Preparation, structure, and ethylene polymerization behavior of bis(imino)pyridyl chromium(III) complexes

Article abstract of DOI:10.1021/om020561u

The synthesis, characterization, and ethylene polymerization behavior of a family of chromium(III) complexes of formula [2,6-bis(imino)pyridyl]CrCl₃ is reported. The X-ray diffraction studies of two of the new compounds show that the geometry around the chromium atom is octahedral, with the three chlorine ligands in a mer disposition. The distance between the metal and one of the trans-disposed chlorine atoms is significantly longer than the other two Cr-Cl distances. Treatment of the complexes [2,6-bis(imino)pyridyl]CrCl₃ with methylaluminoxane (MAO) leads to very active ethylene polymerization catalysts that afford highly linear polyethylene. The substituents at the ortho position of the N-aryl groups of the 2,6-bis(imino)pyridyl ligands modulate both the catalytic activity and the molecular weights of the resulting polyethylene. The most active catalysts are those with two substituents at the ortho position of the N-aryl groups (activities up to 4 × 10⁷ g (mol of Cr)^-1 bar^-1 h^-1 are achieved). Regarding the size of the substituents, the activity and the molecular weights follow an opposite trend. Systems with two small substituents lead to very active systems, but the molecular weight of the polyethylene is lower than when bulkier substituents are present.

Full text of DOI:10.1021/om020561u

Organometallics 2003, 22, 395-406
395
P r ep a r a tion , Str u ctu r e, a n d Eth ylen e P olym er iza tion
Beh a vior of Bis(im in o)p yr id yl Ch r om iu m (III) Com p lexes
Miguel A. Esteruelas,*,† Ana M. Lo´pez,† Luis Me´ndez,‡ Montserrat Oliva´n,† and
Enrique On˜ate†
Departamento de Quı´mica Inorga´nica, Instituto de Ciencia de Materiales de Arago´n,
Universidad de Zaragoza-CSIC, 50009 Zaragoza, Spain, and Repsol-YPF, Centro de
Tecnologı´a, Carretera Extremadura N-V, Km 18, 28930 Mo´stoles, Madrid, Spain
Received J uly 15, 2002
The synthesis, characterization, and ethylene polymerization behavior of a family of
chromium(III) complexes of formula [2,6-bis(imino)pyridyl]CrCl3 is reported. The X-ray
diffraction studies of two of the new compounds show that the geometry around the chromium
atom is octahedral, with the three chlorine ligands in a mer disposition. The distance between
the metal and one of the trans-disposed chlorine atoms is significantly longer than the other
two Cr-Cl distances. Treatment of the complexes [2,6-bis(imino)pyridyl]CrCl3 with methyl-
aluminoxane (MAO) leads to very active ethylene polymerization catalysts that afford highly
linear polyethylene. The substituents at the ortho position of the N-aryl groups of the 2,6-
bis(imino)pyridyl ligands modulate both the catalytic activity and the molecular weights of
the resulting polyethylene. The most active catalysts are those with two substituents at the
ortho position of the N-aryl groups (activities up to 4 × 107 g (mol of Cr)-1 bar-1 h-1 are
achieved). Regarding the size of the substituents, the activity and the molecular weights
follow an opposite trend. Systems with two small substituents lead to very active systems,
but the molecular weight of the polyethylene is lower than when bulkier substituents are
present.
In tr od u ction
dienyl-amido,7 and a number of pentamethylcyclopenta-
dienyl chromium(III)8 catalysts have been reported. In
addition, non-cyclopentadienyl systems containing 1,1-bis-
(2-naphtholato),9 salicylaldiminato,10 â-diketiminato,11
The conventional Ziegler-Natta and Phillips catatysts
used in the industrial production of polyolefins are
heterogeneous systems. The active centers for the first
one are usually based on titanium, while the Phillips
catalysts employ chromium. The heterogeneous nature
of these systems is responsible for certain heterogene-
ities in the produced polymers, which might be not
desirable for some applications.1
Kaminsky and Sinn’s initial discovery that methyl-
aluminoxane (MAO) affords extremely active catalysts,
when combined with titanium and zirconium metal-
locenes,2 has led to an explosion of research into the use
of metallocene catalysts. Because the active centers of
those systems are group 4 metals, they are considered
the homogeneous version of the Ziegler-Natta catalysts.
Their homogeneous nature allows the production of
polymers with narrow molecular weight and comonomer
distributions, as well as a better understanding of the
factors determining the final properties of the polymers.3
Homogeneous models of the Phillips catalysts that
parallel the discoveries in group 4 metallocene/MAO
systems have been also developed.4 Thus, cyclopenta-
dienyl-amine,5 cyclopentadienyl-phosphine,6 cyclopenta-
(3) (a) Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.;
Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143. (b)
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P. W.; Børve, K. J . Organometallics 2000, 19, 403. (d) Enders, M.;
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Verlag: Berlin, 2001; p 127. (b) Do¨hring, A.; J ensen, V. R.; J olly, P.
W.; Thiel, W.; Weber, J . C. Organometallics 2001, 20, 2234.
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Theopold, K. H. J . Am. Chem. Soc. 1991, 113, 893. (b) Bhandari, G.;
Kim, Y.; McFarland, J . M.; Rheingold, A. L.; Theopold, K. H. Organo-
metallics 1995, 14, 738. (c) White, P. A.; Calabrese, J .; Theopold, K.
H. Organometallics 1996, 15, 5473.
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Chem. 2002, 648, 226.
† Universidad de Zaragoza.
‡ Repsol-YPF.
(1) (a) Pino, P.; Mu¨lhaupt, R. Angew. Chem., Int. Ed. Engl. 1980,
19, 857. (b) Hlatky, G. G. Chem. Rev. 2000, 100, 1347. (c) Fink, G.;
Steinmetz, B.; Zechlin, J .; Przybyla, C.; Tesche, B. Chem. Rev. 2000,
100, 1377.
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99. (b) Kaminsky, W.; Miri, M.; Sinn, H.; Woldt, R. Makromol. Chem.
Rapid Commun. 1983, 4, 417.
(10) (a) Gibson, V. C.; Newton, C.; Redshaw, C.; Solan, G. A.; White,
A. J . P.; Williams, D. J . J . Chem. Soc., Dalton Trans. 1999, 827. (b)
Gibson, V. C.; Mastroianni, S.; Newton, C.; Redshaw, C.; Solan, G. A.;
White, A. J . P.; Williams, D. J . J . Chem. Soc., Dalton Trans. 2000,
1969. (c) J ones, D. J .; Gibson, V. C.; Green, S. M.; Maddox, P. J . Chem.
Commun. 2002, 1038.
10.1021/om020561u CCC: $25.00 © 2003 American Chemical Society
Publication on Web 01/01/2003

396 Organometallics, Vol. 22, No. 3, 2003
Esteruelas et al.
Sch em e 1
imido,12 and triazacyclohexane13 ligands are also known.
The most active catalysts of those mentioned above are
those stabilized by cyclopentadienylamine groups,5b
which show activities of about 106 g (mol of Cr)-1 h-1
In the search for new polymerization catalysts with
technological application, we have prepared bis(imino)-
pyridyl chromium(III) complexes. In this paper, we
report the synthesis and full characterization of these
compounds, which, in the presence of methylaluminox-
ane and/or triisobutylaluminum, catalyze the polymer-
ization of ethylene with high and very high activities.
We also show the influence of the ligand architecture
and the reaction conditions on the polymerization activ-
ity and the polymer molecular weight.
bar-1
.
Significant recent developments have also occurred
with late-transition-metal systems,14 in particular, the
discovery of exceptionally active catalysts (between
3.7 × 106 and 2.1 × 107 g (mol of Fe)-1 h-1 bar-1) based
on iron and bis(imino)pyridyl ligands, reported inde-
pendently by the groups of Brookhart15 and Gibson.16
Following this discovery, a considerable amount of effort
has been dedicated to investigate the nature of the
active species17 and to design new catalysts based on
these types of ligands.18 However, the effort in this field
has not led to new polymerization catalysts with activi-
ties comparable to those of Brookhart and Gibson’s
complexes.
Resu lts a n d Discu ssion
1. Syn t h esis a n d Ch a r a ct er iza t ion of t h e New
Com p ou n d s. The symmetrical 2,6-bis(imino)pyridyl
ligands 1-4 (Scheme 1) have been prepared by the
catalytic condensation of 2.0 equiv of the corresponding
substituted aniline with 1.0 equiv of 2,6-diacetylpyridine
in refluxing ethanol and in the presence of acetic acid.
The same experimental procedure has been previously
used by Gibson and co-workers to obtain the related
ligands 5-8.16b The 2,6-bis(imino)pyridyl compounds
1-4 are isolated as yellow solids in moderate yield
(about 50%) after 48 h. Under the same experimental
conditions as those mentioned to obtain 5-8, ligands 9
and 10 are formed in very low yield (>5%) even after
long reaction periods (up to 5 days) and with molecular
sieves to trap the water formed in the reaction. How-
ever, we have observed that the use of toluene as
solvent, p-toluenesulfonic acid as catalyst, and a Dean-
Stark apparatus to remove the water formed in the
reaction leads to 9 and 10 in high yields (about 80%)
after a few hours.
(11) (a) Gibson, V. C.; Maddox, P. J .; Newton, C.; Redshaw, C.; Solan,
G. A.; White, A. J . P.; Williams, D. J . Chem. Commun. 1998, 1651. (b)
Kim, W.-K.; Fevola, M. J .; Liable-Sands, L. M.; Rheingold, A. L.;
Theopold, K. H. Organometallics 1998, 17, 4541. (c) Gibson, V. C.;
Newton, C.; Redshaw, C.; Solan, G. A.; White, A. J . P.; Williams, D. J .
Eur. J . Inorg. Chem. 2001, 1895. (d) McAdams, L. A.; Kim, W.-K.;
Liable-Sands, L. M.; Guzei, I. A.; Rheingold, A. L.; Theopold, K. H.
Organometallics 2002, 21, 952.
(12) (a) Coles, M. P.; Gibson, V. C. Polym. Bull. 1994, 33, 529. (b)
Coles, M. P.; Dalby, C. I.; Gibson, V. C.; Little, I. R.; Marshall, E. L.;
Ribeiro da Costa, M. H.; Mastroianni, S. J . Organomet. Chem. 1999,
591, 78.
(13) (a) Ko¨hn, R. D.; Haufe, M.; Mihan, S.; Lilge, D. Chem. Commun.
2000, 1927. (b) Ko¨hn, R. D.; Haufe, M.; Kociok-Ko¨hn, G.; Grimm, S.;
Wasserscheid, P.; Keim, W. Angew. Chem., Int. Ed. 2000, 39, 4337. (c)
Ko¨hn, R. D.; Seifert, G.; Kociok-Ko¨hn, G.; Mihan, S.; Lilge, D.; Mass,
H. In Organometallic Catalysts and Olefin Polymerization; Blom, R.,
Follestad, A., Rytter, E., Tilset, M., Ystenes, M., Eds.; Springer-
Verlag: Berlin, 2001; p 147.
The asymmetrical 2,6-bis(imino)pyridyl ligands 12-
14 (Scheme 2) have been synthesized by the selective
(14) Britovsek, G. J . P.; Gibson, V. C.; Wass, D. F. Angew. Chem.,
Int. Ed. 1999, 38, 429.
(15) (a) Small, B. L.; Brookhart, M.; Bennett, A. M. A. J . Am. Chem.
Soc. 1998, 120, 4049. (b) Small, B. L.; Brookhart, M. J . Am. Chem.
Soc. 1998, 120, 7143. (c) Bennett, A. M. A. CHEMTECH 1999, 29, 24.
(d) Small, B. L.; Brookhart, M. Macromolecules 1999, 32, 2120.
(16) (a) Britovsek, G. J . P.; Gibson, V. C.; Kimberley, B. S.; Maddox,
P. J .; McTavish, S. J .; Solan, G. A.; White, A. J . P.; Williams, D. J .
Chem. Commun. 1998, 849. (b) Britovsek, G. J . P.; Bruce, M.; Gibson,
V. C.; Kimberley, B. S.; Maddox, P. J .; Mastroianni, S.; McTavish, S.
J .; Redshaw, C.; Solan, G. A.; Stro¨mberg, S.; White, A. J . P.; Williams,
D. J . J . Am. Chem. Soc. 1999, 121, 8728. (c) Britovsek, G. J . P.;
Mastroianni, S.; Solan, G. A.; Baugh, S. P. D.; Redshaw, C.; Gibson,
V. C.; White, A. J . P.; Williams, D. J .; Elsegood, M. R. J . Chem. Eur.
J . 2000, 6, 2221. (d) Britovsek, G. J . P.; Gibson, V. C.; Kimberley, B.
S.; Mastroianni, S.; Redshaw, C.; Solan, G. A.; White, A. J . P.; Williams,
D. J . J . Chem. Soc., Dalton Trans. 2001, 1639. (e) Britovsek, G. J . P.;
Gibson, V. C.; Mastroianni, S.; Oakes, D. C. H.; Redshaw, C.; Solan,
G. A.; White, A. J . P.; Williams, D. J . Eur. J . Inorg. Chem. 2001, 431.
(17) (a) Griffiths, E. A. H.; Britovsek, G. J . P.; Gibson, V. C.; Gould,
I. R. Chem. Commun. 1999, 1333. (b) Dias, E. L.; Brookhart, M.; White,
P. S. Organometallics 2000, 19, 4995. (c) Gibson, V. C.; Humpries, M.
J .; Tellmann, K. P.; Wass, D. F.; White, A. J . P.; Willliams, D. J . Chem.
Commun. 2001, 2252.
(18) (a) C¸ etinkaya, B.; C¸ etinkaya, E.; Brookhart, M.; White, P. S.
J . Mol. Catal. A: Chem. 1999, 142, 101. (b) de Bruin, B.; Bill, E.; Bothe,
E.; Weyhermu¨ller, T.; Weighardt, K. Inorg. Chem. 2000, 39, 2936. (c)
Nu¨ckel, S.; Burger, P. Organometallics 2001, 20, 4345. (d) Dias, E. L.;
Brookhart, M.; White, P. S. J . Am. Chem. Soc. 2001, 123, 2442. (e)
Dias, E. L.; Brookhart, M.; White, P. S. Chem. Commun. 2001, 423.
(f) Small, B. L.; Marcucci, A. J . Organometallics 2001, 20, 5738. (g)
Kaul, F. A. R.; Puchta, G. T.; Schneider, H.; Bielert, F.; Mihalios, D.;
Herrmann, W. A. Organometallics 2002, 21, 74. (h) Abu-Surrah, A.
S.; Lappalainen, K.; Piironen, U.; Lehmus, P.; Repo, T.; Leskela¨, M.
J . Organomet. Chem. 2002, 648, 55.

