Living isospecific styrene polymerization by chiral benzyl titanium complexes that contain a tetradentate [OSSO]-type bis(phenolato) ligand

Article abstract of DOI:10.1021/om060047e

Dibenzyl complexes [Ti(OC₆H₂-R¹-6-R ²-4)₂{S(CH₂)₂S}(CH ₂Ph)₂] (2a-c; R¹ = ^tBu, R ² = Me, a; R¹, R² = ^tBu, b; R ¹ = H, R² = Me, c) with a tetradentate dianionic [OSSO]-type ligand were synthesized from the corresponding titanium dichloro complexes [Ti(OC₆H₂-R¹-6-R²-4) ₂{S(CH₂)₂S}Cl₂] and benzylmagnesium chloride in toluene. NMR spectroscopic monitoring of the reaction of the dibenzyl complex 2b with B(C₆F₅)₃ in bromobenzene indicates the formation of a thermally sensitive benzyl cation [Ti(OC₆H₂-^tBu₂-4,6) ₂{S(CH₂)₂S}(CH₂Ph)]⁺. ¹H NMR spectra at -30°C show two C₁-symmetric diastereomers in a 55:45 ratio, suggesting slow epimerization on the NMR time scale at this temperature. The benzyl complex 2c, which does not bear bulky ortho-substituents, was found to be fluxional and unstable in solution. Related benzyl complexes of the 1,5-dithiapentanediyl-linked ligand [Ti(OC ₆H₂-^tBu-6-R-4)₂{S(CH ₂)₃S}(CH₂Ph)₂](4a,b; R = Me, a; R = ^tBu, b) were synthesized in an analogous manner ' and were also shown to be highly fluxional and unstable in solution, decomposing immediately upon addition of B(C₆F₅)₃. Using the 1,4-dithiabutanediyl-linked dibenzyl complexes and the activators [PhNMe ₂H][B(C₆F₅)₄]/AlⁿOct ₃, the living isospecific polymerization of styrene could be achieved for the first time. The resulting isotactic polystyrenes show narrow molecular weight distributions (M_w/M_n < ～1.2). A linear relation between the number-averaged molecular weights M_n and the monomer conversion was observed.

Full text of DOI:10.1021/om060047e

Organometallics 2006, 25, 3019-3026
3019
Living Isospecific Styrene Polymerization by Chiral Benzyl
Titanium Complexes That Contain a Tetradentate [OSSO]-Type
Bis(phenolato) Ligand
Klaus Beckerle, Ramanujachary Manivannan, Thomas P. Spaniol, and Jun Okuda*
Institute of Inorganic Chemistry, RWTH Aachen UniVersity, Landoltweg 1, D-52056 Aachen, Germany
ReceiVed January 17, 2006
t
Dibenzyl complexes [Ti(OC6H2-R1-6-R2-4)2{S(CH2)2S}(CH2Ph)2] (2a-c; R1 ) Bu, R2 ) Me, a; R1,
t
R2 ) Bu, b; R1 ) H, R2 ) Me, c) with a tetradentate dianionic [OSSO]-type ligand were synthesized
from the corresponding titanium dichloro complexes [Ti(OC6H2-R1-6-R2-4)2{S(CH2)2S}Cl2] and benzyl-
magnesium chloride in toluene. NMR spectroscopic monitoring of the reaction of the dibenzyl complex
2b with B(C6F5)3 in bromobenzene indicates the formation of a thermally sensitive benzyl cation
[Ti(OC6H2-tBu2-4,6)2{S(CH2)2S}(CH2Ph)]+. 1H NMR spectra at -30 °C show two C1-symmetric
diastereomers in a 55:45 ratio, suggesting slow epimerization on the NMR time scale at this temperature.
The benzyl complex 2c, which does not bear bulky ortho-substituents, was found to be fluxional and
unstable in solution. Related benzyl complexes of the 1,5-dithiapentanediyl-linked ligand [Ti(OC6H2-
tBu-6-R-4)2{S(CH2)3S}(CH2Ph)2] (4a,b; R ) Me, a; R ) tBu, b) were synthesized in an analogous manner
and were also shown to be highly fluxional and unstable in solution, decomposing immediately upon
addition of B(C6F5)3. Using the 1,4-dithiabutanediyl-linked dibenzyl complexes and the activators
[PhNMe2H][B(C6F5)4]/AlnOct3, the living isospecific polymerization of styrene could be achieved for
the first time. The resulting isotactic polystyrenes show narrow molecular weight distributions (Mw/Mn
< ∼1.2). A linear relation between the number-averaged molecular weights Mn and the monomer
conversion was observed.
defined chiral half-sandwich zirconium complexes.9 The design
of post-metallocene initiators10,11 provides important contribu-
tions to modern macromolecular synthesis, since conventional
living ionic12 or living radical methodologies13 usually do not
allow influencing the stereospecificity during chain propagation.
Whereas syndiospecific styrene polymerization by titanium
half-sandwich titanium complexes has been well established,14
a controlled version of this polymerization has become known
only recently.15 Isotactic polystyrene was already described in
Introduction
The introduction of structurally well-defined R-olefin
polymerization catalysts has rejuvenated the area of initiator
design for the living/controlled polymerization of R-olefins.1-7
Following the pioneering work by Doi et al. on the vanadium-
initiated living polymerization of propylene in the 1980s,8 the
goal of both stereospecific and living polymerization of R-olefins
has been recently achieved by Sita et al. using structurally well-
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10.1021/om060047e CCC: $33.50 © 2006 American Chemical Society
Publication on Web 05/09/2006

3020 Organometallics, Vol. 25, No. 12, 2006
Beckerle et al.
Scheme 1
the early days of Ziegler-Natta catalysis.16 However, only
recently was a post-metallocene catalyst precursor with a
[OSSO]-type ligand introduced that upon methylaluminoxane
(MAO) activation allows the efficient preparation of isotactic
polystyrene of high molecular weight.17,18 Here we show that
living isospecific polymerization of styrene is possible when
dibenzyl titanium complexes with this ligand are used as
structurally characterized precursors.
Figure 1. ORTEP diagram of the molecular structure of 2b.
Hydrogen atoms were omitted for clarity; thermal ellipsoids are
drawn at the 50% probability level.
