Fe(II) and Co(II) pyridinebisimine complexes bearing different substituents on ortho- and para-position of imines: Synthesis, characterization and behavior of ethylene polymerization

Article abstract of DOI:10.1016/j.jorganchem.2004.11.029

A series of 2,6-bis(imino)pyridyl iron(II) and cobalt(II) complexes [2,6-(ArNCMe)₂C₅H₃N]MCl₂ (Ar = 2,6-i-Pr₂C₆H₃, M = Fe: 3a, M = Co: 4a; Ar = 2,4,6-i-Pr₃C₆H₂, M = Fe: 3b, M = Co: 4b; Ar = 2,6-i-Pr₂-4-BrC₆H₂, M = Fe: 3c, M = Co: 4c; Ar = 2,4-i-Pr₂-6-BrC₆H₂, M = Fe: 3d, M = Co: 4d) has been synthesized, characterized, and investigated as precatalysts for the polymerization of ethylene in the presence of modified methylaluminoxane (MMAO). The substituents of pyridinebisimine ligands and their positions located significantly influence catalyst activity and polymer property. It is found that the catalytic activities of the iron complexes/MMAO systems are mainly dominated by electronical effect, while those of the cobalt complexes/MMAO systems are primarily controlled by hindering effect.

Full text of DOI:10.1016/j.jorganchem.2004.11.029

Journal of Organometallic Chemistry 690 (2005) 1233–1239
www.elsevier.com/locate/jorganchem
Fe(II) and Co(II) pyridinebisimine complexes bearing
different substituents on ortho- and para-position of imines:
synthesis, characterization and behavior of ethylene polymerization
*
Jing-Yu Liu, Yi Zheng, Yan-Guo Li, Li Pan, Yue-Sheng Li , Ning-Hai Hu
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences,
5625 Renmin Street, Changchun 130022, China
Received 31 July 2004; accepted 16 November 2004
Abstract
A series of 2,6-bis(imino)pyridyl iron(II) and cobalt(II) complexes [2,6-(ArN@CMe)2C5H3N]MCl2 (Ar = 2,6-i-Pr2C6H3, M = Fe:
3a, M = Co: 4a; Ar = 2,4,6-i-Pr3C6H2, M = Fe: 3b, M = Co: 4b; Ar = 2,6-i-Pr2-4-BrC6H2, M = Fe: 3c, M = Co: 4c; Ar = 2,4-i-Pr2-6-
BrC6H2, M = Fe: 3d, M = Co: 4d) has been synthesized, characterized, and investigated as precatalysts for the polymerization of
ethylene in the presence of modified methylaluminoxane (MMAO). The substituents of pyridinebisimine ligands and their positions
located significantly influence catalyst activity and polymer property. It is found that the catalytic activities of the iron complexes/
MMAO systems are mainly dominated by electronical effect, while those of the cobalt complexes/MMAO systems are primarily con-
trolled by hindering effect.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Iron complex; Cobalt complex; Catalyst; Ethylene polymerization
1. Introduction
the iron (II) and cobalt (II) complexes bearing triden-
tate pyridinebisimine ligands can be activated with
methylaluminoxane (MAO) to afford highly active cat-
alysts for the polymerization of ethylene. The catalyst
activity and the product property depend on the substi-
tution pattern of the ligands used [10–14].
As well known, two factors can affect catalyst activity
and the behavior of olefin polymerization. One is steric
effect, the other is electronical factor of ligands. After
studying the relationship between ligand structures and
catalyst performances, Mo¨hring and Coville [15] con-
cluded that the electronic effect could contribute as
much as 80% of the change in the catalytic activities of
(CpR)2ZrCl2/MAO systems. Yang and coworkers [16–
18] reported that electronical effects considerably influ-
ence the catalytic activities of metallocene and a-diimine
Ni(II) complexes activated with MAO for olefin
polymerization. However, there is a little study on the
The late transition metal catalysts for olefin poly-
merization have attracted intense interest because of
the potential to yield polymers with different micro-
structures and more tolerant of functionalized mono-
mers [1–3]. Most late transition metal systems often
oligomerize olefins due to a strong trend to b-hydride
transfer. The key to getting a late transition metal cat-
alyst with high activity and to obtaining high molecu-
lar weight polymers is incorporating bulky
substituents into the ortho-position of coordinating
nitrogen atoms of ligands [1]. In 1998, Brookhartꢀs
and Gibsonꢀs groups [4–9] independently reported that
*
Corresponding
+864315685653.
