Fluoro-substituted 2,6-bis(imino)pyridyl iron and cobalt complexes: High-activity ethylene oligomerization catalysts

Article abstract of DOI:10.1021/om020818o

Six five-coordinate difluoro-substituted 2,6-bis(imino)pyridyl iron and cobalt complexes, [{2,6-(2,X-F₂C₆H₃N=CCH₃)₂ C₅H₃N}MCl₂] (X = 6, M = Fe (1), Co (2); X = 5, M = Fe (3), Co (4)); X = 4, M = Fe (5), Co (6)), were synthesized by reactions of the corresponding bis-(imino)pyridyl ligands with FeCl₂·4H₂O or CoCl₂ in tetrahydrofuran (THF). However, a reaction between 2,6-diacetylpyridinebis(2,6-difluoroanil) and FeCl₂·4H₂O in CH₃CN provided the ion-pair complex [Fe{2,6-(2,6-F₂C₆H₃ N=CCH₃)₂C₅H₃ N}₂]²⁺[FeCl₄]^2- (7) instead of a five-coordinate complex. The molecular structures of complexes 3 and 6 were determined by X-ray diffraction. The catalytic activities of complexes 1-7 for ethylene oligomerization were studied using modified methylaluminoxane (MMAO) as cocatalyst. At 60°C and 10 atm of ethylene pressure, the iron complexes 1, 3, and 5 show very high activities: 4.07 × 10⁷, 9.33 × 10⁷, and 11.1 × 10⁷ g/((mol of cat.) h), respectively. The oligomers formed consist mainly of dimer, trimer, and tetramer, with approximately 90% of the products being in the range of C₄-C₈. The complexes 1, 3, and 5 also exhibit high selectivity for linear α-olefins: >98% (complex 1) and >93% (complexes 3 and 5). The cobalt complexes 2, 4, and 6 and the ion-pair iron complex 7 are inactive for ethylene oligomerization.

Full text of DOI:10.1021/om020818o

Organometallics 2003, 22, 1231-1236
1231
F lu or o-Su bstitu ted 2,6-Bis(im in o)p yr id yl Ir on a n d Coba lt
Com p lexes: High -Activity Eth ylen e Oligom er iza tion
Ca ta lysts
Yaofeng Chen, Changtao Qian,* and J ie Sun
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry,
Chinese Academy of Science, 354 Fenglin Road, Shanghai 200032, China
Received October 2, 2002
Six five-coordinate difluoro-substituted 2,6-bis(imino)pyridyl iron and cobalt complexes,
[{2,6-(2,X-F2C6H3NdCCH3)2C5H3N}MCl2] (X ) 6, M ) Fe (1), Co (2); X ) 5, M ) Fe (3), Co
(4)); X ) 4, M ) Fe (5), Co (6)), were synthesized by reactions of the corresponding bis-
(imino)pyridyl ligands with FeCl2‚4H2O or CoCl2 in tetrahydrofuran (THF). However, a
reaction between 2,6-diacetylpyridinebis(2,6-difluoroanil) and FeCl2‚4H2O in CH3CN provided
the ion-pair complex [Fe{2,6-(2,6-F2C6H3NdCCH3)2C5H3N}2]2+[FeCl4]2- (7) instead of a five-
coordinate complex. The molecular structures of complexes 3 and 6 were determined by
X-ray diffraction. The catalytic activities of complexes 1-7 for ethylene oligomerization were
studied using modified methylaluminoxane (MMAO) as cocatalyst. At 60 °C and 10 atm of
ethylene pressure, the iron complexes 1, 3, and 5 show very high activities: 4.07 × 107,
9.33 × 107, and 11.1 × 107 g/((mol of cat.) h), respectively. The oligomers formed consist
mainly of dimer, trimer, and tetramer, with approximately 90% of the products being in the
range of C4-C8. The complexes 1, 3, and 5 also exhibit high selectivity for linear R-olefins:
>98% (complex 1) and >93% (complexes 3 and 5). The cobalt complexes 2, 4, and 6 and the
ion-pair iron complex 7 are inactive for ethylene oligomerization.
In tr od u ction
complexes exhibit high activity in ethylene oligomer-
ization, and the oligomers consist of >95% linear
The oligomerization of ethylene is of considerable
academic and industrial interest for the synthesis of
R-olefins. The major use of linear R-olefins is as poly-
ethylene comonomer surfactants and lubricants. Since
Ziegler’s original work on AlR3 catalysis of ethylene
oligomerization, there has been considerable sustained
interest in developing new oligomerization-active cata-
lysts. Various transition metals such as nickel, chro-
mium, titanium, zirconium, and others have been
proven to be powerful oligomerization catalysts.1-11
Recently, iron and cobalt complexes with mono-alkyl-
substituted bis(imino)pyridyl ligands were reported by
Brookhart12 and Gibson.13,14 These iron and cobalt
R-olefins.
Herein, we wish to report the synthesis of a series of
iron and cobalt complexes bearing 2,6-bis(imino)pyridyl
ligands with fluoro substituents in different positions
on the imine aryl and their reactivity in ethylene
oligomerization. The iron complexes oligomerized eth-
ylene to linear R-olefins with high activity and selectiv-
ity, and linear R-olefins obtained in these fluoro-sub-
stituted iron-complex-catalyzed ethylene oligomerizations
contain much fewer high-molecular-weight products
than those found in ethylene oligomerization catalyzed
by the mono-alkyl-substituted iron complexes. The
relation between the structures of the complexes and
their activity and selectivity is also shown.
