Zirconium-catalyzed polymerization of a styrene: Catalyst reactivation mechanisms using alkenes and dihydrogen

Article abstract of DOI:10.1021/ma102835p

Zirconium salicylaldiminates in the presence of AlⁱBu ₃/[Ph₃C][B(C₆F₅)₄] are inactive for the homopolymerization of p-tert-butylstyrene (TBS), but the addition of hexene leads to a highly a

Full text of DOI:10.1021/ma102835p

ARTICLE
pubs.acs.org/Macromolecules
Zirconium-Catalyzed Polymerization of a Styrene: Catalyst
Reactivation Mechanisms Using Alkenes and Dihydrogen
Giles W. Theaker,†,‡ Colin Morton,‡ and Peter Scott*,†
†Department of Chemistry, University of Warwick, Gibbet Hill Road, Coventry, UK CV4 7AL
‡Infineum UK Ltd., Milton Hill, Abingdon, UK OX13 6BB
S Supporting Information
b
ABSTRACT:
Zirconium salicylaldiminates in the presence of AliBu3/[Ph3C][B(C6F5)4] are inactive for the homopolymerization of p-tert-
butylstyrene (TBS), but the addition of hexene leads to a highly active system. Analysis of the polymers by NMR and MALDI
indicates surprisingly that most of the product chains contain no hexene, while some contain a single hexene unit. Addition of
dihydrogen also leads to the production of poly(TBS) without substantial reduction in molecular weight and with main-chain end-
group unsaturation. These and other observations lead us to two related mechanisms for the hexene- and dihydrogen-promoted
reactions. Synthetic and catalytic studies indicate that the active species is not a typical bis(salicylaldiminato) compound but an
amido/alkoxido system. An authentic compound of this class is highly active for the TBS polymerization even in the absence of
added aluminum alkyl.
’ INTRODUCTION
Early copolymerizations of styrene and ethene with CpTiCl3
produced homopolymers of both monomers as mixtures with the
ES copolymer.12 This implies the presence of multiple catalytic
species in the reaction mixture. Studies conducted into the nature
of the active species in titanium-mediated styrene polymeriza-
tions have implicated TiIII in the homopolymerization of styrene
and TiIV in the homopolymerization of ethene, though there is
evidence that the system may not be this simple.13 Regardless,
TiIV species such as CpTiCl3 are readily reduced by the
aluminum alkyls such as AliBu3 or those present in MAO.14 TiIII
species such as (CpTiOMe)2μ-(OMe)2 have been shown to
have activity for sPS production in excess of that of their TiIV
analogues,8 while EPR studies have shown that increased [TiIII]
corresponds with higher activity for PS production.15-17 Overall
then, TiIII is implicated strongly in PS catalysis, and this is
perhaps a good reason why this metal is far more successful than
(d0) zirconium.
The controlled synthesis of polystyrene (PS) has been
achieved using a number of polymerization mechanisms,1,2
leading to various tacticities, regiochemistries, and molecular
weights. Examples include the production of atactic polystyrene
(aPS) on an industrial scale by radical polymerization methods
and the formation of syndio- and isotactic polystyrene (sPS and
iPS) via cationic transition-metal-mediated coordination polym-
erization. The latter area is dominated by titanium catalysts
which give excellent conversion, activity, and stereocontrol for
either sPS or iPS. Indeed, the first synthesis of sPS3 by Ishihara4
used CpTiCl3 activated with methylaluminoxane (MAO), and
this remains a benchmark system today.
Zirconium-based systems have been less successful. Several
studies have looked at styrene polymerizations with simple
zirconium complexes such as Zr(CH2Ph)4,5 ZrCl4,6 and
ZrCl4 THF2,7 alongside metallocenes (Cp2ZrCl2),8 half-sand-
3
wich complexes (CpZrCl3),8 ansa-zirconocenes,9,10 and post-
metallocenes such as “OSSO”-based systems.11 While produc-
tion of both sPS and iPS has been achieved,8 the activities
displayed by these systems are extremely low compared with
their titanium equivalents. The larger radius and lower electro-
philicity of zirconium have been suggested as the reasons behind
this difference in behavior (vide infra).
Ethene/styrene (ES) copolymers are of great interest both
commercially18 and academically, but as noted above, PS produ-
cing catalysts are less useful for ES copolymerization, as
Received: December 13, 2010
Revised:
January 24, 2011
Published: February 14, 2011
r
2011 American Chemical Society
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Scheme 1. Insertions of Styrene in a Metal-Alkyla
salicylaldimine precatalysts when activated by tri-isobutylalumi-
num (AliBu3) and the trityl borate salt [Ph3C][B(C6F5)4] along
with an investigation of the mechanism of such polymerization.
’ EXPERIMENTAL SECTION
General Considerations. Where necessary, the work detailed
below was carried out under an inert atmosphere of argon, using
standard Schlenk techniques. All glassware, cannula, syringes, etc., were
dried at 150 °C for 24 h prior to use. Solvents were dried by reflux over
an appropriate drying agent (pentane: NaK alloy; THF: potassium;
toluene: sodium; dichloromethane: CaH2) for 3 days prior to distillation
and then freeze-thaw-degassed three times before use. Deuterated
solvents for NMR were refluxed over potassium (benzene, toluene,
tetrahydrofuran) or calcium hydride (pyridine, dichloromethane) for 3
days before being vacuum transferred to a fresh ampule and stored under
argon. Unless stated otherwise, reagents were used as purchased. Metal
complexes and pyrophoric reagents were stored in an MBraun glovebox
at <0.5 ppm of O2.
a A 2,1 insertion leads to the benzylic “dormant state”.
NMR spectra of precursors and complexes were recorded on either
Bruker DPX-400 or DRX-500 spectrometers. Residual protio-solvent
was used as an internal reference.35 13C NMR spectra of ethene/styrenic
copolymers were recorded on a Bruker DPX at 400 MHz in 1,1,2,2-
tetrachloroethane (10 000 scans, 4 s relaxation time, 90 °C), ensuring
that the sample was fully dissolved. 13C NMR of P(TBS) was carried out
on a Bruker DPX at 400 MHz in CDCl3 at room temperature. Mass
spectrometry of non-air-sensitive compounds was carried out on a
Bruker Esquire2000 ESI spectrometer. Air-sensitive compounds were
analyzed on a Bruker Ultraflex II TOF/TOF using 9-nitroanthracene as
the organic matrix. Calibration was achieved using a mixture of C60, C78,
and C90. P(TBS) samples were analyzed on the above machine using
either DCTB or 9-nitroanthracene as the organic matrix and 0.1%
AgTFA. Calibration was achieved using poly(ethylene glycol) (PEG)
with 2-5000 Mn. Elemental analysis was performed by Warwick
Analytical Services or Medac Ltd.
tert-Butylstyrene, styrene, all R-olefins, silanes, and additional mono-
mers were purchased from Aldrich and stirred over CaH2 for 48 h and
then vacuum-distilled and stored under argon. Methylaluminoxane
(10% (w/v) in toluene) was purchased from Witco.
High-temperature GPC was run at RAPRA, utilizing a Polymer
Laboratories GPC220 with a PLgel guard column and two 30 cm Mixed
Bed B columns in 1,2,4-trichlorobenzene at 160 °C. Room temperature
GPC analysis was carried out on a Varian 390LC with PLgel mixed
D column in THF/2% triethylamine. Thermal analyses were carried out
on a Perkin-Elmer PC7 series system. Sample masses in each case were
ca. 3 mg, and the samples were purged with dinitrogen.
