New titanium(IV) complexes with 2-cyclopentadienylbenzylamido ligands: Synthesis, characterization, and catalytic properties for ethylene polymerization and copolymerization with 1-hexene

Article abstract of DOI:10.1021/om4003945

A series of new half-sandwich titanium(IV) complexes chelated with 2-(tetramethylcyclopentadienyl)benzylamido ligands, 2-Me₄CpC ₆H₄CH₂(R)NTiCl₂ (R = ⁱPr (1), Cy (2), ⁿPr (3), 4-M

Full text of DOI:10.1021/om4003945

Article
pubs.acs.org/Organometallics
New Titanium(IV) Complexes with 2‑Cyclopentadienylbenzylamido
Ligands: Synthesis, Characterization, and Catalytic Properties for
Ethylene Polymerization and Copolymerization with 1‑Hexene
Xin Tao, Qiaolin Wu, Hang Huo, Wei Gao, and Ying Mu*
The State Key Laboratory for Supramolecular Structure and Materials, School of Chemistry, Jilin University, 2699 Qianjin Street,
Changchun 130012, People’s Republic of China
S
* Supporting Information
ABSTRACT: A series of new half-sandwich titanium(IV)
complexes chelated with 2-(tetramethylcyclopentadienyl)-
i
benzylamido ligands, 2-Me4CpC6H4CH2(R)NTiCl2 (R = Pr
(1), Cy (2), nPr (3), 4-MePh (4)), have been synthesized from
the chlorotrimethylsilane elimination reactions of TiCl4 with
the double-trimethylsilyl-substituted preligands 2-Me4(TMS)-
CpC6H4CH2(R)N(TMS) (R = Pr (TMS2L1), Cy (TMS2L2), Pr (TMS2L3), 4-MePh (TMS2L4)). The free ligands H2L1−
H2L4 were synthesized by reduction of the corresponding imine compounds 2-Me4CpHC6H4CHNR with LiAlH4, while the
imine compounds were formed in situ by a condensation reaction of 2-tetramethylcyclopentadienylbenzaldehyde with the
i
n
1
corresponding amine. The free ligands were characterized by LC-MS and H NMR spectroscopy, and the titanium complexes
1
were characterized by H and 13C NMR, elemental analyses, and single-crystal X-ray crystallography. The X-ray crystallography
analysis reveals that these titanium complexes possess a three-legged piano-stool geometry with the amide N atom in a mitered
six-membered chelating ring and the two chloride atoms as the legs. The angle between the cyclopentadienyl plane and the
attached phenyl plane in these complexes (59.2, 62.7, and 61.9° for complexes 1, 2, and 4, respectively) is much less than 90° in
the solid state. Upon activation with AliBu3 and Ph3CB(C6F5)4, complexes 1−4 exhibit reasonable catalytic activity for ethylene
homopolymerization and copolymerization with 1-hexene at 110 °C, producing high-molecular-weight polyethylenes and
poly(ethylene-co-1-hexenes) with relatively high comonomer incorporation. Complex 4 was found to show higher catalytic
activity for ethylene/1-hexene copolymerization than complexes 1−3 under similar conditions, while complexes 1−3 produce
poly(ethylene-co-1-hexenes) with higher comonomer incorporation.
Chart 1. Typical Monocyclopentadienyl Titanium
Complexes with a Chelating Side Arm
INTRODUCTION
■
Group 4 metallocene catalysts have attracted extensive interest
in the past decades due to their unique properties and
advantages as olefin polymerization catalysts.1−5 Many research
efforts have been focused on the development of new
homogeneous metallocene catalysts for producing a variety of
high-performance polyolefin materials and understanding the
relationship between the structure and their catalytic property
of a type of catalyst with respect to polymer chain composition
and architecture.6−9 Since the so-called constrained-geometry
titanium complexes were reported to exhibit excellent catalytic
performance in the copolymerization of ethylene with α-
olefins,10−12 a variety of monocyclopentadienyltitanium com-
plexes with a chelating side arm containing a nitrogen, oxygen,
or phosphorus donor have been developed.13−17 Several typical
titanium complexes of this type are shown in Chart 1. The
silylene-bridged Cp-amido titanium complexes a, the typical
constrained-geometry catalysts, have been known to show
several advantages over the bis(cyclopentadienyl) metallocene
catalysts in thermal stability, high α-olefin incorporation, and
producing high molecular weight polymers in the ethylene/α-
olefin copolymerization.14 The cyclopentadienyl-phenoxytita-
nium complexes b were reported to exhibit high catalytic
activity and α-olefin incorporation for ethylene/α-olefin
copolymerization but produce polymers with low molecular
weights due to their too open coordination environment.15 The
o-phenylene-bridged Cp-amido titanium complexes c16 and the
Received: May 5, 2013
© XXXX American Chemical Society
A
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Article
so-called PHENICS complexes d (phenoxy induced complex of
Sumitomo),17 with more crowded coordination environments
in both cases, were reported to show good catalytic activity and
efficient comonomer incorporation in ethylene/α-olefin co-
polymerization and produce polymers with relatively high
molecular weights. It is therefore of interest to develop
analogous titanium(IV) complexes with more bulky ligands
and explore their catalytic performance for ethylene/α-olefin
copolymerization. We have recently synthesized a number of
new titanium(IV) complexes of the type 2-
Me4CpC6H4CH2(R)NTiCl2 (R = Pr (1), Cy (2), Pr (3), 4-
MePh (4)) and found that they show good catalytic activity for
ethylene/1-hexene copolymerization at 110 °C and produce
high-molecular-weight poly(ethylene-co-1-hexenes) with high
comonomer incorporation. In this paper we report the
synthesis and characterization of these complexes and their
catalytic performance in ethylene polymerization and ethylene/
1-hexene copolymerization.
