Synthesis, characterization, and ethylene oligomerization and polymerization of ferrous and cobaltous 2-(ethylcarboxylato)-6-iminopyridyl complexes

Article abstract of DOI:10.1021/om0496636

A series of ferrous complexes (L)FeCl₂ (3a-f) and cobaltous complexes (L)CoCl₂ (4a-f) were prepared by the reaction of 2-(carboxylato)-6-iminopyridines 2a-f (2-COOEt-6-(2,6-R₂C ₆H₃N=CCH₃)C₅H₃N: 2a, R = CH₃; 2b, R = Et; 2c, R = i-Pr; 2d, R = F; 2e, R = Cl; 2f, R = Br) with FeCl₂ or Coda. The obtained complexes were characterized by elemental analysis and IR spectroscopy, and the solid-state structures of 2b,c, 3b,c,e,f, and 4c,f were determined by X-ray diffraction analysis. X-ray crystallographic analyses of complexes 3c,e,f and 4c,f reveal a four-coordinated distorted-tetrahedral geometry, except for complex 3b, in which the tridentate ligand is coordinated through a weak bonding between iron and the carbonyl oxygen of the ester group. The complexes were studied for ethylene oligomerization and polymerization in the presence of methylaluminoxane (MAO) under various reaction conditions. It was found that the ferrous complexes exhibit higher activities for ethylene polymerization than for oligomerization, while the cobaltous complexes show higher activities for ethylene oligomerization. In addition, the ferrous catalytic systems predominantly produce linear oligomers and polyethylene with unsaturated end groups.

Full text of DOI:10.1021/om0496636

Organometallics 2004, 23, 5037-5047
5037
Syn th esis, Ch a r a cter iza tion , a n d Eth ylen e
Oligom er iza tion a n d P olym er iza tion of F er r ou s a n d
Coba ltou s 2-(Eth ylca r boxyla to)-6-im in op yr id yl
Com p lexes
Wen-Hua Sun,* Xiubo Tang, Tielong Gao, Biao Wu, Wenjuan Zhang, and
Hongwei Ma
CAS Key Laboratory of Engineering Plastics, Institute of Chemistry, Chinese Academy of
Sciences, Beijing 100080, China, and State Key Laboratory of Structural Chemistry,
Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences,
Fuzhou 350002, China
Received May 12, 2004
A series of ferrous complexes (L)FeCl2 (3a -f) and cobaltous complexes (L)CoCl2 (4a -f)
were prepared by the reaction of 2-(carboxylato)-6-iminopyridines 2a -f (2-COOEt-6-(2,6-
R2C6H3NdCCH3)C5H3N: 2a , R ) CH3; 2b, R ) Et; 2c, R ) i-Pr; 2d , R ) F; 2e, R ) Cl; 2f,
R ) Br) with FeCl2 or CoCl2. The obtained complexes were characterized by elemental
analysis and IR spectroscopy, and the solid-state structures of 2b,c, 3b,c,e,f, and 4c,f were
determined by X-ray diffraction analysis. X-ray crystallographic analyses of complexes 3c,e,f
and 4c,f reveal a four-coordinated distorted-tetrahedral geometry, except for complex 3b,
in which the tridentate ligand is coordinated through a weak bonding between iron and the
carbonyl oxygen of the ester group. The complexes were studied for ethylene oligomerization
and polymerization in the presence of methylaluminoxane (MAO) under various reaction
conditions. It was found that the ferrous complexes exhibit higher activities for ethylene
polymerization than for oligomerization, while the cobaltous complexes show higher activities
for ethylene oligomerization. In addition, the ferrous catalytic systems predominantly produce
linear oligomers and polyethylene with unsaturated end groups.
In tr od u ction
and oligomerization by the SHOP process.5 Recently,
many academic and industrial research laboratories
have engaged in exploring unknown organometallic
precatalysts containing various philological [O-P],6
[O-N],7 [N-N],8 [N-P],9 and [N-N-N]10 ligands. Fol-
lowing the innovative finding of the highly active 2,6-
bis(imino)pyridyl catalysts, numerous investigations
have been conducted in search of the intermediates of
catalytic systems,11 in which the 2,6-bis(imino)pyridyl-
based ferrous and cobaltous catalysts were modified by
varying the substituent on the aryl group of the ligand.12
Unfortunately, these efforts failed to generate active
Research interest in late-transition-metal complex
catalysts for ethylene polymerization has undergone a
phenomenal acceleration over the past decade.1 The
late-transition-metal complex catalysts have long been
developed to produce dimers or low-molecular-weight
oligomers by chain termination via â-hydride elimina-
tion.2 As a milestone of late-transition-metal catalysts
for ethylene polymerization, the discovery of diimine-
based cationic catalysts3 and 2,6-bis(imino)pyridyl-based
cationic catalysts4 resurrected the late-transition-metal
complexes as the catalysts for ethylene polymerization
(5) (a) Keim, W.; Kowaldt, F. H.; Goddard, R.; Kruger, C. Angew.
Chem., Int. Ed. Engl. 1978, 17, 466-467. (b) Keim, W. Angew. Chem.,
Int. Ed. Engl. 1990, 29, 235-244.
* To whom correspondence should be addressed at the Chinese
Academy of Sciences.
(1) (a) Britovsek, G. J . P.; Gibson, V. C.; Wass, D. F. Angew. Chem.,
Int. Ed. 1999, 38, 428-447. (b) Ittel, S. D.; J ohnson, L. K.; Brookhart,
M. Chem. Rev. 2000, 100, 1169-1203. (c) Gibson, V. C.; Spitzmesser,
S. K. Chem. Rev. 2003, 103, 283-315.
(2) (a) Rix, F.; Brookhart, M. J . Am. Chem. Soc. 1995, 117, 1137-
1138. (b) Peuckert, M.; Keim, W. Organometallics 1983, 2, 594-597.
(c) Wilke, G. Angew. Chem., Int. Ed. Engl. 1988, 27, 185-206.
(3) (a) J ohnson, L. K.; Killian, C. M.; Brookhart, M. J . Am. Chem.
Soc. 1995, 117, 6414-6415. (b) J ohnson, L. K.; Mecking, S.; Brookhart,
M. J . Am. Chem. Soc. 1996, 118, 267-268. (c) Mecking, S.; J ohnson,
L. K.; Wang, L.; Brookhart, M. J . Am. Chem. Soc. 1998, 120, 888-
899. (d) Killian, C. M.; Tempel, D. J .; J ohnson, L. K.; Brookhart, M. J .
Am. Chem. Soc. 1996, 118, 11664-11665. (e) Feldman, J .; McLain, S.
J .; Parthasarathy, A.; Marshall, W. J .; Calabrese, J . C.; Arthur, S. D.
Organometallics 1997, 16, 1514-1516.
(6) (a) Komon, Z. J . A.; Bu, X.; Bazan, G. C. J . Am. Chem. Soc. 2000,
122, 1830-1831. (b) Komon, Z. J . A.; Bu, X.; Bazan, G. C. J . Am. Chem.
Soc. 2000, 122, 12379-12380. (c) Kalamarides, H. A.; Iyer, S.; Lipian,
J .; Rhodes, L. F.; Day, C. Organometallics 2000, 19, 3983-3990. (d)
Malinoski, J . M.; Brookhart, M. Organometallics 2003, 22, 5324-5335.
(7) (a) Younkin, T. R.; Connor, E. F.; Henderson, J . I.; Friedrich, S.
K.; Grubbs, R. H.; Bansleben, D. A. Science 2000, 287, 460-462. (b)
Hicks, F. A.; Brookhart, M. Organometallics 2001, 20, 3217-3219. (c)
Bauers, F. M.; Mecking, S. Angew. Chem., Int. Ed. 2001, 40, 3020-
3022. (d) Shim, C. B.; Kim, Y. H.; Lee, B. Y.; Dong, Y.; Yun, H.
Organometallics 2003, 22, 4272-4280. (e) Sun, W.-H.; Yang, H.; Li,
Z.; Li, Y. Organometallics 2003, 22, 3678-3683. (f) Wang, L.; Sun, W.-
H.; Han, L.; Li, Z.; Hu, Y.; He, C.; Yan, C. J . Organomet. Chem. 2002,
650, 59-64. (g) Sun, W.-H.; Zhang, W.; Gao, T.; Tang, X.; Chen, L.; Li,
Y.; J in, X. J . Organomet. Chem. 2004, 689, 917-929. (h) Chen, L.; Hou,
J .; Sun, W.-H. Appl. Catal. A 2003, 246, 11-16. (i) Shim, C. B.; Kim,
Y. H.; Lee, B. Y.; Dong, Y.; Yun, H. Organometallics 2003, 22, 4272-
4280. (j) Hicks, F. A.; J enkins, J . C.; Brookhart, M. Organometallics
2003, 22, 3533-3545.
(4) (a) Small, B. L.; Brookhart, M.; Bennett, A. M. A. J . Am. Chem.
Soc. 1998, 120, 4049-4050. (b) 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, 849-850.
10.1021/om0496636 CCC: $27.50 © 2004 American Chemical Society
Publication on Web 09/10/2004

5038 Organometallics, Vol. 23, No. 21, 2004
Sun et al.
catalysts, and the catalytic activities of these ferrous
and cobaltous complexes are disappointingly poor.13 In
the exploration of the scope of ferrous and cobaltous
complex catalysts for ethylene polymerization, it has
long been a goal to create ferrous catalysts which are
as active as the bidentate chelated nickel analogues.3,8
Indeed, the pyridylimine-based nickel and palladium14
complexes serve as the active catalysts for ethylene
polymerization, but the corresponding ferrous and co-
baltous analogues do not show any activity. Clearly, to
study iminopyridyl-based ferrous and cobaltous com-
plexes for ethylene polymerization, a synthetic protocol
for the preparation of the robust iminopyridyl ligands
must be developed. We have established the procedure
of synthesizing the ligands by preparing ethyl 6-acetylpy-
ridine-2-carboxylate, which further reacts with aryl-
amines to form 2-(carboxylato)-6-iminopyridine deriva-
tives. We prepared a variety of 2-(carboxylato)-6-imi-
nopyridine analogues with ortho-positioned alkyl and
halogen substituents on the aryl rings and subsequently
investigated the catalytic activities of their ferrous and
cobatous complexes for ethylene oligomerization and
polymerization. It was found that the asymmetric
iminopyridyl ferrous and cobaltous complexes prepared,
which are remarkably stable in air, exhibit high activi-
ties for ethylene polymerization and oligomerization.
