Synthesis and characterization of the titanium complexes bearing two regioisomeric trifluoromethyl-containing enaminoketonato ligands and their behavior in ethylene polymerization

Article abstract of DOI:10.1039/b906854f

A series of new titanium complexes bearing two regioisomeric trifluoromethyl-containing enaminoketonato ligands (3a-h and 6a-h), [PhNCRCHC(CF₃)O]₂TiCl₂ (3a, R = Me; 3b, R = n-C₅H₁₁; 3c, R = i-Pr; 3d, R = Cy; 3e, R = t-Bu; 3f, R = CHCHPh; 3g, R = Et; 3h, R = n-C₁₁H₂₃) and [PhNC(CF ₃)CHC(R)O]₂TiCl₂ (6a, R = Ph; 6b, R = n-C ₅H₁₁; 6c, R = i-Pr; 6d, R = Cy; 6e, R = t-Bu; 6f, R = CHCHPh; 6g, R = CHPh₂; 6h, R = CF₃) have been synthesized and characterized. X-ray crystal structures analyses suggest that complexes 3c-e and 6c-d all adopt a distorted octahedral geometry around the titanium center. Complexes 3c, 3d and 6c display a cis-configuration of the two chlorine atoms around the titanium center, while complex 6d shows a trans-configuration of the two chlorine atoms. Especially, the configurational isomers (cis and trans) of complex 3e were identified both in solution and in the solid state by NMR and X-ray analyses. With modified methylaluminoxane as a cocatalyst, all the complexes are active towards ethylene polymerization, and produce high molecular weight polymers. With the variation of the relative position of the imino group and the trifluoromethyl group of the β-enaminoketonato ligands, the polymerization behavior of the catalysts changed remarkably. It is observed that the substituent directly joined to the carbonyl in the ligands plays an important role for both the catalytic activities and the properties of the polymers produced. The Royal Society of Chemistry 2009.

Full text of DOI:10.1039/b906854f

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www.rsc.org/dalton | Dalton Transactions
Synthesis and characterization of the titanium complexes bearing two
regioisomeric trifluoromethyl-containing enaminoketonato ligands and their
behavior in ethylene polymerization†
Wei-Ping Ye,a,b Hong-Liang Mu,a,b Xin-Cui Shi,a,b Yan-Xiang Chenga and Yue-Sheng Li*a
Received 6th April 2009, Accepted 19th August 2009
First published as an Advance Article on the web 11th September 2009
DOI: 10.1039/b906854f
A series of new titanium complexes bearing two regioisomeric trifluoromethyl-containing
=
enaminoketonato ligands (3a–h and 6a–h), [PhN CRCHC(CF3)O]2TiCl2 (3a, R = Me; 3b, R =
=
n-C5H11; 3c, R = i-Pr; 3d, R = Cy; 3e, R = t-Bu; 3f, R = CH CHPh; 3g, R = Et; 3h, R = n-C11H23)
=
and [PhN C(CF3)CHC(R)O]2TiCl2 (6a, R = Ph; 6b, R = n-C5H11; 6c, R = i-Pr; 6d, R = Cy; 6e, R =
=
t–Bu; 6f, R = CH CHPh; 6g, R = CHPh2; 6h, R = CF3) have been synthesized and characterized.
X-ray crystal structures analyses suggest that complexes 3c–e and 6c–d all adopt a distorted octahedral
geometry around the titanium center. Complexes 3c, 3d and 6c display a cis-configuration of the two
chlorine atoms around the titanium center, while complex 6d shows a trans-configuration of the two
chlorine atoms. Especially, the configurational isomers (cis and trans) of complex 3e were identified
both in solution and in the solid state by NMR and X-ray analyses. With modified methylaluminoxane
as a cocatalyst, all the complexes are active towards ethylene polymerization, and produce high
molecular weight polymers. With the variation of the relative position of the imino group and the
trifluoromethyl group of the b-enaminoketonato ligands, the polymerization behavior of the catalysts
changed remarkably. It is observed that the substituent directly joined to the carbonyl in the ligands
plays an important role for both the catalytic activities and the properties of the polymers produced.
including steric and electronic effects, can greatly influence the
performance of the non-metallocene catalysts.
Recently, we reported type of titanium catalysts
Introduction
In recent years, non-metallocene catalysts have further expanded
the realm of polyolefin-based materials since the development
of Ziegler–Natta catalysts and metallocene catalysts.1 Therefore,
more and more attention has been concentrated on the design
and synthesis of highly active, well-defined or single-site tran-
sition metal catalysts for olefin polymerization.2 A great deal
of new non-metallocene catalysts for olefin polymerization have
currently been discovered, including Group 4 metals chelating
Cp-analog ligands,3 diamide ligands,4 amidinate ligands,5 triden-
tate ligands,6 b-diketiminate ligands,7 phosphine-imide ligands,8
pyrrolide-imine ligands,9 and other new ligands.10-17 Especially,
Fujita and Coates found that the bis(phenoxyimine) titanium or
zirconium complexes which showed high activities, comparable to
or exceeding those of metallocene catalysts and highly dependent
on the nature of the substituents in the ortho-positions of the
phenoxy ring and on the imine nitrogen. Also, the titanium
complexes bearing ortho-fluorinated N-aryl groups polymerize
ethylene and propene in a living fashion.18,19 This creative work
promotes the development of a non-metallocene catalyst for olefin
polymerization and demonstrates that subtle changes of ligands,
a
chelating asymmetrical bidentate b-enaminoketonato ligands,
20
=
[ArN C(R2)CHC(R1)O]2TiCl2, for olefin polymerization. As
the b-enaminoketonato ligand has multiple sites for introducing or
changing the substituents, the steric and electronic requirements
of the metal center can be modulated easily by varying the
ligand structure. By variation of the substituents (R1, R2 and
Ar), we produced a series of highly efficient catalysts towards
olefin polymerization.21 It was observed that trifluoromethyl
(CF3) at the R1 or R2 position played an important role in
the olefin polymerization due to its electron-withdrawing nature,
while the relative position of the CF3 and the alkyl or phenyl
was not examined. However, the condensation of b-diketones
and aromatic amines would give rise to one product or two
regioisomeric compounds because asymmetrical b-diketones such
as 1a (Scheme 1) possess two nonequivalent electrophilic centers,
C2 and C4. The catalysts reported previously, 3a (R = Me), 6a (R =
Ph) and 6e (R = t-Bu), in which the relative position of the imino
group and the trifluoromethyl group were dissimilar, displayed
different characteristics in olefin polymerizations under the same
conditions. Due to the existence of the regioisomerism, we can not
elucidate the effect of the substituents R1 and R2 clearly. In general,
regioisomers display different properties in many fields, such
as structure chemistry,22 asymmetry synthesis,23 biochemistry,24
medical chemistry,25 polymer science,26 etc. This prompted us to
synthesize regioisomeric enaminoketonato ligands and the cor-
aState Key Laboratory of Polymer Physics and Chemistry, Changchun
Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun,
130022, China. E-mail: ysli@ciac.jl.cn; Fax: +86–431–85262039
bGraduate School of the Chinese Academy of Sciences, Changchun Branch,
Changchun, 130022, China
=
responding titanium complexes ([PhN C(R)CHC(CF3)O]2TiCl2
† CCDC reference numbers 726031–726036. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b906854f
=
and [PhN C(CF3) CHC(R)O]2TiCl2) to investigate the olefin
9452 | Dalton Trans., 2009, 9452–9465
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Scheme 1 General synthetic route of the titanium complexes 3a–h used in this study.
polymerization behavior of these complexes. Herein, we describe
the synthesis, characterization, and olefin polymerization be-
havior of a series of titanium complexes bearing regioisomeric
b-enaminoketonato ligands.
fluorinated ligands 2e and 5b from ketimine 1e and imidoyl
chloride 4b.28
The comparison of the 13C NMR spectra of the enaminoketones
synthesized in the present work with those of compounds 2a, 5a
and 5e reported previously shows that the carbonylic signals of
regioisomeric isomers 2a–h emerge at 170.41–180.90 ppm, and
the corresponding signals of ketones 5a–h appear at 201.25–
207.68 ppm. Thus the position of the carbonylic signal can be
used to distinguish isomeric enaminoketones 2a–h and 5a–h.
In addition, the maximum absorbance wavelengths of ligands
2a–h and 5a–h in their ultraviolet spectra were also obviously
different. Compounds 2b–2h which are the analogues of 2a
have a maximum absorbance at 327 nm, while complexes 5b–d
and 5g–h which are the analogues of 5g exhibited a maximum
absorbance at 312 nm. The introduction of an extra conjugated
phenyl caused bathochromic spectral shifts in 2f, 5a and 5f.
