Activation of bis(pyrrolylaldiminato) and (salicylaldiminato) (pyrrolylaldiminato) titanium polymerization catalysts with methylalumoxane

Article abstract of DOI:10.1021/om0607752

Cationic intermediates formed upon activation of an olefin polymerization catalyst based on bis[N-phenylpyrrolylaldiminato]titanium(IV) dichloride (L ₂TiCl₂, I) and [N-(3-tert-butylsalicylidene)-2,3,4,5,6- pentafluoroanilinato-N′-phe

Full text of DOI:10.1021/om0607752

288
Organometallics 2007, 26, 288-293
Activation of Bis(pyrrolylaldiminato) and
(Salicylaldiminato)(pyrrolylaldiminato) Titanium Polymerization
Catalysts with Methylalumoxane
Konstantin P. Bryliakov,*,† Evgenii A. Kravtsov,† Lewis Broomfield,‡ Evgenii P. Talsi,† and
Manfred Bochmann*,‡
BoreskoV Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences, 630090 NoVosibirsk,
Russian Federation, and Wolfson Materials and Catalysis Centre, School of Chemical Sciences and
Pharmacy, UniVersity of East Anglia, Norwich NR4 7TJ, United Kingdom
ReceiVed August 25, 2006
Cationic intermediates formed upon activation of an olefin polymerization catalyst based on bis[N-
phenylpyrrolylaldiminato]titanium(IV) dichloride (L2TiCl2, I) and [N-(3-tert-butylsalicylidene)-2,3,4,5,6-
pentafluoroanilinato-N′-phenylpyrrolylaldiminato]titanium(IV) dichloride (L′LTiCl2, II) with methyla-
lumoxane (MAO) have been identified. Outer-sphere ion pairs of the type [L2TiMe(S)]+[MeMAO]- and
[L′LTiMe(S)]+[MeMAO]- capable of ethene polymerization have been characterized by 1H and 13C NMR
spectroscopy. Unlike methyl metallocenium cations, the barrier of the first ethene insertion into the Ti-
Me bonds of these species is not significantly higher than that of subsequent insertions. Surprisingly,
whereas homoligated catalyst precursors L2TiCl2 in the presence of MAO are prone to ligand transfer to
aluminum, under the same conditions the heteroligated system L′LTiCl2/MAO proved resistant to ligand
scrambling.
(comparable to those of metallocenes), whereas activation with
Al(iBu)3/[CPh3]+[B(C6F5)4]- allows the preparation of high
molecular weight polyethene (Mw up to 5 × 106).2 Moreover,
bis(pyrrolylaldiminato) titanium catalysts promote the living
ethene-norbornene copolymerization with high comonomer
incorporation (up to 46.5%) to yield copolymers consisting of
essentially alternating ethene and norbornene units, even though
ethene homopolymerization is not living and norbornene is
not polymerized at all.9 Very recently, heteroligated (salicyl-
aldiminato)(pyrrolylaldiminato) titanium complexes have been
reported that combine the high ethene polymerization activity
of salicylaldiminato systems with the more open structure
required for comonomer incorporation and display significantly
improved activity and high comonomer incorporation compared
to homoligated couterparts.14-17
Introduction
Complexes of group IV metals with pyrrolylaldiminato
ligands1-4 have attracted particular attention as single-site
catalysts of olefin polymerization.5-11 Titanium complexes were
the first to show high catalytic activities and are therefore more
developed to date; however, zirconium and hafnium counterparts
are currently being investigated as well.4,12,13 Bis(pyrrolylaldi-
minato) titanium complexes (“PI catalysts”) show attractive
catalytic properties: when activated with methylalumoxane
(MAO), they demonstrate high ethene polymerization activities
* Corresponding author. Fax: +7 383 3308056. E-mail: bryliako@
catalysis.ru.
† G. K. Boreskov Institute of Catalysis.
‡ University of East Anglia.
On the other hand, the activation processes of pyrrolylaldi-
minato and (salicylaldiminato)(pyrrolylaldiminato) titanium
complexes with commonly used cocatalysts have so far not been
investigated in detail. Recently, we and others published a
spectroscopic study of the cationic intermediates formed upon
activation of a bis(salicylaldiminato) titanium catalyst capable
of promoting living ethene polymerization.18-20 Here we report
the results of a detailed study of the interaction of the catalyst
(1) Male, M. A. H.; Thornton-Pett, M.; Bochmann, M. J. Chem. Soc.,
Dalton Trans. 1997, 2487.
