A biphenylene-bridged dinuclear constrained geometry titanium complex for ethylene and ethylene/1-octene polymerizations

Article abstract of DOI:10.1016/j.jorganchem.2011.10.010

Permethylated cyclopentadienyl dinuclear constrained geometry titanium catalyst, [μ-(C₆H₄)₂-2,2′] {(η⁵-C₅Me₃)[1-Me₂Si(η ¹-N-^tBu)](TiCl₂)}₂ (BPTi ₂) linked by a biphenylene bridge was synthesized and tested in ethylene and ethylene/1-octene polymerizations upon activation by TIBA (triisobutylaluminum)/[Ph₃C][B(C₆F₅) ₄]. When compared with the corresponding highly active, mononuclear analogs, Me₂Si(η⁵-2-PhC₅Me ₃)(η¹-N-^tBu)TiCl₂ (PhTi ₁) and Me₂Si(η⁵-C₅Me ₄)(η¹-N-^tBu)TiCl₂ (MeTi ₁), BPTi₂ exhibits significantly increased molecular weight of polymer (>two-fold), as well as high level of activity and 1-octene incorporations in ethylene and ethylene/1-octene polymerizations. Although the lower activity was observed at high 1-octene feeds, the combined effects of rigidity and electronic conjugation induced by the biphenylene bridge might be responsible for the observed polymerization properties of BPTi₂.

Full text of DOI:10.1016/j.jorganchem.2011.10.010

Journal of Organometallic Chemistry 696 (2012) 4315e4320
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
A biphenylene-bridged dinuclear constrained geometry titanium complex for
ethylene and ethylene/1-octene polymerizations
,
b
a
b
c
Min Hyung Lee a , Myung Hwan Park , Woo Young Sung , Seong Kyun Kim , AuJiRu Son ,
*
,
Youngkyu Do b
**
a Department of Chemistry and Energy Harvest-Storage Research Center, University of Ulsan, Ulsan 680e749, Republic of Korea
b Department of Chemistry, KAIST, Daejeon 305e701, Republic of Korea
c Catalyst Synthetic Laboratory, Kumho Polychem, Yeosu 555-290, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Permethylated cyclopentadienyl dinuclear constrained geometry titanium catalyst, [m -
-(C6H4)2-2,20]{(h5
Article history:
C5Me3)[1-Me2Si(
in ethylene and ethylene/1-octene polymerizations upon activation by TIBA (triisobutylaluminum)/
[Ph3C][B(C6F5)4]. When compared with the corresponding highly active, mononuclear analogs, Me2Si(h5
2-PhC5Me3)(
1-N-tBu)TiCl2 (PhTi1) and Me2Si( 5-C5Me4)( 1-N-tBu)TiCl2 (MeTi1), BPTi2 exhibits signifi-
h
1-N-tBu)](TiCl2)}2 (BPTi2) linked by a biphenylene bridge was synthesized and tested
Received 5 September 2011
Received in revised form
1 October 2011
-
Accepted 6 October 2011
h
h
h
cantly increased molecular weight of polymer (>two-fold), as well as high level of activity and 1-octene
incorporations in ethylene and ethylene/1-octene polymerizations. Although the lower activity was
observed at high 1-octene feeds, the combined effects of rigidity and electronic conjugation induced by
the biphenylene bridge might be responsible for the observed polymerization properties of BPTi2.
Ó 2011 Elsevier B.V. All rights reserved.
Keywords:
Catalyst
Constrained geometry
Dinuclear
Polyolefin
Titanium
1. Introduction
the highly active, prototypical cyclopentadienyl-CGCs, such as
Me2Si(h h
5-C5Me4)( 1-N-tBu)TiCl2 (MeTi1) for a commercial goal
One of the major advances in single-site olefin catalyst systems
is the development of constrained geometry catalysts (CGCs) based
on the linked cyclopentadienyl-amido ancillary ligand, capable of
inducing efficiently the copolymerization of ethylene with higher
(Chart 1). Moreover, it is necessary for dinuclear CGCs to attain high
activity, high molecular weight, and effective comonomer
enchainment, especially for the utilization in a high-temperature
solution process [15,16,33]. Regarding dinuclear cyclopentadienyl-
CGCs, Lee and coworkers have reported an example of the highly
active CGC linked through an o-phenylene ansa-bridge [34].
