Effect of trimethylaluminum on the formation of active sites of the catalytic system bis[N-(3,5-di-tert-butylsalicylidene)-2,3,5,6- tetrafluoroanilinato]titanium(IV) dichloride - MAO and catalytic isomerization of hex-1-ene

Article abstract of DOI:10.1007/s11172-011-0218-4

The transformations of bis[N-(3,5-di-tert-butylsalicylidene)-2,3,5,6- tetrafluoroanilinato]-titanium(IV) dichloride (L₂TiCl₂) occurring in toluene under the action of methylalumoxane (MAO) were studied by ¹H NMR spectroscopy. The commercially available MAO containing trimethylaluminum (AlMe₃) and MAO free of AlMe₃ (the so called "dry" MAO) were used. The catalytic transformations of hex-1-ene involving the systems L₂TiCl₂ - MAO were studied. We proposed the structures of the cationic titanium complexes formed in the absence and in the presence of hex-1-ene under the action of MAO. In the absence of olefin, neutral and cationic titanium complexes are decomposed under the action of AlMe₃ according to the exchange reaction of the complex ligand with the methyl groups of AlMe₃ to form LAlMe₂. The neutral complexes react considerably faster than the cationic ones. In the presence of olefin, decomposition of complexes under the action of AlMe ₃ is suppressed. The titanium complex activated by "dry" MAO isomerizes hex-1-ene to hex-2-ene. In the presence of large amounts of TMA (commercial MAO), this reaction does not take place.

Full text of DOI:10.1007/s11172-011-0218-4

Russian Chemical Bulletin, International Edition, Vol. 60, No. 7, pp. 1461—1468, July, 2011
1461
Effect of trimethylaluminum on the formation of active sites
of the catalytic system bis[Nꢀ(3,5ꢀdiꢀtertꢀbutylsalicylidene)ꢀ2,3,5,6ꢀ
tetrafluoroanilinato]titanium(IV) dichloride—MAO and catalytic isomerization
of hexꢀ1ꢀene
N. M. Bravaya,a E. E. Faingol´d, O. N. Babkina, L. A. Petrova, V. D. Makhaev,
a
a
a
a
b
b
b
S. Ch. Gagieva, V. A. Tuskaev, and B. M. Bulychev
aInstitute of Problems of Chemical Physics, Russian Academy of Sciences,
1
prosp. Akad. Semenova, 142432 Chernogolovka, Moscow region, Russian Federation.
Fax: +7 (496) 522 3507. Eꢀmail: nbravaya@cat.icp.ac.ru
b
M. V. Lomonosov Moscow State University, Department of Chemistry,
1
Leninskie Gory, 119992 Moscow, Russian Federation
The transformations of bis[Nꢀ(3,5ꢀdiꢀtertꢀbutylsalicylidene)ꢀ2,3,5,6ꢀtetrafluoroanilinato]ꢀ
titanium(IV) dichloride (L TiCl ) occurring in toluene under the action of methylalumoxane
2
2
1
(
MAO) were studied by H NMR spectroscopy. The commercially available MAO containing
trimethylaluminum (AlMe ) and MAO free of AlMe3 (the so called "dry" MAO) were
3
used. The catalytic transformations of hexꢀ1ꢀene involving the systems L TiCl —MAO were
2
2
studied. We proposed the structures of the cationic titanium complexes formed in the absence
and in the presence of hexꢀ1ꢀene under the action of MAO. In the absence of olefin, neutral
and cationic titanium complexes are decomposed under the action of AlMe according to the
3
exchange reaction of the complex ligand with the methyl groups of AlMe to form LAlMe . The
3
2
neutral complexes react considerably faster than the cationic ones. In the presence of olefin,
decomposition of complexes under the action of AlMe is suppressed. The titanium complex
3
activated by "dry" MAO isomerizes hexꢀ1ꢀene to hexꢀ2ꢀene. In the presence of large amounts
of TMA (commercial MAO), this reaction does not take place.
Key words: phenoxyimine complex, methylalumoxane, catalytic intermediates, hexꢀ1ꢀene,
1
isomerization, H NMR spectroscopy.
