Silicon-bridged tetramethylcyclopentadienyl-phenoxy complexes of tantalum: Preparation and alkylation of Et2Si(η5-C 5Me4)(3-tBu-5-Me-2-C6H 2O)TaCl3 and generation of its cationic Complex

Article abstract of DOI:10.1021/om100042t

A tantalum complex of a silicon-bridged tetramethylcyclopentadienyl-phenoxy ligand, Et₂Si(η⁵-C₅Me₄)(3- ^tBu-5-Me-2-C₆H₂O)TaCl₃ (2), was prepared by treating TaCl₅ with the dilithium salt generated by reaction of the corresponding ligand 1 with ⁿBuLi in the presence of Et₃N in heptane. The molecular structure of 2, as confirmed by X-ray analysis, showed a four-legged piano-stool geometry around the tantalum atom and slightly twisted ligand architecture with a bridging diethylsilylene unit. The tantalum complex 2 exhibited moderate catalytic activities for copolymerization of ethylene and 1-hexene in the presence of ⁱBu₃Al/Ph ₃C[B(C₆F₅)₄]. The methylation reaction of the trichlorotantalum complex 2 afforded the corresponding trimethyltantalum complex 4. Cationic dimethyltantalum species were generated by treating 4 with an equimolar amount of Ph₃C[B(C₆F ₅)₄] or B(C₆F₅)₃ and found to be thermally stable in o-dichlorobenzene-d₄, even at elevated temperature.

Full text of DOI:10.1021/om100042t

2080 Organometallics 2010, 29, 2080–2084
DOI: 10.1021/om100042t
Silicon-Bridged Tetramethylcyclopentadienyl-Phenoxy Complexes
of Tantalum: Preparation and Alkylation of Et2Si(η5-C5Me4)-
(3-tBu-5-Me-2-C6H2O)TaCl3 and Generation of Its Cationic Complex
Taichi Senda,† Hidenori Hanaoka,† Yoshiaki Oda,*,† Hayato Tsurugi,‡ and
Kazushi Mashima*,‡
†Organic Synthesis Research Laboratory, Sumitomo Chemical Co., Ltd., 1-98, Kasugadenaka 3-chome,
Konohana-ku, Osaka 554-8558, Japan, and ‡Department of Chemistry, Graduate School of Engineering
Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
Received January 19, 2010
A tantalum complex of a silicon-bridged tetramethylcyclopentadienyl-phenoxy ligand, Et2Si-
(η5-C5Me4)(3-tBu-5-Me-2-C6H2O)TaCl3 (2), was prepared by treating TaCl5 with the dilithium salt
generated by reaction of the corresponding ligand 1 with nBuLi in the presence of Et3N in heptane. The
molecular structure of 2, as confirmed by X-ray analysis, showed a four-legged piano-stool geometry
around the tantalum atom and slightly twisted ligand architecture with a bridging diethylsilylene unit.
The tantalum complex 2 exhibited moderate catalytic activities for copolymerization of ethylene and
1-hexene in the presence of iBu3Al/Ph3C[B(C6F5)4]. The methylation reaction of the trichlorotantalum
complex 2 afforded the corresponding trimethyltantalum complex 4. Cationic dimethyltantalum
species were generated by treating 4 with an equimolar amount of Ph3C[B(C6F5)4] or B(C6F5)3 and
found to be thermally stable in o-dichlorobenzene-d4, even at elevated temperature.
Introduction
R-olefin into polyethylene.3 In addition, the isolation and
structural characterization of cationic alkyl species of me-
tallocene of group 4 metals fundamentally provide insight
into the polymerization mechanism and would enable us to
precisely design catalysts suitable for the desired catalytic
performance.4 It has already been demonstrated that the
metallocene and half-metallocene complexes of group 3
metals also became polymerization catalysts for not only
polymerization of ethylene but also the polymerization of
polar monomers such as methyl methacrylate (MMA) and
ε-caprolactone.5 For niobium and tantalum, we have investi-
gated half-metallocene complexes having 1,3-dienes as ancillary
ligands as unique catalyst precursors for the living polymeri-
zation of ethylene6 and MMA,7 and several half-metallocene
Metallocene complexes of early transition metals have
attracted great interest due to their potential applicability
as catalysts of various organic transformations and poly-
merizations.1 In particular, the combination of metallocenes
of group 4 metals with aluminoxane produced highly active
homogeneous catalysts for R-olefin polymerization, and
modification of ligand architecture, including an ansa-type
bridge skeleton, in these metallocene systems produced
stereoregular polymerization.2 Half-metallocene complexes
of group 4 metals, in which one of two cyclopentadienyl
ligands on the metallocenes was replaced by different kinds
of ancillary anionic ligands, have been anticipated as another
attractive system because of their greater flexibility and
feasibility in design together with high incorporation of
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*To whom correspondence should be addressed. E-mail: oday2@
sc.sumitomo-chem.co.jp (Y.O.); mashima@chem.es.osaka-u.ac.jp (K.M.).