In an effort to develop dinuclear catalytic systems, we disclosed
that the dinuclear group 4 metal complexes linked by a rigid and/or
a modulated biphenylene bridge between two cyclopentadienyl
rings can exhibit the enhanced polymerization properties such as
increase of molecular weight and catalytic activity in ethylene and
a
-olefins to form linear low-density polyethylene (LLDPE) [1e12].
In addition to high activity and high molecular weight of polymer,
most marked in CGCs are the catalytic properties involving como-
nomer incorporation and distribution and the formation of long-
chain branching (LCB) [13e17]. In this regard, recent studies on
the dinuclear indenyl-CGCs connected by flexible bridging groups
provided new impetus to the improvement of catalytic perfor-
mance of existing mononuclear CGCs [18e32]. The intriguing
catalytic properties such as higher a-olefin incorporation [30], high
activity in styrene polymerization [26], and branched or signifi-
cantly increased molecular weights in ethylene polymerization
[24,25,31] were reported mainly due to the cooperative interac-
tions between two active centers. Despite their unique properties,
however, the evaluation of catalytic properties of dinuclear systems
has not been clearly described in terms of comparative studies with
N
Cl
Cl
Si
Ti
Si
Si
Ti
Cl
Ti
Cl
Cl
Cl
N
N
Si
Ti
Cl
Cl
N
* Corresponding author. Tel.: þ82 52 259 2335; fax: þ82 52 259 2348.
** Corresponding author. Tel.: þ82 42 350 2829; fax: þ82 42 350 2810.
E-mail addresses: lmh74@ulsan.ac.kr (M.H. Lee), ykdo@kaist.ac.kr (Y. Do).
MeTi1
PhTi1
BPTi2
Chart 1.
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.10.010

4316
M.H. Lee et al. / Journal of Organometallic Chemistry 696 (2012) 4315e4320
styrene polymerizations [35,36]. These results prompted us to
apply the biphenylene bridge to the synthesis of novel dinuclear
CGC possessing two sterically isolated ansa-units. It is anticipated
that the structure could be beneficial to both the stabilization of
cationic active centers by electronic conjugation effect and the
prevention of mutual steric hindrance that may occur between
metal centers located in proximity. Herein we report the synthesis
of a dumbbell-like, permethylated cyclopentadienyl dinuclear Ti-
CGC (BPTi2) and the polymerization behaviors in ethylene and
ethylene/1-octene polymerizations in comparison with the corre-
sponding highly active, mononuclear Ti-CGC analogs.
p-TsOH (ca. 0.1 g) was added as solid into the solution at room
temperature. An ivory solid was immediately formed, and the stir-
ring was further continued for about 0.5 h. The volume of the
resulting reaction mixture was reduced to wet, and 30 mL of n-
hexane was poured in to the flask in order to precipitate the product
and dissolve out unreacted materials. The large amount of an ivory
solid obtained was filtered on a glass frit and successively washed
with ethanol (30 mL), diethyl ether (30 mL), and n-pentane (30 mL).
Drying in vacuo afforded 7.13 g of 1 (Yield: 65%). 1H NMR
(400.13 MHz, CDCl3):
4H, C5Me3H2), 2.11 (s, 6H, C5Me3H2), 2.00 (s, 6H, C5Me3H2), 1.87 (s,
6H, C5Me3H2). 13C NMR (100.62 MHz, CDCl3):
d
¼ 7.58 (d, 4H, C6H4), 7.40 (d, 4H, C6H4), 3.22 (s,
d
¼ 139.43, 137.76,
2. Experimental
137.51, 136.87, 135.40, 135.36, 127.75, 126.62, 46.74 (C5Me3), 13.61
(C5Me3), 13.29 (C5Me3), 11.24 (C5Me3). Anal. Calcd for C28H30: C,
91.75; H, 8.25. Found: C, 92.18; H, 8.38.