E-mail address: ysli@ciac.jl.cn (Y.-S. Li).
author.
Tel.:
+864315262124;
fax:
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.11.029

1234
J.-Y. Liu et al. / Journal of Organometallic Chemistry 690 (2005) 1233–1239
correlation between the activities of iron and cobalt cat-
alyst and the electronical effects of ligands [19].
Here, we wish to report the synthesis and character-
ization of a series of the iron and cobalt pyridinebisi-
mine complexes, in which the ortho- or para-position
on the imine groups were replaced by the substituents
with different electronical effects. We also demonstrate
that the both hindering and electronical effects signifi-
cantly influence the catalytic activities of the pyridineb-
isimine iron and cobalt catalysts and the properties of
the polyethylenes obtained.
N
R2
N
R2
O
O
N
N
+
R2
R1
R3
R3
R1
H N
R3
2
2
2a-d
MCl2
R2
R1
1a-d
R2
N
N
N
M
Cl
Cl
R1
R3
R3
R1
3a-d, 4a-d
2. Results and discussion
a: R1=R2=iPr, R3=H
b: R1=R2=R3=iPr
3a-d: M = Fe
4a-d: M = Co
2.1. Synthesis and characterization of complexes
c: R1=R2=iPr, R3=Br
d: R1=R3=iPr, R2=Br
The ligands 2a–d were prepared in high yield by the
condensation reaction of two equivalents of the appro-
priate aniline 1a–d with one equivalent of 2,6-diacetyl-
pyridine (Scheme 1). The iron complexes 3a–d and
cobalt complexes 4a–d were synthesized in good yield
by treating MX2 (M = Fe, Co; X = Cl) with the corre-
sponding 2,6-bis(imino)pyridyl ligands in tetrahydrofu-
ran (THF) at room temperature, as shown in Scheme
1. All the iron complexes 3a–d are blue in color, while
the cobalt species 4a–d are green–brown. The crystal
3c, grown from a layered CH2Cl2–pentane (1:1) solu-
tion, was subject to single-crystal X-ray diffraction
study. The molecular structure of the iron complex 3c
is shown in Fig. 1. The data collection and refinement
data of the analysis are summarized in Table 1, and
Scheme 1.
the selected bond lengths and angles are presented in
Table 2. For the complex 3c, an orthorhombic crystal
system and a P212121 space group were observed, while
a triclinic crystal system and a P space group, for the
complex 3a, were reported by Brookhartꢀs group [4].
Contrast to the pseudo square pyramidal geometry of
3a, the iron complex 3c displays C2v molecular symme-
try (angles N2–Fe–Cl1 and N2–Fe–Cl2 are almost
equivalent) and has pseudo trigonal bipyramidal geom-
etry in which N1 and N3 occupy apical positions.
Fig. 1. Molecular structure of the iron complex 3c. Thermal ellipsoids at the 30% level are shown. Hydrogen atoms are omitted for clarity.

J.-Y. Liu et al. / Journal of Organometallic Chemistry 690 (2005) 1233–1239
1235
Table 1
Crystal data and structure refinements of the complex 3c
5.5
Empirical formula
Formula mass
Crystal size (mm3)
Crystal system
Space group
C33H41Br2Cl2FeN3
766.26
5.0
4.5
4.0
3.5
3.0
2.5
2.0
0.31 · 0.18 · 0.06
Orthorhombic
P212121
14.648 (6)
˚
a (A)
˚
b (A)
16.110 (7)
21.270 (9)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
90
90
90
5019
3
˚
V (A )
Z
4
1.014
Density (calcd.) (Mg/cm3)
Absorption coefficient (mmꢂ1
F(000)
)
2.017
1560
0
10
20
30
40
50
60
Reaction Temperature (oC)
h range for data collected (ꢁ)
Reflection collected
Data/restrains/parameters
Independent reflections
Final R indices [I > 2r(I)]
R indices (all data)
1.59 to 24.09
23,906
Fig. 2. Plot of reaction temperature versus the catalytic activity of
catalyst 3a ( ), 3b (d), 3c (h) and 3d ( ). Ethylene pressure, 1 bar;
7916/8/356
7916
n
polymerization time, 10 min; Al/Fe = 1200.
