Synthesis and structural analysis of half-titanocenes containing η2-pyrazolato ligands, and their use in catalysis for ethylene polymerization

Article abstract of DOI:10.1021/ic9004246

Cp^*TiCI₂(L) [L = C₃H ₃N₂ (1), 3,5-Me₂C₃HN₂ (2) and 3,5-ⁱPr₂C₃HN₂ (3)], and Cp ^*Ti(C₃H₃N

Full text of DOI:10.1021/ic9004246

Inorg. Chem. 2009, 48,
DOI:10.1021/ic9004246
5011
Synthesis and Structural Analysis of Half-Titanocenes Containing η2-Pyrazolato
Ligands, and Their Use in Catalysis for Ethylene Polymerization
Irfan Saeed, Shohei Katao, and Kotohiro Nomura*
Graduate School of Materials Science, Nara Institute of Science and Technology (NAIST), 8916-5 Takayama,
Ikoma, Nara 630-0101, Japan
Received March 3, 2009
Cp*TiCl2(L) [L = C3H3N2 (1), 3,5-Me2C3HN2 (2) and 3,5-iPr2C3HN2 (3)], and Cp*Ti(C3H3N2)3 (4) were prepared in moderate
yields by treating Cp*TiCl3 with the pyrazoles in the presence of Et3N or with their corresponding lithium salts in Et2O. The
structures of 1 and 2 determined by X-ray crystallography indicate that these complexes fold a distorted tetrahedral geometry
around Ti, and the pyrazolato ligands coordinate to Ti with η2-N,N0-coordination mode. In contrast, one of the pyrazolato ligand
in 4 coordinates to Ti with η1-N-bonding, whereas the other two ligands were bound to Ti with η2-N,N0-fashion. The Cp
analogues, CpTiCl2(L) [L = C3H3N2 (5), 3,5-Me2C3HN2 (6), 3,5-iPr2C3HN2 (7), and 3,5-Ph2C3HN2 (8)], were also prepared by
the reaction of CpTiCl3 with the corresponding lithium salts in Et2O or n-hexane. The crystallographic analyses of 5 and 6
revealed that the pyrazolato ligands coordinate to Ti with η2-N,N0-coordination mode. These complexes (1-3, 5-8) exhibited
moderate catalytic activities for ethylene polymerization in the presence of methylaluminoxane (MAO), and the activities were
highly affected by the substituent on the pyrazolato ligand employed. Complex 1 exhibited the highest activity affording polymer
with uniform molecular weight distribution, suggesting that the polymerization proceeded with uniform catalytically active
species. An increase in the steric bulk in the pyrazolato ligand led to a slight decrease in the activity by the Cp* analogues,
whereas the activity by the Cp analogues increased upon increasing the steric bulk in the pyrazolato ligand employed.
Introduction
candidates for the new efficient catalysts.6-8 This is because
they exhibit unique characteristics for the synthesis of new
The design and synthesis of efficient transition metal
complex catalysts that precisely control olefin coordination
polymerization have attracted considerable attention.1-7
Nonbridged half-metallocenes of group 4 transition metals
of the type, Cp0M(L)X2 (Cp0 = cyclopentadienyl group;
M = Ti, Zr, Hf; L = anionic ligand such as OAr, NR2,
N = CR2, N = PR3, etc.; X = halogen, alkyl), as exempli-
fied in Chart 1, have emerged as one of the promising
(8) Selected examples (except introduced below), see (a) Shah, S. A. A.; Dorn, H.;
Voigt, A.; Roesky, H. W.; Parisini, E.; Schmidt, H. -G.; Noltemeyer, M. Organo-
metallics 1996, 15, 3176. (b) Richter, J.; Edelmann, F. T.; Noltemeyer, M.; Schmidt,
H. -G.; Schmulinson, M.; Eisen, M. S. J. Mol. Catal. A 1998, 130, 149. (c) Doherty,
S.; Errington, R. J.; Jarvis, A. P.; Collins, S.; Clegg, W.; Elsegood, M. R. J.
Organometallics 1998,17, 3408. (d) Sita, L. R.; Babcock, R. Organometallics 1998,17,
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5228. (e) Stephan, D. W.; Stewart, J. C.; Guerin, F.; Spence, R. E. v. H.; Xu, W.;
Harrison, D. G. Organometallics 1999, 18, 1116. (f ) Vollmerhaus, R.; Shao, P.;
~
Taylor, N. J.; Collins, S. Organometallics 1999, 18, 2731. (g) Antinolo, A.; Carrillo-
ꢀ
Hermosilla, F.; Corrochano, A.; Fernandez-Baeza, J.; Lara-Sanchez, A. R.; Ribeiro,
*To whom correspondence should be addressed. E-mail: nomurak@
M.; Lanfranchi, M.; Otero, A.; Pellinghelli, M. A.; Portela, M. F.; Santos, J. V.
Organometallics 2000, 19, 2837. (h) Jayaratne, K. C.; Sita, L. R. J. Am. Chem. Soc.
2000, 122, 958. Sinnema, P.-J.; Spaniol, T. P.; Okuda, J. J. Organomet. Chem. 2000,
598, 179.(i) Zhang, S.; Piers, W. E.; Gao, X.; Parvez, M. J. Am. Chem. Soc. 2000,122,
5499 (synthesis).( j) McMeeking, J.; Gao, X.; Spence, R. E. v. H.; Brown, S. J.;
Jerermic, D. USP 6114481 (2000). (k) Kretschmer, W. P.; Dijkhuis, C.; Meetsma, A.;
Hessen, B.; Teuben, J. H. Chem. Commun. 2002, 608. (l) Nomura, K.; Fujii, K.
Organometallics 2002, 21, 3042. (m) Huang, J.; Lian, B.; Qian, Y.; Zhou, W.; Chen,
W.; Zheng, G. Macromolecules 2002, 35, 4871. (n) Nomura, K.; Fujii, K. Macro-
molecules 2003, 36, 2633. (o) Ishino, H.; Takemoto, S.; Hirata, K.; Kanaizuka, Y.;
Hidai, M.; Nabika, M.; Seki, Y.; Miyatake, T.; Suzuki, N. Organometallics 2004, 23,
454. ( p) Mahanthappa, M. K.; Cole, A. P.; Waymouth, R. M. Organometallics 2004,
23,836.(q)Tamm,M.;Randoll,S.;Bannenberg,T.;Herdtweck,E.Chem. Commun.
2004, 876. (r) Nomura, K.; Fujita, K.; Fujiki, M. Catal. Commun. 2004, 5, 413. (s)
Nomura, K.; Fujita, K.; Fujiki, M. J. Mol. Catal. A 2004, 220, 133. (t) Dias, A. R.;
Duarte, M. T.; Fernandes, A. C.; Fernandes, S.; Marques, M. M.; Martins, A. M.; da
Silva, J. F.; Rodrigues, S. S. J. Organomet. Chem. 2004, 689, 203. (u) Yasumoto, T.;
Yamagata, T.; Mashima, K. Organometallics 2005, 24, 3375. (v) Martins, A. M.;
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©
2009 American Chemical Society
Published on Web 4/17/2009
pubs.acs.org/IC

5012 Inorg. Chem., Vol. 48, No. 11, 2009
Saeed et al.
