Iron(II) complexes ligated by 2-imino-1,10-phenanthrolines: Preparation and catalytic behavior toward ethylene oligomerization

Article abstract of DOI:10.1016/j.molcata.2007.01.008

A series of N,N,N-tridentate iron (II) complexes bearing 2-imino-1,10-phenanthrolines, [2-{(2,6-R¹,R³-4-R²-C₆H₂)N{double bond, long}C(R)}-1,10-phen]FeCl₂, was synthesized and characterized by IR spectroscopy and elemental analysis. One of these complexes (18b) was determined by single-crystal X-ray crystallography for its unambiguous structure. These iron(II) complexes were found to exhibit remarkable activities for ethylene oligomerization in the presence of MAO or MMAO cocatalyst affording α-olefins with high selectivity and the composition of oligomers followed the Schluz-Flory distribution. The effects of substituents on imino fragment on the activity were explored in detail; complexes with mono substituent at the ortho-position of the phenyl ring showed high activities with low K values, suggesting that fine tuning of the steric bulk of substituents on the imino fragment directly affects both the activity and the selectivity.

Full text of DOI:10.1016/j.molcata.2007.01.008

Journal of Molecular Catalysis A: Chemical 269 (2007) 85–96
Iron(II) complexes ligated by 2-imino-1,10-phenanthrolines:
Preparation and catalytic behavior toward ethylene oligomerization
Suyun Jiea, Shu Zhanga, Wen-Hua Suna,∗, Xiaofei Kuanga,
Tianfu Liua, Jianping Guob
a Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Sciences, Institute of Chemistry,
Chinese Academy of Sciences, Beijing 100080, China
b Institute of Modern Chemistry, Shanxi University, Taiyuan 030006, China
Received 4 September 2006; received in revised form 9 January 2007; accepted 10 January 2007
Available online 13 January 2007
Abstract
A series of N,N,N-tridentate iron (II) complexes bearing 2-imino-1,10-phenanthrolines, [2-{(2,6-R1,R3-4-R2-C6H2)N C(R)}-1,10-phen]FeCl2,
was synthesized and characterized by IR spectroscopy and elemental analysis. One of these complexes (18b) was determined by single-crystal X-ray
crystallography for its unambiguous structure. These iron(II) complexes were found to exhibit remarkable activities for ethylene oligomerization in
the presence of MAO or MMAO cocatalyst affording ␣-olefins with high selectivity and the composition of oligomers followed the Schluz–Flory
distribution. The effects of substituents on imino fragment on the activity were explored in detail; complexes with mono substituent at the ortho-
position of the phenyl ring showed high activities with low K values, suggesting that fine tuning of the steric bulk of substituents on the imino
fragment directly affects both the activity and the selectivity.
© 2007 Elsevier B.V. All rights reserved.
Keywords: 2-Imino-1,10-phenanthroline; Iron complex; Ethylene reactivity; ␣-Olefins; Polyethylene wax
1. Introduction
havebeendesigned;however, theycouldnotprovidesatisfactory
results [11–19]. Considering the frameworks of iron complexes
bearingtridentateligands, we previouslyreported a limited num-
ber of iron (II) complexes bearing 2-imino-1,10-phenanthrolines
as highly active catalysts for ethylene oligomerization with high
selectivity for the formation of linear ␣-olefins [20] while their
nickel analogues showed good activities for ethylene oligomer-
ization with low selectivity for linear ␣-olefins [21]. In the
same period, their cobalt analogues were reported to show good
catalytic activities for ethylene oligomerization with good selec-
tivity for linear ␣-olefins [22]. Compared with the different
metal analogues, iron complexes could be the best candidates
for ethylene oligomerization with high catalytic activity and
selectivity for linear ␣-olefins [20]. Consequently, these iron
complexes could be of great potential commercially for the
conversion of ethylene into linear ␣-olefins. For this purpose,
we believe that it is necessary to establish the effects of sub-
stituents on the catalytic activities as well as the distributions of
products in ethylene oligomerization using iron(II) complexes
containing 2-imino-1,10-phenanthroline ligands of this type,
[2-{(2,6-R1,R3-4-R2-C6H2)N C(R)}-1,10-phen]FeCl2, in the
Ethylene oligomerization is currently one of the major indus-
trial processes for producing linear ␣-olefins [1], which are
attractive and valuable for their wide applications, such as
feedstocks for detergents, lubricants, plasticizers, and oil field
chemicals as well as monomers for copolymers of ethylene and
␣-olefins. Since the pioneering work by Ziegler in the presence
of AlR3 [2], considerable attention has been paid to the develop-
ment of the new catalyst systems with various transition metals
(Ti, Zr, Cr, Fe, Ni, etc.) exhibiting high activities toward ethylene
(oligomerization and/or polymerization) in both academic and
industrial fields [3–7]. Especially in recent years, substantive
progress has been made in iron and cobalt complexes bearing
2,6-bis(imino)pyridines as highly active catalysts by the groups
of Brookhart [8] and Gibson [9,10]. As a way of promoting
this system, iron and cobalt complexes containing new ligands
∗
Corresponding author. Tel.: +86 10 62557955; fax: +86 10 62618239.
E-mail address: whsun@iccas.ac.cn (W.-H. Sun).
1381-1169/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2007.01.008

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S. Jie et al. / Journal of Molecular Catalysis A: Chemical 269 (2007) 85–96
presence of cocatalyst. In this paper, we prepared various iron
analogues (18 complexes) and explored the reaction with ethy-
lene in the presence of Al cocatalyst such as MAO and MMAO.
The effects of substituents on the ligand, cocatalysts, the Al/Fe
molar ratio, reaction temperature on the activity and selectivity
have also been described.
2908, 1635, 1595, 1551, 1485, 1456, 1389, 1363, 1320, 1283,
1227, 1189, 1114, 1079, 1042, 850, 829, 789, 746, 657. H
1
NMR (300 MHz, CDCl3): δ 9.25 (d, J = 4.5 Hz, 1H); 8.70 (d,
J = 8.4 Hz, 1H); 8.35 (d, J = 8.7 Hz, 1H); 8.30 (d, J = 8.1 Hz,
1H); 7.88 (s, 2H); 7.68 (dd, J = 8.1 Hz, 1H); 7.23 (m, 2H); 7.06
(t, J = 7.5 Hz, 1H); 6.74 (d, J = 7.8 Hz, 1H); 2.65 (s, 3H, CH3);
2.17 (s, 3H, PhCH3). 13C NMR (75 MHz, CDCl3): δ 167.8,
156.6, 150.9, 150.6, 150.1, 146.3, 145.1, 136.5, 136.3, 130.4,
129.4, 129.0, 127.5, 127.1, 126.4, 123.7, 122.9, 121.0, 118.0,
17.8, 17.0. Anal. Calc. for C21H17N3 (311.38): C, 81.00; H,
5.50; N, 13.49. Found: C, 80.82; H, 5.72; N, 13.27.
2. Experimental
2.1. General considerations and materials
All manipulations for air or moisture-sensitive compounds
were carried out under an atmosphere of nitrogen 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
2.2.2. 2-Acetyl-1,10-phenanthroline(2-ethylanil) (2a)
In a similar manner with 1a, the ligand 2a was prepared as
a yellow solid in 23% yield. mp: 122–124 ◦C. IR (KBr disc,
cm−1): 2961, 2928, 2869, 1633, 1592, 1551, 1484, 1446, 1416,
1390, 1363, 1321, 1283, 1241, 1221, 1186, 1113, 1079, 1050,
usingKBrdiscintherangeof4000–400 cm−1. 1HNMRand13
C
1
NMR spectra were recorded on a Bruker DMX 300 or 400 MHz
instruments with tetramethylsilane (TMS) as the internal stan-
dard. 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 micro-analyzer. The 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 ␮m film thick-
ness) DM-1 silica capillary column, while the GC–MS analysis
was performed with a HP 5890 Series II and a HP 5971 Series
850, 821, 788, 770, 752, 658. H NMR (300 MHz, CDCl3):
δ 9.25 (dd, J = 3.9 Hz, 1H); 8.70 (d, J = 8.4 Hz, 1H); 8.35 (d,
J = 8.4 Hz, 1H); 8.30 (dd, J = 7.5 Hz, 1H); 7.87 (s, 2H); 7.67
(d, J = 8.1 Hz, 1H); 7.29 (d, J = 7.8 Hz, 1H); 7.22 (d, J = 7.2 Hz,
1H); 7.14 (t, J = 7.2 Hz, 1H); 6.72 (d, J = 8.1 Hz, 1H); 2.68 (s, 3H,
CH3); 2.56 (m, 2H, CH2CH3); 1.18 (t, J = 7.5Hz, 3H, CH2CH3).
13CNMR(75 MHz, CDCl3):δ167.5, 156.6, 150.6, 149.3, 146.2,
145.0, 136.4, 136.2, 133.3, 129.3, 128.9, 128.5, 127.4, 126.4,
126.3, 123.8, 122.8, 120.9, 118.1, 24.6, 16.9, 14.0. Anal. Calc.
for C22H19N3 (325.41): C, 81.20; H, 5.89; N, 12.91. Found: C,
81.55; H, 5.72; N, 12.74.
