Iron and cobalt complexes of 2,3,7,8-tetrahydroacridine-4,5(1 H,6 H)-diimine sterically modulated by substituted aryl rings for the selective oligomerization to polymerization of ethylene

Article abstract of DOI:10.1021/om2000629

A new series of Fe(II) and Co(II) complexes of sterically modulated 2,3,7,8-tetrahydroacridine-4,5(1H,6H)-diimine by substituted aryl rings are synthesized. The complex synthesis is achieved through a one-pot methodology by reacting one equivalent of 2,3,

Full text of DOI:10.1021/om2000629

ARTICLE
pubs.acs.org/Organometallics
Iron and Cobalt Complexes of 2,3,7,8-Tetrahydroacridine-4,-
5(1H,6H)-diimine Sterically Modulated by Substituted Aryl Rings for
the Selective Oligomerization to Polymerization of Ethylene
Vinu Krishnan Appukuttan,† Yinshan Liu,† Bong Chul Son,† Chang-Sik Ha,† Hongsuk Suh,‡ and Il Kim*,†
†The WCU Center for Synthetic Polymer Bioconjugate Hybrid Materials, Department of Polymer Science and Engineering,
Pusan National University, Busan 609-735, Korea
‡Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Pusan 609-735, Korea
S Supporting Information
b
ABSTRACT: A new series of Fe(II) and Co(II) complexes of
sterically modulated 2,3,7,8-tetrahydroacridine-4,5(1H,6H)-dii-
mine by substituted aryl rings are synthesized. The complex
synthesis is achieved through a one-pot methodology by reacting
one equivalent of 2,3,7,8-tetrahydroacridine-4,5(1H,6H)-dione
with two equivalents of required aniline derivatives together with
Fe or Co salt in boiling acetic acid. The single-crystal X-ray analyses
of Fe and Co complexes bearing a 2,6-diisopropyl-substituted
ligand, (N,N0E,N,N0E)-N,N0-(2,3,7,8-tetrahydroacridine-4,5-
(1H,6H)-diylidene)bis(2,6-diisopropylaniline), show a distorted
trigonal-bipyramidal geometry for the metal center, a deviation from square-pyramidal geometry due to the opening up of the
coordination sphere originating from structural rigidity of the carbonyl carbon atom achieved through cyclization. All the complexes
show high activity toward ethylene activation when treated with methylaluminoxane as a cocatalyst. The ortho substituents of the
aryl rings and the type of metal have a significant effect on ethylene activation and specifically on product distribution. The Fe
complex with a 2,6-diisopropyl-substituted bis(imino)tetrahydroacridyl ligand produced polyethylene of moderate molecular
weight (18 000). On changing the ortho substitution of the ligand from 2,6-diisopropyl to 2,6-dimethyl, the Co complexes produce
polyethylene waxes and oligomers of predominantly R-olefins simultaneously, obeying SchulzꢀFlory distribution. The Co
complexes bearing ligands with less sterically hindered substituents at the ortho position behave exclusively as dimerization catalysts.
’ INTRODUCTION
complexes.5ꢀ8,14ꢀ16 However, only few reports showed alter-
native models for Fe and Co catalysts with catalytic activity from
moderate to high.17ꢀ19
The market for polyolefins and R-olefins is in the tens of
billions of dollars, both indicating their importance and stimulat-
ing interest in academic and industrial research in this field.
Polyolefins, with an annual market of over 110 million tons, are
half the volume of all synthesized plastics.1 R-Olefins have been
extensively used as substrates for preparing detergents, lubri-
cants, plasticizers, and oil field chemicals or as monomers for
copolymers, etc. Originally linear R-olefins (LAOs) were pro-
duced by the Ziegler (Alfen) process, which consists in a
controlled oligomerization of ethylene in the presence of AlEt3
at 90ꢀ120 °C at a monomer pressure of 100 bar.2ꢀ4 Driven by
academic and industrial considerations of the important process
of ethylene oligomerization for R-olefins, efficient catalysts and
catalytic processes are pursued for high catalytic activity and
selectivity for the formation of linear R-olefins. Over the
past decade, progress has been made in ethylene reactivity
(polymerization and oligomerization) by late transition metal
complex catalysts.5ꢀ9 The Fe and Co systems derived from 2,6-
bis(imino) pyridines, initially discovered by the groups of
Brookhart and Gibson individually, are well known.10ꢀ14 There
are many works on modifying 2,6-bis(imino)pyridyl metal
Gibson replaced the pyridine ring by a pryimidine one,
resulting in a somewhat less active catalyst.20 Bisimines derived
from hydrazines or 1-amino pyrroles instead of anilines were also
found to be efficient in ethylene activation.21 Apart from the
works on derivatizations of 2,6-bis(imino)pyridyl metal com-
plexes, there have been a lot of reports based on alternative
models of catalysts for ethylene reactivity through designing
novel organic compounds as ligands with tridentate N∧N∧N
coordination features such as 2-imino-1,10-phenanthrolines,22
2-(benzimidazol-2-yl)-1,10-phenanthrolines,23 2-oxazoline-1,10-
phenanthrolines,24 2-quinoxalinyl-6-iminopyridines,25 2-
(benzimidazolyl)-6-iminopyridines,26 N-((pyridin-2-yl)methy-
lene)quinolin-8-amine,27
2-methyl-2,4-bis(6-iminopyridin-
2-yl)-1H-1,5-benzodiazepines,28 N-picolylethylenediamines,29
6-(organyl)-2-(imino)pyridines,30 2-(1H-2-benzimidazolyl)-6-
(1-(arylimino)ethyl)pyridines,31 and 2,8-bis(1-aryliminoethyl)-
Received: January 22, 2011
Published: March 24, 2011
r
2011 American Chemical Society
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Scheme 1. Synthesis of Fe and Co Complexes
quinolines.32 In general, Fe and Co complexes not only
show high catalytic activities but also produce oligomers
and polyethylenes (PEs) of high linearity with terminal vinyl
groups.31
derivatives afford high activities, while the methoxy derivative
was inactive.
In this context, in the present work, we are attempting to
modify the central pyridine donor by replacing that with a
2,3,7,8-tetrahydroacridine-4,5(1H,6H)-diimine by using a
2,3,7,8-tetrahydroacridine-4,5(1H,6H)-dione as a carbonyl
source for the bisimine ligand. The dione compound is
combined with two equivalents of required aniline deriva-
tives and then with Fe or Co salt in a one-pot methodology to
give a series of coordination complexes. The linking of the
aldimine group to the pyridyl ring through cyclization could
bring structural rigidity to the bisimino ligand framework,
reducing the flexibility along the imine bond connecting the
pyridyl and aryl rings. Under this circumstance, in order to
investigate the effect of number, nature, and position of the
substituents on the aryl rings toward the catalytic activity,
complexes with different N-aryl substitution are employed.