Our studies have provided an insight into the effects of
the ligands on the ethylene oligomerization and polym-
erization behaviors of the complexes. In addition, the
incorporation of the ester group into the ligand backbone
has been found to affect the coordination environment
around the metal center. We report herein the synthesis
and characterization of 2-(carboxylato)-6-iminopyridine-
based ferrous and cobaltous complexes and the inves-
tigation of their catalytic behaviors for ethylene oligo-
merization and polymerization upon activation with
MAO.
(8) (a) Lee, B. Y.; Bazan, G. C.; Vela, J .; Komon, Z. J . A.; Bu, X. J .
Am. Chem. Soc. 2001, 123, 5352-5353. (b) Domhover, B.; Klaui, W.;
Kermer-Aach, A.; Bell, R.; Mootz, D. Angew. Chem., Int. Ed. 1998, 37,
3050-3052. (c) Li, J .; Gao, T.; Zhang, W.; Sun, W.-H. Inorg. Chem.
Commun. 2003, 6, 1372-1374. (d) Diamanti, S. J .; Ghosh, P.; Shimizu,
F.; Bazan, G. C. Macromolecules 2003, 36, 9731-9735. (e) Sun, W.-
H.; Shao, C.; Chen, Y.; Hu, H.; Sheldon, R. A.; Wang, H., Leng, X.;
J in, X. Organometallics 2002, 21, 4350-4355. (f) Foley, S. R.; Stock-
land, R. A., J r.; Shen, H.; J ordan, R. F. J . Am. Chem. Soc. 2003, 125,
4350-4361. (g) Salo, E. V.; Guan, Z. Organometallics 2003, 22, 5033-
5046.
(9) (a) Chen, H.-P.; Liu, Y.-H.; Peng, S.-M.; Liu, S.-T. Organome-
tallics 2003, 22, 4893-4899. (b) Speiser, F.; Braunstein, P.; Saussine,
L.; Welter, R. Inorg. Chem. 2004, 43, 1649-1658. (c) Sun, W.-H.; Li,
Z.; Hu, H.; Wu, B.; Yang, H.; Zhu, N.; Leng, X.; Wang, H. New J . Chem.
2002, 26, 1474-1478. (d) Shi, P.-Y.; Liu, Y.-H.; Peng, S.-M.; Liu, S.-T.
Organometallics 2002, 21, 3203-3207. (e) Daugulis, O.; Brookhart, M.
Organometallics 2002, 21, 5926-5934. (f) Daugulis, O.; Brookhart, M.;
White, P. S. Organometallics 2002, 21, 5935-5943.
(10) (a) Britovsek, G. J . P.; Gibson, V. C.; Kimberley, B. S.;
Mastroianni, S.; Redshaw, C.; Solan, G. A.; White, A. J . P.; Williams,
D. J . Dalton 2001, 1639-1644. (b) Michiue, K.; J ordan, R. F. Orga-
nometallics 2004, 23, 460-470. (c) Kunrath, F. A.; de Souza, R. F.;
Casagrande, O. L., J r.; Brooks, N. R.; Young, V. G., J r. Organometallics
2003, 22, 4739-4743. (d) Wang, L.; Sun, W.-H.; Han, L.; Yang, H.;
Hu, Y.; J in, X. J . Organomet. Chem. 2002, 658, 62-70.
(11) (a) Gibson, V. C.; Humphries, M. J .; Tellmann, K. P.; Wass, D.
F.; White, A. J . P.; Williams, D. J . Chem. Commun. 2001, 2252-2253.
(b) Ramos, J .; Cruz, V.; Munoz-Escalona, A.; Martinez-Salazar, J .
Polymer 2003, 43, 3635-3645. (c) Britovsek, G. J . P.; Gibson, V. C.;
Spitzmesser, S. K.; Tellmann, K. P.; White, A. J . P.; Williams, D. J .
Dalton 2002, 1159-1171. (d) Talsi, E. P.; Babushkin, D. E.; Semiko-
lenova, N. V.; Zudin, V. N.; Panchenko, V. N.; Zakharov, V. A.
Macromol. Chem. Phys. 2001, 202, 2046-2051. (e) Luo, H.; Yang, Z.-
H.; Mao, B.-Q.; Yub, D.-S.; Tang, R.-G. J . Mol. Catal. A 2002, 177,
195-207. (f) Kooistra, T. M.; Knijnenburg, Q.; Smits, J . M. M.; Horton,
A. D.; Budzelaar, P. H. M.; Gal, A. W. Angew. Chem. 2001, 113, 4855-
4858.
(12) (a) 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.; Stro1mberg, S.; White, A. J . P.; Williams. D. J . J . Am. Chem.
Soc. 1999, 121, 8728-8740. (b) Amort, C.; Malaun, M., Krajete, A.;
Kopacka, H.; Wurst, K.; Christ, M.; Lilge, D.; Kristen, M. O.; Bildstein,
B. Appl. Organomet. Chem. 2002, 16, 506-516. (c) Small, B. L.;
Brookhart, M. J . Am. Chem. Soc. 1998, 120, 7143-7144. (d) Chen, Y.
F.; Qian, C. T.; Sun, J . Organometallics 2003, 22, 1231-1236. (e)
Paulino, I. S.; Schuchardt, U. J . Mol. Catal. A 2004, 211, 55-58. (f)
Ma, Z.; Sun, W.-H.; Zhu, N.; Li, Z.; Shao, C.; Hu, Y. Polym. Int. 2002,
51, 349-352. (g) Abu-Surrah, A. S.; Lappalainen, K.; Piironen, U.;
Lehmus, P.; Repo, T.; Leskela, M. J . Organomet. Chem. 2002, 648,
55-61. (h) Britovsek, G. J . P.; Mastroianni, S.; Solan, G. A.; Baugh,
S. P. D.; Redshaw, C.; Gibson, V. C.; White, A. J . P.; Williams. D.;
Elsegood, M. R. J . Chem. Eur. J . 2000, 6, 2221-2231. (i) Bluhm, M.
E.; Folli, C.; Do¨ring, M. J . Mol. Catal. A 2004, 212, 13-18. (j) Bianchini,
C.; Mantovani, G.; Meli, A.; Migliacci, F.; Zanobini, F.; Laschi, F.;
Sommazzi, A. Eur. J . Inorg. Chem. 2003, 1620-1631. (k) Chen, Y. F.;
Chen, R. F.; Qian, C. T.; Dong, X, C.; Sun, J . Organometallics 2003,
22, 4312-4321.
(13) (a) LePichon, L.; Stephan, D. W.; Gao, X.; Wang, Q. Organo-
metallics 2002, 21, 1362-1366. (b) Qian, M.; Wang, M.; He, R. J . Mol.
Catal. A 2000, 160, 243-247. (c) Qian, M.; Wang, M.; Zhou, B.; He, R.
Appl. Catal. A 2001, 209, 11-15. (d) Bianchini, C.; Mantovani, G.; Meli,
A.; Migliacci, F.; Laschi, F. Organometallics 2003, 22, 2545-2547. (e)
Zhou, M.-S.; Huang, S.-P.; Weng, L.-H.; Sun, W.-H.; Liu, D.-S. J .
Organomet. Chem. 2003, 665, 237-245. (f) Britovsek, G. J . P.; Gibson,
V. C.; Hoarau, O. D.; Spitzmesser, S. K.; White, A. J . P.; Williams, D.
J . Inorg. Chem. 2003, 42, 3454-3465.
Resu lts a n d Discu ssion
1. Syn th esis an d Ch ar acter ization of th e Ligan ds
a n d Com p lexes. Ethyl 6-acetylpyridine-2-carboxylate
(1) was initially synthesized by the reaction of 2,6-
dicarbethoxypyridine with ethyl acetate in the presence
of C2H5ONa using the modified procedure for the
synthesis of 2,6-diacetylpyridine.15 The optimal molar
ratio of C2H5ONa to 2,6-dicarbethoxypyridine was de-
termined to be 1.1-1.5 in order to dominantly afford
compound 1 in an acceptable yield, and with 2-5 equiv
of C2H5Na, 2,6-diacetylpyridine was obtained as the
major product. The pyridineimine ligands 2a -c were
easily prepared in satisfactory yields (68.2-73.0%)
through the Schiff-base condensation of compound 1
with anilines in the presence of a catalytic amount of
p-toluenesulfonic acid (p-TsOH) in refluxing toluene. To
synthesize 2d -f, which are halogen-substituted on the
aryl ring, a small amount of silica-alumina catalyst
support (grade 135) was added to the reaction mixtures
in addition to the catalytic amount of p-TsOH.12d,k
Moreover, the reactions were assisted by the addition
of 4 Å molecular sieves as water absorbent (Scheme 1).
1
Ligands 2a -f were characterized by IR spectra, H
NMR, 13C NMR, and elemental analysis, and 2b,c were
further characterized by X-ray diffraction analysis
(Figure 1). Both 2b and 2c are in the E conformation
with typical imino CdN double bond lengths of 1.266-
(3) and 1.272 Å, respectively. For 2b and 2c in the solid
state, the aryl rings on imine are approximately per-
pendicular to the pyridine rings, and their dihedral
angles are 104.5 and 92.5°, respectively. The ethyl and
ester groups on the ligand 2b are flexible and disor-
dered, due to their free rotation. Additionally, the X-ray
diffraction determination reveals that there are two
(14) (a) Laine, T. V.; Lappalainen, K.; Liimatta, J .; Aitola, E.;
Loefgren, B.; Leskelae, M. Macromol. Rapid Commun. 1999, 20, 487-
491. (b) Laine, T. V.; Piironen, U.; Lappalainen, K.; Klinga, M.; Aitola,
E.; Leskelae, M. J . Organomet. Chem. 2000, 606, 112-124.