Chart 1
Chart 2
both the cyclopentadienyl fragment (Cp0) and the anionic
ancillary donor ligands (L) employed.6
Pyrazolato ligands and their derivatives are capable
of exhibiting a variety of coordination modes such as η1,
μ-η1:η1, η2 and η5 (Chart 2), and many studies are known
about their coordination behaviors.20 The η2-N,N0-pyrazo-
lato coordination is predominant in the chemistry of early
transition metal complexes,21-23 as demonstrated by Erker
and Winter,21 and this feature brings forth the intriguing
possibility of employing pyrazolato ligands as ancillary
donor ligand for better stabilization. It is also known that
those complexes bear significant structural and chemical
resemblance to analogous cyclopentadienyl and β-diketonate
derivatives.21 Although synthesis of zirconocene complexes
containing pyrazolato ligands were known, detailed studies
for synthesis and structural analysis of a series of half-
titanocenes containing pyrazolato ligands have not so far
been reported. Moreover, investigation of their application
as the catalyst precursors for olefin polymerization has not
been explored, although unique stabilization as the anionic
ancillary donor ligand by η2 (or η5) coordination can be
highly expected, as described above.21 Therefore, in the
present contribution, we wish to introduce the synthesis
and structural analysis of half-titanocenes containing a series
of (substituted) pyrazolato ligands of the type, Cp0TiCl2(L)
[Cp0 = Cp* and Cp, L = C3H3N2, 3,5-Me2C3HN2,
3,5-iPr2C3HN2, 3,5-Ph2C3HN2, Chart 1], and their use as
catalyst precursors for ethylene polymerization.24
polymers6,9-20 that are not accessible by conventional
Ziegler-Natta catalysts, ordinary metallocene type,1 and
“constrained geometry” (linked Cp-amide) type catalysts.1,2
Moreover, their syntheses are generally simple involving one
or two steps, and the modification in the steric and/or
electronic environment of the ligand framework is more
facile especially than that in the linked half-metallocene type
complexes.6 We have demonstrated that half-titanocenes
containing an anionic ancillary donor ligand of the type,
Cp0TiCl2(L0) (L0 = O-2,6-iPr2C6H3, N=CtBu2), not only
exhibit notable catalytic activities for olefin polymerization8
but also display unique characteristics especially for copoly-
merization of ethylene with vinylcyclohexane,11 2-methyl-1-
pentene,12 styrene,13,14 and cyclic olefins such as norbor-
nene,15 cyclopentene,16 and cyclohexene.17 More recently, we
reported that these catalysts are also effective for introducing
functional groups into polyolefins in an efficient manner.18,19
It turned out that an efficient catalyst for the desired (co)
polymerization can be modified by simple replacement of
Results and Discussion
(9) (a) Nomura, K.; Naga, N.; Miki, M.; Yanagi, K.; Imai, A. Organo-
metallics 1998, 17, 2152. (b) Nomura, K.; Naga, N.; Miki, M.; Yanagi, K.
Macromolecules 1998, 31, 7588.
(10) (a) Nomura, K.; Oya, K.; Komatsu, T.; Imanishi, Y. Macromolecules
2000, 33, 3187. (b) Nomura, K.; Oya, K.; Imanishi, Y. J. Mol. Catal. A 2001,
174, 127.
(11) Nomura, K.; Itagaki, K. Macromolecules 2005, 38, 8121.
(12) (a) Nomura, K.; Itagaki, K.; Fujiki, M. Macromolecules 2005, 38,
2053. (b) Itagaki, K.; Fujiki, M.; Nomura, K. Macromolecules 2007, 40,
6489.
1. Synthesis and Structural Analysis of Cp*TiCl2(L)
[L = C3H3N2, 3,5-Me2C3HN2 and 3,5-iPr2C3HN2] and
Cp*Ti(C3H3N2)3. The general strategy for the synthesis of
Cp*TiCl2(L) [L = C3H3N2 (1), 3,5-Me2C3HN2 (2) and
3,5-iPr2C3HN2 (3)] is depicted in Scheme 1. Cp*TiCl2
[C3H3N2] (1) could be prepared in 52% yield by treatment
of Cp*TiCl3 with 1.1 equiv of Li(C3H3N2) (prepared in
(13) (a) Nomura, K.; Komatsu, T.; Imanishi, Y. Macromolecules 2000, 33,
8122. (b) Nomura, K.; Okumura, H.; Komatsu, T.; Naga, N. Macromole-
cules 2002, 35, 5388.
(14) (a) Zhang, H.; Nomura, K. J. Am. Chem. Soc. 2005, 127, 9364.
(b) Zhang, H.; Nomura, K. Macromolecules 2006, 39, 5266.
(15) (a) Nomura, K.; Tsubota, M.; Fujiki, M. Macromolecules 2003, 36,
3797. (b) Wang, W.; Tanaka, T.; Tsubota, M.; Fujiki, M.; Yamanaka, S.;
Nomura, K. Adv. Synth. Catal. 2005, 347, 433. (c) Nomura, K.; Wang, W.;
Fujiki, M.; Liu, J. Chem. Commun. 2006, 2659.
(16) Liu, J.; Nomura, K. Adv. Synth. Catal. 2007, 349, 2235.
(17) Wang, W.; Fujiki, M.; Nomura, K. J. Am. Chem. Soc. 2005, 127,
4582.
(18) (a) Nomura, K.; Liu, J.; Fujiki, M.; Takemoto, A. J. Am. Chem. Soc.
2007, 129, 14170. (b) Nomura, K.; Kitiyanan, B. Curr. Org. Synth. 2008
5, 217.
(19) (a) Liu, J.; Nomura, K. Macromolecules 2008, 41, 1070. (b) Nomura,
K.; Kakinuki, K.; Fujiki, M.; Itagaki, K. Macromolecules 2008, 41, 8974.
(20) For reviews, see (a) Halcrow, M. A. Dalton Trans. 2009, 2059. (b)
Sadimenko, A. P. Adv. Heterocycl. Chem. 2001, 80, 157. (c) Nief, F. Eur. J.
Inorg. Chem. 2001, 891. (d) Cosgriff, J. E.; Deacon, G. B. Angew. Chem.
1998, 110, 298. Angew. Chem., Int. Ed. 1998, 37, 286. (e) La Monica, G.;
Ardizzoia, G. A. Prog. Inorg. Chem. 1997, 46, 151. (f ) Sadimenko, A. P.;
Basson, S. S. Coord. Chem. Rev. 1996, 147, 247. (g) Trofimenko, S. Prog.
Inorg. Chem. 1986, 34, 115. (h) Trofimenko, S. Chem. Rev. 1972, 72, 497.
::
(21) For example (Ti, Zr), see (a) Rottger, D.; Erker, G.; Grehl, M.;
::
Frolich, R. Organometallics 1994, 13, 3897. (b) Guzei, I. A.; Baboul, A. G.;
Yap, G. P. A.; Rheingold, A. L.; Schlegel, H. B.; Winter, C. H. J. Am. Chem.
Soc. 1997, 119, 3387. (c) Guzei, I. A.; Winter, C. H. Inorg. Chem. 1997, 36,
4415. (d) Yelamos, C.; Heeg, M. J.; Winter, C. H. Inorg. Chem. 1999, 38,
1871. (e) Yelamos, C.; Heeg, M. J.; Winter, C. H. Organometallics 1999, 18,
:: ::
1168. (f ) Mosch-Zanetti, N. C.; Kratzer, R.; Lehmann, C.; Schneider, T. R.;
ꢀ
ꢀ
ꢀ
ꢀ
Uson, I. Eur. J. Inorg. Chem. 2000, 2, 13. (g) Yelamos, C.; Gust, K. R.;
Baboul, A. G.; Heeg, M. J.; Schlegel, H. B.; Winter, C. H. Inorg. Chem. 2001,
40, 6451.
(22) For example (V, Nb, Ta),21 see (a) Guzei, I. A.; Yap, G. P. A.; Winter,
C. H. Inorg. Chem. 1997, 36, 1738. (b) Gust, K. R.; Knox, J. E.; Heeg, M. J.;
Schlegel, H. B.; Winter, C. H. Eur. J. Inorg. Chem. 2002, 2327.
(23) For example (Cr, Mo, W), see (a) Gust, K. R.; Knox, J. E.; Heeg, M.
J.; Schlegel, H. B.; Winter, C. H. Angew. Chem., Int. Ed. 2002, 41, 1591.
::
::
(b) Most, K.; Kopke, S.; Dall’Antonia, F.; Mosch-Zanetti, N. C. Chem.
Commun. 2002, 1676. (c) Most, K.; Mosch-Zanetti, N. C.; Vidovi, D.; Jrg
Magull, J. Organometallics 2003, 22, 5485. (d) El-Kadri, O. M.; Heeg, M. J.;
Winter, C. H. Inorg. Chem. 2006, 45, 5278.
(24) Our previous report concerning synthesis, structural analysis for half-
titanocenes containing pyrrolide ligands, Saeed, I.; Katao, S.; Nomura, K.
Organometallics 2009, 28, 111.