All the complexes are characterized for their mass and
elemental composition, and the molecular structure was
elucidated by single-crystal X-ray analysis for a few com-
plexes. The complexes are extensively studied for their
ethylene polymerization/oligomerization activity with com-
plete characterization of polymers and oligomers.
Initial studies involving 2,6-bis(imino)pyridines of Fe and Co
have shown that ketimines are relatively more active than
aldimines.13 Also these catalysts have shown a significant stereo-
electronic effect of N-aryl substituents toward ethylene activation
especially in determining the polymer microstructure.16 The 2,6-
diisoproyl-substituted complexes produce strictly linear poly-
ethylene polymer with high molecular weight (MW), and the
MW decreases as the ortho substituents are changed to methyl
through ethyl.10 It was quite interesting to observe that the
introduction of only one ortho substituent to iron-based com-
plexes resulted in the production of linear alpha olefins over
polymer.12 Simultaneous formation of both polyethylene and
linear alpha olefins obeying a SchulzꢀFlory distribution resulted
when a C1-symmetric 2,6-bis(arylimino)pyridyl iron dichloride
precursor was employed.33 Iron complexes of halogen-substi-
tuted 2,6-bis(imino)pyridyl ligands were also found to produce
polymer with simultaneous production of linear alpha olefins,
while their cobalt analogues were totally inactive toward
ethylene.11 Beyond such modifications to the ligand aryl substit-
uents and central donor moiety, there have been only very few
attempts to verify the effect of changes to the substituents at the
imine carbon atoms. Esteruelas reported a chromium-based
ethylene polymerization catalyst having a phenyl group as back-
bone substituent.34 Smit and co-workers have shown the dra-
matic effect of ether and thioether backbone substituents for the
polymerization of ethylene.35 The bulky phenoxides or thioether
’ RESULTS AND DISCUSSION
Synthesis and Structure of Complexes. The procedures for
the synthesis of complexes are summarized in Scheme 1. The
dione compound 2 derived from a 2,3:5,6-dicycloalkeno pyridine
moiety was synthesized according to a previous report.36
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Figure 1. ORTEP representation of complex 5with 50% thermal ellipsoids.
Hydrogen atoms are omitted for clarity. Selected bond lengths [Å] and
angles[deg]:Fe(1)ꢀN(1) 2.087(4), Fe(1)ꢀN(2) 2.313(4), Fe(1)ꢀN(3)
2.320(4), Fe(1)ꢀCl(1) 2.2851(13), Fe(1)ꢀCl(2) 2.2429(13), C(2)ꢀC-
(3) 1.516(6), C(3)-C4) 1.481(9), C(4)ꢀC(5) 1.532(9), C(12)ꢀC(11)
1.518(6), C(11)ꢀC(10) 1.376(14), C(10)ꢀC(9) 1.406(13); N(1)ꢀFe-
(1)ꢀN(2) 73.22(13), N(1)ꢀFe(1)ꢀN(3) 73.01(13), N(2)ꢀFe(1)ꢀ
N(3) 145.78(13), N(1)ꢀFe(1)ꢀCl(1) 111.32(10), N(2)ꢀFe(1)ꢀ
Cl(1) 99.83(10), N(3)ꢀFe(1)ꢀCl(1) 97.34(9), N(1)ꢀFe(1)ꢀCl(2)
139.20(10), N(2)ꢀFe(1)ꢀCl(2) 100.92(10), N(3)ꢀFe(1)ꢀCl(2)
100.9(10), C(2)ꢀC(3)ꢀC(4) 112.8(5), C(3)ꢀC(4)ꢀC(5) 112.4(6),
C(12)ꢀC(11)ꢀC(10) 115.0(7), C(11)ꢀC(10)ꢀC(9) 131.2(11).
Figure 2. ORTEP representation of complex 10 with 50% thermal
ellipsoids. Hydrogen atoms are omitted for clarity. Selected bond lengths
[Å] and angles [deg]: Co(1)ꢀN(1) 2.037(4), Co(1)ꢀN(2) 2.301(4),
Co(1)ꢀCl(1) 2.2383(14), C(2)ꢀC(3) 1.490(6), C(3)ꢀC4) 1.499(7),
C(4)ꢀC(5) 1.492(8); N(1)ꢀCo(1)ꢀN(2) 75.08(9), N(2)ꢀCo(1)ꢀN-
(2A) 150.16(18), N(1)ꢀCo(1)ꢀCl(1) 121.10(5), N(2)ꢀCo(1)ꢀCl(1)
97.59(10), C(2)ꢀC(3)ꢀC(4) 113.0(5), C(3)ꢀC(4)ꢀC(5) 113.2(6).
orientation, C(4) is positioned away from the pyridyl plane. In
the case of complex 5, there is single-bond character in one ring
containing C(2), C(3), C(4), and C(5), with distances in the
range 1.481(9)ꢀ1.532(9) Å and angles 112.4(6)ꢀ112.8°, while
for the other ring the C(11)ꢀC(10) bond shows a double-bond
character (1.376(14) Å) and C(10)ꢀC(9) a partial double-bond
character (1.406(13) Å), making angles of 115.0(7)° and
131.2(11)° between them. This might be an aberration rather
than a structural feature originating from the estimation of
position of the atoms due to the low quality of the microcrystal.
The existence of a nonsymmetric atomic orientation causes
complex 5 to have a C1 point group.
For both complexes, the MꢀN (acridyl) bond length is signifi-
cantly shorter (2.087(4) Å for 5 and 2.037(4) Å for 10) than the
MꢀN (imino) bond (varying from 2.301(4) to 2.320(4) Å).