CpH proton, indicating that these compounds exist in the form
of one major isomer. In addition, the two methylene protons of
PhCH2 in these free ligands are magnetically inequivalent and
1
show two sets of doublets in their H NMR spectra. These
results might be explained by the formation of a C−H···N
hydrogen bond between the acidic H atom of the Cp ring and
the nitrogen atom.19 Similar results have also been observed for
related 2-(tetramethylcyclopentadienyl)phenol15 and 2-(tetra-
methylcyclopentadienyl)-N,N-dimethylaniline19 derivatives,
and the C−H···N hydrogen bond has been confirmed by
single-crystal X-ray crystallography in the latter case.
i
n
Synthesis of Complexes. The new titanium complexes 1−
4 were synthesized in moderate yields (35−50%) from the
chlorotrimethylsilane elimination reactions20 of TiCl4 with the
double-trimethylsilyl-substituted preligands 2-Me4(TMS)-
CpC6H4CH2(R)N(TMS) (R = iPr (TMS2L1), Cy
n
(TMS2L2), Pr (TMS2L3), 4-MePh (TMS2L4)), as shown in
Scheme 2. The double-trimethylsilyl-substituted preligands
were synthesized by treatment of the corresponding free
ligands with 2 equiv of n-BuLi and 2 equiv of Me3SiCl
sequentially in THF. Crude preligands TMS2L1−TMS2L4
were obtained after removal of the formed LiCl by filtration and
used directly for the chlorotrimethylsilane elimination reaction
without further purification due to their poor stability. The
titanium complexes 1−4 were purified by recrystallization from
CH2Cl2/hexane. These complexes are fairly soluble in CH2Cl2
and toluene and slightly soluble in petroleum ether and hexane.
RESULTS AND DISCUSSION
■
Synthesis of Ligands. The free ligands 2-
i
n
Me4CpHC6H4CH2(R)NH (R = Pr (H2L1), Cy (H2L2), Pr
(H2L3), 4-MePh (H2L4)) were synthesized in high yields
(about 60−70%) by a two-step procedure: a condensation
reaction of 2-(tetramethylcyclopentadienyl)benzaldehyde with
the corresponding amine derivatives18 followed by reduction of
the formed imine compounds with LiAlH4, as illustrated in
Scheme 1. The imine compounds were directly reduced in
1
They were all characterized by H and 13C NMR spectroscopy
along with elemental analyses, and the structures of complexes
1, 2, and 4 were confirmed by X-ray crystallography.
Scheme 1. Synthetic Route for the Free Ligands H2L1−H2L4
The 1H NMR spectra of complexes 1−4 all show two sets of
singlets for the CpCH3 protons and one singlet for the PhCH2
protons. In comparison with the corresponding signals of their
free ligands, the signals observed for the methine protons of the
iPr group in complex 1 and the methine protons of the Cy
group in complex 2 shift downfield from 2.54−2.64 and 2.19−
2.29 ppm to 5.82−5.95 and 5.37−5.46 ppm, respectively.
Similarly, the signal of NCH2Et protons in complexes 3 shifts
1
downfield from 2.39−2.43 to 4.25−4.30 ppm. The H and 13C
NMR spectroscopic analysis of these complexes confirms that
the N atom and the Cp ring have been attached to the titanium
metal center of these complexes, and all complexes are Cs-
symmetric in solution.
Crystallographic Analysis of Complexes 1, 2, and 4.
The molecular structures of complexes 1, 2, and 4 were
determined by single-crystal X-ray diffraction analysis. The
molecular structures of these complexes with the atom-
numbering schemes are shown in Figures 1−3, and selected
bond lengths and angles are given in Table 1. Crystallographic
data indicate that crystals of complexes 2 and 4 belong to the
monoclinic system and P21/n space group, while complex 1
aprotic solvent (Et2O or THF) without isolation due to their
poor stability. H2L1 and H2L3 were synthesized from reactions
carried out in Et2O, while the sterically bulkier free ligands
H2L2 and H2L4 could only be obtained from reactions carried
out in THF in high yields, presumably due to the relatively
good solubility of LiAlH4 in THF. These free ligands were
1
characterized by LC-MS and H NMR spectroscopy. LC-MS
shows that these compounds were obtained in about 95%
1
purity, and the [M + H] ions were clearly observed. The H
NMR spectra of all free ligands show mainly three singlets and
one doublet for the CpCH3 protons and one quartet for the
Scheme 2. Synthetic Route for Complexes 1−4
B
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Figure 1. Perspective view of 1 with thermal ellipsoids drawn at the
30% probability level. Hydrogens are omitted for clarity.
Figure 3. Perspective view of 4 with thermal ellipsoids drawn at the
30% probability level. Hydrogens are omitted for clarity.
distances in these complexes are all shorter than the estimated
value (2.02 Å) for a Ti−N single bond according to Pauling’s
covalent radii,22 demonstrating a TiN double-bond character.
