Halogen-substituted 2,6-bis(imino)pyridyl iron and cobalt complexes: Highly active catalysts for polymerization and oligomerization of ethylene

Article abstract of DOI:10.1021/om0302894

A series of halogen-substituted 2,6-bis(imino)pyridyl ligands and their iron and cobalt complexes [{2,6-(2,6-X¹X²C₆H₃ N=CCH₃)₂C₅H₃N}MCl₂] (X¹ = X² = Br, M = Fe (1), Co (2); X¹ = X² = Cl, M = Fe (3), Co (4); X¹ = Cl, X² = H, M = Fe (5), Co (6); X¹ = Br, X² = H, M = Fe (7), Co (8); X¹ = I, X² = H, M = Fe (9), Co (10)) and [M{2,6-(2,6-X¹X²C₆H₃N= CCH₃)₂C₅H₃ N}₂]²⁺-[MCl₄]^2- (X¹ = F, X² = H, M = Fe (11)) have been synthesized. The molecular structures of complexes 1, 8, 9, 10, and 11 were determined by X-ray diffraction. Crystallographic analyses indicate that 1, 8, 9, and 10 are five-coordinate complexes, while 11 is an ion-pair complex with one six-coordinate iron center and one four-coordinate iron center. These metal coordinative complexes, activated by modified methylaluminoxane (MMAO), lead to highly active ethylene polymerization and/or oligomerization catalysts. The catalyst productivity and product properties crucially depended on the metal center and the halogen substituents on the aryl rings. The catalyst productivities are in the range of (0-73.0) × 10⁶ g/mol of cat·h. The species 11, having ion-pair structure, is inactive. In particular, the product molar masses were changed from high molar mass (M_w of 377 000) to low molar mass oligomers by varying the halogen substituents. NMR and thermal analyses reveal the polymer is highly linear. The oligomer products follow a Schulz-Flory distribution with high selectivity for linear α-olefins. The effects of reaction condition on the polymerization and oligomerization have also been studied.

Full text of DOI:10.1021/om0302894

4312
Organometallics 2003, 22, 4312-4321
Ha logen -Su bstitu ted 2,6-Bis(im in o)p yr id yl Ir on a n d
Coba lt Com p lexes: High ly Active Ca ta lysts for
P olym er iza tion a n d Oligom er iza tion of Eth ylen e
Yaofeng Chen,† Ruifang Chen,† Changtao Qian,*,† Xicheng Dong,‡ and J ie Sun†
State Key Laboratory of Organometallic Chemistry, and Laboratory of Computer Chemistry,
Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road,
Shanghai 200032, China
Received April 22, 2003
A series of halogen-substituted 2,6-bis(imino)pyridyl ligands and their iron and cobalt
complexes [{2,6-(2,6-X1X2C6H3NdCCH3)2C5H3N}MCl2] (X1 ) X2 ) Br, M ) Fe (1), Co (2); X1
) X2 ) Cl, M ) Fe (3), Co (4); X1 ) Cl, X2 ) H, M ) Fe (5), Co (6); X1 ) Br, X2 ) H, M ) Fe
(7), Co (8); X1 ) I, X2 ) H, M ) Fe (9), Co (10)) and [M{2,6-(2,6-X1X2C6H3NdCCH3)2C5H3N}2]2+-
[MCl4]2- (X1 ) F, X2 ) H, M ) Fe (11)) have been synthesized. The molecular structures of
complexes 1, 8, 9, 10, and 11 were determined by X-ray diffraction. Crystallographic analyses
indicate that 1, 8, 9, and 10 are five-coordinate complexes, while 11 is an ion-pair complex
with one six-coordinate iron center and one four-coordinate iron center. These metal
coordinative complexes, activated by modified methylaluminoxane (MMAO), lead to highly
active ethylene polymerization and/or oligomerization catalysts. The catalyst productivity
and product properties crucially depended on the metal center and the halogen substituents
on the aryl rings. The catalyst productivities are in the range of (0-73.0) × 106 g/mol of
cat‚h. The species 11, having ion-pair structure, is inactive. In particular, the product molar
masses were changed from high molar mass (Mw of 377 000) to low molar mass oligomers
by varying the halogen substituents. NMR and thermal analyses reveal the polymer is highly
linear. The oligomer products follow a Schulz-Flory distribution with high selectivity for
linear R-olefins. The effects of reaction condition on the polymerization and oligomerization
have also been studied.
1. In tr od u ction
oligomerization12-18 have been synthesized. Due to the
huge commerical value of HDPE and linear R-olefins,
exploring new ethylene polymerization and oligomer-
ization catalysts aimed at controlling the product prop-
erties and reducing the product cost is still of topical
interest. Recently, a new class of iron and cobalt
complexes bearing bis(imino) pyridyl ligands was re-
ported by Brookhart19-21 and Gibson.22 These iron and
Polyethylene (PE) is a very important industrial
plastic material, with more than 100 billion pounds of
polyethylene produced every year.1 Among them, the
production of high-density polyethylene (HDPE) pre-
pared using catalytic ethylene polymerization contrib-
utes over 40 billion pounds. Linear R-olefins are versa-
tile chemical intermediates for a wide range of industrial
and consumer products. The major use of linear R-ole-
fins is polyethylene comonomer, surfactants, and lubri-
cants. Oligomerization of ethylene is currently the
primary resource of linear R-olefins. Since Ziegler’s
original work in TiCl4/AlR3-catalyzed ethylene polym-
erization and AlR3-catalyzed ethylene oligomerization,
many catalysts for ethylene polymerization2-11 and
(8) Younkin, T. R.; Connor, E. F.; Henderson, J . I.; Friedrich, S. K.;
Grubbs, R. H.; Bansleben, D. A. Science 2000, 287, 460.
(9) J ohnson, L. K.; Killian, C. M.; Brookhart, M. J . Am. Chem. Soc.
1995, 117, 6414.
(10) Britovsek, G. P. J .; Gibson, V. C.; Wass, D. F. Angew. Chem.,
Int. Ed. 1999, 38, 428.
(11) Matsui, S.; Mitani, M.; Saito, J .; Tohi, Y.; Makio, H.; Mat-
sukawa, N.; Takagi, Y.; Tsuru, K.; Nitabaru, M.; Nakano, T.; Tanaka,
H.; Kashiwa, N.; Fujita, T. J . Am. Chem. Soc. 2001, 123, 6847.
(12) Keim, W. Angew. Chem., Int. Ed. Engl. 1990, 29, 235.
(13) Cavell, K. J . Aust. J . Chem. 1994, 47, 769.
(14) Killian, C. M.; J ohnson, L. K.; Brookhart, M. Organometallics
1997, 16, 2005.
(15) Komon, Z. J . A.; Bu, X.; Bazan, G. C. J . Am. Chem. Soc. 2000,
122, 12379.
(16) Byrikhina, N. A.; Pechatnikos, E. L. J . Appl. Chem. 1986, 59,
332.
(17) Briggs, J . R. Chem. Commun. 1989, 674.
(18) Vogt, D. In Applied Homogeneous Catalysis with Organometallic
Compounds, Vol. 1; Cornils, B., Herrmann, W. A., Eds.; VCH: New
York, 1996; p 245.
(19) Small, B. L.; Brookhart, M. Polym. Prepr. (Am. Chem. Soc., Div.
Polym. Chem.) 1998, 39, 213.
* Corresponding author. E-mail: qianct@mail.sioc.ac.cn. Fax: 0086-
21-64166128.
† State Key Laboratory of Organometallic Chemistry.
‡ Laboratory of Computer Chemistry.
(1) Ittel, S. D.; J ohnson, L. K.; Brookhart, M. Chem. Rev. 2000, 100,
1169.
(2) J ordan, R. F. Adv. Organomet. Chem. 1991, 32, 325.
(3) Kaminsky, W.; Arndt, M. Adv. Polym. Sci. 1997, 127, 144.
(4) J eske, G.; Lauke, H.; Mauermann, H.; Swepstone, P. N.; Schu-
mann, H.; Marks, T. J . J . Am. Chem. Soc. 1985, 107, 8091.
(5) Van der Linder, A.; Schaverien, C. J .; Meijboom, N.; Ganter, C.;
Orpen, G. A. J . Am. Chem. Soc. 1995, 117, 3008.
(6) Scollard, J . D.; McConville, D. H.; Payne, N. C.; Vittal, J . J .
Macromolecules 1996, 29, 5241.
