Cu(II) complexes with 4,6-bis(3,5-dimethyl-1H-pyrazole-1-yl)pyrimidine, 4-(3,5-dimethyl-1H-pyrazole-1-yl)-6-(3,5-diphenyl-1H-pyrazole-1-yl)pyrimidine: Synthesis and catalytic activity in ethylene polymerization reaction

Article abstract of DOI:10.1134/S107032840708009X

The Cu(II) complexes with 4,6-bis(3,5-dimethyl-1H-pyrazole-1-yl)pyrimidine (L¹) and 4-(3,5-dimethyl-1H-pyrazole-1-yl)-6-(3,5-diphenyl-1H- pyrazole-1-yl)pyrimidine (L²) of the composition Cu₂L ¹Br₄ and Cu₂L²A₄ (A = Cl, Br), respectively, were synthesized and studied by IR and magnetochemical methods. The molecular structure of the complexes is likely to be binuclear. In the presence of cocatalysts methylaluminoxane and triisobutylaluminium, the title complexes exhibit catalytic activity in the ethylene polymerization reaction.

Full text of DOI:10.1134/S107032840708009X

ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2007, Vol. 33, No. 8, pp. 601–606. © Pleiades Publishing, Ltd., 2007.
Original Russian Text © M.B. Bushuev, V.P. Krivopalov, N.V. Semikolenova, Yu.G. Shvedenkov, L.A. Sheludyakova, G.G. Moskalenko, L.G. Lavrenova, V. A. Zakharov, S.V. Lari-
onov, 2007, published in Koordinatsionnaya Khimiya, 2007, Vol. 33, No. 8, pp. 612–617.
Cu(II) Complexes with 4,6-Bis(3,5-dimethyl-1H-pyrazole-
1-yl)pyrimidine, 4-(3,5-dimethyl-1H-pyrazole-1-yl)-6-
(3,5-diphenyl-1H-pyrazole-1-yl)pyrimidine: Synthesis
and Catalytic Activity in Ethylene Polymerization Reaction
M. B. Bushueva, V. P. Krivopalovb, N. V. Semikolenovac, Yu. G. Shvedenkova,
L. A. Sheludyakovaa, G. G. Moskalenkob, L. G. Lavrenovaa, V. A. Zakharovc, and S. V. Larionova
a Nikolaev Institute of Inorganic Chemistry, Siberian Division, Russian Academy of Sciences,
pr. Akademika Lavrent’eva 3, Novosibirsk, 630090 Russia
b Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Division, Russian Academy of Sciences, Novosibirsk, Russia
c Boreskov Institute of Catalysis, Siberian Division, Russian Academy of Sciences,
pr. Akademika Lavrent’eva 3, Novosibirsk, 630090 Russia
Received August 9, 2006
Abstract—The Cu(II) complexes with 4,6-bis(3,5-dimethyl-1H-pyrazole-1-yl)pyrimidine (L1) and 4-(3,5-
dimethyl-1ç-pyrazole-1-yl)-6-(3,5-diphenyl-1ç-pyrazole-1-yl)pyrimidine (L2) of the composition Cu2L1Br4
and Cu2L2A4 (A = Cl, Br), respectively, were synthesized and studied by IR and magnetochemical methods.
The molecular structure of the complexes is likely to be binuclear. In the presence of cocatalysts methylalumi-
noxane and triisobutylaluminium, the title complexes exhibit catalytic activity in the ethylene polymerization
reaction.
DOI: 10.1134/S107032840708009X
The design of novel catalysts for different processes several metal atoms [20]. The synthesis of binuclear
of chemical technology is a topical problem in modern
chemistry. Of great practical importance are the synthe-
ses and studies of new catalytic systems for the produc-
tion of organic polymers with the desired properties
[1, 2]. The extensive investigations are being performed
today into the catalytic activity of the 3d transition
metal complexes with the nitrogen-containing ligands,
i.e., 2,6-bis(organylimino)pyridines, α-diimines, and
bis(benzimidazoles), which in combination with cocata-
lysts (organoaluminium compounds) catalyze the poly-
merization of olefins [1–17]. The catalytic activity of
the Fe(II) and Co(II) complexes with 2,6-di(pyrazole-
2-yl)- and 2,6-di(pyrazole-1-ylmethyl)pyridines in the
presence of methylaluminoxane was reported in [18].
