Effect of ketimide ligand for ethylene polymerization and ethylene/norbornene copolymerization catalyzed by (cyclopentadienyl)(ketimide)titanium complexes-MAO catalyst systems: Structural analysis for Cp*TiCl2(N{double bond, long}CPh2)

Article abstract of DOI:10.1016/j.jorganchem.2007.04.043

Ligand effects on the catalytic activity [and norbornene (NBE) incorporation] for both ethylene polymerization and ethylene/NBE copolymerization using half-titanocenes (titanium half-sandwich complexes) containing ketimide ligand of type Cp′TiCl₂[N{double bond, long}C(R¹)R²] [Cp′ = Cp (1), C⁵Me⁵ (Cp^*, 2); R¹,R² = ^tBu,^tBu (a), ^tBu,Ph (b), Ph,Ph (c)]-methylaluminoxane (MAO) catalyst systems have been investigated. CpTiCl₂[N{double bond, long}C(^tBu)Ph] (1b) CpTiCl₂(N{double bond, long}CPh₂) (1c), and Cp^*TiCl₂(N{double bond, long}CPh₂) (2c) were prepared and identified; the structure of Cp^*TiCl₂(N{double bond, long}CPh₂) (2c) was determined by X-ray crystallography. The catalytic activity for ethylene polymerization increased in the order: 1a > 1b > 1c, suggesting that an electronic nature of the ketimide ligand affects the activity. However, molecular weight distributions for resultant (co)polymers prepared by 1b,c and by 2c-MAO catalyst systems were bi- or multi-modal, suggesting that the ketimide substituent plays a key role in order for these (co)polymerizations to proceed with single catalytically-active species. CpTiCl₂(N{double bond, long}C^tBu₂) (1a) exhibited both remarkable catalytic activity and efficient NBE incorporation for ethylene/NBE copolymerization.

Full text of DOI:10.1016/j.jorganchem.2007.04.043

Journal of Organometallic Chemistry 692 (2007) 4675–4682
www.elsevier.com/locate/jorganchem
Effect of ketimide ligand for ethylene polymerization
and ethylene/norbornene copolymerization catalyzed
by (cyclopentadienyl)(ketimide)titanium complexes–MAO
catalyst systems: Structural analysis for Cp*TiCl2(N@CPh2)
*
Kotohiro Nomura , Junji Yamada, Wei Wang, Jingyu Liu
Graduate School of Materials Science, Nara Institute of Science and Technology (NAIST), 8916-5 Takayama, Ikoma, Nara 630-0101, Japan
Received 30 March 2007; received in revised form 30 April 2007; accepted 30 April 2007
Available online 8 May 2007
Dedicated in honor of Professor Dr. Gerhard Erker on the occasion of his 60th birthday.
Abstract
Ligand effects on the catalytic activity [and norbornene (NBE) incorporation] for both ethylene polymerization and ethylene/NBE
copolymerization using half-titanocenes (titanium half-sandwich complexes) containing ketimide ligand of type Cp0TiCl2[N@C(R1)R2]
[Cp0 = Cp (1), C5Me5 (Cp*, 2); R1,R2 = tBu,tBu (a), tBu,Ph (b), Ph,Ph (c)]–methylaluminoxane (MAO) catalyst systems have been inves-
tigated. CpTiCl2[N@C(tBu)Ph] (1b) CpTiCl2(N@CPh2) (1c), and Cp*TiCl2(N@CPh2) (2c) were prepared and identified; the structure of
Cp*TiCl2(N@CPh2) (2c) was determined by X-ray crystallography. The catalytic activity for ethylene polymerization increased in the
order: 1a > 1b > 1c, suggesting that an electronic nature of the ketimide ligand affects the activity. However, molecular weight distribu-
tions for resultant (co)polymers prepared by 1b,c and by 2c–MAO catalyst systems were bi- or multi-modal, suggesting that the ketimide
substituent plays a key role in order for these (co)polymerizations to proceed with single catalytically-active species. CpTiCl2(N@CtBu2)
(1a) exhibited both remarkable catalytic activity and efficient NBE incorporation for ethylene/NBE copolymerization.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Titanium; Polymerization; Homogeneous catalysis; Ethylene; Norbornene; Copolymerization
1. Introduction
which are not prepared by conventional Zigler-Natta cata-
lysts, ordinary metallocenes [1] and/or so-called ‘con-
strained geometry’ (linked Cp-amide) type catalysts [2].
In particular, nonbridged half-titanocenes (titanium half-
sandwich complexes) containing an aryloxo ligand of the
type, Cp0TiðOArÞX2 (Ar = 2,6-iPr2C6H3, etc.), displayed
the promising characteristics [4,7–14]. For example, effi-
cient catalyst precursors especially for copolymerization
of ethylene with a-olefin [9], styrene [10], norbornene [11],
cyclohexene [12], 2-methyl-1-pentene [13], vinylcyclohex-
ane [14] can be tuned by modification of Cp0.