Results and Discussion
Table 1. Selected Bond Lengths (Å) and Angles (deg) in 2b
Synthesis and Structure of the Dibenzyl Complexes. The
dibenzyl titanium complexes [Ti(OC6H2-R1-6-R2-4)2{S(CH2)2S}-
Ti-O1
Ti-S1
Ti-C31
1.8732(13)
2.8836(7)
2.149(2)
Ti-O2
Ti-S2
Ti-C38
1.8758(13)
2.7472(7)
2.137(2)
(CH2Ph)2] (2a-c; R1 ) Bu, R2 ) Me, a; R1, R2 ) Bu, b; R1
) H, R2 ) Me, c) were isolated as dark red microcrystals in
20-50% yield by reacting the corresponding dichloro complexes
[Ti(OC6H2-R1-6-R2-4)2{S(CH2)2S}Cl2] (1a-c) with an ethereal
solution of benzylmagnesium chloride in toluene at -30 °C
(Scheme 1). In the 1H NMR spectrum of 2a, the benzylic protons
appear as AB doublets at 3.36 and 3.40 ppm with a coupling
t
t
O1-Ti-O2
O1-Ti-S2
O1-Ti-C38
O2-Ti-S2
O2-Ti-C38
S1-Ti-C31
S2-Ti-C31
C31-Ti-C38
Ti-S1-C15
Ti-C31-C32
157.55(6)
86.06(4)
100.77(7)
73.69(4)
96.71(7)
81.67(6)
151.66(6)
90.57(8)
106.27(7)
116.28(13)
O1-Ti-S1
O1-Ti-C31
O2-Ti-S1
O2-Ti-C31
S1-Ti-S2
S1-Ti-C38
S2-Ti-C38
Ti-S1-C2
C2-S1-C15
Ti-C38-C39
72.23(4)
100.59(7)
92.57(4)
93.18(7)
74.14(2)
168.23(6)
115.45(6)
92.27(7)
101.88(9)
97.45(12)
2
constant of JHH ) 9.2 Hz. The protons of the methylene
backbone appear as AA′BB′ doublet-like multiplets at 1.77 and
1
2.27 ppm. The complex 2b shows a similar H NMR spectral
pattern. The 13C NMR spectra of both compounds show a singlet
for the benzylic carbon atoms at 88.36 and 87.57 ppm,
respectively, with a coupling constant of 1JCH ) 132.2 Hz. These
values are higher than the expected values for a η1-coordinated
benzyl group (122 to 126 Hz), suggesting a partial η2-
coordination at the titanium center.19 Variable-temperature NMR
studies (-70 to +90 °C) indicated that both complexes are
thermally robust and maintain their chiral C2-symmetric structure
within this temperature range. Above 90 °C, decomposition
starts under formation of toluene.
Single crystals of 2b were obtained from a toluene/hexane
mixture. The ORTEP diagram for the structure is shown in
Figure 1, and selected bond lengths and bond distances are
provided in Table 1. The molecular structure shows a C2-
symmetrical [OSSO]-type ligand with the two benzyl groups
in the cis-position (C31-Ti-C38 90.57(8)°). The dihedral
angles Ti-C31-C32 and Ti-C38-C39 of 116.28(13)° and
97.45(12)° indicate that η1- as well as η2-coordination is present
in the complex.20 The elongated titanium sulfur bond distance
(Ti-S1 2.8836(7) Å) as compared to the distance Ti-S2 of
(15) (a) Kawabe, M.; Murata, M. Macromol. Chem. Phys. 2001, 202,
2440. (b) Kawabe, M.; Murata, M. Macromol. Chem. Phys. 2001, 202, 1799.
(c) Kawabe, M.; Murata, M.; Soga, K. Macromol. Rapid Commun. 1999,
20, 569.
(16) (a) Natta, G.; Pino, P.; Corradini, P.; Danusso, F.; Mantica, E.,
Mazzanti, G.; Moraglio, G. J. Am. Chem. Soc. 1955, 77, 1708. (b) Natta,
G.; Corradini, P. Makromol. Chem. 1955, 16, 77. (c) Overberger, C.; Mark,
H. J. Polym. Sci. 1959, 35, 381. (d) Kern, R. J.; Hurst, H. G.; Richard, W.
J. J. Polym. Sci. 1960, 45, 195.
(17) (a) Capacchione, C.; Proto, A.; Ebeling, H.; Mu¨lhaupt, R.; Mo¨ller,
K.; Spaniol, T. P.; Okuda, J. J. Am. Chem. Soc. 2003, 125, 4964. (b)
Capacchione, C.; D’Acunzi, M.; Motta, O.; Oliva, L.; Proto, A.; Okuda, J.
Macromol. Chem. Phys. 2004, 205, 370. (c) Capacchione, C.; Manivannan,
R.; Barone, M.; Beckerle, K.; Centore, R.; Oliva, L.; Proto, A.; Tuzi, A.;
Spaniol, T. P.; Okuda, J. Organometallics 2005, 24, 2971. (d) Capacchione,
C.; Proto, A.; Ebeling, H.; Mu¨lhaupt, R.; Mo¨ller, K.; Manivannan, R.;
Spaniol, T. P.; Okuda, J. J. Mol. Catal. A: Chem. 2004, 213, 137. (e)
Beckerle, K.; Capacchione, C.; Ebeling, H.; Manivannan, R.; Mu¨lhaupt,
R.; Proto, A.; Spaniol, T. P.; Okuda, J. J. Organomet. Chem. 2004, 689,
4636.
(18) For other R-olefin polymerization using this type of catalysts, see:
(a) Proto, A.; Capacchione, C.; Venditto, V.; Okuda, J. Macromolecules
2003, 36, 9249. (b) Capacchione, C.; Proto, A.; Okuda, J. J. Polym. Sci.
Part A: Polym. Chem. 2004, 42, 2815. (c) Capacchione, C.; De Carlo, F.;
Zannoni, C.; Okuda, J.; Proto, A. Macromolecules 2004, 37, 8918. (d)
Capacchione, C.; Proto, A.; Ebeling, H.; Mu¨lhaupt, R.; Okuda, J. J. Polym.
Sci., Part A: Polym. Chem. 2006, 44, 1908.
(19) For examples of η2-coordinated benzyl groups at titanium, see: (a)
Latesky, S. L.; McMullen, A. K.; Niccolai, G. P.; Rothwell, I. P.; Huffman,
J. C. Organometallics 1985, 4, 902. (b) Jordan, R. F.; LaPointe, R. E.;
Bajgur, C. S.; Echols, S. F.; Willet, R. J. Am. Chem. Soc. 1987, 109, 4111.
(c) Bochmann, M.; Lancaster, S. J.; Organometallics 1993, 12, 633. (d)
Bochmann, M.; Lancaster, S. J.; Hursthouse, M. B., Malik, A. K. M.