* To whom correspondence should be addressed. E-mail: qianct@
pub.sioc.ac.cn. Fax: 0086-21-64166128.
(1) Keim, W.; Kowaldt, F.; Goddard, R.; Kruger, C. Angew. Chem.,
Int. Ed. Engl. 1978, 17, 466.
Resu lts a n d Discu ssion
Syn th esis a n d Str u ctu r es of Com p lexes. 2,6-
Diacetylpyridinebis(2,6-difluoroanil) (L1), 2,6-diacetyl-
pyridinebis(2,5-difluoroanil) (L2), and 2,6-diacetylpyr-
idinebis(2,4-difluoroanil) (L3) were synthesized in good
yield by condensation of 2,6-diacetylpyridine with the
corresponding aniline using silica-alumina catalyst
support as the catalyst and molecular sieves as the
water adsorbent15 (Scheme 1). The ligands L1, L2, and
(2) Keim, W. Angew. Chem., Int. Ed. Engl. 1990, 29, 235.
(3) Killian, C. M.; J ohnson, L. K.; Brookhart, M. Organometallics
1997, 16, 2005.
(4) Komon, Z. J . A.; Bu, X.; Bazan, G. C. J . Am. Chem. Soc. 2000,
122, 12379.
(5) Langer, A. W. J . Macromol. Sci., Chem. 1970, A4, 775.
(6) Byrikhina, N. A.; Pechatnikos, E. L. J . Appl. Chem. 1986, 59,
332.
(7) Briggs, J . R. J . Chem. Soc., Chem. Commun. 1989, 674.
(8) Ru¨ther, T.; Braussaud, N.; Cavell, K. J . Organometallics 2001,
20, 1247.
(9) Carter, A.; Cohen, S. A.; Cooley, N. A.; Murphy, A.; Scutt, J .;
Wass, D. F. Chem. Commun. 2002, 858.
(10) Al-J arallah, A. M.; Anabtawi, J . A.; Siddiqui, M. A. B.; Aitani,
A. M.; Al-Sa’doun, A. W. Catal. Today 1992, 14, 1.
(11) Rogers, J . S.; Bazan, G. C.; Sperry, C. K. J . Am. Chem. Soc.
1997, 119, 9305.
(13) Britovsek, G. P. J .; Gibson, V. C.; Kimberley, B. S.; Maddox, P.
J .; McTavish, S. J .; Solan, G. A.; White, A. J . P.; Williams, D. J . Chem.
Commun. 1998, 849.
(14) 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.
(12) Small, B. L.; Brookhart, M. J . Am. Chem. Soc. 1998, 120, 7143.
10.1021/om020818o CCC: $25.00 © 2003 American Chemical Society
Publication on Web 02/15/2003

1232 Organometallics, Vol. 22, No. 6, 2003
Chen et al.
Sch em e 1
F igu r e 1. Molecular structure of complex 3. Selected bond
lengths (Å) and angles (deg): Fe-N(2), 2.1099(19); Fe-
N(1), 2.211(2); Fe-N(3), 2.233(2); Fe-Cl(1), 2.2915(8); Fe-
Cl(2), 2.2771(8); C(1)-N(1), 1.276(3); C(7)-N(3), 1.287(3);
N(2)-Fe-Cl(1), 119.13(6); N(2)-Fe-Cl(2), 129.60(6); Cl-
(1)-Fe-Cl(2), 111.25(3); N(2)-Fe-N(1), 73.01(8); N(2)-
Fe-N(3), 73.08(8); N(1)-Fe-N(3), 146.08(8); Cl(1)-Fe-
N(1), 100.55(6); Cl(1)-Fe-N(3), 96.83(6); Cl(2)-Fe-N(1),
97.48(6); Cl(2)-Fe-N(3), 103.03(6).
C5H3N}2]2+ and [Cl3FeOCl3]2- 17
The formation of these
.
two ion-pair complexes in CH3CN is partly due to the
polarity of the organic solvent. In comparison with THF,
an organic solvent of higher polarity, CH3CN, can add
further stability to the ion-pair complex.16 Therefore, it
is better to use an organic solvent of lower polarity for
the synthesis of five-coordinate complexes with less
bulky substituents on the imino nitrogen donors.
L3 were characterized by elemental analysis, 1H NMR,
IR, and mass spectrometry.
Iron and cobalt complexes of these ligands were
synthesized by dissolving FeCl2‚4H2O or CoCl2 in tetra-
hydrofuran (THF) (Scheme 1), followed by addition of 1
equiv of the ligand. The iron and cobalt complexes
precipitated from the reaction solution. After washing
with diethyl ether, the complexes 1-6 were obtained
in good yield and high purity. The complexes were
characterized by elemental analyses and IR spectros-
copy. The elemental analysis results revealed that the
components of all complexes were in accord with the
formula MLCl2, and one solvent molecule of THF was
included in 5 and 6 and one molecule of H2O in 1 and
2. The IR spectra of the free ligands show that the Cd
N stretching frequencies appear at 1636-1642 cm-1. In
complexes 1-6, the CdN stretching vibrations shift
toward lower frequencies between 1616 and 1633 cm-1
and were greatly reduced in intensity, which indicated
the coordination interaction between the imino nitrogen
atoms and the metal ions.