2.1. General considerations
All operations were performed under an inert nitrogen atmo-
sphere using standard Schlenk and glove box techniques. Anhy-
drous grade solvents (Aldrich) were purified by passing through an
activated alumina column. All solvents were stored over activated
molecular sieves (5Å). Chemicals were used without any further
purification after purchasing from Aldrich (4,40-Dibromobiphenyl,
n-BuLi (2.5 M solution in n-hexane), Me2SiCl2, tert-Butylamine,
PhMgBr (3.0 M solution in Et2O), para-Toluenesulfonic acid mon-
ohydrate (p-TsOH,H2O)), and Strem (TiCl3(thf)3, AgCl, Li(C5Me4H)).
2.2.2. Synthesis of [2,20-(C6H4)2][1-Me2Si(NH-tBu)(C5Me3H)]2 (2)
A slurry of 1.83 g (5.0 mmol) of 1 in 30 mL of THF was treated
with two equiv of n-BuLi (4.0 mL) at ꢀ78 ꢁC. The reaction mixture
was allowed to warm to room temperature and stirred for 2 h. To
the resulting yellow slurry was added an excess amount of Me2SiCl2
(1.5 ꢂ 2 equiv, 1.82 mL) at ꢀ78 ꢁC. The reaction mixture was slowly
allowed to warm to room temperature and stirred overnight. The
colorless solution was evaporated to dryness, and then extracted
with 30 mL of CH2Cl2. Filtration followed by removal of the solvent
in vacuo afforded an ivory solid of [2,20-(C6H4)2][1-
Me2SiCl(C5Me3H)]2 in quantitative yield. 1H NMR (400.13 MHz,
2,3,4-Trimethylcyclopent-2-enone [37], Me2Si(
h
5-2-PhC5Me3)(h1
1-N-tBu)TiCl2
-
N-tBu)TiCl2 (PhTi1) [38], and Me2Si( 5-C5Me4)(
h
h
(MeTi1) [11,12,39] were prepared analogously according to the
literature procedures. Polymerization-grade ethylene monomer
from Honam Petrochemical Co. was used after purification by
passing through LabclearÔ and OxiclearÔ filters. 1-Octene
(Aldrich) was purified by passing through an activated alumina
column. Triisobutylaluminum (TIBA, 1.0 M solution in toluene,
Aldrich) and [Ph3C][B(C6F5)4] (Asahi Glass Co.) were used as
received. CDCl3 was dried over activated molecular sieves (5Å), and
used after vacuum transfer to a Schlenk tube equipped with a J.
Young valve. 1H and 13C NMR spectra of compounds were recorded
on a Bruker Avance 400 spectrometer at ambient temperature. All
CDCl3):
d
¼ 7.62 (d, 4H, C6H4), 7.29 (d, 4H, C6H4), 3.81 (s, 2H,
C5Me3H), 2.15 (s, 6H, C5Me3H), 2.08 (s, 6H, C5Me3H), 1.93 (s, 6H,
C5Me3H), ꢀ0.05 (s, 12H, Me2Si). 13C NMR (100.62 MHz, CDCl3):
d
¼ 139.88, 138.06, 137.96, 136.64, 136.36, 134.71, 129.36, 126.45,
54.87 (SiC5Me3), 14.74 (C5Me3), 12.86 (C5Me3), 11.22 (C5Me3), 2.94
(Me2Si), ꢀ2.39 (Me2Si).
The obtained [2,20-(C6H4)2][1-Me2SiCl(C5Me3H)]2 was dis-
solved in 30 mL of THF, and cooled to ꢀ78 ꢁC. Next, the solution
was treated with
a
three-fold excess amount of tBuNH2
(3 ꢂ 2 equiv, 3.15 mL). Upon warming, colorless salts were grad-
ually formed. The reaction mixture was stirred overnight and then
evaporated to dryness. Extraction with 30 mL of Et2O and filtration
followed by removal of the solvent in vacuo afforded light yellow
chemical shifts are reported in d units with reference to the residual
peaks of CDCl3 for proton (7.24 ppm) and carbon (77.0 ppm)
chemical shifts. Elemental analyses (FISONS EA 1110) and HR EIMS
measurement (FISONS VG Auto Spec) were carried out at KAIST.
