Iron complexes bearing 2-imino-1,10-phenanthrolinyl ligands as highly active catalysts for ethylene oligomerization

Article abstract of DOI:10.1021/om050891p

A series of iron complexes ligated by 2-imino-1,10-phenanthrolinyl ligands, LFeCl₂ (L = 2-(ArN=CR)-1,10-phen), were synthesized and sufficiently characterized by elemental and spectroscopic analysis along with X-ray diffraction analysis. Activated with methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), these iron(II) complexes show high catalytic activities up to 8.95 × 10⁷ g mol^-1(Fe) h ^-1 for ethylene oligomerization. The distribution of oligomers produced follows Schluz-Flory rules with high selectivity for α-olefins. Both the steric and electronic effects of coordinative ligands affect the catalytic activity and the properties of the catalytic products. The parameters of the reaction conditions were also investigated to explore the catalytic potentials of these complexes.

Full text of DOI:10.1021/om050891p

666
Organometallics 2006, 25, 666-677
Iron Complexes Bearing 2-Imino-1,10-phenanthrolinyl Ligands as
Highly Active Catalysts for Ethylene Oligomerization
Wen-Hua Sun,* Suyun Jie, Shu Zhang, Wen Zhang, Yingxia Song, and Hongwei Ma
Key Laboratory of Engineering Plastics, Institute of Chemistry, Chinese Academy of Sciences,
Beijing 100080, China
Jiutong Chen
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter,
Chinese Academy of Sciences, Fuzhou 350002, China
Katrin Wedeking and Roland Fro¨hlich
Organisch-Chemisches Institut der UniVersita¨t Mu¨nster, Corrensstrasse 40, 48149 Mu¨nster, Germany
ReceiVed October 16, 2005
A series of iron complexes ligated by 2-imino-1,10-phenanthrolinyl ligands, LFeCl2 (L ) 2-(ArNd
CR)-1,10-phen), were synthesized and sufficiently characterized by elemental and spectroscopic analysis
along with X-ray diffraction analysis. Activated with methylaluminoxane (MAO) or modified methyla-
luminoxane (MMAO), these iron(II) complexes show high catalytic activities up to 8.95 × 107 g mol-1(Fe)
h-1 for ethylene oligomerization. The distribution of oligomers produced follows Schluz-Flory rules
with high selectivity for R-olefins. Both the steric and electronic effects of coordinative ligands affect
the catalytic activity and the properties of the catalytic products. The parameters of the reaction conditions
were also investigated to explore the catalytic potentials of these complexes.
tant role in large-scale industry. The full-range process of
ethylene oligomerization was originally achieved with the
Ziegler (Alfen) process, while currently the catalysts widely
employed in industrial processes are alkylaluminum compounds,
a combination of alkylaluminum compounds with early transi-
tion metal compounds, or nickel(II) complexes.5 Homogeneous
nickel-based catalysts with monoanionic [P,O] ligands (A, Chart
1) for ethylene oligomerization were developed as the well-
known Schell Higher Olefin Process (SHOP) and have been
extensively investigated.6 In the past decade significant progress
was achieved in the development of late transition metal
catalysts for the oligomerization of ethylene. Nickel and
palladium complexes based on R-diimine ligands (B, Chart 1)7
1. Introduction
R-Olefins are major industrial reactants that are extensively
used in the preparation of detergents, lubricants, plasticizers,
oil field chemicals, and monomers for copolymerization. The
R-olefin industry’s increasing demand for higher fractions has
been growing at around 5% per year, and the oligomerization
of ethylene is currently one of the major industrial processes
for the production of R-olefins. R-Olefin production falls into
two categories: the full range process of ethylene oligomer-
ization with a range of C4/C6 up to C20+ generated, and the
deliberate dimerization and trimerization of ethylene. The
selective dimerization reaction was first described in 1954 by
Ziegler,1 and later the selectivity was improved by modification
of the catalysts and optimization of the reaction conditions.2
Phillips has developed chromium-based catalysts, which can
selectively trimerize ethylene to 1-hexene with high selectivity.3
On the basis of chromium catalysts, the tetramerization of
ethylene has also been developed with reasonable selectivity.4
However, these processes could not provide higher order
R-olefins, and the full-range process of ethylene oligomerization
provides various chemical substances and plays a more impor-
(5) Vogt, D. In Applied Homogeneous Catalysis with Organometallic
Compounds; Cornils, B., Herrmann, W. A., Eds.; VCH: Weinheim, 2002;
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Keim, W.; Behr, A.; Limbacker, B.; Kru¨ger, C. Angew. Chem., Int. Ed.
Engl. 1983, 22, 503. (c) Keim, W.; Behr, A.; Kraus, G. J. Organomet. Chem.
1983, 251, 377-391. (d) Grenouillet, P.; Neibecker, D.; Tkatchenko, I. J.
Organomet. Chem. 1983, 243, 213-222. (e) Peuckert, M.; Keim, W.
Organometallics 1983, 2, 594-597. (f) Peuckert, M.; Keim, W. J. Mol.
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* Corresponding author. Tel: +86 10 62557955. Fax: +86 10 62618239.
E-mail: whsun@iccas.ac.cn.
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10.1021/om050891p CCC: $33.50 © 2006 American Chemical Society
Publication on Web 12/24/2005

Iron-Based Catalysts for Ethylene Oligomerization
Organometallics, Vol. 25, No. 3, 2006 667
Chart 1. Complex Models of Ethylene Oligomerization
Catalyst
center (iron), which is a necessary site for the coordination of
ethylene for oligomerization and polymerization.15 To verify
this hypothesis, the additional imino group in F should be
eliminated. The synthesis of 2-formyl-, 2-acetyl-, and 2-benzoyl-
1,10-phenanthrolines would be required for this work, but the
multistep syntheses have thus blocked further work. Fortunately,
a convenient synthetic method for 2-acetyl-1,10-phenanthroline
has been developed in our group, and accordingly the various
2-imino-1,10-phenanthrolinyl ligands and their corresponding
iron(II) complexes have been synthesized. The catalytic inves-
tigation showed that these iron(II) complexes could oligomerize
ethylene to linear R-olefins with high activity and selectivity.
Herein the syntheses of 2-formyl-, 2-acetyl-, and 2-benzoyl-1,-
10-phenanthrolines are reported along with an improved syn-
thetic method for 2-acetyl-1,10-phenanthroline. The 2-imino-
1,10-phenanthrolinyl ligands and corresponding iron(II) complexes
are investigated and discussed regarding ethylene oligomeriza-
tion with various catalytic reaction parameters.
and iminophosphines (C and D, Chart 1)8 were reported to be
very active and selective catalysts for ethylene oligomerization.
In 1998, extremely active iron- and cobalt-based catalysts
bearing 2,6-bis(imino)pyridyl ligands for the linear polymeri-
zation of ethylene were reported independently by Brookhart9
and Gibson.10 By tuning the steric and electronic properties of
the ligands, the catalytic products of these metal complexes
varied from polyethylene to oligomers (E, Chart 1),11 in which
both the catalytic activity and selectivity of R-olefins are highly
interesting.
Extending the iron complexes including other tridentate
ligands, however, commonly leads to lower catalytic activities
for ethylene oligomerization and polymerization.12 In scanning
suitable tridentate metal complexes, the late transition metal
complexes ligated by 2,9-bis(imino)-1,10-phenanthrolinyl ligands
were investigated in our group.13 The nickel and cobalt
complexes showed considerable to good catalytic activities for
ethylene oligomerization and polymerization, but the iron
complexes (F, Chart 1) showed only negligible activities for
ethylene polymerization. This result was confirmed by Gibson’s
group.14 It could be argued that the nitrogen atom of the
additional imino group can coordinate to the active catalytic
2. Results and Discussion
2.1. Preparation of 2-Formyl-, 2-Acetyl-, and 2-Benzoyl-
1,10-phenanthroline. The 2-formyl, 2-acetyl, and 2-benzoyl
1,10-phenanthroline derivatives are not commercially available,
nor are their synthetic intermediates, except 1,10-phenanthroline.
Therefore the literature procedures and improved synthetic
methods have been explored to prepare the three reactants
(Scheme 1). First, 1,10-phenanthroline was oxidized with 30%
hydrogen peroxide in glacial acetic acid to form 1,10-phenan-
throline 1-oxide.16 (Caution: An explosion easily happened
during the concentration of the resulting acetic acid solution.
The modified method included the least amount of acetic acid
to dissolve 1,10-phenanrhroline and no rotary evaporation before
being neutralized and extracted.) Following the procedure in
the same report,16 the oxide was converted to 2-cyano-1,10-
phenanthroline through cyanation using KCN and benzoyl
chloride. Further treatment gave 2-carbomethoxy-1,10-phenan-
throline. Subsequently the ester was reduced to the carbinol with
NaBH4,17 and the resulting carbinol was oxidized by SeO2 to
produce the aldehyde, 2-formyl-1,10-phenanthroline.18 The
attempts to convert 2-cyano-1,10-phenanthroline into the alde-
hyde by employing the reported one-step reaction employing
Raney nickel and sodium hypophosphite were not successful.19
In the preparation of 2-acetyl-1,10-phenanthroline, the literature
procedure through a Claisen condensation reaction of 2-car-
bomethoxy-1,10-phenanthroline gave the highest total yield of
36% from 2-cyano-1,10-phenanthroline due to multistep reac-
tions and manipulations.20 To shorten the synthetic route and
improve the total yield, an alternative synthetic methodology
was established through the direct reaction of 2-cyano-1,10-
phenanthroline and trimethylaluminum (Scheme 1) for preparing
2-acetyl-1,10-phenanthroline in 60% yield in a somewhat scaled-
up reaction. However, other methyl metal reagents such as
methyllithium or methylmagnesium iodide did not work well.
(8) (a) van den Beuken, E. K.; Smeets, W. J. J.; Spek, A. L.; Feringa, B.
L. Chem. Commun. 1998, 223-224. (b) Guan, Z.; Marshall, W. J.
Organometallics 2002, 21, 3580-3586.
(9) Small, B. L.; Brookhart, M.; Bennett, A. M. A. J. Am. Chem. Soc.
1998, 120, 4049-4050.
(10) Britovsek, G. J. P.; Gibson, V. C.; Kimberley, B. S.; Maddox, P.
J.; McTavish, S. J.; Solan, G. A.; White, A. J. P.; Williams, D. J. Chem.
Commun. 1998, 849-850.
(11) (a) Small, B. L.; Brookhart, M. J. Am. Chem. Soc. 1998, 120, 7143-
7144. (b) Britovsek, G. J. P.; Bruce, M.; Gibson, V. C.; Kimberley, B. S.;
Maddox, P. J.; Mastroianni, S.; McTavish, S. J.; Redshaw, C.; Solan, G.
A.; Stromberg, S.; White, A. J. P.; Williams, D. J. J. Am. Chem. Soc. 1999,
121, 8728-8740. (c) Britovsek, G. J. P.; Mastroianni, S.; Solan, G. A.;
Baugh, S. P. D.; Redshaw, C.; Gibson, V. C.; White, A. J. P.; Williams, D.
J.; Elsegood, M. R. J. Chem. Eur. J. 2000, 6, 2221-2231. (d) Chen, Y.;
Chen, R.; Qian, C.; Dong, X.; Sun, J. Organometallics 2003, 22, 1231-
1236. (e) Chen, Y.; Chen, R.; Qian, C.; Dong, X.; Sun, J. Organometallics
2003, 22, 4312-1321.
(12) (a) Qian, M.; Wang, M.; He, R. J. Mol. Catal. A 2000, 160, 243-
247. (b) Qian, M.; Wang, M.; Zhou, B.; He, R. Appl. Catal. A 2001, 209,
11-15. (c) LePichon, L.; Stephan, D. W.; Gao, X.; Wang, Q. Organome-
tallics 2002, 21, 1362-1366. (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. (g) Cowdell, R.; Davies, C. J.; Hilton, S. J.; Mare´chal,
J.-D.; Solan, G. A.; Thomas, O.; Fawcett, J. Dalton Trans. 2004, 3231-
3240.
(13) Wang, L.; Sun, W.-H.; Han, L.; Yang, H.; Hu, Y.; Jin, X. J.
Organomet. Chem. 2002, 658, 62-70.
(14) Britovsek, G. J. P.; Baugh, S. P. D.; Hoarau, O.; Gibson, V. C.;
Wass, D. F.; White, A. J. P.; Williams, D. J. Inorg. Chim. Acta 2003, 345,
279-291.
(15) Ameerunisha, S.; Schneider, J.; Meyer, T.; Zacharias, P. S.; Bill,
E.; Henkel, G. Chem. Commun. 2000, 2155-2156.
(16) Corey, E. J.; Borror, A. L.; Foglia, T. J. Org. Chem. 1965, 30, 288-
290.
(17) Sigman, D. S.; Wahl, G. M.; Greighton, D. J. Biochemistry 1972,
11, 2236-2242.
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98, 4619-4624.
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(b) Staskun, B.; Backeberg, O. G. J. Chem. Soc. 1964, 5880-5881. (c)
van Es, T.; Staskun, B. J. Chem. Soc. 1965, 5775-5777.
(20) Case, F. H.; Schilt, A. A. J. Heterocycl. Chem. 1979, 16, 1135-
1139.