1
mass detector. H and 13C NMR spectra of the waxes were
recorded on a Bruker DMX 400 MHz instrument at 135 ◦C in
o-dichlorobenzene-d4 using TMS as the internal standard.
Toluene and tetrahydrofuran (THF) were refluxed over
sodium-benzophenone and distilled under nitrogen prior to
use. Methylaluminoxane (MAO, 1.46 M in toluene) and
modified methylaluminoxane (MMAO, 1.93 M in heptane)
were purchased from Akzo Corp (USA). Trimethylalu-
minum (2 M in toluene), diethylaluminum chloride (Et2AlCl,
1 M in hexane) and ethylaluminum dichloride (EtAlCl2,
1 M in hexane) were purchased from Acros Chemicals. 2-
Acetyl-1,10-phenanthroline, 2-formyl-1,10-phenanthroline and
2-benzoyl-1,10-phenanthroline were prepared according to our
previous report [20]. All other chemicals were obtained com-
mercially and used without further purification unless otherwise
stated.
2.2.3. 2-Acetyl-1,10-phenanthroline(2-isopropylanil) (3a)
In a similar manner with 1a, the ligand 3a was prepared as
a yellow solid in 40% yield. mp: 125–127 ◦C. IR (KBr disc,
cm−1): 2958, 2926, 2866, 1630, 1591, 1551, 1483, 1446, 1417,
1388, 1362, 1313, 1279, 1223, 1188, 1115, 1082, 1032, 849, 783,
754, 659. 1H NMR (300 MHz, CDCl3): δ 9.25 (dd, J = 4.2 Hz,
1H); 8.71 (d, J = 8.4 Hz, 1H); 8.35 (d, J = 8.4 Hz, 1H); 8.30 (d,
J = 7.5 Hz, 1H); 7.87 (s, 2H); 7.67 (dd, J = 8.1 Hz, 1H); 7.36
(d, J = 8.1 Hz, 1H); 7.23 (m, 1H); 7.14 (t, J = 7.2 Hz, 1H); 6.70
(d, J = 7.5 Hz, 1H); 3.08 (sept, J = 6.6 Hz, 1H, CH(CH3)2); 2.70
(s, 3H, CH3); 1.21 (d, J = 6.6 Hz, 6H, CH(CH3)2). 13C NMR
(75 MHz, CDCl3): δ 167.9, 157.0, 151.0, 149.1, 146.7, 145.4,
138.5, 136.8, 136.6, 129.8, 129.3, 127.8, 126.8, 126.5, 126.0,
124.5, 123.3, 121.4, 118.7, 28.8, 23.3, 17.4. Anal. Calc. for
C23H21N3 (339.43): C, 81.38; H, 6.24; N, 12.38. Found: C,
81.10; H, 6.40; N, 12.20.
2.2. Synthesis of 2-imino-1,10-phenanthroline ligands
(1a–18a)
2.2.4. 2-Acetyl-1,10-phenanthroline(2-ethyl-6-methylanil)
(4a)
2.2.1. 2-Acetyl-1,10-phenanthroline(2-methylanil) (1a)
A
reaction mixture of 2-acetyl-1,10-phenanthroline
In a similar manner with 1a, the ligand 4a was prepared as
a yellow solid in 56% yield. mp: 154–156 ◦C. IR (KBr disc,
cm−1): 3059, 3014, 2966, 2930, 2870, 1636, 1587, 1551, 1490,
1456, 1417, 1389, 1362, 1322, 1283, 1248, 1202, 1137, 1115,
(0.445 g, 2.0 mmol), 2-methylaniline (0.289 g, 2.7 mmol),
p-toluenesulfonic acid (0.040 g) and anhydrous sodium sulfate
in 30 mL toluene were refluxed under nitrogen for 30 h. After
filtration, the solvent was removed by a rotary evaporator and
the resulting solid was eluted with petroleum ether/ethyl acetate
(4:1, v/v) on an alumina column. The second eluting fraction
was collected and concentrated to give a yellow solid in 23%
yield (0.143 g). mp: 94–96 ◦C. IR (KBr disc, cm−1): 2988,
1
887, 864, 821, 782, 743, 661. H NMR (300 MHz, CDCl3):
δ 9.25 (d, J = 3.9 Hz, 1H); 8.80 (d, J = 8.4 Hz, 1H); 8.35 (d,
J = 8.4 Hz, 1H); 8.29 (d, J = 7.8 Hz, 1H); 7.89 (s, 2H); 7.67 (dd,
J = 8.1 Hz, 1H); 7.12 (t, J = 7.5 Hz, 2H); 7.02 (t, J = 7.5 Hz, 1H);
2.58 (s, 3H, CH3); 2.45 (m, 2H, CH2CH3); 2.08 (s, 3H, PhCH3);

S. Jie et al. / Journal of Molecular Catalysis A: Chemical 269 (2007) 85–96
87
1.17 (t, J = 7.5Hz, 3H, CH2CH3). 13C NMR (75 MHz, CDCl3):
δ 166.7, 154.9, 149.4, 147.2, 145.1, 143.9, 135.2, 135.0, 130.1,
128.3, 127.7, 126.7, 126.3, 125.2, 124.8, 123.8, 122.0, 121.7,
119.6, 23.4, 16.8, 15.9, 12.5. Anal. Calc. for C23H21N3 (339.43):
C, 81.38; H, 6.24; N, 12.38. Found: C, 81.30; H, 6.27; N, 12.11.
1H NMR (300 MHz, CDCl3): δ 9.25 (dd, J = 4.2 Hz, 1H); 8.67
(d, J = 8.1 Hz, 1H); 8.37 (d, J = 8.4 Hz, 1H); 8.31 (dd, J = 8.1 Hz,
1H); 7.88 (s, 2H); 7.80 (s, 1H); 7.68 (q, J = 4.2 Hz, 1H); 7.47
(dd, J = 8.4 Hz, 1H); 6.74 (d, J = 8.4 Hz, 1H); 2.68 (s, 3H, CH3).
13C NMR (75 MHz, CDCl3): δ 170.6, 155.7, 153.1, 150.6,
148.8, 146.2, 145.0, 136.6, 136.2, 135.0, 134.3, 131.0, 128.9,
127.7, 126.3, 123.0, 121.1, 116.4, 114.3, 17.5. Anal. Calc. for
C20H13Br2N3 (455.15): C, 52.78; H, 2.88; N, 9.23. Found: C,
52.71; H, 2.97; N, 9.25.
2.2.5. 2-Acetyl-1,10-phenanthroline(2-bromoanil) (5a)
In a similar manner with 1a, the ligand 5a was prepared as
a yellow solid in 40% yield. mp: 138–140 ◦C. IR (KBr disc,
cm−1): 3045, 2994, 1643, 1584, 1552, 1489, 1462, 1393, 1363,
1320, 1276, 1221, 1115, 1078, 1023, 886, 853, 818, 776, 745,
2.2.9. 2-Acetyl-1,10-phenanthroline
(2,4,6-trifluoroanil) (9a)
1
659. H NMR (300 MHz, CDCl3): δ 9.24 (d, J = 4.1 Hz, 1H);
8.70 (dd, J = 8.4 Hz, 1H); 8.36 (dd, J = 8.4 Hz, 1H); 8.29 (d,
J = 7.8 Hz, 1H); 7.87 (s, 2H); 7.68 (d, J = 4.5 Hz, 1H); 7.65 (d,
J = 9.0 Hz, 1H); 7.34 (t, J = 7.5 Hz, 1H); 7.01 (t, J = 7.5 Hz, 1H);
6.86 (d, J = 7.8 Hz, 1H); 2.67 (s, 3H, CH3). 13C NMR (75 MHz,
CDCl3): δ 169.7, 156.0, 150.4, 149.5, 146.1, 144.9, 136.3, 136.0,
132.7, 129.3, 128.7, 127.8, 127.4, 126.2, 124.4, 122.7, 121.0,
119.7, 113.3, 17.3. Anal. Calc. for C20H14BrN3 (376.25): C,
63.84; H, 3.75; N, 11.17. Found: C, 63.84; H, 3.76; N, 11.09.
In a similar manner with 1a, the ligand 9a was prepared as
a yellow solid in 40% yield. mp: 211–213 ◦C. IR (KBr disc,
cm−1): 3102, 3033, 1629, 1595, 1553, 1492, 1444, 1391, 1368,
1320, 1284, 1216, 1119, 1080, 1036, 998, 856, 804, 778, 728,
659. 1H NMR (300 MHz, CDCl3): δ 9.25 (dd, J = 4.2 Hz, 1H);
8.67 (d, J = 8.4 Hz, 1H); 8.36 (d, J = 8.4 Hz, 1H); 8.30 (dd,
J = 8.4 Hz, 1H); 7.87 (s, 2H); 7.68 (dd, J = 7.8 Hz, 1H); 6.81 (m,
2H); 2.76 (s, 3H, CH3). 13C NMR (75 MHz, CDCl3): δ 171.8,
159.7, 147.6, 146.5, 141.5, 139.5, 137.8, 129.9, 128.8, 125.9,
124.8, 123.3, 122.0, 117.8, 35.3, 34.2, 31.3, 29.5. Anal. Calc.
for C20H12F3N3 (351.32): C, 68.37; H, 3.44; N, 11.96. Found:
C, 68.00; H, 3.51; N, 11.67.