::

Article
Inorg. Chem., Vol. 48, No. 11, 2009
5013
Scheme 1
Scheme 2
advance by treating pyrazole with nBuLi with in hexane,
and isolated as the white solid)25 and was isolated as deep
red microcrystals from the chilled CH2Cl2/n-hexane solu-
tion (-20 °C). The corresponding 3,5-dimethylpyrazola-
to and 3,5-diisopropylpryazolato complexes (2 and 3)
could be isolated by following the same procedure (yield
60% and 82%, respectively). The observed reactivity of
lithium pyrazolides toward Cp*TiCl3 lies in stark con-
trast to those of lithium pyrrolides,24 which afforded
bis- and tris-pyrrolide complexes along with the desired
monopyrrolide complex thus making the isolation of the
pure complex cumbersome. Moreover, the observed
trend is quite different from what has been reported in
the synthesis of Cp*TiCl2[N(Me)(cyclohexyl)]8 where
optimization of the reaction conditions (temperature,
equiv of lithium salts, etc.) was necessary probably
because of the gradual decomposition of the lithium salt
in the reaction solution. Complexes 1-3 could also be
synthesized by the reaction of Cp*TiCl3 with pyrazole
derivatives (LH) in the presence of Et3N (Scheme 1), and
this observation also lies in stark contrast to pyrrole
derivatives, which were not reactive toward Cp*TiCl3
under the same conditions.24 Attempts for preparations
of half-titanocenes containing 3,5-diphenylpyrazolato,
3-methylpyrazolato, and 4-bromopyrazolato ligands
were not successful by either method.
The attempted synthesis of bis-pyrazolato complex
Cp*TiCl(C3H3N2)2 by the reaction of Cp*TiCl3 with
2.2 equiv of Li(C3H3N2) was not successful, and the
monopyrazolato complex (1) was isolated instead. The
use of toluene as a solvent at higher temperatures led to
the formation of a mixture of products thus rendering the
isolation of pure complex difficult. In contrast, all the
three chlorine atoms in Cp*TiCl3 could be smoothly
replaced with pyrazolato ligand, when Cp*TiCl3 was
treated with 3.3 equiv of Li(C3H3N2) in Et2O at room
temperature, affording Cp*Ti(C3H3N2)3 (4) in 56% yield
(Scheme 2). Synthesis of 4 could also be accomplished by
the reaction of Cp*TiCl3 with pyrazole (3.3 equiv) in the
presence of excess Et3N in toluene at 50 °C. However, the
reaction of Cp*TiCl3 with lithium salts of 3-methylpyr-
azole, 3,5-dimethylpyrazole, and 3,5-diisopropylpyrazole
(>3.0 equiv) in either Et2O (at room temperature) or
toluene (50-80 °C) resulted in the formation of a mixture
of products, and attempted isolations of the desired
tris-pyrazolato complexes from the mixtures were not suc-
cessful even after repeated recrystallization procedures.
1
All the complexes (1-4) were identified based on H
and 13C NMR spectra and elemental analyses, and the
structures of 1, 2, and 4 were determined by X-ray
crystallography, as described below. Resonances ascribed
to protons in pyrazole were observed at 6.92 and 7.80 ppm
1
in the H NMR spectrum of 1, which were downfield
shifted with respect to those in free pyrazole (6.29 and
7.61 ppm) caused by the decrement of electron density on
the five-membered heterocyclic ring because of coordina-
tion. In a similar fashion, pyrazolato ring protons in 2 and
3 were observed at 6.43 and 6.50 ppm, respectively, which
are downfield shifted with respect to those in the corre-
sponding free ligands (5.81 and 5.85 ppm, respectively).
As mentioned above, pyrazolato ligands coordinate to
metals in a variety of fashions as depicted in Chart 2.
Although it is difficult to distinguish various coordination
modes of pyrazolato ligand to Ti solely by their NMR
spectra, the η5-bonding mode seems unlikely because the
ring protons were slightly downfield shifted (1: Δδ0.14 and
0.19, 2: Δδ 0.62, 3: Δδ 0.65) whereas the protons in a
η5-pyrazolato Ru complex [Cp*Ru(η5-3,5-dimethylpyra-
zolato) showed a large upfield shift (Δδ 1.42).26
The structures of 1 and 2 were determined by X-ray
crystallographic analysis (Figure 1), and the selected bond
lengths and the angles are summarized in Table 1.27 The
pyrazolato and 3,5-dimethylpyrazolato ligands are coordi-
nated in η2-N,N0 fashion with almost identical Ti-N bond
˚
lengths [2.031(2)-2.0474(13) A], which are comparable with
most of the reported Ti complexes bearing η2-N,N0-coordi-
nated pyrazolato ligands,21-21 but are slightly longer than
those in half-titanocenes containing pyrrolide ligands
˚
[1.969(4) and 1.965(2) A for Cp*TiCl2(2,4-Me2C4H2N)
and Cp*TiCl2(3-Et-2,4-Me2C4HN), respectively].24 More-
over, the Ti-N bond distances are significantly longer than
those in (1,3-Me2C5H3)TiCl2[N(2,6-Me2C6H3)(SiMe3)]
8
8
˚
˚
[1.898(2) A], Cp*TiCl2[N(Me)(cyclohexyl)] [1.870(3) A],
28
and in Cp*TiCl2(N=CPh2) [1.827 (2) A], and the dis-
˚
tance is close to the estimated value (2.02 A) for a tita-
˚
nium-nitrogen single bond according to Pauling’s covalent
radii.29 These results thus suggest that titanium forms
(26) Perera, J. R.; Heeg, M. J.; Schlegel, H. B.; Winter, C. H. J. Am. Chem.
Soc. 1999, 121, 4536.
(27) Detailed structural analysis results including structure rportes and
CIF files are shown in the Supporting Information.
(28) Nomura, K.; Yamada, J.; Wang, W.; Liu, J. J. Organomet. Chem.
2007, 692, 4675.
(29) Pauling, L. The Nature of the Chemical Bond, 3rd ed.; Cornell
University Press: Ithaca, NY, 1960.
(25) For example (preparation of the lithium salts of pyrazole), (a) Campora,
J.; Lopez, J. A.; Palma, P.; Ruiz, C.; Carmona, E. Organometallics 1997, 16,
2709. (b) Campora, J.; Lopez, J. A.; Maya, C. M.; Palma, P.; Carmona, E.;
Ruiz, C. Organometallics 2000, 19, 2707.

5014 Inorg. Chem., Vol. 48, No. 11, 2009
Saeed et al.
