Mechanochemical synthesis of zirconium and hafnium phenoxyimine complexes L2MCl2 (L = N-(3,5-di-tert-butylsalicylidene)-2,3,5,6-tetrafluoroanilinate anion) and their catalytic properties in ethylene polymerization

Article abstract of DOI:10.1007/s11172-014-0631-6

A new method for preparation of zirconium and hafnium phenoxyimine complexes L₂MCl₂ (L is N-(3,5-di-tert-butylsalicylidene)-2,3,5,6-tetrafluoroanilinate anion, M = Zr, Hf) by the solid state interaction of N-(3,5-di-tert-butylsalicylidene)-2,3,5,6-tetrafluoroaniline, the corresponding metal chlorides, and sodium hydride under mechanical activation followed by heating of the activated mixture was developed. The obtained complexes have a high catalytic activity in the reaction of ethylene polymerization.

Full text of DOI:10.1007/s11172-014-0631-6

Russian Chemical Bulletin, International Edition, Vol. 63, No. 7, pp. 1533—1538, July, 2014
1533
Mechanochemical synthesis of zirconium and hafnium phenoxyimine
complexes L2МCl2 (L = Nꢀ(3,5ꢀdiꢀtertꢀbutylsalicylidene)ꢀ
2,3,5,6ꢀtetrafluoroanilinate anion) and their catalytic properties
in ethylene polymerization*
V. D. Makhaev,a L. A. Petrova,a N. M. Bravaya,a E. E. Faingol´d,a E. V. Mukhina,a A. N. Panin,a
S. Ch. Gagieva,b V. A. Tuskaev,b and B. M. Bulychevb
aInstitute of Problems of Chemical Physics, Russian Academy of Sciences,
1 prosp. Akad. Semenova, 142432 Chernogolovka, Moscow Region, Russian Federation.
Fax: +7 (495) 785 7048. Eꢀmail: vim@icp.ac.ru
bChemical Department, M. V. Lomonosov Moscow State University,
1/3 Leninskie Gory, 119992 Moscow, Russian Federation.
Fax: +7 (095) 932 8846. Eꢀmail: b.bulychev@highp.chem.msu.ru
A new method for preparation of zirconium and hafnium phenoxyimine complexes L2MCl2
(L is Nꢀ(3,5ꢀdiꢀtertꢀbutylsalicylidene)ꢀ2,3,5,6ꢀtetrafluoroanilinate anion, M = Zr, Hf) by the
solid state interaction of Nꢀ(3,5ꢀdiꢀtertꢀbutylsalicylidene)ꢀ2,3,5,6ꢀtetrafluoroaniline, the corꢀ
responding metal chlorides, and sodium hydride under mechanical activation followed by
heating of the activated mixture was developed. The obtained complexes have a high catalytic
activity in the reaction of ethylene polymerization.
Key words: phenoxyimine complexes, zirconium, hafnium, mechanochemical synthesis,
1H NMR spectra, catalysis, ethylene polymerization.
Complexes of 4 Group metals with phenoxyimine
ligands play a special role in a series of postꢀmetallocene
catalysts of olefin polymerization based on coordination
compounds of transition metals (precatalysts).1—13 Attenꢀ
tion to them is due to quite a number of unique properties