(15) (a) Singer, A. W.; McElvain, S. M. J . Am. Chem. Soc. 1935, 57,
1135-1136. (b) Barnes, R. A.; Fales, H. M. J . Am. Chem. Soc. 1953,
75, 3830-3831.

Fe and Co 2-(Ethylcarboxylato)-6-iminopyridyl Complexes
Organometallics, Vol. 23, No. 21, 2004 5039
Sch em e 1a
F igu r e 2. Molecular structure of 3b. Hydrogen atoms have
been omitted for clarity. Selected bond lengths (Å) and
angles (deg): Fe-N(1) ) 2.1015(15), Fe-N(2) ) 2.2117-
(15), Fe-Cl(2) ) 2.2714(7), Fe-Cl(3) ) 2.2545(9), Fe-O(1)
) 2.3769(15); N(1)-Fe-N(2) ) 74.53(6), N(1)-Fe-Cl(3) )
125.44(5), N(2)-Fe-Cl(3) ) 101.79(5), N(1)-Fe-Cl(2) )
107.25(5), N(2)-Fe-Cl(2) ) 103.94(5), Cl(2)-Fe-Cl(3) )
125.72(3), N(1)-Fe-O(1) ) 72.25(6), N(2)-Fe-O(1) )
146.21(5), Cl(3)-Fe-O(1) ) 92.44(5), Cl(2)-Fe-O(1) )
91.72(5).
a
Reagents and conditions: (i) ligands 2a -c, toluene, p-
TsOH; (ii) ligands 2d -f, toluene, p-TsOH, silica-alumina
catalyst support, 4 Å molecular sieves; (iii) FeCl2 for complexes
3a -f and CoCl2 for complexes 4a -f in ethanol. Note: there is
a bonding interaction between iron and the carbonyl oxygen
in 3b.
ethanol but did not dissolve in diethyl ether. Therefore,
anhydrous diethyl ether was added to precipitate the
complexes. After they were washed with diethyl ether,
complexes 3a -f were obtained as blue powders in good
yields (typically 80.0-85.0%) and high purities. These
complexes are air-stable in the solid state, but the
solutions of these complexes turned from blue to brown
when exposed to air for a few minutes, probably due to
the oxidation of Fe(II) into Fe(III). The structures of
these complexes were determined by elemental analysis
and IR. NMR data were not obtained, due to the
paramagnetic nature of these complexes. The elemental
analysis results reveal that the components of these
complexes are in accord with the formula MLCl2. The
IR spectra of the ligands show that the CdN stretching
frequencies appear in the range of 1640-1655 cm-1
,
while the CdN stretching vibrations in complexes 3a -f
shift toward lower frequencies between 1619 and 1625
cm-1 with weak intensities. This result indicates the
coordinating interaction between the imino nitrogen
atom and the metal center. In addition, the slight
wavenumber shift of 10-20 cm-1 in the CdO stretching
vibrations in IR spectra suggests the presence of a weak
bonding interaction between the iron and the carbonyl
oxygen of the ester group in complexes 3a -f.
Crystals of 3b,c,e,f suitable for single-crystal X-ray
diffraction analysis were grown by layering pentane on
a dichloromethane solution at room temperature under
a nitrogen atmosphere. Crystal structures of 3b,c,e,f are
shown in Figures 2-5, respectively. As shown in Figure
2, the carbonyl oxygen atom in 3b coordinates with iron.
The geometry around the metal center can be described
as a distorted trigonal bipyramidal with the pyridyl
nitrogen atom and the two chlorine atoms forming an
equatorial plane. The deviation of the iron atom from
the equatorial plane is 0.160 Å. The phenyl ring is
oriented perpendicularly (90.1°) to the coordination
plane containing the ligand backbone and the iron atom.
The CdN bond in 3b displays clear double-bond char-
acter (1.282(2) Å) and is only 0.016 Å longer than that
in the free ligand 2b, indicating that imine is not
involved in bond delocalization within the ligand back-
bone. The Fe-N(imino) and Fe-N(pyridyl) bond lengths
F igu r e 1. Molecular structure of 2b and one of the two
molecules in an asymmetric unit of 2c. Hydrogen atoms
have been omitted for clarity. Selected bond lengths (Å)
and angles (deg) are as follows. 2b: N(2)-C(9) ) 1.266(3);
C(9)-N(2)-C(11) ) 120.3(2), N(2)-C(9)-C(8) ) 117.6(2),
N(1)-C(8)-C(9) ) 115.7(2). 2c: N(12)-C(9) ) 1.272(3);
C(9)-N(12)-C(11) ) 120.7(2), N(12)-C(9)-C(8) ) 116.8-
(2). Note: in the crystal state of 2b, C(19) and C(20) in the
disordered ethyl group, as well as C(2), O(1), and O(2) in
the disordered ester group, may vibrate to another position.
For clarity, only one position of these atoms is shown.
crystallographically independent, closely similar mol-
ecules in one asymmetric unit of 2c.
The ferrous complexes 3a -f were prepared by stirring
an ethanol solution of anhydrous FeCl2 and the corre-
sponding pyridineimine ligands at room temperature
(Scheme 1). The obtained complexes were soluble in

5040 Organometallics, Vol. 23, No. 21, 2004
Sun et al.
F igu r e 5. Molecular structure of 3f. Hydrogen atoms and
the CH2Cl2 solvate molecule have been omitted for clarity.
Selected bond lengths (Å) and angles (deg): Fe-N(1) )
2.103(3), Fe-N(2) ) 2.197(3), Fe-Cl(2) ) 2.2453(13), Fe-
Cl(1) ) 2.2548(13), Fe- - -O(1) ) 2.452; N(1)-Fe-N(2) )
74.48(11), N(1)-Fe-Cl(2) ) 121.74(9), N(2)-Fe-Cl(2) )
102.89(8), N(1)-Fe-Cl(1) ) 115.06(9), N(2)-Fe-Cl(1) )
109.25(9), Cl(2)-Fe-Cl(1) ) 120.04(5).
F igu r e 3. Molecular structure of 3c. Hydrogen atoms have
been omitted for clarity. Selected bond lengths (Å) and
angles (deg): Fe-N(1) ) 2.187(2), Fe-N(2) ) 2.093(2), Fe-
Cl(1) ) 2.2187(9), Fe-Cl(2) ) 2.2360(10), Fe- - -O(1) )
2.610; N(2)-Fe-N(1) ) 75.85(9), N(2)-Fe-Cl(1) ) 130.50-
(7), N(1)-Fe-Cl(1) ) 106.66(7), N(2)-Fe-Cl(2) ) 107.65-
(7), N(1)-Fe-Cl(2) ) 108.49(7), Cl(1)-Fe-Cl(2) ) 117.29-
(4), C(14)-N(1)-Fe ) 115.45(19), C(15)-N(2)-Fe )
115.32(19).
group orients toward the iron center in 3c,e,f, and the
distances between oxygen and iron are 2.610, 2.454, and
2.452 Å, respectively, which are slightly longer than the
Fe-O(1) bond length in 3b. A perusal of the bond angles
around the metal center of complexes 3c,e,f shows that
their coordination geometries are greatly distorted from
an idealized tetrahedron, which may be attributable to
the effect of the carbonyl oxygen atom on the coordina-
tion environment.
The cobaltous complexes 4a -f were conveniently
prepared via stirring an ethanol solution of anhydrous
CoCl2 and the corresponding ligands (Scheme 1). These
complexes were obtained as green powders in good
yields (63.0-73.4%) and are stable in both solution and
the solid state. The structures of the complexes were
characterized by elemental analysis and IR spectros-
copy. Similar to the ferrous complexes, all the cobaltous
complexes show lowered frequencies of ν(CdN) with
wavenumber shifts of 20-30 cm-1 and decreased in-
tensity in their IR spectra, relative to the corresponding
ligands. Attempts to characterize these complexes by
NMR failed due to the paramagnetism of these com-
plexes.
Crystals of complex 4c suitable for X-ray diffraction
were grown by slowly diffusing diethyl ether into a
dichloromethane solution (Figure 6). Complex 4c has
the same distorted-tetrahedral geometry as its ferrous
analogue 3c. The sterically bulky isopropyl groups hold
the N-aryl ring nearly perpendicular to the plane of the
coordinated ring (85.9°), which may provide efficient
blocking of the axial sites on the cobalt center. Crystals
of 4f suitable for X-ray determination were obtained by
layering its dichloromethane solution with diethyl ether
(Figure 7). One dichloromethane molecule was found to
be involved in the crystal lattice, as revealed by an X-ray
determination. Complex 4f is four-coordinated with a
distorted-tetrahedral geometry around the central metal.
The phenyl ring is oriented nearly perpendicular to the
coordination ring, and the dihedral angle is 89.5°.
Similar to the four-coordinated ferrous complexes, the
oxygen in the carbonyl group in complex 4f orients
toward the metal center, and the distance between them
is 2.460 Å.
F igu r e 4. Molecular structure of 3e. Hydrogen atoms and
the CH2Cl2 solvate molecule have been omitted for clarity.
Selected bond lengths (Å) and angles (deg): Fe-N(1) )
2.104(2), Fe-N(2) ) 2.192(2), Fe-Cl(1) ) 2.2566(10), Fe-
Cl(2) ) 2.2532(10), Fe- - -O(1) ) 2.454; N(1)-Fe-N(2) )
74.92(8), N(1)-Fe-Cl(2) ) 121.30(6), N(2)-Fe-Cl(2) )
102.46(6), N(1)-Fe-Cl(1) ) 116.38(6), N(2)-Fe-Cl(1) )
108.15(6), Cl(2)-Fe-Cl(1) ) 119.62(4).
(2.2217(15) and 2.1015(15) Å, respectively) are similar
to the corresponding Fe-N bond lengths of diisopropyl
2,6-bis(imino)pyridyl ferrous complexes reported by
Brookhart et al.4a It is noted that the Fe-O(1) bond
length (2.3769(15) Å) is substantially longer than the
reported Fe-O bond distance (2.212(4) Å),16 which
indicates the weak interaction between the iron and
carbonyl oxygen atom in 3b.
