Iron(II) and cobalt(II) 2-(benzimidazolyl)-6-(1-(arylimino)ethyl)pyridyl complexes as catalysts for ethylene oligomerization and polymerization

Article abstract of DOI:10.1021/om0700819

A series of iron(II) (7a-11a) and cobalt(II) (7b-11b) 2-(1-methyl-2- benzimidazolyl)-6-(1-(arylimino)ethyl)pyridyl complexes were synthesized, as well as bidentate iron(II) and cobalt(II) complexes ligated by 2-(2-benzimidazolyl)-6-methylpyridine, 2-(carboethoxyl)-6-(2-benzimidazolyl) pyridine, and 2-(1-methyl-2-benzimidazolyl)-6-acetylpyridine. All organic compounds were fully characterized by NMR and IR spectroscopy and elemental analysis, while the metal complexes were carefully examined by IR spectroscopy and elemental analysis. Their molecular structures were determined by single-crystal X-ray diffraction analysis. The bidentate metal complexes display a distorted-tetrahedral coordination geometry; however, 2a is an exception, with a distorted-trigonal-bipyramidal geometry due to coordination of one DMF molecule. The X-ray crystallographic studies on all of the tridentate metal complexes revealed the coordination geometry as a distorted trigonal bipyramid. Upon activation with MAO or MMAO, the iron(II) 2-(2-benzimidazolyl)-6-(1- (arylimino)ethyl)pyridyl complexes showed high activities with good α-olefin selectivity, while the cobalt(II) analogues displayed moderate to good catalytic activities. However, other bidentate metal complexes showed considerable moderate catalytic activity. The oligomers and polyethylene waxes obtained were α-olefins, and the distribution of oligomers resembled Schulz-Flory rules with some exceptions. Various reaction parameters were investigated, and the results revealed that both the steric and electronic effects of ligands affect the catalytic activities of their metal complexes as well as the distribution of products.

Full text of DOI:10.1021/om0700819

2720
Organometallics 2007, 26, 2720-2734
Iron(II) and Cobalt(II)
2-(Benzimidazolyl)-6-(1-(arylimino)ethyl)pyridyl Complexes as
Catalysts for Ethylene Oligomerization and Polymerization
Wen-Hua Sun,* Peng Hao, Shu Zhang, Qisong Shi, Weiwei Zuo, and Xiubo Tang
Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Sciences, Institute
of Chemistry, Chinese Academy of Sciences, Beijing 100080, People’s Republic of China
Xiaoming Lu
Department of Chemistry, Capital Normal UniVersity, Beijing 100037, People’s Republic of China
ReceiVed January 28, 2007
A series of iron(II) (7a-11a) and cobalt(II) (7b-11b) 2-(1-methyl-2-benzimidazolyl)-6-(1-(arylimino)-
ethyl)pyridyl complexes were synthesized, as well as bidentate iron(II) and cobalt(II) complexes ligated
by 2-(2-benzimidazolyl)-6-methylpyridine, 2-(carboethoxyl)-6-(2-benzimidazolyl)pyridine, and 2-(1-
methyl-2-benzimidazolyl)-6-acetylpyridine. All organic compounds were fully characterized by NMR
and IR spectroscopy and elemental analysis, while the metal complexes were carefully examined by IR
spectroscopy and elemental analysis. Their molecular structures were determined by single-crystal X-ray
diffraction analysis. The bidentate metal complexes display a distorted-tetrahedral coordination geometry;
however, 2a is an exception, with a distorted-trigonal-bipyramidal geometry due to coordination of one
DMF molecule. The X-ray crystallographic studies on all of the tridentate metal complexes revealed the
coordination geometry as a distorted trigonal bipyramid. Upon activation with MAO or MMAO, the
iron(II) 2-(2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridyl complexes showed high activities with good
R-olefin selectivity, while the cobalt(II) analogues displayed moderate to good catalytic activities. However,
other bidentate metal complexes showed considerable moderate catalytic activity. The oligomers and
polyethylene waxes obtained were R-olefins, and the distribution of oligomers resembled Schulz-Flory
rules with some exceptions. Various reaction parameters were investigated, and the results revealed that
both the steric and electronic effects of ligands affect the catalytic activities of their metal complexes as
well as the distribution of products.
have been achieved with the Ziegler (Alfen) process,5 chromium-
based complexes6 and the Shell Higher Olefin Process (SHOP).7
Breakthroughs in organometallic chemistry and its catalytic
applications have completely transformed our view of designing
new complexes as Robot catalysts for ethylene oligomerization
and polymerizations. The rapid progress in the use of metal
complexes have been termed a “metal complex revolution” for
ethylene activation. First, metallocenes (zirconocene and half-
metallocene) were used as single-site catalysts in the 1980s,4c,d,8
followed by late-transition-metal catalysts9 in the mid-1990s;
at present, various catalysts of complexes of early10 and late
transition metals dominate the scene. However, the strong defect
of “deactivation” caused by the oxophilicity of early-transition-
1. Introduction
The US market for polyolefins and R-olefins is in the tens of
billions of dollars, both indicating their importance and stimulat-
ing interest in academic and industrial research in this field.
Polyolefins, with an annual market of over 110 million tons,
are half the volume of all synthesized plastics.1 Linear R-olefins,
on the other hand, with more than 5 million tons annual
production, are important substances used in the preparation of
detergents, lubricants, plasticizers, oil field chemicals, and
monomers for copolymerization. One challenge is to design
catalysts with higher catalytic activity and performance for
advanced polyolefins. With ethylene as the feedstock, ethylene
activation has provided fast-growing polyethylenes made up of
60% polyolefins and is the major source of linear R-olefins (a
range of C4/C6 up to C20+). The industrial processes of ethylene
polymerization have developed with catalysts of titanium,2
chromium,2b,3 and recently zirconium,4 while the processes of
ethylene oligomerization (including on purpose and full range)
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* To whom correspondence should be addressed. Tel: +86 10
62557955. Fax: +86 10 62618239. E-mail: whsun@iccas.ac.cn.
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Springer-Verlag: Berlin, Heidelberg, Germany, 1999. (b) Pullukat, T. J.;
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10.1021/om0700819 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 04/04/2007

Fe and Co Catalysts for Ethylene ReactiVity
Organometallics, Vol. 26, No. 10, 2007 2721
metal complexes during storage paved the way for stable late-
transition-metal complexes as catalysts for ethylene reactivity
with the expectation of high activity.
transition-metal catalysts to ethylene oligomerization for linear
R-olefins;14a in addition, iron catalysts have shown the advan-
tages of high activities and exceptional selectivity of R-olefins
to produce new olefin waxes.14a,17 The valuable catalysts are
potentially useful as new drop-in catalysts in the current
commercial processes operated by BP, Chevron Phillips, and
Shell.18 Apart from iron(II) catalysts ligated by bis(imino)-
pyridines, a few new models of iron catalysts were reported to
have limited activity,19 but iron complexes based on 1,10-
phenanthroline20 provided an alternative iron model with very
high activity.21 During our extensive research on metal com-
plexes with iminopyridines,22 2-imino-1,10-phenanthrolines,23
and 2,6-bis(2-benzimidazole)pyridines,24 a new challenge has
been to develop a catalyst model of complexes bearing novel
ligands as the hybrids of bis(1-(arylimino)ethyl)pyridines and
bis(2-benzimidazolyl)pyridines, 2-(benzimidazolyl)-6-(1-(arylim-
ino)ethyl)pyridines. The proposed metal complexes ligated by
The strategy of late-transition-metal catalysts in olefin activa-
tion started with the “nickel effect” in the 1950s, and optimiza-
tion of the reaction conditions resulted in the development of
the SHOP process. In contrast to the case for the development
of early-transition-metal catalysts, the late-transition-metal
catalysts have been less investigated because of major â-hy-
drogen elimination occurring in competition with ethylene
insertion and chain propagation of the polymer. The resurrection
of late-transition-metal catalysts was initially induced by the
development of bidentate nickel and palladium diimino halides
by the Brookhart group,11 and tridentate iron and cobalt 2,6-
bis(imino)pyridyl halides by both the Brookhart group12 and
the Gibson group.13 Late-transition-metal complexes as catalysts
for ethylene oligomerization and polymerization have currently
drawn much attention in the design of new catalysts and
optimization of the standard catalyst models.14 The progress in
the use of late-transition-metal catalysts has been well docu-
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insights into their active intermediates and catalytic mecha-
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longstanding consideration and promising application of late-
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2722 Organometallics, Vol. 26, No. 10, 2007
Sun et al.
Scheme 1. Synthesis of
2-(1-Methyl-2-benzimidazolyl)-6-acetylpyridine and Its
Intermediates
2-(benzimidazolyl)-6-(1-(arylimino)ethyl)pyridines would po-
tentially have the advantage of high activities and flexibilities
in producing R-olefins or R-olefin waxes through adapting their
structural features. To verify this hypothesis, a convenient
synthetic methodology was developed to prepare the ligand
model of 2-(2-benzimidazolyl)-6-acetylpyridine in good yield
on the laboratory scale of tens of grams through intermediate
compounds of 2-(2-benzimidazolyl)-6-methylpyridine and 2-(car-
boethoxyl)-6-(2-benzimidazolyl)pyridine. The 2-(benzimida-
zolyl)-6-(1-(arylimino)ethyl)pyridines were routinely prepared
by the condensation reactions of 2-(2-benzimidazolyl)-6-
acetylpyridine with corresponding substituted anilines; thereafter,
their iron and cobalt complexes were synthesized and character-
ized. As expected, upon activation with organoaluminum, the
catalytic systems of 2-(benzimidazolyl)-6-(1-(arylimino)ethyl)-
pyridyl complexes demonstrated very high activities in ethylene
oligomerization and polymerization to produce R-olefins and
waxes. In addition, metal complexes ligated by 2-(2-benzimi-
dazolyl)-6-methylpyridine, 2-(carboethoxyl)-6-(2-benzimidazolyl)-
pyridine, and 2-(1-methyl-2-benzimidazolyl)-6-acetylpyridine
were also synthesized and characterized, and their catalytic
performance in ethylene activation was examined. Herein the
synthesis and characterization of 2-(1-methyl-2-benzimidazolyl)-
6-(1-(arylimino)ethyl) pyridines and their synthetic intermediates
as well as of their iron and cobalt complexes are reported, along
with a detailed investigation of the catalytic behavior of metal
complexes to ethylene activation under various reaction condi-
tions.
Scheme 2. Reaction of MCl2 with
2-(Benzimidazolyl)pyridine Derivatives
2. Results and Discussion
2.1. Preparation of 2-(1-Methyl-2-benzimidazole)-6-acetylpy-
ridine and Its Synthetic Intermediates. The design of
functional organic compounds as suitable ligands is an interest-
ing prerequisite for new complexes in coordination chemistry
and homogeneous catalysis. In order to obtain 2-(2-benzimi-
dazole)-6-acetylpyridine, with two functional groups, it is
necessary to employ multistep synthetic procedures. The
literature synthetic methods for constructing 2-benzimida-
zolylpyridine include the condensation reaction of o-phenylene-
diamine and pyridine-2-carboxylic acid in the presence of
phosphoric acid (PPA)25 or the oxidation reaction by sulfur of
o-phenylenediamine and 2,6-lutidine.26 Accordingly, the solid
reaction of o-phenylenediamine and 2,6-lutidine in the presence
of sulfur oxidant was employed to prepare 2-(2-benzimidazolyl)-
6-methylpyridine (1) in an acceptable yield.26 Though several
oxide reagents were tried, it was necessary to use SeO2 in the
oxidation of 2-(2-benzimidazolyl)-6-methylpyridine (1) into
6-(2-benzimidazolyl)pyridine-2-carboxylic acid (3).27 In the
presence of a catalytic amount of H2SO4, its esterification with
ethanol was carried out to form 2-(carboethoxy)-6-(2-benzimi-
dazolyl)pyridine (4).19g,28 Perhaps due to the reaction of benz-
imidazole with a strong base, the transformation of its carbox-
ylate into an acetyl group to form 6-(2-benzimidazolyl)-2-
acetylpyridine could not be achieved by direct reflux with ethyl
acetate in the presence of C2H5ONa and the following workup.
Therefore, the N-methylation of the 2-benzimidazolyl compound
to 2-(carboethoxy)-6-(1-methyl-2-benzimidazolyl)pyridine (5)
was carried out with the reaction of methyl iodide in acetonitrile
and K2CO3 at room temperature.29 Then, the routine transforma-
tion of a carboxylate group into an acetyl group,19g through a
Claisen reaction with ethyl acetate under basic conditions and
then proceeding in acidic solution, gave 2-(1-methyl-2-benz-
imidazolyl)-6-acetylpyridine (6) in an appropriate yield. Simi-
larly, 2-(1-methyl-2-benzimidazolyl)-6-methylpyridine (2) was
also synthesized in good yield through the N-methylation
reaction. All synthesized compounds were well characterized
and confirmed by elemental analysis and 1H and 13C NMR and
IR spectrometry. The synthetic procedures from 2,6-lutidine to
6-(1-methyl-2-benzimidazolyl)-2-acetylpyridine are summarized
in Scheme 1.
2.2. Synthesis and Characterization of Iron and Cobalt
Complexes Bearing Various 6-Substituted 2-Benzimida-
zolylpyridines. The synthesized 6-substituted 2-benzimida-
zolylpyridine derivatives 2-(1-R′-2-benzimidazolyl)-6-R′′-
pyridine (R′ ) H, R′′ ) Me, 1; R′ ) Me, R′′ ) Me, 2; R′ ) H,
R′′ ) carboethoxyl, 4; R′ ) Me, R′′ ) carboethoxyl, 5; R′ )
Me, R′′ ) acetyl, 6) could be good bidentate or tridentate ligands
for coordination with transition metals. Guided by our previous
works on bidentate iron and cobalt catalysts for ethylene
activation,22,30 the complexes were synthesized in proper yields
by equimolar reactions of the synthesized 2-benzimidazolyl-
pyridine derivatives with FeCl2‚4H2O or CoCl2 in ethanol
(Scheme 2).
(25) Barni, E.; Savarino, P. J. Heterocycl. Chem. 1977, 14, 937.
(26) Tsukamoto, G.; Yoshino, K.; Kohno, T.; Ohtaka, H.; Kagaya, H.;
Ito, K. J. Med. Chem. 1980, 23, 734.
These complexes were characterized by elemental analysis
and IR spectrometry. In comparison with the IR spectrometry
(27) Piguet, C.; Bu¨nzli, J. G.; Bernardinelli, G.; Hopfgartner, G.;
Williams, A. F. J. Am. Chem. Soc. 1993, 115, 8197.
(28) Piguet, C.; Bocquet, B.; Hopfgartner, G.; HelV. Chim. Acta 1994,
77, 931.
(29) Kikugawa, Y. Synthesis 1981, 2, 124.
(30) Shao, C.; Sun, W.-H.; Li, Z.; Hu, Y.; Han, L. Catal. Commun. 2002,
3, 405.

