Ansa-titanocene catalysts for α-Olefin polymerization. Syntheses, structures, and reactions with methylaluminoxane and boron-based activators

Article abstract of DOI:10.1021/om0492496

The racemic isomers of C₂H₄(1-Ind) ₂TiCl₂ and Me₂Si(2-Me-Benzind) ₂TiMe₂ were synthesized and structurally characterized. Reactions of these and related ansa-titanocene complexes

Full text of DOI:10.1021/om0492496

894
Organometallics 2005, 24, 894-904
ansa-Titanocene Catalysts for r-Olefin Polymerization.
Syntheses, Structures, and Reactions with
Methylaluminoxane and Boron-Based Activators
Konstantin P. Bryliakov,† Dmitrii E. Babushkin,† Evgenii P. Talsi,*,†
Alexander Z. Voskoboynikov,‡ Holger Gritzo,§ Lars Schro¨der,§
Hans-Robert H. Damrau,§ Ulrich Wieser,§ Frank Schaper,§ and
Hans H. Brintzinger*,§
Boreskov Institute of Catalysis, Russian Academy of Sciences, and Department of Natural
Sciences, Novosibirsk State University, 630090 Novosibirsk, Russian Federation, Department
of Chemistry, Moscow State University, Lomonosovsky Prospect 1, Moscow 113000, and
Fachbereich Chemie, University of Konstanz, D-78457 Konstanz, Germany
Received September 29, 2004
The racemic isomers of C2H4(1-Ind)2TiCl2 and Me2Si(2-Me-Benzind)2TiMe2 were synthe-
sized and structurally characterized. Reactions of these and related ansa-titanocene
complexes with methylaluminoxane or with the cationizing reagent [CPh3]+[B(C6F5)4]-/Al2-
Me6 were monitored by UV/vis, 1H NMR, and EPR methods. Under conditions approaching
those typically used in olefin polymerizations, heterobinuclear cations of the type [DianTiIV(µ-
Me)2AlMe2]+ (with Dian ) bridged ligand dianion) dominate in each of these reaction systems,
which catalyze the polymerization of propene at temperatures below ambient. Above 0 °C,
these cations are reduced, mainly to neutral heterobinuclear species DianTiIII(µ-Me)2AlMe2,
which appear to be inactive with regard to polymerization catalysis. In the absence of
monomer, the main reducing agent appears to be ethyl aluminum admixtures in Al2Me6.
Addition of monomer increases the rate of reduction rather drastically, probably via formation
of titanium hydrides.
Introduction
In this article, we report syntheses and crystal
structures for the Ti analogues of two prototypical ansa-
zirconocene complexes, rac-C2H4(1-Ind)2TiX2 (1) and rac-
Me2Si(2-Me-Benzind)2TiX2 (2), with X ) Cl or CH3,
results of UV/vis, 1H NMR, and EPR spectroscopic
studies on the formation and decay of reactive species
upon reaction of these and related ansa-titanocene
complexes with MAO and boron-based activators, and
preliminary observations on the properties of these
catalyst systems with regard to olefin polymerization.
A great numbers of ansa-metallocene complexes,1
activated by methylaluminoxane (MAO) or boron-based
activators,2 have been studied as olefin-polymerization
catalysts. Titanocene-based catalyst systems are gener-
ally more easily deactivated than their zirconium ana-
logues, especially at higher temperatures. A more facile
reduction of their Ti(IV) centers is sometimes invoked
in this regard,3 but has apparently not been investigated
in any detail so far. The possibility to monitor reactive
Ti(IV) intermediates in titanocene/MAO and related
reaction systems by 1H NMR methods has recently been
demonstrated.4 The stability of catalytically relevant
intermediates, formed upon activation of ansa-ti-
tanocene complexes with MAO or boron-based activa-
tors, is thus amenable to direct evaluation now.
† Boreskov Institute of Catalysis and Novosibirsk State University.
‡ Moscow State University.
§ University of Konstanz.
(1) Resconi, L.; Cavallo, L.; Fait, A.; Piemontesi, F. Chem. Rev. 2000,
100, 1253.
Results and Discussion
1. Complex Syntheses and Structures. Although
alternative syntheses of their Zr analogues have been
studied in detail,5-7 no syntheses have been reported
so far for the rac isomers of the ansa-titanocene com-
plexes 1 and 2. To prepare the titanocene complex 1-Cl2,
we had to modify our previously described racemose-
(2) Chen, E.; Marks, T. J. Chem. Rev. 2000, 100, 1391.
(3) (a) Ewen, J. A.; Jones, R. L.; Razavi, A.; Ferrara, J. D. J. Am.
Chem. Soc. 1984, 106, 6355. (b) Miyake, S.; Okumura, Y.; Inazawa, S.
Macromolecules 1995, 28, 3074. (c) Bravakis, A. M.; Bailey, L. E.;
Pigeon, M.; Collins, S. Macromolecules 1998, 31, 1000. (d) Lee, M. H.;
Han, Y.; Kim, D.; Hwang J.-W., Do, Y. Organometallics 2003, 22, 2790.
(4) (a) Bryliakov, K. P.; Talsi, E. P.; Bochmann, M. Organometallics
2004, 23, 149. (b) Bryliakov, K. P.; Semikolenova, N. V.; Zakharov V.
A.; Talsi, E. P. J. Organomet. Chem. 2003, 683, 23. (c) Bryliakov, K.
P.; Semikolenova, N. V.; Yudaev, D. V.; Zakharov V. A.; Brintzinger,
H. H.; Ystenes, M.; Rytter, E.; Talsi, E. P. J. Organomet. Chem. 2003,
683, 93.
(5) (a) Wild, F.; Wasiucionek, M.; Huttner, G.; Brintzinger, H. H. J.
Organomet. Chem. 1985, 288, 63. (b) Lee, I. M.; Gauthier, W. J.; Ball,
J. M.; Iyengar, B.; Collins, S. Organometallics 1992, 11, 2115.
10.1021/om0492496 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 01/27/2005

ansa-Titanocene Catalysts for Polymerization
Organometallics, Vol. 24, No. 5, 2005 895
Table 1. Selected Bond Distances (Å) and Angles (deg) for TiCl2(O2biphen)‚2THF,
rac-C2H4(1-Ind)2Ti(O2biphen), rac-C2H4(1-Ind)2TiCl2 (1-Cl2), and rac-Me2Si(2-Me-Benz[e]Ind)2ZrMe2 (2-Me2)
rac-C2H4(1-Ind)2TiCl2
(1-Cl2)
rac-Me2Si(2-Me-
Benz[e]Ind)2ZrMe2 (2-Me2)
TiCl2(O2biphen) ‚2THF
rac-C2H4(1-Ind)2Ti(O2biphen)
Ti-O(1, 2)
1.819(3)
2.163(3)
2.3526(10)
1.902(3), 1.867(3)
Ti-O(3)
Ti-Cl(1)
2.3275(8)
2.127
Ti-C(31, 32)
2.136(5), 2.146(5)
2.131, 2.138
Ti-Z(1, 2)a
2.117, 2.171
1.359(5), 1.370(5)
91.28(14)
O(1, 2)-C
1.381(4)
92.5(2)
167.76(6)
O(1)-Ti-O(1A,2)
Cl(1)-Ti-Cl(1A)
C(31)-TiC(32)
Z(1)-Ti-Z(2)a
Ti-O(1, 2)-C
Ph(1)-Ph(2)b
95.89(4)
129.0
90.4(2)
131.7
126.5
125.8(3), 129.9(3)
41.8
132.7(2)
40.0
a Z(1), Z(2): indenyl C5-ring centroids. b Ph(1), Ph(2): mean planes of biphenolate C6-rings
Figure 2. Molecular structure of rac-C2H4(1-Ind)2Ti(O2-
biphen) (thermal ellipsoids drawn at the 50% probability
level, hydrogen atoms omitted for clarity).
Figure 1. Molecular structure of TiCl2(O2biphen)‚2THF
in the crystalline state (thermal ellipsoids drawn at the
50% probability level, hydrogen atoms omitted for clarity).
1
lective syntheses of ansa-zirconocene complexes.7b For
this purpose, the biphenolate precursor TiCl2(O2biphen)‚
2THF was prepared in ca. 90% yield by reaction of 1,1′-
bi-2-phenol with TiCl4 in toluene, followed by addition
of THF.8 Single crystals of TiCl2(O2biphen)‚2THF were
obtained by recrystallization from THF/hexane at -80
°C. A diffractometric structure determination (Figure
1, Table 1) revealed a monomeric, C2-symmetric, dis-
torted octahedral geometry in the crystalline state, with
trans-positioned Cl ligands, cis-positioned THF ligands,
and a twisted seven-membered chelate ring.9
were no longer apparent in the H NMR spectrum of
the product mixture, while signals assignable to rac-
C2H4(1-Ind)2Ti(O2biphen) and further broadened signals
appeared in the aromatic region.10 After workup (see
Experimental Section) crude rac-C2H4(1-Ind)2Ti(O2-
biphen) was isolated in 12% yield as a dark orange
powder, which was used to prepare the dichloro complex
rac-C2H4(1-Ind)2TiCl2 (1-Cl2), described below. Analyti-
cally and NMR-spectrally pure rac-C2H4(1-Ind)2Ti(O2-
biphen) was obtained by recrystallization from toluene/
pentane. By keeping a toluene solution at 4 °C, we
obtained crystals suitable for an X-ray diffraction
analysis, which revealed a slight deviation from the
expected C2 symmetry, (Figure 2, Table 1) in that the
lines from the Ti center to the midpoints of the ethano
bridge and the biphenolate fragment are not quite
collinear.11 The indenyl rings adopt a forward orienta-
tion, as found for other ethylene-bridged metallocenes
with bis-indenyl ligands.12 The S-conformer of the
twisted biphenolate ligand appears to fit favorably the
When TiCl2(O2biphen)‚2THF was reacted with 1
equiv of the ligand salt C2H4(1-Ind)2Li2(THF)2 in toluene/
THF at room temperature, the signals of the reactants
(6) (a) Spaleck, W.; Ku¨ber, F.; Winter, A.; Rohrmann, J.; Bachmann,
B.; Antberg, M.; Dolle, V.; Paulus, E. F. Organometallics 1994, 13, 954.