Figure 3 shows that the iron atom is coordinated in a
distorted-tetrahedral environment in 3c. The diisopro-
pyl-substituted phenyl ring is oriented nearly perpen-
dicular to the coordination plane, and the dihedral angle
is 86.5°. Similarly, complexes 3e,f are four-coordinated
with a distorted-tetrahedral geometry around the metal
center. One dichloromethane molecule was observed in
the crystal lattices of 3e,f. The phenyl rings in 3e,f are
oriented orthogonally to the coordination rings (88.9 and
89.0°, respectively). The Fe-N(imino) bond lengths in
3c,e,f (2.187(2), 2.192(2), and 2.197(3) Å, respectively)
are slightly shorter than that in pentacoordinated 3b,
reflecting the subtle effect of the coordination fashion
on the electronic properties of the metal center. It should
be pointed out that the oxygen atom in the carbonyl
2. Eth ylen e Oligom er iza tion a n d P olym er iza -
tion . 2.1. Eth ylen e Oligom er iza tion a n d P olym er -
iza tion Beh a vior of th e F er r ou s Com p lexes. The
(16) Chiou Y.-M.; Que, L., J r. J . Am. Chem. Soc. 1995, 117, 3999-
4013.

Fe and Co 2-(Ethylcarboxylato)-6-iminopyridyl Complexes
Organometallics, Vol. 23, No. 21, 2004 5041
explanation for these results is based upon the steric
bulk of the substituent on the ortho position of the aryl
ring that decreasing the bulk on the aryl ring of the
complex leads to higher activity, which is in line with
previous reports regarding bis(imino)pyridyl iron cata-
lysts.7,11j Complex 3e, with dichloro-substituted ligands,
displays higher ethylene oligomerization activity than
its analogue 3d , which contains difluoro-substituted
ligands, and the same result was obtained for the
cobaltous counterparts. From the point of view of
electronic effects, fluoro substitution on the ortho posi-
tion of the aryl ring results in a more electrophilic metal
center, which may increase the catalytic activity of the
complex for ethylene oligomerization and polymeriza-
tion.17 However, the less bulky fluoro substituent ren-
ders the active sites of the catalyst exposed to not only
ethylene but also other reactive species, and the latter
actually leads to the deactivation of the active species.
Indeed, Gibson has shown that the catalytic intermedi-
ates formed from the precursors containing pyridyldi-
imine ligands which lack sufficient steric bulk in the
ortho aryl positions are more easily deactivated through
the interaction with alkylaluminum reagent.12h Al-
though electronic effects on the activities of catalysts
were emphasized in previous studies,12d,k our results
clearly indicate that the electronic effect is not signifi-
cant in the catalyst systems we studied. In addition, the
five-coordinate nature of 3b in the solid state has little
effect on its ethylene catalytic behavior, and in solution,
the coordination mode of 3b may change to four-
coordinate due to the weak Fe-O bond. In the litera-
ture, an N∧N∧O-coordinated ferrous complex bearing
an acetyliminopyridine ligand shows much lower cata-
lytic activity for ethylene oligomerization than the
corresponding bis(imino)pyridine complex.12i
The effect of the steric bulk on the oligomer distribu-
tion is not as remarkable as the effect on the catalytic
activity, and no conclusive trend can be determined.
Analysis of the obtained oligomers by GC and GC-MS
reveals that the selectivities for linear R-olefin are
higher than 93% in all cases at 1 atm of ethylene.
Effects of Al/F e Mola r Ra tio a n d Rea ction Tem -
p er a tu r e on Ca ta lyst Activity. The influences of the
Al/Fe molar ratio and the reaction temperature on
ethylene oligomerization and polymerization were in-
vestigated in detail with complex 3c. Increasing the Al/
Fe molar ratio from 200 to 1500 leads to a slight
enhancement of complex 3c’s ethylene oligomerization
activity (entries 3 and 7-9 in Table 1). Elevation of the
ethylene oligomerization and polymerization reaction
temperature from 0 to 40 °C results in a sharp decrease
in productivity, which may be attributed to catalyst
decomposition and lower ethylene solubility at higher
temperature.12a,h
F igu r e 6. Molecular structure of 4c. Hydrogen atoms have
been omitted for clarity. Selected bond lengths (Å) and
angles (deg): Co(1)-N(1) ) 2.039(3), Co(1)-N(2) ) 2.133-
(3), Co(1)-Cl(1) ) 2.2240(12), Co(1)-Cl(2) ) 2.2020(12),
Co- - -O(1) ) 2.610; N(1)-Co(1)-N(2) ) 77.81(12), N(1)-
Co(1)-Cl(2) ) 131.35(9), N(2)-Co(1)-Cl(2) ) 107.11(9),
N(1)-Co(1)-Cl(1) ) 109.60(8), N(2)-Co(1)-Cl(1) ) 109.01-
(8), Cl(2)-Co(1)-Cl(1) ) 113.67(5).
F igu r e 7. Molecular structure of 4f. Hydrogen atoms and
the CH2Cl2 solvate molecule have been omitted for clarity.
Selected bond lengths (Å) and angles (deg): Co-N(1) )
2.050(3), Co-N(2) ) 2.126(3), Co-Cl(1) ) 2.2316(15), Co-
Cl(2) ) 2.2316(15), Co- - -O(1) ) 2.460; N(1)-Co-N(2) )
77.27(13), N(1)-Co-Cl(2) ) 122.43(11), N(2)-Co-Cl(2) )
103.97(10), N(1)-Co-Cl(1) ) 116.07(11), N(2)-Co-Cl(1)
) 117.20(6), Cl(2)-Co-Cl(1) ) 117.20(6).
ferrous complexes 3a -f were initially studied for their
catalytic activities of ethylene oligomerization and po-
lymerization using methyaluminoxane (MAO) as the
cocatalyst. The results are summarized in Table 1 with
1 atm of ethylene and in Table 2 with 10 atm of
ethylene.
Effect of th e Liga n d En vir on m en t on th e Ca ta -
lytic Beh a vior . Complexes 3a -f show considerable
activities for ethylene oligomerization at a pressure of
1 atm of ethylene, producing butenes and hexenes and
small amounts of higher oligomers. In addition, the
catalytic systems 3a ,b generate isolable amounts of
polyethylene. A variety of ortho-substituted aryl-ring-
containing ligands were employed, including electron-
donating alkyl groups and electron-withdrawing halo-
gen groups, and the studies of these complexes have
provided an insight into the steric and electronic effects
of the aryl ring on the catalytic behaviors of the
complexes, including the catalytic activity and product
distribution. The ethylene catalytic results for com-
plexes 3a -f were obtained under identical reaction
conditions and are listed in entries 1-6 in Table 1. As
shown in Table 1, the ethylene oligomerization activity
varies in the orders of 3a > 3b > 3c and 3e > 3d > 3f,
and a similar trend of polymerization activity was
observed for the alkyl-substituted complexes 3a -c. The
Solven t Effect on th e Ca ta lyst Activity. The effect
of solvent on the catalytic activity was studied with
complex 3f. As shown in Table 1, 3f exhibits about a 4
times higher activity of ethylene oligomerization in
dichloromethane (entry 13) than in toluene (entry 6).
The obtained oligomers were analyzed by GC and GC-
MS, and only the dimers were detected. The selectivity
for 1-butene is higher than 97%.
(17) (a) Chan, M. S. W.; Deng, L. Q.; Ziegler, T. Organometallics
2000, 19, 2741-2750. (b) Zhang, T. Z.; Sun, W.-H.; Li, T.; Yang, X. Z.
J . Mol. Catal. A 2004, 218, 119-124.

5042 Organometallics, Vol. 23, No. 21, 2004
Ta ble 1. P olym er iza tion a n d Oligom er iza tion of 1 a tm of Eth ylen e w ith 3a -f/MAOa
oligomer distribnb (%) activity (104 g (mol of Fe)-1 h-1
Sun et al.
)
entry
complex
Al/Fe (mol)
temp (°C)
C4/∑C
C6/∑C
C
g8/∑C
linear R-olefin
oligomerb
polymer
1
2
3
4
5
6
7
8
3a
3b
3c
3d
3e
3f
3c
3c
3c
3c
3c
3c
3f
1000
1000
1000
1000
1000
1000
200
15
15
15
15
15
15
15
15
15
0
92.40
71.15
98.20
84.04
35.42
77.96
4.25
28.84
1.50
0.90
57.74
2.89
3.35
>99
97.1
>99
94.6
97.7
93.3
>99
97.2
>99
>99
>99
>99
97.8
>99
2.17
1.61
1.39
2.60
6.04
1.80
0.76
1.15
2.46
6.98
0.66
0.48
7.18d
2.45
9.44
0.91
trace
no
trace
trace
no
trace
trace
trace
no
0.3
15.06
6.84
19.15
500
9
1500
1000
1000
1000
1000
1000
10
11
12
13c
14e
40
60
15
15
no
no
no
100d
100
3f
a
b
General conditions: 5 µmol of precatalyst; 30 mL of toluene; reaction time 30 min. Determined by GC. ∑C means the total amounts
of oligomers. c CH2Cl2 as solvent. Determined by GC and GC-MS; approximate result. e 2 equiv of PPh3 as auxiliary ligand.
d
Ta ble 2. Oligom er iza tion a n d P olym er iza tion of 10 a tm of Eth ylen e w ith 3a -f/MAOa
activity (104 g (mol of Fe)-1 h-1
)
complex
(amt (µmol))
polymer
yield (g)
linear
R-olefin (%)
d
entry
oligomerb
polymer
Mnc (103)
PDIc
Tm (°C)
K
1
2
3
3a (42.3)
3b (53.9)
3c (36.5)
3d (34.1)
3e (42.5)
3f (36.9)
24.00
1.15
1.13
trace
1.67
3.50
6.20
1.44
1.90
4.06
30.60
3.90
56.70
2.10
3.20
4.7
1.3
1.0
32.7
90.3
4.2
132
122
124
88.8
82.1
92.1
78.3
92.0
95.8
0.83
0.93
0.96
0.73
0.81
0.81
4
5e
6
3.90
9.50
0.5
0.7
2.4
2.4
88
110
a
b
d
General conditions: Al/Fe molar ratio 1000; 20 °C; 1 h, 700 mL of toluene. Determined by GC. c Determined by GPC. Determined
by DSC. e The oligomers were determined by GC and GC-MS.
