Mono- And dinuclear cyclopentadienylsiloxo titanium complexes: Synthesis, reactivity, and catalytic polymerization applications

Article abstract of DOI:10.1021/om800492e

Hydrolysis of the (dichloromethylsilyl)cyclopentadienyl titanium compound [Ti(η⁵-C₅Me₄SiMeCl₂)Cl ₃] gave the metallasiloxane dinuclear complex [(TiCl ₂)₂(μ- {(η⁵-C

Full text of DOI:10.1021/om800492e

5588
Organometallics 2008, 27, 5588–5597
Mono- and Dinuclear Cyclopentadienylsiloxo Titanium Complexes:
Synthesis, Reactivity, and Catalytic Polymerization Applications
Lorena Postigo,† Ana B. Va´zquez,† Javier Sa´nchez-Nieves,† Pascual Royo,*,† and
Eberhardt Herdtweck§
Departamento de Qu´ımica Inorga´nica, UniVersidad de Alcala´, Campus UniVersitario, E-28871 Alcala´ de
Henares (Madrid), Spain, and Anorganisch-Chemisches Institut der Technischen UniVersita¨t Mu¨nchen,
Lichtenbergstrasse 4, D-85747 Garching bei Mu¨nchen, Germany
ReceiVed May 29, 2008
Hydrolysis of the (dichloromethylsilyl)cyclopentadienyl titanium compound [Ti(η5-C5Me4SiMeCl2)Cl3]
gave the metallasiloxane dinuclear complex [(TiCl2)2(µ-{(η5-C5Me4SiMeO)2(µ-O)})] (1a). Addition of 4
equiv of RMgCl (R ) Me, Bz) to 1a afforded the corresponding tetraalkyl dititanium derivatives [(TiR2)2(µ-
{(η5-C5Me4SiMeO)2(µ-O)})] (R ) Me 1b, Bz 1c). The benzyl compound 1c reacted with E(C6F5)3 (E )
B, Al) and [Ph3C][B(C6F5)4] to give the bridged dititanium compounds [(TiBz)2(µ-{(η5-C5Me4SiMeO)2(µ-
O)})(µ-X)][Q] (Q ) BzB(C6F5)3; X ) Br, 2Br; Cl, 2Cl; F, 2F; Q ) BzAl(C6F5)3; X ) Cl, 3Cl; Q )
B(C6F5)4; X ) Bz, 4Bz; Cl, 4Cl) by benzyl abstraction and further reaction with the corresponding
halogenated solvents. The addition of excess B(C6F5)3 to 1c gave the bis(zwitterionic) benzyl intermediate
[(TiBz{η6-PhCH2B(C6F5)3})2(µ-{(η5-C5Me4SiMeO)2(µ-O)})] (6), which evolved into the bis(zwitterionic)
fulvene derivative [(Ti{η6-PhCH2B(C6F5)3})2(µ-{(η5-C5Me3(η1-CH2)SiMeO)2(µ-O)})] (5). Related mono-
nuclear siloxo compounds [TiCp*R2(OSiiPr3)] (Cp* ) η5-C5Me5; R ) Cl, 7a; Me, 7b) were obtained
from the reaction of [TiCp*R3] (R ) Cl, Me) with HOSiiPr3. Compound 7b reacted with E(C6F5)3 (E )
B, Al) in C6D6, affording the thermally stable ion-paired derivatives [TiCp*Me(OSiiPr3){MeE(C6F5)3}]
(E ) B, 8B; Al, 8Al). The chloro dinuclear 1a and mononuclear 7a complexes were tested as ethylene
polymerization catalysts and the alkyl complexes 1b, 1c, and 7b as methylmethacrylate polymerization
catalysts.
late polymerization may follow a dinuclear mechanism, and thus,
the employment of bimetallic systems can be of interest to
modify the polymer’s properties.14,15
Introduction
The cooperative effect between two metal atoms has been
shown to induce important modifications in polymerization
behavior with respect to related mononuclear systems where
the metal atoms are far enough from each other. It has been
reported that several types of bimetallic group 4 metal com-
pounds produced a significant increase in the content of branches
in ethylene polymerization, and also a significantly enhanced
R-olefin incorporation was observed in ethylene-R-olefin
copolymerization processes.1-13 Conversely, methylmethacry-
One of the most efficient methods used to bring two metal
centers in close proximity generates covalent bridges between
two monometallic compounds to give dinuclear systems. Func-
tionalization of cyclopentadienyl rings with chlorosilyl groups
has been a particularly useful procedure to synthesize dinuclear
compounds through hydrolysis of the Si-Cl bonds. Depending
on the metal atom and its environment, two types of dinuclear
derivatives have been isolated, one with Si-O-Si oxo bridges
for Nb,16-18 Mo,19 and W19 and other with Si-O-M bridges
for group 4 metals20-23 and Nb.17,18 Related dinuclear com-
pounds containing Si-O-Si bridges have also been described
* Corresponding author. E-mail: pascual.royo@uah.es. Fax: 00 34 91
885 4683.
† Universidad de Alcala´.
§ Universita¨t Mu¨nchen.
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2008 American Chemical Society
Publication on Web 10/07/2008

Dinuclear Titanium Complexes
Organometallics, Vol. 27, No. 21, 2008 5589
Scheme 1a
by introducing a biscyclopentadienyl ligand linked by Si-O-Si
moieties for Ti,24,25 Zr,25 and Hf.25
Continuing with our interest in chlorosilylcyclopentadienyl
complexes,16,18,26-31 we describe in this work the use of the
[Ti(C5Me4SiMeCl2)Cl3]28 derivative with a SiCl2 moiety in the
cyclopentadienyl ring as the starting material to generate
dinuclear compounds with both types of Si-O-Si and Si-O-Ti
bridges by a hydrolysis reaction. Complexes containing these
types of bridges can be useful as models for titania-silica
materials, as it facilitates the study of the active Ti centers with
well-defined and soluble monomeric compounds.32-39
The reactivity of the new dinuclear compounds with different
molar ratios of Lewis acids has been explored with the aim of
studying the influence of the dinuclear system in the activation
of each titanium atom. We have also compared the behavior of
the dinuclear compounds with related mononuclear siloxo
derivatives. Finally, comparative studies related to ethylene and
methylmethacrylate polymerization processes were carried out
with both dinuclear and mononuclear compounds.
Results and Discussion
Neutral Dinuclear Compounds. Hydrolysis of the dichlo-
rosilyl-functionalized cyclopentadienyl mononuclear compound
[Ti(C5Me4SiMeCl2)Cl3]28 in ethyl ether solution afforded the
dinuclear siloxo complex [(TiCl2)2(µ-{(η5-C5Me4SiMeO)2(µ-
O)})] (1a) in high yield (Scheme 1). Formation of the dinuclear
compound with η5-C5Me4SiMeO bridges between the metal
atoms follows the behavior reported previously for the hydroly-
sis of related monochlorosilyl-functionalized cyclopentadienyl
derivatives.16-18 However, simultaneous hydrolysis of the
second Si-Cl bond in the starting product gave rise to the
formation of an additional Si-O-Si bridge. Compound 1
showed remarkable stability to possible further hydrolysis
processes. Although compound 1 contains two diastereogenic
Si atoms, the intrinsically diastereoselective formation of the
Si-O-Si bridge is responsible for the generation of only one
a
(i) H2O, Et2O, 120 °C, 24 h; (ii) RMgCl (R ) Me, Bz), Et2O.
1
diastereoisomer of C2 symmetry, consistent with the H and
13C NMR spectra observed for the resulting reaction product.
Thus, both cyclopentadienyl η5-C5Me4Si ligands were equiva-
lent, presenting an ABCD system, and also only one resonance
was observed for both equivalent Si-Me groups.
Figure 1. ORTEP plot of the molecular structure of [(TiCl2)2(µ-
{(η5-C5Me4SiMeO)2(µ-O)})] (1a) in the solid state. Thermal
ellipsoids are drawn at the 30% probability level. Hydrogen atoms
are omitted for clarity. Symmetry code ′ ) 1-x, y, 0.5-z.
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The molecular structure of 1a is illustrated in Figure 1, and
selected bond lengths and angles are listed in Table 1. It consists
of a dinuclear molecule formed by two [TiCl2(µ-{η5-
C5Me4SiMeO})] units in which the oxygen atoms link both
metal fragments through a pair of Si-O-Ti bridges. The
molecule is located on a crystallographic 2-fold axis that bisects
the Si-O2-Si′ angle. Furthermore, one additional oxygen atom
also links both silicon atoms through a Si-O-Si bridge. The
presence of this Si-O-Si bridge causes a slight elongation of
the Ti-O bond and a reduction of ca. 10° for the Si-O-Ti
angle compared with related Si-O-Ti bridges in the dinuclear
compounds [(TiCl2)2(µ-{η5-C5R4SiMe2O}2)] (R ) H,20 A; Me,23
B). A similar reduction was observed in the structure of
[(TiMe2)2(µ-{η5-C5Me4SiMe2O}2)(µ-CH2)]41 (C), with one ad-
ditional bridge between the titanium atoms. However, the Ti-Ti
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5590 Organometallics, Vol. 27, No. 21, 2008
Postigo et al.