Design and synthesis of efficient transition metal com-
plex catalysts for precise olefin polymerization attract con-
siderable 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, Cp0MðLÞX2 (Cp0 = cyclopentadienyl group;
M = Ti, Zr, Hf; L = anionic ligand such as OAr, NR2,
and NPR3; X = halogen, alkyl), display unique characteris-
tics as olefin polymerization catalysts, because these cata-
lysts are effective for production of new polyolefins [4]
Half-titanocenes containing ketimide ligand of the type,
Cp0TiCl2ðN@CtBu2Þ [15–21], also exhibited high catalytic
activities for ethylene polymerization. The complexes also
showed catalytic activities for syndiospecific styrene
*
Corresponding author. Tel.: +81 743 72 6041; fax: +81 743 72 6049.
E-mail address: nomurak@ms.naist.jp (K. Nomura).
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.04.043

4676
K. Nomura et al. / Journal of Organometallic Chemistry 692 (2007) 4675–4682
according to the reported procedure [15a]. CpTiCl2[N@C
cat.1-4
(tBu)Ph] (1b), CpTiCl2(N@CPh2) (1c), and Cp*TiCl2
(N@CPh2) (2c) were prepared similarly in moderate yields
(69–93%) from Cp0TiCl3 by treating with Li[N@C(tBu)Ph]
[22] or Li(N@CPh2) [23] in toluene. The resultant com-
1-x
x
+
MAO cocat.
NBE
poly(ethylene-co-NBE)
cat.
1
plexes were identified by H and 13C NMR spectra and
Ti
Ti
Ti
tBu
Cl
Cl
Cl
Cl
Ph
Ph
N
N
N
Cl
Cl
C
elemental analyses.
C
C
1a
The structure of Cp*TiCl2(N@CPh2) (2c) was deter-
mined by X-ray crystallography (Fig. 1), and the selected
bond distances and angles are summarized in Table 1.
The structure showed that 2c has a distorted tetrahedral
geometry around the titanium metal center. Ti–N(keti-
1b
1c
tBu
tBu
Ph
Cl
Cl
Ti
Ti
Ti
Ti
tBu
Ph
Cl
Cl
Me2Si
Cl
Cl
Cl
Cl
N
N
O
N
C
C
3
2a
2c
4
tBu
Ph
tBu
˚
˚
mide) distance (1.828 A) is close to those in 2a (1.844 A)
t
˚
[21a], (indenyl)TiCl2(N@C Bu2) (1.814 A) [21a]. The dis-
tance is shorter than those in a series of Cp0TiCl2-
Scheme 1.
½NðR1ÞR2ꢀ ðCp0 ¼ Cpꢁ; 1; 3-Me2C5H3;
R1,R2 = Me,Cy,
˚
polymerization, but the observed activities were much
lower than those with Cp*TiCl3 under the same conditions
[17]. We also reported that both CpTiCl2(N@CtBu2) and
(indenyl)TiCl2(N@CtBu2) exhibited remarkable catalytic
activities (ca. activity 728–1270 kg-polymer/mmol-Ti h,
ethylene 4–8 atm, 1-hexene 2.01 mmol/mL in toluene,
MAO cocatalyst) as well as efficient 1-hexene incorpora-
tion for ethylene/1-hexene copolymerization [18]. More
recently, we reported that ethylene/styrene copolymeriza-
tion by Cp*TiCl2(N@CtBu2)–MAO catalyst system
proceeded in a living manner [19]. Moreover, we communi-
cated that CpTiCl2(N@CtBu2) exhibits both remarkable
catalytic activity and efficient norbornene (NBE) incorpo-
ration for ethylene/NBE copolymerization, and the NBE
incorporation by Cp0TiCl2ðXÞðX ¼ N@CtBu2; O-2; 6-iPr2
C6H3; Cp0 ¼ Cp; C5Me5, indenyl) was related to the cal-
culated coordination energy aft0er ethylene insertion [20].
Although syntheses of Cp TiX2ðN@CtBu2Þ (X = Cl,
Me) and the reaction chemistry especially with B(C6F5)3,
[PhN(H)Me2][B(C6F5)4] [15] as well as their use as the cat-
alyst precursors for ethylene (co)polymerizations [18,20]
were known, however, there are few reports concerning
effect of the ketimide substituents on the activity (and
comonomer incorporations) in ethylene (co)polymeriza-
tions. In this paper we thus prepared various half-titanoc-
enes containing ketimide ligands of type, Cp0TiCl2½N
@CðR1ÞR2ꢀ ½Cp0 ¼ Cp ð1Þ; C5Me5 ðCpꢁ; 2Þ; R1,R2 = tBu,
Cy,Cy, 1.861–1.873 A) [24] and that in (1,3-Me2C5H3)TiCl2
˚
[N(SiMe3)(2,6-Me2C6H3)] (1.898 A) [25]. The Ti–N dis-
Fig. 1. ORTEP drawings for Cp*TiCl2(N@CPh2) (2c). Thermal ellipsoids
are drawn at the 50% probability level and H atoms are omitted for
clarity.
tBu (a), Bu,Ph (b), Ph,Ph (c)], and explored effect of the
t
ketimide substituents for ethylene polymerization and eth-
ylene/NBE copolymerization (Scheme 1). Structure of
Cp*TiCl2(N@CPh2) (2c) was also determined by X-ray
crystallography.
