Effect of aryloxide ligand in 1-hexene, styrene polymerization catalyzed by nonbridged half-titanocenes of the type, Cp′TiCl2(OAr) (Cp′ = C5Me5, tBuC5H4).

Article abstract of DOI:10.1016/j.molcata.2006.03.030

Various (aryloxo)(pentamethylcyclopentadienyl)titanium(IV) dichloride complexes of the type, Cp^*TiCl₂(OAr) [Cp^* = C₅Me₅, Ar = 2,6-Me₂C₆H₃ (1), 2,4,6-Me₃C

Full text of DOI:10.1016/j.molcata.2006.03.030

Journal of Molecular Catalysis A: Chemical 254 (2006) 197–205
Effect of aryloxide ligand in 1-hexene, styrene polymerization
catalyzed by nonbridged half-titanocenes of the type,
CpꢀTiCl2(OAr) (Cpꢀ = C5Me5, tBuC5H4)
Structural analyses for Cp*TiCl2(O-2,6-tBu2C6H3)
and Cp*TiCl2(O-2,6-iPr2-4-tBuC6H2)
Kotohiro Nomura∗, Aki Tanaka, Shohei Katao
Graduate School of Materials Science, Nara Institute of Science and Technology (NAIST),
8916-5 Takayama, Ikoma, Nara 630-0101, Japan
Available online 2 May 2006
Abstract
Various (aryloxo)(pentamethylcyclopentadienyl)titanium(IV) dichloride complexes of the type, Cp*TiCl2(OAr) [Cp* = C5Me5, Ar = 2,6-
Me2C6H3 (1), 2,4,6-Me3C6H2 (2), 2,6-iPr2C6H3 (3), 2,6-iPr2-4-tBuC6H2 (4), 2,6-tBu2C6H3 (5), 2,6-tBu2-4-MeC6H2 (6)], have been prepared,
and structures for 4 and 5 have been determined by X-ray crystallography. The Ti O C (phenyl) bond angles for the Cp* analogues con-
taining the 2,6-diisopropyl-substituted phenoxo ligands (3–4, 173.0–174.6◦) were larger than those for other Cp* analogues (155.5–162.3◦),
suggesting that both Cp* and 2,6-diisopropyl-substituted aryloxo ligand force the unique bond angle leading to more O → Ti ␲ donation into
Ti. Effect of aryloxide ligand in 1-hexene polymerization catalyzed by Cp*TiCl2(OAr)—MAO catalysts were explored, and 3–4 exhibited the
exceptionally high catalytic activities. Various tert-BuCp analogues of the type, (tBuC5H4)TiCl2(OAr) [Ar = 2,6-Me2C6H3 (7), 2,4,6-Me3C6H2
(8), 2,6-iPr2C6H3 (9), 2,6-iPr2-4-tBuC6H2 (10), 2,6-tBu2C6H3 (11), 2,6-tBu2-4-MeC6H2 (12)], have also been prepared, and explored effect of
the aryloxide ligand in syndiospecific styrene polymerization in the presence of MAO cocatalyst. The catalytic activity increased in the order: 10
(activity 2680 kg sPs/mol Ti h) > 7, 9 (1370) > 8 (534) > 11 (258) > 12 (54), strongly suggesting that role of anionic donor ligand was present in this
catalysis.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Titanium; Olefin polymerization; Structure analysis; Ligand effect; Half-titanocene
1. Introduction
N = CR2, etc.; X = halogen, alkyl, etc.; R = alkyl, aryl, etc.), have
been one of the promising candidates as the efficient catalysts
[2–24], because this type of complex catalysts recently dis-
played unique characteristics as olefin polymerization catalysts
producing new polymers that had never been prepared by con-
ventional Zigler–Natta catalysts, by ordinary metallocene type
[1] and/or so-called ‘constrained geometry’ (linked Cp-amide)
type catalysts [1d–e]. We reported that half-titanocenes contain-
ing an aryloxo ligand of the type, CpꢀTiCl2(OAr) (OAr = aryloxy
group), exhibited high catalytic activities for both olefin poly-
merization [4] and syndiospecific styrene polymerization [5].
In particular, these complex catalysts exhibited unique charac-
teristics for copolymerization of ethylene with ␣-olefin [4b,6],
styrene [7], norbornene [8a,b], and revealed that an efficient
catalyst for desired polymerization can be tuned by modification
of the cyclopentadienyl fragment, Cpꢀ. More recently, we had
Design and synthesis of efficient transition metal complex
catalysts for precise olefin polymerization are one of the most
attractive subjects not only in the field of organometallic chem-
istry, catalysis, butalsointhefieldofpolymerchemistry, because
evolution of new polyolefins that have never been prepared by
conventional catalysts can be highly expected by designing the
new catalysts [1]. Nonbridged half-metallocene type group 4
transition metal complexes containing anionic donor ligand of
the type, CpꢀM(L)X2 (Cpꢀ = cyclopentadienyl group; M = Ti,
Zr, Hf; L = anionic donor ligand such as OAr, NR2, NPR3,
∗
Corresponding author. Tel.: +81 743 72 6041; fax: +81 743 72 6049.
E-mail address: nomurak@ms.naist.jp (K. Nomura).
1381-1169/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2006.03.030

198
K. Nomura et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 197–205
Scheme 1. Effect of substituents on cyclopentadienyl and aryloxide ligands in ethylene polymerization [4a,b].