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pubs.acs.org/Organometallics
Published on Web 04/07/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 9, 2010 2081
Chart 1
Scheme 1
complexes of tantalum have been studied for the polymeriza-
tion of nonpolar8 and polar monomers.9
Bridged cyclopentadienyl-phenoxy complexes (PHENICS:
phenoxy-induced complex of Sumitomo) of group 4 metals are
industrially important half-metallocene catalyst systems that
produce high-molecular-weight copolymers of ethylene and
R-olefin with high comonomer content (Chart 1).10 As an
extension of our continuous synthesis of PHENICS of group 4
metals, we have synthesized the silicon-bridged PHENICS of
tantalum (PHENICS-Ta), although there are some representa-
tive examples of tantalum-based nonmetallocene polymeriza-
tion catalysts.11 Thus, we report herein the structural fea-
tures along with catalytic capability of these PHENICS-Ta
complexes in comparison with the precedented silicon-bridged
PHENICS of titanium (PHENICS-Ti). The isolation and char-
acterization of a trialkyl complex and cationic dialkyl com-
pounds of silicon-bridged PHENICS-Ta are also provided.
˚
Table 1. Selected Bond Distances (A) and Angles (deg) for
Complex 2
Bond Distances
Ta-Cl(1)
Ta-Cl(3)
Ta-C(2)
Ta-C(4)
Ta-Cpcent
Si-C(1)
2.3696(12)
2.4033(11)
2.423(4)
2.485(4)
2.094
Ta-Cl(2)
Ta-C(1)
Ta-C(3)
Ta-C(5)
Ta-O
2.3877(11)
2.319(4)
2.509(5)
2.363(4)
1.875(3)
1.882(5)
1.898(5)
Si-C(10)
Bond Angles
Results and Discussion
O-Ta-C(1)
87.15(14)
82.91(4)
142.34(4)
84.21
Ta-O-C(11)
150.5(3)
81.56(4)
113.08
63.91
Cl(1)-Ta-Cl(2)
Cl(1)-Ta-Cl(3)
C(1)-Cpcent-Ta
Cl(2)-Ta-Cl(3)
Cpcent-Ta-O
Cpcent-C(1)-Ta
Synthesis and Characterization of Silicon-Bridged PHE-
NICS of Tantalum. The silicon-bridged cyclopentadienyl-
phenoxy ligand 1 was prepared by following modified pro-
cedures for the corresponding titanium and zirconium com-
plexes.10a Treatment of 1 with nBuLi (2.1 equiv) in the
presence of Et3N (4.5 equiv) followed by reaction with TaCl5
(1.2 equiv) gave the corresponding tantalum complex Et2Si-
(η5-C5Me4)(3-tBu-5-Me-2-C6H2O)TaCl3 (2) in very low
yield (2%). We thus chose a stepwise synthetic route, in
Torsion Angles
C(1)-Si-C(10)-C(11)
Ta-O-C(11)-C(10)
10.9(5)
20.7(8)
Dihedral Angle
θa
63.41
a θ denotes the dihedral angle between the best plane of cyclopenta-
dienyl ring and that of phenyl ring carbons.
(8) (a) Antonelli, D. M.; Leins, A.; Stryker, J. M. Organometallics
1997, 16, 2500–2502. (b) Decker, J. M.; Geib, S. J.; Meyer, T. Y. Organo-
metallcs 1999, 18, 4417–4420. (c) Coles, M. P.; Dalby, C. I.; Gibson, V. C.;
Little, I. R.; Marshall, E. L.; da Costa, M. H. R.; Mastroianni, S.
J. Organomet. Chem. 1999, 591, 78–87. (d) Feng, S.; Roof, G. R.; Chen,
which the dilithium salt 3 generated in heptane was collected
by filtration and washed with hexane. When a toluene slurry
of 3 was treated with 1 equiv of TaCl5, the color of the
mixture immediately changed to brown and the orange
complex 2 was isolated in moderate yield (16%) (Scheme 1).
The formulation and structure of 2 was revealed by
elemental analysis and NMR spectroscopy along with a
single-crystal X-ray analysis. Single crystals suitable for
X-ray analysis were grown by slow evaporation of a toluene
solution at room temperature. Selected bond distances and
angles of 2 are summarized in Table 1. The crystal data
and data collection parameters are provided in Table S1
(Supporting Information). Figure 1 shows the crystal struc-
ture of 2, which adopts a four-legged piano-stool geometry.
