Palladium complex of 6-(2-hydroxy-5-methylphenyl)-3-(pyridin-2-yl)-1,2,4- triazin-5(2H)-one: Synthesis, structure, and catalytic activity

Article abstract of DOI:10.1134/S1070428011090181

Palladium(II) complex with 6-(2-hydroxy-5-methylphenyl)-3-(pyridin-2-yl)-1, 2,4-triazin-5(2H)-one was synthesized for the first time. The ligand was prepared from 3-(pyridin-2-yl)-1,2,4-triazin-5(2H)-one and 4-methylphenol via nucleophilic substitution of hydrogen (S_N^H reaction). The complex was readily soluble in basic medium, and it effectively catalyzed Mizoroki-Heck reaction. Pleiades Publishing, Ltd., 2011.

Full text of DOI:10.1134/S1070428011090181

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2011, Vol. 47, No. 9, pp. 1366–1369. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © A.V. Mekhaev, A.V. Pestov, P.A. Slepukhin, Yu.G. Yatluk, M.G. Pervova, M.A. Samorukova, O.N. Chupakhin, 2011, published in
Zhurnal Organicheskoi Khimii, 2011, Vol. 47, No. 9, pp. 1345–1347.
Dedicated to Full Member of the Russian Academy of Sciences
V.N. Charushin on his 60th anniversary
Palladium Complex of 6-(2-Hydroxy-5-methylphenyl)-
3-(pyridin-2-yl)-1,2,4-triazin-5(2H)-one: Synthesis, Structure,
and Catalytic Activity
A. V. Mekhaev, A. V. Pestov, P. A. Slepukhin, Yu. G. Yatluk, M. G. Pervova,
M. A. Samorukova, and O. N. Chupakhin
Postovskii Institute of Organic Synthesis, Ural Division, Russian Academy of Sciences,
ul. S. Kovalevskoi/Akademicheskaya 22/20, Yekaterinburg, 620041
e-mail: mehaev@ios.uran.ru
Received February 4, 2011
Abstract—Palladium(II) complex with 6-(2-hydroxy-5-methylphenyl)-3-(pyridin-2-yl)-1,2,4-triazin-5(2H)-one
was synthesized for the first time. The ligand was prepared from 3-(pyridin-2-yl)-1,2,4-triazin-5(2H)-one and
4-methylphenol via nucleophilic substitution of hydrogen (SNH reaction). The complex was readily soluble in
basic medium, and it effectively catalyzed Mizoroki–Heck reaction.
DOI: 10.1134/S1070428011090181
Mizoroki–Heck reaction [1, 2], i.e., cross coupling
of aryl halides with alkenes in the presence of palla-
dium complexes (Scheme 1), has found wide applica-
tion in modern organic synthesis [3].
1,2,4-triazin-5(2H)-one and p-methylphenol via SNH re-
action [5] (Scheme 2). The reaction of H2L with PdCl2
in aqueous dimethylformamide gave the complex
Me2NH2+ [C15H11Cl2N4O2Pd]– (II). Its structure was
studied by X-ray diffraction. The complex is mono-
nuclear (see figure), the central metal ion has planar
square configuration. The coordination entity is formed
by two chlorine atoms and N,N-chelating moiety of the
ligand. The latter is deprotonated at the N2 atom, so
that the complex is anionic. The counterion is outer-
sphere dimethylammonium which is likely to be gen-
erated by partial hydrolysis of dimethylformamide
during crystallization process. Contrary to the expecta-
tions, phenolic hydroxy group is not involved in coor-
dination, as reported previously for copper(II) com-
plexes [6]. The principal bond lengths and bond angles
are given in table.
Additional analysis of the ligand structure in com-
plex II showed that all three rings therein are planar,
i.e. they are aromatic. The pyridine and triazine rings
lie in one plane and are conjugated with each other.
The substituted benzene ring deviates from that plane,
the corresponding dihedral angle being 15.49°. The
C–C bond lengths in the benzene and pyridine rings
range from 1.353 to 1.413 Å; the N–C bonds in the
triazine ring range from 1.366 to 1.376 Å.
Scheme 1.
[Pd]
–X–
R
R
X +
R'
R'
CH2
The possibility for building up new C–C bond via
simple experimental procedure makes this reaction
a powerful tool for organic chemists. It should be em-
phasized that in the past year R.F. Heck was awarded
the Nobel Prize for this reactions. Mizoroki–Heck re-
action generally implies the use of palladium com-
plexes with phosphine-containing ligands. Huang et al.
[4] recently showed that palladium complexes with
2,2′-bipyridine ligands are very efficient catalysts in
Mizoroki–Heck reaction [4]. Taking into account that
these reactions require basic medium, anionic palladi-
um complex is desirable or an acid residue should be
present in one ring of the ligand. We synthesized
a complex which met the above requirements.
The ligand, 6-(2-hydroxy-5-methylphenyl)-3-(pyri-
din-2-yl)-1,2,4-triazin-5(2H)-one (I, H2L), was synthe-
sized by us for the first time from 3-(pyridin-2-yl)-
1366

