Titanium complexes bearing a hemilabile heteroscorpionate ligand: Synthesis, reactivity, and olefin polymerization activity

Article abstract of DOI:10.1021/om050063w

A series of titanium complexes (bpzmp)TiR¹R²R ³ (bpzmp = (3,5-^tBu₂-2-phenoxo)bis(3,5-Me ₂-pyrazol-1-yl)methane; R¹ = R² = R³ = Cl (2); R¹ = R² = R³ = NMe₂ (3); R¹ = Cl; R² = R³ = NMe₂ (4); R ¹ = R² = Cl; R³= NMe₂ (5); R ¹ = R² = R³ = Me (6)) has been synthesized and characterized by VT NMR spectroscopy and X-ray diffraction analysis (2, 3, 5). The complexes 2-6 adopt in the solid state an octahedral structure in which the bpzmp ligand is κ³-coordinated to the metal via the phenoxy group and the imino nitrogens of the two pyrazolyl rings. The investigation of the solution structure of 3 by means of VT ¹H NMR spectroscopy revealed a fluxional behavior of the bpzmp ligand that produces an equilibrium between the octahedral and tetrahedral form of the titanium complex, the latter resulting from the η¹-coordination of the ligand through exclusively the phenolate group. The thermodynamic and kinetic parameters of this process were evaluated by VT NMR spectroscopy. The selective replacement of chloride for dimethylamide in 4 and 5 shifts the equilibrium toward the octahedral complex, which is the favorite configuration at room temperature. Site exchange of the nonequivalent methyl groups in 6 was observed at room temperature in the slow-regime ¹H NMR time scale: ΔH? and ΔS? values of 22.3 ± 1.1 kcal·mol^-1 and -19.6 ± 3.7 cal mol^-1 K^-1 were respectively determined for the isomerization process occurring with a rate constant of 3 s^-1 and ΔG? of 28.1 ± 0.1 kcal·mol ^-1 at 293 K. Complexes 2 and 6 are active olefin polymerization catalysts after activation with MAO or [Ph₃C] [B(C₆F ₅)₄]. Linear polyethylene and atactic polypropylene were obtained in the polymerization experiments catalyzed by 6-[Ph₃C] [B(C₆F₅)₄]. Highest polymerization activities were found with the 2-MAO catalyst, where leaching of the ligand due to MAO excess was suspected. Reaction of 6 with [Ph₃C] [B(C ₆F₅)₄] in the presence of THF readily produces the ionic complex [(bpzmp)TiMe₂(THF)][B(C₆F ₅)₄], proposed as a model of the active species in this class of olefin polymerization catalysts.

Full text of DOI:10.1021/om050063w

Organometallics 2005, 24, 4915-4925
4915
Titanium Complexes Bearing a Hemilabile
Heteroscorpionate Ligand: Synthesis, Reactivity, and
Olefin Polymerization Activity
Stefano Milione,† Valerio Bertolasi,‡ Toma´s Cuenca,§ and Alfonso Grassi*,†
Dipartimento di Chimica, Universita` di Salerno, 84081 Baronissi, Italy, Centro di
Strutturistica Diffrattometrica and Dipartimento di Chimica, Universita` di Ferrara, 44100
Ferrara, Italy, and Departamento de Qu´ımica Inorga´nica, Universidad de Alcala´, Campus
Universitario, Edificio de Farmacia, 28871 Alcala´ de Henares, Spain
Received January 31, 2005
A series of titanium complexes (bpzmp)TiR1R2R3 (bpzmp ) (3,5-tBu2-2-phenoxo)bis(3,5-
Me2-pyrazol-1-yl)methane; R1 ) R2 ) R3 ) Cl (2); R1 ) R2 ) R3 ) NMe2 (3); R1 ) Cl; R2 )
R3 ) NMe2 (4); R1 ) R2 ) Cl; R3) NMe2 (5); R1 ) R2 ) R3 ) Me (6)) has been synthesized
and characterized by VT NMR spectroscopy and X-ray diffraction analysis (2, 3, 5). The
complexes 2-6 adopt in the solid state an octahedral structure in which the bpzmp ligand
is κ3-coordinated to the metal via the phenoxy group and the imino nitrogens of the two
1
pyrazolyl rings. The investigation of the solution structure of 3 by means of VT H NMR
spectroscopy revealed a fluxional behavior of the bpzmp ligand that produces an equilibrium
between the octahedral and tetrahedral form of the titanium complex, the latter resulting
from the η1-coordination of the ligand through exclusively the phenolate group. The
thermodynamic and kinetic parameters of this process were evaluated by VT NMR
spectroscopy. The selective replacement of chloride for dimethylamide in 4 and 5 shifts the
equilibrium toward the octahedral complex, which is the favorite configuration at room
temperature. Site exchange of the nonequivalent methyl groups in 6 was observed at room
1
temperature in the slow-regime H NMR time scale: ∆Hq and ∆Sq values of 22.3 ( 1.1
kcal‚mol-1 and -19.6 ( 3.7 cal mol-1 K-1 were respectively determined for the isomerization
process occurring with a rate constant of 3 s-1 and ∆Gq of 28.1 ( 0.1 kcal‚mol-1 at 293 K.
Complexes 2 and 6 are active olefin polymerization catalysts after activation with MAO or
[Ph3C][B(C6F5)4]. Linear polyethylene and atactic polypropylene were obtained in the
polymerization experiments catalyzed by 6-[Ph3C][B(C6F5)4]. Highest polymerization activities
were found with the 2-MAO catalyst, where leaching of the ligand due to MAO excess was
suspected. Reaction of 6 with [Ph3C][B(C6F5)4] in the presence of THF readily produces the
ionic complex [(bpzmp)TiMe2(THF)][B(C6F5)4], proposed as a model of the active species in
this class of olefin polymerization catalysts.
Introduction
attention has been paid to mono- and polydentate
ligands bearing oxygen and nitrogen donors. These
ligands are synthesized in a simple manner and modi-
fied by well-established synthetic procedures, yielding
group 4 metal complexes with tunable electronic proper-
ties, flexible coordination geometry, and coordination
number higher than four, typically found in metal-
locenes. Examples of these ligands include bis-phenoxy-
imine,3 amidinate,4 and pyrazolylborate.5 Some recent
reports highlighted the olefin polymerization perfor-
mances of titanium complexes of the tris(pyrazolyl)-
borate ligand carrying sterically demanding substitu-
Olefin polymerization catalysis has been widely domi-
nated in the past decades by group 4 metallocenes,
which allow the synthesis of stereoregular poly-1-olefins
with properties rivalling those of the polymers by
classical heterogeneous Ziegler-Natta catalysts.1 Re-
cently research efforts have been produced to enlarge
the typology of the ligands used in the coordination
chemistry of the group 4 metals, opening the so-called
postmetallocene era.2 In this framework considerable
* To whom correspondence should be addressed. E-mail: agrassi@
unisa.it.
† Universita` di Salerno.
(3) (a) Matsui, S.; Tohi, Y.; Mitani, M.; Saito, J.; Makio, H.; Tanaka,
H.; Nitabaru, M.; Nakano, T.; Fujita, T. Chem. Lett. 1999, 1065. (b)
Matsui, S.; Mitani, M.; Saito, J.; Matsukawa, N.; Tanaka, H.; Nakano,
T.; Fujita, T. Chem. Lett. 2000, 554. (c) Matsui, S.; Mitani, M.; Saito,
J.; Tohi, Y.; Makio, H.; Matsukawa, N.; Takagi, Y.; Tsuru, K.; Nitabaru,
M.; Nakano, T.; Tanaka, H.; Kashiwa, N.; Fujita, T. J. Am. Chem. Soc.
2001, 123, 6847. (d) Saito, J.; Mitani, M.; Mohri, J.-I.; Yoshida, Y.;
Matsui, S.; Ishii, S.-I.; Kojoh, S.-I.; Kashiwa, N.; Fujita, T. Angew.
Chem., Int. Ed. 2001, 40, 2918. (e) Suzuki, Y.; Terao, H.; Fujita, T.
Bull. Chem. Soc. Jpn. 2003, 76, 1493. (f) Tian, J.; Coates, G. W. Angew.
Chem., Int. Ed. 2000, 39, 3626.
‡ Universita` di Ferrara.
§ Universidad de Alcala´.
(1) (a) Bochmann, M. J. Chem. Soc., Dalton Trans. 1996, 255. (b)
Brintzinger, H.-H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.; Waymouth,
R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143. (c) Marks, T. J.
Acc. Chem. Res. 1992, 25, 57. (d) Coates, G. W. Chem. Rev. 2000, 100,
1223.
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Int. Ed. 1999, 38, 428. (b) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev.
2003, 103, 283.
10.1021/om050063w CCC: $30.25 © 2005 American Chemical Society
Publication on Web 09/07/2005

4916 Organometallics, Vol. 24, No. 21, 2005
Milione et al.