The torsion angles C(1)-Si-C(10)-C(11) (10.9(4)°) and
Ta-O-C(11)-C(10) (20.7(8)°) and dihedral angle (θ) be-
tween the cyclopentadienyl ring and the phenyl ring of 2 (θ =
63.41°) indicate that 2 has a slightly twisted ligand backbone.
Different from the case for the parent titanium complex
Et2Si(η5-C5Me4)(3-tBu-5-Me-2-C6H2O)TiCl2,10e both ethyl
groups on the silicon atom are located on the upper side
ꢀ
E. Y.-X. Organometallics 2002, 21, 832–839. (e) Sanchez-Nieves, J.; Royo,
P.; Mosquera, M. E. G. Organometallics 2006, 25, 2331–2336.
(9) (a) Mariott, W. R.; Gustafson, L. O.; Chen, E. Y.-X. Organome-
ꢀ
tallics 2006, 25, 3721–3729. (b) Sanchez-Nieves, J.; Royo, P. Organome-
tallics 2007, 26, 2880–2884.
(10) (a) Hanaoka, H.; Hino, T.; Souda, H.; Yanagi, K.; Oda, Y.;
Imai, A. J. Organomet. Chem. 2007, 692, 4059–4066. (b) Hanaoka, H.;
Hino, T.; Nabika, M.; Kohno, T.; Yanagi, K.; Oda, Y.; Imai, A.; Mashima, K.
J. Organomet. Chem. 2007, 692, 4717–4724. (c) Nabika, M.; Katayama, H.;
Watanabe, T.; Kawamura-Kuribayashi, H.; Yanagi, K.; Imai, A. Organome-
tallics 2009, 28, 3785–3792. (d) Senda, T.; Hanaoka, H.; Hino, T.; Oda, Y.;
Tsurugi, H.; Mashima, K. Macromolecules 2009, 42, 8006–8009. (e) Senda,
T.; Hanaoka, H.; Okado, Y.; Oda, Y.; Tsurugi, H.; Mashima, K. Organome-
tallics 2009, 28, 6915–6926. (f) Senda, T.; Hanaoka, H.; Nakahara, S.; Oda,
Y.; Tsurugi, H.; Mashima, K. Macromolecules 2010, 43, 2299–2306.
(11) (a) Rodriguez, G.; Bazan, G. C. J. Am. Chem. Soc. 1995, 117,
€
10155–10156. (b) Hakala, K.; Lofgren, B. Macromol. Rapid Commun.
1997, 18, 635–638. (c) Murtuza, S.; Harkins, S. B.; Long, G. S.; Sen, A.
J. Am. Chem. Soc. 2000, 122, 1867–1872. (d) Redshaw, C.; Rowan, M.;
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Homden, D. M.; Elsegood, M. R. J.; Yamato, T.; Perez-Casas, C. Chem. Eur.
J. 2007, 13, 10129–10139. (e) Yinghuai, Z.; Nong, L. C.; Zhao, L. C.;
Widjaja, E.; Hwei, C. S.; Cun, W.; Tan, J.; Meurs, M. V.; Hosmane, N. S.;
Maguire, J. A. Organometallics 2009, 28, 60–64. (f) Michiue, K.; Oshiki, T.;
Takai, K.; Mitani, M.; Fujita, T. Organometallics 2009, 28, 6450–6457.

2082 Organometallics, Vol. 29, No. 9, 2010
Senda et al.
the tantalum complex 2, a methylation reaction of 2 was con-
ducted. Thus, treatment of a toluene solution of 2with3equivof
a diethyl ether solution of MeLi resulted in the formation of the
corresponding trimethyltantalum complex 4 (eq 1). Recrystalli-
zation from pentane at -20 °C gave 4 as a yellow solid in
moderate isolated yield (48%). The 1H NMR spectrum of 4 in
CDCl3 exhibited one singlet signal at δ 0.28 assignable to three
methyl protons bound to the tantalum atom, suggesting flux-
ional behavior of the three Ta methyl groups. Equivalent
protons of Ta-Me3 were also observed for trimethyltantalum
complexes with a diamine8d or linked bis(phenoxy)16 ligand.
Figure 1. Molecular structure of the tantalum complex 2. All
hydrogen atoms are omitted for clarity. Key atoms are labeled.