The catalytic systems based on the group IV transition
metal bis(phenoxyimine) (FI) complexes are a novel postꢀ
metallocene generation of olefin polymerization catalysts
nium diamide complex [ArN(CH ) NAr]Ti in the πꢀdoꢀ
2 3
nor solvent (toluene) when the catalyst is activated with
MAO containing up to 30 mass.% of amphiprotic (acꢀ
[
see Reviews 1—3]. These catalysts possess high activity in
cording to Lewis) trimethylaluminum (AlMe ) is characꢀ
3
1
,4—8
ethylene polymerization
pylene polymerization.9
and stereoselectivity in proꢀ
Catalytic properties of comꢀ
terized by a low activity, low molecular weight of the polyꢀ
—14
19
mer, and broadened polydispersity indices. Upon actiꢀ
plexes are easily modified by selection of an organic ligand,
transition metal, or a certain activator (coꢀcatalyst), and
that allows one to use these modifiers for the directed
synthesis of a certain polyolefin.
vation of the same catalyst in heptane or cyclohexane with
"dry" MAO containing a small amount of AlMe , the catꢀ
3
alyst exhibited a high activity in living polymerization of
propylene. We observed a negative effect of trialkylalumiꢀ
num on ethylene polymerization on the example of the
fluorinated titanium complex, viz., bis[Nꢀ(3,5ꢀdiꢀtertꢀbuꢀ
tylsalicylidene)ꢀ2,3,5,6ꢀtetrafluoroanilinato]titanium(IV)
dichloride (L TiCl ), activated with the commercial
Among the group IV postꢀmetallocene catalysts with
varying composition, the titanium FI catalysts containing
the fluorine atoms in the phenyl group of the =NPh fragꢀ
ments are of special interest. In the presence of polymethylꢀ
alumoxane (MAO), these catalysts provide the activity
in living polymerization of ethylene and propylene even at
2
2
2
0
MAO. In the presence of AlMe , retardation of the chain
3
growth occurs and lowꢀmolecularꢀweight components on
the molecularꢀweight distribution curves at the low total
value of the polydispersity index M : M = 1.3—1.4 apꢀ
1
0,11,15—18
elevated reaction temperatures.
However, the
presence of some substances in the reaction mixture can
significantly decrease the efficiency of these catalysts. Proꢀ
pylene polymerization in the presence of the chelate titaꢀ
w
n
pear. At the same time, when the catalyst was activated
with "dry" MAO under the same conditions, the ultraꢀ
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1438—1445, July, 2011.
066ꢀ5285/11/6007ꢀ1461 © 2011 Springer Science+Business Media, Inc.
1

1
462
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 7, July, 2011
Bravaya et al.
highꢀmolecularꢀweight polyethylene insoluble in 1,2,4ꢀtriꢀ
chlorobenzene at 135 °C is formed.
The important factor affecting the activity of the cataꢀ
lytic system is its stability in the presence of trialkylꢀ
aluminum. Using NMR spectroscopy on the example of
bis[Nꢀ(3ꢀtertꢀbutylsalicylidene)ꢀ2,3,4,5,6ꢀpentafluoroꢀ
anilinato]titanium(IV) dichloride activated with MAO (see
Refs 21 and 22) or the system AlMe —Ph CB(C F ) (see
3
3
6 5 4
Ref. 22), it was shown that one of the routes for deactivaꢀ
tion of titanium FI catalysts is exchange of the phenoxyꢀ
imine ligands of the complex for the methyl group of AlMe3
to give LAlMe2.
In the present work, we used H NMR spectroscopy
to study transformations of the tetrafluorinated FI
1
Fig. 1. Atomic numbering scheme in the H NMR spectra in the
ligand L on the example of L2TiCl2.
1
catalyst), and catalytic intermediates that formed in the
presence of hexꢀ1ꢀene is given in Fig. 1 on the example of
L TiCl .
The H NMR spectra of the ligand and precursor in
tolueneꢀd contain narrow wellꢀresolved signals (Table 1).
catalysts based on bis[Nꢀ(3,5ꢀdiꢀtertꢀbutylsalicylidene)ꢀ
2
2
2,3,5,6ꢀtetrafluoroanilinato]titanium(IV) dichloride, which
1
occur in toluene in the presence of the commercial MAO
and "dry" MAO, as well as catalytic isomerization of hexꢀ
8
1
In the H NMR spectrum of the precursor, the greatest
1
ꢀene to hexꢀ2ꢀene under the action of this system.
shifts compared to those of the free ligand are observed for
the signals of the groups that are the most closely adjacent
to the complexing metal, namely, for the singlet signals of
the imine proton and the signals of the protons H(5) of the
tertꢀbutyl groups (Table 1). The doublet signal of the aroꢀ
matic proton H(3) and the singlet signal of the protons
H(6) of the tertꢀbutyl group are slightly shifted to the lowꢀ
er field. For the signal of aromatic protons H(2), a small
shift to the higher field was observed.