Previously [19], we synthesized and studied the Cu(II)
chloride and bromide complexes with pyrazolylpyrim-
idine ligand, 2-(3,5-diphenyl-1ç-pyrazole-1-yl)-4,6-
diphenylpyrimidine, and established their significant
catalytic activity in the ethylene polymerization reac-
tion in the presence of cocatalysts, methylaluminoxane
(MAO) and triisobutylaluminium (TIBA). It has been
shown for the first time that pyrazolylpyrimidine
ligands (L) are promising reagents in the synthesis of
transition metal complexes exhibiting catalytic proper-
ties. The molecules of compounds studied in [1–18]
contain only one metal atom. However, a great number
of catalytic reactions involve complexes containing
and polynuclear complexes depends significantly on
success in the synthesis of organic reagents, which can
function as the polydentate bridging ligands. Such
ligands include the earlier synthesized compound
4,6-bis(3,5-dimethyl-1ç-pyrazole-1-yl)pyrimidine (L1)
[21] and 4-(3,5-dimethyl-1H-pyrazole-1-yl)-6-(3,5-
diphenyl-1ç-pyrazole-1-yl)pyrimidine (L2), whose
synthesis is described in this work:
N
N
N
N
N
N
N
(L1)
4'
4"
N
N
N
5
2
N
N
(L2)
601

602
BUSHUEV et al.
The binuclear complex Rh(I) with L1 containing refluxed for 5 h. The reaction mixture was cooled, the
diolefine was reported in [21]. The goal of this work precipitate formed was filtered with suction, washed
was to synthesize L2 and Cu(II) complexes with L1 and with ethanol, and the product was formed almost in
L2 and to study the catalytic properties of the above quantitative yield; mp = 161.5–163°C. A high-resolu-
complexes in the ethylene polymerization reaction.
tion mass spectrum: found m/z 392.1752 [M]+. For
1
C24H20N6 anal. calcd.: M = 392.1749. The H NMR
spectrum (200.13 MHz, CDCl3), δ, ppm: 8.55 (d, 1H, J
= 1 Hz, H(2)), 8.40 (d, 1H, J = 1 Hz, H(5)), 8.10−7.92
(m, 2H, Ph), 7.51–7.32 (m, 8H. Ph), 6.82 (s 1H, H(4")),
6.02 (s, 1H, H(4')), 2.70 (s, 3H, Me(5')), 2.30 (s, 3H,
Me(3')).
Synthesis of Cu2L1Br4 (I). To a hot solution of
CuBr2 (0.45 g, 2 mmol) in 15 ml ethanol, a hot solution
of ligand L1 (0.28 g, 1 mmol) in 20 ml ethanol was
added dropwise with stirring to give red-brown bulky
precipitate. The mother solution with the precipitate
was stirred for 1.5 h on heating, the precipitate was fil-
tered with suction, washed with ethanol, and dried in
air. The yield was 0.69 g (96%).
EXPERIMENTAL
The pure grade CuCl2 · 2H2O and CuBr2, MAO
Witco Gm1H (Berghamen) (a solution in toluene with
a total content ofAl 1.8 mol/l), TIBA (a solution in hep-
tane, commercial grade) were used. The reagents
4-hydrazino-6-chloropyrimidine and 4,6-dihydrazi-
nopyrimidine were prepared by a known procedure
[22] and [23], respectively.
Synthesis of L1. A mixture of 4,6-dihydrazinopyri-
midine (2.20 g, 16 mmol) and acetylacetone (4.0 g,
40 mmol) was refluxed in 20 ml ethanol for 5 h. After
cooling, the precipitate obtained was filtered off,
washed with ethanol, and dried. The product yield was
3.90 g (93%). A high-resolution mass spectrum (the
direct introduction of a sample to the ionic source):
found m/z 450.1855 [M]+. For C31H22N4 anal. calcd.:
For C14H14Br4Cu2N6
anal. calcd., %:
Found, %:
C, 23.5; H, 2.3; Cu, 17.8; N, 11.8.
C, 22.5; H, 2.6; Cu, 17.8; N, 11.4.
1
M = 450.1844. The H NMR spectrum (200.13 MHz,
CDCl3) is identical to that reported in [21].