Formation of a Cationic Dimethyltantalum Compound. One
equivalent of TB mixed with the neutral trimethyltantalum
complex 4 in o-dichlorobenzene-d4 (ODCB-d4) at room
temperature afforded clean conversion to the corresponding
cationic dimethyltantalum species 5 (eq 2). Although some
cationic complexes of group 4 metals were reported to react
with aryl halides,19 the cationic compound 5 was thermally
stable under an inert atmosphere for long periods, even in
halogenated solvent. The 1H NMR spectrum of compound 5
showed one narrow signal due to the two equivalent Ta-Me
groups (Figure S1b), indicating that the structure of 5 has a
three-legged piano-stool geometry.
of the cyclopentadienyl plane due to the steric repulsion
between Cl(3) and C(24). The observed bond distance
˚
Ta-O (1.875(3) A) is shorter than those of the nonbridged
cyclopentadienyl-phenoxy tantalum complex (η5-Cp*)(2,6-
12
Ph2-3,5-tBu2-C6HO)TaCl3 (1.902(3) A) and the directly
˚
bridged indenyl-phenoxy tantalum complex with 4-phenyl-
pyridine donor ligand [2-(η5-C9H6)-4,6-tBu2-C6H2O]TaCl3-
13
˚
(4-Ph-C5H4N) (1.963(3) A). An almost identical Ta-O
bond distance was reported for the bis(phenoxy) tantalum
complexes Ta(OC6H3-tBu2-2,6)2Cl3,14 TaCl3[(OC6H3-Ph)2-
CH2](C5H5N),15 and TaCl2(CH3)[(OC6H2-tBu2)2C6H4].16
The bond angle Ta-O-C(11) (150.5(3)°) of 2 is nearly
identical with those of Et2Si(η5-C5Me4)(3-tBu-5-Me-2-C6-
H2O)TiCl2 (151.29(13)°)10e and (η5-Cp*)(2,6-Ph2-3,5-tBu2-
C6HO)TaCl3 (149.9(3)°)12 and is larger than that of [2-(η5-
C9H6)-4,6-tBu2-C6H2O]TaCl3(4-Ph-C5H4N) (129.0(3)°).13
Copolymerization of Ethylene and 1-Hexene Catalyzed by
PHENICS-Ta. The tantalum complex 2 was used as a
catalyst precursor for the copolymerization of ethylene and
1-hexene.17 The tantalum complex 2 showed moderate
activity (1.02 kg (mmol of Ta)-1 h-1) upon activation with
iBu3Al (TIBA) and Ph3C[B(C6F5)4] (TB) (Al/B/Ta = 400/
3/1) in toluene at 40 °C to afford ethylene/1-hexene copoly-
mer (Mw = 154 000; Mw/Mn = 1.4) with moderate 1-hexene
content (6 short chain branches per 1000 carbon atoms).18
Alkylation of the Trichlorotantalum Complex. To gain in-
sight into the active species of the polymerization catalyzed by
The methyl abstraction of 4 also proceeded cleanly using an
equimolar amount of B(C6F5)3 in ODCB-d4 at room tempera-
ture to give the corresponding cationic species with the coun-
teranion [MeB(C6F5)3]- (6) (Figure S1c). The 19F NMR
spectrum of the mixture showed a small Δδ(Fmeta-Fpara) value
of 2.45 ppm, indicating the presence of the solvent-separated,
noncoordinated anion [MeB(C6F5)3]- (Figure S6).20
(12) Vilardo, J. S.; Salberg, M. M.; Parker, J. R.; Fanwick, P. E.;
Rothwell, I. P. Inorg. Chim. Acta 2000, 299, 135–141.
(13) Thorn, M. G.; Parker, J. R.; Fanwick, P. E.; Rothwell, I. P.
Organometallics 2003, 22, 4658–4664.
(14) Chamberlain, L. R.; Rothwell, I. P.; Huffman, J. C. Inorg. Chem.
1984, 23, 2575–2578.
(15) Mulford, D. R.; Fanwick, P. E.; Rothwell, I. P. Polyhedron 2000,
19, 35–42.
(16) Agapie, T.; Day, M. W.; Bercaw, J. E. Organometallics 2008, 27,
6123–6142.
Treatment of 4 with 3 equiv of TB also gave 5, and no further
methyl abstraction reaction occurred even at 150 °C(FigureS7).21
(17) Preliminary polymerization of ethylene using 2 was conducted
using various cocatalysts at 40 °C. The polymerization activities were as
follows: MMAO (Al/Ta = 1000/1), 0.24 kg (mmol of Ta)-1 h-1; TIBA/
B(C6F5)3 (Al/B/Ta = 400/3/1), 0.09 kg (mmol of Ta)-1 h-1; TIBA/TB
(Al/B/Ta = 400/3/1), 2.55 kg (mmol of Ta)-1 h-1; TIBA/[Me2NHPh]-
(19) (a) Wu, F.; Dash, A. K.; Jordan, R. F. J. Am. Chem. Soc. 2004,
126, 15360–15361. (b) Ma, K.; Piers, W. E.; Parvez, M. J. Am. Chem. Soc.
2006, 128, 3303–3313.
(20) (a) Horton, A. D.; de With, J.; van der Linden, A. J.; van de Weg,
H. Organometallics 1996, 15, 2672–2674. (b) Klosin, J.; Roof, G. R.; Chen,
E. Y.-X.; Abboud, K. A. Organometallics 2000, 19, 4684–4686. For related
arguments, also see ref 8d, 8e, and 9a.