(2) Yoshida, Y.; Matsui, S.; Takagi, Y.; Mitani, M.; Nitabaru, M.;
Nakano, T.; Tanaka, H.; Fujita, T. Chem. Lett. 2000, 1270.
(3) Yoshida, Y.; Matsui, S.; Takagi, Y.; Mitani, M.; Nakano, T.; Tanaka,
H.; Kashiwa, N.; Fujita, T. Organometallics 2001, 20, 4793.
(4) Dawson, D. M.; Walker, D. A.; Thornton-Pett, M.; Bochmann, M.
J. Chem. Soc., Dalton Trans. 2000, 459.
(5) Yoshida, Y.; Nakano, T.; Tanaka, H.; Fujita, T. Isr. J. Chem. 2002,
42, 353.
(6) Yoshida, Y.; Saito, J.; Mitani, M.; Takagi, Y.; Matsui, S.; Ishii, S.;
Nakano, T.; Kashiwa, N.; Fujita, T. Chem. Commun. 2002, 1298.
(7) Matsui, S.; Spaniol, T. P.; Takagi, Y.; Yoshida, Y.; Okuda, J. J. Chem.
Soc., Dalton Trans. 2002, 4529.
(8) Yoshida, Y.; Nakano, T.; Tanaka, H.; Fujita, T. Isr. J. Chem. 2002,
42, 353.
(9) Matsui, S.; Yoshida, Y.; Takagi, Y.; Spaniol, T. P.; Okuda, J. J.
Organomet. Chem. 2004, 689, 1155.
(10) Yoshida, Y.; Mohri, J.; Ishii, S.; Mitani, M.; Saito, J.; Matsui, S.;
Makio, H.; Nakano, T.; Tanaka, H.; Onda, M.; Yamamoto, Y.; Mizuno,
A.; Fujita, T. J. Am. Chem. Soc. 2004, 126, 12023.
(11) Yoshida, Y.; Matsui, S.; Fujita, T. J. Organomet. Chem. 2005, 690,
4382.
1
precursors I and II with MAO by H and 13C NMR spectros-
(14) Pennington, D. A.; Coles, S. J.; Hursthouse, M. B.; Bochmann, M.;
Lancaster, S. J. Chem. Commun. 2005, 3150.
(15) Pennington, D. A.; Coles, S. J.; Hursthouse, M. B.; Bochmann, M.;
Lancaster, S. J. Macromol. Rapid Commun. 2006, 27, 599.
(16) Matsuo, Y.; Mashima, K.; Tani, K. Chem. Lett. 2000, 1114.
(17) Tsurugi, H.; Yamagata, T.; Tani, K.; Mashima, K. Chem. Lett. 2003,
32, 756.
(18) Bryliakov, K. P.; Kravtsov, E. A.; Pennington, D. A.; Lancaster, S.
J.; Bochmann, M.; Brintzinger, H. H.; Talsi, E. P. Organometallics 2005,
24, 5660.
(12) Matsui, S.; Spaniol, T. P.; Takagi, Y.; Yoshida, Y.; Okuda, J. J.
Chem. Soc., Dalton Trans. 2002, 4017.
(13) Tsurugi, S.; Mashima, K. Organometallics 2006, 25, 5210.
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(20) Makio, H.; Oshiki, T.; Takai, K.; Fujita, T. Chem. Lett. 2005, 34,
1382.
10.1021/om0607752 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 12/09/2006

ActiVation of Pyrrolylaldiminato Ti Polymerization Catalysts
Organometallics, Vol. 26, No. 2, 2007 289
1
Table 1. Selected 13C and H NMR Chemical Shifts (ppm), Line Widths ∆T1/2 (Hz), Multiplicities, and J1 Coupling Constants
CH
(Hz) for Complexes I and I2-I4 in Toluene-d8/1,2-Difluorobenzene
species
Al:Ti
T, °C
1H (Ti-Me)
1H (NdCH)
1H (L)
13C (Ti-Me)
L2TiCl2 (I)
20
7.82
5.89 (dd, J ) 2.3, 3.5),
6.05 (d, J ) 3.5)
6.22
L2TiClMe (I2)
L2TiClMe (I2)
15
15
50
-10
-60
-20
2.37
(∆ϑ1/2 ) 3)
8.04 (∆ϑ1/2 ) 30)
92.1
7.33a
(J1CH ) 127),
(∆ν1/2 ) 9)
b
2.37
(∆ϑ1/2 ) 10)
8.20 (∆ϑ1/2 ) 9)
7.25a
9.0
(∆ϑ1/2 ) 100)
7.5-8.0
n.r.d.f
[L2TiMe(S)]+
[MeMAO]- (I3)
I4
1.85
(∆ϑ1/2 ) 8)
1.65
6.0
82.0 (J1CH ) 125)
50
50
-20
-30
83.4 (J1CH ) 125)
c
[L2TiP(S)]+
[MeMAO]- (I3′)
LAlMe2
n.r.d.