Synthesis of Cu2L2Cl4 (II) and Cu2L2Br4 (III). A
hot solution of L2 (0.20 g, 0.5 mmol) in 25 ml ethanol
was added dropwise with heating to a hot solution of
1.5 mmol of the corresponding Cu(II) salt (0.26 g of
CuCl2 · 2H2O, 0.34 g of CuBr2) in 5–8 ml ethanol to give
the precipitates (beige Cu2L2Cl4 and dark brown
Cu2L2Br4). The mother solutions with the precipitates
were stirred for 1–2 h with heating (the final volume of
the solution was 8–10 ml), the precipitates were filtered
with suction, washed with ethanol, and dried in air. The
yield of II was 0.29 g (88%), the yield of III was 0.40 g
(95%).
Synthesis of 4-(3,5-diphenyl-1H-pyrazole-1-yl)-
6-chloropyrimidine. A mixture of 4-hydrazino-6-
chloropyrimidine (1.44 g, 10 mmol) and dibenzoyl-
methane (2.40 g, 10 mmol) was refluxed in 25 ml etha-
nol for 12 h. The solvent was evaporated in a rotary
evaporator and the residue was passed through a col-
umn with silica gel (CHCl3eluent) The product yield
was 3.13 g (90%); mp = 143–144°C (from the hexane–
benzene mixture, 1 : 1 v/v). A high-resolution mass
spectrum: found m/z 332.0825 [M]+. For C19H13ClN4
1
anal. calcd.: M = 332.0829. The H NMR spectrum
(200.13 MHz, CDCl3), δ, ppm: 8.50 (d, 1 H, J = 0.9 Hz,
H(2)pyrimidine), 8.01 (d, 1 H, J = 0.9 Hz, H(5)pyrimidine),
7.97–7.88 (2 H, Ph), 7.52–7.35 (8 H, Ph), 6.80 (s, 1 H,
H(4)pyrazole).
For C24H20Cl4Cu2N6 (II)
anal. calcd., %:
Found, %:
C, 43.6; H, 3.0; Cu, 19.2; N, 12.7.
C, 43.6; H, 3.1; Cu, 18.7; N, 12.5.
Synthesis of 4-hydrazino-6-(3,5-diphenyl-1H-
pyrazole-1-yl)pyrimidine. A solution of 4-(3,5-
diphenyl-1H-pyrazole-1-yl)-6-chloropyrimidine (5.0 g,
15 mmol) and 3 ml hydrazine hydrate in 30 ml ethanol
was refluxed for 4 h. After cooling the solution to room
temperature, the precipitate was formed. Then, the
reaction mixture was diluted with twofold water quan-
tity and cooled in a refrigerator for a night. The precip-
itate was filtered with suction and washed with water.
The product yield was 4.80 g (98%). A high-resolution
mass spectrum: found m/z 328.1440 [M]+. For C19H16N6
anal. calcd.: M = 328.1436. A high-resolution mass
spectrum of the minor component, 3,5-diphenyl-1H-
pyrazole: found m/z 220.1007 [M]+. For C15H12N2 anal.
calcd.: M = 220.1000.
For C24H20Br4Cu2N6 (III)
anal. calcd., %:
Found, %:
C, 34.4; H, 2.4; Cu, 15.1; N, 10.0.
C, 34.5; H, 1.9; Cu, 15.0; N, 10.1.
The Cu content in the complexes was determined by
complexometric titration after decomposition of the
sample in a mixture of concentrated H2SO4 and HNO3.
The analysis for C, H, N was performed on Carlo Erba
analyzer.
The IR spectra of the samples were measured on a
Scimitar
FTS
2000
spectrophotometer
at
375−4000 cm−1 (Nujol and fluorinated oil mulls) and
on
a
BOMEM MB-102 spectrophotometer at
Synthesis of L2. A mixture of 4-hydrazino-6-(3,5- 200−400 cm–1 in polyethylene. A high-resolution mass
diphenyl-1ç-pyrazole-1-yl)pyrimidine (4.40 g, 13 mmol) spectrum was recorded on a Finnigan MAT-8200 spec-
and acetylacetone (2 g, 20 mmol) in 20 ml ethanol was trometer, electronic impact, 70 eV. The 1H NMR spec-
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 33 No. 8 2007

Cu(II) COMPLEXES
603
tra were recorded on the Bruker WP-200SY and AC- condensation of 2 with acetylacetonate in a 10% HCl solu-
200 spectrometers.