sticky foam of 2 in 96% yield. 1H NMR (400.13 MHz, CDCl3):
d
¼ 7.59
(d, 4H, C6H4), 7.28 (d, 4H, C6H4), 3.59 (s, 2H, C5Me3H), 2.08 (s, 6H,
C5Me3H), 2.05 (s, 6H, C5Me3H), 1.90 (s, 6H, C5Me3H), 0.94 (s, 18H,
NHCMe3), 0.32 (s, 2H, NHCMe3), ꢀ0.13 (s, 6H, Me2Si), ꢀ0.30 (s, 6H,
2.2. Synthesis of catalyst
Me2Si). 13C NMR (100.62 MHz, CDCl3):
d
¼ 138.02, 137.94, 137.61,
2.2.1. Synthesis of 4,40-(C5Me3H2)2(C6H4)2 (1)
137.14, 136.81, 136.02, 129.55, 126.42, 55.52 (NCMe3), 49.24
(SiC5Me3), 33.49 (NCMe3), 15.06 (C5Me3), 12.66 (C5Me3), 11.18
(C5Me3), 0.29 (Me2Si). HR EIMS: m/z calcd for C40H60N2Si2,
624.4295; found, 624.4272.
A slurry of 9.36 g (30.0 mmol) of 4,40-dibromobiphenyl in 40 mL
of diethyl ether was treated with two equiv of n-BuLi (24.0 mL) at
ꢀ30 ꢁC. Upon warming, the reaction mixture became a clean solu-
tion, and was allowed to warm to 0 ꢁC. A slow formation of a white
precipitate was observed, and further stirred for an additional 0.5 h
at this temperature. The reaction mixture was finally allowed to
warm to room temperature and stirred for another 2 h. A colorless
solutionover theprecipitatewasthen decantedoff, and 30mLof THF
was added to the resulting dilithium salt. The mixture was cooled to
ꢀ78 ꢁC, and subsequently two equiv of 2,3,4-trimethylcyclopent-2-
enone (7.46 g) in 20 mL of THF was slowly added via cannula at
ꢀ78 ꢁC. The reaction mixture was slowly allowed to warm to room
temperature and stirred overnight. The resulting light orange solu-
tion was treated with 30 mL of saturated aqueous solution of NH4Cl
to stop the reaction. Next, the organic portion was separated and the
aqueous layer was further extracted with diethyl ether (50 mL). The
combined organic portions were dried over MgSO4, filtered, and
evaporated to dryness, affording a colorless oily product. The crude
product was redissolved in CH2Cl2 (30 mL), and a catalytic amount of
2.2.3. Synthesis of [
N-tBu)](TiCl2)}2 (BPTi2)
m h -
-(C6H4)2-2,20]{( 5-C5Me3)[1-Me2Si(h1
A solution of 2.50 gof [2,20-(C6H4)2][1-Me2Si(NH-tBu)(C5Me3H)]2
(4.0 mmol) in 40 mL of THF was treated with four equiv of n-BuLi
(6.4 mL) at ꢀ78 ꢁC. The reaction mixture was allowed to warm to
room temperature and stirred for an additional 2 h. The resulting
dark brownish-green solution was then added via cannula to the
pre-cooled flask containing THF (40 mL) slurry of TiCl3(THF)3 (2.96 g,
8.0 mmol)at ꢀ78 ꢁC with vigorousstirring. Thereactionmixturewas
slowly allowed to warm to room temperature and stirred overnight.
Tothe resulting darkgreen solutionwas transferred 2.2 equivof AgCl
(1.26 g) as solid. An immediate color change to dark orange-brown
with the gradual precipitation of Ag0 was observed. After stirring
for 1 h, the reaction mixture was evaporated to dryness. The
resulting dark sticky residue was redissolved in 50 mL of a mixed

M.H. Lee et al. / Journal of Organometallic Chemistry 696 (2012) 4315e4320
4317
solvent of n-hexane/CH2Cl2 (v/v ¼ 2:1), and filtered. Removal of the
solvent followed by thorough washing with n-hexane several times
resulted in a bright brown powder. Drying in vacuo afforded 2.43 g of
formed after the addition of EtOH was obtained by decanting the
solution followed by washing with EtOH. The waxy poly(1-octene)s
were acquired differently as described above; After quenching by
ca. 1 mL of 10% HCl solution of EtOH, the bulk polymerization
mixture was evaporated to dryness under vacuum. The residue was
then extracted with CHCl3 and washed with aqueous solution of
10% HCl to remove any insoluble materials. The organic phase was
separated, evaporated, and finally dried in a vacuum oven at 70 ꢁC.