The 2,5-difluoroanil-substituted complex 3 could also
be synthesized in a strongly polar solvent, CH3CN.
However, the solvent polarity is a factor in the type of
complex formed for 2,6- and 2,4-difluoroanil substitu-
tion. The reaction of 2,6-diacetylpyridinebis(2,6-difluo-
roanil) with FeCl2‚4H2O in CH3CN gave the ion-pair
complex [Fe{2,6-(2,6-F2C6H3NdCCH3)2C5H3N}2]2+[Fe-
Cl4]2- (7), and the reaction of the 2,4-substituted ligand
with FeCl2‚4H2O in CH3CN provided an unexpected ion-
pair complex composed of [Fe{2,6-(2,4-F2C6H3NdCCH3)2-
Single crystals of complexes 3 and 6 suitable for X-ray
diffraction analysis were obtained from CH3CN solution
(3) or from THF solution (6). The molecular structures
of complexes 3 and 6 are shown in Figures 1 and 2,
respectively.
Complex 3 displays an approximate C2 symmetry
about a plane containing the iron atom, the two chloro
atoms, and the pyridyl nitrogen atom. The dihedral
angles between the phenyl rings and the plane formed
by three coordinated nitrogen atoms are 76.9 and 66.3°,
respectively. The iron atom deviates by 0.034 Å from
this coordinated plane. The coordination geometry of the
central iron can be best described as distorted trigonal
bipyramidal, with the pyridyl nitrogen atom and the two
chloro atoms forming the equatorial plane. The equato-
rial angles range between 111.25(3) and 129.60(6)°, and
the two axial Fe-N bonds subtend an angle of 146.08-
(8)°. As previously observed,14,18 the Fe-N(imino) bonds
(2.211(2) and 2.233(2) Å) are longer than the Fe-
N(pyridyl) bond (2.1099(19) Å). The two imino CdN
bonds have distinctive double-bond character, with C-N
distances of 1.276(3) and 1.287(3) Å.
(16) Morassi, R.; Bertini, I.; Sacconi, L. Coord. Chem. Rev. 1973,
11, 343.
(17) Chen. Y.; Qian, C.; Sun. J . Submitted for publication in
Polyhedron.
(18) Britovsek, G. J . P.; Bruce, M. S.; Gibson, V. C.; Kimberley, B.
S.; Maddox, P. J .; McTavish, S. J .; Redshaw, C.; Solan, G. A.,
Stro¨mberg, S.; White, A. J . P.; Williams, D. J . J . Am. Chem. Soc. 1999,
121, 8728.
(15) Qian, C.; Gao, F.; Chen, Y.; Gao, L. Submitted for publication
in Tetrahedron Lett.

2,6-Bis(imino)pyridyl Iron and Cobalt Complexes
Organometallics, Vol. 22, No. 6, 2003 1233
Ta ble 1. Resu lts of Oligom er iza tion of Eth ylen e w ith Com p lexes 1-7/MMAO
complex
(amt (µmol))
amt of toluene
(mL)
Al/M
(mol/mol)
temp
(°C)
pressure
(atm)
time
(min)
yield
(g)
activity (107g/
((mol of cat.) h)
linear R-olefina
run
R
(%)
1
2
3
4
5
6
7
8
1 (0.8)
1 (1)
1 (1)
50
150
150
150
200
200
150
200
200
200
200
200
1250
2000
2000
2000
1800
1800
2000
1800
1800
1800
1800
1800
0
25
40
60
60
60
40
60
60
60
60
60
1
10
10
10
5
10
10
10
10
10
10
10
30
60
60
60
15
15
60
15
30
15
30
30
0.32
34.9
45.1
38.4
4.8
0.08
3.49
4.51
3.84
3.20
4.07
inactive
9.33
inactive
11.1
0.70
0.59
0.49
0.42
0.44
0.44
>91
>98
>98
>98
>98
>98
1 (1)
1 (0.6)
1 (0.6)
2 (1)
3 (0.6)
4 (2)
5 (0.6)
6 (2)
7 (0.6)
6.1
14.0
16.6
0.33
0.34
>94
>93
9
10
11
12
inactive
inactive
a
Determined by GC.
The molecular structure of complex 7 was also deter-
mined by X-ray diffraction. It exists as an ion pair
composed of [Fe{2,6-(2,6-F2C6H3NdCCH3)2C5H3N}2]2+
and [FeCl4]2-. The iron center of the cation is coordi-
nated by six nitrogen atoms from two ligands, while that
in the anion is coordinated by four chloro ligands.19
Unfortunately, the refinement results for the structure
are poor, with an R value above 12%. Crystallographic
data for this complex is provided in the Supporting
Information.