Crystallography. Crystals were coated in inert oil prior to transfer
to a cold nitrogen gas stream on an Oxford Diffraction Gemini four-
circle system with Ruby CCD area detector and held at 100(2) K with
the Oxford Cryosystem Cryostream Cobra. The structure was solved by
direct methods (SHELXTL) with additional light atoms found by
Fourier methods. Hydrogen atoms were added at calculated positions
and refined using a riding model with freely rotating methyl groups.
General Procedure for Polymerizations with Monitored
Gas Uptake. Polymerizations were carried out in a jacketed 500 mL
vessel equipped with a Pt thermocouple and buret system for the
monitoring of gas delivery at a fixed pressure. Toluene, comonomer,
and MAO (1000 equiv) were charged into a measuring ampule and
transferred by cannula into the jacketed vessel. The argon atmosphere
was replaced by ethene at 1.2 bar. The vessel was heated by a
thermostatic recirculator unit. The precatalyst was dissolved in toluene
no more than 5 min prior to use and injected into the jacketed vessel to
begin the polymerization. Reactions were terminated by addition of
methanol (5 mL), and the polymer was precipitated by pouring into
Figure 1. Bis(salicylaldimine)zirconium precatalysts 1-5.
homopolymer blends are a likely result. With non-PS producing
catalysts, production of P(E/S) is hampered due to the adverse
effects of styrene on the catalyst involved. For example, the classic
metallocene Cp2ZrCl2/MAO system is essentially inactive for
styrene homopolymerization, and correspondingly addition of
styrene comonomer to an ethene polymerization results in a
dramatic decrease in activity despite there being only minor
incorporation of styrene into the polymer formed.19 The con-
strained geometry catalyst (CGC) [(Me2SiCp0NtBu)TiCl2]/
MAO also suffers from addition of styrene, but less so than for
Cp2ZrCl2. Copolymers with up 35 mol % styrene have been
recorded when using this catalyst system in the presence of
extremely high styrene concentrations,20,21 while recent mod-
ifications to the Cp ring resulted impressively in a 31 mol %
styrene copolymer under more conventional conditions.22
Both experimental and theoretical approaches to the styrene
problem have indicated that this adverse effect is the result of a
2,1 insertion of styrene into a growing polymer chain. The
resulting benzylic species is resistant to further monomer inser-
tion as a result of coordination of the arene to the cationic metal
center and is regarded as a “dormant state” (Scheme 1).20 The
contrast with PS producing catalysts such as CpTiCl3 is inter-
esting, however; here, 2,1 insertion of styrene is the norm, and
high activity is evident.
The use of substituted styrene monomers can have an effect on
the rate or insertion mode of the monomer into the growing
polymer chain.23,24 Oliva and co-workers have shown in a model
system that the ratio of styrenic 1,2 to 2,1 insertions varies with the
electronic effect of para-substitution.25 We have exploited this effect
and shown that tert-butylstyrene (TBS) readily forms ethene-co-
TBS polymers with up to 44 mol % comonomer at low TBS
concentrations using Ti CGC.26 Furthermore, while the zirconium
salicylaldimine systems (Figure 1) developed by Fujita27-29 and
Coates30-32 are inactive in the presence of styrene,33 precatalysts
1-3 in combination with MAO produce unimodal ethene-co-TBS
polymers with very high activity and long catalyst life.34
Here we will describe our discovery of very high and un-
expected TBS homopolymerization activity by zirconium
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MeOH/5% HCl(aq). The sample was filtered on a glass sinter and dried
in a vacuum oven at 70 °C for 16 h.
was transferred via filter cannula directly to a Schlenk vessel charged with
ZrCl4 THF2 (0.31 g, 0.81 mmol) and cooled to -78 °C. After stirring
3
General Procedure for Schlenk-Based Polymerizations. A
Schlenk vessel equipped with stirrer bar was charged with the required
comonomers and toluene under argon. A toluene solution of first
[Ph3C][B(C6F5)4] and then triisobutylaluminum (AliBu3) was added
via cannula. The reaction mixture was stirred and warmed to reaction
temperature using an aluminum heating block. The precatalyst was
dissolved in toluene no more than 5 min prior to use and was added via
syringe. If required, the Schlenk vessel was carefully evacuated and
refilled twice with H2(g) at 1.1 bar. Reactions were terminated by
addition of methanol (5 mL), and the polymer was precipitated by
pouring into MeOH/5% HCl(aq). The sample was filtered on a glass
sinter and dried in a vacuum oven at 70 °C for 16 h.
overnight, the solvent was removed in vacuo. The residue was dissolved
in hot toluene, filtered, and allowed to cool to room temperature. The
resulting precipitate was removed by filtration and washed in cold
pentane, to yield an off white solid (220 mg, 38%). 1H NMR (400 MHz,
CD2Cl2): δ 7.26 (4H, s, Ar), 7.15 (1.5H, m, toluene Ar), 4.29 (2H, d,
2J = 8.5 Hz, COCH2), 3.82 (6H, s, OCH3), 2.36 (1.5H, s, toluene CH3),
1.59 (6H, s, CH3), 1.57 (18H, s, tBu), 1.20 (6H, s, CH3). 13C NMR (100
MHz, CD2Cl2): δ 169.2 (CdN), 157.0, 152.6, 141.8 (Ar q), 129.0,
128.5 (toluene), 123.0 (Ar), 115.6 (Ar q), 109.4 (Ar), 79.4 (CH2), 70.3
(CMe2), 56.0 (OCH3), 35.5 (tBu q), 30.0 (CMe3), 29.0 (CH3), 26.5
(CH3), 21.5 (toluene). Anal. Calcd for C32H44Cl2N2O6Zr 1/2(C7H8)
3
C: 56.04, H: 6.36, N: 3.68. Found C: 56.26, H: 6.43, N: 3.55. MS
(MALDI) m/z: 714.05 [M]þ, 679.09 [M - Cl]þ.
Synthesis. Precatalysts 1-3 and 5, proligands HL,1-3,5,6 and
precursors were synthesized as previously reported,34,36 as was zirco-
nium tetrabenzyl.37 Ligands HL4 and H2L738 and precatalysts 4, 6,36 and
H2L7. Proligand HL2 (1.10 g, 3.88 mmol) was charged into a round-
bottom flask and purged with argon for ca. 5 min. Dry THF (80 mL) was
added, followed by LiAlH4 (0.73 g, 19.4 mmol), and the solution was
stirred for 1.5 h. Diethyl ether was added, and the solution was cooled to
-78 °C. Ice was carefully added, and the solution was allowed to warm
to ambient temperature, with stirring. Further diethyl ether (100 mL)
and NaOH(aq) (1 M, 100 mL) were added; the organic layer was
separated and washed with water and then dried over Na2SO4. The
diethyl ether was removed in vacuo, and the residue was dissolved in
methanol. The solution was cooled to -30 °C overnight, and the
resulting white crystals were collected by filtration (0.795 g, 71%). 1H
NMR (400 MHz, CDCl3): δ 8.21 (1H, s, OH), 7.18 (2H, t, 3J = 7 Hz,
Ar), 6.85 (1H, t, 3J = 7 Hz, Ar), 6.80 (1H, d, 3J = 3 Hz, Ar), 6.79 (1H, s,
NH), 6.51 (1H, d, 3J = 3 Hz, Ar), 4.28 (2H, d, 3J = 6 Hz, CH2N), 3.70
(3H, s, OMe), 1.33 (9H, s, tBu). 13C NMR (100 MHz, CDCl3): δ 152.3,
149.7, 147.2, 138.6 (Ar q), 129.4 (Ar), 123.5 (Ar q), 120.9, 116.1, 113.3,
111.1 (Ar), 55.7 (OMe), 49.6 (CH2), 35.0 (tBu q), 29.5 (tBu). Anal.