BPTi2 in 71% yield. 1H NMR (400.13 MHz, CDCl3):
d
¼ 7.60 (br d, 8H,
C6H4), 2.29 (s, 6H, C5Me3H), 2.24 (s, 6H, C5Me3H), 2.17 (s, 6H,
C5Me3H), 1.38 (s, 18H, NHCMe3), 0.65 (s, 6H, Me2Si), ꢀ0.12 (s, 6H,
Me2Si). 13C NMR (100.62 MHz, CDCl3):
d
¼ 147.30, 142.56, 139.83,
137.76, 137.21, 134.69, 126.14 (2C), 104.37 (SiC5Me3), 63.16 (NCMe3),
32.59 (NCMe3), 16.79 (C5Me3), 13.38 (C5Me3), 13.31 (C5Me3), 4.92
(Me2Si), 4.26 (Me2Si). Anal. Calcd for C40H56Cl4N2Si2Ti2: C, 55.95; H,
6.57; N, 3.26. Found: C, 55.28; H, 6.96; N, 3.04.
2.4. Polymer characterization
13C NMR spectra of the polymers were recorded on either a Bruker
Avance 400 (13C; 100.62 MHz) or a Bruker AMAX 500 (13C;
125.77 MHz) spectrometer at 120 ꢁC with 90ꢁ pulse angle, 2 s
acquisition time, and 8 s relaxation delay. The samples were dissolved
in 1,1,2,2,-tetrachloroethane-d2 to forma 10 wt.-% solution (ca. 90mg/
0.5 mL) in 5-mm tubes. All the measurements were performed after
complete dissolution by pre-heating the samples to about 110 ꢁC in an
oil bath. The chemical shift value of main backbone methylene
2.3. Polymerization procedure
Into a well-degassed 250 mL-glass reactor equipped with
a 3 cm-egg shaped magnetic bar, freshly dried toluene (98.0 mL)
was transferred, and the reactor was adjusted to the desired reac-
tion temperature using an external bath. Ethylene monomer was
then saturated at 1 bar with vigorous stirring for at least 10 min
after degassing with it several times. In the case of copolymeriza-
tion, 1-octene was charged via a syringe at the initial stage of
ethylene saturation and the saturation was further continued for
10 min. During the period of ethylene saturation, catalyst activation
was separately carried out; a toluene solution of catalyst (0.01 M of
[Ti]) was first treated with 50 equiv of TIBA, which was allowed to
react for 10 min, providing 6.67 mM of in situ alkylated Ti solution.
The measured volume of this solution which fixes the final
concentration of an activated catalyst solution at 2.00 mM based on
[Ti] was then added to a toluene solution, typically 3.00 mM
concentration, of 1.1 equiv of [Ph3C][B(C6F5)4]. The slightly excess
amount of [Ph3C][B(C6F5)4] was employed in order to ensure
complete catalyst activation. Next, the activated catalyst solution
(
dþdþ ¼ 29.98 ppm) was used as an internal standard. Peak assign-
ments and the estimation of 1-octene content in the polymers were
made according to the reported literatures [40,41]. The molecular
weight (Mw) and molecular weight distribution (Mw/Mn) of the
polymers were analyzed by high-temperature gel-permeation chro-
matography (GPC) using a Polymer Laboratories PL 220 at 140 ꢁC in
1,2,4-trichlorobenzenewithaflowrateof1.00 mL/min.Themolecular
weight (Mw) measured was calibrated using narrow polystyrene
standards as a reference. The melting transition (Tm) of the polymers
from BPTi2 was measured by differential scanning calorimetry (DSC,
TA Instrument Q100) at a heating rate of 10 ꢁC/min. Any thermal
history in the polymers was eliminated by the first heating the
samples to 180 ꢁC at 20 ꢁC/min, cooling to ꢀ80 ꢁC at 20 ꢁC/min, and
then recording the second DSC scan from ꢀ80 ꢁC to 180 ꢁC.