6.26d
50
-10
7.3d,e
a Overlapping with toluene. Not measured. c13C: 106.5 (-H213C-Ti). Peak position is dependent on temperature and Al/Ti ratio. Al-CH3 peak at δ
b
d
e
-0.24; peak position is dependent on temperature and Al/Ti ratio. f n.r.d. ) not reliably detected.
copy, which provide experimental evidence for structures and
reaction pathways of relevant intermediates in these catalyst
systems.
Results and Discussion
1
The I/MAO System. The H NMR spectrum of the initial
complex I in toluene-d8/1,2-difluorobenzene (5:1) at 20 °C
displays sharp and well-resolved peaks (Table 1). After addition
of MAO (Al:Ti ) 10-15), the major part of I is converted to
another complex identified as L2TiMeCl (I2) (Figure 1a, Table
1). At 20 °C, the imine resonance of I2 is broadened and thus
unobservable; however, lowering the temperature below -10
°C results in clear signal decoalescence into two peaks, in
agreement with the expected nonequivalence of two pyrrole-
imine protons in L2TiMeCl. The apparent exchange value ∆Gq
ex
was estimated to be 13.6 kcal mol-1 at the coalescence
1
temperature of 15 °C (cf. ref 16). The H NMR peak of the
Ti-CH3 group of I2 was observed at δ 2.37, and an experiment
with 13C-enriched MAO revealed the corresponding Ti-13CH3
resonance at δ 92.1 (q, J1 ) 127 Hz, ∆ν1/2 ) 9 Hz, 10 °C,
CH
Table 1). We note that the active species in bis(pyrrolylaldi-
minato) titanium systems are thermally less stable than those
Figure 1. 1H NMR spectra (-20 °C) of I/MAO samples: (a) Al:
Ti ) 10; (b) Al:Ti ) 50; (c) Al:Ti ) 50 after storing at -20 °C
in bis(salicylaldiminato) titanium systems;18 therefore the
spectroscopic measurements of the samples with higher Al/Ti
ratios should be conducted at temperatures below -10 °C.
In all cases the formation of varying amounts of the aluminum
complex LAlMe2 (where L ) N-phenylpyrrolylaldiminate) was
observed, formed via ligand transfer to AlMe3. The compound
LAlMe2 was also generated independently by interaction of I
with AlMe3 at Al/Ti ) 20 and was identified by its CHdN and
Al-CH3 resonances that fall in the region typical for L′ lMe2
complexes with L′ ) salicylaldiminato ligands.18,21
overnight. Asterisks mark peaks assignable to the elusive L2TiMe2
complex. 13C NMR spectra of I/MAO-13C samples: (d) Al:Ti )
10, -10 °C; (e) Al:Ti ) 50, -20 °C.
1
I2. In contrast to I2, compound I3 is characterized by an H
NMR resonance for the Ti-CH3 group at δ 1.86 (-20 °C),
which corresponds to the 13C NMR signal for Ti-13CH3 at δ
82.0 (1JCH ) 125 Hz; Table 1). I3 becomes the predominant
species at Al:Ti ) 50 (Figure 1b). Further increases of the Al:
Ti ratio to 100-200 do not give rise to any new complexes.
By analogy with the bis(salicylaldiminato) titanium system,18
I3 is likely to be the cationic outer-sphere intermediate
[L2TiMe]+[MeMAO]-. Although one should expect two non-
equivalent imine peaks for I3, a single broadened signal is
At higher Al:Ti ratios of 20-30, formation of a new complex
I3 could be observed in the I/MAO system, along with complex
(21) Pappalardo, D.; Tedesco, C., Pellecchia, C. Eur. J. Inorg. Chem.
2002, 621.

290 Organometallics, Vol. 26, No. 2, 2007
BryliakoV et al.
Scheme 1. Formation and Deactivation of the Active Sites in the System I/MAO* (MAO* ) MAO-13C, NkN )
pyrrolylaldiminato ligand, X ) unidentified monoanionic ligand)
observed at temperatures from -60 to -10 °C (δ 9.0, ∆ϑ1/2
)
contains an as yet unidentified negatively charged ligand X
(methyl?). Species I4 is far less reactive toward ethene than I3
(see below).