Organometallics 1994, 13, 2335.

LiVing Isospecific Styrene Polymerization
Organometallics, Vol. 25, No. 12, 2006 3021
Scheme 2
Scheme 3
2.7472(7) Å can be explained by the stronger trans-influence
of the η2-coordinated benzyl group in the solid state. The two
oxygen ligands of the phenol are in the apical position, and the
O1-Ti-O2 angle of 157.55(6)° significantly differs from
linearity. The overall structure of 2b is virtually analogous to
that found for the hafnium complex [Hf(OC6H2-tBu2-4,6)2-
{S(CH2)2S}(CH2Ph)2].17a
In contrast, complex 2c, which does not carry bulky ortho-
1
substituents, was found to be highly fluxional. The H NMR
spectrum at ambient temperature shows only one singlet at 3.36
ppm for the methylene protons of the benzyl group. The
CH2CH2 protons of the backbone within the bis(phenolato)
ligand appear as a broad singlet at 1.98 ppm, overlapping with
the signals of the para methyl groups. At temperatures below
-20 °C, the CH2CH2 protons of the backbone appear as two
broad doublets at 1.78 and 2.23 ppm. The benzylic protons still
are recorded as a singlet at -20 °C, but at -55 °C, they appear
as an AB quartet, which at -80 °C give rise to two broad
singlets at 3.02 and 3.08 ppm. Consistent with these results,
the 13C NMR spectrum at ambient temperature shows one signal
at 36.92 ppm for the carbon atoms of the backbone and a single
resonance at 89.87 ppm for the η2-coordinated CH2 group (1JCH
) 134 Hz). At temperatures above 40 °C, the complex starts to
decompose under formation of 1,2-diphenylethane, indicating
low stability in solution. Even at room temperature, 2c was not
stable in solution for more than 4 h. The decomposition resulted
in the formation of a dark-colored solid that was insoluble in
hydrocarbon solvents and CHCl3.
3a,17c the dibenzyl complex 4a was configurationally fluxional
within the temperature region of -70 to +80 °C with Cs-
symmetry in solution. At room temperature, the 1H NMR spectra
show singlets for the benzylic protons at 3.59 ppm and the
central CH2 protons of the backbone appear as a higher order
multiplet at 1.00 ppm; the SCH2 protons are recorded as a triplet-
like higher order multiplet at 2.13 ppm. At -70 °C, the benzylic
protons appear as two broad singlets at 3.38 and 3.58 ppm and
coalesce to a broad singlet at -35 °C. In the 13C NMR spectrum
the benzylic carbon atom is recorded at 95.15 ppm (1JCH ) 132.4
Hz). The 1H NMR spectrum of 4b is similar to that of 4a. Upon
standing at room temperature for more than 8 h, solutions of
the complexes 4a,b decompose under formation of toluene,
indicating that these complexes are less stable than their 1,4-
dithiabutanediyl-bridged counterparts 2a,b. The high solubility
of this complex in all common solvents precluded us from
isolating this compound in pure form.
Related benzyl complexes of the 1,5-dithiapentanediyl-linked
ligand [Ti(OC6H2-tBu-6-R-4)2{S(CH2)3S}(CH2Ph)2] (4a,b; R )
t
Me, a; R ) Bu, b) were synthesized in an analogous manner
(Scheme 2). Similar to the highly fluxional dichloro complex
(20) For bond angles, bond distances, and NMR spectroscopic data of
other titanium dibenzyl complexes, see Table 2 and the following refer-
ences: (a) Bassi, I. W.; Allegra, G.; Scordamaglia, R.; Chioccola, G. J.
Am. Chem. Soc. 1971, 93, 3787. (b) Scholz, J.; Rehbaum, F.; Thiele, K.
H.; Goddard, R.; Betz, P.; Kru¨ger, C. J. Organomet. Chem. 1993, 443, 93.
(c) Groysman, S.; Tshuva, E. Y.; Goldberg, I.; Kol, M.; Goldschmidt, Z.;
Shuster, M. Organometallics 2004, 23, 5291. (d) van der Linden, A.;
Schaverien, C. J.; Meijboom, N.; Ganter, C.; Orpen, A. G. J. Am. Chem.
Soc. 1995, 117, 3008. (e) Thorn, M. G.; Etheridge, Z. C.; Fanwick, P. E.;
Rothwell, I. P. J. Organomet. Chem. 1999, 591, 148. (f) Reimer, V.; Spaniol,
T. P.; Okuda, J.; Ebeling, H.; Tuchbreiter, A.; Mu¨lhaupt, R. Inorg. Chim.
Acta 2003, 345, 221. (g) Fokken, S.; Reichwald, F.; Spaniol, T. P.; Okuda,
J. J. Organomet. Chem. 2002, 663, 158. (h) Duchateau, R.; Cremer, U.;
Harmsen, R. J.; Mohamud, S. I.; Abbenhuis, H. C. L.; van Santen, R. A.;
Meetsma, A.; Thiele, S. K. H.; van Tol, M. F. H.; Kranenburg, M.
Organometallics 1999, 18, 5447. (i) Carpentier, J. F.; Martin, A.; Swenson,
D. C.; Jordan, R. F.; Organometallics 2003, 22, 4999. (j) Jeon, Y.-M.; Heo,
J.; Lee, W. M.; Chang, T.; Kim, K. Organometallics 1999, 18, 4107. (k)
Siemeling, U.; Ko¨lling, L.; Stammler, A.; Stammler, H.-G. J. Chem. Soc.,
Dalton Trans. 2002, 3277. (l) Tsuie, B.; Swenson, D. C.; Jordan, R. F.;
Petersen, J. L. Organometallics 1997, 16, 1392. (m) Minhas, R. K.; Scoles,
L.; Wong, S.; Gambarotta, S. Organometallics 1996, 15, 1113.
Generation of Benzyl Cations. For the MAO-activated
dichloro complexes 1a,b, we assume that an alkyl cation
[Ti(OC6H2-tBu2-4,6)2{S(CH2)2S}R]+ is generated as catalyti-
cally active species, similar to related nonmetallocene polym-
erization catalysts.11 Adding B(C6F5)3 to the dibenzyl complex
2b in bromobenzene-d5 at -30 °C immediately produced an
1
orange solution. The H NMR spectrum shows the signals of
the ion pair [Ti(OC6H2tBu2-4,6)2{S(CH2)2S}(CH2Ph)][(PhCH2)B-
(C6F5)3], together with a small amount of free bis(phenol) as
1
an impurity. Two-dimensional H NMR spectra allowed us to
assign the signals. At low temperature (-30 °C), two sets of
signals of intensity ratio 55:45 are found; coalescence is
observed at ca. 0 °C, where only one broad signal is observed
for the tBu methyl groups. At elevated temperatures, the signals

3022 Organometallics, Vol. 25, No. 12, 2006
Beckerle et al.
