Ethylene polymerization and ethylene/1-octene copolymerization using group 4 half-metallocenes containing aryloxo ligands, Cp*MCl2(OAr) [M= Ti, Zr, Hf; Ar = O-2,6-R2C6H3, R= tBu, Ph]-MAO catalyst syst

Article abstract of DOI:10.1016/j.molcata.2009.01.001

Effect of the centered metal toward the catalytic activity as well as comonomer incorporation has been explored in ethylene (co)polymerization using a series of Cp*MCl₂(O-2,6-R₂C₆H ₃) [M=Ti (1), Zr (2), Hf (3);

Full text of DOI:10.1016/j.molcata.2009.01.001

Journal of Molecular Catalysis A: Chemical 303 (2009) 102–109
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Ethylene polymerization and ethylene/1-octene copolymerization using group 4
half-metallocenes containing aryloxo ligands, Cp*MCl2(OAr)
[M = Ti, Zr, Hf; Ar = O-2,6-R2C6H3, R = tBu, Ph]—MAO catalyst systems
Koji Itagaki, Shinya Hasumi, Michiya Fujiki, Kotohiro Nomura∗
Graduate School of Materials Science, Nara Institute of Science and Technology (NAIST), 8916-5 Takayama, Ikoma, Nara 630-0101, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Effect of the centered metal toward the catalytic activity as well as comonomer incorporation has been
Received 13 December 2008
Received in revised form
26 December 2008
explored in ethylene (co)polymerization using a series of Cp*MCl2(O-2,6-R2C6H3) [M = Ti (1), Zr (2), Hf
i
(3); R = Ph (a), tBu (b), Pr (c)] in the presence of methylaluminoxane (MAO) cocatalyst. Complexes 2a,
3a,b were prepared and identified, and the structures for 2–3a,b were determined by X-ray crystallog-
raphy as a distorted tetrahedral geometry around the metal center. The catalytic activity in ethylene
polymerization was affected by the centered metal employed [Ti > Zr > Hf]; the complexes containing
2,6-diphenylphenoxy ligand (1–3a) showed higher catalytic activities than the complexes containing
2,6-di-tert-butylphenoxy analogues (1–3b). The molecular weights in the resultant polymers prepared
by the Zr and the Hf analogues were lower than those prepared by the Ti–Ph (1a) and the Ti–iPr (1c) ana-
logues. Although the copolymerizations of ethylene with 1-octene afforded the copolymers with uniform
molecular weight distributions (except 1b), both the catalytic activities and the 1-octene incorporation
were highly affected by the centered metal employed; the Ti–iPr analogue (1c) seems to be the most suited
in terms of both the catalytic activity and the 1-octene incorporation. The attempted copolymerization
of ethylene with 2-methyl-1-pentene using 2a,b and 3a—MAO catalysts afforded linear polyethylene.
© 2009 Elsevier B.V. All rights reserved.
Accepted 5 January 2009
Available online 9 January 2009
Keywords:
Ethylene polymerization
Titanium
Zirconium
Hafnium
Coordination polymerization
1. Introduction
be tuned by modification of the cyclopentadienyl fragment
(Cpꢀ).
Syntheses of Cp*ZrCl2(O-2,6-tBu2C6H3) and Cp*Zr(O-2,4,6-
Me3C6H2)3 and their use as the catalyst precursors for ethylene
polymerization in the presence of methylaluminoxane (MAO)
cocatalyst were reported [15]. Moreover, synthesis of Cp*TiCl2(O-
2,6-Ph2C6H3) and application in cyclization (intramolecular
Pauson-Khand) reaction was reported [16]. We demonstrated that
the aryloxo substituent plays an important role especially toward
the catalytic activity in ethylene (␣-olefin) polymerization [7] as
well as in copolymerization of ethylene with ␣-olefin [9c], 2-
methyl-1-pentene [13b]. However, synthesis of a series of group 4
half-metallocenes containing aryloxo ligands and the study con-
cerning effect of centered metal not only toward the catalytic
activity in ethylene polymerization, but also toward the monomer
reactivities in ethylene copolymerization have not so far been
reported. In this paper, we thus explored an effect of centered metal
in ethylene (co)polymerization using a series of Cp*MCl2(O-2,6-
Design and synthesis of efficient transition metal complex
catalysts for precise olefin polymerization attract considerable
attention in the fields of catalysis, organometallic chemistry,
and polymer chemistry [1–6]. Nonbridged half-metallocene type
group
4
transition metal complexes of the type, CpꢀM(L)X2
(Cpꢀ = cyclopentadienyl group; M = Ti, Zr, Hf; L = anionic ligand
such as OAr, NR2, NPR3, etc.; X = halogen, alkyl), display unique
characteristics as olefin polymerization catalysts, because these
catalysts are effective for production of new polyolefins [4a]
which are not prepared by conventional Ziegler-Natta catalysts,
ordinary metallocenes [1] and/or so-called ‘constrained geome-
try’ (linked Cp-amide) type catalysts [2]. In particular, nonbridged
half-titanocenes (titanium half-sandwich complexes) containing
an aryloxo ligand of the type, CpꢀTi(OAr)X2 (Ar = 2,6-iPr2C6H3,
etc.), display promising characteristics [4a,7–14]. For example,
efficient catalyst precursors especially for copolymerization of
ethylene with ␣-olefin [9], styrene [10], norbornene [11], cyclo-
hexene [12], 2-methyl-1-pentene [13], vinylcyclohexane [14] can
t
i
R2C6H3) [M = Ti (1), Zr (2), Hf (3); R = Ph (a), Bu (b), Pr (c)] in the
presence of MAO cocatalyst (Scheme 1) [17,18].