(b) Stehling, U.; Diebold, J.; Kirsten, R.; Ro¨ll, W.; Brintzinger, H. H.;
Juengling, S.; Mu¨lhaupt, R.; Langhauser, F. Organometallics 1994,
13, 964.
(7) (a) Zhang, X.; Zhu, Q.; Guzei, I. A.; Jordan, R. F. J. Am. Chem.
Soc. 2000, 122, 8093. (b) Damrau, H. R. H.; Royo, E.; Obert, S.; Schaper,
F.; Weeber, A.; Brintzinger, H. H. Organometallics 2001, 20, 5258.
(8) A THF-free, probably polymeric form of TiCl2O2biphen and its
use for racemoselective preparation of ansa-titanocenes has been
described: McLaughlin, M. L.; Erickson, M. S.; Fronczek, F. R. J.
Organomet. Chem. 1991, 415, 75.
(9) For a related Zr biphenolate complex, which contains tert-butyl
groups in 3,3′-positions and methyl groups in 5,5′-positions, a similar
crystal structure has been described in ref 7b.
(10) An EPR measurement indicated the presence of some Ti(III)
species.
(11) Similar distortions have been observed for other ansa-ti-
tanocenes with substituents in â-position of their C5-rings: Gutmann,
S.; Burger, P.; Hund, H. U.; Hofmann, J.; Brintzinger, H. H. J.
Organomet. Chem. 1989, 369, 343. Burger, P.; Diebold, J.; Gutmann,
S.; Hund, H. U.; Brintzinger, H. H. Organometallics 1992, 11, 1319.

896 Organometallics, Vol. 24, No. 5, 2005
Bryliakov et al.
Figure 4. Molecular structure of complex 2-Me2 (thermal
ellipsoids drawn at the 50% probability level, hydrogen
atoms omitted for clarity).
Figure 3. Molecular structure of 1-Cl2 (thermal ellipsoids
drawn at the 50% probability level, hydrogen atoms omit-
ted for clarity).
Table 2. Selected Bond Distances (Å) and Angles
(deg) for Different rac-C2H4(1-Ind)2MCl2
Complexes with M ) Ti, Zr, and Hf
mental Section) is in accord with the expected C2
symmetry
For complex 2, we have chosen a preparation that
yields, instead of the exceedingly insoluble dichloride
complex 2-Cl2, directly the more soluble dimethyl de-
rivative 2-Me2 in a one-pot reaction.13 As a convenient
synthon, we have used a methylmagnesium salt of the
dimethylsilyl-bridged 2-methylbenzindenyl ligand, Me2-
Si(2-Me-benz[e]indMgMe)2, which was prepared in situ
by transmetalating the ligand dilithium salt6 with 2
equiv of MeMgBr. Reaction of a suspension of the
methylmagnesium ligand salt with TiCl4(Et2O)n in
diethyl ether, first at -78 °C, then at ambient temper-
ature, gave, after appropriate workup (see Experimental
Section), complex 2-Me2 in 28% yield. Crystals suitable
for X-ray analysis were obtained by slow evaporation
from a concentrated diethyl ether solution at room
temperature.
A diffractometric structure determination of complex
2-Me2 revealed an almost perfect C2 symmetry (Figure
4, Table 1), with the TiMe2 and Me2Si fragments aligned
in the molecular mid-plane. As with other Me2Si-bridged
bis-indenyl complexes, both 2-Me-benz[e]indenyl ligands
are coordinated via their C5-rings in an η5 fashion. Some
strain is apparent by a deviation of the Si-C(ring) bonds
from the C5-ring planes by 20° and by a rather small
(ring)C-Si-C(ring) angle of ca. 94°. The Ti-Cp centroid
distances of 2.131 and 2.138 Å as well as the Ti-methyl
distances of 2.136 and 2.146 Å are similar to those
reported for comparable ansa-titanocene structures.14
The dichloride rac-Me2Si(2-Me-benz[e]ind)2TiCl2 (2-
Cl2) was obtained in 58% yield by reaction of 2-Me2 with
AlCl3‚THF and appropriate workup (see Experimental
Section).
Ti
Zra
Hfb
M-Cl
2.3275
2.127
95.89
129.0
2.3884
2.219
99.09
125.3
2.396
2.217
96.39
125.7
M-Zc
Cl-M-Cl
Z-M-Zc
a Ref 12a. b Ref 12b. c Z: centroids of indenyl C5-ring.
spatial requirements of the S,S-configurated bridgehead
carbon atoms and the ensuing λ conformation of the Ti-
C(1),C(10),C(20),C(11) chelate ring.
Crude rac-C2H4(1-Ind)2Ti(O2biphen) was converted to
rac-C2H4(1-Ind)2TiCl2 (1-Cl2) by reaction with MeAlCl2
in toluene and extraction of the crude reaction product
1
with CH2Cl2. As indicated by its H NMR (see Experi-
mental Section), pure 1-Cl2 was obtained in 42% yield.
Recrystallization from toluene afforded red crystals
suitable for X-ray analysis.
A structure with crystallographic C2 symmetry was
revealed by X-ray diffraction analysis for complex 1-Cl2
(Table 1, Figure 3). In the stereoisomer shown in Figure
3, the ansa-ligand assumes the λ-1S,1′S conformation,
which was also found for the biphenolate complex rac-
C2H4(1-Ind)2Ti(O2biphen) and for the analogous metal-
12a
locene complexes rac-C2H4(1-Ind)2ZrCl2
and rac-
C2H4(1-Ind)2HfCl2.12b All of these complexes have in
common a forward orientation of their indenyl rings.
Due to the trend of metal radii, complex 1-Cl2 has the
shortest M-Cl and M-centroid bonds in this series; the
Z-Ti-Z angle is the largest and, hence, the Cl-Ti-Cl
angle the smallest among these group 4 metallocenes
(Table 2).
From the dichloride 1-Cl2, the dimethyl derivative
1-Me2 is obtained, in near-quantitative yield, by reaction
with 2 equiv of methyllithium in diethyl ether solution.
(13) An alternative direct synthesis of metallocene dimethyl com-
pounds, in this case by use of excess methyllithium, has been
reported: Balboni, D.; Camurati, I.; Prini, G.; Resconi, L.; Galli, S.;
Mercandelli, P.; Sironi, A. Inorg. Chem. 2001, 40, 6588
(14) (a) Cano, A.; Cuenca, T.; Go´mez-Sal, P.; Manzanero, A.; Royo,
P. J. Organomet. Chem. 1996, 526, 227. (b) Lee, H.; Bonanno, J. B.;
Hascall, T.; Cordaro, J.; Hahn, J. M.; Parkin, G. J. Chem. Soc., Dalton
Trans. 1999, 1365. (c) Agarkov, A. Y.; Izmer, V. V.; Riabov, A. N.;
Kuz’mina, L. G.; Howard, J. A. K.; Beletskaya, I. P.; Voskoboynikov,
A. Z. J. Organomet. Chem. 2001, 619, 280.
1
The H NMR spectrum of complex 1-Me2 (see Experi-
(12) (a) Piemontesi, F.; Camurati, I.; Resconi, L.; Balboni, D.; Sironi,
A.; Moret, M.; Zeigler, R.; Piccolrovazzi, N. Organometallics 1995, 14,
1256. (b) Ewen, J. A.; Haspeslagh, L.; Atwood, J. L.; Zhang, H. J. Am.
Chem. Soc. 1987, 109, 6544.