Comparing the complexes 5 and 10 with the well-known bisimino-
pyridyl Fe and Co complexes, where the MꢀN (pyridyl) bond is
2.088(4) Å for Fe and 2.051(3) Å for Co, it could be seen that the
metal is more closely placed to the acridyl N atom in the present
system. On the other hand for the present complexes the MꢀN
(imino) bond was found to be significantly longer than the
bisiminopyridyl complexes, where the distances between the two
MꢀN (imino) bonds for Fe are 2.238 and 2.50 Å, respectively, and
that for Co is 2.11 Å each.10 This variation is probably due to linking
the aldimino group to the pyridyl ring through cyclization. In
addition the distance (4.483 Å) between the two imino N atoms
of the Co complex 10 is longer than that (4.173 Å) of the Co
complex bearing 2,6-bis(imino)pyridyl ligands.13 This elongation
slightly opens up the coordination sphere and thus gives a space
incorporating the central metal atom within the N3 plane. In fact the
cobalt atom lies within the N3 plane, while iron is deviated by a
distance of 0.16 Å. Thus this structural variation of the ligand gives a
distorted trigonal-bipyramidal geometry to the metal center, which is
comparable to a square-pyramidal geometry of analogous Fe and Co
complexes of 2,6-bis(imino)pyridine. The double-bond nature of the
imino bond is kept intact for both complexes (ranging from 1.268(6)
to 1.282(5) Å). The chloride atoms, Cl(1) and Cl(2), are bonded to
In order to avoid a complex purification procedure and to
maximize the yield, a one-pot methodology is employed for the
synthesis of complexes based on previous reports.27,37,38 The reac-
tion is performed in boiling acetic acid for 8 h by taking stoichio-
metric amounts of diketone, corresponding aniline, and metal
chlorides. Along with the condensation of the diketone and the
amines, the central metal atom is incorporated to the ligands to give
the desired complexes. The complexes were precipitated in diethyl
ether and filtered, dissolved in CH2Cl2, reprecipitated in diethyl
ether, separated, and dried to get pure complexes. All the complexes
3ꢀ15 were synthesized in good yields and were air-stable. The
isopropyl derivatives of Fe and Co complexes 5 and 10 were
characterized by single-crystal X-ray crystallography.
Crystals of complexes 5 and 10 suitable for X-ray crystal-
lography were grown by slow diffusion of diethyl ether into a
solution of complexes in CH2Cl2. The molecular structures and
selected bond lengths and angles of the isopropyl derivatives of
iron (5) and cobalt complexes (10) are shown in Figures 1 and 2,
respectively. The metal center of both complexes is isostructural,
having distorted trigonal-bipyramidal geometry. The basal plane
is formed by the acridyl N atom and the two chloride atoms,
while the two imino N atoms occupy the apical position. The
essential difference between the two complexes arises from the
variation of the structural orientation of the ligand backbone.
The cobalt complex, 10, possesses a C2 axis passing through
C(7)ꢀN(1)ꢀCo(1) and a inversion plane (iσh) passing through
C(7)ꢀN(1)ꢀCo(1), making a symmetrical spatial orientation
of the atoms along the plane with identical bond lengths and
angles. Thus the two symmetry elements give 10 a near C2h point
group. The two cyclic rings on the pyridine show a single-bond
character with bond distances ranging from 1.490(6) to 1.499(7)
Å and bond angles in the range 113.0(5)ꢀ113.2(6)°. Since the
sp3-hybridized C(4) is bonded to two adjacent sp3 carbon
atoms (C(2) and C(5)), in order to attain a near-tetrahedral
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the Fe atom by a distance of 2.2852(13) and 2.2429(13) Å,
respectively, for 5, and those bonded with the Co atom are at a
equidistance of 2.2383(14) Å for 10. The phenyl rings in both
complexes essentially lie orthogonal to the plane of the backbone
with dihedral angles ranging from 76° to 87°.
Effect of Catalyst Structure on Ethylene Oligomerization/
Polymerization. All the catalysts were examined for their
ethylene oligomerization and polymerization capability em-
ploying MAO as a cocatalyst and toluene as a solvent under
semibatch conditions. The effect of catalyst structure on
oligomerization/polymerization behavior has been investi-
gated by conducting the reactions with variable parameters
such as cocatalyst concentration and temperature.
The polymerization rate (Rp) of ethylene under constant
pressure using Fe (3ꢀ6) and Co (8ꢀ11) complexes combined
with MAO ([Al]/[M] = 250; M = Fe or Co) changes markedly
with time, as illustrated by the rate curves in Figure 3. The kinetic
curves obtained with the Fe complexes show an induction or
buildup period probably due to low solubility of the complexes,
where the Rp increases to a maximum followed by a decay period
during which the rate decreases gradually to the stationary state.
In the case of kinetic curves obtained by the Co complexes there
is almost no induction period, followed by a rapid decay. The
kinetic curves show that it takes longer to form active sites from
the reaction of Fe complexes with MAO in the presence of
ethylene monomer than the corresponding Co complex systems.
The polymerization results are also summarized in Table 1.
Note that the type of metal center has a significant effect not only
on the kinetic curve but also on the catalyst activity. Although the
Co catalysts show a higher maximum rate of polymerization than
the corresponding Fe analogues, they show a lower average rate
of polymerization than the corresponding Fe analogues since the
Co catalysts deactivate very rapidly. The results also show that
the polymerization activity is strongly influenced by 2,6-substit-
uents on the N-aryl ring as observed in the other catalyst
system.13 The less bulky methyl-substituted complexes are more
active than the bulkier isopropyl one, and the activity of ethyl-
substituted complexes lies in between (Table 1). This observa-
tion is the direct consequence of the effect of the size of the ortho
substituents toward the insertion of monomer; bulkier substitu-
ents offer maximum resistance to incoming monomers to the
active metal center. In order to determine the electronic effect of
the substituents, we replaced the 4-position of the N-aryl ring by
keeping the 2,6-substituents as methyl to generate the Fe
complex 6 and the Co complex 11. To our surprise both complexes
showed relatively lower productivities in ethylene activation
(Table 1, entries 4, 6) than those observed for 2,6-bis(imino)-
tetrahydroacridine catalysts, 3 and 8, demonstrating that the
electron-donating methyl groups on the 4-position of the N-aryl
ring probably have a negative effect on the catalytic activity.
The steric bulk offered by ortho imino-aryl sustituents has a
significant influence on the polymer properties and has been a
subject of many investigations. Bulky ortho substituents usually
result in high molecular weight polymers, and the MW usually
depends on the size of those substituents. Brookhart and co-
workers demonstrated that 2,6-isopropyl-substituted complex
produced PE with the highest MW, and as the 2,6-substituent
was changed to ethyl and methyl, the MW also decreased
accordingly.13 The introduction of only one ortho substituent
on the aryl ring resulted in oligomerization producing R-olefins.
For the Cs and C1 symmetric bis(imino)pyridyl complexes of Fe
and Co containing one alkyl-imine and one aryl-imine, Bianchini
and co-workers found the formation of ethylene oligomers with
high selectivity for R-olefins.15 The significant influence of the
slight variation of the bulkiness of the 2,6-arylimino substituent
on the product microstructure was established by Qian and co-
workers utilizing halogens as ortho aryl groups.39 The Fe complex
Figure 3. Ethylene polymerization rate profiles obtained by different
complexes. Polymerization conditions: catalyst = 2.5 μmol, [Al]/[M] =
250 (Mt = Fe or Co), PC2H4 = 1.3 bar, toluene = 80 mL, T = 30 °C, and
time = 30 min.