Effect of th e Au xilia r y Liga n d on Ca ta lyst Ac-
tivity. Previous studies on nickel-based catalysts have
demonstrated that incorporating PPh3 into catalytic
systems leads to higher activity and longer catalyst
lifetime.7g,18 We were curious whether such effects would
apply to our ferrous catalyst systems. Therefore, the
oligomerization reaction with the 3f/MAO system was
carried out in the presence of 2 equiv of PPh3 (entry 14,
Table 1). However, as shown in Table 1, only a slight
increase of catalyst activity was observed relative to the
catalytic system of 3f/MAO (entry 6, Table 1).
E ffect s of E t h ylen e P r essu r e on t h e Ca t a lyst
Beh a vior . Ethylene oligomerization and polymerization
with complexes 3a -f in the presence of MAO were also
studied under an ethylene pressure of 10 atm, and the
results are listed in Table 2. As is apparent, the ethylene
concentration significantly affects the catalytic behav-
iors of the complexes. For the alkyl-substituted ferrous
complexes 3a -c, the effects of the steric bulk of the
ortho aryl substituent on the catalyst’s ethylene polym-
erization activities at 10 atm of ethylene pressure are
quite consistent with those observed at 1 atm of ethyl-
ene. As shown in Table 2 (entries 1-3), higher polym-
erization activity was observed for the complex contain-
ing a ligand with less bulky substituents. In addition,
the dibromo-substituted complex 3f shows higher po-
lymerization activity and lower oligomerization activity
than the dichloro-substituted complex 3e.
F igu r e 8. Oligomer distribution obtained in entries 4-6
in Table 2.
obtained with the catalytic systems of 3d -f under 10
atm of ethylene. The distribution of olefin oligomers
follows the Schulz-Flory rules19 and is characterized
by the constant K as defined in eq 1, where K represents
K ) kprop/(kprop + kch-transfer) )
(mol of Cn+2 oligomers)/(mol of Cn oligomers) (1)
the probability of chain propagation. The K values
determined by the molar ratio of C14 and C16 fractions
for each run are listed in Table 2. As shown in Table 2,
increasing the bulk at the ortho position of the aryl
group on the complex leads to an increase in the K value
(entries 1-3 in Table 2). GC and GC-MS analysis of the
oligomers indicates that the selectivities for linear
R-olefins are higher than 78% for 3a -f at 10 atm of
ethylene.
In comparison with the results obtained with 1 atm
of ethylene, the distribution of oligomers formed at 10
atm of ethylene pressure shifts to higher carbon number
olefins. Figure 8 shows the distributions of the oligomers
(18) (a) Carlini, C.; Isola, M.; Liuzzo, V.; Galletti, A. M. P.; Sbrana,
G. Appl. Catal. A: Gen. 2002, 231, 307-320. (b) J enkins, J . C.;
Brookhart, M. Organometallics 2003, 22, 250-256.
(19) (a) Flory, P. J . J . Am. Chem. Soc. 1940, 62, 1561-1565. (b)
Schulz, G. V. Z. Phys. Chem. B 1935, 30, 379-399. (c) Schulz, G. V. Z.
Phys. Chem. B 1939, 43, 25-46.

Fe and Co 2-(Ethylcarboxylato)-6-iminopyridyl Complexes
Organometallics, Vol. 23, No. 21, 2004 5043
which implies that chain termination occurs with â-hy-
dride elimination for the polymeric R-olefin. The Mn
value calculated from 1H NMR and 13C NMR spectra
for the PE sample generated by 3e is approximately 700,
which is slightly higher than that obtained by GPC.
However, the Mn value obtained from NMR may be
more accurate, due to the fact that GPC may afford an
ambiguous characterization of low-molecular-weight
polyethylene.6d Moreover, DSC studies determine that
the Tm values of the PE samples are in the range of 88-
132 °C, which correlates well with the linear charac-
teristics of low-molecular-weight PE.
2.2. Eth ylen e Oligom er iza tion a n d P olym er iza -
tion Beh a vior s of th e Coba ltou s Com p lexes. The
cobaltous complexes 4a -f were systematically investi-
gated for their ethylene oligomerization and polymeri-
zation behavior upon activation with MAO, and the
results are summarized in Table 3 (with 1 atm of
ethylene) and Table 4 (with 10 atm of ethylene).
Previous studies on the 2,6-bis(imino)pyridine-based
iron and cobalt catalyst systems demonstrated that
cobalt complexes usually display much lower productiv-
ity than iron complexes.12h,j,k However, the cobaltous
catalysts in our study exhibit remarkably higher eth-
ylene oligomerization activities than their ferrous coun-
terparts at 1 atm. We noted rapid consumption of
ethylene in the experiments when MAO was injected
into the catalytic systems, which indicates that no initial
time of ethylene oligomerization and polymerization is
required. GC and GC-MS analysis of the obtained
oligomers reveals that dimers and trimers are the major
products, plus a small amount of higher carbon number
olefins, and the linear R-olefins are the predominant
products.
F igu r e 9. GPC traces of PE samples obtained in entries
1, 2, 3, 5, and 6 in Table 2.
F igu r e 10. 13C NMR spectra of the PE sample obtained
Effects of th e Ar yl Su bstitu en ts on th e Ca ta lyst
Beh a vior s. The ligand environment has a significant
effect on productivity. The less bulky methyl-substituted
complex 4a displays higher total conversion of ethylene
than the sterically bulky isopropyl-substituted complex
4c. Nevertheless, 4c produces more polyethylene than
4a under identical reaction conditions (Table 3, entry 1
vs entry 9). In addition, the dibromo-substituted com-
plex 4f generates a trace amount of polyethylene, while
the difluoro-substituted complex 4d and the dichloro-
substituted complex 4e produce only oligomers (Table
3, entries 10, 11, and 15). The effect of aryl substituents
on the cobaltous complexes’ catalytic behavior is well
in line with the reported result.4a,12d,h Similar to the
results obtained with the ferrous complexes, the elec-
tronic effect on the catalyst productivity is not signifi-
cant.
in entry 5 in Table 2.
The polyethylene produced by 3a -c,e,f was isolated
as a white powder. The GPC analysis indicates that the
obtained polyethylene has a relatively low molecular
weight, with the Mn value in the range of 500-4700.
As shown by the GPC traces in Figure 9, the PE samples
obtained from 3a ,b display bimodal molecular weight
distribution. The observed bimodal distribution is at-
tributed to the formation of the different types of active
species when the complexes are activated by MAO and
the rate difference between chain transfer and chain
propagation of these active species. The Mn value of the
PE produced by 3a is much higher than those obtained
from 3b,c, which is surprising in view of previous
reports,4a,12h which demonstrated a higher molecular
weight for PE produced with a ligand of greater steric
bulk. However, in our study, repeated ethylene polym-
erization reactions with 3a -c under 10 atm demon-
strate consistent results for both the catalyst activity
and the molecular weight of the obtained PE. In
addition, the PE produced by dihalogen-substituted
complexes 3e,f has a lower Mn value than the PE
produced by dialkyl-substituted 3a -c. Analysis of the
Effects of Al/Co Mola r Ra tio a n d Rea ction Tem -
p er a tu r e on Ca ta lyst Activity. The Al/Co molar ratio
slightly affects the oligomerization and polymerization
activity of complex 4b. Complex 4b shows the highest
activity when the Al/Co ratio is 1000 (Table 3, entries
2-5). For complexes 4b,f, increasing the reaction tem-
perature in the range of -10 to +40 °C leads to reduced
oligomerization activities, suggesting that the active
species may be less stable at higher temperature.
1
product by H NMR and 13C NMR shows that the PE
samples are strictly linear and the end groups are
mainly R-olefin.20 The 13C NMR spectra for the PE
sample listed in entry 5 of Table 2 is shown in Figure
10. Furthermore, the IR spectroscopic analysis of the
obtained PE confirms the presence of end vinyl groups,
(20) (a) Kokko, E.; Lehmus, P.; Leino, R.; Luttikhedde, H. J . G.;
Ekholm, P.; Na¨sman, J . H.; Seppa¨la¨, J . V. Macromolecules 2000, 33,
9200-9204. (b) Galland, G. B.; Quijada, R.; Rolas, R.; Bazan, G.;
Komon, Z. J . A. Macromolecules 2002, 35, 339-345.

5044 Organometallics, Vol. 23, No. 21, 2004
Ta ble 3. P olym er iza tion a n d Oligom er iza tion of 1 a tm of Eth ylen e w ith 4a -f/MAOa
oligomer distribnb (%) activity (104 g (mol Co)-1 h-1
Sun et al.