ansa-Titanocene Catalysts for Polymerization
Organometallics, Vol. 24, No. 5, 2005 897
2. Reactions of Complexes 1 and 2 with MAO
and with [CPh3]+[B(C6F5)4]-. As was shown for their
zirconium analogues,15-17 activation reactions of these
complexes are conveniently studied by UV/vis and by
1H NMR spectroscopy.4 When a toluene solution of MAO
is added to a ca. 1 mM solution of complex 1-Cl2 in
toluene at a ratio of [Al]/[Ti] ) 3 at room temperature,
the absorption band of 1-Cl2 at 652 nm is rapidly
diminished in size concomitantly with the appearance
of a new band at 533 nm, which is complete within 3-4
min. By its 1H NMR spectrum the new species is
identified as the methyl chloride complex rac-C2H4(1-
Ind)2Ti(Cl)Me.18 Upon further addition of MAO to [Al]/
1
[Ti] ) 6, H NMR spectra indicate the presence of rac-
C2H4(1-Ind)2Ti(Cl)Me, rac-C2H4(1-Ind)2TiMe2 (1-Me2),18
and another, presumably cationic species, which be-
comes dominant at [Al]/[Ti] ) 9, where the signals of
the two neutral complexes have completely disap-
peared.19
Further increase of the [Al]/[Ti] ratios causes a
bathochromic shift of the lowest-energy band to λmax
≈
620 nm. While an isosbestic point at λ ) 586 nm would
indicate a single reaction at room temperature; its lack
at -20 °C points to the occurrence of a reaction
intermediate. When 1-Cl2 is reacted with MAO at -50
°C, a first bathochromic shift to λmax ) 606 nm, which
requires ca. 2 h for completion, is observed at a ratio of
[Al]/[Ti] ≈ 16-30. A second bathochromic shift to λmax
) 643 nm occurs upon further addition of MAO to a ratio
of [Al]/[Ti] ) 100. An isosbestic point at λ ) 631 nm
indicates a clean conversion to the new complex species.
Figure 5. Reaction of rac-C2H4(1-Ind)2TiCl2 (1-Cl2) with
MAO at -50 °C: Slow formation of species with λmax ) 606
nm at [Al]/[Ti] ) 16 (top) and conversion to species with
λmax ) 643 nm at [Al]/[Ti] > 30 (bottom, spectra taken after
10-15 min).
1H NMR signals of the reaction system rac-C2H4(1-
Ind)2TiCl2/MAO, recorded at a ratio of [Al]/[Ti] ) 200
in d8-toluene at 20 °C, indicate the presence of the het-
erobinuclear ion pair [rac-C2H4(1-Ind)2Ti(µ-Me)2AlMe2]+-
[Me-MAO]-. The close similarity of these signals to
those of the heterobinuclear ion pair [rac-C2H4(1-Ind)2-
Ti(µ-Me)2AlMe2]+[B(C6F5)4]-, prepared via reaction of
1-Cl2 with Al2Me6 and [CPh3][B(C6F5)4] in a 1:20:1 ratio
(Figure 6), shows that the cationic AlMe3 adduct [rac-
C2H4(1-Ind)2Ti(µ-Me)2AlMe2]+ dominates in these reac-
tion systems. Nonuniformly broadened signals, typical
of contact ion pairs of the type rac-C2H4(1-Ind)2TiMe+‚
‚‚MeMAO-,4 were detected at [Al]/[Ti] ratios below 100.
While some uncertainty remains especially with regard
to the nature of the counteranion MAOX-,20 the close
similarity of the NMR spectra shown in Figure 6
Figure 6. 1H NMR spectra (toluene-d8, 20 °C) of the
systems rac-C2H4(1-Ind)2TiCl2/MAO, with [Al]:[Ti] ) 200
-
(a, top) and rac-C2H4(1-Ind)2TiCl2/Al2Me6/CPh3+B(C6F5)4
with [Ti]:[Al]:[B] ) 1:20:1 (b, bottom).
,
indicates that the species with λmax ) 606 nm observed
at [Al]/[Ti] ) 16-30 is indeed the contact ion pair rac-
C2H4(1-Ind)2TiMe+‚‚‚MAOX-, while that with λmax
)
643 nm, formed at higher [Al]/[Ti] ratios, represents an
outer-sphere ion pair of the cationic AlMe3 adduct [rac-
C2H4(1-Ind)2Ti(µ-Me)2AlMe2]+ with its MAOX- coun-
teranion (Scheme 1).16
While the reaction sequence thus established for the
activation of complex 1-Cl2 with MAO (Scheme 1) is
rather similar to activation sequences previously estab-
lished for related ansa-zirconocene/MAO systems,15-17
several differences are to be noted: First, much lower
(15) (a) Coevoet, D.; Cramail, H.; Deffiex, A. Macromol. Chem. Phys.
1998, 199, 1451. (b) Pedeutour, J. N.; Coevoet, D.; Cramail, H.; Deffiex,
A. Macromol. Chem. Phys. 1999, 200, 1215. (c) Deffieux, A.; Cramail,
H.; Pedeutour, J. N. Polym. Prepr. 2000, 41, 1887.
(16) Babushkin, D. E.; Semikolenova N. V.; Zakharov, V. A.; Talsi,
E. P. Macromol. Chem. Phys. 2000, 201, 558.
(17) (a) Wieser, U.; Brintzinger, H. H. In Organometallic Catalysts
and Olefin Polymerization; Blom, E., Follestad, A., Rytter, E., Tilset,
M., Ystenes, M., Eds.; Springer: Berlin, 2001; p 3. (b) Wieser, U.
Dissertation, Universita¨t Konstanz, 2002. (c) Wieser, U. Schaper, F.;
Brintzinger, H. H.; Ma¨kela¨, N. I.; Knuuttila, H. R.; Leskela¨, M.
Organometallics 2002, 21, 541.
(18) Identified by spectral comparison with authentic rac-C2H4(1-
Ind)2Ti(Cl)Me (λmax ) 533 nm) and rac-C2H4(1-Ind)2TiMe2 (λmax ) 452
nm), obtained by reaction of complex 1-Cl2 with 1 and 2 equiv of
methyllithium, respectively.
(19) For the system 1-Cl2/MAO, no evidence was obtained for the
formation of a series of homobinuclear cations of the type [DianTiMe-
(µ-X)XTiDian]+ with X ) Cl or Me at 20 °C, which were identified by
Bryliakov et al. in the reaction system (C5H5)2TiCl2/MAO at -15 °C.4a
(20) The MAO-derived anions MAOX-, assumed to be formed upon
activation of a metallocene dichloride with MAO,16 are not sufficiently
characterized yet to warrant an unambiguous identification of the
entity X as either Cl or Me;21 exchange of the primarily abstracted
Cl- anion with a neutral Al-Me unit might form a neutral Al-Cl species
and a MAOMe- anion.

898 Organometallics, Vol. 24, No. 5, 2005
Bryliakov et al.
Scheme 1. Reaction Sequence for the Activation of
the Dichloride Complex 1-Cl2 with Increasing
MAO Concentrations (X ) Cl or Me)20
excess ratios of MAO are required for each reaction step
of the ansa-titanocene/MAO systems studied here.
Independent experiments show that complete formation
of the monomethyl complex requires just 1 equiv of
AlMe3, while an excess of AlMe3 is required to complete
the analogous transformation of the Zr congener.22
Formation of the dimethyl complex goes to completion
upon addition to 1-Cl2 of just 2 equiv of AlMe3, while
an analogous reaction has not been reported for reac-
tions of a zirconocene dichloride with MAO. Very modest
[Al]:[Zr] ratios are also required for each of the cation-
ization steps represented in Scheme 1. This observation
could have its origin in a higher compressibility of a CH3
than of a Cl ligand, which would favor CH3 over Cl as
a ligand in the more narrow titanocene coordination
gap.22,23
Figure 7. Decay of absorption bands of rac-C2H4(1-Ind)2-
TiMe+‚‚‚MeMAO- at 606 nm (top) and of [rac-C2H4(1-Ind)2-
Ti(µ-Me)2AlMe2]+[MeMAO]- at 643 nm (bottom) in toluene
at 20 °C.
Another difference concerns the tendency of the
cationic activation products to undergo decomposition:
While their zirconocene analogues are stable for about
1 week at room temperature,15-17 the cationic complexes
formed in the reaction system rac-C2H4(1-Ind)2TiCl2/
MAO are unstable at room temperature. Especially the
characteristic absorption band at 606 nm associated
with the contact ion pair rac-C2H4(1-Ind)2TiMe+‚‚‚
MeMAO- begins to decay within minutes at room
temperature; it is stable for extended periods only at
temperatures below -20 °C. The AlMe3-containing
outer-sphere ion pair [rac-C2H4(1-Ind)2Ti(µ-Me)2AlMe2]+-
[Me-MAO]-, on the other hand, is reasonably stable over
several hours at room temperature; at this temperature
its absorption band at 643 nm decays with a half-life of
several days (Figure 7). In the reaction system rac-
C2H4(1-Ind)2TiCl2/Al2Me6/CPh3B(C6F5)4 ([Ti]:[Al]:[B] )
1:20:1), the concentration of [rac-C2H4(1-Ind)2Ti(µ-
Me)2AlMe2]+[B(C6F5)4]- likewise decreases by a factor
of 3 during 2 days at room temperature. The products
of this decay reaction will be further characterized
below.
As a congener to another prototypical ansa-zirconocene/
MAO system, we have studied reactions of the sterically
more encumbered complex Me2Si(2-Me-Benz[e]Ind)2TiCl2
(2-Cl2) and its dimethyl derivative 2-Me2 with MAO.
