Synthesis and ethylene polymerization behavior of a new titanium complex having two imine-phenoxy chelate ligands

Article abstract of DOI:10.1246/cl.2002.358

A novel (N-benzylidene-2-hydroxy-3,5-di-t-butyl-ani-line)₂TiCl₂ complex was synthesized and investigated for its potential as an ethylene polymerization catalyst in the presence of MAO or Ph₃C⁺B^-(C

Full text of DOI:10.1246/cl.2002.358

358
Chemistry Letters 2002
Synthesis and Ethylene Polymerization Behavior of a New Titanium Complex Having
Two Imine–Phenoxy Chelate Ligands
Yasuhiko Suzuki, Norio Kashiwa, and Terunori Fujitaꢀ
R&D Center, Mitsui Chemicals, Inc., 580-32 Nagaura, Sodegaura, Chiba 299-0265
(Received November 16, 2001; CL-011160)
A
novel (N-benzylidene-2-hydroxy-3,5-di-t-butyl-ani-
2,4-Di-t-butylphenol was transformed in three steps (i:
nitration, ii: hydrogenation, iii: condensation with benzaldehyde)
to the ligand in 28% yield.7 Lithiation of the ligand (77%)
followed by reaction with 0.5 equiv of TiCl4 in diethyl ether
yielded complex 1 (reddish brown powder, 87%).
line)2TiCl2 complex was synthesized and investigated for its
potential as an ethylene polymerization catalyst in the presence of
MAO or Ph3CþBÀ(C6F5Þ4/iBu3Al as a cocatalyst. Upon activa-
tion with Ph3CþBÀ(C6F5Þ4/iBu3Al, the complex displayed
higher activities at higher temperatures, and the activity reached
a very high value of 5784 kg-PE/mol-TiÁh at 75 ꢁC under
atmospheric pressure.
Complex 1 was characterized by elemental analysis and mass
spectrometry.8 1H NMR spectroscopy revealed complicated
spectra, indicating that the complex 1 exists as an isomeric
1
mixture in solution.9 Further studies using H NMR at varying
temperatures suggested the presence of mutually convertible
isomers, which may originate from the following; (1) attached/
detached state of imine nitrogens, (2) syn/anti imine double
bonds, and (3) coordination geometry of ligands around the
central metal.
Upon activation with methylaluminoxane (MAO) cocatalyst,
complex 1 was found to be active towards ethylene polymeriza-
tion to give solid polyethylenes (Table 1). The activities are
moderate in the temperature range of 25–75 ꢁC (101–124 kg-PE/
mol-TiÁh) though the molecular weights of the polyethylenes are
very high (Mv: 2130000–2320000).10
Enormous advances in the chemistry of well-defined group 4
metallocene complex catalysts have made a significant impact in
the manufacture of polyolefins. Recently, therefore, the search for
new olefin polymerization catalysts based on well-defined
transition metal complexes has been a field of major interest
involving many academic and industrial research groups.1;2
In our own efforts, previously, we have acquired transition
metal complexes having non-symmetric [O,N] or [N,N] chelate
ligand(s), as catalysts for the polymerization of ethylene and/or ꢀ-
olefins.3{6 In this paper, we report on a new titanium complex 1
bearing two non-symmetric imine–phenoxy chelate ligands for
ethylene polymerization, which displays different catalytic
performance from the previously reported complex 2 having
ligands that are structurally different yet contain the same
coordination sites (Figure 1).
Table 1. Ethylene polymerization results with MAO cocatalyst
Entry
Temp/ꢁC
Yield/mg
321
Activitya
124
Mv=104
b
1
2
3
25
50252 1
75
—
10232
268
107
213
Conditions: reaction time, 30min; toluene 250mL; ethylene gas
flow, 100 L/h; pressure, 0.1 MPa; complex, 0.005 mmol; MAO,
a
1.25 mmol. Activity: kg-PE/mol-TiÁh. bNot available due to low
yield of polyethylene.
When activated with Ph3CþBÀ(C6F5Þ4/iBu3Al cocatalyst,
however, complex 1 displayed considerably increased activities
at raised polymerization temperatures and produced high
molecular weight polyethylenes (Mv: 1170000, 560000, Table
2). Thus, the polymerization behavior of complex 1 is totally
different from that of the previously reported complex 2, which
exhibited higher activity with MAO (max. 4150kg-PE/mol-Ti Áh,
50 ꢁC) relative to the activity with Ph3CþBÀ(C6F5Þ4/iBu3Al
Figure 1. Structures of new complex 1 and previously
reported 2.3
The preparation of the imine–phenoxy ligand, N-benzyli-
dene-2-hydroxy-3,5-di-t-butylaniline, and its conversion to the
desired complex, starting from commercially available 2,4-di-t-
butylphenol, are shown in Scheme 1.
Table 2. Ethylene polymerization results with Ph3CþBÀ(C6F5)4/
iBu3Al cocatalyst
Entry
Temp/ꢁC
Yield/mg
Activitya
Mv=104
b
1
2
3
25
50576
75
34
1382
72
—
117
24105784
56
Conditions: reaction time, 5 min; toluene 250mL; ethylene gas flow,
100 L/h;
pressure,
0.1 MPa;
complex,
0.005 mmol;
a
Ph3CþBÀ(C6F5)4, 0.006 mmol; iBu3Al, 0.25 mmol. Activity: kg-
Scheme 1.
PE/mol-TiÁh. bNot available due to low yield of polyethylene.
Copyright Ó 2002 The Chemical Society of Japan