668 Organometallics, Vol. 25, No. 3, 2006
Scheme 1. Synthesis of 2-Formyl-, 2-Acetyl-, and 2-Benzoyl-1,10-phenanthroline
Sun et al.
Scheme 2. Synthesis of the Ligands 1-20 and the Iron(II) Complexes 1a-20a
2-Benzoyl-1,10-phenanthroline was first synthesized from 1,-
10-phenanthroline-2-carbonyl chloride followed by a Friedel-
Crafts acylation reaction of benzene with AlCl3 as catalyst.
2.2. Synthesis of 2-Imino-1,10-phenanthrolinyl Ligands
and Their Iron Complexes. The 2-imino-1,10-phenanthrolinyl
ligands (1-20, 2-(ArNdCR)-1,10-phen) were prepared through
the condensation reaction of aldehydes or ketones and the
corresponding substituted anilines using p-toluenesulfonic acid
as catalyst (Scheme 2). Because of the difference in the reactive
nature between aldehydes and ketones and alkyl- and halogen-
substituted anilines, various solvents such as ethanol, toluene,
and tetraethyl silicate were employed in order to improve the
product yields. The 2-imino-1,10-phenanthrolinyl ligands can
be classified according to the nature of R on the imino-C as
methyl-ketimine (R ) Me, 1-11), aldimine (R ) H, 12-17),
and phenyl-ketimine (R ) Ph, 18-20), and all compounds were
sufficiently characterized and confirmed by the analysis of IR
and 1H and 13C NMR spectra as well as their elemental analysis.
The iron(II) complexes 1a-20a were easily prepared by
mixing the corresponding ligand and 1 equiv of FeCl2‚4H2O in
THF at room temperature under argon (Scheme 2). The resulting
complexes were precipitated from the reaction solution and
separated as blue, purple, or brown air-stable powders. All the
complexes were characterized by FT-IR spectra and elemental
analysis. In the IR spectra, the stretching vibration bands of
CdN of these iron(II) complexes (1602-1614 cm-1) apparently
shifted to lower wavenumber and the peak intensity was greatly
reduced, as compared to the corresponding ligands (1618-1656
cm-1), indicating the coordination interaction between the imino
nitrogen atom and the metal cation. Some elemental data of
complexes showed incorporation of a solvent molecule because
the samples were prepared through the recrystallization. These
iron(II) complexes are paramagnetic. As one representative
species, complex 2a was characterized in its methanol-d4
solution by the Evans method21 and afforded a magnetic moment
of 5.5 µB, consistent with four unpaired electrons of the high-
spin iron(II). Their unambigious structures were confirmed by
single-crystal X-ray diffraction analysis.
2.3. Crystal Structures. Single crystals of complexes 2a,
4a, 7a, and 8a suitable for X-ray diffraction analysis were
individually obtained by slow diffusion of diethyl ether into
their methanol solutions under argon atmosphere, while crystals
of 14a suitable for X-ray diffraction analysis were grown
through slow layering of the chloroform solution of ligand 14
over the ethanol solution of FeCl2 in a Schlenk tube under argon
atmosphere. According to their structures, the coordination
geometry around the iron center can be described as distorted
trigonal bipyramidal, in which the nitrogen (next to the imino-
C) of the phenanthrolinyl group and two chlorides compose an
equatorial plane. Their crystal structures are shown in Figures
(21) (a) Evans, D. F. J. Chem. Soc. 1959, 2003-2005. (b) Lo¨liger, J.;
Scheffold, R. J. Chem. Educ. 1972, 49, 646-647. (c) Sur, S. K. J. Magn.
Reson. 1989, 82, 169-173.

Iron-Based Catalysts for Ethylene Oligomerization
Organometallics, Vol. 25, No. 3, 2006 669
Figure 2. ORTEP drawing of complex 4a with thermal ellipsoids
at the 60% probability level. Hydrogen atoms have been omitted
for clarity.
Figure 1. ORTEP drawing of complex 2a with thermal ellipsoids
at the 30% probability level. Hydrogen atoms have been omitted
for clarity.
1-5, individually, and selected bond lengths and angles are
collected in Table 1.
In the structure of 2a (Figure 1), the iron atom slightly
deviates by 0.0465 Å from the triangular plane of N2, Cl1, and
Cl2 with equatorial angle ranges between 103.06(8)° and
146.74(8)°, deviating from 120°. This equatorial plane is nearly
perpendicular to the phenanthrolinyl plane, with a dihedral angle
of 91.2°. The dihedral angle between the phenyl ring and the
phenanthrolinyl plane is 79.8°. The Fe-N(2)(phenanthrolinyl)
bond (2.110(3) Å) is shorter by about 0.16 Å than the
Fe-N(1)(phenanthrolinyl) (2.271(3) Å) and Fe-N(3)(imino)
(2.275(3) Å) bonds, which is similar to the 2,6-bis(imino)pyridyl
iron(II) complexes.10 The two Fe-Cl bond lengths show a slight
difference between the Fe-Cl(2) (2.3046(13) Å) and
Fe-Cl(1) (2.2806(11) Å). The imino N(3)-C(13) bond length
is 1.273(5) Å, with the typical character of a CdN double bond.
According to complex 4a (Figure 2), the phenanthrolinyl
nitrogen atom (N2) and two chlorides form the equatorial plane,
and the iron atom slightly deviates by 0.0330 Å from this plane.
The three equatorial angles N(2)-Fe-Cl(1), N(2)-Fe-Cl(2),
and Cl(1)-Fe-Cl(2) are respectively 150.53(5)°, 99.54(4)°, and
109.86(2)°, with the larger distortion of N(2)-Fe-Cl(1), and
the axial Fe-N bonds subtend an angle of 143.38(6)° (N(1)-
Fe-N(3)). The dihedral angles between the equatorial plane
and the phenanthrolinyl plane, and the phenyl plane and the
phenanthrolinyl plane, are 85.5° and 77.3°, respectively. Their
two axial Fe-N bond lengths, 2.2643(16) and 2.2296(16) Å,
are longer than that of Fe-N(2) of the equatorial plane
(2.1262(15) Å), which is similar to that observed in the bis-
Figure 3. ORTEP drawing of complex 7a with thermal ellipsoids
at the 50% probability level. Hydrogen atoms have been omitted
for clarity.
(2,4,6-trimethylphenylimino)pyridyliron(II) complex,11b also
with a trigonal bipyramical geometry at the iron center. The
difference of the two Fe-Cl linkages, Fe-Cl(2) (2.3321(5) Å)
and Fe-Cl(1) (2.2923(5) Å), is about 0.04 Å. The imino N(3)-
C(13) bond length is 1.286(2) Å with the typical character of a
CdN double bond, but slightly longer than that of 2a
(1.273(5) Å). The difference is probably due to the less bulky
methyl at the ortho-positions of the phenyl ring in 4a. This steric
effect of the substituents also influences the Fe-N(imino) bonds.
For instance, the Fe-N(imino) bond length of 4a (2.2296(16)
Å) is noticeably shorter than that of 2a (2.275(3) Å), with the
relatively bulkier ethyl groups at the ortho-positions of the
phenyl ring.
Complex 7a (Figure 3) with 2,6-dichlorophenyl and complex
8a (Figure 4) with 2,6-dibromophenyl almost have the same
structural characters, as shown in Figures 3 and 4 (their bond
distances and angles are listed in Table 1). One nitrogen atom
Table 1. Selected Bond Lengths (Å) and Angles (deg) for Complexes 2a, 4a, 7a, 8a, and 14a
2a 4a 7a 8a
14a
Bond Lengths
2.2387(17)
Fe-N(1)
2.271(3)
2.110(3)
2.275(3)
2.2806(11)
2.3046(13)
1.273(5)
1.438(4)
2.2643(16)
2.1262(15)
2.2296(16)
2.2923(5)
2.3321(5)
1.286(2)
2.241(4)
2.128(4)
2.279(4)
2.2727(16)
2.3228(17)
1.283(6)
1.419(6)
2.259(3)
2.097(2)
2.276(2)
2.2496(12)
2.2921(12)
1.277(3)
Fe-N(2)
2.1223(17)
2.2750(17)
2.2760(6)
2.3292(7)
1.288(3)
Fe-N(3)
Fe-Cl(1)
Fe-Cl(2)
N(3)-C(13)
N(3)-C(15)
1.437(2)
1.419(3)
1.449(3) (N3-C14)
Bond Angles
N(2)-Fe-N(1)
N(2)-Fe-N(3)
N(1)-Fe-N(3)
N(1)-Fe-Cl(1)
N(2)-Fe-Cl(1)
N(3)-Fe-Cl(1)
N(1)-Fe-Cl(2)
N(2)-Fe-Cl(2)
N(3)-Fe-Cl(2)
Cl(1)-Fe-Cl(2)
73.80(10)
71.86(10)
144.10(10)
97.95(7)
146.74(8)
104.97(8)
98.20(8)
103.06(8)
99.37(8)
110.04(4)
73.36(6)
71.86(6)
143.38(6)
99.57(4)
150.53(5)
105.01(4)
98.35(4)
99.54(4)
98.32(4)
109.86(2)
74.34(6)
71.30(6)
74.19(16)
71.21(15)
144.14(16)
101.21(12)
148.98(12)
103.49(11)
93.87(12)
99.02(11)
100.47(11)
111.96(7)
73.83(10)
72.58(9)
145.10(10)
101.26(8)
139.89(8)
98.26(7)
144.52(6)
101.91(5)
148.63(5)
102.72(5)
93.62(5)
100.50(5)
100.97(5)
110.85(3)
94.10(8)
103.50(8)
102.63(7)
116.60(5)