Figure 2. Variable-temperature 13C NMR spectra of the benzyl cation prepared from 2b and B(C6F5)3 in bromobenzene. The expanded
region shows the benzyl carbon signals.
become sharp. Above ca. 70 °C, slow decomposition sets in.
The proton signals of the BCH2 group at 3.4 ppm as well as
the 19F and 11B NMR spectra suggest the presence of a solvent-
separated ion pair.21
tion of the alkyl radical to give Ti(III) species than the
corresponding complex with a 1,4-dithiabutane bridge.22
Styrene Polymerization. Polymerization data of styrene
using the dibenzyl titanium complex 2a activated with
[PhNMe2H][B(C6F5)4] in the presence of the trialkylaluminum
compound AlnOct3 are presented in Table 3. The molecular
weight of the polymers increases linearly with the conversion
up to ca. 70% (Figure 3). The semilogarithmic plot of monomer
conversion against time also shows linearity (Figure 4). In all
of these experiments, the polydispersity remains low (Mw/Mn
< ∼1.2), and there is no consistent trend toward a broader
molecular weight distribution upon increasing conversion. The
larger molecular weight distribution of some samples is caused
by varying amounts of a byproduct of higher molecular weight.
Closer examination of these bimodal distributions shows that
both fractions have a narrow molecular weight distribution (Mw/
Mn < ∼1.1) and that the molecular weight of the byproduct is
twice the molecular weight of the main fraction. We assume
that this byproduct is formed during aerobic workup by coupling
of two polymer chains via a radical mechanism.23 The initiator
efficiencies < 100% result in molecular weights higher than
the calculated values.
The two diastereomers can be distinguished in the 13C NMR
spectrum at low temperature (-30 °C), where the signal for
the TiCH2 carbon appears at 97.22 and 97.36 ppm (of equal
1
intensity). The JCH value of 151 Hz indicates an η2-bonding
nature of the benzyl group. The 13C NMR spectra at -30 °C
show that the ratio of both C1-symmetric diastereomers is nearly
equal and suggests that epimerization does not occur on the
NMR time scale at this temperature (Scheme 3). Coalescence
is observed at -5 °C. Above this temperature, only one signal
is observed, corresponding to only one species with C2-
symmetry (Figure 2). The free energy of activation for this
epimerization process was estimated to be ∆Gq ) 52 ( 4 kJ/
mol. We explain this fluxional behavior by the formation of an
η2-bonded benzyl cation that coordinates either a solvent
molecule or the anion, leading to diastereomeric pairs with
pseudo-seven-coordinate configuration. We assume that the
helicity change or ∆,Λ interconversion does not occur, but
cannot exclude it conclusively at this time.
Activation of the benzyl complex with B(C6F5)3 is pos-
sible, but leads to slightly broader molecular weight distribu-
tions, most probably because of the stronger coordinating
character of the anion compared to that of the perfluorinated
borate. The presence of aluminum alkyl is essential for the
polymerization, although an excess does not influence the
polymerization behavior. It is probably involved in “masking”
the N,N-dimethylaniline that would coordinate at the active
center.
DSC measurements of the polymers show melting temper-
atures of ca. 210 °C. These Tm values are slightly lower than
those of high molecular weight isotactic polystyrenes,17a,c but
given the relatively low molecular weight of the samples, these
values can be regarded as typical. 13C NMR spectroscopic
analysis of the samples revealed perfect isotacticity with [rr]
Similar NMR spectra were obtained for the cation generated
from 2a. The benzyl cations derived from the complexes 2a
and 2b were stable within the same temperature range and
decompose slowly at elevated temperature, giving 1,2-diphenyl-
ethane and toluene.
Complex 2c immediately decomposed upon reaction with
B(C6F5)3 with formation of 1,2-diphenylethane and toluene, as
1
indicated by the H NMR spectrum. Activation of 4a and 4b
with B(C6F5)3 in bromobenzene at -30 °C led to a color change
of the initially dark red solution to pale red; only broad
resonances attributable to (paramagnetic) decomposition prod-
1
ucts could be observed in the H NMR spectrum. We suspect
that the alkyl cation derived from the longer 1,5-dithiapentane
bridge more readily undergoes reduction by homolytic dissocia-
(21) For coordination of [(PhCH2)B(C6F5)3]- at a cationic group 4 metal
center, see: (a) Pellecchia, C.; Immirzi, A.; Grassi, A.; Zambelli, A.
Organometallics 1993, 12, 4473. (b) Pellecchia, C.; Grassi, A.; Immirzi,
A. J. Am. Chem. Soc. 1993, 115, 1160. (c) Horton, A. D.; de With, J.; van
der Linden, A. J.; van de Weg, H. Organometallics 1996, 15, 2672. (d)
Horton, A. D.; de With, J. Organometallics 1997, 16, 5424.
(22) Borkowsky, S. L.; Baenziger, N. C.; Jordan, R. F. Organometallics
1993, 12, 486.
(23) (a) Odian, G. Principles of Polymerization, 3rd ed.; John Wiley:
New York, 1991; p 403. (b) Takaki, M.; Asami, R.; Kuwata, R.
Macromolecules 1979, 12, 378. (c) Asami, R.; Takaki, M.; Hanahata, H.
Macromolecules 1983, 16, 628.

LiVing Isospecific Styrene Polymerization
Organometallics, Vol. 25, No. 12, 2006 3023
Table 2. Structural Comparisons of Some Benzyl Titanium Complexes
> 95%. Finally, we have confirmed by acetone extraction that
the polymer samples are not contaminated with atactic poly-
styrene that might have been formed by radical or cation
initiation.
solvent/anion coordination and η2-bonding of the benzyl group
rather than by helicity change of the tetradentate ligand. When
the dibenzyl complexes were activated with B(C6F5)3 or
[PhNMe2H][B(C6F5)] in the presence of trialkylaluminum,
isospecific polymerization of styrene could be performed in a
living fashion for the first time. Complexes that do not bear
ortho substituents in the aromatic ring of the phenol moiety
are fluxional in solution and rapidly decompose in solution. The
corresponding dibenzyl complexes with 1,5-dithiapentanediyl-
linked bis(phenolato) ligands are also fluxional and unstable in
solution. Reaction of these dibenzyl complexes with B(C6F5)3
results in decomposition.