(20) Small, B. L.; Brookhart, M.; Bennett, A. M. A. J . Am. Chem.
Soc. 1998, 120, 4049.
(21) Small, B. L.; Brookhart, M. J . Am. Chem. Soc. 1998, 120, 7143.
(7) Baumann, R.; Davis, W. M.; Schrock, R. B. J . Am. Chem. Soc.
1997, 119, 3830.
10.1021/om0302894 CCC: $25.00 © 2003 American Chemical Society
Publication on Web 09/11/2003

Halogen-Substituted 2,6-Bis(imino)pyridyl Complexes
Organometallics, Vol. 22, No. 21, 2003 4313
Sch em e 1
cobalt complexes exhibit high activities in ethylene
polymerization and oligomerization. The product is
strictly linear polymer with high density. The oligomers
consist of g95% linear R-olefins. The product molar
mass is dependent on the size of alkyl substituents at
the ortho postion of imine aryl rings and ranges from
high molar mass to low molar mass oligomers.
polymerization and oligomerization using MMAO as
cocatalyst has shown that these iron and cobalt com-
plexes are very active for ethylene polymerization and
oligomerization, and the product molar masses are
closely dependent on the different halogen atoms as
substituents. Herein, we report our research results.
2. Resu lts a n d Discu ssion
Halogens are a family of interesting substituents. The
electronegativities decrease from fluorine to iodine with
the values of 4.0, 3.0, 2.8, and 2.5, respectively, while
the covalent radius (Å) increases in the same order:
0.72, 0.99, 1.14, and 1.33, respectively.23 The halogen
substituents lead to not only steric effects but also
electronic effects. Compared to the small difference in
electronic effect originating from changing the alkyl
groups, the electronic effect from varying halogens is
much more significant due to the large difference in
their electronegativities. The halogens are generally
electron-attracting, while the alkyls are electron-donat-
ing. Our previous results showed that difluoro-substi-
tuted 2,6-bis(imino)pyridyl iron complexes were very
highly active catalysts for ethylene oligomerization.24
Employing different halogens as the substituents on the
imine aryl rings in the catalysts and studying the
relationship between catalyst productivity, product
properties and halogen subsituents are expected to be
of interest. Nevertheless, to the best of our knowledge,
no such work has been published.25 Recently, we syn-
thesized a series of halogen-substituted 2,6-bis(imino)-
pyridyl ligands and their iron and cobalt complexes. The
investigation of their catalytic activities in ethylene
2.1. Syn th esis a n d Ch a r a cter iza tion of Liga n d s
a n d Cor r esp on d in g Meta l Com p lexes. The 2,6-bis-
(imino)pyridyl ligands with alkyl substituents at the
ortho position of aryl groups can be readily prepared
by condensation of the appropriate aniline with 2,6-
diacetylpyridine using formic acid (or glacial acetic acid)
as catalyst.20,21,26 However, these conditions are not
optimal for the preparation of 2,6-bis(imino)pyridyl
ligands with halogen substituents. The ligands L1 and
L2 were synthesized by the reaction of diketone with
the corresponding halogenated aniline in the presence
of a catalytic amount of p-toluene sulfonic acid in
toluene with removal of water by azeotropic distillation
(Scheme 1). Ligands L3-L6 were synthesized in satis-
factory yield (56-75%) in the presence of a catalytic
amount of silica-alumina catalyst support with molec-
ular sieves as the water adsorbent. This technique also
offers the advantages of mild reaction conditions and
use of much less solvent.27 Ligands L1-L6 were char-
(25) We applied for a China patent (CN 1322717) in J anuary 2001.
Basf Company promulgated a WO Patent (01/07491) in February 2001,
in which two halogen-substituted 2,6-bis(imino)pyridyl iron complexes,
2,6-bis-diacetylpyridinebis(2,6-dibrom-4-methylanil)FeCl2 and 2,6-bis-
diacetylpyridinebis(2,6-dichloroanil)FeCl2, appeared, but there was no
characterization of the complexes.
(26) Britovsek, G. J . P.; Bruce, M. S.; Gibson, V. C.; Kimberley, B.
S.; Maddox, P. J .; 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.
(22) Britovsek, G. P. J .; 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.
(23) Linus Pauling. The Nature of The Chemical Bond, 3rd ed.;
Carnell University Press: Ithaca, NY, 1973.
(24) Chen, Y.; Qian, C.; Sun, J . Organometallics 2003, 22, 1231.
(27) Qian, C.; Gao, F.; Chen, Y.; Gao, L. Synlett. (in press).

4314 Organometallics, Vol. 22, No. 21, 2003
Chen et al.
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Com p lexes 1, 8, 9, a n d 10
1 [M ) Fe] 8 [M ) Co] 9 [M ) Fe] 10 [M ) Co]
M-N(1)
M-N(2)
M-N(3)
M-Cl(1)
M-Cl(2)
C(6)-N(2)
C(8)-N(3)
N(1)-M-Cl(1) 146.3(3)
N(1)-M-Cl(2) 106.6(2)
Cl(1)-M-Cl(2) 107.0(1)
N(1)-M-N(2) 71.6(3)
N(1)-M-N(3) 72.3(3)
N(2)-M-N(3) 141.1(3)
Cl(1)-M-N(2) 95.8(2)
Cl(1)-M-N(3) 106.2(2)
Cl(2)-M-N(2) 105.4(2)
Cl(2)-M-N(3) 98.4(2)
2.120(8)
2.240(9)
2.230(8)
2.275(3)
2.307(4)
1.27(1)
2.022(5)
2.215(6)
2.217(6)
2.247(2)
2.2569(18) 2.292((4)
1.295(7)
1.285(8)
134.16(12) 127.8(3)
107.38(16) 113.8(3)
118.45(7) 118.27(16) 120.5(2)
75.3(3)
75.1(3)
150.0(3)
98.18(17) 103.3(3)
98.89(19) 96.2(3)
95.78(14) 95.8(3)
97.48(16) 97.3(3)
2.119(9)
2.189(11) 2.22(1)
2.210(11) 2.23(1)
2.04(1)
2.265(4)
2.247(5)
2.255(4)
1.250(13) 1.28(2)
1.271(17) 1.25(2)
1.29(1)
F igu r e 1. Molecular structure of ligand L1. Selected bond
lengths (Å) and angles (deg): N(2)-C(6) 1.284(7), N(3)-
C(8) 1.261(7); C(1)-C(6)-N(2) 116.5(6), C(5)-C(8)-N(3)
116.2(6), N(1)-C(1)-C(6) 114.6(5), N(1)-C(5)-C(8) 114.9.
132.9(3)
106.6(3)
73.8(4)
73.9(5)
147.8(4)
75.1(4)
74.6(4)
149.5(4)
97.8(3)
100.5(4)
94.9(3)
96.5(4)
acterized by elemental analysis, 1H NMR, IR, and mass
spectrometry. Ligand L1 was further characterized by
X-ray diffraction (Figure 1). It is observed that the
ligand L1 is in the (E, E) conformation with typical
1
imino CdN double bonds, 1.284(7) and 1.261(7) Å. H
NMR spectra of ligands L3-L6 indicate that the aryl
groups bearing only a single ortho substituent on each
aryl ring can rotate around the carbon-nitrogen bond
to interconvert syn and anti isomers.28
The corresponding iron and cobalt complexes were
synthesized by dissolving FeCl2‚4H2O or CoCl2 in tet-
rahydrofuran (THF) (Scheme 1), followed by addition
of the appropriate ligand. The iron and cobalt complexes
precipitated from the reaction solution. After washing
with diethyl ether, the complexes 1-11 were obtained
in good yield and high purity. The complexes were
characterized by elemental analyses and IR spectrom-
etry. The elemental analyses results reveal that the
components of all complexes are in accord with the
formula MLCl2, and in some cases one solvent molecule
of THF or water molecule is found in the complex. The
IR spectra of the free ligands show that the CdN
stretching frequencies appear in the range from 1634
to 1646 cm-1. For complexes 1-11, the CdN stretching
vibrations shift toward lower frequencies between 1614
and 1627 cm-1 and are greatly reduced in intensity,
which indicate the coordination interaction between the
imine nitrogen atoms and the metal center. Further
characterization of these complexes was difficult be-
cause of their poor solubility in organic solvents. For-
tunately, single crystals of complexes 1, 8, 9, 10, and
11 suitable for X-ray diffraction analysis were obtained
and characterized. The crystal structures of complexes
1, 9, and 10 (isomorphous with 8) are shown in Figures
2, 3, and 4, respectively, and selected bond lengths and
angles are listed in Table 1.