670 Organometallics, Vol. 25, No. 3, 2006
Sun et al.
Table 2. Results of Ethylene Oligomerization by Complexes
1a-20a/MAOa
oligomers
waxes
c
d
entry
cat.
Al/Fe
Tb(°C)
Ao
1.20
21.2
R
% R-Oe
Aw
1
2
3
4
5
6
7
8
2a
2a
2a
2a
2a
2a
2a
2a
2a
1a
3a
4a
5a
6a
7a
8a
200
500
40
40
40
40
40
20
30
50
60
40
40
40
40
40
40
40
40
40
40
40
40
40
40
40
40
40
40
40
0.68
0.64
0.62
0.62
0.64
0.49
0.55
0.61
0.44
0.67
0.50
0.72
0.67
0.37
0.52
0.61
0.73
0.49
0.64
0.58
0.54
0.48
0.39
0.59
0.62
0.57
0.52
0.50
>99
>96
>94
>97
>98
>96
>95
>93
>95
>96
>98
>96
>91
>79
>79
>80
>80
>90
>87
>94
>99
>97
>97
>97
>99
>91
>95
>98
1.01
1.56
14.6
9.13
1.25
10.1
26.3
5.87
4.88
102
1000
1500
2000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
49.1
25.5
7.50
16.4
21.4
35.5
14.4
38.9
9
Figure 4. ORTEP drawing of complex 8a with thermal ellipsoids
at the 30% probability level. Hydrogen atoms have been omitted
for clarity.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
9.42
0.21
138
12.4
48.2
23.7
35.1
40.6
38.9
19.6
22.2
13.3
174
trace
trace
65.5
241
14.6
64.1
48.6
trace
0.88
trace
4.51
trace
304
9a
10a
11a
12a
13a
14a
15a
16a
17a
18a
19a
20a
1.60
9.00
6.99
7.30
1.08
12.7
23.0
1.31
3.25
3.18
a General conditions: cat.: 2 µmol; reaction time: 1 h; solvent: toluene
Figure 5. ORTEP drawing of complex 14a with thermal ellipsoids
at the 30% probability level. Hydrogen atoms have been omitted
for clarity.
(100 mL); ethylene pressure: 10 atm. b Reaction temperature. c Activity for
oligomers: 106 g mol-1(Fe) h-1 d Activity for low-molecular-weight
.
waxes: 105 g mol-1(Fe) h-1
GC-MS.
.
e % R-olefin content determined by GC and
(N2) of the phenanthrolinyl group and two chlorides form the
equatorial plane, while the iron atom lies 0.0155 and 0.0246 Å
out of the equatorial plane in 7a and 8a, respectively. The bond
angles N(1)-Fe-N(3) are nearly identical for the two com-
plexes, (144.52(6)° (7a) and 144.14(16)° (8a)), as well as the
N(2)-Fe-Cl angles of 8a (148.98(12)° and 99.02(11)°) and
those of 7a (148.63(5)° and 100.50(5)°) and the angles Cl(1)-
Fe-Cl(2) of 7a and 8a (110.85(3)° and 111.96(7)°, respec-
tively). The equatorial planes of these two complexes are nearly
orthogonal to the phenanthrolinyl plane, with dihedral angles
of 83.3° in 7a and 84.7° in 8a. The dihedral angles between
the phenyl plane and the phenanthrolinyl plane are 103.9° in
7a and 102.0° in 8a, which are different from the corresponding
alkyl-substituted analogues 2a (79.8°) and 4a (77.3°). The
difference in bond distance is about 0.05 Å between the Fe-
Cl(1) and Fe-Cl(2) bonds, such as 2.2760(6) and 2.3292(7) Å
in 7a and 2.2727(16) and 2.3228(17) Å in 8a, respectively.
Interestingly, the Fe-Cl distances on the same sides of the
complex frame are almost equal. The two imino CdN bonds
have distinctive double-bond character, with C-N distances of
1.288(3) Å (7a) and 1.283(6) Å (8a). The electronic properties
of the substituents at the ortho-positions of the phenyl ring also
have some influence on the adjacent N(3)-C(15)(phenyl) bond
length. The N(3)-C(15) bonds of 7a (1.419(3) Å) and 8a
(1.419(6) Å) with 2,6-dihalogenphenyl are shorter by 0.02 Å
than those of 2a (1.438(4) Å) and 4a (1.437(2) Å) with 2,6-
dialkylphenyl.
N(1)-Fe-N(3) angle is 145.10(10)°. Both the equatorial plane
and the phenyl plane are almost perpendicular to the phenan-
throlinyl plane, with dihedral angles of 87.3° and 81.3°,
respectively. The two axial Fe-N bond lengths, 2.259(3) and
2.276(2) Å, are longer than that of Fe-N(2) in the equatorial
plane (2.097(2) Å). The two Fe-Cl distances show an obvious
difference, 2.2496(12) and 2.2921(12) Å. Furthermore, they are
shorter than those of the ketimine complexes, as shown in Table
1. The imino C(13)-N(3) bond has typical CdN double-bond
character, with a bond length of 1.277(3) Å, and it also has a
longer N(3)-C(14)(phenyl) (1.449(3) Å), which is slightly
longer than that of the ketimine analogues.
2.4. Ethylene Oligomerization. All the synthesized iron(II)
complexes, when activated with methylaluminoxane (MAO),
display high catalytic activities for ethylene oligomerization with
high selectivity for R-olefins at 10 atm of ethylene pressure.
The detailed results are summarized in Table 2. The distribution
of oligomers obtained in all cases follows Schulz-Flory rules,
which is characteristic of the constant R, where R represents
the probability of chain propagation (R ) rate of propagation/
((rate of propagation) + (rate of chain transfer)) ) (moles of
C
n+2)/(moles of Cn)).22 The R values are determined by the
molar ratio of C12 and C14 fractions.
2.4.1. Effects of the Molar Ratio of Al/Fe and Reaction
Temperature. The catalytic system of 2a/MAO was typically
investigated with varying reaction conditions, such as the molar
ratio of Al/Fe and reaction temperature. When the Al/Fe molar
ratio was enhanced from 200 to 2000, the catalytic activities of
Complex 14a (Figure 5) has a structural character similar to
complex 2a. One phenanthrolinyl nitrogen atom and two
chlorides form the equatorial plane, with the iron atom slightly
deviating by 0.012 Å from this plane. The three equatorial angles
are respectively 139.89(8)°, 103.50(8)°, and 116.60(5)°, with a
smaller N(2)-Fe-Cl(1) angle and a larger Cl(1)-Fe-Cl(2)
angle than those of the ketimine analogues, while the axial
(22) (a) Schulz, G. V. Z. Phys. Chem., Abt. B 1935, 30, 379-398. (b)
Schulz, G. V. Z. Phys. Chem., Abt. B 1939, 43, 25-46. (c) Flory, P. J. J.
Am. Chem. Soc. 1940, 62, 1561-1565. (d) Henrici-Olive´, G.; Olive´, S.
AdV. Polym. Sci. 1974, 15, 1-30.

Iron-Based Catalysts for Ethylene Oligomerization
Organometallics, Vol. 25, No. 3, 2006 671
Table 3. Ethylene Oligomerization with Complexes 1a-4a
and 6a-8a/MMAOa
2a for both oligomers and low-molecular-weight waxes initially
increased and then decreased, while the R value showed little
change. With increasing reaction temperature, both the catalytic
activity and R value initially increased and then decreased;
however, the activity showed no great change. Complex 2a
exhibited an activity of 4.91 × 107 g mol-1(Fe) h-1 at the Al/
Fe molar ratio of 1000:1 and 40 °C under 10 atm of ethylene
pressure.
oligomers
waxes
yield (g) Aw
b
c
entry
cat.
t (min)
Ao
a
% R-Od
1
2
3
4
5
6
7
8
1a
1a
1a
1a
1a
2a
3a
4a
6a
7a
8a
5
10
20
30
60
30
30
30
30
30
30
8.95
4.77
2.99
2.97
1.22
1.70
1.37
2.07
1.72
1.80
1.87
0.67
0.65
0.67
0.68
0.70
0.64
0.46
0.55
0.42
0.65
0.62
>98
>98
>98
>97
>97
>97
>98
>98
>95
>96
>93
0.67
0.73
1.88
2.63
3.99
0.06
trace
2.55
40.2
22.1
28.2
26.3
20.0
2.4.2. Effect of the Ligand Environment. The variation of
the R substituent on the imino-C of ligands, 2-(ArNdCR)-1,-
10-phen, resulted in changes of the catalytic performance.
Aldimine (R ) H) and phenyl-ketimine (R ) Ph) complexes
showed relatively lower catalytic activities than the correspond-
ing methyl-ketimine (R ) Me) complexes. Furthermore, the R
substituent had different influences on the catalytic performances
of methyl- or phenyl-ketimine and aldimine analogues. Consider
the 2,6-dialkyl-substituted ketimine and aldimine complexes as
examples. Both the methyl-ketimine complex 2a and the phenyl-
ketimine complex 19a have 2,6-diethyl groups on the phenyl
ring of the imino nitrogen and showed the highest activity
among their analogues. However, the corresponding aldimine
complex 13a showed much lower activity under the same
reaction conditions (entries 3, 27, and 21 in Table 2). Comparing
the complexes ligated by the ketimine or aldimine containing
the 2,6-diisopropylphenyl group on the imino nitrogen, both 3a
and 14a (entries 11 and 22 in Table 2) showed much better
catalytic activity than 20a (entry 28 in Table 2), which also
showed lower activity than its analogues (entries 26 and 27 in
Table 2), perhaps due to the bulky phenyl-ketimine. In general,
all methyl-ketimine complexes bearing electron-donating alkyl
groups showed high catalytic activity and good selectivity for
R-olefins. On the contrary, relatively lower selectivity was
observed with the complexes containing electron-withdrawing
halogen groups, such as complexes 6a-9a, despite their good
productivity.
0.61
25.5
9
10
11
0.13
0.15
1.32
1.45
a General conditions: cat.: 2 µmol; reaction temperature: 40 °C; solvent:
toluene (100 mL); ethylene pressure: 10 atm. b Activity for oligomers: 107
g mol-1(Fe) h-1 c % R-olefin content determined by GC and GC-MS.
.
d Activity for low-molecular-weight waxes: 105 g mol-1(Fe) h-1
.
group at the 4-position of the aryl ring. However, complex 5a,
bearing 4-bromo-2,6-dimethyl groups, showed higher oligo-
merization activity than 2,4,6-trimethyl-substituted complex 4a.
For the aldimine complexes 12a-17a, 2,6-dimethyl-substi-
tuted complex 12a displayed the higher catalytic activity of 1.33
× 107 g mol-1(Fe) h-1 (entry 20 in Table 2), while a much
lower catalytic activity was obtained for 2,6-diethyl-substituted
complex 13a (entry 21 in Table 2) under the same reaction
conditions. For the 2,6-dihalogen-substituted complexes 15a-
17a, complex 17a, with bromine atoms at the ortho-positions
of the imino N-aryl ring, gave the lower activity, while the 2,6-
dichloro-substituted complex 16a displayed a higher oligomer-
ization activity with some waxes produced and 2,6-difluoro-
substituted complex 15a showed comparable oligomerization
activity with a lower R value. This probably resulted from the
interaction of their steric and electronic effects. For the phenyl-
ketimine complexes, complex 20a, bearing bulkier isopropyl
groups at the ortho-positions of the aryl ring, had much lower
oligomerization activity than the 2,6-dimethyl-substituted 18a
and the 2,6-diethyl-substituted 19a, probably because of the
cooperative interaction of bulkier isopropyl groups on the
imino-N aryl ring and bulkier phenyl on the imino-C.
2.4.3. Effect of Different Cocatalysts. When modified
methylaluminoxane (MMAO) was employed as cocatalyst,
methyl-ketimine complexes 1a-4a and 6a-8a also displayed
high catalytic activity for ethylene oligomerization with high
selectivity for R-olefins at 10 atm, and the distribution of
oligomers obtained in all cases followed Schulz-Flory rules.
The detailed results are listed in Table 3.
In the presence of MMAO, ethylene was consumed very
quickly over the first 5 min, but after this time, the consumption
rate slowed gradually. In the presence of MAO, the consumption
rate of ethylene slightly decreased during the reaction time. As
an example, the lifetime of the complex 1a/MMAO system was
studied by varying the reaction time from 5 to 60 min. The
highest activity of 8.95 × 107 g mol-1(Fe) h-1 was obtained at
5 min (entry 1 in Table 3). With prolonged reaction time, the
oligomerization activity decreased and the yield of low-
molecular-weight waxes increased progressively, while the R
value and the activity for waxes had no remarkable change
(entries 1-5 in Table 3). However, under the same reaction
conditions, complex 1a showed a lower catalytic activity (1.22
× 107 g mol-1(Fe) h-1) than that using MAO as cocatalyst (3.89
× 107 g mol-1(Fe) h-1, entry 5 in Table 3 and entry 10 in Table
2). On treatment with MMAO, the other alkyl- and halogen-
substituted methyl-ketimine complexes displayed comparable
The substituents on the imino-N aryl ring had a great
influence on the catalytic performances of both the ketimine
and aldimine complexes. For the 2,6-dialkyl-substituted methyl-
ketimine complexes 1a-3a, somewhat reduced catalytic activity
was observed for the sterically bulkier catalyst systems. This
could be demonstrated by comparing the 2,6-diisopropyl-
substituted 3a with the 2,6-dimethyl-substituted 1a or 2,6-
diethyl-substituted 2a (entry 11 vs entry 10 or 3 in Table 2).
The greater bulkiness of the isopropyl groups at the ortho-
positions of the imino-N aryl ring of complex 3a may prevent
the access of ethylene to the active center in the catalytic system,
therefore resulting in the decrease of catalytic activity. Further-
more, the bulkier the substituents, the smaller R value and a
smaller amount of low-molecular-weight waxes produced.
Complexes 5a-11a, which bear mono- or multi-halogen groups,
exhibited comparable catalytic activity and relatively lower
selectivity for R-olefins in the oligomerization of ethylene than
complexes 1a-4a, bearing only alkyl groups. In the catalytic
systems of complexes 6a-8a, containing a 2,6-dihalogen-
substituted ligand, the bulkier substituents at the ortho-positions
of the imino-N aryl ring resulted in higher catalytic activities
as well as higher R values (bromo- > chloro- > fluoro-, entries
14-16 in Table 2). In addition, the substituent at the 4-position
of the aryl ring had an obvious influence on the catalytic activity
and R value. The 2,6-dibromo-substituted complex 9a, which
also bears an electron-donating methyl group at the 4-position
of the aryl ring, exhibited higher catalytic activity and a larger
R value than the corresponding complexes 10a (4-chloro) and
11a (4-bromo), which bear an electron-withdrawing halogen