2.2.6. 2-Acetyl-1,10-phenanthroline(2-bromo-4-
methylanil) (6a)
In a similar manner with 1a, the ligand 6a was prepared as
a yellow solid in 30% yield. mp: 166–168 ◦C. IR (KBr disc,
cm−1): 3204, 2917, 1641, 1556, 1506, 1361, 1313, 1271, 1117,
2.2.10. 2-Acetyl-1,10-phenanthroline
(2,4,6-trichloroanil) (10a)
1
853, 818, 739, 657. H NMR (300 MHz, CDCl3): δ 9.26 (s,
1H); 8.70 (d, J = 8.4 Hz, 1H); 8.36 (d, J = 8.4 Hz, 1H); 8.30 (d,
J = 7.8 Hz, 1H); 7.87 (s, 2H); 7.68 (m, 1H); 7.49 (s, 1H); 7.15 (d,
J = 7.5 Hz, 1H); 6.76 (t, J = 7.8 Hz, 1H); 2.68 (s, 3H, CH3), 2.36
(s, 3H, PhCH3). 13C NMR (75 MHz, CDCl3): δ 170.1, 156.3,
150.6, 147.1, 146.3, 145.1, 136.6, 136.3, 134.7, 133.2, 129.5,
129.0, 128.8, 127.6, 126.5, 123.0, 121.3, 120.0, 113.4, 20.5,
17.5. Anal. Calc. for C21H16BrN3 (390.28): C, 64.63; H, 4.13;
N 10.77. Found: C, 64.64; H, 4.22; N, 10.48.
2-Acetyl-1,10-phenanthroline (0.445 g, 2.0 mmol), 2,4,6-
trichloroaniline (0.491 g, 2.5 mmol) and p-toluenesulfonic acid
(0.040 g) were combined with tetraethyl orthosilicate (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 orthosilicate was removed
at reduced pressure and the resulting solid was eluted with
petroleum ether/ethyl acetate (4:1, v/v) on an alumina column.
The second eluting fraction was collected and concentrated to
give a yellow solid in 15% yield (0.120 g). mp: 188–190 ◦C. IR
(KBr disc, cm−1): 3049, 1643, 1587, 1543, 1490, 1450, 1430,
2.2.7. 2-Acetyl-1,10-phenanthroline(2-bromo-4-
fluoroanil) (7a)
1
1362, 1322, 1285, 1229, 1135, 1114, 854, 798, 706. H NMR
In a similar manner with 1a, the ligand 7a was prepared
as a yellow solid in 39% yield. mp: 206–208 ◦C. IR (KBr
disc, cm−1): 3045, 1641, 1589, 1554, 1479, 1396, 1366, 1321,
(300 MHz, CDCl3): δ 9.26 (d, J = 4.2 Hz, 1H); 8.74 (d, J = 8.4Hz,
1H); 8.38 (d, J = 8.4 Hz, 1H); 8.31 (dd, J = 7.8 Hz, 1H); 7.89 (s,
2H); 7.69 (dd, J = 7.8 Hz, 1H); 7.41 (s, 2H); 2.67 (s, 3H, CH3).
13CNMR(75 MHz, CDCl3):δ173.3, 155.4, 151.1, 145.6, 145.0,
137.1, 136.7, 130.2, 129.4, 129.0, 128.5, 128.4, 126.8, 125.3,
121.7, 18.5. Anal. Calc. for C20H12Cl3N3 (400.69): C, 59.95;
H, 3.02; N, 10.49. Found: C, 59.65; H, 3.07; N, 10.20.
1
1253, 1234, 1193, 1118, 1078, 854, 825, 763, 740, 654. H
NMR (300 MHz, CDCl3): δ 9.25 (dd, J = 4.2 Hz, 1H); 8.63 (d,
J = 8.4 Hz, 1H); 8.36 (d, J = 8.1 Hz, 1H); 8.29 (dd, J = 7.5 Hz,
1H); 7.88 (s, 2H); 7.69 (q, J = 4.5 Hz, 1H); 7.34 (t, J = 7.5 Hz,
2H); 6.86 (t, J = 8.7 Hz, 1H); 2.72 (s, 3H, CH3). 13C NMR
(75 MHz, CDCl3): δ 171.8, 155.8, 150.6, 149.5, 146.2, 150.0,
136.5, 136.2, 129.5, 128.9, 127.7, 127.5, 126.3, 123.0, 121.0,
119.7, 119.4, 17.6. Anal. Calc. for C20H13BrFN3 (394.24): C,
60.93; H, 3.32; N, 10.66. Found: C, 61.08; H, 3.41; N, 10.46.
2.2.11. 2-Acetyl-1,10-phenanthroline
(2-bromo-4,6-difluoroanil) (11a)
In a similar manner with 10a, the ligand 11a was prepared
as a yellow solid in 40% yield. mp: 173–175 ◦C. IR (KBr disc,
cm−1): 3041, 1631, 1603, 1583, 1553, 1489, 1464, 1419, 1366,
1324, 1290, 1206, 1164, 1109, 1080, 992, 886, 851, 793, 739,
659. 1H NMR (300 MHz, CDCl3): 1H NMR (300 MHz, CDCl3):
δ 9.24 (d, J = 3.6 Hz, 1H); 8.71 (d, J = 8.4 Hz, 1H); 8.34 (d,
J = 8.4 Hz, 1H); 8.26 (d, J = 8.1 Hz, 1H); 7.84 (s, 2H); 7.66
2.2.8. 2-Acetyl-1,10-phenanthroline(2,4-dibromoanil) (8a)
In a similar manner with 1a, the ligand 8a was prepared as
a yellow solid in 45% yield. mp: 150–152 ◦C. IR (KBr disc,
cm−1): 3419, 3054, 1636, 1587, 1551, 1488, 1458, 1391, 1365,
1319, 1284, 1253, 1219, 1116, 1077, 1042, 859, 831, 742, 686.

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S. Jie et al. / Journal of Molecular Catalysis A: Chemical 269 (2007) 85–96
(dd, J = 7.8 Hz, 1H); 7.24 (s, 1H); 6.94 (m, 1H); 2.70 (s, 3H,
CH3). 13C NMR (100 MHz, CDCl3): δ 173.1, 155.1, 151.9,
146.0, 144.8, 136.3, 135.9, 129.4, 128.7, 127.6, 126.0, 122.7,
121.0, 115.4, 115.1, 103.8, 103.6, 103.3, 17.8. Anal. Calc. for
C20H12BrF2N3 (412.20): C, 58.27; H, 2.93; N, 10.19. Found:
C, 57.94; H, 3.06; N, 10.13.
2.2.15. 2-Formyl-1,10-phenanthroline(2,4,6-trimethylanil)
(15a)
In a similar manner with 14a, the ligand 15a was prepared
as a yellow solid in 82% yield. mp: 99–101 ◦C. IR (KBr disc,
cm−1): 3445, 2915, 2856, 1635, 1587, 1554, 1485, 1394, 1210,
1144, 1091, 855, 835, 739. 1H NMR (300 MHz, CDCl3): δ 9.24
(s, 1H); 8.85 (s, 1H, CH N); 8.70 (d, J = 8.4 Hz, 1H); 8.37 (d,
J = 8.1 Hz, 1H); 8.28 (d, J = 7.8 Hz, 1H); 7.88 (s, 2H), 7.67 (dd,
J = 8.1 Hz, 1H); 6.92 (s, 2H); 2.31 (s, 3H, PhCH3); 2.17 (s, 6H,
PhCH3). 13C NMR (100 MHz, CDCl3): δ 164.1, 154.8, 150.7,
147.9, 146.1, 145.8, 136.8, 136.3, 133.4, 129.8, 129.0, 128.8,
127.7, 126.6, 126.5, 123.2, 120.3, 20.8, 18.3. Anal. Calc. for
C22H19N3·EtOH (371.47): C, 77.60; H, 6.78; N, 11.31. Found:
C, 77.83; H, 6.63; N, 11.44.
2.2.12. 2-Acetyl-1,10-phenanthroline(2-bromo-6-chloro-4-
fluoroanil) (12a)
In a similar manner with 10a, the ligand 12a was prepared
as a yellow solid in 39% yield. mp: 197–198 ◦C. IR (KBr disc,
cm−1): 3076, 2986, 1657, 1586, 1562, 1491, 1440, 1389, 1362,
1
1319, 1284, 1252, 1195, 1137, 1115, 928, 858, 772, 658. H
NMR (300 MHz, CDCl3): δ 9.25 (d, J = 3.3 Hz, 1H); 8.76 (d,
J = 8.4Hz, 1H); 8.37 (d, J = 8.4 Hz, 1H); 8.30 (d, J = 7.8 Hz, 1H);
7.88 (s, 2H); 7.68 (dd, J = 7.8 Hz, 1H); 7.35 (d, J = 6.9 Hz, 1H);
7.23 (d, J = 8.1 Hz, 1H); 2.66 (s, 3H, CH3). 13C NMR (75 MHz,
CDCl3): δ 173.4, 155.5, 151.1, 146.7, 145.6, 137.1, 136.7, 130.2,
129.4, 128.3, 126.8, 124.6, 123.4, 121.7, 119.3, 118.9, 117.0,
116.6, 114.2, 18.4. Anal. Calc. for C20H12BrClFN3 (428.68):
C, 56.04; H, 2.82; N, 9.80. Found: C, 55.76; H, 2.78; N, 9.64.
