Bis(alkylphenylaminopyridinato) titanium dichlorides as ethylene polymerization catalysts

Article abstract of DOI:10.1016/j.molcata.2007.10.029

Four titanium complexes derived from 2-(2-ethylanilino)-, 2-(3,5-dimethylanilino)pyridine, 2-(4-n-butylanilino)- and 2-(2-t-butylanilino)pyridine were synthesized and characterized by spectroscopic methods. These complexes were used to catalyze the polyme

Full text of DOI:10.1016/j.molcata.2007.10.029

Available online at www.sciencedirect.com
Journal of Molecular Catalysis A: Chemical 280 (2008) 102–105
Bis(alkylphenylaminopyridinato) titanium dichlorides
as ethylene polymerization catalysts
∗
¨
Markku Talja , Mika Polamo, Markku Leskela
Laboratory of Inorganic Chemistry, Department of Chemistry, University of Helsinki,
P.O. Box 55, Helsinki FIN-00014, Finland
Received 24 April 2007; received in revised form 24 October 2007; accepted 25 October 2007
Available online 4 November 2007
Abstract
Four titanium complexes derived from 2-(2-ethylanilino)-, 2-(3,5-dimethylanilino)pyridine, 2-(4-n-butylanilino)- and 2-(2-t-butylanilino)
pyridine were synthesized and characterized by spectroscopic methods. These complexes were used to catalyze the polymerization of ethylene
in the presence of MAO as cocatalyst. The effect of the complex structures on the polymerization behavior was studied. All the alkylpheny-
laminopyridinato titanium complexes used in this study yielded higher molar masses than the unsubstituted bis(phenylaminopyridinato) titanium
dichloride complex. Correspondingly, activities were lower and molar mass distributions were broader than those in the case of the unsubstituted
bis(phenylaminopyridinato) titanium catalyst. The fluxional behavior of alkylphenylaminopyridinato titanium catalysts is probably the reason for
the broad molar mass distributions. This might be due to the electron-donating effect from the alkyl substituent because the alkyl substituent
enhances the active site isomerization rate.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Aminopyridinato; Titanium; Polyethylene; Catalysis; Polymerization
1. Introduction
complexes on the catalytic activity in ethylene polymerization
(Fig. 1). The alkyl substituents should increase the bulkiness of
the phenyl group in the phenylaminopyridinato titanium cata-
lyst and thus should affect the length of the polyethylene chain
produced by the catalyst. We claim that in the case of alkyl
substituents the propagation/elimination ratio would increase to
produce a higher molar mass than with the unsubstituted pheny-
laminopyridinato titanium catalyst. Also, the activity should
increase if the alkyl substituent does not prevent the coordi-
nation of ethylene. Furthermore, the less bulky catalysts should
produce more branched polyethylene than the catalysts with the
more sterically demanding ligand framework.
The development of the olefin polymerization catalysts forms
one of the most impressive examples in organometallic chem-
istry. Usually, the catalytic properties of the organometallic
complexes are highly dependent on the structure of the ligand
framework around the metal centre [1–4]. As an alternative to the
metallocenes, aminopyridinato complexes have gained interest
in the field of catalysis of ␣-olefin polymerization [5,6]. Com-
monly, substituents include phenyl [7], aryl [8,9], silyl [10] and
alkyl [11] groups. Scott et al. claimed that the alkyl substituents
are better than trialkylsilyl substituents to control the stoichiom-
etry and structure of aminopyridinato complexes [10,11]. The
bis(N-adamantyl-2-aminopyridinato) zirconium dichloride used
by them produced the activity of 20 kg mol−1 h−1 bar−1 in ethy-
lene polymerization [11].
2. Experimental
2.1. Chemicals
Our aim was to study the effect of alkyl group in the phenyl
group of the bis(phenylaminopyridinato) titanium dichloride
Methylaluminoxane (30%) was acquired from Borealis Poly-
mers. Toluene (Lab Scan, an analytical grade) was refluxed
with sodium and distilled under argon. Polymerization-grade
ethylene was purchased from AGA and used without further
purification.