[B(C6F5)4] (Al/B/Ta = 400/3/1), 1.92 kg (mmol of Ta)-1 h-1
.
(18) For copolymerization results of related titanium complexes, see
ref 10a.
(21) For a reaction of Cp2TaMe3 with 2 equiv of TB, see ref 8d.

Article
Organometallics, Vol. 29, No. 9, 2010 2083
The result indicates that coordination of ODCB-d4 to the
tantalum metal center is strong enough to separate Ta-Me
bonds of cationic species from an excess amount of TB.22 The
mixture of 4 and 3 equiv of TB in ODCB-d4 was added to 500
equiv of 1-hexene at room temperature, giving low-molecular-
weight poly(1-hexene) (Mw = 1430; Mw/Mn = 1.2) in 65.9%
yield after 5 days. The low activity toward 1-hexene polymeri-
zation suggested that coordination of ODCB-d4 to vacant site
hampered the 1-hexene approach.23
Although cationic alkyl complexes of early transition
metals are generally thermally unstable, the cationic di-
methyltantalum complex derived from 4 is very stable in
ODCB-d4 even at elevated temperature.24 The high tempera-
ture stability is attributable to the coordination of ODCB-d4
and the bridged cyclopentadienyl-phenoxy framework, for
which the characteristic ligand effects have been demon-
strated by high-temperature ethylene/1-hexene copolymeri-
zation catalyzed by titanium derivatives.10 The relatively low
catalytic activity of PHENICS-Ta toward olefin polymeri-
zation is ascribed to the larger atom radius of tantalum as
compared to that of titanium, which causes coordination of
the aromatic solvent.25,26
to the lower Lewis acidity of the cationic species and the
larger atom radius of tantalum as compared to that of the
corresponding titanium-based PHENICS.
Experimental Section
General Procedures. All manipulations of air- and moisture-
sensitive materials were performed under dry nitrogen using
a glovebox or standard Schlenk line techniques. Solvents
(heptane, pentane, and toluene) were purchased from Kanto
Chemical Co., Inc. (anhydrous grade) and used as received.
nBuLi was purchased from Kanto Chemical Co., Inc. TaCl5 was
purchased from Sigma-Aldrich. Et3N was purchased from
Nacalai Tesque Co., Inc. C6D4Cl2 (o-dichlorobenzene-d4) was
i
purchased from Wako Pure Chemical Industries, Ltd. Bu3Al
(TIBA) was purchased from Tosoh Finechem. Co., Ltd. Ph3C-
[B(C6F5)4] (TB) was purchased from Asahi Glass Co., Ltd. The
bridged cyclopentadienyl-phenoxy ligand 1 was prepared by
the reported method.10d 1H NMR (270 MHz) and 13C NMR
(68 MHz) were measured on a JEOL EX270 spectrometer. 19
F
NMR spectra (282 MHz) were measured on a Bruker DPX-300
spectrometer. Chemical shifts for 1H and 13C NMR spectra were
referenced using internal solvent resonances and are reported
relative to TMS. 19F NMR spectra were referenced to external
CFCl3. When C6D4Cl2 was used as the solvent, the spectra were
referenced to the resonance of the 3,6-positions of the residual
solvent protons at δ 7.40 or that of the 4,5-positions at δ 7.14 in
the 1H NMR spectra. Elemental analyses were performed using
an Elementar element analyzer at Sumika Chemical Analysis
Service, Ltd. All melting points were measured in sealed alumi-
num pans under a nitrogen atmosphere by differential scanning
calorimetry (DSC) on a TA Instruments Q2000 at a heating rate
of 10 °C/min. Molecular weights (Mw and Mn) and molecu-
lar weight distributions (Mw/Mn) were determined by high-
temperature gel permeation chromatography (GPC). GPC ana-
Conclusion
In summary, we demonstrated the preparation of a tri-
chlorotantalum complex bearing a bridged tetramethylcy-
clopentadienyl-phenoxy ligand, Et2Si(η5-C5Me4)(3-tBu-5-
Me-2-C6H2O)TaCl3 (2), and the molecular structure of 2 was
revealed by X-ray analysis. The alkylation reaction of 2 with
MeLi afforded the corresponding trimethyltantalum com-
plex 4. The reaction of 4 with an equimolar amount of