of the catalytic systems involving these compounds (FI
catalysts). For example, they are comparable or even surꢀ
pass the most active metallocene catalysts in activity in
ethylene polymerization. Various types of polyolefins were
obtained with participation of FI catalysts: ultraꢀhighꢀ
molecularꢀweight linear polyethylene (UHMWPE), lowꢀ
molecularꢀweight PE with terminal vinyl groups, highly
regular isotactic and syndiotactic polypropylene, highꢀ
molecularꢀweight atactic polypropylene, polyꢀꢀolefins,
ultaꢀhighꢀmolecularꢀweight random and block copolymers
of ethylene with propylene, ethylene copolymers with nonꢀ
bornene, and a series of other polyolefins. Among interꢀ
esting properties of catalysts of this class are the ability to
provide "living" ethylene and propylene polymerization
even at high reaction temperatures1 and the possibility to
change the catalytic properties of the phenoxyimine comꢀ
plexes due to the variation of the electronic and steric
characteristics of substituents in both the amine and pheꢀ
nol groups of the FI ligands ("tuning" to the synthesis of
polyolefin with certain characteristics).1—13 These propꢀ
erties of the phenoxyimine catalysts caused the choice of
similar compounds as objects of the present study.
The FI complexes (as many other coordination comꢀ
pounds) are usually synthesized in solution in several
steps.14,15 Processes aimed at interacting of the solid iniꢀ
tial substances in the absence of a solvent (solventless reꢀ
actions) are of great interest at present.16 Mechanical acꢀ
tivation is used in many cases to accelerate the solid state
reactions.17,18 Using this method, we earlier obtained varꢀ
ious types of coordination compounds: metal diketoꢀ
nates19; Ga and Cr acetylacetoneiminates20; cyclopentaꢀ
dienyl complexes of 3, 4, and 8 Group metals21; and Fe,
Co, and Cr bis(dicarbollyl) complexes.22 A convenient
method was developed for the preparation of triphenylmeꢀ
thylium tetrakis(pentafluoro)borate Ph3C[B(C6F5)4] wideꢀ
ly used as an initiator in metallocene catalysis, and tripheꢀ
nylcyclopropenylium tetrakis(pentafluorophenyl)borate
Ph3C3[B(C6F5)4].23
As for the reactions in solutions, in the case of solid
state synthesis optimization is required for the goals of
selecting optimal conditions (solvent, reactant ratio, duꢀ
ration, temperature of the process, etc.), for thorough studꢀ
* Dedicated to Academician of the Russian Academy of Sciences
O. N. Chupakhin on the occasion of his 80th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1533—1538, July, 2014.
1066ꢀ5285/14/6307ꢀ1533 © 2014 Springer Science+Business Media, Inc.