Experimental
Tolueneꢀd (Aldrich) and hexꢀ1ꢀene dried by multiple disꢀ
8
tillation over activated molecular sieves (4Å), the commercially
available MAO (Aldrich) as a 10 wt.% solution in toluene (hereꢀ
after referred to as MAO) were used in the work. "Dry" MAO
(
the content of AlMe is about 5%) was prepared by evacuation
3
of MAO at room temperature for 8 h followed by dissolution of
the dry glassy product in tolueneꢀd . The precursor (L TiCl )
Reactions of the ligand LH with MAO. The main deꢀ
activation products of the catalytic systems involving strucꢀ
turally similar titanium and zirconium FI catalysts under
the action of TMAꢀcontaining activators, such as MAO or
AlMe —Ph CB(C F ) , are the products of exchange of
8
2
2
and the ligand were synthesized according to the described proꢀ
cedure.23
All procedures for the preparation of the starting reagents
and reaction products were performed under dry argon using the
standard operation technique in the inert atmosphere, 5 mm
NMR tubes with rubber septa, gastight syringes, and glass vacuꢀ
um assembly. Reagents were mixed in NMR tubes and the liquid
components of the systems under study were introduced through
septa by means of gastight syringes. The measurements were
performed both immediately after mixing reagents (2—3 min)
and after a time interval specified in the text.
1H NMR spectra were recorded with a DPXꢀ200 (Bruker)
spectrometer (200.13 MHz) at room temperature (20 °C). The
chemical shifts are given in the δ scale relatively to the signals of
residual protons in a deuterated solvent (δH 2.09).
3
3
6 5 4
the oxoimine ligand by the methyl groups of AlMe . This
3
reaction is evidenced by the appearance of the complex
2
1—24
LAlMe in the reaction mixture.
A reference comꢀ
2
pound, LAlMe , required for the assignment of the signals
2
in the NMR spectra of a multicomponent system using
our precursor was synthesized by the reaction of the ligand
LH with both MAO containing about 35 mol.% AlMe3
and "dry" MAO containing about 5 mol.% AlMe . In
3
the first case, the reaction was performed in a solution of
MAO in toluene at the molar ratio AlMAO : LH = 20 : 1
ESR spectra were recorded with a SE/X 2544 (Radiopan)
(
AlAlMe3 : LH ≈ 7 : 1). In the second case, the reaction was
–2
–1
instrument for the systems L TiCl —MAO ([Ti] = 2•10 mol L
,
2
2
carried out in a solution of "dry" MAO in deuterated toluꢀ
the molar ratio Al
: Ti = 50 : 1) at room temperature. The
contents of the Ti paramagnetic complexes were determined
by comparison of the second integrals of the signals of Ti with
those of the organic radical TEMPO.
MAO
III
ene at AlMAO : LH = 30 : 1 (Al
: LH ≈ 1.5 : 1).
AlMe3
1
III
In both cases, in the H NMR spectra, the signals of
the protons of the starting ligand disappear and an identiꢀ
cal set of novel signals assigned to LAlMe2 appear among
the reaction products. After the reaction of "dry" MAO
with LH, the signal intensity of the methyl groups of the
Results and Discussion
residual AlMe decreases significantly, while the broad
3
The starting dichloride complex. Numbering scheme of
1
IV
the atoms in the H NMR spectra of the Ti dichloride
complex (catalyst precursor), reaction products of the
ligand (LH) with MAO, the precursor with MAO (preꢀ
Hereinafter in the text and in Figs 3—6, the signals assigned to
LAlMe are designated by the symbol "*".