Scheme 1
ents in the 3,5-positions.6 These ligands were expected
to stabilize, better than cyclopentadienyl, the Ti(IV)
metal center toward reduction to lower oxidation states
after treatment with MAO excess.6b
The use of polydentate ligands with fluxional coordi-
nation properties also permitted intriguing and novel
reactivity patterns at the metal center.9 The presence
of a neutral pendant group, chemically linked to the
cyclopentadienyl ligand, increased the thermal stability
of the corresponding olefin polymerization catalysts.9b
More remarkably, the coordination of a properly sub-
stituted aryl group switched the properties of (η5-C5H4-
CMe2Ar)TiCl3 (Ar ) Ph, 3,5-Me2C6H3) from an ethylene
polymerization catalyst to a selective ethylene trimer-
ization catalyst, and 1-hexene was thus selectively
obtained under proper conditions.10
When compared to titanocenes, the bis-phenoxy-imine
titanium complexes exhibit a significant improvement:
the corresponding MAO-activated polymerization cata-
lysts show living properties in propene polymerization
at room temperature, and olefin block copolymers with
unprecedented architectures were successfully synthe-
sized.7 The syndiospecificity of the bis-phenoxy-imine
titanium catalysts in propene polymerization was at-
tributed to the chain end stereocontrol mediated by the
fluxional behavior of the ligands, in turn controlled by
the site chirality.7a,b,8
(7) (a) Saito, J.; Mitani, M.; Onda, M.; Mohri, J.-I.; Ishii, S.-I.;
Yoshida, Y.; Nakano, T.; Tanaka, H.; Matsugi, T.; Kojoh, S.-I.; Kashiwa,
N.; Fujita, T. Macromol. Rapid Commun. 2001, 22, 1072. (b) Mitani,
M.; Furuyama, R.; Mohri, J.-I.; Saito, J.; Ishii, S.; Terao, H.; Nakano,
T.; Tanaka, H.; Fujita, T. J. Am. Chem. Soc. 2003, 125, 4293. (c) Mitani,
M.; Furuyama, R.; Mohri, J.-I.; Saito, J.; Ishii, S.; Terao, H.; Kashiwa,
N.; Fujita, T. J. Am. Chem. Soc. 2002, 124, 7888. (d) Ishii, S.-I.;
Furuyama, R.; Matsukawa, N.; Saito, J.; Mitani, M.; Tanaka, H.;
Fujita, T. Macromol. Rapid Commun. 2003, 24, 452. (e) Tian, J.;
Hustad, P. D.; Coates, G. W. J. Am. Chem. Soc. 2001, 123, 5134.
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124, 13368. (b) Lamberti, M.; Pappalardo, D.; Zambelli, A.; Pellecchia,
C. Macromolecules 2002, 35, 658. (c) Hustad, P. D.; Tian, J.; Coates,
G. W. J. Am. Chem. Soc. 2002, 124, 3614.
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M. S.; Chien, J. C. W.; Rausch, M. D. Organometallics 1998, 17, 3775.
(c) Sassmannshausen, J.; Powell, A. K.; Anson, C. E.; Wocadlo, S.;
Bochmann, M. J. Organomet. Chem. 1999, 592, 84. (d) Amor, F.; Butt,
A.; du Plooy, K. E.; Spanoil, T. P.; Okuda, J. Organometallics 1998,
17, 5836.
(4) (a) Volkis, V.; Shmulinson, M.; Averbuj, C.; Lisovskii, A.;
Edelmann, F. T.; Eisen, M. S. Organometallics 1998, 17, 3155. (b)
Volkis, V.; Nelkenbaum, E.; Lisovskii, A.; Hasson, G.; Semiat, R.;
Kapon, M.; Botoshansky, M.; Eishen, Y.; Eisen, M. S. J. Am. Chem.
Soc. 2003, 125, 2179.
(5) (a) Nakazawa, H.; Ikai, S.; Imaoka, K.; Kai, Y.; Yano, T. J. Mol.
Catal. A 1998, 132, 33. (b) Obara, T.; Ueki, S. Jpn. Kokai Tokkyo Koho
01 095 110, 1989. (c) Jens, K. J.; Tilset, M.; Heuman, A. PCT Int. Appl.
WO 97 17379, 1997. (d) Matsunaga, P. T.; Rinaldo, S. PCT Int. Appl.
WO 99 29739, 1999. (e) Ikai, S.; Kai, Y.; Murakami, M.; Nakazawa,
H. Jpn. Kokai Tokkyo Koho 11 228 614, 1999.
(6) (a) Furlan, L. G.; Gil, M. P.; Casagrande, O. L. Macromol. Rapid
Commun. 2000, 21, 1054. (b) Murtuza, S.; Casagrande, O. L.; Jordan,
R. F. Organometallics 2002, 21, 1882. (c) Michiue, K.; Jordan, R. F.
Macromolecules 2003, 36, 9707. (d) Michiue, K.; Jordan, R. F.;
Organometallics 2004, 23, 460. (e) Gil, M. P.; Casagrande, O. L. J.
Organomet. Chem. 2004, 286.

Titanium Complexes with a Heteroscorpionate Ligand
Organometallics, Vol. 24, No. 21, 2005 4917
Scheme 2
The fluxionality of the ligand can also tune the
electronic and steric properties of the metal center
during the polymerization process and control the
monomer incorporation in the growing polymer chain;
thus interesting results could be expected in the field
of olefin copolymerization with electron-rich monomers
such as styrene and 1,3-conjugated dienes.
Figure 1. ORTEP diagram of the molecular structure of
(bpzmp)TiCl3 (2). Thermal ellipsoids are drawn at the 40%
probability level.
lization of the crude product from dichloromethane/
hexane gave 2 as a bright dark red microcrystalline
solid, sparingly soluble in aromatic (toluene, benzene)
and aliphatic (n-pentane, n-heptane) hydrocarbon sol-
vents but soluble in polar solvents, such as dichlo-
romethane and tetrahydrofuran. Complex 2 was ther-
mally stable when exposed to the air in the solid state.
The 1H and 13C NMR spectra of 2 are consistent with
an octahedral Cs symmetric structure resulting from the
κ3-N,N,O coordination of the ligand to the metal center.
Actually one set of 1H NMR resonances, downfield
shifted from those of the free ligand, was observed for
the pyrazolyl protons. The 1H-1H NOESY experiments
permitted the univocal attribution of the 1H resonances,
in particular those of the methyls of the pyrazolyl groups
and of the t-Bu groups of the phenoxy ring. The chemical
shift of the methine proton of the bpzmp bridge was a
good probe for the assessment of the ligand coordination.
When bpzmp is κ3-coordinated to the metal, the methine
1H signal is upfield shifted from 7.5 ppm, whereas it is
found downfield shifted from this values for the ligand
exhibiting η1-coordination (vide infra). Upon warming
of a 1,1,2,2-tetrachloroethane-d2 solution of 2 up to 373
K, no broadening of the proton resonances was observed,
in agreement with the high coordination energy of the
ligand to the metal and the lack of any in-out fluxional
equilibrium of the two N,N donors (Scheme 2).
Crystals of 2 were grown from a dichloromethane/
hexane solution: the molecular structure, determined
by X-ray diffraction, is in fine agreement with the
solution structure observed in the NMR experiments.
The ORTEP15 view of complexes 2 is shown in Figure
1, and crystallographic data and selected interatomic
distances and angles are given in Tables 1 and 2. The
titanium geometry is distorted octahedral in which the
heteroscorpionate ligand is coordinated via the two
nitrogens of the pyrazole rings and the oxygen of the
phenolate group, and three chlorine atoms occupy the
other three sites of the octahedron. The Ti-Cl bond
lengths in the N,N plane, namely, 2.278(1) and 2.290-
(1) Å, are shorter than Ti-Cl1 (2.332(1) Å); the former
values are very similar to those observed in the pseudo-
In this framework we explored the performances of
the monoanionic tridentate heteroscorpionate ligand,11
(3,5-tBu2-2-phenoxo)bis(3,5-Me2-pyrazol-1-yl)methane
(bpzmp-H). A stable trialkyl zirconium derivative,
(bpzmp)ZrBn3, was synthesized and found active in
ethylene polymerization after activation with B(C6F5)3.12
The polydispersity index of polyethylene samples was
found to be temperature dependent with values ap-
proaching that of a single-site catalyst at -40 °C.
Recently a titanium complex of the bis(3,5-dimeth-
ylpyrazol-1-yl)acetate (bdmpza) ligand was successfully
synthesized by Otero et al. and found to be highly active
in ethylene polymerization: unfortunately alkyl deriva-
tives, modeling the active species, were not reported.13
Herein we describe the synthesis and solution proper-
ties of a series of heteroscorpionate titanium(IV) com-
plexes of the bpzmp ligand as well as preliminary
results on the performances of these catalysts in olefin
polymerization.
Results and Discussion
1. Synthesis and Reactivity of the Complexes
(bpzmp)TiR1R2R3 (R1 ) R2 ) R3 ) Cl (2); R1 ) R2 )
R3 ) NMe2 (3); R1 ) Cl; R2 ) R3 ) NMe2 (4); R1 ) R2
) Cl; R3 ) NMe2 (5); R1 ) R2 ) R3 ) Me (6); R1 ) R2
) Me; R3 ) THF (8)). The ligand bpzmp-H (1) was
synthesized according to the literature14 and the corre-
sponding sodium salt prepared by reaction with NaH
in toluene at room temperature. Treatment of a toluene
solution of TiCl4 with the sodium salt of 1 (Scheme 1)
afforded (bpzmp)TiCl3 (2) in good yield (61%). Crystal-
(10) (a) Deckers, P. J. W.; Hessen, B.; Teuben, J. H. Angew. Chem.,
Int. Ed. 2001, 40, 2516. (b) Deckers, P. J. W.; Hessen, B.; Teuben, J.