Table 1
˚
Selected bond distances (A) and angles (ꢁ) for Cp*TiCl2(N@CPh2) (2c)
˚
Bond distances in A
Ti(1)–Cl(1)
Ti(1)–N(1)
Ti(1)–C(1)
C(11)–C(12)
N(1)–C(11)
2.2844(8)
1.827(2)
2.361(2)
1.495(3)
1.276(3)
Ti(1)–Cl(2)
Ti(1)–Cpcent.
Ti(1)–C(2)
2.2735(10)
2.024
2.351(2)
1.491(3)
2. Results and discussion
C(11)–C(18)
2.1. Syntheses of Cp0TiCl2½N@CðR1ÞR2ꢀ ½Cp0 ¼ Cp ð1Þ;
C5Me5 ðCpꢁ; 2Þ; R1,R2 = tBu,tBu (a), Bu,Ph (b), Ph,Ph
t
Bond angles in ꢁ
Cl(1)–Ti(1)–Cl(2)
Cl(1)–Ti(1)–N(1)
Cl(2)–Ti(1)–N(1)
Ti(1)–Cpplane
(c)], and structural analysis for Cp*TiCl2(N@CPh2)
102.53(3)
102.44(7)
105.27(7)
89.826
Ti(1)–N(1)–C(11)
N(1)–C(11)–(12)
N(1)–C(11)–(18)
C(12)–C(11)–C(18)
170.5(2)
120.4(2)
121.2(2)
118.3(2)
Cp0TiCl2ðN@CtBu2Þ ½Cp0 ¼ Cp ð1aÞ; Cpꢁð2aÞꢀ were pre-
pared by reaction of Cp0TiCl3 with Li(N@CtBu2) in toluene

K. Nomura et al. / Journal of Organometallic Chemistry 692 (2007) 4675–4682
4677
tance is also shorter than that in Cp2Zr(N@CPh2)2 (2.058–
trend was observed between 2a and 2c, and the activities
by the Cp* analogues were higher than that by the Cp ana-
logues (ex. R1R2 = tBu,tBu, runs 1 and 4; R1R2 = tBu,Ph,
runs 3 and 5). These results would suggest that an elec-
tronic nature of the ketimide ligand affects the catalytic
activity. However, the molecular weight distributions for
the resultant PEs prepared by 1b–c, 2c–MAO catalyst sys-
tems were multi-modal, consisting of a mixture of high and
low molecular weight polymers. The complexes with the
ketimide ligand containing two tert-Bu substituents,
Cp0TiCl2(N@CtBu2), were thus effective for the ethylene
polymerization to give polymers with unimodal molecular
weight distributions, in other words, to proceed with sole
catalytically-active species.
˚
˚
2.063 A) [26]. The N(1)–C(11) distance (1.276 A) in 2c is
˚
close to those in 2a (1.266 A) [21a], Cp2Zr(N@CPh2)2
˚
(1.259 and 1.266 A) [26], and is comparable to those in a
series of (arylimido)(ketimide)vanadium complexes
˚
(1.250–1.270 A) [27]. Ti–N(ketimide)–C bond angle,
[Ti(1)–N(1)–C(11) = 170.58ꢁ], in 2c is slightly larger than
those in 2a (166.4ꢁ) [21a], (indenyl)TiCl2(N@CtBu2)
(167.6ꢁ) and Cp2Zr(N@CPh2)2 (164.1ꢁ, 163.7ꢁ) [26]; the
angle is within a range of those in a series of (arylim-
ido)(ketimide)vanadium complexes (169.4–177.3ꢁ) [27].
These results strongly suggest that strong p-donation of
the nitrogen atom to Ti would be thus present.
2.2. Ethylene polymerization catalyzed by Cp0TiCl2½N@
ðR1ÞR2ꢀ ½Cp0 ¼ Cp ð1Þ, C5Me5 (Cp*, 2); R1,R2 = tBu,tBu
2.3. Copolymerization of ethylene with norbornene (NBE)
catalyzed by Cp0TiCl2[N@(R1)R2] [Cp0 = Cp (1), C5Me5
t
(a), Bu,Ph (b), Ph,Ph (c)]–MAO catalyst systems
t
(Cp*, 2); R1,R2 = tBu,tBu (a), Bu,Ph (b), Ph,Ph (c)]–
MAO catalyst systems
Ethylene polymerizations by 1–2–MAO catalyst systems
were performed in toluene at 25 ꢁC, and Cp*TiCl2(O-
2,6-iPr2C6H3) (3) was also chosen for comparison [7].