2.2.16. 2-Formyl-1,10-phenanthroline(4-bromo-2,6-
dimethylanil) (16a)
In a similar manner with 14a, the ligand 16a was prepared
as a yellow solid in 36% yield. mp: 190–192 ◦C. IR (KBr disc,
cm−1): 3443, 2966, 2911, 1635, 1587, 1553, 1492, 1465, 1393,
1
1191, 856, 815, 742. H NMR (300 MHz, CDCl3): δ 9.25 (d,
J = 3.3 Hz, 1H); 8.82 (s, 1H, CH N); 8.68 (d, J = 8.4 Hz, 1H);
8.40 (d, J = 8.4 Hz, 1H); 8.31 (d, J = 7.5 Hz, 1H); 7.90 (s, 2H);
2.2.13. 2-Acetyl-1,10-phenanthroline(2-bromo-4-chloro-6-
fluoroanil) (13a)
7.69 (dd, J = 8.1 Hz, 1H); 7.24 (s, 2H); 2.15 (s, 6H, PhCH3). 13
C
In a similar manner with 10a, the ligand 13a was prepared
as a yellow solid in 43% yield. mp: 117–118 ◦C. IR (KBr disc,
cm−1): 3061, 2919, 1639, 1587, 1554, 1504, 1490, 1455, 1418,
1401, 1392, 1372, 1323, 1286, 1266, 1246, 1212, 1170, 1136,
1118, 1080, 921, 887, 857, 822, 775, 762, 742, 710, 659, 625.
1H NMR (300 MHz, CDCl3): δ 9.25 (d, J = 3.3 Hz, 1H); 8.71
(d, J = 7.5 Hz, 1H); 8.36 (d, J = 7.8 Hz, 1H); 8.30 (d, J = 7.2 Hz,
1H); 7.87 (s, 2H); 7.68 (s, 1H); 7.48 (s, 1H); 7.18 (d, J = 8.1 Hz,
1H); 2.70 (s, 3H, CH3). 13C NMR (100 MHz, CDCl3): δ 173.3,
155.3, 150.7, 146.3, 145.1, 137.1, 136.7, 136.3, 129.8, 129.2,
129.0, 128.1, 128.0, 126.4, 123.1, 121.4, 116.1, 115.9, 115.6,
18.3. Anal. Calc. for C20H12BrClFN3 (428.68): C, 56.04; H,
2.82; N, 9.80. Found: C, 55.78; H, 2.83; N, 9.71.
NMR (75 MHz, CDCl3): δ 164.8, 154.3, 150.8, 149.4, 146.0,
145.9, 136.9, 136.3, 130.7, 129.9, 129.0, 128.9, 128.0, 126.4,
123.3, 120.2, 116.7, 18.1. Anal. Calc. for C21H16BrN3 (390.28):
C, 64.63; H, 4.13; N, 10.77. Found: C, 64.34; H, 4.07; N, 10.52.
2.2.17. 2-Benzoyl-1,10-phenanthroline(2,4,6-
trimethylanil) (17a)
In a similar manner with 10a, while 2-benzoyl-1,10-
phenanthroline and 2,4,6-trimethylaniline were alternatively
used, the ligand 17a was prepared as a yellow solid in 44%
yield. mp: 210–212 ◦C. IR (KBr disc, cm−1): 3054, 2913, 1623,
1589, 1551, 1487, 1447, 1389, 1322, 1215, 1140, 967, 877,
1
845, 789, 693. H NMR (300 MHz, CDCl3): δ 9.20–6.59 (m,
14H); 2.22 (d, J = 8.4 Hz, 6H), 2.25 (d, J = 8.1 Hz, 3H). 13C
NMR (100 MHz, CDCl3): δ 166.8, 156.8, 151.4, 147.2, 146.9,
146.5, 138.8, 137.3, 136.7, 136.6, 132.8, 131.6, 130.8, 130.2,
129.8, 129.4, 129.1, 128.8, 128.3, 128.1, 127.1, 127.0, 126.2,
123.9, 122.7, 21.5, 19.7, 19.3. Anal. Calc. forC28H23N3·0.5H2O
(410.51): C, 81.92; H, 5.89; N, 10.24. Found: C, 82.21; H, 5.63;
N, 10.12.
2.2.14. 2-Formyl-1,10-phenanthroline(2-methylanil) (14a)
A
reaction mixture of 2-formyl-1,10-phenanthroline
(0.208 g, 1.0 mmol), 2-methylaniline (0.129 g, 1.2 mmol),
p-toluenesulfonic acid (0.040 g) and absolute ethanol (10 mL)
was refluxed under nitrogen for 6 h. The solvent was thereafter
removed by a rotary evaporator and the resulting solid was
eluted with petroleum ether/ethyl acetate (1:1, v/v) on an
alumina column. The second eluting fraction was collected and
concentrated to afford a yellow solid in 41% yield (0.122 g).
mp: 196–198 ◦C. IR (KBr disc, cm−1): 3255, 3061, 2912,
1637, 1591, 1555, 1495, 1461, 1412, 1128, 861, 823, 751.
1H NMR (300 MHz, CDCl3): δ 9.18 (d, J = 3.0 Hz, 1H); 8.27
(d, J = 7.8 Hz, 2H); 7.83 (s, 2H), 7.67 (dd, J = 4.2 Hz, 1H);
7.06–6.78 (m, 5H); 6.58 (d, J = 7.5 Hz, 1H); 2.24 (s, 3H,
PhCH3). 13C NMR (75 MHz, CDCl3): δ 164.3, 154.6, 150.5,
146.0, 145.6, 136.2, 133.2, 129.9, 129.0, 128.6, 127.7, 126.3,
126.0, 125.9, 125.8, 125.7, 125.6, 123.3, 122.1, 18.6. Anal.
Calc. for C20H15N3 (297.35): C, 80.78; H, 5.08; N, 14.13.
Found: C, 80.54; H, 5.38; N, 13.97.
2.2.18. 2-Benzoyl-1,10-phenanthroline(4-bromo-2,6-
dimethylanil) (18a)
In a similar manner with 17a, the ligand 18a was prepared
as a yellow solid in 25% yield. mp: 194–196 ◦C. IR (KBr disc,
cm−1): 3056, 2918, 1625, 1588, 1574, 1551, 1487, 1465, 1447,
1
1388, 1321, 1206, 1159, 966, 878, 845, 785, 692. H NMR
(400 MHz, CDCl3): δ 9.18 (d, J = 4.0 Hz, 1H); 8.18 (d, J = 8.0Hz,
1H); 8.07 (d, J = 8.0 Hz, 1H); 7.95 (d, J = 7.6 Hz, 2H); 7.74 (d,
J = 8.8 Hz, 1H); 7.67 (d, J = 8.8 Hz, 1H); 7.59 (dd, J = 8.0 Hz,
1H); 7.46 (t, J = 7.2 Hz, 1H); 7.39 (t, J = 7.2 Hz, 2H); 7.30 (dd,
J = 8.4 Hz, 2H); 6.89 (s, 2H); 2.24 (s, 6H, PhCH3). 13C NMR
(100 MHz, CDCl3): δ 166.3, 154.9, 150.1, 147.4, 145.8, 145.2,

S. Jie et al. / Journal of Molecular Catalysis A: Chemical 269 (2007) 85–96
89
137.1, 136.1, 135.7, 135.5, 130.7, 130.1, 129.6, 129.0, 128.6,
128.3, 127.9, 127.1, 125.8, 122.8, 123.0, 114.9, 18.4. Anal. Calc.
for C27H20BrN3 (466.37): C, 69.53; H, 4.32; N, 9.01. Found: C,
69.45; H, 4.46; N, 8.89.
3466, 3061, 2910, 1613, 1578, 1548, 1514, 1491, 1438, 1405,
1375, 1286, 1232, 1152, 859, 799, 739, 656. Anal. Calc. for
C20H12Cl5FeN3 (527.44): C, 45.54; H, 2.29; N, 7.97. Found:
C, 45.29; H, 2.34; N, 7.89. 11b: Dark blue powder in 81%
yield. IR (KBr disc, cm−1): 3449, 3065, 1607, 1586, 1516,
1465, 1425, 1398, 1287, 1213, 1174, 1114, 1063, 996, 861, 738,
658. Anal. Calc. for C20H12BrCl2F2FeN3 (538.98): C, 44.57;
H, 2.24; N, 7.80. Found: C, 44.82; H, 2.31; N, 7.52. 12b: Dark
purple powder in 99% yield. IR (KBr disc, cm−1): 3482, 3059,
2969, 2908, 1612, 1589, 1570, 1515, 1493, 1448, 1407, 1376,
1286, 1266, 1200, 1178, 936, 861, 779, 734, 657. Anal. Calc.
for C20H12BrCl3FFeN3 (555.44): C, 43.25; H, 2.18; N, 7.57.