2. Results and discussion
∗
Cp*ZrCl2(O-2,6-Ph2C6H3) (2a) could be prepared by treat-
ing Cp*ZrCl3 with Li(O-2,6-Ph2C6H3) in a mixed solution of
Corresponding author. Fax: +81 743 72 6049.
E-mail address: nomurak@ms.naist.jp (K. Nomura).
1381-1169/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2009.01.001

K. Itagaki et al. / Journal of Molecular Catalysis A: Chemical 303 (2009) 102–109
103
Scheme 2.
Scheme 1.
Li(O-2,6-R2C6H3) in toluene or Et2O (Scheme 2). These complexes
were identified based on 1H, 13C NMR spectra and elemental anal-
yses. As shown in Fig. 1, the structures for 2a,b and 3a,b could be
determined by X-ray crystallography [19], and their selected bond
distances and angles are summarized in Table 1.
toluene/n-hexane according to an analogous procedure for
Cp*ZrCl2(O-2,6-tBu2C6H3) (2b) reported previously (Scheme 2)
[15]. The Hf analogues, Cp*HfCl2(O-2,6-R2C6H3) [R = Ph (3a), tBu
(3b)], could also be prepared similarly by treating Cp*HfCl3 with
Fig. 1. ORTEP drawings for Cp*MCl2(O-2,6-R2C6H3) [top: M = Zr, R = Ph (2a, left), tBu, (2b, right); bottom: M = Hf, R = Ph (3a, left), tBu (3b, right)]. Thermal ellipsoids are drawn
at the 50% probability level and H atoms are omitted for clarity [18].

104
K. Itagaki et al. / Journal of Molecular Catalysis A: Chemical 303 (2009) 102–109
Table 1
Summary of selected bond distances (Å) and angles (◦) for Cp*MCl2(O-2,6-R2C6H3) [M = Ti (1), Zr (2), Hf (3); R = Ph (a), R = tBu (b), iPr (c)]a.
Complex (M, R)
1ab (Ti, Ph)
1bc (Ti, tBu)
1cd (Ti, iPr)
2a (Zr, Ph)
2b (Zr, tBu)
3a (Hf, Ph)
3b (Hf, tBu)
Selected bond distances (Å)
M–Cl1
M–Cl2
M–O
2.2693(13)
2.2865(14)
1.811(3)
2.2674(10)
2.2674(10)
1.804(2)
2.305(2)
2.239(2)
1.772(3)
2.4008(4)
2.3881(5)
1.9349(12)
2.3961(3)
2.3963(3)
1.9431(9)
2.3640(7)
2.3751(7)
1.9224(15)
2.3714(6)
2.3710(8)
1.9280(19)
Selected bond angles (◦)
M–O–C(Phenyl)
Cl1–M–Cl2
Cl1–M–O
Cl2–M–O
160.6(3)
98.70(5)
104.33(10)
105.20(10)
155.5(2)
98.10(4)
103.22(6)
103.22(6)
173.0(3)
103.45(5)
99.1(2)
160.99(11)
99.629(17)
107.37(3)
105.73(3)
169.95(8)
98.234(12)
103.72(2)
105.52(3)
160.97(14)
99.40(2)
104.71(4)
106.25(4)
169.64(16)
98.04(2)
104.60(6)
103.10(5)
104.1(2)
a
Detailed analysis conditions and results for 2a,b, and 3a,b are shown in the Supplementary materials.
b
c
Cited from reference [16].
Cited from reference [7].
Cited from reference [7].
d
These complexes show a rather distorted tetrahedral geome-
try around zirconium/hafnium, as seen in Cp*TiCl2(O-2,6-R2C6H3)
1.9280(19) Å] and the Ti–O [1.811(3), 1.804(2) Å] bond distances
[7c,16]. The M–O–C(phenyl) bond angles in the Zr–Ph (2a) and the
t
i
t
[R = Ph (1a), Bu (1b), Pr (1c)] [7a,c,16]. The Zr–Cl bond distances
[2a,b: 2.3881(5)–2.4008(4) Å] are slightly longer than the Hf–Cl
bond distances [3a,b: 2.3640(78)–2.3751(7) Å], and are longer than
the Ti–Cl bond distances [1a,b: 2.2674(10)–2.2865(14) Å] [7c,16],
probably influenced by the atomic radii [20]. In contrast, no sig-
nificant differences are observed in the Cl–M–Cl bond angles,
except that the angles in the Ph analogues (1–3a) are larger
Hf–Ph analogues (3a) are smaller than those in the Bu analogues
(2–3b), whereas opposite trend is observed in the Ti analogues
(1a,b) [7c,16]. As reported previously [7a], the Ti–iPr analogue
(1c), which showed exceptionally high catalytic activities in ethy-
lene (co)polymerizations, possesses large Ti–O–C(phenyl) bond
angle [173.0(3) ◦], along with a rather short Ti–O bond distance
[1.772(3) Å]; the fact suggests that these distances and angles are
influenced by a combination of both the centered metal and sub-
stituent in the aryloxo group.
t
than those in the Bu analogues (1–3b). The Zr–O bond distances
[1.9349(12), 1.9431(9) Å] are also longer than the Hf–O [1.9224(15),
Table 2
Ethylene polymerization by Cp*MCl2(O-2,6-R2C6H3) [M = Ti (1), Zr (2), Hf (3); R = Ph (a), R = tBu (b), iPr (c)]—MAO catalyst systemsa.