Fe and Co Catalysts for Ethylene ReactiVity
Organometallics, Vol. 26, No. 10, 2007 2723
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
Complexes 1b, 2a, 2b, and 5b (M ) Co, Fe)
1b
2b
2a
5b
Bond Lengths
M-N1
2.0197(1)
2.0701(1)
2.2132(5)
2.2286(5)
1.392(2)
1.327(2)
1.358(2)
1.347(2)
1.468(2)
2.0003(2)
2.0744 (2)
2.2174(5)
2.2174(5)
1.384(3)
1.331(3)
1.366(3)
1.339(3)
1.476(3)
2.0989(2)
2.3322(2)
2.3179(7)
2.3232(7)
1.392(3)
1.327(3)
1.358(3)
1.334(3)
1.472(3)
2.1702(2)
2.0627(2)
2.0912(2)
2.2854(8)
2.2404(7)
1.381(3)
1.327(3)
1.346(3)
1.335(3)
1.474(3)
M-N2
M-Cl1
M-Cl2/1A
N1-C1
N1-C7
N2-C8
N2-C12
C7-C8
M-O1
Bond Angles
80.56(7)
N2-M-N1
81.56(6)
74.71(7)
98.54(5)
117.75(6)
125.07(3)
116.48(6)
87.46(5)
77.36(8)
Figure 1. Molecular structure of 1b. Thermal ellipsoids are shown
at the 30% probability level. Hydrogen atoms have been omitted
for clarity.
N2-M-Cl1
114.44(5)
116.97(5)
111.27(2)
118.91(5)
110.27(4)
115.05(3)
117.13(3)
109.52(3)
117.13(3)
115.05(3)
104.18(6)
106.55(6)
112.79(3)
106.08(6)
139.55(6)
N1-M-Cl1
Cl1-M-Cl2/1A
N1-M-Cl2/1A
N2-M-Cl2/1A
of free organic compounds, the absorption bands of complexes
were shifted to lower frequencies, indicating the coordination
effects. The complexes are stable in their solid state; however,
the color of the iron complex solutions slowly changed because
of oxidation. To understand their real structures, the single
crystals of complexes 1b, 2a,b, and 5b were determined by
single-crystal X-ray diffraction. Their molecular structures are
discussed with their structural features, while their selected bond
lengths and angles are collected in Table 1.
In the structure of 1b (Figure 1), the geometry around the
cobalt center can be described as a distorted tetrahedron, in
which the cobalt was coordinated with the sp2 N1 instead of
sp3 N3 in the benzimidazole ring. In this structure, the pyridine
ring is almost coplanar with the benzimidazole ring (the dihedral
angle is 2.3°). The Co-Nbenzimidazole bond length of 2.0197(1)
Å is slightly shorter than the Co-Npyridine length of 2.0701(1)
Å.
Figure 2. Molecular structure of 2a. Thermal ellipsoids are shown
at the 30% probability level. Hydrogen atoms have been omitted
for clarity.
Single crystals of 2a were obtained by diffusing a diethyl
ether layer into its solution mixture of ethanol and DMF. The
molecular structure of five-coordinated 2a consists of a distorted-
trigonal-bipyramidal geometry in which the iron atom is
surrounded by one ligand, two chlorides, and one DMF molecule
coordinated by an oxygen atom linkage (Figure 2). The axial
positions are occupied by N2pyridine and O1 from the DMF
molecule (N2-Fe1-O1 ) 167.42(6)°), while the equatorial
plane is formed by the nitrogen (N1) atom of benzimidazole
and two chlorides with the deviation of the iron center from
the equatorial plane by 0.1086 Å. The axial plane and the
equatorial plane make a dihedral angle of 88.7°. The Fe1-
N2pyridine bond (2.1702(2) Å) is significantly longer than the
Fe1-N1benzimidazole bond (2.0989(2) Å), which can be attributed
to the coordination of the DMF molecule. It is noteworthy that
the benzimidazole ring and pyridyl ring are not coplanar, having
a dihedral angle of 26.6°, which is different from the observation
in complex 1b and the following 2b because of the different
geometries around the metal center.
Figure 3. Molecular structure of 2b. Thermal ellipsoids are shown
at the 30% probability level. Hydrogen atoms have been omitted
for clarity.
In the molecular structure of 5b (Figure 4), the geometry
around the cobalt center can be described as a distorted
tetrahedron. The distance between the oxygen and cobalt atoms,
Co1‚‚‚O1, is 2.428 Å, which is substantially longer than the
normal Co1-O1 bond distance (2.2191(2) Å).31 The same
observation was found in the (2-(ethylcarboxylato)-6-iminopy-
ridyl)iron(II) and -cobalt(II) complexes, which indicated a weak
interaction between the cobalt and carbonyl oxygen atoms.18
In comparison with those in the cobalt complexes 1b and 2b,
both the Co1-N1 and Co1-N2 bonds in 5b are slightly longer,
which can be attributed to the weak interaction between the
The molecular structure of 2b showed the geometry of a
distorted tetrahedron (Figure 3). In this structure, the Co-
Nbenzimidazole bond length of 2.0003(2) Å is slightly shorter than
the Co-Npyridine length of 2.0744(2) Å. However, different from
the case for complex 1b, 2b displays an approximate Cs
symmetry about the plane containing the cobalt atom and all
the non-hydrogen atoms of 2. The distortion from a regular
tetrahedron is not as remarkable as that in the cobalt complexes
which contain a steric substituent at the 6-position of the pyridine
ring.19c
(31) March, R.; Clegg, W.; Coxall, R. A.; Gonza´lez-Duarte, P. Inorg.
Chim. Acta, 2003, 346, 87.

2724 Organometallics, Vol. 26, No. 10, 2007
Sun et al.
The obtained complexes were precipitated from the reaction
solution and separated as blue powders in good yields (70-
96%) with good purity. These complexes are air-stable in the
solid state but turned from blue to yellow in solution when
exposed to air for a few minutes, indicating their oxidation in
solution. The formation of these complexes was confirmed by
elemental analysis and IR. In comparison with the IR spectra
of the free ligands with CdN stretching frequencies in the range
of 1639-1650 cm-1, the CdN stretching vibrations in com-
plexes 7a-11a were shifted toward lower frequencies in the
range of 1591-1595 cm-1 with the reduced peak intensity,
which indicated an effective coordination interaction between
the imino nitrogen atom and the iron center.
By using the same synthetic method, the cobalt complexes
7b-11b were conveniently prepared as green powders in
isolated yields (46-73%) (Scheme 3). These cobalt complexes
are stable in both solution and the solid state. Similar to the
case for the iron analogues, all of the cobalt complexes showed
lower frequencies of ν(CdN) with wavenumber shifts of 40-
50 cm-1 along with a decreased peak intensity, in contrast to
the signals for the corresponding free ligands.
Figure 4. Molecular structure of 5b. Thermal ellipsoids are shown
at the 30% probability level. Hydrogen atoms have been omitted
for clarity.
Scheme 3. Synthesis of
2-(1-Methyl-2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridines
and Their Metal Complexes
Moreover, single crystals of 7 and 10 suitable for X-ray
analysis were obtained by slow evaporation of their individual
saturated ethyl acetate solutions. Single crystals of complexes
7a, 10a, 7b, and 8b were individually obtained by slow diffusion
of diethyl ether into their methanol solutions under a nitrogen
atmosphere, while single crystals of 10b were obtained by the
slow diffusion of diethyl ether into a saturated solution of the
compound in methanol and DMF.
The crystal study of 7 and 10 revealed their E conformations
as free molecules (Figure 4). The dihedral angles of the phenyl
ring on imine with pyridine are 76.5° in 7 and 69.7° in 10. Two
planes of the benzimidazole and the pyridine are nearly coplanar
with a dihedral angle of 0.2° in 7; however, this phenomenon
was not observed in 10, in which the dihedral angle is 8.2°.
The imino groups with a bond length of 1.2656(2) Å in 7 and
1.277(2) Å in 10 are in the range of typical CdN double-bond
lengths. Their selected bond lengths and angles are listed below
Figure 5.
cobalt and carbonyl oxygen atoms. The pyridine ring was nearly
coplanar with the benzimidazole ring, having a dihedral angle
of 5.1°.
2.3. Synthesis and Characterization of 2-(1-Methyl-2-
benzimidazolyl)-6-(1-(arylimino)ethyl)pyridines (7-11) and
Their Iron and Cobalt Complexes (7a-11a, 7b-11b). The
2-(1-methyl-2-benzimidazolyl)-6-(1-(arylimino)ethyl)py-
ridines 7-9 were easily prepared in satisfactory yields (68-
89%) through the condensation reactions of 2-(1-methyl-2-
benzimidazoleyl)-6-acetylpyridine ketones and the appropriate
substituted anilines using p-toluenesulfonic acid as the catalyst;32
however, the analogues 10 and 11 with halogen substituents
on the phenyl ring were necessarily synthesized with a small
amount of 4 Å molecular sieves as a water absorber (Scheme
3). The synthetic method with 4 Å molecular sieves as a water
absorber offers the advantages of mild reaction conditions and
smaller amount of solvent. The 2-(2-benzimidazolyl)-2-(1-
(arylimino)ethyl) pyridines 7-11 were routinely characterized
by elemental analysis and 1H and 13C NMR, IR, and ESI mass
spectrometry. The IR spectra of the ligands showed that the
CdN stretching frequencies appeared in the range of 1639-
An X-ray crystallographic study on the iron complex 7a
revealed the coordination geometry around metal center as a
distorted trigonal bipyramid with the pyridyl nitrogen atom and
the two chlorides forming an equatorial plane; the molecular
structure is shown in Figure 6 with selected bond lengths and
angles being given in Table 2. The deviation of the iron center
from equatorial plane is 0.0075 Å, and the iron atom is nearly
in this triangular plane with equatorial angles ranging between
133.00(1) and 115.68(1)°. The two nitrogen atoms (N1 and N3)
occupy the axial coordination sites with a bond angle of 145.23-
(2)° for N1-Fe1-N3. The benzimidazole ring and the pyridyl
ring are nearly coplanar, with a dihedral angle of 6.0°. The
equatorial plane is oriented perpendicularly (86.6°) to the
pyridine, and the dihedral angle between the phenyl ring and
the pyridine is 83.3°. Nonetheless, the phenyl ring lies almost
perpendicular to the plane formed by the coordinated nitrogen
atoms (86.7°), which is similar to the case for the (2,6-bis-
(imino)pyridyl)iron(II) complexes12,13 and (2-imino-1,10-phenan-
throlinyl)iron(II) complexes.21 Furthermore, the iron atom
deviates by 0.2115 Å from this coordinated plane and the two
Fe-Cl bond lengths show a slight difference between Fe-Cl1
(2.3131(1) Å) and Fe-Cl2 (2.2911(2) Å). The difference usually
appears in tridentate N∧N∧N iron(II) complexes and may be
ascribed to apical elongation in the square-pyramidal complex.32b
The Fe-N2(pyridyl) (2.153(4) Å) bond is shorter (by about 0.13
1650 cm-1
.
Their iron complexes 7a-11a were prepared by stirring an
ethanol solution of 1 equiv of FeCl2·4H2O and the corresponding
ligands 7-11 at room temperature under nitrogen (Scheme 3).
(32) (a) Chen, Y.; Qian, C.; Sun, J. Organometallics 2003, 22, 1231.
(b) Chen, Y.; Chen, R.; Qian, C.; Dong, X.; Sun, J. Organometallics 2003,
22, 4312.