Table 1. Results of Ethylene Polymerization with Various Fe and Co Catalystsa
entry
cat.
Rp,max ꢁ 10ꢀ6b
Rp,av ꢁ 10ꢀ6b
Mnc (g/mol)
PDIc
oligomerd (%)
Ke
Tmf (°C)
1
2
3
4
5
6
7
8
3
5.60
3.08
2.06
4.11
6.42
5.59
3.36
5.15
3.71
2.17
1.29
2.92
2.98
1.33
0.66
2.54
7700
8300
18 000
7200
640g
3.6
4.6
7.2
6.4
1.4
1.6
6.6
1.5
131.9
136.9
138.2
132.1
4
5
6
8
63.6
63.5
0.88
0.88
9
1000
5200
620g
120.1
137.8
10
11
a Polymerization conditions: catalyst = 2.5 μmol, cocatalyst = MAO, [Al]/[M] = 250, PC2H4 = 1.3 bar, toluene = 80 mL, and time = 30 min. b The
maximum rate of polymerization (Rp,max) and the average rate of polymerization over 30 min (Rp,av) in (g-product) (mol-metal)ꢀ1 hꢀ1 barꢀ1
.
3
3
3
c Number average molecular weight (Mn) and polydispersity index (PDI) determined by GPC. d From methanol-soluble fraction. SchulzꢀFlory
e
distribution constant, K = (moles of C14)/(moles of C12). f Determined by DSC. g From methanol-insoluble portion.
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Table 2. Results of Ethylene Polymerization with Complex 5 at Different Reaction Conditionsa
c
entry
catalyst (μmol)
[Al]/[Fe]
Tp (°C)
yield (g)
Rp,av ꢁ 10ꢀ6 b
Mnc (g/mol)
Mw/Mn
Tmd (°C)
1
2
3
4
5
6
7
8
9
2.5
2.5
2.5
2.5
2.5
2.5
5
50
100
30
30
30
30
30
30
30
50
70
0.34
0.52
2.52
2.05
1.79
1.20
7.15
5.40
4.94
0.21
0.32
1.55
1.26
1.10
0.74
2.20
1.66
1.52
49 800
32 500
18 000
5800
3.9
6.2
141.9
141.1
138.2
132.8
131.5
127.9
131.6
129.9
127.6
250
7.2
500
21.1
42.0
19.9
27.5
7.0
1000
2000
500
2100
1100
2800
5
500
1700
5
500
1600
2.0
a Polymerization conditions: PC2H4 = 1.3 bar, toluene = 80 mL, and time = 30 min. b The average rate of polymerization over 30 min (Rp,av) in
(g-PE) (mol-Fe)ꢀ1 hꢀ1 barꢀ1. c Determined by GPC. d Determined by DSC.
3
3
3
Figure 4. GPC curves of polyethylene samples obtained by complex 5 at different [MAO]/[5] ratios: (a) 250, (b) 500, (c) 1000, and (d) 2000.
Polymerization conditions: catalyst = 2.5 μmol, PC2H4 = 1.3 bar, toluene = 80 mL, T = 30 °C, and time = 30 min.
having the larger bromide groups as 2,6-substituent produced
PEs with high MW (101 000), while the Fe complex with smaller
chloride groups yielded PEs with lower MW by 10-fold, and
finally the Fe complex substituted by fluoride groups produced
LAOs with a K value (SchulzꢀFlory constant for oligomer
distribution) of 0.7 under identical reaction conditions. On the
contrary, the meta and para substituents on the aryl rings had
only an electronic effect on the polymerization, the product
distribution remaining similar.
For the present catalytic system, all the polymers were character-
ized by moderate to low MW with broad distribution, which is
generally associated with bisimino complexes of Fe and Co.13 The Fe
complexes with the 2,6-dimethyl (3) and 2,4,6-trimethyl (6) sub-
stituted bis(imino)tetrahydroacridyl ligand produced linear PE with
the number average molecular weight (Mn) of 7700 and 7200,
respectively, while the Fe complex with a 2,6-diisopropyl-substituted
bis(imino)tetrahydroacridyl ligand yielded PE with an Mn of 18 000.
A similar steric effect on the product distribution was also observed
for the Co complexes, even though the Co complexes produce PEs
with lower MW than Fe homologues. Thus, complexes 8 and 10
produce PEs with Mn's of 640 and 5800, respectively. Note that
complex 8 also produces LAO together with low MW PE (Table 1,
entry 5). The product analysis reveals that the LAO content is 63.6
wt % of the total product with a distribution that closely resembles
SchulzꢀFlory rules, having a K value of 0.89.40ꢀ44 Complex 11
shows similar product distribution to complex 8 (Table 1, entry 8).
Detailed simultaneous oligo- and polymerizations by using complex
8 will be discussed later.
All the polymers were found to be highly linear according to
the microstructural analysis by NMR spectroscopy. A slightly
higher melting temperature (Tm) values are observed for Fe
complexes than their Co analogues. The PE produced by 5 shows
a Tm of 138.2 °C and that by 3 shows a Tm of 131.9 °C. For Co
complexes, 10 produce PEs with a Tm of 137.8 and 9 produces
waxes melting at 120.1 °C, respectively. High Tm values for
isopropyl derivatives are due to the strictly linear nature of the
polymer coupled with high MW.
Effect of Reaction Conditions on Ethylene Polymerization.
The effect of MAO concentration and temperature on the polym-
erization behavior has been investigated by using complex 5 as a
representative catalyst, and the results are summarized in Table 2.
The polymerizations conducted at different MAO concentrations
([Al]/[Fe] = 50ꢀ2000) show that the catalytic activity increases
from an [Al]/[Fe] ratio of 50 to 250 and then starts to decrease at
higher ratios (Table 2, entries 1ꢀ6). Complex 5 combined with a
low [Al]/[Fe] ratio of 50 produces PE with higher MW (Mn =
49 800); however, the Mn value decreases to 1100 at a high
[Al]/[Fe] ratio of 2000, due to the facilitated chain transfer to
aluminum. The GPC trace is monomodal in nature for [Al]/[Fe] =
50, and the characteristic bimodal nature of Fe catalysts started to
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Table 3. Simultaneous Oligo- and Polymerizations of Ethylenea
entry
catalyst
[Al]/[Co]
Tp (°C)
activity kg/molCo h bar
total yield (g)
oligomer yield (%)
% R-olefinb
Rc
β
3
3
1
2
3
4
5
6
7
8
8
8
8
8
8
8
8d
7
250
500
30
30
30
30
50
70
30
30
4093
4936
5742
5096
3882
1022
9316
575
7.97
8.02
9.33
8.28
7.56
1.66
2.02
1.12
63.6
63.9
64.2
65.3
65.9
70.2
78.3
99>
99>
99>
99>
95
0.88
0.91
0.91
0.89
0.90
0.87
0.88
0.50
0.14
0.10
0.10
0.12
0.11
0.15
0.14
1.00
1000
2000
1000
1000
1100
250
98
97
90
99>
a Polymerization conditions: PC2H4 = 1.3 bar, toluene = 80 mL, and time = 30 min. b Determined by GC. c SchulzꢀFlory distribution constant,
K = (moles of C14)/(moles of C12). d Conditions: cocatalyst =100 MAO þ 1000TMA, time = 10 min.