∗
Corresponding author. Fax: +358 9 191 50198.
E-mail address: markku.talja@helsinki.fi (M. Talja).
1381-1169/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2007.10.029

M. Talja et al. / Journal of Molecular Catalysis A: Chemical 280 (2008) 102–105
103
no gas was evolved. The yellow ether solution of sodium ami-
dopyridine was filtrated through the glass filter and then added
dropwisely to the orange toluene solution of TiCl4 (5 mmol in
40 ml) and stirred one hour at room temperature. The reaction
mixture was filtrated through Kieselguhr and the solvent was
evaporated under vacuum.
2.5. Pre-catalyst characterization
2.5.1. Bis[2-(2-Ethyl)phenylaminopyridinato]TiCl2
1H NMR (CDCl3) δ: 1.11 (t, 6H), 2.39–2.63 (q, 4H), 5.93
(d, 2H), 6.12 (d, 2H) 6.68 (dd, 2H), 7.09–7.24 (m, 6H), 7.46 (t,
2H), 7.96 (br s, 2H).
Fig. 1. Bis(alkylphenylaminopyridinato) titanium dichloride complexes: R = 2-
Et; 2-t-Bu; 3,5-Me; 4-n-Bu.
2.2. Proligand preparation
13C NMR (CDCl3) δ: 14.64, 24.30, 104.86, 114.67, 121.67,
126.27, 126.81, 129.00, 139.16, 142.16, 144.31, 147.72, 167.09.
Anal. Calc. For C26H26Cl2N4Ti C(60.84%), H(5.11),
N(10.92%). Found C(59.94%), H(5.89), N(10.15%).
2-Phenylaminopyridine is commercially available. The other
proligands were synthesized from 2-chloropyridine and from the
desired alkylaniline hydrochloride. Corresponding hydrochlo-
ride salt was made from the alkyl aniline and dried in a
vacuum. 2-Chloropyridine and the alkylaniline hydrochloride
were heated for 2 h at 180 ◦C. The resulting alkylaminopyri-
dine hydrochloride was suspended to the sodium carbonate. The
proligand was crystallized from a diethyl ether/heptane solution.
2.5.2. Bis[2-(3,5-dimethyl)phenylaminopyridinato]TiCl2
1H NMR (CDCl3) δ: 2.22 (s, 12H), 6.51 (s, 2H), 6.59 (s,
4H), 6.83-6.94 (m, 4H), 7.49 (t, 2H), 7.89 (d, 2H).13C NMR
(CDCl3) δ: 21.34, 105.26, 115.14, 119.08, 127.21, 138.40,
142.01, 142.24, 148.96, 168.90.
Anal. Calc. For C26H26Cl2N4Ti C(60.84%), H(5.11),
N(10.92%). Found C(60.24%), H(5.71), N(10.10%).
2.3. Proligand characterization
2.3.1. 2-[(2-Ethyl)phenylamino]pyridine [12]
1H NMR (CDCl3) δ: 1.21 (t, 3H), 2.65 (q, 2H), 6.41 (br s,
1H), 6.63 (d, 1H), 6.69 (d, 1H), 7.09–7.47 (m, 5H), 8.17 (d, 1H).
13C NMR (CDCl3) δ: 14.24, 24.43, 107.15, 114.45, 123.97,
124.93, 126.72, 129.25, 137.66, 137.85, 145.48, 148.51, 157.32.
2.5.3. Bis[2-(4-n-Butyl)phenylaminopyridinato]TiCl2
1H NMR (CDCl3) δ: 0.87 (t, 6H), 1.32 (sept, 4H), 1.54 (sept,
4H), 2.53 (t, 4H), 6.45 (dd, 2H), 6.48 (dd, 2H), 6.87–7.18 (m,
8H), 7.47 (t, 2H), 7.87 (br s, 2H).