Calcd C: 75.76, H: 8.12, N: 4.91. Found C: 75.80, H: 8.17, N: 4.82. MS
(EI) m/z: 286.1 [M]þ.
7
38 were synthesized as reported below.
HL4. 2-Hydroxy-3-tert-butylbenzaldehyde (2.02 g, 11.35 mmol) and
anisidine (2.09 g, 17.0 mmol) were dissolved in methanol (40 mL) and
heated to reflux for 12 h. The solution was cooled to 4 °C, and the pale
orange powder precipitate was collected by vacuum filtration (1.15 g, 35%).
1H NMR (400 MHz, CDCl3): δ 13.97 (1H, s, OH), 8.59 (1H, s, CHN),
7.30 (1H, s, Ar), 7.28 (3H, m, Ar), 7.02 (1H, d, 3J = 2 Hz, Ar) 6.97 (1H, s,
Ar), 6.95 (1H, s, Ar), 3.86 (3H, s, OMe), 1.49 (9H, s, tBu). 13C NMR (100
MHz, CDCl3): δ161.3 (CN), 158.7, 141.4, 137.6 (Ar-q), 130.9 (Ar), 130.6
(Ar-q), 130.0 (Ar), 122.27 (Ar), 119.0 (Ar-q), 114.6 (Ar), 55.5 (OMe),
34.9 (tBu q), 29.4 (tBu). Anal. Calcd C: 76.29, H: 7.47, N: 4.94. Found C:
76.29, H: 7.31, N: 4.49. MS (CI) m/z: 284.4 [M þ H]þ.
L4 ZrCl2 (4). HL4 (0.90 g, 3.17 mmol) and NaH (excess) were
2
charged into a Schlenk vessel and cooled to -78 °C. Dry THF (40 mL)
was added, and the solution was stirred at ambient temperature for 18 h.
The resulting solution was filtered via cannula directly onto
ZrCl4 THF2 (0.54 g, 1.42 mmol) in dry THF (20 mL) at -78 °C.
3
L7ZrBn2 (7). H2L7 (104.6 mg, 0.37 mmol) and ZrBn4 (168.2 mg,
0.37 mmol) were charged into a Schlenk vessel under argon and then
cooled to -78 °C. DCM (20 mL) was added, and the solution stirred for
1 h. The solvent was removed in vacuo, and the residue was washed with
cold pentane. The resulting light yellow solid (165 mg, 80%) was stored
at -30 °C under argon to avoid decomposition. 1H NMR (400 MHz,
CD2Cl2): δ 7.34 (2H, t, 3J = 8 Hz, Ar), 7.26 (1H, d, 3J = 7 Hz, Ar), 7.14
(2H, m, Ar), 7.06 (3H, m, Ar), 6.83 (2H, t, 3J = 7 Hz, Ar), 6.66 (2H, m,
Ar), 6.53 (3H, m, Ar), 6.34 (2H, m, Ar), 5.31 (1H, s, DCM), 4.56, 3.54
(1H, d, 2J = 17 Hz, CH2N), 3.79 (3H, s, OCH3), 2.66, 2.31 (1H, d, 2J =
11 Hz, CH2Ph), 1.75, 1.55 (1H, d, 2J = 11 Hz, CH2Ph), 1.25 (9H, s, tBu).
13C NMR (100 MHz, CD2Cl2): δ 152.2, 151.8, 149.0, 140.1, 136.9,
135.4, 129.0 (Ar q), 130.3, 129.9, 128.8, 128.5, 127.6, 126.5, 126.0,
125.7, 125.2, 121.4, 112.1 (Ar), 67.5, 64.0 (CH2Ph), 55.5 (OCH3), 53.2
(DCM), 50.8 (CH2N), 34.5 (tBu q), 28.9 (tBu). Anal. Calcd for
After stirring overnight, the solvent was removed in vacuo, yielding a
yellow solid. This was further purified via sublimation (5 ꢀ 10-6 mbar,
260 °C) to give 0.7 g, 68%. Crystals suitable for X-ray diffraction were
obtained from DCM at -30 °C. 1H NMR (400 MHz, -60 °C,
3
CD2Cl2): δ 8.14 (2H, s, CHN), 7.46 (2H, d, J = 8 Hz, Ar), 7.14
(2H, d, 3J = 8 Hz, Ar), 7.00 (4H, d, 3J = 9 Hz, Ar), 6.86 (2H, t, 3J = 8 Hz,
Ar), 6.59 (4H, d, 3J = 9 Hz, Ar), 3.65 (6H, s, OMe), 1.40 (18H, s, tBu).
13C NMR (100 MHz, Pyr): δ 137.4, 136.0, 135.8, 126.4, 116.0 (Ar),
57.11 (OMe), 36.8 (tBu q), 31.6 (tBu). Solubility of this complex is poor
and quaternary aromatic peaks were not visible. Anal. Calcd for C36H40
Cl2N2O4Zr C: 59.49, H: 5.55, N: 3.85. Found C: 58.68, H: 5.39, N: 3.52.
MS (MALDI) m/z: 689.1 [M - Cl]þ.
L6 ZrCl2 (6). A Schlenk vessel equipped with stirrer bar was
2
charged with HL6 (0.40 g, 1.61 mmol) and NaH (0.077 g, 3.24 mmol)
and cooled to -78 °C. Dry THF (30 mL) was added, and the solution
was allowed to warm to room temperature with stirring. After 4 h,
stirring was stopped and the precipitate allowed to settle. The solution
C32H35NO2Zr 1/2(CH2Cl2) C: 65.87, H: 6.11, N: 2.37. Found C:
3
65.84, H: 6.15, N: 2.37. MS (MALDI) m/z: 538.63 [M - Me]þ.
Table 1. Initial Polymerization Resultsa
run
cat.
cat. (mol)/10-6
monomer system
yield (g)
mass prodb
TBS % conv
PDI
66
TM (°C)
1
2
3
4
5
6
1
2
3
2
2
2
9.00
7.02
8.43
6.88
8.12
4.54
E/TBS
E/TBS
E/TBS
E/TBS
E/St
1.8
12.0
1.7
200.0
1710.2
201.7
3750.5
49.3
n/d
40
96.5, 125.7
91.0, 124.4
109.1, 117.1
112.7, 119.3
n/d
41
4.3
0.4
n/d
TBS
0.1
22.0
n/d
a Conditions: [Ph3C][B(C6F5)4] = 1.1 equiv to Zr; AliBu3 = 100 equiv to Zr; ethene at 1.2 bar; [TBS] = 0.07 M; volume = 100 mL (runs 1-5) or 50 mL
(run 6); run time = 60 min (except run 44, 10 min); T = 40 °C. b In kg-polymer/(mol-catalyst h).
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’ RESULTS AND DISCUSSION
regular polymer. Figure 3b shows the spectrum of ethene-co-TBS
produced by 2/MAO, indicating isolated TBS units (Tδδ, SRδ/
SRγ, and Sβδ at 45.0, 36.5, and 27.5 ppm, respectively).
Also visible are the peaks associated with a terminal CH3 from
PE (14.0 ppm) and the CH2 adjacent to this (22.3 ppm).