Bis(imino)pyridyl Chromium(III) Complexes
Organometallics, Vol. 22, No. 3, 2003 397
F igu r e 1. Molecular diagram of the complex {2,6-bis[1-((2,6-diisopropylphenyl)imino)ethyl]pyridine}CrCl3 (22). Thermal
ellipsoids are shown at 50% probability.
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Com p lex 22
Sch em e 2
Cr-N(1)
Cr-N(2)
Cr-N(3)
N(1)-C(13)
2.142(3)
1.981(3)
2.142(3)
1.308(4)
Cr-Cl(1)
Cr-Cl(2)
Cr-Cl(3)
N(3)-C(20)
2.3415(9)
2.2821(9)
2.2856(9)
1.294(4)
N(1)-Cr-N(2)
N(2)-Cr-N(3)
N(1)-Cr-Cl(2)
N(2)-Cr-Cl(1)
N(2)-Cr-Cl(3)
N(3)-Cr-Cl(2)
Cl(1)-Cr-Cl(2)
Cl(2)-Cr-Cl(3)
77.55(10)
77.15(10)
101.00(7)
82.27(8)
89.49(8)
104.69(8)
93.40(3)
94.87(3)
N(1)-Cr-N(3)
N(1)-Cr-Cl(1)
N(1)-Cr-Cl(3)
N(2)-Cr-Cl(2)
N(3)-Cr-Cl(1)
N(3)-Cr-Cl(3)
Cl(1)-Cr-Cl(3)
153.97(10)
92.28(7)
87.23(7)
175.35(8)
90.31(7)
86.52(7)
171.65(4)
brown solid in 89% yield after 4 h. The addition of
aminopropyl silica gel to a dichloromethane solution of
16 gives rise to ligand 17, as a yellow solid in 51% yield.
Attempts to obtain 17 by direct condensation of 15 with
2,4,6-trimethylaniline were unsuccessful.
The chromium complexes 18-31 (Scheme 4) have
been prepared by reaction of CrCl3(THF)3 with the
stoichiometric amount of the corresponding 2,6-bis-
(imino)pyridyl ligand in acetone under reflux (com-
pounds 19, 21-25, 28, and 29) or in dichloromethane
at room temperature (compounds 18, 20, 26, 27, 30, and
31). They are isolated as green air-stable solids in high
yield (60-97%) and were characterized by elemental
analysis, FAB mass spectrometry, and IR. Complexes
22 and 31 were further characterized by X-ray crystal-
lography.
Crystals of 22 suitable for X-ray structural determi-
nation were grown from a dichloromethane solution
layered with pentane. The molecular structure is shown
in Figure 1, whereas selected bond lengths and angles
are listed in Table 1. The geometry around the chro-
mium atom could be described as a distorted octahedron
with the chlorine ligands in a mer disposition. The Cl-
Cr-Cl and N-Cr-N angles are 93.40(3), 171.65(40),
and 94.87(3)° and 77.55(10), 153.97(10), and 77.15(10)°,
respectively. The Cr-N(pyridyl) bond distance (Cr-N(2)
) 1.981(3) Å) is about 0.16 Å shorter than the Cr-
N(imino) bond distances (2.142(3) Å, Cr-N(1) and Cr-
and consecutive condensations of 1.0 equiv of 2,4,6-
trimethylaniline and 1.0 equiv of the corresponding
aniline with 1.0 equiv of 2,6-diacetylpyridine. Initially,
the treatment of 2,6-diacetylpyridine with 0.85 equiv
of 2,4,6-trimethylaniline, under the experimental condi-
tions used to prepare 9 and 10, leads to 11. This
intermediate, which is isolated as a yellow solid in 38%
yield after 45 min, subsequently reacts with 2,6-diiso-
propylaniline, 2-tert-butylaniline, and 2-(trifluoromethyl)-
aniline to afford 12-14, which are isolated as yellow
solids in 70-80% yield, after 12 h.
The 2,6-bis{1-[(2,4,6-trimethylphenyl)imino]benzyl}-
pyridine ligand (17) has been prepared by starting from
2,6-dicarbonylpyridine dichloride according to Scheme
3. Initially, this compound was transformed into 2,6-
dibenzoylpyridine (15) by a Friedel-Crafts acylation of
benzene with AlCl3 as catalyst. Treatment of 15 with
1.0 equiv of anhydrous nickel dichloride and 2.0 equiv
of 2,4,6-trimethylaniline in acetic acid under reflux
affords the nickel complex 16, which is isolated as a

398 Organometallics, Vol. 22, No. 3, 2003
Esteruelas et al.
Sch em e 3
Sch em e 4
N(3)), with the formal double-bond character of the
imino linkages N(1)-C(13) (1.308(4) Å) and N(3)-C(20)
(1.294(4) Å) having been retained. The planes of the
phenyl rings are oriented essentially orthogonal to the
coordination plane of the bis(imino)pyridine unit with
angles of 76.67(0.08) and 87.44(0.10)°. Interestingly, the
separations between the metal and the mutually trans-
disposed chlorine atoms are significantly different. The
Cr-Cl(2) bond length (2.2821(9) Å) is statistically
identical with the separation between the metal and the
chlorine atom disposed trans to the pyridinic nitrogen
atom (Cr-Cl(3) ) 2.2856(9) Å). However, it is about 0.06
Å shorter than the Cr-Cl(1) distance (2.3415(9) Å).
Crystals of 31 suitable for X-ray structural determi-
nation were grown from a dichloromethane solution
layered with diethyl ether. The molecular structure of
this complex is shown in Figure 2, whereas selected
bond lengths and angles are listed in Table 2. The
presence of phenyl substituents instead of methyl
groups at the CdN carbon atoms of the imino functional
groups, as well as the presence of methyl groups instead
of isopropyl groups in the N-Ph substituents, does not
appear to have any significant influence on the molec-
ular geometry. The most noticeable difference between
both structures is the length of the longest Cr-Cl bond
(Cr-Cl(1) ) 2.326(2) Å), which is shortened about 0.02
Å in 31 with regard to 22.
2. Eth ylen e P olym er iza tion . The chromium(III)
complexes 18-31 were tested for ethylene polymeriza-
tion under diverse sets of conditions, as shown in Table