Fe and Co Catalysts for Ethylene ReactiVity
Organometallics, Vol. 26, No. 10, 2007 2725
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
Complexes 7a, 10a, 7b, 8b, and 10b (M ) Co, Fe).
7a
10a
7b
8b
10b
Bond Lengths
M-N1
2.160(4) 2.157(2) 2.1326(1) 2.132(2) 2.1293(2)
2.153(4) 2.138(2) 2.0801(1) 2.079(2) 2.0889(1)
2.283(4) 2.286(2) 2.2323(1) 2.209(2) 2.2661(2)
2.3131(1) 2.2887(8) 2.2716(5) 2.2723(1) 2.2683(5)
2.2911(2) 2.3197(8) 2.2790(5) 2.2643(1) 2.2978(5)
1.365(6) 1.383(3) 1.378(2) 1.384(4) 1.381(2)
1.316(6) 1.324(3) 1.329(2) 1.315(4) 1.326(2)
1.368(6) 1.354(3) 1.3462(2) 1.345(4) 1.342(2)
1.334(5) 1.328(3) 1.336(2) 1.333(4) 1.332(2)
1.272(6) 1.281(3) 1.280(2) 1.279(4) 1.278(2)
1.441(6) 1.429(3) 1.4400(2) 1.442(4) 1.427(2)
M-N2
M-N3
M-Cl1
M-Cl2
N1-C1
N1-C7
N2-C8
N2-C12
N3-C13
N3-C15
Bond Angles
N2-M-N1 73.95(2) 74.24(8) 75.95(5) 75.26(1) 75.65(6)
N2-M-N3 72.20(1) 71.65(8) 73.98(5) 74.12(9) 72.85(6)
N1-M-N3 145.23(2) 142.45(8) 147.76(5) 146.20(9) 144.46(6)
N2-M-Cl1 133.00(1) 147.68(6) 142.45(4) 98.34(8) 149.33(4)
N1-M-Cl1 97.55(1) 104.86(6) 98.31(4) 97.46(7) 102.17(4)
N3-M-Cl1 99.65(1) 95.81(6) 98.41(4) 100.80(8) 96.67(4)
Cl1-M-Cl2 111.32(6) 114.14(3) 115.71(2) 115.87(5) 113.93(2)
N1-M-Cl2 100.31(1) 96.92(6) 98.43(4) 98.16(7) 97.38(4)
N2-M-Cl2 115.68(1) 97.85(6) 101.83(4) 145.77(8) 96.58(4)
N3-M-Cl2 101.19(1) 102.79(6) 98.82(4) 99.07(8) 102.13(4)
Figure 5. Molecular structures of 7 and 10. Thermal ellipsoids
are shown at the 30% probability level. Hydrogen atoms have been
omitted for clarity. Selected bond distances (Å) and angles (deg)
are as follows. 7: N2-C8, 1.3372(2); N2-C12, 1.3387(2); N3-
C13, 1.2656(2); N3-C15, 1.4237(2); N1-C7, 1.3189(2); N1-C1,
1.3798(2); C8-N2-C12, 118.04(1); C13-N3-C15, 121.16(1);
C7-N1-C1, 104.67(1). 10: N2-C8, 1.341(2); N2-C12, 1.348-
(2); N3-C13, 1.277(2); N3-C15, 1.410(2); N1-C7, 1.319(2); N1-
C1, 1.383(2); C8-N2-C12, 117.99(2); C13-N3-C15, 120.61(2);
C7-N1-C1, 105.10(2).
electronic effects of chloro and methyl substituents. Similarly,
the imino N3-C13 bond in 10a displays clear double-bond
character (1.281(3) Å) and is slightly longer than that of the
free ligand 10.
The cobalt analogues 7b, with a 2,6-dimethylphenyl group,
and 8b, with a 2,6-diethylphenyl group, have the same structural
character, as shown in Figure 8, along with the selected bond
distances and angles given in Table 2. The coordination
geometry around the cobalt center can be described as distorted
trigonal bipyramidal, in which the nitrogen of the pyridyl group
and two chlorides compose the equatorial plane, while the cobalt
atom lies slightly out of the equatorial plane in 7b (0.0110 Å)
and 8b (0.0143 Å). The axial planes are occupied by N1-Co1-
N3, and the bond angles N1-Co1-N3 are nearly identical in
the two complexes (147.76(5)° (7b) and 146.20(9)° (8b)). The
equatorial planes of these two complexes are nearly perpen-
dicular to the benzimidazole ring, with dihedral angles of 88.8°
in 7b and 88.3° in 8b. The dihedral angles between the phenyl
plane and the benzimidazole ring are 83.8° in 7b and 85.6° in
8b. The two imino CdN bonds have distinctive double-bond
character, with C-N distances of 1.280(2) Å (7b) and 1.279-
(4) Å (8b). The CdN bond in 7b is about 0.015 Å longer than
that of the corresponding free ligand, indicating coordination
effects in the iron analogues. The steric effect of the substituents
at the ortho positions of the phenyl ring are slightly reflected
in the adjacent bond lengths. The Co1-N(imino) bond length
of 7b (2.2323(1) Å) is noticeably longer than that of 8b (2.209-
(2) Å). This effect is due to the relatively bulkier ethyl groups
at the ortho positions of the phenyl ring in 8b.
The molecular structure of complex 10b is shown in Figure
9. The cobalt atom slightly deviates by 0.0458 Å from the
equatorial plane. The three equatorial angles N2-Co1-Cl1,
N2-Co1-Cl2, and Cl1-Co1-Cl2 are 149.33(4), 96.58(4), and
113.93(2)°, respectively, while the larger distortion of N2-
Co1-Cl1 and the axial Co1-N bonds subtend an angle of N1-
Co1-N3 (144.46(6)°). The dihedral angle between the equa-
torial plane and the benzimidazole plane is 84.2°, while the
dihedral angle between the phenyl plane and the benzimidazole
plane is 93.0°. Its two axial Co1-N bond lengths (2.1293(2)
and 2.2661(2) Å) are longer than Co1-N2 in the equatorial
plane (2.0889(1) Å), which is usually observed in (bis(imino)-
Figure 6. Molecular structure of 7a. Thermal ellipsoids are shown
at the 30% probability level. Hydrogen atoms and solvent molecules
have been omitted for clarity.
Å) than the Fe-N3(imino) (2.283(4) Å) bond and is only
slightly shorter than the Fe-N1(benzimidazole) (2.160(4) Å)
bond. The imino N3-C13 bond in 7a displays clear double-
bond character (1.272(6) Å).
With structural features similar to those of 7a, the molecular
structure of complex 10a is shown in Figure 7. According to
Table 2, its Fe-N and Fe-Cl bond lengths are nearly the same
as those of 7a. In 10a, the deviation of the iron center from the
equatorial plane is 0.0678 Å. The two nitrogen atoms (N1 and
N3) occupy the axial coordination sites with a bond angle of
142.45(8)° for N1-Fe1-N3. The equatorial plane is oriented
perpendicularly (83.2°) to the pyridyl plane, and the dihedral
angles between the phenyl ring and the pyridyl plane and
between the phenyl ring and the benzimidazole plane are 86.7
and 92.1°, respectively. The phenyl ring also lies almost
perpendicular to the plane formed by the coordinated nitrogen
atoms. However, a slight difference exists between the two
structures. The dihedral angle of the benzimidazole ring and
the pyridyl ring is 9.5°, which is wider than that of complex
7a. The deviation (0.4154 Å) of the iron atom from the
coordinated plane is much greater than that observed in 7a.
These structural differences may be due to the different

2726 Organometallics, Vol. 26, No. 10, 2007
Sun et al.
Table 3. Ethylene Oligomerization by Metal Complexes
Ligated with 1, 2 and 4-6 and Their Oligomer Distributiona
oligomer distribn (%)c
entry cat.
cocat.
Al/M activityb
C4/∑C
C6/∑C
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
1a
1a
1a
1a
2a
4a
5a
6a
6a
1b
1b
2b
4b
5b
6b
MMAO
Et2AlCl
Et2AlCl
MAO
1000
500
200
1000
1000
1000
1000
1000
200
500
200
200
200
0.86
0.56
0.38
0.26
0.78
5.15
3.33
0.90
1.29
1.29
1.41
0.80
1.13
0.76
0.80
81.4
58.7
60.2
53.9
68.3
96.3
96.3
75.0
76.2
67.4
70.5
37.4
81.6
77.9
48.5
18.6
41.3
39.8
46.1
31.7
3.4
MMAO
MMAO
MMAO
MMAO
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
3.7
25.0
23.8
32.6
29.5
62.6
18.4
22.1
51.5
Figure 7. Molecular structure of 10a. Thermal ellipsoids are shown
at the 30% probability level. Hydrogen atoms have been omitted
for clarity.
200
200
a Conditions: 5 µmol of catalyst; 30 min; 20 atm of ethylene, 20 °C,
100 mL of toluene. b In units of 104 g (mol of M)-1 h-1 atm-1 c Determined
.
by GC; ∑C signifies the total amounts of oligomers.
that the introduction of electron-withdrawing substituents on
the phenyl rings slightly affects the structural properties.
Moreover, the difference between the two Co1-Cl linkages,
Co1-Cl2 (2.2978(5) Å) and Co1-Cl1 (2.2683(5) Å), is about
0.03 Å.
2.4. Ethylene Oligomerization and Polymerization. 2.4.1.
Ethylene Oligomerization by Bidentate Metal Complexes.
Different functional groups and coordinated environments of
the complexes affected their catalytic behaviors toward ethylene
activation. Prior to investigating the titled complexes, the metal
complexes bearing bidentate N∧N coordinated ligands of various
6-substituted 2-benzimidazolylpyridines such as 1, 2, and 4-6
were also synthesized and investigated for their ethylene
oligomerzation. When different organoaluminum were used at
an ambient pressure of ethylene, these iron and cobalt complexes
showed very low catalytic activities; therefore, 20 atm of
ethylene was fixed for the reaction. Considerable catalytic
activities of iron complexes were obtained with cocatalysts such
as MAO, MMAO, and Et2AlCl. As a matter of fact, in general,
the catalytic system with MAO showed activities lower than
those with MMAO or Et2AlCl on the basis of the results of 1a
(Table 3). However, their cobalt analogues showed low activities
toward ethylene reactivity with cocatalysts of MAO and MMAO
but good activities with Et2AlCl (Table 3).
Figure 8. Molecular structures of 7b and 8b. Thermal ellipsoids
are shown at the 30% probability level. Hydrogen atoms have been
omitted for clarity.
In comparison with the metal complexes ligated by 2 as
catalysts (entries 5 and 12 in Table 3), the catalytic systems of
complexes 1a,b had relatively higher activities (entries 1 and
11 in Table 3), and the same tendency was also observed in the
complexes ligated by 4 and 5 (entry 6 vs 7 and entry 13 vs 14
in Table 3). These results, which concurred with the literature
reports,24,33 can be attributed to the deprotonation of the N-H
group to give anionic amide ligands and form N-Al species to
increase their catalytic activity when activated by the orga-
noaluminum cocatalyst. The iron complexes 4a and 5a, contain-
ing a carboxylate group at the 6-position of the pyridine ring,
exhibited reactivities higher than those of their analogues ligated
by 1 and 2, even better than those containing 6. This phenom-
enon could be assumed to be the result of the better solubility
of complexes or the electron-withdrawing effect of the car-
boxylate group and the weak metal-oxygen interaction.19c
Furthermore, when iron complexes with an ester group were
Figure 9. Molecular structure of 10b. Thermal ellipsoids are shown
at the 30% probability level. Hydrogen atoms have been omitted
for clarity.
pyridyl)cobalt(II) complexes.12,13 In comparison with the 2,6-
dialkylphenyl complexes 7b and 8b, Co1-N1 and Co1-N2
have almost identical bond lengths, while the Co1-N3(imino)
bond length of 10b is relatively longer than that of 7b and 8b.
The imino N3-C13 bond length is 1.278(2) Å, having the
typical character of a CdN double bond. These facts suggest
(33) McGuinness, D. S.; Wasserscheid, P.; Morgan, D. H.; Dixon, J. T.
Organometallics 2005, 24, 552.