672 Organometallics, Vol. 25, No. 3, 2006
Sun et al.
1
Figure 6. NMR spectra of the waxes obtained by complex 1a/MAO. (a) 13C NMR; (b) H NMR.
ethylene oligomerization activities and high selectivities for
R-olefins. However, the 2,6-diisopropyl-substituted complex 3a
and the 2,6-difluoro-substituted complex 6a gave lower R values
and no waxes were formed.
4. Experimental Section
4.1. General Considerations. All manipulations of air- or
moisture-sensitive compounds were carried out under an atmosphere
of argon using standard Schlenk techniques. Melting points (mp)
were measured with a digital electrothermal apparatus without
calibration. IR spectra were recorded on a Perkin-Elmer FT-IR 2000
spectrometer by using KBr disks in the range 4000-400 cm-1. 1H
NMR and 13C NMR spectra were recorded on a Bruker DMX-300
instrument with TMS as the internal standard. Splitting patterns
are designated as follows: s, singlet; d, doublet; dd, double doublet;
t, triplet; quad, quadruplet; sept, septet; m, multiplet. Elemental
analysis was performed on a Flash EA1112 microanalyzer. GC
analysis was performed with a Carlo Erba 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.
Toluene and tetrahydrofuran were refluxed over sodium-ben-
zophenone and distilled under argon prior to use. Trimethylalumi-
num was purchased from Acros Chemicals and diluted to 2 M with
dried toluene. Methylaluminoxane (MAO, 1.46 M in toluene) and
modified methylaluminoxane (MMAO, 1.93 M in heptane) were
purchased from Akzo Nobel Corp. (Gallipolis Ferry, WV). All the
anilines were purchased from Aldrich or Acros Chemicals. Iron-
(II) chloride tetrahydrate was synthesized from reduced iron power
and aqueous hydrogen chloride and kept under inert atmosphere.
All other chemicals were obtained commercially and used without
further purification unless otherwise stated.
2.4.4. Characterization of Low-Molecular-Weight Waxes.
In many cases, some low-molecular-weight waxes as higher
oligomers were obtained in addition to lower oligomers.
Characterized by IR spectra recorded using KBr disks in the
range 4000-400 cm-1, the waxes can be confirmed to be mainly
linear R-olefins from the characteristic vibration absorption
1
bands of CdC and various C-H bonds. H and 13C NMR
spectra of the waxes obtained by complex 1a/MAO were
recorded in o-dichlorobenzene-d4 using TMS as the internal
standard. NMR spectra of the waxes are shown in Figure 6,
and the assignments were determined according to the litera-
ture.23,24 The 13C NMR spectra further demonstrated that linear
R-olefins of the waxes absolutely predominated in the waxes,
and the single peaks at δ 139.14 and 114.17 ppm showed the
property of a vinyl-unsaturated chain end. The obtained average
molecular weight from 1H NMR indicated that the carbon
number of the waxes was about 40.
3. Conclusions
A series of tridentate iron(II) complexes bearing 2-imino-1,-
10-phenanthrolinyl ligands have been synthesized and fully
characterized. Upon treatment with MAO or MMAO, these
iron(II) complexes showed high catalytic activities of up to 8.95
× 107 g mol-1(Fe) h-1 for ethylene oligomerization with high
selectivity for R-olefins. However, MAO was found to be a more
effective cocatalyst than MMAO. Both the R on the imino-C
and the substituents on the N-aryl rings had an obvious influence
on the catalytic activity, distribution of oligomers, and selectivity
for R-olefins due to their different steric and electronic proper-
ties. The methyl ketimine complexes were proved to be
relatively more active than either the corresponding aldimine
or phenyl ketimine complexes under the same reaction condi-
tions. Electron-donating groups placed on the N-aryl rings
increased the selectivity for R-olefins. The placement of bulkier
o-alkyl groups on the N-aryl rings led to reduced activity
because of steric interaction; however, bulkier halogen groups
gave the reverse effect.
4.2. Preparation of the Starting Materials (aldehyde and
ketones). 4.2.1. Preparation of 2-Formyl-1,10-phenanthroline.
1,10-Phenanthroline 1-oxide. A 30 mL portion of 30% hydrogen
peroxide was added dropwise to a solution of 50.0 g (0.25 mol) of
1,10-phenanthroline monohydrate in 60 mL of glacial acetic acid.
The reaction mixture was maintained at 70-75 °C for 3 h, after
which an addition 30 mL of 30% hydrogen peroxide was
added dropwise and the heating continued for 3 h. After
cooling, the mixture was neutralized to pH
≈
10 with
saturated aqueous potassium hydroxide and then was extracted
repeatedly with chloroform. The combined chloroform extracts
were dried over anhydrous sodium sulfate and evaporated to give
a yellow solid (39.0 g) in 79% yield. Mp: 178-180 °C [lit.16 176-
179 °C].
2-Cyano-1,10-phenanthroline. To a solution consisting of 25.0
g (0.13 mol) of 1,10-phenanthroline 1-oxide and 25.0 g of potassium
cyanide dissolved in 200 mL of water was added dropwise 25 mL
of benzoyl chloride under magnetic stirring. The total addition
required 1 h, and the reaction mixture was stirred for an additional
2 h. The resulting precipitate was collected by suction filtration,
washed with water, and dried as a brown solid in 87% yield. Mp:
230-232 °C [lit.16 233-234 °C].
(23) Galland, G. B.; De Souza, R. F.; Mauler, R. S.; Nunes, F. F.
Macromolecules 1999, 32, 1620-1625.
(24) Galland, G. B.; Quijada, R.; Rojas, R.; Bazan, G. C.; Komon, Z. J.
A. Maromolecules 2002, 35, 339-345.