Ph3C[B(C6F5)4] or B(C6F5)3 led to the quantitative forma-
tion of the cationic dimethyltantalum complexes 5 and 6,
lyses were carried out at 160 °C using a Symyx Rapid GPCTM
,
equipped with three Plgel 10 μm mixed-B columns, and a Tosoh
HLC-8121GPC/HT gel permeation chromatograph, equipped
with TSKgel GMHHR-H(S)HT mixed bed columns. GPC
columns were calibrated using commercially available polysty-
rene standards (Polymer Laboratories). FT-IR measurements
were performed on a Bruker Equinox 55 þ PIKE Mapp IR
spectrometer to determine 1-hexene content in the copolymer.27
Preparation of Et2Si(η5-C5Me4)(3-tBu-5-Me-2-C6H2O)TaCl3
(2). To a heptane (40 mL) solution of Et3N (2.44 g, 24.15 mmol)
and 1 (1.98 g, 4.83 mmol) at -78 °C was added a hexane solution
of nBuLi (1.55 M, 7.79 mL, 12.07 mmol). The mixture was
warmed to room temperature and then stirred for 3 h. The
solvent was evaporated, and the resulting solids were collected
by filtration and washed with hexane. The dilithium salt 3 was
obtained as a pale yellow powder (1.23 g). To a toluene (10 mL)
slurry of TaCl5 (0.94 g, 2.61 mmol) at -30 °C was added a
toluene (10 mL) slurry of 3 (1.00 g, 2.61 mmol). The resulting
mixture was warmed to room temperature and then stirred
overnight. Insoluble materials were removed by filtration. Re-
moval of the solvent followed by washing with pentane gave 2 as
orange solids (0.42 g, 16% yield). Mp: 229-232 °C dec. 1H
NMR (CDCl3): δ 1.00-1.32 (m, 10H, Si-Et2), 1.40 (s, 9H,
Ar-tBu), 2.38 (s, 3H, Ar-Me), 2.53 (s, 6H, Cp-Me2), 2.57 (s,
6H, Cp-Me2), 7.08 (s, 1H, Ar-H), 7.29 (s, 1H, Ar-H). 13C NMR
(CDCl3): δ 5.1 (Si-CH2CH3), 7.6 (Si-CH2CH3), 13.4 (Cp-Me2),
15.5 (Cp-Me2), 21.2 (Ar-Me), 31.0 (Ar-CMe3), 34.9 (Ar-CMe3),
110.3, 126.0, 130.1, 133.5, 133.6, 135.4, 139.5, 140.9, 164.0.
Anal. Calcd for C24H36Cl3OSiTa: C, 43.95; H, 5.53. Found:
C, 44.04; H, 5.70.
1
respectively, which were fully characterized by H and 13C
NMR analyses. The 19F NMR spectrum of 6 showed a small
Δδ(Fmeta-Fpara) value of [MeB(C6F5)3]- and indicated the
presence of a separated ion pair in o-dichlorobenzene-d4. The
cationic dimethyltantalum species was found to be thermally
stable in o-dichlorobenzene-d4 even at 150 °C in the presence
of an excess amount of Ph3C[B(C6F5)4], giving no further
methyl abstraction. The observed ion separation and high
temperature stability suggested a strong coordination of
o-dichlorobenzene-d4 to the vacant coordination site of
the cationic tantalum metal center. The relatively lower
polymerization activity of PHENICS-Ta is attributable
(22) For coordination of a halogenated solvent to a cationic early-
transition-metal center, see: (a) Bochmann, M.; Jaggar, A. J.; Nicholls,
J. C. Angew. Chem., Int. Ed. Engl. 1990, 29, 780–782. (b) Bouwkamp,
M. W.; de Wolf, J.; del Hierro Morales, I.; Gercama, J.; Meetsma, A.;
Troyanov, S. I.; Hessen, B.; Teuben, J. H. J. Am. Chem. Soc. 2002, 124,
12956–12957. (c) Hayes, P. G.; Piers, W. E.; Parvez, M. J. Am. Chem. Soc.
2003, 125, 5622–5623. (d) Bouwkamp, M. W.; Budzelaar, P. H. M.;
Gercama, J.; Morales, I. D. H.; de Wolf, J.; Meetsma, A.; Troyanov, S. I.;
Teuben, J. H.; Hessen, B. J. Am. Chem. Soc. 2005, 127, 14310–14319.
(23) The cationic species 5 was insoluble in toluene. Generation of the
cationic species 5 and the following polymerization of 1-hexene was
attempted in toluene under more dilute conditions; however, no polymer
was obtained.
(24) For a review, see: Chen, E. Y.-X.; Marks, T. J. Chem. Rev. 2000,
100, 1391–1434.
Preparation of Et2Si(η5-C5Me4)(3-tBu-5-Me-2-C6H2O)Ta-
Me3 (4). To a toluene (11 mL) solution of 2 (210 mg, 0.32 mmol)
(25) For decreased polymerization activities by the coordination of
toluene, see: Scollard, J. D.; McConville, D. H. J. Am. Chem. Soc. 1996,
118, 10008–10009.