Fe and Co Catalysts for Ethylene ReactiVity
Organometallics, Vol. 26, No. 10, 2007 2727
Table 4. Ethylene Oligomerization of the 6a/Et2AlCl Systema
Table 5. Selection of a Suitable Cocatalyst Based on 7aa
oligomer distribn (%)c
oligomer
activityb
oligomer
distribn
polymer
activityb
entry
cocat.
Al/Fe
entry
Al/Fe
P/atm
T/°C
activityb
C4/∑C
C6/∑C
1
2
3
MAO
MMAO
Et2AlCl
1000
1000
200
9.2
12.0
C4-C28
C4-C26
1.0
trace
1
2
3
4
5
6
7
8
9
50
100
200
300
500
200
200
200
200
200
20
20
20
20
20
10
30
20
20
20
20
20
20
20
20
20
20
40
60
80
0.54
1.03
1.29
1.07
1.00
1.43
1.01
2.40
0.91
0.48
33.8
66.2
76.2
60.0
64.8
73.4
75.0
86.3
72.6
47.7
66.2
33.8
23.8
40.0
35.2
26.6
25.0
13.7
27.4
52.3
a Reaction conditions: 5 µmol of 7a, 10 atm of ethylene; 30 min; 20
°C; 100 mL of toluene. b In units of 104 g (mol of Fe)-1 h-1 atm-1
.
2.4.2.1. Catalytic Behavior of the Tridentate Iron Com-
plexes. Cocatalyst Selection. The catalytic activities of iron-
(II) complexes for ethylene activation were evaluated in the
presence of different cocatalysts such as methylaluminoxane
(MAO), modified methylaluminoxane (MMAO), and Et2AlCl.
Because of the low catalytic activity at ambient pressure of
ethylene, it is hard to evaluate the effect of the cocatalyst. An
elevated pressure of ethylene (10 atm) was used, and the effects
of cocatalysts were studied in detail with 7a (Table 5). The
results showed that MAO and MMAO could be promising
cocatalysts for ethylene activation.
2.4.2.2. Ethylene Activation in the Presence of MAO. After
routine selection of the ratio of MAO to iron catalyst, good
catalytic activity was observed at an Al/Fe molar ratio of 1000.
Therefore, the catalytic behaviors of all tridentate iron complexes
were investigated with a fixed Al/Fe molar ratio of 1000, and
their resultant data are summarized in Table 6. All of the
complexes displayed high catalytic activities for ethylene
oligomerization with high R-olefin selectivity (>99%) at 30 atm
of ethylene pressure. The distribution of obtained oligomers
resembled Schulz-Flory rules, and the probability of chain
propagation is represented with the constant K, where K ) rate
of propagation/((rate of propagation) + (rate of chain transfer))
) (moles of Cn+2)/(moles of Cn); the K values are determined
by the molar ratio of C12 and C14 fractions.36 The distribution
of the oligomers (entries 4-6 of Table 6) are shown in detail
in Figure 10.
10
a Conditions: 5 µmol of catalyst; 30 min; 100 mL of toluene. b In units
of 104 g (mol of M)-1 h-1 atm-1
total amounts of oligomers.
.
c Determined by GC; ∑C signifies the
used as the catalysts, the C6 proportion in the products was much
lower than that for the other catalytic systems; the possible
reason for this could be the occurrence of faster elimination.
Nevertheless, the catalytic activities of the cobalt complexes
were hardly different with different substituents on the pyridyl
group. This indicates that different coordination environments
for cobalt complexes in benzimidazole derivatives exhibit little
influence on ethylene activation. In general, the cobalt com-
plexes generally exhibited activities 1 order of magnitude lower
than those of the iron analogues. In comparison with similar
catalytic systems of complexes bearing acetyliminopyridine34
and 2-(ethylcarboxylato)-6-iminopyridine ligands,19g the cata-
lysts in this work gave oligomers with shorter carbon chains
(C4 and C6).
Varying catalytic conditions such as the reaction temperature
and pressure of ethylene were also investigated. Since compa-
rable catalytic activities by cocatalysts of MMAO and Et2AlCl
were observed, Et2AlCl was selected in the catalytic system of
6a, which also avoided the effect of MMAO on the contribution
of C4 in their products (Table 4). According to the data in Table
4, the optimum catalytic activity was obtained in the system
with an Al/Fe molar ratio of 200. Both increasing and decreasing
the Al/Fe molar ratio led to lower activity (entries 1-5 in Table
4). No obvious change in catalytic activities was observed by
elevating the ethylene pressure from 10 to 30 atm (entries 3, 6,
and 7 in Table 4). In addition, the highest activity was obtained
at 40 °C; higher reaction temperatures resulted in a sharp
decrease in activity (entries 8-10 in Table 4), which can be
explained by the decomposition of reactive species and lower
ethylene solubility at higher temperature.35 Additionally, for the
above catalytic reactions, C4 and C6 were produced as the main
products and no wax was obtained.
As depicted in Table 6, the higher the ethylene pressure, the
higher the catalytic activity. The ethylene concentration sig-
nificantly affected the catalytic behaviors. At ambient ethylene
pressure, only C4 and C6 were produced; the higher pressure,
however, increased the chain propagation, leading to longer
chain oligomers up to the range of C4-C28 in addition to the
improved activity. At 30 atm, all iron complexes had high
activity toward ethylene oligomerization with some amount of
polyethylene waxes produced.
The steric effect of ligands on the activities of iron complexes
is easily observed. As indicated by entry 6 of Table 6, 9a,
containing 2,6-diisopropyl substituents, showed the highest
2.4.2. Ethylene Reactivity Catalyzed by the Tridentate
Iron Complexes. Generally, the catalytic activities of the title
tridentate complexes were scanned in the presence of various
cocatalysts such as MAO, MMAO, and Et2AlCl, and the
catalytic systems with MAO or MMAO had high activity and
were worthy of careful investigation. It has commonly been
observed that the catalytic behaviors of iron and cobalt
complexes toward ethylene oligomerization and polymerization
are similar; however, in our investigation, there are some
differences in their catalytic activities. Therefore, the discussion
of their reactivity with ethylene is separated into two parts.
oligomerization activity at 47.7 × 104 g (mol of Fe)-1 h-1 atm-1
.
This could be explained by the less bulky substituents rendering
the active sites of the catalyst exposed to not only ethylene but
also other reactive species, and the latter actually lead to the
deactivation of the active species. Indeed, Gibson has proved
that the catalytic intermediates formed from precursors contain-
ing pyridyldiimine ligands are more easily deactivated through
the interaction with alkylaluminum reagent if they lack sufficient
steric bulk in the aryl ring.35b Meanwhile, with higher catalytic
activity, the content of C4 is obviously increased, and the
distribution of obtained oligomers did not resemble Schulz-
Flory rules (entries 5 and 6 in Table 6). The electronic effect
of ligands on the activities of iron complexes was also
(34) Bluhm, M. E.; Folli, C.; Do¨ring, M. J. Mol. Catal. A 2004, 212,
13.
(35) (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.; Stro¨mberg, S.; White, A. J. P.; Williams, D. J. J. Am. Chem. Soc. 1999,
121, 8728. (b) 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.
(36) (a) Schulz, G. V. Z. Phys. Chem., Abt. B 1935, 30, 379. (b) Schulz,
G. V. Z. Phys. Chem., Abt. B 1939, 43, 25. (c) Flory, P. J. J. Am. Chem.
Soc. 1940, 62, 1561. (d) Henrici-Olive´, G.; Olive´, S. AdV. Polym. Sci. 1974,
15, 1.

2728 Organometallics, Vol. 26, No. 10, 2007
Table 6. Polymerization and Oligomerization of Ethylene with 7a-11a/MAOa
activityb oligomer distribn (%)c
oligomer
Sun et al.
entry
cat.
P/atm
K
amt of wax/g
wax
C4/∑C
C6/∑C
C8/∑C
C10/∑C
Cg12/∑C
1
2
3
4
5
6
7
8
7a
9a
7a
7a
8a
9a
10a
11a
1
1
3.10
3.50
9.20
22.2
24.6
47.7
83.7
95.0
20.0
26.0
41.7
42.3
37.3
32.3
16.3
5.0
10
30
30
30
30
30
0.65
0.58
0.58
0.58
0.48
0.46
0.25
0.67
1.02
0.77
1.00
0.90
1.37
1.03
trace
trace
17.3
21.2
23.6
24.8
25.8
21.2
13.8
17.7
13.0
12.7
14.2
14.7
10.5
10.9
8.1
7.0
8.9
38.4
24.0
13.6
13.2
13.6
21.9
1.07
3.87
9.9
a Reaction conditions: 5 µmol of catalyst; Al/Fe ) 1000; 30 atm of ethylene; 30 min; 20 °C, 100 mL of toluene. b In units of 104 g (mol of Fe)-1 h-1
atm-1 c Determined by GC; ∑C signifies the total amounts of oligomers.
.
Al/Fe molar ratio to 1500 led to lower activity. This observation
could be traced to the increasing amount of isobutyl groups,
and the generated species hinder the insertion reaction of
ethylene due to steric bulkiness.37
To ascertain the relationship between catalytic activity and
ethylene pressure, the catalytic system of 7a with 1000 equiv
of MMAO at room temperature was investigated by varying
the ethylene pressure (entries 3, 5, and 6 in Table 7). The
phenomena were found to be the same as those with MAO as
cocatalyst. The higher the ethylene pressure, the higher the
catalytic activity. It is also worth mentioning that the ethylene
pressure affects the distribution of oligomers (Figure 11). This
point could be considerably useful in future industrial processes,
and the distribution of oligomers will be slightly changed with
changing ethylene pressure.
As the ethylene oligomerization and polymerization are highly
exothermic reactions, the reaction temperature significantly
affects the catalytic activity. To understand this influence, the
catalytic system of 7a with 1000 equiv of MMAO at 30 atm of
ethylene was investigated with changing reaction temperature
(entries 3, 11, and 12 in Table 7). Elevation of the reaction
temperature from 20 to 60 °C resulted in a sharp decrease of
catalytic activity, which can be explained as catalyst decomposi-
tion and lower ethylene solubility at higher temperature.35
Moreover, the oligomer distribution became narrower, along
with a decreased reactivity. The proportion of C4 and other short-
chain oligomers was greatly increased at higher temperature
because â-hydrogen elimination was faster than ethylene
propagation and the distribution of obtained oligomers did not
resemble Schulz-Flory rules (entries 11 and 12 in Table 7).
Figure 10. Oligomer distribution obtained in entries 4-6 in Table
6.
considered. Complexes 10a and 11a, bearing halogen groups,
exhibited lower activity than complexes bearing alkyl groups
(entries 4-8 in Table 6). Furthermore, the bromo-substituted
complex 11a showed much higher oligomerization activity than
10a, which can be explained as the total result of the electronic
and steric effects and the influence of the reaction between the
halogen substituent catalyst and the Lewis acidic activators. It
is noteworthy that only trace waxes were produced by the
complexes with electron-withdrawing groups. Therefore, bulky
ligands with electron-donating substituents would be helpful in
increasing the catalytic activity of the tridentate iron complexes
in the presence of MAO.
The natural catalytic behaviors of these tridentate iron
complexes with MMAO are rooted in their ligands with different
substituents. In the presence of MMAO as cocatalyst, complexes
7a-11a also showed high activities for ethylene oligomerization
along with moderate activities for ethylene polymerization
(entries 3 and 7-10 in Table 7). On the basis of these data,
their oligomerization activity varied in the order of 9a (with an
i-Pr substituent) < 8a (with Et) < 7a (with Me) and 11a (with
Br) < 10a (with Cl), and this order was reversed in catalytic
systems with MAO as cocatalyst. In the catalytic system with
MMAO, it is assumed that the factor controlling the reaction
speed mostly relies on the insertion of ethylene at the active
metal center, and a more bulky group causes a slower insertion
reaction and consequently lower activity. This observation could
be traced to the isobutyl group, and therefore, the generated
species hinder the insertion reaction of ethylene due to steric
2.4.2.3. Ethylene Activation in the Presence of MMAO.
In the presence of MMAO as cocatalyst, the tridentate iron
complexes were carefully investigated under various reaction
conditions, including changing the ethylene pressure, molar ratio
of MMAO to iron, and reaction temperature. In a pattern similar
to that with MAO, the oligomers range from C4 to C28 with
high selectivity for R-olefins (>99%), and the results are given
in Table 7 (K ) (moles of Cn+2)/(moles of Cn) and is determined
by the molar ratio of C12 and C14 fractions36).
Guided by the experience of the catalytic system with MAO,
the various Al/Fe molar ratios were studied with 7a at 30 atm
of ethylene. When the Al/Fe molar ratio was varied from 200
to 1500, the catalytic activities for both oligomers and poly-
ethylene waxes initially increased and then decreased (entries
1-4 in Table 7). Notably, the catalytic activity increased sharply
from 200 to 500, which may be attributed to the fact that
MMAO scavenged adventitious water and impurities in the
solvent at an Al/Fe ratio of 200 and the iron catalysts require
more cocatalyst to be active. At an Al/Fe ratio of 1000, the
catalytic activities for both ethylene oligomerization and po-
lymerization were attained at the highest value. Increasing the
(37) (a) Chen, E. Y.; Marks, T. J. Chem. ReV. 2000, 100, 1391. (b)
Karam, A. R.; Catar´ı, E. L.; Lo´pez-Linares, F.; Agrifoglio, G.; Albano, C.
L.; D´ıaz-Barrios, A.; Lehmann, T. E.; Pekerar, S. V.; Albornoz, L. A.;
Atencio, R.; Gonza´lez, T.; Ortega, H. B.; Joskowics, P. Appl. Catal. A:
Gen. 2005, 280, 165.