Found: C, 43.60; H, 2.51; N, 7.23. 13b: Dark blue powder in 85%
yield. IR (KBr disc, cm−1): 3459, 3060, 2909, 1612, 1562, 1513,
1491, 1454, 1405, 1374, 1587, 1216, 1174, 928, 860, 791, 740,
657. Anal. Calc. for C20H12BrCl3FFeN3 (555.44): C, 43.25; H,
2.18; N, 7.57. Found: C, 43.46; H, 2.46; N, 7.28. 14b: Dark blue
powder in 64% yield. IR (KBr disc, cm−1): 3431, 3059, 3016,
1603, 1580, 1512, 1487, 1405, 1296, 1185, 1143, 1116, 965,
862, 760. Anal. Calc. for C20H15Cl2FeN3·0.5H2O (433.11): C,
55.46; H, 3.72; N, 9.70. Found: C, 55.29; H, 3.64; N, 9.44.
15b: Dark blue powder in 70% yield. IR (KBr disc, cm−1):
3436, 3053, 2917, 1608, 1582, 1512, 1481, 1406, 1297, 1198,
1142, 964, 860, 738, 646. Anal. Calc. for C22H19Cl2FeN3·H2O
(470.17): C, 56.20; H, 4.50; N, 8.94. Found: C, 56.52; H, 4.31;
N, 8.88. 16b: Gray blue powder in 95% yield. IR (KBr disc,
cm−1): 3436, 3056, 2976, 1606, 1582, 1512, 1494, 1470, 1436,
1406, 1297, 1182, 1140, 963, 859, 840, 738, 644. Anal. Calc. for
C21H16BrCl2FeN3 (517.03): C, 48.78; H, 3.12; N, 8.13. Found:
C, 49.04; H, 3.26; N, 7.94. 17b: Dark brown powder in 89%
yield. IR (KBr disc, cm−1): 3443, 3060, 2913, 1601, 1583, 1510,
1491, 1442, 1402, 1289, 1223, 1000, 866, 701. Anal. Calc. for
C28H23Cl2FeN3·0.5EtOH (551.29): C, 63.18; H, 4.75; N, 7.62.
Found: C, 62.94; H, 4.49; N, 7.58. 18b: Dark brown powder in
95% yield. IR (KBr disc, cm−1): 3447, 3043, 2966, 1619, 1590,
1509, 1494, 1463, 1441, 1404, 1290, 1217, 1158, 1113, 1000,
856, 701. Anal. Calc. for C27H20BrCl2FeN3·CH3OH (625.16):
C, 53.79; H, 3.87; N, 6.72. Found: C, 53.71; H, 3.97; N, 6.51.
2.3. Preparation of iron(II) complexes
2.3.1. General procedure
The ligand and FeCl2·4H2O were added together in a Schlenk
tube, previously purged three times with argon and then charged
with THF. The reaction mixture was stirred at room tempera-
ture for 9 h. The resulting precipitate was filtered, washed with
diethyl ether and dried in vacuum. All of the complexes were
prepared in high yield in this manner.
2.3.2. Synthesis of complexes 1b–18b
1b: Dark blue powder in 70% yield. IR (KBr disc, cm−1):
3420, 3056, 2918, 1667, 1605, 1578, 1511, 1488, 1401,
1287, 1260, 1226, 1150, 864, 742, 656. Anal. Calc. for
C21H17Cl2FeN3 (438.13): C, 57.57; H, 3.91; N, 9.59. Found:
C, 57.80; H, 3.54; N, 9.24. 2b: Dark blue powder in 90% yield.
IR (KBr disc, cm−1): 3482, 3059, 2966, 2934, 2876, 1608, 1579,
1513, 1484, 1447, 1405, 1370, 1337, 1286, 1223, 1147, 858, 786,
742, 657. Anal. Calc. for C22H19Cl2FeN3 (489.22): C, 58.44; H,
4.24; N, 9.29. Found: C, 58.19; H, 4.36; N, 8.93. 3b: Dark blue
powder in 95% yield. IR (KBr disc, cm−1): 3447, 3060, 2962,
2922, 2869, 1610, 1578, 1514, 1486, 1445, 1406, 1371, 1286,
1228, 1195, 1145, 1089, 1033, 858, 835, 790, 756, 741, 656.
Anal. Calc. for C23H21Cl2FeN3 (466.18): C, 59.26; H, 4.54; N,
9.01. Found: C, 58.89; H, 4.54; N, 8.83. 4b: Dark blue powder in
88% yield. IR (KBr disc, cm−1): 3446, 1974, 2912, 1609, 1581,
1509, 1489, 1456, 1403, 1372, 1285, 1203, 1143, 1095, 894,
862, 783, 741, 656. Anal. Calc. for C24H23Cl2FeN3 (480.21):
C, 60.03; H, 4.83; N, 8.75. Found: C, 59.91; H, 4.61; N, 8.62.
5b: Gray blue powder in 79% yield. IR (KBr disc, cm−1): 3468,
3059, 3015, 2910, 1612, 1580, 1514, 1492, 1464, 1426, 1406,
1373, 1333, 1287, 1223, 1149, 1137, 1027, 862, 834, 789, 762,
739, 657. Anal. Calc. for C20H14BrCl2FeN3 (503.00): C, 47.76;
H, 2.81; N, 8.35. Found: C, 47.43; H, 2.56; N, 8.05. 6b: Dark
green powder in 89% yield. IR (KBr disc, cm−1): 3440, 3058,
2917, 1610, 1578, 1512, 1485, 1398, 1337, 1288, 1232, 1154,
1047, 843, 857, 739, 655. Anal. Calc. for C21H16BrCl2FeN3
(517.03): C, 48.78; H, 3.12; N, 8.13. Found: C, 48.42; H, 3.34;
N, 8.25. 7b: Dark blue powder in 87% yield. IR (KBr disc,
cm−1): 3449, 3055, 2912, 1614, 1596, 1513, 1479, 1405, 1374,
1289, 1260, 1193, 1039, 856, 787, 740, 655. Anal. Calc. for
C20H13BrCl2FFeN3 (520.99):C, 46.11;H, 2.52;N, 8.07. Found:
C, 45.83; H, 2.73; N, 7.87. 8b: Dark green powder in 92% yield.
IR (KBr disc, cm−1): 3449, 3065, 1607, 1586, 1516, 1465, 1425,
1399, 1375, 1287, 1213, 1174, 1114, 1063, 996, 861, 738, 658.
Anal. Calc. for C20H13Br2Cl2FeN3 (581.90): C, 41.28; H, 2.25;
N, 7.22. Found: C, 40.97; H, 2.38; N, 7.14. 9b: Dark blue pow-
der in 92% yield. IR (KBr disc, cm−1): 3452, 3051, 2910, 1631,
1599, 1579, 1514, 1495, 1447, 1404, 1285, 1227, 1124, 1043,
998, 847, 741, 660. Anal. Calc. for C20H12Cl2F3FeN3 (478.08):
C, 50.25; H, 2.53; N, 8.79. Found: C, 49.97; H, 2.81; N, 8.48.
10b: Dark blue powder in 75% yield. IR (KBr disc, cm−1):
2.4. General procedure for ethylene reactivity
Ethylene oligomerization under atmospheric pressure of
ethylene was carried out as follows: the catalyst precursor was
dissolved in toluene in a Schlenk tube. The mixture was inten-
sively stirred at a controlled temperature under one atmospheric
ethylene. The reaction was thereafter initiated by the addition of
the desired amount of cocatalyst. After the set period of time,
an aliquot amount of the solution was collected with a syringe
and quenched by the addition of 5% aqueous hydrogen chlo-
ride. The composition and distribution of obtained oligomers
were analyzed by gas chromatography (GC).