Conclusion
Chiral titanium dibenzyl complexes with bulky ortho sub-
stituents in the 1,4-dithiabutanediylbis(phenolato) ligand do not
undergo ∆,Λ interconversion on the NMR time scale. Reaction
of these complexes with B(C6F5)3 gives rise to two diastereo-
meric benzyl cations in a 55:45 ratio at lower temperatures.
However, at higher temperatures epimerization occurs, by labile

3024 Organometallics, Vol. 25, No. 12, 2006
Beckerle et al.
Table 3. Styrene Polymerization by 2a Activated by
a
[PhNMe2H][B(C6F5)] and AlnOct3
Al
%
Mn (× 103 g
Tm
run equivb t (h) conv
mol-1
)
Mw/Mn efficiencyc (°C)
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
2
3
0.5
1
1.5
2
3
4
5
2
2
12.2
22.3
30.1
42.4
62.4
65.8
90.8
78.9
71.3
18.3
27.1
35.1
49.9
1.19
1.15
1.09
1.08
1.18
1.13
1.27
1.19
1.20
35
43
44
48
50
50
45
57
55
n.d.
n.d.
n.d.
n.d.
n.d.
207e
210
215
217
64.1d
67.1d
106.1d
72.5
67.0
a Conditions: [Ti] ) 10-3 M, [B] ) 0.9 × 10-3 M in 10 mL of toluene;
[styrene]/[Ti] ) 500; T ) 25 °C. b AlnOct3. c Efficiency defined as the
percentage of active initiators, calculated from the observed number of
polymer chains relative to the theoretical ones, assuming that each titanium
complex initiates one polymer chain. d Bimodal. e [rr] > 95% by 13C NMR
spectroscopy (see Supporting Information).
Figure 4. Semilogarithmic plot of styrene conversion against time
using 2a activated by [PhNMe2H][B(C6F5)4] and AlnOct3 (linear
fit, R ) 0.988).
in 50 mL of toluene at -78 °C was added a 1.0 M solution of
PhCH2MgCl in diethyl ether (0.89 g, 5.9 mL, 5.9 mmol) dropwise
over a period of 15 min, and the dark red colored mixture stirred
for 1 h at -78 °C. The dark red colored solution was then gradually
allowed to warm to 0 °C and stirred for 2 h at the same temperature.
After filtration the solution was concentrated to 3 mL, an equal
volume of hexane was added, and the mixture was stored at -20
°C to afford 0.83 g of a red-brown powder in 46% yield. 1H
2
NMR: δ 1.71 (s, 18 H, C(CH3)3), 1.77 (d, 2 H, JHH ) 10.0 Hz,
SCH2), 2.07 (s, 6 H, 4-CH3), 2.27 (d, 2 H, 2JHH ) 10.0 Hz, SCH2),
3.36 (d, 2 H, 2JHH ) 9.2 Hz, TiCH2), 3.40 (d, 2 H, 2JHH ) 9.2 Hz,
4
3
TiCH2), 6.68 (d, 2 H, JHH ) 1.2 Hz, 5-CH), 6.85 (t, 2 H, JHH
)
7.2 Hz, p-CH2Ph), 7.06 (t, 4 H, 3JHH ) 7.6 Hz, m-CH2Ph), 7.17 (s,
2 H, 3-CH, overlap with solvent signal), 7.20 (d, 4 H, o-CH2Ph).
13C{1H} NMR (25 °C, C6D6): δ 20.79 (CH3), 29.78 (C(CH3)3),
35.45 (C(CH3)3), 37.48 (SCH2), 88.36 (TiCH2), 120.92 (C-2),
123.70 (p-CH2Ph), 129.55 (m-CH2Ph), 129.90 (C-4), 130.08 (C-
3), 130.47 (o-CH2Ph), 131.07 (C-5), 137.49 (C-6), 144.17 (ipso-
CH2Ph), 166.26 (C-1). Anal. Calcd for C44H58O2S2Ti: C, 70.57;
H, 7.17; S, 9.92. Found: C, 69.95; H, 7.30; S, 9.62.
Figure 3. Plot of number-averaged molecular weights Mn and
polydispersity index versus conversion during isospecific styrene
polymerization using 2a activated by [PhNMe2H][B(C6F5)4] and
AlnOct3.
Dibenzyl{1,4-dithiabutanediyl-2,2′-bis(4,6-di-tert-butyl-
phenoxy)}titanium (2b). To a solution of 1b (1.70 g, 2.74 mmol)
in toluene at -78 °C was added a 1.0 M solution of PhCH2MgCl
in diethyl ether (0.83 g, 5.5 mL, 5.50 mmol) dropwise over a period
of 15 min, and the dark red colored mixture stirred for 1 h at -78
°C. The dark red colored solution was then gradually allowed to
warm to 0 °C and stirred for 2 h at 0 °C. After filtration the solution
was concentrated to 3 mL, an equal volume of n-hexane was added,
and the mixture was stored at -20 °C to afford 0.88 g of dark red
Experimental Section
General Considerations. All operations were performed under
an inert atmosphere of argon using standard Schlenk-line or
glovebox techniques. Diethyl ether was distilled from sodium
benzophenone ketyl; hexane and toluene were purified by distillation
from sodium/triglyme benzophenone ketyl. Titanium tetrachloride
(ALFA or Strem), 25 wt % tri-n-octylaluminum solution in hexane,
and 1 M benzylmagnesium chloride solution in diethyl ether
(Aldrich) were used as received. Dichloro titanium complexes of
1,4-dithiabutanediyl- (1a-c) and 1,5-dithiapentanediyl-derived
(3a,b) ligands were prepared according to published procedures.17c
All other chemicals were commercially available and used after
appropriate purification. NMR spectra were recorded on a Bruker
DRX 400 spectrometer (1H, 400 MHz; 13C, 101 MHz) in C6D6 at
25 °C, unless otherwise stated. All variable-temperature NMR
measurements were carried out in toluene-d8. Chemical shifts for
1H and 13C spectra were referenced internally using the residual
solvent resonances and reported relative to tetramethylsilane.
Assignments were verified by correlated spectroscopy. Elemental
analyses were performed by the Microanalytical Laboratory of this
department.