F igu r e 2. Molecular structure of complex 1.
As shown in Figure 2, the complex 1 possesses a
structure with approximate Cs symmetry about a plane
containing the iron atom, the two chloro atoms, and the
pyridyl nitrogen atom. One dibromophenyl ring lies
almost perpendicular (81.9°) to the plane formed by the
coordinated nitrogen atoms, while the other dibro-
mophenyl ring forms a dihedral angle of 69.4° with the
plane. The iron atom deviates 0.40 Å from this coordi-
nated plane. The geometry at the iron center can be
better described as distorted square pyramidal (Figure
5). The Fe-Cl(2) bond length (2.307(4) Å) is longer than
that of Fe-Cl(1) (2.275(3) Å), which can be ascribed to
apical elongation in the square-pyramidal complex. The
F igu r e 3. Molecular structure of the dominant conforma-
tion present in the crystals of 9 (one THF molecule in the
lattice is not included).
two N(1)-M-Cl angles are unsymmetrical; one is 146.3-
(3)°, while the other is 106.6(2)°.
The solid-state structures of the complexes with only
one ortho substituent on the imine aryls are observed
to be disordered with “up” or “down” orientation of the
aryl rings. The dominant conformation of the complexes
9 (ca. 85%) displays C2 symmetry about a plane con-
taining the iron atom, the two chloro groups, and the
pyridyl nitrogen atom. However, the dominant conform-
ers of the complexes 8 (ca. 80%) and 10 (ca. 70%) are
isomorphous (Figure 3), both having approximate Cs
(28) Gates, D. P.; Svejda, S. A.; On˜ate, E.; Killian, C. M.; J ohnson,
L. K.; White, P. S.; Brookhart, M. Macromolecules 2000, 33, 2320.

Halogen-Substituted 2,6-Bis(imino)pyridyl Complexes
Organometallics, Vol. 22, No. 21, 2003 4315
F igu r e 4. Molecular structure of the dominant conforma-
tion present in the crystals of 10 (that of the bromine-
substituted analogue 8 is isomorphous, and one THF
molecule in the lattice is not included).
F igu r e 7. Molecular structure of complex 11 (one water
molecule in the lattice is not included). Selected bond
lengths (Å) and angles (deg): Fe(1)-N(1) 1.863(8), Fe(1)-
N(2) 1.968(7), Fe(1)-N(3) 1.995(7), Fe(1)-N(4) 1.844(8), Fe-
(1)-N(5) 1.952(6), Fe(1)-N(6) 1.979(7), Fe(2)-Cl(1) 2.295-
(3), Fe(2)-Cl(2) 2.302(3), Fe(2)-Cl(3) 2.303(4), Fe(2)-Cl(4)
2.313(3); N(1)-Fe(1)-N(2) 79.9(3), N(1)-Fe(1)-N(3) 81.6-
(3), N(2)-Fe(1)-N(3) 161.5(4), N(4)-Fe(1)-N(5) 78.9(3),
N(4)-Fe(1)-N(6) 79.6(3), N(5)-Fe(1)-N(6) 158.4(4), N(4)-
Fe(1)-N(1) 176.8(2).
F igu r e 5. Coordination geometry of complex 1.
118.27(16)° in 9, 120.5(2)° in 10) and much larger than
the value of 107.0(1)° for complex 1. The N(1)-M-Cl
angles of complex 9 (127.8(3)° and 113.8(3)°) are differ-
ent from those in complexes 8 (134.16(12)° and 107.38-
(16)°) and 10 (132.9(3)° and 106.6(3)°). It is worth noting
that the N(1)-M-Cl angle on the same side as the
halide substituents (134.16(12)° in 8 and 132.9(3)° in
10) is much larger than the other N(1)-M-Cl angle
(107.38(16)° in 8 and 106.6(3)° in 10).
The X-ray diffraction analysis indicates that complex
11 exists as an ion pair comprised of [FeL2]2+ and
[FeCl4]2- (Figure 7). In the cation, the iron atom is
coordinated by six nitrogen atoms from two ligands, and
its coordination geometry at the iron center of [FeL2]2+
can be described as distorted octahedron. The Fe-
N(imino) bonds and Fe-N(pyridyl) bonds are shorter
than those in the complexes 1, 9, and other reported
five-coordinate iron complexes by 0.2-0.3 Å26,29 and
comparable to those in the six-coordinate iron complexes
with a similar type of ligand.30 The geometry at the iron
center of [FeCl4]2- can be described as a distorted
tetrahedron with Fe-Cl distances of 2.295(3)-2.313(3)
Å and Cl-Fe-Cl angles of 101.21(8)-115.82(15)°. There
is one molecule of water in the lattice, which is not
coordinated with the metal ion.
F igu r e 6. Coordination geometry of complex 9 (those of
complexes 8 and 10 are isomorphous).
symmetry (Figure 4). The deviations of the metal ion
from the plane formed by the coordinated nitrogen
atoms in 8, 9, and 10, 0.006, 0.080, and 0.006 Å,
respectively, are much less than that in 1. As shown in
Figure 6, the geometry at the metal center in these three
complexes can be described as distorted trigonal bipy-
ramidal with the equatorial plane formed by the pyridyl
nitrogen atom, the two chloro ligands, and the two axial
Fe-N bonds (Figure 6). The metal ions lie only 0.013,
0.041, and 0.025 Å out of the equatorial plane in 8, 9,
and 10, respectively. The Cl(1)-M-Cl(2) angles are very
similar for these three complexes (118.45(7)° in 8,
(29) 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.
(30) Scheer, C.; Chautemps, P.; Gautier-Luneau, I.; Pierre, J .;
Serratrice, G. Polyhedron 1996, 15, 219.

4316 Organometallics, Vol. 22, No. 21, 2003
Ta ble 2. Eth ylen e P olym er iza tion Resu lts fr om Com p lexes 1-4 a n d 12/MMAOa
Chen et al.
temp
(°C)
Al/M
(mol/mol)
yield
(g)
activity
mp
(°C)
run
complex
(106g/mol of cat‚h)
Mw
Mn
Mw/Mn
1
2
3
4
5
6
7
8
9
1
1
2
3
4
0
40
0
0
0
0
0
15
15
1250
1250
1250
1250
1250
2500
2500
1500
1500
3.44
2.73
0.25
5.13
0.47
4.87
2.16
28.8
29.2
8.6
6.8
0.6
12.8
1.2
12.2
5.4
101 000
52 300
12 200
13 300
370
65 100
144 000
377 000
27 700
1860
1570
3580
2570
320
1350
1380
14300
7650
54.3
33.3
3.41
5.18
1.15
48.2
104.3
26.4
3.62
128
129
128
1
12b
1c
3c
72.0
73.0
133
132
a
b
Toluene solvent 50 mL, 1 atm of ethylene, reaction time 0.5 h, cat. 0.8 µmol. Precatalyst 2,6-bis-diacetylpyridinebis(2,6-
diisopropylanil)FeCl2 (12) was prepared according to the literature.20 c Toluene solvent 500 mL, 6 atm of ethylene, triisobutylaluminum
scavenger, reaction time 0.5 h, cat. 0.8 µmol.
Ta ble 3. Resu lts of Oligom er iza tion of Eth ylen e w ith Com p lexes 5-11 a n d 13/MMAO
complex
(µmol)
toluene
(mL)
Al/M
(mol/mol)
temp
(°C)
press.
(atm)
time
(min)
yield
(g)
activity
linear R-olefin
run
(10 6g/mol of cat‚h)
R
(%)
1
2
3
4
5
6
7
8
13a (0.8)
13a (1)
5 (0.8)
5 (1)
5 (1)
6 (2)
7 (0.8)
7 (2)
8 (2)
9 (2)
9 (2)
50
150
50
150
150
150
50
150
150
50
150
150
150
150
1250
2000
1250
2000
2000
1500
1250
1500
1500
1250
1500
1500
1500
1500
0
60
0
40
60
60
0
60
60
0
60
60
60
60
1
10
1
10
10
10
1
10
10
1
10
10
10
10
30
60
30
60
60
60
30
60
60
30
60
60
25
40
0.32
38.4
2.4
25.3
51.9
0.08
38.4
6.0
25.3
51.9
inactive
4.3
29.5
inactive
0.70
0.42
0.69
0.70
0.59
>91
>98
>94
>98
>98
1.7
58.1
0.83
0.63
>94
>98
9
10
11
12
13
14
trace
18.5
9.3
0.67
>98
10 (2)
11 (1)
11 (1)
inactive
inactive
inactive
a
2,6-Bis-diacetylpyridinebis(2,6-difluoroanil)FeCl2 (13).