(1), 2,4,6-Me3C6H2 (2), 2,6-iPr2C6H3 (3), 2,6-iPr2-4-tBuC6H2
(4), 2,6-tBu2C6H3 (5), 2,6-tBu2-4-MeC6H2 (6); Cpꢀ = tBuC5H4
and Ar = 2,6-Me2C6H3 (7), 2,4,6-Me3C6H2 (8), 2,6-iPr2C6H3
(9), 2,6-iPr2-4-tBuC6H2 (10), 2,6-tBu2C6H3 (11), 2,6-tBu2-4-
MeC6H2 (12)] (Chart 1), and explored effect of the arylox-
ide ligand in both 1-hexene polymerization and syndiospe-
cific styrene polymerization in the presence of MAO cocata-
lyst. Through this study, we explored effect of anionic donor
ligand for precise olefin polymerization using these half-
titanocenes.
shown that efficient copolymerizations of ethylene with cyclo-
hexene (CHE) [8c], 2-methyl-1-pentene (2M1P) [9], and with
vinylcyclohexane [10] had been achieved as the first examples
by using these complex catalysts.
We previously reported that the catalytic activities for
the ethylene polymerization were dependent upon the sub-
stituent on both cyclopentadienyl and the aryloxide ligands
employed (Scheme 1) [4]. Since, as summarized in Table 1
[4a,b], the bond angle (173.0◦) of Ti O C (phenoxy) for
Cp*TiCl2(O-2,6-iPr2C6H3) which was the most effective cat-
alyst precursor is significantly different from those for the
other Cp derivatives, CpꢀTiCl2(O-2,6-iPr2C6H3) (Cpꢀ = Cp, 1,3-
tBu2C5H3, 163.0–163.1◦) and for Cp*TiCl2(O-2,6-Me2C6H3)
(162.3◦), we assumed that both Cp* and the diisopropyl group
sterically force the more open Ti O C bond angle, which
leads to more O → Ti ␲ donation into Ti; this along with the
more electron donating Cp* (as compared with Cp, BuCp,
t
Me2Cp) stabilizes the active species, leading to higher activ-
ity [25]. Recently, it also turned out that the role of anionic
donor ligand plays an essential role especially for ethylene
copolymerizations such as 2M1P, CHE, styrene incorpora-
tions [8c,9,23b]. Therefore, we prepared various Cp* and
tert-BuCp derivatives containing various aryloxide ligands of
the type, CpꢀTiCl2(OAr) [Cpꢀ = Cp* and Ar = 2,6-Me2C6H3
Table 1
ꢀ
i
˚
Selected bond distances (A) and angles for Cp TiCl2(O-2,6- Pr2C6H3) [4a]
Cpꢀ = Cp Cpꢀ = 1,3-tBu2C5H3 Cpꢀ = Cp*
˚
Bond distances (A)
Ti(1) Cl(1)
2.262(1)
2.2553(8)
2.379(3)
2.378(3)
2.410(2)
1.773(3)
2.305(2)
2.367(7)
2.345(7)
2.368(7)
1.772(3)
Ti(1) C(1) in Cp
Ti(1) C(2) in Cp
Ti(1) C(3) in Cp
Ti(1) O(1)
2.282(8)
2.299(5)
2.325(5)
1.760(4)
Bond angles (◦)
Cl(1) Ti Cl(2)
Cl(1) Ti O(1)
Cl(2) Ti O(1)
104.23(7)
102.53(9)
102.53(9)
103.46(3)
103.45(5)
99.1(2)
104.1(2)
173.0(3)
103.62(6)
98.57(6)
163.1(2)
Ti
O C(6)in phenyl 163.0(4)
Chart 1.

K. Nomura et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 197–205
199
2. Results and discussion
The red platelet microcrystals of 4, 5 were grown from the
concentrated hot toluene solution layered by n-hexane upon
standing at room temperature in the drybox, and their struc-
tures were determined at −30 ◦C. The molecular structures for
4 and 5 are shown in Figs. 1 and 2, respectively, and these
structures showed that both complexes fold a rather distored
tetrahedral geometry around the titanium metal center. Selected
bond distances, and bond angles for various Cp*TiCl2(OAr) are
summarized in Table 2, and these values in some reported Cp*
analogues [26–29] are also shown for comparison. No signifi-
cant differences in bond lengths among these complexes were
2.1. Syntheses of various Cp*TiCl2(OAr) (1–6),
(tBuC5H4)TiCl2(OAr) (7–12), and structural analyses for
Cp*TiCl2(O-2,6-iPr-4-tBu-C6H2) (4) and
Cp*TiCl2(O-2,6-tBu2C6H3) (5)
Various Cp* derivatives (1–4) of the type, Cp*TiCl2(OAr),
could be prepared in high yields from Cp*TiCl3 by adding
1.0 equiv. of the corresponding lithium phenoxides in Et2O
according to the reported procedure [4b], and the various
tert-BuCp derivatives (7–10) could also be prepared from
(tBuC5H4)TiCl3 in the same manner. However, attempts to iso-
late the 2,6-di-tert-butyl analogues (5–6, 11–12) from Cp*TiCl3
or (tBuC5H4)TiCl3 were not successful, and the reaction mixture
consisting of a certain amount of Cp*TiCl3 or (tBuC5H4)TiCl3
and the desired product were thus obtained. The desired com-
plexes, CpꢀTiCl2(O-2,6-tBu2C6H3) (5, 11), CpꢀTiCl2(O-2,6-
tBu2-4-MeC6H2) (6, 12) were found to be repared in high yields
if CpꢀTiCl3 was treated with 1.0 equiv. of the corresponding
LiOAr in toluene at 70 ◦C. The reaction at 70 ◦C was found to
be important, and the reaction of Cp*TiCl3 with LiO-tBu2C6H3
at 50 ◦C after 10 h still afforded a mixture of 5 and Cp*TiCl3.