Chemistry Letters 2002
359
(max. 670kg-PE/mol-Ti Áh, 75 ꢁC).3f
in this case.
The activity value of 5784 kg-PE/mol-TiÁh exhibited at 75 ꢁC
represents one of the highest reported activities to date for
ethylene polymerization catalysts based on titanium complexes
with no Cp ligands at atmospheric pressure conditions.
Studies on the rate profile of complex 1/Ph3CþBÀ(C6F5Þ4/
iBu3Al catalyst system revealed that there is an induction period
for the polymerization (Figure 2).
In summary, new ethylene polymerization catalyst systems
based on Ti complex having two imine–phenoxy chelate ligands
have been introduced. The discovery of the 1/Ph3CþBÀ(C6F5Þ4/
iBu3Al catalyst system exhibiting high activities at high
polymerization temperatures is of great significance. The results
introduced herein demonstrate that a dramatic effect can be
obtained on catalytic performance by only changing chelate
architecture in the complex. Successful polymerization and
copolymerization of olefins and further preparation of derivatives
are underway.
References and Notes
1
a) H. Sinn, W. Kaminsky, H. J. Vollmer, and R . Woldt, Angew. Chem.,
Int. Ed. Engl., 19, 390(1980). b) H. H. Brintzinger, D. Fischer, R.
Mulhaupt, B. Rieger, and R. M. Waymouth, Angew. Chem., Int. Ed.
¨
Engl., 34, 114 (1995).
2
a) G. J. P. Biritovsek, V. C. Gibson, and D. F. Wass, Angew. Chem., Int.
Ed., 38, 428 (1999). b) S. D. Ittel, L. K. Johnson, and M. Brookhart,
Chem. Rev., 100, 1169 (2000). c) T. R. Younkin, E. F. Connor, J. I.
Henderson, S. K. Friedrich, R. H. Grubbs, and D. A. Bansleben, Science,
2000, 1114. d) Y. Matsuo, K. Mashima, and K. Tani, Chem. Lett., 2000,
1114. e) K. Nomura, A. Sagara, and Y. Imanishi, Chem. Lett., 2001, 36.
a) T. Fujita, Y. Tohi, M. Mitani, S. Matsui, J .Saito, M. Nitabaru, K. Sugi,
H. Makio, and T. Tsutsui, European Patent 087405 (1998); Chem.
Abstr., 129, 331166 (1998). b) 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. c) 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 Patent 01 55231 A1
(2001). d) J. Saito, M. Mitani, J. Mohri, Y. Yoshida, S. Matsui, S. Ishii,
S. Kojoh, N. Kashiwa, and T. Fujita, Angew. Chem., Int. Ed., 40, 2918
(2001). e) 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. Raid Commun., 22, 1072 (2001). f) J. Saito, M. Mitani, S.
Matsui, Y. Tohi, H. Makio, T. Nakano, H. Tanaka, N. Kashiwa, and T.
Fujita, Macromol. Chem. Phys., 203, 59 (2002). g) J. Tian, P. D. Hustad,
and G. W. Coates, J. Am. Chem. Soc. 123, 5134 (2001).
Figure 2. Time dependence of PE yield with 1/
Ph3CþBÀ(C6F5)4/iBu3Al. Conditions: toluene 250mL;
ethylene gas flow, 100 L/h; pressure, 0.1 MPa; temperature,
75 ꢁC; 1, 0.005 mmol; Ph3CþBÀ(C6F5)4, 0.006 mmol;
iBu3Al, 0.25 mmol.
3
An elucidation for the presence of the induction period is