100 Hz at -20 °C). The width of the Ti-CH3 resonance is
highly temperature dependent (∆ϑ1/2 ) 8 Hz at -20 °C, 15 Hz
at -30 °C, and 30 Hz at -40 °C), indicative of slow exchange
of the Ti-Me group between the two coordination sites of [L2-
TiMe]+. The remaining site of I3 is probably occupied by a
weakly coordinated solvent molecule (S), and we therefore
formulate I3 as [L2TiMe(S)]+[Me-MAO]- (Scheme 1). The
To corroborate the role of I3 as the ethene polymerizing
species, we injected 13C-labeled ethene into the NMR tubes
containing I3 and I4 (at ca. 1:2 ratio) at low temperatures.
Addition of 13C2H4 (ethene:Ti ) 8) into this sample at -30 °C
resulted in the immediate disappearance of the Ti-CH3 and
Ti-13CH3 peaks of I3, whereas those of I4 remained unaffected
(see Supporting Information). At the same time a very small
13C NMR peak was observed at δ 106.5 that, in analogy with
the Ti-13CH2 signal in the bis(salicylaldiminato) system,18 might
be assigned to the Ti-13CH2- carbon of the titanium polymeryl
species.31 After warming the sample to room temperature, the
13C NMR signal of polyethene was observed (δ 30.1), and all
ethene was found to be consumed. In contrast, when ethene
was injected into a separate sample containing only I4, even
after 5 min at -10 °C only partial consumption of ethene was
1
relatively sharp H and 13C NMR peaks of I3 indicate that the
[Me-MAO]- counterion is placed in the outer coordination
sphere of titanium.22 The reactive nature of I3 will be further
illustrated by the reaction with 13C2H4.
We note that, just as was the case of the bis(salicylaldiminato)
titanium system,18 the dimethyl product L2TiMe2 could not be
reliably detected in the I/MAO system. We did observe a small
1
sharp H peak at δ 2.30 (-10 °C) that might be ascribed to
L2Ti(CH3)2 protons in samples of I/MAO at Al:Ti ) 20-50 in
the course of conversion of I2 to I3 (Figure 1b); however, its
concentration was too low for a reliable identification.
1
detected by H NMR spectroscopy.
Thus, the active intermediate in the system I/MAO is an
outer-sphere ion pair, [L2TiMe(S)]+[Me-MAO]- (I3). In the
absence of ethene, it converts to another titanium species, I4,
which is far less reactive toward ethene, and even less so to
LAlMe2. This is likely to be the major route of catalyst
deactivation of system I.
Apart from the formation of I4, a major catalyst deactivation
pathway is the reduction of Ti(IV) to Ti(III). EPR spectra
(toluene-d8/1,2-difluorobenzene, 20 °C) of the samples of
I/MAO, recorded after the decay of the Ti(IV) species was
confirmed by NMR spectroscopy, are a superposition of two
types of signals: a sharp isotropic signal at g 1.967 and an
axially anisotropic one (gx ) 1.992, gy ) 1.966, gz ) 1.966).
As distinct from the bis(salicylaldiminato)TiCl2/MAO system,
with time the ion pair I3 irreversibly converts into another
(presumably cationic) titanium(IV) species I4, which is char-
acterized by 1H and 13C NMR peaks close to those of I3 (Figure
1c, Table 1). I4 is far more stable than I3: traces of I4 can be
observed even at +20 °C. Taking into account the fact that
formation of I4 is always accompanied by the appearance of
LAlMe2 and that decomposition of I4 at room temperature results
in further increase in the LAlMe2 concentration, one can
conclude that the pyrrolylaldiminato ligand in I4 remains
unaffected (i.e., no reduction of the imine functionality is
apparent).30 It is likely therefore that I4 is a cationic titanium-
(IV) complex derived from ligand transfer to Al and also
(22) For zwitterion-like inner-sphere ion pairs formed by MAO and
metallocenes,23-25,27 half-titanocenes,26 and constrained-geometry com-
plexes,27 broad non-uniform NMR peaks are observed.
(23) Babushkin, D. E.; Semikolenova, N. V.; Zakharov, V. A., Talsi, E.
P. Macromol. Chem. Phys. 2000, 201, 558.
(24) 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, 92.
(28) Although one might expect that I4 may be formed by a reaction of
MAO with the CHdN functional group of I3 (in analogy with the imine to
amine reduction by Al(iBu)3 as previously described by Fujita and
co-workers for bis(salicylaldimine) titanium complexes29,30), the CHdN
group seems to be unaffected under our experimental conditions.