The Ti−Cl bond distances (2.276−2.305 Å) in these
complexes are in agreement with those observed for related
N- or O-functionalized cyclopentadienyl titanium dichloride
complexes.14−17,21 Ti−Cp(cent) distances are close to each
other for complexes 1 (2.020 Å), 2 (2.019 Å), and 4 (2.023 Å).
Similarly, the Ti−CCp(av) (av = average) distances (2.353 Å for
1, 2.354 Å for 2, and 2.357 Å for 4) are also close to each other.
In these complexes, the individual Ti−CCp bond distances
range from 2.321 to 2.376 Å, with the Ti−C3 and Ti−C4
distances (2.3755(18) and 2.3726(18) Å for 1, 2.3688(19) and
2.3762(18) Å for 2, and 2.3744(18) and 2.3681 Å for 4) being
obviously longer than the remaining Ti−CCp bond lengths
(average 2.3386, 2.3411, and 2.3470 Å for 1, 2, and 4,
respectively), indicating that the central titanium atom is not
located exactly below the center of the Cp ring due to the
coordination of the amido N atom. The N−Ti−Cp(cent)
angles of complexes 1, 2, and 4 (110.5° for 1 and 4 and 110.4°
for 2) are obviously larger than those observed in the known N-
functionalized titanocene complexes a (107.0−107.6°)21 and c
(104.6−106.1°),16 which is indicative of these complexes
possessing a more crowded coordinating environment
surrounding the central titanium atom than the reported
similar complexes. The two N−Ti−Cl angles (104.9(5) and
106.4(5)° for 1, 105.7(5) and 107.0(5)° for 2, and 105.0(5)
and 109.3(5)° for 4) in each complex are different, since these
complexes are not Cs-symmetric in the solid state, with the
angles between the Cp plane and the attached phenyl plane
(59.2° for 1, 62.7° for 2, and 61.9° for 4) being much less than
the 90° of ideal Cs-symmetric molecules. The Cl−Ti−Cl angles
(104.3(3)° for 1, 103.8(2)° for 2, and 102.3(2)° for 4) change
in the order 1 > 2 > 4. In addition, the sum of the bond angles
around the amido nitrogen atom is 359.6° for 1, 359.4° for 2,
and 358.9° for 4, respectively, indicating π donation of an
electron pair onthe N atom to the titanium through sp2
hybridization. These structural features may affect their catalytic
performance by influencing the rate of olefin molecule
coordination to the titanium atom and insertion into the
Figure 2. Perspective view of 2 with thermal ellipsoids drawn at the
30% probability level. Hydrogens are omitted for clarity.
crystallizes in the monoclinic system and C2/c space group. All
three complexes possess a three-legged piano-stool geometry
with a distorted-octahedral coordination environment around
the central titanium atom. As can be seen from their crystal
structures, the coordination of the nitrogen atom to the central
metal in these complexes builds a six-membered chelating ring
in a position approximately vertical to the cyclopentadienyl
ring. The six-membered chelating ring, together with the group
at the nitrogen atom, constructs a relatively crowded
coordinating environment surrounding the central titanium
atom. The Ti−N distances in complexes 1, 2, and 4 (1.868(15)
Å for 1, 1.869(16) Å for 2, and 1.895(15) Å for 4) are slightly
shorter than those observed for complexes a (1.901−1.907 Å)21
and c (1.900−1.923 Å)16 in Chart 1. Complex 4 has the longest
Ti−N bond distance among these complexes, which is
reasonable, since the amido N atom with the 4-methylphenyl
group in complex 4 has relatively poor electron-donating ability
in comparison to those in complexes 1 and 2. The Ti−N bond
C
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Table 1. Selected Bond Lengths (Å) and Bond Angles (deg) for Complexes 1, 2, and 4
1
2
4
Ti(1)−N(1)
Ti(1)−Cl(1)
Ti(1)−Cl(2)
1.868(15)
2.301(6)
2.302(6)
1.869(16)
2.297(6)
2.305(6)
1.895(15)
2.276(6)
2.295(6)
Ti(1)−CCp (range)
Ti(1)−CCp (av)
Ti(1)−Cp(cent)
C(16)−N(1)
2.321(17)−2.376(18)
2.353
2.328(17)−2.376(18)
2.354
2.334(17)−2.374(18)
2.357
2.020
2.019
2.023
1.458(2)
1.493(2)
104.32(3)
104.88(5)
106.36(5)
110.5
1.463(2)
1.480(2)
103.82(2)
105.74(5)
106.95(5)
110.4
1.474(2)
1.451(2)
102.34(2)
105.00(5)
109.27(5)
110.5
C(17)−N(1)
Cl(1)−Ti(1)−Cl(2)
N(1)−Ti(1)−Cl(1)
N(1)−Ti(1)−Cl(2)
Cp(cent)−Ti−N(1)
C(16)−N(1)−Ti(1)
C(17)−N(1)−Ti(1)
C(16)−N(1)−C(17)
N(1)−C(16)−C(15)
140.93(13)
104.84(12)
113.84(15)
115.66(16)
59.2
141.81(12)
103.49(11)
114.09(15)
114.85(17)
62.7
140.34(12)
108.02(11)
110.51(14)
115.66(16)
61.9
a
Cp∠Ph
a
Angle between a cyclopentadienyl plane and an attached phenyl plane.
growing polymer chain, as well as the rate of the polymer chain
termination.