H. Organometallics 2002, 21, 5122.
(11) For a recent review on heteroscorpionate ligands see: Otero,
A.; Fernandez-Baeza, J.; Antinolo, A.; Tejeda, J.; Lara-Sanchez A.
Dalton Trans. 2004, 1499.
(12) Milione, S.; Montefusco, C.; Cuenca, T.; Grassi, A. Chem.
Commun. 2003, 1176.
(13) (a) Otero, A.; Fernandez-Baeza, J.; Antinolo, A.; Carrillo-
Hermosilla, F.; Tejeda, J.; Diez-Barra, E.; Lara-Sanchez, A.; Sanchez-
Barba, L.; Lopez-Solera, I. Organometallics 2001, 20, 2428. (b) Otero,
A.; Fernandez-Baeza, J.; Antinolo, A.; Carrillo-Hermosilla, F.; Tejeda,
J.; Lara-Sanchez, A.; Sanchez-Barba, L.; Fernandez-Lopez, M.; Rod-
riguez, A. M.; Lopez-Solera, I. Inorg. Chem. 2002, 41, 5193.
(14) (a) The, K. I.; Peterson, L. K. Can. J. Chem. 1973, 51, 422. (b)
Hammes, B. S.; Carrano, C. J. Inorg. Chem. 1999, 38, 3562.
(15) Burdett, M. N.; Johnson, C. K. ORTEP III, Report ORNL-6895;
Oak Ridge National Laboratory: Oak Ridge, TN, 1996.

4918 Organometallics, Vol. 24, No. 21, 2005
Milione et al.
Table 1. Experimental Data for the Crystal Structure Determination of (bpzmp)TiCl3 (2), (bpzmp)Ti(NMe2)3
(3), and (bpzmp)Ti(NMe2)Cl2 (5)
2
3
5
formula
C
25H35Cl3 N4OTi
C31H53N7OTi‚1/2(C6H14
630.79
triclinic
P1h
)
C27H41Cl2N5OTi‚C7H8
662.58
monoclinic
P21/c
12.8927(2)
17.6351(3)
16.4832(3)
90
M
561.82
monoclinic
P21/n
system
space group
a/Å
11.6958(2)
18.5980(3)
13.0171(2)
90
96.706(1)
90
10.7759(2)
13.7408(3)
14.4792(3)
108.529(1)
107.328(1)
103.069(1)
1814.58(6)
2
b/Å
c/Å
R/deg
â/deg
94.777(1)
90
γ/deg
U/Å3
2812.09(8)
4
3734.7(1)
4
Z
Dc/g cm-3
1.327
1.154
1.178
µ/cm-1
6.14
2.71
4.04
T/K
295
100
295
θmin-θmax/deg
unique reflns
Rint
3.7-30.0
8086
2.1-30.0
10 303
3.0-28.0
8961
0.037
0.054
0.044
obs. reflns [I>2σ(I)]
R (obsd reflns)
wRw (all reflns)
S
5766
7818
6120
0.0468
0.1258
1.03
0.0464
0.0545
0.1629
1.04
0.1188
1.03
∆Fmax; ∆Fmin/e Å-3
0.65; -0.35
0.51; -0.45
0.48;-0.35
rine atoms are trans to the pyrazolyl nitrogens.16 The
Ti1-Cl1 lengthening was ascribed to a trans effect17 of
the phenolate oxygen that is stronger than that pro-
duced by the neutral pyrazolyl nitrogens. The C-sub-
stituted pyrazolyl groups coordinated to the titanium
atom form six-membered rings, N1-N2-C7-N4-N3-
Ti1, in boat conformation.
Table 2. Selected Bond Distances (Å) and Angles
(deg) for Compounds 2, 3, and 5
2
3
5
Ti1-Cl1
2.332(1)
2.278(1)
2.290(1)
1.798(1)
2.248(2)
2.204(2)
2.376(1)
2.337(1)
Ti1-Cl2
Ti1-Cl3
Ti1-O1
1.986(1)
2.387(2)
2.398(1)
1.965(2)
1.954(2)
1.944(1)
1.840(2)
2.211(2)
2.323(2)
1.923(2)
Ti1-N1
We attempted the synthesis of the amido derivatives
in order to get access to a wider family of heteroscor-
pionate titanium complexes. Treatment of a toluene
solution of Ti(NMe2)4 with 1 affords the triamido
derivative (bpzmp)Ti(NMe2)3 (3) (Scheme 1) in good
yield (62%).18 1H NMR monitoring of the reaction in a
NMR tube showed that this is fast and quantitative in
a few minutes. Complex 3 is very soluble in hexane, and
crystals suitable for X-ray analysis were grown from this
solvent at 253 K. The molecular structure of 3 (Figure
2) is very similar to that found for 2; the only difference
is the very strong trans effect exerted by the dimethyl-
amido ligand, which produces bond lengths for Ti-N1
and Ti-N3 (2.39 Å on average) and for Ti-O(phenolate)
[1.986(1) Å in 3 vs 1.798(1) Å in 2] longer than in 2.
The relative orientation of the three amido groups,
approximately orthogonal to each other, fits with the
optimal disposition and better overlap of the nitrogen
lone pairs with the d metal orbitals suitable for the one-
to-one metal(d)-NMe2(p) π-bonding interaction.19 The
O-Ti-N1 angle observed in 3 is smaller than in 2,
likely as a result of the steric congestion between the
-NMe2 groups and the tBu substituent of the phenolate
group. Weaker interaction of the ligand with the metal
Ti1-N3
Ti1-N5
Ti1-N6
Ti1-N7
Cl1-Ti1-Cl2
Cl1-Ti1-Cl3
Cl1-Ti1-O1
Cl1-Ti1-N1
Cl1-Ti1-N3
Cl1-Ti1-N5
Cl2-Ti1-Cl3
Cl2-Ti1-O1
Cl2-Ti1-N1
Cl2-Ti1-N3
Cl2-Ti1-N5
Cl3-Ti1-O1
Cl3-Ti1-N1
Cl3-Ti1-N3
O1-Ti1-N1
O1-Ti1-N3
N1-Ti1-N3
O1-Ti1-N5
O1-Ti1-N6
O1-Ti1-N7
N1-Ti1-N5
N1-Ti1-N6
N1-Ti1-N7
N3-Ti1-N5
N3-Ti1-N6
N3-Ti1-N7
N5-Ti1-N6
N5-Ti1-N7
N6-Ti1-N7
Ti1-O1-C1
Ti1-N1-N2
Ti1-N1-C8
Ti1-N3-N4
Ti1-N3-C13
N2-C7-N4
95.01(2)
93.19(2)
166.13(5)
83.74(4)
85.34(5)
91.76(3)
166.01(5)
85.26(5)
83.80(5)
95.18(7)
95.06(2)
94.85(4)
173.99(5)
93.20(5)
95.53(5)
171.36(6)
92.65(5)
95.72(7)
95.63(5)
90.89(5)
171.71(5)
85.44(6)
84.39(6)
80.85(6)
74.86(5)
85.51(5)
77.54(5)
159.44(6)
91.95(6)
99.61(6)
86.39(6)
161.18(6)
101.17(6)
82.22(6)
88.26(5)
174.26(6)
104.05(7)
92.13(7)
94.14(6)
149.0(1)
123.1(1)
132.0(1)
122.8(1)
128.8(1)
110.2(1)
85.80(7)
83.95(7)
78.98(7)
95.95(8)
92.63(9)
171.60(8)
(16) Antinolo, A.; Carrillo-Hermosillo, F.; Corrochano, A. E.; Fernan-
dez-Baeza, J.; Lanfranchi, M.; Otero, A.; Pellinghelli, M. A. J. Orga-
nomet. Chem. 1999, 577, 174.
154.8(1)
120.4(1)
133.8(1)
120.6(1)
133.4(1)
110.3(2)
154.7(1)
122.0(2)
132.8(3)
119.9(1)
135.2(2)
111.1(2)
(17) Coe, B. J.; Glenwright, S. J. Coord. Chem. Rev. 2000, 203, 5.
(18) For examples of amine elimination from Ti(NR2)4 see: (a)
Pritchett, S.; Gantzel, P.; Walsh, P. J. Organometallics 1997, 16, 5130.
(b) Pritchett, S.; Woodmansee, D. H.; Gantzel, P.; Walsh, P. J. J. Am.
Chem. Soc. 1998, 120, 6423. (c) Armistead, L. T.; White, P. S.; Gagne,
M. R. Organometallics 1998, 17, 216. (d) Kim, I.; Nishihara, Y.; Jordan,
R. F.; Rogers, R. D.; Rheingold, A. L.; Yap, G. P. A. Organometallics
1997, 16, 3314.
octahedral structure of the hydrido-tris(pyrazol-1-yl)-
borate titanium trichloride complex in which the chlo-
(19) Chisholm, M.; Hammond, C.; Huffman, J. Polyhedron 1988, 7
(24), 2515.