Table 1. Selected Bond Distances (Å) and Angles (deg) for Compounds 1a, [(TiCl2)2(µ-{η5-C5R4SiMe2O}2)] (R ) H, A;20 Me, B23), and
[(TiMe2)2(µ-{η5-C5Me4SiMe2O}2)(µ-CH2)]41 (C)
complex
Ti-O1
Si-O1
Si-O2
Ti · · · Cp
Ti · · · Ti′
Ti-O1-Si
Si-O-Si′
Si · · · Si
1a
A
B
1.803(1)
1.767(19)
1.771(4)
1.827(1)
1.643(1)
1.653(1)
1.650(4)
1.640(1)
1.640(1)
2.038
2.026
2.031
2.058
5.193
5.255
5.099
3.371
147.96(9)
160.2(1)
159.8(2)
150.09(7)
120.2(1)
2.845
4.700
4.829
4.535
C
Scheme 2a
case, the result was dependent on the reaction conditions,
temperature, solvent, and Lewis acid molar amount.
Reaction of 1c with B(C6F5)3 in CD2Cl2 at -70 °C gave the
neutral oxo-borane adduct [(TiBz2)2(µ-{(η5-C5Me4SiMeO)2(µ-
O · B(C6F5)3)})] (1cB) as the main product (Scheme 2). Moni-
toring of this solution while the temperature was increased
showed the slow transformation of 1cB into the chloro-bridged
compound [(TiBz)2(µ-{(η5-C5Me4SiMeO)2(µ-O)})(µ-Cl)][BzB-
(C6F5)3] (2Cl), which was the only product at 25 °C. It may be
reasonably expected that this transformation occurred by reaction
with the chlorinated solvent of the intermediate benzyl bridged
cation [(TiBz)2(µ-{(η5-C5Me4SiMeO)2(µ-O)})(µ-Bz)]+. This
putative tribenzyl intermediate derivative was identified by
NMR spectroscopy as [(TiBz)2(µ-{(η5-C5Me4SiMeO)2(µ-O)})-
(µ-Bz)][B(C6F5)4] (4Bz) in the reaction of 1c with
[Ph3C][B(C6F5)4] in CD2Cl2 at -70 °C (Scheme 2), which also
showedtheevolutionof4B+to[(TiBz)2(µ-{(η5-C5Me4SiMeO)2(µ-
O)})(µ-Cl)]+ (4Cl+) at higher temperature.
The same reaction of 1c with B(C6F5)3 in C6D6 gave a
brownish insoluble oil, which after dissolution in halogenated
solvents gave the related halide-bridged cationic compounds
[(TiBz)2(µ-{(η5-C5Me4SiMeO)2(µ-O)})(µ-X)]+ (X ) Br, 2Br+
(BrC6D5); Cl, 2Cl+ (ClC6D5 or CD2Cl2); F, 2F+ (FC6D5))
(Scheme 2), which were characterized by NMR spectroscopy.
These cationic compounds were also formed when the reaction
of 1c with B(C6F5)3 was carried out directly in the halogenated
solvents. The transformation was immediate when CD2Cl2 was
used as solvent, whereas slower reactions were observed for
the other deuterated halobenzenes according to the following
sequence: FC6D5 (2 h) > BrC6D5 (24 h) > ClC6D5 (48 h). The
reaction rate is consistent with the X-C energy bond for BrC6D5
and ClC6D5. However, the surprisingly faster activation of the
stronger C-F bond could be justified by the favored formation
of a thermodynamically more stable fluoride bridge, as a
consequence of its smaller size, which allows better overlapping
of the orbitals involved in the bridge formation.
a
(i) Al(C6F5)3; (ii) B(C6F5)3, -70 °C, CD2Cl2; (iii) Ph3C[B(C6F5)4],
-70 °C, CD2Cl2; (iv) E(C6F5)3 (E ) B, Al), CD2Cl2 or XC6D5.
distance, over 5 Å in 1a, is similar to that found in complexes
A and B, whereas a clear approach of both titanium atoms to
ca. 3 Å was observed for compound C. In contrast, both silicon
atoms are clearly closer in compound 1a due to the presence of
the oxo bridge. As a consequence of the Si-O-Si and
Ti-CH2-Ti bridges in 1a and C, respectively, the angle formed
by the planes containing both cyclopentadienyl rings is close
to 30°, whereas both rings are parallel in A and B. A lower
π-bonding contribution in the Ti-O and/or Si-O bonds of the
Ti-O-Si bridging system would be consistent with the closer
angle observed for 1a with respect to complexes A and B.
When Al(C6F5)3 and [Ph3C][B(C6F5)4] were employed as
Lewis acids, the analogous ionic compounds [(TiBz)2(µ-{(η5-
C5Me4SiMeO)2(µ-O)})(µ-Cl)][Q] (Q ) BzAl(C6F5)3, 3Cl;
B(C6F5)4, 4Cl) were obtained. Generation of toluene and 1,2-
diphenylethane in all of these reactions suggests that the
benzyl-halide exchange proceeded via homolytic bond cleav-
age.42 Compounds 2-4 were stable in XC6D5 solutions, but in
CD2Cl2 evolved to give the neutral chloride derivative 1a as
the only final product.
Alkylation of compound 1a with RMgCl (R ) Me, Bz)
provided the corresponding tetraalkyl complexes [(TiR2)2(µ-
{(η5-C5Me4SiMeO)2(µ-O)})] (R ) Me, 1b; Bz, 1c) (Scheme
1), which were sensitive to light and decomposed slowly at
ambient temperature. The NMR spectra of these complexes
presented a similar pattern to that observed for 1a, with two
new sets of resonances corresponding to the new diastereotopic
alkyl groups bound to each titanium atom.
The 1H and 13C NMR spectra of the oxo-borane adduct 1cB
showed resonances very close to the starting compound 1c, the
most significant difference being observed in the 19F NMR
spectrum, which showed resonances corresponding to a tetra-
coordinated boron atom.43-46
Cationic Dinuclear Compounds. The tetrachloro compound
1a reacted with Al(C6F5)3, but not with B(C6F5)3, to give the
neutral oxo-alane adduct [(TiCl2)2(µ-{(η5-C5Me4SiMeO)2(µ-
O · Al(C6F5)3)})] (1aAl), which was unaltered at ambient
temperature (Scheme 2). In contrast, reactions of the tetramethyl
derivative 1b with different Lewis acids (E(C6F5)3 (E ) B, Al),
[Ph3C][B(C6F5)4]) unfortunately failed to give any characterized
compound even at low temperature, whereas more easily
identifiable compounds were observed when similar reactions
were carried out using the tetrabenzyl derivative 1c. In this last
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1993, 12, 486.
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Chem. 2006, 45, 487.

Dinuclear Titanium Complexes
Organometallics, Vol. 27, No. 21, 2008 5591
Scheme 3a
The cationic complexes 2+-4+, in addition to the two
stereogenic Si centers, present two additional stereogenic Ti
atoms. However, the formation of these cationic compounds
was also diastereoselective, as evidenced by the NMR spectra
that showed resonances for only one diastereoisomer of C2
symmetry, which corresponds with the formation of the halide
bridge opposite the Si-O-Si bridge. Hence, an ABCD spin
system similar to that discussed for complexes 1 was observed
in their NMR spectra for the C5Me4Si substituent. The 1H NMR
spectra also showed two doublets for the diastereotopic Ti-CH2
protons. The benzyl group attached to the titanium atoms was
η2-coordinated, in accordance with the value observed for the
coupling constant JC-H about 147 Hz.47-50 The 19F NMR
spectra of the ionic derivatives 2X demonstrated that no ion-
pair interaction is present, in line with a ∆δ(Fp - Fm) of 2.8
ppm.51 Furthermore, the 19F NMR spectrum of 2F+ showed a
broad resonance at negative values (δ -77.0) corresponding to
the Ti-F-Ti bridge.52,53
In contrast, compound 4Bz+ has the same NMR pattern as
those observed for related halogen-bridged compounds 2+-4+,
1
with an additional broad resonance in the H NMR at δ 1.87
a
corresponding to the CH2 group bridging both titanium atoms.
(i) >2 B(C6F5)3, - MeC6H5; toluene or BrC6D5.
The terminal benzyl groups were η1-coordinated, in accordance
1
with the value observed for the coupling constant JC-H about
used to characterize the reaction product as a mixture of the
bis-zwitterionic fulvene derivative [(Ti{η6-PhCH2B(C6F5)3})2(µ-
{(η5-C5Me3(η1-CH2)SiMeO)2(µ-O)})] (5) as the major product
(>65%) (Scheme 3) and of the monocationic halogen-bridged
compound 2X+. Unfortunately, longer reaction times did not
improve the yield of 5, nor did higher amounts of B(C6F5)3,
with only decomposition of the starting materials occurring.
Compound 5 has each titanium atom stabilized by η6-C6H5
coordination of the benzylborate anion. Such an interaction is
of prime importance59-61 because only decomposition, rather
than formation of the dinuclear compound, could be observed
when 2 equiv of the noncoordinating anion salt [Ph3C][B(C6F5)4]
was employed. It is remarkable that compound 5 contains two
fulvene ligands, which were formed by hydrogen abstraction
from a cyclopentadienyl-methyl group by both benzyl ligands
bound to the titanium atoms on the proposed monobenzyl
intermediate [(TiBz{η6-PhCH2B(C6F5)3})2(µ-{(η5-C5Me4SiMeO)2-
(µ-O)})] (6).