Fe and Co Catalysts for Ethylene ReactiVity
Table 7. Polymerization and Oligomerization of Ethylene with 7a-11a/MMAOa
activityb oligomer distribn (%)c
oligomer
0.60
Organometallics, Vol. 26, No. 10, 2007 2729
entry
cat.
Al/Fe
P/atm
K
T/oC
amt of wax/g
wax
C4/∑C
C6/∑C
C8/∑C
C10/∑C
∑Cg12/∑C
1
2
7a
7a
7a
7a
7a
7a
8a
9a
10a
11a
7a
7a
7a
200
500
30
30
30
30
10
20
30
30
30
30
30
30
30
0.52
0.44
0.53
0.54
0.62
0.59
0.55
0.51
0.56
0.52
0.47
0.57
0.45
20
20
20
20
20
20
20
20
20
20
40
60
20
0.08
0.10
0.90
0.25
0.10
0.13
1.20
0.33
trace
0.10
0.43
1.13
trace
trace
trace
trace
trace
46.1
35.7
35.0
37.3
38.5
42.5
26.3
59.6
28.2
46.9
65.5
68.0
47.3
22.1
28.7
27.8
24.7
14.9
21.0
22.5
21.3
26.4
26.1
16.3
18.9
20.8
11.5
16.7
15.2
14.6
11.6
13.7
18.0
9.1
6.5
8.7
8.1
8.9
9.3
8.2
12.4
3.9
11.1
6.1
5.0
4.2
7.1
13.8
10.2
13.9
14.5
25.7
14.6
20.8
6.1
15.8
9.1
4.5
3.0
10.3
19.0
26.4
7.57
12.0
8.20
22.3
4.67
12.9
7.07
3
4
5
6
7
8
9
10
11
12
13d
1000
1500
1000
1000
1000
1000
1000
1000
1000
1000
1000
0.05
0.32
0.85
18.5
11.8
8.7
0.77
0.50
2.20
6.1
14.4
a Reaction conditions: 5 µmol of catalyst; 30 min; 100 mL of toluene. b In units of 104 g (mol of Fe)-1 h-1 atm-1
.
c Determined by GC; ∑C signifies the
total amounts of oligomers. d Five equivalents of PPh3.
1
bands of various C-H and CdC bonds. H and 13C NMR
spectra of the polyethylene waxes obtained by 8a/MAO were
recorded at 110 °C in o-dichlorobenzene-d4 using TMS as the
internal standard. NMR spectra are shown in Figure 12, and
the assignments were determined according to the literature.39
The 13C NMR spectra further demonstrated that linear R-olefins
of the waxes absolutely predominated in the polymers, and the
single peaks at δ 140.0 and 115.1 ppm showed the property of
a vinyl-unsaturated chain end. The obtained average molecular
weight from 13C NMR indicated that the carbon number of the
polymeric waxes is about 60. Other ethylene waxes showed very
similar NMR spectra, to confirm the linear R-olefin fashion of
polymeric alkenes.
To briefly summarize, cocatalysts of both MAO and MMAO
could activate the tridentate iron complexes to be highly active
toward ethylene activation. The selectivity of forming R-olefins
is generally very high; even the ethylene waxes showed high
selectivity to be vinyl-terminal long-chain alkenes. However,
the catalytic activities of MAO and MMAO are quite different,
especially with regard to the bulky effect of substituents in their
ligands, such as that caused by a bulky isobutyl group in
MMAO.
2.4.3. Ethylene Oligomerization by Tridentate Cobalt
Complexes. Similar to the case for the iron complexes above,
all of the cobalt(II) analogues displayed moderate catalytic
activities for ethylene oligomerization with high selectivity for
R-olefins (>98%) at 30 atm of ethylene pressure in the presence
of MAO (Table 8). Though MMAO or Et2AlCl could also be
used as the cocatalyst, these catalytic systems yielded lower
catalytic activities (entries 6 and 7 in Table 8). Therefore, further
detailed investigation was carried out using MAO as the
cocatalyst. The obtained oligomers were only C4 and C6 without
polymeric products. As reported in previous studies, the cobalt
catalyst system displayed activities that are an order of
magnitude lower than that of their iron analogues.32,35b,40
The catalytic activities of cobalt complexes are significantly
affected by their ligands’ environment. As shown in Table 8,
the ethylene oligomerization activity varied in the order 7b >
8b > 9b and 10b > 11b. The catalysts bearing less bulky
substituents displayed higher activity than those with sterically
bulky substituents. This can perhaps be attributed to a weaker
interaction between the cobalt atom and the π-electrons of the
Figure 11. Oligomer distribution obtained in entries 3, 5, and 6
in Table 7.
bulkiness.37 Complex 10a, with a dichloro-substituted ligand,
displayed ethylene oligomerization activity higher than that of
its analogue 11a, containing a dibromo-substituted ligand.
Similar to the case for the catalytic system with MAO, the
distribution of obtained oligomers did not resemble Schulz-
Flory rules with a sterically large, bulky group on the N-aryl
ring (entries 8 and 10 in Table 7).
Previous studies reported that nickel-based catalysts incor-
porated PPh3 in catalytic systems, resulting in higher activity
and longer catalyst lifetime.22a,23a,38 Therefore, the oligomer-
ization reaction with the 7a/MMAO system was carried out in
the presence of 5 equiv of PPh3 (entry 13 of Table 7). However,
a sharp decrease in catalyst activity was observed and no
polyethylene waxes were produced. This can be explained by
the fact that the stronger Fe-P bond prevented the insertion of
ethylene at the active metal center.
2.4.2.4. Characterization of Low-Molecular-Weight Waxes.
In addition to high selectivity for R-olefins, polyethylene waxes
were also obtained in some catalytic systems. As characterized
by IR spectra recorded using KBr disks in the range of 4000-
400 cm-1, the polyethylene waxes were confirmed to be highly
linear R-olefins, from the characteristic vibration absorption
(38) (a) Carlini, C.; Isola, M.; Liuzzo, V.; Galletti, A. M. R.; Sbrana, G.
Appl. Catal. A: Gen. 2002, 231, 307. (b) Jenkins, J. C.; Brookhart, M.
Organometallics 2003, 22, 250. (c) Sun, W.-H.; Zhang, W.; Gao, T.; Tang,
X.; Chen, L.; Li, Y.; Jin, X. J. Organomet. Chem. 2004, 689, 917. (d) Tang,
X.; Zhang, D.; Jie, S.; Sun, W.-H.; Chen, J. J. Organomet. Chem. 2005,
690, 3918.
(39) (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. (b)
Galland, G. B.; Quijada, R.; Rojas, R.; Bazan, G.; Komon, Z. J. A.
Macromolecules 2002, 35, 339.
(40) Bianchini, C.; Mantovani, G.; Meli, A.; Migliacci, F.; Zanobini,
F.; Laschi, F.; Sommazzi, A. Eur. J. Inorg. Chem. 2003, 8, 1620.

2730 Organometallics, Vol. 26, No. 10, 2007
Sun et al.
Figure 12. 1H NMR (a) and 13C NMR (b) spectra of the waxes obtained by complex 8a in entry 5 in Table 6.
Table 8. Oligomerization of Ethylene by 7b-11ba
catalysts toward ethylene activation, 2-(benzimidazolyl)-6-(1-
(arylimino)ethyl)pyridines have been successively synthesized
and used to form their iron and cobalt complexes. In the
presence of either MAO or MMAO, the tridentate iron
complexes had very high catalytic activities, up to 47.7 × 104
g (mol of-1Fe)-1 h-1 atm-1, in producing R-olefins (C4-C28)
with high selectivity. The tridentate cobalt complexes showed
moderate activities when activated by MAO cocatalysts. In
synthesizing 2-(benzimidazolyl)-6-(1-(arylimino)ethyl)pyridines,
the intermediates of 2-(benzimidazolyl)-6-substituted-pyridines
could be used as bidentate ligands to form their iron and cobalt
complexes. The bidentate metal complexes could provide
moderate to good catalytic activities toward ethylene oligomer-
ization. In addition, the ethylene pressure affects the distribution
of oligomers significantly. In some cases, the waxes have been
obtained and confirmed to be vinyl-terminal long-chain alkenes.
Finally, we can conclude that these tridentate iron complexes
could be promising catalysts for industrial consideration in
ethylene oligomerization for full-range processes.
oligomer
distribn (%)c
P/
T/
entry cat.
cocat.
Al/Co atm °C activityb C4/∑C C6/∑C
1
2
3
4
5
6
7
8
9
7b
9b
7b
7b
7b
7b
7b
8b
9b
MAO
MAO
MAO
MAO
MAO
MMAO 1000
Et2AlCl
MAO
1000
1000
1000
1000
1000
1
1
20
20
0.88
0.82
1.40
1.58
100
100
100
10 20
20 20
30 20
30 20
30 20
30 20
30 20
30 20
30 20
30 20
30 20
30 40
30 60
77.8
22.2
10.0
15.0
15.0
11.8
90.0
85.0
85.0
94.6
89.3
83.3
75.8
88.6
74.7
70.6
91.5
2.37
2.33
8.60
4.67
2.80
1.87
4.67
2.10
3.00
2.37
200
1000
1000
1000
1000
1500
500
5.40
MAO
10.7
16.7
24.2
11.4
25.3
29.4
10
11
12
13
14
15
10b MAO
11b MAO
7b
7b
7b
7b
MAO
MAO
MAO
MAO
1000
1000
8.50
a Reaction conditions: 5 µmol of catalyst; 30 min; 100 mL of toluene.
b In units of 103 g (mol of Co)-1 h-1 atm-1
.
c Determined by GC; ∑C
signifies the total amounts of oligomers.
4. Experimental Section
ethylene monomer, due to bulkier groups on the phenyl ring,
which resulted in a decrease in the rate of ethylene insertion in
the chain-growth steps. For 10b and 11b, as a consequence of
electronegativity Cl > Br; 10b displayed higher reactivity than
11b when the central metal positive charge was increased.
When reaction parameters were varied, the catalytic activities
of cobalt complexes were also affected. When the Al/Co molar
ratio was increased from 500 to 1500, the catalytic activities
initially increased and then decreased, with the optimum activity
being at an Al/Co molar ratio of 1000 (entries 5, 12, and 13 in
Table 8). Elevating the reaction temperature from 20 to 60 °C
resulted in decreasing catalytic activity (entries 5, 14, and 15
in Table 8), which might be caused by instability of the active
species or a lower concentration of ethylene in the reaction
solution. Commonly, a lower catalytic activity was observed at
lower pressure and only butenes were produced at an ethylene
pressure lower than 10 atm (entries 1 and 3-5 in Table 8).
4.1. General Considerations. All manipulations of air- and
moisture-sensitive compounds were performed under a nitrogen
atmosphere using standard Schlenk techniques. Toluene was
refluxed over sodium-benzophenone and distilled under argon prior
to use. Methylaluminoxane (MAO, a 1.46 M solution in toluene)
and modified methylaluminoxane (MMAO, 1.93 M in heptane, 3A)
were purchased from Akzo Nobel Corp. Diethylaluminum chloride
(Et2AlCl, 1.7 M in toluene) was purchased from Acros Chemicals.
Other reagents were purchased from Aldrich or Acros Chemicals;
the boiling range of light petroleum is 30-60 °C and the type of
1
silica gel used is 200-300 mesh. H 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 spectrometer.
Elemental analysis was carried out using an HPMOD 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. The yield of oligomers was calculated by
referencing to the mass of the solvent on the basis of the prerequisite
that the mass of each fraction was approximately proportional to
its integrated area in the GC trace. Selectivity for the linear R-olefin
3. Conclusion
Inspired by the success of bis(imino)pyridyliron dihalide12,13
and 2-imino-1,10-phenanthrolyliron dihalide21,23 as highly active