Titanium Complexes with a Heteroscorpionate Ligand
Organometallics, Vol. 24, No. 21, 2005 4919
chloride-amide mixed coordination sphere compounds.
Amide-halide exchange reaction is well documented in
group 4 metal amide complexes: some representative
examples are the reaction of CpTi(NMe2)3, Cp2Zr-
(NMe2)2, or Cp2Zr(NMe2)2 with MCl4 (M ) Si or Ge)20
or Me3SiCl21 as a chlorinating reagent. Reaction of 3
with Me3SiCl yielded the selective formation of the
chloro derivatives 4 and 5 with varied reaction condi-
tions. The addition of 1 equiv of Me3SiCl to a benzene-
d6 solution of 3 turned the color from red-orange to dark
red, and the selective and quantitative formation of
(bpzmp)Ti(NMe2)2Cl (4) and Me3SiNMe2 (Scheme 1) was
observed in 18 h. 1H NMR analysis of the solution
structure of 4 permitted the Cs symmetric structure to
be identified in which the ligand is κ3-N,N,O-coordinated
to the titanium, the chloride atom is trans to the oxygen,
and the four nitrogen atoms are in the equatorial plane.
The methine of the ligand bridge was observed at 6.80
ppm, and the two pyrazolyl rings produce a unique
symmetric 1H pattern. The sharpness of the line width
Figure 2. ORTEP diagram of the molecular structure of
(bpzmp)Ti(NMe2)3 (3). Thermal ellipsoids are drawn at the
40% probability level.
1
of the H NMR signals suggests that the ligand dis-
center is thus expected, and an increased fluxional
sociation does not occur in this case. When reaction of
3 with Me3SiCl was monitored at room temperature by
1H NMR spectroscopy, the 50% mol conversion of the
reagents was observed in 10 min and two species, with
Cs and C1 symmetry, respectively, were detected in 3:2
molar ratio. The structural differences between the two
isomers consist in the chloride placement that is trans
to the nitrogen atom of the pyrazolyl ring in the C1
isomer and trans to the oxygen atom of the phenoxy ring
in the Cs form (see Scheme 3). The C1 symmetric form
exhibits two nonequivalent pyrazolyl rings: two 1H
signals were indeed observed for the H4 of the pyrazolyl
groups at 5.23 and 5.46 ppm, and the chemical shift for
the methine of the ligand bridge at 6.75 ppm confirms
the κ3 coordination of the ligand to the metal. When the
reaction mixture was left for 18 h at room temperature,
the Cs isomer was detected pure and was the thermo-
dynamically favored product of this reaction. Possibly
the kinetic product displays the amide group trans to
the oxygen atoms, but it is slowly converted to the more
stable Cs symmetric isomer in which it is in the N,N
plane. When 3 was treated at room temperature in
benzene solution with a 3.5 equiv excess of Me3SiCl, the
selective and quantitative synthesis of the dichloride
derivative (bpzmp)Ti(NMe2)Cl2 (5) (Scheme 1) was
observed in 1 h. The excess of Me3SiCl does not further
react with 5, even after 1 day at room temperature. The
complex 5 is observed in the octahedral coordination
behavior of 3 in dichloromethane-d2 solution was actu-
1
ally observed. In the room-temperature H NMR spec-
trum, the pattern of the resonances is consistent with
a Cs symmetric structure corresponding to the η1
coordination of the ligand. Actually the methine 1H
signal is detected at 7.76 ppm as well as two singlets at
2.12 and 1.83 ppm for the four Me groups of the
pyrazolyl rings and only one signal for the three NMe2
groups at 3.06 ppm. Thus complex 3 adopts at room
temperature a tetrahedral geometry with the het-
eroscorpionate ligand coordinated exclusively through
the phenolate oxygen. The fast rotation of the amido
groups about the Ti-N and Ti-O bonds produces the
equivalence of the methyl groups of -NMe2. The broad-
1
ness of the H singlets for the 5-pyrazolyl methyls, H6
of the phenoxy ring, and the methine of the ligand
bridge at 1.83, 6.54, and 7.76 ppm, respectively, suggests
an equilibrium between the tetrahedral species (the
most abundant) and a minor species in fast exchange
regime in proton time scale at room temperature.
Actually a new set of sharp resonances appeared in the
1H NMR spectrum of 3 at 193 K, attributed to the
octahedral form observed in the X-ray molecular struc-
ture. Indeed the methine resonance of the ligand bridge
is now at 6.84 ppm (vs 7.62 ppm in the tetrahedral form
t
at 193 K), the Bu groups of the phenolate yield two
singlets at 1.23 and 1.33 ppm, and the 3- and 5-pyrazolyl
methyls are detected at 2.43 and 2.05 ppm, respectively.
The octahedral and tetrahedral forms are in 7:3 molar
ratio at 193 K. Noteworthy the NMe2 protons still result
as one singlet at 2.96 ppm, independently of their
position in the octahedron. Although the kinetic con-
stant kd of the equilibrium reaction between the octa-
hedral and tetrahedral forms at 193 K is small and
yields sharp and well-resolved resonances for the two
species, the kinetics of the intramolecular ligand ex-
change is so fast (on the NMR time scale) to produce a
1
environment, as indicated by the presence of one H
signal for the methine of the bridgehead at 6.77 ppm.
Moreover the two pyrazolyl groups are not equivalent
and produce two signals for the H4 at 5.38 and 5.13 ppm,
respectively. The C1 stereoisomer did not convert to Cs
in 24 h, suggesting that the former is the thermody-
namically favored species. The molecular structure of
5 (Figure 3), determined by X-ray diffraction analysis,
confirmed that both pyrazolyl ligands are coordinated
to the metal in the solid state and the Ti-N3 bond
length assumes an intermediate value between that
observed in 2 and 3. A consistent trans effect of the
1
unique slightly broad H resonance for the equatorial
and axial amide groups.
Aiming to get a closer insight into the aforementioned
fluxional behavior of the heteroscorpionate titanium
complexes, particularly pronounced in the case of the
triamide derivative, we attempted the synthesis of
(20) (a) Benzing, E.; Kornicker, W. Chem. Ber. 1961, 94, 2263. (b)
Wade, S. R.; Willey, G. R. J. Chem. Soc., Dalton Trans. 1981, 1264.
(21) Diamond, G. M.; Jordan R. F.; Petersen, J. L. J. Am. Chem.
Soc. 1996, 118, 8024.

4920 Organometallics, Vol. 24, No. 21, 2005
Milione et al.
Scheme 3
amido ligand is well documented by the differences
between the Ti-N1 (trans to chloride) and Ti-N3 (trans
to the amido group) bond distances of 1.840(2) and
2.211(2) Å, respectively. Interestingly the Ti-N5 bond
length is the shortest value observed for the amido
groups in this class of heteroscopionate titanium com-
plexes, suggesting a strong dπ-pπ interaction of the lone
pair of the amido group with the d orbitals of the metal.
Finally, the chloro derivative 2 can be achieved by
treatment of 3 with 3 equiv of Me3SiCl at 353 K after 5
h in 1,1,2,2-tetrachloroethane-d2.
1 equiv of 1 at this temperature. Under this condition
the methyl complex 6 was isolated in higher yield (28%).
Twinned crystals not suitable for a single-crystal X-ray
diffraction analysis were grown from cold hexane.
However the solution structure of 6 was definitively
1
assessed by H NMR, 13C NMR, and gHMQC experi-
ments and found corresponding to the Cs symmetric
structure in which the heteroscorpionate ligand κ3-
N,N,O-coordinated to the metal. Actually one set of
resonances are observed for the two pyrazolyl rings, and
the methine signal of the ligand is observed at 7.04 ppm.
1
Alkyl derivatives of hydrido-tris(pyrazol-1-yl)borate
group 4 metal complexes are relatively rare,22 and their
presence in olefin polymerization processes is typically
postulated in the reaction of the chloride, alkoxy, or
amide derivatives with MAO. Aiming to explore the
olefin polymerization catalysis promoted by the afore-
mentioned titanium heteroscorpionates, we attempted
the synthesis of alkyl derivatives. In situ alkylation of
3 with trialkylaluminum compounds as AlMe3 or
Al-iBu3 were unsuccessful. The treatment of 2 with 3
equiv of methyllithium gave the expected methyl com-
plex (bpzmp)TiMe3 (6), as a crystalline yellow solid, in
very low yield (10%). A black-green material was
additionally obtained and attributed to side-products
resulting from reduction of the Ti(IV) precursor to Ti
The sharpness of the H signals suggests an elevated
coordination energy of the ligand to the metal center
and the absence of any fluxional equilibrium of the two
N,N donors at room temperature. A comparable thermal
stability of the solution structure was previously ob-
served for the heteroscorpionate trialkylzirconium com-
plex (bpzmp)Zr(CH2Ph)3.12 Noteworthy, the Ti-Me groups
produce two broad singlets at 1.78 and 1.55 ppm in 1:2
molar ratio, respectively, attributed to the methyl group
trans to the oxygen atom and to the nitrogen atoms,
respectively. EXSY experiments revealed a site-ex-
change reaction between the nonequivalent methyl
groups of the octahedral complex in the temperature
range 303-333 K (see below for more details).