Figure 3c is the spectrum of polymer formed with
2/AliBu3/[Ph3C][B(C6F5)4] (run 4). Here the Tδδ peak is
not present. Instead, we see the Tββ peak at 40.0 ppm, indicative
of sequential TBS units. Unlike Figure 3a, this peak is broad and
its associated SRR peak at 43.1 ppm is lost almost entirely in the
baseline, suggesting atactic polymer. The few remaining peaks
are readily assigned as belonging to either from P(TBS) (31.5
Ethene/tert-Butylstyrene Copolymerizations. We have
previously shown that salicylaldimine catalysts 1-3 on activation
with MAO cleanly gave E/TBS copolymers.34 In contrast, on
activation of the same precatalysts with AliBu3/[Ph3C]
[B(C6F5)4] (Table 1 runs 1-4) led to production of mixtures
of PE and P(TBS) (vide infra).
Catalyst 2 (run 2) was substantially more active and stable
than catalysts 1 and 3 (runs 1 and 3), giving continuous ethene
uptake over a 1 h period (Figure 2). Fractionation of the products
by Soxhlet extraction into pentane failed to separate the compo-
nents sufficiently, and GPC analysis returned traces with broad,
multimodal distributions. The observation of two distinct melt-
ing points for sample 4 is consistent with a mixture of compo-
nents in the system. The lower TM can be assigned to p(TBS)
(vide infra), and the higher TM is consistent with PE.
t
t
and 34.2 ppm, Bu (CH3)3 and Bu quaternary carbon, re-
spectively) or PE (29.5 ppm, Sδδ). No peaks for ethene/TBS
copolymers are observed.
Thus, a combination of NMR, DSC, and GPC data point
toward a the formation of a blend of PE and P(TBS). Evidently
then, the catalyst formed from 2/MAO has very different
selectivity to that formed from 2/AliBu3/[Ph3C][B(C6F5)4].
In order to exclude the possibility that the PE contaminant was
being produced by the system at low concentrations of TBS
toward the end of the 1 h reaction period, run 4 was conducted
for 10 min. Analysis of the crude product and the Soxhlet
fractions by NMR and DSC indicated that the polymer composi-
tion was broadly similar to that of run 2.
Analysis of the 13C NMR spectrum of polymer produced in
run 4 shows several striking differences compared with that of the
11 mol % ethene-co-TBS produced with 2/MAO.
Figure 3a shows the 13C NMR spectrum of high molecular
weight, syndiotactic P(TBS) produced using CpTiCl3/MAO in
our laboratory. The SRR and Tββ peaks (at 43.6 and 40.0 ppm,
respectively) are sharp and solitary, indicating a highly stereo-
Run 5 shows that styrene is inactive in this system in place of
TBS; ethene uptake dropped rapidly to near zero, and only traces
of polymer were obtained from the system. This result corre-
sponds with previous observations that the relative rates of the
various styrenic monomer insertions are strongly affected by the
substituents on the styrene ring, with alkylated styrenes favoring
1,2 insertion.25,26,41 A number of further control experiments
were carried out, and it was found that all three components
(precatalyst 2, AliBu3, and [Ph3C][B(C6F5)4]) are required to
furnish a catalytic system since removal of any one led to a
complete loss of activity. Most interestingly, when the polymer-
ization was repeated in the absence of ethene, very little polymer
was produced (run 6). These results also exclude the possibility
of a cationic/radical mechanism mediated by trityl or a Lewis
acid-catalyzed process (via AliBu3).
tert-Butylstyrene Homopolymerizations. Given that
ethene is required to produce a catalytic system, but that a
homopolymer of TBS is the major mass product, we considered
that ethene may be acting as a chain transfer agent (vide infra)
and might be conveniently replaced by a monomer that would
Figure 2. Ethene uptake profiles for runs 1-5.
Figure 3. 13C NMR spectra of P(TBS) produced by (a) CpTiCl3, (b) ethene-co-TBS produced with 2/MAO,34 and (c) 2/AliBu3/[Ph3C][B(C6F5)4]
(run 2), with assignments.19,21,39,40
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Table 2. P(TBS) Polymerization Results with Catalyst 2a
run
cat. (mol)/10-6
monomer system
yield (g)
mass prodb
TBS % conv
Mn
PDI
TM (°C)
7
3.44
3.43
4.27
3.58
5.50
3.71
3.34
2.98
3.03
TBS/Hex
TBS/Hex
TBS/Hex
TBS/H2(g)
TBS/D2(g)
TBS/Et3SiH
TBS/Pent
TBS/St
4.1
5.0
0.1
4.2
5.1
0.2
1.1
7.3
6.3
1192.0
1453.7
23.4
76
3194
4028
2284
4357
4977
n/d
2.8
2.8
1.8
3.2
2.6
n/d
2.5
3.2
n/d
119.5
127.4
8
87
9
n/d
77
10
11
12
13
14
15
1174.1
926.7
53.9
124.5
137.1
n/d
87
n/d
21
329.3
2447.5
2079.0
3320
2556
n/d
121.1
104.0
140.5
95
TBS/DVB
92
a Conditions: [Ph3C][B(C6F5)4] = 1.1 equiv to Zr; AliBu3 = 100 equiv to Zr; ethene at 1.2 bar; [TBS] = 0.07 M; volume = 50 mL; run time = 60 min; T =
40 °C. b In kg-polymer/(mol-catalyst h).
Figure 4. MALDI spectra of polymer obtained from run 7.
not itself also be homopolymerized in this system. We selected
1-hexene for this purpose, given that only titanium salicylaldi-
mine systems activated with AliBu3/[Ph3C][B(C6F5)4] had
been shown to homopolymerize this monomer.42
conventional comonomer. As we have described above, benzylic
dormant species are prevalent in E/S copolymerizations, and
Chung has exploited this in the production of p-methylstyrene-
terminated PE simply by addition of dihydrogen.44 This pro-
duces an alkyl-terminated polymer and regenerates the catalyst
by the mechanism shown in Figure 6. We were thus pleased to
find that under 1 atm of H2, with no additional olefin “promoter”,
P(TBS) was formed (run 10, Table 2). This run gave 4.2 g of free-
flowing polymer and a conversion of 80% after 1 h, but interest-
ingly we were unable to detect a loss of partial pressure of H2
during the run.
GPC showed also that despite the presence of dihydrogen the
homopolymer produced was very similar in Mw to that produced
above using hexene as a promoter. 13C NMR spectra also show
olefinic end groups (vide infra). Replacing H2 with D2 gave a
yield of 5.1 g of polymer (run 11), comparable to that obtained in
runs 7, 8, and 10. The MALDI spectra of P(TBS) from runs 10
and 11 indicated only vinyl-terminated polymer with no detect-
able incorporation of deuterium.
Run 7 (Table 2) shows the effect of adding 1-hexene to a TBS
homopolymerization by 2/AliBu3/[Ph3C][B(C6F5)4]. After 1 h
1
at 40 °C, 76% of the TBS had been converted. H NMR
suggested that P(TBS) had been formed exclusively. MALDI
mass spectrometry (Figure 4) however showed two polymers:
(i) P(TBS) with peaks spaced 160 Da apart as expected and (ii)
P(TBS) with mass corresponding to a single unit of hexene
having been incorporated—peaks spaced 160 Da apart but offset
from P(TBS) by 84 Da (mass of hexene). On the basis of the
masses observed, all polymers observed contain one in-chain
double bond (vide infra).