Figure 5. GC traces of ethylene oligomers obtained by complex 8 at polymerization conditions of catalyst = 2.5 μmol, PC2H4 = 1.3 bar, toluene = 80 mL,
T = 30 °C, time = 30 min, and (top) [MAO]/[Co] = 1000 and (bottom) [MAO]/AlMe3]/[Co] = 100/1000/1.
appear from [Al]/[Fe] g 250; hence a broadening of MWD is
observed. The GPC curves of PEs produced at [Al]/[Fe] ratios
250ꢀ2000 are illustrated in Figure 4. At [Al]/[Fe] ratios of 500 and
1000, bimodal distributions can be clearly observed, and at the
[Al]/[Fe] ratio of 2000 the high MW fraction almost disappeared.
The formation of a low MW fraction is evidently due to the chain
transfer to aluminum.11,12
polymerization temperature is smaller than that induced by the
variation of MAO concentration, demonstrating that chain
transfer to aluminum is a major transfer reaction and a viable
route for the formation of low molecular weight materials. The
PEs produced by 5 catalysts usually have high Tm values owing to
their linear structure. The polymer produced at [Al]/[Fe] = 50
has a high Tm value of 141.9 °C. As the ratio increases, Tm
decreases, reaching a low value of 127.9 °C at 2000 ratio, due to
the decrease in MW and broadening of its distribution.
Simultaneous Oligo- and Polymerizations of Ethylene.
The simultaneous oligomerization and polymerization behavior
has been investigated by using complex 8 at various conditions,
since complex 8 was found to produce both waxy PE and LAOs
ranging from C4 to C38 in the presence of MAO. The LAO
percentage ranges between 63.6% and 70.2%, as summarized in
Table 3. Complex 8 gives a SchulzꢀFlory distribution of LAOs,
which can be quantified by the R value. The R value represents
the probability of chain propagation and is experimentally
determined by the molar ratio of two neighboring LAO fractions,
The effect of temperature was also investigated between 30
and 70 °C (Table 2, entries 7ꢀ9). The catalytic activity decreases
monotonically as the temperature increases. The Rp value
decreases from 2.20 ꢁ 106 (g-PE) (mol-Fe)ꢀ1 hꢀ1 barꢀ1 at
3
3 ꢀ1 3
30 °C to 1.52 ꢁ 106 (g-PE) (mol-Fe)ꢀ1 hꢀ1 bar at 70 °C, a
3
3
3
drop of activity about 31%. The typical Fe(II) catalyst based on
tridentate pyridine bis-imine ligand [(2,6-C6H3(i-Pr)2Nd
C(Me))2C5H3N]FeCl2 showed a much more severe decrease
of activity, by about 90%, in the same temperature range.10 The
MW of PE decreases as the polymerization temperature increases
due to the facilitated chain-transfer reactions at elevated tem-
peratures. Note that the decrease of the MW value according to
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Organometallics
ARTICLE
Table 4. Dimerization Results of Ethylene Obtained by
Various Cobalt Complexesa
entry
catalyst
yield (g)
C4b (%)
R-C4b (%)
1
2
3
4
5
12
13
14
15
16
0.21
0.82
0.81
0.73
0.27
95.3
95.6
96.0
96.1
95.4
96.3
94.4
96.7
95.4
95.9
a Dimerization conditions: catalyst = 2.5 μmol, [Al]/[Co] = 250, PC2H4
=
1.3 bar, toluene = 80 mL, and time = 30 min. b Determined by GC.
present system producing LAOs, with the operation of
β-hydrogen transfer as the chain-transfer mechanism.14,45 The
chain transfer to aluminum cocatalyst has been detected as a
minor chain-transfer mechanism; in this case odd-numbered
oligomers were almost negligible [see Figure 5 (top)]. However,
the odd-numbered oligomers are clearly seen by adding an excess
amount of a strong transfer agent such as trimethylaluminum
(TMA), due to the activated chain transfer to aluminum [see
Figure 5 (bottom)]. TMA may form methyl-bridged dinuclear
species that promote chain transfer. In this case, TMA acts as a
separate chain-transfer agent and reduces the MW of the poly-
mer. Although chain transfer to Al is the dominant chain-transfer
mechanism at high TMA concentration, it is clear that chain
transfer to Al is only a minor contribution at the general
polymerization conditions employed in this study.
Dimerization of Ethylene by Cobalt Complexes. To pro-
vide insights into ethylene activation, the present catalytic
system, a cobalt complex (12) bearing no substituents on the
aryl rings, was synthesized and tested for its activity. Surprisingly
the complex produces 95.3% dimer with 96.3% selectivity to
1-butene, but the overall catalytic activity is lower than the cobalt
complexes bearing ligands with 2,6-alkyl-substituted aryl rings
and the iron systems (Table 4, entry 1). But a similar iron
complex (7) produced LAOs rather than dimer with K = 0.50
(Table 3, entry 8). The cobalt complexes bearing ligands of
aniline rings with unsymmetrical dimethyl substituents [2,3-
dimethyl- (13), 2,4-dimethyl- (14), and 2,5-dimethyl-substituted
(15)] and with a 3,5-dimethyl substituent (16) were also
synthesized and tested for ethylene oligomerization. As shown
in Table 4, all the catalysts were active in selective dimerization to
1-butene, with the selectivity in the range 94.4ꢀ96.7%. Catalysts
show high initial activity with rapid deactivation within 10 min of
reaction time, and those without any ortho substitution deacti-
vated much faster. These results demonstrate that, in cobalt
complexes of bisimines, 2,6-dialkyl substituents on the aryl rings
are a prerequisite condition to achieve higher R-olefins and/or
high MW PEs.
Figure 6. Molar distribution of oligomers produced by 8 at [Al]/[Co]
ratios from 250 to 1000. Polymerization conditions: catalyst = 2.5 μmol,
PC H = 1.3 bar, toluene = 80 mL, T = 30 °C, and time = 30 min.