)
entry complex Al/Co (mol) temp (°C) time (min)
C4/∑C
C6/∑C
C
g8/∑C linear R-olefin
2.93
oligomerb
polymer
1
4a
4b
4b
4b
4b
4b
4b
4b
4c
4d
4e
4e
4f
4f
4f
4f
4f
4f
4f
4f
4f
1000
200
15
15
15
15
15
-10
0
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
15
30
60
15
30
81.80
67.37
61.03
74.25
78.98
76.56
72.97
67.84
55.34
93.28
83.76
100d
70.00
66.00
72.11
66.86
71.67
100d
15.27
15.96
20.13
14.89
13.06
19.33
21.46
18.71
27.17
1.39
96.2
90.3
95.9
75.0
83.2
83.2
95.6
89.0
98.1
78.6
82.0
96.8
90.4
94.7
95.6
81.5
87.1
92.8
90.0
87.5
92.2
14.70
4.71
6.95
8.22
8.10
19.50
13.05
3.58
5.32
7.98
14.50
135.00d
36.20
24.70
18.90
4.42
34.90
46.90d
9.92
0.670
trace
1.04
1.04
trace
trace
0.972
trace
3.50
no
2
16.68
18.84
10.86
7.96
4.11
5.57
13.45
17.49
5.33
4.95
-
5.53
9.90
4.10
13.86
5.79
-
3
500
4
5
6
7
8
9
10
11
12c
13
14
15
16
17
18c
19e
20f
21f
1000
1500
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
40
15
15
15
15
-10
0
1.79
-
no
no
24.47
24.10
23.78
19.27
22.57
trace
trace
trace
trace
trace
trace
trace
no
15
40
15
15
15
15
15
72.24
73.83
71.28
22.74
20.57
23.28
5.03
5.60
5.23
16.60
31.70
no
a
b
General conditions: 5 µmol of precatalyst; 30 mL of toluene. Determined by GC. ∑C signifies the total amounts of oligomers. c CH2Cl2
as solvent. Determined by GC and GC-MS; approximate result. e Determined by GC-MS. f 2 equiv of PPh3 as auxiliary ligand.
d
Ta ble 4. Oligom er iza tion a n d P olym er iza tion of 10 a tm of Eth ylen e w ith 4c a n d 4fa
activity (104 g (mol of Co)-1 h-1
)
d
entry complex (amt (µmol)) polymer yield (g)
oligomerb
polymer
Mnc (×103) linear R-olefin (%) PDIc Tm (°C)
1
2
4c (32.8)
4f (49.6)
0.18
0.44
3.63
23.40
0.53
0.90
1.9
1.7
84.6
97.9
36.4
16.7
125
125
a
b
d
General conditions: Al/Fe molar ratio 1000; 20 °C, 1 h, 700 mL of toluene. Determined by GC. c Determined by GPC. Determined
by DSC.
Lifetim e of th e Active Ca ta lytic Sp ecies. All the
cobaltous catalysts have been found to show very short
lifetimes even at low temperature. As an example, the
lifetime of 4f/MAO was studied by varying the reaction
time, and it was found that the oligomerization activity
of 4f at 30 min of reaction (Table 3, entry 15) was about
half of that at 15 min of reaction (Table 3, entry 17),
indicating that the majority of active catalytic species
were deactivated after 15 min of reaction.
Au xilia r y Liga n d a n d Solven t Effects on th e
Ca ta lyst Beh a vior . Oligomerization activities of the
cobaltous complexes were also studied in the presence
of 2 equiv of PPh3. The results show that addition of
PPh3 to the reaction has no significant impact on the
activity of 4f/MAO. It is noted that the oligomerization
activity of 4f in the presence of PPh3 remains high when
the reaction time is prolonged from 15 to 30 min (Table
3, entries 20 and 21). The prolonged catalyst lifetime
may be ascribed to the formation of more stable catalytic
intermediates with the addition of PPh3. Solvent effects
on ethylene oligomerization were also investigated with
4e,f. As shown in Table 3, using dichloromethane as the
solvent leads to a significant increase of the oligomer-
ization activities of 4e,f, and as determined by GC and
GC-MS, only butenes were detected when dichlo-
romethane was employed as the solvent (Table 3, entries
12 and 18).
F igu r e 11. GPC traces of the PE samples obtained by 4c,f
at 10 atm.
produce PE with low molecular weight. In addition, the
molecular weight distributions of the obtained PE are
considerably wide, which is characterized by a broad
peak in the GPC trace (Figure 11). The polymers display
Tm values of 125 °C, as measured by DSC. The IR
spectra of the PE samples produced by 4c,f to some
extent demonstrate the PE’s linear characteristics and
the presence of the vinyl end groups. Further analysis
of the PE was not performed, due to the low polymer
productivity.
Su m m a r y
Eth ylen e P r essu r e Effects on Ca ta lyst P er for -
m a n ce. Cobaltous complexes 4c,f were studied for
ethylene oligomerization and polymerization under 10
atm of ethylene with MAO activation (Table 4). It is
observed that the activity of 4c,f does not change
significantly with the ethylene pressure. 4c,f both
A series of 2-(carboxylato)-6-iminopyridine-based fer-
rous and cobaltous complexes have been synthesized.
In the presence of MAO, these complexes exhibit good
activities for oligomerization and polymerization. The
steric bulk dependence of the activities was observed

Fe and Co 2-(Ethylcarboxylato)-6-iminopyridyl Complexes
Organometallics, Vol. 23, No. 21, 2004 5045
1H, J 1 ) 1.2 Hz, J 2 ) 6.6 Hz, Py Hm); 8.20 (q, 1H, J 1 ) 1.2 Hz,
J 2 ) 6.6 Hz, Py Hm); 7.99 (t, 1H, J ) 7.8 Hz, Py Hp); 4.50 (q,
2H); 2.81 (s, 3H); 1.47 (t, 3H). 13C NMR (75.45 MHz, CDCl3;
δ): 199.72; 164.70; 153.61; 147.85; 138.01; 128.16; 124.43;
62.12; 25.71; 14.33. IR (KBr; cm-1): 1727 (vCdO); 1704; 1585;
for both the ferrous and cobaltous catalyst systems. A
decrease in the steric bulk of the substituent on the
ligand leads to a higher activity of the catalyst, except
for the difluoro-substituted complexes. The electronic
effects on the catalytic activities are less significant. The
cobaltous complexes 4a -f display very short lifetimes,
due to deactivation of the active catalytic sites. Analysis
of the products shows that the majority of obtained
oligomers are linear R-olefins, and the polymers ob-
tained in some cases are linear polymeric R-olefins.
1474; 1455; 1321; 1367; 1237; 1155. Anal. Calcd for C10H11
-
NO3: C, 62.17; H, 5.74; N, 7.25. Found: C, 62.14; H, 5.75; N,
7.17.
Syn th esis of Liga n d s. Eth yl 6-[1-((2,6-Dim eth ylp h en -
yl)im in o)eth yl]p yr id in e-2-ca r boxyla te (2a ). A solution of
2,6-dimethylaniline (0.267 g, 2.2 mmol), ethyl 6-acetylpyridine-
2-carboxylate (0.386 g, 2.0 mmol), and a catalytic amount of
p-toluenesulfonic acid in toluene (25 mL) were refluxed for 24
h. After solvent evaporation, the crude product was purified
by column chromatography on silica gel with petroleum ether/
ethyl acetate (15/1) as eluent to afford the product as a yellow
powder in 69.5% yield. 1H NMR (300 MHz, CDCl3; δ): 8.58
(d, 1H, J ) 7.9 Hz, Py Hm); 8.20 (d, 1H, J ) 7.6 Hz, Py Hm);
7.95 (t, 1H, J ) 7.9 Hz, Py Hp); 7.07 (d, 2H, J ) 7.4 Hz, Ar H);
6.95 (t, 1H, J ) 7.4 Hz, Ar H); 4.49 (q, 2H); 2.26 (s, 3H); 2.03
(s, 6H); 1.46 (t, 3H, J ) 7.1 Hz). 13C NMR (75.45 MHz, CDCl3;
δ): 166.98; 165.15; 156.45; 148.57; 147.39; 137.32; 126.16;
125.27; 124.33; 123.18; 61.88; 17.92; 16.51; 14.31. IR (KBr;
cm-1): 1720 (νCdO); 1640 (νCdN); 1587; 1469; 1370; 1324. Anal.
Calcd for C18H20N2O2: C, 72.95; H, 6.80; N, 9.45. Found: C,
72.46; H, 6.77; N, 9.29.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations of air- and/
or moisture-sensitive compounds were performed under a
nitrogen atmosphere using standard Schlenk techniques.
Solvents were dried by the literature methods. Methylalumi-
noxane (MAO) was purchased from Albemarle as a 1.4 M
solution in toluene. Other reagents were purchased from
Aldrich or Acros Chemicals. 1H and 13C NMR spectra were
recorded on a Bruker DMX 300 MHz instrument at ambient
temperature using TMS as an internal standard. IR spectra
were recorded on a Perkin-Elmer System 2000 FT-IR spec-
trometer. Elemental analysis was carried out using an HP-
MOD 1106 microanalyzer. GC analysis was performed with a
Carlo Erba Strumentazione gas chromatograph equipped with
a flame ionization detector and a 30 m (0.25 mm i.d., 0.25 µm
film thickness) DM-1 silica capillary column. GC-MS analysis
was performed with HP 5890 SERIES II and HP 5971 SERIES
mass detectors. The yield of oligomers was calculated by
referencing with the mass of the solvent on the basis of the
prerequisite that the mass of each fraction is approximately
proportional to its integrated areas in the GC trace. Selectivity
for the linear R-olefin is defined as (amount of linear R-olefin
of all fractions)/(total amount of oligomer products) in percent.
1H and 13C NMR spectra of the PE samples were recorded on
E t h yl 6-[1-((2,6-Diet h ylp h en yl)im in o)et h yl]p yr id in e-
2-ca r boxyla te (2b). Using the same procedure as for the
synthesis of 2a , 2b was obtained as a yellow powder in 68.2%
1
yield. H NMR (300 MHz, CDCl3; δ): 8.49 (d, 1H, J ) 7.8 Hz,
Py Hm); 8.12 (d, 1H, J ) 7.5 Hz, Py Hm); 7.87 (t, 1H, J ) 7.8
Hz, Py Hp); 7.15 (d, 2H, J ) 7.5 Hz, Ar H); 6.96 (t, 1H, J ) 6.3
Hz, Ar H); 4.42 (q, 2H); 2.71 (m, 4H); 2.18 (s, 3H); 1.39 (t, 3H);
1.05 (t, 6H). 13C NMR (75.45 MHz, CDCl3; δ): 166.66; 165.17;
156.43; 147.57; 147.38; 137.31; 131.03; 126.11; 125.94; 124.26;
123.45; 61.87; 24.54; 16.81; 14.29; 13.67. IR (KBr; cm-1): 1722
(νCdO); 1640 (νCdN); 1580; 1540; 1454; 1394. Anal. Calcd for
C
20H24N2O2: C, 74.04; H, 7.46; N, 8.64. Found: C, 73.95; H,
a
Bruker DMX 400 MHz instrument at 135 °C in 1,2-
7.49; N, 8.52.
dichlorobenzene-d4 using TMS as the internal standard. The
molecular weight and polydispersity index (PDI) of PE were
determined by a PL-GPC220 instrument at 150 °C with 1,2,4-
trichlorobenzene as the eluent. Melting points of the polymers
were obtained on a Perkin-Elmer DSC-7 instrument in the
standard DSC run mode. The instrument was initially cali-
brated for the melting point of an indium standard at a heating
rate of 10 °C/min. The polymer sample was first equilibrated
at 0 °C and then heated to 160 °C at a rate of 10 °C/min to
remove thermal history. The sample was then cooled to 0 °C
at a rate of 10 °C/min. A second heating cycle was used for
collecting DSC thermogram data at a ramping rate of 10 °C/
min.