Addition of increasing amounts of MAO to a toluene
solution of 2-Cl2 at 20 °C causes a hypsochromic shift
of the lowest-energy absorption band, from λmax ) 651
nm to λmax ≈ 550 nm. We assign this change, which
requires an [Al]/[Ti] ratio of ca. 30, to the formation of
rac-Me2Si(2-Me-Benz[e]Ind)2Ti(Cl)Me by a first Me/Cl
exchange with the AlMe3 contained in MAO. Addition
of further amounts of MAO, up to an [Al]/[Ti] ratio of
ca. 6-8:1, causes a second hypsochromic shift, due to
the formation of the dimethyl complex with λmax ) 489
nm. As in the system 1-Cl2/MAO, both chlorides are
replaced by methyl groups by exchange with the AlMe3
content of MAO; here, however, a higher excess of MAO
is required for each exchange step than in the case of
1-Cl2/MAO. Further addition of MAO causes, again, two
successive bathochromic shifts of the lowest-energy
absorption bands to 654 and then to 667 nm. The same
observations pertain, as expected, if a toluene solution
of rac-Me2Si(2-Me-Benz[e]Ind)2TiMe2 is treated with
excess MAO at -50 °C (Figure 8).
In analogy with the previous case, we can safely
assume that the ion pairs rac-Me2Si(2-Me-Benz[e]-
Ind)2TiMe+‚‚‚Me-MAO- and [rac-Me2Si(2-Me-Benz[e]-
Ind)2Ti(µ-Me)2AlMe2]+Me-MAO- are formed at [Al]/[Ti]
ratios of ca. 140:1 and ca. 400:1, respectively. Isosbestic
points found at λ ) 516 nm and at λ ) 516 and 650 nm
for the first and the second step, respectively, document
clean reactions without intermediates or side products.
While the reaction steps in the system 2-Cl2/MAO thus
appear to follow closely those described in Scheme 1 for
1-Cl2/MAO, it is remarkable that the formation of each
species in this system requires much higher MAO
concentrations than in the system 1-Cl2/MAO (Table 3).
We ascribe this observation to an opening of the
coordination gap aperture by the shorter Me2Si bridge,23
which reduces the pressure on the Ti-bound ligands and,
hence, the advantage of a more easily compressible CH3
over a Cl ligand. No significant differences are to be
noted, however, between the systems 2-Cl2/MAO and
2-Me2/MAO: Abstraction of Cl- and Me- units by MAO
appears to require practically identical [Al]:[Ti] ratios.
(21) Babushkin, D. E.; Brintzinger, H. H. J. Am. Chem. Soc. 2002,
124, 12869.
To check on the identity of the species formed from
2-Cl2 or 2-Me2 at high [Al]/[Ti] ratios, the heterobi-
nuclear ion pair [rac-Me2Si(2-Me-Benz[e]Ind)2TiMe2(µ-
Me)2AlMe2]+(C6F5)4B- was generated by reaction of
(22) (a) Beck, S.: Brintzinger, H. H. Inorg. Chim. Acta 1998, 270,
376. (b) Wieser, U.; Babushkin, D.; Brintzinger, H. H. Organometallics
2002, 920.
(23) Hortmann, K.; Brintzinger, H. H. New J. Chem. 1992, 16, 51.

ansa-Titanocene Catalysts for Polymerization
Organometallics, Vol. 24, No. 5, 2005 899
scribed above, we have first studied by EPR the interac-
tion of rac-C2H4(1-Ind)2TiCl2 with Al2Me6 in toluene ([Ti]
) 0.001 M, [Al]/[Ti] ) 20). EPR spectra recorded 1 day
after the onset of the decay reaction at room tempera-
ture display a signal at g0 ) 1.978 with hyperfine
structure (hfs) from Ti (aTi ) 12 G, Figure 9a) and
partially resolved hfs from Al (aAl ) 2.3 G). The intensity
of the EPR signal indicates, within an accuracy of 20-
30%, essentially complete reduction of Ti(IV) to Ti(III).
The hfs due to Al indicates that the signal at g0 ) 1.978
belongs to a heterobinuclear complex containing tita-
nium(III) and aluminum atoms, most likely to the
species rac-C2H4(1-Ind)2TiIII(µ-Me)2AlMe2 (type A).24
With regard to the nature of the reducing agent in
solutions of rac-C2H4(1-Ind)2TiCl2 and Al2Me6, we as-
sume that Me2AlEt admixtures of the latter might
generate, by elimination of C2H4, a metal hydride
species that would be capable of causing reduction of
Ti(IV).27 In accord with an estimate that the Al2Me6
used in our study contains ca. 2% of ethyl instead of
methyl groups,28 only partial conversion of Ti(IV) to Ti-
(III) was observed at an [Al]:[Ti] ratio of 5, whereas at
[Al]:[Ti] ) 20, complete reduction occurred. To cor-
roborate our hypothesis, we have used as a reducing
agent triisobutylaluminum (TIBA) instead of Al2Me6.
TIBA always contains some HAl(iBu)2,29 which should
lead to immediate reduction of Ti(IV). Addition of 10
equiv of TIBA to a solution of rac-C2H4(1-Ind)2TiCl2 in
toluene caused indeed an immediate and complete
reduction of Ti(IV) to Ti(III). The EPR spectrum ob-
served displays an EPR signal at g0 ) 1.978 with hfs
from Al of 1.8 G and a doublet at g0 ) 1.986 from a Ti-
(III) hydride complex with aH ) 5.5 G (Figure 9b).26 By
analogy with the system rac-C2H4(1-Ind)2TiCl2/Al2Me6,
the signal at g0 ) 1.978 with hfs from Al can be
attributed to a heterobinuclear complex of type A,
containing some isobutyl aluminum fragment, while the
hydride signal indicates that a surplus of hydride
species remains in this reaction system even after
reduction of all TiIV species.
Figure 8. Reaction of rac-Me2Si(2-Me-Benz[e]Ind)2TiMe2
(2-Me2) with excess MAO at -50 °C: First bathochromic
shift to λmax ) 654 nm at [Al]/[Ti] ) 40-140 (top) and
second bathochromic shift to λmax ) 667 at [Al]/[Ti] > 140
(bottom, spectra taken after ca. 10-15 min).
2-Me2 with 1.1 equiv of trityl perfluorotetraphenyl
borate in the presence of excess Al2Me6 in toluene
solution at room temperature. The absorption band at
668 nm formed under these conditions closely coincides
with that at 667 nm, generated by MAO activation of
either 2-Cl2 or 2-Me2. This indicates that the same
heterobinuclear cation, [rac-Me2Si(2-Me-Benz[e]Ind)2Ti-
(µ-Me)2AlMe2]+, is formed in all of these reaction
systems.
These assignments are supported by 1H NMR signals
obtained from solutions containing complex 2-Me2 to-
gether with an excess of MAO ([Al]:[Ti] ≈ 500) or with
an equivalent amount of (C6H5)3C+B(C6F5)4- and excess
trimethyl aluminum, in C6D6 at room temperature
(Table 4).
When 1 equiv of (C6H5)3C+B(C6F5)4 is added to a
-
mixture of rac-C2H4(1-Ind)2TiCl2 and Al2Me6 ([Al]:[Ti]
) 20) in toluene, we observe, besides the signal of
complex A, a weaker singlet signal at g0 ) 1.965. Clues
to the nature of this species are apparent from the
literature: Four-coordinated complexes of the type Cp2-
TiIIIL2, where L2 are bidentate ligands such as acetate,
2-hydroxypyridine, or bipyridyl, exhibit EPR signals at
To check on conceivable effects of different lengths of
the interannular bridges on the stability of cationic
species in these reaction systems, we have included in
this series also a congener of complex 1-Cl2 with only
one bridging CH2 unit, rac-CH2(1-Ind)2TiCl2 (3-Cl2).14c
As shown in Table 4, the cationic AlMe3 adduct [rac-
CH2(1-Ind)2Ti(µ-Me)2AlMe2]+, formed from 3A with
excess MAO, falls in line with the other species of this
type derived from complexes 1-Cl2 and 2-Cl2. It can thus
be safely assumed that formation of these species at
elevated MAO concentrations is a general characteristic
for ansa-titanocene as for ansa-zirconocene complexes.
The UV/vis bands and 1H NMR signals characteristic
for these cationic AlMe3 adducts, generated in the
presence of excess MAO, are completely formed within
ca. 5-10 min at room temperature and remain stable
for some time. After 20-30 min, some decay of these
characteristics becomes noticeable at room temperature;
in the course of several days they finally disappear
altogether.
(24) A related complex, (C5H5)2TiIII(µ-Me)2AlMe2, has been reported
to give an EPR signal at g0 ) 1.977 with unresolved hfs from Al in
toluene solution at -40 °C (ref 25), while a similar EPR spectrum with
g0 ) 1.975 and hfs from Al of 3.7 G has been reported for (C5H5)2-
TiIII(µ-Cl)2AlEtCl (ref 26). That species A is rac-C2H4(1-Ind)2TiIII(µ-
Me)2AlMe2, rather than a chloride-containing analogue rac-C2H4(1-
Ind)2TiIII(µ-Me)x(µ-Cl)(2-x)AlMe2, is indicated by the observation that
higher ratios of [Al]:[Ti] ) 50, at which all Ti-bound Cl- ions are likely
to be replaced by Me- units, do not cause any changes in the EPR
spectrum.
(25) Holton, J.; Lappert, M. F.; Ballard, D. G. H.; Pearce, R.; Atwood,
J. L.; Hunter, W. E. J. Chem. Soc., Dalton Trans. 1979, 45.
(26) Henrici-Olive´, G.; Olive´, S. Adv. Polym. Sci. 1969, 6, 421.
(27) Formation of C2H4 was always detected by 1H NMR in 1-Cl2/
Al2Me6 reaction mixtures.