The resultant complexes were identified by 1H, 13C NMR spec-
tra, elemental analysis, and X-ray crystallography as shown
below.
˚
observed, and Ti O bond distances (1.772–1.811 A) were some-
˚
what shorter than that (1.978 A) for Ti O (in CF3SO3) bond
distance in Cp*TiMe(CF3SO3)(O-2,6-iPr2C6H3) [30] due to
the ␲ donation from oxygen to titanium. The Cl(1) Ti Cl(2)
bond angles were found to be influenced by the substituents
on the aryloxide ligand, and rather bulky di-tert-butyl ana-
logue (5) possessed the smallest angle (98.10◦) among these
complexes.
It should be noted that the bond angles of Ti O C (phenyl)
in 3–4 (173.0, 174.6◦) were larger than those in the other
Cp* derivatives (155.5–162.3◦) except Cp*TiCl2(O-2,6-Ph2-
3,5-tBu2C6H) (14, 176.9◦) [31]. Although we assumed in the
previous reports [4a,b] that both Cp* and diisopropyl group
sterically force the more open Ti O C bond angle, the bond
angle for the di-tert-butyl analogue (5) was small (155.5◦). The
Fig. 1. ORTEP drawings for Cp*TiCl2(O-2,6-iPr2-4-tBuC6H2) (left: side view; right: front view). Thermal ellipsoids are drawn at a 50% probability level, and hydro-
˚
gen atoms were omitted for clarity. Selected bond length (A): Ti(1) Cl(1) 2.263(2), Ti(1) Cl(2) 2.2673(15), Ti(1) O(1) 1.777(4), Ti(1) C(1) 2.403(7), Ti(1) C(2)
2.337(5), O(1) C(11) 1.376(8), C(1) C(2) 1.441(9), C(1) C(5) 1.383(8), C(1) C(6) 1.508(14), C(2) C(3) 1.419(12), C(2) C(7) 1.481(6), C(11) C(12)
1.404(5). Selected bond angles (◦): Cl(1) Ti(1) Cl(2) 103.71(7), Cl(1) Ti(1) O(1) 101.54(13), Cl(2) Ti(1) O(1) 102.86(12), Ti(1) O(1) C(11) 174.0(3),
C(2) C(1) C(5) 108.7(7), C(1) C(2) C(3) 106.8(4), O(1) C(11) C(12) 118.6(6), O(1) C(11) C(16) 119.1(3), C(12) C(11) C(16) 122.2(6).

200
K. Nomura et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 197–205
Selected bond angles and distances for Cp*Ti(X)(Y)(O-2,6-
iPr2-4-RꢀC6H2) (X,Y = Cl,Cl, Me,Me, Me,CF3SO3, Rꢀ = H or
tBu) are summarized in Table 3. Although no significant dif-
ferences in the bond distances were observed among these
complexes, the bond angles in X–Ti–Y were influenced by the
anionic ligands (X,Y), probably due to the increased steric bulk
of Me, CF3SO3 ligands compared to Cl. It should be noted that
the bond angles in Ti O C (phenyl) were somewhat large in all
cases (166.2–174.6◦), clearly suggesting that both Cp* and the
2,6-diisopropyl-substituted aryloxo ligand form the unique bond
angle, leading to more O → Ti ␲ donation into the titanium.
2.2. Effect of aryloxide ligand in 1-hexene polymerization
catalyzed by Cp*TiCl2(OAr) (1–6)—MAO catalyst systems
Table 4 summarizes 1-hexene polymerization results by 3
under various Al/Ti molar ratios. As reported previously [4c],
the catalytic activity was affected by the Al/Ti molar ratio,
and the ratio of 6000 showed the highest activity under these
conditions. The resultant polymers were poly(1-hexene)s with
atactic stereo-regularity [4c], and the polymers possessed high
molecular weights with unimodal molecular weight distribu-
tions (Mn = 3.01–4.61 × 105, Mw/Mn = 1.42–1.74). These poly-
merizations proceeded at remarkable rates, and the Mn values
for the resultant polymers slightly increased for longer times
(runs 4, 6–8). Fig. 3 shows time course plots of ln[1-hexene]/[1-
hexene]0 in the polymerization [32]. Since a first order relation-
ship between the monomer concentration and the reaction rate
was seen, it is thus clear that the apparent decrease in the activity
is not due to the deactivation of catalytically-active species but
due to the decrease in the 1-hexene concentration.
Fig. 2. ORTEP drawings for Cp*TiCl2(O-2,6-tBu2C6H3). Thermal ellipsoids
are drawn at a 50% probability level, and hydrogen atoms were omitted for clar-
ity. Selected bond length (A): Ti(1) Cl(1) 2.2674(10), Ti(1) Cl(1)ꢀ 2.2674(10),
˚
Ti(1) O(1) 1.804(2), Ti(1) C(1) 2.359(4), Ti(1) C(2) 2.375(3), Ti(1) C(3)
2.370(3), O(1) C(7) 1.380(4), C(1) C(2) 1.405(4), C(1) C(4) 1.499(7),
C(2) C(3) 1.391(5), C(2) C(5) 1.508(6), C(7) C(8) 1.409(3). Selected
bond angles (◦): Cl(1) Ti(1) Cl(1)ꢀ 98.10(4), Cl(1) Ti(1) O(1) 103.22(6),
Ti(1) O(1) C(7) 155.5(2), C(1) C(2) C(3) 107.6(3), O(1) C(7) C(8)
119.05(18), C(7) C(8) C(9) 115.8(3).
similar large bond angle was observed in 14 whereas the value
in Cp*TiCl2(O-2,6-Ph2C6H3) (13) was rather small (160.6◦).