1
microcrystals; yield 45%. H NMR: δ 1.22 (s, 18 H, C(CH3)3),
2
1.75 (s, 18 H, C(CH3)3), 1.87 (d, 2 H, JHH ) 10.0 Hz, SCH2),
2.37 (d, 2 H, 2JHH ) 10.0 Hz, SCH2), 3.27 (d, 2 H, 2JHH ) 8.8 Hz,
TiCH2), 3.34 (d, 2 H, 2JHH ) 8.8 Hz, TiCH2), 6.84 (t, 2 H, 3JHH
)
7.2 Hz, p-CH2Ph), 7.02 (t, 4 H, 3JHH ) 7.5 Hz, m-CH2Ph), 7.03 (d,
2 H, 4JHH ) 2.4 Hz, 5-CH), 7.16 (d, 4 H, 3JHH ) 7.2 Hz, o-CH2Ph,
4
overlap with solvent signal), 7.52 (d, 2 H, JHH ) 2.4 Hz, 3-CH).
13C{H} NMR: δ 30.01 (C(CH3)3), 31.65 (C(CH3)3), 34.51 (C(CH3)3),
35.75 (C(CH3)3), 37.84 (SCH2), 87.57 (TiCH2), 120.75 (C-2),
123.71 (p-CH2Ph), 125.99 (C-3), 127.87 (C-5), 128.2 (m-CH2Ph,
overlap with solvent signal), 130.14 (o-CH2Ph), 136.96 (C-4),
143.19 (C-6), 144.05 (ipso-CH2Ph),166.22 (C-1). Anal. Calcd for
C44H58O2S2Ti: C, 72.30; H, 8.00, S, 8.77. Found: C 71.57; H,
7.98; S, 8.75.
Dibenzyl{1,4-dithiabutanediyl-2,2′-bis(6-tert-butyl-4-methyl-
phenoxy)}titanium (2a). To a solution of 1a (1.51 g, 2.80 mmol)
Dibenzyl{1,4-dithiapentanediyl-2,2′-bis(4-methylphenoxy)}-
titanium (2c). To a suspension of 1c in 2 mL diethyl ether (1.01

LiVing Isospecific Styrene Polymerization
Organometallics, Vol. 25, No. 12, 2006 3025
Table 4. Experimental Data for the Crystal Structure
Determinations of 2b
filtered and concentrated to afford a dark red oil. Repeated attempts
to crystallize failed. 1H NMR: δ 1.25 (s, 18 H, C(CH3)3), 1.49 (m,
2
2 H, CH2), 1.57 (s, 18 H, C(CH3)3), 2.21 (t, 4 H, JHH ) 7 Hz,
formula
fw
C47.50H62O2S2Ti
777.02
SCH2), 3.49 (s, 4 H, TiCH2), 6.68 (s, 2 H, 5-CH), 7.01 (t, 2 H,
3JHH ) 6 Hz, p-CH2Ph), 7.14 (m, 4 H, overlap with solvent signal,
m-CH2Ph), 7.18 (m, 4 H, partial overlap with solvent signal,
o-CH2Ph), 7.52 (d, 2 H, 4JHH ) 2.4 Hz, 3-CH). 13C{H} NMR (C6D6,
25 °C): δ 30.00 (C(CH3)3), 31.65 (C(CH3)3), 34.51 (C(CH3)3),
35.75 (C(CH3)3), 37.84 (SCH2), 87.57 (TiCH2), 120.75 (p-CH2Ph),
123.71 (C-2), 125.98 (C-3), 127.39 (o-CH2Ph, overlap with solvent
signal), 127.76 (m-CH2Ph), 136.95 (C-4), 143.91 (C-6), 144.04
(ipso-CH2Ph), 166.21 (C-1).
cryst size, mm
cryst color
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
0.63 × 0.26 × 0.14
dark red
triclinic
P1h (no. 2)
9.4075(18)
15.683(3)
16.292(3)
104.389(5)
102.912(5)
103.148(5)
2165.1(7)
2
Reaction of 2a with B(C6F5)3. To a solid mixture of 2a (30
mg, 46 µmol) and B(C6F5)3 (28 mg, 55 µmol) in an NMR tube
was added a cooled solution of bromobenzene-d5 at -30 °C, and
the reaction was monitored at different temperatures. 1H NMR
(C6D5Br, -30 °C): δ 1.33 (s, 9 H, C(CH3)3), 1.35 (s, 18 H,
C(CH3)3), 1.46 (s, 9 H, C(CH3)3), 1.81 (m, 2 H, SCH2), 2.0-2.1
(br m, SCH2, overlap with CH3 signals), 2.05 (s, 3 H, CH3), 2.09
(s, 3 H, CH3), 2.13 (s, 3 H, CH3), 2.18 (s, 3 H, CH3), 2.47 (d, 1 H,
Z
F
calcd, g cm-3
1.192
0.330
834
µ, mm-1
F(000)
2θmax, deg
1.35 to 26.06
h, -11 to 11
k, -19 to 19
l, -20 to 20
25 373
index ranges
no. of reflns measd
2
2JHH ) 9 Hz, SCH2), 2.53 (d, 1 H, JHH ) 9 Hz, SCH2), 2.74 (d,
no. of indep reflns
no. of params
8507 [R(int) ) 0.0428]
548
1 H, 2JHH ) 9 Hz, SCH2), 3.06 (d, 1 H, 2JHH ) 9 Hz, SCH2), 3.39
(s, 1 H, TiCH2) overlap with 3.41 (br s, 4 H, BCH2), 3.76 (br s, 2
H, TiCH2), 3.89 (br, 1 H, TiCH2), 6.31 (s, 1 H), 6.43 (br d, 1 H),
6.56 (d, 2 H), 6.74-6.85 (m), 6.98-7.05 (m, overlap with solvent
signals), 7.12 (m), 7.17-7.21 (m), 7.38 (m, 1 H), 7.48 (m, 2 H).
1H NMR (C6D5Br, +50 °C): δ 1.42 (s, 18 H, C(CH3)3), 2.05 (d,
2 H, 2JHH ) 6.5 Hz, SCH2), 2.17 (s, 6 H, CH3), 2.79 (d, 2 H, 2JHH
) 6.5 Hz, SCH2), 3.31 (br s, 2 H, BCH2), 3.79 (d, 1 H, 2JHH ) 6.5,
TiCH2), 3.94 (d, 1 H, 2JHH ) 6.5, TiCH2), 6.7 (s, 2 H, 5-CH), 6.98
(m, 2 H, m-TiCH2Ph), 7.06 (m, 1 H, p-TiCH2Ph), 7.1-7.2 (m, 5
H, BCH2Ph), 7.15 (m, 2 H, o-TiCH2Ph), 7.34 (s, 2 H, 3-CH).