Polymerization. Ethylene polymerizations using complexes
1−4 as precatalysts under different conditions were examined,
and the results are summarized in Table 2. Upon activation
catalytic activity of complex 4 with a bulkier but less electron
donating L4 ligand is higher than that of complex 2 with a less
bulky but more electron-donating L2 ligand further demon-
strates the importance of the steric effect of the ligand. As
observed in other olefin polymerization catalyst systems, the
catalytic activity of these titanium catalyst systems is dependent
on the Al/Ti molar ratio. The maximum catalytic activity data
were obtained at Al/Ti molar ratios of about 180. The catalytic
performance of these catalyst systems was also examined at
different polymerization temperatures (80 and 110 °C), and
relatively high catalytic activities were observed at 110 °C,
demonstrating good thermal stability of these catalyst systems.
It was found that the molecular weight of the resultant
polyethylenes is remarkably dependent on the structure of the
catalyst, with the highest molecular weight polyethylenes being
produced by catalyst 4, due probably to the relatively large
steric hindrance of its ligand in the chain-transfer reaction.24
The influence of the Al/Ti molar ratio and the polymerization
temperature on the polymer molecular weight was also
investigated. As expected, the molecular weight of the obtained
polyethylenes decreases with the increase in Al/Ti molar ratio
and the elevation in polymerization temperature due to the
acceleration of both the chain transfer reaction to alkylalumi-
num and the β-hydride elimination reaction. In addition, the
melting temperature of the resultant polyethylenes (137.2−
141.3 °C) is in the normal range for linear polyethylene.
Copolymerization reactions of ethylene with 1-hexene using
complexes 1−4 as precatalysts, activated with AliBu3 and
Ph3CB(C6F5)4, were also explored, and the experimental results
are summarized in Table 3. As observed in the ethylene
homopolymerization, the catalytic activity of these catalyst
systems for the ethylene/1-hexene copolymerization under
similar conditions also changes in the order 4 > 2 > 1 > 3. It is
worth noting that the catalytic activity data of these catalytic
systems for most copolymerization reactions are higher than
those observed for the ethylene homopolymerization reactions
due to the comonomer effect. The comonomer effect for these
catalyst systems can be clearly seen from the data in Table 3.
Similar results have previously been observed in the ethylene/1-
hexene copolymerization reaction with other half-sandwich
titanium(IV) catalyst systems.23,25 The obtained poly(ethylene-
Table 2. Summary of Ethylene Polymerization Catalyzed by
a
1−4/AliBu3/Ph3CB(C6F5)4 Systems
c
d
Al/
Ti
temp
(°C)
yield
(g)
Mη
Tm
b
entry cat.
activity
(×104)
(°C)
1
1
1
1
1
1
1
2
2
3
3
4
4
120
150
180
210
240
180
180
180
180
180
180
180
110
110
110
110
110
80
0.41
0.68
0.85
0.79
0.61
0.71
1.39
1.26
0.58
0.41
1.78
1.66
820
1360
1700
1580
1220
1420
2780
2520
1160
820
92.6
82.8
78.2
73.6
63.2
96.5
85.7
102.6
65.4
82.3
101.1
116.4
139.2
139.8
140.1
138.5
138.9
140.4
140.1
139.6
137.2
138.0
141.3
141.1
2
3
4
5
6
7
110
80
8
9
110
80
10
11
12
110
80
3560
3320
a
Polymerization conditions: solvent, 60 mL of toluene; catalyst, 2 ×
10−6 mol; B/Ti molar ratio, 1.5; ethylene pressure, 5 bar; time, 15 min.
b
c
In units of kg of PE (mol of Ti)−1 h−1
.
Measured in
d
decahydronaphthalene at 135 °C. Determined by DSC at a heating
rate of 10 °C min−1.
with AliBu3 and Ph3CB(C6F5)4, complexes 1−4 all exhibit
moderate catalytic activity for the ethylene polymerization
reaction. Under similar conditions, the catalytic activity
decreases in the order 4 > 2 > 1 > 3, which indicates that
the catalytic activity of these complexes is notably influenced by
the nature of the substituents on their amido N atoms. As is
known for group 4 metallocene catalysts, electron-donating
substituents on the ligands stabilize the catalytically active
cationic species during the polymerization and improve the
catalytic activity of the catalyst; bulky ligands weaken the
interaction between the catalytically active cationic species and
the anionic cocatalyst15b,c,23 and therefore could increase the
catalytic activity of the catalyst as well. The fact that the
D
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Article
geometry catalyst systems.27 GPC analysis on the copolymers
reveals that the poly(ethylene-co-1-hexenes) produced by these
catalysts possess relatively high molecular weights (Mw = (8−
23) × 104) in comparison to those formed by similar catalyst
systems16a,17f and that the molecular weight distribution is
basically unimodal and narrow, being characteristic for
metallocene polyolefins. The aforementioned capability of the
new catalyst systems to efficiently catalyze the copolymerization
of ethylene with α-olefins and produce high-molecular-weight
copolymers with high comonomer incorporation is just what is
required for this type of catalyst.