When the same type of reaction was carried out in CD2Cl2,
only the monocationic derivative 2Cl+ was formed, as the
substitution of the benzyl bridge in the intermediate complex
2Bz+ was faster than abstraction of a second benzyl ligand.
However, the use of XC6D5 (X ) Br, Cl) as solvents also
allowed the formation of 5, although a higher proportion of the
respective monocationic derivatives 2X+ was observed com-
pared with the products of reactions in toluene or benzene. It is
also important to note that monocations 2X+ did not react with
excess B(C6F5)3 or [Ph3C][B(C6F5)4].
127 Hz. In this case, we did not observe exchange between
both types of bridging and terminal benzyl ligands54 because
thepresenceoftheSi-O-Sibridgepreventssucharearrangement.
The behavior described here for compound 1c parallels that
observed for the related dinuclear titanium compound [(TiBz2)2(µ-
{η5-C5H4SiMe2O}2)], for which the benzyl-bridged intermediate
was unstable in aromatic solvents, decomposing to give
unidentified paramagnetic species.54 The substitution of the
benzyl by a halide bridge occurring in halogenated solvents is
clearly favored by the π-donating ability of this substituent,
which increases the electron density, reducing their positive
charge.54-56 Cationic dinuclear group 4 complexes with halide
bridges have also been formed by rearrangement of mononuclear
cationic derivatives in halogenated solvents.53,57,58
The dinuclear nature of compound 1c could be helpful to
synthesize dinuclear dicationic derivatives by abstraction of one
benzyl substituent from each titanium atom. This goal was
successfully achieved by stirring 1c with excess B(C6F5)3 in
toluene or benzene to give an insoluble oil after 3 days at 20
°C. Solutions of this oil obtained in halogenated solvents were
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(52) Perdih, F.; Pevec, A.; Petricek, S.; Petric, A.; Lah, N.; Kogej, K.;
Demsar, A. Inorg. Chem. 2006, 45, 7915.
(53) Chen, M. C.; Roberts, J. A. S.; Seyam, A. M.; Li, L.; Zuccaccia,
C.; Stahl, N. G.; Marks, T. J. Organometallics 2006, 25, 2833.
(54) Jime´nez, G.; Royo, P.; Cuenca, T.; Galakhov, M. Organometallics
2001, 20, 5237.
(55) Royo, E.; Royo, P.; Cuenca, T.; Galakhov, M. Organometallics
2000, 19, 5559.
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Bochmann, M. J. Organomet. Chem. 1997, 543, 209.
(57) Deckers, P. J. W.; van der Linden, A. J.; Meetsma, A.; Hessen, B.
Eur. J. Inorg. Chem. 2000, 929.
The NMR spectra of compound 5 correspond to a C2
symmetry complex and confirm the presence of only three
methyl substituents at the cyclopentadienyl ring. The main
1
features of its H NMR spectrum are the two doublets for the
diastereotopic fulvene CH2 moiety and the multiplets corre-
(59) Sassmannshausen, J.; Green, J. C.; Stelzer, F.; Baumgartner, J.
Organometallics 2006, 25, 2796.
(60) Green, M. L. H.; Sassmannshausen, J. Chem. Commun. 1999, 115.
(61) Bosch, B. E.; Erker, G.; Frohlich, R.; Meyer, O. Organometallics
1997, 16, 5449.
(62) Pellecchia, C.; Immirzi, A.; Grassi, A.; Zambelli, A. Organome-
tallics 1993, 12, 4473.
(58) Yang, X.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1994, 116,
10015.
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115, 1160.

5592 Organometallics, Vol. 27, No. 21, 2008
Postigo et al.
Table 2. Ethylene Polymerization with Complexes 1a and 7aa
Scheme 4a
d
d
run complex
cocat.
MAO (sol)b traces
dry-MAO traces
MAO (sol)b 8.3
dry-MAO 11.7
yield (g) Ac 105 Mw Mw/Mn Tm (°C)e
1
2
3
4
1a
1a
7a
7a
664
4.63
2.58
2.09
136.0
141.9
936 12.84
a Polymerization conditions: P(ethylene) ) 5 bar, T ) 50 °C, solvent
) toluene (200 mL), t ) 30 min, [1a] ) 2.5 µmol, [7a] ) 5 µmol, Al/
Ti ) 500. b MAO in solution 1.5 M in toluene. c Activity ) g PE/
(mmol compd · bar · h). d Determined by GPC in trichlorobenzene at 140
°C vs polystyrene standards. e Determined by DSC measurement.
aryloxo ligand,70-72 although the related alkoxo derivative
[TiCp*Me2(OtBu)] was unstable upon addition of B(C6F5)3
probably by activation of the tBu group.73,74
Ethylene Polymerization. The dinuclear [(TiCl2)2(µ-{(η5-
C5Me4SiMeO)2(µ-O)})] (1a) and mononuclear [TiCp*Cl2-
(OSiiPr3)] (7a) dichloro complexes were studied as ethylene
polymerization catalysts in the presence of MAO and dry MAO
(Al/Ti ) 500, 5 bar, 50 °C). The dinuclear compound 1a showed
negligible activity under these conditions (runs 1 and 2). The
steric characteristics of this bimetallic compound and its
tendency to form bridges between the titanium atoms decrease
the electronic and coordinative deficiency of the active species,
making monomer incorporation and chain growth more difficult.
A similar result was observed with a imido-bridged dititanium
compound,7 contrasting with the activity reported for dinuclear
compounds with longer chains that keep the metal centers
separate.1-6,8-13
Conversely, the mononuclear siloxo compound 7a exhibited
high activity, giving HDPE with a narrow polydispersity (runs
3 and 4). When dry MAO was employed as cocatalyst (run 4),
the activity, polydispersity, and Mw were improved to give high
molecular weight PE (HMWPE) with low branching, in ac-
cordance with the Tm value and the polydispersity values
corresponding to single-site catalysts. These results are similar
to those reported for aryloxo derivatives [TiCp*Cl2(OAr)]
reported by Nomura et al.75,76
a
(i) HOSiiPr3; (ii) E(C6F5)3 (E ) B, Al).
sponding to the η6-C6H5 fragment, which are high-field shifted
with respect to the noncoordinated phenyl rings.47,62,63 The
resonance observed in the 13C NMR spectroscopy at δ 87.6 for
1
the fulvene CH2 and the coupling constant JC-H confirm the
presence of this activated methylene group.64-67 The 19F NMR
spectrum shows a ∆δ(Fp - Fm) over 4 ppm, which is consistent
with the presence of an ion-pair interaction.
The nonfulvene intermediate 6 was detected by NMR
spectroscopy as a minor product in the mixture obtained by
reaction of 1c with excess B(C6F5)3 in BrC6D5, together with
compounds 2Br and 5, confirming that abstraction of the benzyl
1
ligand occurred before activation of the methyl group. The H
MMA Polymerization. The neutral dinuclear [(TiR2)2(µ-
{(η5-C5Me4SiMeO)2(µ-O)})] (R ) Me, 1b; Bz, 1c) and mono-
nuclear [TiCp*Me2(OSiiPr3)] (7b) compounds were studied as
catalysts for MMA polymerization in the presence of the Lewis
acids E(C6F5)3 (E ) B, Al). As we have described above, total
transformation of 1c by abstraction of two benzyl ligands into
NMR spectrum of compound 6 showed four resonances of the
η5-C5Me4 ring, two doublets for the diastereotopic CH2-Ti
protons, and a broad signal for the CH2-B protons, consistent
with a C2 symmetry compound.
Mononuclear Compounds. The mononuclear siloxo deriva-
tives [TiCp*R2(OSiiPr3)] (R ) Cl, 7a; Me, 7b) were isolated
as referential model compounds for the dinuclear siloxo-bridged
complexes described above. These compounds were obtained
in good yields by alcoholysis of the Ti-Cl and Ti-Me bonds32
of [TiCp*R3] (R ) Cl, Me) when treated with HOSiiPr3
(Scheme 4) at 100 °C for 7 days for 7a and at 25 °C for 2 h for
7b, respectively.
(64) Pellny, P. M.; Kirchbauer, F. G.; Burlakov, V. V.; Baumann, W.;
Spannenberg, A.; Rosenthal, U. Chem. Eur. J. 2000, 6, 81.
(65) Lee, H.; Bonanno, J. B.; Hascall, T.; Cordaro, J.; Hahn, J. M.;
Parkin, G. J. Chem. Soc., Dalton Trans. 1999, 1365.
(66) Schock, L. E.; Brock, C. P.; Marks, T. J. Organometallics 1987,
6, 232.
(67) Bulls, A. R.; Schaefer, W. P.; Serfas, M.; Bercaw, J. E. Organo-
metallics 1987, 6, 1219.
(68) Amo, V.; Andre´s, R.; de Jesu´s, E.; de la Mata, F. J.; Flores, J. C.;
Go´mez, R.; Go´mez-Sal, M. P.; Turner, J. F. C. Organometallics 2005, 24,
2331.