(26) For cyclopentadienyl tantalum complexes with a pendant η6-
arene ligand, see: Otten, E.; Meetsma, A.; Hessen, B. J. Am. Chem. Soc.
2007, 129, 10100–10101.
(27) Blitz, J. P.; McFaddin, D. C. J. Appl. Polym. Sci. 1994, 51, 13–20.

2084 Organometallics, Vol. 29, No. 9, 2010
Senda et al.
at -78 °C was added dropwise an Et2O solution of MeLi
(1.12 M, 0.90 mL, 1.01 mmol). The mixture was warmed to
room temperature and then stirred for 1 h. After evaporation of
the solvent, hexane was added and insoluble materials were
removed by filtration. The solvent was evaporated, and recrys-
tallization from pentane at -20 °C gave 4 as yellow solids
(91.3 mg, 48% yield). Mp: 175-177 °C dec. 1H NMR
(CDCl3): δ 0.28 (s, 9H, Ta-Me3), 0.84-1.09 (m, 10H, Si-Et2),
1.39 (s, 9H, Ar-tBu), 2.00 (s, 6H, Cp-Me2), 2.03 (s, 6H, Cp-Me2),
2.28 (s, 3H, Ar-Me), 6.95 (d, J = 2.1 Hz, 1H, Ar-H), 7.18 (d, J =
2.1 Hz, 1H, Ar-H). 13C NMR (CDCl3): δ 5.2 (Si-CH2CH3), 7.5
(Si-CH2CH3), 11.5 (Cp-Me2), 13.8 (Cp-Me2), 21.1 (Ar-Me),
30.6 (Ar-CMe3), 34.8 (Ar-CMe3), 57.2 (Ta-Me3), 101.0, 124.6,
125.6, 126.2, 129.8, 130.0, 133.5, 138.3, 162.9. Anal. Calcd for
C27H45OSiTa: C, 54.53; H, 7.63. Found: C, 54.79; H, 7.73.
Preparation of [Et2Si(η5-C5Me4)(3-tBu-5-Me-2-C6H2O)-
TaMe2]þ[B(C6F5)4]- (5). In a glovebox, C6D4Cl2 (0.5 mL) was
added to a mixture of 4 (7.7 mg, 12.9 μmol) and Ph3C[B(C6F5)4]
(11.9 mg, 12.9 μmol) at room temperature, and then the NMR
were injected into each reaction vessel through a valve. The total
volume of the reaction mixture was adjusted with toluene to
5 mL. The temperature was then set to 40 °C, the stirring speed
was set to 800 rpm, and the mixture was pressurized with
ethylene to 0.6 MPa. Polymerization was started by addition
of a toluene solution of tantalum complex 2 (0.1 μmol, 1 mM
toluene solution) followed by a toluene solution of TB
(0.3 μmol, 1 mM toluene solution). Ethylene pressure in the cell
and the temperature setting were maintained by computer
control until the end of the polymerization experiment. After
the polymerization reaction, the reaction mixture was cooled to
room temperature and the ethylene pressure in the cell was
slowly vented. The glass vial insert was then removed from the
pressure cell, and the volatile components were removed using a
centrifuge vacuum evaporator to give the polymeric product.
Polymerization of 1-Hexene Catalyzed by 5. In a glovebox, a
mixture of 4 (8.5 mg, 14.3 μmol) with TB (39.6 mg, 42.9 μmol)
in ODCB-d4 (0.5 mL) was added to 1-hexene (606.5 mg, 7.21
mmol) at room temperature. The reaction mixture was stirred
for 5 days at room temperature. The reaction was quenched by
adding MeOH, and the mixture was dried. The polymer was
extracted by hexane, and the hexane extract was purified by
passing through silica gel. Polymer was obtained by evaporating
hexane and drying at 60 °C. The result is provided in the main
text.
1
spectrum was obtained. The H NMR spectrum indicated the
quantitative formation of the title compound. 1H NMR (C6D4-
Cl2): δ 0.92-1.05 (m, 10H, Si-Et2), 1.20 (s, 6H, Ta-Me2), 1.60 (s,
9H, Ar-tBu), 2.14 (s, 6H, Cp-Me2), 2.25 (s, 6H, Cp-Me2), 2.51 (s,
3H, Ar-Me), 7.48 (d, J = 1.5 Hz, 1H, Ar-H); one aryl proton
signal was overlapped with Ph3CMe resonances. 13C NMR
(C6D4Cl2): δ 5.2 (Si-CH2CH3), 7.4 (Si-CH2CH3), 11.8 (Cp-
Me2), 13.1 (Cp-Me2), 21.5 (Ar-Me), 30.4 (Ar-CMe3), 35.1 (Ar-
CMe3), 71.1 (Ta-Me2), 105.6, 126.8, 131.3, 133.5, 134.0, 134.6,
137.1 (br d, JCF = 247.5 Hz, C6F5), 137.6, 137.9, 139.0 (br d,
JCF = 245.4 Hz, C6F5), 149.2 (br d, JCF = 243.4 Hz, C6F5),
160.6. The ipso carbon of the C6F5 group could not be assigned
with confidence due to overlapping with the NMR solvent peaks.