1534
Russ.Chem.Bull., Int.Ed., Vol. 63, No. 7, July, 2014
Makhaev et al.
ies on the selection of the activating device with the correꢀ
sponding energy potential, determination of the optimum
ratio "activating filling/useful load (overall weight of actiꢀ
vated compounds)," elucidation of the necessity and
choosing the regime of the subsequent thermal treatment
of an activated mixture, and optimization of other paramꢀ
eters. They are needed in each particular case for the solid
state synthesis reactions using mechanochemical activaꢀ
tion to establish the principal possibility of the synthesis,
optimize the process, and prevent mechanical destruction
of the starting compounds. The use of solid state methods
allows one to exclude the application of solvents in the
synthesis, obtain nonꢀsolvated products, reduce the amount
of waste, and thus enhance ecological compatibility of the
process.17
In this work, we describe a new method for the syntheꢀ
sis of zirconium and hafnium chloride complexes with
Nꢀ(3,5ꢀdiꢀtertꢀbutylsalicylidene)ꢀ2,3,5,6ꢀtetrafluoroaniliꢀ
nate ligands L2MCl2 by the solid state interaction of zirꢀ
conium or hafnium tetrachlorides, ligand, and sodium hyꢀ
dride under the mechanochemical activation conditions.
The results of studying the catalytic properties of the obꢀ
tained compounds in ethylene polymerization reactions
are presented. Neither synthesis, nor properties of the obꢀ
tained hafnium complex were described earlier.
result is observed for the interaction in an LH—sodium
hydride—zirconium (hafnium) tetrachloride ternary system.
Thus, it was found that the chemical reaction occurred
upon the mechanical action on the reaction mixture.
To reveal the optimum conditions for the synthesis of
target products, we studied the influence of the activation
time, ratio of reagents (from 1 : 1 : 1 to 2 : 2 : 1), and paraꢀ
meters of heating of activated mixtures on their catalytic
activity in ethylene polymerization.
Along with the reflections of sodium chloride, the difꢀ
fraction patterns contain a broad hump at 2  20, indiꢀ
cating that the mixtures include an Xꢀray amorphous phase
(Fig. 1). The nature of this phase remains unclear, but we
tend to consider it as some intermediate substance rather
than desired complex L2MCl2 (M = Zr, Hf). This viewꢀ
point is substantiated by the fact that the mixture obtained
by mechanical activation exhibits no catalytic activity in
ethylene polymerization and dichloride complexes L2MCl2
cannot be isolated from this mixture by extraction with an
organic solvent. To induce the catalytic activity, the obꢀ
tained mixture should be heated to ~150 C. However, no
reflections from the expected complex L2MCl2 (M = Zr,
Hf) or from any other substances, except for sodium chlorꢀ
ide, appear before or after heating; i.e., the reaction prodꢀ
uct still remains in the reaction mixture in the Xꢀray amorꢀ
Results and Discussion
I (rel. units)
a
12000
The influence of conditions of the mechanical action
on LH—sodium hydride and LH—sodium hydride—zirꢀ
conium (hafnium) tetrachloride mixtures (LH is (3,5ꢀdiꢀ
tertꢀbutylsalicylidene)ꢀ2,3,5,6ꢀtetrafluoroaniline) using
a ball vibromill was studied to reveal the stability of the
used substances under mechanical load and establish the
principal possibility of the synthesis followed by the optiꢀ
mization of mechanical activation parameters. It was
found, as a result, that the reaction is very sensitive to the
purity and ratio of the initial reagents. Traces of the solꢀ
vent (petroleum ether) in phenoxyimine, which is used for
the recrystallization of LH, lead to the inhibition of the
reaction. When using pure reagents for the treatment of an
LH—sodium hydride mixture at a reagent ratio of 1 : 1,
the color of the substance changes from white to yellow
just after 10 min of activation. The diffraction pattern
of the activated mixture shows a decrease in the reflection
intensity of the initial reagents and the appearance of new
reflections corresponding to the formation of (3,5ꢀdiꢀtertꢀ
butylsalicylidene)ꢀ2,3,5,6ꢀtetrafluoroaniline sodium salt.
After 1 h of mechanical treatment, the reflections of the
starting substances almost completely disappear. Upon
the addition of a zirconium or hafnium tetrachloride to
the obtained reaction mixture followed by the mechanical
action for 1—2 h, the reflections of the sodium salt of the
ligand disappear from the diffraction pattern and easily
identified reflections of sodium chloride appear. A similar
8000
4000
1250
b
1000
750
500
250
1250
c
1000
750
500
250
750
500
250
d
20
40
60
80 2/deg
Fig. 1. Diffraction patterns of the initial substances and reaction
mixtures: а, LH; b, NaH; c, mixture LH + NaH after mechanical
activation for 1 h; d, mechanically activated mixture LH + NaH
after ZrCl4 addition and mechanical activation for 1 h.