(29) Saito, J.; Mitani, M.; Matsui, S.; Tohi, Y.; Makio, H.; Nakano, T.;
Tanaka, H.; Kashiwa, N.; Fujita, T. Macromol. Chem. Phys. 2002, 203,
59.
(25) Tritto, I; Donetti, R.; Sacchi, M. C.; Locatelli, P.; Zannoni, G.
Macromolecules 1997, 30, 1247.
(26) Bryliakov, K. P.; Semikolenova, N. V.; Zakharov, V. A.; Talsi, E.
P. J. Organomet. Chem. 2003, 683, 23.
(27) Bryliakov, K. P.; Talsi, E. P.; Bochmann, M. Organometallics 2004,
23, 149.
(30) Saito, J.; Suzuki, Y.; Makio, H.; Tanaka, H.; Onda, M.; Fujita, T.
Macromolecules 2006, 39, 4023.
(31) In distinction to the “living” bis(salicylaldimine) titanium system
(where titanium polymeryl species are stable at -20 °C),18 in the I/MAO
system the Ti-13CH2- peak is expected to be elusive because of â-hydrogen
elimination/chain transfer processes.

ActiVation of Pyrrolylaldiminato Ti Polymerization Catalysts
Organometallics, Vol. 26, No. 2, 2007 291
Scheme 2. Formation and Deactivation of the Active Sites in the System II/MAO* (MAO* ) MAO-13C
1
Table 2. Selected 13C and H NMR Chemical Shifts (ppm), Line Widths ∆T1/2 (Hz), Multiplicities, and J1 Coupling Constants
CH
(Hz) for Complexes II, II2, and II3 in Toluene-d8/1,2-Difluorobenzene
species
Al:Ti
T, °C
1H (NdCH)
1H (Ti-Me)
1H (L′, L)
1H (tBu)
13C (Ti-Me)
13C (tBu)
L'LTiCl2 (II)
L'LTiClMe (II2)
-20
-20
7.86, 7.78
5.86, 6.22
n.r.d.b
1.36
a
29.4
12
12
50
50
8.29 (∆ϑ1/2 ) 11)
7.60 (∆ϑ1/2 ) 8)
8.21 (∆ϑ1/2) 27)
7.66 (∆ϑ1/2 ) 21)
8.08 (∆ϑ1/2 ) 35)
7.72 (∆ϑ1/2 ) 30)
8.08 (∆ϑ1/2 ) 20)
7.72 (∆ϑ1/2 ) 20)
1.97 (∆ϑ1/2 ) 8)
1.97 (∆ϑ1/2 ) 25)
2.24 (∆ϑ1/2 ) 30)
2.27 (∆ϑ1/2 ) 18)
1.46 (∆ϑ1/2 ) 8)
1.48 (∆ϑ1/2 ) 25)
1.57 (∆ϑ1/2 ) 30)
1.55
82.1 (J1CH ) 127,
∆ν1/2 ) 13)
L'LTiClMe (II2)
0
-20
-10
6.16, 6.27
n.r.d.
a
a
[L′LTiMe(S)]+
[MeMAO]- (II3)
[L′LTiMe(S)]+
[MeMAO]- (II3)
102.9
29.9
30.0
n.r.d.
102.6 (∆ν1/2 ) 27)
a Not measured. b n.r.d. ) not reliably detected.
The fraction of the latter increases with increasing Al/Ti ratio.
The former peak probably belongs to a free titanium(III) species
in solution. The latter signal may be associated with a titanium-
(III) complex coordinated to bulky MAO molecules, which leads
to restricted tumbling of the Ti(III) species. The giso values of
1.975 are close to those measured for Ti(III) species observed
in ansa-titanocene/MAO systems.32
The II/MAO System. The activation of complex II with
MAO (Scheme 2) proceeds quite similarly to the system I/MAO.
At low Al:Ti ratios of 5-15, the monomethylated complex II2
(L′LTiClMe) is observed (Table 2 and Figure 2a). Since the
ligands L′ and L are different in II, two separate imine protons
are observed for II2 at temperatures from -60 to +20 °C. Slow
exchange (on the NMR time scale) between Ti-Cl and Ti-
Me ligands is apparent at -20 °C, since at higher temperatures
(e.g., 0 °C, Table 2) rather broader 1H NMR peaks are observed
for II2.
However, in the system II/MAO we did not detect the formation
of ligand-to-aluminum transfer products of the type LAlMe2
18
(vide supra) or L′AlMe2 in the course of II3 decomposition.
The main catalyst deactivation pathway in this system therefore
appears to be the reduction of Ti(IV) to Ti(III).