ꢀ
R1 = 0.0997, wR2 = 0.2689
R1 = 0.2161, wR2 = 0.3504
Semi-empirical from equivalents
0.961
Absorption correction.
Goodness-of-fit on F2
Max./min. transmission
Largest peak/hole in
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
0.8818 and 0.5700
1.067 and ꢂ0.670
3
˚
final diff. map (e/A )
Table 2
Selected bond lengths (A) and angles (ꢁ) for complex 3c
˚
Fe–N(2)
Fe–N(3)
2.068(4)
2.280(8)
1.911(13)
2.264(7)
1.289(12)
72.7(3)
Fe–N(1)
2.260(9)
1.878(6)
2.250(7)
1.268(14)
C(1)–Br(1)
Fe–Cl(1)
C(13)–N(1)
C(25)–Br(2)
Fe–Cl(2)
C(20)–N(3)
N(2)–Fe–N(1)
N(1)–Fe–N(3)
N(1)–Fe–Cl(1)
N(2)–Fe–Cl(2)
N(3)–Fe–Cl(2)
N(2)–Fe–N(3)
N(2)–Fe–Cl(1)
N(3)–Fe–Cl(1)
N(1)–Fe–Cl(2)
Cl(1)–Fe–Cl(2)
73.2(3)
145.8(3)
99.6(5)
124.3(6)
100.2(5)
98.4(5)
124.4(6)
99.9(5)
800
1000
1200
1400
1600
1800
2000
111.34(17)
Al/Fe molar ratio
Fig. 3. Plot of Al/Fe molar ratio versus the catalytic activity of catalyst
3a ( ), 3b ( ), 3c (h) and 3d ( ). Ethylene pressure, 1 bar;
2.2. Ethylene polymerization with the iron complexes
3a–d
n
ꢁ
ꢀ
polymerization time, 10 min; temperature, 0 ꢁC.
On treatment with MMAO, all the iron complexes
3a–d are active towards ethylene polymerization. The
strong temperature dependence of the catalytic activi-
ties is their common characteristic. For example, the
catalyst activities decrease monotonously with the in-
crease of polymerization temperature, as shown in
Fig. 2. In addition, Al/Fe molar ratio can also show
a significant influence upon the catalyst activities.
Hence, several experiments were carried out to deter-
mine the effect of the Al/Fe molar ratio on the catalyst
activities. Fig. 3 shows the results of these experiments
in a range of Al/Fe from 800 to 2000. The catalyst
activities increase with an increase in the Al/Fe molar
ratio from 800 to 1600, nevertheless, the Al/Fe molar
ratio has a little influence on the catalyst activities with
further increase.