Heating a 1,1,2,2-tetrachloroethane-d2 solution of 6
at 353 K produces in a few minutes the selective
formation of 2. The concomitant formation of methane
detected by the presence of a 1H resonance at 0.26 ppm
suggests a radical mechanism as a possible pathway for
this decomposition reaction.
1
species in lower oxidation state. Actually the H NMR
spectrum of the green mixture in benzene exhibited only
very broad featureless resonances. On the contrary the
one-pot synthesis of in situ preformed TiMe4(Et2O)2 with
1 via alkane elimination was successful. The methyl
complex was synthesized by metathesis of TiCl4 with
MeLi at 193 K in diethyl ether23 and in situ treated with
Compound 6 was not reactive with 1 or sterically
hindered phenols such as 2,6-di-tBu-4-Me-1-phenol (BHT).
The 1H NMR spectrum of a mixture of 6 with 1 equiv of
BHT or 1 remained unchanged also after 24 h at room
temperature. A similar behavior was previously ob-
served for the tribenzyl heteroscorpionate zirconium
complex and assumed as a result of the relative bulki-
(22) (a) Reger, D. L.; Tarquini, M. E.; Lebioda, L. Organometallics
1983, 2, 1763. (b) Ipaktischi, J.; Sulzbach, W. J. Organomet. Chem.
1992, 426, 59.
(23) (a) Kleihenz, S.; Seppelt, K. Chem. Eur. J. 1999, 5 (12), 3573.
(b) Berger, S.; Bock, W.; Frenking, G.; Jonas, V.; Muller, F. J. Am.
Chem. Soc. 1995, 117, 3820.

Titanium Complexes with a Heteroscorpionate Ligand
Organometallics, Vol. 24, No. 21, 2005 4921
Figure 3. ORTEP diagram of the molecular structure of
(bpzmp)Ti(NMe2)Cl2 (5). Thermal ellipsoids are drawn at
the 40% probability level.
ness of the ligand and complex.12 On the contrary,
Tp*TiCl3 was reactive with 1.5 equiv of 2-tBu-phenol
at room temperature in dichloromethane in the presence
of triethylamine, and the expected monophenoxo dichlo-
ro derivative was isolated from the reaction mixture.6
The generation of the cationic heteroscorpionate di-
methyl titanium complex was attempted by reacting
complex 6 with 1 equiv of [PhC3]+[B(C6F5)4]- in benzene.
The expected ionic species [(bpzmp)TiMe2]+[B(C6F5)4]-
(7) precipitated as a red oil in the NMR tube and was
analyzed after dissolution in chlorobenzene-d5. The 1H
NMR spectrum exhibits a 1H signal at 2.14 ppm for the
two equivalent Ti-Me groups, downfield shifted from the
neutral complex 6 (1.78 and 1.55 ppm), and a 1H signal
at 7.00 ppm for the methine of the ligand bridge.
Moreover, the presence of two equivalent pyrazolyl rings
suggests a Cs symmetric octahedral structure in which
the ligand is κ3-coordinated to the metal. The ionic
species is thermally unstable and decomposes in a few
minutes at room temperature. When 6 was treated with
1 equiv of THF and then reacted with [PhC3]+[B(C6F5)4]-
(B/Ti ) 1; C6D6; 25°C), the formation of the Lewis base
adduct [(bpzmp)TiMe2(THF)]+[B(C6F5)4]- (8) is straight-
forward and selective. The pattern of 1H resonances for
the ligand was similar to that of 7; the only difference
is the presence of a singlet at 1.85 ppm for the Ti-Me
and two broad singlets at 3.77 and 2.08 ppm for the
methylene protons of coordinated THF, found in a rapid
equilibrium with uncoordinated THF. The Lewis acid-
catalyzed ring-opening reaction of THF was not ob-
served at room temperature after overnight aging of the
solution at room temperature.
1
Figure 4. Experimental and simulated H NMR spectra
showing the resonances for the -NMe2 group of (bpzmp)-
Ti(NMe2)Cl2 (5) in TCDE.
according to eq 1:
Keq ) [T]/[O] ) IT/IO
(1)
in which [T] and [O] stand for the concentration of the
tetrahedral (T) and octahedral (O) species and IT and
IO for the intensities of the H4 of the pyrazolyl reso-
nances assumed as diagnostic of the tetrahedral and
octahedral forms, respectively. The thermodynamic
parameters, namely, the standard enthalpy (∆H°) and
entropy (∆S°) values of 4.0 ( 0.6 kcal‚mol-1 and 18.9 (
2.6 cal mol-1 K-1, were respectively determined. The
∆H° value is smaller than expected for the dissociation
reaction of the two neutral imino parts of the ligand and
likely accounts for the reorganization energy from the
octahedral to the tetrahedral coordination sphere. In the
latter the relief of interligand steric repulsion, docu-
mented by the high ∆S° value, stabilizes the species
with lower coordination number.
Replacement of Cl for NMe2 increased the coordina-
tion energy of the heteroscorpionate ligand as a result
of lower trans effect of the halide vs the amide. The
stereorigid octahedral environment is stable up to 373
K, where no fluxional behavior of the ligand was
detected by 1H NMR spectroscopy. Noteworthy, a higher
energetic barrier to rotation of the amide group about
the Ti-N bond was observed in 5, in agreement with
the shorter bond distance detected in the X-ray molec-
2. Dynamic NMR Behavior of the Solution Struc-
tures 3-6. The fluxional behavior of the hemilabile
heteroscorpionate ligand has been studied in the solu-
tion structures of 3-6 by VT 1H NMR spectroscopy. The
strong trans effect exerted by the amido groups in 3
produces partial dissociation of the ligand, and the
equilibrium between the tetrahedral and octahedral
forms of 3 in benzene-d6 or dichloromethane-d2 solution
was observed in the temperature range 193-303 K
(Scheme 2). The integral ratio of the 1H resonances
diagnostic of the two species permitted the equilibrium
constant Keq to be evaluated at different temperature
1
ular structure (Figure 4). Two broad H NMR signals
at 4.23 and 3.58 ppm have been detected for the two
nonequivalent methyls of -NMe2, whose coalescence
was observed at 323 K. No broadening of the bpzmp
signals was observed at this temperature, suggesting
that the rotation about the Ti-N bond does not involve

4922 Organometallics, Vol. 24, No. 21, 2005
Table 3. Ethylene and Propylene Polymerization Results
Milione et al.
entrya
precatalyst
temp (°C)
Al/Ti
monomer
time (min)
yield (g)
Mw × 103
1
2
3
4
(bpzmp)TiCl3/MAO
(bpzmp)TiCl3/MAO
(bpzmp)TiCl3/MAO
(bpzmp)TiCl3/MAO
(bpzmp)TiCl3/Al-Bu3/[Ph3C][B(C6F5)4]
(bpzmp)TiCl3/AliBu3/[Ph3C][B(C6F5)4]
(bpzmp)TiMe3/[Ph3C][B(C6F5)4]
(bpzmp)TiCl3/MAO
25
25
25
25
25
-40
25
25
100
300
500
500
20
E
E
E
E
E
E
E
P
P
15
15
15
60
30
30
60
60
60
0.50
0.98
1.04
1.43
0.93
0.54
0.35
2.69e
0.06f
796
1163
1116
1140
36
368
730
178
24
5
6b
7c
8d
9c
20
500
(bpzmp)TiMe3/[Ph3C][B(C6F5)4]
25
a Polymerization conditions: precatalyst ) 20 µmol ([Ti] ) 2.5 × 10-4 M); 80 mL of toluene; monomer pressure ) 6 atm; cocatalyst )
10 mmol of MAO (Al/Zr molar ratio ) 500); alternatively, 20 µmol of [Ph3C][B(C6F5)4] (B/Ti ) 1) and 400 µmol of Al-iBu3 (Al/Ti ) 20).b 40
mL of toluene ([Ti] ) 5.0 × 10-4 M); monomer pressure ) 1 atm. c Precatalyst ) 40 µmol ([Ti] ) 5.0 × 10-4 M); cocatalyst ) 40 µmol of
[Ph3C][B(C6F5)4] (B/Ti ) 1), 0.1 mL (0.4 mmol) of Al-iBu3 as scavenger. d Precatalyst ) 40 µmol ([Ti] ) 5.0 × 10-4 M); cocatalyst ) 20
mmol of MAO (Al/Zr molar ratio ) 500). e Microstructure: mm ) 0.46, mr ) 0.28, rr ) 0.26; 13% of region-errors. f Microstructure: mm
) 0.36, mr ) 0.33, rr ) 0.31; 9% of region-errors.
ligand dissociation. A rate constant of 98 s-1 was
evaluated for this isomerization at 293 K by comparison
of the experimental and simulated VT 1H NMR spectra
obtained with a full line shape calculation program.24
An activation free energy (∆Gq) of 12.7 ( 0.1 kcal‚mol-1
and the corresponding ∆Hq and ∆Sq of 13.6 ( 0.2 kcal
mol-1 and 3.1 ( 0.5 cal mol-1 K-1 were determined at
293 K. Noteworthy, previous theoretical studies carried
out on the group 4 hydrotris(pyrazol-1-yl)borate com-
plexes TpM(NMe2)3 (M ) Ti or Zr) showed that the
NMe2 rotation in the octahedral complex is almost
barrierless (1-2 kcal mol-1) because of the extreme
flatness of the potential-energy curve as a result of a
compromise between the electronic and steric factors.25
The methyl complex 6 was configurationally not
stable. The methyl 1H signals are broad at room
temperature in 1,1,2,2-tetrachloroethane-d2 solution
because of rapid exchange between the axial and
equatorial positions, and the coalescence of these two
signals was observed at 333 K. The VT 1H NMR analysis
was carried out in the slow exchange region because of
thermal decomposition of 6 at temperature higher than
333 K. ∆Hq and ∆Sq values of 22.3 ( 1.1 kcal‚mol-1 and
-19.6 ( 3.7 cal mol-1 K-1 were calculated, respectively,
and the rate constant of 3 s-1 with ∆Gq of 28.1 ( 0.1
kcal‚mol-1 was found at 293 K.
in the range 2.1-16 (depending on the condition) and
thus larger than 2, as expected for a single-site catalyst.