The formation of a second cationic titanium-methyl species
analogous to I4 has also not been observed in this system, and
we can thus conclude that the heteroligated (salicylaldiminato)-
(pyrrolylaldiminato) titanium system is much less prone to
ligand scrambling than the bis(salicylaldiminato) and bis-
(pyrrolylaldiminato) catalysts.
The reactivity of II3 toward ethene was probed by addition
of ethene-13C. In agreement with the high reactivity of the II/
MAO catalyst,14 even immediately after the injection at -20
°C of 8 equiv of ethene to the sample containing predominantly
II3 (Al:Ti ) 50), there were no traces of ethene-13C observed
1
in the H NMR spectrum and the Ti-Me peak of II3 was not
apparent any more either. At the same time 13C NMR spectro-
scopy showed the formation of free ethene oligomers (inner
methylene groups at δ 30.6, â and γ carbons of the polymer
chain at δ 23.5 and 32.7)33,34 (see Supporting Information).
In contrast to the bis(salicylaldiminato) system,18 in the bis-
(pyrrolylaldiminato) catalyst the Ti-13CH2- peak of the
titanium-polymeryl moiety was not detected in the 13C NMR
spectrum, in part due to fast â-hydrogen elimination and chain
transfer processes and, probably, significant line broadening at
low temperatures. Spectra of II/MAO samples (Al:Ti ) 50)
recorded at -20 °C after the addition of 8 equiv of 13C2H4 show
only a vinyl-terminated ethene oligomer chain (see Supporting
Information, Figure S4). The same sample warmed to room
temperature and recooled to -20 °C shows the formation of at
least one other type of vinyl end groups. A possible explanation
At higher Al:Ti ratios (g50), the cationic intermediate
[L′LTiMe(S)]+[Me-MAO]- (II3) was detected as the main
species (Table 2 and Figure 2b). It is characterized by two
1
separate H peaks of imine protons from the salicylaldiminato
and pyrrolylaldiminato ligands (δ 8.08 and 7.72 at -20 °C)
and the Ti-CH3 peak at δ 2.24 (which corresponds to a Ti-
13CH3 peak at δ 102.9). The widths of NMR lines of II3 are
also temperature sensitive: lowering the temperature to -40
1
°C results in the disappearance of the imine and Ti-Me H
signals, whereas at -10 °C II3 has sharper 1H resonances; thus,
at -20 to -10 °C the case of fast exchange (on the NMR time
scale) is realized. Again we note that in the II/MAO system
we could not reliably detect the dimethyl species L′LTiMe2;
apparently, once formed, the latter rapidly converts into II3.
Like I3, intermediate II3 is thermally unstable and decomposes
within 3 h at -10 °C, or within several minutes at +10 °C.
(33) Tritto, I.; Sacchi, M. C.; Locatelli, P.; Zannoni, G. Macromolecules
1995, 28, 5358.
(34) Tritto, I.; Donetti, R.; Sacchi, M. C.; Locatelli, P.; Zannoni, G.
Macromolecules 1999, 32, 264.
(32) Bryliakov, K. P.; Babushkin, D. E.; Talsi, E. P.; Voskoboynikov,
A. Z.; Gritzo, H.; Shro¨der, L.; Damrau, H-R.; Wieser, U.; Schaper, F.;
Brintzinger, H.-H. Organometallics 2005, 24, 894.

292 Organometallics, Vol. 26, No. 2, 2007
BryliakoV et al.
(III). This absence of ligand scrambling may contribute to the
high ethene polymerization activity of catalysts based on II.
Experimental Section
All operations were carried out under dry argon by standard
Schlenk techniques. Methylalumoxane (MAO) was purchased from
Witco GmbH (Bergkamen, Germany) as a toluene solution (total
Al content 1.8 M, Al as AlMe3 0.5 M). Ethene-13C2 (99% 13C)
was purchased from Aldrich. Toluene-d8 and 1,2-difluorobenzene
were dried over molecular sieves (4 Å), degassed in vacuo, and
stored under dry argon. Toluene was distilled over sodium or
sodium benzophenone under nitrogen and degassed in vacuo. Solids
and toluene-d8 were transferred and stored in a glovebox. Bis(N-
phenylpyrrolylaldiminato)titanium(IV) dichloride2 (L2TiCl2, I) and
[N-(3-tert-butylsalicylidene)-2,3,4,5,6-pentafluoroanilinato-N′-phe-
nylpyrrolylaldiminato]titanium(IV) dichloride14 (L′LTiCl2, II) were
1
prepared as described (one can find its H NMR spectrum in the
Supporting information, Figure S1). 1H and 13C{1H} NMR spectra
were recorded at 300.130 and 75.473 MHz, respectively, on a
Bruker Avance-300 MHz NMR spectrometer. Typical operating
conditions for 13C NMR measurements were as follows: spectral
width 20 kHz; spectrum accumulation frequency 0.2-0.1 Hz; 100-
2000 transients, 90° pulse at 7 µs. Multiplicities and coupling
constants were derived from analysis of gated decoupled spectra.