In order to evaluate the effect of ligand structure on
the performances of the iron precatalysts, we polymerize
ethylene with the precatalysts 3a–d under the fixed con-
ditions (atmospheric pressure, 0 ꢁC, and Al/Fe (molar
ratio) = 1200). The typical results are summarized in Ta-
ble 3. The data in Table 3 indicate that the variation of
the ortho- or para-substituents of pyridinebisimine li-
gands has a pronounced effect not only on the catalyst
activity, but also on the molecular weight of the result-
ing polymer. The replacement of the para-aryl proton
(3a) with an electron-donating isopropyl group (3b)

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J.-Y. Liu et al. / Journal of Organometallic Chemistry 690 (2005) 1233–1239
Table 3
Results of ethylene polymerization with the iron and cobalt complexesa
b
c
c
ꢀ
ꢀ
ꢀ
Entry
Catalyst
Yield (g)
Activity (kg PE/molFe h bar)
Tm (ꢁC)
Mw ðkg=molÞ
Mw=Mn
1
2
3
4
5
6
7
8
a
3a
3b
3c
3d
4a
4b
4c
4d
1.54
1.41
1.71
1.79
0.62
1.03
0.91
1.11
4620
4230
5130
5380
1860
3090
2730
3330
129.4
128.0
132.3
127.6
128.8
131.9
131.5
126.7
60.4
41.6
87.1
36.9
57.8
80.3
79.1
30.1
38.2
23.8
46.8
58.3
3.58
9.56
6.30
3.04
Polymerization condition: 2 lmol catalyst, Al/Fe = 1200 (molar ratio), polymerization reaction at 0 ꢁC and under 1 bar for 10 min.
Determined by DSC (heating rate: 10 ꢁC/min).
Determined by GPC.
b
c
ꢀ
results in the decrease of catalyst activity and Mw of the
polyethylene obtained (the catalyst activity from 4620 to
ionic species more unstable. This makes for ethylene
insertion. Thus, the precatalyst 3c presents higher activ-
ity and yields higher molecular weight polyethylenes, in
comparison with the precatalyst 3a.
ꢀ
4230 kg PE/molFe h, Mw from 60.4 to 41.6 kg/mol).
However, an electron-withdrawing Br on the para-posi-
tion of imines (3c) increases the catalyst activity to 5130
ꢀ
By comparing the molecular structures of the com-
plex 3c and 3a, we found that the electron-withdrawing
ability of Br atom on the p-position of the imines in the
complex 3c increased the bond distances of Fe–N(1) and
kg PE/molFe h, and Mw to 87.1 kg/mol.
It is noteworthy that the precatalysts 3a–c have the
same substituents on the ortho-position of the imines in
the tridentate ligands, as a result, the rates of b-H elimi-
nations for these systems should be the same. The exclu-
sive difference among these precatalysts is the
substituents on the para-position of the imines. There
are two sides which might explain the differences of the
catalyst activities and the polymer mass. One is the bulk
of the substituents, the other is the electronic effect of the
substituents. According to Cossee [8,20], the mechanism
of the homogeneous polymerizations with iron catalysts
should involve cationic intermediate species, and the ac-
tive centers of iron catalysts are generally considered as
[LFe–R]+. The eclectrophilic character of the center iron
atom is one of the key factors determining the rate of
chain propagation. A more eclectrophilic character of
center iron atom favors the insertion of ethylene. In addi-
tion, an important feature of iron catalyst is the chain
transfer to aluminum. The competition between the
chain propagation and the chain-transfer to Al can play
a decisive role on the molecular weight of polymer. We
consider tentatively that the electronic effect is more
important for the precatalysts 3a–c, although the substi-
tuent in the para-position can provide a certain extent
steric effect. The existence of the electron-donating group
on the para-position of coordinative nitrogen atom can
enhance the electron releasing ability and weaken the
electrophilic character of the center iron atom of the pre-
catalyst 3b, which is unfavorable to chain propagation
relative to chain transfer. As a result, the precatalyst 3b
displays a lower activity, and produces lower molecular
weight polymers than the precatalyst 3a. With respect
to the precatalyst 3c containing the electron-withdrawing
group, due to the strong electron-withdrawing ability of
halogen atom, the electrophilic character on the center
iron atom is enhanced remarkably, which makes the cat-
˚
˚
Fe–N(3) [3c, Fe–N(1), 2.260(9) A; Fe–N(3), 2.280(8) A.
˚
˚
3a, Fe–N(1), 2.222(4) A; Fe–N(3), 2.225(5) A]. The in-
crease of the bond length of Fe–N(1) and Fe–N(3) indi-
cates that the density of electron cloud of the metallic
center decreases, namely, the electron-withdrawing
group can indeed enhance the electrophilic character
of the center iron atom. The acceleration of chain prop-
agation restrains the chain transfer reaction, resulting in
the increase of the catalyst activity and the molecular
weight of the polymers obtained. Therefore, the precat-
alyst 3c exhibits higher activity and yields higher molec-
ular weight polyethylenes than the precatalyst 3a.