13C NMR (CDCl3) δ: 13.95, 22.33, 33.63, 35.16, 104.95,
115.05, 121.13, 128.67, 140.22, 141.92, 142.15, 146.75, 165.84.
Anal. Calc. For C30H34Cl2N4Ti C(63.28%), H(6.02),
N(9.84%). Found C(62.51%), H(5.89), N(9.41%).
2.3.2. 2-[(3,5-Dimethyl)phenylamino]pyridine
1H NMR (CDCl3) δ: 2.22 (s, 6H), 6.69 (t, 1H), 6.87 (s, 1H),
6.91 (s, 2H), 7.26 (br s, 1H), 7.43 (t, 1H), 8.18 (d, 1H).13C
NMR (CDCl3) δ: 21.34, 108.01, 114.53, 118.26, 124.60, 137.56,
138.87, 140.42, 148.32, 156.41.
2.5.4. Bis[2-(2-t-Butyl)phenylaminopyridinato]TiCl2
1H NMR (CDCl3) δ: 1.27 (s, 18H), 5.8 (dd, 2H), 6.41 (d, 2H),
6.69 (d, 2H), 7.05–7.26 (m, 6H), 7.43 (t, 2H), 7.89 (br s, 2H).
13C NMR (CDCl3) δ: 30.79, 35.12, 106.88, 115.23, 125.20,
126.68, 127.84, 128.13, 141.42, 141.95, 145.12, 151.60,
166.01.
2.3.3. 2-[(4-n-Butyl)phenylamino]pyridine
1H NMR (CDCl3) δ: 0.93 (t, 3H), 1.36 (sept, 2H), 1.60 (sept,
2H), 2.58 (t, 2H), 6.67 (dd, 1H), 6.83 (d, 1H), 7.05 (br s, 1H),
7.18 (m, 4H), 7.44 (td, 1H), 8.17 (dd, 1H).13C NMR (CDCl3)
δ: 13.93, 22.29, 33.70, 34.98, 107.63, 114.45, 121.04, 129.13,
137.57, 137.74, 137.95, 148.33, 156.59.
Anal. Calc. For C30H34Cl2N4Ti C(63.28%), H(6.02),
N(9.84%). Found C(62.98%), H(6.44), N(9.51%).
2.3.4. 2-[(2-t-Butyl)phenylamino]pyridine
2.6. Polymerization procedure
1H NMR (CDCl3) δ: 1.42 (s, 9H), 6.32 (br s, 1H), 6.45 (d,
1H), 6.64 (dd, 1H), 6.73 (dd, 1H), 7.13–7.50 (4m, H), 8.16 (d,
1H).
Toluene (250 ml) and the cocatalyst (MAO) were charged
into the argon-purged reactor. Once the polymerization tem-
perature had been reached, the vessel was pressurized with
ethylene to the appropriate pressure. Introduction of the catalyst
precursor solution (20 ml) into the reactor started the polymer-
ization. After a desired polymerization time the reactor was
depressurized and the contents of the vessel were poured into
methanol acidified with a small amount of HCl. The solid poly-
mer was filtered off, washed with methanol and dried under
vacuum.
13C NMR (CDCl3) δ: 30.56, 35.00, 106.98, 114.04, 125.85,
127.06, 127.23, 128.59, 137.59, 138.58, 145.69, 148.52, 158.12.
2.4. Pre-catalyst preparation
The general procedure for preparing bis(amidopyridinato)
titanium complexes: The amidopyridine ligand was let to react
with NaH (excess) in dry Et2O (40 ml) at room temperature until

104
M. Talja et al. / Journal of Molecular Catalysis A: Chemical 280 (2008) 102–105
Table 1
Results of ethylene polymerizations promoted by complexes 1–5 with MAOa
b
Run
Cat.
