Zirconium complexes having phenoxy/cycloalkylimine chelate ligands for the polymerization of ethylene for vinyl-terminated low molecular weight polyethylenes

Article abstract of DOI:10.1246/cl.2002.740

Zirconium complexes bearing phenoxy/cyclopropyl-, cyclobutyl- or cyclopentyl-imine chelate ligands, when activated with methylalumoxane (MAO), produced vinyl-terminated low molecular weight polyethylenes (M_w < 5000) with higher activities than Cp₂ZrCl₂ at 25°C. The complex having a cyclobutyl group provided the lowest molecular weight polyethylene (M_w 2100).

Full text of DOI:10.1246/cl.2002.740

740
Chemistry Letters 2002
Zirconium Complexes Having Phenoxy/Cycloalkylimine Chelate Ligands for the
Polymerization of Ethylene for Vinyl-Terminated Low Molecular Weight Polyethylenes
Sei-ichi Ishii, Makoto Mitani, Junji Saito, Sadahiko Matsuura, Shin-ichi Kojoh,
Norio Kashiwa, and Terunori Fujitaꢀ
R&D Center, Mitsui Chemicals, Inc., 580-32 Nagaura, Sodegaura, Chiba 299-0265
(Received April 19, 2002; CL-020340)
Zirconium complexes bearing phenoxy/cyclopropyl-, cyclo-
prepared in quantitative yields via the condensation of the
appropriate cycloalkylamine with 3-tert-butylsalicylaldehyde.
The ligands A–D were deprotonated using n-BuLi and the anions
allowed to react with 0.5 equiv of ZrCl4 to afford the target
complexes 1–4 as yellow solids in moderate to good yields (1;
35%, 2; 64%, 3; 41%, 4; 42%).
butyl- or cyclopentyl-imine chelate ligands, when activated with
methylalumoxane (MAO), produced vinyl-terminated low mo-
lecular weight polyethylenes (Mw < 5000) with higher activities
than Cp2ZrCl2 at 25 ꢁC. The complex having a cyclobutyl group
provided the lowest molecular weight polyethylene (Mw 2100).
The ethylene polymerization behavior of complexes 1–4 has
been investigated with methylalumoxane (MAO) cocatalyst at
25 ꢁC under atmospheric pressure. A summary of polymerization
results is shown in Table 1. Complexes 1–4 had high catalytic
activities exceeding that seen by Cp2ZrCl2 under similar
conditions. Complex 3 bearing a cyclopentyl group on the
imine-nitrogen exhibited the highest activity with a turnover
frequency (TOF) of 69,000 minꢂ1 atmꢂ1. Although there is no
clear relationship between the catalytic activity and the
substituent on the imine-nitrogen, it appears that the steric bulk
of the substituents is sufficiently large that extremely high
activities are achieved (entries 3 and 4).
GPC analyses indicate that the PEs formed with complexes
1–4 possess narrow molecular weight distributions (Mw=Mn) in
the range of 1.52–1.82, as expected for a polymer generated from
a chemically homogeneous catalyst. A comparison of PE
molecular weights shows that the substituent on the imine-
nitrogen has a considerable effect on molecular weights, ranging
from 2100 to 13800. The lowest molecular weight PE (Mw 2100)
was given by complex 2 having a cyclobutyl group on the imine-
nitrogen. It is worth noting that complexes 1, 2, and 3 produce low
molecular weight PEs (Mw 2100–4700) with higher activities
than Cp2ZrCl2 at ambient temperature. Considering that a
molecular weight is determined by the relative rate of chain
propagation and chain termination, complex 3, with a cyclopentyl
group on the imine-nitrogen, displays faster chain termination
rates than complex 2 though complex 2 produces the lowest
molecular weight PE (Mw 2100) among the complexes investi-
gated, as described above. This can be associated with the size and
location of a cyclopentyl group, an appropriate size and location
which encourages chain termination while maintaining chain
propagation rate.
The selective synthesis of vinyl-terminated low molecular
weight (Mw < 5000) polyethylenes (PEs) has been one of the
challenging subjects of practical interest (many potential
applications) as well as of fundamental interest (precise control
of chain termination). This is because such PEs can be
transformed by chain-end functionalizations to terminally-
functionalized polymers.1 In addition, these PEs may serve as
macromonomers in copolymerizations with ethylene or ꢀ-olefins
to yield long-chain branched polymers.2 There are, however, only
a few examples of transition metal complexes producing low
molecular weight PEs containing vinyl-end groups with high
activities under mild conditions.3{5
Previously, based on ligand-oriented catalyst design re-
search6 we obtained a new family of group 4 transition metal
complexes featuring phenoxy/imine chelate ligands, named FI
Catalysts, which display high catalytic performance for olefin
polymerization including living olefin polymerization.7;8
Although we successfully developed highly active FI Catalysts
giving moderate to high molecular weight PEs, we did not attain
FI Catalysts producing low molecular weight PEs (Mw < 5000)
with high efficiency. Consequently, we have performed further
research on FI Catalysts to yield highly active FI Catalysts
capable of providing low molecular weight PEs, preferably
having vinyl-end groups.
Here, we describe new zirconium complexes with phenoxy/
cycloalkylimine [O, N] chelate ligands, zirconium FI Catalysts,
which promote the polymerization of ethylene for vinyl-
terminated low molecular weight PEs with very high activities.
The synthetic route to the zirconium complexes described
herein, bis[N-(3-tert-butylsalicylidene)cycloalkylaminato]zirco-
nium(IV)dichloride 1–4, is summarized in Scheme 1.9 The
phenoxy/cycloalkylimine ligands of structures A–D are readily
13C NMR as well as IR analyses indicate that the PEs arising
from complexes 1–4 have linear structures with virtually no
branching. End group analyses of the PEs using 1H NMR show
the presence of vinyl (1; 45%, 2; 45%, 3; 45%, 4; 39%) and
saturated end (1; 55%, 2; 55%, 3; 55%, 4; 61%), suggesting that
ꢁ-hydrogen transfer is a predominant mechanism for chain
termination. Therefore, the PEs obtained from complexes 1–4
have 78–90% vinyl-terminated chain ends. It is of great
significance that complexes 1, 2, and 3 promote the polymeriza-
tion of ethylene to produce vinyl-terminated (90%) low molecular
weight (Mw < 5000) linear PEs having narrow molecular weight
Scheme 1. Synthetic route to zirconium complexes 1–4.
Copyright Ó 2002 The Chemical Society of Japan