MAO white solid [prepared by removing toluene and
AlMe3 from the commercially available MAO (PMAO,
Tosoh Finechem Co.)] was chosen as the cocatalyst,
because this MAO is effective for preparing poly(ethylene-
co-1-butene)s with narrow molecular weight distributions
as well as with relatively high molecular weights when 3
and [Me2Si(C5Me4)(NtBu)]TiCl2 (4) were employed as the
catalyst precursors [9a,10]. The results under the optimized
Al/Ti ratios are summarized in Table 2.
As reported previously, 2a showed the remarkable cata-
lytic activity affording high molecular weight linear poly-
ethylene (PE) with unimodal molecular weight
distribution (run 4), and the Cp analogue (1a) also showed
the high catalytic activity (run 1). The observed activities
by 1a, 2a are in the similar level to that by the Cp*-aryloxo
analogue (3). The catalytic activities with a series of
CpTiCl2[N@C(R1)R2]–MAO catalyst systems increased in
the order: 1a (5880 kg-PE/mol-Ti h, R1R2 = tBu,tBu, run
1) > 1b (90.0 kg-PE/mol-Ti h, R1R2 = tBu,Ph, run 2) > 1c
(56.4 kg-PE/mol-Ti h, R1R2 = Ph,Ph, run 3). The same
As communicated previously [20], 1a showed notable
both catalytic activity and norbornene (NBE) incorpora-
tion for ethylene/NBE copolymerization in the presence
of MAO, and it is possible to prepare high molecular
weight poly(ethylene-co-NBE)s with high NBE contents
(>50 mol%) as well as with unimodal molecular weight dis-
tributions. The copolymerization results by 1a–MAO cata-
lyst system under various conditions are summarized in
Table 3, and the results by Cp*TiCl2(O-2,6-iPr2C6H3) (3),
[Me2Si(C5Me4)(NtBu)]TiCl2 (4)–MAO catalyst systems
under the same conditions are also shown for comparison.
The copolymerization by 1a–MAO catalyst system pro-
ceeded at remarkable rate, and the activity (calculated
based on the polymer yields vs. amount of 1a charged)
after 20 min was the same as that after 30 min (runs 13
and 14), suggesting that no distinct decrease in the activity
was seen under these conditions. The activity increased
upon increasing the initial NBE concentration [5880 kg-
PE/mol-Ti h (run 1) vs. 40200 kg-polymer/mol-Ti h (run
12)], whereas the activities by 3, 4–MAO catalyst systems
decreased upon increasing the NBE concentration (runs
Table 2
t
Ethylene polymerization by Cp0TiCl2[N@C(R1)R2] [Cp0 = Cp (1), Cp* (2); R1,R2 = tBu,tBu (a), Bu,Ph (b), Ph,Ph (c)] or Cp*TiCl2(O-2,6-iPr2C6H3) (3)–
a
MAO catalyst systems
Run
Complex (lmol)
Cp0
R1;R2
Yield (mg)
Activityb
Mn · 10ꢂ4c
Mw/Mcn
1
2
3
4
5
6
a
1a (0.1)
1b (5.0)
1c (5.0)
2a (0.05)
2c (5.0)
3 (0.2)
Cp
Cp
Cp
Cp*
Cp*
Cp*
tBu;tBu
tBu;Ph
Ph;Ph
tBu;tBu
Ph;Ph
–
98
75
47
164
105
280
5880
90.0
56.4
19680
126
8400
45.2
2.30
Multi-modald
Multi-modald
42.2
2.45
1.90
Multi-modald
65.2
Conditions: toluene 50 mL, MAO white solid (prepared by removing AlMe3, toluene from PMAO, MAO: methylaluminoxane) 3.0 mmol, ethylene
4 atm, 25 ꢁC, 10 min.
b
Activity in kg-PE/mol-Ti h.
c
GPC data in o-dichlorobenzene vs. polystyrene standards.
Multi-modal molecular weight distributions [Mn = 4.16 · 104, Mw/Mn = 21.1 (run 3); Mn = 9.91 · 103, Mw/Mn = 25.9 (run 5)].