b
c
c
Run
Cat. (␮mol)
MAO/mmol (Al/M × 10−3
)
Yield/mg
Activity/kg-PE/mol-M h
Mn (×10−4
)
Mw/Mn
1
2
3
4
5
1a (0.01)
1a (0.01)
1a (0.01)
1a (0.01)
1a (0.01)
1.0 (100)
2.0 (200)
3.0 (300)
4.0 (400)
5.0 (500)
133
145
144
161
151
79800
87000
86400
96600
90600
120
3.2
67.8d
67.0d
54.4d
3.3
2.9
3.4
6
7
8
9
1b (0.1)
1b (0.1)
1b (0.1)
1b (0.1)
1.0 (10.0)
2.0 (20.0)
3.0 (30.0)
4.0 (40.0)
93
113
127
140
5580
6780
7620
8400
3.74
2.9
2.5
2.3
2.4
2.63e
1.78e
2.67e
10
1b (0.1)
5.0 (50.0)
125
7500
2.35
242
2.9
2.0
11
1c (0.01)
3.0 (300)
72
43200
189
2.4
12
13
14
15
16
17
2a (0.2)
2a (0.2)
2a (0.2)
2a (0.2)
2a (0.2)
2a (0.2)
1.0 (5.0)
5
3
85
295
205
14
200
90
2600
8850
6150
420
2.0 (10.0)
2.5 (12.5)
3.0 (15.0)
4.0 (20.0)
5.0 (25.0)
0.59
2.31
2.43
2.1
2.2
2.0
18
19
20
21
22
2b (0.5)
2b (0.5)
2b (0.5)
2b (0.5)
2b (0.5)
1.0 (2.0)
2.0 (4.0)
3.0 (6.0)
4.0 (8.0)
5.0 (10.0)
181
278
217
81
2170
3340
2600
970
35.1
21.3
16.3
13.4
13.5
1.9
2.3
2.3
2.2
2.0
103
1240
23
24
25
26
27
3a (1.0)
3a (1.0)
3a (1.0)
3a (1.0)
3a (1.0)
1.0 (1.0)
2.0 (2.0)
3.0 (3.0)
4.0 (4.0)
5.0 (5.0)
20
24
108
125
86
120
140
648
750
520
0.79
0.56
0.49
0.50
0.40
2.8
2.0
2.0
1.9
2.0
28
3b (5.0)
3.0 (0.6)
65
78
2.33
4.2
a
b
c
Conditions: toluene 30 mL, MAO (prepared by removing toluene and AlMe3 from ordinary MAO) 1–5 mmol, ethylene 6 atm, 25 ◦C, 10 min.
Molar ratio of Al/M.
GPC data in o-dichlorobenzene vs. polystyrene standards.
Low molecular weight shoulder was observed in small amount in the GPC trace.
High molecular weight shoulder was observed in small amount in the GPC trace.
d
e

K. Itagaki et al. / Journal of Molecular Catalysis A: Chemical 303 (2009) 102–109
105
Table 3
Effect of temperature in ethylene polymerization by Cp*MCl2(O-2,6-R2C6H3) [M = Ti (1), Zr (2), Hf (3); R = Ph (a), R = tBu (b), iPr (c)]—MAO catalyst systemsa.
b
c
c
Run
Cat. (␮mol)
MAO/mmol (Al/M × 10−3
)
Temperature/◦C
Yield/mg
Activity/kg-PE/mol-M h
Mn (×10−4
)
Mw/Mn
4
29
30
1a (0.01)
1a (0.01)
1a (0.01)
4.0 (400)
4.0 (400)
4.0 (400)
25
40
55
161
88
67
97000
52800
40200
67.0d
61.1d
40.7d
2.9
2.9
3.2
9
31
1b (0.1)
1b (0.1)
4.0 (40.0)
4.0 (40.0)
25
40
140
63
8400
3780
2.67e
2.54e
2.4
2.2
32
1b (0.1)
4.0 (40.0)
55
82
4920
2.32
90.8
1.7
1.9
15
33
34
2a (0.2)
2a (0.2)
2a (0.2)
3.0 (15.0)
3.0 (15.0)
3.0 (15.0)
25
40
55
295
20
15
8850
600
450
2.31
Insoluble
Insoluble
2.2
19
35
36
2b (0.5)
2b (0.5)
2b (0.5)
2.0 (4.0)
2.0 (4.0)
2.0 (4.0)
25
40
55
278
36
37
3340
430
440
21.3
Insoluble
Insoluble
2.3
26
37
38
3a (1.0)
3a (1.0)
3a (1.0)
4.0 (4.0)
4.0 (4.0)
4.0 (4.0)
25
40
55
125
140
270
750
840
1620
0.50
0.38
0.41
1.9
2.1
2.0
a
b
c
Conditions: toluene 30 mL, MAO (prepared by removing toluene and AlMe3 from ordinary MAO) 1–5 mmol, ethylene 6 atm, 25 ◦C, 10 min.
Molar ratio of Al/M.
GPC data in o-dichlorobenzene vs. polystyrene standards.
Low molecular weight shoulder was observed in small amount in the GPC trace.
High molecular weight shoulder was observed in small amount in the GPC trace.
d
e
2.1. Ethylene polymerization by Cp*MCl2(O-2,6-R2C6H3)—MAO
catalyst systems
tant polyethylene prepared by 1a—MAO catalyst, runs 1,3,5, and
30), the Al/Ti ratio affected the molecular weight distributions in
the resultant polyethylenes; peaks corresponding to trace or small
amount of low molecular weight polymers were observed if the
polymerizations were conducted at high Al/Ti molar ratios or at
55 ◦C.
The catalytic activity with a series of Cp*MCl2(O-2,6-R2C6H3) (1-
3a,b) under the optimized Al/M molar ratios increased in the order:
1a (96600 kg-PE/mol-Ti h, run 4) » 2a (8850, run 15), 1b (8400, run
9) > 2b (3340, run 19) > 3a (750, run 26) > 3b (78, run 28). The results
suggest that the complexes containing 2,6-diphenylphenoxy ligand
(1–3a) showed higher catalytic activities than the complexes con-
taining 2,6-di-tert-butylphenoxy ligand (1–3b), probably due to a
steric bulk around the metal center. The activity by the Zr–Ph ana-
logue (2a) was sensitive toward the Al/Zr molar ratio (runs 12–17).