Lowering the concentration of 1-hexene in the system (run 8,
0.1 equiv to TBS) gave P(TBS) only (within the detection limits
of the MALDI experiment). Increasing the concentration of
hexene (run 9, 10 equiv to TBS) lowered both the yield and the
DoP but increased the proportion of hexene-terminated chains.
Figure 5 shows MALDI spectra of both run 7 and run 9. In the
spectra of run 7 the intensities of the peaks attributed to hex-
P(TBS) are lower than those of P(TBS). In the spectra of run 9,
this is reversed.43
The use of silanes in olefin polymerization has been previously
shown to produce end-capped PE and PS with both lanthanide
and group IV transition metal catalysts.45,46 Run 12 used
triethylsilane in place of hexene/H2/D2. In accordance with
previous results,47 a significantly lower productivity rate was
recorded than with either hexene, H2, or D2; however, Et3Si
was incorporated onto the end of some P(TBS) chains. MALDI
Evidently then, hexene is in some way involved with the
production of catalytic centers, i.e., as a promoter rather than a
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Figure 5. MALDI spectra of polymer obtained from runs 7 and 9.
formed in the presence of ethene (vide supra) was of lower
molecular weight than those formed in the presence of hexene or H2.
Mechanism. We will begin by proposing a mechanism to
account for our observations of the TBS homopolymerization by
2/AliBu3/[Ph3C][B(C6F5)4] in the presence of H2 (Scheme 2).
Cationic species A containing a polymeryl group (p) and
coordinated TBS undergoes 1,2-insertion (a1,2) to give B which
may either add further TBS to regenerate A or may, given the
presence of a free coordination site at the metal, undergo
β-elimination to give the 2-styrenyl-terminated polymer P(TBS)-
2-sty. A may also undergo 2,1-insertion (a2,1) to give benzylic
species C. This species is unlikely to undergo β-elimination or
insertion since it does not have a suitable free coordination site
for either of these processes (a dormant state; vide supra).
Coordination of the arene as shown also orients the β-hydrogen
atoms so that they may not coordinate to the metal to form the
necessary transition state. Nevertheless, H2 (or D2) can regen-
erate the catalytic species through hydrogenolysis of the dormant
state C (step c), releasing a P(TBS) chain. The coproduct from
step c, hydride D, adds and inserts TBS (d) to regenerate A.
Without H2 (run 6) ca. 100 mg of polymer is produced before
the catalyst becomes dormant or otherwise inactive. This equates
to several polymer chains being produced through bβH, i.e., the
rate of bβH . a2,1, making P(TBS)-2-sty the major product, and
P(TBS)-2H the minor. End-group analysis of the 13C NMR
spectra (see Supporting Information) shows minor peaks at
111.5 and 145.3 ppm (CH2 and CCH2, respectively), corre-
sponding to polymer produced by bβH (the major product).
Alkyl peaks corresponding to the minor component P(TBS)-2H
are not seen.
Figure 6. Chain transfer to H2 exemplified in the Chung system.44
of the resulting polymer shows two sets of peaks as with TBS/
hexene, with an offset of 115 Da from each other (Figure 7).
1H NMR shows no ethyl peaks, indicating that incorporation of
Et3SiH is low. Polymerizations were also undertaken with
vinyltrimethylsilane and diphenylsilane, though neither allowed
the formation of P(TBS).
In an attempt to exploit the single monomer addition for use in
postpolymerization functionalization reactions, copolymeriza-
tions with several hexene monomers were run: 5-hexenyl acetate,
5-hexen-2-one, 6-bromo-1-hexene, and 1,5-hexadiene. Of these,
only the 1,5-hexadiene/TBS copolymerization yielded polymer
(ca. 1.5 g). MALDI of this sample showed only peaks corre-
sponding to P(TBS); i.e., no hexadiene addition was seen.
Further comonomers tried included 1-pentene, 1-heptene,
1-octene, 1-dodecene, divinylbenzene (DVB), and styrene. Un-
expectedly, neither heptene, octene, nor dodecene showed
addition to the P(TBS) formed, which was of low yield. Pentene
fared better (run 13), producing 1.1 g of polymer, though
MALDI suggested that there were fewer pentene-terminated
chains than hexene-terminated chains under the same condi-
tions. Polymerization of styrene/TBS was surprisingly successful
(run 14), forming P(TBS) with ca. 18 mol % styrene incorpo-
Our proposed mechanism for the hexene-cocatalyzed process
(Scheme 3) is necessarily more complex. Species A undergoes
propagation by 1,2-insertions of TBS (a1,2) with the possibility
of termination by β-elimination (bβH) to give the observed
P(TBS)-2-sty or 2,1 “mis-insertion” (a2,1) to give C, a “dormant
state” as before. At step cBHT, 1-hexene—which is not homo-
polymerized by this system (vide supra) but is rather less
sterically demanding and more nucleophilic than TBS—ap-
proaches the dormant state and initiates a β-hydrogen transfer
1
rated according to H NMR spectra. This was confirmed by
MALDI which showed P(TBS) chains with 1-3 styrene units
each. Run 15 used 2 mol % DVB/TBS with which P(TBS) was
formed in good yield, but without DVB addition according to
MALDI. The high TM for this run thus suggests a higher Mn,
similar to that of 11, rather than cross-linking due to DVB.
The melting points shown for runs 7, 8, 10, and 11 generally
increase with increased Mn. This may suggest that the p(TBS)
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Figure 7. MALDI spectra of polymer obtained from run 12.
can then begin polymerization of TBS again via step d. Alter-
natively at E, a hexene-containing polymer chain is produced by
addition and 1,2-insertion of TBS (e1,2) to give A0. This chain is
subsequently propagated through B0 via a01,2. TBS mis-insertion
(step a02,1) gives dormant state C0 which, being resistant to
β-elimina0tion, undergoes β-hydride transfer to monomer as
before (c BHT) to re-form E and eliminate hexyl-initiated and
1-styrenyl polymer hex-P(TBS)-1-sty.
Scheme 2. Proposed Mechanism of P(TBS) Formation
Involving Chain Transfer to Dihydrogen
In this mechanism, the molecular weight of the -1-sty polymers
is determined by the relative rates of a1,2 to a2,1 and a01,2 to a02,1
.
Since species A and A0 are identical in the region of the metal
center following propagation, we would fully expect the rate
constants for monomer insertions to be the same, i.e., k(a1,2) =
k(a01,2) and k(a2,1) = k(a02,1). Hence, the observation of a similar
molecular weight distribution, whether the chain contains hexene
or not, is consistent with this mechanism. Similarly, the molec-
ular weights of the -2-sty pol0ymers are determined by the ratios of
a1,2 to bβH and a01,2 to b βH; again, as species B and B0 are
identical, molecular weights for -2-sty polymers will be the same.
The ratio of hexyl- to non-hexyl-terminated polymer chains is
determined by the relative rates of steps eβH and e1,2, with the
rate of eβH . e1,2 as indicated by the lack of resolvable hexyl
peaks in either 13C or 1H NMR.
From the mechanism outlined in Scheme 3 we would expect a
higher hexene concentration (cf. run 7 and run 9, 1, and 10 equiv
of hexene, respectively) to produce significantly more hexyl-
terminated polymer, and this was confirmed by MALDI spectro-
metry (Figure 5). Figure 8 shows GPC traces obtained for
polymer from runs 7 and 9. The polymer from run 9 has a lower
PDI (1.4) compared with that of run 7 (2.8), and the main peak
corresponds to a shoulder of run 7. It is thus tentatively suggested
that the major peak in run 7 is that of P(TBS)-2H while the major
peak in run 9 is that of hex-P(TBS).