d

4678
K. Nomura et al. / Journal of Organometallic Chemistry 692 (2007) 4675–4682
Table 3
Copolymerization of ethylene with norbornene (NBE) by CpTiCl2(N@CtBu2) (1a), Cp*TiCl2(O-2,6-iPr2C6H3) (3), [Me2Si(C5Me4)(N tBu)]TiCl2 (4)–MAO
a
catalyst systems
Run Complex
NBE (mmol/
mL)b
Ethylene
(atm)
Temperature
(ꢁC)
Time (min) Activity · 10ꢂ3c Mn · 10ꢂ4d Mw/
NBE (mol%)e
(lmol)
Mnd
7
8
9
3 (0.2)
3 (0.2)
0.2
1.0
0.2
1.0
0.2
1.0
1.0
1.0
1.0
1.0
1.0
2.5
5.0
10.0
4
4
4
4
4
4
4
4
4
4
4
2
2
2
25
25
25
25
25
25
25
25
40
60
80
25
25
25
10
10
10
10
10
10
20
30
10
10
10
10
10
10
6.54
2.64
2.46
2.00
57.9
29.6
21.1
12.8
70.6
71.9
53.4
61.3
62.0
47.5
33.8
32.3
34.0
44.4
1.61
1.46
1.88
2.15
1.85
2.92
2.11
2.18
2.37
2.20
2.34
2.09
2.00
2.01
8.2
21.7
9.6
4 (0.50)
4 (0.50)
1a (0.02)
1a (0.02)
1a (0.02)
1a (0.02)
1a (0.02)
1a (0.02)
1a (0.02)
1a (0.01)
1a (0.01)
1a (0.02)
10
11
12
13
14
15
16
17
18f
19f
20f
a
26.5
17.8
40.7
41.5
41.0
45.9
51.2
61.7
58.8g
65.8g
73.5g
21.6
40.2
60.2
59.7
48.9
194
133
90.0
85.8
31.5
Conditions: toluene 50 mL, MAO white solid (prepared by removing AlMe3, toluene from PMAO) 3.0 mmol.
Initial NBE concentration in mmol/mL.
Activity in kg-polymer/mol-Ti h.
GPC data in o-dichlorobenzene vs. polystyrene standards.
NBE content in mol% estimated by 13C NMR spectra.
Ethylene 2 atm, toluene 10 mL.
b
c
d
e
f
g
Glass transition temperature measured by DSC were 185 (run 18), 202 (run 19), 214 (run 20) ꢁC, respectively.
7–10). The NBE contents in the copolymers prepared by 1a
were higher than those prepared by 3, 4 under the same
conditions. Note that both the activity (by 1a) and the
NBE contents in the copolymer increased at higher temper-
ature (runs 15–17, 40–80 ꢁC), and the resultant copolymers
possessed large Mn values with unimodal molecular weight
distributions (Mn = 3.38–6.20 · 105, Mw/Mn = 2.20–2.37).
The increases in the NBE contents at higher temperatures
(45.9–61.7 mol%) would be due to an decrease in the ethyl-
ene concentration in toluene.
The efficient syntheses of high molecular weight copoly-
mers with high NBE contents (58.8–73.5 mol%) could thus
be achieved upon increasing the NBE concentration at low
ethylene pressure (2 atm, runs 18–20), and glass transition
temperature (Tg) for the resultant copolymers increased lin-
early upon increasing the NBE content (ex. 185, 202, and
214 ꢁC at the NBE contents in the copolymers are 58.8,
65.8, and 73.3 mol%, respectively). Note that the activities
at higher NBE/ethylene feed ratios (ethylene 2 atm, NBE
2.5–5.0 mmol/mL, runs 18 and 19) were higher than those
at lower NBE/ethylene feed ratios (ethylene 4 atm, NBE
1.0 mmol/mL, runs 12–14), although the activity decreased
upon increasing the NBE concentration (runs 18–20). The
observed facts are unique contrast to those in the copoly-
merization using ordinary metallocenes or linked half-
titanocenes.
onances ascribed to the NBE repeating units) were
observed for the copolymers prepared by 1a, and the
microstructures thus possessed a mixture of two and/or
three NBE repeat units (including dyads, triads) in addition
to alternating, isolated NBE sequences (Fig. 2b). The inten-
sity of resonances ascribed to NBE dyads, triads increased
upon increasing the NBE contents (Fig. 2c).
The results for ethylene/NBE copolymerization by half-
titanocenes containing various ketimide ligands,
Cp0TiCl2[N@(R1)R2] [Cp0 = Cp (1), C5Me5 (Cp*, 2);
t
R1,R2 = tBu,tBu (a), Bu,Ph (b), Ph,Ph (c)], MAO catalyst
systems under the same conditions are summarized in
Table 4. Cp*TiCl2(N@CtBu2) (2a) showed high catalytic
activities, but the activity decreased upon increasing the
NBE concentration (runs 25 and 26); the NBE contents
for the resultant copolymers prepared by 2a were lower
than those by 1a under the same conditions. The observed
trend is somewhat similar to that seen in the copolymeriza-
tion by 3–MAO catalyst system.
The ethylene/NBE copolymerization by using 1b,c and
2c–MAO catalyst systems were conducted to explore effect
of the ketimide substituents toward both the activity and
NBE incorporation. However, the observed catalytic activ-
ities were lower than those by Cp0TiCl2(N@CtBu2) (1a,
2a)–MAO catalyst systems. The resultant polymers pos-
sessed bimodal molecular weight distributions consisting
of low and high molecular weight polymers. The order in
the activity was somewhat different that for ethylene poly-
merization; 1c showed higher catalytic activity than 1b, and
we have no clear reason to explain the observed results at
this moment.