Chemistry Letters 2002
741
Table 1. Results of ethylene polymerization with complexes 1–4 and Cp2ZrCl2
Chain-end groupc
vinyl/methyl
b
b
Entry
Complexa
Yield
/g
TOF
/minꢂ1 atmꢂ1
Mw=Mn
Mw
/103
Vinyl-terminated
chain end/mol%
1
2
3
4
5
1
2
3
4
0.64
0.51
1.94
1.89
1.13
22,800
18,000
69,000
67,800
16,200
1.81
1.52
1.82
1.75
2.61
4.7
2.1
3.8
13.8
636.0
45/55
45/55
45/55
39/61
(26/74)d
90
90
90
78
(52)d
Cp2ZrCl2
Conditions: solvent, toluene (250 mL); polymerization temperature, 25 ꢁC; ethylene pressure, 0.1MPa; ethylene feed 100 L/h;
a
b
polymerization time, 5 min. complex 1–4 0.2 ꢃmol, Cp2ZrCl2 0.5 ꢃmol, MAO (Albemarle) 1.25 mmol. Determined by GPC using
polythylene calibration. cDetermined by 1H NMR. dCalculated based on IR analysis (vinyl chain-end 0.03 per 1000 carbon atoms).
Chem. Eur. J., 6, 2221(2000).
distributions (Mw=Mn 1.52–1.82) with high activities. To our
knowledge, these are the first examples of group 4 olefin
polymerization catalysts generating such PEs with high efficiency
at ambient temperature.
6
a) Y. Yoshida, S. Matsui, Y. Takagi, M. Mitani, T. Nakano, H.
Tanaka, N. Kashiwa, and T. Fujita, Organometallics, 20, 4793
(2001). b) Y. Inoue, T. Nakano, H. Tanaka, N. Kashiwa, and T.
Fujita, Chem. Lett., 2001, 1060. c) Y. Suzuki, N. Kashiwa, and T.
Fujita, Chem. Lett., 2002, 358. d) T. Matsugi, S. Matsui, S. Kojoh,
Y. Takagi, Y. Inoue, T. Nakano, T. Fujita, and N. Kashiwa,
Macromolecules, in press. e) Y. Yoshida, J. Saito, M. Mitani, Y.
Takagi, S. Matsui, S. Ishii, T. Nakano, N. Kashiwa, and T. Fujita
Chem. Commun., in press.
a) T. Fujita, Y. Tohi, M. Mitani, S. Matsui, J. Saito, M. Nitabaru, K.
Sugi, H. Makio, and T. Tsutsui, Europe Patent, EP-0874005
(1998); Chem. Abstr., 129, 331166 (1998). b) M. Mitani, Y.
Yoshida, J. Mohri, K. Tsuru, S. Ishii, S. Kojoh, T. Matsugi, J. Saito,
N. Matsukawa, S. Matsui, T. Nakano, H. Tanaka, N. Kashiwa, and
T. Fujita, WO 01/55231 A1 (2001); Chem. Abstr., 135, 137852
(2001).
In summary, we have prepared new zirconium complexes
having two phenoxy/imine chelate ligands, zirconium FI
Catalysts, in which the imine-nitrogen possesses a cycloalkyl
group. These complexes having a cyclopropyl, cyclobutyl, or
cyclopentyl group on the imine-nitrogen, combined with MAO,
are highly active catalysts for the polymerization of ethylene to
generate low molecular weight linear PEs having predominantly
vinyl chain ends with higher activities than Cp2ZrCl2 at 25 ꢁC.
The influence of substitution groups of the ligands and cocatalysts
on molecular weights and vinyl-end group selectivity as well as
the applications of these vinyl-terminated PEs is currently under