Oligom er iztion of Eth ylen e. The catalytic activities
of complexes 1-7 for the oligomerization of ethylene
were evaluated employing modified methylaluminoxane
(MMAO) as cocatalyst. The results are listed in Table
1. The iron complexes 1, 3, and 5 are highly active for
the oligomerization of ethylene, under the conditions
employed. At 60 °C and 10 atm of ethylene pressure,
their activities are 4.07 × 107, 9.33 × 107, and 11.1 ×
107 g/((mol of cat.) h), respectively. However, their cobalt
analogues 2, 4, and 6 are inactive for the ethylene
oligomerization. The distribution of oligomers obtained
in 1-, 3-, and 5-catalyzed ethylene oligomerization
follows Schulz-Flory rules, which can be characterized
by the constant R; here R represents the probability of
chain propagation (R ) rate of propagation/((rate of
propagation) + (rate of chain transfer)) ) (moles of
F igu r e 2. Molecular structure of complex 6 (one THF
molecule in the lattice is not included). Selected bond
lengths (Å) and angles (deg): Co-N(1), 2.045(3); Co-N(2),
2.211(3); Co-N(3), 2.225(3); Co-Cl(1), 2.2602(12); Co-Cl-
(2), 2.2533(11); C(1)-N(2), 1.273(4); C(7)-N(3), 1.283(4);
N(1)-Co-Cl(1), 111.87(9); N(1)-Co-Cl(2), 134.75(9); Cl-
(1)-Co-Cl(2), 113.28(5); N(1)-Co-N(2), 75.29(13); N(1)-
Co-N(3), 74.42(13); N(2)-Co-N(3), 149.54(13); Cl(1)-Co-
N(2), 95.88(8); Cl(1)-Co-N(3), 98.26(9); Cl(2)-Co-N(2),
102.72 (9); Cl(2)-Co-N(3), 96.24(9).
C
n+2)/(moles of Cn)).20-23 The R value can be determined
The complex 6 possesses a structure with approxi-
mate Cs symmetry about a plane containing the cobalt
atom, the two chloro atoms, and the pyridyl nitrogen
atom. One difluorophenyl ring is oriented almost per-
pendicular (77.3°) to the plane formed by the coordi-
nated nitrogen atoms, while the other difluorophenyl
ring forms a dihedral angle of 55.7° with this plane. The
cobalt atom lies on this coordinated plane. The coordi-
nation geometry at the cobalt center is also distorted
trigonal bipyramidal, with the equatorial plane formed
by the pyridyl nitrogen atom and the two chloro ligands,
and two axial Co-N bonds. The Cl(1)-Co-Cl(2) angle
is 113.28(5)°. Two N(1)-M-Cl angles are unsymmetri-
cal: one is 134.75(9)°, while the other is 111.87(9)°. The
“axial” Co-N bonds subtend an angle of 149.54(13)°.
The Co-N(pyridyl) bond (2.045(3) Å) of 6 is shorter than
the Fe-N(pyridyl) bond (2.1099(19) Å) of 3, while the
distances between the metal atom and the imino nitro-
gens in the two complexes are almost the same (2.211-
(2) and 2.233(2) Å in 3 and 2.211(3) and 2.225(3) Å in
6). The two imino CdN bonds in 6 have typical double-
bond character with CdN bond lengths of 1.283(4) and
1.273(4) Å.
by the molar ratio of C12 and C14 fractions. When the
complexes with fluoro groups in different positions of
the aryl rings are compared, it is found that the 2,5-
difluoro-substituted complex 3 and 2,4-difluoro-substi-
tuted complex 5 show much higher activity than the 2,6-
difluoro-substituted complex 1, and the activity of 5 is
slightly higher than that of 3. The R values obtained in
1-, 3- and 5-catalyzed ethylene oligomerization, 0.44
(Table 1, run 6), 0.33 (Table 1, run 8), and 0.34 (Table
1, run 10), are much lower than those found in the
ethylene oligomerization catalyzed by the mono-alkyl-
substituted iron complexes; the alkyl-substituted iron
complexes give R values of 0.70-0.85.12,14 The small size
of the fluoro group is responsible for the small R value
here. The products provided by the complexes 1, 3, and
5 consist mainly of dimer, trimer, and tetramer, with
approximately 90% of the product being in the range of
(19) Scheer, C.; Chautemps, P.; Gautier-Luneau, I.; Pierre, J .;
Serratrice, G. Polyhedron 1996, 15, 219.
(20) Schulz, G. V. Z. Phys. Chem., Abt. B 1935, 30, 379.
(21) Schulz, G. V. Z. Phys. Chem., Abt. B 1939, 43, 25.
(22) Flory, P. J . J . Am. Chem. Soc. 1940, 62, 1561.
(23) Henrici-Olive´, G.; Olive´, S. Adv. Polym. Sci. 1974, 15, 1.

1234 Organometallics, Vol. 22, No. 6, 2003
Chen et al.