Fe and Co Catalysts for Ethylene ReactiVity
Organometallics, Vol. 26, No. 10, 2007 2731
was 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 a Bruker DMX 300 MHz
instrument at 110 °C in 1,2-dichlorobenzene-d4 using TMS as the
internal standard.
Py), 7.82 (s, 1H, Ar), 7.45 (s, 1H, Ar), 7.27 (m, 2H, Ar), 4.45 (q,
2H, CH2), 1.42 (t, 3H, CH3). IR (KBr; cm-1): 3068, 1720, 1662,
1594, 1460, 1405, 1367, 1300, 1250, 1228, 1117, 1098, 997, 925,
836, 743, 378.
2-(Carboethoxy)-6-(1-methyl-2-benzimidazolyl)pyridine (5).
A solution of 4 (300 mg, 1.12 mmol) in 30 mL of acetonitrile was
refluxed with 2 equiv of K2CO3 (310 mg, 2.24 mmol) for 0.5 h.
After the mixture was cooled to room temperature, iodomethane
(100 µL, 1.56 mmol) was added to the reaction mixture and the
mixture stirred for 24 h. The solvent was evaporated at reduced
pressure before water (20 mL) was added, and the aqueous phase
was extracted with CH2Cl2 (4 × 15 mL). The combined extracts
were dried over anhydrous Na2SO4 and filtered, and the solvent
was finally evaporated at reduced pressure. The desired compound
5 was obtained as a white solid in 75% yield after purification by
column chromatography (silica gel, 3/1 (v/v) petroleum ether/ethyl
4.2. Preparation of the Starting Materials. 4.2.1. Preparation
of the Precursor Compounds. 2-(2-Benzimidazolyl)-6-methylpy-
ridine (1). A mixture of equivalent molar amounts of o-phenylene-
diamine (21.6 g, 0.20 mol) and 2,6-lutidine (21.4 g, 0.20 mol) with
excess sulfur (22.5 g, 0.70 mol) was heated to 170 °C and stirred
for 10 h. After the mixture was cooled to room temperature, 250
mL of methanol was added, and the precipitated solid (including
unreacted sulfur) was filtered off. The filtrate was evaporated and
recrystallized in benzene to get yellow needlelike crystals as the
target compound, yield 26.8 g (1) (64%). Mp: 228-230 °C (lit.26
1
mp 222.5-223 °C). H NMR (300 MHz, CDCl3, TMS): δ 11.2
1
(s, 1 H, NH), 8.30 (d, 1H, J ) 7.9 Hz, Py), 7.70 (m, 2H, Py), 7.20
(m, 4H, Ar), 2.53 (s, 3H, CH3). IR (KBr; cm-1): 3047, 1598, 1576,
1465, 1416, 1385, 1315, 1279, 1226, 1017, 993, 904, 808, 743,
423.
acetate). Mp: 140-141 °C. H NMR (300 MHz, CDCl3, TMS):
δ 8.62 (d, 1H, J ) 6.6 Hz, Py), 8.14 (d, 1H, J ) 6.6 Hz, Py), 8.00
(t, 1H, J ) 7.8 Hz, Py);, 7.82 (d, 1H, J ) 7.5 Hz, Ar), 7.44 (d, 1H,
J ) 7.2 Hz, Ar), 7.35 (m, 2H, Ar), 4.48 (q, 2H, J ) 7.2 Hz, CH2),
4.40 (s, 3H, CH3), 1.47 (t, 3H, J ) 7.2 Hz, CH3). 13C NMR (75
MHz, CDCl3, TMS): δ 165.0, 150.8, 149.2, 147.2, 142.6, 137.9,
137.6, 127.5, 124.8, 123.8, 122.9, 120.3, 110.2, 61.9, 33.0, 14.4.
ESI-MS (m/z): 282.2 (M + H+), 320.1 (M + K+). IR (KBr; cm-1):
3366, 3052, 2978, 2926, 2856, 1730 (νCdO), 1590, 1473, 1403,
1386, 1300, 1251, 1165, 740. Anal. Calcd for C16H15N3O2
(281.3): C, 68.31; H, 5.37; N, 14.94. Found: C, 68.42; H, 5.37;
N, 14.86.
2-(1-Methyl-2-benzimidazolyl)-6-methylpyridine (2). A solu-
tion of 1 (500 mg, 2.39 mmol) in 30 mL of acetonitrile was refluxed
with 2 equiv of K2CO3 (700 mg, 5.00 mmol) for 0.5 h. Iodomethane
(220 µL, 3.35 mmol) was added to this system after the mixture
was cooled to room temperature and reacted for 24 h. The mixture
was evaporated at reduced pressure, and water (20 mL) was then
added, which was extracted with CH2Cl2 (4 × 15 mL), and the
combined extracts were dried over anhydrous Na2SO4 and filtered.
The solvent was evaporated at reduced pressure, and the desired
compound 2 was obtained as a white solid in 96% yield after
purification by column chromatography (silica gel, 3/1 petroleum
ether/Et3N). Mp: 110-111 °C. 1H NMR (300 MHz, CDCl3,
TMS): δ 8.17 (d, 1H, J ) 7.8 Hz, Py), 7.82 (d, 1H, J ) 8.1 Hz,
Py), 7.72 (t, 1H, J ) 7.8 Hz, Ph), 7.41 (m, 1H, Ph), 7.30 (m, 2H,
Ph), 7.19 (d, 1H, J ) 7.8 Hz, Py), 4.26 (s, 3H, CH3), 2.63 (s, 3H,
CH3). 13C NMR (75 MHz, CDCl3, TMS): δ 157.5, 150.7, 150.0,
142.6, 137.4, 137.1, 123.3, 123.2, 122.5, 121.8, 120.0, 109.9, 32.8,
24.6. ESI-MS (m/z): 224.0 (M + H+). IR (KBr; cm-1): 3058, 2954,
1577, 1472, 1433, 1392, 1372, 1255, 1157, 1077, 1009, 805, 743.
Anal. Calcd for C14H13N3 (223.3): C, 75.31; H, 5.87; N, 18.82.
Found: C, 74.99; H, 5.79; N, 18.54.
2-(1-Methyl-2-benzimidazolyl)-6-acetylpyridine (6). A solution
of 5 (10.8 g, 43.2 mmol) in 15 mL of freshly distilled ethyl acetate
was added dropwise to 5.8 equiv of dried C2H5ONa (17.0 g, 250
mmol) with stirring to afford a yellow mixture, which was refluxed
for 12 h and allowed to stand overnight. Concentrated HCl (50
mL) was added dropwise with stirring, and the mixture was refluxed
for another period of 6 h to complete the reaction. With addition
of 200 mL of water, the mixture turned into an orange solution;
the aqueous phase was then extracted with CH2Cl2 (4 × 50 mL),
and the combined extracts were washed with 5% aqueous Na2CO3.
The organic phase was dried over anhydrous Na2SO4 and filtered
before the solvent was evaporated at reduced pressure. The desired
compound 6 was obtained as a white solid in 59% yield after
purification by column chromatography (silica gel, 3/1 (v/v)
6-(2-Benzimidazolyl)pyridine-2-carboxylic acid (3). 1 (1.50 g,
7.17 mmol) and selenium dioxide (3.60 g, 32.4 mmol) were refluxed
in dry pyridine for 36 h. After it was cooled, the mixture was filtered
to remove solid Se and the clear solution was evaporated to dryness.
The crude residue was suspended in water (50 mL), and the pH
was adjusted to 11.0 with NaOH (5 M). The resulting clear yellow
solution was extracted with dichloromethane (3 × 25 mL), and
the aqueous phase was filtered and neutralized to pH 3.4 with
concentrated hydrochloric acid. Thereafter the precipitate was
collected by filtration and crystallized from 1/1 dimethyl sulfoxide/
water (100 °C) to give 1.12 g (4.68 mmol, yield 66%). Mp: 299-
1
petroleum ether/ethyl acetate). Mp: 189-190 °C. H NMR (300
MHz, CDCl3, TMS): δ 8.62 (d, 1H, J ) 7.8 Hz, Py), 8.08 (d, 1H,
J ) 7.5 Hz, Py), 7.99 (t, 1H, J ) 7.5 Hz, Py), 7.83 (d, 1H, J ) 7.2
Hz, Ar), 7.45 (d, 1H, J ) 7.8 Hz, Ar), 7.35 (m, 2H, Ar), 4.34 (s,
3H, CH2), 2.78 (s, 3H, CH3). 13C NMR (75 MHz, CDCl3, TMS):
δ 199.4, 152.4, 150.0, 149.3, 142.5, 138.0, 137.4, 128.1, 123.8,
123.0, 121.7, 120.3, 110.0, 33.1, 26.2. ESI-MS (m/z): 252.3 (M +
H+), 274.2 (M + Na+). IR (KBr; cm-1): 3369, 3059, 2960, 1696
(νCdO), 1583, 1469, 1435, 1387, 1353, 1300, 1261, 1214, 1149,
1106, 1020, 817, 748. Anal. Calcd for C15H13N3O (251.3): C, 71.70;
H, 5.21; N, 16.72. Found: C, 71.98; H, 5.30; N, 16.70.
1
301 °C. H NMR (300 MHz, DMSO, TMS): δ 8.55 (d, 1 H, J )
7.6 Hz, Py), 8.20 (m, 2H, Py), 7.71 (m, 2H, Ar), 7.31 (m, 2H, Ar).
Synthesis of [2-(2-Benzimidazolyl)-6-methylpyridine]dichlor-
oiron (1a). The ligand 1 (400 mg, 1.91 mmol) and FeCl2‚4H2O
(362 mg, 1.82 mmol) were placed in a Schlenk tube, followed by
the addition of freshly distilled ethanol (3 mL) with rapid
stirring at room temperature. The solution turned yellow im-
mediately, and a yellow powder precipitated after 1 min. The
reaction mixture was stirred for 12 h, and after the mixture stood
for 30 min, the supernatant was removed. The precipitate was
washed with diethyl ether twice and dried under vacuum to give
the pure product as a yellow powder in 92% yield. IR (KBr; cm-1):
3229, 1606, 1576, 1492, 1475, 1446, 1401, 1378, 1321, 1247,
1152, 1107, 987, 911, 801, 746, 431. Anal. Calcd for C13H11Cl2-
FeN3 (336.0): C, 46.47; H, 3.30; N, 12.51. Found: C, 46.76; H,
3.66; N, 12.26.
2-(Carboethoxy)-6-(2-benzimidazolyl)pyridine (4). 3 (0.50 g,
2.09 mmol) and 1 mL of H2SO4 (98%) were refluxed in 40 mL of
ethanol for 4 h. After the mixture was cooled to room temperature,
it was filtered into 50 mL of water, and then the pH was adjusted
to 7.0 with saturated NaHCO3 solution. Then ethanol was evapo-
rated and the aqueous phase was extracted with dichloromethane
(3 × 25 mL), the combined organic phases were dried over
anhydrous Na2SO4 and filtered, and the solvent was evaporated at
reduced pressure. The solid was collected and recrystallized from
dichloromethane to give 0.44 g (1.63 mmol, yield 78%) of pure
1
compound. Mp: 152-154 °C (lit.28 mp 148-149 °C). H NMR
(300 MHz, CDCl3, TMS): δ 12.06 (s, 1 H, NH), 8.60 (d, 1H, J )
7.9 Hz, Py), 8.10 (d, 1H, J ) 7.6 Hz, Py), 7.95 (t, 1H, J ) 7.7 Hz,