Iron-Based Catalysts for Ethylene Oligomerization
Organometallics, Vol. 25, No. 3, 2006 673
2-Carboxy-1,10-phenanthroline. A solution of 10.0 g of sodium
hydroxide in 60 mL of water was added to a solution of 12.0 g
(59.0 mmol) of 2-cyano-1,10-phenanthroline in 120 mL of 95%
ethanol, and the reaction mixture was refluxed for 2 h. Some of
ethanol was removed at reduced pressure, and the residue was made
slightly acidic with concentrated hydrochloric acid in an ice-water
bath. The precipitate was filtrated, washed with water, and dried
in a vacuum, and a yellow-brown solid (10.4 g) was obtained in
79% yield. Mp: 212-214 °C [lit.16 209-210 °C].
2-Carbomethoxy-1,10-phenanthroline. A 6.10 g (27.0 mmol)
amount of 2-carboxy-1,10-phenanthroline was suspended in 250
mL of thionyl chloride and refluxed until the solid had dissolved
to give a red solution (about 4 h), and then the residual SOCl2 was
removed at reduced pressure. To the residue was added 200 mL of
anhydrous methanol, and the mixture was stirred overnight at room
temperature. The resulting red solution was eluted through a basic
alumina column, and the methanol effluent was then concentrated
to approximately 10 mL on a rotatory evaporator. The addition of
200 mL of water caused the ester to precipitate from the solution.
And the product was collected by filtration, washed with water,
and dried as a yellow solid (5.10 g) in 80% yield. Mp: 110-112
°C [lit.17 112-114 °C].
2-Carbinol-1,10-phenanthroline. To a red solution of 6.30 g
(26.4 mmol) of 2-carbomethoxy-1,10-phenanthroline dissolved in
60 mL of anhydrous methanol was slowly added 7.0 g of sodium
borohydride over 30 min at 0-5 °C. The reaction solution was
stirred for 1 h at room temperature and then refluxed for 2 h. After
the solution was allowed to cool, 100 mL of distilled water was
added, and methanol was removed on the rotatory evaporator. The
resulting solution was then extracted four times with chloroform,
and the extracts were combined and dried over sodium sulfate. The
chloroform was evaporated and the residue was eluted with ethanol
on an alumina column. The second eluting part was collected and
concentrated to give an orange solid (4.0 g) in 72% yield. Mp:
136-138 °C [lit.17 139-143 °C].
2-Formyl-1,10-phenanthroline. A 1.40 g (12.5 mmol) portion
of selenium dioxide was added to a solution of 5.25 g (25.0 mmol)
of 2-carbinol-1,10-phenanthroline in 200 mL of pyridine with
constant stirring. The mixture was then heated for 4 h at 80-90
°C, and the color changed from orange to a dirty brown,
characteristic of selenium metal precipitate. After cooling to room
temperature, the selenium precipitate was removed by filtration.
Pyridine of the filtrate was removed at reduced pressure, and the
residue was eluted with methanol on an alumina column. The eluent
was concentrated to give a yellow solid (4.70 g) in 90% yield.
Mp: 152-154 °C [lit.18 152-153 °C]. FT-IR (KBr disk, cm-1):
1705 (νCdO).
with thionyl chloride (250 mL) for 6 h, and the residual SOCl2
was removed at reduced pressure. The resulting yellowish solid
was refluxed with anhydrous aluminum chloride (9.00 g, 66.0
mmol) in benzene (70 mL) for 4 h. The resulting red solution was
cooled to room temperature, and it was stirred for 12 h and then
refluxed for 6 h. After the solution was cooled to room temperature,
it was poured into distilled water (125 mL) at 0 °C. The aqueous
layer was extracted with chloroform (20 mL × 4). The combined
organic phases were dried over anhydrous sodium sulfate and
evaporated in a vacuum to afford a white solid in 48% yield. Mp:
110-112 °C. FT-IR (KBr disk, cm-1): 1655 (νCdO). 1H NMR (300
MHz, CDCl3): δ 9.18 (dd, J ) 2.1 Hz, 1H); 8.44 (s, 1H); 8.41 (s,
1H); 8.39 (d, J ) 3.3 Hz, 1H); 8.27-8.23 (m, 2H); 7.86-7.83 (m,
2H), 7.66-7.58 (m, 2H); 7.54-7.49 (m, 2H). 13C NMR (100 MHz,
CDCl3): δ 193.2, 154.8, 150.7, 146.3, 144.8, 136.9, 136.1, 135.9,
133.1, 131.8, 129.5, 129.0, 128.4, 128.2, 126.0, 123.1, 122.9. Anal.
Calc for C19H12N2O (284.31): C, 80.27; H, 4.25; N, 9.85. Found:
C, 80.24; H, 4.24; N, 9.83.
4.3. Synthesis of the 2-Imino-1,10-phenanthroline Ligands
1-20. 2-Acetyl-1,10-phenanthroline(2,6-dimethylanil) (1). A
reaction mixture of 2-acetyl-1,10-phenanthroline (0.445 g, 2.00
mmol), 2,6-dimethylaniline (0.315 g, 2.60 mmol), p-toluenesulfonic
acid (0.040 g), and absolute ethanol (20 mL) was refluxed under
N2 atmosphere for 2 days. The solvent was rotary evaporated and
the resulting solid was eluted with petroleum ether/ethyl acetate
(v/v ) 2:1) on an alumina column. The second eluting part was
collected and concentrated to give a yellow solid in 72% yield.
Mp: 170-172 °C. FT-IR (KBr disk, cm-1): 3435, 2970, 2933,
1645, 1590, 1553, 1490, 1469, 1446, 1366, 1324, 1207, 1138, 1117,
1091, 866, 777, 747. 1H NMR (300 MHz, CDCl3): δ 9.24 (t, J )
2.1 Hz, 1H); 8.80 (dd, J ) 8.7 Hz, 1H); 8.34 (dd, J ) 8.4 Hz, 1H);
8.27 (d, J ) 7.8 Hz, 1H); 7.85 (s, 2H); 7.65 (m, 1H); 7.10 (d, J )
7.5 Hz, 2H); 6.96 (t, J ) 7.5 Hz, 1H); 2.56 (s, 3H, CH3); 2.08 (s,
6H, PhCH3). 13C NMR (75 MHz, CDCl3): δ 168.0, 156.0, 150.6,
148.9, 146.2, 145.0, 136.4, 136.2, 129.4, 128.9, 127.8, 127.5, 126.4,
125.2, 123.0, 122.9, 120.8, 17.9, 16.9. Anal. Calc for C22H19N3
(325.41): C, 81.20; H, 5.89; N, 12.91. Found: C, 80.99; H, 5.94;
N, 12.87.
2-Acetyl-1,10-phenanthroline(2,6-diethylanil) (2). In a manner
similar to that described for 1, the ligand 2 was prepared as a yellow
solid in 68% yield. Mp: 188-190 °C. FT-IR (KBr disk, cm-1):
3424, 2966, 2930, 2870, 1639, 1587, 1553, 1491, 1453, 1363, 1322,
1257, 1197, 1138, 1116, 1079, 867, 824, 782, 747. 1H NMR (300
MHz, CDCl3): δ 9.25 (dd, J ) 3.0 Hz, 1H); 8.80 (d, J ) 8.3 Hz,
1H); 8.35 (d, J ) 8.3 Hz, 1H); 8.27 (dd, J ) 7.8 Hz, 1H); 7.86 (s,
2H); 7.66 (m, 1H); 7.15 (d, J ) 7.6 Hz, 2H); 6.96 (t, J ) 7.5 Hz,
1H); 2.58 (s, 3H, CH3); 2.43 (m, 4H, CH2CH3), 1.16 (t, J ) 7.5
Hz, 6H, CH2CH3). 13C NMR (75 MHz, CDCl3): δ 167.8, 156.2,
150.7, 148.0, 146.4, 145.2, 136.5, 131.1, 129.5, 129.0, 127.5, 126.5,
126.0, 123.4, 122.9, 120.8, 24.6, 17.3, 13.7. Anal. Calc for C24H23N3
(353.46): C, 81.55; H, 6.56; N, 11.89. Found: C, 80.88; H, 6.59;
N, 11.78.
4.2.2. Preparation of 2-Acetyl-1,10-phenanthroline. To a
suspension of 2-cyano-1,10-phenanthroline (2.10 g, 10.0 mmol) in
50 mL of toluene was added dropwise 2 equiv of trimethylaluminum
(10 mL, 20.0 mmol) toluene solution at -78 °C, and then the
temperature was slowly elevated to room temperature. After stirring
for 12 h at room temperature, a small amount of water was added
dropwise to the reaction mixture in an ice-water bath and a yellow
precipitate appeared. Then the mixture was extracted with dilute
aqueous hydrogen chloride. The combined water layer was made
alkaline with solid potassium hydroxide, and the resulting precipitate
was filtered, dried, and then purified through a basic alumina
column. The desired product was obtained as an ivory-white solid
(1.37 g) in 60% yield. Mp: 152-154 °C. FT-IR (KBr disk, cm-1):
2-Acetyl-1,10-phenanthroline(2,6-diisopropylanil) (3). In a
manner similar to that described for 1, the ligand 3 was prepared
as a yellow solid in 72% yield. Mp: 196-198 °C. FT-IR (KBr
disk, cm-1): 3434, 2961, 2870, 1646, 1588, 1552, 1490, 1459, 1363,
1321, 1191, 1115, 861, 821, 772, 745. 1H NMR (300 MHz,
CDCl3): δ 9.25 (d, J ) 2.7 Hz, 1H); 8.82 (d, J ) 8.7 Hz, 1H);
8.33 (m, 2H); 7.85 (s, 2H); 7.65 (m, 1H); 7.17 (m, 3H); 2.86 (sept,
J ) 6.6 Hz, 2H, CH(CH3)2), 2.60 (s, 3H, CH3); 1.17 (d, 12H, CH-
(CH3)2). 13C NMR (75 MHz, CDCl3): δ 167.7, 156.1, 150.7, 146.7,
146.4, 145.2, 136.5, 136.3, 135.7, 129.5, 129.0, 127.5, 126.5, 123.7,
123.0, 122.9, 120.9, 28.3, 23.3, 22.9, 17.6. Anal. Calc for C26H27N3
(381.51): C, 81.85; H, 7.13; N, 11.01. Found: C, 81.82; H, 7.25;
N, 10.71.
1
1693 (νCdO). H NMR (300 MHz, CDCl3): δ 9.26 (d, J ) 3.9
Hz, 1H); 8.37 (s, 2H); 8.29 (d, J ) 8.1 Hz, 1H); 7.87 (dd, J ) 8.7
Hz, 2H); 7.69 (dd, J ) 7.8 Hz, 1H); 3.09 (s, 3H, CH3). Anal. Calc
for C19H10N2O (222.24): C, 75.66; H, 4.54; N, 12.60. Found: C,
75.50; H, 4.64; N, 12.41.
4.2.3. Preparation of 2-Benzoyl-1,10-phenanthroline. 1,10-
Phenanthroline-2-carboxylic acid (12.0 g, 53.0 mmol) was refluxed
2-Acetyl-1,10-phenanthroline(2,4,6-trimethylanil) (4). In a
manner similar to that described for 1, the ligand 4 was prepared