The molecular weight in the resultant polymers prepared by the Zr
and Hf analogues were lower than those prepared by Ti–Ph (1a) and
Ti–iPr (1c) analogues, although the polymers possessed unimodal
molecular weight distributions, as seen in the polymer prepared by
1c—MAO catalyst under the same conditions (run 11).
Table 3 summarizes the results in the ethylene polymeriza-
tion employed at higher temperature. The catalytic activity by the
Ti complexes (1a,b) decreased at higher temperature (40, 55 ◦C),
and significant decreases in the activities were observed in case
of Zr complex catalysts (2a,b, runs 33–36). In contrast, the activ-
ity increased at higher temperature, if the Hf–Ph complex (3a) was
employed as the catalyst precursors (runs 37–38). The fact (temper-
ature dependence) should be a unique contrast as effect of centered
metal toward the catalytic activity.
Ethylene polymerizations using a series of Cp*MCl2(O-2,6-
R2C6H3) [M = Ti (1), Zr (2), Hf (3); R = Ph (a), tBu (b)] were conducted
in toluene in the presence of MAO cocatalyst, and Cp*TiCl2(O-
2,6-iPr2C6H3) (1c) was also chosen for comparison. MAO white
solids prepared by removing AlMe3 and toluene from the com-
mercially available samples [PMAO-S, 9.5 wt% (Al) toluene solution,
Tosoh Finechem Co.] were chosen, because it was effective for the
preparation of high molecular weight ethylene/␣-olefin copoly-
mers with unimodal molecular weight distributions when 1c and
[Me2Si(C5Me4)(NtBu)]TiCl2 were used as the catalyst precursor
[9a]. The results are summarized in Tables 2 and 3.
Table 2 summarizes the results conducted at 25 ◦C with vari-
ous Al/M molar ratios. The Ti–Ph analogue (1a) showed notable
catalytic activity in the ethylene polymerization (runs 1–5), and
the activity was somewhat higher than that by the Ti–iPr analogue
(1c, run 11) under the same conditions. As reported previously [7c],
the activities by the Ti-tBu analogue (1b) were lower (runs 6–10)
than those by 1c under the same conditions. The observed activi-
ties by 1a,b were not strongly dependent upon the Al/Ti molar ratios
employed, however, as exemplified in Fig. 2 (GPC charts in the resul-
2.2. Copolymerization of ethylene with 1-octene and
2-methyl-1-pentene by Cp*MCl2(O-2,6-R2C6H3)—MAO catalyst
systems
Table 4 summarizes the results in copolymerization of ethy-
lene with 1-octene, 2-methyl-1-pentene (2M1P) using a series
of Cp*MCl2(O-2,6-R2C6H3) [M = Ti (1), Zr (2), Hf (3); R = Ph (a),
tBu (b), iPr (c)]—MAO catalyst systems. Fig. 3 shows typical 13C
NMR spectra in the resultant polymers. As reported previously
[9b,c], the Ti–iPr complex (1c) exhibited notable catalytic activ-
Fig. 2. GPC traces for resultant polyethylene prepared by Cp*TiCl2(O-2,6-Ph2C6H3)
(1a)—MAO catalyst.

106
K. Itagaki et al. / Journal of Molecular Catalysis A: Chemical 303 (2009) 102–109
Table 4
Copolymerization of ethylene with 1-octene (OC), 2-methyl-1-pentene (2M1P) by Cp*MCl2(O-2,6-R2C6H3) [M = Ti (1), Zr (2), Hf (3); R = Ph (a), R = tBu (b), iPr (c)]—MAO catalyst
systemsa.
Run
Cat. (␮mol)
MAO/mmol
Comonomer
(mmol/mL)
Temperature/◦C
Yield/mg
Activity/kg-PE/mol-M h
Mn (×10−4
c
)
Mw/Mn
Comonomerd/mol%
c
b
(Al/M × 10−3
)
4
1a (0.01)
1a (0.01)
1a (0.01)
1a (0.01)
1a (0.01)
1b (0.1)
1b (1.0)
1b (1.0)
1b (5.0)
1c (0.01)
1c (0.02)
1c (0.5)
2a (0.2)
2a (0.2)
2a (0.2)
2a (0.2)
2a (0.1)
2b (0.5)
2b (0.5)
2b (0.5)
2b (0.5)
2b (0.5)
3a (1.0)
3a (1.0)
3a (1.0)
3a (1.0)
3a (1.0)
4.0 (400)
4.0 (400)
4.0 (400)
4.0 (400)
4.0 (400)
4.0 (40.0)
4.0 (4.0)
4.0 (4.0)
4.0 (0.8)
3.0 (300)
3.0 (150)
4.5 (9.0)
3.0 (15.0)
3.0 (15.0)
3.0 (15.0)
3.0 (15.0)
3.0 (30.0)
2.0 (4.0)
2.0 (4.0)
2.0 (4.0)
2.0 (4.0)
2.0 (4.0)
4.0 (4.0)
4.0 (4.0)
4.0 (4.0)
4.0 (4.0)
4.0 (4.0)
–
25
25
55
25
55
25
25
55
25
25
25
25
25
25
55
25
55
25
25
55
25
55
25
25
55
25
55
161
53
97000
32000
–
67.0e
4.70
–
2.9
1.9
–
–
27.0
–
39
40
41
42
9
OC (1.06)
OC (1.06)
2M1P (1.35)
2M1P (1.35)
–
OC (1.06)
OC (1.06)
2M1P (1.35)
–
OC (1.06)
2M1P (1.35)
–
OC (1.06)
OC (1.06)
2M1P (1.35)
2M1P (1.35)
–
OC (1.06)
OC (1.06)
2M1P (1.35)
2M1P (1.35)
–
OC (1.06)
OC (1.06)
2M1P (1.35)
2M1P (1.35)
Trace
Trace
222
140
68
127
99
72
308
705
295
Trace
431
24
400
278
263
219
150
204
125
128
139
80
–
–
–
–
133000
8400
410
1.64
2.67f
3.86
3.70
1.50
189
12.8
11.8
2.31
–
1.41
Insoluble
194j
21.3
26.1
1.24
6.80
156
0.50
0.50
0.65
0.42
0.32f
4.8
2.4
3.8
3.3
5.6
2.4
2.1
2.1
2.2
–
Trace
–
27.8
34.3
Trace
–
27.9
3.3
–
43
44
45
11
46g
47h
15
48
49
50
51i
19
52
53
54
55
26
56
57
58
59
762
120
43200
154000
8460
8850
–
12930
720
2.2
3.2
48000
3340
3200
2600
1800
2450
750
768
834
480
1240
2.2
2.3
2.3
2.9
1.3
2.4
1.9
2.0
1.8
2.2
2.6
None
–
9.4
15.9
None
–
9.9
16.4
None
206
a
Conditions: toluene 25 mL + 1-octene (OC) or 2-methyl-1-pentene (2M1P) 5 mL, MAO (prepared by removing toluene and AlMe3 from ordinary MAO) 1–5 mmol, ethylene
6 atm, 25 ◦C, 10 min.