13C{1H} NMR (C6D5Br, -30 °C): δ 20.90, 20.95 (CH3), 29.11,
29.22, 29.41 (C(CH3)3), 32.12 (br s, BCH2), 36.18, 38.31, 39.32,
41.58 (SCH2), 97.19 (TiCH2), 97.57 (TiCH2), 122.4-149.8 (aro-
matic signals and solvent signals), 162.58 (s, C-1), 162.79 (s, C-1),
163.61 (s, C-1), 164.06 (s, C-1). 13C{1H} NMR (C6D5Br, +50
°C): δ 20.64 (CH3), 29.57 (C(CH3)3), 31.9 (br s, BCH2), 34.17
(C(CH3)3), 37.94 (SCH2), 41.17 (SCH2), 98.11 (TiCH2), 122.4-
140.4 (aromatic signals, overlap with solvent signals), 147.49 (ipso-
CH2Ph), 163.38 (C-1). 11B NMR (C6D5Br, -30 °C): δ -12.15
GOF
1.024
final R indices R1, wR2 (obsd data)
final R indices R1, wR2 (all data)
largest e-max., e-min., e Å-3
0.0422/0.1011
0.0561/0.1083
0.477/-0.229
g, 2.38 mmol) at -30 °C was added dropwise a 1.0 M solution of
PhCH2MgCl in diethyl ether (0.76 g, 5.0 mL, 5.01 mmol) and stirred
for 1 h at the same temperature. Then, 15 mL of diethyl ether was
added at -30 °C, and the solution was then gradually allowed to
warm to ambient temperature and stirred for 4 h. The solution was
filtered, concentrated, and stored at -30 °C to afford a dark red
powder; yield 0.27 g (22%). 1H NMR: δ 1.98 (br s, 10 H, 4-CH3
4
and SCH2), 3.37 (s, 4 H, TiCH2), 6.65 (d, 2 H, JHH ) 1.5 Hz,
C5), 6.86 (d, 2 H, 3JHH ) 7.5 Hz, C3), 6.87 (t, 2 H, 3JHH ) 7.5 Hz,
3
3
p-CH2Ph), 6.94 (d, 2 H, JHH ) 7.5 Hz, C6), 7.07 (t, 4 H, JHH
)
7.5 Hz, m-CH2Ph), 7.22 (d, 4 H, 3JHH ) 7.5 Hz, o-CH2Ph). 13C{1H}
NMR: δ 20.35 (4-CH3), 36.92 (SCH2), 89.27 (TiCH2), 116.41 (C-
6), 119.80 (C-2), 123.76 (p-CH2Ph), 128.58 (m-CH2Ph), 129.95
(C-4), 130.67 (o-CH2Ph), 132.55 (C-3), 133.37 (C-5), 142.0 (ipso-
CH2Ph), 167.64 (C-1).
3
(s). 19F NMR (C6D5Br, -30 °C): δ -130.25 (d, JFF ) 14 Hz,
Dibenzyl{1,5-dithiapentanediyl-2,2′-bis(6-tert-butyl-4-methyl-
phenoxy)}titanium (4a). To a solution of 3a (0.63 g, 1.13 mmol)
in diethyl ether at -30 °C was added dropwise 1.0 M PhCH2MgCl
in diethyl ether (0.34 g, 2.3 mL, 2.30 mmol), and the mixture was
stirred for 1 h at the same temperature. The solution was then
gradually allowed to warm to ambient temperature and stirred for
6 h. The solution was filtered and concentrated to give 0.28 g of
dark red powder; yield 37%. Analytical samples were obtained from
o-C6F5), -162.95 (t, 3JFF ) 14 Hz, p-C6F5), -165.78 (d, 3JFF ) 14
Hz, m-C6F5).
Reaction of 2b with B(C6F5)3. To a solid mixture of 2b (32
mg, 43 µmol) and B(C6F5)3 (27 mg, 52 µmol) in an NMR tube
was added a cooled solution of bromobenzene-d5 at -30 °C, and
the reaction was monitored at different temperatures. 1H NMR
(C6D5Br, -30 °C): δ 1.15 (s, 9 H, C(CH3)3), 1.21 (s, 9 H, C(CH3)3),
1.24 (s, 9 H, C(CH3)3), 1.29 (s, 9 H, C(CH3)3), 1.39 (s, 9 H,
C(CH3)3), 1.42 (s, 18 H, C(CH3)3), 1.54 (s, 9 H, C(CH3)3), 1.68 (d,
1
a toluene/diethyl ether mixture at 0 °C. H NMR: δ 1.00 (quint,
3JHH ) 5.8 Hz, 2 H, CH2), 1.84 (s, 18 H, C(CH3)3), 2.13 (t, 2JHH
)
2
1 H, JHH ) 8 Hz, SCH2), 1.89 (m, 2 H, SCH2), 2.06 (m, 1 H,
5.8 Hz, 4 H, SCH2), 2.23 (s, 6 H, CH3), 3.59 (s, 4 H, TiCH2), 6.85
2
4
3
SCH2), 2.22 (m, 1 H, SCH2), 2.52 (m, 1 H, JHH ) 8 Hz, SCH2),
(d, 2 H, JHH ) 1.2 Hz, 5-CH), 6.95 (t, JHH ) 7.3 Hz, 2 H,
p-CH2Ph), 7.18 (t, 4 H, 3JHH ) 7.3 Hz, m-CH2Ph), 7.26-7.28 (m,
4 H, overlap with solvent signal, o-CH2Ph), 7.29 (s, 2 H, 3-CH).
13C{H} NMR: δ 20.93 (CH3), 22.84 (CH2), 30.03 (C(CH3)3), 34.76
(SCH2), 35.52 (C(CH3)3), 95.15 (TiCH2), 123.06 (C-2), 124.92 (p-
CH2Ph), 128.38 (m-CH2Ph), 128.52 (C-4), 128.86 (C-3), 129.74
(C-5), 130.38 (o-CH2Ph), 137.51 (C-6), 146.41 (ipso-CH2Ph),
164.79 (C-1). Anal. Calcd for C39H48O2S2Ti: C, 70.89; H, 7.32;
S, 9.70. Found: C, 69.49; H, 7.12; S, 9.85.