(28) Al-Et units in trimethyl aluminum give rise to 1H NMR signals
at 1.05 (t, 3H, CH3) and 0.02 ppm (q, 2H, CH2), 3JHH ) 8.1 Hz, at 250
MHz in C6D6 at 20 °C.
3. EPR Studies on the Reductive Decay of Cat-
ionic Titanocene Species. To identify the products
that arise from the decay of the cationic species de-
(29) Al-H units in tri-isobutyl aluminum give a broad (ν1/2 ≈ 15 Hz)
singlet at 4.07 ppm in d8-toluene at 20 °C; isobutene signals: 4.76 (sept,
4
2H, CH2) and 1.61 ppm (t, 6H, CH3), JHH ) 1.2 Hz.

900 Organometallics, Vol. 24, No. 5, 2005
Bryliakov et al.
Table 3. Positions of Lowest-Energy UV/Vis Absorption Bands and [Al]/[Ti] Ratios Required for the
Formation of Individual Species in the Reaction Systems 1-Cl2/MAO, 2-Cl2/MAO, and 2-Me2/MAO
λmax/nm
2-(Cl2,Me2)/MAO
[Al]/[Ti]
2-(Cl2,Me2)/MAO
speciesa
1-Cl2/MAO
1-Cl2/MAO
DiAnTiCl2
652
533
452
606
643
651
550
491
654
667
DiAnTi(Cl)Me
3
6-8
16
28
44
100
424
DiAnTiMe2
[DiAnTiMe]+[MeMAO]-
[DiAnTi(µ-Me)2AlMe2]+[MAOCl]-
100
a DiAn: rac-C2H4(1-Ind)2 for 1-Cl2, rac-Me2Si(2-Me-Benz[e]Ind)2 for 2-Cl2 and 2-Me2.
1
Table 4. Selected H NMR Signals for Heterobinuclear Methyl Titanocenium Cations (at room
temperature, δ in ppm)
species
Cp-H
bridge
Al-CH3
Ti-CH3-Al
[rac-C2H4(1-Ind)2Ti(µ-Me)2AlMe2]+[Me-MAO]-a
[rac-C2H4(1-Ind)2Ti(µ-Me)2AlMe2]+[B(C6F5)4]-b
[rac-Me2Si(2-Me-Benzind)2Ti(µ-Me)2AlMe2]+ [Me-MAO]-c
[rac-Me2Si(2-Me-Benzind)2Ti(µ-Me)2AlMe2]+ [B(C6F5)4]-d
[rac-CH2(1-Ind)2Ti(µ-Me)2AlMe2]+[Me-MAO]-e
5.65, 4.78
5.57, 4.74
6.42
3.27f
3.24f
1.16g
0.85g
4.31h
-0.69
-0.76
-0.81
-0.83
-0.65
-1.26
-1.33
-1.72
-1.71
-1.65
6.31
5.92, 4.20
a In toluene-d8, [Al]:[Ti] ) 200. b In toluene-d8, [B]:[Al]:[Ti] ) 1:20:1. c In benzene-d6, [Al]:[Ti] ) 500. d In benzene-d6, [B]:[Al]:[Ti] )
1:20:1. e In toluene-d8, [Al]:[Ti] ) 200. f -C2H4-. g -Si(CH3)2-. h -CH2-.
For [(C5H2Me3)2TiCl] in methyltetrahydrofuran (mthf)
solution, for example, Mach and Reynor have assigned
two well-separated isotropic EPR signals at g0 ) 1.979
and at g0 ) 1.965 to a complex with a mthf molecule in
its fourth coordination site (g0 ) 1.979) and a three-
coordinated complex without coordinated solvent (g0 )
1.965), respectively.32 By analogy, the singlet at g0 )
1.965 in the reaction system C2H4(1-Ind)2TiCl2/Al2Me6/
[CPh3]+[B(C6F5)4]- might be due to a three-coordinated
complex of the type C2H4(1-Ind)2TiIIIMe (type B), which
has lost from its fourth coordination site the AlMe3 unit
contained in complex A (Scheme 2).33
EPR signals assignable to complexes of type A and
type B were observed also in toluene solutions contain-
ing rac-Me2Si(2-Me-Benzind)2TiMe2 and Al2Me6/[CPh3]-
[B(C6F5)4] ([Ti] ) 10-3 M; Ti:Al:B ) 1:20:1) 1 day after
onset of the reaction.34
When MAO is added to a toluene solution of rac-
C2H4(1-Ind)2TiCl2, we observe that pronounced amounts
of precipitate settle on the bottom of the EPR tube
during 1 day after onset of the reaction at room
temperature. By analogy with the corresponding zir-
conocene reaction systems, we can assume that this
precipitate contains some MAO-bound, insoluble Ti(IV)
species. At the same time, EPR spectra indicate reduc-
tion of ca. 10% of total titanium to Ti(III). EPR spectra
of the solution decanted from the upper part of the EPR
tube display a superposition of two rhombic anisotropic
signals from titanium complexes A′ and B′ with the
(30) (a) Francesconi, L. C.; Corbin, D. R.; Clauss, A. W.; Hendricson,
D. N.; Stucky, G. D. Inorg. Chem. 1981, 20, 2059. (b) Fieselmann, B.
F.; Hendrickson, D. N.; Stucky, G. D. Inorg. Chem. 1978, 17, 1841. (c)
Fieselmann, B. F.; Hendrickson, D. N.; Stucky, G. D. Inorg. Chem.
1978, 17, 2078.
(31) (a) Teuben, J. H.; De Liefde Meijer, H. J. J. Organomet. Chem.
Figure 9. EPR spectra (toluene-d8, 20 °C) of (a) rac-
1972, 46, 313. (b) Luinstra, G. A.; ten Cate, L. C.; Heeres, H. J.;
C2H4(1-Ind)2TiCl2/Al2Me6, [Al]:[/Ti] ) 20, 1 day after onset
of the reaction and (b) rac-C2H4(1-Ind)2TiCl2/Al(iBu)3, [Al]:
[Ti] ) 10, 10 min after onset of the reaction b; dashed lines
represent simulations of the experimental spectra.
Pattiasina, J. W.; Meetsma, A.; Teuben, J. H. Organometallics 1991,
10, 3227.
(32) Mach, K.; Raynor, J. B. J. Chem. Soc., Dalton Trans. 1992, 683.
(33) That B is an ion pair with positively charged titanium(III)
center appears less probable, since the zwitterionic complex rac-(ebthi)-
Ti+-η2-Me3SiC2B(C6F5)3}-] (ebthi ) 1,2-ethylene-1,1′-bis(η5-tetrahy-
droindenyl) has been reported to give an EPR signal at g0 )1.98:
Arndt, P.; Baumann, W.; Spannenberg, A.; Rosenthal, U.; Burlakov,
V. V.; Shur, V. B. Angew. Chem. 2003, 115, 1455.
g0 ) 1.978-1.980,30 whereas EPR signals at g0 ) 1.950-
1.957 are associated with three-coordinated complexes
such as (C5Me5)2TiIIIMe or (C5H5)2TiIIIL1, which contain
a monodentate ligand L1 ) Ph or o-, m-, p-CH3C6H4.31
(34) In this reaction mixture, we observe also the EPR signal of the
trityl radical.35 Possibly, Ti(III) reacts with (C6H5)3C+ to afford
(C6H5)3C• and Ti(IV).

ansa-Titanocene Catalysts for Polymerization
Organometallics, Vol. 24, No. 5, 2005 901
Table 5. Polymerization of Propene with 1-Cl2/
MAO and with 2-Me2/MAOa
catalyst/amount Al:Ti temp (°C) time (h) g PP activityb
Scheme 2. Reactions of the Complex 1-Cl2, in
toluene at 20 °Ca
1-Cl2/40 µmol
1-Cl2/40 µmol
2-Me2/40 µmol 375:1
2-Me2/44 µmol 190:1
450:1
400:1
-20
20
-20
30
1.5
1
9.7
0
11.9
5.4
161
0
100
50
3
2.5
a Propene pressure 1 bar. b g PP/(mol Ti‚h‚bar).
EPR spectra recorded several hours after onset of the
reactions of rac-Me2Si(2-Me-Benzind)2TiMe2 or of rac-
CH2(1-Ind)2TiCl2 with MAO ([Ti] ) 10-3 M, [Al]/[Ti] )
100) likewise display a superposition of anisotropic
signals from complexes A′ and B′, as observed in the
case of the system rac-C2H4(1-Ind)2TiCl2/MAO.
Preliminary data for propene polymerization with rac-
C2H4(1-Ind)2TiCl2/MAO and rac-Me2Si(2-Me-Benzind)2Ti-
Me2/MAO show that these catalysts are reasonably
active at -20 °C but less so at room temperature. 1-Cl2/
MAO in particular is totally inactive at 20 °C (Table 5).
At first glance, this appears to be at variance with the
relatively slow reductions of the heterobinuclear ion
pairs formed upon reaction with MAO, which require
several hours or even days at room temperature. Ap-
parently, catalyst deactivation is accelerated in the
presence of monomer.
a
(i) 20 equiv of Al2Me6; (ii) 20 equiv of Al2Me6 and 1 equiv
of (C6H5)3C+B(C6F5)4-; (iii) MAO at [Al]:[Ti] ) 200.