Furthermore, the single-crystal X-ray structure analyses of the
corresponding titanium complexes further clarified the structures
of the regioisomeric ligands.
Results and discussion
Synthesis and characterization of new titanium complexes
The titanium complexes 3a–h and 6a–h used here were synthesized
according to the modified procedures reported previously, as
shown in Scheme 1 and Scheme 2.20 A tandem sequence of Claisen
condensation between methyl ketones and ethyl trifluoroacetate
and the condensation of the resulting b-diketone with aniline
in acidic toluene was used to synthesize most of the new
b-enaminoketones (except 2e, 5b and 5h) in moderate to high
yields. When R was a primary alkyl, the major condensation
products were b-enaminoketones 2a–b and 2g–h, in which the
amino group was attached to the b-carbon atom with respect to
the carbonyl group. When R was a secondary alkyl (i-Pr or Cy)
or a styryl, regioisomeric ligands 2c, 5c, 2d, 5d, 2f, 5f can be
synthesized by the condensation of b-diketones 1c, 1d and 1f with
aniline in one pot, respectively. When R was phenyl, tert-butyl
or diphenylmethyl, the major products were b-enaminoketones
5a, 5e, 5g with the amino group and trifluoromethyl located at
the same carbon atom. However, b-enaminoketone 5h was not
obtained via the same method because aniline was deactivated due
to the formation of anilinium trifluoroacetate.27 This compound
was prepared in moderate yield by the reaction of 1,1,1,5,5,5-
hexafluoroacetylacetone with aniline in toluene using TiCl4 as a
catalyst. According to the literature, we synthesized regioisomeric
Titanium complexes 3a–h and 6a–h were prepared under facile
conditions in good yields by the reaction of TiCl4 with two
equivalents of the lithium salts of b-enaminoketones 2a–h and
5a–h in dry diethyl ether. The molecular structures of complexes
3c–e and 6c–d were confirmed by X-ray crystal analysis. The
crystallographic data together with the collection and refinement
parameters are summarized in Table 1. The molecular structures
of these complexes are shown in Figs. 1–6, respectively, and the
selected bond lengths and bond angles are summarized in Table 2.
In the solid state, six-coordinate complexes 3c, 3d and 6c all
adopt distorted octahedral geometry around the titanium center
with trans oxygen atoms, cis nitrogen atoms and cis chlorine
atoms, which is the same as the case of complexes 3a and 6e
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Scheme 2 General synthetic route of the titanium complexes 6a–h used in this study.
Table 1 Crystal data and structure refinements of complexes 3c–e and 6c–d
2 ¥ 3c 3d 6c
C26H26Cl2F6N2O2Ti C32H34Cl2F6N2O2Ti C26H26Cl2F6N2O2Ti C32H34Cl2F6N2O2Ti C28H30Cl2F6N2O2Ti C28H30Cl2F6N2O2Ti
6d
3e-I
3e-II
Empirical formula
Formula weight
Crystal system
Space group
631.29
Orthorhombic
Pca2(1)
16.3779(17)
16.9660(17)
21.199(2)
90
5890.4(10), 8
1.424
711.41
631.29
Monoclinic
P2(1)/c
17.9733(8)
9.2121(4)
17.4099(8)
97.6240(10)
2857.1(2), 4
1.468
711.41
Monoclinic
P2(1)/c
6.2203(5)
16.5443(12)
15.5413(11)
94.5850(10)
1594.2(2), 2
1.482
659.31
Monoclinic
P2(1)/c
9.5394(4)
37.7491(15)
8.9319(4)
113.4400(10)
2951.0(2), 4
1.484
659.31
Monoclinic
P2(1)/c
6.1707(5)
19.7949(16)
12.4053(10)
100.7780(10)
1488.6(2), 2
1.471
Orthorhombic
Pna2(1)
21.8133(13)
8.0499(5)
19.0926(12)
90
˚
a (A)
˚
b (A)
˚
c (A)
b (◦).
3
˚
V (A ), Z
3352.6(4), 4
1.409
Densitycalcd (Mg/m3)
Absorption coefficient 0.536
0.479
0.552
0.504
0.538
0.533
(mm-1)
F (000)
2576
0.24 ¥0.16 ¥ 0.05
1.20 to 25.04
1464
1288
776
1352
720
Crystal size (mm)
q range for data
collection (◦)
0.15 ¥ 0.14 ¥ 0.10 0.15 ¥ 0.14 ¥ 0.12 0.12 ¥ 0.09 ¥ 0.07
0.13 ¥ 0.12 ¥ 0.10 0.17 ¥ 0.14 ¥ 0.12
1.87 to 26.09
17678
1.14 to 26.10
15494
1.80 to 26.13
9215
1.08 to 25.98
16997
1.96 to 26.09
8165
Reflections collected
29355
Independent reflections 10163 (Rint = 0.0960) 6100 (Rint = 0.0674) 5665 (Rint = 0.0302) 3176 (Rint = 0.0604) 5767 (Rint = 0.0303) 2954 (Rint = 0.0342)
Data/restraints/
parameters
10163/1/711
6100/1/416
5665/0/356
3176/0/205
5767/0/376
2954/0/190
Goodness-of-fit on F2 0.996
0.987
0.0477, 0.0955
1.016
0.0397, 0.0959
1.024
0.0456, 0.0752
1.004
0.0371, 0.1017
1.051
0.0496, 0.1450
Final R indices [I >
2s(I)]: R1, wR2
0.0783, 0.1554
Largest diff. Peak and 0.879 and -0.345
0.322 and -0.263
0.856 and -0.255
0.332 and -0.367
0.362 and -0.337
0.902 and -0.602
-3
˚
hole (e A )
reported.20,21 Theoretically, chelate complexes [N,O]2MCl2 may
form five configurational isomers, as shown in Scheme 3. Our
previous work20 and the results in the literature18,19 suggest that
these titanium complexes bearing two b-enaminoketonato chelate
ligands tend to form isomer cis-I. Herein, complexes 3c, 3d and
6c adopt this configuration, as shown in Figs. 1–3. In previous
research, it was found that the homologous titanium complex
bearing a large substituent (CF3) on the ortho position of the
aniline, isomer trans-II, in which two oxygen atoms, two nitrogen
atoms and two chlorine atoms were all in trans configuration,
displayed the lowest RFE, and was the most stable. Herein for
complex 6d (R= Cy), isomer trans-II (Cl–Ti–Cl angle, 180.00◦; N–
Ti–N angle, 180.00◦; O–Ti–O angle, 180.00◦) was the most stable
structure (Fig. 4). It was noticed that cyclohexyl in complexes 3d
and 6d was all in the chair conformation and the substituents
were in the equatorial position. Especially, for complex 3e, the
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Fig. 1 Molecular structure of complex 3c with thermal ellipsoids at 30% probability level. Hydrogen atoms are omitted for clarity.
Fig. 2 Molecular structure of complex 3d with thermal ellipsoids at 30% probability level. Hydrogen atoms are omitted for clarity.
structures of two configurational isomers 3e-I and 3e-II were
identified (Fig. 5 and 6). The isomer 3e-I adopted a distorted
octahedral geometry around the titanium center with trans oxygen
atoms, cis nitrogen atoms and cis chlorine atoms, while two oxygen
atoms, two nitrogen atoms, and two chlorine atoms were all in
the trans position of the isomer 3e-II. The transformation of the
configuration of 3e probably originates from the steric hindrance
between the trifluoromethyl, the tert-butyl and the phenyl. Based
on the structures of complexes 3e-II and 6d, the configurational
isomerization should be considered if a large substituent was
introduced to the R position of these titanium complexes.
and 6e, the 1H NMR spectra displayed a single sharp resonance for
=
the methine proton (-CH C-) of the b-enaminoketonato chelate
ligands in accordance with only one isomer of the octahedral
coordination structure.20 In contrast, the 1H NMR spectra of
complex 3e showed two resonances (6.38 and 6.09 ppm) in the
ratio of 7:10 for the two olefinic protons of the ligands (Fig. 7).
Therefore, the ratio of the two configurational isomers should
be 7:10. In the 13C NMR spectra of 3e, there were also two
resonances (105.14, 103.46) for the two methine carbons. The
increased number of signals as compared with the previous results
reveal that there are two isomers in the solution, because one C2-
1
Besides the solid-state structure, the solution structure of
symmetric isomer should show only one signal in the H NMR
1
complex 3e was also studied carefully by NMR. The H and 13C
spectrum for two equivalent methine protons.16,20
NMR data of 3e in CDCl3 solution at 25 ◦C also suggests that
there were two isomers in the solution. For titanium complexes 3a
The solution structure of complex 3e was also investigated
in other deuterated solvent, especially, in toluene-d8, in which
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Fig. 3 Molecular structure of complex 6c with thermal ellipsoids at 30% probability level. Hydrogen atoms are omitted for clarity.