b
Molar ratio of Al/M.
GPC data in o-dichlorobenzene vs. polystyrene standard.
Comonomer content in copolymer estimated by 13 C NMR spectra.
Low molecular weight shoulder was observed in small amount in the GPC trace.
High molecular weight shoulder was observed in small amount in the GPC trace.
Cited from reference [13b], polymerization 6 min.
Cited from reference [13a].
c
d
e
f
g
h
i
Polymerization time 5 min.
Sample was hardly soluble even in hot o-dichlorobenzene.
j
ity in ethylene/1-octene copolymerization (run 46); the activity
in the copolymerization was higher than that in the ethylene
homopolymerization. The resultant polymer prepared by 1c was
high molecular weight poly(ethylene-co-1-octene) with unimodal
molecular weight distribution. The 1-octene contents in the resul-
tant copolymers prepared by 1a, 1b were very close to that prepared
by 1c, when the copolymerization was conducted under the same
conditions at 25 ◦C (runs 39,43). However, the activities by 1a,b
decreased upon the presence of 1-octene in the copolymerization;
the Mn value in the copolymer prepared by 1a was lower than that
in the polyethylene (runs 4 vs. 39) and the resultant copolymer
prepared by 1b possessed broad molecular weight distribution.
It also turned out that the copolymerization using a series of
Cp*MCl2(O-2,6-R2C6H3) (1–2a,b, and 3a)—MAO catalysts afforded
the copolymer, poly(ethylene-co-1-octene)s, with unimodal molec-
ular weight distributions (Mw/Mn = ca. 2) except 1b. However,
notable increases in the activity in the copolymerization from the
ethylene homopolymerization as observed by 1c were not observed
in all cases. Note that the 1-octene contents in the resultant copoly-
mers were dependent upon the centered metal employed rather
than the phenoxy substituent (Ph or tBu), and the Ti complexes
(1a,c) showed better 1-octene incorporation. Both the catalytic
activities and 1-octene contents in the copolymers by the Zr (2a,b)
and the Hf (3a) complexes increased at higher temperatures (55 ◦C,
runs 49, 53, 57), whereas the extremely low catalytic activity by the
Ti–Ph analogue (1a) was observed at 55 ◦C in the copolymerization
(run 40) and the activities in the ethylene homopolymerizations
by the Zr analogues (2a,b) decreased at higher temperature (runs
33–34, 35–36). The Zr complex (2b) showed similar 1-octene incor-
poration to those by 3a, however, these showed less efficient
1-octene incorporations than the Ti complexes (1a,c) under these
conditions; 2a showed the lowest 1-octene incorporation. No sig-
nificant differences in microstructures in the resultant copolymers
prepared by 1–3a were observed, although some resonances were
not seen due to the low 1-octene contents in the copolymers pre-
pared by 2–3a and resonances ascribed to the polymer chain ends
were seen due to the low molecular weight in the copolymer by
3a. Taking into account these results, it is thus suggested that the
Ti analogues (1a,c) seem to be more suited as the catalyst precur-
sors in terms of both the activity and the 1-octene incorporation in
the ethylene/1-octene copolymerization; the Ti–iPr analogue (1c)
exhibits exceptionally high catalytic activity with efficient 1-octene
incorporation, as reported previously [9c].
As also reported previously [13], 1c showed moderate catalytic
activity in ethylene/2M1P copolymerization, and the resultant
polymer was poly(ethylene-co-2M1P) that possesses rather high
molecular weight with uniform molecular weight distribution (run
47, Mn = 1.18 × 105, Mw/Mn = 2.1, 2M1P 3.3 mol%). In contrast, the
activities by the Ti–Ph (1a), the Ti–tBu (1b) analogues at 25 ◦C were
low (runs 41, 45). Although a significant increase in the activity was
observed by 1a at 55 ◦C, the resultant polymers contained trace
amount of 2M1P. Therefore, only the Ti–iPr complex (1c) could
incorporate 2M1P in the copolymerization under these copolymer-
ization conditions.