These results might suggest that the unique bond angle would
be dependent upon the ligand set employed. Based on the anal-
ysis results in 3–4, it is thus suggested that the unique bond
angles in Ti O C (phenyl) were affected by substituents in both
cyclopentadienyl and aryloxo ligands.
Undertheoptimizedconditionsbytheaboveexperiments, the
1-hexene polymerizations by Cp*TiCl2(OAr) (1–6) were per-
formed in the presence of MAO cocatalyst. The results are sum-
marized in Table 5. The activities by the Cp*-aryloxo analogues
(3–4) containing two isopropyl group in 2,6-position were much
higher than those by the others (1–2, 5–6), and the significant
difference in the activity was not observed between 3 and 4. The
Table 2
*
ꢀ
˚
Selected bond distances (A) and angles for Cp TiCl2(O-2,6-R2-4-R C6H2) (1–5)
1a (R,Rꢀ = Me,H) 2b (R,Rꢀ =Me,Me) 3c (R,Rꢀ =iPr,H) 4 (R,Rꢀ =iPr,tBu) 5 (R,Rꢀ =tBu,H) 13d (R,Rꢀ =Ph,H) 14e (R,Rꢀ =Ph,3,5-tBu2)
˚
Bond distances (A)
Ti(1) Cl(1)
2.273(6)
2.329(3)
2.341(2)
2.398(2)
1.785(2)
2.262(2)
2.344(6)
2.389(7)
2.374(7)
1.781(4)
2.305(2)
2.367(7)
2.345(7)
2.368(7)
1.772(3)
2.268(1)
2.345(4)
2.417(4)
2.399(4)
1.779(3)
2.2674(10)
2.359(4)
2.375(3)
2.370(3)
1.804(2)
2.2693(13)
2.355(4)
2.348(4)
2.377(4)
1.811(3)
2.258(1)
2.340(3)
2.369(3)
2.420(3)
1.804(2)
Ti(1) C(1) in Cp
Ti(1) C(2) in Cp
Ti(1) C(3) in Cp
Ti(1) O(1)
Bond angles (◦)
Cl(1) Ti Cl(2)
Cl(1) Ti O(1)
Cl(2) Ti O(1)
103.3(2)
101.7(1)
101.7(1)
103.2(1)
103.45(5)
99.1(2)
104.1(2)
173.0(3)
103.68(5)
102.73(10)
101.83(10)
174.6(3)
98.10(4)
103.22(6)
103.22(6)
155.5(2)
98.70(5)
104.33(10)
105.20(10)
160.6(3)
100.44(4)
103.68(7)
104.34(7)
176.90(19)
102.0(1)
101.6(1)
162.1(4)
Ti
O C(6)in phenyl 162.3(2)
a
b
c
d
e
Cp*TiCl2(O-2,6-Me2C6H3) (1) cited from ref. [26].
Cp*TiCl2(O-2,4,6-Me3C6H2) (2) cited from ref. [27].
Cp*TiCl2(O-2,6-iPr2C6H3) (3) cited from ref. [4a].
Cp*TiCl2(O-2,6-Ph2C6H3) (13) cited from ref. [28].
Cp*TiCl2(O-2,6-Ph2-3,5-tBu2C6H) (14) cited from ref. [29].

K. Nomura et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 197–205
201
Table 3
Selected bond distances (A) and angles ( ) for Cp Ti(X)(Y)(O-2,6- Pr2-4-R C6H2)
◦
*
i
ꢀ
˚
Rꢀ = Ha, X,Y = Cl,Cl
Rꢀ = tBu, X,Y = Cl,Cl
Rꢀ = Hb, X,Y = Me,Me
Rꢀ = Hb, X,Y = Me,CF3SO3
˚
Bond distances (A)
Ti(1) Cl(1) or C in Me
Ti(1) C(1) in Cp
Ti(1) C(2) in Cp
Ti(1) C(3) in Cp
Ti(1) O(1)
2.305(2)
2.367(7)
2.345(7)
2.368(7)
1.772(3)
2.268(1)
2.345(4)
2.417(4)
2.399(4)
1.779(3)
2.101(3)
2.338(3)
2.350(2)
2.374(2)
1.790(2)
2.093(8)
2.346(6)
2.377(6)
2.353(6)
1.778(4)
Bond angles (◦)
X
X
Y
Ti
Ti
Y
103.45(5)
99.1(2)
104.1(2)
173.0(3)
103.68(5)
102.73(10)
101.83(10)
174.6(3)
99.8(1)c
101.9(1)e
102.9(1)
168.7(1)
97.4(3)d
102.1(2)e
106.6(2)
166.2(4)
Ti O(1), X = Cl or C in Me
Ti O(1)
O
C in phenyl
a
b
c
d
e
Cp*TiCl2(O-2,6-iPr2C6H3) (3) cited from ref. [4a].
Cp*TiMe(Y)(O-2,6-iPr2C6H3) (Y = Me, CF3SO3) cited from ref. [30].
Me Ti Me bond angle.
Me Ti O in CF3SO3 bond angle.
O(1) Ti C in Me bond angle.