Fig. 4 Molecular structure of complex 6d with thermal ellipsoids at 30% probability level. Hydrogen atoms are omitted for clarity.
the ethylene polymerization experiments were carried out. It was
observed that there were also two isomers in these solvents and
the molar ratio of the configurational isomers changed (in CDCl3,
3e-I:3e-II = 10:7, in o-C6D4Cl2, 3e-I:3e-II = 6.25:1, in toluene-
d8, 3e-I:3e-II = 1:1). It suggests that the isomers exchange for
each other and the dynamic phenomena are operative at room
temperature. The equilibrium constants (Keq) and the activation
barriers at the room temperature for this interconversion (3e-
(o-C6D4Cl2) and Keq = 1.0, DG = 0 kJ/mol (toluene-d8). Variable
temperature 1H NMR experiments were also conducted to assess
the dynamic transformation and the equilibrium constants and
the activation barriers in toluene-d8 and o-C6D4Cl2 for this
interconversion. The fluxional dynamic process associated with
1
isomerization of complex 3e was observed by VT H NMR in
the temperature range 25 to 60 ◦C in toluene-d8 (Fig. 8). The
equilibrium constant for the interconversion (3e-Iꢀ3e-II) was
about 1.0 at the two temperatures and the breadth of signals
broaden with the increase in the temperature.29 The dynamic
Iꢀ3e-II) were calculated by the DG = -RTlnK equation: Keq
=
0.70, DG = 0.88 kJ/mol (CDCl3), Keq = 0.16, DG = 4.54 kJ/mol
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Fig. 6 Molecular structure of complex 3e-II with thermal ellipsoids at
30% probability level. Hydrogen atoms are omitted for clarity.
Fig. 5 Molecular structure of complex 3e-I with thermal ellipsoids at
30% probability level. Hydrogen atoms are omitted for clarity.
=
process associated with isomerization of complex 3e was◦ also
observed by VT 1H NMR in the temperature range 25 to 60 C in
o-C6D4Cl2 (Fig. 9). The equilibrium constant for the interconver-
sion (3e-Iꢀ3e-II) was 6.25 (298 K) and 3.70 (333 K).
arising from CH C ligand protons (5.93 and 5.74 ppm) were
together with the aromatic signals in different regions (7.35 and
7.44 ppm). This suggests that the cis-configuration is the major
configuration for complex 6d in solution because the olefinic
proton of the referenced complex 6c is at 5.75 ppm which is very
close to the major resonance (5.78 ppm) of 6d (in the beginning,
we considered the resonance at 5.93 ppm to be an unidentified
impurity for there are no other resonances corresponding to
it). With increasing temperature, the proportion of the trans-
configuration increased slightly. These 1H NMR data suggest that
the dynamic phenomena also exists in solution for complex 6d, of
which the solution structure is quite different from its solid state
structure.
We have also noticed that the NMR data of complexes 6c and
1
6d look very much the same. It was observed that the H and
13C NMR data for complex 6c in CDCl3 at room temperature
contains only a single set of resonances, which suggested that
the cis configuration observed in the solid state was retained
1
in solution. For complex 6d, the H NMR spectra showed two
resonances (5.92 and 5.78 ppm) in the ratio of 1:10 for the two
olefinic protons of the ligands. In addition, we studied the solution
structure of the complexes 6c and 6d in toluene (Fig. 10). It was
observed that the 1H NMR data also contain only a single set of
resonances for complex 6c in toluene-d8, but there are also two
resonances (5.92 and 5.71 ppm) in the ratio of 1:10 for the two
olefinic protons of complex 6d. At the same time, these resonances
All the complexes, 3e-II and 6d, in which two chlorine atoms are
in a trans configuration, displayed longer Ti–Cl and Ti–O bond
distances and shorter Ti–N bond distances than those of other
complexes in which two chlorine atoms are in a cis configuration.
◦
˚
Table 2 Selected bond lengths (A) and angles ( ) for complexes 3c–e and 6c–d
3c
3d
6c
6d
3e-I
3e-II
Bond distances
Ti–O(1)
Ti–O(2)
Ti–N(1)
Ti–N(2)
Ti–Cl(1)
Ti–Cl(2)
1.884(5)
1.908(6)
2.209(6)
2.205(8)
2.257(3)
2.261(3)
1.890 (3)
1.900 (3)
2.198(3)
2.210(3)
2.2582 (14)
2.2679(15)
1.8874(15)
1.8699(16)
2.223(2)
2.204(2)
2.2780(8)
2.2660(8)
1.9039(17)
1.9039(17)
2.132(2)
2.132(2)
2.2970(7)
2.2970(7)
1.8837(15)
1.8925(15)
2.2600(18)
2.2367(18)
2.2466(7)
2.2639(7)
1.9021(19)
1.9021(19)
2.184(2)
2.184(2)
2.2882(7)
2.2882(7)
Bond angles
N(1)–Ti–N(2)
O(1)–Ti–O(2)
Cl(1)–Ti–Cl(2)
83.2 (2)
171.0 (2)
100.27 (11)
82.36 (12)
173.51 (11)
101.29 (5)
83.86 (7)
167.66 (7)
98.90 (3)
180.00(10)
180.00(10)
180.00(10)
82.99(6)
171.50(7)
101.54(3)
179.999(1)
180.00(13)
180.0
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Scheme 3 Structures of five configurational isomers of the titanium complex.
Fig. 7 1H NMR spectra of 3e in CDCl3. The resonances (6.38, 6.09 ppm) are for the methine protons of the ligands in 3e-I and 3e-II, and those (7.31–7.15
and 6.75 ppm) are for the aromatic protons.
Fig. 8 Variable-temperature 1H NMR spectra of 3e in toluene-d8.
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Table 3 Polymerization of ethylene by complexes 3a–h and 6a–h/MMAO
systema
c
d
Complex Polymer
Tm
Activityb (◦C)
Mn
(kg/mol) Mw/Mn
Entry (mmol)
(g)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
3a (1.0)
3b (1.0)
3c (1.0)
3d (1.0)
3e (1.0)
3f (3.0)
3g (1.0)
3h (1.0)
6a (1.0)
6b (1.0)
6c (1.0)
6d (3.0)
6e (1.0)
6f (3.0)
6g (1.0)
6h (3.0)
0.141
0.186
0.216
0.280
0.057
0.116
0.160
0.190
0.110
0.037
0.259
0.124
0.360
0.046
0.312
0.049
1.68
2.23
2.59
3.36
0.68
0.46
1.92
2.28
1.32
0.44
3.11
0.50
4.32
0.18
3.74
0.20
137
139
141
138
135
137
140
139
134
135
139
136
139
136
135
138
82
115
136
134
44
40
97
124
61
42
117
27
221
17
1.93
1.39
1.55
1.53
1.12
1.60
1.75
1.37
1.27
1.24
1.73
1.56
1.80
1.10
3.00
4.40
Fig. 9 Variable-temperature 1H NMR spectra of 3e in o-C6D4Cl2.
For instance, the configurational isomer 3e-II showed longer
91
64
˚
Ti–Cl and Ti–O bond distances of 2.2882(7) and 1.9021(13) A,
˚
respectively, and shorter Ti–N bond distance of 2.184(2) A than
a Reaction conditions: 1 atm ethylene pressure, Al/Ti (mol ratio) = 2000,
toluene 50 mL, polymerization for 5 min, the results shown for each entry
are representative of at least two reproducible runs. b kg of PE/mmolTi·h.
c Melting temperature measured by DSC. d Number-average molecular
weight and polydispersity index of the resultant polyethylene determined
by GPC using polystyrene standard.
the isomer 3e-I (average bond distances: Ti–Cl = 2.2553(7),
˚
Ti–O = 1.8881(15), Ti–N = 2.2484(18) A). Crystals of 3c consist
of two crystallographically independent molecules in the unit cell,
with only minor differences from each other (e.g., bond angles
Cl(1)–Ti(1)–Cl(2) and Cl(3)–Ti(2)–Cl(4) are 100.27◦ and 101.19◦,
respectively). For complexes 3c and 3d, in which imino groups
and alkyl substituents are located at the same carbon atoms, the
bond distances of Ti–O, Ti–N, Ti–Cl and the bond angles of
N–Ti–N, O–Ti–O, Cl–Ti–Cl were very similar to each other. For
complexes 3c and 6c, which were from the regioisomeric ligands,
the corresponding bond angles are slightly different from each
other: Complex 3c showed wider O–Ti–O (171.0(2)◦) and Cl–
Ti–Cl (100.27(11)◦) bond angles than complex 6c (O–Ti–O =
167.66(7)◦, Cl–Ti–Cl = 98.90(3)◦).