2

Effect of AlMe on hexꢀ1ꢀene isomerization
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 7, July, 2011
1463
3
1
Table 1. The chemical shifts of the protons in the H NMR spectra (tolueneꢀd ) of the ligand (LH), complex (L TiCl ), product of the
8
2
2
LAlMe ligand exchange, and cationic complexes 1—3 formed under the action of MAO in the absence and presence of hexꢀ1ꢀene
2
Compound or system
Complex
δ (J/Hz)
H(3)
H(1)
s)
H(2)
(m)
H(4)
(d)
H(5) H(6)
(s) (s)
(
(d)
LHa
8.11
7.48
7.31
7.31
8.20
7.31
6.09
6.07
6.08
6.08
6.17
6.08
7.61
J = 2.0)
7.63
J = 2.3)
7.66
J = 2.2)
7.66
(J = 2.2)
8.01
J = 2.0)
7.66
J = 2.2)
7.83
7.79
—b
1.56 1.26
1.44 1.24
1.43 1.21
1.43 1.21
1.51 1.26
1.43 1.21
(
(
(
L2TiCl2
LAlMe2
6.92
(J = 2.5)
6.72
(J = 2.0)
6.72
L TiCl —MAO
LAlMe2
2
2
(
"dry" MAO)
(J = 2.0)
7.37
L Ti Me...XMAO (1)c
+
–
2
(
(
L TiCl —hexꢀ1ꢀene—MAO
LAlMe2
6.72
2
2
(J = 2.0)
+
–
b
—b
—b
b
L Ti Me...(hexꢀ1ꢀene)...XMAO (2)7.95
6.33
6.39
—
—
2
+
–
d
b
b
L TiCl —hexꢀ1ꢀene—"dry" MAO
L Ti Y...XMAO (3)
7.95
—
—
2
2
2
a
b
The signal of the OH group of the free ligand LH is observed at δ 13.13. The signal overlaps with the signals of toluene and the
signals of the other components of the catalytic system. c X = Cl, Me. d Y is alkyl, allyl, or H.
signal of the methyl groups of MAO shows no changes
Fig. 2). This fact allows one to conclude that the methyl
nals of the protons of the reaction products overlapped in
the first case with signals of toluene.
(
groups of AlMe react more readily with the ligand as
In the systems involving L TiCl , MAO and "dry"
3
2
2
compared with the methyl groups of MAO.
MAO, cationic complexes of the same structure are
formed. In the aromatic region of the spectrum obtained
immediately after mixing L TiCl with MAO (or "dry"
Systems L TiCl —MAO, L TiCl —"dry" MAO. In
2
2
2
2
some instances, the reaction products of the titanium
dichloride complex with MAO and "dry" MAO (AlMAO : Ti
2
2
MAO) two sets of signals were observed. One of them
≈
70 : 1) were analyzed immediately after mixing reagents
is attributable to the complex LAlMe (see Table 1) and
2
or after 1 h following the preparation of the system. In
other cases when the changes in the spectra were slow, the
analysis was conducted several hours later. Since MAO is
used in reactions as a solution in toluene, in a series of
experiments some signals of the products and the solꢀ
vent signals overlap. Solution of preꢀcatalysts obtained
in the reactions of the precursor with the "dry" MAO were
the second one — to a novel titanium complex, which in
the low field exhibits a broad singlet of the imine proton
H(1), doublets of the aromatic protons H(3) and H(4)
(see Table 1 and Fig. 3, a, c). The multiplets of the protons
H(2) and H(2*) overlap in the region of δH 5.8—6.3.
In the system containing a solution of MAO in toluene,
the signals of H(4), H(1*), and H(4*) are overlapped
by the signals of the aromatic protons of toluene. The
low field signals of the novel titanium complex are apparꢀ
analyzed in tolueneꢀd , which revealed the low field sigꢀ
8
+
–
ently related to the cationic complex L Ti Me...XMAO
2
AlMe3
(
1, X = Cl, Me). The low field shifts of all signals comꢀ
pared to the signals of starting dichloride complex provide
evidence in favor of this fact (see Table 1). In addition, for
the system L TiCl —"dry" MAO in the high field spectral
MAO
2
2
region, we observed the signal at δH 1.98 (see Fig. 3, c)
with integral intensity 1.5ꢀfold higher than that of the
signal of the proton H(3) of complex 1, which supports its
assignment to the protons of the methyl group linked to
the titanium atom.