(4.0 mmol of Ti, 2.0 mL) was quickly injected into the reactor. As
soon as catalyst injection, rapid increase of viscosity in the reaction
medium was observed, particularly in ethylene homopolymeriza-
tion by BPTi2. All the reactions were quenched after 1 min by the
injection of ca. 1 mL of 10% HCl solution of EtOH. The resultant
mixture was then poured into the large volume of EtOH (500 mL)
and stirred for 1 h. The precipitated polymer was subsequently
collected by filtration, and washed with EtOH several times (ca.
200 mL). The resulting polymers were finally dried in a vacuum
oven at 70 ꢁC to constant weight. In the case of sticky polymers,
usually copolymers of high 1-octene content, the sticky residue
3. Results and discussion
A new biscyclopentadienyl ligand, 4,40-(C5Me3H2)2(C6H4)2 (1)
was designed to achieve the biphenylene-bridged permethylated
dinuclear CGC (BPTi2) inwhich the biphenylene group is linked toan
a-position to the bridgehead carbon atom of the Cp ring to maintain
a sterically open nature. 1 was prepared from the reaction of
dilithium salt of 4,40-dibrombiphenyl and two equiv of 2,3,4-
trimethylcyclopent-2-enone followed by dehydration (Scheme 1).
1. 2 n-BuLi
1. 2 n-BuLi
Br
Br
O
2. 2 Me2SiCl2
3. 4 tBuNH2
2. 2
1
3. p-TsOH
NH
H
N
Cl
Cl
Si
Si
Ti
1. 4 n-BuLi
2. 2 TiCl3(thf)3
3. 2 AgCl
H
Si
Si
Ti
Cl
Cl
HN
N
2
BPTi2
Scheme 1. Synthesis of a biphenylene-bridged dinuclear Ti-CGC (BPTi2).

4318
M.H. Lee et al. / Journal of Organometallic Chemistry 696 (2012) 4315e4320
Table 1
Ethylene and ethylene/1-octene polymerization results with BPTi2, PhTi1, MeTi1/Al(iBu)3/[Ph3C][B(C6F5)4] catalytic systemsa.
mol) 1-Octene feed (mL) Tp (ꢁC) Yield (g) Activityc
10ꢀ3 Mwd (g molꢀ1
)
Mw/Mn
1-Octene contente (mol%) Tm (ꢁC)
d
f
Run Catalyst Amt of cat. (
m
1
2
3
4
5
6
7
8
BPTi2
BPTi2
BPTi2
PhTi1
PhTi1
PhTi1
MeTi1
BPTi2
BPTi2
BPTi2
BPTi2
BPTi2
PhTi1
PhTi1
PhTi1
PhTi1
PhTi1
MeTi1
2.0
2.0
2.0
4.0
4.0
4.0
4.0
2.0
2.0
2.0
2.0
2.0
4.0
4.0
4.0
4.0
4.0
4.0
0
0
0
0
0
25
50
75
25
50
75
50
50
50
50
50
50
50
50
50
50
50
50
0.48
0.64
0.68
0.73
0.60
0.56
0.57
0.97
1.15
1.27
1.46
0.12
1.06
1.30
1.82
2.59
0.15
1.26
7.20 ꢂ 106 1329
2.61
2.38
2.84
2.36
2.36
3.01
3.19
2.65
2.59
2.19
2.12
1.34
3.21
3.10
2.65
2.24
1.42
3.04
134.6
134.5
133.8
9.60 ꢂ 106
1.02 ꢂ 107
1.10 ꢂ 107
9.00 ꢂ 106
8.40 ꢂ 106
8.55 ꢂ 106
1.46 ꢂ 107
1.73 ꢂ 107
1.91 ꢂ 107
2.19 ꢂ 107
1.80 ꢂ 106
1.59 ꢂ 107
1.95 ꢂ 107
2.73 ꢂ 107
3.89 ꢂ 107
2.25 ꢂ 106
1.89 ꢂ 107
661
348
450
305
211
266
322
243
227
137
15
132
90
54
43
17
g
ꢀ
e
e
e
0
0
0.5
1.0
2.0
5.0
30.0
0.5
1.0
2.0
5.0
30.0
1.0
6.3
12.1
21.5
43.7
87.8
59.4
n/oh
n/o
9
10
11
12b
13
14
15
16
17b
18
6.3
11.3
20.6
43.1
e
e
e
e
e
e
138
11.3
a
Polymerization conditions: PE ¼ 1 bar; [Al]/[Ti] ¼ 50; [B]/[Ti] ¼ 1.1; solvent ¼ 100 mL of toluene; tp ¼ 1.0 min.