(69) Phomphrai, K.; Fenwick, A. E.; Sharma, S.; Fanwick, P. E.;
Caruthers, J. M.; Delgass, W. N.; Abu-Omar, M. M.; Rothwell, I. P.
Organometallics 2006, 25, 214.
(70) Sa´nchez-Nieves, J.; Royo, P. Organometallics 2007, 26, 2880.
(71) Mayer, J. M.; Curtis, C. J.; Bercaw, J. E. J. Am. Chem. Soc. 1983,
105, 2651.
(72) Kubacek, P.; Hoffmann, R.; Havlas, Z. Organometallics 1982, 1,
180.
(73) Pinkas, J.; Varga, V.; Cisarova, I.; Kubista, J.; Horacek, M.; Mach,
K. J. Organomet. Chem. 2007, 692, 2064.
The mononuclear siloxo derivative 7b reacted with the Lewis
acids E(C6F5)3 (E ) B, Al) to give the ion-paired compounds
[TiCp*Me(OSiiPr3)(MeE(C6F5)3)] (E ) B, 8B; Al, 8Al) (Scheme
4), which were soluble in C6D6. The methyl group bridging the
1
titanium and E atoms was observed in the H NMR spectra at
δ 0.49 for 8B and at δ 0.08 for 8Al. The 19F NMR spectrum of
8B shows a value of ∆δ(Fp - Fm) over 4 ppm, consistent with
the presence of an ion-pair interaction.51 These siloxo zwitte-
rionic methyl compounds 8 were stable for several days,68
contrasting with the decomposition observed when the methyl
compound 1b was reacted with E(C6F5)3 and also with the
instability observed for analogous aryloxo derivatives.69 Ap-
parently, this stability difference among the mononuclear siloxo
and aryloxo complexes could be related to the higher π-donor
ability of the oxygen atom in the siloxo substituent than in the
(74) Stoebenau, E. J.; Jordan, R. F. J. Am. Chem. Soc. 2006, 128, 8162.
(75) Nomura, K.; Liu, J. Y.; Padmanabhan, S.; Kitiyanan, B. J. Mol.
Catal. A: Chem. 2007, 267, 1.
(76) Nomura, K.; Tanaka, A.; Katao, S. J. Mol. Catal. A: Chem. 2006,
254, 197.

Dinuclear Titanium Complexes
Organometallics, Vol. 27, No. 21, 2008 5593
Table 3. Polymerization of MMAa with Complexes 1b, 1c, and 7b
7b,5,14,77-80 although further kinetic studies are required to
assess the mechanism of this process.
with E(C6F5)3 (E ) B, Al)
t
yield 104
104 Mn Mw/ [mm] [mr] [rr]
c
run complex
E
(min) (%) Mn calcb (g/mol)c Mn (%)d (%)d (%)d
Conclusions
1
1b
1b
1b
1b
1c
1c
1c
7b
7b
7b
B
B
B
Al
5
30
30
30
70
70
60
20
0
34
25
60
0
0.12
0.12
0.09
0.03
6.40 1.20
1.81 1.03
13.50 1.42
8.54 1.83
5
5
4
8
25
33
25
30
70
62
71
62
2e
3f
4
Hydrolysis of both Si-Cl bonds of complex [Ti(η5-
C5Me4SiMeCl2)Cl3] generated the dinuclear derivative [(TiCl2)2-
(µ-{(η5-C5Me4SiMeO)2(µ-O)})] (1a) with two siloxo η5-
C5Me4SiMeO units linking both Ti atoms and one oxo bridge
linking both Si atoms. Alkylation of 1a with RMgCl (R ) Me,
Bz)affordedthedialkylderivatives[(TiR2)2(µ-{(η5-C5Me4SiMeO)2(µ-
O)})] (R ) Me, 1b; Bz, 1c). The dimethyl compound 1b was
unstable in the presence of the Lewis acids. However, the
dibenzyl complex 1c generated monocationic complexes with
bridging halogen [(TiBz)2(µ-{(η5-C5Me4SiMeO)2(µ-O)})(µ-
X)]+ (X ) Br, Cl, F) by reaction with E(C6F5)3 (E ) B, Al)
and [Ph3C][B(C6F5)4] in halogenated solvents, as a consequence
of the activation of the highly reactive benzyl bridge in the
cationic compound [(TiBz)2(µ-{(η5-C5Me4SiMeO)2(µ-O)})(µ-
Bz)]+. Abstraction of one Ti-Bz bond of each Ti atom of 1c
was partially possible using excess B(C6F5)3 in aromatic solvents
or BrC6D5 to give a bis-zwitterionic compound, [(TiBz{η6-
PhCH2B(C6F5)3})2(µ-{(η5-C5Me4SiMeO)2(µ-O)})], which was
further transformed by activation of one C-H bond of a η5-
C5Me4 methyl group of both Ti fragments to give the bis-
zwitterionic bisfulvene derivative [(Ti{η6-PhCH2B(C6F5)3})2(µ-
{(η5-C5Me3(η1-CH2)SiMeO)2(µ-O)})]. The stabilization of these
zwitterionic compounds was derived from η6-phenyl coordina-
tion of the anion generated. These results showed that the close
proximity of the two metal centers hindered the formation of
dicationic compounds, due to the easy formation of a halogen
bridge between the metal atoms or to the instability of the
resulting dicationic compound.
The mononuclear siloxo compounds [TiCp*R2(OSiiPr3)] (Cp*
) C5Me5; R ) Cl, 7a; Me, 7b) were synthesized by reaction
of [TiCp*R3] (R ) Cl, Me) with HOSiiPr3. In contrast with the
dinuclear methyl compound 1b, 7b gave the stable zwitterionic
compounds [TiCp*Me(OSiiPr3)(MeE(C6F5)3)] when reacted
with the Lewis acids E(C6F5)3 (E ) B, Al). This stability stems
from the presence of the siloxo group, compared with the
instability previously described for similar alkoxo and aryloxo
derivatives.
The chloro compounds 1a and 7a were studied as catalysts
for ethylene polymerization with MAO and dry MAO as
cocatalysts. Only traces of PE were obtained in the case of 1a,
whereas 7a showed high activity. The lack of activity of
compound 1a may be due to the difficult activation of both Ti
atoms of the dinuclear system, which would generate less active
centers, and also to the easy formation of bridges between these
two Ti atoms as a consequence of their proximity, which would
make the insertion and chain-growing reaction difficult.
The methyl derivatives 1b and 7b polymerized MMA when
activated with B(C6F5)3, although the yield and degree of
syndiotacticity of the PMMA obtained was higher with 1b.
When Al(C6F5)3 was used as cocatalyst, the yield was clearly
lower. Furthermore, the benzyl derivative 1c also showed low
activity, probably as a consequence of the lower reactivity of
the Ti-benzyl versus the Ti-Me bond. Finally, the PDI of the
5
6
7
8
B or Al 60
B
Al
B
Al
B
180
180
30
60
30
0.05
0.03
0.04
6.90 1.31 12
16.11 1.30
1.51 1.01
28
23
28
60
72
63
5
9
9
10g
10
n.d.
n.d.
n.d.
8
29
63
a Polymerization conditions: dinuclear complexes [1b] ) [1c] ) 0.06
mmol and [E(C6F5)3] ) 0.06 mmol premixed in toluene (2 mL), then
MMA (1 mL, [MMA]:[dinuclear complex] ) 155, 25 °C; mononuclear
complex [7b] ) 0.12 mmol and [E(C6F5)3] ) 0.12 mmol premixed in
toluene (2 mL), then MMA (1 mL, [MMA]:[7b] ) 78), 25 °C. b Mn
calc values ) conv × [MMA]/n[Ti] × 100.81 g mol-1 (n ) number of
Ti atoms per molecule; fw MMA ) 100.81). c Determined by GPC in
THF vs polystyrene standard. d Determined by 1H NMR in CDCl3. e 5
mL of toluene. f T (°C) ) -20 °C. g [7b] ) 0.12 mmol and [B(C6F5)3]
) 0.06 mmol.
a dinuclear dicationic compound was not achieved even in the
presence of excess E(C6F5)3 and after several days of reaction
at ambient temperature. However, to avoid possible interference
from dicationic compounds, MMA polymerization studies were
carried out using a dinuclear compound/cocatalyst molar ratio
of 1:1. For the mononuclear compound 7b we have used the
double molar amounts with regard to dinuclear 1b or 1c, aiming
to introduce to the solution an equal number of metal centers
in each experiment and then to compare the behavior of the
dinuclear and mononuclear systems.
MMA polymerization with the dinuclear 1b/B(C6F5)3 system
was fast at ambient temperature, giving a slurry after 5 min
(run 1). The experiment was then run with a larger amount of
solvent to help stirring (run 2). The PMMA obtained in both
cases was 70% syndiotactic, but with narrow polydispersity
(PDI) for the more diluted polymerization (1.03). The experi-
ment was repeated at -20 °C, giving a lower yield after 30
min (run 3), although the PMMA had a higher molecular weight
and a higher polydispersity. When Al(C6F5)3 was used as
cocatalyst (run 4), both the yield and the syndiotacticity were
lower, while the polydispersity was as high as 1.83. Conversely,
polymerization with the benzyl system 1c/E(C6F5)3 (runs 5-7)
required longer times as a consequence of the bulk and kinetic
requirements of the benzyl ligand. In this case, the syndiotac-
ticity was higher for Al(C6F5)3 than for B(C6F5)3, and the
PMMA obtained was of high molecular weight for Al(C6F5)3,
although again the yield was lower.