For the precatalyst 3d, not only the electronic effect
but also the steric effect should be considered. First, the
electron-withdrawing ability of halogen atom on the o-
position of the imines (3d) is stronger than that on the
p-position (3c), which enhances the electrophilic charac-
ter on center iron atom. As a result, the rate of chain
propagation increases. Second, the reduction of the steric
bulk at the o-aryl position causes the increase of the rate
of b-H elimination reaction. Thus, the precatalyst 3d
shows the higher activity and produces lower molecular
weight polymer than the precatalyst 3c (Table 3).
2.3. Ethylene polymerization with the cobalt complexes
4a–d
Since iron is a metal in group 8, and cobalt is a metal
in group 9, the electronic environments are different be-
tween their pyridinebisimine complexes. It is expected
that electronical effect of the pyridinebisimine ligands
on the preferences of the two type catalysts might also
be different. In comparison with the iron precatalysts,
the corresponding cobalt precatalysts show lower

J.-Y. Liu et al. / Journal of Organometallic Chemistry 690 (2005) 1233–1239
1237
activities and produce lower molecular weight polymers
(Table 3). Both the precatalyst 4b with an electron-
donating substituent and the precatalyst 4c with an elec-
tron-withdrawing substituent on the para-position of the
imines display higher activities and produce higher
molecular weight polymers (4b (Entry 6 in Table 3):
tane solution) was purchased from Akzo Nobel Chemi-
cal Inc. All other chemicals were commercially available
and used without further purification. The iron com-
plexes 3a–d and the cobalt complexes 4a–d were pre-
pared according to the procedure reported by Gibson
and coworkers [8].
ꢀ
activity, 3090 kg PE/molFe h, Mw, 80.3 kg/mol; and 4c
The NMR data of the polymers were obtained on a
Varian Unity-400 MHz spectrometer at 110 C with o-
C6D4Cl2 as the solvent. The NMR data of the ligands
were obtained on a Bruker 300 MHz spectrometer at
ambient temperature, CDCl3 as solvent. Mass spectra
were obtained using electron impact (EI-MS). Elemental
analyses were obtained using Carlo Erba 1106 and ST02
apparatus. The FT-IR spectra were recorded on a
Bio-Rad FTS-135 spectrophotometer. The DSC mea-
surements were performed on a Perkin–Elmer Pyris 1
differential scanning calorimeter at a rate of 10 ꢁC/min.
The molecular weights and the molecular weight distri-
butions of the polymer samples were determined at
150 ꢁC with a PL-GPC 220 type high temperature chro-
matograph equipped with three PLgel 10 lm Mixed-B
LS type columns. 1,2,4-Trichlorobenzene (TCB) was
employed as the solvent at a flow rate of 1.0 mL/min.
The calibration was made by polystyrene standard Easi-
Cal PS-1 (PL Ltd.).
ꢀ
(Entry 7 in Table 3): activity, 2730 kg PE/molFe h, Mw,
79.1 kg/mol) than the corresponding precatalyst 4a (En-
try 5 in Table 3, activity, 1860 kg PE/molFe h, 57.8 kg/
mol). It is noteworthy that the order of catalyst activities
increases (4a < 4c < 4b) accords with that of the bulk of
substituents (H < Br < i-Pr). This indicates that the hin-
dering effect of para-substituent is the main factor to
determine catalyst activities and polymer mass. Similar
to the iron precatalysts, due to the reduction of steric
bulk on the ortho-position of the imines, the precatalyst
4d, displays higher catalytic activity toward ethylene
polymerization and produces lower molecular weight
polymers than the precatlayst 4a.