Syn th esis of Eth yl 6-Acetylp yr id in e-2-ca r boxyla te (1).
According to the traditional method, 2,6-dicarbethoxypyridine
was prepared by the esterification of dipicolinic acid with
ethanol with a yield of 70%. Mp: 41.0-41.5 °C. A solution of
2,6-dicarbethoxypyridine (18.9 g, 0.085 mol) in 70 mL of freshly
distilled ethyl acetate was added dropwise to 1.1 equiv of dried
C2H5ONa (6.4 g, 0.094 mol) with stirring to afford a yellow
mixture, which was refluxed for 12 h and then allowed to stand
overnight. Concentrated HCl (35 mL) was added dropwise with
stirring, and the mixture was refluxed for a period of 6 h to
complete the reaction. Water (100 mL) was then added, and
the mixture turned orange. The aqueous phase was extracted
with CH2Cl2 (4 × 25 mL), and the combined extract was
washed with 5% aqueous Na2CO3. The combined organic phase
was dried over anhydrous Na2SO4 and filtered, and the solvent
was evaporated under reduced pressure. The desired com-
pound 6-acetylpyridine-2-carboxylate (1) was obtained as a
white solid in 40.0% yield after purification by column chro-
matography (silica gel, petroleum ether/ethyl acetate 8/1).
Mp: 50.0-51.5 °C. 1H NMR (300 MHz, CDCl3; δ): 8.27 (q,
E t h yl 6-[1-((2,6-Diisop r op ylp h en yl)im in o)et h yl]p yr -
id in e-2-ca r boxyla te (2c). Using the same procedure as for
the synthesis of 2a , 2c was obtained as a yellow powder in
1
71.5% yield. H NMR (300 MHz, CDCl3; δ): 8.56 (d, 1H, J )
7.8 Hz, Py Hm); 8.19 (d, 1H, J ) 7.5 Hz, Py Hm); 7.93 (t, 1H, J
) 7.8 Hz, Py Hp); 7.15 (q, 1H, J 1 ) 6.3 Hz, J 2 ) 2.1 Hz, Ar H);
7.10 (q, 1H, J 1 ) 6.0 Hz, J 2 ) 3.0 Hz, Ar H); 7.04 (t, 1H, J )
7.8 Hz, Ar H); 4.48 (q, 2H); 2.71 (m, 2H); 2.28 (s, 3H); 1.45 (t,
3H); 1.36 (t, 12H). 13C NMR (75.45 MHz, CDCl3; δ): 166.67;
165.19; 156.40; 147.39; 146.24; 137.31; 135.64; 126.10; 124.31;
123.71; 123.00; 61.87; 28.24; 23.22; 17.11; 14.28. IR (KBr;
cm-1): 1722 (νCdO); 1643 (νCdN); 1584; 1548; 1460; 1368. Anal.
Calcd for C22H28N2O2: C, 74.97; H, 8.01; N, 7.95. Found: C,
74.71; H, 7.99; N, 7.69.
Eth yl 6-[1-((2,6-Diflu or op h en yl)im in o)eth yl]p yr id in e-
2-ca r boxyla te (2d ). A solution of 2,6-difluoroaniline (0.575
g, 4.34 mmol), ethyl 6-acetylpyridine-2-carboxylate (0.700 g,
3.62 mmol), p-toluenesulfonic acid (0.060 g), and silica-
alumina catalyst (grade 135, 0.120 g) in toluene (25 mL) was
refluxed for 15 h, and 4 Å molecular sieves (2 g) were added
to remove water. After filtration and solvent evaporation, the
crude product was purified by column chromatography on
silica gel with petroleum ether/ethyl acetate (6/1) as eluent to
afford the product as a viscous yellow oil in 44.5% yield. 1H
NMR (300 MHz, CDCl3; δ): 8.52 (d, 1H, J ) 7.8 Hz, Py Hm);
8.21 (d, 1H, J ) 7.5 Hz, Py Hm); 7.94 (t, 1H, J ) 7.8 Hz, Py
Hp); 6.9-7.1 (m, 3H, Ar H); 4.49 (q, 2H); 2.47 (s, 3H); 1.46 (t,
3H). 13C NMR (75.45 MHz, CDCl3; δ): 172.47; 165.06; 155.98;
147.51; 145.49; 137.58; 128.25; 126.70; 125.07; 124.53; 124.45;
61.98; 17.60; 14.31. IR (KBr; cm-1): 1721 (νCdO); 1647 (νCdN);
1583; 1471; 1425; 1369. Anal. Calcd for C16H14F2N2O2: C,
63.15; H, 4.64; N, 9.21. Found: C, 63.06; H, 4.52; N, 9.10.

5046 Organometallics, Vol. 23, No. 21, 2004
Sun et al.
Ta ble 5. Cr ysta llogr a p h ic Da ta a n d Refin em en t Deta ils for 2b,c, 3b,c, 3e·CH2Cl2, 3f·CH2Cl2, 4c, a n d
4f·CH2Cl2
2b
2c
3b
3c
formula
fw
cryst syst
space group
a (Å)
b (Å)
c (Å)
C
20H24N2O2
C
22H28N2O2
C
20H24Cl2F N2O2
C
22H28Cl2F N2O2
324.41
monoclinic
P21/c
352.46
triclinic
P1h
451.16
monoclinic
P21/c
479.21
monoclinic
P21/n
10.881(2)
21.536(4)
7.9300(16)
90
90.73(3)
90
8.566(3)
11.233(3)
22.545(7)
103.851(5)
91.796(6)
93.920(6)
2098.8(11)
4
18.572(4)
8.1783(16)
14.677(3)
90
107.50(3)
90
9.8641(2)
18.0236(4)
13.0853(3)
90
93.224(3)
90
R (deg)
â (deg)
γ (deg)
V (Å3)
1853.8(6)
4
2126.1(7)
4
2322.71(9)
4
Z
Dcalcd (g cm-3
)
1.162
1.115
1.409
1.370
abs coeff, µ (mm-1
F(000)
)
0.075
0.071
0.977
0.899
696
760
936
1000
θ range (deg)
2.66-26.39
10 204
3778
0.93-25.00
10 951
7382
1.15-27.48
2.26-27.75
no. of data collected
4840
5129
no. of unique data
4840
2064
R
Rw
0.0661
0.1803
1.005
0.0624
0.1371
1.006
0.0339
0.0926
1.024
0.0414
0.0513
0.691
goodness of fit
3e‚CH2Cl2
3f‚CH2Cl2
4c
4f‚CH2Cl2
formula
fw
cryst syst
space group
a (Å)
b (Å)
c (Å)
C
17H16Cl6FeN2O2
C
17H16Br2Cl4FeN2O2
C
22H28Cl2CoN2O2
C
17H16Br2Cl4CoN2O2
548.87
triclinic
P1h
637.79
monoclinic
P1h
482.29
monoclinic
P21/n
640.87
triclinic
P1h
8.1888(16)
8.9943(18)
16.108(3)
100.49(3)
98.71(3)
94.71(3)
1145.8(4)
2
8.1968(16)
8.9615(18)
16.470(3)
102.26(3)
98.51(3)
94.46(3)
1161.7(4)
2
9.840(2)
17.844(4)
13.178(3)
90
92.85(3)
90
8.1368(16)
8.9650(18)
16.349(3)
102.23(3)
98.36(3)
94.28(3)
1146.2(4)
2
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
2311.1(8)
4
Dcalcd (g cm-3
)
1.591
1.823
1.386
1.857
abs coeff, µ (mm-1
F(000)
)
1.373
4.564
0.994
4.717
552
624
1004
626
θ range (deg)
1.30-27.48
1.28-27.45
2.37-27.48
1.29-27.33
no. of data collected
5212
5245
4725
5012
no. of unique data
5212
5245
1929
5012
R
Rw
0.0459
0.1288
1.039
0.0436
0.1042
1.021
0.0432
0.0538
0.708
0.0519
0.1374
1.045
goodness of fit
Eth yl 6-[1-((2,6-Dich lor op h en yl)im in o)eth yl]p yr id in e-
2-ca r boxyla te (2e). Using a procedure analogous to that used
for the synthesis of 2d , 2e was obtained as a viscous yellow
for 3a can be described as follows. The ligand 2a (0.100 g, 0.338
mmol) and FeCl2 (0.043 g, 0.338 mmol) were added to a
Schlenk tube, followed by the addition of freshly distilled
ethanol (4 mL) with rapid stirring at room temperature. The
solution turned deep blue immediately. The reaction mixture
was stirred for 10 h, and absolute diethyl ether (10 mL) was
added to precipitate the complex. After the mixture stood for
30 min, the supernatant was removed. The precipitate was
washed with diethyl ether twice and dried in vacuo to furnish
the pure product as a blue powder in 82.0% yield. Anal. Calcd
for C18H20Cl2FeN2O2: C, 51.10; H, 4.76; N, 6.62. Found: C,
50.43; H, 4.84; N, 6.15. IR (KBr; cm-1): 1708 (νCdO); 1624 (νCd
N); 1590; 1468; 1374 cm-1. Data for 3b are as follows. Yield:
80.0%. IR (KBr; cm-1): 1699 (νCdO); 1623 (νCdN); 1588; 1448;
1376. Anal. Calcd for C20H24Cl2FeN2O2: C, 53.24; H, 5.36; N,
6.21. Found: C, 52.71; H, 5.33; N, 6.09. Data for 3c are as
follows. Yield: 83.0%. IR (KBr; cm-1): 1719 (νCdO); 1619 (νCd
N); 1590; 1464; 1371. Anal. Calcd for C22H28Cl2FeN2O2: C,
55.14; H, 5.89; N, 5.85. Found: C, 54.82; H, 5.86; N, 5.61. Data
for 3d are as follows. Yield: 80.0%. IR (KBr; cm-1): 1711 (νCd
O); 1620 (νCdN); 1591; 1472; 1375. Anal. Calcd for C16H14Cl2F2-
FeN2O2: C, 44.58; H, 3.27; N, 6.50. Found: C, 45.06; H, 3.44;
N, 6.36. Data for 3e are as follows. Yield: 81.0%. IR (KBr;
cm-1): 1701 (νCdO); 1624 (νCdN); 1589; 1564; 1436. Anal. Calcd
for C16H14Cl4FeN2O2: C, 41.42; H, 3.04; N, 6.04. Found: C,
41.32; H, 3.06; N, 5.99. Data for 3f are as follows. Yield: 80.3%.