1
2
0
.05
–0.15
–0.35
–0.55
–0.75
δ
In the case of the reaction product of L TiCl with
2
2
1
MAO, the ratio of the signal intensities for the protons
H(3) and H(3*) measured immediately after mixing reꢀ
agents was close to 1 : 2. Considering that, the titanium
Fig. 2. Fragments of H NMR spectra of "dry" MAO (1) and the
product of its reaction with LH (2) at the molar ratio of
AlMAO : LH = 30 : 1 (AlAlMe3 : LH ≈ 1.5 : 1).

1
464
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 7, July, 2011
a
Bravaya et al.
b
H(3*)
H(3) H(3*)
H(2), H(2*)
H(2*)
6.0
H(1)
8
.4
8.0
7.6
6.4
6.0
5.6 δ
8.4
8.0
7.6 6.4
5.6 δ
c
H(4),
H(1*)
H(3)
8.0
Ti*—Me
H(4*)
H(2), H(2*)
H(1)
H(3*)
7.6
8
.4
7.2
6.8
6.4
6.0
2.32 2.16 2.00
δ
d
H(1*)
H(3*)
H(4*)
6.8
Ti*—Me
H(2*)
H(3)
8.0
8
.4
7.6
7.2
6.4
6.0
2.32 2.16 2.00 δ
1
Fig. 3. Fragments of H NMR spectra of the systems L TiCl —MAO (a, b) and L TiCl —"dry" MAO (c, d) recorded immediately after
2
2
2
2
mixing (a, c) and 4 h (b, d) after mixing reagents. The spectra (a, b) were recorded in toluene, the spectra (c, d) were recorded in
+
tolueneꢀd . The signals H(1)—H(3) ascribed to the cationic complex L Ti Me...XMAO (1, X = Cl, Me).
8
2
complex 1 has two ligands and LAlMe has one ligand,
viz., LAlMe (see Fig. 3). Taking into account that AlMe
2
2
3
such a ratio suggests that about 65% of the titanium comꢀ
is a strong Lewis acid, one can expect that the attack of
plex undergoes ligand exchange with AlMe during the
AlMe , which results in degradation of neutral and catꢀ
3
3
preparation of the complex (several minutes). During next
ionic complexes, occurs at the oxygen atom of the ligand
bearing a lone pair of electrons.
4
h, complex 1 quantitatively changes its ligands with the
methyl groups of AlMe to form LAlMe , which is reflectꢀ
The detailed mechanism of transformation of preꢀcatꢀ
alysts requires additional studies; however, based on the
experimental data (Scheme 1) one can even now make
some assumptions. The processes occurring in the system
L TiCl —MAO can be divided into relatively fast and slow.
3
2
ed in a slow disappearance of the signal of the proton H(3)
of the complex and an increase in the intensity of the
signal of the proton H(3*) (see Fig. 3, a, b).
In the reaction product of L TiCl and "dry" MAO,
2
2
2
2
the intensity ratio of the signals of H(3) and H(3*) meaꢀ
sured after the interval required for the sample preparation
is 3 : 1, which corresponds to the transformation of only
During the first minutes of the reaction, LAlMe and
2
+
L Ti Me...XMAO (1) form due to fast processes. The forꢀ
2
+
mation of the cationic complex L Ti Me...XMAO (1)
2
2
5 mol.% of the starting preꢀcatalyst. These values can
should be preceded by the formation of the alkylated inꢀ
1
presumably be explained by a lower concentration of AlMe3
in "dry" MAO. However, 4 h after the preparation of the
system with "dry" MAO all signals of preꢀcatalyst 1, as
well as the signal of the Ti—Me group disappear and the
spectrum exhibits only the signals of the reaction product,
termediate [L TiMeX], whose identification by H NMR
2
spectroscopy failed. The reason can be found in a high rate
of the subsequent fragmentation. It is possible that dimeꢀ
thylation occurs in our system, i.e., in complex 1 (X = Me).