MMA polymerization with the mononuclear 7b/E(C6F5)3
systems showed the same tendency with regard to E, giving a
moderate yield for B(C6F5)3 (run 8) but negligible activity for
Al(C6F5)3 (run 9). However, the yield and syndiotacticity for
the system 7b/B(C6F5)3 (run 8) were lower than those observed
for 1b, although the polydispersity was as narrow as that
observed for 1b in run 2.
An experiment with half of the molecular amount of B(C6F5)3
(run 10), corresponding to a Ti:B molar ratio of 2:1, as in the
dinuclear system, gave a rather poor yield of PMMA. The
difference observed in the behavior of MMA polymerization
with 1b and with 7b when a Ti:B molar ratio of 2:1 was
employed could be related to the different bimetallic pathway
followed by the dinuclear compound15 instead of the monome-
tallic mechanism exhibited by the mononuclear derivative
(77) Tomasi, S.; Weiss, H.; Ziegler, T. Organometallics 2006, 25, 3619.
(78) Cameron, P. A.; Gibson, V. C.; Graham, A. J. Macromolecules
2000, 33, 4329.
(79) Deng, H.; Soga, K. Macromolecules 1996, 29, 1847.
(80) Collins, S.; Ward, D. G.; Suddaby, K. H. Macromolecules 1994,
27, 7222.

5594 Organometallics, Vol. 27, No. 21, 2008
Postigo et al.
[(TiBz2)2(µ-{(η5-C5Me4SiMeO)2(µ-O)})] (1c). A suspension of
1a (2.00 g, 3.27 mmol) in diethyl ether (50 mL) at -78 °C was
treated with 4 equiv of a THF solution of BzMgCl (2 M, 6.55 mL,
13.10 mmol). The reaction mixture was warmed to room temper-
ature and stirred overnight in the absence of light. Hexane (20 mL)
was then added, and the solution was filtered. The red residue was
extracted again into a mixture of diethyl ether/hexane (40 mL/20
mL). The volatiles were evaporated, and the remaining solid was
washed with 10 mL of hexane to isolate 1c as a red solid (2.31 g,
85%). 1H NMR (C6D6): 0.38 (s, 6 H, SiMe), 1.56 (s, 6 H, C5Me4),
PMMA obtained with both the dinuclear 1b and mononuclear
7b complexes showed features of living polymerization.
Two different polymerization pathways are proposed for the
dinuclear and mononuclear compounds. For the first, coordina-
tion of free MMA and chain growth proceed alternatively on
each Ti atom, whereas for the second, both processes occur at
the same Ti atom. This last assertion was confirmed by the low
yield of PMMA obtained when polymerization was attempted
with a Ti:B molar ratio of 2:1.
2
1.79 (s, 6 H, C5Me4), 1.87 (s, 6 H, C5Me4), 2.06 (d, 2 H, J ) 9
Hz, PhCH2-Ti), 2.20 (d, 2 H, 2J ) 9 Hz, PhCH2-Ti), 2.24 (d, 2 H,
2J ) 9 Hz, PhCH2-Ti), 2.28 (s, 6 H, C5Me4), 3.05 (d, 2 H, 2J ) 9
Hz, PhCH2-Ti), 6.81-7.20 (m, 20 H, C6H5). 13C NMR (C6D6):
0.0 (SiMe), 11.4, 12.1, 13.8 and 14.0 (C5Me4), 86.5 and 86.9
(PhCH2-Ti, JCH ) 125 Hz), 122.8, 123.1, 126.8, 127.9, 128.2, 128.5,
148.8 (Ci), and 150.4 (Ci) (C6H5), 113.4, 131.8, 132.8, 133.9, and
134.2 (C5Me4). Anal. Calc for C48H58O3Si2Ti2 (833.6): C, 69.09;
H, 6.95. Found: C, 69.37; H, 7.15.
Experimental Section
General Considerations. All manipulations were carried out
under an argon atmosphere, and solvents were purified from
appropriate drying agents. NMR spectra were recorded at 400.13
(1H), 376.70 (19F), and 100.60 (13C) MHz on a Bruker AV400.
Chemical shifts (δ) are given in ppm. 1H and 13C resonances were
measured relative to solvent peaks considering TMS ) 0 ppm, while
19F resonance were measured relative to external CFCl3. Assign-
ment of resonances was made from HSQC and HMBC NMR
experiments. Elemental analyses were performed on a Perkin-Elmer
240C. Distilled water was deoxygenated prior to its use and stored
under argon. iPr3SiOH was purchased from Aldrich, degassed, and
stored under Ar with molecular sieves. Compounds [Ti(C5-
Me4SiMeCl2)Cl3],28 [TiCp*R3] (R ) Cl,81 Me82), B(C6F5)3,83
0.5(toluene) · Al(C6F5)3,84 and [Ph3C][B(C6F5)4]85 were prepared by
literature methods. Ethylene (AGA polymer grade) was passed over
columns with supported copper scavenger (BASF R3-11) and
molecular sieves (4 Å) before being passed to the reactor. MMA
was purchased from Aldrich, dried over CaH2 overnight, and
distilled under vacuum. The purified monomer was stored at
-30 °C.
[(TiCl2)2(µ-{(η5-C5Me4SiMeO)2(µ-O · Al(C6F5)3)})] (1a-Al). [(Ti-
Cl2)2(µ-{(η5-C5Me4SiMeO)2(µ-O)})] (1a) (0.100 g, 0.16 mmol) and
0.5(toluene) · Al(C6F5)3 (0.093 g, 0.16 mmol) were stirred in toluene
(5 mL) for 5 min. The volatiles were removed under vacuum,
leaving a red solid, which was washed with hexane (2 × 2 mL) to
give 1a-Al (0.180 g, 85%). 1H NMR (C6D6): 0.29 (s, 6 H, SiMe),
1.93 (s, 6 H, C5Me4), 1.95 (s, 6 H, C5Me4), 1.99 (s, 6 H, C5Me4),
2.20 (s, 6 H, C5Me4). 13C NMR (C6D6): -2.2 (SiMe), 13.0, 13.4,
15.2, and 16.3 (C5Me4), 120.7, 141.8, 141.9, 143.9, and 147.6
(C5Me4), 137.5, 142.3, and 150.5 (m, C6F5). 19F NMR (C6D6):
-120.4 (o-C6F5), -150.5 (p-C6F5), -160.1 (m-C6F5). Anal. Calc
for C38H30O3Si2Ti2Cl4AlF15 (1139.68): C, 40.01; H, 2.63. Found:
C, 40.85; H, 2.58.
[(TiBz2)2(µ-{(η5-C5Me4SiMeO)2(µ-O · B(C6F5)3)})] (1c-B). A
0.5 mL sample of CD2Cl2 previously cooled at -78 °C was added
to a mixture of 1c (0.030 g, 0.03 mmol) and B(C6F5)3 (0.018 g,
0.03 mmol) in a NMR tube cooled at -78 °C. NMR spectroscopy
run after 5 min at -70 °C showed the formation of 1c-B as a unique
product. 1H NMR (CD2Cl2): 0.15 (s, 6 H, SiMe), 1.66 (s, 6 H,
C5Me4), 1.78 (s, 6 H, C5Me4), 1.84 (d, 4 H, 2J ) 9 Hz, PhCH2-Ti),
1.99 (d, 2 H, 2J ) 9 Hz, PhCH2-Ti), 2.14 (s, 6 H, C5Me4), 2.15 (s,
[(TiCl2)2(µ-{(η5-C5Me4SiMeO)2(µ-O)})] (1a). A solution of
[Ti(η5-C5Me4SiMeCl2)Cl3] (2.00 g, 5.12 mmol) in diethyl ether (50
mL) was treated with 2 equiv of deoxygenated water (0.19 mL,
10.24 mmol) at room temperature. The reaction mixture was heated
at 135 °C for 20 h. The volatiles were then removed under vacuum,
and the remaining solid was washed with hexane (2 × 30 mL) to
give 1a as an orange solid (1.41 g, 90%). 1H NMR (CDCl3): 0.47
(s, 6 H, SiMe), 2.34 (s, 6 H, C5Me4), 2.35 (s, 6 H, C5Me4), 2.37 (s,
6 H, C5Me4), 2.38 (s, 6 H, C5Me4). 13C NMR (CDCl3): -1.7 (SiMe),
13.1, 13.7, 15.6 and 16.1 (C5Me4), 119.5, 139.1, 139.4, 141.7, and
144.8 (C5Me4). Anal. Calc for C20H30O3Si2Ti2Cl4 (612.16): C, 39.24;
H, 4.94. Found: C, 39.21; H, 5.11.
2
6 H, C5Me4), 2.40 (d, 2 H, J ) 9 Hz, PhCH2-Ti), 6.75-7.20 (m,
20 H, C6H5). 19F NMR (CD2Cl2): -127.7 (o-C6F5), -156.3 (p-
C6F5), -163.2 (m-C6F5).