C4-C8. It is also found that the 2,5-difluoro-substituted
complex 3 and 2,4-difluoro-substituted complex 5 give
very similar R values (0.33 and 0.34), while the 2,6-
difluoro-substituted complex 1 gives a higher R value
of 0.44. There are two factors which might explain the
higher R value provided by 1. One is that the fluorine
atom is slightly larger than the hydrogen atom, and the
other is that there might be an interaction between the
fluoro group in the ortho position of the aryl ring and
the â-hydrogen of the propagation chain in the active
species, suppressing the â-hydrogen transfer to the iron
center and favoring the chain propagation. In compari-
son with the 2,5-difluoro-substituted complex 3 and 2,4-
difluoro-substituted complex 5, the 2,6-difluoro-substi-
tuted complex 1 has more fluoro groups in the ortho
positions of the aryl ring; therefore, 1 gives a higher R
value. Recently, Fujita et al. found that such interac-
tions also existed in the titanium complexes bearing
fluorine-containing phenoxy-imine ligands and pre-
vented â-hydrogen elimination.24 The fluoro groups in
meta or para positions of the aryl rings have little effect
on the selectivity for linear R-olefins. The percentages
of linear R-olefins generated in the 3- and 5-catalyzed
ethylene oligomerizations are 94% and 93%, respec-
tively. These values are lower than that for the 2,6-
difluoro-substituted complex 1 (98%). The effects of
reaction temperature on 1-catalyzed ethylene oligomer-
ization were also studied (Table 1, runs 2-4). The R
value can be tuned by varying the reaction temperature.
Decreasing the temperature results in an increase of R
value, which is due to a decrease in the rate of
â-hydrogen transfer relative to the rate of propagation
when the temperature is lowered. In contrast to the high
activity of the five-coordinate complex [{2,6-(2,6-F2C6-
H3NdCCH3)2C5H3N}FeCl2] (1), the ion-pair complex
[Fe{2,6-(2,6-F2C6H3NdCCH3)2C5H3N}2]2+[FeCl4]2- (7)
is inactive for ethylene oligomerization.
Flory R values than complex 1, and the percentages of
linear R-olefins obtained in the 3- and 5-catalyzed
ethylene oligomerizations are lower than that found in
the ethylene oligomerization catalyzed by complex 1.
Exp er im en ta l Section
All manipulations of air- and/or moisture-sensitive com-
pounds were performed under an atmosphere of argon using
standard Schlenk techniques. 1H NMR was recorded on a
Varian XL 300 MHz spectrometer. Mass spectra were carried
out with a HP5989A spectrometer. IR spectra were recorded
using a Nicolet AV-360 spectrometer. Elemental analyses were
performed by the Analytical Laboratory of the Shanghai
Institute of Organic Chemistry. Oligomer products were
analyzed by Varian CP-3800 GC and Finnigan MD-800 GC-
MS. The Varian CP-3800 GC was equipped with an SPB-5
capillary column (30 m × 0.32 mm) and a flame ionization
detector. The analytical conditions used were as follows:
injector and detector temperature, 280 °C; oven temperature
program, 40 °C/6 min, 10 °C/min ramp, 250 °C/15 min. C6
olefin isomer was used to determine the percentage of linear
R-olefins. 2,4-Difluoroaniline, 2,5-difluoroaniline, and 2,6-
difluoroaniline were purchased from Acros and used as
received. A toluene solution of modified methylaluminoxane
(MMAO) was purchased from Akzo Nobel. Silica-alumina
catalyst support (grade 135) was purchased from Aldrich
Chemical Co. 2,6-Diacetylpyridine was prepared according to
a published procedure.25 Tetrahydrofuran and CH3CN were
degassed to remove oxygen prior to use. Toluene used as an
oligomerization solvent was distilled under argon from sodium-
benzophenone.
2,6-Dia cetylp yr id in ebis(2,6-d iflu or oa n il) (L1). Meth od
a . A solution of 2,6-difluoroaniline (1.61 g, 12.5 mmol), 2,6-
diacetylpyridine (0.81 g, 5 mmol), and p-toluenesulfonic acid
(0.02 g) in toluene (100 mL) was refluxed for 3 days, with
azeotropic removal of water using a Dean-Stark trap. Then
the reaction mixture was cooled to room temperature, and the
solvent was removed in vacuo. The crude product was purified
by column chromatography. L1 was obtained as a yellow
powder in 13% yield.
Con clu sion
Meth od b. A solution of 2,6-diacetylpyridine (0.41 g, 2.5
mmol), 2,6-difluoroaniline (0.77 g, 6 mmol), silica-alumina
catalyst support (0.2 g), and molecular sieves 4 Å (1.0 g) in
toluene (8 mL) was stirred at 30-40 °C for 24 h. Then the
reaction mixture was filtered, and the molecular sieves were
washed with toluene several times. The toluene of the com-
bined filtrates was removed in vacuo. Anhydrous methanol (8
mL) was added to the residue. A yellow solid was filtered off
to give L1 in 65% yield. 1H NMR (300 MHz, CDCl3): δ 8.47
(d, 2H, J ) 7.8 Hz, Py Hm); 7.93 (t, 1H, J ) 7.9 Hz, Py Hp);
7.07 (m , 4H, Ar H); 6.99 (t, 2H, J ) 7.6 Hz, Ar H); 2.46 (s,
6H, NdCMe). IR (KBr): 1636 (νCdN), 1576, 1465, 1369, 1277,
1237, 1215, 1126, 1032, 1002, 827, 789, 759 cm-1. EI mass
spectrum: m/z 385 [M+]. Anal. Calcd for C21H15N3F4: C, 65.45;
H, 3.92; N, 10.90. Found: C, 65.51; H, 4.08; N, 10.62.