Table 4
1-Hexene polymerization by Cp*TiCl2(O-2,6-iPr2C6H3) (3)—MAO catalyst systema
Al/Tib
Time (min)
Yield (mg)
Activityc
TONd
Mn (×10−4
)
Mw/Mn
e
e
Run no.
1
2
3
4
5
2000
3000
4000
6000
8000
20
20
20
20
20
162
210
384
445
327
972
1260
2300
2670
1960
3850
4990
9130
10600
7770
28.4
30.1
37.2
46.1
40.0
1.74
1.74
1.65
1.42
1.64
6
4
7
8
6000
6000
6000
6000
10
20
30
60
192
445
518
588
2300
2670
2070
1180
4560
10600
12300
14000
38.2
46.1
47.6
57.6
1.47
1.42
1.48
1.40
a
Polymerization conditions: 1-hexene 10 mL, n-hexane 10 mL, catalyst 0.5 ␮mol (3 2.0 ␮mol/mL toluene), MAO (prepared by removing toluene and AlMe3),
25 ◦C.
b
c
d
e
Molar ratio of Al/Ti.
Activity in kg polymer/mol Ti h.
TON (turnover numbers) = (molar amount of 1-hexene consumed)/(mol Ti).
GPC data in THF vs. polystyrene standards.
results clearly indicate that both Cp* and aryloxo ligand contain-
ing diisopropyl group in 2,6-position are very important factors
for exhibiting the high activity. These results would also sug-
gest that the unique bond angles in Ti O C (phenyl) for 3–4
affect the high catalytic activity by more O → Ti ␲ donation
into the titanium, which leads to stabilize the catalytically active
species for exhibiting the higher catalytic activity in 1-hexene
polymerization.
Table 5
1-Hexene polymerization by Cp*TiCl2(OAr) [OAr = O-2,6-Me2C6H3 (1), O-
2,4,6-Me3C6H2 (2), O-2,6-iPr2C6H3 (3), O-2,6-iPr2-4-tBuC6H2 (4), O-2,6-
tBu2C6H3 (5), O-2,6-tBu2-4-MeC6H2 (6)]—MAO catalyst systemsa
c
c
Run no.
Catalyst
Yield (mg)
Activityb
Mn (×10−4
)
Mw/Mn
9
10
4
11
12
13
1
2
3
4
5
6
40
58
445
448
26
240
348
2670
2690
156
14.2
13.2
46.1
26.1
23.7
28.4
1.66
1.66
1.42
1.80
1.93
1.63
36
216
a
Polymerization conditions: 1-hexene 10 mL, n-hexane 10 mL, catalyst
0.5 ␮mol (complex 2.0 ␮mol/mL toluene), MAO (prepared by removing toluene
and AlMe3) 3.0 mmol, 25 ◦C, 20 min.
Fig. 3. Time course plots vs. ln[1-hexeme]/[1-hexene]0 for 1-hexene polymer-
ization by 1—MAO catalyst system, and [1-hexene] is the 1-hexene concentra-
tion at the prescribed time and [1-hexene]0 is the initial concentration.
b
Activity in kg polymer/mol Ti h.
c
GPC data in THF vs. polystyrene standards.

202
K. Nomura et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 197–205
Table 6
Effect of aryloxide ligand for styrene polymerization by (tBuC5H4)TiCl2(OAr) [OAr = O-2,6-Me2C6H3 (7), O-2,4,6-Me3C6H2 (8), O-2,6-iPr2C6H3 (9), O-2,6-iPr2-
4-tBuC6H2 (10), O-2,6-tBu2C6H3 (11), O-2,6-tBu2-4-MeC6H2 (12)]—MAO catalyst systemsa
Run no.
Catalyst
Acetone insolubleb
Yield, mg (%)c
Acetone solublef (mg)
Activityd
Mn (×10−4
)
Mw/Mn
e
e
14
15
16
17
18
19
7
8
9
10
11
12
228(92)
89(79)
229(91)
446(83)
43(33)
9(25)
1370
534
1370
2680
258
5.3
5.9
5.7
5.2
5.1
4.6
2.05
1.91
2.05
2.18
2.01
1.98
20
23
22
91
87
27
54
a
Conditions: catalyst 1.0 ␮mol, styrene/toluene = 5/9 mL, MAO 3.0 mmol (Al/Ti = 3000), 10 min at 25 ◦C.
Syndiotactic polystyrene (sPS).
Yield (%) = yield (mg) of sPS/polymer yield (mg) in whole polystyrene produced.
Activity in kg sPS/mol Ti h.
GPC data in THF vs polystyrene standards.
Atactic polystyrene prepared by MAO.
b
c
d
e
f
2.3. Effect of aryloxide ligand in syndiospecific styrene
3. Experimental
polymerization catalyzed by (tBuC5H4)TiCl2(OAr)
(7–12)—MAO catalyst systems
3.1. General procedure
Table
6
summarizes the results for syndiospecific
All experiments were carried out under a nitrogen atmo-
sphere in a vacuum atmospheres drybox unless otherwise spec-
ified. Anhydrous grade of toluene (Kanto Kagaku Co. Ltd) was
transferred into a bottle containing molecular sieves (mixture
of 3A and 4A 1/16, and 13X) in the drybox, and was used
without further purification. Styrene of polymerization grade
(Idemitsu Petrochemicals Co.) was stored in a freezer after pass-
ing through alumina short column under nitrogen flow in the
dry box, and the styrene was further purified by the same pro-
cedure in the dry box prior to use. Cp*TiCl2(O-2,6-Me2C6H3)
(1) [26], Cp*TiCl2(O-2,4,6-Me3C6H2) (2) [4b], Cp*TiCl2(O-
2,6-iPr2C6H3) (3) [4b], (tBuC5H4)TiCl2(O-2,6-iPr2C6H3) (7)
[4b] were prepared according to the previous reports. Toluene
and AlMe3 in the commercially available methylaluminoxane
[PMAO-S, 9.5 wt.% (Al) toluene solution, Tosoh Finechem Co.]
were taken to dryness 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.