674 Organometallics, Vol. 25, No. 3, 2006
Sun et al.
as yellow solid in 80% yield. Mp: 146-148 °C. FT-IR (KBr disk,
cm-1): 3011, 2966, 1639, 1625, 1587, 1550, 1503, 1489, 1448,
1426, 1391, 1365, 1323, 1284, 1263, 1220, 1194, 1137, 1118, 1080,
889, 855, 818, 775, 759, 739, 725, 658. 1H NMR (300 MHz,
CDCl3): δ 9.26 (d, J ) 4.2 Hz, 1H); 8.81 (d, J ) 8.4 Hz, 1H);
8.39 (d, J ) 8.4 Hz, 1H); 8.31 (d, J ) 8.1 Hz, 1H); 7.89 (s, 2H);
7.69 (dd, J ) 8.1 Hz, 1H); 7.60 (d, J ) 8.1 Hz, 2H); 6.88 (t, J )
8.1 Hz, 1H); 2.67 (s, 3H, CH3). 13C NMR (75 MHz, CDCl3): δ
172.0, 155.2, 150.7, 148.3, 146.3, 145.2, 136.7, 136.4, 132.0, 129.9,
129.0, 127.9, 126.5, 125.3, 123.1, 121.5, 113.5, 18.1. Anal. Calc
for C20H13Br2N3 (455.15): C, 52.78; H, 2.88; N, 9.23. Found: C,
52.78; H, 2.92; N, 9.16.
cm-1): 2937, 1634, 1586, 1551, 1480, 1364, 1323, 1216, 1136,
1
1115, 824, 773, 744. H NMR (400 MHz, CDCl3): δ 9.25 (dd, J
) 4.5 Hz, 1H); 8.80 (d, J ) 8.4 Hz, 1H); 8.35 (d, J ) 8.4 Hz, 1H);
8.30 (dd, J ) 8.1 Hz, 1H); 7.88 (s, 2H); 7.68 (quad, J ) 4.5 Hz,
1H); 6.93 (s, 2H); 2.56 (s, 3H, CH3); 2.32 (s, 3H, PhCH3); 2.05 (s,
6H, PhCH3). 13C NMR (75 MHz, CDCl3): δ 168.3, 156.2, 150.5,
146.4, 146.2, 145.0, 136.4, 136.3, 132.2, 129.4, 128.9, 128.5, 127.4,
126.4, 125.1, 122.9, 120.9, 20.7, 17.9, 16.9. Anal. Calc for C23H21N3
(339.43): C, 81.38; H, 6.24; N, 12.38. Found: C, 81.42; H, 6.26;
N, 12.14.
2-Acetyl-1,10-phenanthroline(2,6-dibromo-4-methylanil) (9).
In a manner similar to that described for 7, the ligand 9 was prepared
as a yellow solid in 37% yield. Mp: 213-215 °C. FT-IR (KBr
disk, cm-1): 2966, 2921, 1628, 1585, 1551, 1486, 1449, 1388, 1363,
1319, 1284, 1229, 1195, 1116, 1079, 853, 775, 740, 658. 1H NMR
(300 MHz, CDCl3): δ 9.26 (dd, J ) 4.2 Hz, 1H); 8.80 (d, J ) 8.4
Hz, 1H); 8.38 (d, J ) 8.4 Hz, 1H); 8.31 (dd, J ) 7.5 Hz, 1H); 7.89
(s, 2H); 7.68 (d, J ) 8.1 Hz, 1H); 7.43 (s, 2H); 2.66 (s, 3H, CH3);
2.18 (s, 3H, PhCH3). 13C NMR (75 MHz, CDCl3): δ 172.2, 155.4,
150.7, 146.3, 145.7, 145.2, 136.7, 136.3, 135.4, 132.5, 129.8, 129.0,
127.8, 126.5, 123.0, 121.4, 113.1, 20.2, 18.0. Anal. Calc for C21H15-
Br2N3 (469.17): C, 53.76; H, 3.22; N, 8.96. Found: C, 53.95; H,
3.49; N, 8.80.
2-Acetyl-1,10-phenanthroline(4-bromo-2,6-dimethylanil) (5).
A reaction mixture of 2-acetyl-1,10-phenanthroline (0.445 g, 2.00
mmol), 4-bromo-2,6-dimethylaniline (0.520 g, 2.60 mmol), p-
toluenesulfonic acid (0.040 g), and anhydrous sodium sulfate in
30 mL of toluene was refluxed under N2 atmosphere for 30 h. After
filtration, the solvent was removed through rotary evaporation and
the resulting solid was eluted with petroleum ether/ethyl acetate
(v/v ) 4:1) on an alumina column. The second eluting part was
collected and concentrated to give a yellow solid in 65% yield.
Mp: 196-198 °C. FT-IR (KBr disk, cm-1): 3036, 2969, 2913,
1641, 1584, 1550, 1462, 1397, 1366, 1323, 1284, 1201, 1113, 1077,
1
997, 880, 853, 780, 743, 710, 661. H NMR (300 MHz, CDCl3):
δ 9.25 (dd., J ) 4.2 Hz, 1H); 8.76 (d, J ) 8.4 Hz, 1H); 8.37 (d, J
) 8.4 Hz, 1H); 8.31 (dd, J ) 7.8 Hz, 1H); 7.89 (s, 2H); 7.68 (dd,
J ) 7.8 Hz, 1H); 7.25 (d, J ) 5.7 Hz, 2H); 2.55 (s, 3H, CH3); 2.05
(s, 6H, PhCH3). 13C NMR (75 MHz, CDCl3): δ 168.6, 155.5, 150.4,
147.7, 146.0, 1449, 136.3, 136.0, 130.2, 129.3, 128.7, 127.4, 127.3,
126.1, 122.7, 120.5, 115.3, 17.5, 16.8. Anal. Calc for C22H18BrN3
(404.30): C, 65.36; H, 4.49; N, 10.39. Found: C, 64.97; H, 4.49;
N, 10.39.
2-Acetyl-1,10-phenanthroline(4-chloro-2,6-dibromoanil) (10).
In a manner similar to that described for 7, the ligand 10 was
prepared as a yellow solid in 22% yield. Mp: 214-216 °C. FT-IR
(KBr disk, cm-1): 3070, 3045, 2987, 1656, 1619, 1587, 1552, 1531,
1491, 1450, 1439, 1425, 1390, 1365, 1322, 1285, 1229, 1190, 1137,
1
1117, 1081, 858, 821, 773, 742, 699, 659. H NMR (300 MHz,
CDCl3): δ 9.25 (d, J ) 3.3 Hz, 1H); 8.77 (d, J ) 8.4 Hz, 1H);
8.38 (d, J ) 8.4 Hz, 1H); 8.31 (d, J ) 7.8 Hz, 1H); 7.89 (s, 2H);
7.69 (dd, J ) 7.8 Hz, 1H); 7.62 (s, 2H); 2.66 (s, 3H, CH3). 13C
NMR (75 MHz, CDCl3): δ 172.7, 155.0, 150.7, 147.2, 146.3, 145.2,
136.7, 136.4, 131.6, 129.9, 129.2, 129.0, 128.0, 126.4, 123.1, 121.4,
113.6, 18.2. Anal. Calc for C20H12Br2ClN3 (489.59): C, 49.06; H,
2.47; N, 8.58. Found: C, 49.17; H, 2.49; N, 8.43.
2-Acetyl-1,10-phenanthroline(2,6-difluoroanil) (6). In a manner
similar to that described for 5, the ligand 6 was prepared as a yellow
solid in 54% yield. Mp: 180-182 °C. FT-IR (KBr disk, cm-1):
3429, 3015, 1637, 1585, 1556, 1473, 1421, 1391, 1368, 1322, 1277,
1237, 1121, 1066, 1027, 999, 888, 852, 821, 766, 744, 697, 658.
1H NMR (300 MHz, CDCl3): δ 9.25 (dd, J ) 4.2 Hz, 1H); 8.70
(d, J ) 8.4 Hz, 1H); 8.36 (d, J ) 8.7 Hz, 1H); 8.30 (dd, J ) 8.7
Hz, 1H); 7.88 (s, 2H); 7.68 (dd, J ) 7.8 Hz, 1H); 7.11-6.97 (m,
3H); 2.76 (s, 3H, CH3). 13C NMR (75 MHz, CDCl3): δ 173.6,
155.7, 154.5, 151.3, 151.2, 150.7, 146.3, 145.1, 136.6, 136.3, 129.7,
129.0, 127.8, 126.4, 124.1, 123.0, 121.4, 111.8, 111.5, 18.2. Anal.
Calc for C20H13F2N3 (333.33): C, 72.06; H, 3.93; N, 12.61.
Found: C, 71.89; H, 3.90; N, 12.87.
2-Acetyl-1,10-phenanthroline(2,4,6-tribromoanil) (11). In a
manner similar to that described for 7, the ligand 11 was prepared
as a yellow solid in 22% yield. Mp: 206-208 °C. FT-IR (KBr
disk, cm-1): 3066, 1644, 1586, 1551, 1529, 1489, 1450, 1421, 1393,
1363, 1323, 1286, 1225, 1192, 1136, 1114, 1079, 887, 854, 829,
1
775, 741, 681, 658. H NMR (300 MHz, CDCl3): δ 9.25 (d, J )
3.3 Hz, 1H); 8.77 (d, J ) 8.4 Hz, 1H); 8.38 (d, J ) 8.4 Hz, 1H);
8.30 (d, J ) 7.8 Hz, 1H); 7.88 (s, 2H); 7.75 (s, 2H); 7.68 (dd, J )
7.8 Hz, 1H); 2.66 (s, 3H, CH3). 13C NMR (100 MHz, CDCl3): δ
172.5, 154.9, 150.7, 147.6, 146.3, 145.2, 136.7, 136.3, 134.3, 129.9,
129.0, 128.0, 126.4, 123.1, 121.3, 116.0, 113.9, 18.2. Anal. Calc
for C20H12Br3N3 (534.04): C, 44.98; H, 2.26; N, 7.87. Found: C,
45.16; H, 2.32; N, 7.94.
2-Acetyl-1,10-phenanthroline(2,6-dichloroanil) (7). 2-Acetyl-
1,10-phenanthroline (0.445 g, 2.00 mmol), 2,6-dichloroaniline
(0.388 mg, 2.40 mmol), and p-toluenesulfonic acid (0.040 g) were
combined with tetraethyl silicate (5 mL) in a flask. The flask was
equipped with a condenser along with a water knockout trap, and
the mixture was heated at 140-150 °C under nitrogen for 36 h.
Tetraethyl silicate was removed at reduced pressure, and the
resulting solid was eluted with petroleum ether/ethyl acetate
(v/v ) 4:1) on an alumina column. The second eluting part was
collected and concentrated to give a yellow solid in 32% yield.
Mp: 184-186 °C. FT-IR (KBr disk, cm-1): 2966, 2926, 1641,
1629, 1585, 1554, 1489, 1448, 1432, 1390, 1367, 1324, 1285, 1260,
2-Formyl-1,10-phenanthroline(2,6-dimethylanil) (12). In a
manner similar to that described for 1, the ligand 12 was prepared
as a yellow solid in 78% yield. Mp: 164-166 °C. FT-IR (KBr
disk, cm-1): 3513, 3446, 2956, 2917, 1628, 1590, 1556, 1490, 1470,
1394, 1192, 1089, 855, 764, 743. 1H NMR (300 MHz, CDCl3): δ
9.23 (s, 1H); 8.89 (s, 1H, CHdN); 8.69 (d, J ) 8.4 Hz, 1H); 8.32
(d, J ) 8.4 Hz, 1H); 8.21 (d, J ) 7.8 Hz, 1H); 7.79 (s, 2H), 7.63
(s, 1H); 7.10 (d, J ) 7.2 Hz, 2H); 7.00 (dd, J ) 6.9 Hz, 1H); 2.21
(s, 6H, PhCH3). 13C NMR (100 MHz, CDCl3): δ 164.3, 154.7,
150.8, 150.5, 146.2, 146.0, 137.0, 136.4, 129.9, 129.1, 128.3, 128.0,
126.7, 126.6, 124.2, 123.4, 120.4, 18.5. Anal. Calc for C21H17N3‚
0.5H2O (320.39): C, 78.72; H, 5.66; N, 13.12. Found: C, 78.23;
H, 5.70; N, 12.84.
1
1223, 1119, 1079, 854, 782, 761, 738, 658. H NMR (300 MHz,
CDCl3): δ 9.26 (d, J ) 4.2 Hz, 1H); 8.78 (d, J ) 8.4 Hz, 1H);
8.38 (d, J ) 8.4 Hz, 1H); 8.31 (d, J ) 7.8 Hz, 1H); 7.89 (s, 2H);
7.69 (dd, J ) 8.1 Hz, 1H); 7.39 (d, J ) 8.1 Hz, 2H); 7.02 (t, J )
8.1 Hz, 1H); 2.68 (s, 3H, CH3). 13C NMR (75 MHz, CDCl3): δ
172.3, 155.4, 150.7, 136.7, 136.4, 129.8, 129.0, 128.3, 127.9, 126.5,
124.4, 123.1, 121.5, 18.1. Anal. Calc for C20H13Cl2N3 (366.24):
C, 65.59; H, 3.58; N, 11.47. Found: C, 65.29; H, 3.70; N, 11.28.
2-Formyl-1,10-phenanthroline(2,6-diethylanil) (13). In a man-
ner similar to that described for 1, the ligand 13 was prepared as
a yellow solid in 70% yield. Mp: 94-96 °C. FT-IR (KBr disk,
cm-1): 3507, 3436, 2964, 2933, 2875, 1631, 1589, 1556, 1505,
2-Acetyl-1,10-phenanthroline(2,6-dibromoanil) (8). In a man-
ner similar to that described for 7, the ligand 8 was prepared as a
yellow solid in 22% yield. Mp: 170-172 °C. FT-IR (KBr disk,