Figure 1. Oak Ridge Thermal Ellipsoid Program (ORTEP) drawings for Cp*TiCl2(C3H3N2) (1, left) and Cp*TiCl2(3,5-Me2C3HN2) (2, right). Thermal
ellipsoids are drawn at the 50% probability level and H atoms are omitted for clarity.27
[2.114(2) and 2.157(2) A].30 The pyrazolato ligand is planar
˚
˚
Table 1. Selected Bond Distances (A) and Angles (deg) for Cp*TiCl2(C3H3N2) (1)
and Cp*TiCl2(3,5-Me2C3HN2) (2)27
and close to a regular pentagon in both cases, for example,
all the bond distances within the heterocyclic ring are almost
identical in complex 1 [N(1)-C(11) 1.341(2), C(11)-C(12)
1.381(2), C(12)-C(13) 1.388(2), N(2)-C(13) 1.337(2),
N(1)-N(2) 1.3679(18)] and bond angles are close to 108°
(see Supporting Information). The coordination spheres
around the Ti possess an approximate tetrahedral geometry
in both complexes if the center of the nitrogen-nitrogen
bond in pyrazolato ligand is considered as a monodentate
ligand. As a result of η2-N,N0-coordination of pyrazolato
ligands, the Cl(1)-Ti-Cl(2) bond angles in 1, 2 were
constrained [1; 95.684(18)° and 2; 97.24(3)°], and these
showed unique contrast to those in the half-titanocenes
containing pyrrolide ligands in η1 coordination mode
(>100°).24
1
2
˚
Bond Distances (A)
Ti(1)-Cl(1)
Ti(1)-Cl(2)
Ti(1)-N(1)
Ti(1)-N(2)
Ti(1)-C(1)
Ti(1)-C(2)
Ti(1)-C(3)
N(1)-C(11)
C(11)-C(12)
C(12)-C(13)
N(2)-C(13)
N(1)-N(2)
Ti(1)-Cp
2.3088(4)
2.3028(5)
2.0429(14)
2.0474(13)
2.3579(16)
2.3697(16)
2.3620(17)
1.341(2)
1.381(2)
1.388(2)
1.337(2)
1.3679(18)
2.037
2.3047(13)
2.3027(13)
2.031(2)
2.0185(16)
2.376(2)
2.378(2)
2.347(3)
1.339(2)
1.392(5)
1.399(6)
1.337(2)
1.381(6)
2.029
˚
The Ti-Cl bond lengths [2.3027(13)-2.3088(4) A] are
Bond Angles (deg)
somewhat longer than those in the Cp*-pyrrolide
Cl(1)-Ti(1)-Cl(2)
Cl(1)-Ti(1)-N(1)
Cl(2)-Ti(1)-N(1)
Cl(1)-Ti(1)-N(2)
Cl(2)-Ti(1)-N(2)
N(1)-Ti(1)-N(2)
Cp-Ti(1)-Cl(1)
95.684(18)
91.46(4)
119.25(4)
125.34(4)
93.70(4)
97.24(3)
91.27(9)
complexes
[Cp*TiCl2(2,4-Me2C4H2N):
2.2458(19) A; Cp*TiCl2(3-Et-2,4-Me2C4HN): 2.2548(19),
2.2639(19),
˚
123.90(8)
122.05(9)
92.48(10)
39.87(16)
112.46(6)
114.05(6)
113.93(6)
114.15(6)
24
2.2578(11) A]. The observed slight differences in the
˚
Ti-Cl bond lengths (in between the pyrrolide and the
pyrazolato analogues) are probably the outcome of
better electron donation of the η2-N,N0-coordinated
pyrazolato ligands than the η1-coordinated pyrrolide
ligands. Moreover, the Ti-Cl bond lengths are compar-
39.07(5)
112.86(2)
113.16(2)
118.86(4)
112.20(4)
Cp-Ti(1)-Cl(2)
Cp-Ti(1)-N(1)
Cp-Ti(1)-N(2)
i
6
˚
able with those in Cp*TiCl2(2,6- Pr2C6H3) [2.305(2) A]
and Cp*TiCl2[N(Me)(cyclohexyl)] [2.302(1), 2.304(1)
˚
σ-bonds to both nitrogen atoms in the pyrazolato ligand as a
result of delocalization of negative charge over five-mem-
bered ring. On the basis of these results, these complexes
would be considered as 14e complexes (by 3e donation
with the pyrazolato ligand) rather than 16e complexes
(by 5e donation). The bonding behavior in the pyrazolato
ligand is somewhat similar to that in the amidinate ligands,
exemplified by Cp*Ti[η2-PhCH(Me)NCH(Me)NCH(Me)
Ph]Cl2 in which amidinate ligand exhibits η2-coordination
mode with both nitrogen atoms attached with Ti through
σ-bonds as indicated by almost equal Ti-N bond lengths
8
A], but are slightly longer than those in (1,3-Me2C5H38)
TiCl2[N(2,6-Me2C6H3)(SiMe3)] [2.2662(9), 2.2770(9) A],
and Cp*TiCl2(N = CPh2) [2.2844 (8) and 2.2735(10)
˚
28
˚
˚
A]. The N-N distances [1, 1.3679(18); 2, 1.381(6) A]
and the N(1)-Ti(1)-N(2) bite angles [1, 39.07(5)°; 2,
39.87(16)°] in the pyrazolato ligands are similar to those
in the η2-N,N0-pyrazolato complexes of several early
transition metals.21-23
(30) Koterwas, L. A.; Fettinger, J. C.; Sita, L. A. Organometallics 1999,
18, 4183.

Article
Inorg. Chem., Vol. 48, No. 11, 2009
5015
Scheme 3
CH2Cl2/n-hexane solution (-20 °C). It was found that the
by-production of undesired bis-pyrazolato complex
can be avoided if reaction of CpTiCl3 with the lithium
salt, Li(C3H3N2), is carried out in cold n-hexane. In case
of the other pyrazolato derivatives 6-8, reactions of the
corresponding lithium salts with CpTiCl3 in Et2O took
place cleanly without formation of any undesired bis- or
tris-pyrazolato complexes (Scheme 3). The desired com-
plexes (6-8) were thus isolated in moderate yields
(6, 53%; 7, 63%; and 8, 57%). Complexes 6-8 were also
accessible through the reaction of the corresponding
pyrazole derivatives with Et3N in Et2O. Several attempts
to prepare the Cp complexes containing 3-methylpyrazo-
lato and 4-bromopyrazolato complexes were not success-
ful, as observed in the Cp* complexes. The reaction of
CpTiCl3 with 2.2 and 3.3 equiv of Li(C3H3N2) resulted in
the formation of oily products, and the isolation of the
pure bis- and tris-pyrazolato complexes could not be
accomplished. Furthermore, attempted syntheses of
the tris-pyrazolato complexes with 3-methylpyrazolato,
3,5-dimethylpyrazolato, and 3,5-diisopropylpyrazolato
ligands were not successful either.
Figure 2. ORTEP drawings for Cp*Ti(C3H3N2)3 (4). Thermal ellipsoids
are drawn at the 50% probability level, and H atoms are omitted for
clarity.27
The structure of Cp*Ti(C3H3N2)3 (4) is shown in
Figure 2, and the selected bond distances and the angles
are summarized in Table 2.27 Two of the three pyrazolato
ligands coordinate to Ti with η2-N,N0-bonding modes and
the one binds to Ti through η1-N-coordination. The
geometry around Ti can be envisioned as a distorted
tetrahedral if the center of the nitrogen-nitrogen bond
in η2-N,N0-coordinated pyrazolato ligand is considered as
a monodentate ligand. The Ti-N bond distances in η2-N,
N0-coordinated pyrazolato ligand [2.0503(16)-2.0735(13)
1
Complexes 5-8 were identified based on H and 13C
˚
A] are slightly longer than those in complexes 1 and 2
˚
NMR spectra and elemental analyses, and the structures
of 5 and 6 were determined by X-ray crystallography, as
described below. As observed in the Cp* analogues (1, 2),
resonances ascribed to the ring protons in pyrazole were
downfield shifted (7.00 and 7.81 ppm) with respect to
those in free pyrazole (6.29 and 7.61 ppm). The protons
corresponding to pyrazolato ligands in Cp complexes
seemed more downfield shifted than those in their Cp*
counterparts [1, 6.93 and 7.80; 4, 7.00 and 7.81 ppm;
2, 6.43; 5, 6.55 ppm; 3, 6.50; 6, 6.60 ppm]. Despite the
fact that the magnitude of downfield shift in Cp com-
plexes is greater than those in Cp* analogues, η5-bonding
mode is ruled out on the grounds that Δδ lies in the range
0.23-0.75 ppm well below the value of 1.42 ppm observed
in a η5-pyrazolato Ru complex.26
[2.031(2)-2.0474(13) A]. In contrast, Ti-N bond length in
η1-N-coordinated pyrazolato ligand was significantly
2
0
˚
longer [2.1136(13)A] than those with the η -N,N -coordi-
nated pyrazolato ligands. On the basis of these crystal-
lographic results, the complex 4 should be considered as a
16 electron complex.
Although two different bonding modes (η2-N,N0 and
η1-N) of three pyrazolato ligands in 4 were observed in
the crystallographic analysis, only two types of ring
protons corresponding to these pyrazolato ligands were
observed as triplet (6.52 ppm) and doublet (7.81 ppm) in
CDCl3. The variable temperature 1H NMR spectra
were measured in toluene-d8 to investigate any possible
dynamic process taking place in 4, but the spectra did
not show any changes in the temperature range of
between -80 and 100 °C.