Syn th esis of 2,6-Dia cetylp yr id in ebis(2,5-d iflu or oa n il)
(L2). Following the above procedure (L1 method b), 2,6-
diacetylpyridine (0.49 g, 3.0 mmol), 2,6-difluoroaniline (0.91
g, 7.0 mmol), silica-alumina catalyst support (0.2 g), and
molecular sieves 4 Å (1.5 g) were used. L2 was obtained as a
yellow powder in 70% yield. 1H NMR (300 MHz, CDCl3): δ
8.38 (d, J ) 7.9 Hz, 2H, Py Hm); 7.91 (t, J ) 7.9 Hz, 1H, Py
Hp); 7.07 (m , 2H, Ar H); 6.80 (m, 2H, Ar H); 6.69 (m, 2H, Ar
H); 2.43 (s, 6H, NdCMe). IR (KBr): 1642 (νCdN), 1617, 1578,
1492, 1367, 1323, 1268, 1245, 1196, 1142, 1098, 1080, 863, 822,
806, 760, 742, 721 cm-1. EI mass spectrum: m/z 385 [M+].
Reactions of the difluoro-substituted 2,6-bis(imino)
pyridyl ligands (2,X-F2C6H3NdCCH3)2C5H3N (X ) 6, 5,
4) with FeCl2‚4H2O or CoCl2 in THF provided the five-
coordinate 2,6-bis(imino)pyridyl iron and cobalt com-
plexes [{2,6-(2,X-F2C6H3NdCCH3)2C5H3N}MCl2] (X )
6, M ) Fe (1), Co (2); X ) 5, M ) Fe (3), Co (4); X ) 4,
M ) Fe (5), Co (6)). Complex 3 was also obtained in a
organic solvent of higher polarity, CH3CN, while a
reaction between 2,6-diacetylpyridinebis(2,6-difluoro-
anil) and FeCl2‚4H2O in CH3CN produced the ion-pair
complex [Fe{2,6-(2,6-F2C6H4NdCCH3)2C5H3N}2]2+[Fe-
Cl4]2- (7). When modified methylaluminoxane (MMAO)
is employed as cocatalyst, the iron complexes 1, 3, and
5 show very high activities for ethylene oligomerization,
while the cobalt complexes 2, 4, and 6 and the ion-pair
iron complex 7 are inactive. For the five-coordinate iron
complexes [{2,6-(2,X-F2C6H3NdCCH3)2C5H3N}FeCl2]
(X ) 6, M ) Fe (1); X ) 5, M ) Fe (3); X ) 4, M ) Fe
(5)), the activity, distribution of oligomers, and selectiv-
ity for linear R-olefins closely depend on the position of
fluorine on the imine aryl. The complexes 3 and 5 show
much higher activities and give much smaller Schulz-
(24) Mitani, M.; Mohri, J .; Yoshida, Y.; Saito, J .; Ishil, S.; Tsuru,
K.; Matsui, S.; Furuyama, R.; Nakano, T.; Tanaka, H.; Kojon, S.;
Matsugi, T.; Kashiwa, N.; Fujita, T. J . Am. Chem. Soc. 2002, 124, 3327.
(25) Alyes, E. C.; Merrel, P. H. Synth. React. Inorg. Met.-Org. Chem.
1974, 4, 53510.

2,6-Bis(imino)pyridyl Iron and Cobalt Complexes
Organometallics, Vol. 22, No. 6, 2003 1235
Anal. Calcd for C21H15N3F4: C, 65.45; H, 3.92; N, 10.90.
Found: C, 65.51; H, 4.12; N, 10.44.
Syn th esis of [F e(2,6-d ia cetylp yr id in ebis(2,6-d iflu or o-
a n il))2]2+[F eCl4]2- (7). 2,6-Diacetylpyridinebis(2,6-difluoro-
anil) (22 mg, 0.056 mmol) was added to a solution of FeCl2‚
4H2O (11 mg, 0.056 mmol) in CH3CN (5 mL) at room
temperature with rapid stirring. After the mixture was stirred
at room temperature for 2 h, the reaction volume was reduced
to about 3 mL and the mixture left to stand at 0 °C for several
days. Dark blue crystals of the product formed and were
separated from the solution (18 mg, 63%). Anal. Calcd for
Syn th esis of 2,6-Dia cetylp yr id in ebis(2,4-d iflu or oa n il)
(L3). Following the above procedure (L1 method b), L3 was
obtained as a yellow powder in 72% yield. 1H NMR (300 MHz,
CDCl3): δ 8.38 (d, J ) 7.9 Hz, 2H, Py Hm); 7.90 (t, J ) 7.9 Hz,
1H, Py Hp); 6.93 (m, 6H, Ar H); 2.41 (s, 6H, NdCMe). IR
(KBr): 1639 (νCdN), 1596, 1575, 1497, 1426, 1366, 1322, 1261,
1199, 1140, 1094, 1080, 960, 848, 825, 778, 726 cm-1. EI mass
spectrum: m/z 385 [M+]. Anal. Calcd for C21H15N3F4: C, 65.45;
H, 3.92; N, 10.90. Found: C, 65.83; H, 4.14; N, 10.57.
C
42H30N6F8Fe2Cl4: C, 49.26; H, 2.95; N, 8.21. Found: C, 48.58;
H, 3.31, N, 7.86.