Molecular weights and the molecular weight distributions
of the poly(1-hexene), polystyrenes were measured by gel-
permeation chromatography (GPC). HPLC grade THF was used
for GPC and were degassed prior to use. GPC were performed
at 40 ◦C on a Shimazu SCL-10A using a RID-10A detector
(Shimazu Co. Ltd.) in THF (containing 0.03 wt.% 2,6-di-tert-
butyl-p-cresol, flow rate 1.0 mL/min). GPC columns (ShimPAC
GPC-806, 804 and 802, 30 cm × 8.0 mmØ, spherical porous gel
made of styrene/divinylbenzene copolymer, ranging from <102
to 2 × 107 MW) were calibrated versus polystyrene standard
samples. Elemental analyses were performed by using PE2400II
Series (Perkin-Elmer Co.).
styrene polymerization by various tert-BuCp analogues,
(tBuC5H4)TiCl2(OAr) (7–12), under the optimized condi-
tions according to the previous report [5b]. The tert-BuCp
analogues were chosen because the molecular weight distri-
butions for resultant syndiotactic polystyrenes (as the acetone
insoluble fraction) prepared by (1,3-Me2C5H3)TiCl2(OAr)
(Ar = 2,6-Me2C6H3, 3,5-Me2C6H3) complexes were bimodal
in the presence of MAO [5a], or AliBu3-Al(n-C8H17)3/borate
cocatalyst [33]. In contrast, the resultant polymers prepared
by 7–12—MAO catalysts possessed high molecular weights
with unimodal molecular weight distributions as well as with
perfect syndiotactic stereo-regularity (Mn = 4.6–5.9 × 104,
Mw/Mn = 1.91–2.18). No significant differences in the Mn
values were observed, and the facts may be explained
by our previous assumption that these values (dominant
chain-transfer reactions) were not influenced by the anionic
donor ligand but highly influenced by the Cpꢀ employed
[5b].
It is important to note that the catalytic activity
increased in the order: 10 (activity 2680 kg sPS/mol Ti h) > 7,
9(1370) > 8(534) > 11(258) > 12(54). These results clearly indi-
cate that the catalytic activities are strongly influenced by
both ortho- and para- substituents in the aryloxide ligand
[34,35]. Although it has been invoked that cationic Ti(III)
plays an essential role for syndiospecific styrene polymeriza-
tion by CpꢀTiXꢀ3 (Xꢀ = Cl, OMe, etc.) [36], the role of anionic
donor ligands towards the activity was present in this catal-
ysis. This would suggest a possibility that a neutral Ti(III)
or a cationic Ti(IV) species also plays a role for this poly-
merization with this unique catalyst system, as we previously
suggested [5b]. We believe that the contents in this paper
should be helpful for understanding the reaction mechanism for
both syndiospecific styrene polymerization and ethylene/styrene
copolymerization.
3.2. Synthesis of Cp*TiCl2(O-2,6-iPr2-4-tBuC6H2) (4)
Into a Et2O solution (30 mL) containing Cp*TiCl3 (1.00 g,
3.46 mmol), LiO-2,6-iPr2-4-tBuC6H2 (1.0 equiv.) was added in

K. Nomura et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 197–205
203
one portion at −25 ◦C, and the reaction mixture was warmed
slowly to room temperature, was stirred for 10 h. The mixture
was then filtered through Celite pad, and the filter cake was
washed with Et2O (2× 15 mL). The combined filtrate and the
wash were taken to dryness under reduced pressure to give a red-
orange solid. The solid was then dissolved in a minimum amount
of CH2Cl2 layered by n-hexane in the freezer (−25 ◦C). The
chilled solution gave red (platelet) microcrystals. Yield 1.363 g
(81%). 1HNMR(C6D6):δ1.31(s, 9H, (CH3)3C ), 1.34(d, 12H,
J = 7.0 Hz, (CH3)2CH ), 1.91 (s, 15H, C5(CH3)5 ), 3.40–3.58
(m, 2H, (CH3)2CH ), 7.28 (s, 2H, C6H2). 13C NMR (C6D6): δ
12.7, 24.4, 27.1, 31.7, 34.3, 120.3, 131.9, 139.0, 146.3, 158.1.
Anal. calcd. for C26H40Cl2OTi: C, 64.06; H, 8.27. Found: C,
64.29; H, 8.14 (%).
J = 7.5 Hz, C6H3), 6.80 (d, 2H, J = 7.3 Hz, C6H3). 13C NMR
(C6D6): δ 17.7, 31.0, 34.0, 119.4, 119.6, 124.3, 128.1, 129.1,
150.9, 167.2. Anal. calcd. for C17H23Cl2OTi: C, 56.38; H, 6.40.
Found: C, 56.69; H, 6.20 (%).