K. Itagaki et al. / Journal of Molecular Catalysis A: Chemical 303 (2009) 102–109
107
Fig. 3. 13 C NMR spectra (in C6D6/1,2,4-trichlorobenzene 1/4 (v/v), at 110 ◦C) for poly(ethylene-co-1-octene)s prepared by (a) Cp*TiCl2(O-2,6-Ph2C6H3) (1a), (b) Cp*ZrCl2(O-
2,6-Ph2C6H3) (2a), and (c) Cp*HfCl2(O-2,6-Ph2C6H3) (3a) in the presence of MAO cocatalyst.
The polymerizations of ethylene using the Zr (2a,b) and the
Hf (3a) were also explored in the presence of 2M1P, and notable
increase in the activity at 55 ◦C was observed in the polymerization
using the Zr–Ph analogue (run 51). However, the resultant poly-
mers were linear polyethylene in all cases and resonances ascribed
to incorporation of 2M1P were not observed in the 13C NMR spec-
tra even in a trace amount. Taking into account of these results, the
Ti–iPr (1c) analogue should be most suited as the catalyst precursor
in terms of both the catalytic activity and 2M1P incorporation.
tert-butylphenoxy analogues (1–3b). The molecular weights in the
resultant polymers prepared by the Zr and the Hf analogues were
lower than those prepared by the Ti–Ph (1a) and the Ti–iPr (1c) ana-
logues. Although the copolymerizations of ethylene with 1-octene
afforded the copolymer with uniform molecular weight distribu-
tions (except 1b), both the activities and 1-octene incorporation
were highly affected by the centered metal employed; the Ti–iPr
analogue (1c) seems to be the most suited in terms of both the cat-
alytic activity and the 1-octene incorporation. The Ti–iPr analogue
(1c) only showed rather efficient comonomer incorporation in the
copolymerization of ethylene with 2M1P. We believe that the infor-
mation should be helpful for designing efficient catalyst precursors
for precise, controlled olefin polymerization.
3. Conclusion
A series of Cp*MCl2(O-2,6-R2C6H3) [Ti (1), Zr (2), Hf (3); R = Ph
t
(a), Bu (b)] have been prepared and effect of the centered metal
toward the catalytic activity as well as comonomer incorporation
has been explored in ethylene (co)polymerization in the presence
of MAO cocatalyst. Structures for 2–3a,b were determined by X-ray
crystallography as a rather distorted tetrahedral geometry around
the metal center. The catalytic activity in ethylene polymerization
was affected by the centered metal employed [Ti > Zr > Hf], and the
complexes containing 2,6-diphenylphenoxy ligand (1–3a) showed
higher catalytic activities than the complexes containing 2,6-di-
4. Experimental section
4.1. General procedure
All experiments were carried out under a nitrogen atmosphere
in a Vacuum Atmospheres drybox or using standard Schlenk tech-
niques. All chemicals used were of reagent grade and were purified
by standard purification procedures. Anhydrous grade toluene and

108
K. Itagaki et al. / Journal of Molecular Catalysis A: Chemical 303 (2009) 102–109
n-hexane (Kanto Chemical Co., Inc.) were stored in drybox in the
presence of molecular sieves (mixture of 3A 1/16 and 4A 1/8,
and 13X 1/16) after passing through an alumina short column
under nitrogen. Anhydrous grade dichloromethane and diethyl
ether (Kanto Kagaku Co., Ltd.) were stored in drybox in the pres-
ence of molecular sieves (mixture of 3A 1/16 and 4A 1/8, and 13X
1/16). Cp*TiCl3 (Wako Pure Chemical Ind., Ltd.), Cp*ZrCl3 (Aldrich),
Cp*HfCl3 (Aldrich) were used as received. Cp*TiCl2(O-2,6-Ph2C6H3)
(1a) [16], Cp*TiCl2(O-2,6-tBu2C6H3) (1b) [7c], Cp*TiCl2(O-2,6-
iPr2C6H3) (1c) [7a], and Cp*ZrCl2(O-2,6-tBu2C6H3) (2b) [15] were
prepared according to the published procedures.
octene)s were measured by gel permeation chromatography (GPC,
Tosoh HLC-8121GPC/HT) using a RI-8022 detector (for high temper-
ature, Tosoh Co.) with polystyrene gel column (TSK gel GMHHR-H
HT × 2, 30 cm × 7.8 mm␾ ID), ranging from <102 to <2.8 × 108 MW)
at 140 ◦C using o-dichlorobenzene containing 0.05 wt/v% 2,6-di-
tert-butyl-p-cresol as the solvent. The molecular weight was
calculated by a standard procedure based on the calibration with
standard polystyrene samples.
4.2. Synthesis of Cp*ZrCl2(O-2,6-Ph2C6H3) (2a)
Ethylene of polymerization grade (Sumitomo Seika Chemicals,
Ltd.) was used as received without further purification. 1-Octene
(Wako Pure Chemical Ind., Ltd.) and 2-methyl-1-pentene (TCI Co.,
Ltd.) were stored in dryboxinthepresenceofmolecularsieves (mix-
ture of 3A 1/16 and 4A 1/8, and 13X 1/16) after passing through
alumina short column under nitrogen. Toluene and AlMe3 in
the commercially available methylaluminoxane [PMAO-S, 9.5 wt%
(Al) toluene solution, Tosoh Finechem Co.] were removed under
reduced pressure (at ca. 50 ◦C for removing toluene, AlMe3, and
then heated at >100 ◦C for 1 h for completion) in the drybox to give
white solids.
Into a toluene/n-hexane suspension containing Cp*ZrCl3 303 mg
(0.910 mmol), LiO-2,6-Ph2C6H3 (0.928 mmol) was added at −30 ◦C.
The reaction mixture was warmed slowly up to room tempera-
ture, and the mixture was stirred for 5 h. The solvent was removed
in vacuo after addition of CH2Cl2, and the resultant residue was
extracted with hot toluene. The toluene extract was then dried in
vacuo to give a pale yellow solid. The solid was then dissolved in a
minimum amount of CH2Cl2 layered by a small amount of n-hexane.