Yield (g)
Tm (◦C)
Activityc
Mw (g mol−1
)
Mw/Mn
Xc (%)d
1
2
3
4
5
2-EtPh (1)
3,5-MePh (2)
4-n-BuPh (3)
2-t-BuPh (4)
Ph (5)
0.27
0.47
0.48
0.30
0.80
136.8
136.1
132.9
135.2
135.9
27
47
48
30
80
630000
390000
500000
390000
250000
20.0
20.3
26.6
22.9
2.5
59
33
22
48
55
a
Polymerization conditions: [Al]:[Ti] = 3000:1; ncat = 20 ␮mol; tp = 3600 s; Tp = 60 ◦C; Pp = 5 bar C2H4.
b
c
d
Melting point determined by DSC. These values have been obtained from remelted samples at heating rate of 10 ◦C min−1
.
Activity of catalyst in kg PE mol−1 Ti−1 h−1
.
Xc (%): Crystallinity = 100(ꢀHm/ꢀHm∗ ); ꢀHm∗ = 290 J/g.
2.7. Polymer characterization
titanium catalyst produced the most branched polyethylene in
this study (Run 3). This conclusion is based on the information
that melting points of polyethylenes decrease nearly linearly
with the branching degree, i.e. one branch per 1000 carbon atoms
in the chain reduces the melting point by approximately 1 C◦
[15]. This would mean that in the polyethylene produced by the
catalyst 3 there are about 4 branches per 1000 carbon atoms more
than in the polyethylene produced by the catalyst 1. As in the
case of the catalyst 3, phenylaminopyridinato titanium catalyst
5 leaves the titanium centre open but it produced polyethylene
which has the higher crystallinity and the melting point (Runs 3
and 5). In contrast, 2-ethylphenylaminopyridinato titanium cat-
alyst 1 produced the most linear polyethylene in this study. The
open titanium aminopyridinato catalyst structure (5) produced
the more linear polyethylene than the catalyst (4).
For the analysis of polymer molar masses and molar mass
distributions a Waters 150C GPC chromatograph was used.
1,2,4-Trichlorobenzene was used as eluent at 145 ◦C and the
calibration of the system was done with linear polystyrene stan-
dards. Melting temperatures of preheated and cooled samples
were determined by differential scanning calorimetry using a
PerkinElmer DSC-2 calorimeter. Heat of fusion was measured
by DSC with a heating rate of 10 ◦C min−1 using a Mettler
Toledo Stare System. Crystallinity was calculated by using
290 J g−1 for the specific heat of fusion of polyethylene crys-
tallites [13].
3. Results and discussion
The molar mass distributions of polyethylenes produced by
alkylphenylaminopyridinato titanium catalysts 1–4 refer to the
several existing active centres. On these kinds of co-ordination
catalysts both mono- and dimeric titanium complex might
appear as in the case of pyridyldiamines [16]. The catalytic cycle
can also be complex because of possible other oxidation states
of the titanium. In addition, it is known that amidopyridines
form complexes with aluminum and hence the broadening of
the observed molar mass distribution can be caused by the
transfer of the amide to aluminum [17,18]. The most prob-
able explanation for the broad molar mass distributions is,
however, the rotation of the phenyl group of the phenylaminopy-
ridinato titanium catalyst and thus several conformations can
exist in solution. It is already known that in solution aminopy-
ridinato titanium complexes have different configurations due
to the weak pyridine nitrogen coordination to titanium cen-
tre [19,20]. The broad molecular weight distribution might
also be due to the electron-donating effect from the alkyl sub-
stituent. The electron-donating effect from the alkyl substituent
makes the Ti center more electron rich, thus significantly weak-
ening the N· · ·Ti coordination strength between the pyridine
and the Ti center, therefore the rotation around the pyridine-
amidonitrogen bond would be activated. This situation produces
multiple Ti active sites with different coordination spheres,
which makes polymer fractions with different molecular
weights.
The polymerization activities of the catalyst precursors 1–5
were studied in the ethylene polymerization. With MAO as a
cocatalyst, catalysts 1–5 yielded polyethylene with moderate
activity (Table 1).