In agreement with this assumption, addition of pro-
pene (200 equiv) to a freshly prepared solution of rac-
C2H4(1-Ind)2TiCl2 and MAO in toluene ([Ti] ) 10-3 M,
Al/Ti ) 200) gave immediately a 5-fold increase of the
Ti(III) concentration as measured by EPR. We propose
that hydride species, assumed to arise as side products
or reaction intermediates in the course of titanocene-
catalyzed polymerization, are responsible for rapid
catalyst reduction and deactivation.
No well-defined neutral titanium(III)-based molecular
systems with established activity for catalytic olefin
polymerization have been reported in the literature so
far. Reduction of the predominant Ti(IV) species [Di-
AnTi(µ-Me)2AlR2]+, with R ) methyl or polymeryl, to
the Ti(III) congener DiAnTi(µ-Me)2AlR2 thus appears to
be the main, although possibly not the only,36 cause for
deactivation of titanocene-based polymerization cata-
lysts. Since all three catalyst systems studied, rac-
C2H4(1-Ind)2TiCl2/MAO, rac-CH2(1-Ind)2TiCl2/MAO, and
rac-Me2Si(2-Me-Benzind)2TiMe2/MAO, show closely simi-
lar activation and deactivation behavior, useful clues
with regard to structural features that might stabilize
the catalytically active Ti(IV) state are not available yet.
It remains to be elucidated which circumstances are
responsible for the stability of some titanium-containing
constrained-geometry and titanocene-based olefin po-
lymerization catalysts, which remain highly active for
olefin polymerization at elevated temperatures.40,41
Figure 10. EPR spectrum (toluene-d8, 20 °C) of the system
1-Cl2/MAO in toluene ([Ti] ) 10-3 M, [Al]/[Ti] ) 200) 1 day
after onset of the reaction.
following parameters: A′ (g1 )2.000, g2 ) 1.980, g3
)1.940) and B′ (g1 ) 2.000, g2 )1.980, g3 ) 1.882)
(Figure 10). The anisotropy of the spectra indicates that
the tumbling of the titanium(III) species is restricted,
presumably by coordination to the bulky MAO mol-
ecules.21 The corresponding isotropic g-values (g0 ) (g1
+ g2 + g3)/3) for complexes A′ and B′ (g0 ) 1.973 and g0
) 1.954, respectively) are close to those for complexes
A and B, discussed above.
When solutions of [TiIII(C5H2Me3)2Cl] in methyltet-
rahydrofuran (mthf) are frozen, the isotropic EPR
signals at g0 ) 1.979 and at g0 ) 1.965 discussed above
are replaced by two rhombic signals similar to those of
B′ and A′, assigned to the uncoordinated starting
complex (g1 ) 2.000, g2 ) 1.984, g3 )1.909) and the same
complex coordinated with mthf (g1 ) 2.000, g2 )1.984,
g3 ) 1. 954).34 It is thus tempting to assign complex A′
to a heterobinuclear complex similar to rac-C2H4(1-Ind)2-
TiIII(µ-Me)2AlMe2, the mobility of which is reduced due
to some kind of attachment to MAO. For the assignment
of B′, we propose that B′ is a neutral complex C2H4(1-
Ind)2TiIIIMe somehow attached to a molecule of MAO
(Scheme 2).
(35) Maki, A. U.; Alendoerfer, R. D.; Danner, J. C.; Keys, R. T. J.
Am. Chem. Soc. 1968, 90, 4225.
(36) As with the corresponding zirconocene reaction systems, pos-
sible deactivation processes might also be C-H activation, metathesis,
aryl transfer from the counteranion to the metal, and double cation-
ization of the precatalyst.37-39
(37) Zhang, S.; Piers, W. E.; Gao, X.; Parvez, M. J. Am. Chem. Soc.
2000, 122, 5499.
(38) Kickham, J. E.; Gue´rin, F.; Stephan, D. W. J. Am. Chem. Soc.
2002, 124, 11486.
(39) Wondimagegn, T.; Vanka, K.; Xu, Z.; Ziegler, T. Organometallics
2004, 23, 2651.
(40) McKnight, A. L.; Waymouth, R. M. Chem. Rev. 1998, 98, 2587.

902 Organometallics, Vol. 24, No. 5, 2005
Bryliakov et al.
toluene, and 0.76 mL of MeAlCl2 (1 M in hexane, 0.76 mmol)
was added. The solvent was removed under reduced pressure.
Diethyl ether was added, and the resulting suspension was
filtered. The precipitate was washed with diethyl ether until
the filtrate was essentially colorless. The resulting brown
residue was extracted with methylene chloride, which gave a
dark green solution. The solvent was removed in vacuo to yield
0.12 g (42%) of pure rac-C2H4(Ind)2TiCl2. Recrystallization from
toluene at room temperature afforded red crystals suitable for
X-ray analysis. 1H NMR (600 MHz, CD2Cl2, 25 °C, δ, ppm):
7.62 (2H, d, JHH ) 8.6 Hz, 7,7′-Ind-H); 7.44 (2H, d, JHH ) 8.5
Hz, 4,4′-Ind-H); 7.36 (2H, m, 5,5′-Ind-H); 7.26 (2H, m, 6,6′-
Ind-H); 6.69 (2H, d, JHH ) 3.2 Hz, 3,3′-Ind-H); 6.12 (2H, d,
JHH ) 3.2 Hz, 2,2′-Ind-H); 3.70-3.94 (4H, m, C2H4). 13C NMR
(CD2Cl2, 25 °C, δ, ppm): 131.5, 130.0, 128.7, 128.5, 126.7,
126.1, 122.8, 120.2, 115.7 (Ind-C3a/3a′, -C7a/7a′, -C6/6′, -C5/
5′, -C1/1′, -C4/4′, -C7/7′, -C3/3′, -C2/2′); 29.7 (C2H4). EI-MS
(70 eV): m/e 374 (M+). Anal. Calcd for C20H16Cl2Ti (375.11):
C, 64.04; H, 4.30. Found: C, 64.88; H, 4.42.
Experimental Section
Toluene-d8 and benzene-d6 were dried over molecular sieves
(4 Å) prior to use. All operations were carried out under dry
nitrogen (99.999%) in a glovebox. MAO was prepared from
commercial MAO (Witco) by removal of the solvent in vacuo
at 20 °C. The solid product obtained (polymeric MAO with total
Al content 40 wt % and Al as residual AlMe3 ca. 5 wt %) was
used for the preparation of the samples. 1H NMR and 13C NMR
spectra were recorded on Bruker AMX 250 (250 MHz) or
Bruker Avance 600 (600 MHz) instruments.
C2H4(1-Ind)2Li2(THF)2. C2H4(1-Ind)2Li2 was prepared ac-
cording to ref 5b. From the resulting reaction mixture, the
solvent was removed under vacuum. The precipitate formed
by addition of pentane was collected by filtration and dried
under reduced pressure. The pure lithium salt contained 2
THF per molecule as indicated by NMR spectroscopy.
(1,1′-Bi-2-phenolate)TiCl2(THF)2. To a solution of 13.0 g
(70 mmol) of 1,1′-bi-2-phenol in 50 mL of toluene was slowly
added 7.6 mL (70 mmol) of TiCl4. Excess HCl gas pressure
was allowed to escape via a bubbler. After stirring at room
temperature for 4 h, the solvent was removed under vacuum.
The resulting brown powder was washed with pentane and
dried under reduced pressure. THF (100 mL) was added, and
the solution was kept at room temperature for 2 days. The
solvent was removed under vacuum, and pentane was added.
The suspension was filtered, and the precipitate was washed
with pentane and dried in vacuo to yield 28.4 g (91%) of a dark
orange powder. Single crystals suitable for X-ray analysis were
obtained from THF/pentane at -80 °C. 1H NMR (CD2Cl2, 600
MHz, 25 °C, δ, ppm): 7.49 (2H, d, JHH ) 7.4 Hz, 6,6′-
biphenolate-H); 7.30 (2H, t, JHH ) 7.2 Hz, 4,4′-biphenolate-
H); 7.14 (2H, m, 5,5′-biphenolate-H); 6.82 (2H, bs, 3,3′-
biphenolate-H); 4.26 (8H, bs, THF); 1.97 (8H, bs, THF). 13C
NMR (CD2Cl2, 25 °C, δ, ppm): 166.2, 131.6, 128.8, 127.4, 124.3,
115.1 (biphenolate-C2,2′, -C,6,6′, -C4,4′, -C1,1′, -C5,5′, -C3,3′);
73.7, 25.9 (THF). EI-MS (70 eV): m/e 302 (M+ - 2THF). Anal.
Calcd for C20H24O4Cl2Ti (447.18): C, 53.72; H, 5.41. Found:
C, 53.37; H, 5.16.
rac-Me2Si(2-Me-Benzind)2TiMe2 (2-Me2). At room tem-
perature, 1.8 g of TiCl4 (9.49 mmol) was dissolved in 20 mL of
pentane. The solution was cooled to -78 °C, and 60 mL of Et2O
was slowly added. The yellow suspension was then warmed
to room temperature. Me2Si(2-Me-benz[e]indH)2 (3.95 g, 9.49
mmol) was dissolved at room temperature in 60 mL of Et2O,
and 12 mL (19 mmol) of MeLi (solution in Et2O, 1.6 M) was
slowly added, yielding a brown solution. After stirring the
reaction mixture for 2 h, 6.2 mL (19 mmol) of MeMgBr (3.06
M solution in Et2O) was added. The solution was stirred for
an additional 2 h while a white material, presumably LiBr,
precipitated. Both reaction mixtures were then cooled to -78
°C and combined via cannula. The resulting dark suspension
was allowed to come to room temperature overnight. 1H NMR
spectra of the crude product mixture showed a rac-meso ratio
of about 1:1. The dark precipitate was collected by filtration,
dried in vaccuo, and then extracted with CH2Cl2. Evaporation
of the solvent yielded 1.05 g (22.5%) of pure racemic 2-Me2.