Iron-Based Catalysts for Ethylene Oligomerization
Organometallics, Vol. 25, No. 3, 2006 675
1491, 1454, 1395, 1324, 1185, 1093, 867, 748. 1H NMR (300 MHz,
CDCl3): δ 9.31 (dd, J ) 4.2 Hz, 1H); 8.85 (s, 1H, CHdN); 8.72
(d, J ) 8.4 Hz, 1H); 8.40 (d, J ) 8.4 Hz, 1H); 8.36 (d, J ) 7.8 Hz,
1H); 7.90 (s, 2H), 7.72 (dd, J ) 8.1 Hz, 1H); 7.12 (m, 2H); 6.98
(d, J ) 7.5 Hz, 1H); 2.57 (q, J ) 7.5 Hz, 4H, CH2CH3), 1.15 (t, J
) 7.5 Hz, 6H, CH2CH3). 13C NMR (100 MHz, CDCl3): δ 163.6,
154.8, 150.2, 149.4, 145.2, 137.1, 136.9, 132.5, 129.9, 129.0, 127.6,
126.8, 126.2, 126.1, 124.3, 123.3, 120.6, 24.7, 14.4. Anal. Calc
for C23H21N3‚0.5EtOH (362.47): C, 79.53; H, 6.67; N, 11.59.
Found: C, 79.45; H, 6.45; N, 11.47.
CDCl3): δ 9.21-6.67 (m, 15H); 2.26 (s, 6H, PhCH3). 13C NMR
(100 MHz, CDCl3): δ 165.8, 155.6, 150.5, 148.6, 146.2, 145.6,
137.7, 136.4, 135.8, 135.7, 130.8, 129.9, 129.3, 128.9, 128.2, 127.8,
127.4, 127.2, 126.3, 126.1, 125.4, 123.2, 123.0, 122.7, 121.6, 18.9,
18.5. Anal. Calc for C27H21N3 (387.48): C, 83.69; H, 5.46; N, 10.84.
Found: C, 83.56; H, 5.47; N, 10.68.
2-Benzoyl-1,10-phenanthroline(2,6-diethylanil) (19). In a man-
ner similar to that described for 7, the ligand 19 was prepared as
a yellow solid in 76% yield. Mp: 178-180 °C. FT-IR (KBr disk,
cm-1): 3433, 3058, 2966, 2931, 1618, 1587, 1552, 1489, 1449,
1324, 1159, 964, 854, 695. 1H NMR (300 MHz, CDCl3): δ 9.17-
6.80 (m, 15H); 2.85-2.71 (m, 2H, CH2CH3); 2.56-2.44 (m, 2H,
CH2CH3); 1.17 (t, J ) 7.5 Hz, 6H, CH2CH3). 13C NMR (100 MHz,
CDCl3): δ 165.1, 155.5, 150.5, 147.7, 146.3, 145.6, 137.9, 136.5,
135.9, 135.7, 131.9, 130.8, 130.1, 129.5, 129.0, 128.3, 127.9, 127.5,
127.3, 126.3, 125.6, 125.1, 123.7, 123.1, 122.0, 24.9, 24.6, 13.5.
Anal. Calc for C29H25N3 (415.53): C, 83.82; H, 6.06; N, 10.11.
Found: C, 83.56; H, 6.10; N, 9.98.
2-Formyl-1,10-phenanthroline(2,6-diisopropylanil) (14). In a
manner similar to that described for 1, the ligand 14 was prepared
as a yellow solid in 88% yield. Mp: 192-194 °C. FT-IR (KBr
disk, cm-1): 3426, 3063, 2960, 2868, 1639, 1587, 1555, 1490, 1455,
1395, 1321, 1182, 1090, 859, 787, 751. 1H NMR (300 MHz,
CDCl3): δ 9.25 (d, J ) 1.5 Hz, 1H); 8.84 (s, 1H, CHdN); 8.73
(d, J ) 8.4 Hz, 1H); 8.39 (d, J ) 8.1 Hz, 1H); 8.29 (d, J ) 7.8 Hz,
1H); 7.87 (s, 2H), 7.67 (m, 1H); 7.17 (m, 3H); 3.06 (sept, J ) 3.3
Hz, 2H, CH(CH3)2); 1.17 (d, J ) 4.5 Hz, 12H, CH(CH3)2). 13C
NMR (100 MHz, CDCl3): δ 163.4, 154.6, 150.7, 148.2,
146.1, 145.9, 136.8, 136.3, 129.8, 128.9, 127.8, 126.4, 124.3,
123.4, 123.1, 122.8, 120.4, 27.9, 23.2. Anal. Calc for C25H25N3
(367.49): C, 81.71; H, 6.86; N, 11.43. Found: C, 81.36; H, 6.82;
N, 11.31.
2-Benzoyl-1,10-phenanthroline(2,6-diisopropylanil) (20). In a
manner similar to that described for 7, the ligand 20 was prepared
as a yellow solid in 82% yield. Mp: 224-226 °C. FT-IR (KBr
disk, cm-1): 3060, 2963, 1630, 1449, 1285, 1159, 974, 850, 766,
1
698. H NMR (300 MHz, CDCl3): δ 9.21-6.84 (m, 15H); 3.30
(sept, J ) 6.6 Hz, 2H, CH(CH3)2); 1.19 (d, J ) 6.3 Hz, 6H, CH-
(CH3)2); 0.98 (d, J ) 6.3 Hz, 6H, CH(CH3)2). 13C NMR (100 MHz,
CDCl3): δ 164.2, 155.3, 150.4, 146.1, 145.6, 137.9, 136.4, 135.9,
135.6, 130.6, 129.2, 128.9, 128.2, 127.7, 127.4, 127.2, 126.2, 123.4,
123.0, 122.4, 122.2, 28.4, 24.0, 21.7. Anal. Calc for C31H29N3
(443.58): C, 83.94; H, 6.59; N, 9.47. Found: C, 82.99; H, 6.59;
N, 9.29.
2-Formyl-1,10-phenanthroline(2,6-difluoroanil) (15). In a
manner similar to that described for 5, the ligand 15 was prepared
as a yellow solid in 36% yield. Mp: 156-158 °C. FT-IR (KBr
disk, cm-1): 3072, 3037, 1634, 1584, 1555, 1469, 1397, 1316, 1274,
1
1239, 1012, 970, 793, 741. H NMR (300 MHz, CDCl3): δ 9.32
(s, 1H, CHdN); 9.26 (d, J ) 3.6 Hz, 1H); 8.67 (d, J ) 8.4 Hz,
1H); 8.35 (d, J ) 8.4 Hz, 1H); 8.28 (d, J ) 7.5 Hz, 1H); 7.85 (s,
2H); 7.67 (dd, J ) 8.1 Hz, 1H); 7.14 (m, 1H); 7.01 (m, 2H). 13C
NMR (100 MHz, CDCl3): δ 167.7, 156.5, 152.2, 150.6, 146.0,
145.9, 137.3, 136.7, 131.1, 129.4, 128.0, 126.4, 123.6, 123.2, 120.5,
119.6, 116.5. Anal. Calc for C19H11F2N3 (319.31): C, 71.47; H,
3.47; N, 13.16. Found: C, 70.64; H, 3.56; N, 12.76.
4.4. Synthesis of the Complexes 1a-20a. General Procedure.
The ligand and 1 equiv of FeCl2‚4H2O were added together in a
Schlenk tube that was purged three times with argon and then
charged with THF. The reaction mixture was stirred at room
temperature for 9 h. The resulting precipitate was filtered, washed
with diethyl ether, and dried in a vacuum. All the iron(II) complexes
were prepared in high yield in this manner.
2-Acetyl-1,10-phenanthroline(2,6-dimethylanil)FeCl2 (1a). This
complex was isolated as a dark blue powder in 96% yield. FT-IR
(KBr disk, cm-1): 3436, 3407, 2978, 2915, 1612, 1584, 1512, 1491,
1467, 1406, 1374, 1287, 1209, 1153, 1093, 864, 790, 772, 742,
657. Anal. Calc for C22H19Cl2FeN3 (452.16): C, 58.44; H, 4.24;
N, 9.29. Found: C, 58.51; H, 4.49; N, 9.07.
2-Acetyl-1,10-phenanthroline(2,6-diethylanil)FeCl2 (2a). This
complex was isolated as a dark blue powder in 89% yield. FT-IR
(KBr disk, cm-1): 3436, 2965, 2933, 2876, 1609, 1583, 1513, 1493,
1447, 1406, 1374, 1287, 1194, 874, 836, 786, 741, 658. Anal. Calc
for C24H23Cl2FeN3 (480.21): C, 60.03; H, 4.83; N, 8.75. Found:
C, 59.86; H, 4.88; N, 8.58.
2-Formyl-1,10-phenanthroline(2,6-dichloroanil) (16). In a
manner similar to that described for 5, the ligand 16 was prepared
as a yellow solid in 58% yield. Mp: 116-118 °C. FT-IR (KBr
disk, cm-1): 3523, 3419, 1634, 1619, 1586, 1558, 1507, 1492, 1434,
1395, 1216, 1083, 856, 781, 743. 1H NMR (300 MHz, CDCl3): δ
9.25 (d, J ) 3.9 Hz, 1H); 9.00 (s, 1H, CHdN); 8.70 (d, J ) 8.1
Hz, 1H); 8.39 (d, J ) 8.1 Hz, 1H); 8.29 (d, J ) 8.1 Hz, 1H); 7.87
(s, 2H); 7.68 (dd, J ) 7.8 Hz, 1H); 7.38 (d, J ) 8.1 Hz, 2H); 7.04
(t, J ) 8.1 Hz, 1H). 13C NMR (100 MHz, CDCl3): δ 194.0, 152.2,
150.9, 146.0, 140.0, 137.3, 136.3, 131.1, 129.3, 129.0, 128.3, 127.7,
126.1, 123.6, 119.6, 119.5, 118.0. Anal. Calc for C19H11Cl2N3
(352.22): C, 64.79; H, 3.15; N, 11.93. Found: C, 65.14; H, 3.50;
N, 11.79.
2-Acetyl-1,10-phenanthroline(2,6-diisopropylanil)FeCl2 (3a).
This complex was isolated as a dark blue powder in 89% yield.
FT-IR (KBr disk, cm-1): 3440, 2967, 2928, 2869, 1605, 1512,
1464, 1446, 1407, 1289, 1191, 1146, 850, 789, 759, 655. Anal.
Calc for C26H27Cl2FeN3 (508.26): C, 61.44; H, 5.35; N, 8.27.
Found: C, 61.44; H, 5.58; N, 8.05.
2-Acetyl-1,10-phenanthroline(2,4,6-trimethylanil)FeCl2 (4a).
This complex was isolated as a dark blue powder in 63% yield.
FT-IR (KBr disk, cm-1): 2915, 1606, 1580, 1513, 1480, 1406,
1286, 1221, 1161, 857, 785, 741, 657. Anal. Calc for C23H21Cl2-
FeN3 (466.18): C, 59.26; H, 4.54; N, 9.01. Found: C, 58.24; H,
4.54; N, 8.56.
2-Acetyl-1,10-phenanthroline(4-bromo-2,6-dimethylanil)-
FeCl2 (5a). This complex was isolated as a purple powder in 80%
yield. FT-IR (KBr disk, cm-1): 3048, 2952, 2911, 1618, 1580,
1515, 1494, 1466, 1436, 1406, 1286, 1206, 854, 796, 738, 657.
Anal. Calc for C22H18BrCl2FeN3 (531.05): C, 49.76; H, 3.42; N,
7.91. Found: C, 49.89; H, 3.53; N, 7.83.
2-Formyl-1,10-phenanthroline(2,6-dibromoanil) (17). In a
manner similar to that described for 5, the ligand 17 was prepared
as a yellow solid in 51% yield. Mp: 198-200 °C. FT-IR (KBr
disk, cm-1): 3417, 3043, 1639, 1614, 1585, 1550, 1504, 1490, 1451,
1426, 1390, 1334, 1211, 854, 781, 737. 1H NMR (300 MHz,
CDCl3): δ 9.25 (dd, J ) 4.8 Hz, 1H); 8.93 (s, 1H, CHdN); 8.71
(d, J ) 8.4 Hz, 1H); 8.38 (d, J ) 8.1 Hz, 1H); 8.27 (dd, J ) 8.4
Hz, 1H); 7.85 (s, 2H); 7.67 (dd, J ) 8.1 Hz, 1H); 7.59 (d, J ) 8.1
Hz, 2H); 6.89 (t, J ) 8.1 Hz, 1H). 13C NMR (100 MHz, CDCl3):
δ 170.4, 156.0, 153.1, 151.5, 148.4, 148.3, 139.3, 138.7, 134.5,
132.5, 131.3, 130.6, 128.7, 128.6, 125.7, 123.1, 116.6. Anal. Calc
for C19H11Br2N3 (441.12): C, 51.73; H, 2.51; N, 9.53. Found: C,
51.28; H, 2.45; N, 9.34.
2-Benzoyl-1,10-phenanthroline(2,6-dimethylanil) (18). In a
manner similar to that described for 7, the ligand 18 was prepared
as a yellow solid in 56% yield. Mp: 206-208 °C. FT-IR (KBr
disk, cm-1): 3420, 3057, 2917, 1618, 1589, 1550, 1487, 1446, 1387,
1323, 1208, 1161, 1091, 969, 851, 777, 693. 1H NMR (300 MHz,