given by the structural change of the imine–phenoxy ligand,
which is suggested by 1H NMR studies using complex 1/iBu3Al
mixture (Figure 3). Thus, the treatment of 1 with iBu3Al resulted
in the appearance of AB system peaks at 4.40ppm and 4.51 ppm,
assigned to diastereotopic benzyl protons, as well as a sharp
multiplet peak centered at 4.78 ppm, assigned to isobutene
protons,11 indicating that the imine–phenoxy ligand was
converted to an amine–phenoxy ligand by the reduction with
iBu3Al, which co-produced isobutene during the reaction. This is
further confirmed by the fact that the protonolysis of a similar
mixture of complex 1 and iBu3Al (0.25 mmol and 2.80 mmol in
12 mL of toluene, 50 ꢁC, 30min) gave N-benzyl-2-hydroxy-3,5-
di-t-butylaniline quantitatively.12 Therefore, a highly active
species derived from complex 1/Ph3CþBÀ(C6F5Þ4/iBu3Al is
suggested to have an amine–phenoxy ligand.13 Although we have
reported a similar reduction of an imine-containing ligand,3b it is
noteworthy that the reduced species exhibits much higher activity
4
5
6
7
Y. Yoshida, S. Matsui, Y. Takagi, M. Mitani, T. Nakano, H. Tanaka, N.
Kashiwa, and T. Fujita, Organometallics, 20, 4793 (2001).
T. Matsugi, S. Matsui, S. Kojoh, Y. Takagi, Y. Inoue, T. Fujita, and N.
Kashiwa, Chem. Lett., 2001, 566.
Y. Inoue, T. Nakano, H. Tanaka, N. Kashiwa, and T. Fujita, Chem. Lett.,
2001, 1060.
1H NMR data for N-benzylidene-2-hydroxy-3,5-di-t-butylaniline (ꢁ,
ppm, CDCl3, 25 ꢁC): 8.70(s, 1H), 7.96–7.92 (m, 2H), 7.73 (s, 1H), 7.48–
7.43 (m ,3H), 7.25 (d, 1H, 2 Hz), 7.17 (d, 1H, 2 Hz), 1.46 (s, 9H), 1.35 (s,
9H).
8
9
Anal. Found: C, 68.72; H, 6.91; N, 3.83%. Calcd for C42H52Cl2N2O2Ti:
C, 68.57; H, 7.12; N, 3.81%. FD-MS (m=z): 734 (Mþ), and the relative
intensities of the other peaks are less than 5%.
1H NMR (ꢁ, C6D6): At least 10major singlet peaks attributed to tBu
groups appeared in the region of 0.8–2.2 ppm at room temperature. The
number of the peaks was reduced to 6 when the temperature was raised
to 75 ꢁC.
10 Mv values were calculated from the following equation, ½ꢂŠ ¼
6:2 ꢂ 10À4Mv0:7; R. Chiang, J. Polymer Sci., 36, 91 (1959). Intrinsic
viscosity [ꢂ] was measured in decalin at 135 ꢁC using an Ubbelohde
viscometer.
11 The NMR was identified by comparison with authentic isobutene.
12 1H NMR (ꢁ, CDCl3): 7.32 (m, 5H), 6.85 (m, 1H), 6.73 (m, 1H), 5,95 (bs,
1H), 4.12 (s, 2H), 3.20(bs, 1H), 1.39 (s, 9H), 1.20(s, 9H). FD-MS ( m=z):
311 (Mþ).
13 This conclusion is confirmed by the fact that the mixture, which gave N-
benzyl-2-hydroxy-3,5-di-t-butylaniline by protonolysis, displayed
7704 kg-PE/mol-TiÁh of activity without any induction period under
the conditions given in Table 2.
Figure 3. 1H NMR spectra of 1/iBu3Al in toluene-d8 at 50 ꢁC.