PALLADIUM COMPLEX OF 6-(2-HYDROXY-5-METHYLPHENYL)-...
1367
Scheme 2.
HO
N
HN
N
OH
CF3COOH, O2
N
Me
N
+
N
O
N
Me
N
H
O
I
HO
N
Cl Cl
Pd
PdCl2, DMF
Me2NH2
N
Me
N
N
O
II
Analysis of shortened O···O contacts showed that
the crystalline structure of complex II is stabilized by
both inter- and intramolecular hydrogen bonds. The
phenolic hydroxy proton is infolved in bifurcate intra-
molecular hydrogen bond with the N2 atom in the
triazine ring [O2–H2 0.76(4), H2···N2 1.94(4), O2···N2
2.582(4) Å, ∠O2H2N2 141(3)°] and chlorine atom
[H2 ···Cl2 2.77(4), O2 ···Cl2 3.357(4) Å, ∠O2H2Cl2
135(3)°]. The cation–anion interaction is characterized
by intermolecular hydrogen bonding between the NH
protons in dimethylammonium ion and carbonyl
oxygen atom in the neighboring molecule: N1S–H1SD
0.900, H1SD · · · O1 [–x + 2, –y + 1, –z] 1.822(4),
N1S···O1 [–x + 2, –y + 1, –z] 2.708(4) Å, ∠N1SH1SDO1
[–x + 2, –y + 1, –z] 167.6(4)°; in addition, intermolec-
ular hydrogen bond between the NH proton and Cl2
is formed: N1S–H1SE 0.900, H1SE · · · Cl2 2.394(4),
N1S···Cl2 3.229(4) Å.
acrylate with chlorobenzene. Using the reaction with
iodobenzene as model we found that the amount of
the catalyst can be reduced to 0.01 mol % without
loss in the yield. Further reduction of its amount to
0.001 mol % was accompanied by decrease of the
yield to 90% according to the GC–MS data.
Butyl acrylate reacted with substituted iodoben-
zenes (o-iodotoluene, 1-iodo-3,4-dimethoxybenzene,
and p-iodonitrobenzene) in the presence of 0.1 mol %
of the catalyst to give the corresponding substituted
butylcinnamates in quantitative yield.
We also tried 2-vinylpyridine as activated alkene.
The reaction of iodobenzene with 2-vinylpyridine
gave (E)-2-styrylpyridine in 80% yield (GC–MS;
O1
C15
C4
N3
C7
C3
C2
C12
C13
C8
C6 C5
The catalytic efficiency of the newly synthesized
complex was studied in reactions of phenyl halides
with butyl acrylate (Scheme 3). The products were
identified by GC–MS and 1H NMR. The reactions of
butyl acrylate with iodo- and bromobenzenes quanti-
tatively afforded butyl cinnamate. However, no cou-
pling product was detected in the reaction of butyl
C14
C11
N1
C9
O2
C1
N4
N2
C10
Pd1
Cl2
Cl1
c
Scheme 3.
Hlg
N1S
O
C2S
+
H2C
C1S
OBu
a
b
O
Structure of the molecule of dimethylammonium [6-(2-hy-
droxy-5-methylphenyl)-5-oxo-3-(pyridin-2-yl)-5H-1,2,4-tri-
azin-4-ido]dichloropalladate(II) (II) according to the X-ray
diffraction data.
Bu3N, DMF, catalyst
140°C, 16 h
OBu
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 47 No. 9 2011