The data in Table 3 demonstrate that the relative position of the
N-aryl moieties plays a great role in the catalytic activities of
the complexes and the properties of the polymers. The melting
temperatures of the resultant polyethylene indicate the polymers
are linear polyethylenes.
Previous research showed that complex 3a, of which the imino
group abuts upon the methyl (Scheme 1), displayed an excellent
ability to copolymerize ethylene with a-olefin or cycloolefin, and
produced high molecular weight polymers. However, since it
was difficult to dissolve in toluene, the “real” catalytic activity
might be much higher. In order to increase the solubility to
increase the catalytic activity of the catalysts, some longer alkyl
Ethylene polymerization by the new titanium complexes
With MMAO as a cocatalyst, all the titanium complexes are
active towards ethylene polymerization at room temperature under
atmospheric pressure. Typical results are summarized in Table 3.
Fig. 10 (a) 1H NMR spectra of 6d in CDCl3 (b) 1H NMR spectra of 6d in toluene-d8 (c) 1H NMR spectra of 6c in toluene-d8.
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chains, such as ethyl, n-pentyl and n-undecyl were introduced,
and the new complexes 3g, 3b and 3h were synthesized. It was
observed that the solubilities of the new complexes in toluene were
increased obviously with the increase of the length of the carbon
chains. As a result, complexes 3g, 3b and 3h all displayed higher
catalytic activities toward ethylene polymerization (1.92, 2.23 and
2.28 kg PE/mmolTi·h, respectively) than complex 3a (1.68 kg
PE/mmolTi·h). Furthermore, 3b and 3h produced much narrower
molecular weight distribution (PDI = 1.39 and 1.37, respectively)
polyethylenes than that produced by 3a (PDI = 1.93). This result
indicated that the substituents of the ligands considerably affect
the performance of the enaminoketonato titanium catalysts.
Besides the primary alkyl, the larger substituents including
iso-propyl, cyclohexyl and tert-butyl were also introduced, and
complexes 3c, 3d and 3e were synthesized. The effect of these
substituents were more complicated than the primary alkyl.
Complexes 3c and 3d showed higher catalytic activity (2.59 and
3.36 kg PE/mmolTi·h, respectively) than complexes 3a, 3b, 3g and
3h. This result shows that the catalytic activities towards ethylene
polymerization can be increased to some extent by increasing the
size of the saturated alkyl substituent R in the position of the
methyl of complex 3a. However, complex 3e (R = t-Bu) only
exhibited a low catalytic activity of 0.68 kg PE/mmolTi·h under
the same conditions. One rational explanation is that the isomers
3e-I and 3e-II are in equilibrium in the toluene solution, and the
trans-configurational isomer 3e-II was not suitable for ethylene
polymerization.
Titanium complexes 6a (R = Ph) and 6e (R = t-Bu) with the
imino group and the trifluoromethyl joined to the same carbon
atom were previously reported to show high activities for ethylene
polymerization.20 In order to further understand the effect of the
substituent R on the catalytic behavior, a series of new complexes
were designed and synthesized successfully. It is noticed that
complex 6c (R = i-Pr) showed a much higher catalytic activity
(3.11 kg PE/mmolTi·h, entry 11), about eight times more than
complex 6b (R = n-pentyl, 0.44 kg PE/mmolTi·h, entry 10).
Complex 6d (R = Cy) showed a much lower activity (0.50 kg
PE/mmolTi·h, entry 12) than complex 6c though the solution
structure of 6c and 6d is similar (1H NMR data look very much
the same for 6c and 6d). The other reaction conditions, such as
reaction temperature, catalyst dosage, Al/Ti molar ratio, are all
the same, and the solution structure is similar, one of the possible
reasons for this quite different result is the difference between i-Pr
and cyclohexyl. Although the steric effect of i-Pr and cyclohexyl
is almost the same in organic chemistry, the i-Pr can freely rotate
in solution, and the cyclohexyl can not freely rotate in solution
due to the constraints of a ring structure. Perhaps, the cyclohexyl
can not cause the effective separation between the cationic active
species and the anionic cocatalysts, which permits more space
for ethylene to coordinate to the metal and thus enhances the
catalytic activity.30 Considering that complex 6e (R = t-Bu) showed
the highest activity (4.32 kg PE/mmolTi·h, entry 13) among all
the complexes, the bulky diphenylmethyl was also introduced
into the ligands to form complex 6g which also showed a high
catalytic activity (3.74 kg PE/mmolTi·h, entry 15). In this series
of complexes, the order of the catalytic activities (6e > 6g > 6c >
6b) was almost the same as the order of the steric effect of the
substituent Rc, (tertiary alkyl (6e) > secondary alkyl (6c and
6g) > primary alkyl (6b)). The reason for the enhancement of
the activity is probably that the introduction of the large group
at the R position causes effective separation between the cationic
active species and the anionic cocatalysts, which permits more
space for ethylene to coordinate to the metal and thus increase
the catalytic activity.30 In addition, in order to comprehend the
electronic effect of the substituent R on the property of the
enaminoketonato titanium catalysts, 6f and 6h were designed
and synthesized. Complex 6f (R = styryl) showed lower activity
(0.18 kg PE/mmolTi·h, entry 14) than complex 6b in which R was a
saturated primary alkyl. It produced narrower distribution (PDI =
1.10) PE than that of catalyst 6a (PDI = 1.27), which exhibited
the characteristics of a living polymerization of ethylene and
copolymerization of ethylene and norbornene.20 Another strong
electron withdrawing group CF3 was introduced to synthesize
complex 6h. An unexpected low catalytic activity of 0.20 kg
PE/mmolTi·h was observed (entry 16), and a wide molecular
weight distribution (PDI = 4.4) polymer was produced. This result
might be attributed to its stronger electrophilic titanium center
and the lower stability of the catalytic species originating from the
strong electron-withdrawing effect of the second trifluoromethyl
group. In a word, for complexes 6a–h, substitutents R have much
more influence on the behavior of ethylene polymerization than
those in complexes 3a–h.
Generally, the regioisomeric ligands in these titanium complexes
would show similar electronic effects. Thus, the diversity of
the catalytic activities of the complexes may originate from the
steric effect of the substituents around the titanium center. The
substituents which are situated directly adjacent to the catalytic
center and along the path of the incoming olefin will have more
influence than those that are away from the titanium center.31
In these new titanium complexes, N-Phenyl and the substituent,
labeled as Rc which is joined to the carbonyl directly, are in the
proximity of the titanium center according to their molecular
structures determined by X-ray analysis. The N-Phenyl in different
complexes should display almost the same steric effect, so the
substituent Rc would play a more important role on the catalytic
performance of this type of titanium complex. In order to further
clarify this point, the five pairs of titanium complexes bearing
regioisomeric enaminoketonato ligands (3b vs 6b, 3c vs 6c, 3d vs
6d, 3e vs 6e and 3h vs 6h) were synthesized, and their behavior in
the ethylene polymerization is described above. The comparison
of the catalytic activities of every pair will be discussed below.
Complex 3b (Rc = CF3) showed a much higher activity for ethylene
polymerization than complex 6b (Rc = n-pentyl), while the steric
effect of CF3 was greater than n-pentyl.32 Complexes 3c (Rc =
CF3) and 6c (Rc = i-Pr) showed similar activity, while the steric
effect of CF3 is similar to iso-propyl.32 Complex 6e (Rc = t-Bu)
showed a much higher activity than complex 3e (Rc = CF3), while
the steric effect of t-Bu is greater than CF3. When Rc was CF3,
complexes 3b, 3c and 3d showed similar catalytic activities. Based
on these comparisons, for these regioisomeric enaminoketonato
titanium complexes, the catalytic activities were more influenced
by the steric effect of Rc, when Rc is a saturated alkyl. The order
of the catalytic activities (6e >3g ª 3c ª 6c ª 3a > 6b) was almost
the same as the order of the steric effect of the substituent Rc,
(t-Bu (6e) > CF3 (3g and 3a) ª i-Pr (3c) > n-pentyl (6b)). With the
increase of the steric effect of the Rc, the catalytic activity increased
without reference to the relative position of the imino group and
the trifluoromethyl group.