It is known that microstructures for poly(ethylene-co-
NBE)s prepared by 3, 4 estimated by 13C NMR spectra
possesses few NBE repeat units and contained both meso
and racemo alternating ethylene-NBE sequences as well
as isolated NBE units (33.0–33.5 ppm) [11,28], and the
NBE dyads were also observed as a tiny trace. In contrast,
as shown in Fig. 2, resonances ascribed to NBE dyads (res-
We reported effect of the ketimide substituent on the
activity for ethylene polymerization using VCl2(N-2,6-

K. Nomura et al. / Journal of Organometallic Chemistry 692 (2007) 4675–4682
4679
nated) to give another catalytically-active species. We
also found that 5a showed much higher catalytic activity
than 5b for ring-opening metathesis polymerization of
NBE in the presence of MeMgBr/PMe3 [30], and specu-
lated that a stability of V–N@C bond toward the MeMgBr
might affect the catalytic activity. It is also reported that
imino (ArN@CH–Ar0) group in zirconium complexes con-
taining two phenoxy-imine, [N-(3-tert-butylsalicylid-
ene)anilinato], ligand was reacted with AliBu3 to afford
another zirconium complexes containing phenoxy-amide
ligands [31]. Taking into account the above facts, it is thus
assumed that the observed difference in the activity
between 1a and 1b,c might be due to the stability of imino
group, N@C(R1)R2, toward the Al cocatalyst in the reac-
tion mixture.
We have prepared half-titanocenes containing various
ketimide ligands of type, Cp0TiCl2[N@C(R1)R2] [Cp0 = Cp
(1), C5Me5 (Cp*, 2); R1,R2 = tBu,Ph (b), Ph,Ph (c)], and the
structure of 2c was determined by X-ray crystallography.
The catalytic activities for ethylene polymerization by
1b,c, 2c–MAO catalyst systems were lower than those
reported by 1a, 2a–MAO catalyst systems [17,18], and
the resultant polymers possessed multi-modal molecular
weight distributions. Although 1a–MAO catalyst system
showed both notable catalytic activities and efficient
norbornene (NBE) incorporations for ethylene/NBE copo-
lymerization, the observed activities for the copolymeriza-
tion by 1b,c, 2c–MAO catalyst systems were low and the
resultant polymers consisted of a mixture of high and low
molecular weight polymers. Although the polymerization
results by 1b,c and by 2c–MAO catalyst systems were not
promising, however, the results presented here should
afford important information for designing efficient cata-
lysts with half-titanocenes for precise olefin polymeri-
zation.
3. Experimental
3.1. General procedure
All experiments were carried out under nitrogen atmo-
sphere in a Vacuum Atmospheres drybox or using standard
Schlenk techniques unless otherwise specified. Anhydrous
grade of toluene, hexane (Kanto Chemical Co., Inc.) were
stored in a Schlenk tube in the drybox in the presence of
molecular sieves (a mixture of 3A 1/16, 4A 1/8, and 13X
1/16). Ethylene for polymerization was of polymerization
grade (purity >99.9%, Sumitomo Seika Co. Ltd.) and
was used as received. All chemicals used were reagent-
grades and purified by standard purification procedures.
Toluene and AlMe3 in the commercially available MAO
[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. Syntheses of CpTiCl2(N@CtBu2) (1a), Cp*TiCl2(N
@CtBu2) (2a) were according to the previous report [15a].
Fig. 2. 13C NMR spectra for poly(ethylene-co-NBE)s prepared by 1a–
MAO catalyst system. NBE contents: (a) 17.8 (run 11), (b) 40.7 (run 12),
(c) 58.8 mol% (run 18).
Me2C6H3)[N@C(R1)tBu] [R1 = tBu (5a), CH2SiMe3 (5b)]–
MAO catalyst systems [29]. The activity by 5b at 25 ꢁC
was higher than that by 5a [activity 985 kg-PE/mol-V h
vs. 666 kg-PE/mol-V h, ethylene 8 atm in toluene], but
the activity by 5b decreased at 50 ꢁC whereas increase in
the activity was observed in 5a [543 kg-PE/mol-V h vs.