Mechanochemical synthesis of phenoxyimines
Russ.Chem.Bull., Int.Ed., Vol. 63, No. 7, July, 2014
1535
phous state. Nevertheless, the fact of formation of phenꢀ
oxyimine complexes L2MCl2 was reliably established when
studying the NMR spectra of the solutions obtained after
the extraction with hexane of the activated mixtures heatꢀ
ed to 150 С and was confirmed by the elemental analysis
data for the products isolated from the solutions.
The IR spectra of the zirconium and hafnium comꢀ
plexes are nearly identical; i.e., the nature of the metal in
the studied frequency range weakly affects the shape of the
spectra. The main distinctions of the IR spectra of the
reaction products from the spectrum of the initial LH are
that the intensity of the absorption band at 1619 cm–1
probably corresponding to vibrations of the C=N group of
phenoxyimine24 considerably decreases and the band shifts
to 1604 cm–1. Absorption bands at 545 and 470 cm–1 apꢀ
pear in the lowꢀfrequency spectral range and can be assigned
to vibrations of M—O and M—N bonds. The diffraction
patterns of the zirconium and hafnium complexes obtained
after extraction with hexane indicate the crystalline state of
the products. The positions of reflections in the diffraction
patterns almost coincide for both complexes, indicating
their isostructural character. Unfortunately, we failed yet
to grow crystals for Xꢀray structure analysis.
It follows from the NMR spectral data that the purꢀ
est complexes L2MCl2 are formed by the activation of
LH—NaH—MCl4 mixtures (M = Zr, Hf; LH is (3,5ꢀdiꢀ
tertꢀbutylsalicylidene)ꢀ2,3,5,6ꢀtetrafluoroaniline) with the
ratio LH : МCl4 = 1 : 1 rather than 2 : 1 as it is required by
their stoichiometry. The same mixtures exhibit the highꢀ
est catalytic activity in polymerization. The observed deꢀ
pendences of the run of the process and purity of the prodꢀ
ucts on the reagent ratio and the necessity in the step of
heating the activated mixture indicate a complicated
mechanism of the solid state reaction, which needs further
studies. As can be seen from the presented NMR spectra,
the nature of the metal (Zr or Hf) exerts an insignificant
effect on the electron density distribution in the protonꢀ
containing groups of the ligands in the considered comꢀ
plexes. The assignment of signals in the 1H NMR spectra
of the zirconium and hafnium complexes (Fig. 2, c, d)
corresponds to the numeration of atoms presented in the
formula of L2MCl2. The fragments of the 1Н NMR specꢀ
tra of the initial phenoxyimine LH (spectrum a) and the
corresponding titanium complex (spectrum b) described
earlier25 are presented in Fig. 2 for comparison. It should
be mentioned that for all three complexes of the triad (Ti,
Zr, Hf) the maximum upfield shifts compared to the startꢀ
ing LH are observed in the 1H NMR spectra for protons of
the groups arranged most closely to the complexꢀforming
metal, namely, for the imine proton H(1) (shift 0.62 ppm
(Ti, Zr) and 0.59 ppm (Hf)), and the protons of the tertꢀ
butyl substituent H(5) (0.13 ppm (Ti), 0.15 ppm (Zr), and
0.16 ppm (Hf)).
M = Zr, Hf
ethylene polymerization, but after heating to 150 С they
demonstrate high activity (toluene, 30 С, overall pressure
of ethylene and toluene vapor 1 atm, polymerization time
20 min, MAO as an activator (AlMAO/M = 1000 mol mol–1)).
For example, for the mixture based on zirconium chloride
the activity based on 1 mole of metal ion M (M = Zr, Hf)
is 5500 (kg of PE) (mol h atm)–1, whereas for the mixture
based on hafnium chloride this value is 1100 (kg of
PE) (mol h atm)–1. The catalytic systems based on indiꢀ
vidual complexes L2MCl2 isolated by extraction from the
heated mixtures showed a substantially higher activity:
10 200 and 2900 (kg of PE) (mol h atm)–1 for the Zr and
Hf complexes, respectively. Under analogous conditions,
the activity of the titanium complex with the same ligand
has an intermediate value of 7800 (kg of PE) (mol h atm)–1
.
The decrease in the activity in the order Zr > Ti > Hf is
typical of the most part of structural analogs of the metalꢀ
locene catalysts.1
We have earlier shown25 for the titanium and zirconiꢀ
um complexes with the same ligand that trimethylalumiꢀ
num present in MAO favors the deactivation of the cataꢀ
lyst due to the exchange reaction of the ligands of the
complexes with TMA. Probably, similar reactions occur
in the course of polymerization involving the hafnium catꢀ
alyst. Figure 3 compares the dependences of the specific
activity of the hafnium complex when it is activated by
MAO and "dry" MAO (from which TMA was removed by
prolong evacuation). It is seen that ethylene polymerizaꢀ
tion with the activation of the catalyst by MAO is accomꢀ
panied by the gradual deactivation of the catalyst (see Fig. 3,
curve 1), whereas the catalytic system with "dry" MAO
performs the process with the stationary rate (curve 2). An
induction period (~3 min) is observed in experiment with
"dry" MAO, which probably indicates a lower efficiency of
methylation of L2HfCl2 under the action of "dry" MAO,
and the step of alkylation of the dichloride complex is the
necessary stage preceding the formation of cationic metꢀ
al—alkyl complexes, the latter being active sites leading
the polymerization process.
Thus, we developed the new (for this class of comꢀ
pounds) mechanochemical method of synthesis of the FI
complexes of 4 Group metals by the direct interaction of
As mentioned above, the mixtures obtained directly by
mechanical activation exhibit no catalytic properties in