Bis(imino)pyridyl Chromium(III) Complexes
Organometallics, Vol. 22, No. 3, 2003 399
F igu r e 2. Molecular diagram of the complex {2,6-bis[1-((2,4,6-trimethylphenyl)imino)benzyl]pyridine}CrCl3 (31). Thermal
ellipsoids are shown at 50% probability.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Com p lex 31
hexyl groups with no substituents in the 2- and 6-posi-
tions attached to the nitrogen atom of the imines, has
a low activity (8.30 × 103 g of PE (mol of Cr)-1 bar-1
h-1, entry 1), those with aromatic groups (19-31)
substituted at least in one of their ortho positions show
much higher activities (ranging from 1.25 × 105 to 4.14
× 107 g of PE (mol of Cr)-1 bar-1 h-1, entries 2-26).
The highest activities achieved in the tested set of
compounds are obtained for those which bear ligands
derived from 2,4,6-trimethylaniline (24 and 28-31,
entries 12-16 and 20-26). It seems that the methyl
group in the para position has a beneficial influence on
the activity (compare entries 11 and 14). On the other
hand, an increase of the bulkiness of the groups in the
ortho positions of the anilines renders a less active
catalyst (compare entries 6, 8, and 11).
Cr-N(1)
Cr-N(2)
Cr-N(3)
N(1)-C(10)
2.113(3)
1.987(3)
2.108(3)
1.308(7)
Cr-Cl(1)
Cr-Cl(2)
Cr-Cl(3)
N(3)-C(22)
2.326(2)
2.283(2)
2.296(2)
1.292(8)
N(1)-Cr-N(2)
N(2)-Cr-N(3)
N(1)-Cr-Cl(2)
N(2)-Cr-Cl(1)
N(2)-Cr-Cl(3)
N(3)-Cr-Cl(2)
Cl(1)-Cr-Cl(2)
Cl(2)-Cr-Cl(3)
77.89(8)
77.71(10)
103.06(9)
82.77(9)
90.14(9)
101.48(9)
94.78(8)
92.29(8)
N(1)-Cr-N(3)
N(1)-Cr-Cl(1)
N(1)-Cr-Cl(3)
N(2)-Cr-Cl(2)
N(3)-Cr-Cl(1)
N(3)-Cr-Cl(3)
Cl(1)-Cr-Cl(3)
155.31(13)
91.10(9)
88.60(10)
177.41(11)
89.54(10)
87.75(9)
172.81(9)
3. In all experiments the chromium complexes were
previously dissolved and preactivated in a methylalu-
minoxane/toluene solution. This treatment acts in two
ways: first, it helps to solubilize the poorly soluble
complexes and, second, it preforms the actual catalytic
species. We have observed that, by doing so, activities
are enhanced and there is not an induction polymeri-
zation period. These complex/MAO/toluene solutions
remain stable for weeks if kept under an inert atmo-
sphere, although it has been observed that in order to
reach a high and constant value of activity the solutions
must be employed after a period of ca. 30-60 min from
their preparation. During this period the complex dis-
solves and the color of the solution changes from the
original green to that of brown tea. This suggests that
the formation of the actual catalytic species needs a
period of several minutes to be formed at room temper-
ature. To check if a Cr(II) species could be formed during
this preactivation period, a similar experiment was
performed using [2,6-bis{1-[2,6-(diisopropylphenyl)-
imino]ethyl}pyridine]CrCl2 (32), the Cr(II) analogue of
complex 24. This catalyst has also shown the need for
a preactivation time (even longer than the time needed
for 24) with MAO in order to achieve high and stable
catalytic activities, suggesting that activation of Cr(III)
does not occur by reduction to Cr(II). Under exactly the
same conditions (including the same preactivation time,
60 min), 32 is ca. half as active as 24 (entries 16 and 27).
The substituents of the ligands influence the catalytic
behavior of complexes 18-31, with regard to both
activity and the molecular weight of the resulting
polyethylene. Thus, while complex 18, which has cyclo-
The electronic nature of the aromatic substituents has
also a marked influence on the activity. Thus, substitu-
tion of one methyl (complex 23) by a methoxy group
(complex 26) in the ortho position leads to a nonactive
species (compare entries 11 and 18). However, the
replacement of a tert-butyl group (complex 25) by a
trifluoromethyl group at the ortho position (complex 20)
does not seem to affect the catalytic activity (entries 5
and 17).
Changing the substituent on the imine functional
group from a methyl to a phenyl has little or no effect
on the activity. Thus, complexes 24 (methyl) and 31
(phenyl) render polyethylene with similar productivity.
The molecular weight (Mw) of the polyethylene ob-
tained with catalyst 25 is 257 500. All the other cata-
lysts give polyethylene whose molecular weights (Mw)
are between 1630 and 35 900.19 In most cases, after the
reaction is quenched with methanol/HCl, part of the
polymer remains dissolved in the heptane used for the
assays, and after filtration of the solid fraction and
separation of the phases, a waxy fraction is recovered
from the heptane layer by evaporation under vacuum.
In Table 3 the percentage of waxes obtained in most
cases is given. The amount of wax produced is depend-
(19) Usually, a molecular weight distribution smaller than 2 is an
indication of the occurrence of some living polymerization processes
(ideally Mw/Mn ) 1). However, the fact that we have not observed any
dependence of Mw on the polymerization time rules out this possibility.

400 Organometallics, Vol. 22, No. 3, 2003
Ta ble 3. Resu lts of th e Eth ylen e P olym er iza tion Assa ysa
Esteruelas et al.
amt of Cr AlMAO/Cr
Al/Cr
t
total wt of waxes
c
entry complex
(µmol)
(pref sol) coactivator coactivator (min) polymer (g)
(%)
activityb
Mw
Mn
Mw/Mn
1
2
3
4
5
6
7
8
18
19
19
19
20
21
21
22
22
22
23
24
24
24
24
24
25
26
27
28
29
29
30
30
31
31
32
32
3.9
1.0
4.6
4.6
5.2
2.3
2.3
7.5
14.1
7.5
1.9
1.9
1.0
0.9
0.9
0.5
3.8
10.3
8.4
3.3
5.8
5.8
2.2
0.5
0.6
0.6
0.5
4.8
110
450
190
190
200
190
190
50
MAO
MAO
TIBA
MAO
TIBA
MAO
TIBA
MAO
TIBA
TIBAO
MAO
MAO
MAO
MAO
TIBA
TIBA
MAO
MAO
TIBAO
TIBAO
TIBA
TIBAO
MAO
TIBAO
MAO
TIBAO
TIBA
MAO
550
780
810
800
800
820
830
400
400
400
680
700
1080
1110
1050
810
170
650
235
830
860
850
520
960
1840
840
805
1120
60
30
30
30
10
30
30
30
30
30
30
0.13
1.76
34.69
15.13
1.56
14.82
34.98
12.9
28.6
13.6
45.9
17.7
5.85
46.6
29.0
11.4
1.89
traces
traces
14.85
13.4
11.8
40.5
12.2
27.9
11.6
5.02
81.5
d
24
10
15
33
7.1
4.4
0.9
1.2
0
15
d
d
d
d
8.30 × 103
9.18 × 105
3.80 × 106
1.66 × 106
4.53 × 105
3.23 × 106
7.66 × 106
8.57 × 105
1.02 × 106
9.06 × 105
1.21 × 107
4.14 × 107
9.20 × 106
2.51 × 107
1.52 × 107
1.24 × 107
d
d
d
d
d
d
1.50
1.86
d
d
2.17
d
1.58
1.31
1.54
1.31
1.48
1.29
1.48
d
2170
2690
d
1450
1450
d
d
d
5390
d
12900
2480
d
8150
9
400
25
10
11
12
13e
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
35900 27400
140
140
140
140
140
400
120
200
60
2130
2100
2660
1980
1630
d
1380
1600
1800
1540
1100
d
3.5
10
30
30
30
60
30
30
30
30
30
60
30
30
30
30
15
22
d
1.25 × 105 257500
4180 61.6
50
3.2
34
41
36
36
21
34
30
13
2.22 × 106
1.16 × 106
1.01 × 106
4.53 × 106
1.19 × 107
2.38 × 107
9.83 × 106
5.44 × 106
1.70 × 107
d
d
d
d
d
d
d
d
d
d
d
d
d
d
d
d
d
d
d
d
d
d
990
990
680
680
730
730
400
110
d
d
1740
1130
1.54
a
Conditions: solvent heptane; temperature 70 °C; ethylene pressure 4 bar. The complexes were dissolved and preactivated in a MAO/
toluene solution (ca. 10%); the actual concentration of AlMAO for each solution was estimated from its 1H NMR spectrum. Activity is
b
expressed in units of g of PE (mol of Cr)-1 bar-1 h-1
.
c Determined by GPC. Refers only to the polymer separated from the wax phase.
Not recorded. e Temperature 90 °C.
d
ent on the structure of the catalyst and the nature of
the cocatalyst.
The structure of the ligands also influences the
molecular weights of the polyethylene. Complexes hav-
ing bulkier ortho substituents in the phenyl groups give
rise to higher molecular weights. This is in agreement
with the results observed for the iron and cobalt
catalysts with the same types of ligands.15,16 In this
aspect, the molecular weight and molecular weight
distribution of the polymer obtained with complex 25
are remarkable. A high molecular weight distribution
value has been also observed for the related iron
complex.16b
F igu r e 3. Influence of the AlMAO/Cr ratio of the preformed
complex solution on the activity of catalyst 19. General
The polymers obtained with these chromium com-
plexes are highly linear, and this is reflected in their
physical properties: for example, the polymer obtained
with 22 (entry 10) has a calculated degree of crystal-
linity of 80% (Tm ) 134 °C, ∆Hm ) -232 J g-1).
The copolymerization ability of these complexes has
been also tested. Copolymerization with 1-hexene oc-
curs, rendering a branched polyethylene, although the
activity results diminished in comparison with those for
the production of homopolyethylene. Thus, under the
same conditions as those employed in entry 14, but
adding 15 mL of 1-hexene (see Experimental Section),
complex 24 copolymerizes 1-hexene and ethylene, yield-
conditions employed for the assays: 4.3 µmol of Cr, AlTIBA
/
Cr ) 820, 4 bar, 70 °C, 30 min.
3 shows the variation of the activity of complex 19 as a
result of the increase of the ratio AlMAO/Cr in the
complex/MAO/toluene solution prepared before it is
injected in the polymerization reactor. All the polym-
erization assays were performed under the same condi-
tions, the AlTIBA/Cr (TIBA stands for triisobutylalumi-
num) ratio being equal to 820. The activity increases
slightly when the ratio of MAO increases from 50 to 200,
and then it remains stable up to a ratio of 400.
Figure 4 shows the trend in activity, also for complex
19, when the AlTIBA/Cr ratio is changed keeping constant
the AlMAO/Cr ratio (190). The activity shows a maximum
around an AlTIBA/Cr ratio of 800.
ing 34.8 g (activity 1.83 × 107 g (mol of Cr)-1 h-1 bar-1
)
of branched polyethylene (Mw ) 1470, Mw/Mn ) 2.13)
having 1.13 butyl branches per 1000 C (Tm ) 105 °C,
∆Hm ) - 246 J g-1).
The effect of the cocatalyst in the productivity and
nature of the polymer has been also studied. We have
observed that a minimum of MAO is needed for reaching
acceptable activities, but then, it can be substituted in
part by aluminum alkyls or other aluminoxanes. Figure
Three kinds of terminal groups are detected by 13C
NMR spectroscopy: vinyl, isopropyl (denoted here as
ISOF), and methyl (denoted here as CH3F).20 The first
one denotes â-hydrogen elimination or â-hydrogen
transfer to the monomer21 and the isopropyl end group
shows the occurrence of chain transfer to triisobutyl-