It is worth noting that salicylaldimine catalysts/MAO give
multimodal GPC traces for PE. This has been attributed to
multiple catalytic isomers present in the reaction,49-51 though
our catalyst studies suggest this is not the case here (vide infra).
We also note our previous work showed that ethene/TBS
copolymers produced with 2/MAO were formed by a single site
mechanism, with a PDI of 2.34
to monomer step. This releases the observed P(TBS)-1-sty and
generates a hexyl species E. β-Hydride elimination at step eβH re-
releases 1-hexene and forms a metal hydride D.48 This species
We also note that the dominant 1,2 propagation steps in these
mechanisms is likely to lead to atactic or syndio-rich polymer.
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Scheme 3. Mechanism Outline of Chain Transfer to Monomer Providing P(TBS) with and without Hexene Termination
ARTICLE
NMR spectra of the products are consistent with the former,
suggesting a sterically unencumbered catalytic site (vide infra). In
Figure 9 we have plotted TM versus Mn for authentic homo-
polymers described in this work. TM appears to reach a plateau
well below the melting points of syndiotactic and isotactic
p(TBS) (310 and 308 °C, respectively).8
Catalyst Modifications. After our initial success with runs 7
and 10, TBS/H2 homopolymerizations with catalysts 1 and 3
were initially undertaken alongside catalyst 2 (runs 16 and 17,
Table 3). While no polymer precipitated in methanol as with run
10, organic work-up (DCM/1 M HCL(aq)) yielded several grams
of low weight P(TBS). The melting points for these two
polymers are also noticeably lower than run 10. This suggests
the OMe group para to the O-Zr is important for formation of
higher polymers either through a direct interaction with the
cocatalyst or through its electron donation into the phenyl ring.
To probe this, we synthesized zirconium dichloride precatalysts
based on 4 and 5 (Figure 1) (runs 18-23, Table 3). Precatalyst 4
(L4 ZrCl2) was synthesized with a methoxy group para to the
2
imine nitrogen. The molecular structure was determined by
X-ray diffraction (Figure 10). The asymmetric unit contains half
a complex composed of a phenoxyimine ligand and a chloride
ligand attached to half a Zr atom which lies on a 2-fold axis. The
angle between mean planes through the methoxyphenyl group
and the chelate ring is 49.69(4)°. The angle between mean planes
through the two chelate rings is 61.05(3)°. There is some
possible π stacking between methoxy arene and phenoxide with
closest C-C contact of 3.3237(23) Å and centroid-centroid
distance of ca. 3.78 Å, but the angle between least-squares planes
of these rings is rather high at ca. 20.9°.52 Nevertheless, there
does not seem to be any steric reason why the rather “flattened”
structure as shown in Figure 10 is adopted, with N(1)-Zr-
N(10) of 72.17(6) Å and corresponding Cl(1)-Zr(1)-Cl(10) of
100.95(2).
Perhaps as a result of this unusual structure, this catalyst was
found to give only a modest yield of ethene homopolymer
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(run 18). 13C NMR spectra of the polymer produced using 4 in
the ethene/TBS run 19 showed the sample to have a low
incorporation of TBS (ca. 5%) with isolated TBS units. Corre-
spondingly, this catalyst did not homopolymerize TBS under
H2 (run 20).
Precatalyst 5 (L5 ZrCl2) was synthesized with a tert-butyl
2
group para to the O-Zr unit. This catalyst system gives low
yields of PE (run 21). Interestingly, while TBS/H2 homopoly-
merization produced only traces of polymer with this catalyst
(run 23), TBS/ethene copolymerization produced P(TBS) (ca.
46% conversion) and traces of PE (run 22).
Nature of the Catalytic Site. Previous work on salicylaldi-
minate systems has shown that replacing MAO with a combina-
tion of AliBu3/[Ph3C][B(C6F5)4] can have profound effects on
the polymers produced. Zirconium salicylaldiminate catalysts
activated with MAO produce low-weight PE, whereas when
activated with AliBu3/[Ph3C][B(C6F5)4] high-molecular-weight
PE is formed.53 This catalyst system also produces polypropene
(PP), unlike its MAO equivalent. Many of these changes are
thought to be due not to the presence of a [B(C6F5)4]-
counterion, but to the effect of aluminum alkyls on the pre-
catalyst. Reduction of salicylaldimines to their correspond
ing amines has been shown to occur in situ upon addition of
Figure 8. GPC spectra of selected polymers.
Figure 10. Molecular structure of 4 (H atoms omitted). Thermal ellipsoids
shown at 50% probability. Selected bond lengths (deg) and angles (Å):
Zr(1)-O(1) 1.9902(10), Zr(1)-N(1) 2.3480(13), Zr(1)-Cl(2)
2.4325(4), O(1)-Zr(1)-O(1)0 167.59(6), N(1)-Zr(1)-N(1)0
72.17(6), Cl(2)-Zr(1)-Cl(2)0 100.95(2).
Figure 9. TM vs Mn for selected TBS polymers.
Table 3. Polymerizations with Functional Group-Modified Catalystsa
run
cat.
cat. (mol)/10-6
monomer system
yield (g)
mass prodb
TBS % conv
Mn
PDI
TM (°C)
16
17
18
19
20
21
22
23
1
3
4
4
4
5
5
5
3.30
5.83
7.02
6.88
4.27
7.86
6.44
4.64
TBS/H2(g)
TBS/H2(g)
ethene
2.1
3.4
1.5
3.6
0.0
1.5
4.7
0.4
636.0
950.5
213.8
523.3
0.0
36
2139
2276
1.9
2.0
63.7
73.5
56
n/a
5
120.8
91.3
E/TBS
TBS/H2(g)
ethene
n/a
n/a
46
190.9
729.7
86.3
114.9
E/TBS
88.9, 123.6
TBS/H2(g)
n/d
a Conditions: [Ph3C][B(C6F5)4] = 1.1 equiv to Zr; AliBu3 = 100 equiv to Zr; ethene at 1.2 bar; [TBS] = 0.07 M; volume = 100 mL (runs 18, 19, 21, and
22) or 50 mL (runs 16, 17, 20, and 23); run time = 60 min.; T = 40 °C. b In kg-polymer/(mol-catalyst h).
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Table 4. Polymerizations with Salicyloxazoline- and Salicylamine-Based Catalystsa
run
cat.
cat. (mol)/10-6
monomer system
yield (g)
mass prodb
TBS % conv
Mn
n/d
PDI
TM (°C)
24
25
26
27
28
29
30
31
2
6
6
6
7
7
7
7
4.68
6.85
7.13
3.50
9.01
5.22
4.68
5.04
E/TBS
2.2
3.9
3.0
0.0
0.3
0.0
4.6
2.3
469.8
568.9
420.5
0.0
40
n/d
n/d
n/d
127.3, 152.6
128.5
ethene
n/a
3
n/d
n/d
E/TBS
126.6
TBS/H2(g)
ethene
n/a
n/a
n/a
82
33.3
n/d
n/d
n/d
E/TBS
1.9
TBS/H2(g)
TBS/Hex
982.2
13 899
6745
1.6
2.1
154.6
142.0
483.8
41
a Conditions: [Ph3C][B(C6F5)4] = 1.1 equiv to Zr; AliBu3 = 100 equiv to Zr; ethene at 1.2 bar; [TBS] = 0.07 M; volume = 100 mL (runs 24-26, 28, and
29) or 50 mL (runs 27, 30, and 31); run time = 60 min; T = 40 °C. b In kg-polymer/(mol-catalyst h).