743 kg-PE/mol-V h]. We speculated that two tert-butyl
group in 5a may be necessary to improve the stability of
V–N@C bond under these conditions, especially minimiz-
ing the reaction of 5a,b with MAO (or AlMe3 contami-

4680
K. Nomura et al. / Journal of Organometallic Chemistry 692 (2007) 4675–4682
Table 4
Copolymerization of ethylene with norbornene (NBE) by Cp0TiCl2[N@C(R1)R2] [Cp0 = Cp (1), Cp* (2); R1,R2 = tBu,tBu (a), tBu,Ph (b), Ph,Ph (c)]–MAO
catalyst systemsa
Run
Complex (lmol)
NBE (mmol/mL)b
Activityc
Mdn · 10ꢂ4
Mw/Mdn
NBE (mol%)e
1
11
12
2
1a (0.10)
1a (0.02)
1a (0.02)
1b (5.0)
1b (5.0)
–
5880
21600
40200
90.0
45.2
70.6
71.9
Multi-modal
151
2.30
1.85
2.92
–
17.8
40.7
0.2
1.0
–
21
0.2
106
2.24
5.80
1.71
0.19
22
3
23
1b (5.0)
1c (5.0)
1c (5.0)
1.0
–
0.2
161
56.4
154
2.06g
Multi-modalf
110
2.63
2.84
2.75
2.14
2.45
2.47
2.04
6.60
8.37
1.89
42.2
52.3
97.0
Multi-modalf
1.40h
–
24
1c (5.0)
1.0
389
4
25
26
5
27
28
a
2a (0.05)
2a (0.05)
2a (0.05)
2c (5.0)
2c (5.0)
2c (5.0)
–
19680
31700
22200
126
245
Trace
–
12.7
20.3
0.2
1.0
–
0.2
1.0
6.09
–
Conditions: toluene 50 mL, ethylene 4 atm, 25 ꢁC, 10 min, MAO white solid (prepared by removing AlMe3, toluene from PMAO) 3.0 mmol.
Initial NBE concentration in mmol/mL.
Activity in kg-polymer/mol-Ti h.
GPC data in o-dichlorobenzene vs. polystyrene standards.
NBE content in mol% estimated by 13C NMR spectra.
Multimodal molecular weight distributions [Mn = 4.16 · 104, Mw/Mn = 21.1 (run 3); Mn = 9.91 · 103, Mw/Mn = 25.9 (run 5)].
A trace amount of peak ascribed to high molecular weight polymer (PE) was seen in the GPC trace.
High molecular weight shoulder peak was observed in the GPC trace.
b
c
d
e
f
g
h
Li[N@C(tBu)Ph] [22] or Li(N@CPh2) [23] were prepared
were prepared by dissolving polymers in a mixed solution
of 1,3,4-trichlorobenzene/benzene-d6 (90/10 wt), and the
spectrum was measured at 130 ꢁC.
according to the reported procedures. Elemental analyses
were performed by using PE2400II Series (Perkin–Elmer
Co.), and some analysis runs were employed twice to con-
firm the reproducibility in the independent analysis/synthe-
sis runs.
3.1.1. Synthesis of CpTiCl2[N@C(tBu)Ph] (1b)
To a toluene solution (10 mL) containing CpTiCl3
(439 mg, 2.0 mmol) was added Li[N@C(tBu)Ph] (351 mg,
2.1 mmol) at ꢂ30 ꢁC. The reaction mixture was warmed
slowly to room temperature (25 ꢁC), and the mixture was
then stirred for additional 4 h. The solution was filtered
through Celite pad, and the solvent was removed in vacuo.
The residue was then dissolved in minimal amount of
CH2Cl2 and the solution was covered with n-hexane. The
chilled solution (ꢂ30 ꢁC) yielded 602 mg (88%) of the titled
complex as red microcrystals. 1H NMR (CDCl3): d 1.32 (s,
9H, CH3C), 6.55 (s, 5H, Cp), 7.36 (m, 3H, Ph), 7.43 (m,
2H, Ph). 13C NMR (CDCl3): d 29.1, 45.4, 117.3, 127.1,
128.2, 129.7, 138.3, 196.1. Anal. Calc. for C16H19Cl2NTi:
C, 55.85; H, 5.57; N, 4.07. Found (1): C, 55.69; H, 5.24;
N, 3.83%. Found (2): C, 55.47; H, 5.39; N, 3.88%.
Molecular weights and molecular weight distributions
for polyethylene and poly(ethylene-co-norbornene)s were
measured by gel permeation chromatography (Tosoh
HLC-8121GPC/HT) with polystyrene gel column (TSK
gel GMHHR-H HT · 2, 30 cm · 7.8 mmB ID), ranging
from <102 to <2.8 · 108 MW at 140 ꢁC using o-dichloro-
benzene containing 0.05 wt/v% 2,6-di-tert-butyl-p-cresol
as solvent. The molecular weight was calculated by a stan-
dard procedure based on the calibration with standard
polystyrene samples.