Bis(imino)pyridyl Chromium(III) Complexes
Organometallics, Vol. 22, No. 3, 2003 401
Ta ble 4. Effect of th e Su bstitu tion of TIBA by
TIBAO in th e Ca ta lytic Activity a n d Na tu r e of
Ch a in En d s of th e P olyeth ylen e Obta in ed w ith
Com p lex 22a
amt of activity (g of PE
PE
(g)
(mol of Cr)-1
TIBA/Cr TIBAO/Cr
bar-1 h-1
)
CH3Fb ISOFb
410
200
0
0
200
400
800
14.66
15.06
16.39
18.40
1.07 × 106
1.09 × 106
1.18 × 106
1.33 × 106
5.99
5.44
2.26
2.92
1.91
1.64
0.40
0.63
0
a
Conditions: 6.9 µmol of Cr; AlMAO/Cr ) 200 for the preformed
complex solution; temperature 70 °C; ethylene pressure 4 bar; 30
F igu r e 4. Influence of the AlTIBA/Cr ratio on the activity
of complex 19. General conditions employed for the as-
says: 4.6 µmol of Cr, AlMAO/Cr ) 190, 4 bar, 70 °C, 30 min.
min. Results from 13C NMR spectroscopy, given per 1000 carbon
b
atoms.
F igu r e 6. Dependence of the activity (b) and percentage
of wax formed (2) on temperature for complex 19. General
F igu r e 5. Dependence of the number and nature of the
polymer chain-end groups (9, vinyl; b, CH3F; 2, ISOF) on
the AlTIBA/Cr ratio for ethylene polymerization for complex
19 using the set of conditions shown in Figure 4.
conditions employed for the assays: 4.6 mmol of Cr, AlMAO
/
Cr ) 190, AlTIBA/Cr ) 810, 4 bar, 70 °C, 30 min.
aluminum (TIBA), while the methyl end group can have
several origins: from the initial methylation step with
MAO, from chain transfer to MAO followed by hydroly-
sis during the workup of the polymer, and from methyl
groups formed after insertion of ethylene into the Cr-H
bond formed after â-hydrogen elimination and/or trans-
fer to monomer (Scheme 5). As is shown in Figure 5,
when the TIBA/Cr ratio is increased, the number of
isopropyl end groups (ISOF) grows. The number of
methyl groups (CH3F) increases also parallel to the
number of ISOF, while the number of vinyl groups
decreases, reflecting an increase in the number of
saturated chains.
To reduce the alkylating power of the cocatalyst, TIBA
was substituted by tetraisobutylaluminoxane (TIBAO)
in some of the assays. Table 4 shows the influence of
the substitution of TIBA by TIBAO on the catalytic
activity and nature of the chain ends of the polyethylene
obtained with complex 22. This procedure resulted in
lower numbers of ISOF and CH3F groups per 1000 C
chain ends and comparable, if not higher, activities. In
other experiments, the amount of MAO was reduced and
it was substituted by TIBAO. In these cases, the
termination reaction by alkyl-transfer processes to
aluminum is not favored and, consequently, the molec-
ular weights increase (Table 3, entry 10).22
The influence of the temperature on the catalyst
behavior has been studied. Figure 6 shows the effect of
the temperature on the catalytic performance for com-
plex 19 upon increasing the temperature within the
range 60-90 °C. The activity decreases gradually, and
there is an increase on the percentage of waxes ob-
tained. This is similar to what is observed with the bis-
(imino)pyridyl iron and cobalt complexes, where a
significant decrease in productivity and molecular weight
is reported when the temperature is increased from 35
to 70 °C.16b However, according to our results, the
stability at high temperatures (over 70 °C) of the
chromium complexes seems to be higher than that of
the iron and cobalt complexes.
As is known, the application of homogeneous olefin
polymerization catalysts in gas-phase or slurry reactions
would cause problems such as reactor fouling. This
problem could be overcome via heterogeneization of the
homogeneous catalysts. Therefore, we have pursued the
heterogeneization of our system. An active catalytic
system was obtained by prepolymerization of complex
24 with ethylene together with MAO supported on silica
(see the Experimental Section). The catalytic system
thus obtained was employed for the polymerization of
ethylene at a total pressure of 38 bar in isobutane at
80 °C, using TIBA as cocatalyst. The consumption of
ethylene was very stable during the assay (60 min),
yielding a linear polymer (Mw of 1470, Mw/Mn ) 2.13)
with high productivity (ca. 1300 kg of PE (g of Cr)-1 h-1),
superior to most Phillips type catalysts.23
(20) Vinyl and CH3F groups assigned according to: Randall, J . C.
J . Macromol. Sci. Rev. Macromol. Chem. Phys. 1989, C29, 201. The
ISOF groups were assigned according to: Sarpal, A. S.; Kapur, G. S.;
Chopra, A.; J ain, S. K.; Srivastava, S. P.; Bhatnagar, A. K. Fuel 1996,
75, 483.
(21) We cannot be certain which mechanism for the formation of
vinyl groups is favored: â-hydrogen elimination or transfer to mono-
mer. However, the fact that the molecular weight of the polymer
obtained at high pressure (38 bar) with the supported catalyst (see
text) is similar to that obtained at lower pressure (4 bar) provides an
indication that â-hydrogen elimination could predominate.
(22) We have observed (unpublished results) that, by reduction of
the trimethylaluminum present in MAO by evaporation, the molecular
weights of the polymer are also increased.

402 Organometallics, Vol. 22, No. 3, 2003
Sch em e 5. P ossible Ch a in P r op r oga tion a n d Ter m in a tion P a th w a ys
Esteruelas et al.
Con clu d in g Rem a r k s
due to chain-transfer processes to aluminum, as has
been demonstrated by NMR analysis of chain end
groups. The general trend observed is that the molecular
weights increase when the alkylating power of the
cocatalyst is reduced.
A family of air-stable chromium(III) complexes bear-
ing bis(imino)pyridine has been synthesized and char-
acterized. In the presence of methylaluminoxane and/
or triisobutylaluminum, these compounds are the most
active chromium catalysts reported to date for ethylene
polymerization, showing activities up to 4.14 × 107 g of
PE (mol of Cr)-1 bar-1 h-1. The thermal stability of these
systems is also remarkable, reaching a maximum of
activity at 60-70 °C. Linear polyethylene of molecular
weights (Mw) ranging from 35 900 to 1630 are obtained.
In the presence of an R-olefin comonomer such as
1-hexene incorporation is observed.
The catalytic activity and the molecular weights of
the polyethylene depend greatly on the structure and
electronic properties of the ligands. The complexes with
two substituents in the ortho positions of the parent
anilines are more active than those with only one.
However, the increase of the steric hindrance of these
subtituents produces a decrease in the catalytic activity.
Thus, the most active complexes are those bearing two
ortho methyl groups. An opposite trend has been
observed for the molecular weights of the obtained
polyethylene, which increase as the steric requirement
of the substituents at the ortho positions increases. The
presence of donor groups, such as methoxy, in ortho or
para positions of the aryl groups renders nonactive
systems.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations were carried
out under an inert atmosphere, using standard Schlenk
techniques. Solvents were refluxed over an appropriate drying
agent and distilled prior to use. C, H, and N analyses were
measured on a Perkin-Elmer 2400 CHNS/O analyzer. Infrared
spectra were recorded on Perkin-Elmer 883 or Spectrum One
spectrometers as solids (Nujol mull). 1H, 13C{1H}, and 19F
spectra were recorded on a Varian Gemini 2000 or Bruker ARX
300. 13C{1H} NMR (1,2,4-trichlorobenzene, 378 K) polymer
analyses were recorded on a Bruker DRX 500 NMR spectrom-
eter. Chemical shifts are referenced to residual solvent peaks
(1H, 13C{1H}) or external CFCl3. Coupling constants are given
in hertz. Mass spectral analyses were performed with a VG
Auto Spec instrument. The ions were produced, FAB+ mode,
with the standard Cs+ gun at ca. 30 kV, and 3-nitrobenzyl
alcohol (NBA) was used as the matrix. Electron impact MS
(operating at 70 eV) was used for the ligands. Molecular
weights of the polymers were determined by gel permeation
chromatography employing universal calibration in a Waters
150c instrument with differential refractive index (DRI) detec-
tor and a Viscotek 150R DV detector and thermal analysis by
differential scanning calorimetry employing a Mettler Toledo
DSC822E with a scan speed of 10 °C/min. Data given are for
the second melt. The chromium content of the prepolymerized
catalyst was measured by ion-coupled plasma (ICP) techniques
employing an ICP-AES Perkin-Elmer 4300 instrument. Methyl-
aluminoxane (MAO, 10% in toluene), triisobutylaluminum
(TIBA, 1 M in heptane), and tetraisobutylaluminoxane (TIBAO,
20% in heptane) were purchased from Witco (now Crompton).
2,6-Bis{1-[2,6-(diisopropylphenyl)imino]ethyl}pyridine (5), 2,6-
bis{1-[(2,6-dimethylphenyl)imino]ethyl}pyridine (6), 2,6-bis-
The molecular weight of the polymer is also influenced
by the nature and amount of the employed cocatalyst
(23) Typical Phillips catalyst polyethylenes contain 1.5-2.5 ppm of
Cr, thus corresponding to productivities in the range of 400-700 kg
of PE/g of Cr (see for example: Maduen˜o Casado, M.; Del Amo
Ferna´ndez, B.; Ferna´ndez Sibo´n, F. J .; Herna´ndez-Vaquero AÄ lvarez,
J .; Rodriguez Sinoga, J . (Repsol Qu´ımica), Eur. Pat. Appl. 1153943,
2001.