2
2
2.75 (d, 1 H, JHH ) 8 Hz, SCH2), 3.15 (d, 1 H, JHH ) 8 Hz,
SCH2), 3.35 (m, 1 H, TiCH2), 3.44 (br s, BCH2), 3.78 (s, 1 H,
TiCH2), 3.82 (s, 1 H, TiCH2), 3.89 (m, 1 H, TiCH2), 6.48 (br d, 1
H), 6.55 (br s, 1 H), 6.68 (br d, 1 H), 6.86 (br), 6.94-7.02 (br m),
1
7.29 (br), 7.44 (br), 7.48 (br), 7.53 (aromatic signals). H NMR
(C6D5Br, +60 °C): δ 1.32 (s, 18 H, C(CH3)3), 1.52 (s, 18 H,
C(CH3)3), 2.14 (d, 2 H, 2JHH ) 7 Hz, SCH2), 2.88 (d, 2 H, 2JHH
)
2
7 Hz, SCH2), 3.37 (br s, 2 H, BCH2), 3.85 (d, 1 H, JHH ) 4 Hz,
2
TiCH2), 4.01 (d, 1 H, JHH ) 4 Hz, TiCH2), 6.75-6.90 (m), 6.98
Dibenzyl{1,5-dithiapentanediyl-2,2′-bis(4,6-di-tert-butyl-
phenoxy)}titanium (4b). To a solution of 3b (0.64 g, 1.0 mmol)
in toluene at -78 °C was added dropwise PhCH2MgCl in diethyl
ether (0.35 g, 2.2 mL, 2.2 mmol), and the mixture was stirred for
1 h at the same temperature. The reaction mixture was gradually
allowed to warm to 0 °C and stirred for 2 h. The solution was
(br), 7.05 (s), 7.15 (br m), 7.40 (br), 7.53 (br) (aromatic signals).
13C NMR (C6D5Br, -30 °C): δ 29.14, 29.28, 29.51, C(CH3)3),
31.34, 31.41, C(CH3)3), 34.60, 34.73, 34.82, 44.88 (C(CH3)3), 35.4
(br, BCH2), 36.0, 37.5, 39.96, 41.73 (SCH2), 97.22 (TiCH2), 97.36
(TiCH2), 119.96-136.42 (aromatic signals, overlap with solvent

3026 Organometallics, Vol. 25, No. 12, 2006
Beckerle et al.
signals), 146.52, 147.33, 149.01, 149.72 (ipso-CH2Ph), 162.74,
163.58, 164.19 (s, C-1). 13C NMR (C6D5Br, +50 °C): δ 29.53
(C(CH3)3), 31.25 (C(CH3)3), 34.68 (C(CH3)3), 34.91 (C(CH3)3),
37.81 (br, BCH2), 41.54 (SCH2), 89.35 (TiCH2), 121.08-149.80
representation, ORTEP-III for Windows was used as implemented
in the program system WINGX.24d
Styrene Polymerization. A 25 mL Schlenk tube was charged
with toluene (calculated for an overall volume of 10 mL; toluene
and styrene were dried over sodium and calcium hydride, respec-
tively, and degassed three times before use). A 0.01 M solution of
2a in toluene (1 mL, 10 µmol) was added, followed by a 4.5 mM
solution of [PhNMe2H][B(C6F5)] in toluene (2 mL; 9.0 µmol) and
a 5 mM solution of tri(n-octyl)aluminum in hexane/toluene (1-3
mL; 5-15 µmol). This mixture was stirred for 20 min, 500 mg of
styrene (4.80 mmol), if not stated otherwise in Table 3, was added,
and the mixture was stirred for the time given in Table 3. The
reaction mixture was quenched by addition of 0.1 mL of acidified
methanol, and the polymer was precipitated from 100 mL of
acidified methanol and dried in vacuo at 60 °C for several hours.
(aromatic signals, overlap with solvent signals), 163.30 (C-1). 11
B
NMR (C6D5Br, -30 °C): δ -12.23 (s). 19F NMR (C6D5Br, -30
°C): δ -130.23 (d, 3JFF ) 14 Hz, o-C6F5), -162.98 (t, 3JFF ) 14
3
Hz, p-C6F5), -165.80 (d, JFF ) 14 Hz, m-C6F5).
Crystal Structure Analysis of 2b. Crystallographic data for 2b
are summarized in Table 1. Single-crystals suitable for X-ray crystal
structure analysis were obtained by slow evaporation of toluene as
toluene solvate inside the glovebox at ambient temperature. The
data collection was performed using ω scans on a Bruker AXS
diffractometer with graphite-monochromated Mo KR radiation at
120(2) K. The data collection as well as the data reduction and
correction for absorption was carried out using the program system
SMART.24a The structure was solved using the program SHELXS-
8624b and was found to be isotypic to [Hf(OC6H2-tBu2-4,6)2-
{S(CH2)2S}(CH2Ph)2].17a From the measured reflections, all inde-
pendent reflections were used, and the parameters were refined by
Acknowledgment. Financial support by the EU Commission
(FP6 project: NMP3-CT-2005-516972), the Deutsche For-
schungsgemeinschaft, and the Fonds der Chemischen Industrie
is gratefully acknowledged. R.M. thanks the Alexander von
Humboldt Foundation for a postdoctoral fellowship.
2
full-matrix least-squares against all Fo data (SHELXL-97)24c and
refined with anisotropic thermal parameters. For the graphical
Supporting Information Available: Tables of all crystal data
and refinement parameters, atomic parameters including hydrogen
atoms, thermal parameters, and bond lengths and angles for 2b.
Variable-temperature 1H and 13C NMR spectra of the reaction
mixture of 2a with B(C6F5)3. 1H and 13C NMR spectra of isotactic
polystyrene obtained by titanium complex 2a activated with
[PhNMe2H][B(C6F5)4]/AlnOct3. This material is available free of
charge via the Internet at http://pubs.acs.org.
(24) (a) Siemens. ASTRO, SAINT, and SADABS. Data Collection and
Processing Software for the SMART System; Siemens Analytical X-ray
Instruments Inc.: Madison, WI, 1996. (b) Sheldrick, G. M. SHELXS-86,
Program for Crystal Structure Solution; University of Go¨ttingen: Go¨ttingen,
Germany, 1986. (c) Sheldrick, G. M. SHELXL-97, Program for Crystal
Structure Refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(d) Farrugia, L. J. WinGX-Version 1.64.02, An Integrated System of
Windows Programs for the Solution, Refinement and Analysis of Single-
Crystal X-Ray Diffraction Data. J. Appl. Crystallogr. 1999, 32, 837.
OM060047E