TBS (run 26) a copolymer was produced (ca. 3 mol % TBS,
isolated TBS units by 13C NMR and further suggested by the
high TM). This latter behavior is the same as that of 2/MAO.
Correspondingly, no polymer is formed during attempted TBS
homopolymerization by 6/AliBu3/[Ph3C][B(C6F5)4] under an
atmosphere of dihydrogen (run 27).
The above results are consistent with a reduced Schiff base
catalyst system being produced from 2. We thus synthesized 7
(L7ZrBn2), a new member of a class of salicylamido zirconium
compounds introduced by Gibson.38 We first confirmed Gib-
son’s reports38,58 that the aluminum-free catalyst system
7/[Ph3C][B(C6F5)4] is inactive for PE (run 28, Table 4) and
then showed that it is highly active for TBS polymerization in the
presence of H2 or hexene (runs 30 and 31, respectively).
Interestingly, P(TBS) is not formed in the presence of ethene
(run 29). Productivities are comparable to those of 2/AliBu3
/[Ph3C][B(C6F5)4] (compare runs 10/30 and 7/31), as are the
molecular weight and PDI of the polymers produced.
’ CONCLUSIONS
In the presence of AliBu3/[Ph3C][B(C6F5)4] the zirconium
precatalysts 1-3 are converted to a catalytic species which act in
essentially the same manner as the aluminum-free 7/[Ph3C][B-
Figure 11. Salicyloxazoline and salicylamido complexes.
AliBu3 or in the case of metal dibenzyl species through a 1,2
(C6F5)4] system. The implication is that the catalyst in both cases
migratory insertion of a benzyl group from the metal center.54,55
Furthermore, Pellecchia and co-workers have synthesized com-
is closely related to the propagating cationic species 8. The lack of
activity in the absence of added aliphatic monomer or dihydro-
gen is accounted for by two related mechanisms. Hexene
awakens a benzylic dormant state by a familiar β-hydrogen
transfer to monomer (BHT) process,59,60 and this leads to the
observed products (some containing one hexene unit, and some
none, plus two different unsaturated end groups). Dihydrogen
takes part in a “chain transfer to hydrogen” mechanism, allowing
catalyst regeneration (Scheme 2).
The catalytic activity in this system is finely balanced. For
example, substituents on the catalyst affect the activity and Mw of
the polymer produced (cf. 2 with I and 3). Styrene itself is not
polymerized, presumably because the benzylic dormant species
formed by this unsubstituted monomer is more stable than its
TBS analogue.34 There is also a striking similarity in terms of
functionality between 8 and the proposed active species 9 from
Ishihara’s classic sPS catalyst,3,4 the chief difference between the
two being that 9 produces syndiotactic PS due to the prevalence
of the 2,1 insertion,3 whereas in 8, 1,2 insertions lead to
formation of atactic polymer.
plementary salen(imine) and salen(amine) complexes. When
activated with AliBu3 and MAO, respectively, these systems gave
comparable results for polymerization of several different
monomers.56
Our investigation into this phenomenon and the nature of the
active site in our Zr system began with run 24 (Table 4). Catalyst
2 was premixed with 5 equiv of AliBu3 in toluene for 30 min prior
to injection into the reaction vessel to allow any imine reduction
to take place. Although the yield of P(TBS) was relatively low, no
ethene uptake was seen, and no evidence of PE was found by
NMR spectroscopy. This result indicates that while a catalyst for
PE synthesis is produced on first activation of 2, this converts to a
catalyst for production of P(TBS). This is of course consistent
with the results in Table 1.
Our bis-salicyloxazoline group 4 complexes have been shown
to be resistant to reduction and when activated with either MAO
or borates are capable of very high activity polymerization of
olefins.36,57 The salicyloxazoline catalyst
6
(L6 ZrCl2)
2
(Figure 11) polymerized ethene in the presence of
These new catalytic systems for polymerization of TBS are
exceptionally active considering the usual poor performance of
AliBu3/[Ph3C][B(C6F5)4] (run 25), while in the presence of
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Zr compared with Ti for PS catalysis as reviewed above. The
results indicate how we might in future be able to produce
practical Zr catalysts for PS catalysis; it may be that many known
poorly active (or perhaps dormant) systems could be awakened
using dihydrogen or alkenes as chain transfer agents.
(18) Chum, P. S.; Kruper, W. J.; Guest, M. J. Adv. Mater. 2000, 12
(23), 1759–1767.
(19) Arai, T.; Ohtsu, T.; Suzuki, S. Macromol. Rapid Commun. 1998,
19 (6), 327–331.
(20) Sernetz, F. G.; Mulhaupt, R.; Amor, F.; Eberle, T.; Okuda, J.
J. Polym. Sci., Part A: Polym. Chem. 1997, 35 (8), 1571–1578.
(21) Sernetz, F. G.; Mulhaupt, R.; Waymouth, R. M. Macromol.
Chem. Phys. 1996, 197 (3), 1071–1083.
’ ASSOCIATED CONTENT
(22) Arriola, D. J.; Bokota, M.; Campbell, R. E.; Klosin, J.; LaPointe,
R. E.; Redwine, O. D.; Shankar, R. B.; Timmers, F. J.; Abboud, K. A.
J. Am. Chem. Soc. 2007, 129 (22), 7065–7076.
(23) Chirik, P. J.; Bercaw, J. E. Organometallics 2005, 24 (22), 5407–
5423.
Supporting Information. 13C spectra of p(TBS) and
S
b
crystallographic data for complex 4 in .cif format. This material
is available free of charge via the Internet at http://pubs.acs.org.
(24) Naga, N.; Wakita, Y.; Murase, S. J. Appl. Polym. Sci. 2008, 110
(6), 3770–3777.
(25) Correa, A.; Galdi, N.; Izzo, L.; Cavallo, L.; Oliva, L. Organome-
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: Peter.Scott@warwick.ac.uk.
tallics 2008, 27 (6), 1028–1029.
(26) Theaker, G. W.; Morton, C.; Scott, P. J. Polym. Sci., Part A:
Polym. Chem. 2009, 47 (12), 3111–3117.
’ ACKNOWLEDGMENT
(27) Matsui, S.; Mitani, M.; Saito, J.; Tohi, Y.; Makio, H.; Matsukawa,
N.; Takagi, Y.; Tsuru, K.; Nitabaru, M.; Nakano, T.; Tanaka, H.; Kashiwa,
N.; Fujita, T. J. Am. Chem. Soc. 2001, 123 (28), 6847–6856.
(28) Matsui, S.; Mitani, M.; Saito, J.; Tohi, Y.; Makio, H.; Tanaka, H.;
Fujita, T. Chem. Lett. 1999, 12, 1263–1264.
(29) Matsui, S.; Tohi, Y.; Mitani, M.; Saito, J.; Makio, H.; Tanaka, H.;
Nitabaru, M.; Nakano, T.; Fujita, T. Chem. Lett. 1999, 10, 1065–1066.
(30) Hustad, P. D.; Tian, J.; Coates, G. W. J. Am. Chem. Soc. 2002,
124 (14), 3614–3621.
An Oxford Diffraction Gemini XRD system and polymer
characterization equipment were obtained through the Science
City Advanced Materials project 1 and 2, respectively, with
support from Advantage West Midlands (AWM) and part
funded by the European Regional Development Fund
(ERDF). We thank EPSRC and Infineum for funding through
a Warwick Collaborative Training Account and Warwick Knowl-
edge Transfer Secondments (G.W.T.).