2
2
For example, according to the literature the complex
Scheme 1
X = Cl, Me
P are the decomposition products of the precursors and preꢀcatalyst

Effect of AlMe on hexꢀ1ꢀene isomerization
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 7, July, 2011
1465
3
+
–
[
L TiMe(S)] [MeMAO ], where S is the solvent moleꢀ
small shifts to higher field compared to the signals of the
cationic complex 1 were observed (see Table 1). A higher
stability of the neutral complexes in the presence of olefin
can be seen in a much lower content of the ligand exꢀ
2
cule, forms in the presence of the structurally close comꢀ
plex, bis[Nꢀ(3ꢀtertꢀbutylsalicylidene)ꢀ2,3,4,5,6ꢀpentaꢀ
fluoroanilinato]titanium(IV) dichloride, under the action
of MAO. The formation of LAlMe can occur by ligand
change product, viz., LAlMe (the signal of H(3*)), in the
2
2
exchange of AlMe with both dichloride and alkylated
ternary system than in the binary one. The conversion of
this complex in the system with hexꢀ1ꢀene observed 1 h
after mixing components was only about 15 mol.% comꢀ
pared to 65 mol.% in the analogous system without hexꢀ1ꢀ
ene. No changes in the intensities of the signals of the
3
forms of the titanium complex. The cationic complex deꢀ
composes slowly (for several hours) under the action of
AlMe to give LAlMe , which was the only detected deacꢀ
3
2
tivation product. Thus, the neutral complex decomposes
much faster than the cationic one. Decrease in the amount
proton H(3*) of LAlMe and cationic titanium complexes
2
of AlMe with a use of "dry" MAO leads to a decrease in
the decomposition rate of both the neutral preꢀcatalyst
were observed for 5 h of monitoring (see Fig. 4), which
evidences a high stability of the latter in the presence of
a higher olefin. No significant transformations of hexꢀ1ꢀene
in the presence of this catalytic system were observed for
a longer interval of time. It was only 5 h after mixing
reagents, when trace amounts of hexꢀ2ꢀene formed in
a solution. It should be noted that the chemical shifts of
the protons of the cationic complexes formed in the binary
and ternary systems are significantly different and the catꢀ
ionic complex shows a higher stability in the presence of
hexꢀ1ꢀene. In addition, no catalytic transformations of
αꢀolefin occur in these systems in contrast to the system
with "dry" MAO (see below). All these facts imply that the
complex formed under these conditions is the olefinꢀsepaꢀ
3
and cationic complex, i.e., it is AlMe that results in deꢀ
3
composition of preꢀcatalysts.
The results outlined above agree with the NMR specꢀ
tral data of the reaction products for the structurally close
titanium complexes with MAO.2
1,22
It was found that durꢀ
ing the reaction mononuclear cationic complexes are
formed followed by ligand exchange of the cationic comꢀ
plex with the methyl group of AlMe to give LAlMe .
3
2
According to our data, neutral titanium complexes more
readily involved in the exchange reaction L—Me comꢀ
pared with the cationic ones.
Another deactivation pathway of the catalytic system is
IV
+
–
also possible, which is associated with the reduction of Ti
rated ion pair L Ti Me...(hexꢀ1ꢀene)...MeMAO (2).
2
III
to Ti (see Ref. 22). To check this assumption, we studied
A specific feature of this system includes the presence of
–
2
–1
the systems L TiCl —MAO ([Ti] = 1.4•10 mol L
,
2
2
Al : Ti = 50 : 1) and L TiCl —hexꢀ1ꢀene—MAO ([Ti] =
=
2
2
1.5•10– mol L , Al : Ti = 50 : 1, hexꢀ1ꢀene : Ti = 50 : 1).
2
–1
C6ꢀ1
a
The organic radical TEMPO was used as the reference.
It was found that 2 h after preparation, the concentration
of paramagnetic compounds containing the Ti atoms
H(1)
H(3)
H(3*)
C6ꢀ2
H(2), H(2*)
III
(
g = 1.968) did not exceed 2 mol.% in both systems. Thereꢀ
IV
fore, one can assume that if the reduction of Ti under the
experimental conditions nevertheless occurs, compounds
with an oxidation state less than Ti are formed. Such
8
.0
7.6 6.4
6.0
5.6
5.2 4.8
δ
III
b
reduction can involve neutral titanium complexes, for exꢀ
ample, via the formation of thermally unstable methyl
derivatives, e.g., tetramethyltitanium, which decomposes
at –78 °C.2 However, we failed to obtain a direct confirꢀ
mation of this assumption.