9460 | Dalton Trans., 2009, 9452–9465
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7% aluminium in heptane solution) was purchased from Akzo
Nobel Chemical Inc. Commercial ethylene was directly used for
polymerization without further purification. Complexes 3a, 6a
and 6e were synthesized according to the procedure reported
previously.20
Conclusions
A series of novel titanium complexes (3a–h and 6a–h) bearing
two regioisomeric trifluoromethyl-containing enaminoketonato
ligands have been synthesized and characterized. In the solid
state, complexes 3c, 3d, 3e and 6c, all adopt a distorted octahedral
geometry around the titanium center. For complexes 3c, 3d and 6c,
the two chlorine atoms are in the cis-position to each other, and
for complex 6d, the two chlorine atoms are in the trans-position
around the central titanium metal. Especially, for complex 3e,
two configurational isomers existed both in the solid state and
in solution. With MMAO as a cocatalyst, titanium complexes
3a–h and 6a–h are active for ethylene polymerization. Catalytic
activity and polymer property are influenced significantly by
the structure of the b-enaminoketonato ligands. For complexes
6a–h, substituents R have much more influence on the behavior
of ethylene polymerization than those in complexes 3a–h. The
comparable study displays that the catalytic activities are more
influenced by the steric effect of Rc, joined directly to the carbonyl
in the ligands. The order of the catalytic activities (6e >3g ª
3c ª 6c ª 3a > 6b) is almost the same as the order of the steric
effect of the substituent Rc, (t-Bu (6e) > CF3 (3g and 3a) ª
i-Pr (3c) > n-pentyl (6b)). With the increase of the steric effect
of the Rc, the catalytic activity increased without reference to the
relative position of the imino group and the trifluoromethyl group.
A more detailed study of ethylene/a-olefin copolymerization and
propylene polymerization using these precatalysts is underway.
Synthesis of PhNHC(n-C5H11)CHCOCF3 (2b)
To a stirred suspension of t-BuOK (2.8 g, 24 mmol) in dried ether
(60 mL), were added ethyl trifluoroacetate (3.6 mL, 30 mmol)
in THF (30 mL). The solution was stirred for 45 min at room
temperature. A solution of 2-heptanone (1.8 mL, 20 mmol) in
THF (50 mL) was added, and the solution was stirred overnight.
The reaction mixture was poured onto a saturated ammonium
chloride solution, and then extracted with ether. The combined
organic layer was washed with brine, dried over anhydrous sodium
sulfate, filtered, and evaporated under reduced pressure to afford
a deep yellow oil. To a stirred solution of this crude product
in toluene (50 mL) were added aniline (1.86 mL, 20 mmol)
and p-toluenesulfonic acid (ca. 20 mg) as a catalyst at room
temperature. The mixture was heated and refluxed, and the water
formed was removed azotropically using a Dean–Stark apparatus
for 24 h. During the stirring period, a light-yellow solution was
formed. Evaporation of toluene gave a deep yellow oil. The crude
product was purified by column chromatography on silica gel
with petroleum ether/ethyl acetate mixture (200:1) as an eluent,
affording 2b (3.69 g) as a light yellow oil in 65 % yield. 1H NMR
(300 MHz, CDCl3): d 12.66 (s, 1H, N–H), 7.45–7.32 (m, 3H, Ph–
Experimental
=
H), 7.18–7.16 (m, 2H, Ph–H), 5.56 (s, 1H, CH), 2.35 (t, 2H,
CH2), 1.51 (m, 2H, CH2), 1.21 (m, 4H, (CH2)2), 0.83 (t, 3H, CH3).
All air and moisture-sensitive compounds were manipulated
using standard Schlenk techniques or in a glove box under
an argon atmosphere. The NMR data of the ligands and the
complexes were obtained on a Bruker 300 MHz spectrometer
at ambient temperature with CDCl3 as a solvent (dried by MS
13C NMR (100 MHz, CDCl3): d 176.92, 173.10, 137.17, 129.84,
127.96, 125.95 118.13, 89.74, 32.45, 31.80, 27.73, 22.77, 13.94.
EtOH
UVl
327.1 nm. Anal. Calcd for C15H18F3NO: C, 63.15; H,
max
6.36; N, 4.91. Found: C, 63.25; H, 6.42; N, 4.85.
˚
4A). Melting points were determined on a Thomas–Hoover
melting point apparatus. The NMR data of the polymers were
obtained on a Varian Unity 400-MHz spectrometer at 125 ◦C
with o-C6D4Cl2. UV/Vis absorbance spectra were obtained by
a Cary 50 spectrophotometer (Varian) equipped with a quartz
micro-colorimetric vessel of 1-cm path length. Elemental analyses
were performed on a Perkin-Elmer Series II CHN/O analyzer
2400. DSC measurements were performed on a Perkin-Elmer
Pyris 1 Differential Scanning Calorimeter. Melting temperatures
were recorded in the second heating run at a heating rate of
10 ◦C/min. The number-average molecular weights (Mn) and
polydispersity indices (PDI) of the polymers were determined in
1,2,4-trichlorobenzene at 150 ◦C on a high temperature GPC using
PL-GPC 220 instrument equipped with three PLgel 10-mm mixed-
B LS columns.20
Synthesis of PhNHC(i-Pr)CHCOCF3 (2c)
Compound 2c was prepared via a procedure similar to that for 2b
as an off-white solid in 32 % yield. 1H NMR (300 MHz, CDCl3): d
12.78 (s, 1H, N–H), 7.46–7.36 (m, 3H, Ph–H), 7.19–7.16 (m, 2H,
=
Ph–H), 5.59 (s, 1H, CH), 2.87 (m, 1H, -CH), 1.16 (d, 6H, -CH3).
13C NMR (100 MHz, CDCl3): d 179.13, 177.41, 136.95, 129.96,
EtOH
127.20, 126.40, 118.04, 86.06, 29.52, 21.83. UV l
max 327.0 nm.
m.p. 29–30 ◦C. Anal. Calcd for C13H14F3NO: C, 60.70; H, 5.49; N,
5.44. Found: C, 60.53; H, 5.47; N, 5.36.
Synthesis of PhNHC(C6H11)CHCOCF3 (2d)
Dried diethyl ether, hexane and toluene were purified from
an MBraun SPS system. Methyl ketones, ethyl trifluoroacetate,
1,1,1,5,5,5-hexafluoroacetylacetone and aniline for ligand synthe-
sis were purchased from Aldrich Chemical or Acros Organics,
and used without further purification. Ketimine 1e and imidoyl
chloride 4b were prepared according to the methods described in
the literature.33 Commercial titanium tetrachloride was distilled
prior to use. The 1.6 M n-butyllithium solution in hexane was
purchased from Acros. Modified methylaluminoxane (MMAO,
Compound 2d was prepared via a procedure similar to that for 2b
as a white solid in 26 % yield. H NMR (300 MHz, CDCl3): d
12.78 (s, 1H, N–H), 7.46–7.33 (m, 3H, Ph–H), 7.46–7.33 (m, 3H,
1
=
Ph–H), 7.16–7.14 (m, 2H, Ph–H), 5.58 (s, 1H, CH), 2.51 (m, 1H,
CH), 1.77–1.03 (m, 10H, -(CH2)5-). 13C NMR (100 MHz, CDCl3):
d 175.61, 175.17, 135.59, 128.53, 126.65, 124.74, 116.71, 85.78,
EtOH
38.64, 30.72, 24.64, 24.41. UV l
327.9 nm. m.p. 78–80 ◦C.
max
Anal. Calcd for C16H18F3NO: C, 64.64; H, 6.10; N, 4.71. Found:
C, 64.48; H, 6.13; N, 4.68.
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Synthesis of PhNHC(t-Bu)CHCOCF3 (2e)
cooled to -78 ◦C, and then imidoyl chloride 4b (4.2 g, 20 mmol)
in THF was added. The solution was allowed to warm to room
temperature. After 5 h, the reaction was quenched by addition of
a saturated ammonium chloride solution. The aqueous layer was
extracted with dichloromethane. The combined organic extracts
were washed with brine and then dried (Na2SO4) and evaporated
under reduced pressure to furnish the crude product. The crude
product was purified by column chromatography on silica gel
with petroleum ether/ethyl acetate mixture (200:1) as an eluent,
affording 5b (2.9 g, 10.0 mmol) as a light yellow oil in 50 % yield. 1H
NMR (300 MHz, CDCl3): d 11.77 (s, 1H, N–H), 7.37–7.18 (m, 5H,
A solution of ketimine 1e (3.5 g, 20 mmol) in THF (50 mL) was
added under argon to LDA (2.0 M in ether, 20.0 mL, 40 mmol)
in THF (50 mL). The solution was stirred for 30 min at room
temperature. Ethyl trifluoroacetate (3.6 mL, 30 mmol) in THF
(30 mL) was added and the solution was stirred overnight. The
reaction mixture was poured onto a saturated ammonium chloride
solution extracted with ether. The combined organic layers were
washed with brine, dried over anhydrous sodium sulfate, filtered,
and evaporated under reduce pressure to afford a deep yellow oil.