[(TiBz)2(µ-Cl)(µ-{(η5-C5Me4SiMeO)2(µ-O)})][BzB(C6F5)3]
(2Cl). A solution of 1c (0.100 g, 0.11 mmol) and B(C6F5)3 (0.061
g, 0.11 mmol) in CH2Cl2 (3 mL) was stirred for 5 min. The volatiles
were removed under vacuum, leaving an oil, which was washed
with hexane (2 × 2 mL) to give 2Cl as a brownish oil (0.120 g,
85%). 1H NMR (CD2Cl2): 0.38 (s, 6 H, SiMe), 1.70 (s, 6 H, C5Me4),
1.96 (s, 6 H, C5Me4), 2.14 (s, 6 H, C5Me4), 2.52 (s, 6 H, C5Me4),
2.83 (bs, 2 H, PhCH2-B), 2.85 (d, 2 H, 2J ) 8 Hz, PhCH2-Ti),
[(TiMe2)2(µ-{(η5-C5Me4SiMeO)2(µ-O)})] (1b). MeMgCl (3 M,
0.86 mL, 2.58 mmol) was injected into a solution of 1a (0.38 g,
0.62 mmol) in diethyl ether (50 mL) at -78 °C. The reaction
mixture was warmed to room temperature and stirred overnight.
The volatiles were removed under vacuum to yield a yellow residue,
which was extracted into hexane (2 × 25 mL). The volume was
concentrated to ca. 20 mL and cooled to -35 °C, yielding 1b as a
yellow solid (0.19 g, 58%). 1H NMR (C6D6): 0.44 (s, 6 H, SiMe),
0.67 (s, 12 H, Me-Ti), 1.88 (s, 6 H, C5Me4), 1.97 (s, 6 H, C5Me4),
1.99 (s, 6 H, C5Me4), 2.39 (s, 6 H, C5Me4). 13C NMR (C6D6): -0.2
(SiMe), 12.0, 12.1, 13.7, and 14.3 (C5Me4), 54.7 and 56.6 (Me-Ti),
112.0, 127.3, 129.8, 130.4, and 132.9 (C5Me4). Anal. Calc for
C24H42O3Si2Ti2 (529.6): C, 54.34; H, 7.98. Found: C, 54.07; H,
7.96.
2
3.56 (d, 2 H, J ) 8 Hz, PhCH2-Ti), 6.56-7.36 (m, 15 H, C6H5).
13C NMR (CD2Cl2): -1.0 (SiMe), 12.8, 13.7, 16.3, and 16.7
(C5Me4), PhCH2-B was not observed, 85.9 (PhCH2-Ti, JCH ) 147
Hz), 122.5, 127.0, 128.9, 131.7, 133.3, and 135.7 (C6H5), 117.9,
130.1, 132.8, 137.9, and 139.5 (C5Me4), 135.7, 137.8, and 149.5
(m, C6F5), 137.1 (PhCH2-Ti, Ci), 149.9 (PhCH2-B, Ci). 19F NMR
(CD2Cl2): -129.6 (o-C6F5), -163.3 (p-C6F5), -166.1 (m-C6F5).
Anal. Calc for C59H51BF15O3Si2Ti2Cl (1290.1): C, 54.89; H, 3.95.
Found: C, 54.41; H, 3.80.
(81) Llinas, G. H.; Mena, M.; Palacios, F.; Royo, P.; Serrano, R. J.
Organomet. Chem. 1988, 340, 37.
(82) Mena, M.; Royo, P.; Serrano, R.; Pellinghelli, M. A.; Tiripicchio,
A. Organometallics 1989, 8, 476.
(83) Lancaster, S. Synthetic Pages 2003, 215, http://www.syntheticpages.
org/pages/215.
(84) Feng, S. G.; Roof, G. R.; Chen, E. Y. X. Organometallics 2002,
21, 832.
[(TiBz)2(µ-X)(µ-{(η5-C5Me4SiMeO)2(µ-O)})][Q] (Q ) BzB-
(C6F5)3; X ) Br, 2Br; F, 2F; Q ) BzAl(C6F5)3; X ) Cl, 3Cl;
Q ) B(C6F5)4; X ) Cl, 4Cl). [(TiBz2)2(µ-{(η5-C5Me4SiMeO)2(µ-
O)})] (1c) (0.030 g, 0.03 mmol) and the required cocatalyst in 1:1
molar ratio (B(C6F5)3 0.018 g, 0.03 mmol; 0.5(toluene) · Al(C6F5)3
0.020 g, 0.03 mmol; [Ph3C][B(C6F5)4] 0.033 g, 0.03 mmol) were
loaded into a NMR tube, and 0.5 mL of the corresponding solvent
(85) Lancaster, S. Synthetic Pages 2003, 216, http://www.syntheticpages.
org/pages/216.

Dinuclear Titanium Complexes
Organometallics, Vol. 27, No. 21, 2008 5595
was added (BrC6D5 for 2Br, FC6D5 for 2F, CD2Cl2 for 3Cl and
4Cl). Each sample was then shaken vigorously, and the reaction
was monitored by NMR spectroscopy at 25 °C, showing the
formation of 2Br after 24 h, 2F after 2 h, and 3Cl and 4Cl
immediately.
mL) to give a mixture of compounds 5 and 2Br in 5.5:1 molar
ratio. Method B: Compounds 1c (0.030 g, 0.03 mmol) and
B(C6F5)3 (0.055 g, 0.10 mmol) were mixed in 0.5 mL of BrC6D5
in a NMR tube. The reaction was monitored by NMR spectros-
copy, which showed the formation of a mixture of 5 and 2Br in
ca. 3:1 molar ratio after three days at ambient temperature.
1
Data for 2Br. H NMR (BrC6D5): 0.17 (s, 6 H, SiMe), 1.36
1
(s, 6 H, C5Me4), 1.55 (s, 6 H, C5Me4), 1.76 (s, 6 H, C5Me4),
Data for 5. H NMR (BrC6D5): 0.07 (s, 6 H, SiMe), 0.92 (s,
2
1.99 (s, 6 H, C5Me4), 2.48 (d, 2 H, J ) 8 Hz, PhCH2-Ti), 3.02
6H, C5Me3), 1.21 (s, 6H, C5Me3), 1.73 (s, 6H, C5Me3), 2.39 (d, 2
H, C5Me3CH2-Ti, 2J ) 2.4 Hz), 2.80 (d, 2 H, C5Me3CH2-Ti, 2J )
2.4 Hz), 2.83 (bs, 4 H, PhCH2-B), 4.82 (t, 2 H, p-PhCH2-B), 5.73
(t, 2 H, m-PhCH2-B), 5.89 (t, 2 H, m-PhCH2-B), 6.87 (d, 2 H,
o-PhCH2-B), 7.32 (d, 2 H, o-PhCH2-B). 13C NMR (BrC6D5): -0.8
(d, 2 H, 2J ) 8 Hz, PhCH2-Ti), 3.25 (bs, 2 H, PhCH2-B),
6.56-7.36 (m, 15 H, C6H5). 13C NMR (BrC6D5): -2.3 (SiMe),
10.6, 12.8, 14.7, and 15.8 (C5Me4), 30.1 (PhCH2-B), 85.6
(PhCH2-Ti, JCH ) 148 Hz), 121.3, 125.6, 127.6, 130.0, 131.13,
and 134.5 (C6H5), 115.6, 132.8, 135.2, 137.2, and 138.0 (C5Me4),
135.7, 137.8, and 149.5 (m, C6F5), 137.5 (PhCH2-Ti, Ci), 147.7
(PhCH2-B, Ci). 19 NMR (BrC6D5): -129.1 (o-C6F5), -162.8 (p-
C6F5), -165.5 (m-C6F5).
(SiMe), 11.2, 12.2, and 13.6 (C5Me3), 87.6 (C5Me3CH2-Ti, JCH
)
160 Hz), 119.8, 121.4, 123.6, 129.9, 131.4, and 162.8 (Ci) (PhCH2-
B), 118.0, 136.4, 137.3, 138.4, and 140.0 (C5Me3), 135.7, 137.8,
and 149.5 (m, C6F5), PhCH2-B was not observed. 19F NMR
(BrC6D5): -129.1 (o-C6F5), -159.2 (p-C6F5), -163.2 (m-C6F5).
1
Data for 2F. H NMR (FC6D5): 0.19 (s, 6 H, SiMe), 1.40 (s,
6 H, C5Me4), 1.47 (s, 6 H, C5Me4), 1.82 (s, 6 H, C5Me4), 2.03
[(TiBz{η6-PhCH2B(C6F5)3})2(µ-{(η5-C5Me4SiMeO)2(µ-O)})] (6).
Compound 1c (0.030 g, 0.03 mmol) and 3 equiv of B(C6F5)3 (0.055
g, 0.10 mmol) were mixed in 0.5 mL of BrC6D5 in a NMR tube.
The reaction was monitored by NMR spectroscopy at room
temperature, and formation of 6 was detected after 30 min as a
minor product together with 5 and 2Br in a mixture of compounds.
After three days, total transformation of 6 into 5 was observed.