4
8
.0
7.6 6.4
6.0
5.6
5.2 4.8
δ
Systems L TiCl —hexꢀ1ꢀene—MAO and L TiCl —
2
2
2
2
hexꢀ1ꢀene—"dry" MAO. Hexꢀ1ꢀene was used to elucidate
the role of a πꢀdonor in the formation of a true catalyst
and its catalytic transformations in the presence of MAO
and "dry" MAO. The molar ratio hexꢀ1ꢀene : Ti was about
c
20 : 1 in all experiments. The ternary systems were moniꢀ
tored at the same time intervals as in the analysis of the
binary systems discussed above.
8
.0
7.6 6.4
6.0
5.6
5.2 4.8
δ
1
Fig. 4. Fragments of H NMR spectra of the systems L TiCl —
hexꢀ1ꢀene—MAO recorded 1 (a), 2 (b), and 5 h (c) after
the sample preparation. Hexꢀ1ꢀene : Ti = 20 : 1. The signals
H(1)—H(3) ascribed to the cationic complex L Ti Me...(hexꢀ
1
2
2
The H NMR spectrum of a solution obtained upon
mixing the components of the system L TiCl —hexꢀ1ꢀ
2
2
ene—MAO (Fig. 4) exhibited new signals: a broadened
signal of the imine proton at δH 7.95 and a signal of aroꢀ
matic proton H(3) at δH 7.83. For both these signals,
+
2
1ꢀene)...XMAO (2). Here and in Figs 4 and 5 C ꢀ1 is hexꢀ1ꢀene
6
and C ꢀ2 is hexꢀ2ꢀene.
6

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Bravaya et al.
hexꢀ1ꢀene in the coordination sphere of the complex that
hinders the exchange reaction of the phenoxyimine ligands
bulky hexꢀ1ꢀene, the predominant catalytic reaction
is isomerization proceeding at a low rate rather than insertion.
We observed slight differences in the values of the
chemical shifts of the protons of the complexes with MAO
and "dry" MAO in the presence of hexꢀ1ꢀene and isomerꢀ
ization of hexꢀ1ꢀene on the system with "dry" MAO as
well. These facts when combined with commonly acceptꢀ
ed concepts of the mechanism of olefin isomerization via
formation of the metalꢀalkyl or allyl complexes,26 the
structure of the cationic titanium complex can be repreꢀ
of the complex with the methyl groups of AlMe and,
3
thereby, provides its enhanced stability. It is also of note
that a probable coordination of AlMe to the oxygen atom
3
of the phenoxyimine ligand is likely to prevent catalytic
transformations of hexꢀ1ꢀene.
In the system L TiCl —hexꢀ1ꢀene—"dry" MAO, the
2
2
chemical shifts of the signal of the protons H(1)—H(3) in
the formed cationic complex 3 (see Table 1) are close to
those of complex 2. One can note only a small high field
shift of the signal of H(3) (ΔδH = 0.04 ppm) and a low
field shift of the signal of H(2) (ΔδH = 0.06 ppm) comꢀ
pared to the corresponding signals of complex 2. Trace
+
–
sented as the ion pair L Ti Y...XMAO (3), where Y is an
2
alkyl, hydride, or allyl group. The Ti—H bond formation
is caused by hydride shift observed during isomerization.
The effect of the AlMe content in MAO on the effiꢀ
3
amount of complex LAlMe was detected even 24 h after
ciency of hexꢀ1ꢀene isomerization is shown in Fig. 6. Three
2
the preparation of the system (Fig. 5, a—c).
types of MAO with different content of AlMe were used
3
A significant feature of the catalytic system with a low
for activation of the complex (see Fig. 6, a). The time
interval of isomerization of hexꢀ1ꢀene was 4 h in each
experiment. It is seen from Fig. 6, b that an increase in the
content of AlMe is its ability to isomerize hexꢀ1ꢀene to
3
hexꢀ2ꢀene (see Fig. 5, d—f). Catalytic activity of the sysꢀ
tem L TiCl —"dry" MAO in the reaction with hexꢀ1ꢀene
content of AlMe is accompanied by a decrease in the
2
2
3
was evaluated by the integral intensities of the signals of
hexꢀ1ꢀene and hexꢀ2ꢀene taking into account the duration
of the reaction. It was revealed that at the initial reaction step,
efficiency of isomerization. It is obvious that AlMe preꢀ
vents isomerization, for example, due to the outersphere
coordination in the cationic complex. To reveal the nature
3
–1
catalytic activity was about 0.3 mol ((mol Ti) min [C H ])
of catalytic intermediates and channels of AlMe influꢀ
6
12
3
and it decreases exponentially with time as hexꢀ1ꢀene
undergoes transformation. This catalyst exhibits a very
high activity in the ethylene polymerization
ence more detailed studies are required.