Gen er a l P r oced u r e for Eth ylen e Oligom er iza tion . (a )
High -P r essu r e Oligom er iza tion . A mechanically stirred 500
mL stainless steel reactor was heated under vacuum for at
least 2 h at >85 °C and then cooled to the reaction temperature
under an ethylene atmosphere. A 150 mL portion of toluene
and 0.48 mmol of MMAO were charged into the reactor. The
reactor was sealed, and ethylene was added (5 atm). The
solution was stirred for about 10 min, during which time the
desired reaction temperature was established. The ethylene
pressure was then released, 10 mL of catalyst solution
prepared by combination of 0.6 µmol of the complex in toluene
and 0.6 mmol of MMAO was injected into the reactor, and then
40 mL of toluene was added. The reactor was then sealed and
pressurized with ethylene to 10 atm. The reaction mixture was
stirred under constant ethylene pressure for 15 min, after
which time the reactor was resealed and the catalyst quenched
with dilute hydrochloric acid. The organic layer was separated
and dried over anhydrous Na2SO4. An aliquot of this solution
was analyzed by GC. The integrated areas of the C12 and C14
oligomers were used to calculate the Schulz-Flory R constant.
The standard solution containing precise known masses of
1-hexene, 1-octene, 1-decene, and 1-dodecene in toluene was
prepared and chromatographed, and the mass percents of
these olefins in this solution should be prepared close to those
in the sample. The masses of C6, C8, C10, and C12 oligomers
produced can be calculated by using the formula
Syn th esis of[2,6-d ia cetylp yr id in ebis(2,6-d iflu or oa n il)]-
F eCl2‚H2O (1). Ligand L1 (63 mg, 0.16 mmol) was added to a
solution of FeCl2‚4H2O (27 mg, 0.14 mmol) in THF (8 mL) at
room temperature with rapid stirring. The solution turned
deep blue immidiately. The dark blue product precipitated
from the solution after several minutes. After it was stirred
at room temperature for 12 h, the reaction volume was reduced
to about 4 mL. The reaction mixture was allowed to stand at
room temperature for several hours, and then the supernatant
liquid was removed. The product was washed with 4 × 5 mL
of Et2O and dried in vacuo. The desired product (62 mg) was
obtained as a dark blue powder in 89% yield. IR (KBr): 3422,
1616 (νCdN), 1587, 1464, 1374, 1260, 1240, 1006, 784, 752 cm-1
.
Anal. Calcd for C21H15N3F4FeCl2‚H2O: C, 47.58; H, 3.23; N,
7.92. Found: C, 48.42; H, 3.36; N, 7.66.
Syn th esis of[2,6-d ia cetylp yr id in ebis(2,6-d iflu or oa n il)]-
CoCl2‚H2O (2). The procedure as above, using ligand L1 (53
mg, 0.12 mmol) and CoCl2 (13 mg, 0.10 mmol), gave 2 as a
golden brown powder (42 mg, 81%). IR (KBr): 3457, 1619 (νCd
N), 1589, 1471, 1376, 1283, 1262, 1241, 1229, 1006, 783, 751
cm-1. Anal. Calcd for C21H15N3F4CoCl2‚H2O: C, 47.30; H, 3.21;
N, 7.88. Found: C, 47.27; H, 3.16; N, 7.68.
Syn th esis of[2,6-d ia cetylp yr id in ebis(2,5-d iflu or oa n il)]-
F eCl2 (3). Meth od a . The procedure as above, using ligand
L2 (92 mg, 0.26 mmol) and FeCl2‚4H2O (51 mg, 0.26 mmol),
gave 3 as a blue powder (100 mg, 76%). IR (KBr): 1629 (νCd
N), 1617, 1595, 1496, 1377, 1265, 1250, 1212, 1194, 1158, 813,
765 cm-1. Anal. Calcd for C21H15N3F4FeCl2: C, 49.25; H, 2.95;
N, 8.20. Found: C, 49.15; H, 3.18, N, 8.16.
W ′C VC V ′TolWTol
n
n
WC
)
n
V ′C VTolW ′Tol
n
Meth od b. Ligand L2 (68 mg, 0.17 mmol) was added to a
solution of FeCl2‚4H2O (35 mg, 0.17 mmol) in CH3CN (7 mL)
at room temperature with rapid stirring. The solution turned
deep blue immidiately. After the mixture was stirred at room
temperature for 2 h, the reaction volume was reduced to about
4 mL and left to stand at 0 °C for several days. Dark blue
crystals of the product 3 formed and were separated from the
solution (69 mg, 77%). Anal. Calcd for C21H15N3F4FeCl2: C,
49.25; H, 2.95; N, 8.20. Found: C, 49.19; H, 3.10; N, 8.23.
where W ′C ) mass of Cn in the standard solution, W ′Tol
)
n
mass of toluene in the standard solution, V ′C ) integrated
n
area of Cn in the standard solution, V ′Tol ) integrated area of
toluene in the standard solution, VC ) integrated area of Cn
n
in the sample, VTol ) integrated area of toluene in the sample,
and WTol ) mass of toluene used as the solvent in the
oligomerization. The mass of C4 was calculated by the mass
of C6 and the Schulz-Flory R constant:
Syn th esis of[2,6-d ia cetylp yr id in ebis(2,5-d iflu or oa n il)]-
CoCl2 (4). The procedure is similar to that of complex 1, using
ligand L2 (96 mg, 0.25 mmol) and CoCl2 (32 mg, 0.25 mmol)
gave 4 as a yellow-green powder (98 mg, 77%). IR (KBr): 1633
(νCdN), 1617, 1595, 1496, 1377, 1262, 1251, 1212, 1194, 1158,
813, 765 cm-1. Anal. Calcd for C21H15N3F4CoCl2: C, 48.96; H,
2.93; N, 8.16. Found: C, 48.87; H, 3.18; N, 8.06.