When the filtrate of the original reaction mixture was con-
centrated to about the half its volume under reduced pressure,
an additional 0.26 g (5.6%) of racemic 2-Me2 was obtained after
several days by the same procedure. Dissolving this product
in CH2Cl2, filtering, removal of solvent in vaccuo, and repeating
the same procedure in toluene gave analytically pure complex.
Crystals suitable for X-ray analysis were obtained by slow
evaporation of a concentrated ether solution at room temper-
ature. 1H NMR (δ in ppm, CD2Cl2, 298 K, 600 MHz): 8.17 (d,
2H, 3JHH ) 7.84 Hz, 4,4’-benzindH2), 7.77 (d, 2H, 3JHH ) 7.92
Hz, 7,7′-benzindH2), 7.68 (s, 2H, 3,3′-benzindH2), 7.59 (dd, 2H,
rac-C2H4(1-Ind)2Ti(1,1′-bi-2-phenolate). To a dry mixture
of 2.76 g (6.2 mmol) of (1,1′-Bi-2-phenolate)TiCl2(THF)2 (1) and
2.55 g (6.2 mmol) of C2H4(1-Ind)2Li2(THF)2 were added 30 mL
of toluene and 10 mL of THF. After stirring at room temper-
ature for 1 h 100 mL of pentane was added and the reaction
mixture was kept at -80 °C for 1 h. The brown suspension
was filtered, and the solvent was removed from the filtrate
under vacuum. A crude dark orange powder (0.37 g, 12%) was
obtained and was used without further purification for the
preparation of complex 3 (see below). An analytically pure
sample of 2 was obtained by cooling a solution of crude product
in toluene/pentane at 4 °C. The red precipitate was filtered,
washed with pentane, and dried in vacuo. Crystals suitable
for X-ray diffraction analysis were obtained from a toluene
3
3JHH ) 7.53 Hz, JHH ) 7.38 Hz, 5,5′-benzindH2), 7.48 (dd,
3
2H,3JHH ) 7.47 Hz, JHH ) 7.41 Hz, 6,6′-benzindH2), 7.39 (d,
2H, 3JHH ) 9.15 Hz, 9,9′-benzindH2), 7.21 (d, 2H, 3JHH ) 9.14
Hz, 8,8′-benzindH2), 1.93 (s, 6H, 2-CH3, 1.05 (s, 6H, Si-CH3),
-1.18 (s, 6H, Ti-CH3). 13C NMR (CD2Cl2 as internal standard,
298 K, 150 MHz, ppm): 132.7, 132.5, 131.6, 130.3, 128.7, 127.4,
126.8, 126.3, 125.0, 124.6, 124.5, 122.9, 87.1 (benz[e]ind-C);
51.0 (Ti-CH3), 18.5 (2-benz[e]ind-CH3), 2.2 (-Si-CH3). Anal.
Calcd for C32H32SiTi: C, 78.02; H, 6.54. Found: C, 77.90; H,
6.20. MS: 477 [M]+ - CH3 (40%), 462 [M]+ - 2CH3 (100%).
1
solution at 4 °C. H NMR (600 MHz, CD2Cl2, 25 °C, δ, ppm):
7.73 (2H, d, JHH ) 8.6 Hz, 7,7′-Ind-H); 7.16 (4H, m, 4,4′-
biphenolate-Hand 6,6′-Ind-H); 7.06 (2H, d, JHH ) 7.5 Hz, 6,6′-
biphenolate-H); 6.89 (2H, m, 5,5′-Ind-H); 6.84 (2H, m, 5,5′-
biphenolate-H); 6.47 (4H, m, 3,3′-biphenolate-H and 4,4′-Ind-
H); 6.21 (2H, d, JHH ) 3.0 Hz, 2,2′-Ind-H); 5.72 (2H, d, JHH
)
rac-Me2Si(2-Me-Benz[e]ind)2TiCl2 (2-Cl2). AlCl3(THF)
was prepared by slowly adding 0.55 mL of THF to a suspension
of 0.89 g (6,67 mmol) of AlCl3 in 30 mL of toluene at -30 °C.
The resulting clear solution was allowed to come to room
temperature, and the solvent was removed in vaccuo. The
white powder was used without further purification. At room
temperature, 230 mg (0,467 mmol) of solid Me2Si(2-Me-Benz-
[e]ind)TiMe2 (2-Me2) and 200 mg (0.97 mmol) of solid AlCl3-
(THF) were mixed, and 20 mL of CH2Cl2 was added. The dark
solution was stirred for 2 days while some dark precipitate
was formed. The 1H NMR spectra of the reaction mixture
indicated a clean conversion to Me2Si(2-Me-Benz[e]ind)TiCl2.
The solvent was evaporated, and the solid residue was washed
3.0 Hz, 3,3′-Ind-H); 3.79-4.01 (4H, m, C2H4). 13C NMR (CD2-
Cl2, 25 °C, δ, ppm): 165.7, 131.2, 128.4, 126.2, 117.1 (biphe-
nolate-C2/2′, -C6/6′, -C4/4′, -C5/5′, -C3/3′); 131.3, 127.2,
127.0, 125.9 (biphenolate, Ind); 126.4, 124.0, 121.4, 120.3,
114.8, 111.5 (Ind-C6/6′, -C4/4′, -C7/7′, -C5/5′, -C2/2′, -C3/
3′); 29.4 (C2H4). EI-MS (70 eV): m/e 488 (M+). Anal. Calcd for
C32H24O2Ti (488.42): C, 78.69; H, 4.95. Found: C, 78.50; H,
5.00.
rac-C2H4(1-Ind)2TiCl2. Crude rac-C2H4(1-Ind)2Ti(1,1′-bi-2-
phenolate) (0.37 g, 0.76 mmol) was dissolved in 10 mL of
(41) Ewen, J. A.; Zambelli, A.; Longo, P.; Sullivan, J. M. Macromol.
Rapid Commun. 1998, 19, 71.

ansa-Titanocene Catalysts for Polymerization
Organometallics, Vol. 24, No. 5, 2005 903
Table 6. Crystallographic Data for Complexes (1,1′-bi-2-phenolate)TiCl2(THF)2,
rac-C2H4(1-Ind)2Ti(1,1′-bi-2-phenolate), rac-C2H4(1-Ind)2TiCl2 (1-Cl2), and rac-Me2Si(2-Me-Benzind)2TiMe2
(2-Me2)
(1,1′-bi-2-phenolate)-
rac-C2H4 (1-Ind)2Ti(1,1′-
rac-C2H4(1-Ind)2TiCl2
(1-Cl2)
rac-Me2Si(2-Me-
Benzind)2TiMe2 (2-Me2)
TiCl2(THF)
bi-2-phenolate)
a
formula
C
13H12ClO2Ti0.5
C
32H24O2Ti
C20H16Cl2Ti
Enraf Nonius CAD 4
red rhombohedron
monoclinic
C2/c
C32H32SiTi
Enraf Nonius CAD 4
red plates
monoclinic
P21/c
8.6895(14)
23.235(3)
12.4943(19)
90
diffractometer
cryst color and form
cryst syst
Siemens P4
red plates
monoclinic
C2/c
Siemens P4
red plates
monoclinic
P21/n
space group
a [Å]
12.945(2)
17.144(3)
12.512(2)
90
91.560(10)
90
8, 2775.9(7)
0.2 × 0.3 × 0.4
243, 1.242
0.527, 1072
ω, 1.97-25.00
2706
11.055(7)
13.841(11)
15.851(17)
90
108.19(8)
90
4, 2304(3)
0.25 × 0.3 × 0.3
193, 1.408
0.401, 1016
ω, 1.99-25.00
4990
15.333(5)
b [Å]
10.4415(18)
11.797(5)
c [Å]
R [deg]
90
â [deg]
122.49(3)
97.09(2)
90
γ [deg]
90
Z, V [Å3]
4, 1593.2(9)
0.3 × 0.3 × 0.6
183, 1.564
0.868, 768
ω, 2.51-27.08
1921
4, 2530.4(7)
0.05 × 0.25 × 0.6
183, 1.307
0.868, 768
ω, 2.36-27.06
5927
cryst size [mm]
T [K], dcalcd [g/cm3]
µ [mm-1], F(000)
scan mode, θ range [deg]
no. of reflns collected
no. of ind reflns (Rint
solution
)
2279 (2.22%)
direct
4035 (5.04%)
direct
1749 (6.93%)
direct
5467 (3.17%)
direct
refinement
Shelxl-93b
145, 1.090
5.97%, 16.85%
0.1125, 3.1876
0.872
Shelxl-97b
316, 1.007
5.63%, 11.62%
0.0600, 0.7858
0.402
Shelxl-97b
137, 1.108
4.58%, 11.83%
0.0842, 1.2532
0.646
Shelxl-97b
307, 1.008
6.92%, 14.15%
0.0690, 2.4145
0.509
no. of params, GOF (F2)
R(F), Rw(F2)c
weighting scheme (a,b)d
largest diff peak [e-/Å3]
abs corr
Ψ-scan
Ψ-scan
Ψ-scan
Ψ-scan
a One disordered molecule of hexane was found per Ti and refined with geometrical restraints. Due to the high disorder, H atoms were
neglected. b G. Sheldrick, University of Go¨ttingen, 1993 and 1997. c Observed data (I > 2σ(I)). d Weighting scheme: w-1 ) σ2(Fo)2 + (aP)2
2
2
+ bP, where P ) (Fo + 2Fc )/3.