Figure 3 shows the structure for 5, 6 determined by
X-ray crystallographic analysis, and the selected bond
lengths and the angles are summarized in Table 3.27 The
analysis results indicate that the pyrazolato ligands
coordinate to Ti with η2-N,N0 mode. The Ti-N
2. Synthesis and Structural Analysis of CpTiCl2(L) [L
= C3H3N2, 3,5-Me2C3HN2, 3,5-iPr2C3HN2, and 3,5-
Ph2C3HN2]. Initial attempts for the synthesis of
CpTiCl2(C3H3N2) (5) by the reaction of CpTiCl3 with
1.1 equiv of Li(C3H3N2) in Et2O were not successful, and
the resulting product was a mixture consisting of bis-
pyrazolato complex (major) along with the desired mono-
pyrazolato complex. In contrast, the reaction of CpTiCl3
with pyrazole in the presence of Et3N resulted in the clean
formation of the desired complex (5) in 60% yield, which
was obtained as yellow microcrystals from the chilled
˚
bond lengths [2.007(3)-2.030(2) A] in 5, 6 are slightly
shorter than those in the Cp* counterpart [2.031(2)-
2.0474(13) A], and the facts indicate a better electron
˚
donation from Cp* consistent with the NMR data. As
observed in the Cp* complexes (1, 2), the Ti-N bond
lengths in 5 and 6 are longer than those in the
˚
Cp-pyrrolide complexes, CpTiCl2(C4H4N) [1.956(19) A]

5016 Inorg. Chem., Vol. 48, No. 11, 2009
Saeed et al.
Table 2. Selected Bond Distances (A) and Angles (deg) for Cp*Ti(C3H3N2)3 (4)27
˚
˚
Bond Distances (A)
Ti(1)-N(1)
Ti(1)-N(2)
Ti(1)-N(3)
Ti(1)-N(4)
Ti(1)-N(5)
Ti(1)-C(1)
Ti(1)-C(2)
Ti(1)-C(3)
2.0735(13)
2.0587(12)
2.0635(13)
2.0503(16)
2.1136(13)
2.3714(14)
2.3933(14)
2.3870(14)
Ti(1)-Cp*
2.049
C(15)-C(16)
N(4)-C(16)
N(3)-N(4)
N(5)-C(17)
C(17)-C(18)
C(18)-C(19)
N(6)-C(19)
N(5)-N(6)
1.379(2)
1.336(2)
1.353(19)
1.349(2)
1.377(2)
1.390(2)
1.335(2)
1.374(17)
N(1)-C(11)
C(11)-C(12)
C(12)-C(13)
N(2)-C(13)
N(1)-N(2)
1.344(2)
1.377(2)
1.387(2)
1.3369(19)
1.347(2)
1.334(2)
1.396(3)
N(3)-C(14)
C(14)-C(15)
Bond Angles (deg)
Cp*-Ti(1)-N(1)
Cp*-Ti(1)-N(2)
Cp*-Ti(1)-N(3)
Cp*-Ti(1)-N(4)
Cp*-Ti(1)-N(5)
N(2)-Ti-N(4)
N(2)-Ti-N(5)
N(3)-Ti-N(4)
120.12(4)
108.23(4)
109.34(4)
113.63(4)
110.32(4)
86.52(5)
N(1)-Ti-N(2)
N(1)-Ti-N(3)
N(1)-Ti-N(4)
N(1)-Ti-N(5)
N(2)-Ti-N(3)
N(3)-Ti-N(5)
N(4)-Ti-N(5)
38.03(5)
130.33(5)
110.52(6)
81.71(5)
122.31(6)
85.73(5)
117.06(5)
119.15(4)
38.39(5)
Scheme 4
˚
and CpTiCl2(2,4-Me2C4H2N) [1.968(13) A]. The pyrazo-
lato ligand in 5 is planar and close to a regular pentagon
as indicated by approximately identical bond distances
within the heterocyclic ring [N(1)-C(6) 1.341(3), C(6)-
C(7) 1.385(4), C(7)-C(8) 1.381(3), N(2)-C(8) 1.337(2),
N(1)-N(2) 1.363(2)], and the bond angles are close to
108° (see Supporting Information); similar trends were
seen in 6. The coordination sphere around the Ti
atom fold an approximate distorted tetrahedral in both
complexes. As a result of η2-N,N0-coordination of the
pyrazolato ligands, the Cl(1)-Ti-Cl(2) bond angles
in 5, 6 become constrained [5, 95.48(2)°, and 6, 96.63(5)°],
and these showed unique contrast to those in the
half-titanocenes containing pyrrolide ligands in η1-N-co-
ordination mode (>100°).24
˚
The Ti-Cl bond lengths [2.2760(16)-2.3134(9) A] are
Note that 1 showed remarkable catalytic activities for
the ethylene polymerization and the activities by
Cp*TiCl2(C3H3N2) (1, activity = 6300-9000 kg-PE/
longer than those in the Cp-pyrrolide complexes
˚
[CpTiCl2(C4H4N): 2.2587(7), 2.252(13) A; CpTiCl2
24
(2,4-Me2C4H2N): 2.244(4), 2.2561(4) A]. The slight
˚
mol-Ti h) were higher than those by Cp*TiX2(C4H4N)
3
(X = Cl, Me, activity = 5400-5970 kg-PE/mol-Ti h).24
difference in the Ti-Cl bond length is most probably an
outcome of better electron donation of η2-N,N0-coordi-
nated pyrazolato ligands as compared to η1-N-coordi-
nated pyrrolide ligands, although the Ti-N bond lengths
in the pyrazolato complexes are longer than those in the
pyrrolide complexes. The N-N distances [5, 1.363(2);
3
The resultant polymers under the optimized Al/Ti molar
ratios possessed unimodal molecular weight distributions
(although their Mn values were somewhat low compared
with those obtained by the reported Cp*-aryolox analo-
gues,6,9,10,12 Mn = 2.46-3.52 ꢀ 104, Mw/Mn = 2.17-
2.47, runs 2,4,5), and these observations are in unique
contrast to the facts that resultant polymers prepared by
the Cp*-pyrrolide analogue contained a small amount of
high molecular weight fraction.24 Since the by-produc-
tion of the high molecular weight shoulders by using the
Cp*-pyrrolide analogue-MAO catalysts was considered
to be due to dissociation of the pyrrolide ligand (pyrrolide
transfer from Ti to Al), the formation of unimodal
polymers in the present case clearly suggest that the
dissociation of the pyrazolato ligand did not take place
under these conditions, probably because of an improved
stability of the pyrazolato ligand in 1 with η2-N,N0
coordination mode rather than that of the pyrrolide
ligand (η1-N coordination).