Table 3. Summary of Ethylene/1-Hexene Copolymerization
a
Catalyzed by 1−4/AliBu3/Ph3CB(C6F5)4 Systems
amt of 1-
hexene
(mol/L)
1-hexene
c
d
yield
(g)
content
Mw
M /
wd
b
entry cat.
activity
(mol %)
(×104) Mn
13
14
15
16
17
18
10
20
21
22
23
24
1
1
1
2
2
2
3
3
3
4
4
4
0.5
1.0
1.5
0.5
1.0
1.5
0.5
1.0
1.5
0.5
1.0
1.5
0.69
0.91
0.76
0.82
1.43
1.05
0.22
0.34
0.27
2.18
2.59
2.32
1380
1820
1520
1640
2860
2010
440
14.7
21.4
30.0
12.6
19.5
27.9
13.8
20.6
28.7
3.6
13.16
11.88
9.71
3.13
3.48
3.92
2.61
2.88
3.11
2.63
2.96
3.13
2.48
2.67
2.98
15.56
13.90
10.24
9.16
CONCLUSION
680
8.74
■
540
8.19
A series of new titanium(IV) complexes with chelated 2-
(tetramethylcyclopentadienyl)benzylamido ligands, 2-
Me4CpC6H4CH2(R)NTiCl2, have been synthesized from the
reactions of TiCl4 with the double-trimethylsilyl-substituted
preligands 2-Me4(TMS)CpC6H4CH2(R)N(TMS). The free
ligands H2L1−H2L4 can be synthesized by reduction of the
corresponding in situ formed imine compounds 2-
4360
5180
4640
22.98
21.58
21.33
5.3
7.9
a
Polymerization conditions: toluene + 1-hexene, total 60 mL; catalyst,
2 × 10−6 mol; Al/Ti molar ratio, 180; B/Ti molar ratio, 1.5; time, 15
b
min; temperature, 110 °C; ethylene pressure, 5 bar. In units of kg of
c
polymer (mol of Ti)−1 h−1. Calculated on the basis of 13C NMR
1
Me4CpHC6H4CHNR with LiAlH4. H NMR spectroscopic
d
spectra. Measured by GPC analysis.
analysis indicates that the free ligands exist mainly in one form
of their three isomers due to the formation of a C−H···N
hydrogen bond between the acidic H atom of the Cp ring and
the nitrogen atom. X-ray crystallographic analysis demonstrates
that the half-metallocene titanium(IV) complexes adopt a
pseudo-octahedral coordination environment, with the N atom
bonding to the Ti metal center. Upon activation with AliBu3
and Ph3CB(C6F5)4, complexes 1−4 exhibit moderate catalytic
activity for ethylene homopolymerization and copolymerization
with 1-hexene at 110 °C, producing high-molecular-weight
polyethylenes and poly(ethylene-co-1-hexenes) with high
comonomer incorporation. Complex 4 shows a higher catalytic
activity for ethylene/1-hexene copolymerization than com-
plexes 1−3 under similar conditions, while complexes 1−3
produce poly(ethylene-co-1-hexenes) with higher comonomer
incorporation.
co-1-hexenes) were analyzed by 13C NMR and GPC. The 13C
NMR spectra for typical copolymer samples are shown in the
Supporting Information. On the basis of the 13C NMR
analysis,26 the comonomer content in the poly(ethylene-co-1-
hexenes) was calculated and the data are given in Table 4. It
can be seen from these results that the comonomer
incorporation ability of these catalyst systems is evidently
dependent on the structure of the catalyst. The comonomer
contents of the copolymers obtained with complexes 1−3 are
quite high, being comparable to those produced by similar N-
or O-functionalized titanocene catalyst systems under similar
conditions.16a,17f In comparison, complex 4 produces copoly-
mers with relatively low comonomer contents due probably to
the relatively large steric hindrance of its ligand. It has been
known that the comonomer incorporation ability of a catalyst
system can be affected by several factors. In the present work,
the steric bulk of the ligands in these complexes seems to be a
major issue. A large steric hindrance from the ligands would
block the coordination of the comonomer to the metal center
of the catalyst. Table 4 summarizes the monomer sequence
distribution and the rErH values for typical poly(ethylene-co-1-
hexene) samples estimated on the basis of 13C NMR
spectroscopy. The calculated rErH values of about 0.2 imply
that the 1-hexene incorporation in the present system does not
proceed in a random manner as observed in the constrained-
EXPERIMENTAL SECTION
■
All manipulations involving air- and/or moisture-sensitive compounds
were carried out under a nitrogen atmosphere (ultrahigh purity) using
either standard Schlenk techniques or glovebox techniques. Toluene,
diethyl ether, THF, and n-hexane were distilled under nitrogen in the
presence of sodium and benzophenone. CH2Cl2 and 1-hexene were
purified by distilling over calcium hydride before use. 2-
(Tetramethylcyclopentadienyl)benzaldehyde18 and Ph3CB(C6F5)4
were prepared according to literature procedures. Polymerization
grade ethylene was further purified by passage through columns of 5 Å