MEKHAEV et al.
1368
Principal bond lengths and bond angles in molecule II
fragment of a single crystal on an Xcalibur 3 automatic
diffractometer (CCD detector, MoKα irradiation,
graphite monochromator). Absorption by the crystal
was taken into account analytically according to the
multifaceted crystal model [7]. Monoclinic crystal
system, space group P21/n; unit cell parameters: a =
12.9723(14), b = 7.3095(8), c = 20.859(3) Å; β =
98.991(9)°; V = 1953.6(4) Å3; C17H19Cl2N5O2Pd; Z =
4; dcalc = 1.709 g/cm3. Total of 12528 reflection inten-
sities were measured in the ranges –17 ≤ h ≤ 16, –9 ≤
k ≤ 9, –15 ≤ l ≤ 27; 4668 reflections were independent.
The structure was solved by the direct method and was
refined by the full-matrix least-squares procedure in
anisotropic approximation for non-hydrogen atoms
using SHELX-97 software package [8]. The final
refinement parameters were: S = 1.008, R1 = 0.0344,
wR2 = 0.0558 [for reflections with I > 2σ(I)] and R1 =
0.0859, wR2 = 0.0598 (for all reflections). The maxi-
mal and minimal residual electron density peaks were
0.632 and –0.382 ē/Å3.
Bond
d, Å
Bond angle
φ, deg
Pd1–Cl1
Pd1–Cl2
Pd1–N1
Pd1–N4
2.2934(9)
2.2940(9)
1.990(2)0
2.024(3)0
N4Pd1N1
Cl1Pd1N1
Cl1Pd1N4
Cl2Pd1N1
080.25(10)
175.44(8)
095.31(8)
094.48(8)
Scheme 4). However, in the reaction with p-iodonitro-
benzene the yield of 2-(4-nitrostyryl)pyridine was as
poor as 8% (GC–MS).
Scheme 4.
I
+
H2C
R
N
Bu3N, DMF, catalyst
140°C, 16 h
N
R
6-(2-Hydroxy-5-methylphenyl)-3-(pyridin-2-yl)-
1,2,3-triazin-5(2H)-one (I). Air was passed over
a period of 15 h through a mixture of 0.3 g (1.73 mmol)
of 3-(pyridin-2-yl)-1,2,4-triazin-5(2H)-one, 12 ml of
trifluoroacetic acid, and 0.187 g (1.73 mmol) of
4-methylphenol. The mixture was evaporated, the
residue was treated with 5 ml of water, and the precip-
itate was filtered off, washed with water (3×5 ml), and
dried under reduced pressure. Yield 0.158 g (33%),
R = H, NO2.
EXPERIMENTAL
1
The H NMR spectra were recorded on a Bruker
BioSpin Avance DRX-400 spectrometer at 400 MHz
using CDCl3 as solvent and tetramethylsilane as inter-
nal reference. Quantitative analysis of the products was
performed by GLC (internal normalization technique)
on a Shimadzu GC 2010 chromatograph equipped with
a flame-ionization detector and a ZB-5 capillary col-
umn, 30 m×0.25 mm, film thickness 0.25 μm (poly-
methylsiloxane containing 5% of phenyl groups);
carrier gas nitrogen, split ratio 1:30, flow rate 1.0 ml×
min–1; oven temperature programming from 40°C
(3 min) to 290°C at a rate of 10 deg/min; injector tem-
perature 280°C, detector temperature 320°C.
The products were identified by gas chromatog-
raphy–mass spectrometry using an Agilent GC
7890A–MS 5975C system (quadrupole detector); elec-
tron impact, 70 eV; HP-5MS capillary column, 30 m×
0.25 mm, film thickness 0.25 μm; carrier gas helium,
split ratio 1:50, flow rate 1.0 ml/min; oven tempera-
ture programming from 40°C (3 min) to 290°C at
a rate of 10 deg/min (20 min at the final temperature);
injector temperature 250°C, ion source temperature
230°C, quadrupole temperature 150°C, interface tem-
perature 280°C.
1
mp 247–249°C (from MeCN). H NMR spectrum
(DMSO-d6), δ, ppm: 2.07 s (3H, CH3), 6.81 m (1H,
Harom), 7.14 m (1H, Harom), 7.39 s (1H, Harom), 7.74 m
(1H, pyridine), 8.13 m (1H, pyridine), 8.36 d (1H,
pyridine), 8.84 d (1H, pyridine). Found, %: C 64.44;
H 4.54; N 19.76. C15H12N4O2. Calculated, %: C 64.29;
H 4.29; N 20.00.
Dimethylammonium [6-(2-hydroxy-5-methyl-
phenyl)-5-oxo-3-(pyridin-2-yl)-5H-1,2,4-triazin-4-
ido]dichloropalladate(II) (II). A solution of 0.0105 g
(0.06 mmol) of palladium(II) chloride in 2 ml of water
was added to a solution of 0.0166 g (0.06 mmol) of
ligand I in 5 ml of DMF. The product separated from
the resulting solution upon slow evaporation at 70°C.
Found, %: C 43.22; H 4.03; Cl 15.04, N 14.83;
Pd 22.45. C17H19Cl2N5O2Pd. Calculated, %: C 43.37;
H 4.15; N 14.64; Cl 14.86; Pd 22.06.
Reaction of iodobenzene with butyl acrylate.
Palladium complex (II), 0.001 mmol, was dissolved in
3.0 ml of DMF, 0.2040 g (1 mmol) of iodobenzene,
0.1923 g (1.5 mmol) of butyl acrylate, and 0.3707 g
(2 mmol) of tributylamine were added, and the mixture
The X-ray diffraction data for complex II were
acquired at 295(2) K from a 0.27×0.09×0.01-mm
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 47 No. 9 2011

PALLADIUM COMPLEX OF 6-(2-HYDROXY-5-METHYLPHENYL)-...
1369
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was heated for 16 h at 140°C in a sealed ampule. The
ampule was opened, the mixture was evaporated under
reduced pressure (10 mm) at 40°C, the residue was
treated with 6 ml of toluene, and the toluene extract
was washed with 3 ml of 0.5 M aqueous sodium
hydroxide and water (2×6 ml) and dried over sodium
sulfate.
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Reactions of other halobenzenes with alkenes were
carried out in a similar way.
This study was performed under financial support
by the Ural Division of the Russian Academy of
Sciences (project no. 09-S-3-1016).
7. Clark, R.C. and Reid, J.S., Acta Crystallogr., Sect. A,
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