WC (Mw of C4)
6
WC
)
4
(Mw of C6)R
The masses of C14 and C16 oligomers were obtained by
comparing their integrated areas with that of the C12 oligomer,
and the mass of oligomers in the C18-C40 range was calculated
by the formula
Syn th esis of[2,6-d ia cetylp yr id in ebis(2,4-d iflu or oa n il)]-
F eCl2‚THF (5). The procedure as above, using ligand L3 (103
mg, 0.27 mmol) and FeCl2‚4H2O (53 mg, 0.27 mmol), gave 5
as a dark blue powder (108 mg, 69%). IR (KBr): 1619 (νCdN),
1587, 1502, 1429, 1374, 1266, 1219, 1145, 1093, 966, 875, 806,
715 cm-1. Anal. Calcd for C21H15N3F4FeCl2‚THF: C, 51.40; H,
3.97; N, 7.19. Found: C, 51.36; H, 4.27; N, 7.16.
WC (Mw of Cn)Rn-16/2
16
WC
)
n
Mw of C16
The total product mass was obtained by adding the mass of
oligomers in the C4-C40 range; therefore, the activity numbers
were generated.
(b) Oligom er iza tion a t 1 a tm P r essu r e. A 100 mL flame-
dried Schlenk flask equipped with a stirrer bar was placed in
an ice-water bath and purged with ethylene (1 atm), followed
by charging with 40 mL of toluene and 1 mmol of MMAO. The
required temperature was ensured by stirring the mixture for
Syn th esis of[2,6-d ia cetylp yr id in ebis(2,4-d iflu or oa n il)]-
CoCl2‚THF (6). The procedure as above, using ligand L3 (96
mg, 0.25 mmol) and CoCl2 (32 mg, 0.25 mmol), gave 6 as a
brown powder (107 mg, 73%). IR (KBr): 1627 (νCdN), 1587,
1429, 1374, 1265, 1220, 1144, 1092, 966, 877, 808, 715 cm-1
.
Anal. Calcd for C21H15N3F4CoCl2‚THF: C, 51.12; H, 3.95; N,
7.15. Found: C, 50.99; H, 4.09; N, 7.10.

1236 Organometallics, Vol. 22, No. 6, 2003
Chen et al.
Ta ble 2. Cr ysta llogr a p h ic Da ta a n d Refin em en t
for Com p lexes 3 a n d 6
pressure for 0.5 h, the oligomerization was stopped by the
injection of diluted hydrochloric acid. The oligomers were
collected and worked up as described as in the oligomerization
under high pressure.
3
6
formula
fw
C21H15N3F4FeCl2 C21H15N3F2CoCl2‚C4H8O
X-r a y Str u ctu r e Deter m in a tion . Data collections for
complexes 3 and 6 were performed at 20 °C on a Bruker
SMART diffractometer with graphite-monochromated Mo KR
radiation (λ ) 0.710 73 Å). The SMART program package was
used to determine the unit-cell parameters. A SADABS
absorption correction was applied. The structures were solved
by direct methods and refined on F2 by full-matrix least-
squares techniques with anisotropic thermal parameters for
non-hydrogen atoms. Hydrogen atoms were placed at calcu-
lated positions and were included in the structure calculation
without further refinement of the parameters. All calculations
were carried out using the SHELXS-97 program. Crystal data
and processing parameters for complexes 3 and 6 are sum-
marized in Table 2.
512.11
587.29
color
dark-blue
monoclinic
P21/c
10.6387(8)
13.0812(10)
16.3810(12)
106.770(2)
2182.7(3)
4
brown
monoclinic
P21/n
12.7337(11)
16.1664(15)
12.8804(11)
101.808(2)
2595.4(4)
4
cryst syst
space group
a, Å
b, Å
c, Å
â, deg
V, Å3
Z
D
calcd, g/cm3
1.558
1.503
F(000)
1032
0.983
2.00-28.32
1196
0.919
2.05-28.29
15 696
µ(Mo KR), mm-1
θ range, deg
no. of rflns collected 13 195
no. of unique rflns
no. of obsd rflns
(I > 2σ(I))
5119
2074
6066
1997
Ack n ow led gm en t. We are grateful to the Chinese
Academy of Science and the Natural Science Foundation
of China for financial support.
no. of params
goodness of fit
final R, Rw
340
0.609
0.0378, 0.0487
0.419, -0.293
327
0.678
0.0458, 0.0735
0.644, -0.365
∆Fmax,min/e Å-3
Su p p or tin g In for m a tion Ava ila ble: Tables giving X-ray
crystallographic data for 3, 6, and 7. This material is available
free of charge via the Internet at http://pubs.acs.org.
about 20 min in the water bath. A 0.8 µmol amount of
precatalyst in 10 mL of toluene was injected via syringe. After
the reaction mixture was stirred under 1 atm of ethylene
OM020818O