molecular sieves and MnO. AliBu3, n-BuLi, TMSCl, LiAlH4, and TiCl4
Table 4. Monomer Sequence Distributions for Poly(ethylene-co-1-hexenes) Obtained with the 1−4/AliBu3/Ph3CB(C6F5)4
a
Systems
c
d
triad (%)
dyad (%)
b
e
entry cat. content of 1-hexene (mol %)
EEE
EEH + HEE
HEH
EHE
EHH + HHE
HHH
EE
EH + HE
HH
rErH
13
15
18
21
24
1
1
2
3
4
14.7
30.0
27.9
28.7
7.9
64.8
32.9
37.6
36.7
80.6
11.7
21.3
18.5
18.1
7.2
trace
2.8
23.5
36.0
36.1
36.3
12.2
trace
7.0
trace
trace
trace
trace
trace
70.7
43.6
46.9
45.7
84.2
29.3
52.9
50.4
51.1
15.8
trace
3.5
0.22
0.20
0.22
2.3
5.5
2.7
2.6
6.4
3.2
trace
trace
trace
a
b
c
For polymerization condition,: see Table 3. 1-Hexene content in mol % estimated on the basis of 13C NMR spectra. Calculated by 13C NMR
d
spectra. [EE] = [EEE] + 1/2[EEH + HEE], [EH + HE] = [HEH] + [EHE] + /2{[EEH + HEE] + [HHE+EHH]}, [HH] = [HHH] + /2[HHE
1
1
+EHH]. rErH = 4[EE][HH]/[EH + HE].2
e
E
dx.doi.org/10.1021/om4003945 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
were purchased from Aldrich or Acros. 1H and 13C NMR spectra were
measured using a Varian Mercury-300 NMR spectrometer. 13C NMR
spectra of the copolymers were recorded on a Varian Unity-400 NMR
spectrometer at 135 °C with o-C6D4Cl2 as the solvent. LC-MS were
recorded on a DIONEX Ultimate 3000 liquid chromatograph and a
Bruker HCT mass spectrometer in ESI mode. The molecular weight of
the polyethylenes was measured in decahydronaphthalene at 135 °C
by a Ubbelohde viscometer according to the following equation: [η] =
(6.77 × 10−4)Mη0.67. Molecular weights and molecular weight
distributions of the copolymer samples were measured on a PL-
GPC 220 instrument at 150 °C with 1,2,4-trichlobenzene as the
eluent. The melting points of the polymers were measured by
differential scanning calorimetry (DSC) on a NETZSCH DSC 204
instrument at a heating/cooling rate of 10 °C/min from 35 to 160 °C,
and the data from the second heating scan were used.
Synthesis of Complex 1. To a solution of free ligand H2L1 (1.35
g, 5.00 mmol) in 20 mL of THF was added dropwise a solution of n-
butyllithium (5.43 mL, 10.0 mmol) in n-hexane at −78 °C. The
reaction mixture was warmed to room temperature and stirred for 3 h.
Trimethylsilyl chloride (1.27 mL, 10.0 mmol) was added, and the
mixture was then heated at 60 °C for 5 h. The solvents were removed
under reduced pressure, and the residue was redissolved in toluene (20
mL). The LiCl precipitate was filtered off, and the solution was slowly
added to a solution of TiCl4 (0.55 mL, 5.00 mmol) in toluene (30 mL)
at room temperature. The reaction mixture was stirred at room
temperature for 1 h and then at 70 °C overnight. The precipitate was
filtered off, and the solvent was removed under reduced pressure to
leave an orange residue. Recrystallization from CH2Cl2/hexane gave
pure product 1 (0.938 g, 48.6%) as orange crystals. Anal. Calcd for
C19H25Cl2NTi (385.08): C, 59.09; H, 6.53; N, 3.63. Found: C, 59.19;
1
Synthesis of 2-Me4CpHC6H4CH2(iPr)NH (H2L1). To a solution
of 2-(2,3,4,5-tetramethylcyclopentadienyl)benzaldehyde (2.26 g, 10.0
mmol) in absolute diethyl ether (30 mL) were added isopropylamine
(0.591 g, 10.0 mmol), 4 Å molecular sieves (MS), and formic acid (2
drops), and the mixture was stirred at room temperature under a
nitrogen atmosphere. After the disappearance of the aldehyde was
confirmed by 1H NMR spectroscopy, the molecular sieves were
filtered off. To the solution was slowly added LiAlH4 at 0 °C, and the
reaction mixture that formed was warmed to room temperature and
stirred for 1 h under a nitrogen atmosphere. After the reaction mixture
changed color from orange to colorless, the reaction was quenched
with 1 mL of water and the insoluble solids were filtered off. Further 3
M NaOH (1 mL) and H2O (3 mL) were added to the filtrate, and the
product was extracted with diethyl ether. The organic layer was dried
over anhydrous MgSO4, and the solvent was evaporated under
reduced pressure. The obtained oily substance was purified by silica gel
chromatography to give the pure product (1.76 g, 6.54 mmol, 65.4%)
H, 6.62; N, 3.71. H NMR (CDCl3, 300 MHz, 298 K): δ 7.42−7.34
(m, 4H, ArH), 5.95−5.82 (m, 1H, NCH(CH3)2), 4.55 (s, 2H,
ArCH2N), 2.27 (s, 6H, CpCH3), 1.85 (s, 6H, CpCH3), 1.21 (d, J = 6.1
Hz, 6H, NCH(CH3)2) ppm. 13C NMR (CDCl3, 75 MHz, 298 K): δ
141.7, 131.1, 130.6, 130.5, 128.3, 128.2, 127.4, 127.1, 57.7, 49.7, 18.4,
13.6, 13.2 ppm.