Bis(imino)pyridyl Chromium(III) Complexes
Organometallics, Vol. 22, No. 3, 2003 403
{1-[(2,4,6-trimethylphenyl)imino]ethyl}pyridine (7), and 2,6-
bis{1-[2-(tert-butylphenyl)imino]ethyl}pyridine (8) were prepared
according to published methods.16b CrCl3(THF)324 and [2,6-bis-
{1-[2,6-(diisopropylphenyl)imino]ethyl}pyridine]CrCl2 (32)
were prepared as previously reported.
13C{1H} NMR (CDCl3, 75.4 MHz, plus APT): δ 167.3 (NdC),
155.3 (py Co), 147.7 (Ar Cip), 136.9 (py Cp), 136.4 (Ar Co), 127.8
(Ar Cp), 125.1 (Ar Co), 123.4 (Ar Cm), 123.2 (Ar Cm), 122.3 (py
Cm), 28.2 (CH(CH3)2), 23.0 (CH(CH3)2), 22.7 (CH(CH3)2), 18.0
(NdCMe), 16.7 (Me).
25
P r epa r a tion of 2,6-Bis{1-[(2-m eth yl-6-m eth oxyp h en yl)-
im in o]eth yl}p yr id in e (9). 2-Methyl-6-methoxyaniline (841
mg, 6.13 mmol) was added to a solution of 2,6-diacetylpyridine
(500 mg, 3 mmol) in toluene (12 mL). After the addition of 0.1
mg of p-toluenesulfonic acid, the solution was refluxed for 12
h. During this time the water of the solution was removed
using a Dean-Stark apparatus. When this solution was cooled
to room temperature, it was concentrated in vacuo to afford a
yellow solid, which was washed with methanol and dried in
P r ep a r a tion of 2,6-Bis{1-(cycloh exylim in o)eth yl}-
p yr id in e (1). Cyclohexylamine (1.4 mL, 12 mmol) was added
to a solution of 2,6-diacetylpyridine (500 mg, 3 mmol) in
absolute ethanol (10 mL). After the addition of several drops
of glacial acetic acid the solution was refluxed for 48 h. When
this solution was cooled to room temperature, the product
crystallized from ethanol. The pale yellow solid that formed
was washed with cold ethanol (4 × 4 mL) and dried in vacuo.
Yield: 421.2 mg (42%). MS (EI): m/z 325.5 (M+). 1H NMR
(CDCl3, 300 MHz): δ 8.04 (d, 2H, J H-H ) 7.8, py Hm), 7.66 (t,
1H, J H-H ) 7.8, py Hp), 3.55 (m, 2H, -CH, Cy), 2.39 (s, 6H,
NdCMe), 1.84-1.24 (m, 20H, -CH2-, Cy). 13C{1H} NMR
(CDCl3, 75.4 MHz, plus APT): δ 164.4 (NdC), 156.9 (py Co),
136.8 (py Cp), 121.3 (py Cm), 60.3 (NCH), 33.5 (-CH2-), 25.8
(-CH2-), 24.9 (-CH2-), 13.5 (NdCMe).
1
vacuo. Yield: 984 mg (80%). MS (EI): m/z 401 (M+). H NMR
(CDCl3, 300 MHz): δ 8.49 (d, 2H, J H-H ) 7.8, py Hm), 7.88 (t,
1H, J H-H ) 7.8, py Hp), 7.00 (t, 2H, J H-H ) 7.8, Ar Hp), 6.87
(d, 2H, J H-H ) 7.8, Ar Hm), 6.81 (d, 2H, J H-H ) 7.8, Ar Hm),
3.77 (s, 6H, OMe), 2.27 (s, 6H, NdCMe), 2.10 (s, 6H, Me). 13C-
{1H} NMR (CDCl3, 75.4 MHz): δ 168.9 (NdC), 155.3 (py Co),
148.0 (Ar Cip), 138.8 (py Cp), 136.8 (Ar), 128.4 (Ar), 123.7 (Ar),
122.6 (Ar), 122.4 (py Cm), 108.9 (Ar), 55.5 (OMe), 17.6 (Me),
16.5 (NdCMe).
P r ep a r a tion of 2,6-Bis{1-[2,6-(d ieth ylp h en yl)im in o]-
eth yl}p yr id in e (2). 2,6-Diethylaniline (1.5 mL, 9.2 mmol) was
added to a solution of 2,6-diacetylpyridine (500 mg, 3 mmol)
in absolute ethanol (12 mL). After the addition of several drops
of glacial acetic acid, the solution was refluxed for 48 h. When
this solution was cooled to room temperature, the product
crystallized from ethanol. The yellow solid that formed was
washed (3 × 5 mL) with cold ethanol, and it was dried in vacuo
at 60 °C for 1 day. Yield: 540 mg (48%). MS (EI): m/z 425
P r epar ation of 2,6-Bis{1-[(2,4-dim eth oxyph en yl)im in o]-
eth yl}p yr id in e (10). 2,4-Dimethoxyaniline (939 mg, 6.12
mmol, previously purified from the commercial source by
sublimation) was added to a solution of 2,6-diacetylpyridine
(500 mg, 3 mmol) in toluene (12 mL). After the addition of 0.1
mg of p-toluenesulfonic acid, the solution was refluxed for 2
h. During this time the water of the solution was removed
using a Dean-Stark apparatus. When this solution was cooled
to room temperature, it was concentrated in vacuo to afford a
yellow solid, which was washed with methanol and dried in
1
(M+). H NMR (CDCl3, 300 MHz): δ 8.47 (d, 2H, J H-H ) 7.8,
py Hm), 7.91 (t, 1H, J H-H ) 7.8, py Hp), 7.12-7.00 (m, 6H, Ph),
2.37 (m, 8H, -CH2CH3), 2.23 (s, 6H, NdCMe), 1.13 (m, 12H,
-CH2CH3). 13C{1H} NMR (CDCl3, 75.4 MHz): δ 167.1 (Nd
C), 155.3 (py Co), 147.9 (Ar Cip), 137.0 (py Cp), 131.3 (Ar Co),
126.0 (Ar Cm), 123.4 (Ar Cp), 122.3 (py Cm), 24.5 (CH2CH3),
16.7 (NdCMe), 13.6 (CH2CH3).
1
vacuo. Yield: 690 mg (52%). MS (EI): m/z 433 (M+). H NMR
(CDCl3, 300 MHz): δ 8.36 (d, 2H, J H-H ) 7.8, py Hm), 7.83 (t,
1H, J H-H ) 7.8, py Hp), 6.73 (d, 2H, J H-H ) 8.4, Ar), 6.56 (s,
2H, Ar), 6.52 (d, 2H, J H-H ) 8.4, Ar), 3.82 (s, 6H, OMe), 3.78
(s, 6H, OMe), 2.35 (s, 6H, NdCMe). 13C{1H} NMR (CDCl3, 75.4
MHz): δ 169.4 (NdC), 157.4, 155.6, 150.1, 136.7, 133.8, 122.4,
120.8, 104.2, 99.6 (py and Ar), 55.5 (OMe), 55.4 (OMe), 16.5
(NdCMe).
P r ep a r a tion of 2,6-Bis{1-[(2-(tr iflu or om eth yl)p h en yl)-
im in o]eth yl}p yr id in e (3). 2-(Trifluoromethyl)aniline (1.15
mL, 9.2 mmol) was added to a solution of 2,6-diacetylpyridine
(500 mg, 3 mmol) in absolute ethanol (12 mL). After the
addition of several drops of glacial acetic acid, the solution was
refluxed for 48 h. When this solution was cooled to room
temperature, the reaction volume was reduced to afford a pale
yellow solid, which was washed with ethanol at 0 °C and dried
P r ep a r a tion of 2-Acetyl-6-[1-(2,4,6-tr im eth ylp h en yl-
im in o)eth yl]p yr id in e (11). 2,4,6-Trimethylaniline (731 µL,
5.2 mmol) was added to a solution of 2,6-diacetylpyridine (1
g, 6.1 mmol). After the addition of 0.1 mg of p-toluenesulfonic
acid, the solution was refluxed for 45 min. During this time
the water of the solution was removed using a Dean-Stark
apparatus. When this solution was cooled to room temperature,
it was concentrated in vacuo and methanol added to afford a
yellow solid that was washed with methanol and dried in
1
in vacuo. Yield: 668 mg (48.5%). MS (EI): m/z 449 (M+). H
NMR (CDCl3, 300 MHz): δ 8.35 (d, 2H, J H-H ) 7.8, py Hm),
7.90 (t, 1H, J H-H ) 7.8, py Hp), 7.67 (d, 2H, J H-H ) 7.8, Ph),
7.51 (d, 2H, J H-H ) 7.7, Ph), 7.17 (d, 2H, J H-H ) 7.7, Ph), 6.79
(d, 2H, J H-H ) 7.8, Ph), 2.35 (s, 6H, NdCMe). 19F NMR (CDCl3,
279 MHz): δ -64.3 (CF3). 13C{1H} NMR (CDCl3, 75.4 MHz):
δ 168.7 (NdC), 155.0 (py Co), 149.7 (Ar, Cip), 137.3 (py Cp),
132.7 (Ar), 126.5 (q, J F-C ) 5 Hz, Ar), 124 (q, J F-C ) 273 Hz,
CF3), 123.3 (Ar), 123.1 (py Cm), 119.8 (Ar), 16.7 (NdCMe).
1
vacuo. Yield: 560 mg (38%). MS (EI): m/z 280 (M+). H NMR
(CDCl3, 300 MHz): δ 8.56 (d, 1H, J H-H ) 7.8, py Hm), 8.12 (d,
J H-H ) 7.8, 1H, py Hm), 7.93 (t, J H-H ) 7.8, 1H, py Hp), 6.89
(s, 2 H, ArMe3), 2.78 (s, 3H, Me), 2.29 (s, 3H, Me), 2.22 (s, 3H,
Me), 1.99 (s, 6H, 2 Me). 13C{1H} NMR (CDCl3, 75.4 MHz): δ
199.9 (CdO), 166.7 (CdN), 155.6, 152.4, 145.9, 137.2, 132.3,
128.5, 125.2, 124.4, 122.5 (py and Ar), 25.6, 20.6, 17.8, 16.2
(Me).
P r epar ation of 2,6-Bis{1-[(2-m eth yl-6-isopr opylph en yl)-
im in o]eth yl}p yr id in e (4). 2-Methyl-6-isopropylaniline (1.45
mL, 9.2 mmol) was added to a solution of 2,6-diacetylpyridine
(500 mg, 3 mmol) in absolute ethanol (12 mL). After the
addition of several drops of glacial acetic acid, the solution was
refluxed for 48 h. When this solution was cooled to room
temperature, the product crystallized from ethanol. The pale
yellow solid that formed was washed with cold ethanol (2 × 6
mL), and it was dried in vacuo at 60 °C for 2 days. Yield: 1.02
P r ep a r a t ion of 2-{1-[(2,6-Diisop r op ylp h en yl)im in o]-
eth yl}-6-{1-[(2,4,6-tr im eth ylp h en yl)im in o]eth yl}p yr id in e
(12). 2,6-Diisopropylaniline (336 µL, 1.78 mmol) was added
to a solution of 11 (500 mg, 1.78 mmol) in toluene (10 mL).
After the addition of 0.1 mg of p-toluenesulfonic acid, the
solution was refluxed for 15 h. During this time the water of
the solution was removed using a Dean-Stark apparatus.
When this solution was cooled to room temperature, it was
concentrated in vacuo to afford a yellow solid, which was
washed with methanol and dried in vacuo. Yield: 611 mg
1
g (78%). MS (EI): m/z 425 (M+). H NMR (CDCl3, 300 MHz):
δ 8.46 (d, 2H, J H-H ) 7.9, py Hm), 7.90 (t, 1H, J H-H ) 7.9, py
Hp), 7.17-6.98 (m, 6H, Ar), 2.81 (spt, 2H, J H-H ) 6.8,
CH(CH3)2), 2.24 (s, 6H, NdCMe), 2.02 (s, 6H, Me), 1.18 (d, 6H,
J H-H ) 6.8, CH(CH3)2), 1.12 (d, 6H, J H-H ) 6.8, CH(CH3)2).
1
(78%). MS (EI): m/z 440 (M+). H NMR (CDCl3, 300 MHz): δ
(24) Boudjouk, P.; So, J .-H. Inorg. Synth. 1992, 29, 108.
(25) Devore, D. D.; Feng, S. S.; Frazier, K. A.; Patton, J . T. (Dow)
WO 00/69923, 2000.
8.46 (d, J H-H ) 7.8, 1H, py Hm), 8.45 (d, J H-H ) 7.8, 1H, py
Hm), 7.90 (t, J H-H ) 7.8, 1H, py Hp), 7.18-7.06 (m, 3H, AriPr2),