b
c
Bulk polymerization of 1-octene.
Activity given in units of g polymer (mol Ti h bar)ꢀ1
Determined by GPC.
.
d
e
f
Determined by 13C NMR.
Determined by DSC.
g
h
Not determined.
Not observed.
This synthetic route is quite straightforward and the crystalline 1
was obtained in good yield freed from any mono-substituted side
products. Despite poor solubility in common organic solvents such
as THF, ether, and CH2Cl2, 1 can be readily converted into the cor-
responding dilithium salt in THF, which subsequently reacted with
two equiv Me2SiCl2 and then excess tBuNH2 to afford the final CGC
ligand (2) as sticky foam in high yield (96%). Synthesis of the dinu-
clear BPTi2 was directed by a usual method applied to the synthesis
of mononuclear CGCs using tetralithium salt of 2 and two equiv of
TiCl3(thf)3 in THF. The formation of BPTi2 was confirmed by the 1H
and 13C NMR spectroscopy and elemental analysis. However,
attempts to obtain single crystals of BPTi2 have failed due to poor
crystallinity. Along with BPTi2, the corresponding mono-CGCs,
PhTi1 and MeTi1 were prepared analogously for a comparison study.
To investigate the catalytic properties of BPTi2 in olefin poly-
merization, ethylene polymerization behavior was first examined.
In situ alkylation using triisobutylaluminum (TIBA) followed by
borate ([Ph3C][B(C6F5)4]) activation of BPTi2 afforded a highly
active catalytic system in ethylene polymerization (Table 1).
According to the comparative result with the PhTi1 system, the
overall activity of BPTi2 is almost in a similar range, but the
retention of high activity at elevated temperatures is particularly
observed. In contrast, the activity of PhTi1 decreases with
increasing temperature as reported [42], implying an enhanced
thermal stability of BPTi2. Moreover, the activity of BPTi2 is even
larger than that of MeTi1 under the identical conditions. It is
interesting to note that the molecular weight of polyethylenes by
BPTi2 is nearly 2e3 times greater than those by PhTi1 and MeTi1 in
a whole reaction temperature range. From the fact that PhTi1
produces polyethylenes having slightly increased molecular weight
than MeTi1 at 50 ꢁC (run 5 vs. run 7), the much increased molecular
weight by BPTi2 is quite remarkable (Fig. 1). The narrow molecular
weight distribution (Mw/Mn) from BPTi2, as similar to that of
polyethylenes obtained with the mononuclear CGCs, also indicates
that the two titanium active centers behave as single active sites.
Based on the foregoing ethylene polymerization results, the
detailed ethylene/1-octene copolymerization was performed,
especially at 50 ꢁC where BPTi2 and PhTi1 exhibited nearly same
Fig. 1. GPC curves of polyethylenes from BPTi2, PhTi1, and MeTi1 at 50 ꢁC (runs 2, 5,
and 7, respectively in Table 1).
Fig. 2. Comparison of molecular weight (Mw) of polyethylenes and poly(ethylene-co-
1-octene)s from BPTi2, PhTi1, and MeTi1 at 50 ꢁC.