The ethylene polymerization activity of alkylpheny-
laminopyridinates 1–4 decreased compared with pheny-
laminopyridinato 5. This might be due to the electron-donating
effectfromthealkylsubstituent. Thelongerthedistancebetween
the alkyl substituent and metal center the more active is the
alkylphenylaminopyridinato titanium catalyst. This refers to the
fact that the alkyl substituents at the 2 position of phenyl group
of the phenylaminopyridinato ligand inhibit the coordination of
the monomer to the metal centre, i.e. the steric factors affect the
polymerization activity (Runs 1, 4 and 5).
All the present alkylphenylaminopyridinato titanium cat-
alysts 1–4 produced higher molar masses than the pheny-
laminopyridinato titanium catalyst 5. The alkyl substituent
significantly enhances the active site isomerization rate. This
might also be due to the electron-donating effect from the alkyl
substituent. When the activity decreases the length of the poly-
mer chain increases and its molar mass distribution broadens.
Obviously, this is caused by the alkyl substituents preventing
the ␤-elimination and thus by the increase in the propaga-
tion/elimination ratio. Furthermore, the electron donating alkyl
substituents lead to an increase in the length of the polymer
chain, i.e. they lower the ethylene insertion transition state [14].
Concluding from the crystallinities and the melting points
of the polymers the 4-n-Bu-substituted phenylaminopyridinato
The broad 1H NMR signals of the alkylphenylaminopy-
ridinato titanium complexes refer to the fact that in solution
rotation takes place around the amido titanium bond. Further-

M. Talja et al. / Journal of Molecular Catalysis A: Chemical 280 (2008) 102–105
105
Fig. 2. Possible rotation modes of alkylphenylaminopyridinato titanium complexes in solution.
more, rotation around the pyridine-amidonitrogen bond and the
aryl-amidonitrogen bond is possible (Fig. 2). In other words, the
rotation rate of the alkylphenylaminopyridinato ligand changes
in relation to the polymerization rate and thus the molar mass
distribution broadens. In the case of ansa-aminopyridinato cat-
alysts only the rotation of the pyridine part should be possible
and thus the molar mass distribution should be narrower but no
data has been reported [10,21].
The comparison of activities with the trialkylsilyl and
adamantyl aminopyridinates is not simple because the values
that have been experimentally determined depend on the used
devices and their settings. The activation time or the lifetime
of the catalyst is not often reported, the length of the polymer
chain should be also a reliable indicator about catalyst behavior
because the electronic effects have usually stronger influence on
the molar mass than to the activity. In the case of trialkylsilyl
and adamantyl aminopyridinato catalysts the published infor-
mation about the molar masses of polymers is not available
[10,11].
nato catalyst centre does not necessarily produce polyethylene
which has more branches.
Several rotation modes of the alkylphenylaminopyridinato
titanium catalyst in solution are most probably responsible for
the broad molar mass distribution due to the electron-donating
effect from the alkyl substituent. A bridged phenylaminopyrid-
inato titanium catalyst should be used to make the molar mass
distribution narrow. On the other hand, the bridged aminopyrid-
inato catalysts do not necessarily improve activity significantly
according to known examples [10,11].
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4. Conclusion
It is clear that the properties of polyethylene are related
to the molecular structure of the alkylphenylaminopyridinato
titanium catalyst used. The alkyl substitution of the phenyl
group in the phenylaminopyridinato titanium complexes did not
produce a better activity and narrow molar mass distribution
compared with the phenylaminopyridinato titanium complex.
This might be due to the electron-donating effect from the alkyl
substituent.
The alkyl substituted phenylaminopyridinato titanium cata-
lysts produced longer polyethylene chains than the unsubstituted
reference titanium catalyst because bulky substituents reduced
the probability of ␤-elimination and because the electron donat-
ing alkyl substituents lead to an increase in the length of the
polymer chain. The alkyl substituent significantly enhanced the
active site isomerization rate. This might also be due to the
electron-donating effect from the alkyl substituent. When the
concentration of the branches in the polyethylene decreases, the
crystallinity and the melting point of the polyethylene increases
and thus approaches the melting point of the known linear
polyethylene and vice versa. The open titanium aminopyridi-
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