404 Organometallics, Vol. 22, No. 3, 2003
Esteruelas et al.
6.88 (s, 2 H, ArMe3), 2.75 (spt, J H-H ) 6.9, 2H, -CH(CH3)2),
2.28 (s, 3H, Me), 2.25 (s, 3H, Me), 2.22 (s, 3H, Me), 2.00 (s,
6H, ArMe2), 1.14 (d, J H-H ) 6.9, 12H, -CH(CH3)2). 13C{1H}
NMR (CDCl3, 75.4 MHz): δ 167.1 (NdC), 167.06 (NdC), 155.4,
155.2, 146.6, 146.4, 136.9, 135.8, 132.3, 128.6, 125.3, 123.6,
123.1, 122.3, 122.2 (py and Ar), 28.2 (CH(CH3)2), 23.1 (CH-
(CH3)2), 22.8 (CH(CH3)2), 20.6 (Me), 17.7 (Me2), 16.9 (NdCMe),
16.2 (NdC-Me).
P r ep a r a tion of 2-{1-[(2-ter t-Bu tylp h en yl)im in o]eth yl}-
6-{1-[(2,4,6-tr im eth ylp h en yl)im in o]eth yl}p yr id in e (13).
2-tert-Butylaniline (278 µL, 1.78 mmol) was added to a solution
of 11 (500 mg, 1.78 mmol) in toluene (10 mL). After the
addition of 0.1 mg of p-toluenesulfonic acid, the solution was
refluxed for 15 h. During this time the water of the solution
was removed using a Dean-Stark apparatus. When this
solution was cooled to room temperature, it was concentrated
in vacuo and methanol added to afford a yellow solid that was
washed with methanol and dried in vacuo. Yield: 580 mg
(79%). MS (EI): m/z 413 (M+ + 1). 1H NMR (CDCl3, 300
MHz): δ 8.46 (d, 1H, J H-H ) 7.8, py Hm), 8.40 (d, J H-H ) 7.8,
(665 mg, 2.31 mmol), and 2,4,6-trimethylaniline (650 µL, 4.63
mmol) in acetic acid (15 mL) was refluxed for 4 h, giving a
brown solution. The brown solution was filtered through Celite
and concentrated in vacuo to ca. 0.5 mL. Addition of diethyl
ether afforded a brown solid, which was washed with diethyl
ether (3 × 5 mL) and dried in vacuo. Yield: 1.34 g (89%). Anal.
Calcd for C37H35N3NiCl2: C, 68.23; H, 5.42; N, 6.45. Found:
C, 68.19; H, 5.03; N, 6.62. IR (Nujol, cm-1): 1579, 1266, 1025,
703. MS (FAB+): m/z 614 (M+ - Cl), 579 (M+ - 2Cl).
P r epar ation of 2,6-Bis{1-[(2,4,6-tr im eth ylph en yl)im in o]-
ben zyl}p yr id in e (17). A solution of 16 (1 g, 1.53 mmol) in
50 mL of CH2Cl2 was stirred over aminopropyl silica gel for
18 h. During this time the color of the solution changed from
brown to yellow. The aminopropyl silica gel was filtered and
the solution concentrated to ca. 0.5 mL under vacuum.
Methanol was added to afford a yellow solid, which was
washed with methanol and dried in vacuo. Yield: 408 mg
(51%). MS (EI): m/z 521 (M+), 506 (M+ - Me), 444 (M+ - Ph),
404 (M+ - C6H2Me3), 388 (M+ - NC6H2Me3). IR (Nujol, cm-1):
1627, 1578, 1562, 1292, 1214, 1173, 1140. 1H NMR (CDCl3,
300 MHz): δ 8.48-6.60 (m, 16H, Ar), 2.20-1.82 (m, 18H, Me).
13C{1H} NMR (CDCl3, 75.4 MHz): δ 165.9 (NdC), 155.2, 149.6,
146.2, 137.9, 136.1, 135.6, 131.7, 130.6, 128.8, 128.0, 125.6,
121.5, 20.7 (ArMe), 18.5 (ArMe2).
P r ep a r a tion of {2,6-Bis[1-(cycloh exylim in o)eth yl]-
p yr id in e}Cr Cl3 (18). A solution of CrCl3(THF)3 (500 mg, 1.33
mmol) and 1 (435 mg, 1.33 mmol) in dichloromethane (20 mL)
was refluxed for 12 h, giving a green solution. During this time
a green solution was obtained, which was filtered through
Celite. The reaction volume was concentrated, and diethyl
ether was added to afford a green solid, which was washed
repeatedly with diethyl ether and dried in vacuo. Yield: 549
mg (82%). Anal. Calcd for C21H31N3CrCl3‚1.5H2O: C, 49.37;
H, 6.71; N, 8.22. Found: C, 49.24; H, 6.83; N, 7.96. IR (Nujol,
cm-1): 1579, 1282, 1200, 891, 805, 350, 290. MS (FAB+): m/z
447 (M+ - Cl).
P r ep a r a tion of {2,6-Bis[1-(2,6-(d ieth ylp h en yl)im in o)-
eth yl]p yr id in e}Cr Cl3 (19). A solution of CrCl3(THF)3 (500
mg, 1.33 mmol) and 2 (568 mg, 1.33 mmol) in acetone (15 mL)
was refluxed for 6 h, giving a green suspension. The reaction
volume was concentrated, and diethyl ether was added to
afford a green solid, which was washed repeatedly with diethyl
ether and dried in vacuo. Yield: 756 mg (97%). Anal. Calcd
for C29H35N3CrCl3: C, 59.65; H, 6.04; N, 7.19. Found: C, 59.32;
H, 6.43; N, 7.38. IR (Nujol, cm-1): 1579, 1263, 1043, 817, 399,
353. MS (FAB+): m/z 547 (M+ - Cl).
P r ep a r a tion of {2,6-Bis[1-((2-(tr iflu or om eth yl)p h en yl)-
im in o)eth yl]p yr id in e}Cr Cl3 (20). A solution of CrCl3(THF)3
(500 mg, 1.33 mmol) and 3 (600 mg, 1.33 mmol) in dichloro-
methane (20 mL) was stirred at room temperature for 5 h.
During this time a green solution was obtained, which was
filtered through Celite. The reaction volume was concentrated,
and diethyl ether was added to afford a green solid, which was
washed repeatedly with diethyl ether and dried in vacuo.
Yield: 446 mg (52%). Anal. Calcd for C23H17F6N3CrCl3‚2H2O:
C, 42.91; H, 3.29; N, 6.53. Found: C, 43.07; H, 3.07; N, 6.26.
IR (Nujol, cm-1): 1604, 1584, 1318, 1175, 1121, 1060, 1038,
767, 363. MS (FAB+): m/z 571 (M+ - Cl).
1H, py Hm), 7.91 (t, J H-H ) 7.8, 1H, py Hp), 7.43 (d, J H-H
)
7.5, 1H, ArtBu), 7.19 (d, J H-H ) 7.5, 1H, ArtBu), 7.08 (d, J H-H
) 7.5, 1H, ArtBu), 6.90 (s, 2 H, ArMe3), 6.54 (d, J H-H ) 7.5,
1H, ArtBu), 2.40 (s, 3H, Me), 2.29 (s, 3H, Me), 2.23 (s, 3H, Me),
t
2.01 (s, 6H, ArMe2), 1.36 (s, 9H, Bu). 13C{1H} NMR (CDCl3,
75.4 MHz): δ 167.4 (NdC), 165.3 (NdC), 155.6, 155.2, 149.6,
146.2, 139.7, 136.8, 132.1, 128.5, 126.4, 126.4, 126.3, 125.3,
123.7, 122.4, 122.0, 119.7 (py and Ar), 35.1 (s, C(CH3)3), 29.6
(s, C(CH3)3), 20.7 (ArMe), 17.9 (ArMe2), 16.9 (NdCMe), 16.4
(NdCMe).
P r ep a r a t ion of 2-{1-[(2-(t r iflu or om et h yl)p h en yl)-
im in o]eth yl}-6-{1-[(2,4,6-tr im eth ylp h en yl)im in o]eth yl}-
p yr id in e (14). 2-(Trifluoromethyl)aniline (134 µL, 1.07 mmol)
was added to a solution of 11 (300 mg, 1.07 mmol) in toluene
(10 mL). After the addition of 0.1 mg of p-toluenesulfonic acid,
the solution was refluxed for 15 h. During this time, the water
of the solution was removed using a Dean-Stark apparatus.
When this solution was cooled to room temperature, it was
concentrated in vacuo and methanol added to afford a yellow
solid, which was washed with methanol and dried in vacuo.
Yield: 326 mg (72%). MS (EI): m/z 423 (M+). 1H NMR (CDCl3,
300 MHz): δ 8.47 (dd, J H-H ) 7.8, J H-H ) 3.8, 1H, py), 8.37
(d, J H-H ) 7.7, J H-H ) 3.8, 1H, py), 7.91 (t, J H-H ) 7.8, 1H,
py), 7.69 (d, J H-H ) 7.5, 1H, ArCF3), 7.53 (t, J H-H ) 7.7, 1H,
ArCF3), 7.19 (t, J H-H ) 7.7, 1H, ArCF3), 6.90 (s, 2 H, ArMe3),
6.82 (d, J H-H ) 7.7, 1H, ArCF3), 2.38 (s, 3H, Me), 2.30 (s, 3H,
Me), 2.24 (s, 3H, Me), 2.02 (s, 6H, ArMe2). 19F NMR (CDCl3,
279 MHz): δ -62.5. 13C{1H} NMR (CDCl3, 75.4 MHz): δ 168.7
(NdC), 167.4 (NdC), 167.2, 155.2, 154.9, 149.6, 146.2, 136.9,
132.5, 132.2, 128.4, 126.4 (q, J F-C ) 5 Hz), 125.2, 123.1, 122.7,
122.5, 122.1, 119.7 (py and Ar), 20.7 (ArMe), 17.8 (ArMe2), 16.8
(NdCMe), 16.4 (NdCMe).
P r ep a r a tion of 2,6-Diben zoylp yr id in e (15). An orange
reddish suspension of 2,6-dicarbonylpyridine dichloride (1 g,
4.9 mmol) and AlCl3 (1.63 g. 12.25 mmol) in benzene (12.5 mL)
was heated at reflux for 4 h, giving a red solution. The red
solution was cooled to room temperature, and it was stirred
for 12 h and then refluxed for 6 h. After the solution was cooled
to room temperature, it was poured into distilled water (25
mL) at 0 °C. The organic layer was separated, and the aqueous
phase was extracted with diethyl ether (5 mL × 2). The
combined organic phases were dried over Na2SO4 and evapo-
rated in vacuo. Addition of diethyl ether afforded a white solid,
which was washed with cold diethyl ether and dried in vacuo.
Yield: 0.95 g (67%). MS (EI): m/z 288 (M+). 1H NMR (acetone-
d6, 300 MHz): δ 8.38-8.28 (m, 3H), 8.12-8.09 (m, 4H), 7.65-
7.47 (m, 6H). 13C{1H} NMR (acetone-d6, 75.4 MHz): δ 193.3,
154.7, 139.7, 137.0, 133.7, 131.6, 128.8, 127.5.
P r epar ation of {2,6-Bis[1-((2-m eth yl-6-isopr opylph en yl)-
im in o)eth yl]p yr id in e}Cr Cl3 (21). A solution of CrCl3(THF)3
(500 mg, 1.33 mmol) and 4 (568 mg, 1.33 mmol) in acetone
(15 mL) was heated to 56 °C overnight, giving a green
suspension. The reaction volume was concentrated, and diethyl
ether was added to afford a green solid, which was washed
repeatedly with diethyl ether (5 × 10 mL) and dried in vacuo.
Yield: 670 mg (94%). Anal. Calcd for C29H35N3CrCl3‚1.5H2O:
C, 57.01; H, 6.27; N, 6.88. Found: C, 56.75; H, 6.41; N, 6.75.
IR (Nujol, cm-1): 1579, 1515, 1273, 1219. 357. MS (FAB+): m/z
547 (M+ - Cl).
P r ep a r a t ion of {2,6-Bis[1-((2,4,6-t r im et h ylp h en yl)-
im in o)ben zyl]p yr id in e}NiCl2 (16). An orange suspension
of anhydrous NiCl2 (300 mg, 2.31 mmol), 2,6-dibenzoylpyridine
P r ep a r a t ion of {2,6-Bis[1-((2,6-d iisop r op ylp h en yl)-
im in o)eth yl]p yr id in e}Cr Cl3 (22). A solution of CrCl3(THF)3