˚
6, 1.396(4) A] and the N(1)-Ti(1)-N(2) angles [5, 39.07
(5)°; 6, 40.56(12)°] in the pyrazolato ligands are compar-
able with those in the Cp* derivatives (1, 2), and these are
in a generally observed range for η2-N,N0-pyrazolato
complexes of several early transition metals.21-23
3. Polymerization of Ethylene Cp0TiCl2(L) [Cp0 =
Cp*, Cp; L = C4H4N, 2,5-Me2C4H2N, 2,4-Me2C4H2N,
2,4-Me2-3-EtC4HN] - MAO Catalyst Systems. Ethylene
polymerizations using the Cp*TiCl2(C3H3N2) (1) were
conducted in toluene in the presence of methylaluminox-
ane (MAO) at 25 °C (Scheme 4), and the results are
summarized in Table 4. MAO white solid prepared by
removing AlMe3 and toluene from the commercially
available samples (PMAO-S, 6.8 wt % in toluene, Tosoh
Finechem Co.) was chosen because it was effective in the
preparation of high molecular weight ethylene/R-olefin
copolymers with unimodal molecular weight distribu-
tions when the Cp*TiCl2(O-2,6-iPr2C6H3) was used as
the catalyst precursor.9
Ethylene polymerization using a series of the Cp* and
Cp analogues containing different pyrazolato ligands
(2, 3, 5-8) were also conducted under the same condi-
tions, and the results are summarized in Table 4. It turned
out that 2, 3 and 5-8 also exhibited moderate catalytic

Article
Inorg. Chem., Vol. 48, No. 11, 2009
5017
Figure 3. ORTEP drawings for CpTiCl2(C3H3N2) (5, left) and CpTiCl2(3,5-Me2C3HN2) (6, right). Thermal ellipsoids are drawn at the 50% probability
level, and H atoms are omitted for clarity.27
˚
Table 3. Selected Bond Distances (A) and Angles (deg) for CpTiCl2(C3H3N2) (5)
and CpTiCl2(3,5-Me2C3HN2) (6)27
Table 4. Ethylene Polymerization by Cp0TiCl2(L) [Cp0 = Cp*; L = C3H3N2 (1),
3,5-Me2C3HN2 (2), 3,5-iPr2C3HN2 (3): Cp0 = Cp; L = C3H3N2 (5), 3,5-Me2
C3HN2 (6), 3,5-iPr2C3HN2 (7), 3,5-Ph2C3HN2 (8)] - MAO Catalyst Systemsa
5
6
c
catalyst
run Cp0; L
amount MAO polymer
Mn ꢀ Mw/
( μmol) (mmol) yield (mg) activityb 10-4 Mn
c
˚
Bond Distances (A)
Ti(1)-Cl(1)
Ti(1)-Cl(2)
Ti(1)-N(1)
Ti(1)-N(2)
Ti(1)-C(1)
Ti(1)-C(2)
Ti(1)-C(3)
N(1)-C(6)
C(6)-C(7)
C(7)-C(8)
N(2)-C(8)
N(1)-N(2)
Ti(1)-Cp
2.3018(7)
2.2904(7
2.023(2)
2.0159(19)
2.330(2)
2.322(4)
2.333(4)
1.341(3)
1.385(4)
1.381(3))
1.336(3)
1.363(2)
2.023
2.2760(16)
2.3146(10)
2.022(3)
2.007(3)
2.332(5)
2.331(7)
2.321(7)
1.336(4)
1.407(5)
1.373(4)
1.335(5)
1.396(4)
2.013
1
Cp*;
C3H3N2 (1)
0.2
3.0
241
7230
2
3
4
5
6
7
0.2
0.1
0.1
0.1
0.1
0.1
3.0
3.0
3.0
2.0
2.0
1.0
247
105
106
150
147
25
7410
6300
6360
9000
8820
1500
2.46
2.47
2.81
3.52
2.40
2.17
62.0
0.92
2.40
2.01
8
9
0.1
Cp*; 3,5- 0.1
Me2C3HN2
(2)
1.0
2.0
23
122
1380
7320
2.91
2.62
10
0.1
2.0
2.0
120
145
7200
8700
11 Cp*; 3,5-i 0.1
Pr2C3HN2
(3)
2.40
2.44
Bond Angles (deg)
Cl(1)-Ti(1)-Cl(2)
Cl(1)-Ti(1)-N(1)
Cl(2)-Ti(1)-N(1)
Cl(1)-Ti(1)-N(2)
Cl(2)-Ti(1)-N(2)
N(1)-Ti(1)-N(2)
Cp-Ti(1)-Cl(1)
Cp-Ti(1)-Cl(2)
Cp-Ti(1)-N(1)
Cp-Ti(1)-N(2)
95.48(2)
92.25(6)
121.03(6)
123.40(6)
91.65(6)
96.63(5)
93.93(11)
125.65(9)
120.86(11)
90.35(8)
40.56(12)
112.81(10)
112.27(8)
111.97(12)
118.19(14)
12
13 Cp;
0.1
0.1
2.0
2.0
141
7
8460
420
C3H3N2 (5)
14
15 Cp; 3,5-
0.1
0.1
2.0
2.0
9
10
540
600
130.6 2.31
124.4 2.29
39.07(5)
113.53(6)
113.87(6)
115.82(7)
114.20(8)
Me2C3HN2
(6)
16
17 Cp; 3,5-
iPr2C3HN2
(7)
0.1
0.1
2.0
2.0
13
14
780
840
97.4
3.07
activities for ethylene polymerization in the presence of
MAO, and the activities were affected by the substituent
on the pyrazolato ligands employed. The activities using
a series of the Cp* analogues increased in the order:
0.36
89.5
2.04
3.03
18
19 Cp; 3,5-
Ph2C3HN2
(8)
0.1
0.1
2.0
2.0
14
20
840
1200
L = C3H3N2 (1, 9000 kg-PE/mol-Ti h) > 3,5-iPr2-
3
C3HN2 (3, 8700) > 3,5-Me2-C3HN2 (2, 7320). Complex
1 exhibited the highest activity among the Cp* analogues,
and introduction of two methyl groups in the pyrazola
to ligand (in 2) led to a slight decrease in activity, whereas
the 3,5-diisopropyl analogue exhibited the similar cata-
lytic activity. The facts should thus be an interesting
contrast to the facts using the Cp*-pyrrolide analogues,
where an introduction of the alkyl substituents into the
20
0.1
2.0
19
1140
a Reaction Conditions: toluene total 30 mL, ethylene 6 atm, 10 min,
25 °C, 100 mL scale autoclave, d-MAO (prepared by removing AlMe3
and toluene from commercially available MAO). b Activity = kg-PE/
mol-Ti h. c GPC data in o-dichlorobenzene vs polystyrene standards.
3
pyrrolide ligand resulted in the significant decrease in the
activity.24 Moreover, the activity using a series of
CpTiCl2(L) increased in the order: L = 3,5-Ph2-C3HN2

5018 Inorg. Chem., Vol. 48, No. 11, 2009
Saeed et al.
Table 5. Crystal Data and Structure Refinement Parameters for Cp*TiCl2(C3H3N2) (1), Cp*TiCl2(3,5-Me2C3HN2) (2), Cp*Ti(C3H3N2)3 (4), CpTiCl2(C3H3N2) (5), and
CpTiCl2(3,5-Me2C3HN2) (6)27
1
2
4
5
6a
formula
fw
C13H18Cl2N2Ti
321.10
C15H22Cl2N2Ti
349.16
C19H24N6Ti
384.34
C8H8Cl2N2Ti
250.97
C40.50H48Cl9N8Ti4
1157.56
cryst color, habit
cryst size (mm)
cryst syst
red, block
0.40 ꢀ 0.40 ꢀ 0.35
monoclinic
P21/n (No. 14)
6.8153(3)
16.1063(6)
13.2599(5)
1454.87(10)
4
red, block
0.40 ꢀ 0.35 ꢀ 0.20
triclinic
P1 (No. 2)
7.6897(4)
15.4162(7)
15.6337(8)
834.34(7))
2
red, block
0.40 ꢀ 0.35 ꢀ 0.20
monoclinic
C2/c (No. 15)
18.0253(8)
13.2856(5)
16.7750(6)
3807.4(2)
8
yellow, block
0.25 ꢀ 0.20 ꢀ 0.18
orthorhombic
Pbca (No. 61)
7.2026(3)
12.0375(5)
23.2951(8)
2019.72(13)
8
orange, block
0.50 ꢀ 0.40 ꢀ 0.30
triclinic
P1 (No. 2)
9.0137(3)
10.2644(4)
15.0913(7)
1313.36(9)
1
space group
˚
a (A)
˚
b (A)
˚
c (A)
3
V (A )
˚
Z value
Dcalcd (g/cm3)
F000
no. of reflns meads.
no. of observations
no. of variables
R1
1.466 g/cm3
664.00
11789
1.390 g/cm3
364.00
6930
2831
203
0.0289
0.1108
1.001
1.341 g/cm3
1616.00
15269
1.651 g/cm3
1008.00
15074
1.463 g/cm3
588.00
11031
4373
303
0.0631
0.1377
1.001
2424
181
0.0244
0.0840
1.002
3115
259
0.0287
0.1010
1.016
1583
126
0.0293
0.0971
1.004
wR2
goodness of fit
a The crystal consisted of [CpTiCl2(3,5-Me2C3HN2)]4 1/2CH2Cl2. The details are shown in the Supporting Information.
3
(8, 1200 kg-PE/mol-Ti h) > 3,5-iPr2-C3HN2 (7, 840) >
accompanied in the polymerization using the Cp*-pyrrolide
analogue in the presence of MAO cocatalyst.24
3
3,5-Me2-C3HN2 (6, 780) > C3H3N2 (5, 540), suggesting
that the activity by the Cp analogues increased upon
increasing the steric bulk in the pyrazolato ligand. The
latter trend by the Cp analogues seems similar to that
in the Cp0-aryloxo analogues9 as well as Cp0-pyrrolide
analogues24and that in ordinary metallocenes,31 in which
an introduction of electron donating substituents would
stabilize the catalytically active species leading to the
higher activity.