investigation.
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8
a) S. Matsui, M. Mitani, J. Saito, Y. Tohi, H. Makio, N. Matsukawa,
Y. Takagi, K. Tsuru, M. Nitabaru, T. Nakano, H. Tanaka, N.
Kashiwa, and T. Fujita, J. Am. Chem. Soc., 123, 6847 (2001) and
references therein. b) N. Matsukawa, S. Matsui, M. Mitani, J. Saito,
K. Tsuru, N. Kashiwa, and T. Fujita, J. Mol. Catal. A: Chem., 169,
99 (2001). c) S. Ishii, J. Saito, M. Mitani, J. Mohri, N. Matsukawa,
Y. Tohi, S. Matsui, N. Kashiwa, and T. Fujita, J. Mol. Catal. A:
Chem., 179, 11 (2002). d) J. Saito, M. Mitani, S. Matsui, N.
Kashiwa, and T. Fujita, Macromol. Rapid Commun., 21, 1333
(2000). e) S. Kojoh, T. Matsugi, J. Saito, M. Mitani, T. Fujita, and
N. Kahiwa, Chem. Lett., 2001, 822. f) J. Saito, M. Mitani, M. Onda,
J. Mohri, S. Ishii, Y. Yoshida, T. Nakano, H. Tanaka, T. Matsugi, S.
Kojoh, N. Kashiwa, and T. Fujita, Macromol. Rapid Commun., 22,
1072 (2001). g) M. Mitani, J. Mohri, Y. Yoshida, J. Saito, S. Ishii,
K. Tsuru, S. Matsui, R. Furuyama, T. Nakano, H. Tanaka, S. Kojoh,
T. Matsugi, N. Kahiwa, and T. Fujita, J. Am. Chem. Soc., 124, 3327
(2002) and references therein.
We wish to thank Dr. M. Mullins for fruitful discussions and
suggestions.
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9
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1H: NMR (270 MHz, CDCl3, TMS): ꢂ 1.42 (s, 18H, t-Bu), 0.50–
1.54 (m, 8H, CH2Þ, 3.22 (br s, 2H, CH), 6.80–7.55 (m, 6H, Ar H),
8.48 (s, 2H, CH=N). Anal. Calcd. for ZrC28H36N2O2Cl2: C, 56.55;
H, 6.10; N, 4.71; Zr, 15.34%. Found: C, 56.48; H, 5.90; N, 4.43; Zr,
15.06%. FD-MS: 592 (Mþ). 2: 1H NMR (270 MHz, CDCl3, TMS):
ꢂ 1.21–2.22 (m, 18H; t-Bu þ 12H; CH2,), 4.55 (br s, 2H, CH),
6.87–7.64 (m, 6H, Ar H), 8.27 (s, 2H, CH=N). Anal. Calcd. for
ZrC30H40N2O2Cl2: C, 57.86; H, 6.47; N, 4.50; Zr, 14.60%. Found:
C, 57.77; H, 6.43; N, 4.24; Zr, 14.40%. FD-MS: 622 (Mþ). 3: 1H
NMR (270 MHz, CDCl3, TMS): ꢂ 1.57 (s, 18H, t-Bu), 1.18–2.16
(m, 16H, CH2), 4.30–4.50 (m, 2H, CH), 6.89–7.57 (m, 6H, Ar H),
8.28 (s, 2H, CH=N), Anal. Calcd. for ZrC32H44N2O2Cl2: C, 59.05;
H, 6.81; N, 4.30; Zr, 14.02%. Found: C, 59.20; H, 6.93; N, 4.37; Zr,
14.23%. FD-MS: 650 (Mþ). 4: 1H NMR (270 MHz, CDCl3, TMS):
ꢂ 1.55 (s, 18H, t-Bu), 0.80–2.40 (m, 20H, CH2), 3.80–4.00 (m, 2H,
CH), 6.79–7.64 (m, 6H, Ar H), 8.31(s, 2H, CH=N). Anal. Calcd.
for ZrC34H48N2O2Cl2: C, 60.15; H, 7.13; N, 4.71; Zr, 13.44%.
Found: C, 60.35; H, 7.07; N, 4.50; Zr, 13.30%. FD-MS: 678 (Mþ).
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¨
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