Bis(imino)pyridyl Chromium(III) Complexes
Organometallics, Vol. 22, No. 3, 2003 405
(500 mg, 1.33 mmol) and 5 (643 mg, 1.33 mmol) in acetone
(15 mL) was refluxed for 12 h, giving a green solution. The
reaction volume was concentrated, and pentane was added to
afford a green solid, which was washed repeatedly with
pentane. This solid was recrystallized from CH2Cl2/diethyl
ether and dried in vacuo. Yield: 769 mg (90%). Anal. Calcd
for C33H43Cl3CrN3: C, 61.92; H, 6.77; N, 6.56. Found: C, 61.96;
H, 6.82; N, 5.97. IR (Nujol, cm-1): 1579, 1274, 1215, 937, 802,
778, 399, 371. MS (FAB+): m/z 603 (M+ - Cl), 568 (M+ - 2 Cl).
P r ep a r a tion of {2,6-Bis[1-((2,6-d im eth ylp h en yl)im in o)-
eth yl]p yr id in e}Cr Cl3 (23). A solution of CrCl3(THF)3 (500
mg, 1.33 mmol) and 6 (493 mg, 1.33 mmol) in acetone (15 mL)
was refluxed for 5 h, giving a green suspension. The reaction
volume was concentrated, and the green solid was washed
repeatedly with acetone (4 × 5 mL) and dried in vacuo. Yield:
521 mg (74%). Anal. Calcd for C25H27N3CrCl3: C, 56.89; H,
5.16; N, 7.96. Found: C, 56.55; H, 5.46; N, 7.61. IR (Nujol,
cm-1): 1575, 1271, 1220, 1106, 1067, 1043, 817, 785, 766, 406,
356. MS (FAB+): m/z 491 (M+ - Cl), 456 (M+ - 2 Cl).
P r ep a r a t ion of {2,6-Bis[1-((2,4,6-t r im et h ylp h en yl)-
im in o)eth yl]p yr id in e}Cr Cl3 (24). A solution of CrCl3(THF)3
(500 mg, 1.33 mmol) and 7 (530 mg, 1.33 mmol) in acetone
(15 mL) was refluxed overnight, giving a green suspension.
The reaction volume was concentrated, and the green solid
was washed repeatedly with acetone (4 × 5 mL) and dried in
vacuo. Yield: 482 mg (65%). Anal. Calcd for C27H31N3CrCl3:
C, 58.34; H, 5.62; N, 7.56. Found: C, 58.24; H, 5.68; N, 7.17.
IR (Nujol, cm-1): 1577, 1269, 1224, 1210, 1100, 1042, 862, 855,
809, 402, 350. MS (FAB+): m/z 519 (M+ - Cl), 484 (M+ - 2 Cl).
P r ep a r a tion of {2,6-Bis[1-((2-ter t-bu tylp h en yl)im in o)-
eth yl]p yr id in e}Cr Cl3 (25). A solution of CrCl3(THF)3 (500
mg, 1.33 mmol) and 8 (568 mg, 1.33 mmol) in acetone (10 mL)
was refluxed overnight. The resulting green solution was
evaporated to ca. 0.5 mL, and diethyl ether was added to afford
a green solid that was washed repeatedly with diethyl ether
(4 × 5 mL) and dried in vacuo. Yield: 584 mg (75%). Anal.
Calcd for C29H35Cl3CrN3: C, 59.65; H, 6.04; N, 7.20. Found:
C, 59.36; H, 6.42; N, 7.35. IR (Nujol, cm-1): 1578, 1286, 1088,
1043, 817, 760, 399, 352. MS (FAB+): m/z 547 (M+ - Cl), 512
(M+ - 2 Cl).
P r epar ation of {2,6-Bis[1-((2-m eth yl-6-m eth oxyph en yl)-
im in o)eth yl]p yr id in e}Cr Cl3 (26). A solution of CrCl3(THF)3
(500 mg, 1.33 mmol) and 9 (536 mg, 1.33 mmol) in dichloro-
methane (20 mL) was stirred at room temperature for 2 h.
During this time a green solution was obtained, which was
filtered through Celite. The reaction volume was concentrated,
and diethyl ether was added to afford a green solid, which was
washed repeatedly with diethyl ether and dried in vacuo.
Yield: 665 mg (89%). Anal. Calcd for C25H27N3O2CrCl3: C,
53.63; H, 4.86; N, 7.50. Found: C, 53.30; H, 4.79; N, 6.95. IR
(Nujol, cm-1): 1646, 1579, 1271, 1082, 775, 528. MS (FAB+):
m/z 525 (M+ - Cl).
P r epar ation of {2,6-Bis[1-((2,4-dim eth oxyph en yl)im in o)-
eth yl]p yr id in e}Cr Cl3 (27). A solution of CrCl3(THF)3 (500
mg, 1.33 mmol) and 10 (578 mg, 1.33 mmol) in dichlo-
romethane (20 mL) was stirred at room temperature for 2 h.
During this time a green suspension was obtained. The
reaction volume was concentrated, and diethyl ether was
added to afford a green solid, which was washed repeatedly
with diethyl ether and dried in vacuo. Yield: 687 mg (87%).
Anal. Calcd for C25H27N3O4CrCl3: C, 50.73; H, 4.60; N, 7.10.
Found: C, 50.48; H, 4.42; N, 6.94. IR (Nujol, cm-1): 1603, 1581,
1504, 1209, 1162, 1025. MS (FAB+): m/z 555 (M+ - Cl).
P r ep a r a tion of {2-[1-((2,6-Diisop r op ylp h en yl)im in o)-
eth yl]-6-[1-((2,4,6-tr im eth ylph en yl)im in o)eth yl]pyr idin e}-
Cr Cl3 (28). A solution of CrCl3(THF)3 (500 mg, 1.33 mmol)
and 12 (587 mg, 1.33 mmol) in acetone (20 mL) was refluxed
for 2 h, giving a green solution. The reaction volume was
concentrated to ca. 1 mL, and diethyl ether was added to afford
a green solid, which was washed repeatedly with diethyl ether
and dried in vacuo. Yield: 686 mg (86%). Anal. Calcd for
C30H37N3CrCl3‚1.5H2O: C, 60.25; H, 6.24; N, 7.03. Found: C,
59.84; H, 6.13; N, 6.67. IR (Nujol, cm-1): 1665, 1574, 1270,
1218, 1042, 801, 399, 357. MS (FAB+): m/z 561 (M+ - Cl).
P r ep a r a tion of {2-[1-((2-ter t-Bu tylp h en yl)im in o)eth yl]-
6-[1-((2,4,6-t r im e t h y lp h e n y l)im in o )e t h y l]p y r id in e }-
Cr Cl3 (29). A solution of CrCl3(THF)3 (500 mg, 1.33 mmol)
and 13 (549 mg, 1.33 mmol) in acetone (20 mL) was refluxed
for 2 h 30 min, giving a green solution. The reaction volume
was concentrated to ca. 1 mL, and diethyl ether was added to
afford a green solid, which was washed repeatedly with diethyl
ether (2 × 10 mL) and dried in vacuo. Yield: 715 mg (94%).
Anal. Calcd for C28H33N3CrCl3‚1.5H2O: C, 59.00; H, 5.84; N,
7.37. Found: C, 58.56; H, 6.12; N, 7.31. IR (Nujol, cm-1): 1698,
1664, 1574, 1286, 1086, 855, 815, 757. MS (FAB+): m/z 535
(M+ - Cl).
P r ep a r a t ion of {2-[1-((2-(Tr iflu or om et h yl)p h en yl)-
im in o)et h yl]-6-[1-((2,4,6-t r im et h ylp h en yl)im in o)et h yl]-
p yr id in e}Cr Cl3 (30). A solution of CrCl3(THF)3 (250 mg, 0.67
mmol) and 14 (282 mg, 0.67 mmol) in dichloromethane (10
mL) was stirred at room temperature for 6 h, giving a green
suspension. The reaction volume was concentrated to ca. 1 mL,
and pentane was added to afford a green solid, which was
washed repeatedly with pentane and dried in vacuo. Yield: 307
mg (79%). Anal. Calcd for C25H24Cl3F3CrCl3: C, 51.61; H, 4.16;
N, 7.22. Found: C, 52.04; H, 4.38; N, 6.91. IR (Nujol, cm-1):
1578, 1319, 1270, 1175, 1122, 1060, 1037, 357. MS (FAB+):
m/z 546 (M+ - Cl), 520 (M+ - 2 Cl), 485 (M+ - 3 Cl).
P r ep a r a t ion of {2,6-Bis[1-((2,4,6-t r im et h ylp h en yl)-
im in o)ben zyl]p yr id in e}Cr Cl3 (31). A solution of CrCl3-
(THF)3 (200 mg, 0.53 mmol) and 17 (278 mg, 0.53 mmol) in
dichloromethane (20 mL) was stirred at room temperature for
18 h. During this time a green suspension was obtained. The
reaction volume was concentrated, and pentane was added to
afford a green solid, which was washed repeatedly with
pentane and dried in vacuo. Yield: 327 mg (90%). Anal. Calcd
for C37H35N3CrCl3: C, 65.35; H, 5.19; N, 6.18. Found: C, 64.92;
H, 5.14; N, 5.72. IR (Nujol, cm-1): 1578, 1557, 1283, 1044, 855,
407. MS (FAB+): m/z 643 (M+ - Cl).
P olym er iza tion Assa ys. P r ep a r a tion of Ca ta lyst Solu -
tion s. The weighed amount of chromium complex is charged
into a Schlenk tube. Air is eliminated from the Schlenk tube
by successive vacuum/nitrogen (SEO, N2 B50, further purified
over molecular sieves and alumina beds) steps. Then the
desired volume of MAO/toluene solution (10%) is added. The
solution is then stirred at 500 rpm for the time set.
P olym er iza tion Assa ys a t 4 ba r . Gen er a l P r oced u r e.
A 1.3 L glass autoclave reactor vessel is employed. Air and
polar impurities are eliminated from the reactor previous to
every polymerization experiment by washing at 70 °C with
heptane (650 mL) and TIBA (5 mL, 1 M in heptane) under
nitrogen (SEO, N2 B50, further purified over molecular sieves
and alumina beds) for 30 min with stirring. After washing,
the reactor is charged with 600 mL of heptane, degassed, and
saturated with ethylene to a pressure of 4 bar at the set
temperature. Then, first, the required volume of the cocatalyst
solution and, second and immediately, the catalyst solution
are added. Polymerizations are effected at constant pressure,
the consumption of ethylene being monitored by means of a
Tylan Model FM 380 mass flowmeter. The temperature is
measured by means of a PT-100 probe immersed in the
reaction solvent. Regulation of the temperature is provided
by a combination of heating and cooling systems operating
simultaneously by passing two fluids through two external
jackets at the walls of the reactor vessel. The heating is
effected with oil from a circulating oil bath (Haake N3).
Refrigeration is obtained from cold tap water controlled by an
electrovalve connected to a Toho TM-104 controller. Ethylene
(SEO, N35) is further purified by passing it through activated
molecular sieves (13 X, 4 Å) and activated alumina beds
previous to its introduction in the polymerization reactor.
Stirring is carried out at 1200 rpm. After the time set for the