2.2. Eth ylen e P olym er iza tion a n d Oligom er iza -
tion . Ethylene polymerization and oligomerization cata-
lyzed by these iron and cobalt coordination complexes
using modified methylaluminoxane (MMAO) as cocata-
lyst have been systematically investigated. The results
are listed in Tables 2 and 3.
positions are very close, -0.2859 and -0.2854, respec-
tively. The charge on the iron center in the chloro-
substituted complex 3 (-0.2354) is more positive than
that in the bromo-substituted complex 1 (-0.2502), and
compared with the complexes with alkyl substitutes, the
halogen-substituted complexes 3 and 1 have relatively
more positive iron centers. When the ortho positions of
the aryl rings of the ligand are filled by fluoro groups,
the corresponding complex 13 generates oligomer in-
stead of polymer (Table 3, runs 1 and 2).24 The small
size and strong electron-withdrawing nature of the
fluoro group are responsible for the small R value. The
atomic (Mulliken) charge on the iron in complex 13 with
fluoro substiuents is -0.1862, which is comparable to
that in the complex with -CF3 substituents, -0.1813.
The cobalt complexes show the same trends as iron
complexes, with higher activity and lower molar mass
product for chloro-subsituted complexes than those of
bromo-subsituted complexes, although their activities
are much lower than those of the iron analogues.
Compared with 1 and 3, in which both ortho positions
of the aryl rings are substituted by bromo and chloro
groups, respectively, the iron complexes with only one
ortho substituent on the aryl rings, 5 and 7, show lower
activity and provide much lower molar mass products
in the ethylene polymerization. The distribution of
oligomers obtained by 5 and 7 follows Schulz-Flory
2.2.1. Su bstitu en t Effects of Ar yl Rin g on Ca ta -
lyst Activity a n d P r od u ct P r op er ties. Ligand envi-
ronment has a great influence on the catalyst behaviors,
such as activity and product properties. The iron
complexes bearing a 2,6-bis(imino)pyridyl ligand with
bromo (1) and chloro (3) substituents at both ortho
positions of the aryl rings, respectively, activated with
MMAO produce high molar mass polyethylene. The
molar mass is strictly substituent dependent; the molar
mass Mw decreases from 101 000 generated by bromo-
substituted iron complex 1 to 13 300 by the chloro-
substituted iron complex 3 under the conditions of 0 °C,
1 atm ethylene pressure, and 1250 Al/Fe molar ratio.
Complex 3 shows higher activity than that of 1: 12.8 ×
106 g/mol of cat‚h for 3 vs 8.6 × 106 g/mol of cat‚h for 1.
Complex 1 is more active in ethylene polymerization
(12.2 × 106 g/mol of cat‚h) than the corresponding
isopropyl-substituted iron complex 1220,22,26 (5.4 × 106
g/mol of cat‚h) reported by Brookhart and Gibson under
identical conditions of 0 °C, 1 atm, and Al/Fe molar ratio
2500. The electron-withdrawing nature of chloro and
bromo substituents, which results in a more electro-
philic iron center in the complexes, may increase the
corresponding activity in the ethylene polymerization.
The semiempirical calculation31 indicates the atomic
(Mulliken) charges on the irons in the complexes with
isopropyl or methyl substituents in both ortho aryl
(31) Semiempirical PM3 calculations were carried out on complexes
8, 10, 12, 21, a complex with -CH3 substituents in both ortho aryl
positions, and a complex with -CF3 substituents in both ortho aryl
positions. Their geometries were fully optimized for the quintet state
of each compound,26,29 using the standard procedure with conventional
gradient techniques. The atomic (Mulliken) charge on the iron atom
was thus obtained.

Halogen-Substituted 2,6-Bis(imino)pyridyl Complexes
Organometallics, Vol. 22, No. 21, 2003 4317
Ta ble 4. Effects of Al/F e Mola r Ra tio on Eth ylen e
P olym er iza tion w ith Com p lex 1a
rules, which can be characterized by a constant R, where
R represents the probability of chain propagation [R )
rate of propagation/(rate of propagation + rate of chain
transfer) ) mol of Cn+2/mol of Cn].32-36 The R value can
be determined by the molar ratio of C12 and C14
fractions. Under the conditions of 0 °C, 1 atm, and Al/
Fe molar ratio of 1250, the activities of mono ortho-
substituted complexes 5 and 7 (6.0 × 106 and 4.3 × 106
g/mol of cat‚h) are about half of the corresponding
double ortho-substituted complexes 3 (12.8 × 106 g/mol
of cat‚h) and 1 (8.6 × 106 g/mol of cat‚h). In addition,
the bromo-substituted complex 7 exhibits lower activity
than the chloro-substituted complex 5, but the molar
mass of products produced by 7 are higher than those
produced by 5. Similar trends are observed for these
complexes under other conditions, such as at 60 °C and
10 atm of ethylene pressure. Changing the substituents
to iodo groups, complex 9, results in a great decrease
in activity. The activity of 9 is too low to yield meaning-
ful product at 1 atm. When the ethylene pressure was
raised to 10 atm, the activity increases to 9.3 × 106 g/mol
of cat‚h with the oligomer’s R value of 0.67, which is
higher than the R values of oligomers generated by 5
(0.59) and 7 (0.63) under similar conditions. GC-MS
and GC analyses indicate that complexes 5, 7, and 9
produced linear R-olefins with a selectivity higher than
98% at 10 atm. Complex 11, containing the ligand with
only one fluoro group on the ortho aryl position, is found
to be inactive for ethylene oligomerization (Table 3, runs
13, 14), which is probably due to the ion-pair structure.
The iron complex bearing a bis(imino)pyridyl ligand
without substituents on either of the ortho aryl positions
is also prepared for comparison. It is inactive for
ethylene oligomerization, which may also be associated
with the ion-pair structure of the complex.37-39
2.2.2. Meta l Cen ter Effects on th e Ca ta lyst Ac-
tivity a n d P r od u ct P r op er ties. Similar to the obser-
vation in metal coordinative complexes with alkyl
substituents on the ortho positions of the aryl rings of
the ligands, the cobalt complexes show much lower
activity and yield product with lower molar mass than
their iron analogues. The activities of cobalt complexes
2 and 4 are approximately an order of magnitude less
active than those of their iron analogues 1 and 3. The
molar masses Mw of polyethylene generated from 2 and
4 dropped to 12 200 and 370, respectively, compared to
those for the corresponding iron anologues 1 (101 000)
and 3 (13 300). The cobalt complexes 6, 8, and 10 all
gave unsuccessful results in ethylene polymerization.
NMR analyses reveal that the iron and cobalt com-
plexes 1-4 generated highly linear polymers. The end
groups of polyethylene yielded from iron complexes are
mainly saturated end groups, whereas the cobalt com-
plexes generate polymers with unsaturated chain ends.
This is probably because of different chain transfer
mechanisms during the reaction. For the iron com-
plexes, matured polymer chains formed in the polym-
activity
Al/Fe
(106g/mol of
run (mol/mol) yield (g)
cat‚h)
Mw
Mn
Mw/Mn
1
2
3
4
250
1250
2500
5000
1.27
3.44
4.87
4.02
3.2
8.6
12.2
10.1
184 000 15 600 11.8
101 000
65 100
19 400
1860 54.3
1350 48.2
840 23.0
a
Toluene solvent 50 mL, 1 atm of ethylene, 0 °C, reaction time
0.5 h, cat. 0.8 µmol.
F igu r e 8. Effect of Al/Fe molar ratio on the molar masses
of polymers produced with complex 1. A: Al/Fe ) 250; B:
Al/Fe ) 1250; C: Al/Fe ) 2500; D: Al/Fe ) 5000.
erization mainly transfer to aluminum complexes; sub-
sequent quenches with ethanol generate saturated
polyethylene. For the cobalt complexes, â-H elimination
is the major factor in chain transfer, which gives
unsaturated polymer chain ends. The linearity was also
reflected in the thermal properties of the polymers. The
melting points are found to be in the range 128-133
°C for complexes 1-3 (Table 2, runs 1, 3, 4, 8, 9).