The broad PDIs are consistent with a variable concen-
tration of the active sites during the polymerization
time, probably as a result of the reaction or leaching of
the ligand promoted by the excess of MAO. Hydrido-
tris(pyrazol-1-yl)borate titanium complexes, for which
the olefin polymerization mechanism was studied in
great detail,6 exhibited similar PDI values and perfor-
mances in ethylene polymerization. The decrease of the
polymerization activity with time (entry 3: A ) 35 gPE
mmol-1 h-1 atm-1; entry 4: A ) 12 gPE mmol-1 h-1
atm-1) confirms the poor thermal stability of the active
species under polymerization conditions, in agreement
with the 1H NMR monitoring of the reaction of the
methyl complex 6 with [Ph3C][B(C6F5)4]. Second, the
octahedral and the tetrahedral forms of the catalyst,
resulting from the dissociation of the nitrogen donors
of the pyrazolyl groups, exhibit different propagation
and termination rate constants, also contributing to the
enlargement of the PDIs. The high molecular weight of
1
the polymers precluded H NMR analysis of the end
groups of the polymer chain; however the elevated
values of the molecular mass suggest for the terminat-
ing reaction a prevailingly chain transfer of the polymer
chain to the acidic aluminum center of the cocatalyst
or of the scavenger employed.
3. Olefin Polymerization Catalyzed by 2 and 6.
Preliminary ethylene polymerization experiments cata-
lyzed by 2 and 6 were carried out in toluene at room
temperature using MAO or [Ph3C][B(C6F5)4] as cocata-
lyst. The results are summarized in Table 3.
In situ alkylation of 2 with Al-iBu3 (Al/Ti molar ratio
of 20) followed by reaction with 1 equiv of [Ph3C]-
[B(C6F5)4] produced ethylene polymerization catalysts
with activity values comparable to that of the MAO-
based catalyst. The excess of trialkyl aluminum com-
pound produces an increase of the chain transfer rate,
and low molecular weight polyethylene was correspond-
ingly obtained. When the polymerization temperature
was lowered to -40 °C, a significant increase of the
molecular weight, of about 1 order of magnitude, was
observed, in agreement with a reduced chain transfer
rate to aluminum. The broad PDI (Mw/Mn ) 8.2)
confirms the decomposition of the catalyst also at very
low temperature.
A control polymerization experiment in the presence
of 6 activated with 1 equiv of [Ph3C][B(C6F5)4] was
carried out to assess the nature of the active species.
Polyethylene with the same molecular mass of run 1
was obtained but in lower yield. The broad PDI (Mw/
Mn ) 4.5) and low yield confirm the poor thermal
The chloride derivative 2 activated with MAO showed
good activity in ethylene polymerization and exhibits
activity values comparable to that of CpTiCl3 or Tp-
5
TiCl3 but lower than the heteroscorpionate complex
(bdmpza)TiCl3.13 The polymerization activity increases
as the Al/Ti molar ratio is increased from 100 to 300
and gives a plateau at higher ratios; the same trend was
observed for the average molecular mass Mw’s, which
reach the value of about 1 × 106 Da or higher at an Al/
Ti ratio of 500. All polyethylene samples are linear and
show a melting point of 135 °C. The molecular weight
distributions of the polymer samples from runs 1-6 are
broad and multimodal curves with PDI (Mw/Mn) values
(24) Reich, H. J. WinDNMr: Dynamic NMR Spectra for Windows.
J. Chem. Educ.: Software, Ser. D 1996, Vol. 3D, No. 2.
(25) Cai, H.; Lam, W. H.; Yu, X.; Liu, X.; Wu, Z. Chen, T.; Lin, Z.;
Chen, X.; You, X.; Xue, Z. Inorg. Chem. 2003, 42, 3008.

Titanium Complexes with a Heteroscorpionate Ligand
Organometallics, Vol. 24, No. 21, 2005 4923
stability of the active species in the presence of the
trialkylaluminum compounds.
with 1 equiv of [Ph3C][B(C6F5)4] in the presence of Al-
iBu3 as alkylating agent and/or scavenger. The 2-MAO
catalyst was more active and produces linear high
molecular weight polyolefins characterized by broad
PDIs. A similar trend was found for other non-Cp Ti
complexes, such as the hydrotrispyrazolyl borate tita-
nium complex by Jordan et al. and (bdmpza)TiCl3 by
Otero et al. The methyl complex 6 activated with the
trityl salt is moderately active in ethylene polymeriza-
tion and fairly active in propene polymerization: linear
polyethylene and atactic polypropylene were respec-
tively produced in the polymerization experiments. The
reaction of 6 with [Ph3C][B(C6F5)4] permitted the syn-
thesis of the ionic species 7, proposed as a model of the
active species in this class of olefin polymerization
catalysts.
Propylene polymerization runs catalyzed by 2 were
also carried out: the corresponding results are listed
in Table 3. The 2/MAO catalyst exhibited low but
significant activity in propene polymerization, and high
molecular weight polypropylene was thus produced: it
is worth noting that corresponding data for the hydrido-
tris(pyrazol-1-yl)borate titanium complex and (bdmpza)-
TiCl3 were not reported. The crude polymer was sub-
stantially stereoirregular in the 13C NMR analysis, in
agreement with the symmetry of the catalyst precursor
(mm ) 0.46, mr ) 0.28, rr ) 0.26; entry 8). However a
small fraction of crystalline stereoregular polymer was
isolated by exhaustive fractionating with hot heptane
(16 wt % of the raw polymer). This fraction stayed
isotactic during 13C NMR analysis (mm ) 58), and the
relative intensity of the stereoirregualr methyl pentads
(mmmr:mmrr:mrrm ) 2:2:1) showed that it is produced
via an enantiomorphic site polymerization mechanism.
Considering that traces of isotactic polypropylene by
enantiomorphic site mechanism are often produced via
Ziegler-Natta catalysis when group 4 metal complexes
carrying labile ligands are treated with excess MAO,
we propose that the stereoregular fraction arises from
side reactions of the titanium precursor with MAO.
Actually ZrCl4-MAO gave isotactic polypropylene with
the same 13C NMR fingerprint and comparable yield
under the same conditions.26 To confirm this hypothesis,
we carried out propene polymerization catalyzed by the
methyl complex 6 activated with [Ph3C][B(C6F5)4]. The
crude polymer was completely atactic with relative
intensities of the monomer triads of mm ) 0.36, mr )
0.33, and rr ) 0.31 (entry 9), as expected from the
symmetry of the catalyst precursor.
Experimental Section
3.1. General Information. All organic preparations were
carried out under aerobic conditions. Organometallic manipu-
lations were performed in dry nitrogen or argon atmospheres
using standard Schlenk line techniques and a glovebox.
Solvents were distilled from the appropriate drying agents
(sodium/benzophenone for hydrocarbon solvents, CaH2 for
ethyl ether and THF). The bpzmp-H ligand was synthesized
according to the literature procedure.14 TiCl4, Ti(NMe2)4, MeLi,
MeMgCl (Aldrich), [CPh3][B(C6F5)4] (Boulder SPA Company),
and B(C6F5)3 (Strem Chemicals) were used as received. Me3-
SiCl (Aldrich) was distilled from CaH2. Ethylene (S.O.N.,
polymerization grade) was dried by passing over activated 4
Å molecular sieves. Methylalumoxane (MAO) (Witco, 10 wt %
solution in toluene) was dried in a vacuum at 50 °C to remove
the uncoordinated AlMe3, washed with hexane, and used as
solid. Elemental analyses were performed with a Perkin-Elmer
240-C. 1H and 13C NMR spectra were recorded with a Bruker
Avance 300 and Bruker Avance 400 operating at 300 and 400
1
1
MHz for H, respectively. The H NMR chemical shifts were
referred to TMS as external standard using the residual protio
impurities of the deuterated solvents as reference.