3. Conclusions
The synthesis and characterization of a series of iron
and cobalt precatalysts for ethylene polymerization have
been described. For iron precatalysts, not only the steric
bulk but also the electronic effect of the substituents on
the ortho- or para-position of the imines in pyridinebisi-
mine ligands plays an important role on the catalyst activ-
ities and the properties of the resulting polyethylenes. The
electron-withdrawing group can increase the electrophilic
character of the center iron atom, which favors the chain
propagation. The acceleration of chain propagation re-
sults in the increase of catalyst activity. Contrarily, elec-
tron-donating group weakens the electrophilic character
of the center iron atom, which decreases the rate of chain
propagation relative to chain transfer, leading to the de-
crease in the molecular weight of the polyethylenes ob-
tained. The substituents in pyridinebisimine ligands also
affect considerably cobalt catalyst activity and polyethyl-
ene property. For the para-substituents, hindering effect is
more important to determine catalyst activities and poly-
mer mass than electronic effect.
4.2. Synthesis of aniline derivatives (1b–d)
4.2.1. 2,4,6-Triisopropylaniline (1b)
The mixture of fuming HNO3 (16 g, 0.25 mol),
CH3COOH (10 g), Ac2O (10 g) was dropped into a solu-
tion of 1,3,5-triisopropylbenzene 32 g (0.16 mol) and
Ac2O (30 g) at 0 ꢁC in 2 h. The precipitate was filtration
and recrystallized in methanol and dried to afford 2,4,6-
triisopropyl nitrobenzene as yellow crystal 27 g (68%).
1H NMR (CDCl3): d 6.91 (s, 2H, Ar–H), 2.85 (m, 3H,
CHMe2), 1.28 (d, 18H, CHMe2).
A 500 ml Schlenk flash containing 200 ml of degassed
ethanol was charged with above product (12.5 g, 0.05
mol), 5% Pd/C (12 g) and 150 ml NH2NH2 ÆH2O. The
reaction mixture was refluxed for 18 h. After the reac-
tion mixture was cooled to room temperature, the Pd–C
catalyst was filtrated and the solvent was removed.
The residual was washed with 20% aqueous NaOH, ex-
tracted with diethyl ether (100 ml) and dried over
Na2SO4. The diethyl ether was vaporized to give 1b as
1
4. Experimental
a colorless liquid (11 g, 100%). H NMR (CDCl3): d
6.99 (s, 2H, Ar–H), 3.60 (s, 2H, NH2), 2.95 (m, 3H,
CHMe2), 1.36 (d, 18H, CHMe2).
4.1. General procedures and materials
All manipulations of water and/or moisture sensitive
compounds were performed by means of standard high
vacuum Schlenk and cannula techniques under a N2
atmosphere. Toluene was refluxed and distilled from so-
dium/benzophenone under dry nitrogen. Modified
methylaluminoxane (MMAO) (7% aluminum in hep-
4.2.2. 4-Boromo-2,6-diisopropylaniline (1c)
Br2 (15 g, 0.094 mol) was dropped into the solution of
2,6-diisopropylaniline (18 g, 0.102 mol) and Fe (0.056 g, 1
mmol) in 2 h. The precipitate was separated by filtration,
recrystallized in ethanol. The white solid was washed with
20% aqueous NaOH, extracted with diethyl ether (100

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J.-Y. Liu et al. / Journal of Organometallic Chemistry 690 (2005) 1233–1239
mL) and dried over Na2SO4. The solvent was removed to
1
give product 1c as a colorless powder (9.8 g, 41%). H
in tetrahydrofuran (THF) (20 mL). The mixture was
stirred at room temperature for 5 h under nitrogen
atmosphere, and then a blue solid was isolated by filtra-
tion and washed several times by cold THF to yield iron
complex 3b as a blue powder 0.292 g (84.4%). EI-MS (70
eV): m/z = 691 [M+]. Anal. Calcd. for C39H55Cl2FeN3:
C, 67.63; H, 8.00; N, 6.07. Found: C, 67.32; H, 7.91;
N, 6.00%.
NMR (CDCl3): d 7.14 (s, 2H, Ar–H), 3.52 (s, 2H, NH2),
2.91 (m, 2H, CHMe2), 1.27 (d, 12H, CH-CH3).