2.2.3. Effects of Rea ction Con d ition s on th e
Ca ta lyst Activity a n d P r od u ct P r op er ties. Effects
of Al/F e Mola r Ra tio. It has been found that Al/Fe
molar ratio has a significant effect on the ethylene
polymerization behavior for alkyl-substituted iron com-
plexes.20,26 The experiments were carried out to eluci-
date effects of Al/Fe molar ratio on ethylene polymeri-
zation using halogen-substituted iron complexes as
precatalysts activated with MMAO. Complex 1 was
selected as an example, and the Al/Fe values were
systematically varied from 250 to 5000. The results are
summarized in Table 4, and the curvatures of GPC
analyses are shown in Figure 8.
The molar mass distributions of the samples obtained
at different Al/Fe molar ratios are bimodal. Raising the
Al/Fe molar ratio results in an increase of the lower
molar mass fraction. For example, the lower molar mass
fraction of about 50% of the sample obtained at an Al/
Fe molar ratio of 250 increases to 60% at an Al/Fe of
1250 and 75% at an Al/Fe of 2500. Raising the Al/Fe
molar ratio to 5000, the lower molar mass fraction is
most prominent, accounting for over 90% of the sample.
It is also found that the average polymer molar mass
of the lower molar mass fraction decreases with increas-
ing Al/Fe molar ratio. These evidenced that the molec-
ular chains transferred to the aluminum complexes
during the polymerization and the higher Al/Fe value
increase the rate of chain transfer to the Al complex.
When the polymerization is quenched, it gives the satu-
rated polymer product. This is in good agreement with
polymer analysis results disscussed in section 2.2.2.
(32) Svejda, S. A.; Brookhart, M. Organometallics 1999, 18, 65.
(33) Schulz, G. V. Z. Phys. Chem., Abt. B. 1935, 30, 379.
(34) Schulz, G. V. Z. Phys. Chem., Abt. B. 1939, 43, 25.
(35) Flory, P. J . J . Am. Chem. Soc. 1940, 62, 1561.
(36) Henrici-Olive´, G.; Olive´, S. Adv. Polym. Sci. 1974, 15, 1.
(37) Curry, J . D.; Robinson, M. A.; Busch, D. H. Inorg. Chem. 1967,
6, 1570.
(38) Figgins, P. E.; Busch, D. H. J . Am. Chem. Soc. 1960, 82, 820.
(39) Lions, F.; Martin, K. V. J . Am. Chem. Soc. 1957, 79, 2733.

4318 Organometallics, Vol. 22, No. 21, 2003
Chen et al.
Ta ble 5. Effects of Eth ylen e P r essu r e on
P olym er iza tion w ith Com p lex 2a
pressure, while the molar mass and molar mass distri-
bution of polymers remain essentially invariant. These
results suggest that both chain propagation and chain
transfer increase equally with ethylene pressure. The
different effects of ethylene pressure on the molar mass
of polymers observed using iron complex 1 and cobalt
complex 2 as precatalysts are due to the different chain
transfer mechanisms during the reaction. For the iron
complex, the chain transfer to aluminum is the main
chain transfer process, at least at lower pressure and
higher Al/Fe molar ratio. But for the cobalt complex,
the â-H transfer to the monomer is the major chain
transfer process. The different chain transfer mecha-
nism is also reflected in the polymer structure: the end
groups of the polymers generated from iron complexes
are mainly saturated end groups, whereas for polymers
generated from the cobalt complexes, the ratio of vinyl
end groups to methyl groups is approximately 1:1.
pressure yield
activity
run
(atm)
(g)
(106g/mol of cat‚h) Mw
Mn Mw/Mn
1
2
3
4
8
12
1.00
1.67
2.07
3.33
5.57
6.90
5100 2080
5190 2090
5300 2060
2.46
2.49
2.57
a
Toluene solvent 200 mL, Al/Co molar ratio of 1000, 25 °C,
reaction time 20 min, cat. 1 µmol.
Tem p er a tu r e Effects on th e P olym er iza tion . It
is well known that temperature has great effects on
olefin polymerization, particularly on catalyst activity
and polymer molar mass. For example, molar mass Mw
of polymer generated by 1 drops from 101 000 at 0 °C
(Table 2, run 1) to 52 300 at 40 °C (Table 2, run 2). The
variation of molar mass with reaction temperature
suggests an increase in the rate of chain transfer
relative to the rate of propagation. In general, the
reaction temperature will increase the catalyst activity
in polymerization. However, for 1 the catalytic activity
drops from 8.6 × 106 g/mol of cat‚h to 6.8 × 106 g/mol of
cat‚h when the temperature increases from 0 °C (Table
2, run 1) to 40 °C (Table 2, run 2). The decrease in
activity with increasing reaction temperature is mainly
caused by catalyst decomposition and lower ethylene
solubility at higher temperature.26
Eth ylen e P r essu r e Effects on th e P olym er iza -
tion . For iron complexes 1 and 3, increasing the
monomer pressure results in increases in activity and
molar mass of polymers. At 6 atm, the activity of
complex 1 increases to 72.0 × 106 g/mol of cat‚h and
Mw of the polyethylene obtained is up to 377 000 (Table
2 run 8). Complex 3 shows an activity of 73.0 × 106
g/mol of cat‚h with the polyethylene molar mass Mw of
27 700 (Table 2 run 9). The pressure dependence of the
molar mass is associated with chain propagation, alu-
minum chain transfer, and â-H transfer. For iron
complexes, the aluminum chain transfer is an important
chain transfer process. When the polymerization tests
were carried out at 1 atm and Al/Fe molar ratio > 1250,
aluminum chain transfer became the dominant process
(see section 2.2.3). The increase of ethylene pressure
results in an increase in rate of propagation and also
the rate of the â-H transfer process but not the rate of
aluminum chain transfer. Therefore, the rate of propa-
gation relative to the rate of chain transfer (the rate of
chain transfer ) the rate of â-H transfer + the rate of
aluminum chain transfer) increases with the ethylene
pressure and is responsible for the higher molar mass
of polymers at higher pressure.
3. Su m m a r y
Six new halogen-substituted 2,6-bis(imino)pyridyl
ligands have been synthesized. Reactions of these
halogen-substituted 2,6-bis(imino)pyridyl ligands with
MCl2‚nH2O (M ) Fe, n ) 4; M ) Co, n ) 0) provided
two types of complexes: five-coordinate complex and
ion-pair complex, which is dependent on the halogen
substitutents. On treatment with MMAO, all the five-
coordinate iron complexes are very active for ethylene
polymerization and oligomerization, while the ion-pair
complex is inactive. The catalyst productivity and
product properties are strictly substituent dependent.
The molar mass of the product can be easily changed
from high molar mass polymers to very low molar mass
oligomers by using different halogen atoms as substit-
uents.
4. Exp er im en ta l Section
4.1. Gen er a l P r oced u r es. All manipulations of air- and/
or moisture-sensitive compounds were performed under an
1
atmosphere of argon using standard Schlenk techniques. H
NMR and 13C NMR were recorded on Bruker Am-300 or
Varian XL-300 MHz spectrometers. Mass spectra were carried
out with a HP5989A spectrometer. IR spectra were recorded
using Perkin-Elmer 983 or Nicolet AV-360 spectrometers.
Elemental analyses were performed by the Analytical Labora-
tory of the Shanghai Institute of Organic Chemistry. Oligomer
products were analyzed by Varian CP-3800 GC and Finnigan
MD-800 GC-MS. The Varian CP-3800 GC was equipped with
an SPB-5 capillary column (30 m × 0.32 mm) and a flame
ionization detector. The analytic conditions used were as
follows: injector and detector temperature, 280 °C; oven
temperature program, 40 °C/6 min, 10 °C/min ramp, 250 °C/
15 min. C6 olefin isomer was used in determining the percent-
age of linear R-olefins. 1H NMR and 13C NMR spectra of
polyethylene were taken in 1,2-dichlorobenzene-d4 at 100 or
135 °C. High-temperature gel permeation chromatography
(GPC) was performed on PL-GPC 220 in 1,2,4-trichlorobenzene
at 135 °C using polystyrene calibration. Melting temperatures
of preheated samples were determined by differential scanning
calorimetry (DSC) with a Perkin-Elmer pryris at a heating rate
of 10 °C/min. 2,6-Diacetylpyridine40 and 2,6-bis-diacetylpyri-
dine bis(2,6-diisopropylanil)FeCl2 (12)20 were prepared accord-
ing to published procedures. 2-Iodoaniline was purchased from
Acros and purified by recrystallization from petroleum ether.