Ethylene oligomerization at 10 atm of ethylene was carried
out as follows: 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. On cooling
to the required reaction temperature under ethylene, it was
charged with toluene solution (100 mL total volume) of catalyst

90
S. Jie et al. / Journal of Molecular Catalysis A: Chemical 269 (2007) 85–96
Table 1
Crystal data and structure refinement for [2-{(2,6-Me2-4-Br–C6H2)N C(Ph)}-1,10-phen]FeCl2 (18b)
Formula
Temperature(K)
Crystal system
C27H20BrCl2FeN3·CH3OH
Formula weight
624.15
0.71073
P-1
˚
293(2)
Wavelength (A)
Triclinic
Space group
˚
˚
a (A)
8.2536(16)
19.678(4)
88.482(4)
1333.0(4)
1.555
b (A)
8.5313(16)
84.533(4)
75.124(3)
2
c (A)
α (◦)
γ (◦)
Z
˚
β (◦)
3
˚
Volume (A )
Dcalc (Mg m−3
F(0 0 0)
θ range (◦)
Reflections collected
Completeness to θ (%)
Goodness-of-fit on F2
R indices (all data)
)
μ (mm−1
)
2.292
630
Crystal size (mm)
Limiting indices
Unique reflections
Number of parameters
Final R indices [I > 2σ(I)]
0.20 × 0.15 × 0.10
2.08–25.01
5524
98.0 (θ = 25.01◦)
1.053
−9 ≤ h ≤ 8, −10 ≤ k ≤ 6, −22 ≤ l ≤ 23
4598
327
R1 = 0.0891, wR2 = 0.1795
0.815, −0.351
−3
)
˚
R1 = 0.1579, wR2 = 0.2103
Largest diffraction peak, hole (einstein A
precursor and the desired amount of cocatalyst. Ethylene at
10 atm pressures was then introduced to start the reaction. At the
lapse of the reaction set time, the pressure was released and an
aliquot amount of the solution was collected, terminated by the
addition of 5% aqueous hydrogen chloride and then analyzed
by gas chromatography (GC) for composition and distribution
of oligomers. The residual solution was finally quenched with
5% hydrochloric acid ethanol. The precipitated low-molecular-
weight waxes were collected by filtration, washed with ethanol,
dried in vacuum at 60 ◦C to constant weight.
tallographic data have been deposited within the Cambridge
Crystallographic Data Center, CCDC 624452.
3. Results and discussion
3.1. Synthesis and characterization of the ligands and
iron(II) complexes
The 2-formyl, 2-acetyl and 2-benzoyl-1,10-phenanthroline
derivatives were prepared according to our previous work
[20]. The 2-imino-1,10-phenanthrolines, 2-{(2,6-R1,R3-4-
R2-C6H2)N C(R)}-1,10-phen (1a–18a), were conveniently
prepared through the condensation reaction of the aldehyde
or ketones of 1,10-phenanthroline with the corresponding sub-
stituted anilines using p-toluene sulfonic acid as a catalyst
(Scheme 1). The reaction solvents were varied according to dif-
ferent substances in order to improve the yields of products. All
the compounds were characterized and confirmed by IR, 1H and
13C NMR spectra as well as their elemental analysis.
The 2-imino-1,10-phenanthrolines as ligands reacted with
one equivalent of FeCl2·4H2O to form their corresponding iron
complexes precipitately at room temperature under nitrogen
(Scheme 1). The resultant precipitates were collected and
separated by filtration and subsequently washed with diethyl
ether to obtain the complexes as blue, green or brown air-stable
2.5. X-ray crystallography measurements
Single-crystal X-ray diffraction studies for 18b were car-
ried out on a Bruker SMART 1000 CCD diffractometer with
˚
graphite monochromated Mo K␣ radiation (λ = 0.71073 A). Cell
parameters were obtained by global refinement of the posi-
tions 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-
matrixleast-squaresonF2. Allnon-hydrogenatomswererefined
anisotropically. All hydrogen atoms were placed in calculated
positions. Structure solution and refinement were performed by
using the SHELXL-97 Package [23]. Its crystallographic data
and processing parameters are summarized in Table 1. The crys-
Scheme 1. Synthesis of 1a–18a and their iron (II) complexes 1b–18b.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
R
Me
Me
H
Me
Et
H
Me
i-Pr
H
Me
Me
H
Me
Br
H
Me
Br
Me
H
Me
Br
F
Me
Br
Br
H
Me
F
F
Me
Cl
Cl
Me
Br
F
Me
Br
F
Me
Br
Cl
F
H
Me
H
H
H
Me
Br
Ph
Ph
Me
Br
R1
R2
R3
Me
Me
Me
Me
Me
Me
H
H
H
Et
H
H
F
Cl
F
Cl
H
Me
Me

S. Jie et al. / Journal of Molecular Catalysis A: Chemical 269 (2007) 85–96
91
Table 2
◦
˚
Selected bond lengths (A) and angles ( ) for [2-{(2,6-Me2-4-Br-C6H2)N
C(Ph)}-1,10-phen]FeCl2 (18b)
Bond lengths
Fe–N(1)
Fe–N(2)
Fe–N(3)
Fe–Cl(1)
Fe–Cl(2)
N(3)–C(13)
N(3)–C(14)
Br–C(17)
2.223(7)
2.107(6)
2.303(6)
2.275(3)
2.304(3)
1.269(9)
1.431(1)
1.893(9)
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)
74.6(3)
71.9(2)
146.4(2)
95.9(2)
136.74(2)
106.24(2)
97.24(2)
110.84(2)
97.35(2)
112.21(1)
Fig. 1. ORTEP drawing of 18b with thermal ellipsoids at 30% probability level.
One methanol molecule and all hydrogen atoms have been omitted for clarity.
powders in good yields and in high purity. All the complexes
were characterized by IR spectra and elemental analysis. In
addition, the solid structure was confirmed by the single-crystal
X-ray diffraction analysis of complex 18b.
Single crystals of complex 18b suitable for X-ray diffraction
analysis were obtained by slow diffusion of diethyl ether into its
methanol solution under nitrogen. The crystal structure is shown
in Fig. 1 and the selected bond lengths and angles are collected
in Table 2.
plane and the phenanthrolinyl plane is 87.2◦. The two phenyl
rings are nearly perpendicular to the equatorial plane with the
dihedral angles of 89.2◦ and 90.4◦. The two axial Fe–N bonds,
˚
In the structure of complex 18b, the coordination geom-
etry around the iron center can be described as a distorted
trigonal bipyramidal. The nitrogen atom (N(2) in Fig. 1)
of the phenanthrolinyl group and two chlorine atoms com-
pose an equatorial plane and the central iron atom slightly
2.223(7) (Fe–N(1)) and 2.303(6) A (Fe–N(3)), are much longer
˚
than Fe–N(2) of the equatorial plane (2.107(6) A), which is simi-
lartothatobservedinthealdimineormethyl-ketimineanalogues
[20]. Differently, Fe–N(1)(phenanthroline) is shorter by about
˚
0.08 A than that of Fe–N(3)(imino) probably due to the exis-
˚
deviates by 0.0567 A from this plane. The three equato-
tence of the phenyl group on the imino-C. The difference of the
˚ ˚
two Fe–Cl linkages is that Fe–Cl(2) (2.304(3) A) is about 0.03 A
rial angles N(2)–Fe–Cl(1), N(2)–Fe–Cl(2) and Cl(1)–Fe–Cl(2)
are 106.24(18)◦, 110.84(19)◦ and 112.21(11)◦, respectively
and the axial Fe–N bonds subtend an angle of 146.4(2)◦
(N(1)–Fe–N(3)). The dihedral angle between the equatorial
˚
longer than Fe–Cl(1) (2.275(3) A). The imino N(3)–C(13) bond
˚
length is 1.269(9) A with the typical character of C N double
bond.
Table 3
Ethylene oligomerization using [2-{(2-i-Pr-C6H4)N = C(Me)}-1,10-phen]FeCl2 (3b) with different co-catalystsa
b
Entry
Co-catalyst
Al/Fe
t (min)
Ao
% ␣-Oc
Distribution of oligomers (%)d
ꢀ
ꢀ
ꢀ
C4/
C
C6/
C
≥C8/
C
1
2
3
4
5
6
7
8
9
10
11
12
13
14
EtAlCl2
EtAlCl2
Et2AlCl
Et2AlCl
AlEt3
AlEt3
AlEt3
AlEt3
AlEt3
20
100
100
200
100
200
500
750
1000
500
500
500
500
500
30
30
30
30
30
30
30
30
30
30
5
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
11.3
–
4.0
7.0
9.7
–
–
–
4.47
8.17
10.3
7.90
4.57
8.93
385
291
158
>99
>99
>99
>99
>99
>96
>81
>83
>87
>87
100
100
100
100
100
MAO
57.6
31.1
35.4
36.0
35.4
34.6
MMAO
MMAO
MMAO
MMAO
64.6
64.0
57.6
55.7
10
20
30
87.2
a
General conditions—catalyst: 5 ␮mol; solvent: toluene (30 mL); reaction temperature: 20 ◦C; ethylene pressure: 1 atm.
b
c
d
Activity for oligomers: 104 g mol−1 (Fe) h−1
.
% ␣-olefin content determined by GC and GC–MS.
ꢀ
C: total amount of oligomers.