The crude product was purified by column chromatography on
silica gel with petroleum ether/ethyl acetate mixture (200:1) as
an eluent, affording 2e (3.8 g, 14.0 mmol) as a light yellow oil
=
Ph–H), 5.71 (s, 1H, CH), 2.48 (t, 2H, CH2), 1.66 (m, 2H, CH2),
1.34 (m, 4H, -(CH2)2-), 0.92 (t, 3H, CH3). 13C NMR (100 MHz,
CDCl3): d 201.25, 145.67, 136.93, 127.91, 125.80, 124.65, 119.13,
1
in 70 % yield. H NMR (300 MHz, CDCl3): d 13.32 (s, 1H, N–
EtOH
94.14, 42.19, 30.82, 24.04, 21.40, 12.80. UV l
312.9 nm.
max
H), 7.40–7.38 (m, 3H, Ph–H), 7.25–7.24 (m, 2H, Ph–H), 5.72 (s,
Anal. Calcd for C15H18F3NO: C, 63.15; H, 6.36; N, 4.91. Found:
C, 63.63; H, 6.31; N, 4.93.
1H, CH), 1.17 (s, 9H, -C(CH3)3). 13C NMR (100 MHz, CDCl3):
=
d 180.90, 176.84, 138.82, 129.34, 128.54, 128.39, 118.39, 87.77,
◦
EtOH
38.66, 30.63. UV l
326.1 nm. m.p. 90–91 C. Anal. Calcd
max
Synthesis of PhNHC(CF3)CHCO(i-Pr) (5c)
for C14H16F3NO: C, 61.98; H, 5.94; N, 5.16. Found: C, 62.16; H,
5.90; N, 5.11.
Compound 5c was prepared via a procedure similar to that for
2b as a light yellow oil in 42 % yield. 1H NMR (300 MHz,
CDCl3): d 11.80 (s, 1H, N–H), 7.37–7.18 (m, 5H, Ph–H), 5.75
=
Synthesis of PhNHC(PhCH CH)CHCOCF3 (2f)
(s, 1H, CH), 2.67 (m, 1H, -CH), 1.17 (d, 6H, -CH3). 13C NMR
=
Compound 2f was prepared via a procedure similar to that for
2b as a yellow oil in 34 % yield. H NMR (300 MHz, CDCl3):
d 12.31 (s, 1H, N–H), 7.67–7.57 (m, 3H, Ph–H), 7.41–7.23 (m,
8H, Ph–H and Ph–CH ), 6.85 (d, 1H, CH), 5.95 (s, 1H, CH).
13C NMR (300 MHz, CDCl3): d 176.85, 163.23, 139.58, 137.10,
1
(100 MHz, CDCl3): d 204.93, 146.20, 136.92, 127.90, 124.81,
EtOH
123.65, 119.10, 92.67, 39.85, 17.93. UV l
312.0 nm. Anal.
max
Calcd for C13H14F3NO: C, 60.70; H, 5.49; N, 5.44. Found: C, 60.53;
H, 5.47; N, 5.37.
=
=
=
134.77, 130.32, 129.54, 129.10, 127.87, 127.03, 124.70, 120.25,
EtOH
117.76, 87.20. UVl
max 334.0 nm Anal. Calcd for C18H14F3NO:
Synthesis of PhNHC(CF3)CHCO(C6H11) (5d)
C, 68.13; H, 4.45; N, 4.41. Found: C, 68.33; H, 4.39; N, 4.48.
Compound 5d was prepared via a procedure similar to that for
1
2b as a light yellow solid in 57 % yield. H NMR (300 MHz,
Synthesis of PhNHC(Et)CHCOCF3 (2g)
CDCl3): d 11.83 (s, 1H, N–H), 7.37–7.18 (m, 5H, Ph–H), 5.74
Compound 2g was prepared via a procedure similar to that for 2b
as a light yellow oil in 76 % yield. 1H NMR (300 MHz, CDCl3): d
12.62 (s, 1H, N–H), 7.45–7.32 (m, 3H, Ph–H), 7.19–7.16 (m, 2H,
=
(s, 1H, CH), 2.39 (m, 1H, -CH), 1.92–1.20 (m, 10H, -(CH2)5-).
13C NMR (100 MHz, CDCl3): d 204.20, 147.00, 136.97, 127.90,
125.74, 124.79, 119.05, 93.04, 50.00, 28.25, 24.87, 24.79. UV
◦
EtOH
=
Ph–H), 5.58 (s, 1H, CH), 2.40 (q, 2H, CH2), 1.14 (t, 3H, CH3).
l
312.9 nm. m.p. 40–41 C. Anal. Calcd for C16H18F3NO:
max
13C NMR (100 MHz, CDCl3): d 176.95, 173.72, 136.74, 130.24,
C, 64.64; H, 6.10; N, 4.71. Found: C, 64.48; H, 6.15; N, 4.65.
EtOH
127.61, 125.55, 117.63, 89.01, 25.52, 12.02. UV l
max 327.0 nm.
Anal. Calcd for C12H12F3NO: C, 59.26; H, 4.97; N, 5.76. Found:
C, 58.98; H, 4.93; N, 5.78.
=
Synthesis of PhNHC(CF3)CHCO(CH CH–Ph) (5f)
Compound 5f was prepared via a procedure similar to that for 2b
as a deep yellow oil in 32 % yield. 1H NMR (300 MHz, CDCl3):
Synthesis of PhNHC(n-C11H23)CHCOCF3 (2h)
=
d 12.71 (s, 1H, N–H), 7.46–7.15 (m, 11H, Ph–H and Ph–CH ),
Compound 2h was prepared via a procedure similar to that for 2b
as a light yellow oil in 57 % yield. 1H NMR (300 MHz, CDCl3): d
12.65 (s, 1H, N–H), 7.45–7.31 (m, 3H, Ph–H), 7.18–7.16 (m, 2H,
6.76 (d, 1H, CH), 5.74 (s, 1H, CH). 13C NMR (100 MHz,
=
=
CDCl3): d 189.57, 148.02, 141.26, 137.88, 134.95, 130.22, 129.23,
EtOH
129.03, 128.30, 127.26, 126.70, 125.61, 120.08, 96.00. UV l
max
=
Ph–H), 5.56 (s, 1H, CH), 2.35 (t, 2H, CH2), 1.52–1.19 (m, 18H,
361.9 nm. Anal. Calcd for C18H14F3NO: C, 68.13; H, 4.45; N, 4.41.
9CH2), 0.88 (t, 3H, CH3). 13C NMR (100 MHz, CDCl3): d 177.04,
Found: C, 68.28; H, 4.39; N, 4.47.
173.01, 137.24, 129.85, 127.51, 126.03, 118.00, 89.80, 32.54, 32.04,
30.49, 29.98, 29.87, 29.67, 29.35, 28.89, 28.35, 23.04, 14.41. UV
EtOH
Synthesis of PhNHC(CF3)CHCO(CHPh2) (5g)
l
max 327.3 nm. Anal. Calcd for C21H30F3NO: C, 68.27; H, 8.18;
N, 3.79. Found: C, 68.12; H, 8.16; N, 3.72.
Compound 5g was prepared via a procedure similar to that for
2b as a light yellow solid in 45 % yield. H NMR (300 MHz,
1
Synthesis of PhNHC(CF3)CHCO(n-C5H11) (5b)
CDCl3): d 11.87 (s, 1H, N–H), 7.38–7.17 (m, 15H, Ph–H), 5.79
13
=
To a solution of LDA (2 M in ether, 20 mL, 40 mmol), 2-heptanone
(2.8 mL, 20 mmol) in THF (40 mL) was added dropwise under
argon. The mixture was stirred at 0 ◦C for 2 h. The solution was
(s, 1H, CH), 5.18 (s, 1H, CHPh2). C NMR (100 MHz, CDCl3):
d 199.70, 148.01, 139.30, 137.62, 129.19, 129.04, 128.72, 127.25,
127.12, 125.87, 119.95, 95.60, 64.15. UV l
EtOH
319.1 nm. m.p.
max
9462 | Dalton Trans., 2009, 9452–9465
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90–92 ◦C. Anal. Calcd for C23H18F3NO: C, 72.43; H, 4.76; N, 3.67.