It is different from iron complexes; there are two
observations about the effects of ethylene pressure on
polymerization with cobalt complexes. One is that the
activity of cobalt complexes increases with ethylene
pressure;26 the other is that the activity of cobalt
precatalyst does not change markedly with ethylene
pressure.1 To clarify the effects of ethylene pressure on
polymerization catalyzed by halogen-substituted cobalt
complexes, the experiments were carried out using
cobalt complex 2 as precatalyst in the ethylene polym-
erization. Results with different ethylene pressure from
4 to 12 atm are listed in Table 5. The results show that
the activity of ethylene polymerization catalyzed by
cobalt complex 2 increases with increasing ethylene
(40) Alyes, E. C.; Merrel, P. H. Synth. React. Inorg. Metal-Org. Chem.
1974, 4, 53510.

Halogen-Substituted 2,6-Bis(imino)pyridyl Complexes
Organometallics, Vol. 22, No. 21, 2003 4319
Other anilines were purchased from TCL, Acros Organics, or
Aldrich Chemical Co. and used as received. Silica-alumina
catalyst support (grade 135) was purchased from Aldrich
Chemical Co. Modified methylaluminoxane (MMAO) was
purchased from Akzo Nobel. Tetrahydrofuran was degassed
to remove oxygen prior to use. Toluene used as solvent in
polymerization or oligomerization was distilled under argon
over sodium-benzophenone.
2,6-Dia ctylp yr id in ebis(2-br om oa n il) (L5). Using a pro-
cedure analogous to that used for the synthesis of L3, L5 was
obtained as a yellow powder in 75% yield. 1H NMR (300 MHz,
CDCl3): δ 8.47 (d, 2H, J ) 7.7 Hz, Py-Hm); 7.94 (t, 1H, J )
7.7 Hz, Py-Hp); 7.62 (dd, 2H, J ) 8.0 Hz, Ar-H); 7.34 (pseudo
t, 2H, J ) 7.6 Hz, Ar-H); 7.01 (pseudo t, 2H, J ) 7.6 Hz, Ar-
H); 6.85 (dd, 2H, J ) 7.9 Hz, Ar-H); 2.38 (s, 6H, NdCMe). IR
(KBr): 1634 (νCdN), 1574, 1430, 1360, 1252, 1220, 1025, 816,
770, 754, 734 cm-1. EI-MS: m/z 469 [M+]. Anal. (C21H17N3-
Br2) Calcd: C, 53.53; H, 3.64; N, 8.92. Found: C, 53.66; H,
3.65; N, 8.88.
4.2. Syn th esis of Liga n d s. 2,6-Dia cetylp yr id in ebis(2,6-
d ibr om oa n il) (L1). A solution of 2,6-dibromoaniline (1.23 g,
5.0 mmol), 2,6-diacetylpyridine (0.41 g, 2.5 mmol), and p-
toluenesulfonic acid (0.020 g) in toluene (100 mL) was refluxed
for 24 h, with azeotropic removal of water using a Dean-Stark
trap. The mixture was cooled to room temperature, and the
solvent was removed under reduced pressure. The crude
product was dissolved in Et2O (100 mL), and the organic layer
was washed twice with water (50 mL) and once with saturated
NaCl solution (50 mL) and dried over MgSO4. The solvent was
removed under reduced pressure, and the crude product was
recrystallized from MeOH to give the desired product in 35%
2,6-Dia ctylp yr id in ebis(2-iod oa n il) (L6). Using a proce-
dure analogous to that used for the synthesis of L3, after 48
h, the reaction mixture was filtered and the molecular sieve
was washed with toluene several times. The toluene of the
filtrate was removed in vacuo. Petroleum ether (10 mL) was
added to the residue. A yellow solid formed, which was filtered
1
off to afford L6 in 64% yield. H NMR (300 MHz, CDCl3): δ
8.52 (d, 2H, J ) 7.5 Hz, Py-Hm); 7.96 (t, 1H, J ) 8.0 Hz, Py-
Hp); 7.90 (dd, 2H, J ) 7.8 Hz, Ar-H); 7.37 (pseudo t, 2H, J )
7.5 Hz, Ar-H); 6.85 (pseudo t, 2H, J ) 7.6 Hz, Ar-H); 6.80
(dd, 2H, J ) 7.8 Hz, Ar-H); 2.37 (s, 6H, NdCMe). IR (KBr):
1645 (νCdN), 1568, 1457, 1431, 1364, 1252, 1218, 1116, 1017,
830, 813, 772, 656 cm-1. EI MS: m/z 565 [M+]. Anal.
(C21H17N3I2) Calcd: C, 44.63; H, 3.03; N, 7.43. Found: C, 44.95;
H, 3.06; N, 7.30.
1
yield. H NMR (300 MHz, CDCl3): δ 8.55 (d, 2H, J ) 7.8 Hz,
Py-Hm); 7.97 (t, 1H, J ) 7.8 Hz, Py-Hp); 7.58 (d, 4H, J ) 8.0
Hz, Ar-H); 6.86 (t, 2H, J ) 8.0 Hz, Ar-H); 2.36 (s, 6H, Nd
CMe). IR (KBr): 1638(νCdN), 1565, 1546, 1450, 1426, 1366,
1323, 1304, 1259, 1222, 1198, 1143, 1123, 1076, 969, 881, 822,
824, 762, 769, 652 cm-1. EI-MS: m/z 625 [M+]. Anal. (C21H15N3-
Br4) Calcd: C, 40.06; H, 2.38; N, 6.68. Found: C, 40.47; H,
2.73; N, 6.37.
4.3. Syn th esis of Com p lexes. 2,6-Bis-d ia cetylp yr id in e-
bis(2,6-d ibr om oa n il)F eCl2 (1). Ligand L1 (191 mg, 0.30
mmol) was added to a solution of FeCl2‚4H2O (56 mg, 0.28
mmol) in THF (12 mL) at room temperature with rapid
stirring. The solution turned to deep blue immediately. The
dark blue product precipitated from the solution after several
minutes. After being stirred at room temperature for 12 h, the
reaction volume was reduced to about 6 mL. The reaction
mixture was allowed to stand at room temperature for several
hours, then the supernatant liquid was removed. The product
was washed with 4 × 5 mL of Et2O and dried in vacuo. The
desired product (0.170 mg) was obtained as a blue powder in
80% yield. IR (KBr): 1614(νCdN), 1587, 1555, 1429, 1371, 1265,
817, 771, 730 cm-1. Anal. (C21H15N3Br4FeCl2) Calcd: C, 33.37;
H, 2.00; N, 5.56. Found: C, 33.67; H, 2.14; N, 5.47.
2,6-Bis-d ia cetylp yr id in ebis(2,6-d ibr om oa n il)CoCl2 (2).
This golden brown complex was prepared as above in 80%
yield, using ligand L1 (397 mg, 0.63 mmol) and CoCl2 (82
mg,0.63 mmol). IR (KBr): 1617(νCdN), 1584, 1551, 1428, 1368,
1319, 1267, 1234, 1194, 1022, 824, 816, 769, 726 cm-1. Anal.
(C21H15N3Br4CoCl2) Calcd: C, 33.25; H, 1.98; N, 5.54. Found:
C, 33.18; H, 2.17; N, 5.58.
2,6-Bis-d ia cetylp yr id in ebis(2,6-d ich lor oa n il)F eCl2 (3).
This blue complex was prepared as above in 85% yield, using
ligand L2 (285 mg, 0.63 mmol) and FeCl2‚4H2O (125 mg, 0.63
mmol). IR (KBr): 1623(νCdN), 1583, 1558, 1435, 1373, 1267,
1235, 1099, 1023, 819, 793, 773 cm-1. Anal. (C21H15N3FeCl6)
Calcd: C, 43.60; H, 7.27; N, 2.60. Found: C, 43.76; H, 7.31;
N, 2.86.
2,6-Bis-d ia cetylp yr id in ebis(2,6-d ich lor oa n il)CoCl2 (4).
This golden brown complex was prepared as above in 80%
yield, using ligand L2 (285 mg, 0.63 mmol) and CoCl2 (82
mg,0.63 mmol). IR (KBr): 1626(νCdN), 1583, 1557, 1436, 1373,
1268, 1236, 1096, 1025, 820, 793, 773 cm-1. Anal. (C21H15N3-
CoCl6) Calcd: C, 43.45; H, 2.59; N, 7.24. Found: C, 43.13; H,
2.71; N, 7.21.