3.6. Synthesis of (tBuC5H4)TiCl2(O-2,4,6-Me3C6H2) (8)
Synthetic procedure for 8 was the same as that for 7
except that LiO-2,4,6-Me3C6H2 was used in stead of LiO-
2,6-Me2C6H3 and (tBuC5H4)TiCl3 (1.00 g, 3.63 mmol) was
1
used. Yield 1.057 g (78%). H NMR (C6D6): δ 1.21 (s, 9H,
(CH3)3C ), 2.08 (s, 3H, CH3C6H2), 2.24 (s, 6H, CH3C6H2),
t
5.81 (t, 2H, J = 3.3 Hz, BuC5H4), 6.37 (t, 2H, J = 3.3 Hz,
tBuC5H4), 6.59 (s, 2H, C6H2). 13C NMR (C6D6): δ 17.7, 21.0,
31.0, 34.0, 119.3, 119.5, 127.8, 129.6, 133.6, 150.6, 165.9. Anal.
calcd. for C18H24Cl2OTi: C, 57.63; H, 6.45. Found: C, 57.89;
H, 6.51 (%).
3.3. Synthesis of Cp*TiCl2(O-2,6-tBu2C6H3) (5)
Into a toluene solution (30 mL) containing Cp*TiCl3 (1.00 g,
3.46 mmol) equipped with a sealed Schlenck tube, LiO-2,6-
tBu2C6H3 (1.0 equiv.) was added in one portion at room tem-
perature. The reaction mixture was stirred at 70 ◦C for 10 h.
The mixture was then filtered through Celite pad, and the fil-
ter cake was washed with toluene (2× 15 mL). The combined
filtrate and the wash were taken to dryness under reduced pres-
sure to give a red-orange solid. The solid was then dissolved
in a minimum amount of CH2Cl2 layered by n-hexane in the
freezer (−25 ◦C). The chilled solution gave red microcrys-
3.7. Synthesis of (tBuC5H4)TiCl2(O-2,6-iPr2-4-tBuC6H2)
(10)
Synthetic procedure for 10 was the same as that for 8 except
that LiO-2,6-iPr2-4-tBuC6H2 was used in stead of LiO-2,4,6-
Me3C6H2. Yield 1.362 g (79%). 1H NMR (C6D6): δ 1.23 (s, 9H,
(CH3)3C ), 1.30 (s, 9H, (CH3)3C ), 1.34 (d, 12H, J = 6.6 Hz,
(CH3)2CH ), 3.53–3.58 (m, 2H, (CH3)2CH ), 5.87 (t, 2H,
t
t
J = 2.7 Hz, BuC5H4), 6.43 (t, 2H, J = 2.7 Hz, BuC5H4), 7.29
(s, 2H, C6H2). 13C NMR (C6D6): δ 24.0, 27.4, 30.8, 31.6,
33.8, 34.9, 119.0, 120.4, 138.0, 147.2, 150.6, 163.3. Anal.
calcd. for C25H38Cl2OTi: C, 63.43; H, 8.09. Found: C, 63.30;
H, 7.92 (%).
1
tals. Yield 1.235 g (78%). H NMR (C6D6): δ 1.44 (s, 18H,
(CH3)3C ), 1.82 (s, 15H, C5(CH3)5 ), 6.82 (t, 1H, J = 7.7 Hz,
C6H3), 7.16 (d, 2H, J = 7.7 Hz, C6H3). 13C NMR (C6D6): δ
13.8, 32.1, 36.3, 121.8, 125.3, 133.5, 139.9, 166.9. Anal. calcd.
for C24H36Cl2OTi: C, 62.76; H, 7.90. Found: C, 62.36; H, 7.73
(%).
3.8. Synthesis of (tBuC5H4)TiCl2(O-2,6-tBu2C6H3) (11)
3.4. Synthesis of Cp*TiCl2(O-2,6-tBu2-4-MeC6H2) (6)
Synthetic procedure for 11 was the same as that for 5
except (tBuC5H4)TiCl3 (0.51 g, 1.85 mmol)) was used instead
of Cp*TiCl3. Yield 0.666 g (81%). 1H NMR (C6D6): δ 1.28 (s,
9H, (CH3)3C ), 1.48 (s, 18H, (CH3)3C C6H2), 5.76 (t, 2H,
J = 2.7 Hz, tBuC5H4), 6.40 (t, 2H, J = 2.7 Hz, tBuC5H4), 6.84 (t,
1H, J = 7.9 Hz, C6H3), 7.19 (d, 2H, J = 7.7 Hz, C6H3). 13C NMR
(C6D6): δ 31.2, 32.4, 34.4, 36.3, 120.4, 123.1, 126.0, 139.7,
151.9, 171.4. Anal. calcd. for C23H34Cl2OTi: C, 62.03; H, 7.70.
Found: C, 62.12; H, 7.85 (%).
Synthetic procedure for 6 was the same as that for 5
except LiO-2,6-tBu2-4-MeC6H2 was used in stead of LiO-2,6-
tBu2C6H3 and amount of Cp*TiCl3 was 0.85 g (2.94 mmol).
Yield 1.232 g (89%). 1H NMR (C6D6): δ 1.47 (s, 18H,
(CH3)3C ), 1.85 (s, 15H, C5(CH3)5 ), 2.20 (s, 3H, CH3C6H2),
7.04 (s, 2H, C6H2). 13C NMR (C6D6): δ 13.4, 21.1, 32.3,
36.2, 126.0, 130.6, 133.3, 139.9, 165.4. Anal. calcd. for
C25H38Cl2OTi: C, 63.43; H, 8.09. Found: C, 63.31; H, 8.05
(%).