We highly believe that the results presented here should
be promising not only from the viewpoint of basic under-
standing of the chemistry of half-titanocenes containing
pyrazolato ligands but also from the standpoint of designing
efficient transition metal catalysts for precise olefin polymer-
ization (e.g., improved stabilization of the catalytically active
species to avoid the ligand transfer from Ti to Al, etc.). We
are exploring a possibility for efficient preparation of new
polymers by ethylene copolymerization with strictly encum-
bered comonomers. We are also exploring syntheses of
a series of half-titanocenes containing both pyrazolato and
the other anionic ancillary donor ligands for better under-
standing concerning coordination modes and reactivity in
these complexes.
Concluding Remarks
In summary, we have established a systematic route for the
synthesis of various half-titanocenes containing pyrazolato
ligands of the types Cp0TiCl2(L) [Cp0 = Cp* and L =
C3H3N2 (1), 3,5-Me2C3HN2 (2) and 3,5-iPr2C3HN2 (3);
Cp0 = Cp and L = C3H3N2 (5), 3,5-Me2C3HN2 (6),
3,5-iPr2C3HN2 (7), and 3,5-Ph2C3HN2 (8)]. The structural
analysis results clearly indicate that these complexes are
14e Ti(IV) species, and the pyrazolato ligand coordinates to
Ti with η2-N,N0-fashion. The tris(pyrazolato) analogue,
Cp*Ti(C3H3N2)3, was also cleanly prepared by treating
Cp*TiCl3 with C3H3N2Li in Et2O, and the crystallographic
analysis result indicates that one of the pyrazolato ligand
coodinates to Ti with η1-N fashion and the other two
coordinate to Ti with η2-N,N0 fashion.
These complexes (1-3, 5-8) exhibited moderate/notable
catalytic activities for ethylene polymerization in the presence
of MAO, and the activities were affected by the substituent
on the pyrazolato ligand. Complex 1 exhibited the highest
activity, and the activity was higher than that by the
Cp*-pyrrolide analogue under the same conditions. The
resultant polymers possessed rather low molecular weights
with uniform molecular weight distributions, suggesting that
the polymerization proceeded with uniform catalytically
active species. The facts thus showed unique contrast to
those prepared by the Cp*-pyrrolide analogue, in which
certain degree of pyrrolide transfer (from Ti to Al) was
Experimental Section
General Procedures. All experiments were carried out under
a nitrogen atmosphere in a Vacuum Atmospheres drybox unless
otherwise specified. All chemicals used were of reagent grade
and were purified by the standard purification procedures.
Anhydrous grade tetrahydrofuran, diethyl ether, n-hexane,
dichloromethane, and toluene (Kanto Chemical Co., Inc.) were
transferred into bottles containing molecular sieves (mixture of
˚
˚
3 A 1/16 and 4 A 1/8, and 13X 1/16) under a nitrogen stream in
the drybox and were used without further purification. Reagent
grade pyrazole, 3,5-dimethylpyrazole, 3,5-diisopropylpyrazole,
3,5-diphenylpyrazole, CpTiCl3 and Cp*TiCl3 were purchased
from Wako Pure Chemical Ind., Ltd., and were used as received.
Ethylene for polymerization was of polymerization grade
(purity >99.9%, Sumitomo Seika Co., Ltd.) and was used as
received. Elemental analyses were performed by using a
PE2400II Series (Perkin-Elmer Co.). Some analysis runs were
employed twice to confirm the reproducibility in independent
analysis/synthesis runs.
All 1H and 13C NMR spectra were recorded on a JEOL
JNMLA400 spectrometer (399.65 MHz, 1H; 100.40 MHz, 13C).
All deuterated NMR solvents were stored over molecular sieves
under a nitrogen atmosphere, and all chemical shifts are given in
ppm and are referenced to residual solvent peaks.
Molecular weights and molecular weight distributions for
the polyethylene samples were measured by gel permeation
chromatography (Tosoh HLC-8121GPC/HT) using a RI-8022
(31) Influence of cyclopentadienyl fragment in ethylene polymerization by
substituted zirconocenes, Mohring, P. C.; Coville, N. J. J. Organomet. Chem.
1991, 479, 1.
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Article
Inorg. Chem., Vol. 48, No. 11, 2009
5019
detector (for high temperature, Tosoh Co.) with a polystyrene gel
column (TSK gel GMHHR-H HT ꢀ 2, 30 cm ꢀ 7.8 mm i.d.),
ranging from <102 to <2.8 ꢀ 108 MW) at 140 °C using
o-dichlorobenzene containing 0.05 wt/v% 2,6-di-tert-butyl-p-cre-
sol. The molecular weight was calculated by a standard procedure
based on the calibration with standard polystyrene samples.
Synthesis of Li(C3H3N2). Li(C3H3N2) was prepared ac-
cording to the following procedure.25 Into a n-hexane (50 mL)
solution containing pyrazole (2.04 g, 0.03 mol) precooled at
-20 °C (in the freezer), n-hexane solution containing n-BuLi
(18.9 mL of 1.58 mol/L solution, 0.03 mol) was added slowly in
small portions. Immediate formation of voluminous white
precipitates was observed. The reaction mixture was then
warmed slowly to room temperature and was stirred for 4 h.
The resultant precipitates were thus collected on a glass
filter and were adequately washed with n-hexane twice and
dried in vacuo. Yield 89%. 1H NMR (THF-d8): δ 6.19
(br, 1H, NCHCH), 7.65 (br, 2H, NCH). 13C NMR (THF-d8):
δ 101.52, 137.66.
Lithium salts of 3,5-dimethylpyrazole, 3,5-diisopropylpyra-
zole, and 3,5-diphenylpyrazole were prepared similarly.25
Synthesis of Cp*TiCl2(C3H3N2) (1). All the complexes
could be synthesized by following either of the two methods,
which have been described in detail for the synthesis of complex 1.
Method 1. Into an Et2O solution (10 mL) containing
Cp*TiCl3 (289 mg, 1.0 mmol) was added Li(C3H3N2) (81 mg,
1.1 mmol) at -20 °C. The reaction mixture was stirred for
16 h at 25 °C followed by addition of a small amount of
CH2Cl2 (0.5 mL) to quench the remaining lithium salt. The
reaction mixture was filtered through a Celite pad using a
glass filter. The filtercake was washed with Et2O, and the
combined filtrate and the washings were taken to dryness
under reduced pressure to give a solid red residue. The
residue was dissolved in a minimum amount of CH2Cl2 and
layered with hexane. The chilled solution (-20 °C) afforded red
microcrystals. Yield 167 mg (52%). δ 2.09 (15H, C5Me5), 6.93
(t, 1H, J = 1.5 Hz, N NCHCH), 7.81 (d, 2H, J = 1.5 Hz,
NCHCH). 13C NMR (CDCl3): δ 13.18, 119.29, 133.95, 134.20.
Anal. Calcd for C13H18Cl2N2Ti: C, 48.63; H, 5.65; N, 8.73%.
Found: C, 48.57; H, 5.83; N, 8.50%.
Cp*Ti(C3H3N2)3 (4). The synthetic procedure of 8 was the
same as that for 1 except that 3.3 equiv of lithium pyrazolato
(244 mg, 3.3 mmol) was used, and the desired complex was
purified by recrystallization from chilled ether solution. In
case of method 2, approximately 10 equiv of pyrazole and
Et3N were employed, and reaction was carried out in toluene
at 50 °C for 16 h. Yield 216 mg (method 1: 56%, method 2: 48%).
1H NMR (CDCl3): δ 1.75 (s, 15H, C5Me5), 6.52 (t, 1H, J =
1.5 Hz, NCHCH), 7.81 (d, 2H, J = 1.5 Hz, NCHCH). 13C NMR
(CDCl3): δ 11.57, 13.21, 111.31, 129.33, 134.71. Anal. Calcd for
C19H24N6Ti: C, 59.38; H, 6.29; N, 21.87%. Found: C, 59.04; H,
6.21; N, 21.51%.
CpTiCl2(C3H3N2) (5). The synthetic procedure of 4 was the
same as that for 1 except that CpTiCl3 (219 mg, 1.1 mmol) was
used in place of Cp*TiCl3, and the reaction was carried out in
hexane in case of method 1. Yield 150 mg (method 1: 60%,
method 2: 62%). 1H NMR (CDCl3): 1H NMR (CDCl3): δ 6.65
(s, 5H, C5H5), 7.00 (t, 1H, J = 1.5 Hz, NCHCH), 7.81 (d, 2H,
J = 1.5 Hz, NCH). 13C NMR (CDCl3): δ 120.21, 121.16, 136.29.