In conclusion, we can discuss the results outlined
above. They show a specific role of the titanium phenoxyꢀ
imine complex in the formation of active sites under the
action of MAO. We found also that the complex is unstaꢀ
–
1
(
~60000 mol ((mol Ti) min [C H ]) ), but much lower
2 4
activity
in
the
propylene
polymerization
–
1 25
(
~30 mol ((mol Ti) min [C H ]) ). In the case of a more
ble in the presence of AlMe . Moreover, we succeeded to
3
6
3
H(1)
a
C6ꢀ2
b
H(3)
C ꢀ1
6
H(2)
C ꢀ1
6
8
.0 7.6 7.2
6.8
6.4 6.0
δ
6.0 5.8 5.4 5.2 5.0 4.8
δ
c
d
8
.0 7.6 7.2
6.8 6.4 6.0 δ
6.0 5.8 5.4 5.2 5.0 4.8
δ
e
f
8
.0 7.6 7.2
6.8 6.4 6.0
δ
6.0 5.8 5.4 5.2 5.0 4.8 4.6
δ
1
Fig. 5. Fragments of H NMR spectra of the system L TiCl —hexꢀ1ꢀene—"dry" MAO recorded 1 (a, b), 5 (c, d), and 24 h (e, f) after the
2
2
+
sample preparation. Hexꢀ1ꢀene : Ti = 20. The signals H(1)—H(3) ascribed to the cationic complex L Ti Y...XMAO (3, Y = alkyl,
2
allyl, H). a, c, e, The region of the signals of complex 3; b, d, f, the region of the signals of the double bond in hexenes.

Effect of AlMe on hexꢀ1ꢀene isomerization
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 7, July, 2011
1467
3
a
C ꢀ2
b
AlMe3
6
3
1
2
2
*
3
1
0
.2
0
–0.2
–0.4
–0.6
δ
5.9
5.7
5.5
5.2
5.1
4.9
δ
1
Fig. 6. a, Fragments of H NMR spectra of MAO samples containing 35 (1), 25 (2), and 5 mol.% of AlMe (3). The symbol «*»
3
1
designates the signal of protons of methane. b, The region of the signals of the double bonds in hexenes in the H NMR spectra of the
catalytic system L TiCl —hexꢀ1ꢀene—MAO at the content of AlMe in MAO equal to 35 (1), 25 (2), 5 mol.% (3). The reaction
2
2
3
time is 4 h.
disclose specific catalytic properties of the complex in
the transformation of hexꢀ1ꢀene and evaluate the effect
tion of the precursor with MAO free of AlMe , hexꢀ1ꢀene
3
isomerizes selectively to hexꢀ2ꢀene. If AlMe presents in
3
of AlMe on the catalytic processes. The reactions of
the amount of 35 mol.% (commercial MAO), this process
is inhibited.
3
L TiCl with MAO at room temperature at the molar raꢀ
2
2
tio Al : Ti = 70 : 1 proceed along two parallel routes. The
first route is deactivation and it is realized in the presence
The authors are grateful to V. I. Shestov (Institute of
Physiologically Active Substances, Russian Academy of
Sciences) for recording H NMR spectra.
of AlMe and absence of olefin. Under these conditions,
3
1
the exchange reaction of the phenoxyimine ligands of the
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 10ꢀ03ꢀ00926ꢀa)
and the Ministry of Education and Science of the Russian
Federation (State Contract No. 02.740.11.0646).
neutral complexes with the methyl groups of AlMe ocꢀ
3
curs followed by decomposition of methyl titanium derivꢀ
atives. The presence of hexꢀ1ꢀene hinders this exchange
reaction. The second route is activation and, under the
action of MAO, it leads to the formation of cationic comꢀ
2
2
plexes. Based on the spectral analysis and literature data ,
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in revised form April 19, 2011