2732 Organometallics, Vol. 26, No. 10, 2007
Sun et al.
Synthesis of [2-(2-Benzimidazolyl)-6-methylpyridine]dichlo-
rocobalt (1b). 1b was synthesized by the same method as for 1a;
the green powder was produced in 79% yield. IR (KBr; cm-1):
3228, 1609, 1575, 1493, 1477, 1440, 1387, 1320, 1297, 1231, 1119,
1102, 985, 934, 800, 761, 744, 429. Anal. Calcd for C13H11Cl2-
CoN3 (339.1): C, 46.05; H, 3.27; N, 12.39. Found: C, 46.06; H,
3.36; N, 12.37.
Synthesis of [2-(1-Methyl-2-benzimidazolyl)-6-methylpyridine]-
dichloroiron (2a). 2a was synthesized by the same method as for
1a; the yellow powder was produced in 94% yield. IR (KBr; cm-1):
3123, 3064, 1605, 1487, 1443, 1390, 1347, 1249, 1162, 1010,
797, 747. Anal. Calcd for C14H13Cl2FeN3 (350.0): C, 48.04; H,
3.74; N, 12.00. Found: C, 48.11; H, 3.76; N, 11.80.
Synthesis of [2-(1-Methyl-2-benzimidazolyl)-6-methylpyridine]-
dichlorocobalt (2b). 2b was synthesized by the same method as
for 1a; the green powder was produced in 77% yield. IR (KBr;
cm-1): 3121, 3066, 1606, 1488, 1440, 1392, 1347, 1250, 1163,
1014, 796, 747. Anal. Calcd for C14H13Cl2CoN3 (353.1): C, 47.62;
H, 3.71; N, 11.90. Found: C, 47.42; H, 3.82; N, 11.75.
Synthesis of [2-(Carboethoxy)-6-(2-benzimidazolyl)pyridine]-
dichloroiron (4a). 4a was synthesized by the same method as for
1a; the brown powder was produced in 89% yield. IR (KBr; cm-1):
3056, 1668, 1602, 1575, 1476, 1414, 1374, 1334, 1274, 1149,
1077, 993, 815, 762, 374. Anal. Calcd for C15H13Cl2FeN3O2
(394.0): C, 45.72; H, 3.33; N, 10.66. Found: C, 45.42; H, 3.13;
N, 11.15.
Synthesis of [2-(Carboethoxy)-6-(2-benzimidazolyl)pyridine]-
dichlorocobalt (4b). 4b was synthesized by the same method as
for 1a; the green powder was produced in 72% yield. IR (KBr;
cm-1): 3064, 1743, 1698, 1602, 1471, 1422, 1373, 1326, 1271,
1202, 1153, 1089, 990, 856, 754, 434. Anal. Calcd for C15H13Cl2-
CoN3O2 (397.1): C, 45.37; H, 3.30; N, 10.58. Found: C, 45.00;
H, 3.39; N, 10.49.
Synthesis of [2-(Carboethoxy)-6-(1-methyl-2-benzimidazolyl)-
pyridine]dichloroiron (5a). 5a was synthesized by the same
method as for 1a; the purple powder was produced in 98% yield.
IR (KBr; cm-1): 3419, 3063, 1697 (νCdO), 1597, 1486, 1403, 1376,
1328, 1256, 1013, 862, 754. Anal. Calcd for C16H15Cl2FeN3O2
(408.1): C, 47.09; H, 3.71; N, 10.30. Found: C, 46.78; H, 3.66;
N, 10.45.
Synthesis of [2-(Carboethoxy)-6-(1-methyl-2-benzimidazolyl)-
pyridine]dichlorocobalt (5b). 5b was synthesized by the same
method as for 1a; the green powder was produced in 79% yield.
IR (KBr; cm-1): 3382, 3063, 1703 (νCdO), 1598, 1487, 1403, 1376,
1327, 1256, 1201, 1093, 1017, 835, 754. Anal. Calcd for C16H15-
Cl2CoN3O2 (411.1): C, 46.74; H, 3.68; N, 10.22. Found: C, 46.50;
H, 3.83; N, 10.24.
Synthesis of [2-Acetyl-6-(1-methyl-2-benzimidazolyl)pyridine]-
dichloroiron (6a). 6a was synthesized by the same method as for
1a; the purple powder was produced in 88% yield. IR (KBr; cm-1):
3420, 3035, 1659 (νCdO), 1593, 1486, 1423, 1347, 1330, 1272,
1249, 1191, 1149, 807, 765, 749. Anal. Calcd for C15H13Cl2FeN3O
(378.0): C, 47.66; H, 3.47; N, 11.12. Found: C, 47.61; H, 3.72;
N, 10.90.
Synthesis of [2-Acetyl-6-(1-methyl-2-benzimidazolyl)pyridine]-
dichlorocobalt (6b). 6b was synthesized by the same method as
for 1a; the green powder was produced in 85% yield. IR (KBr;
cm-1): 3430, 3036, 1673 (νCdO), 1594, 1487, 1424, 1365, 1330,
1269, 1247, 1191, 1149, 1020, 807, 768. Anal. Calcd for C15H13-
Cl2CoN3O (381.1): C, 47.27; H, 3.44; N, 11.03. Found: C, 47.51;
H, 3.76; N, 10.89.
amount of p-toluenesulfonic acid in toluene (25 mL) was refluxed
for 24 h. After solvent evaporation, the crude product was purified
by column chromatography on silica gel with petroleum ether/ethyl
acetate (3/1 v/v) as eluent to afford the product as a yellow powder
1
in 68% yield. Mp: 170-172 °C. H NMR (300 MHz, CDCl3,
TMS): δ 8.55 (d, 1H, J ) 7.8 Hz, Py), 8.46 (t, 1H, J ) 7.5 Hz,
Py), 7.96 (t, 1H, J ) 7.8 Hz, Py), 7.85 (m, 1H, Ph), 7.44 (d, 1H,
Ph), 7.34 (m, 2H, Ph), 7.08 (d, 2H, J ) 7.5 Hz, Ph), 6.95 (t, 1H,
J ) 7.2 Hz, Ph), 4.35 (s, 3H, CH3), 2.25 (s, 3H, CH3), 2.06 (s, 6H,
CH3). 13C NMR (75 MHz, CDCl3, TMS): δ 166.7, 155.3, 150.0,
149.6, 148.6, 142.7, 137.6, 137.4, 128.0, 125.9, 125.4, 123.6, 123.3,
122.8, 121.4, 120.2, 110.0, 33.1, 18.1, 16.9. ESI-MS (m/z): 355.5
(M + H+), 377.3 (M + Na+). IR (KBr; cm-1): 3421, 2944, 1645
(νCdN), 1592, 1571, 1541, 1468, 1384, 1361, 1328, 1205, 1149,
1115, 770, 747. Anal. Calcd for C23H22N4 (354.5): C, 77.94; H,
6.26; N, 15.81. Found: C, 77.71; H, 6.37; N, 15.52.
(E)-2,6-Diethyl-N-(1-(6-(1-methyl-1H-benzo[d]imidazol-2-yl)-
pyridin-2-yl)ethylidene)benzenamine (8). Using the same proce-
dure as for the synthesis of 7, 8 was obtained as a yellow powder
1
in 89% yield. Mp: 181-182 °C. H NMR (300 MHz, CDCl3,
TMS): δ 8.56 (d, 1H, J ) 7.8 Hz, Py), 8.45 (d, 1H, J ) 8.1 Hz,
Py), 7.98 (t, 1H, J ) 7.8 Hz, Ph), 7.86 (m, 1H, Ph), 7.45 (d, 1H,
J ) 6.0 Hz, Ph), 7.35 (m, 2H, Ph), 7.14 (d, 2H, J ) 8.1 Hz, Ph),
7.05 (m, 1H, Ph), 4.36 (s, 3H, CH3), 2.40 (q, 4H, J ) 7.5 Hz,
CH2), 2.27 (s, 3H, CH3), 1.15 (t, 6H, J ) 7.5 Hz, CH3). 13C NMR
(75 MHz, CDCl3, TMS): δ 166.4, 155.4, 150.0, 149.5, 147.7, 142.5,
137.6, 137.3, 131.2, 126.1, 125.9, 123.6, 123.5, 122.9, 121.4, 120.2,
110.0, 33.1, 24.7, 17.3, 13.9. ESI-MS (m/z): 383.5 (M + H+). IR
(KBr; cm-1): 3060, 2965, 2931, 2872, 1917, 1639 (νCdN), 1588,
1570, 1469, 1453, 1432, 1396, 1358, 1329, 1252, 1198, 1153, 1113,
1072, 758, 741. Anal. Calcd for C25H26N4 (382.5): C, 78.50; H,
6.85; N, 14.65. Found: C, 78.20; H, 6.84; N, 14.55.
(E)-2,6-Diisopropyl-N-(1-(6-(1-methyl-1H-benzo[d]imidazol-
2-yl)pyridin-2-yl)ethylidene)benzenamine (9). Using the same
procedure as for the synthesis of 7, 9 was obtained as a yellow
1
powder in 86% yield. Mp: 222 -223 °C. H NMR (300 MHz,
CDCl3, TMS): δ 8.44 (d, 1H, J ) 7.8 Hz, Py), 8.35 (t, 1H, J )
7.5 Hz, Py), 7.85 (t, 1H, J ) 7.8 Hz, Ph), 7.76 (d, 1H, J ) 6.1 Hz,
Ph), 7.33 (d, 1H, J ) 6.1 Hz, Ph), 7.22 (m, 2H, Ph), 7.09 (m, 2H,
Ph), 7.00 (m, 1H, Ph), 4.24 (s, 3H, CH3), 2.68 (m, 2H, CH), 2.19
(s, 3H, CH3), 1.09 (d, 12H, J ) 6.6 Hz, CH3). 13C NMR (75 MHz,
CDCl3, TMS): δ 166.5, 155.4, 150.0, 149.6, 146.4, 142.7, 137.6,
137.4, 135.8, 125.9, 123.9, 123.5, 123.2, 122.8, 121.4, 120.2, 110.0,
33.2, 28.5, 23.3, 23.0, 17.7. ESI-MS (m/z): 411.5 (M + H+), 433.5
(M + Na+). IR (KBr; cm-1): 2961, 1643 (νCdN), 1570, 1467, 1432,
1393, 1359, 1330, 1262, 1193, 1153, 1110, 1069, 784, 758, 732.
Anal. Calcd for C27H30N4 (410.6): C, 78.99; H, 7.37; N, 13.65.
Found: C, 79.24; H, 7.11; N, 13.31.
(E)-2,6-Dichloro-N-(1-(6-(1-methyl-1H-benzo[d]imidazol-2-
yl)pyridin-2-yl)ethylidene)benzenamine (10). Using the same
procedure as for the synthesis of 7, 10 was obtained as a yellow
1
powder in 22% yield. Mp: 178-179 °C. H NMR (300 MHz,
CDCl3, TMS): δ 8.59 (d, 1H, J ) 7.2 Hz, Py), 8.47 (d, 1H, J )
7.2 Hz, Py), 8.00 (t, 1H, J ) 7.5 Hz, Py), 7.87 (m, 1H, Ph), 7.45
(m, 1H, Ph), 7.36 (m, 4H, Ph), 7.03 (m, 1H, Ph), 4.36 (s, 3H, CH3),
2.38 (s, 3H, CH3).13C NMR (75 MHz, CDCl3, TMS): δ 170.77,
154.5, 149.8, 149.7, 145.6, 142.6, 137.7, 137.4, 128.3, 126.5, 124.6,
124.5, 123.6, 122.8, 122.1, 120.3, 109.9, 33.1, 18.01. ESI-MS (m/
z): 396.2 (M + H+), 418.0 (M + Na+). IR (KBr; cm-1): 2924,
1650 (νCdN), 1587, 1470, 1433, 1393, 1361, 1311, 1265, 1223,
1150, 1112, 1073, 771, 742. Anal. Calcd for C21H16Cl2N4 (395.3):
C, 63.81; H, 4.08; N, 14.17. Found: C, 63.61; H, 4.14; N, 13.94.
4.3. Synthesis of 2-(1-Methyl-2-benzimidazolyl)-2-(1-(aryl-
imino)ethyl)pyridines (7-11) and Their Iron and Cobalt Com-
plexes. 4.3.1. Synthesis of Tridentate Ligands 7-11. (E)-2,6-
Dimethyl-N-(1-(6-(1-methyl-1H-benzo[d]imidazol-2-yl)pyridin-
2-yl)ethylidene)benzenamine (7). A mixture of 2,6-dimethylaniline
(106 mg, 0.88 mmol), 6 (200 mg, 0.80 mmol), and a catalytic
(E)-2,6-Dibromo-N-(1-(6-(1-methyl-1H-benzo[d]imidazol-2-
yl)pyridin-2-yl)ethylidene)benzenamine (11). Using the same
procedure as for the synthesis of 7, 11 was obtained as a yellow
1
powder in 25% yield. Mp: 157-158 °C. H NMR (300 MHz,
CDCl3, TMS): δ 8.50 (d, 1H, J ) 7.2 Hz, Py), 8.39 (d, 1H, J )