Found: C, 72.28; H, 4.71; N, 3.68.
Synthesis of titanium complex [PhNC(Cy)CHC O(CF3)]2TiCl2
(3d)
=
Complex 3d was prepared via a procedure similar to that for 3b as
1
red crystals in 65% yield. H NMR (300 MHz, CDCl3): d 7.46–
7.04 (m, 8H, Ph–H), 6.58 (d, 2H, Ph–H), 5.87 (s, 2H, CH), 2.09
Synthesis of PhNHC(CF3)CHCO(CF3) (5h)
=
According to the literature,34 to a well-stirred solution of
1,1,1,5,5,5-hexafluoroacetylacetone (2.8 mL, 20 mmol) and aniline
(9.2 mL, 100 mmol) in dry toluene (100 mL) under N2 was added
dropwise TiCl4 (1.6 mL, 15 mmol) in 30 mL dry toluene over a
period of 1 h. The dark brown reaction mixture was stirred for 1 h
and then heated to 130 ◦C overnight. After being cooled to room
temperature, the reaction mixture was diluted with ether (200 mL)
and stirred until the color of the precipitate totally changed to
(t, 2H, CH), 1.75–1.58 (m, 12H, 3CH2), 1.40–0.86 (m, 8H, 2CH2).
13C NMR (100 MHz, CDCl3): d 177.00, 156.51, 147.07, 128.57,
127.19, 125.49, 124.28, 119.53, 117.12, 101.26, 43.38, 28.97, 28.80,
24.05. Anal. Calc. for C32H34Cl2F6N2O2Ti: C, 54.03; H, 4.82; N,
3.94. Found: C, 54.12; H, 4.77; N, 3.88.
Synthesis of titanium complex [PhNC(t-Bu)CHCO(CF3)]2TiCl2
(3e)
R
light yellow. The mixture was filtered through Celiteꢀ, and the
collected precipitate was washed with ether. Concentration of the
combined filtrate gave the crude product. The crude product was
purified by column chromatography on silica gel with petroleum
ether/ethyl acetate mixture (200:1) as an eluent, affording 5h (2.5 g,
9.0 mmol) as a light yellow solid in 45 % yield. 1H NMR (300 MHz,
DMSO): d 11.53 (s, 1H, N–H), 7.62–7.04 (m, 5H, Ph–H), 6.02
Complex 3e was prepared via a procedure similar to that for 3b as
1
red crystals in 53% yield. H NMR (300 MHz, CDCl3): d 7.31–
7.15 (m, 8H, Ph–H in 3e-I and 3e-II), 6.75 (d, 2H, Ph–H in 3e-I),
=
=
6.38 (s, 2H, CH in 3e-II), 6.09 (s, 2H, CH in 3e-I), 1.03 (s, 18H,
t-Bu in 3e-I), 1.00 (s, 18H, t-Bu in 3e-II). 13C NMR (300 MHz,
CDCl3): d 178.94, 105.14, 41.90, 29.19 (For 3e-II) 178.12, 103.46,
42.25, 29.85 (For 3e-I), 158.97, 158.51, 147.45, 144.91, 127.86,
127.38, 126.84, 126.43, 126.29, 126.07, 125.90, 125.55, 121.12,
119.27, 117.42, 117.40, (For both 3e-I and 3e-II). Anal. Calc. for
C28H30Cl2F6N2O2Ti: C, 51.01; H, 4.59; N, 4.25. Found: C, 49.92;
H, 4.56; N, 4.19.
(s, 1H, CH). 13C NMR (100 MHz, CDCl3): d 180.51, 153.09,
=
EtOH
136.03, 129.28, 128.54, 126.15, 119.04, 116.51, 87.87. UV l
max
327.0 nm. m.p. 29–30 ◦C. Anal. Calcd for C11H7F6NO: C, 46.66;
H, 2.49; N, 4.95. Found: C, 45.62; H, 2.56; N, 5.01.
Synthesis of titanium complex
[PhNC(n-C5H11)CHCO(CF3)]2TiCl2 (3b)
Synthesis of titanium complex
=
[PhNC(Ph–CH CH)CHCO(CF3)]2TiCl2 (3f)
To a stirred solution of compound 2b (1.14 g, 4 mmol) in dried
diethyl ether (20 mL) at -78 C, a 1.6 M n-butyllithium hexane
solution (2.6 mL, 4.2 mmol) was added dropwise over 5 min. The
mixture was allowed to warm to room temperature and stirred for
3 h. Then, the mixture was added dropwise to TiCl4 (2 mmol) in
Complex 3f was prepared via a procedure similar to that for 3b as
a red solid in 61% yield. 1H NMR (300 MHz, CDCl3): d 7.51–7.46
(m, 20H, Ph–H), 6.85 (d, 2H, CH), 6.42 (d, 2H, CH), 6.03 (d,
◦
=
=
=
2H, CH). Anal. Calc. for C36H26Cl2F6N2O2Ti: C, 57.55; H, 3.49;
N, 3.73. Found: C, 57.34; H, 3.43; N, 3.66.
◦
dried diethyl ether (30 mL) at -78 C with stirring over 30 min.
The mixture was allowed to warm to room temperature and stirred
overnight. The evaporation of the solvent in reduced pressure
yielded a crude product. Dried CH2Cl2 and n-hexane were added
to the solid residue, and the mixture was stirred for 10 min. The
filtration of the mixture gave complex 3b as a deep red solid in 65
% yield. 1H NMR (300 MHz, CDCl3): d 7.46–7.06 (m, 8H, Ph–H),
=
Synthesis of titanium complex [PhNC(Et)CHC O(CF3)]2TiCl2
(3g)
Complex 3g was prepared via a procedure similar to that for 3b
as a red solid in 62% yield. 1H NMR (300 MHz, CDCl3): d 7.44–
7.10 (m, 8H, Ph–H), 6.63 (d, 2H, Ph–H), 5.81 (s, 2H, CH), 2.10
(t, 4H, CH2), 1.08 (d, 6H, CH3). 13C NMR (100 MHz, CDCl3):
d 176.85, 157.81, 148.64, 130.94, 129.05, 127.13, 125.86, 121.18,
120.36, 118.51, 30.86, 12.57. Anal. Calc. for C24H22Cl2F6N2O2Ti:
C, 47.79; H, 3.68; N, 4.64. Found: C, 47.58; H, 3.71; N, 4.56.
=
=
6.61 (d, 2H, Ph–H), 5.80 (s, 2H, CH), 2.04 (t, 4H, CH2), 1.45 (m,
4H, CH2), 1.14 (m, 8H, CH2CH2), 0.81 (t, 6H, CH3).13C NMR
(100 MHz, CDCl3): d 175.61, 156.91, 148.28, 129.62, 128.22,
126.72, 125.63, 120.92, 118.15, 105.34, 37.02, 31.52, 27.66, 21.93,
13.65. Anal. Calc. for C30H34Cl2F6N2O2Ti: C, 52.42; H, 4.99; N,
4.08. Found: C, 52.61; H, 4.93; N, 4.02.
Synthesis of titanium complex
[PhNC(n-C11H23)CHCO(CF3)]2TiCl2 (3h)
Synthesis of titanium complex [PhNC(i-Pr)CHCO(CF3)]2TiCl2
(3c)
Complex 3h was prepared via a procedure similar to that for 3b
as a red solid in 42% yield. H NMR (300 MHz, CDCl3): 7.41–
1
=
Complex 3c was prepared via a procedure similar to that for 3b
7.09 (m, 8H, Ph–H), 6.60 (d, 2H, Ph–H), 5.79 (s, 2H, CH), 2.04
1
as red crystals in 85% yield. H NMR (CDCl3): d 7.42–7.06 (m,
(t, 4H, CH2), 1.45–1.13 (m, 36H, -(CH2)9-), 0.87 (t, 6H, CH3).
13C NMR (100 MHz, CDCl3): d 174.61, 155.11, 147.26, 128.57,
127.55, 126.06, 124.70, 119.96, 117.15, 104.35, 36.03, 31.35, 28.38,
28.28, 28.19, 27.95, 27.83, 26.96, 26.66, 21.65, 13.07. Anal. Calcd.
for C42H58Cl2F6N2O2Ti: C, 58.95; H, 6.83; N, 3.27. Found: C,
58.69; H, 6.76; N, 3.23.