4.2.3. 2-Boromo-4,6-diisopropylaniline (1d)
2-Bromo-4,6-diisopropylnitrobenzene was prepared
by nitration of 1,3-diisopropylbenzo using the procedure
described in above (4.2.1) as yellow liquid (yield, 90.6%),
1H NMR (CDCl3): d 7.68 (d, 1 H, Ar–H), 7.29 (s, 1 H,
Ar–H), 7.14 (d, 1 H, Ar–H), 3.49 (m, 1 H, CHMe2), 2.98
(m, 1 H, CHMe2), 1.27 (d, 12H, CH–CH3) and 1d as a
4.4.2. [2,6-Diacetylpyridinebis(2,6-diisopropylanil)]
FeCl2 (3a)
The procedure as above using ligand 2a (0.241 g, 0.5
mmol) and FeCl2 Æ4H2O (0.099 g, 0.5 mmol) gave iron
complex 3a as a blue powder 0.266 g (87.6%). EI-MS
(70 eV): m/z = 607 [M+]. Anal. Calcd. for
C33H43Cl2FeN3: C, 65.14; H, 7.12; N, 6.91. Found: C,
65.32; H, 7.04; N, 6.82%.
1
colorless liquid (11.5 g, 89.8%), H NMR (CDCl3): d
7.04 (s, 1H, Ar–H), 7.00 (d, 1H, Ar–H), 6.66 (d, 1H,
Ar–H), 3.59 (s, 2H, NH2@C), 2.86 (m, 2H, CHMe2),
1.28 (d, 12H, CHMe2).
4.3. Synthesis of ligands (2b–d)
4.4.3. [2,6-Diacetylpyridinebis(4-boromo-2,6-
diisopropylanil)]FeCl2 (3c)
4.3.1. 2,6-Diacetylpyridinebis(2,4,6-triisopropylanil)
(2b)
The procedure as above using ligand 2c (0.320 g, 0.5
mmol) and FeCl2 Æ4H2O (0.099 g, 0.5 mmol) gave iron
complex 3c as a blue powder 0.332g (86.8%). EI-MS
(70 eV): m/z = 763 [M+]. Anal. Calcd. for
C33H41Br2Cl2FeN3: C, 51.73; H, 5.39; N, 5.48. Found:
C, 51.86; H, 5.27; N, 5.37%.
A solution of 2,6-diacetylpyridine (0.6 g, 4 mmol), 1b
(1.97 g, 9 mmol), and p-toluenesulfonic acid (0.02 g) in
toluene (100 mL) was refluxed for 3 days, with azeotro-
pic removal of water using a Dean-Stark trap. Upon
cooling to room temperature, the product was precipi-
tated from ethanol. After filtration the yellow solid
was washed with cold ethanol and dried in a vacuum
oven (50 ꢁC) over night. The ligand 2b as a yellow
powder was obtained in 79% yield. The other ligands
2c and 2d were prepared by the same procedure with
4.4.4. [2,6-Diacetylpyridinebis(2-boromo-4,6-
diisopropylanil)]FeCl2 (3d)
The procedure as above using ligand 2d (0.320 g, 0.5
mmol) and FeCl2 Æ4H2O (0.099 g, 0.5 mmol) gave iron
complex 3d as a blue powder 0.335 g (87.4%). EI-MS
(70 eV): m/z = 763 [M+]. Anal. Calcd. for
C33H41Br2Cl2FeN3: C, 51.73; H, 5.39; N, 5.48. Found:
C, 51.62; H, 5.28; N, 5.45%.
1
similar yields. H NMR (CDCl3): d 8.47 (d, 2H, Py–
Hm), 7.91 (t, 1H, Py–Hp), 7.02 (s, 4H, Ar–H), 2.85
(m, 6H, CHMe2), 2.28 (s, 6H, N@CCH3), 1.20 (d, 36H,
CH–CH3).