1536
Russ.Chem.Bull., Int.Ed., Vol. 63, No. 7, July, 2014
Makhaev et al.
*
a
1.27
1.57
H(1)
H(6)
13.14
8.11
H(3)
7.61
7.62
H(2)
6.09
H(5)
*
2.09
8.0
7.5
5.0
7.0
6.5
3.0

8.0
7.0
6.0
4.0
2.0
1.0

*
H(4)
6.93
H(3)
7.63
b
H(6)
H(1)
7.49
1.24
6.92
7.64
H(5)
1.44
H(2)
6.07
*
2.09
8.0
7.5
7.0
6.5
4.0

8.0
7.0
6.0
5.0
3.0
2.0
1.0

*
7.16
c
H(6)
1.26
H(1)
7.49
H(5)
1.42
H(4)
6.89
H(3)
7.67
H(2)
6.06
8.0
6.0
7.5
5.0
7.0
6.5
6.0

8.0
7.0
4.0
3.0
2.0
1.0

*
d
7.16
1.26
H(6)
H(5)
1.41
H(1)
7.52
7.70
H(4)
6.89
H(3)
7.71
H(2)
6.06
8.0
7.5
5.0
7.0
4.0
6.5
3.0
6.0

8.0
7.0
6.0
2.0
1.0

Fig. 2. Fragments of the 1Н NMR spectra of solutions of the initial LH (a) and titanium complex (b) in tolueneꢀd8 (see Ref. 16) and the
zirconium (с) and hafnium (d) complexes in benzeneꢀd6.
anhydrous chlorides of these metals with Nꢀ(3,5ꢀdiꢀtertꢀ
butylsalicylidene)ꢀ2,3,5,6ꢀtetrafluoroaniline and sodium
hydride followed by heating of the activated mixture and
showed that the obtained complexes have a high catalytic
activity of in ethylene polymerization.
Experimental
The starting commercial substances ZrCl4, HfCl4, and NaH
were used without additional purification. Nꢀ(3,5ꢀDiꢀtertꢀbutylꢀ
salicylidene)ꢀ2,3,5,6ꢀtetrafluoroaniline was synthesized according