All 1H and 13C NMR spectra were recorded on a JEOL
1
JNM-LA400 spectrometer (399.65 MHz, H). All deuter-
ated NMR solvents were stored over molecular sieves
under nitrogen atmosphere in the drybox, and all chemical
shifts are given in ppm and are referenced to Me4Si. All
spectra were obtained in the solvent indicated at 25 ꢁC
unless otherwise noted. 13C NMR spectra for poly(ethyl-
ene-co-norbornene)s and polyethylene were recorded on a
JEOL JNM-LA400 spectrometer (100.40 MHz, 13C) with
proton decoupling. The pulse interval was 5.2 s, the acqui-
sition time was 0.8 s, the pulse angle was 90ꢁ, and the num-
ber of transients accumulated was ca. 6000. The analysis
samples of polyethylene, poly(ethylene-co-norbornene)s
3.1.2. Synthesis of CpTiCl2(N@CPh2) (1c)
The titled compound was synthesized according to the
same procedure as for 1b except that CpTiCl3 (230 mg,
1.05 mmol) and Li(N@CPh2) (206 mg, 1.10 mmol) in place
of Li[N@C(tBu)Ph] were used. Yield 250 mg (69%). 1H
NMR (CDCl3): d 6.65 (s, 5H, Cp), 7.43 (t, 4H, meta),
7.52 (t, 2H, para), 7.60 (d, 4H, ortho). 13C NMR (CDCl3):
d 117.3, 128.5, 130.3, 131.9, 136.7, 181.9.

K. Nomura et al. / Journal of Organometallic Chemistry 692 (2007) 4675–4682
4681
3.1.3. Synthesis of Cp*TiCl2(N@CPh2) (2c)
MAO solid (174 mg, 3.0 mmol) were added into the auto-
clave (100 mL scale stainless steel) in the drybox, and was
filled with ethylene (1 atm). A toluene solution (1.0 mL)
containing 1a (0.1 lmol) was then added into the auto-
clave, and the reaction apparatus was then immediately
pressurized to 3 atm (ethylene total 4 atm). The mixture
was magnetically stirred for 10 min, ethylene remained
was purged after the reaction, and the mixture was then
poured into EtOH (50 mL) containing HCl (5 mL). The
resultant polymer was collected on a filter paper by filtra-
tion, and was adequately washed with EtOH, and was then
dried in vacuo. Basic experimental procedure in the ethyl-
ene/norbornene copolymerization was the same as that in
ethylene homopolymerization except that norbornene was
added in toluene in the drybox.
Titled compound was synthesized according to the same
procedure as for 1b except that Cp*TiCl3 (246 mg,
0.92 mmol) and Li(N@CPh2) (206 mg, 1.10 mmol) was
used in place of CpTiCl3 and Li[N@C(tBu)Ph], respec-
1
tively. Yield 371 mg (93%). H NMR (CDCl3): d 2.11 (s,
15H, CH3), 7.40 (t, 4H, meta), 7.47 (t, 2H, para), 7.62 (d,
4H, ortho). 13C NMR (CDCl3): d 13.2, 128.4, 129.5,
131.1, 137.0, 180.2. Anal. Calc. for C23H25Cl2NTi: C,
63.62; H, 5.80; N, 3.23. Found (1): C, 3.31; H, 5.63; N,
3.16%. Found (2): C, 63.29; H, 5.55; N, 3.27%.
3.1.4. Crystallographic analysis for Cp*TiCl2(N@CPh2)
(2c)
All measurements were performed on a Rigaku RAXIS-
RAPID Imaging Plate diffractometer with graphite mono-
chromated Mo Ka radiation. The selected crystal collec-
tion parameters are listed in Table 5, and the detailed
results were described in the reports attached below. All
structures were solved by direct method and expanded
using Fourier techniques [32], and the non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were
included but not refined. All calculations for complex 2c
were performed using the Crystal Structure [33,34] crystal-
lographic software package.
Acknowledgements
The present research is partly supported by Grant-in-
Aid for Scientific Research (B) from the Japan Society
for the Promotion of Science (JSPS, No.18350055). We
are grateful to Prof. Michiya Fujiki (NAIST) for discus-
sion, to Mr. Shohei Katao (NAIST) for his assistance in
the crystallographic analysis, and to Tosoh Finechem Co.
for donating MAO. W.W. and J.L. express their thanks
to JSPS (Japan Society for the Promotion of Science) for
a postdoctoral fellowship (P03295, P05397), and J.Y. ex-
presses his thanks to the JSPS for a predoctoral fellowship
(No. 5042).
3.1.5. Ethylene polymerization, ethylene/norbornene
copolymerization
The typical reaction procedure for ethylene polymeriza-
tion (Table 2, run 1) is as follows. Toluene (49 mL), and d-
Appendix A. Supplementary material
Table 5
Crystal and data collection parameters for Cp*TiCl2(N@CPh2) (2c)a
CIF file and structure report for structural determina-
tion for Cp*TiCl2(N@CPh2) (2c). Supplementary data
associated with this article can be found, in the online ver-
sion, at doi:10.1016/j.jorganchem.2007.04.043.
Complex
Cp*TiCl2(N@CPh2) (2c)
Formula; formula weight
Habits; crystal size (mm)
C23H25Cl2NTi; 434.26
Red, platelet;
0.80 · 0.30 · 0.10
Orthorhombic
Pbca (#61)
8.5825(18); 18.048(6);
28.745(6)
4452.6(18)
8
1.296
1808.00
243
0.71075
Total: 40434, unique: 5091
(0.042)
Crystal system
Space group
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