92
S. Jie et al. / Journal of Molecular Catalysis A: Chemical 269 (2007) 85–96
3.2. Ethylene oligomerization under atmospheric pressure
of ethylene
3.2.2. Effects of Al/Fe molar ratio and reaction temperature
The influence of the Al/Fe molar ratio and reaction tempera-
ture was investigated in detail with the precursor 2b and MMAO
as cocatalyst (Table 4). In many cases, the composition of
obtained oligomers follows the Schulz–Flory distribution which
is characteristic of the constant K, where K represents the prob-
ability of chain propagation (K = rate of propagation/((rate of
propagation) + (rate of chain transfer)) = (moles of Cn+2)/(moles
of Cn)) [24–27]. The K values are determined by the molar
ratio of C12 and C14 fractions. By fixing the reaction tem-
perature at room temperature (20 ◦C) and changing the Al/Fe
molar ratio from 100 to 2000, the catalytic activity was observed
increasing initially with increasing molar ratio and later decreas-
ing with further increment. The optimum activity was up to
9.1 × 105 g mol−1 (Fe) h−1 at the ratio of 500 (entry 4). At the
lower Al/Fe molar ratios (such as 100), complex 2b showed
lower catalytic activity and the oligomers produced consisted
of only butene and hexene (entry 2). In addition, by fixing
the Al/Fe molar ratio at 500 and changing the reaction tem-
perature in the range of −10 to 60 ◦C, the highest activity
(1.34 × 106 g mol−1 (Fe) h−1) was observed at 0 ◦C with larger
3.2.1. Effects of different co-catalysts and reaction time
Complex 3b, [2-{(2-i-Pr–C6H4)N C(Me)}-1,10-phen]
FeCl2, has been chosen to explore the effect of Al cocatalyst
for ethylene oligomerization and the results are summarized
in Table 3. Negligible catalytic activities were observed when
Et2AlCl or EtAlCl2 was used as cocatalyst even at various
Al/Fe molar ratios. In contrast, remarkable catalytic activities
were seen in the presence of MMAO; whereas moderate
activities were observed in the presence of MAO or AlEt3. In
particular, MMAO was the best one among the series of Al
cocatalysts employed in the oligomerization. Time course plots
for ethylene oligomerization with 3b/MMAO catalyst were
employed (entries 11–14) and the observed activities turned
out to be high especially at the beginning (<10 min) and then
decreased gradually. The product in the oligomerization with
3b/AlEt3 catalyst was C4 olefin as the major product, and the
3b/MAO catalyst afforded higher oligomers with a similar
␣-olefin selectivity and distribution.
Table 4
Ethylene reactivity with [2-{(2,6-R1,R3-4-R2-C6H2)N C(R)}-1,10-phen]FeCl2 (1b–18b)/MMAO under atmospheric pressure of ethylenea
Entry
Catalyst
Al/Fe
Tb (◦C)
Oligomers
Waxes
% ␣-Od
Distribution (%)e
Aw
c
f
Ao
K
ꢀ
ꢀ
ꢀ
C4/
C
C6/
C
≥C8/
C
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
1b
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
3b
4b
5b
6b
7b
8b
500
100
200
500
1000
1500
2000
500
500
500
500
500
500
500
500
500
500
500
500
500
500
500
500
500
500
500
500
20
20
20
20
20
20
20
-10
0
40
60
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
93.3
4.90
46.9
91.0
73.0
63.8
55.1
34.8
134
86.2
41.3
87.2
81.5
99.3
41.1
92.4
26.3
108
46.9
73.3
79.6
104
86.1
94.7
58.9
80.0
71.7
0.45
–
–
>92
>96
>90
>87
>89
>93
>93
>93
>93
>92
>92
>87
>93
>90
>91
>91
>92
>90
>91
>94
>89
>91
>94
>93
>92
>95
>91
31.8
73.2
48.4
44.3
43.1
53.2
54.6
34.6
30.9
43.2
54.7
55.7
20.2
35.2
36.5
43.6
29.3
38.4
19.1
36.7
35.0
42.1
35.7
23.7
18.1
21.0
18.8
34.1
26.8
30.8
33.5
32.5
27.6
25.0
45.4
35.6
42.0
44.0
34.6
45.0
43.2
53.5
42.2
61.2
40.4
40.1
50.6
46.8
44.0
49.8
44.4
45.0
29.8
28.6
34.1
-
–
–
–
–
–
–
–
–
–
–
–
–
5.18
–
–
20.8
22.2
24.4
19.2
20.4
20.0
33.5
14.8
1.3
–
0.44
0.37
0.40
0.47
0.52
–
–
–
0.60
0.48
–
9.7
35.8
21.6
10.0
14.2
9.5
21.2
40.8
12.7
18.2
13.9
14.5
31.9
37.0
49.2
52.6
–
–
–
9b
0.40
0.45
–
0.52
0.42
0.38
0.65
0.70
0.62
0.71
–
1.20
–
0.33
0.35
–
1.84
2.77
7.47
15.9
10b
11b
12b
13b
14b
15b
16b
17b
18b
a
General conditions—catalyst: 5 ␮mol; solvent: toluene (30 mL); reaction time: 30 min.
b
c
d
e
Reaction temperature.
Activity for oligomers: 104 g mol−1 (Fe) h−1
.
% ␣-olefin content determined by GC and GC–MS.
ꢀ
C: total amount of oligomers.
Activity for low-molecular-weight waxes: 104 g mol−1 (Fe) h−1
.
f

S. Jie et al. / Journal of Molecular Catalysis A: Chemical 269 (2007) 85–96
93
amount of longer oligomers (higher K value) (entry 9). When
the reaction temperature was increased, both catalytic activity
and amount of longer oligomers were gradually decreased.
However, complex 15b with three methyl groups resulted in the
increase in oligomerization activity and the K value along with
the production of waxes. Complex 16b containing a bromine
atom at the para-position of the phenyl ring displayed higher K
value along with more waxes although a little lower oligomer-
ization activity was observed, in comparison to its analogues.
Phenylketimine (R = Ph) complexes 17b and 18b exhibited sim-
ilar ethylene reactivity with their aldimine analogues except that
much more low-molecular-weight waxes obtained.
3.2.3. Effects of ligand environment
All the iron(II) complexes were investigated under atmo-
spheric pressure of ethylene and the variation of R group on
the imino-C and substituents on the imino-N aryl rings had
significant influences on the catalytic properties (Table 4).
For monoalkyl-substituted methylketimine (R = Me) complexes
1b–3b, the larger the bulkiness of the alkyl group, the lower the
oligomerization activity and the less amount of longer oligomers
produced. In addition, complex 4b with two alkyl groups at
the ortho-positions of the phenyl ring led to a slightly lower
oligomerization activity; at the same time, higher K value was
observed as well as some low-molecular-weight waxes pro-
duced with the activity of 5.18 × 104 g mol−1 (Fe) h−1 (entry
13). Under the same reaction conditions, complexes 5b–13b
bearing mono- or multi-halogen groups on the phenyl ring
displayed comparable oligomerization activities to their ana-
logues without obvious regularity. Aldimine (R = H) complexes
14b–16b and phenylketimine complexes 17b–18b also showed
comparable oligomerization activity and similar ␣-olefin selec-
tivity. Differently, complex 14b with only one methyl group gave
slightly lower oligomerization activity and a smaller K value.
3.3. Ethylene oligomerization at 10 atm of ethylene
3.3.1. Effects of the amount of catalyst and Al/Fe molar
ratio with MMAO
The catalytic system of 3b/MMAO was examined to deter-
mine the optimal amount of catalyst and the Al/Fe molar ratio
at 10 atm of ethylene (Table 5). The highest activity for ethylene
oligomerization (2.41 × 107 g mol−1 (Fe) h−1) was obtained
with 2 ␮mol catalyst at the Al/Fe molar ratio of 1000. When less
amount of catalyst (1 ␮mol) or lower Al/Fe molar ratio (500)
was used, the catalytic system produced higher contents of C4
with higher selectivity for ␣-olefins (entries 1 and 5). However,
when the amount of catalyst was increased, the selectivity for
␣-olefins decreased. It is worthy to note that the amount of
catalyst and the Al/Fe molar ratio had no significant influence
Table 5
Ethylene reactivity with [2-{(2,6-R1,R3-4-R2-C6H2)N C(R)}-1,10-phen]FeCl2 (1b–18b)/MMAO at 10 atm of ethylenea
Entry
Catalyst (␮mol)
Oligomers
Waxes
b
e
Ao
K
% ␣-Oc
Distribution (%)d
Aw
ꢀ
ꢀ
ꢀ
C4/
C
C6/
C
≥C8/
C
1
2
3b(1)
3b(2)
21.7
24.1
15.1
11.8
8.21
20.8
18.5
22.2
28.6
24.7
22.6
24.9
18.6
20.6
29.8
22.3
22.0
24.3
16.8
25.7
17.5
19.7
29.1
0.27
0.26
0.30
0.28
0.27
0.33
0.46
0.38
0.70
0.56
0.51
0.54
0.51
0.30
0.65
0.48
0.60
0.52
0.33
0.69
0.60
0.67
0.69
>93
>93
>78
>76
>93
>76
>96
>90
>96
>90
>93
>95
>95
>92
>89
>96
>93
>94
>96
>95
>96
>98
>97
56.9
31.2
33.2
26.7
51.6
31.1
21.7
23.7
15.4
19.6
21.8
20.5
28.0
44.5
14.9
21.6
22.4
31.3
43.7
12.6
16.6
13.3
8.8
30.9
49.8
48.8
52.8
34.8
52.1
37.2
42.3
19.1
37.8
30.6
33.7
32.6
32.8
21.3
34.4
26.9
31.7
32.5
18.4
24.3
15.9
17.3
12.2
19.0
18.0
20.5
13.6
16.8
41.1
34.0
65.5
42.6
47.6
45.8
39.4
22.7
63.8
44.0
50.7
37.0
23.8
69.0
59.1
70.8
73.9
–
–
–
–
–
–
–
–
37.6
–
3
3b(4)
4
5
6
7
3b(5)
3b(2)f
3b(5)f
1b(2)
8
2b(2)
9
4b(2)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
5b(2)
6b(2)
7b(2)
8b(2)
–
–
–
–
9b(2)
10b(2)
11b(2)
12b(2)
13b(2)
14b(2)
15b(2)
16b(2)
17b(2)
18b(2)
23.1
–
3.72
0.30
–
40.7
82.0
142
174
a
General conditions—solvent: toluene (100 mL); Al/Fe: 1000; reaction temperature: 20 ◦C; reaction time: 30 min; ethylene pressure: 10 atm.