The chilled solution gave colorless crystal. Yield: 359 mg (72.7%). 1H
NMR (CDCl3): ı 7.55 (d, 4H, J = 8.1), 7.44 (t, 4H, J = 7.5), 7.32 (t, 2H,
J = 7.3), 7.27 (d, 2H, J = 7.7), 7.11 (t, 1H, J = 7.5), 1.57 (s, 16H). 13C NMR
(CDCl3): ı 154.9, 138.8, 133.3, 130.4, 130.3, 128.9, 127.1, 126.2, 122.3,
All 1H and 13C NMR spectra were recorded on a JEOL JNM-
LA400 spectrometer (399.78 MHz for 1H and 100.53 MHz for 13C).
All spectra were obtained in the solvent indicated at room temper-
ature unless otherwise noted. Chemical shifts are given in ppm and
are referenced to SiMe4 (ı 0.00, 1H, 13C). 13C NMR spectra for the
resultant polymers [polyethylene, poly(ethylene-co-1-octene), and
poly(ethylene-co-2-methyl-1-pentene)] were measured at 110 ◦C
in C6D6/1,2,4-trichlorobenzene (1/4, v/v). The relaxation delay was
5.2 s, the acquisition time was 1.3 s, the pulse angle was 90◦, and
the number of transients accumulated was ca. 6000. Elemental
analyses were performed by using a PE2400II Series (PerkinElmer
Co.), and some analytical runs were performed twice to confirm the
reproducibility in the independent analysis/synthesis runs. Certain
C values were somewhat lower than those calculated, whereas their
N, H, values were close; this is due to incomplete combustion (to
form titanium carbide).
10.9. Anal. Calcd. for C28
C, 61.20; H, 5.31; N, 0%.
H28Cl2ZrO: C, 61.97; H, 5.20; N, 0%. Found:
4.3. Synthesis of Cp*HfCl2(O-2,6-Ph2C6H3) (3a)
To a toluene solution (10 mL) containing Cp*HfCl3 506 mg
(1.20 mmol), LiO-2,6-Ph2C6H3 313 mg (1.24 mmol) was added at
−30 ◦C. The reaction mixture was warmed slowly to room tem-
perature, and the mixture was stirred for additional 12 h. The
solvent was removed in vacuo after addition of CH2Cl2, and the
resultant white tan residue was extracted with hot toluene. The
toluene extract was then dried in vacuo, and the resulting white
was dissolved in a minimum amount of CH2Cl2 layered by a small
amount of n-hexane. The chilled solution gave colorless crystal.
Yield 430 mg (56.7%). 1H NMR (CDCl3): ı 7.52 (dd, 4H, J = 7.5, 1.4),
7.41 (t, 4H, J = 7.5), 7.31 (tt, 2H, J = 7.5, 1.4), 7.26 (d, 2H, J = 7.4),
7.08 (t, 1H, J = 7.4), 1.61 (s, 15H). 13C NMR (CDCl3): ı 154.9, 138.3,
Molecular weights and molecular weight distributions for the
poly(ethylene-co-2-methyl-1-pentene)s and poly(ethylene-co-1-
Table 5
Crystal and data collection parameters [19] a
.
Complex
2a
2b
3a
3b
Formula; formula weight
Habits
Crystal size (mm)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
ˇ (Deg)
V (Å3)
C28H28Cl2OZr; 542.65
Colorless, block
0.35 × 0.15 × 0.15
Monoclinic
P21/n (#14)
9.0510(3)
7.5984(2)
36.2051(10)
93.0128(12)
2486.51(13)
4
C24H36Cl2OZr; 502.67
Colorless, block
0.40 × 0.30 × 0.18
Monoclinic
P21/n (#14)
9.6805(4)
15.5345(5)
17.0748(5)
107.1917(11)
2453.01(15)
4
C28H28Cl2HfO; 629.92
Colorless, block
0.30 × 0.25 × 0.18
Monoclinic
P21/n (#14)
9.0287(3)
7.61072(18)
36.2190(8)
92.9237(12)
2485.54(12)
4
C24H36Cl2HfO; 589.94
Colorless, block
0.40 × 0.40 × 0.30
Monoclinic
P21/n (#14)
9.6678(3)
15.5309(4)
17.0507(4)
107.1726(8)
2446.02(11)
4
Z value
Dcalcd (g/cm3)
F000
1.449
1112.00
1.361
1048.00
1.683
1240.00
1.602
1176.00
Temperature (K)
193
6.747
193
6.773
193
44.223
193
44.871
␮ (Mo K␣) (cm−1
)
No. of reflections measured
Total: 33034; Unique:
5624; Rint = 0.027
4870
Total: 23994; Unique:
5594; Rint = 0.020
5117
Total: 19782; Unique:
5361; Rint = 0.026
4823
Total: 19523; Unique:
4464; Rint = 0.042
4327
No. of observations (I > −3.00 ı(I))
No. of variables
317
289
317
289
Residuals: R1; Rw
GOF
Max (minimum) peak In final diff. map (e-/Å3)
0.0290
1.004
0.55 (−0.61)
0.0209
1.009
0.30 (−0.35)
0.0195
1.006
0.99 (−0.84)
0.0261
1.008
0.80 (−2.53)
a
Diffractometer: Rigaku RAXIS-RAPID Imaging Plate. Structure solution: direct methods. Refinement: full-matrix least-squares. Function minimized: ꢀw(|Fo| − |Fc|)2
(w = Least-squares weights, Chebychev polynomial). Standard deviation of an observation of unit weight: [ꢀw(|Fo| − |Fc|)2/(No − Nv)]1/2 (No = number of observations,
Nv = number of variables).