676 Organometallics, Vol. 25, No. 3, 2006
Table 4. Crystal Data and Structure Refinement for Complexes 2a, 4a, 7a, 8a, and 14a
Sun et al.
2a
4a
7a
8a
14a
formula
fw
C24H23Cl2FeN3
480.20
C23H21Cl2FeN3
466.18
C20H13Cl4FeN3
492.98
C20H13Br2Cl2FeN3
581.90
C25H25Cl2FeN3
494.23
temperature (K)
wavelength (Å)
cryst syst
space group
a (Å)
293(2)
0.71073
triclinic
P1h
8.3051(17)
8.9970(18)
16.173(3)
103.05(3)
91.74(3)
108.94(3)
1106.4(4)
2
293(2)
0.71073
198(2)
0.71073
monoclinic
P2(1)/c
7.925(1)
18.526(1)
13.606(1)
90.00
104.17(1)
90.00
1936.8(3)
4
1.691
293(2)
0.71073
293(2)
0.71073
monoclinic
P2(1)/c
7.8710(5)
20.0610(11)
13.3304(8)
90.00
104.979(2)
90.00
2033.3(2)
4
monoclinic
P2(1)/c
8.0359(16)
18.611(4)
13.788(3)
90.00
103.90(3)
90.00
2001.8(7)
4
orthorhombic
Pbca
14.974(5)
15.993(5)
19.474(6)
90.00
90.00
90.00
4663(3)
8
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
volume (Å3)
Z
D
calc (Mg m-3
)
1.441
0.939
496
1.523
1.019
960
1.931
5.024
1136
1.408
0.893
2048
µ (mm-1
F(000)
)
1.342
992
cryst size (mm)
θ range (deg)
0.56 × 0.19 × 0.10
1.30-25.01
0 e h e 9,
-10 e k e 10,
-19 e l e 19
9031
3616
3152
0.0317
0.53 × 0.20 × 0.12
3.16-27.48
-10 e h e 10,
-25 e k e 26,
-17 e l e 17
15 428
4611
4324
0.0230
0.15 × 0.15 × 0.10
1.90-28.26
-10 e h e 10,
-22 e k e 24,
-18 e l e 17
15 954
4747
3706
0.029
0.29 × 0.23 × 0.21
1.87-27.48
0 e h e 10,
0 e k e 24,
-17 e l e 17
14 828
4448
2512
0.0702
0.18 × 0.17 × 0.15
2.50-27.56
-19 e h e 14,
-20 e k e 20,
-25 e l e 25
34 649
5373
3375
0.0599
limiting indices
no. of rflns collected
no. of unique rflns
no. of obsd rflns (I>2σ(I))
Rint
completeness to θ (%)
92.8 (θ) 25.01°)
empirical
251
99.1 (θ)27.48°)
empirical
262
98.8 (θ)28.26°)
empirical
254
96.8 (θ)27.48°)
empirical
253
99.7 (θ)27.56°)
empirical
280
absorp corr
no. of params
goodness-of-fit on F2
final R indices [I>2σ(I)]
1.086
0.940
1.030
0.969
1.079
R1)0.0467,
wR2)0.1266
R1)0.0531,
wR2)0.1311
0.602, -0.470
R1)0.0353,
wR2)0.0947
R1)0.0379,
wR2)0.0969
0.552, -0.537
R1)0.0354,
wR2)0.0744
R1)0.0541,
wR2)0.0811
0.309, -0.382
R1)0.0561,
wR2)0.1045
R1)0.1045,
wR2)0.1202
0.454, -0.582
R1)0.0565,
wR2)0.0925
R1)0.1102,
wR2)0.1130
0.358, -0.274
R indices (all data)
largest diff peak, hole (e Å-3
)
2-Acetyl-1,10-phenanthroline(2,6-difloroanil)FeCl2 (6a). This
complex was isolated as a dark blue powder in 97% yield. FT-IR
(KBr disk, cm-1): 3447, 3056, 2969, 2868, 1612, 1587, 1514, 1472,
1405, 1373, 1284, 1241, 1227, 1150, 1061, 1026, 1005, 861, 775,
743, 658. Anal. Calc for C20H13Cl2F2FeN3 (460.08): C, 52.21; H,
2.85; N, 9.13. Found: C, 52.32; H, 3.43; N, 8.83.
2-Acetyl-1,10-phenanthroline(2,6-dichloroanil)FeCl2 (7a). This
complex was isolated as a purple powder in 88% yield. FT-IR (KBr
disk, cm-1): 3447, 3066, 2992, 2911, 1614, 1580, 1561, 1516, 1495,
1439, 1407, 1376, 1332, 1286, 1231, 1209, 1160, 1150, 1090, 859,
832, 788, 749, 684, 657. Anal. Calc for C20H13Cl4FeN3‚Et2O
(567.11): C, 50.83; H, 4.09; N, 7.41. Found: C, 50.86; H, 3.75;
N, 7.49.
2-Acetyl-1,10-phenanthroline(2,6-dibromoanil)FeCl2 (8a). This
complex was isolated as a purple powder in 96% yield. FT-IR (KBr
disk, cm-1): 3462, 3059, 2969, 2909, 1614, 1578, 1551, 1515, 1493,
1432, 1406, 1376, 1331, 1286, 1266, 1231, 1204, 1150, 863, 833,
784, 732, 658. Anal. Calc for C20H13Br2Cl2FeN3 (581.90): C, 41.28;
H, 2.25; N, 7.22. Found: C, 41.07; H, 2.46; N, 7.15.
2-Acetyl-1,10-phenanthroline(2,6-dibromo-4-methylanil)-
FeCl2 (9a). This complex was isolated as a purple powder in 77%
yield. FT-IR (KBr disk, cm-1): 3469, 3057, 2911, 1611, 1579,
1537, 1515, 1492, 1449, 1407, 1376, 1333, 1287, 1235, 1149, 860,
744, 658. Anal. Calc for C21H15Br2Cl2FeN3 (595.92): C, 42.33;
H, 2.54; N, 7.05. Found: C, 41.76; H, 2.68; N, 6.77.
(KBr disk, cm-1): 3450, 3050, 2910, 1613, 1581, 1562, 1538, 1512,
1491, 1430, 1408, 1369, 1288, 1155, 1138, 876, 856, 789, 746,
732, 692, 658. Anal. Calc for C20H12Br3Cl2FeN3 (660.79): C, 36.35;
H, 1.83; N, 6.36. Found: C, 35.47; H, 2.11; N, 6.31.
2-Formyl-1,10-phenanthroline(2,6-dimethylanil)FeCl2 (12a).
This complex was isolated as a dark blue powder in 94% yield.
FT-IR (KBr disk, cm-1): 3436, 3061, 2918, 1607, 1512, 1472,
1406, 1297, 1182, 1142, 1117, 1093, 963, 861, 780, 737. Anal.
Calc for C21H17Cl2FeN3 (438.13): C, 57.57; H, 3.91; N, 9.59.
Found: C, 57.09; H, 4.20; N, 9.06.
2-Formyl-1,10-phenanthroline(2,6-diethylanil)FeCl2 (13a). This
complex was isolated as a gray-blue powder in 63% yield. FT-IR
(KBr disk, cm-1): 3436, 3059, 2965, 2934, 1605, 1584, 1514, 1452,
1405, 1177, 1141, 963, 860, 769, 737. Anal. Calc for C23H21Cl2-
FeN3 (466.18): C, 59.26; H, 4.54; N, 9.01. Found: C, 59.05; H,
4.50; N, 8.83.
2-Formyl-1,10-phenanthroline(2,6-diisopropylanil)FeCl2 (14a).
This complex was isolated as a dark blue powder in 99% yield.
FT-IR (KBr disk, cm-1): 3395, 3.60, 2964, 2868, 1601, 1580, 1514,
1494, 1462, 1447, 1407, 1175, 1117, 849, 806, 766. Anal. Calc
for C25H25Cl2FeN3 (494.24): C, 60.75; H, 5.10; N, 8.50. Found:
C, 60.36; H, 5.49; N, 8.00.
2-Formyl-1,10-phenanthroline(2,6-difluoroanil)FeCl2 (15a).
This complex was isolated as a gray-green powder in 90% yield.
FT-IR (KBr disk, cm-1): 3397, 3060, 3019, 1610, 1588, 1513,
1470, 1434, 1404, 1363, 1342, 1284, 1236, 1198, 1144, 1117, 1058,
1015, 963, 862, 786, 736. Anal. Calc for C19H11Cl2F2FeN3
(446.06): C, 51.16; H, 2.49; N, 9.42. Found: C, 51.17; H, 2.90;
N, 9.07.
2-Acetyl-1,10-phenanthroline(4-chloro-2,6-dibromoanil)-
FeCl2 (10a). This complex was isolated as a purple powder in 95%
yield. FT-IR (KBr disk, cm-1): 3449, 3050, 2910, 1613, 1572,
1539, 1512, 1491, 1433, 1407, 1372, 1288, 1263, 1232, 1155, 1138,
875, 858, 842, 792, 747, 732, 699, 658. Anal. Calc for C20H12Br2-
Cl3FeN3 (616.34): C, 38.97; H, 1.96; N, 6.82. Found: C, 39.34;
H, 2.30; N, 6.44.
2-Formyl-1,10-phenanthroline(2,6-dichloroanil)FeCl2 (16a).
This complex was isolated as a dark blue powder in 56% yield.
FT-IR (KBr disk, cm-1): 3370, 3063, 3005, 1607, 1580, 1563,
1513, 1441, 1405, 1360, 1342, 1297, 1200, 1117, 963, 863, 788,
2-Acetyl-1,10-phenanthroline(2,4,6-tribromoanil)FeCl2 (11a).
This complex was isolated as a gray powder in 80% yield. FT-IR

Iron-Based Catalysts for Ethylene Oligomerization
Organometallics, Vol. 25, No. 3, 2006 677
737, 643. Anal. Calc for C19H11Cl4FeN3 (478.97): C, 47.64; H,
2.31; N, 8.77. Found: C, 47.05; H, 2.66; N, 8.30.
hydrogen chloride, 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 ethanol (5%). The precipitated
low-molecular-weight waxes were collected by filtration, washed
with ethanol, and dried in a vacuum until constant weight.
4.6. X-ray Crystallography Measurements. Single-crystal
X-ray diffraction studies for 2a and 8a were carried out on a Rigaku
RAXIS Rapid IP diffractometer with graphite-monochromated Mo
KR radiation (λ ) 0.71073 Å). Intensity data for crystals of 4a
and 14a were collected on a Bruker SMART 1000 CCD diffrac-
tometer with graphite-monochromated Mo KR radiation (λ )
0.71073 Å). The data set for 7a was collected with a Nonius Kappa
CCD diffractometer, equipped with a Nonius FR591 rotating anode
generator. 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 aniso-
tropically. All hydrogen atoms were placed in calculated positions.
Structure solution and refinement were performed by using the
SHELXL-97 package.25 Crystallographic data and processing
parameters for complexes 2a, 4a, 7a, 8a, and 14a are summarized
in Table 4.
2-Formyl-1,10-phenanthroline(2,6-dibromoanil)FeCl2 (17a).
This complex was isolated as a dark gray powder in 86% yield.
FT-IR (KBr disk, cm-1): 3420, 3058, 1606, 1579, 1555, 1512,
1435, 1405, 1298, 1199, 1142, 1116, 961, 863, 780, 740, 643. Anal.
Calc for C19H11Br2Cl2FeN3 (567.87): C, 40.19; H, 1.95; N, 7.40.
Found: C, 40.25; H, 2.11; N, 7.35.
2-Benzoyl-1,10-phenanthroline(2,6-dimethylanil)FeCl2 (18a).
This complex was isolated as a dark brown powder in 97% yield.
FT-IR (KBr disk, cm-1): 3409, 3060, 2908, 1602, 1511, 1492,
1442, 1402, 1297, 1216, 1000, 866, 790, 701. Anal. Calc for C27H21-
Cl2FeN3‚0.5H2O (523.24): C, 61.98; H, 4.24; N, 8.03. Found: C,
61.95; H, 4.05; N, 8.03.
2-Benzoyl-1,10-phenanthroline(2,6-diethylanil)FeCl2 (19a).
This complex was isolated as a dark brown powder in 87% yield.
FT-IR (KBr disk, cm-1): 3436, 3065, 2972, 1605, 1583, 1508,
1444, 1403, 1284, 1001, 881, 783, 703. Anal. Calc for C29H25Cl2-
FeN3 (542.28): C, 64.23; H, 4.65; N, 7.75. Found: C, 64.04; H,
4.70; N, 7.66.
2-Benzoyl-1,10-phenanthroline(2,6-diisopropylanil)FeCl2 (20a).
This complex was isolated as a dark brown powder in 64% yield.
FT-IR (KBr disk, cm-1): 2964, 2867, 1604, 1586, 1510, 1437,
1402, 1292, 1209, 1112, 999, 863, 783, 701. Anal. Calc for C31H29-
Cl2FeN3‚EtOH (616.40): C, 64.30; H, 5.72; N, 6.82. Found: C,
64.27; H, 5.27; N, 7.04.
4.5. General Procedure for Ethylene Oligomerization. A 250
mL autoclave stainless steel reactor equipped with a mechanical
stirrer and a temperature controller was heated in vacuo for at least
2 h over 80 °C, allowed to cool to the required reaction temperature
under ethylene atmosphere, and then charged with toluene, the
desired amount of cocatalyt, and toluene solution of catalytic
precursor; the total volume was 100 mL. At the reaction temper-
ature, the reactor was sealed and pressurized to 10 atm of ethylene
pressure, and the ethylene pressure was kept with feeding of
ethylene. After the reaction was carried out for the required time,
the pressure was released and a small amount of the reaction
solution was collected and terminated by the addition of 5% aqueous
Acknowledgment. This project was supported by NSFC
Nos. 20272062 and 20473099 along with National 863 Project
(2002AA333060), and partly sponsored by CNPC Innovation
Fund (04E7054). We thank Dr. Jinkui Niu and Mr. Steven
Scheltz for English correction.
Supporting Information Available: X-ray crystallographic data
(CIF) for complexes 2a, 4a, 7a, 8a, and 14a. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM050891P
(25) Sheldrick, G. M. SHELXTL-97, Program for the Refinement of
Crystal Structures; University of Gottingen: Germany, 1997.