Mechanochemical synthesis of phenoxyimines
Russ.Chem.Bull., Int.Ed., Vol. 63, No. 7, July, 2014
1537
Qsp/(kg of PE) (mole of Hf)–1
finely crystalline substance L2ZrCl2 was 0.26 g. The yield with
respect to the starting LH was 87% based on the amount of the
reaction mixture taken for extraction. Found (%): C, 54.78;
H, 4.97; Cl, 7.75; F, 15.05; N, 3.11; Zr, 9.28. C42H44Cl2F8N2O2Zr.
Calculated (%): C, 54.65; H, 4.60; Cl 7.68; F, 16.5; N 3.03;
Zr, 9.88. IR, /cm–1: 2958 w, 2923 m, 2854 w, 1604 m, 1588 s,
1560 w, 1546 s, 1514 vs, 1469 m, 1435 w, 1391 br.m, 1364 w,
1274 m, 1253 m, 1177 m, 1041 s, 939 s, 851 s, 777 w, 757 w,
600 w, 550 s, 470 m. 1H NMR (tolueneꢀd8), : 1.25 (s, But); 1.39
(s, But); 6.06 (m, C6F4H); 6.90 (d, Ar, J = 2.43 Hz); 7.58
(s, CH=N); 7.65 (d, Ar, J = 2.43 Hz). Xꢀray phase analysis, d/Å
(Irel (%)): 11.63 (66), 9.46 (21), 8.19 (88), 6.99 (19), 4.54 (100),
4.09 (55), 3.97 (55), 3.67 (43), 3.49 (35), 2.69 (19), 2.49 (20),
2.39 (17).
1000
800
1
600
2
400
200
Synthesis of bis[Nꢀ(3,5ꢀdiꢀtertꢀbutylsalicylidene)ꢀ2,3,5,6ꢀ
tetrafluoroanilinato]hafnium(IV) dichloride. The reaction was carꢀ
ried out similarly to the previous example using LH (0.265 g,
0.695 mmol), NaH (0.035 g, 1.46 mmol), and HfCl4 (0.225 g,
0.700 mmol). The target product was extracted with hexane
(3×25 mL) from the heated mixture (0.34 g). The yield of the
bright yellow finely crystalline substance L2HfCl2 was 0.17 g
(75%). Found (%): C, 49.39; H, 4.96. C42H44Cl2F8HfN2O2.
Calculated (%): C, 49.94; H, 4.39. IR, /cm–1: 2958 w, 2923 m,
2854 w, 1604 m, 1588 s, 1560 w, 1546 s, 1514 vs, 1469 m, 1435 w,
1391 br.m, 1364 w, 1274 m, 1253 sh, 1177 m, 1041 s, 939 s, 851 s,
777 w, 757 w, 600 w, 545 s, 470 m. 1H NMR (benzeneꢀd6),
: 1.26 (s, But); 1.41 (s, But); 6.06 (m, C6F4H); 6.89 (d, Ar, J =
= 2.43 Hz); 7.52 (s, CH=N); 7.71 (d, Ar, J = 2.43 Hz). Xꢀray
phase analysis, d/Å (Irel (%)): 11.56 (57), 9.40 (13), 8.15 (100),
6.99 (25), 5.16 (12), 4.53 (67), 4.09 (30), 3.96 (29), 3.65 (19),
3.48 (17), 2.69 (10), 2.49 (15), 2.42 (12), 2.38 (16).
5
10
15
20 t/min
Fig. 3. Specific activity of hafnium complex L2HfCl2 vs time in
ethylene polymerization for the activation of the catalyst by
MAO (1) and "dry" MAO (2). Polymerization conditions: toluꢀ
ene, 30 С, total pressure of ethylene and toluene vapors 1 atm,
and Al/Hf mole ratio = 1000.
to a described procedure.26 Hexane and benzene (reagent grade)
were distilled over lithium alumohydride in the presence of cetylꢀ
trimethylammonium bromide. Toluene was doubly distilled over
LiAlH4 in an argon atmosphere. Methylaluminoxane (MAO)
as a solution in toluene with a content of ~35 mol.% trimethylꢀ
aluminum (TMA) (Aldrich) was used as received. Ethylene
(polymerization purity) was additionally purified passing through
columns packed with activated molecular sieves 4 Å and Al2O3.
All procedures with compounds sensitive to the action of air and
moisture were carried out in a helium box or using Schlenk
technique.
The mechanical treatment of the reaction mixture was carꢀ
ried out using an eccentric vibromill (working frequency 12 Hz,
amplitude 11 mm) in stainless steel reactors with a volume of
~85 cm3. The activating filling was 20 steel balls with a diameter
of 12.3 mm and a total weight of ~150 g.
Ethylene polymerization. Polymerization of ethylene was carꢀ
ried out using an earlier described procedure.25
The obtained products were identified by the data of chemiꢀ
cal analysis and physicochemical methods of investigation. The
chemical analysis, thermal studies, and detection of diffraction
patterns and IR and NMR spectra were carried out at the Multiꢀ
user Analytical Center of the Institute of Problems of Chemical
Physics, Russian Academy of Sciences.
The Xꢀray phase analysis of the samples was carried out on
an ADNꢀ2ꢀ01 diffractometer (CuꢀK radiation, Ni filter) using
the XꢀRay program developed for the automation of the proꢀ
cesses of obtaining, processing, and analysis of data on Xꢀray
diffractometers (series DRON). The IR spectra of the initial
substances, reaction mixtures, and reaction products were recordꢀ
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 12ꢀ03ꢀ00974ꢀa).
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.
Samples for the studies were prepared as suspensions in Nujol
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a PerkinElmer Spectrum 100 FTꢀIR spectrometer in the range
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Received March 20, 2014;
in revised form June 2, 2014