Anal. Calcd for C8H8Cl2N2Ti: C, 38.29; H, 3.21; N, 11.16%.
Found: 38.63; H, 3.12; N, 11.07%.
CpTiCl2(3,5-Me2C3HN2) (6). The synthetic procedure
of 5 was the same as that for 2 except that CpTiCl3 (219 mg,
1.1 mmol) was used in place of Cp*TiCl3, and the product was
purified by recrystallization from chilled ether solution. Yield
1
147 mg (method 1: 53%, method 2: 48%). H NMR (CDCl3):
δ 2.33 (s, 6H, Me), 6.49 (s, 1H, NCHCH), 6.62 (s, 5H, C5H5).
13C NMR (CDCl3): δ 12.34, 119.75, 120.37, 147.86. Anal. Calcd
for C10H12Cl2N2Ti: C, 43.05 or 38.74 (+TiC); H, 4.34; N,
10.04%. Found: 40.92; H, 4.08; N, 9.68%.
CpTiCl2(3,5-iPr2C3HN2) (7). The synthetic procedure of 6
was the same as that for 3 except that CpTiCl3 (219 mg, 1.1 mmol)
was used in place of Cp*TiCl3. Yield 208 mg (method 1: 63%,
method 2: 58%). 1H NMR (CDCl3): δ 1.31 (d, 12H, J = 6.96 Hz,
Me), 3.01 (sep, 2H, J = 6.96 Hz, CHMe2), 6.55 (s, 1H, NCHCH)
6.60 (s, 5H, C5H5). 13C NMR (CDCl3): δ 22.50, 27.37, 115.27,
120.34, 158.06. Anal. Calcd for C14H22Cl2N2Ti: C, 50.18; H, 6.02;
N, 8.36%. Found: 50.44; H, 6.22; N, 8.49%.
CpTiCl2(3,5-Ph2C3HN2) (8). The synthetic procedure of
6 was the same as that for 1 except that CpTiCl3 (219 mg,
1.1 mmol) was used in place of Cp*TiCl3 and lithum
3,5-diphenylpyrazolato was used instead of Li(C3H3N2). Yield
Method 2. A suspension of Cp*TiCl3 (289 mg, 1.0 mmol)
and Et2O (10 mL) was cooled in a refrigerator to -20 °C.
A mixture of pyrazole (75 mg, 1.1 mmol) and Et3N (110 mg,
1.1 mmol) was added to the above cooled mixture in small
portions. The reaction mixture was stirred for 16 h at room
temperature, the reaction mixture was then filtered through a
Celite pad using a glass filter. The solid residue was washed with
Et2O; the filtrate and the washings were combined and evapo-
rated to dryness. Recrystallization of the solid residue with
CH2Cl2 layered with n-hexane afforded red microcrystals of 1.
1
234 mg (57%). H NMR (CDCl3): δ 6.65 (s, 5H, C5H5), 7.03
(s, 1H, NCHCH), 7.37-7.52 (m, 6H, Ar) 7.92-7.94 (m, 4H, Ar).
13C NMR (CDCl3): δ 112.24, 121.04, 123.39, 125.93, 129.13,
130.14, 152.12. Anal. Calcd for C20H16Cl2N2Ti: C, 59.59; H,
4.00; N, 6.95%. Found: 59.87; H, 4.13; N, 6.81%.
Crystallographic Analysis. All measurements were
made on a Rigaku RAXIS-RAPID Imaging Plate diffract-
ometer with graphite monochromated Mo KR radiation.
The selected crystal collection parameters are listed below
(Table 5), and the detailed results were described in the
reports in the Supporting Information. All structures were
solved by direct method and expanded using Fourier
techniques,32 and the non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were included but not re-
fined. All calculations for complexes 1, 2, 4-6 were performed
using the Crystal Structure33,34 crystallographic software
package.
1
Yield 157 mg (49%). H and 13C NMR data was exactly the
same with the sample prepared by method 1.
Cp*TiCl2(3,5-Me2C3HN2) (2). The synthetic procedure
of 2 was the same as that for 1 except that lithium salt of
3,5-dimethylpyrazole (114 mg, 1.1 mmol) was used in place of
Li(C3H3N2). Yield 209 mg (method 1: 60%, method 2: 53%).
1H NMR (CDCl3): δ 2.10 (15H, C5Me5), 2.33 (6H, Me), 6.43
(s, 1H, NCHCH). 13C NMR (CDCl3): δ 12.35, 13.21, 119.05,
133.33, 145.20. Anal. Calcd for C15H22Cl2N2Ti: C, 51.60; H,
6.35; N, 8.02%. Found: C, 51.27; H, 6.19; N, 8.10%.
Cp*TiCl2(3,5-iPr2C3HN2) (3). The synthetic procedure of
3 was the same as that for 1 except that lithium 3,5-diispropyl-
pyrazolato (173 mg, 1.1 mmol) was used in place of Li(C3H3N2).
Yield 332 mg (method 1: 82%, method 2: 79%). 1H NMR
(CDCl3): δ 1.31 (d, 12H, J = 7.0 Hz, CHMe2), 2.11 (s, 15H,
C5Me5), 3.05 (sep, 2H, J = 7.0 Hz, CHMe2), 6.50 (s, 1H,
NCHCH). 13C NMR (CDCl3): δ 13.34, 22.71, 27.49, 113.59,
133.27, 156.05. Anal. Calcd for C19H30Cl2N2Ti: C, 56.31; H,
7.46; N, 6.91%. Found: C, 56.30; H, 7.24; N, 6.98%.
(32) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; de
Delder, R.; Israel, R.; Smits, J. M. M. DIRDIF94; The DIRDIF94 program
system, Technical report of the crystallography laboratory; University of
Nijmegen: The Netherlands, 1994.
(33) CrystalStructure 3.6.0, Crystal Structure Analysis Package; Rigaku
and Rigaku/MSC: The Woodlands, TX, 2000-2004.
(34) Watkin, D. J., Prout, C. K. Carruthers, J. R.; Betteridge, P. W.
CRYSTALS, Issue 10; Chemical Crystallography Laboratory: Oxford,
U.K., 1996.

5020 Inorg. Chem., Vol. 48, No. 11, 2009
Saeed et al.
Ethylene Polymerization Procedures. Ethylene polymer-
izations were conducted in toluene by using a 100 mL
scale autoclave. Solvent (29.0 mL) and MAO white solid
(174 mg, 3.0 mmol), prepared by removing toluene and
AlMe3 from commercially available MAO (PMAO-S,
Tosoh Finechem Co.), were charged into the autoclave in
the drybox, and the apparatus was placed under ethylene
atmosphere (1 atm). After the addition of a toluene solution
(1.0 mL) containing a prescribed amount of 1 via a syringe,
the reaction apparatus was pressurized to 5 atm (total 6 atm),
and the mixture was stirred magnetically for 10 min. After
the above procedure, ethylene was purged, and the
mixture was then poured into MeOH (150 mL) contain-
ing HCl (10 mL). The resultant polymer was collected on a
filter paper by filtration and was adequately washed with MeOH
and then dried in vacuo.
Acknowledgment. The present research is partly supported
by Grant-in-Aid for Scientific Research (B) from the Japan
Society for the Promotion of Science (JSPS, No.18350055),
and I.S. expresses his thanks to the JSPS for a postdoctoral
fellowship (No. 07061). The authors also thank Tosoh
Finechem Co. for donating MAO, and Sumitomo Chemicals
for GPC analysis of polyethylene.
Supporting Information Available: 1H-, 13C NMR spectra for
Cp*TiCl2(C3H3N2) (1), Cp*TiCl2(3,5-Me2C3HN2) (2), Cp*Ti
(C3H3N2)3 (4), and CpTiCl2(3,5-Me2C3HN2) (6). VT 1H NMR
spectra for 4. Crystal structure determinations, reports for 1, 2,
4-6, and the crystallographic data are also given as CIF files,
ORTEP drawing for [CpTiCl2(3,5-Me2C3HN2)]4 1/2CH2Cl2.
3
This material is available free of charge via the Internet at
http://pubs.acs.org.