K. Itagaki et al. / Journal of Molecular Catalysis A: Chemical 303 (2009) 102–109
109
(2a), Cp*ZrCl2(O-2,6-Ph2C6H3) (2b), Cp*HfCl2(O-2,6-tBu2C6H3)
(3a), Cp*HfCl2(O-2,6-Ph2C6H3) (3b). These data (including CIF files)
were also deposited in Cambridge Crystallographic Data Centre as
CCDC 712658-712661, respectively. The data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html or
e-mail deposit@ccdc.cam.ac.uk.
133.4, 130.4, 130.3, 128.8, 127.1, 123.8, 122.1, 10.7. Anal. Calcd. for
28H28Cl2HfO: C, 53.39; H, 4.48; N, 0%. Found: C, 52.62; H, 4.27; N,
0.05%.
C
4.4. Synthesis of Cp*HfCl2(O-2,6-tBu2C6H3) (3b)
Synthesis of 3b was carried out by the same procedure as that
for 1b except that Cp*HfCl3 250 mg (0.595 mmol), LiO-2,6-tBu2C6H3
132 mg (0.622 mmol) and Et2O as solvent were used. Yield: 94 mg
(27%). 1H NMR (CDCl3): ı 7.19 (d, 2H, J = 7.7 Hz), 6.82 (t, 1H, J = 7.7 Hz),
2.10 (s, 15H), 1.37 (s, 18H). 13C NMR (CDCl3): ı 160.6, 139.2, 125.5,
124.8, 120.8, 35.3, 31.9, 12.2. Anal. Calcd. for C24H36Cl2HfO: C, 48.86;
H, 6.15; N, 0%. Found: C, 49.12; H, 6.25; N, 0.10%.
References
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A typical procedure (Table 2, run 3) for ethylene polymeriza-
tion was performed as follows: the prescribed amounts of toluene
(29.0 mL), d-MAO (174 mg, 3.0 mmol) were added into the auto-
clave (100 mL scale) in the drybox, and the apparatus was then
purged with ethylene. The reaction mixture was then pressurized
to 5 atm (total ethylene 6 atm) soon after the addition of a toluene
solution (1.0 mL) containing 1a (0.01 ␮mol). The mixture was mag-
netically stirred for 10 min, the ethylene remaining was purged after
reaction, and the mixture was then poured into EtOH (50 mL) con-
taining HCl (5 mL). The resultant polymer was collected on a filter
paper by filtration, and was adequately washed with EtOH, and was
then dried in vacuo at 60 ◦C for several hours. Copolymerizations of
ethylene with 1-octene or 2-methyl-1-pentene were conducted in
the same manner as that for ethylene polymerization except that a
mixture of toluene (24.0 mL) and 1-octene or 2-methyl-1-pentene
(5.0 mL) was used in place of toluene (29.0 mL).
Acknowledgements
(b) T.A. Manz, S. Sharma, K. Phomphrai, K.A. Novstrup, A.E. Fenwick, P.E. Fanwick,
G.A. Medvedev, M.M. Abu-Omar, W.N. Delgass, K.T. Thomson, J.M. Caruthers,
Organometallics 27 (2008) 5504.
This research was partly supported by Grant-in-Aid for Scientific
Research (B) from the Japan Society for the Promotion of Science
(JSPS, No. 18350055). The authors would like to express their thanks
to Sumitomo Chemical Co., Ltd. for GPC analyses of some polyethy-
lene samples. K.N. and K.I. express their thanks to Mr. Shohei Katao
and Mr. Fumio Asanoma (Nara Institute of Science and Technology)
for help in X-ray crystallographic analyses. K.I. thanks to JSPS for a
predoctoral fellowship (18-7944). K.N. thanks to Tosoh Finechem
Co. for donating MAO.
[18] (a) Part of these results were presented at the following symposium: S. Hasumi,
K. Itagaki, M. Fujiki, K. Nomura, Abstract in 17th annual symposium in the Japan
Petroleum Institute, December 2008, Kyoto, Japan.;
(b) More recently, results for improvement in the catalytic activity in the ethy-
lene polymerization using Cp*TiCl2(OAr) had been presented: T.-J. Kim, S.K.
Kim, J.-S. Hahn, M.-A. Ok, J.H. Song, D.-H. Shin, J. Ko, C. Minserk, M. Mitoraj,
M. Srebro, A. Michalak, S.O. Kang, Abstract in 102nd Korean Chemical Society
National Meeting, October 2008, Jeju, Korea.
[19] Their structure analysis reports are shown in the Supplementary Materials,
and the crystallographic data (including CIF files) for 2a,b and 3a,b were also
deposited in Cambridge Crystallographic Data Centre as CCDC 712658-712661,
respectively.
[20] L. Pauling, J. Am. Chem. Soc. 69 (1947) 542.
Appendix A. Appendix A. Supplementary Material
[21] DIRDIF94: P.T. Beurskens, G. Admiraal, G. Beurskens, W.P. Bosman, R. de Delder,
R. Israel, J.M.M. Smits, The DIRDIF94 Program System, Technical report of crys-
tallography laboratory, University of Nijmegen, The Netherlands, 1994.
[22] (a) Crystal Structure 3.6.0, Crystal Structure Analysis Package, Rigaku and
Rigaku/MSC, The Woodlands, TX, 2000–2004.;
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molcata.2009.01.001.
Structure reports including crystal data and crystallographic
(b) D.J. Watkin, C.K. Prout, J.R. Carruthers, P.W. Betteridge, CRYSTALS Issue 10,
Chemical Crystallography Laboratory, Oxford, UK, 1996.
parameters for structural analyses for Cp*ZrCl2(O-2,6-tBu2C6H3)