tion [23]. We prepared the above ligand using the latter
method but with boiling in ethanol in a neutral medium. In
the synthesis of 4-hydrazino-6-(3,5-diphenyl-1ç-pyrazol-
1-yl)pyrimidine (5) by the reaction of 4-(3,5-diphenyl-
1ç-pyrazole-1-yl)-6-chloropyrimidine (4) with hydrazine
hydrate, the nucleofuge lability of 3,5-diphenyl-1ç-pyra-
zole-2-yl group was observed, since a high-resolution
mass spectrum of the product contained, in addition to the
line of compound 5, the line due to the molecular ion of
3,5-diphenyl-1H-pyrazole (~3%). The latter is registered
as a major compound at the initial spectral recording,
while the intensity ratio of the observed peaks of the ions
agrees with the data of compound itself [24, 25]. The latter
is inert as the subsequent stage of the synthesis of the
ligand L2. It was also reported recently that the heating of
2-(3,5-dimethylpyrazole-1-yl)-4-methyl-5-ethoxycarbon-
ylpyrimidine with ethanol solution of hydrazine hydrate
gave 2-hydrazino-4-methyl-5-ethoxycarbonylpyrimidine
(in 82% yield) in the absence of both the product of pyri-
midine ring recyclization and hydrazine of the starting
compound [26].
The magnetic properties of the complexes were
studied on a MPMS-5s SQUID-magnetometer (Quan-
tum Design) at 2–300 K and external magnetic filed
strength of about 5 kOe. The molar magnetic suscepti-
bility (c) was calculated with the account for atomic
diamagnetism using Pascal additive scheme. The effec-
tive magnetic moment was calculated as µef
=
[(3k/NAβ2)χ T]1/2 ≈ (8χT)1/2, where k is the Boltzmann
constant, NA is the Avogadro number, and β is the Bohr
magneton.
Estimation of catalytic properties in ethylene
polymerization reaction. The verification of the cat-
alytic activity of Cu(II) complexes in ethylene poly-
merization reaction was performed in a temperature-
controlled reactor (0.2 l in volume) equipped with a
stirrer. MAO and TIBA were used as cocatalysts. The
temperature and pressure of ethylele in the course of the
reaction (1 h) were constant. The polyethylene (PE)
powder obtained was dried in air and weighed.
The complex compounds I, II were synthesized by
the reaction of Cu(II) salts with L in the ethanol solu-
RESULTS AND DISCUSSION
The starting reagents for the synthesis of pyrazolylpy- tions on heating. Taking into account the possible bridg-
rimidines L1 and L2, i.e., 4,6-dihydrazinopyrimidine (2) ing functions of L1 and L2, the molar ratios Cu : L = 2 : 1
and 4-hydrazino-6-chloropyrimidine (3), were obtained and 3 : 1 were used in the synthesis.As follows from the
by the reaction of available 4,6-dichloropyrimidine (1) chemical analysis data, the Cu : L ratio in compounds
with hydrazine hydrate. Previously, ligand L1 was synthe- I–III is 2 : 1, which suggests the binuclear structure of
sized by two methods: a) by the interaction of 1 with the the complexes. The following scheme of transforma-
sodium salt of 3,5-dimethylpyrazole [21] and b) by cyclo- tions was performed:
NH HN
2
NHNH
2
(MeCO) CH2
2
N
N
N
N
CuBr2
N
N
Cu2L1Br4
(I)
N
N
(2)
(1)
(L1)
NH2NH2
Cl
N
Cl
N
NH2NH2
NH HN
2
N
Cl
N
N
N
Cl
N
NHNH
NH2NH2
2
(PhCO)2CH2
N
N
N
N
N
(4)
(3)
(5)
(MeCO)2CH2
N
N
N
N
CuX2
2
Cu L X
2
4
(X = Cl (II), Br (III))
N
N
(L2)
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 33 No. 8 2007

604
BUSHUEV et al.
Table 1. The main vibration frequencies in IR spectra (cm–1)
of ligands L1, L2, and complexes I–III
Cl (I) and Cu–Br (I, III), for which the characteristic
relationship is fulfilled ν(Cu–Br)/ν(Cu–Cl) = 0.77–0.80.
Complexes I–III have identical magnetic properties
and therefore, the µeff(T) and χ(T) curves are plotted
only for complex III (see in the figure). At room tem-
perature, the µeff values are equal to 2.59, 2.53, and
2.45 µB for I, II, and III, respectively. As the tempera-
ture is lowered, the µeff values increase to indicate the
predominant antiferromagnetic exchange interactions
between the Cu2+ ions.