19F NMR (C6D4Cl2): δ -131.28 (o-C6F5), -161.74 (p-C6F5),
-165.57 (m-C6F5).
Crystallographic Data Collection and Structure Determination
of 2. The crystal was mounted on a CryoLoop (Hampton
Research Corp.) with a layer of light mineral oil and placed in
a nitrogen stream at 113(2) K. The measurement was made on a
Rigaku AFC7R/Mercury CCD detector with graphite-mono-
˚
chromated Mo KR (0.710 75 A) radiation. Crystal data and
structure refinement parameters are summarized in Table S1
(Supporting Information). The structure was solved by direct
methods (SIR 92)28 and refined on F2 using full-matrix least-
squares methods (SHELXL-97).29 Non-hydrogen atoms were
anisotropically refined. H atoms were included in the refinement
Preparation of [Et2Si(η5-C5Me4)(3-tBu-5-Me-2-C6H2O)-
TaMe2]þ[MeB(C6F5)3]- (6). In a glovebox, C6D4Cl2 (0.5 mL)
was added to a mixture of 4 (19.9 mg, 33.5 μmol) and B(C6F5)3
(17.1 mg, 33.5 μmol) at room temperature, and then the NMR
on calculated positions riding on their carrier atoms. The
P
2
2 2
function minimized was [ w(Fo - Fc ) ] (w = 1/[σ2(Fo2) þ
spectrum was obtained. The H NMR spectrum indicated the
(aP)2 þ bP]), where P = (Max(Fo2,0) þ 2Fc )/3 with σ2(Fo2) from
1
2
P
quantitative formation of the title compound. 1H NMR (C6D4-
Cl2): δ 0.92-1.05 (m, 10H, Si-Et2), 1.19 (s, 6H, Ta-Me2), 1.25 (s,
3H, B-Me), 1.58 (s, 9H, Ar-tBu), 2.13 (s, 6H, Cp-Me2), 2.24 (s,
6H, Cp-Me2), 2.50 (s, 3H, Ar-Me), 7.22 (d, J = 1.5 Hz, 1H,
Ar-H), 7.47 (d, J = 1.5 Hz, 1H, Ar-H). 13C NMR (C6D4Cl2):
δ 5.1 (Si-CH2CH3), 7.4 (Si-CH2CH3), 11.8 (Cp-Me2), 13.1
(Cp-Me2), 21.5 (Ar-Me), 30.4 (Ar-CMe3), 35.1 (Ar-CMe3),
71.1 (Ta-Me2), 105.6, 126.8, 131.2, 133.5, 134.0, 134.6, 137.2
counting statistics. The functions R1 and wR2 were ( ||Fo| -
P
P
P
|Fc||)/( |Fo|) and [{ w(Fo - Fc ) }/{ (wFo4)}]1/2, respec-
tively. The ORTEP-3 program (for Windows, version 2.02)30
was used to draw the molecule.
2
2 2
Acknowledgment. We thank Mr. Takahiro Hino (Sumi-
tomo Chemical) and Mr. Takuto Nakayama (Sumitomo
Chemical) for polymerization experiments.
(br d, JCF = 249.5 Hz, C6F5), 137.5, 137.9, 138.2 (br d, JCF
=
243.4 Hz, C6F5), 149.4 (br d, JCF = 235.3 Hz, C6F5), 160.6. The
ipso carbon of the C6F5 group could not be assigned with
confidence due to overlapping with the NMR solvent peaks.
19F NMR (C6D4Cl2): δ -131.21 (o-C6F5), -163.57 (p-C6F5),
-166.02 (m-C6F5).
Supporting Information Available: Figures showing NMR
spectra of 5 and 6 and a table and CIF file giving crystal data for
2. This material is available free of charge via the Internet at
http://pubs.acs.org.
Copolymerization of Ethylene and 1-Hexene Catalyzed by 2. A
Symyx Parallel Pressure Reactor (PPR) system was used for
polymerization experiments. A prewashed glass vial insert and
disposable stirring paddle were fitted to each reaction vessel of
the reactor. The reactor was then closed, and TIBA (40 μmol,
160 μL, 0.25 M toluene solution), 1-hexene (60 μL), and toluene
(28) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.;
Burla, M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27,
435.
(29) Sheldrick, G. M.; Schneider, T. R. Methods Enzymol. 1997, 277,
319–343.
(30) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.