=
8H, Ph–H), 6.60 (d, 2H, Ph–H), 5.84 (s, 2H, CH), 2.49 (m,
2H, CH), 1.02 (d, 12H, CH3). 13C NMR (100 MHz, CDCl3):
d 178.57, 156.60, 147.13, 128.78, 127.39, 125.65, 124.40, 119.56,
117.19, 100.32, 32.59, 19.10. Anal. Calc. for C26H26Cl2F6N2O2Ti:
C, 49.47; H, 4.15; N, 4.44. Found: C, 49.13; H, 4.09; N, 4.38.
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Dalton Trans., 2009, 9452–9465 | 9463
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Synthesis of titanium complex
[PhNC(CF3)CHCO(n-C5H11)]2TiCl2 (6b)
139.16, 129.55, 129.21, 128.97, 128.68, 128.49, 127.68, 127.25,
126.65, 119.34, 103.35, 58.99. Anal. Calc. for C46H34Cl2F6N2O2Ti:
C, 62.82; H, 3.90; N, 3.19. Found: C, 62.67; H, 3.83; N, 3.25.
Complex 6b was prepared via a procedure similar to that for 3b as
a red solid in 51% yield. 1H NMR (300 MHz, CDCl3): 7.47–6.56
Synthesis of titanium complex [PhNC(CF3)CHCO(CF3)]2TiCl2
(6h)
=
(m, 10H, Ph–H), 6.27 (s, 2H, CH), 2.38 (t, 2H, CH2), 1.57 (m,
2H, CH2), 1.31(m, 4H, -(CH2)2-), 1.00 (t, 3H, CH3). 13C NMR
(100 MHz, CDCl3): d 185.77, 155.09, 146.95, 130.74, 129.92,
127.92, 126.55, 121.58, 119.87, 117.17, 35.96, 30.79, 29.03, 22.18,
12.55. Anal. Calc. for. C30H34Cl2F6N2O2Ti: C, 52.42; H, 4.99; N,
4.08. Found: C, 52.51; H, 5.03; N, 4.01.
Complex 6h was prepared via a procedure similar to that for 3b
as red needle crystals in 72% yield. 1H NMR (300 MHz, CDCl3):
d 7.41–7.07 (m, 8H, Ph–H), 6.85 (d, 2H, Ph–H), 6.15 (d, 2H,
13
=
CH). C NMR (100 MHz, CDCl3): d 175.25, 159.42, 145.67,
129.05, 128.08, 127.55, 126.94, 124.60, 118.07, 115.39, 98.79. Anal.
Calc. for C22H12Cl2F12N2O2Ti: C, 38.68; H, 1.77; N, 4.10. Found:
C, 38.48; H, 1.73; N, 4.04.
Synthesis of titanium complex [PhNC(CF3)CHCO(i-Pr)]2TiCl2
(6c)
Complex 6c was prepared via a procedure similar to that for
1
3b as red crystals in 45% yield. H NMR (CDCl3): d 7.37–7.21
(m, 8H, Ph–H), 6.76 (d, 2H, Ph–H), 5.80 (s, 2H, CH), 2.06
X-ray crystallography studies
=
(m, 2H, CH), 0.98 (d, 6H, CH3), 0.89 (d, 6H, CH3). 13C NMR
(100 MHz, CDCl3): d 189.72, 156.26, 146.68, 127.10, 126.80,
125.74, 125.46, 121.02, 118.00, 99.07, 35.36, 18.72, 18.32. Anal.
Calc. for C26H26Cl2F6N2O2Ti: C, 49.47; H, 4.15; N, 4.44. Found:
C, 49.23; H, 4.08; N, 4.39.
Single crystals of complexes 3c–e and 6c–d suitable for X-ray
structure determination were grown from hexane solution at
-20 ◦C in a glove box, thus maintaining a dry, O2-free environment.
X-ray intensities of complexes 3c–e and 6c–d were collected on
a Bruker Smart CCD diffractometer equipped with graphite
˚
monochromated Mo Ka radiation (l = 0.71073 A) at 187 K.
=
Synthesis of titanium complex [PhNC(CF3)CHC O(Cy)]2TiCl2
(6d)
Empirical absorption corrections were applied to the data using
the SADABS program.35 The structures were solved by the direct
method and refined by the full-matrix least-squares on F2 using the
SHELXTL-97 program.36 The Flack parameter is 0.5 and 0.47 for
structures 726031 and 726032, which means that the crystals are
thus twinned by inversion and the ratios of the two configurations
are 1:1 and 0.53:0.47, respectively. All of the non-hydrogen atoms
were refined anisotropically. The positions of the hydrogen atoms
were calculated theoretically and included in the final cycles of
refinement in a riding model along with the attached carbons.
Complex 6d was prepared via a procedure similar to that for 3b as
red crystals in 81% yield. H NMR (300 MHz, CDCl3): d 7.37–
7.20 (m, 8H, Ar), 6.74 (d, 2H, Ar), 5.93, (s, 2H, CH, trans-
1
=
=
configuration), 5.78 (s, 2H, CH, cis-configuration), 1.73–1.59 (m,
10H, CH(CH2)2), 1.24–0.88 (m, 12H, (CH2)3).1H NMR (300 MHz,
toluene-d8): d 7.44 (d, 2H, Ar, cis-configuration), 7.26 (d, 2H, Ar,
trans-configuration), 7.10–6.81 (m, 8H, Ar), 5.92 (s, 2H, CH,
trans-configuration), 5.71 (s, 2H, CH, cis-configuration), 1.73–
=
=
1.59 (m, 10H, CH(CH2)2), 1.24–0.88 (m, 12H, (CH2)3). 13C NMR
(100 MHz, CDCl3): d 189.04, 156.03, 145.20, 126.80, 126.67,
125.79, 125.37, 121.03, 118.03, 98.74, 44.82, 28.57, 28.25, 24.54.
Anal. Calc. for C32H34Cl2F6N2O2Ti: C, 54.03; H, 4.82; N, 3.94.
Found: C, 53.82; H, 4.75; N, 3.88.
Ethylene polymerization
Polymerization was carried out under atmospheric pressure in
toluene in a 150 ml glass reactor equipped with a mechanical
stirrer. Toluene (50 mL) was introduced into the argon-purged
reactor and stirred vigorously (600 rpm). The toluene was kept
at a prescribed polymerization temperature, and then the ethylene
gas feed was started. After 15 min, the polymerization was initiated
by the addition of a heptane solution of MMAO and a toluene
solution of one of the titanium complexes into the reactor with
vigorous stirring (600 rpm). After a prescribed time, isobutyl
alcohol (10 mL) was added to terminate the polymerization
reaction, and the ethylene gas feed was stopped. The resulting
mixture was added to acidic methanol. The solid polyethylene was
Synthesis of titanium complex
=
[PhNC(CF3)CHCO(PhCH CH)]2TiCl2 (6f)
Complex 6f was prepared via a procedure similar to that for 3b as
purple crystals in 66% yield. 1H NMR (300 MHz, CDCl3): d 7.59
(m, 4H, Ph–H), d 7.50–7.46 (m, 8H, Ph–H) 7.20–7.15 (m, 4H, Ph–
=
H), 7.59 (m, 4H, Ph–H), 6.98 (t, 4H, Ar), 6.78 (d, 2H, CH), 6.32
13
=
=
(d, 2H, CH), 5.92 (d, 2H, CH). C NMR (100 MHz, CDCl3):
d 188.89, 173.16, 155.50, 142.95, 141.16, 131.53, 129.64, 128.60,
128.01, 127.48, 126.81, 125.71, 125.43, 124.93, 119.62, 101.95.
Anal. Calc. for C36H26Cl2F6N2O2Ti: C, 57.55; H, 3.49; N, 3.73.
Found: C, 57.34; H, 3.43; N, 3.67.
◦
isolated by filtration, washed with methanol, and dried at 60 C
for 24 h in a vacuum oven.
Acknowledgements
Synthesis of titanium complex
=
[PhNC(CF3)CHC O(CHPh2)]2TiCl2 (6g)
The authors are grateful for the subsidy provided by the Na-
tional Natural Science Foundation of China (Nos. 20734002
and 50525312), and by the Special Funds for Major State Basis
Research Projects (No. 2005CB623800) from the Ministry of
Science and Technology of China.
Complex 6g was prepared via a procedure similar to that for 3b
as a brown solid in 70% yield. H NMR (300 MHz, CDCl3):
1
=
d 7.40–7.25 (m, 30H, Ph–H), 5.85 (s, 2H, CH), 5.08 (s, 2H,
CHPh2). 13C NMR (100 MHz, CDCl3): d 185.45, 156.97, 147.43,
9464 | Dalton Trans., 2009, 9452–9465
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©

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Mohri, J. Saito, S. Ishii, H. Terao, T. Nakano, H. Tanaka and T. Fujita,
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