Conclusion
A series of novel titanium complexes 2-6 of the
tridentate N,N,O heteroscorpionate ligand (3,5-tBu2-2-
phenoxo)bis(3,5-Me2-pyrazol-1-yl)methane have been
prepared and the corresponding solution structures
investigated by NMR spectroscopy. All complexes ex-
hibit in the solid state an octahedral geometry in which
the ligand is κ3-coordinated to the metal. A fluxional
coordinative behavior of the bpmpz ligand was moni-
tored with different ancillary ligands (-Cl, -NMe2,
-Me). The amide ligands in 3 exert a strong trans effect
toward pyrazolyl groups that are involved in a dissocia-
tive equilibrium producing the tetrahedral isomer of 3
as the major species at room temperature. The chloride-
amide mixed coordination sphere complexes 4 and 5 are
configurationally more stable, and the octahedral form
is the main species in benzene solution. The methyl
complex (bpzmp)TiMe3 was successfully obtained and
was thermally more stable than the corresponding alkyl
derivatives of mono-tris(pyrazolyl)borate or mono-cy-
clopentadienyl titanium complexes. A site exchange of
the nonequivalent methyl groups of the octahedral form
GPC analyses of the polymers were carried out with a PL-
GPC210 chromatograph equipped with 4 PL-Gel Mixed A
columns, RALLS light-scattering detector PD2040, H502 vis-
cometer (Viscotek) refractive detector, and DM400 data man-
ager (Viscotek). The GPC measurements were conducted at
140 °C, using 1,2,4-trichlorobenzene as solvent and narrow
MWD polystyrene standard samples for the molecular weight
calibration.
Differential scanning calorimetry (DSC) measurements were
carried out with a TA Instrument DSC 2920 at a heating rate
of 10 °C/min.
Synthesis of (bpzmp)TiCl3 (2). bpzmp-H (1) (2.72 g, 6.66
mmol) was deprotonated by treatment with NaH (0.159 g, 6.66
mmol) in toluene at room temperature. The toluene solution
of the sodium salt of 1 (140 mL, 6.66 mmol) was slowly added
to a solution of TiCl4 (6.66 mmol) in toluene (20 mL) at room
temperature, and the resulting red suspension was stirred
overnight at this temperature. The solvent was filtered off by
cannula, and the residue was washed with hexane (50 mL),
dried in vacuo, and then exhaustively extracted with dichlo-
romethane (100 mL). The red-brown dichloromethane solution
was concentrated at 50 mL and layered with hexane (1:1 v/v)
to yield 2.088 g of 2 as a bright red microcrystalline powder
(62%). Anal. Found: C, 53.23; H, 6.30; N, 9.92. Calc for C25H35-
Cl3N4OTi: C, 53.45; H, 6.28; N, 9.97. 1H NMR (400 MHz, CD2-
Cl2, 25 °C): δ 1.33 (s, 9H, 5-tBu-Ph), 1.57 (s, 9H, 3-tBu-Ph),
2.52 (s, 6H, 3-CH3-Pz), 2.73 (s, 6H, 5-CH3-Pz), 6.10 (s, 2H, Pz-
H), 7.17 (d, 1H, J ) 2.1 Hz, 6-H-Ar), 7.18 (s, 1H, -CH-), 7.47
(d, 1H, J ) 2.1 Hz, 4-H-Ar). Selected 13C{1H} NMR data: δ
1
was monitored by EXSY H NMR spectroscopy.
Complexes 2 and 6 are active olefin polymerization
catalysts after activation with excess MAO or treatment
(26) Proto, A.; Capacchione, C.; Motta, O.; De Carlo, F. Macromol-
ecules 2003, 36, 5942. Similar results were obtained with a TiCl4/MAO
catalytic system in our laboratory.

4924 Organometallics, Vol. 24, No. 21, 2005
Milione et al.
12.4, 17.2, 31.5, 35.2, 36.0, 71.1, 109.3, 124.4, 127.4, 128.2,
140.5, 141.0, 147.4, 154.1, 161.4.
left to slowly reach room temperature (overnight). All volatiles
were removed in vacuo, and the black-green residue was
extracted with hexane (80 mL). The pale yellow filtrate was
concentrated to 15 mL and cooled at -10 °C, affording a yellow
Synthesis of (bpzmp)Ti(NMe2)3 (3). A solution of bpzmp-H
(1) (0.500 g 1.22 mmol) in toluene (20 mL, 0,061 M) was slowly
added to a solution of Ti(NMe2)4 (2.88 mL, 1.22 mmol) in
toluene (30 mL, 0.0407 M) at room temperature. Evolution of
dimethylamine was soon observed. The resulting orange
solution was stirred overnight at room temperature. All
volatiles were then removed in vacuo, and the solid was
extracted with hexane (40 mL). The orange-red filtrate was
concentrated, and a bright red crystalline solid was isolated
after cooling of the hexane solution at -10 °C. Yield: 0.438 g
(61%). The crystalline sample spontaneously and slowly
releases the hexane molecules clathrated in the lattice. To
achieve good elemental analysis, the sample was evacuated
overnight at 50 °C and then analyzed. Anal. Found: C, 63.06;
H, 9.02; N, 16.73. Calc for C31H53N7OTi: C, 63.36; H, 9.09; N,
16.68. 1H NMR (400 MHz, CD2Cl2, 25 °C): δ 1.18 (s, 9H, 5-tBu-
Ph), 1.43 (s, 9H, 3-tBu-Ph), 1.83 (bs, 6H, 5-CH3-Pz), 2.12 (s,
6H, 3-CH3-Pz), 3.06 (bs, 18H, TiN-CH3), 5.82 (s, 2H, Pz-H),
6.54 (brs, 1H, 6-H-Ar), 7.30 (d, 1H, J ) 2.4 Hz, 4-H-Ar) 7.76
(brs, 1H, -CH-). Selected 13C{1H} NMR data (63 MHz, CD2-
Cl2, 25 °C): δ 10.9, 14.5, 29.9, 31.8, 34.6, 35.7, 45.2, 72.9, 107.4,
124.2, 124.7, 126.0, 138.7, 141.1, 147.8, 159.7.
Synthesis of (bpzmp)Ti(NMe2)2Cl (4) (reaction in a
NMR tube). Me3SiCl (3.15 µL, 25.5 µmol) dissolved in
benzene-d6 (0.3 mL) was added to a solution of (bpzmp)Ti-
(NMe2)3 (0.015 g, 25.5 µmol) in benzene-d6 (0.3 mL) in a NMR
tube. The color of the resulting solution changed from orange-
red to dark red in a few minutes. Spectroscopic data for
(bpzmp)Ti(NMe2)2Cl (4) in the Cs symmetric form: 1H NMR
(400 MHz, C6D6, 25 °C): δ 1.34 (s, 9H, 5-tBu-Ph), 1.57 (s, 9H,
3-tBu-Ph), 1.74 (s, 3H, 3-CH3-Pz), 2.47 (s, 3H, 5-CH3-Pz), 3.73
(s, 12H, TiN-CH3), 5.37 (s, 2H, Pz-H), 6.80 (s, 1H, -CH-), 7.02
(d, 1H, J ) 2.7 Hz, 6-H-Ar), 7.65 (d, 1H, J ) 2.7 Hz, 4-H-Ar).
Spectroscopic data for (bpzmp)Ti(NMe2)2Cl (4) in the C1
symmetric form: 1H NMR (400 MHz, C6D6, 25 °C): δ 1.28 (s,
9H, 5-tBu-Ph), 1.38 (s, 9H, 3-tBu-Ph), 1.68 (s, 3H, CH3-Pz), 1.82
(s, 3H, CH3-Pz), 1.89 (s, 3H, CH3-Pz), 2.50(s, 3H, CH3-Pz), 3.25
(bs, 6H, TiN-CH3), 3.67 (s, 6H, TiN-CH3), 5.23 (s, 1H, Pz-H),
5.46 (s, 1H, Pz-H), 6.75 (s, 1H, -CH-), 6.97 (d, 1H, J ) 2.7
Hz, 6-H-Ar), 7.63 (d, 1H, J ) 2.7 Hz, 4-H-Ar).
1
microcrystalline powder. Yield: 0.040 g (10%). H NMR (400
MHz, C2D2Cl2, 25 °C): δ 1.30 (s, 9H, 5-tBu-Ph), 1.52 (s, 9H,
3-tBu-Ph), 1.55 (s, 6H, Ti-eq-CH3), 1.78 (s, 3H, Ti-ax-CH3), 2.35
(s, 6H, 5-CH3-Pz), 2.47 (s, 6H, 3-CH3-Pz), 5.96 (s, 2H, Pz-H),
7.04 (s, 1H, -CH-), 7.08 (bs, 1H, 6-H-Ar), 7.40 (bs, 1H, 4-H-
Ar). Selected 13C{1H} NMR data (400 MHz, CD2Cl2, 25 °C): δ
12.2 (3-CH3-Pz), 15.0 (5-CH3-Pz), 30.2 (3-tBu-Ph), 31.6 (5-tBu-
Ph), 54.8 (Ti-ax-CH3), 68.4 (Ti-eq-CH3), 71.9 (-CHPz2-), 108.3
(4-C-Pz), 124 (6-C-Ar), 126.6 (4-C-Ar).
Method 2: One-Pot Synthesis. A solution of methyl-
lithium (4.88 mmol) in diethyl ether (3.5 mL 1.4 M) was added
to a solution of TiCl4 (0.13 mL, 1.22 mmol) in diethyl ether
(25 mL) at -80 °C, and the resulting yellow solution was left
under stirring at -80 °C in argon atmosphere for 7 h. A
precooled (-80 °C) solution of 1 (0.500 g 1.22 mmol) in diethyl
ether (25 mL, 0.049 M) was then added to the reaction mixture.