2
4
C14 and C12 in this case [eq 1].14
Rp
moles of Cn þ 2
moles of Cn
R ¼
¼
ð1Þ
ð2Þ
Rp þ Rtr
Rtr
1 ꢀ R
β ¼
¼
Rp
R
where Rp and Rtr are the rate of propagation and the rate of chain
transfer, respectively. The R value ranging from 0.87 to 0.91
characteristic for the distribution of LAOs obtained with the
precatalyst 8 shows that the polymerization parameters have very
little effect on the LAO distribution, unlike the differences in
activity, and the range encompasses the most desired values for
industrial production of R-olefins.2 Figure 5 (top) shows the
typical gas chromatogram of the LAO product produced by the
8/MAO catalyst system ([Al]/[Co] = 1000) at 30 °C. Quanti-
tative analysis of the LAO product reveals product selectivity for
linear R-olefins greater than 99%. Neither branched oligomers
nor isomerization to internal olefins is observed. By adding
trimethyl aluminum as a chain-transfer agent, formation of odd
carbon number alkanes generated by chain transfer to aluminum
was observed (Table 3, entry 7), and the gas chromatogram is
shown in Figure 5 (bottom). The molar distribution of oligomers
produced by the 8/MAO system ([Al]/[Co] = 250ꢀ1000) is
illustrated in Figure 6. This high selectivity, combined with a
SchulzꢀFlory distribution, is consistent with an oligomerization
mechanism starting from a cobalt alkyl species, which is gener-
ated by the reaction of 8 with MAO, followed by several insertion
steps of ethylene and a chain-transfer process.
’ CONCLUSIONS
In an attempt to find new alternatives for the well-known Fe
and Co catalysts bearing bis(arylimino)pyridine ligands, we
modified the central pyridine donor by replacing it with a
2,3:5,6-dicyclohexano pyridine by using 2,3,7,8-tetrahydroacri-
dine-4,5(1H,6H)-dione as a carbonyl source for the bisimine
ligand. The dione compound is combined with two equivalents
of required aniline derivatives and metal halides in a one-pot
methodology to give a series of Fe(II) and Co(II) complexes.
The use of the cyclized backbone as a ligand changes the
geometry of the metal center from distorted square pyramidal
In the case of late transition metal catalyzed ethylene oligo-
merization, four different transfer processes can be considered:
namely, β-hydrogen to metal, β-hydrogen to monomer, σ-bond
metathesis, and chain transfer to Al. Since the oligomerization
resulted in LAOs in excess of 99%, a Cossee-type mechanism
proposed by Britovsek and co-workers based on their work on Cs
symmetric Co and Fe complexes is envisaged to operate in the
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Organometallics
ARTICLE
for the well-known 2,6-diisopropyl-substituted bis(imino)-
pyridine Fe and Co complexes to a trigonal-bipyramidal struc-
ture, as evidenced from single-crystal X-ray analyses. All the
complexes show high activity toward ethylene activation when
treated with MAO as a cocatalyst. The ortho substitution in the
aryl rings of the complexes and the type of metal had a significant
effect on ethylene activation and more importantly on product
microstructure. Thus, the Fe complex with a 2,6-diisopropyl-
substituted bis(imino)tetrahydroacridyl ligand yielded PE with
the Mn of 18 000, while the Co complexes produced PE waxes
and LAO obeying SchulzꢀFlory distribution simultaneously,
changing their compositions according to the bulk of the ortho
disubstitution. The Co complexes without any ortho substitution
or with only one substitution behave as exclusive dimerization
catalysts with over 97% selectivity toward 1-butene, which is not
common in Co catalyst systems.
Calcd for C33H39Cl2FeN3: C, 65.57; H, 6.50; N, 6.95. Found: C, 65.91;
H, 6.12; N, 7.05. FAB-MS (m/z): 568 [M ꢀ Cl]þ,533 [M ꢀ 2Cl]þ.
(15E)-N-((E)-4-(2,6-Diisopropylphenylimino)-1,2,3,4,7,8-hexahy-
droacridin-5(6H)-ylidene)-2,6-diisopropylbenzenamine Fe(II) Chloride
(5). The complex was obtained as brown-colored crystals in 59.0% yield.
Anal. Calcd for C37H47Cl2FeN3: C, 67.28; H, 7.17; N, 6.36. Found: C,
67.06; H, 7.01; N, 6.55. FAB-MS (m/z): 624 [M ꢀ Cl]þ, 590 [M ꢀ
2Cl]þ.
(15E)-N-((E)-1,2,3,4,7,8-Hexahydro-4-(mesitylimino)acridin-5(6H)-
ylidene)-2,4,6-trimethylbenzenamine Fe(II) Chloride (6). The complex
was obtained as brown-colored crystals in 62.0% yield. Anal. Calcd for
C31H35Cl2FeN3: C, 64.60; H, 6.12; N, 7.29. Found: C, 64.76; H, 6.01;
N, 7.35. FAB-MS (m/z): 540 [M ꢀ Cl]þ,504 [M ꢀ 2Cl]þ.
(15E)-N-((E)-1,2,3,4,7,8-Hexahydro-4-(phenylimino)acridin-5(6H)-
ylidene)benzenamine Fe(II) Chloride (7). The complex was obtained as
deep brown colored crystals in 71.0% yield. Anal. Calcd for
C25H23Cl2FeN3: C, 61.00; H, 4.71; N, 8.54. Found: C, 61.30; H,
4.43; N, 8.74. FAB-MS (m/z): 456 [M ꢀ Cl]þ, 420 [M ꢀ 2Cl]þ.
(15E)-N-((E)-4-(2,6-Dimethylphenylimino)-1,2,3,4,7,8-hexahydroa-
cridin-5(6H)-ylidene)-2,6-dimethylbenzenamine Co(II) Chloride (8).
The complex was obtained as green-colored crystals in 62.0% yield.
Anal. Calcd for C29H31Cl2CoN3: C, 63.17; H, 5.67; N, 7.62. Found: C,
63.12; H, 4.37; N, 7.84. FAB-MS (m/z): 515 [M ꢀ Cl]þ, 480 [M ꢀ
2Cl]þ.
(15E)-N-((E)-4-(2,6-Diethylphenylimino)-1,2,3,4,7,8-hexahydroacri-
din-5(6H)-ylidene)-2,6-diethylbenzenamine Co(II) Chloride (9). The
complex was obtained as green-colored crystals in 60.0% yield. Anal.
Calcd for C33H39Cl2CoN3: C, 65.24; H, 6.47; N, 6.92. Found: C, 65.82;
H, 6.08; N, 6.95. FAB-MS (m/z): 571 [M ꢀ Cl]þ, 534 [M ꢀ 2Cl]þ.