Activity for oligomers: 106 g mol−1 (Fe) h−1
b
c
d
.
% ␣-olefin content determined by GC and GC–MS.
ꢀ
C: total amount of oligomers.
Activity for low-molecular-weight waxes: 105 g mol−1 (Fe) h−1
Al/Fe: 500.
e
f
.

94
S. Jie et al. / Journal of Molecular Catalysis A: Chemical 269 (2007) 85–96
on the K value. When the amount of catalyst was increased
from 2 to 5 ␮mol with the Al/Fe molar ratio fixed at 1000, the
catalytic activities for ethylene reactivity decreased gradually
despite similar K values, oligomers distribution and ␣-olefin
selectivity (entries 2–4). By fixing the Al/Fe molar ratio at 500,
however, a reverse trend was observed (entries 5–6).
of C4 among the oligomers obtained (entry 14); while 2,4,6-
trichloro-subsituted complex 10b showed the highest activity for
ethylene oligomerization (2.98 × 107 g mol−1 (Fe) h−1) along
with a higher K value and the production of low-molecular-
weight waxes with the activity of 2.31 × 106 g mol−1 (Fe) h−1
(entry 15).
The variation of R substituent on the imino-C also resulted in
some changes of the catalytic properties. For aldimine (R = H)
complexes, 15b with 2,4,6-trimethyl groups on the phenyl ring
displayed higher activity for ethylene oligomerization as well
as a much higher K value and amount of low-molecular-weight
waxes than 14b with only one methyl group at the ortho-position
of the phenyl ring. However, when the methyl group at the
para-position of the phenyl ring was replaced by a bromine
atom, complex 16b gave a little lower oligomerization activ-
ity and much more amount of low-molecular-weight waxes
(8.20 × 106 g mol−1 (Fe) h−1, entry 21). The phenyl-ketimine
(R = Ph) complexes bearing the same substituents on the imino-
N phenyl ring as the corresponding aldimine complexes showed
relatively higher total productivity of oligomers and waxes, in
which higher amount of waxes was observed. Complex 18b with
2,6-dimethyl and 4-bromo groups on the phenyl ring gave higher
activity along with higher amount of waxes than complex 17b
bearing 2,4,6-trimethyl groups, which was different from the
corresponding aldimine complexes.
3.3.2. Effects of ligand environment with MMAO
Allthesynthesizediron(II)complexesdisplayedmuchhigher
catalytic activities for ethylene oligomerization with high selec-
tivity for ␣-olefins when activated with MMAO at 10 atm of
ethylene (Table 5). The distribution of oligomers obtained in
all cases followed the Schulz–Flory rules. For methylketimine
complexes 1b–3b with monoalkyl group on the imino-N phenyl
ring, the catalytic activity was increased with the bulkier group,
while the corresponding K value went down. With both of ortho-
positions occupied by alkyl groups, complex 4b showed higher
catalytic activity with a higher K value as well as the production
of low-molecular-weight waxes (3.76 × 106 g mol−1 (Fe) h−1
,
entry 9). When the substituents on the phenyl ring were changed
fromalkyltohalogengroups, thecomplexesshowedcomparable
catalyticactivitiesforethyleneoligomerization. Whentheortho-
position was fixed with a bromine atom in complexes 5b–8b,
the variation of substituent at the para-position just had a little
influence on the catalytic properties including the oligomeriza-
tion activity, the distribution of oligomers and the K value (entry
10–13). Complexes 9b–13b with three halogen groups on the
phenyl ring also exhibited very high catalytic activity for ethy-
lene oligomerization. However, complex 9b bearing less bulky
fluorine atoms had a much smaller K value and higher amount
3.3.3. Effects of ligand environment with MAO
All the iron (II) complexes were also investigated in the
presence of MAO at 10 atm of ethylene (Table 6). These iron
complexes also showed higher oligomerization activities with
Table 6
Ethylene reactivity with [2-{(2,6-R1,R3-4-R2-C6H2)N C(R)}-1,10-phen]FeCl2 (1b–18b)/MAO at 10 atm of ethylenea
Entry
Catalyst
Oligomers
Waxes
b
e
Ao
K
% ␣-Oc
Distribution (%)d
Aw
ꢀ
ꢀ
ꢀ
C4/
C
C6/
C
≥C8/
C
1
2
1b
2b
10.4
17.8
18.9
9.37
26.1
28.6
10.6
22.3
9.93
44.6
9.65
27.1
26.4
9.23
14.7
5.96
5.94
3.66
0.39
0.41
0.30
0.62
0.42
0.51
0.42
0.44
0.41
0.58
0.40
0.48
0.43
0.38
0.56
0.62
0.58
0.57
>95
>82
>83
>92
>88
>92
>93
>94
>91
>87
>94
>86
>94
>91
>93
>95
>96
>92
27.7
22.6
34.9
23.3
38.2
20.7
26.2
42.8
39.4
22.1
24.6
26.7
41.3
37.3
17.2
20.4
19.7
18.2
38.3
43.4
46.5
21.5
43.5
32.3
34.7
39.4
37.8
25.3
40.1
35.5
24.7
34.2
22.4
20.7
21.2
21.2
34.0
34.0
18.6
55.1
18.3
47.0
39.1
17.8
22.8
52.7
35.4
37.8
34.0
28.5
60.4
58.9
59.2
60.6
–
–
–
3
3b
4
4b
52.4
–
5
5b
6
6b
–
–
7
7b
8
8b
1.24
–
64.1
–
1.55
1.44
–
19.9
2.55
2.91
24.6
9
9b
10
11
12
13
14
15
16
17
18
10b
11b
12b
13b
14b
15b
16b
17b
18b
a
General conditions—catalyst: 2 ␮mol; solvent: toluene (100 mL); Al/Fe: 1000; reaction temperature: 40 ◦C; reaction time: 1 h.
Activity for oligomers: 106 g mol−1 (Fe) h−1
b
c
d
.
% ␣-olefin content determined by GC and GC–MS.
ꢀ
C: total amount of oligomers.
Activity for low-molecular-weight waxes: 105 g mol−1 (Fe) h−1
.
e

S. Jie et al. / Journal of Molecular Catalysis A: Chemical 269 (2007) 85–96
95
Fig. 2. NMR spectra of the waxes obtained by 18b/MMAO (entry 23 in Table 5) (a) 13C NMR; (b) 1H NMR.
better selectivity for ␣-olefins as well as the distribution of
oligomers following the Schulz–Flory rules. As in our previous
report [20], the consumption rate of ethylene decreased more
slowly and the oligomerization reaction could last for a longer
time at higher pressure of ethylene. When MAO was employed
as cocatalyst, obviously, the variation in the substitution pattern
onthephenylringsignificantlyinfluencedthecatalystproductiv-
ity. Under the same reaction conditions, the highest activity for
ethylene oligomerization was achieved with complex 10b bear-
ing 2,4,6-trichloro groups (4.46 × 107 g mol−1 (Fe) h−1, entry
10).
10b/MAO catalyst system) and the distribution of the oligomers
obtained followed the Schulz–Flory rules. When MMAO was
employed as cocatalyst, methylketimine complexes bearing
electron-withdrawing halogen groups and electron-donating
alkyl groups displayed comparable catalytic activities, while
2,4,6-trisubstituted aldimine and phenyl-ketimine complexes
produced much more low-molecular-weight waxes and higher
K values with high oligomerization activities kept. The low-
molecular-weight waxes obtained as higher order oligomers
were predominantly linear ␣-olefins.
Acknowledgements
3.3.4. Characterization for low-molecular-weight waxes
In some of catalyst systems examined, low-molecular-weight
waxes as higher order oligomers were obtained in large amounts.
1H and 13C NMR spectra of the waxes produced by complex
18b/MMAO were recorded in o-dichlorobenzene-d4 using TMS
as the internal standard. The corresponding spectra are shown in
Fig. 2 and the assignments were determined according to the lit-
eratures [28,29]. The 13C NMR spectra demonstrated that linear
␣-olefins absolutely predominated among the produced waxes
with the single signals at δ 138.78 and 113.91 ppm, indicating
the property of vinyl-unsaturated C C chain ends.
The project was supported by NSFC No. 20473099. We thank
ourCAS-TWASPostgraduateFellow, Mr. SherrifAdewuyifrom
Nigeria for the English corrections. Prof. Dr. Takashi Tatsumi
is gratefully acknowledged for his kindly editorial and English
corrections.
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