406 Organometallics, Vol. 22, No. 3, 2003
Esteruelas et al.
Ta ble 5. Cr ysta l Da ta a n d Da ta Collection a n d
Refin em en t Deta ils for 22 a n d 31
experiment, the contents of the reactor are discharged and a
methanol/HCl solution is added. Filtration, washing, and
drying of the resulting solid (70 °C/10 mmHg for ca. 20 h) gives
the nonsoluble fraction of the resulting polymer. To collect the
soluble waxes, the filtrates are decanted and the upper layer
evaporated under vacuum.
22
31
Crystal Data
formula
C
33H43Cl3CrN3‚
C
37H35Cl3CrN3‚
CH2Cl2
CH2Cl2‚1/2OC4H10
Cop olym er iza tion Assa y of Eth ylen e a n d 1-Hexen e
w ith Com p lex 24. The temperature was set at 70 °C. A 15
mL portion of 1-hexene was added to the polymerization
medium. MAO in toluene was then added (0.8 mL) to the
vessel before 0.1 mL (0.0009 mmol) of a solution of 24 in MAO/
toluene was added as well. Ethylene was continuously supplied
in order to keep a constant pressure. The consumption of
ethylene was maintained for 30 min. During this period the
temperature reached a maximum of 74 °C for a couple of
minutes, being controlled by the refrigeration system at ca.
70 °C most of the time. Afterward, the polymerization mixture
was added to a methanol/HCl solution. Filtration, washing,
and drying of the resulting solid (70 °C/10 mmHg for ca. 20 h)
gave 34.84 g (activity 1.83 × 107 g of PE (mol of Cr)-1 bar-1
h-1) of a white powder (branched polyethylene according to
the 13C NMR spectrum with 1.13 Bu branches, 12.57 vinyl
mol wt
724.98
802.02
color and habit
green, irregular green, irregular
block block
symmetry, space group monoclinic, P21/c monoclinic, C2/c
a, Å
b, Å
c, Å
13.4267(15)
16.5582(19)
16.5357(19)
101.922(2)
3597.0(7)
4
24.126(11)
21.521(10)
16.378(7)
96.119(12)
8455(6)
8
â, deg
V, Å3
Z
D(calcd), g cm-3
1.339
1.260
Data Collection and Refinement
Bruker Smart APEX
diffractometer
λ(Mo KR), Å
monochromator
scan type
0.710 73
graphite oriented
ω scans
0.618
µ, mm-1
0.717
3-56
100
2θ range, deg
temp, K
3-46
groups, and 13.24 end methyl groups per 1000 C). GPC: Mw
)
.
2290, Mw/Mn ) 1.59. DSC: Tmax ) 105 °C, ∆Hm ) -246 J g-1
100
no. of data collected
no. of unique data
38329
8564
26387
5887
P r ep a r a tion of th e P r ep olym er ized Ca ta lyst. In a
Schlenk tube, 0.5 g of silica-MAO TA02794/HL/PQ (provided
by Witco, now Crompton), 10 mL of dry toluene, and 25 mg of
24 were mixed together under nitrogen. To this mixture was
also added 5.0 mL of MAO/toluene (10%). The Schlenk tube
was then immersed in an ice bath, and the contents were
stirred with a Teflon magnetic bar at 800 rpm. Ethylene was
passed through the Schlenk tube at atmospheric pressure for
4.15 h. The ice bath was then removed, the solvent evaporated
in vacuo, and the solid dried. The total weight of solids was
2.06 g. From ICP measurement the content of Cr was
determined to be 0.11(5) wt % and that of Al 14.6 wt %.
Eth ylen e P olym er iza tion w ith P r ep olym er ized Ca ta -
lyst. In a 2 L stainless steel autoclave heated to reach an
internal temperature of 80 °C charged with isobutane (1 L)
and TIBA (1.0 M, 0.9 mL), ethylene was added up to a total
internal pressure of ca. 35 bar. Then, 100 mg of the prepoly-
merized catalyst prepared above were added by dragging it
with an ethylene current, and the internal pressure in the
reactor increased up to ca. 38 bar. Polymerization started
immediately. Ethylene was added continuously in order to
keep a constant internal pressure. The consumption of the gas
feed was very stable all through the 60 min of duration of the
assay. Afterward, the reactor was vented and cooled to room
temperature. The solids were discharged and washed thor-
oughly with acidified methanol. The total weight of polymer
obtained after drying in vacuo for 20 h was 150.53 g (1309 kg
of PE (g of Cr)-1 h-1). The polyethylene obtained was linear,
according to the 13C NMR spectrum, with 17.7 vinyl groups
and 16.7 end methyl groups per 1000 C. GPC: Mw ) 1470,
Mw/Mn ) 2.13.
X-r a y An a lysis of 22 a n d 31. Two irregular green crystals
of size 0.40 × 0.16 × 0.06 mm (22) and 0.26 × 0.06 × 0.02
mm (31) were mounted on a Bruker Smart APEX CCD
diffractometer at 100.0(2) K equipped with a normal-focus, 2.4
kW sealed-tube source (molybdenum radiation, λ ) 0.710 73
Å) operating at 50 kV and 40 mA. Data were collected over
the complete sphere by a combination of four sets. Each frame
exposure time was 30 s, covering 0.3° in ω. The cell parameters
were determined and refined by a least-squares fit of 4325
(22) or 2704 (31) collected reflections. The first 100 frames
were collected at the end of the data collection to monitor
crystal decay. Absorption correction was performed with the
SADABS program (this is based on the method of Blessing26).
Lorentz and polarization corrections were also performed. The
(Rint ) 0.0874)
(Rint ) 0.1640)
no. of params/restraints 398/0
474/60
0.0605
0.1546
0.839
R1a (F2 > 2σ(F2))
wR2b (all data)
Sc (all data)
0.0442
0.1032
0.790
R1(F) ) ∑||Fo| - |Fc||/∑|Fo|. wR2(F2) ) {∑[w(Fo - Fc2)2]/
a
b
2
2
∑[w(Fo2)2]}1/2
.
c GOF ) S ) {∑[(Fo - Fc2)2]/(n - p)}1/2, where n
is the number of reflections and p is the number of refined
parameters.
structures were solved by Patterson and Fourier methods
and refined by full-matrix least squares using the Bruker
SHELXTL program package27 minimizing w(Fo - Fc2)2. Both
2
compounds crystallize with solvent molecules: dichloromethane
(22) or dichloromethane/diethyl ether (31). The non-hydrogen
atoms were anisotropically refined, and the disordered solvent
molecules (31) were refined with restrained geometry. The
hydrogen atoms were observed or calculated and refined riding
on their bonded carbon atoms. Weighted R factors (Rw) and
goodness of fit (S) are based on F2; conventional R factors are
based on F.
Crystal data and details of the data collection and refine-
ment are given in Table 5.
Ack n ow led gm en t. We acknowledge financial sup-
port from the DGES of Spain (Project PB98-1591).
Repsol-YPF is also acknowledged for financial support
and the permission to publish these results. Thanks are
due to Ms. V. Blasco and Mr. J . M. Ca´rdenas for a part
of the polymerization experimental work and to the
NMR department of Repsol-YPF for the resolution and
assignments of the polymer spectra. Thanks are also
due to the Gidem of the Consejo Superior de Investiga-
ciones Cient´ıficas in Madrid for the polymer character-
ization.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates and equivalent isotropic displacement coefficients,
anisotropic thermal parameters, experimental details of the
X-ray studies, and bond distances and angles for 22 and 31.
This material is available free of charge via the Internet at
http://pubs.acs.org.
OM020561U
(27) SHELXTL, version 6.1; Bruker Analytical X-ray Systems,
Madison, WI.
(26) Blessing, R. H. Acta Crystallogr., Sect. A 1995, 51, 33.