(15E)-N-((E)-4-(2,6-Diisopropylphenylimino)-1,2,3,4,7,8-hexahy-
droacridin-5(6H)-ylidene)-2,6-diisopropylbenzenamine Co(II) Chlor-
ide (10). The complex was obtained as brown-colored crystals in
59.0% yield. Anal. Calcd for C37H47Cl2CoN3: C, 66.96; H, 7.14; N,
6.33. Found: C, 67.06; H, 7.01; N, 6.55. FAB-MS (m/z): 627[M ꢀ Cl]þ,
590 [M ꢀ 2Cl]þ.
’ EXPERIMENTAL SECTION
General Procedures and Materials. All reactions and opera-
tions were performed under a purified nitrogen atmosphere using
standard glovebox and Schlenk techniques. Polymerization grade ethy-
lene (SK Co., Korea) was purified by passing it through columns of
Fisher RIDOX catalyst and molecular sieve 5 Å/13X. Toluene used as
solvent for polymerizations was distilled from Na/benzophenone and
stored over molecular sieves (4 Å). MAO (8.4 wt % total Al solution in
toluene) was donated by LG Chemicals, Korea, and was used without
purification. 1,2,3,4,5,6,7,8-Octahydroacridine was purchased from TCI
Chemicals. All other reagents were purchased from Aldrich Chemical
Co. and used without further purification.
Characterizations. Elemental analyses were carried out using CE
Instruments/Thermo Quest Italia Flash EA 1112 series. 1H NMR
spectra (300 MHz) and 13C NMR spectra (75 MHz) of the ligands
were recorded on a Varian Gemini 2000 spectrometer. Chemical shifts
are reported in parts per million relative to internal (CH3)4Si (1H, 13C).
1H and 13C NMR spectra of polyethylene (PE) samples were taken in
C6H6Cl2 at 135 °C on a Varian Unity Plus 300 (300 and 75 MHz)
spectrometer. Fast atom bombardment mass spectra (FAB-MS) of the
complexes were recorded on a JEOL JMS-700 spectrometer. MW and
polydispersity of PE were determined by GPC (Alliance GPCV2000, RI
detector) at 150 °C column temperature in 1,2,4-trichlorobenzene using
polystyrene as a standard. Thermal analysis of PE was carried out by a
differential scanning calorimeter (Perkin-Elmer DSC, model Pyris 1) at
10 °C/min heating rate under a nitrogen atmosphere. Oligomerization
products were analyzed by an Agilent Technologies 7890 A GC system
with a J&W Scientific 30 m column with 0.25 mm inner diameter.
Synthesis of Complexes. All complexes were prepared in a
similar manner by using FeCl2 4H2O or CoCl2 6H2O as a metal
(15E)-N-((E)-1,2,3,4,7,8-Hexahydro-4-(mesitylimino)acridin-5(6H)-
ylidene)-2,4,6-trimethylbenzenamine Co(II) Chloride (11). The com-
plex was obtained as green crystals in 56.0% yield. Anal. Calcd for
C31H35Cl2CoN3: C, 64.25; H, 6.09; N, 7.25. Found: C, 64.73; H, 6.04;
N, 7.30. FAB-MS (m/z): 543 [M ꢀ Cl]þ, 508 [M ꢀ 2Cl]þ.
(15E)-N-((E)-1,2,3,4,7,8-Hexahydro-4-(phenylimino)acridin-5(6H)-
ylidene)benzenamine Co(II) Chloride (12). The complex was ob-
tained as brown-colored crystals in 65.0% yield. Anal. Calcd for
C25H23Cl2CoN3: C, 60.62; H, 4.68; N, 8.48. Found: C, 61.07; H,
4.55; N, 8.81. FAB-MS (m/z): 459 [M ꢀ Cl]þ, 424 [M ꢀ 2Cl]þ.
(15E)-N-((E)-4-(2,3-Dimethylphenylimino)-1,2,3,4,7,8-hexahydroa-
cridin-5(6H)-ylidene)-2,3-dimethylbenzenamine Co(II) Chloride (13).
The complex was obtained as green-colored crystals in 64.0% yield. Anal.
Calcd for C29H31Cl2CoN3: C, 63.17; H, 5.67; N, 7.62. Found: C, 63.12;
H, 5.59; N, 7.71. FAB-MS (m/z): 515 [M ꢀ Cl]þ, 480 [M ꢀ 2Cl]þ.
(15E)-N-((E)-4-(2,4-Dimethylphenylimino)-1,2,3,4,7,8-hexahydroa-
cridin-5(6H)-ylidene)-2,4-dimethylbenzenamine Co(II) Chloride (14).
The complex was obtained as green-colored crystals in 67.0% yield. Anal.
Calcd for C29H31Cl2CoN3: C, 63.17; H, 5.67; N, 7.62. Found: C, 63.00;
H, 5.48; N, 7.85. FAB-MS (m/z): 515 [M ꢀ Cl]þ, 480 [M ꢀ 2Cl]þ.
(15E)-N-((E)-4-(2,5-Dimethylphenylimino)-1,2,3,4,7,8-hexahydroa-
cridin-5(6H)-ylidene)-2,5-dimethylbenzenamine Co(II) Chloride (15).
The complex was obtained as deep brown colored crystals in 57.0%
yield. Anal. Calcd for C29H31Cl2CoN3: C, 63.17; H, 5.67; N, 7.62.
Found: C, 63.12; H, 5.75; N, 7.66. FAB-MS (m/z): 517 [M ꢀ Cl]þ, 480
[M ꢀ 2Cl]þ.
3
3
source. A suspension of 3 (1.00 mmol) and 2 mmol of corresponding
aniline derivative with metal salt in glacial acetic acid (10 mL) was
refluxed for 6 h. The complex was precipitated by adding excess diethyl
ether, and the precipitate was collected by filtration and washed with 3 ꢁ
5 mL of diethyl ether. Then the collected solid was dried under vacuum
to yield the complex.
(15E)-N-((E)-4-(2,6-Dimethylphenylimino)-1,2,3,4,7,8-hexahydroa-
cridin-5(6H)-ylidene)-2,6-dimethylbenzenamine Fe(II) Chloride (3).
The complex was obtained as deep brown colored crystals in 68.0%
yield. Anal. Calcd for C29H31Cl2FeN3: C, 63.52; H, 5.70; N, 7.66.
Found: C, 63.02; H, 4.35; N, 7.72. FAB-MS (m/z): 512 [M ꢀ Cl]þ, 476
[M ꢀ 2Cl]þ
(15E)-N-((E)-4-(2,6-Diethylphenylimino)-1,2,3,4,7,8-hexahydroacri-
din-5(6H)-ylidene)-2,6-diethylbenzenamine Fe(II) Chloride (4). The
complex was obtained as brown-colored crystals in 64.0% yield. Anal.