M.H. Lee et al. / Journal of Organometallic Chemistry 696 (2012) 4315e4320
4319
activity in ethylene polymerization (Table 1). The polymerization
results upon variation of 1-octene amount in the feed indicate that
BPTi2 acts as a highly active catalyst in ethylene/1-octene copoly-
merization. The activity of both BPTi2 and PhTi systems is higher
than that in the corresponding ethylene homopolymerization, and
that the higher the 1-octene feed, the higher activity results in
[43,44]. However, the lower activity of BPTi2 than PhTi1 is observed
at the increased 1-octene feeds (2.0 and 5.0 mL), while the activity
is in a similar range at the moderate 1-octene feeds (0.5 and
1.0 mL). On the other hand, the molecular weight of copolymers by
BPTi2, which is lower than those of polyethylenes and is decreasing
with increasing 1-octene feed, is 2e4 times greater than those by
PhTi1 and MeTi1 whose values show a slight difference (Fig. 2).
Although the moderate increase in the molecular weight of poly(-
ethylene-co-1-hexene) has recently been observed for the cyclo-
pentadienyl dinuclear Ti-CGCs [34], the consistently observed large
increase of molecular weight by BPTi2 in both polyethylene and
poly(ethylene-co-1-octene) over various reaction conditions could
be an interesting polymerization feature of the present dinuclear
Ti-CGC system.
achievable via a macromolecular reinsertion process [24,25]. Since
the molecular weight of polymer is much governed by electronic
effect of ligand [17,33], the increase of molecular weight by BPTi2
appears to be mainly attributed to the electronic effect of the
biphenylene bridge on both cationic active centers. Exclusion of
mutual steric effect between the active centers caused by the rigid
and isolated ansa-nature in BPTi2 may be supportive of the large
involvement of electronic effect on molecular weight (vide infra).
The similar increase of molecular weight of polyethylene, even
though a less extent to the given system, was previously observed
for the dinuclear zirconocenes linked by a biphenylene bridge
[35,36].
13C NMR analyses of copolymers reveal high 1-octene incorpo-
ration in the copolymers obtained from BPTi2 as comparable to
those from PhTi1 and MeTi1 under identical 1-octene feeds. The
estimation of the comonomer contents at the different comonomer
feeds indicates that the incorporation of 1-octene into the poly-
ethylene backbone gradually increases with increasing comonomer
concentration in the feed. Furthermore the 13C NMR spectra, for
example, obtained at 1-octene feed of 1.0 mL, exhibit almost similar
carbon peak positions and intensities for all three systems (Fig. 3).
In conjunction with the narrow Mw/Mn of all the copolymers from
BPTi2, these results indicate that (co)monomer insertions occur
independently at each isolated metal unit of BPTi2.
Regarding molecular weight of polymer, it was reported that
similar values are typically observed between mono and dinuclear
indenyl Ti-CGCs linked by flexible bridges [30], while significantly
high molecular weight polyethylene from dinuclear Zr-CGCs can be
Fig. 3. 13C NMR spectra of poly(ethylene-co-1-octene)s at a 1-octene feed of 1.0 mL, from (a) BPTi2 (run 9), (b) PhTi1 (run 14), and (c) MeTi1 (run 18 in Table 1). Peak assignments
were made on the carbon atoms contributed from isolated comonomer units.

4320
M.H. Lee et al. / Journal of Organometallic Chemistry 696 (2012) 4315e4320
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cationic active centers via a possible electronic conjugation, but
also steric isolation of two metal centers provided by rigidity
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leading to high molecular weight. The stabilization could also
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is likely that vinyl-terminated macromonomers formed at one Ti
center may interfere with monomer insertion at the proximal Ti.
Although a direct evidence of LCB was not detected by 13C NMR
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Ti center due to the enhanced solubility of the copolymer having
a high amount of 1-octene appears to lead to such interaction. The
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homopolymerization (run 12 vs. 17) may plausibly support this
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We have prepared a novel permethylated cyclopentadienyl
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exhibited high activity and high 1-octene incorporation in ethylene
and ethylene/1-octene polymerizations. Particularly, BPTi2 led to
the significantly increased molecular weight of polymers in both
homo- and copolymerization in comparison with those from the
corresponding mononuclear Ti-CGC analogs. These results appear to
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of two cationic metal centers through the biphenylene group and
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Acknowledgments
This work was supported by the 2010 Research Fund of
University of Ulsan.
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