twice with small amounts of toluene. The dark powder was
dried in vaccuo to yield 0.143 g (58%) of Me2Si(2-Me-Benz[e]-
ind)TiCl2. Resolving of the complex in CH2Cl2, filtering the
solution, and removing the solvent under vaccuo yielded
analytically pure complex. Anal. Calcd for C30H26Cl2SiTi: C,
67.55; H, 4.91. Found: C, 67.54; H, 5.22. MS: 534 [M]+ (76%)
497 [M]+ - Cl (43%). 1H NMR (δ in ppm, in CD2Cl2 as internal
standard, 298 K, 600 MHz): 7.95 (d, 2H, 3JHH ) 7.70 Hz, 4,4′-
benzind-H), 7.79 (d, 2H, 3JHH ) 7.53 Hz, 7,7′-benzind-H), 7.57
(m, 6H, 5,5′-, 6,6′-, 9,9′-benzind-H3), 7.43 (s, 2H, 3,3′-benzind-
[rac-C2H4(1-Ind)2Ti(µ-Me)2AlMe2]+[Me-MAO]-. 1H NMR
(C6D6, 20 °C, δ, ppm): 5.65 (2H, JHH ) 2.7 Hz, 3,3′-ind-H),
4.78 (2H, d, JHH ) 2.7 Hz, 2,2′-ind-H), 3.27 (4H, m, C2H4),
-0.69 (6H, s, Al(CH3)2), -1.26 (6H, s, Ti-(µ-CH3)-Al).
[rac-C2H4(1-Ind)2Ti(µ-Me)2AlMe2]+[B(C6F5)4]-. 1H NMR
(C6D6, 20 °C, δ, ppm): 5.57 (2H, JHH ) 2.7 Hz, 3,3′-ind-H),
4.74 (2H, d, JHH ) 2.7 Hz, 2,2′-ind-H), 3.24 (m, 4H, C2H4),
-0.76 (6H, s, Al-(CH3)2), -1.33 (6H, s, Ti-(µ-CH3)-Al).
1
rac-Me2Si(2-Me-Benzind)2TiMe2. H NMR (C6D6, 20 °C,
δ, ppm): 8.02 (2H, d, 4,4′-benzind-H), 7.63 (2H, d, 7,7′-benzind-
H), 7.54 (2H, s, 3,3′-benzind-H), 7.3-7.4 (4H, m, 5,5′- and 6,6′-
benzind-H), 7.28 (2H, d, 8,8′- or 9,9′-benzind-H), 7.09 (2H, d,
8,8′- or 9,9′-benzind-H), 1.81 (6H, s, 2-CH3), 0.68 (6H, s, Si-
(CH3)2), -0.69 (6H, s, Ti-(CH3)2).
rac-Me2Si(2-Me-Benzind)2TiMe+‚‚‚MeB(C6F5)3-. 1H NMR
(C6D6, 20 °C, δ, ppm): 7.88 (2H, d, 4,4′-benzind-H), 7.18 (2H,
d, 7,7′-benzind-H), 7.27 (2H, s, 3,3′-benzind-H), 7.3-7.4 (4H,
m, 5,5′- and 6,6′-benzind-H), 6.84 (2H + 2H, AB, 8,8′- and 9,9′-
benzind-H), 1.46 (6H, s, 2-CH3), 0.48 (6H, s, Si(CH3)2), 0.32
(3H, s, Ti-CH3), -0.8 (3H, bs, B-(µ-CH3)-Ti).
3
H), 7.32 (d, 2H, JHH ) 9.20 Hz, 8,8′-benzind-H), 2.18 (s, 6H,
2-CH3), 1.38 (s, 6H, Si-CH3). 13C NMR (δ in ppm, in CD2Cl2 as
internal standard, 298 K, 150 MHz): 137.7, 135.8, 133.6, 131.2,
130.2, 128.7, 128.6, 128.3, 128.1, 127.9, 125.4, 123.7, 88.7
(benz[e]ind-C); 19.8 (2-benz[e]ind-CH3), 2.0 (-Si-CH3).
UV/Vis, 1H NMR, and EPR Measurements of Reaction
Systems. UV/vis spectra of the reaction mixtures were
recorded on a Cary 50 Varian spectrometer, using an immer-
sion probe with fiber-optical light guide, placed in a specially
designed Schlenk vessel. Absorbance values were corrected for
dilution by the activator solutions added. 1H NMR spectra were
recorded in standard 5 mm NMR tubes on a Bruker AMX 250
rac-Me2Si(2-Me-Benzind)2TiMe+B(C6F5)4-. 1H NMR (C6D6,
20 °C, δ, ppm): 1.42 (6H, s, 2-CH3), 0.58 (6H, s, Si(CH3)2), 0.46
(3H, s, Ti-CH3).
1
MHz spectrometer. Typical operating conditions for H NMR
measurements: spectral width 5 kHz; spectrum accumulation
frequency 0.2-0.5 Hz; number of transients 32-64. For
[rac-Me2Si(2-Me-Benzind)2Ti(µ-Me)2AlMe2]+[Me-
MAO]-. 1H NMR (C6D6, 20 °C, δ, ppm): 7.83 (2H, d, 4,4′-
benzind-H), 6.42 (2H, s, 3,3′-benzind-H), 1.56 (6H, s, 2-CH3),
1.16 (6H, s, Si(CH3)2), -0.81 (6H, s, Al-CH3), -1.72 (6H, s, Ti-
(µ-CH3)2-Al).
1
calculations of H chemical shifts, the residual solvent peaks
were taken as 2.09 ppm (CHD2 group of deuterated toluene)
and 7.15 ppm (deuterated benzene), respectively. Samples for
NMR and EPR measurements were prepared in standard 5
mm glass NMR tubes as follows: In a glovebox, the appropri-
ate amount of Ti complex was dissolved in deuterated toluene
or benzene, then weighed quantities of MAO or B(C6F5)3 were
added as solids. In the experiments with Al2Me6/[Ph3C]+-
[B(C6F5)4]-, a toluene solution of Al2Me6 was added to the
solution of the titanocene complex first, followed by solid
[Ph3C][B(C6F5)4]. The samples were capped with rubber stop-
pers. The following 1H NMR signals were used to identify and,
where applicable, to quantify the cationic titanocene species
discussed above.
[rac-Me2Si(2-Me-Benzind)2Ti(µ-Me)2AlMe2]+[B-
1
(C6F5)4]-. H NMR (C6D6, 20 °C, δ, ppm): 7.74 (2H, d, 4,4′-
benzind-H), 6.31 (2H, s, 3,3′-benzind-H), 6.92 (2H, d, 8,8′- or
9,9′-benzind-H), 1.42 (6H, s, 2-CH3), 0.85 (6H, s, Si(CH3)2),
-0.83 (6H, s, Al(CH3)2), -1.71 (6H, s, Ti-(µ-CH3)2-Al).
1
[rac-CH2(1-Ind)2Ti(µ-Me)2AlMe2]+[B(C6F5)4]-. H NMR
(C6D6, 20 °C, δ, ppm): 5.92 (2H, JHH ) 2.5 Hz, 3,3′-ind-H),
4.20 (2H, d, JHH ) 2.5 Hz, 2,2′-ind-H), 4.31 (2H, s, CH2), -0.65
(6H, s, Al-(CH3)2), -1.65 (6H, s, Ti-(µ-CH3)2-Al).

904 Organometallics, Vol. 24, No. 5, 2005
Bryliakov et al.
EPR spectra were recorded at 25 °C on a Bruker ER-300D
spectrometer. EPR signals were quantified by double integra-
tion using copper chloride as standard.
as supplementary publications CCDC 230670, 230738, 230750,
and 230753.
Acknowledgment. We thank Dr. Nina Semikole-
nova (Boreskov Institut of Catalysis) for the preparation
of samples for NMR and EPR spectroscopy and Marc
Rudolf (University of Konstanz) for help with EPR
measurements. This work was supported by the Euro-
pean Commission, INTAS grant 00-841. Financial sup-
port from BASELL Polyolefine GmbH (Frankfurt-
Hoechst) is gratefully acknowledged.
Crystal Structures. X-ray diffraction analyses were car-
ried out on a Siemens P4 or an Enraf-Nonius CAD 4 diffrac-
tometer using Mo KR radiation (71.073 pm) and a graphite
monochromator. Crystal decay was monitored by measuring
three standard reflections every 100 reflections. Details of the
X-ray diffraction analysis are given in Table 6. Crystal-
lographic data for the structures in this paper have been
deposited with the Cambridge Crystallographic Data Centre
OM0492496