IR (KBr; cm-1): 1704 (νCdO); 1625 (νCdN); 1590; 1553; 1429.
Anal. Calcd for C16H14Br2Cl2FeN2O2: C, 34.76; H, 2.55; N, 5.07.
Found: C, 35.07; H, 2.57; N, 4.96.
1
oil in 34.4% yield. H NMR (300 MHz, CDCl3; δ): 8.58 (d, 1H,
J ) 7.8 Hz, Py Hm); 8.23 (d, 1H, J ) 7.8 Hz, Py Hm); 7.96 (t,
1H, J ) 7.8 Hz, Py Hp); 7.57 (d, 2H, J 1 ) 8.1 Hz, Ar H); 7.00
(t, 1H, J ) 8.0 Hz, Ar H); 4.50 (q, 2H); 2.38 (s, 3H); 1.46 (t,
3H). 13C NMR (75.45 MHz, CDCl3; δ): 171.19; 165.06; 155.62;
147.509; 145.490; 137.58; 128.25; 126.70; 125.07; 124.53;
124.45; 61.98; 17.60; 14.31. IR (KBr; cm-1): 1721 (νCdO); 1655
(νCdN); 1580; 1556; 1437; 1368. Anal. Calcd for C16H14
-
Cl2N2O2: C, 56.99; H, 4.18; N, 8.31. Found: C, 56.84; H, 4.40;
N, 7.99.
Eth yl 6-[1-((2,6-Dibr om op h en yl)im in o)eth yl]p yr id in e-
2-ca r boxyla te (2f). Using a procedure analogous to that used
for the synthesis of 2d , 2f was obtained as a viscous yellow oil
1
in 63.8% yield. H NMR (300 MHz, CDCl3; δ): 8.59 (d, 1H, J
) 7.8 Hz, Py Hm); 8.23 (d, 1H, J ) 6.9 Hz, Py Hm); 7.97 (t, 1H,
J ) 7.8 Hz, Py Hp); 7.57 (q, 2H, J 1 ) 7.5 Hz, J 2 ) 0.6 Hz, Ar
H); 6.88 (t, 1H, J ) 7.8 Hz, Ar H); 4.49 (m, 2H); 2.37 (s, 3H);
1.46 (t, 3H). 13C NMR (75.45 MHz, CDCl3; δ): 170.89; 164.98;
155.49; 147.87; 147.48; 135.51; 131.93; 126.67; 125.36; 125.01;
113.40; 61.90; 17.55; 14.24. IR (KBr; cm-1): 1720 (νCdO); 1654
(νCdN); 1582; 1548; 1430; 1368. Anal. Calcd for C16H14
-
Br2N2O2: C, 45.10; H, 3.31; N, 6.57. Found: C, 45.12; H, 3.37;
N, 6.34.
Syn th esis of (L)F eCl2 (3a -f; L ) 2a -f). The complexes
3a -f were synthesized by the reaction of FeCl2 with the
corresponding ligands in ethanol. A typical synthetic procedure

Fe and Co 2-(Ethylcarboxylato)-6-iminopyridyl Complexes
Organometallics, Vol. 23, No. 21, 2004 5047
Syn th esis of (L)CoCl2 (4a -f; L ) 2a -f). 4a -f were
prepared by the same synthetic procedure as for 3a -f and
obtained as a green powder. The synthetic procedure of 4a can
be described as follows: to a mixture of ligand 2a (0.150 g,
0.506 mmol) and CoCl2 (0.065 g, 0.500 mmol) was added
freshly distilled ethanol (8 mL) at room temperature. The
solution turned green immediately. The reaction mixture was
stirred for 5 h, and hexane (20 mL) was added to precipitate
the complex. The precipitate was collected by filtration and
washed with hexane, followed by drying in vacuo. The desired
complex was obtained as a green powder in 68.0% yield. IR
(KBr; cm-1): 1713 (νCdO); 1625 (νCdN); 1591; 1468; 1374. Anal.
was isolated via filtration and dried at 60 °C to constant weight
in a vacuum oven.
P r oced u r e for Oligom er iza tion a n d P olym er iza tion s
w ith 10 a tm of Eth ylen e. High-pressure ethylene polymer-
ization was performed in a stainless steel autoclave (2 L
capacity) equipped with a gas ballast through a solenoid clave
for continuous feeding of ethylene at constant pressure. A 700
mL amount of toluene containing the catalyst precursor was
transferred to the fully dried reactor under a nitrogen atmo-
sphere. The required amount of cocatalyst (MAO) was then
injected into the reactor using a syringe. As the prescribed
temperature was reached, the reactor was pressurized to 10
atm. After the reaction mixture was stirred for the desired
period of time, the reaction was quenched and the mixture
worked up using the same method as described above for the
1 atm reaction.
X-r a y Cr ysta llogr a p h ic Stu d ies. Single-crystal X-ray
diffraction studies for ligands 2b,c were carried out on a
Bruker SMART 1000 CCD diffractometer with graphite-
monochromated Mo KR radiation (λ ) 0.710 73 Å). Intensity
data for crystals of 3b,c,e,f and 4c,f were collected on a Rigaku
RAXIS Rapid IP diffractometer with graphite-monochromated
Mo KR radiation (λ ) 0.710 73 Å). Cell parameters were
obtained by global refinement of the positions of all collected
reflections. Intensities were corrected for Lorentz and polar-
ization effects and empirical absorption. The structures were
solved by direct methods and refined by full-matrix least
squares on F2. All non-hydrogen atoms were refined anisotro-
pically. All hydrogen atoms were placed in calculated positions.
Structure solution and refinement were performed by using
the SHELXL-97 package. Crystal data and processing param-
eters for ligands 2b,c and complexes 3b,c,e,f and 4c,f are
summarized in Table 5.
Calcd for
C18H20Cl2CoN2O2: C, 50.73; H, 4.73; N, 6.57.
Found: C, 50.65; H, 4.81; N, 6.39. Data for 4b are as follows.
Yield: 69.2%. IR (KBr; cm-1): 1701 (νCdO); 1624 (νCdN); 1589;
1467; 1375. Anal. Calcd for C20H24Cl2CoN2O2: C, 52.88; H,
5.33; N, 6.17. Found: C, 52.40; H, 5.33; N, 6.04. Data for 4c
are as follows. Yield: 72.0%. IR (KBr; cm-1): 1722 (νCdO); 1620
(νCdN); 1591; 1464; 1371. Anal. Calcd for C22H28Cl2CoN2O2: C,
54.79; H, 5.85; N, 5.81. Found: C, 54.73; H, 5.94; N, 5.45. Data
for 4d are as follows. Yield: 63.3%. IR (KBr; cm-1): 1696 (νCd
O); 1630 (νCdN); 1592; 1471; 1378. Anal. Calcd for C16H14Cl2-
CoF2N2O2: C, 44.27; H, 3.25; N, 6.45. Found: C, 44.22; H, 3.29;
N, 6.19. Data for 4e are as follows. Yield: 63.0%. IR (KBr;
cm-1): 1708 (νvCdO); 1631 (νCdN); 1590; 1563; 1436. Anal. Calcd
for C16H14Cl4CoN2O2: C, 41.15; H, 3.02; N, 6.00. Found: C,
41.17; H, 3.06; N, 5.61. Data for 4f are as follows. Yield: 73.4%.
IR (KBr; cm-1): 1710 (νCdO); 1626 (νCdN); 1591; 1553; 1430.
Anal. Calcd for C16H14Br2Cl2CoN2O2: C, 34.57; H, 2.54; N, 5.04.
Found: C, 34.33; H, 2.57; N, 4.82.
P r oced u r e for Oligom er iza tion s a n d P olym er iza tion s
w ith 1 a tm of Eth ylen e. The complex (5 µmol) was added to
a Schlenk-type flask under nitrogen. The flask was back-filled
three times with N2 and twice with ethylene and then charged
with toluene and MAO solution in turn under an ethylene
atmosphere. In the cases that CH2Cl2 was used as the solvent,
MAO was added first to the dry flask under a nitrogen
atmosphere, and then toluene in the MAO solution was
completely removed in vacuo, followed by addition of complex
and CH2Cl2. At the prescribed temperature, the reaction
solution was vigorously stirred under 1 atm of ethylene for
the desired period of time. The polymerization reaction was
quenched by addition of 60 mL of 10% HCl solution. About 1
mL of organic solution was dried with anhydrous Na2SO4 for
GC determination. The remaining mixture was poured into
100 mL of ethanol to precipitate the polymer. The polyethylene
Ack n ow led gm en t. We are grateful to the National
Natural Science Foundation of China for financial
support under Grant No. 20272062 and National 863
Project (Grant No. 2002AA333060). We thank Dr.
J inkui Niu for the English proofreading.
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
data for 2b,c, 3b,c,e,f, and 4c,f as CIF files. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM0496636