For the acquisition of Ti-13CH3 groups of species I2, II2, I3, II3,
and I4, 13C-enriched MAO was used as activator. Operating
conditions for 1H NMR measurements: spectral width 5 kHz;
spectrum accumulation frequency 0.5-0.2 Hz; number of transients
32-64, ca. 30° pulse at 2 µs. 13C,1H-correlations were established
using double-resonance techniques. For calculations of 1H and 13
C
chemical shifts, the resonances of the methyl group of the toluene-
d8 solvent were taken as δ 2.11 and 20.40, respectively. The sample
temperature measurement uncertainty and temperature reproduc-
ibility were less than (1 °C. EPR spectra were recorded on a Bruker
ER-200D EPR spectrometer at 9.678 GHz in 3 mm outer diameter
quartz tubes at room temperature.
Preparation of MAO and Al2Me6 Samples. Solid MAO was
prepared from commercial MAO (Witko) by removal of the solvent
in vacuo at 20 °C for 1 day. 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. 13CH3-enriched
MAO was prepared by methyl exchange of 99% 13CH3-enriched
Al2Me6 (30 mol % of total Me groups) and solid MAO (70 mol %
of total Me groups) in toluene solution followed by subsequent
removal of volatiles under vacuum at room temperature to give a
sample of 13C-enriched MAO (ca. 30% 13C) with desired Al2Me6
content (polymeric MAO with total Al content of 40% and Al as
residual Al2Me6 ca. 5 wt %). A more detailed description is
presented in ref 27.
Figure 2. 1H NMR spectra (-20 °C) of II/MAO samples: (a)
Al:Ti ) 10; (b) Al:Ti ) 50. 13C NMR spectra of I/MAO-13C
samples: (c) Al:Ti ) 10, -20 °C; (d) Al:Ti ) 50, -10 °C.
Asterisks mark impurities in MAO.
for these observations is that at -20 °C some of the oligomeryl
chains were released via chain transfer to monomer, which
consumes any remaining ethene, while on warming further chain
release via â-H elimination takes place.
Conclusions
The formation of cationic species formed in two nonmetal-
locene catalytic systems based on bis[N-phenylpyrrolylaldimi-
nato]titanium(IV) dichloride (L2TiCl2, I) and [N-(3-tert-
butylsalicylidene)-2,3,4,5,6-pentafluoroanilinato-N′-
phenylpyrrolylaldiminato]titanium(IV) dichloride (L′LTiCl2, II)
has been studied. It was found that the first step of the activation
of the above catalysts with methylalumoxane (MAO) is the
monomethylation to give L2TiMeCl (I2) and L′LTiMeCl (II2),
respectively, whereas there was little evidence for the formation
of titanium dimethyl products. At Al:Ti ratios > 50 these species
quantitatively convert to outer-sphere ion pairs of the type [L2-
TiMe(S)]+[MeMAO]- (I3) and [L′LTiMe(S)]+[MeMAO]- (II3)
(where S is a weakly coordinated solvent molecule). These ion
pairs have been shown to be active for ethene polymerization.
Preparation of I/MAO and II/MAO (+ethene) Samples.
Taking into account that the species of interest (ion pairs I3, I4,
II3) have limited solubility in relatively nonpolar toluene and tend
to form oily precipitates in the NMR tubes, we increased the solvent
polarity by adding 15 vol % of 1,2-difluorobenzene to the
solvent.18,27
The appropriate amounts of I (II) and MAO (generally 10-5 mol
of Ti) were weighed in an NMR tube in a glovebox, and the tube
was closed with a septum stopper. Further addition of toluene-d8
and 1,2-difluorobenzene was performed outside the glovebox with
gastight microsyringes in a flow of argon upon appropriate cooling.
1H NMR (I2, toluene-d8/1,2-difluorobenzene, -20 °C): δ 8.04
(1H, ∆ϑ1/2 ) 30, CHdN), 7.33 (1H, CHdN), 6.22 (1H, pyrrol
ligand), 2.37 (s, 3H, ∆ϑ1/2 ) 3 Hz, Ti-CH3). 13C NMR: δ 92.1
The two systems follow different deactivation pathways.