Synthesis of Complex 2. Complex 2 was synthesized in the same
way as described above for the synthesis of complex 1 with the ligand
H2L2 (1.55 g, 5.00 mmol), n-BuLi (5.43 mL, 10.0 mmol), Me3SiCl
(1.27 mL, 10.0 mmol), and TiCl4 (0.55 mL, 5 mmol) as starting
materials. Pure 2 (0.848 g, 39.8%) was obtained as yellow crystals.
Anal. Calcd for C22H29Cl2NTi (425.12): C, 61.99; H, 6.86; N, 3.29.
1
Found: C, 62.11; H, 6.97 ; N, 3.36. H NMR (CDCl3, 300 MHz, 298
K): δ 7.44−7.30 (m, 4H, ArH), 5.46−5.37 (tt, J = 10.2, 3.3 Hz, 1H,
NCHC5H10), 4.57 (s, 2H, ArCH2N), 2.27 (s, 6H, CpCH3), 1.84 (s,
6H, CpCH3), 1.91−1.08 (m, 10H, NCHC5H10) ppm. 13C NMR
(CDCl3, 75 MHz, 298 K): δ 141.8, 131.0, 130.6, 128.2, 128.1, 127.7,
127.4, 127.1, 59.2, 57.9, 28.9, 26.9, 25.9, 13.6, 13.2 ppm.
1
as a colorless oily substance. H NMR (CDCl3, 300 MHz, 298 K): δ
Synthesis of Complex 3. Complex 3 was synthesized in the same
way as described above for the synthesis of complex 1 with the ligand
H2L3 (1.35 g, 5.00 mmol), n-BuLi (5.43 mL, 10.0 mmol), Me3SiCl
(1.27 mL, 10.0 mmol), and TiCl4 (0.55 mL, 5 mmol) as starting
materials. Pure 3 (0.679 g, 35.2%) was obtained as dark red crystals.
Anal. Calcd for C19H25Cl2NTi (385.08): C, 59.09; H, 6.53; N, 3.63.
7.43−6.95 (m, 4H, ArH), 3.62 (d, J = 13.2 Hz, 1H, ArCH2N), 3.57 (d,
J = 13.2 Hz, 1H, ArCH2N), 2.77−2.65 (m, 1H, CpH), 2.64−2.54 (m,
1H, NCH(CH3)2), 1.88 (s, 3H, CpCH3), 1.70 (s, 3H, CpCH3), 1.55
(s, 3H, CpCH3), 1.13 (d, J = 7.5 Hz, 3H, CpCH3), 0.94 (d, J = 6.2 Hz,
6H, NCH(CH3)2) ppm. MS: m/z 270 [M + H].
Synthesis of 2-Me4CpHC6H4CH2(Cy)NH (H2L2). Compound
H2L2 was synthesized in the same manner as for H2L1 with
cyclohexylamine (0.991 g, 10.0 mmol) as starting material. However,
this reaction was carried out in absolute THF. The pure product (1.91
1
Found: C, 59.21; H, 6.48; N, 3.74. H NMR (CDCl3, 300 MHz, 298
K): δ 7.43−7.28 (m, 4H, ArH), 4.64 (s, 2H, ArCH2N), 4.30−4.25 (t, J
= 7.5 Hz, 2H, NCH2C2H5), 2.27 (s, 6H, CpCH3), 1.86 (s, 6H,
CpCH3), 1.68−1.56 (m, 2H, NCH2CH2CH3), 1.03−0.99 (t, J = 7.5
Hz, 3H, N(CH2)2CH3) ppm. 13C NMR (CDCl3, 75 MHz, 298 K): δ
141.4, 137.2, 130.7, 128.3, 128.1, 127.9, 127.4, 127.2, 65.4, 56.2, 21.4,
20.8, 13.6, 13.2 ppm.
1
g, 6.18 mmol, 61.8%) was obtained as a colorless oily substance. H
NMR (CDCl3, 300 MHz, 298 K): δ 7.43−6.96 (m, 4H, ArH), 3.64 (d,
J = 13.2 Hz, 1H, ArCH2N), 3.59 (d, J = 13.2 Hz, 1H, ArCH2N), 2.75−
2.64 (m, 1H, CpH), 2.29−2.19 (tt, J = 10.1, 3.6 Hz, 1H, NCH in Cy),
1.88 (s, 3H, CpCH3), 1.70 (s, 3H, CpCH3), 1.55 (s, 3H, CpCH3), 1.13
(d, J = 7.7 Hz, 3H, CpCH3), 1.75−0.90 (m, 10H, NCHC5H10) ppm.
MS: m/z 310 [M + H].
Synthesis of Complex 4. Complex 4 was synthesized in the same
way as described above for the synthesis of complex 1 with the ligand
H2L4 (1.59 g, 5.00 mmol), n-BuLi (5.43 mL, 10.0 mmol), Me3SiCl
(1.27 mL, 10.0 mmol), and TiCl4 (0.55 mL, 5 mmol) as starting
materials. Pure 4 (0.827 g, 38.2%) was obtained as orange crystals.