Fe and Co Catalysts for Ethylene ReactiVity
Organometallics, Vol. 26, No. 10, 2007 2733
Table 9. Crystal Data and Structure Refinement Details
1b
2a
2b
5b
7
empirical formula
C13H11Cl2-
CoN3
C17H20Cl2Fe-
N4O
C14H13Cl2-
CoN3
C16H15Cl2Co-
N3O2
C23H22N4
formula wt
cryst color
temp (K)
wavelength (Å)
cryst syst
space group
a (Å)
339.08
blue
293(2)
423.12
brown
293(2)
353.10
blue
293(2)
411.14
green
293(2)
0.710 73
triclinic
354.45
yellow
293(2)
0.710 73
monoclinic
P21/n
7.25050(1)
15.3040(3)
12.4512(2)
90.0
91.2860(1)
90.0
1381.26(4)
4
0.710 73
monoclinic
P21/c
7.8858(2)
16.8075(4)
14.1633(4)
90.0
94.2910(1)
90.0
1871.95(8)
4
0.710 73
monoclinic
P21/m
8.6204(2)
7.4012(2)
12.1953(3)
90.0
107.8400(1)
90.0
740.66(3)
2
0.710 73
monoclinic
P21/c
17.8207(3)
8.34060(1)
13.2319(2)
90
100.7490(1)
90
1932.22(5)
4
P1h
7.7749(3)
8.3615(2)
13.3453(4)
92.052(2)
93.674(2)
99.584(2)
852.76(5)
2
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
D
calcd (g cm-3
)
1.631
1.616
684
1.501
1.104
872
1.583
1.511
358
1.601
1.333
418
1.218
0.074
752
µ (mm-1
F(000)
)
cryst size (mm)
0.32 × 0.23 ×
0.45 × 0.40 ×
0.45 × 0.32 ×
0.35 × 0.25 ×
0.40 × 0.30 ×
0.15
0.40
0.10
0.14
0.30
θ range (deg)
2.11-28.30
-9 e h e8
-20 e k e 20
-16 e l e 16
13 866
1.88-28.29
-10 e h e 9
-21 e k e 22
-18 e l e 18
18 954
2.56-28.28
-11 e h e 11
-9 e k e 9
-16 e l e 15
6510
2.47-28.32
-10 e h e 10
-11 e k e 11
-17 e l e 17
11 290
1.16-28.29
-23 e h e 23
-10 e k e 10
-15 e l e 17
18 748
limiting indices
no. of rflns collected
no. of unique rflns
3286
4650
1963
4193
4745
completeness to θ (%)
95.6 (θ )
28.30°)
99.9 (θ )
28.29°)
99.4 (θ )
28.28°)
98.7 (θ )
28.32°)
99.2 (θ )
28.29°)
abs cor
empirical
176
1.056
R1 ) 0.0278
wR2 ) 0.0766
R1 ) 0.0388
wR2 ) 0.0813
0.381, -0.269
empirical
226
1.063
R1 ) 0.0391
wR2 ) 0.1040
R1 ) 0.0631
wR2 ) 0.1124
0.441, -0.363
empirical
119
0.982
R1 ) 0.0269
wR2 ) 0.0791
R1 ) 0.0327
wR2 ) 0.0825
0.357, -0.282
empirical
217
1.029
R1 ) 0.0367
wR2 ) 0.0927
R1 ) 0.0675
wR2 ) 0.1008
0.442, -0.281
empirical
244
1.042
R1 ) 0.0468
wR2 ) 0.1499
R1 ) 0.0606
wR2 ) 0.1705
0.254, -0.345
no. of params
goodness of fit on F2
final R indices (I > 2σ(I))
R indices (all data)
largest diff peak,
hole (e Å-3
)
10
7a
10a
7b
8b
10b
empirical formula
C21H16Cl2-
N4
C23H22Cl2Fe-
N4O
C21H16Cl4-
FeN4
C23H22Cl2-
CoN4
C25H26Cl2-
CoN4
C21H16Cl4-
CoN4
formula wt
cryst color
temp (K)
wavelength (Å)
cryst syst
space group
a (Å)
395.28
yellow
293(2)
497.20
blue
293(2)
522.03
blue
293(2)
484.28
dark
293(2)
512.33
green
293(2)
525.11
green
293(2)
0.710 73
orthorhombic
Pbcn
17.9085(5)
8.3223(2)
25.3872(7)
90
3783.71(2)
8
1.388
0.710 73
monoclinic
P21/n
12.8592(9)
8.8271(6)
23.0969(2)
101.934(4)
2565.1(3)
4
0.710 73
monoclinic
P21/c
10.2210(3)
15.1437(4)
14.1708(4)
97.857(2)
2172.82(1)
4
0.710 73
monoclinic
P21/c
8.14280(1)
15.0548(2)
18.0755(3)
96.1460(1)
2203.11(5)
4
0.710 73
monoclinic
P21/c
9.57290(1)
14.1768(2)
18.5031(3)
95.5010(1)
2499.55(6)
4
0.710 73
monoclinic
P21/c
10.1894(3)
15.1037(5)
14.1505(4)
98.085(2)
2156.08(1)
4
b (Å)
c (Å)
â (deg)
V (Å3)
Z
D
calcd (g cm-3
)
1.287
0.816
1024
1.596
1.202
1056
1.460
1.039
996
1.361
0.920
1060
1.618
1.308
1060
µ (mm-1
F(000)
)
0.356
1632
cryst size (mm)
0.95 × 0.85 ×
0.32 × 0.21 ×
0.30 × 0.20 ×
0.40 × 0.30 ×
0.30 × 0.20 ×
0.40 × 0.30 ×
0.80
0.15
0.10
0.30
0.10
0.20
θ range (deg)
1.97-28.32
-20 e h e 23
-10 e k e 11
-30 e l e 33
20 694
1.80-28.40
-17 e h e 17
-11 e k e 11
-30 e l e 30
25 506
1.98-28.34
-13 e h e 13
-20 e k e 20
-18 e l e 18
21 486
2.27-28.28
-10 e h e 9
-20 e k e 18
-24 e l e 23
22 817
1.81-28.30
-12 e h e 12
-18 e k e 18
-20 e l e 24
36 642
1.98-28.29
-13 e h e 13
-20 e k e 19
-16 e l e 18
21 694
limiting indices
no. of rflns collected
no. of unique rflns
4702
6347
5404
5419
6200
5338
completeness to θ (%)
99.7 (θ )
28.32°)
98.6 (θ )
28.40°)
99.7 (θ )
28.34°)
99.1 (θ )
28.28°)
99.8 (θ )
28.30°)
99.4 (θ )
28.29°)
abs cor
empirical
244
0.944
R1 ) 0.0447
wR2 ) 0.1215
R1 ) 0.0961
wR2 ) 0.1370
0.301, -0.342
empirical
289
0.822
R1 ) 0.0592
wR2 ) 0.1823
R1 ) 0.1821
wR2 ) 0.2183
0.558, -0.386
empirical
271
1.058
R1 ) 0.0434
wR2 ) 0.1094
R1 ) 0.0803
wR2 ) 0.1234
0.374, -0.432
empirical
271
1.048
R1 ) 0.0317
wR2 ) 0.0897
R1 ) 0.0374
wR2 ) 0.0934
0.565, -0.568
empirical
271
1.087
R1 ) 0.0577
wR2 ) 0.1801
R1 ) 0.0789
wR2 ) 0.1963
1.050, -1.488
empirical
271
1.084
R1 ) 0.0309
wR2 ) 0.0860
R1 ) 0.0415
wR2 ) 0.0910
0.477, -0.503
no. of params
goodness of fit on F2
final R indices (I > 2σ(I))
R indices (all data)
largest diff peak,
hole (e Å-3
)

2734 Organometallics, Vol. 26, No. 10, 2007
Sun et al.
7.2 Hz, Py), 7.93 (t, 1H, J ) 7.2 Hz, Py), 7.79 (d, 1H, J ) 6.3 Hz,
Ph), 7.51 (d, 2H, J ) 7.5 Hz, Ph), 7.25 (m, 3H, Ph), 6.78 (m, 1H,
Ph), 4.28 (s, 3H, CH3), 2.28 (s, 3H, CH3).13C NMR (75 MHz,
CDCl3, TMS): δ 170.6, 154.5, 149.9, 149.8, 148.0, 142.6, 137.8,
137.4, 132.1, 126.5, 125.5, 123.6, 122.9, 122.1, 120.3, 113.7, 101.0,
33.1, 18.1. ESI-MS (m/z): 485.0 (M + H+). IR (KBr; cm-1): 2953,
1647 (νCdN), 1587, 1468, 1428, 1362, 1313, 1265, 1222, 1150,
1114, 1073, 825, 747. Anal. Calcd for C21H16Br2N4 (484.2): C,
52.09; H, 3.33; N, 11.57. Found: C, 52.38; H, 3.53; N, 11.27.
4.3.2. Synthesis of Tridentate Iron Complexes 7a-11a. The
complexes 7a-11a were synthesized by the reaction of FeCl2·4H2O
with the corresponding ligands in ethanol. A typical synthetic
procedure for 7a can be described as follows. The ligand 7 (150
mg, 0.42 mmol) and FeCl2·4H2O (79.5 mg, 0.40 mmol) were added
to a Schlenk tube, followed by the addition of freshly distilled
ethanol (2 mL) with rapid stirring at room temperature. The solution
turned deep blue immediately, and a blue powder was formed after
1 min. The reaction mixture was stirred for 10 h and allowed to
stand for 30 min before the supernatant was removed. The
precipitate was washed with diethyl ether twice and dried under
vacuum to give the pure product as a blue powder in 96% yield.
IR (KBr; cm-1): 3449, 2951, 2915, 1594 (νCdN), 1487, 1470, 1399,
1372, 1284, 1348, 1331, 1259, 1209, 1098, 794, 748. Anal. Calcd
for C23H22Cl2FeN4 (481.2): C, 57.41; H, 4.61; N, 11.64. Found:
C, 57.09; H, 4.30; N, 11.41. Data for 8a are as follows. Yield:
89%. IR (KBr; cm-1): 3398, 2962, 2932, 2875, 1595 (νCdN), 1486,
1445, 1422, 1398, 1371, 1349, 1304, 1284, 1256, 1162, 1126, 792,
754. Anal. Calcd for C25H26Cl2FeN4 (509.3): C, 58.96; H, 5.15;
N, 11.00. Found: C, 59.06; H, 5.08; N, 10.75. Data for 9a are as
follows. Yield: 95%. IR (KBr; cm-1): 3423, 2963, 2929, 2869,
1595 (νCdN), 1487, 1464, 1444, 1399, 1369, 1351, 1283, 1255,
1199, 1106, 792, 757. Anal. Calcd for C27H30Cl2FeN4 (537.3): C,
60.35; H, 5.63; N, 10.43. Found: C, 60.50; H, 5.80; N, 10.16. Data
for 10a are as follows. Yield: 70%. IR (KBr; cm-1): 3423, 3057,
1595 (νCdN), 1562, 1485, 1438, 1396, 1367, 1307, 1282, 1228,
1188, 1159, 1091, 789, 746. Anal. Calcd for C21H16Cl4FeN4
(522.0): C, 48.32; H, 3.09; N, 10.73. Found: C, 48.40; H, 3.02;
N, 10.51. Data for 11a are as follows. Yield: 72%. IR (KBr; cm-1):
3422, 3063, 1595 (νCdN), 1552, 1485, 1432, 1395, 1368, 1307,
1259, 1225, 1159, 815, 786, 749, 729. Anal. Calcd for C21H16Cl2-
Br2FeN4 (610.9): C, 41.28; H, 2.64; N, 9.17. Found: C, 41.26; H,
2.24; N, 9.15.
4.3.3. Synthesis of Tridentate Cobalt Complexes 7b-11b. 7b-
11b were prepared by the same synthetic procedures as for 7a-
11a and were obtained as green powders. The synthetic procedure
of 7b can be described as follows: to a mixture of ligand 7 (150
mg, 0.42 mmol) and CoCl2 (52 mg, 0.40 mmol) was added freshly
distilled ethanol (2 mL) at room temperature. The solution turned
green immediately. The reaction mixture was stirred for 10 h, and
the precipitate was collected by filtration and washed with diethyl
ether, followed by drying under vacuum. The desired complex was
obtained as a green powder in 60% yield. IR (KBr; cm-1): 3440,
2916, 1662, 1594 (νCdN), 1566, 1488, 1399, 1363, 1329, 1257,
1211, 1156, 1097, 1020, 794, 751. Anal. Calcd for C23H22Cl2N4Co
(484.3): C, 57.04; H, 4.58; N, 11.57. Found: C, 56.83; H, 4.75;
N, 11.46. Data for 8b are as follows. Yield: 72%. IR (KBr; cm-1):
3446, 3060, 2961, 2874, 1594 (νCdN), 1487, 1445, 1401, 1369,
1306, 1282, 1256, 1163, 1090, 1024, 793, 757. Anal. Calcd for
C25H26Cl2N4Co (512.3): C, 58.61; H, 5.12; N, 10.94. Found: C,
58.52; H, 5.21; N, 10.73. Data for 9b are as follows. Yield: 48%.
IR (KBr; cm-1): 3449, 3113, 2963, 2869, 1595 (νCdN), 1572, 1488,
1461, 1402, 1384, 1329, 1283, 1256, 1201, 1104, 793, 758. Anal.
Calcd for C27H30Cl2CoN4 (540.4): C, 60.01; H, 5.60; N, 10.37.
Found: C, 60.11; H, 5.75; N, 10.16. Data for 10b are as follows.
Yield: 57%. IR (KBr; cm-1): 3445, 3053, 2362, 1596 (νCdN), 1573,
1488, 1434, 1401, 1365, 1307, 1283, 1258, 1231, 1191, 1160, 1090,
1021, 789, 763. Anal. Calcd for C21H16Cl4N4Co (525.1): C, 48.03;
H, 3.07; N, 10.67. Found: C, 47.78; H, 3.20; N, 10.61. Data for
11b are as follows. Yield: 46%. IR (KBr; cm-1): 3422, 3061, 1595
(νCdN), 1486, 1432, 1370, 1333, 1281, 1259, 1227, 1187, 1160,
1094, 815, 789, 748, 730. Anal. Calcd for C21H16Cl2Br2CoN4
(614.0): C, 41.08; H, 2.63; N, 9.12. Found: C, 41.27; H, 2.27; N,
9.00.
4.6. Procedure for Ethylene Oligomerization and Polymer-
ization. Ethylene oligomerization and polymerization were per-
formed in a stainless steel autoclave (0.5 L capacity) equipped with
a gas ballast through a solenoid clave for continuous feeding of
ethylene at constant pressure. A 100 mL amount of toluene
containing the catalyst precursor was transferred to the fully dried
reactor under a nitrogen atmosphere. The required amount of
cocatalyst (MAO, MMAO, or Et2AlCl) was then injected into the
reactor via a syringe. At the reaction temperature, the reactor was
sealed and pressurized to high ethylene pressure, and the ethylene
pressure was maintained with feeding of ethylene. After the reaction
mixture was stirred for the desired period, the pressure was released
and a small amount of the reaction solution was collected, which
was then analyzed by gas chromatography (GC) for determining
the composition and mass distribution of oligomers obtained. Then
the residual reaction solution was quenched with 5% hydrochloric
acid in ethanol. The precipitated low-molecular-weight waxes were
collected by filtration, washed with ethanol and water, and dried
under vacuum to constant weight.
4.7. X-ray Crystallographic Studies. Single-crystal X-ray
diffraction studies for 1b, 2a, 2b, 5b, 7, 10, 7a, 10a, 7b, 8b, and
10b were carried out on a Bruker SMART 1000 CCD 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 polarization 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 anisotropically.
All hydrogen atoms were placed in calculated positions. Structure
solution and refinement were performed by using the SHELXL-97
package.41 Crystal data and processing parameters for 1b, 2a, 2b,
5b, 7, 10, 7a, 10a, 7b, 8b, and 10b are summarized in Table 9.
Acknowledgment. This work was supported by NSFC No.
20674089 and MOST No. 2006AA03Z553. We thank Mr.
Sherrif Adewuyi for the English corrections.
Supporting Information Available: CIF files giving X-ray
crystallographic data for 1b, 2a, 2b, 5b, 7, 10, 7a, 10a, 7b, 8b,
and 10b, along with text and figures giving representative examples
of π-π stacking and hydrogen bonding between two adjacent
molecules. This material is available free of charge via the Internet
at http://pubs.acs.org.
OM0700819
(41) Sheldrick, G. M. SHELXTL-97, Program for the Refinement of
Crystal Structures; University of Go¨ttingen, Go¨ttingen, Germany, 1997.