Data for 6: 1H NMR (BrC6D5): -0.50 (s, 6 H, SiMe), 1.29 (s, 6 H,
C5Me4), 1.71 (s, 6 H, C5Me4), 1.92 (s, 6 H, C5Me4), 2.33 (s, 6 H,
C5Me4), 2.40 (d, 2 H, 2J ) 8 Hz, PhCH2-Ti), 3.45 (d, 2 H, 2J ) 8
Hz, PhCH2-Ti), 3.10 (bs, 4 H, PhCH2-B), 5.20 (m, 2 H,
p-PhCH2-B), 5.41 (m, 2 H, m-PhCH2-B), 6.80 (m, 2 H, m-PhCH2-
B), 6.88 (m, 2 H, o-PhCH2-B), 7.10 (m, 2 H, o-PhCH2-B). 13C
NMR (BrC6D5): 89.3 (PhCH2-Ti). 19F NMR (BrC6D5): -129.1 (o-
C6F5), -159.2 (p-C6F5), -163.2 (m-C6F5).
2
(s, 6 H, C5Me4), 2.43 (d, 2 H, J ) 9 Hz, PhCH2-Ti), 3.14 (d,
2 H, 2J ) 9 Hz, PhCH2-Ti), 3.28 (bs, 2 H, PhCH2-B), 6.12-7.15
(m, 15 H, C6H5). 13C NMR (FC6D5): -3.0 (SiMe), 10.4, 11.3,
14.2, and 14.7 (C5Me4), 84.5 (PhCH2-Ti, JCH ) 148 Hz), 121.5,
125.9, 128.2, 128.5, 131.1, and 134.2 (C6H5), 116.4, 130.1, 135.4,
137.0, and 138.0 (C5Me4), 135.7, 137.8, and 149.5 (m, C6F5),
137.5 (PhCH2-Ti, Ci), 148.9 (PhCH2-B, Ci), PhCH2-B was not
observed. 19F NMR (FC6D5): -93.8 (Ti-F-Ti), -130.2 (o-C6F5),
-164.2 (p-C6F5), -167.0 (m-C6F5).
1
Data for 3Cl. H NMR (CD2Cl2): 0.38 (s, 6 H, SiMe), 1.70
(s, 6 H, C5Me4), 1.96 (s, 6 H, C5Me4), 2.14 (s, 6 H, C5Me4),
2
2.52 (s, 6 H, C5Me4), 2.85 (d, 2 H, J ) 8 Hz, PhCH2-Ti), 3.20
(bs, 2 H, PhCH2-Al), 3.56 (d, 2 H, 2J ) 8 Hz, PhCH2-Ti),
6.56-7.36 (m, 15 H, C6H5). 13C NMR (CD2Cl2): -1.0 (SiMe),
12.8, 13.7, 16.3, and 16.7 (C5Me4), 29.0 (PhCH2-Al), 85.9
(PhCH2-Ti, JCH ) 147 Hz), 122.5, 127.0, 128.9, 131.7, 133.3,
and 135.7 (C6H5), 117.9, 130.1, 132.8, 137.9, and 139.5 (C5Me4),
135.7, 137.8, and 149.5 (m, C6F5), 137.1 (PhCH2-Ti, Ci), 149.9
(PhCH2-Al, Ci). 19F NMR (CD2Cl2): -118.6 (o-C6F5), -156.6
(p-C6F5), -162.0 (m-C6F5).
[TiCp*Cl2(OSiiPr3)] (7a). A solution of [TiCp*Cl3] (0.525 g,
1.81 mmol) and iPr3SiOH (0.475 g, 2.71 mmol) in toluene (30
mL) was refluxed for seven days. The solvent was completely
removed to give a red solid, which was washed with 20 mL of
1
hexane to afford 7a (0.61 g, 80%). H NMR (CDCl3): 1.10 (m,
21 H, Me2CH and Me2CH), 2.21 (s, 15 H, C5Me5). 13C NMR
(CDCl3): 13.2 (C5Me5), 13.8 (Me2CH), 18.0 (Me2CH), 131.9
(C5Me5). Anal. Calc for C19H36OSiTiCl2 (426.78): C, 53.42; H,
8.43. Found: C, 53.21; H, 8.22.
1
Data for 4Cl. H NMR (CD2Cl2): 0.38 (s, 6 H, SiMe), 1.70
(s, 6 H, C5Me4), 1.96 (s, 6 H, C5Me4), 2.14 (s, 6 H, C5Me4),
2
2.52 (s, 6 H, C5Me4), 2.85 (d, 2 H, J ) 8 Hz, PhCH2-Ti), 3.56
(d, 2 H, 2J ) 8 Hz, PhCH2-Ti), 6.56-7.36 (m, 15 H, C6H5).
13C NMR (CD2Cl2): -1.0 (SiMe), 12.8, 13.7, 16.3, and 16.7
(C5Me4), 85.9 (PhCH2-Ti, JCH ) 147 Hz), 122.5, 127.0, 128.9,
131.7, 133.3, and 135.7 (C6H5), 117.9, 130.1, 132.8, 137.9, and
139.5 (C5Me4), 136.8, 139.7, and 149.4 (m, C6F5), 137.1 (PhCH2-
Ti, Ci). 19F NMR (CD2Cl2): -133.5 (o-C6F5), -162.5 (p-C6F5),
-166.4 (m-C6F5).
[TiCp*Me2(OSiiPr3)] (7b). A toluene solution (10 mL) of
iPr3SiOH (0.585 g, 3.29 mmol) was added dropwise to a toluene
solution (20 mL) of [TiCp*Me3] (0.750 g, 3.29 mmol) at -78
°C. The cooling bath was removed, and the reaction mixture
was allowed to warm to ambient temperature and further stirred
for 2 h. The solution was filtered and the volatiles were removed
1
to yield 7b as a yellowish oil (1.01 g, 80%). H NMR (C6D6):
[(TiBz)2(µ-Bz)(µ-{(η5-C5Me4SiMeO)2(µ-O)})][B(C6F5)4] (4Bz). A
0.5 mL sample of CD2Cl2 previously cooled at -78 °C was
0.55 (Me-Ti), 1.24 (m, 21 H, Me2CH and Me2CH), 1.81 (s, 15
H, C5Me5). 13C NMR (C6D6): 11.7 (C5Me5), 14.3 (Me2CH), 18.5
(Me2CH), 52.5 (Me-Ti), 121.8 (C5Me5). Anal. Calc for
C21H42OSiTi (385.88): C, 65.30; H, 10.88. Found: C, 65.01; H,
10.94.
added to
a mixture of 1c (0.030 g, 0.03 mmol) and
[Ph3C][B(C6F5)4] (0.033 g, 0.03 mmol) in a NMR tube cooled
at -78 °C. The NMR spectra were run at -70 °C, showing the
1
formation of 4Bz as the only product. H NMR (CD2Cl2): 0.12
[TiCp*Me(OSiiPr3){MeE(C6F5)3}] (E ) B, 8B; Al, 8Al).
Compounds 7b (0.100 g, 0.25 mmol) and E(C6F5)3 (B(C6F5)3
0.128 g, 0.25 mmol; Al(C6F5)3 0.143 g, 0.25 mmol) were stirred
in toluene (5 mL) for 5 min. The volatiles were removed under
vacuum and the oil was washed with hexane (4 mL) to give 8B
(0.190 g, 85%) and 8Al (0.194 g, 85%) as yellowish oils.
Data for 8B. 1H NMR (C6D6): 0.49 (bs, 3 H, Me-B), 0.77 (m,
3 H, Me2CH), 0.83 (d, 9 H, J ) 7 Hz, Me2CH), 0.91 (d, 9 H, J
) 7 Hz, Me2CH), 1.43 (s, 3 H, Me-Ti), 1.53 (s, 15 H, C5Me5).
13C NMR (C6D6): 11.9 (C5Me5), 14.3 (Me2CH), 18.4 (Me2CH),
30.1 (Me-B), 73.3 (Me-Ti), 131.5 (C5Me5), 137.2 (C6F5), 148.6
(C6F5). 19F NMR (C6D6): -133.1 (o-C6F5), -159.2 (p-C6F5),
-164.3 (m-C6F5). Anal. Calc for C39H42OSiTiBF15 (897.88): C,
52.12; H, 4.67. Found: C, 52.04; H, 4.56.
(s, 6 H, SiMe), 1.65 (s, 6 H, C5Me4), 1.76 (s, 6 H, C5Me4), 2.10
(s, 6 H, C5Me4), 2.11 (s, 6 H, C5Me4), 1.87 (m, 2 H, TiCH2Ti),
2
2
1.98 (d, 2 H, J ) 8 Hz, PhCH2-Ti), 2.40 (d, 2 H, J ) 8 Hz,
PhCH2-Ti), 6.56-7.36 (m, 15 H, C6H5). 13C NMR (CD2Cl2):
-4.5 (SiMe), 7.6, 8.5, 8.7, and 9.7 (C5Me4), 81.7 (TiCH2Ti, JCH
) 128 Hz), 81.4 (PhCH2-Ti, JCH ) 127 Hz), 120.1-140.3 (C6H5,
C6F5, C5Me4). 19F NMR (CD2Cl2): -133.5 (o-C6F5), -162.5 (p-
C6F5), -166.4 (m-C6F5).