3.9. Synthesis of (tBuC5H4)TiCl2(O-2,6-tBu2-4-MeC6H2)
(12)
3.5. Synthesis of (tBuC5H4)TiCl2(O-2,6-Me2C6H3) (7)
Synthetic procedure for 12 was the same as that for 5 except
that (tBuC5H4)TiCl3 (0.60 g, 2.18 mmol) was used instead of
Cp*TiCl3, and LiO-2,6-tBu2-4-MeC6H2 was used in stead of
Synthetic procedure for 7 was the same as that for 4 except
that (tBuC5H4)TiCl3 (500 mg, 1.82 mmol) was used instead of
Cp*TiCl3, and LiO-2,6-Me2C6H3 was used in stead of LiO-
2,6-iPr2-4-tBuC6H2. The resultant solid after filtration was then
dissolved in a minimum amount of Et2O layered by n-hexane
in the freezer (−25 ◦C). The chilled solution gave red micro-
crystals. Yield 422 mg (64%). 1H NMR (C6D6): δ 1.20 (s, 9H,
(CH3)3C ), 2.22 (s, 6H, CH3C6H2), 5.76 (t, 2H, J = 2.7 Hz,
1
LiO-2,6-tBu2C6H3. Yield 0.656 g (66%). H NMR (C6D6): δ
1.30 (s, 9H, (CH3)3C ), 1.49 (s, 18H, (CH3)3C C6H2), 2.20 (s,
3H, CH3C6H2), 5.81 (t, 2H, J = 2.7 Hz, tBuC5H4), 6.42 (t, 2H,
J = 2.7 Hz, tBuC5H4), 7.08 (s, 2H, C6H2). 13C NMR (C6D6): δ
21.2, 31.0, 32.1, 34.1, 35.9, 119.9, 126.4, 131.7, 139.3, 151.1,
169.8. Anal. calcd. for C24H36Cl2OTi: C, 62.76; H, 7.90. Found:
C, 62.91; H, 7.97 (%).
tBuC5H4), 6.34 (t, 2H, J = 2.6 Hz, BuC5H4), 6.74 (t, 1H,
t

204
K. Nomura et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 197–205
3.10. 1-Hexene polymerization
filtration, and was dried in vacuo. The resultant solid was then
separated into two fractions by using acetone as the extraction
1
Typical procedure for 1-hexene polymerization was as fol-
lows: prescribed amount of MAO, 1-hexene (10.0 mL) and n-
hexane (10.0 mL) were added to a round bottom flask (50 mL) in
the drybox, and the polymerization was started by the addition of
a toluene solution (0.25 mL) containing the catalyst (0.5 ␮mol).
The reaction mixture was stirred for prescribed time at 25 ◦C,
and the polymerization was terminated with the addition of
EtOH. The reaction product was extracted with CHCl3 which
was washed with a mixed solution of EtOH and HCl aqueous
solution and then rinsed with water. The chloroform extract was
dried over Na2SO4, and chloroform and 1-hexene remained was
then removed in vacuo. The resultant poly(1-hexene)s possessed
atacticstereoregularitywithfavoredrepeated1,2-insertionmode
[4c].
solvent, and was dried in vacuo for 6 h at 60 ◦C. Typical H
and 13C NMR spectra for resultant polymer (acetone insoluble
fraction, SPS) were the same as those reported previously [5].
3.12. Crystallographic analysis
All measurements were made on a Rigaku RAXIS-RAPID
Imaging Plate diffractometer with graphite monochromated Mo
K␣ radiation. The selected crystal collection parameters are
listed in Table 7, and the detailed results (CIF files, and X-ray
structure reports) were described in Supplementary materials.
All structures were solved by direct method and expanded
using Fourier techniques [37], and the nonhydrogen atoms were
refined anisotropically. Hydrogen atoms were included but not
refined. All calculations for complexes were performed using
the crystal structure [38,39] crystallographic software package.
3.11. Polymerization of styrene
Typicalpolymerizationprocedure(describedinTable6, com-
plex 7) is as follows: into a 25 mL round bottom flask, MAO
(3.0 mmol, 174 mg), prescribed amount of toluene (9.0 mL), and
then styrene (5.0 mL) were added in the dry box. A toluene
solution containing titanium complex (1.0 ␮mol/mL toluene,
1.0 mL) was added into the solution to start the polymerization
at 25 ◦C, and the reaction mixture was stirred for 10 min. The
polymerization was then terminated with the addition of ethanol
containing HCl, and the resultant white solid was collected by
Acknowledgements
KN would like to express his heartfelt thanks to Tosoh
Finechem Co. for donating MAO (PMAO-S), and KN and AT
express their thanks to Prof. Michiya Fujiki (NAIST) for his
helpful comments through this research project.
Appendix A. Supplementary data
Supplementary data associated with this article can be found,
in the online version, at doi:10.1016/j.molcata.2006.03.030.
Table 7
Crystal and data collection parameters for Cp*TiCl2(OAr) [OAr = O-2,6-iPr2-
4-tBu-C6H2 (4), O-2,6-tBu2C6H3 (5)]a
Complex
4
5
References
Formula
Formula weight
Habits
Crystal size (mm)
Crystal system
Space group
C26H40Cl2OTi
487.41
C24H36Cl2OTi
459.35
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Monoclinic
C2/c (#15)
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12.534(6)
20.261(10)
129.225(19)
5542.3(47)
8
1.168
2080.00
243
0.71069
50.0◦
2741
Red, platelet
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Orthorhombic
Pnma (#62)
7.822(3)
˚
a (A)
˚
b (A)
17.091(8)
18.628(6)
˚
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V (A )
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3
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a
Detailed analysis results are shown in Supplementary data.

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