2,6-Bis-d ia cetylp yr id in ebis(2,6-d ich lor oa n il) (L2). A
solution of 2,6-dichloroaniline (0.79 g, 5.0 mmol), 2,6-di-
acetylpyridine (0.41 g, 2.5 mmol), and p-toluenesulfonic acid
(0.020 g) as well as 4 Å molecular sieves (0.5 g) in toluene (100
mL) was refluxed for 24 h, with azeotropic removal of water
using a Dean-Stark trap. The mixture was cooled to room
temperature, and the solvent was removed under reduced
pressure. Workup as above yielded the desired product in 40%
1
yield. H NMR (300 MHz, CDCl3): δ 8.52 (d, 2H, J ) 7.8 Hz,
Py-Hm); 7.95 (t, 1H, J ) 7.8 Hz, Py-Hp); 7.35 (d, 4H, J ) 8.0
Hz, Ar-H); 7.01 (t, 2H, J ) 8.0 Hz, Ar-H); 2.36 (s, 6H, Nd
CMe). IR (KBr): 1646 (νCdN), 1576, 1555, 1449, 1432, 1362,
1318, 1301, 1272, 1226, 1151, 1120, 1096, 997, 958, 917, 827,
789, 777, 752, 653 cm-1. EI-MS: m/z 449 [M+]. Anal. (C21H15N3-
Cl4) Calcd: C, 55.88; H, 3.33; N, 9.31. Found: C, 55.80; H,
3.47; N, 9.15.
2,6-Dia ctylp yr id in ebis(2-flu or oa n il) (L3). A solution of
2,6-diacetylpyridine (0.41 g, 2.5 mmol), 2-fluoroaniline (0.77
g, 6 mmol), silica-alumina catalyst support (0.2 g) and
molecular sieves 4 Å (1 g) in toluene (8 mL) was stirred at
30-40 °C for 24 h. The reaction mixture was filtered, and the
molecular sieve was washed with toluene several times. The
toluene of the combined filtrates was removed in vacuo.
Anhydrous methanol (5 mL) was added to the residue. L3 was
obtained as a yellow powder in 56% yield. 1H NMR (300 MHz,
CDCl3): δ 8.39 (d, 2H, J ) 8.0 Hz, Py-Hm); 7.90 (t, 1H, J )
7.9 Hz, Py-Hp); 7.19-7.10 (m, 6H, Ar-H); 7.08-6.91 (m, 2H,
Ar-H); 2.42 (s, 6H, NdCMe). IR (KBr): 1634(νCdN), 1601,
1575, 1482, 1364, 1236, 1194, 1123, 1102, 1079, 1031, 844, 825,
780, 760, 744 cm-1. EI-MS: m/z 349 [M+]. Anal. (C21H17N3F2)
Calcd: C, 72.19; H, 4.90; N, 12.03. Found: C, 71.88; H, 4.96;
N, 11.99.
2,6-Dia ctylp yr id in ebis(2-ch lor oa n il) (L4). Using a pro-
cedure analogous to that used for the synthesis of L3, L4 was
obtained as a yellow powder in 65% yield. 1H NMR (300 MHz,
CDCl3): δ 8.44 (d, 2H, J ) 8.0 Hz, Py-Hm); 7.94 (t, 1H, J )
7.8 Hz, Py-Hp); 7.43 (dd, 2H, J ) 8.0 Hz, Ar-H); 7.28 (pseudo
t, 2H, J ) 7.7 Hz, Ar-H); 7.07 (pseudo t, 2H, J ) 7.8 Hz, Ar-
H); 6.86 (dd, 2H, J ) 7.9 Hz, Ar-H); 2.38 (s, 6H, NdCMe). IR
(KBr): 1635 (νCdN), 1582, 1465, 1436, 1362, 1252, 1222, 1120,
1054, 1032, 816, 772, 756, 743, 735, 687 cm-1. EI-MS: m/z
381 [M+]. Anal. (C21H17N3Cl2) Calcd: C, 65.97; H, 4.48; N,
10.99. Found: C, 65.44; H, 4.69; N, 10.88.
2,6-Bis-d ia cetylp yr id in ebis(2-ch lor oa n il)F eCl2 (5). This
blue complex was prepared as above in 75% yield, using ligand
L4 (172 mg, 0.45 mmol) and FeCl2‚4H2O (80 mg, 0.40 mmol).
IR (KBr): 1623 (νCdN), 1587, 1470, 1440, 1373, 1262, 1228,
1060, 1033, 820, 778, 759, 745, 730, 688 cm-1. Anal. (C21H17N3-
Cl2FeCl2) Calcd: C, 49.55; H, 3.37; N, 8.25. Found: C, 49.76;
H, 3.96; N, 7.59.
2,6-Bis-d ia cetylp yr id in ebis(2-ch lor oa n il)CoCl2 (6). This
yellow-green complex was prepared as above in 85% yield,

4320 Organometallics, Vol. 22, No. 21, 2003
Chen et al.
Ta ble 6. Cr ysta llogr a p h ic Da ta a n d Refin em en t for Liga n d L1 a n d Com p lexes 1, 8, 9, 10, a n d 11
L1
1
8
9
10
11
formula
C
21H15 N3Br4 C21H15N3Br4FeCl2 C21H17N3Br2-
C21H17N3I2-FeCl2‚ C4H8O C21H17N3I2-
C42H34N6F4-
CoCl2‚ C4H8O
CoCl2‚ C4H8O Fe2Cl4‚ H2O
fw
629.00
755.74
673.13
764.03
767.14
970.27
color
cryst syst
space group
pale yellow
triclinic
P1h
dark blue
monoclinic
P2(1)/c
(No. 14)
12.793(6)
11.899(8)
16.909(9)
yellow-green
monoclinic
C2/c
dark blue
orthorhomic
P2(1)2(1)2(1)
(No. 19)
10.990(2)
15.509(3)
16.821(3)
yellow-green
monoclinic
C2/c
dark blue
hexagonal
P6(1)
(No. 169)
11.3198(4)
11.3198(4)
62.060(4)
(No. 2)
(No. 15)
(No. 15)
a, Å
b, Å
c, Å
7.9236(10)
11.5210(15)
12.6884(16)
90.566(2)
105.744(3)
79.878(2)
1096.6(2)
2
27.538(2)
12.9011(10)
16.6697(14)
27.960(6)
13.156(4)
16.621(3)
R, deg
â, deg
γ, deg
V, Å3
Z
99.23(4)
112.029(2)
111.73(1)
120.00
6886.8(5)
6
2540(2)
4
1.976
5489.9(8)
8
1.629
2867.0(9)
4
1.770
5679(2)
8
1.794
D
calcd, g/cm3
1.905
1.404
F(000)
604
7.352
1.7-28.2
1448
7.127
2.3-26.0
5494
5255
2493
2680
3.754
1.6-28.2
16 646
6417
1480
2.888
1.8-25.50
14 874
5339
2968
2.990
2.3-25.0
4996
4880
2004
2964
0.919
2.1-28.2
42 039
10026
µ(Mo Ka), mm-1
θ range, deg
no. of reflns collected 6764
no. of unique reflns
no. of obsd reflns
4890
1940
1501
1829
2980
(I >2σ(I))
(I >3σ(I))
(I >2σ(I))
(I >2σ(I))
(I >3σ(I))
(I >2σ(I))
no. of params
goodness of fit
256
281
327
307
276
502
0.766
0.063, 0.140
0.75, -1.31
1.85
0.057, 0.061
1.27, -1.12
0.621
0.049, 0.081
0.65, -0.52
0.773
0.058, 0.130
0.41, -0.39
1.70
0.061, 0.075
0.92, -0.75
0.699
0.056, 0.126
0.54, -0.40
a
final R, Rw
∆Fmax,min/e Å-3
using ligand L4 (57 mg, 0.15 mmol) and CoCl2 (19 mg, 0.15
mmol). IR (KBr): 1627 (νCdN), 1589, 1469, 1439, 1371, 1262,
1229, 1060, 1027, 819, 780, 757, 744, 729, 688 cm-1. Anal.
(C21H17N3Cl2CoCl2) Calcd: C, 49.25; H, 3.34; N, 8.20. Found:
C, 50.02; H, 3.71; N, 7.97.