[(Ti{η6-PhCH2B(C6F5)3})2(µ-{(η5-C5Me3(η1-CH2)SiMeO)2(µ-
O)})] (5). Method A: A solution of 1c (0.030 g, 0.03 mmol) and
excess of B(C6F5)3 (0.073 g, 0.15 mmol) were stirred in toluene
(3 mL) for three days at ambient temperature. The solution was
filtered, and the remaining oil was washed with hexane (2 × 2

5596 Organometallics, Vol. 27, No. 21, 2008
Postigo et al.
1
Table 4. Crystallographic Data for
[(TiCl2)2(µ-{(η5-C5Me4SiMeO)2(µ-O)})] (1a)
Data for 8Al. H NMR (C6D6): 0.08 (bs, 3 H, Me-Al), 0.90
(m, 21 H, Me2CH and Me2CH), 1.20 (s, 3 H, Me-Ti), 1.56 (s,
15 H, C5Me5). 13C NMR (C6D6): 11.8 (C5Me5), 14.3 (Me2CH),
18.4 (Me2CH), 71.3 (Me-Ti), Me-Al was not observed, 131.5
(C5Me5), 137.2 (C6F5), 142.3 (C6F5), 150.6 (C6F5). 19F NMR
(C6D6): -122.4 (o-C6F5), -153.7 (p-C6F5), -161.5 (m-C6F5).
Anal. Calc for C39H42OSiTiAlF15 (914.12): C, 51.19; H, 4.59.
Found: C, 50.85; H, 4.51.
formula
fw
C20H30Cl4O3Si2Ti2
612.16
color/habit
orange/fragment
0.08 × 0.13 × 0.25
monoclinic
C2/c (no. 15)
15.4858(1)
8.3884(1)
21.9165(2)
108.6914(4)
2696.82(4)
4
cryst dimens (mm3)
cryst syst
space group
a, Å
b, Å
c, Å
Polymerization of Ethylene with Dinuclear Complex 1a.
Separate solutions of the mononuclear complex 1a (2.5 µmol)
and MAO (10% Al, 2.5 mmol) or dry MAO (2.5 mmol), in ca.
Al/Ti ) 500 molar ratio, in toluene (10 mL) were prepared in
a glovebox. The catalytic ethylene polymerization reactions were
performed in a stainless steel 1 L autoclave (Medimex) in
semibatch mode (ethylene was added by replenishing flow to
keep the pressure constant). The reactor was temperature- and
pressure-controlled and equipped with separated toluene, catalyst,
and cocatalyst injection systems. In a typical experiment, the
autoclave was evacuated and heated for 1 h at 125 °C prior to
use. The reactor was then brought to the desired temperature
with stirring at 600 rpm and charged with 200 mL of toluene.
After pressurizing with ethylene to reach 5 bar total pressure
the autoclave was equilibrated for 5 min. Subsequently, the
solution of MAO was injected into the reactor (using a
pneumatically operated injector), and the reaction was started
by injecting the 1a solution. The reactor was stirred for 30 min
and then vented. The residual MAO was destroyed by addition
of 20 mL of ethanol. Polymeric product was collected, stirred
in acidified ethanol overnight, and rinsed with ethanol on a glass
frit. The polymer was initially dried in air and then in vacuo at
80 °C. GPC analyses of the polyethylenes were performed on a
Polymer Laboratories Ltd. (PL-GPC210) chromatograph using
1,2,4-trichlorobenzene (TCB) as the mobile phase at 150 °C and
using polystyrene references (full specs: column 4 PL-Gel Mixed
A, Triple Detector RI + visco + LS, 90 °C). The DSC was
measured on a TA Instruments DSC 2920, using a heat/cool/
heat sequence employing 10 °C/min, between 20 and 160 °C.
, deg
V, Å3
Z
T, K
173
1.508
Dcalcd, g cm-3
µ, mm-1
F(000)
1.097
1256
θ range, deg
index ranges (h, k, l)
no. of rflns collected
no. of indep rflns/Rint
no. of obsd rflns (I > 2σ(I))
no. of data/restraints/params
R1/wR2 (I > 2σ(I))a
R1/wR2 (all data)a
GOF (on F2)a
largest diff peak and hole (e Å-3
2.78-25.36
(18, ( 10, ( 26
27 893
2477/0.034
2254
2477/0/201
0.0252/0.0628
0.0294/0.0650
1.061
)
+0.33/-0.25
2
2 2
a R1
∑[w(Fo2)2]}1/2; GOF ) ∑[w(Fo - Fc ) ]/(n - p)}1/2
)
∑(||Fo|
-
|Fc||)/∑|Fo|; wR2
)
∑[w(Fo
.
- Fc ) ]/
2
2 2
a Lindemann capillary, fixed, and sealed. Preliminary examina-
tion and data collection86 were carried out on an area detecting
system (NONIUS, MACH3, κ-CCD) at the window of a rotating
anode (NONIUS, FR591) and graphite-monochromated Mo KR
radiation (λ ) 0.71073 Å). The unit cell parameters were
obtained by full-matrix least-squares refinement of 2657 reflec-
tions. Data collection were performed at 173 K (Oxford
Cryosystems) within a θ-range of 2.78°< θ < 25.36°. The crystal
was measured with eight data sets in rotation scan modus with
∆ꢀ/∆ω ) 1.0°. A total number of 27 893 intensities were
integrated. Raw data were corrected for Lorentz, polarization,
and, arising from the scaling procedure, latent decay and
absorption effects. After merging (Rint ) 0.034) a sum of 2477
(all data) and 2254 [I > 2σ(I)] data, respectively, remained, and
all data were used. The structure was solved by a combination
of direct methods and difference Fourier syntheses. All non-
hydrogen atoms were refined with anisotropic displacement
parameters. All hydrogen atoms were found and refined with
individual isotropic displacement parameters. Full-matrix least-
squares refinements with 201 parameters were carried out by
Polymerization of Ethylene with Mononuclear Complex
7a. Polymerization was carried out as described above except for
the use of a toluene solution of 7a (5 µmol) and 2.5 mmolar equiv
of MAO (Al/Ti ) 500) with the aim of introducing an equal number
of metal centers into the solution in each experiment.
Polymerization of MMA with Complexes 1b and 1c. In a
typical procedure, complex 1b or 1c (0.06 mmol) and E(C6F5)3
(0.08 mmol) were mixed in a flask inside the glovebox and stirred
with 2 mL of toluene for 2 min. MMA was then quickly added.
After the measured time interval, the flask was removed from
the glovebox and quenched by adding 5 mL of MeOH/HCl
diluted. The quenched mixture was precipitated into 150 mL of
methanol, stirred overnight, filtered, and washed with methanol.
The polymer collected was dissolved in acetone, precipitated in
methanol at 0 °C, filtered, and dried in a vacuum oven at 80 °C.
2
2 2
minimizing ∑w(Fo - Fc ) with the SHELXL-97 weighting
scheme and stopped at shift/err < 0.001. The final residual
electron density maps showed no remarkable features. Neutral
atom scattering factors for all atoms and anomalous dispersion
corrections for the non-hydrogen atoms were taken from
International Tables for Crystallography.87 All calculations were
performed on an Intel Pentium 4 PC, with the STRUX-V system,
includingtheprogramsPLATON,88 SIR92,89 andSHELXL-97.90,91
Crystallographic data (excluding structure factors) for the
structures reported in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplementary
publication no. CCDC-702723 (1a). Copies of the data can be
1
A H NMR (CDCl3) spectrum of the polymer was obtained to
determine its tacticity and compared with literature. Gel
permeation chromatography (GPC) analyses of polymer samples
were carried out in THF as solvent at 25 °C (Waters GPCV-
2000) at Alcala´ University.
Polymerization of MMA with Mononuclear Complex 5b.
Polymerization was carried out as described above except for the
use of a toluene solution of 5b (0.12 mmol) and E(C6F5)3 (0.14
mmol) with the aim of introducing an equal number of metal centers
into the solution in each experiment.
(86) Data Collection Software for Nonius CCD DeVices; Delft: The
Netherlands, 2001.
(87) International Tables for Crystallography; Kluwer Academic Pub-
lishers: Dordrecht, 1992; Vol. C.
(88) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool;
Utrecht University: Utrecht, 2007.
(89) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.
Single-Crystal X-ray Structure Determination of Compound
1a. Crystal data and details of the structure determination are
presented in Table 4. Suitable single crystals for the X-ray
diffraction study were grown from hexane. A clear orange
fragment was stored under perfluorinated ether, transferred into

Dinuclear Titanium Complexes
Organometallics, Vol. 27, No. 21, 2008 5597
obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: (+44)1223-336-033; e-mail:
deposit@ccdc.cam.ac.uk).
0328, COMAL-CM) (Spain) for financial support. L.P.
acknowledges DGUI-CM for fellowship.
Supporting Information Available: Crystallographic data for
1a and selected NMR spectra. This material is available free of
charge via the Internet at http://pubs.acs.org.
Acknowledgment. We gratefully acknowledge Ministerio
de Educacio´n y Ciencia (project MAT2007-60997) and
DGUI-Comunidad de Madrid (programme S-0505/PPQ-
OM800492E
(90) Sheldrick, G. M. SHELXL-97; University of Gottingen: Gottingen,
1998.
(91) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307.