4.3.2. 2,6-Diacetylpyridinebis (4-boromo-2,6-
diisopropylanil) (2c)
4.4.5. [2,6-Diacetylpyridinebis(2,4,6-
triisopropylanil)]CoCl2 (4b)
1
Yield: 91.3%. H NMR (CDCl3): d 8.49 (d, 2 H, Py–
To a suspension of ligand 2b (0.226 g, 0.4 mmol) were
added to a solution of CoCl2 Æ6H2O (0.095 g, 0.4 mmol)
in THF (20 mL). The mixture was stirred at room tem-
perature for 5 h under nitrogen atmosphere, and then a
brown powder was isolated by filtration and washed sev-
eral times by cold THF to yield cobalt complex 4b 0.224
g (80.4%). EI-MS (70 eV): m/z = 694 [M+]. Anal. Calcd.
for C39H55Cl2CoN3: C, 67.33; H, 7.97; N, 6.04. Found:
C, 67.17; H, 7.89; N, 5.93%.
Hm), 7.96 (t, 1 H, Py–Hp), 7.30 (s, 4H, Ar–H), 2.91
(m, 4H, CHMe2), 2.28 (s, 6H, N@CCH3), 1.18 (d, 24H,
CH–CH3).
4.3.3. 2,6-Diacetylpyridinebis(2-boromo-4,6-
diisopropylanil) (2d)
1
Yield: 90.1%. H NMR (CDCl3): d 8.43 (d, 2 H, Py–
Hm), 7.86 (t, 1H, Py–Hp), 7.25 (s, 2 H, Ar–H), 7.04 (s, 2
H, Ar–H), 2.81 (m, 4 H, CHMe2), 2.26 (s, 6H,
N@CCH3), 1.19 (d, 24 H, CH–CH3).
4.4.6. [2,6-Diacetylpyridinebis(2,6-
diisopropylanil)]CoCl2 (4a)
4.4. Synthesis of iron and cobalt complexes (3a–d, 4a–d)
The procedure as above using ligand 2a (0.192 g, 0.4
mmol) and CoCl2 Æ6H2O (0.095 g, 0.4 mmol) gave cobalt
complex 4a as a brown powder 0.207 g (84.6%). EI-MS
(70 eV): m/z = 610 [M+]. Anal. Calcd. for C33H43Cl2
CoN3: C, 64.81; H, 7.09; N, 6.87. Found: C, 65.01; H,
7.00; N, 6.80%.
4.4.1. [2,6-Diacetylpyridinebis(2,4,6-triisopropylanil)]
FeCl2 (3b)
To a suspension of ligand 2b (0.283 g, 0.5 mmol) were
added to a solution of FeCl2 Æ4H2O (0.099 g, 0.5 mmol)

J.-Y. Liu et al. / Journal of Organometallic Chemistry 690 (2005) 1233–1239
1239
4.4.7. [2,6-Diacetylpyridinebis(4-boromo-2,6-
diisopropylanil) ]CoCl2 (4c)
e-mail: deposit@ccdc.cam.ac.uk or WWW: http://
ccdc.cam.ac.uk).
The procedure as above using ligand 2c (0.256 g, 0.4
mmol) and CoCl2 Æ6H2O (0.095 g, 0.4 mmol) gave cobalt
complex 4c as a brown powder 0.261 g (84.7%). EI-MS
(70 eV): m/z = 766 [M+]. Anal. Calcd. for C33H41Br2Cl2
CoN3: C, 51.52; H, 5.37; N, 5.46. Found: C, 51.37; H,
5.23; N, 5.59%.
Acknowledgement
The authors are grateful for the financial support by
the National Natural Science Foundation of China and
SINOPEC (No. 20334030).
4.4.8. [2,6-Diacetylpyridinebis(2-boromo-4,6-
diisopropylanil)]CoCl2 (4d)
The procedure as above ligand 2d (0.256 g, 0.4 mmol)
and CoCl2 Æ6H2O (0.095 g, 0.4 mmol) gave cobalt com-
plex 4d as a brown powder 0.271 g (88.2%). EI-MS (70
eV): m/z = 766 [M+]. Anal. Calcd. for C33H41Br2Cl2
CoN3: C, 51.52; H, 5.37; N, 5.46. Found: C, 51.39; H,
5.25; N, 5.37%.
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