The resulting solution was slowly allowed to reach room
temperature (overnight). All volatiles were removed in vacuo,
and the black-green residue was extracted with hexane (80
mL). The pale yellow filtrate was concentrated to 20 mL and
cooled at -10 °C to give a yellow solid, which was isolated by
filtration and dried in vacuo. Yield: 0.170 g (28%).
Synthesis of [(bpzmp)TiMe2][B(C6F5)4] (7) (reaction in
a NMR tube). [Ph3C][B(C6F5)4] (0.010 g, 11.2 µmol) was
dissolved in benzene-d6 (0.5 mL) and added to a solution of
(bpzmp)TiMe3 (0.005 g, 11.2 µmol) in benzene-d6 (0.5 mL) in
a NMR tube at room temperature. After a few minutes a red
oil separated from the reaction mixture. The mother liquor
was filtered off and the red oil analyzed in chlorobenzene-d5
1
solution. H NMR (400 MHz, C6D5Cl, 25 °C): δ 1.54 (s, 9H,
5-tBu-Ph), 1.91 (s, 9H, 3-tBu-Ph), 2.14 (s, 6H, Ti-CH3), 2.25 (s,
6H, 3-CH3-Pz), 2.32 (s, 6H, 5-CH3-Pz), 5.60 (s, 2H, Pz-H), 7.00
(s, 1H, -CH-), 7.88 (d, 1H, J ) 1.7 Hz, 4-H-Ar).
Synthesis of [(bpzmp)TiMe2(THF)][B(C6F5)4] (8) (reac-
tion in a NMR tube). [Ph3C][B(C6F5)4] (0.010 g, 11.2 µmol)
was dissolved in benzene-d6 (0.5 mL) and added at room
temperature to a solution of (bpzmp)TiMe3 (0.005 g, 11.2 µmol)
in benzene-d6 (0.5 mL) containing tetrahydrofuran (0.9 µL,
11.5 µmol). After a few minutes a red oil separated from the
reaction mixture. The mother liquor was filtered off and the
Synthesis of (bpzmp)Ti(NMe2)Cl2 (5). A solution of Me3-
SiCl (0.22 mL, 1.204 mmol) in toluene (5 mL) was slowly added
to a solution of (bpzmp)Ti(NMe2)3 (0.380 g, 0.602 mmol) in
toluene (15 mL) and left under stirring at room temperature
for 5 h. During this time the color of the solution changed
slowly from orange to dark red. All volatiles were then removed
in vacuo, and the residue was washed with hexane (10 mL)
and extracted with toluene (30 mL). The red-brown toluene
solution was concentrated to 15 mL and layered with hexane
(20 mL). A bright red crystalline solid was isolated by
filtration. Yield: 0.180 g (52%). The crystalline sample spon-
taneously and slowly released the toluene molecules clathrated
in the lattice. To achieve good elemental analysis, the sample
was evacuated overnight at 70 °C and then analyzed. Anal.
Found: C, 56.70; H, 7.20; N, 12.34. Calc for C27H41Cl2N5OTi:
1
red oil analyzed in chlorobenzene-d5 solution. H NMR (400
MHz, C6D5Cl, 25 °C): δ 1.58 (s, 9H, 5-tBu-Ph), 1.85 (s, 6H,
Ti-CH3), 1.97 (s, 9H, 3-tBu-Ph), 2.08 (s, 6H, 3-CH3-Pz), 2.20
(s, 6H, 5-CH3-Pz), 3.77 (b, OCH2CH2-THF), 4.46 (b, OCH2CH2-
THF), 5.62 (s, 2H, Pz-H), 7.04 (s, 1H, -CH-), 7.90 (d, 1H, J )
2.2 Hz, 4-H-Ar). Selected 13C{1H} NMR data: δ 11.5 (3-CH3-
Pz), 25.7 (5-CH3-Pz), 30.5 (3-tBu-Ph), 31.5 (5-tBu-Ph), 70,8
(-CHPz2-), 78.9 (Ti-CH3), 109.3 (4-C-Pz), 128,4 (4-C-Ar).
Polymerization Procedure. The polymerization runs
employing MAO cocatalyst were carried out using the following
procedure. A 500 mL Bu¨chi glass reactor equipped with a
mechanical stirrer was charged with toluene (80 mL) contain-
ing the appropriate precatalyst and MAO. The evacuated
reactor was fed with ethylene at 6 atm, and the monomer
pressure was kept constant by feeding on demand. After the
specific reaction time, the polymerization was stopped by
venting the reactor and pouring the polymerization mixture
into ethanol acidified with aqueous HCl. The polymer was
recovered by filtration, washed with an excess of fresh ethanol,
and dried in a vacuum at 80 °C.
1
C, 56.85; H, 7.24; N, 12.28. H NMR (400 MHz, C6D6, 25 °C):
δ 1.32 (s, 9H, 5-tBu-Ph), 1.60 (s, 9H, 3-tBu-Ph), 1.62 (s, 3H,
CH3-Pz), 1.77 (s, 3H, CH3-Pz), 2.14 (s, 3H, CH3-Pz), 3.02 (s,
3H, CH3-Pz), 3.56 (bs, 6H, TiN-CH3), 4.21 (s, 6H, TiN-CH3),
5.13 (s, 1H, Pz-H), 5.38 (s, 1H, Pz-H), 6.77 (s, 1H, -CH-), 7.01
(d, 1H, J ) 2.0 Hz, 6-H-Ar), 7.58 (d, 1H, J ) 2.0 Hz, 4-H-Ar).
Selected 13C{1H} NMR data: 11.5, 11.6, 15.3, 16.6, 32.0, 34.7,
36.4, 71.8, 108.3, 108.9, 124.2, 126.0, 127.5, 128.9, 129.7, 138.7,
139.9, 140.2, 142.4, 152.8, 154.2 161.4.
The polymerization runs employing [Ph3C][B(C6F5)4] cocata-
lyst were carried out using the following procedure. A sealed
glass vial containing the appropriate amount of precatalyst
and [Ph3C][B(C6F5)4] was introduced into a 500 mL Bu¨chi glass
autoclave equipped with a mechanical stirrer. The autoclave
was evacuated and charged with a toluene (80 mL) and Al-
iBu3 (0.4 mL, 1.60 mmol) used as scavenger. After equilibration
Synthesis of (bpzmp)TiMe3 (6). Method 1: Metathesis
with MeLi. An 80 mL sample of a diethyl ether solution of
methyllithium (1.7 M, 2.57 mmol) was added to a slurry of
(bpzmp)TiCl3 (0.400 g, 0.79 mmol) in diethyl ether (1.7 mL)
at -80 °C. The mixture was stirred for 1 h at -80 °C and then

Titanium Complexes with a Heteroscorpionate Ligand
Organometallics, Vol. 24, No. 21, 2005 4925
of the solution with ethylene at 6 atm, the polymerization run
was started by breaking the vial with the mechanical stirrer.
The run was terminated by venting the reactor and pouring
the polymerization mixture into ethanol acidified with aqueous
HCl. The polymer was recovered by filtration, washed with
an excess of fresh ethanol, and dried in a vacuum at 80 °C.
Crystal Structure Determinations. The crystal data for
2, 3, and 5 were collected using a Nonius Kappa CCD
diffractometer using graphite-monochromated Mo KR radia-
tion. The data sets were integrated with the Denzo-SMN
package27 and corrected for Lorentz-polarization and absorp-
tion effects (SORTAV).28 The structures were solved by direct
methods (SIR97)29 and refined using full-matrix least-squares
with all non-hydrogen atoms anisotropic and hydrogens in-
cluded on calculated positions, riding on their carrier atoms.
The crystals of 3 contain molecules of hexane lying in centers
of symmetry, while those of 5 contain disordered molecules of
toluene. Furthermore, the Bu groups linked to C4 in 5 are
disordered, and the three methyl groups were refined over two
positions with occupancy of 0.5.
All calculations were performed using SHELXL-9730 and
PARST31 implemented in the WINGX32 system of programs.
The crystal data and refinement parameters are summarized
in Table 1.
t
Supporting Information Available: 1H NMR spectra of
1-8, 2D NMR experiments, determination of the thermody-
namic parameters for the equilibrium between the octahedral
and tetrahedral isomers of (bpzmp)Ti(NMe2)3 (3), determina-
tion of the kinetic parameters for the rotation of the amide
group about the Ti-N bond in (bpzmp)TiCl2(NMe2)3 (5) and
for the rotation of methyl groups in (bpzmp)TiMe3 (6); full
crystallographic data given in CIF format. This material is
available free of charge via the Internet at http://pubs.acs.org.
(27) Otwinowski, Z.; Minor, W. In Methods in Enzymology; Carter,
C. W., Sweet, R. M., Ed.; Academic Press: London, 1997; Vol. 276,
Part A, p 307.
(28) Blessing, R. H. Acta Crystallogr. Sect. A 1995, 51, 33.
(29) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G.; Polidori, G.; Spagna,
R. SIR97. J. Appl. Crystallogr. 1999, 32, 115.
(30) Sheldrick, G. M. SHELX-97, Program for Crystal Structure
Refinement; University of Gottingen: Germany, 1997.
(31) Nardelli, M. J. Appl. Crystallogr. 1995, 28, 659.
OM050063W
(32) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.