C-2), 126.4 (C-11), 124.7, 124.0, 123.9 (C-4, C-12, C-
14), 117.3 (C-15), 109.1 (C-7) ppm.
α /°
β /°
97.815(2)
90
1742.86(5)
4
1.781
11.233
109.739(2)
90
1873.64(7)
4
1.763
10.534
γ /°
V /Å3
Z
ρcalcd. /gcm–3
3d: From 2d according to the general procedure (yield 95%).
μ /mm–1
C16H13ClN4OPd (419.16): calcd. C 45.85, H 3.13, N 13.37; found
θ range /°
Reflections collected
Independent
reflections
Data/restraints/
parameters
Final R indices
[IϾ 2σ(I)][a]
R indices (all data)
GooF[b]
3.94–62.62
10892
2777
[R(int) = 0.0293]
2777/1/232
4.44–62.62
13076
3004
[R(int) = 0.0304]
3004/1/250
1
C 45.30, H 3.30, N 13.15. H NMR (400.1 MHz, [D6]DMSO): δ =
3
11.02 (br, 1 H, NH), 9.33 (d, JH,H = 4.7 Hz, 1 H, 1-H), 8.95 (d,
3JH,H = 4.7 Hz, 1 H, 8-H), 8.66 (d, 3JH,H = 8.2 Hz, 1 H, 4-H), 8.28
3
4
(t, JH,H = 8.3 Hz, 1 H, 3-H), 8.00 (d, JH,H = 2.7 Hz, 1 H, 12-H),
1
7.91 (d, 1 H, 7-H), 7.88 (dd, 1 H, 2-H), 7.14 (d, JH,H = 8.0 Hz, 1
0.0229, 0.0636
0.0211, 0.0521
H, 15-H), 6.69 (dd, 1 H, 14-H), 3.68 (s, 3 H, OCH3) ppm. 13C
NMR (100.6 MHz, [D6]DMSO): δ = 161.9 (C-6), 160.9 (C-8), 152.6
(C-5), 152.0 (C-13), 149.7 (C-9), 149.2 (C-1), 139.7 (C-3), 130.6 (C-
10), 127.9 (C-2), 125.8 (C-11), 124.1 123.8 (C-4, C-12), 116.4 (C-
14), 111.5 (C-15), 108.2 (C-7), 54.9 (OCH3) ppm.
0.0258, 0.0745
1.189
0.509/–0.854
0.0230, 0.0527
1.069
0.316/–0.677
Δρmax./min. /eÅ3
2
2
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|, ωR2 = [Σω(Fo – Fc )2/ΣωFo
]
2 1/2. [b]
2
2 2
GooF = [Σω(Fo – Fc ) /(n – p)]1/2
.
3e: From 2e according to the general procedure (yield 90%).
C16H10ClN5Pd·DMSO (492.27): calcd. C 43.92, H 3.28, N 14.23;
found C 44.04, H 3.33, N 14.47. 1H NMR (400.1 MHz, [D6]-
Acknowledgments
3
DMSO): δ = 11.54 (br, 1 H, NH), 9.32 (d, JH,H = 4.7 Hz, 1 H, 1-
3
3
This work was supported by the Deutsche Forschungsgemeinschaft
(DFG) through funding for the transregional collaborative research
centre 3MET (Project B2) and by the International PhD program
“Catalysis for Sustainable Synthesis (CaSuS)” funded by the
German Federal State of Lower Saxony (see www.casus.uni-
goettingen.de).
H), 9.11 (d, JH,H = 4.7 Hz, 1 H, 8-H), 8.74 (d, JH,H = 8.0 Hz, 1
3
H, 4-H), 8.73 (s, 1 H, 12-H), 8.35 (t, JH,H = 8.0 Hz, 1 H, 3-H),
3
8.13 (d, 1 H, 7-H), 7.93 (dd, 1 H, 2-H), 7.47 (d, JH,H = 8.2 Hz, 1
H, 14-H), 7.29 (d, 1 H, 15-H) ppm. 13C NMR (100.6 MHz, [D6]-
DMSO): 3e was not soluble enough to obtain a 13C NMR spec-
trum.
X-ray Structure Analyses: The crystal data and refinement param-
eters for 3a and 3d are collected in Table 2. The structures were
solved by direct methods (SIR92[19]), completed by subsequent dif-
ference Fourier syntheses, and refined by full-matrix least-squares
procedures.[20] Semi-empirical absorption corrections from equiva-
lents (multiscan) were applied.[21] The hydrogen atom bound to the
nitrogen atom N-4 was located in the difference Fourier synthesis
and was refined semifreely with the help of a distance restraint,
and its U value was constrained to 1.2 times the Ueq value of N-4.
All the other hydrogen atoms were placed in calculated positions
and refined by using a riding model.
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Received: March 7, 2014
Published Online: April 30, 2014
Eur. J. Inorg. Chem. 2014, 2618–2624
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