Species I3 deactivates predominantly via transfer of a pyrroly-
laldiminato ligand to AlMe3, whereas in the mixed-ligand system
II/MAO such ligand transfer is not evident, and the main
deactivation pathway appears to be reduction of Ti(IV) to Ti-
(1C, J1 ) 125, ∆ν1/2 ) 9 Hz).
CH
1H NMR (II2, toluene-d8/1,2-difluorobenzene, -20 °C): δ 8.29
(1H, ∆ϑ1/2 ) 11, CHdN), 7.60 (1H, ∆ϑ1/2 ) 8, CHdN), 1.97 (s,
3H, ∆ϑ1/2 ) 8 Hz, Ti-CH3), 1.46 (s, 9H, ∆ϑ1/2 ) 8 Hz, C(CH3)3).

ActiVation of Pyrrolylaldiminato Ti Polymerization Catalysts
Organometallics, Vol. 26, No. 2, 2007 293
13C NMR: δ 82.1 (1C, J1 ) 127, ∆ν1/2 ) 13, Ti-CH3), 29.4
13CH-), 110.1 (d, J1 ) 72 Hz, H213Cd13CH-), 38.2 (dd, J1
CH
CC
CC
(3C, C(CH3)3).
) 42 Hz, 33 Hz, H213Cd13CH-13CH2-), 32.7 (unresolved,
1H NMR (I3, toluene-d8/1,2-difluorobenzene, -20 °C): δ 9.0
(2H, ∆ϑ1/2 ) 100 Hz, CHdN), 6.0 (2H, JHH ) 7.5 Hz, pyrrol
ligand), 1.85 (s, 3H, ∆ϑ1/2 ) 100 Hz, Ti-CH3). 13C NMR: δ 153.8
(2C, J1 ) 170 Hz, CHdN), 82.0 (1C, J1 ) 125, Ti-CH3).
-13CH2-13CH2-12CH3), 30.6 (PE×bc {-13CH2-}n), 23.5 (d, J1
CC
) 34 Hz, -13CH2-13CH2-12CH3).
13C NMR (V2, toluene-d8/1,2-difluorobenzene, -20 °C): δ 108.9
(d, J1 ) 72 Hz, H213Cd13CH-), 36.7 (broad triplet, H213Cd13-
CH
CH
CC
1H NMR (II3, toluene-d8/1,2-difluorobenzene, -20 °C): δ 8.08
(1H, ∆ϑ1/2 ) 35 Hz, pyrrole-imine CHdN), 7.72 (1H, ∆ϑ1/2 ) 30
Hz, phenoxy-imine CHdN), 2.24 (s, 3H, ∆ϑ1/2 ) 8 Hz, Ti-CH3),
1.57 (s, 9H, C(CH3)3). 13C NMR: δ 102.9 (1C, Ti-CH3), 29.9
(3C, C(CH3)3).
CH-13CH2-), 32.7 (unresolved, -13CH2-13CH2-12CH3), 30.6
(PE×bc {-13CH2-}n), 23.5 (d, J1 ) 34 Hz, -13CH2-13CH2-
CC
12CH3).
Acknowledgment. This work was supported by the Royal
Society, grant no. 2004/R1-FSU, and Russian Foundation of
Basic Research, grant no. 06-03-32700. We thank Dr. N. V.
Semikolenova and Dr. D. E. Babushkin for the generous gift
of MAO-13C and D. Homden for EPR measurements.
Addition of ethene or 13C2-ethene (ethene:Ti ) 6 or 8) to the
above samples was performed with a gastight syringe by bubbling
the gas through the cooled solutions of I3 and II3. The sample was
placed in the NMR probe thermostated at -20 °C, and the NMR
spectra were run at this temperature and then at higher temperatures,
if appropriate.
Upon polymerization of 13C2H4 by II3 at -20 °C, warming the
sample to room temperature, and recooling to -20 °C, two sets of
13CH2dNMR signals corresponding to two types of vinyl end
groups (V1 and V2) were observed.
13C NMR (V1, toluene-d8/1,2-difluorobenzene, -20 °C): δ 146.1
(partly overlapped with toluene, dd, J1CC ) 72 Hz, 42 Hz, H213Cd
Supporting Information Available: 1H NMR spectrum of
1
species LA1Me2, 13C NMR spectra of species I3, I4; H and 13C
NMR spectra of species II3 before and after addition of ethene-
13C; and EPR spectra. This material is available free of charge via
the Internet at http://pubs.acs.org.
OM0607752