Compound
L1
Cu2L1Br4 (I) 1611, 1542
L2
1589, 1558
(ν + δ)ring
ν(Cu–N) ν(Cu–X)
1594, 1571
260
244
Cu2L2Cl4 (II) 1613, 1565, 1544, 1520
Cu2L2Br4 (III) 1612, 1564, 1542, 1519
280
262
313, 325
249
The χ(T) curves of the complexes are characterized
by the maxima (see in the figure, b). The observed mag-
netic behavior is typical of the compounds, whose
exchange clusters consist of even number of the para-
magnetic centers with the same spin. We analyzed the
relations obtained using the isotropic spin-Hamiltonian
in terms of the approach suggested in [27]. The two-
center exchange cluster was used for approximation
and the “monomer impurity” effect [28], which takes
into account the powdered state of the samples. The
obtained optimal parameters of the effective g-factor of
the Cu2+ ions, the exchange interaction (J), and the stan-
dard deviation values (σ) are listed in Table 2. The the-
oretical curves corresponding to the above parameters
agree well with the experimental curves (shown in the fig-
ure in dotted line is the theoretical curve for complex III).
If g-factor is taken to be 2.1 on the basis of the data
obtained, then the theoretical value of µeff calculated for
two practically noninteracting Cu2+ ions with the spin
S = 1/2 will be 2.57 µB, which is in a good agreement
with the experimental data for complexes I–III synthe-
sized at room temperature.
Table 2. Optimal exchange parameters of complexes I–III
Compound
g
J, cm3/mol
σ
Cu2L1Br4 (I)
2.11 0.01
–5.5 0.1
0.0184
Cu2L2Cl4 (II) 2.12 0.01 –16.3 0.1
Cu2L2Br4 (III) 2.06 0.01 –19.9 0.2
0.00341
0.00681
Complexes I–III are stable in air. They are soluble
in organic solvents, i.e., ethanol, MeCN, isopropyl
alcohol, toluene, CH2Cl2, CHCl3, and their mixtures; the
above complexes are insoluble in water.
Table 1 contains IR data for L1, L2, I–III. The posi-
tions of the stretching-bending vibrations of heterocy-
clic rings in the spectra of complexes change noticeably
On the basis of the results obtained we suggest that
as compared to the spectra of L1 and L2, which indi- the most probable variant of the structure of complexes
cated the coordination of the donor N atoms and mole- I–III is the following. The complexes have the molec-
cules L. This agrees with the presence of the stretching ular binuclear structure: the tetradentate cyclic-bridg-
vibrations of the Cu–N bonds in the low-frequency ing ligands (molecules L) are coordinated by two Cu
region. The spectra of the complexes also contain the atoms through the N atoms of pyrazole and pyrimidine
bands due to the stretching vibrations of the bonds Cu– rings:
N
N
N
N
N
N
N
Cu
X
N
Br Cu
Br
N
N
Cu
N
N
Cu
X
Br
X
X
Br
(I)
(II: X = Cl, III: X = Br)
The coordination surrounding of the Cu atoms is
Estimates of the catalytic activity of complexes
completed to a distorted tetrahedral surrounding by the I−III in the ethylene polymerization reaction are given
halide ions as in the case of the Cu(II) chloride and bro- in Table 3. Under indicated conditions, complexes
mide complexes with the analogous pyrazolylpyrimi- I−III show appreciable activity in the ethylene poly-
dine ligands [19, 29].
merization that noticeably exceeds the activity of the
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 33 No. 8 2007

Cu(II) COMPLEXES
605
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Table 3. Catalytic activity of complexes I–III in the ethylene polymerization reaction*
Conditions
Activity,
kg PE/(mol Cu h atm)
Complex
PE yield, g
cocatalyst
pC H , atm
T, °C
2
4
Cu2L1Br4 (I)
MAO
TIBA
MAO
TIBA
MAO
TIBA
MAO
10
10
10
10
10
10
35
35
35
35
35
35
0.96
1.39
1.04
1.29
1.13
1.18
0.4
48.0
69.5
52.0
64.5
56.5
59.0
4.5
Cu2L2Cl4 (II)
Cu2L2Br4 (III)
Cu(α-diimine)Cl2 [10]**
4.5
25
–5
Notes: * Polymerization conditions: 70 ml of toluene (heptane), c = 3 × 10 mol/l, molar ratio Al
/Cu = 500.
Cu
cocat
–4
** The data of [10] are listed for comparison (c = 2.0 × 10 mol/l).
Cu
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