Anal. Calcd for C23H25Cl2NTi (433.08): C, 63.62; H, 5.80; N, 3.23.
Synthesis of 2-Me4CpHC6H4CH2(nPr)NH (H2L3). Compound
H2L3 was synthesized in the same manner as for H2L1 with
propylamine (0.59 g, 10.0 mmol) as starting material. The pure
product (1.81 g, 6.72 mmol, 67.2%) was obtained as a colorless oily
substance. 1H NMR (CDCl3, 300 MHz, 298 K): δ 7.40−6.99 (m, 4H,
ArH), 3.62 (d, J = 13.5 Hz, 1H, ArCH2N), 3.57 (d, J = 13.5 Hz, 1H,
ArCH2N), 2.75−2.68 (m, 1H, CpH), 2.43−2.39 (t, J = 6.0 Hz, 2H,
NCH2C2H5), 1.87 (s, 3H, CpCH3), 1.69 (s, 3H, CpCH3), 1.54 (s, 3H,
CpCH3), 1.49−1.34 (m, 2H, NCH2CH2CH3), 1.13 (d, J = 9 Hz, 3H,
CpCH3), 0.86−0.81 (t, J = 6.0 Hz, 3H, N(CH2)2CH3) ppm. MS: m/z
270 [M + H].
1
Found: C, 63.77; H, 5.89; N, 3.38. H NMR (CDCl3, 300 MHz, 298
K): δ7.46−7.16 (m, 8H, ArH), 4.93 (s, 2H, ArCH2N), 2.37 (s, 3H,
NArCH3), 2.29 (s, 6H, CpCH3), 2.05 (s, 6H, CpCH3) ppm. 13C NMR
(CDCl3, 75 MHz, 298 K): δ 148.4, 141.3, 137.9, 132.4, 130.7, 130.4,
130.3, 129.7, 128.4, 127.5, 127.4, 127.3, 71.6, 21.5, 13.9, 13.6 ppm.
X-ray Crystallographic Studies. The crystals were mounted on
glass fibers using an oil drop. Data obtained with the ω−2θ scan mode
were collected on a Bruker SMART 1000 CCD diffractometer with
graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). The
structures were solved using direct methods,28 and further refinements
with full-matrix least squares on F2 were obtained with the SHELXTL
program package. All non-hydrogen atoms were refined anisotropi-
cally. Hydrogen atoms were introduced in calculated positions with the
displacement factors of the host carbon atoms. All calculations were
performed using the SHELXTL crystallographic software packages.29
Polymerization Reaction. The ethylene polymerization experi-
ments were carried out as follows: a dry 250 mL steel autoclave with a
magetic stirrer was charged with 60 mL of toluene, thermostated at the
Synthesis of 2-Me4CpHC6H4CH2(4-MePh)NH (H2L4). Com-
pound H2L4 was synthesized in the same manner as for H2L2 with 4-
methylaniline (1.07 g, 10.0 mmol) as starting material. The pure
product (2.03 g, 6.39 mmol, 63.9%) was obtained as a colorless oily
substance. 1H NMR (CDCl3, 300 MHz, 298 K): δ 7.77−6.92 (m, 8H,
ArH), 3.94 (d, J = 13.2 Hz, 1H, ArCH2N), 3.79 (d, J = 13.2 Hz, 1H,
ArCH2N), 2.75−2.68 (m, 1H, CpH), 2.36 (s, 3H, ArCH3), 1.88 (s,
3H, CpCH3), 1.71 (s, 3H, CpCH3), 1.56 (s, 3H, CpCH3), 1.12 (d, J =
7.5 Hz, 3H, CpCH3) ppm. MS: m/z 318 [M + H].
F
dx.doi.org/10.1021/om4003945 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
desired temperature, and saturated with ethylene (1.0 atm). The
polymerization reaction was started by addition of a mixture of catalyst
and AliBu3 in toluene (5 mL) and a solution of Ph3CB(C6F5)4 in
toluene (5 mL) at the same time. The vessel was pressurized to 5 atm
with ethylene immediately, and the pressure was kept by continuous
feeding of ethylene. The reaction mixture was stirred at the desired
temperature for 15 min. The polymerization was then quenched by
injecting acidified ethanol containing HCl (3 M). The polymer was
collected by filtration, washed with water and ethanol, and dried to a
constant weight under vacuum. For the ethylene/1-hexene copoly-
merization experiments, appropriate amounts of 1-hexene were added
in toluene.
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̈
ASSOCIATED CONTENT
■
S
* Supporting Information
Figures giving 13C NMR spectra for typical copolymer samples
and CIF files giving X-ray crystallographic data for complexes 1,
2, and 4. This material is available free of charge via the Internet
at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*Y.M.: tel, (86)-431-85168376; fax, (86)-431-85193421; e-
mail, ymu@jlu.edu.cn.
■
(18) Zhang, L.; Gao, W.; Tao, X.; Wu, Q.; Mu, Y.; Ye, L.
Organometallics 2011, 30, 433.
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Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
■
This research work was supported by the National Natural
Science Foundation of China (Nos. 21074043, 51173061, and
21274050).
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dx.doi.org/10.1021/om4003945 | Organometallics XXXX, XXX, XXX−XXX