(31) Tian, J.; Coates, G. W. Angew. Chem., Int. Ed. 2000, 39 (20),
3626–3629.
(32) Tian, J.; Hustad, P. D.; Coates, G. W. J. Am. Chem. Soc. 2001,
123 (21), 5134–5135.
(33) Weiser, M. S.; Mulhaupt, R. Macromol. Rapid Commun. 2006,
27 (13), 1009–1014.
(34) Theaker, G. W.; Morton, C.; Scott, P. Dalton Trans. 2008, 48,
6883–6885.
’ REFERENCES
(1) Schellenberg, J.; Tomotsu, N. Prog. Polym. Sci. 2002, 27 (9),
1925–1982.
(2) Rodrigues, A. S.; Kirillov, E.; Carpentier, J. F. Coord. Chem. Rev.
2008, 252 (18-20), 2115–2136.
(3) Ishihara, N.; Seimiya, T.; Kuramoto, M.; Uoi, M. Macromolecules
1986, 19 (9), 2464–2465.
(4) Ishihara, N.; Kuramoto, M.; Uoi, M. Macromolecules 1988, 21
(12), 3356–3360.
(5) Grassi, A.; Pellecchia, C.; Longo, P.; Zambelli, A. Gazz. Chim.
Ital. 1987, 117 (4), 249–250.
(6) Ishihara, N.; Kuramoto, M. In Synthesis and Properties of Syndio-
tactic Polystyrene; International Symposium on Catalyst Design for
Tailor-Made Polyolefins, Kanazawa, Japan, Mar 10-12; Soga, K.,
Terano, M., Eds.; Kanazawa, Japan, 1994; pp 339-350.
(7) Proto, A.; Luciano, E.; Capacchione, C.; Motta, O. Macromol.
Rapid Commun. 2002, 23 (3), 183–186.
(35) Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. J. Org. Chem. 1997,
62 (21), 7512–7515.
(36) Bott, R. K. J.; Hammond, M.; Horton, P. N.; Lancaster, S. J.;
Bochmann, M.; Scott, P. Dalton Trans. 2005, 22, 3611–3613.
(37) Scott, P. Alkylation of zirconium tetrachloride with benzyl
Grignard. http://cssp.chemspider.com/1 http://dx.doi.org/10.1039/
SP1.
(38) Oakes, D. C. H.; Kimberley, B. S.; Gibson, V. C.; Jones, D. J.;
White, A. J. P.; Williams, D. J. Chem. Commun. 2004, 19, 2174–2175.
(39) Martinez, S.; Exposito, M. T.; Ramos, J.; Cruz, V.; Martinez,
M. C.; Lopez, M.; Munoz-Escalona, A.; Martinez-Salazar, J. J. Polym. Sci.,
Part A: Polym. Chem. 2005, 43 (4), 711–725.
(8) Tomotsu, N.; Ishihara, N.; Newman, T. H.; Malanga, M. T.
J. Mol. Catal. A: Chem. 1998, 128 (1-3), 167–190.
(9) Rahmani, S.; Abbasian, M.; Moghadam, P. N.; Entezami, A. A.
J. Appl. Polym. Sci. 2007, 104 (6), 4008–4014.
(40) Nomura, K.; Okumura, H.; Komatsu, T.; Naga, N.; Imanishi, Y.
J. Mol. Catal. A: Chem. 2002, 190 (1-2), 225–234.
(41) Chung, T. C.; Lu, H. L. J. Polym. Sci., Part A: Polym. Chem. 1998,
36 (6), 1017–1029.
(10) Caporaso, L.; Izzo, L.; Sisti, I.; Oliva, L. Macromolecules 2002,
35 (13), 4866–4870.
(11) Beckerle, K.; Capacchione, C.; Ebeling, H.; Manivannan, R.;
Mulhaupt, R.; Proto, A.; Spaniol, T. P.; Okuda, J. J. Organomet. Chem.
2004, 689 (24), 4636–4641.
(12) Longo, P.; Grassi, A.; Oliva, L. Makromol. Chem. 1990, 191
(10), 2387–2396.
(13) Williams, E. F.; Murray, M. C.; Baird, M. C. Macromolecules
2000, 33 (2), 261–268.
(42) We have confirmed this experimentally in the current system.
(43) We note that the Mn apparent in the MALDI spectra (ca. 3000
for run 7) is substantially lower than that obtained by GPC (ca. 7000 for
the same run).
(44) Dong, J. Y.; Chung, T. C. Macromolecules 2002, 35 (5), 1622–
1631.
(45) Koo, K. M.; Marks, T. J. J. Am. Chem. Soc. 1998, 120 (16),
4019–4020.
(46) Koo, K.; Marks, T. J. J. Am. Chem. Soc. 1999, 121 (38), 8791–
(14) Po, R.; Cardi, N. Prog. Polym. Sci. 1996, 21 (1), 47–88.
(15) Chien, J. C. W.; Salajka, Z.; Dong, S. Macromolecules 1992, 25
(12), 3199–3203.
8802.
(47) Makio, H.; Koo, K.; Marks, T. J. Macromolecules 2001, 34 (14),
4676–4679.
(16) Ready, T. E.; Gurge, R.; Chien, J. C. W.; Rausch, M. D.
Organometallics 1998, 17 (24), 5236–5239.
(17) Grassi, A.; Zambelli, A.; Laschi, F. Organometallics 1996, 15 (2),
480–482.
(48) Although no polyhexene is formed from this system, hexene
coordination may occur, rendering this step reversible.
(49) Haruyuki Makio, T. F. Macromol. Symp. 2004, 213 (1), 221–
234.
1403
dx.doi.org/10.1021/ma102835p |Macromolecules 2011, 44, 1393–1404

Macromolecules
ARTICLE
(50) Sanz, M.; Cuenca, T.; Cuomo, C.; Grassi, A. J. Organomet.
Chem. 2006, 691 (18), 3816–3822.
(51) Tohi, Y.; Makio, H.; Matsui, S.; Onda, M.; Fujita, T. Macro-
molecules 2003, 36 (3), 523–525.
(52) Janiak, C. Dalton Trans. 2000, 21, 3885–3896.
(53) Makio, H.; Kashiwa, N.; Fujita, T. Adv. Synth. Catal. 2002, 344
(5), 477–493.
(54) Knight, P. D.; O’Shaughnessy, P. N.; Munslow, I. J.; Kimberley,
B. S.; Scott, P. J. Organomet. Chem. 2003, 683 (1), 103–113.
(55) Knight, P. D.; Clarkson, G.; Hammond, M. L.; Kimberley, B. S.;
Scott, P. J. Organomet. Chem. 2005, 690 (23), 5125–5144.
(56) Strianese, M.; Lambert, M.; Mazzeo, M.; Pellecchia, C. Macro-
mol. Chem. Phys. 2008, 209 (6), 585–592.
(57) Coles, S. R.; Clarkson, G. J.; Gott, A. L.; Munslow, I. J.;
Spitzmesser, S. K.; Scott, P. Organometallics 2006, 25 (26), 6019–6029.
(58) Cariou, R.; Gibson, V. C.; Tomov, A. K.; White, A. J. P.
J. Organomet. Chem. 2009, 694 (5), 703–716.
(59) Talarico, G.; Budzelaar, P. H. M. J. Am. Chem. Soc. 2006, 128
(14), 4524–4525.
(60) Talarico, G.; Budzelaar, P. H. M. Organometallics 2008, 27 (16),
4098–4107.
1404
dx.doi.org/10.1021/ma102835p |Macromolecules 2011, 44, 1393–1404