2,6-Bis-diacetylpyr idin ebis(2-br om oan il)FeCl2‚THF (7).
This blue complex was prepared as above in 79% yield, using
ligand L5 (414 mg, 0.88 mmol) and FeCl2‚4H2O (161 mg, 0.81
mmol). IR (KBr): 1623 (νCdN), 1587, 1467, 1375, 1268, 1229,
1028, 816, 778, 759, 743 cm-1. Anal. (C21H17N3Br2FeCl2‚THF)
Calcd: C, 44.81; H, 3.45; N, 6.27. Found: C, 43.72; H, 3.54;
N, 6.27.
2,6-Bis-diacetylpyr idin ebis(2-br om oan il)CoCl2‚THF (8).
This yellow-green complex was prepared as above in 85% yield,
using ligand L5 (71 mg, 0.15 mmol) and CoCl2 (19 mg, 0.15
mmol). IR (KBr): 1627 (νCdN), 1588, 1466, 1366, 1261, 1228,
1027, 817, 774, 759, 744 cm-1. Anal. (C21H17N3Br2CoCl2‚THF)
Calcd: C, 44.61; H, 3.74; N, 6.24. Found: C, 44.54; H, 4.05;
N, 6.17.
2,6-Bis-d ia cetylp yr id in ebis(2-iod oa n il)F eCl2‚THF (9).
This dark blue complex was prepared as above in 85% yield,
using ligand L6 (72 mg, 0.13 mmol) and FeCl2‚4H2O (24 mg,
0.12 mmol). IR (KBr): 1620 (νCdN), 1586, 1457, 1432, 1370,
1263, 1225, 1017, 816, 774, 759, 738, 720 cm-1. Anal.
(C21H17N3I2FeCl2‚THF) Calcd: C, 39.30; H, 3.30; N, 5.50.
Found: C, 39.07; H, 3.18; N, 5.30.
dried Schlenk flask equipped with a stirrer bar was placed in
a water bath and purged with ethylene (1atm), followed by
charging with 40 mL of toluene and 1 mmol of MMAO. The
required temperature was ensured by stirring the mixture for
about 20 min in the water bath. A 0.8 µmol sample of
precatalyst in 10 mL of toluene was injected via syringe.
Polymerization time was measured from that point. After the
reaction mixture was stirred under 1 atm of ethylene pressure
for 0.5 h, the polymerization was stopped by injection of 2 mL
of methanol. The polymer was precipitated by pouring the
reaction mixture into large volume of acidified ethanol (0.5%
HCl), filtered, washed with ethanol, and then dried under
vacuum at 60 °C to a constant weight.
(b) High -P r essu r e P olym er iza tion . A 1 L stainless steel
reactor equipped with a mechanical stirrer was heated under
vacuum for at least 2 h over 85 °C, allowed to cool to the
required reaction temperature under ethylene atmosphere,
and charged with 450 mL of toluene and 0.15 mL of Al(iBu)3.
The reactor was sealed and pressurized to 5 atm of ethylene
pressure. Stirring for about 1 h ensured that the solution was
equilibrated and the required reaction temperature was
established. The ethylene pressure was then released. Then
1.2 mmol MMAO, 0.8 µmol precatalyst in toluene (10 mL), and
40 mL of toluene were added. The reactor was sealed and
pressurized to 6 atm of ethylene pressure. After the reaction
was carried out for 0.5 h, the pressure was released and 2 mL
of methanol was immediately injected to stop the reaction. The
reaction mixture was poured into a large amount of acidified
ethanol (0.5% HCl) to precipitate the resulting polymer. The
polymer was filtered, washed, and dried under vacuum at 60
°C to a constant weight.
2,6-Bis-d ia cetylp yr id in ebis(2-iod oa n il)CoCl2‚THF (10).
This yellow-green complex was prepared as above in 71% yield,
using ligand L6 (36 mg, 0.064 mmol) and CoCl2 (8 mg, 0.062
mmol). IR (KBr): 1625 (νCdN), 1588, 1459, 1432, 1364, 1260,
1226, 1017, 816, 774, 759, 742, 724 cm-1. Anal. (C21H17N3I2-
CoCl2‚THF) Calcd: C, 39.14; H, 3.28; N, 5.48. Found: C, 39.40;
H, 3.03; N, 5.37.
4.5. Gen er a l P r oced u r e for Eth ylen e Oligom er iza tion .
(a ) 1 a tm Oligom er iza tion . Similar to the procedure above
for the ethylene polymerization under 1 atm pressure, the
ethylene oligomerization was carried out under 1 atm of
ethylene pressure at the required temperature and quenched
by the injection of diluted hydrochloric acid. The organic layer
was separated and dried over anhydrous Na2SO4. An aliquot
of this solution was analyzed by GC to determine the content
of oligomers.
[F e(2,6-bis-d ia cetylp yr id in ebis(2-flu or oa n il))2]2+ [F e-
Cl4]2+‚H2O (11). This dark blue complex was prepared as
above in 84% yield, using ligand L3 (157 mg, 0.45 mmol) and
FeCl2‚4H2O (80 mg, 0.40 mmol). IR (KBr): 3448, 1625(νCdN),
1584, 1529, 1487, 1401, 1374, 1320, 1246, 1104, 808, 762 cm-1
.
(C42H34N6F4Fe2Cl4‚H2O) Calcd: C, 52.00; H, 3.73; N, 8.66.
Found: C, 52.63; H, 3.46; N, 8.13.
4.4. Gen er a l P r oced u r e for Eth ylen e P olym er iza tion .
(a ) Nor m a l P r essu r e P olym er iza tion . A 100 mL flame-
(b) High -P r essu r e Oligom er iza tion . The high pressure
of ethylene oligomerization method is similar to the high-

Halogen-Substituted 2,6-Bis(imino)pyridyl Complexes
Organometallics, Vol. 22, No. 21, 2003 4321
pressure ethylene polymerization. The oligomerization was
carried out in a 500 mL stainless steel reactor equipped with
mechanical stirrer under required conditions. The reaction was
terminated by the injection of diluted hydrochloric acid, and
the oligomer was collected and worked up as described as in
the oligomerization under 1 atm.
with graphite-monochromated Mo KR radiation (λ ) 0.71073
Å). The SMART program package was used to determine the
unit-cell parameters. A SADABS absorption correction was
applied, The structures were solved by direct methods and
refined on F2 by full-matrix least-squares techniques with
anisotropic thermal parameters for non-hydrogen atoms.
Hydrogen atoms were placed at the calculated positions and
were included in the structure calculation without further
refinement of the parameters. All calculations were carried
out using the SHELXS-97 program. Crystal data and process-
ing parameters for ligand L1 and complexes 1, 8, 9, 10, and
11 are summarized in Table 6.
4.6. X-r a y Cr ysta llogr a p h ic Stu d ies. Data for complexes
1 and 10 were collected at 20 °C on
a Rigaku AFC7R
diffractometer with graphite-monochromated Mo KR radiation
(λ ) 0.71069 Å). An empirical absorption correction based on
azimuthal scans of several reflections was applied. The data
were corrected for Lorentz-polarization effects. The structures
were solved by heavy-atom Patterson methods for 1 and direct
methods for 10, and expanded using Fourier techniques. The
nonhydrogen atoms were refined anisotropically by full-matrix
least squares. Hydrogen atoms were included but not refined.
Scattering factors were taken from ref 41. All calculations were
performed using the TEXSAN crystallographic software pack-
age.42
Ack n ow led gm en t. We are grateful to the Chinese
Academy of Science and the Nature Science Foundation
of China for financial support. We also thank Dr.
Fuquan Song of the University of Anglia and Prof. Lixin
Dai and Yong Tang of Shanghai Institute of Organic
Chemistry for their helpful discussions.
Data collections for ligand L1 and complexes 8, 9, and 11
were performed at 20 °C on a Bruker SMART diffractometer
Su p p or tin g In for m a tion Ava ila ble: X-ray crystallo-
graphic data for structure determination of L1, 1, 8, 9, 10,
and 11. This material is available free of charge via the
Internet at http://pubs.acs.org.
(41) Cromer, D. T.; Waber, J . T. International Tables for X-ray
Crystallography; Kynoch Press: Birmingham, 1974; Vol. 4, Table 2.2A.
(42) TEXSAN, Crystal Structure Analysis Package; Molecular
Structure Corporation: Houston, TX, 1985 and 1992.
OM0302894