(15E)-N-((E)-4-(3,5-Dimethylphenylimino)-1,2,3,4,7,8-hexahydroacri-
din-5(6H)-ylidene)-3,5-dimethylbenzenamine Co(II) Chloride (16). The
complex was obtained as green-colored crystals in 64.0% yield. Anal. Calcd
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dx.doi.org/10.1021/om2000629 |Organometallics 2011, 30, 2285–2294

Organometallics
ARTICLE
for C29H31Cl2CoN3: C, 63.17; H, 5.67; N, 7.62. Found: C, 63.09; H, 5.89;
N, 7.69. FAB-MS (m/z): 515 [M ꢀ Cl]þ, 480 [M ꢀ 2Cl]þ.
(2) Vogt, D. In Applied Homogeneous Catalysis with Organometallic
Compounds; Cornils, B; Herrmann, W. A., Eds.; VHC: New York, 1996;
Vol. 1, p 245.
Crystallographic Studies. The crystal was picked up with Paraton
N oil and mounted on a Bruker SMART CCD diffractometer equipped
with a graphite-monochromated Mo KR (λ= 0.71073 Å) radiation
source and a nitrogen cold stream (ꢀ100 °C). The data were corrected
for Lorentz and polarization effects (SAINT), and semiempirical
absorption corrections based on equivalent reflections were applied
(SADABS). The structure was solved by direct methods and refined by
full-matrix least-squares on F2 (SHELXTL). All the non-hydrogen
atoms were refined anisotropically, and hydrogen atoms were added
to their geometrically ideal positions. The crystal data for complexes 5
and 10 have been deposited at the Cambridge Crystallographic Data
Center with numbers CCDC 755418 and 755419, respectively. The data
can be obtained free of charge from the Cambridge Crystallographic
Data Centre through www.ccdc.cam.ac.uk/data_request/cif.
(3) Skupinska, J. Chem. Rev. 1991, 91, 613.
(4) Parshall, G. V.; Ittel, S. D. Homogeneous Catalysis. In The
Applications and Chemistry of Catalysis by Soluble Transition Metal
Complexes; John Wiley and Sons: New York, 1992; p 68.
(5) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2003, 103, 283.
(6) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int.
Ed. 1999, 38, 428.
(7) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000, 100, 1169.
(8) Mecking, S. Angew. Chem., Int. Ed. 2001, 40, 534.
(9) Park, S.; Han, Y.; Kim, S. K.; Lee, J.; Kim, H. K.; Do, Y.
J. Organomet. Chem. 2004, 689, 4263.
(10) Small, B. L.; Brookhart, M.; Bennett, A. M. A. J. Am. Chem. Soc.
1998, 120, 4049.
(11) Small, B. L.; Brookhart, M. J. Am. Chem. Soc. 1998, 120, 7143.
(12) Gibson, V. C.; Britovsek, C. J.; Kimberley, B. S.; Maddox, P. J.;
Maddox, P. J.; McTavish, S. J.; Solan, G. A.; White, A. J. P.; Williams, D. J.
Chem. Commun. 1998, 849.
(13) Britovsek, G. J. P.; Bruce, M.; Gibson, V. C.; Kimberley, B. S.;
Maddox, P. J.; Mastroianni, S.; McTavish, S. J.; Redshaw, C.; Solan,
G. A.; Stromberg, S.; White, A. J. P.; Williams, D. J. J. Am. Chem. Soc.
1999, 121, 8728.
(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.
(15) Bianchini, C.; Giambastiani, G.; Rios, I. G.; Mantovani, G.;
Meli, A.; Segarra, A. M. Coord. Chem. Rev. 2006, 250, 1391.
(16) Gibson, V. C.; Redshaw, C.; Solan, G. A. Chem. Rev. 2007,
107, 1745.
Polymerization/Oligomerization Procedure. Ethylene oligo-
merizations/polymerizations were performed in a 250 mL glass reactor
equipped with a septum adapter and a magnetic stir bar. The required
amount of catalyst was added to the reactor and kept under vacuum for
30 min and then purged with N2. The reactor was then charged with
toluene (80 mL) under N2 and then pressurized with ethylene (1.3 bar)
at the desired temperature with stirring. The polymerization was started
by the addition of cocatalyst. The ethylene flow to the reactor was
monitored by a mass flow meter from the rate of consumption, measured
by a hotwire flow meter (model 5850 D from Brooks Instrument Div.)
connected to a personal computer through an A/D converter. After the
given reaction time, for polymerization, the reaction was quenched by
the addition of acidified methanol followed by precipitation in methanol.
The polymer was then washed several times with methanol and dried in a
vacuum oven to constant weight. For oligomerizations, the samples are
collected from the reactor for analysis and passed through a silica column
to remove catalyst and are analyzed by gas chromatography. The
oligomerization rate was determined from a mass flow meter connected
to the computer.
(17) Sun, W.-H.; Zhang, S.; Zuo, W. C. R. Chimie 2008, 11, 307.
(18) Britovsek, G. J. P.; Baugh, S. P. D.; Hoarau, O. D.; Gibson, V. C.;
Wass, D. F.; White, A. J. P.; Williams, D. J. Inorg. Chim. Acta 2003,
345, 279.
(19) Small, B. L.; Rios, R.; Fernandez, E. R.; Carney, M. J. Organo-
metallics 2007, 26, 1744.
(20) Britovsek, G. J. P.; Gibson, V. C.; Hoarau, O. D.; Spitzmesser,
S. K.; White, A. J. P.; Williams, D. J. Inorg. Chem. 2003, 42, 3454.
(21) Britovsek, G. J. P.; Gibson, V. C.; Kimberley, B. S.; Mastroiannni,
S.; Redshaw, C.; Solan, G. A.; White, A. J. P.; Williams, D. J. J. Chem. Soc.,
Dalton Trans. 2001, 1639.
(22) Jie, S.; Zhang, S.; Sun, W.-H.; Kuang, X.; Liu, T.; Guo, J. J. Mol.
Catal. A: Chem. 2007, 269, 85.
(23) Zhang, M.; Hao, P.; Zuo, W.; Jie, S.; Sun, W.-H. J. Organomet.
Chem. 2008, 693, 483.
’ ASSOCIATED CONTENT
S
Supporting Information. Structure refinement and CIF
b
files containing X-ray diffraction data of complexes 5 and 10 and
synthesis of compound 2 are available free of charge via the
Internet at http://pubs.acs.org.
(24) Zhang, M.; Gao, R.; Hao, X.; Sun, W.-H. J. Organomet. Chem.
2008, 693, 3867.
’ AUTHOR INFORMATION
(25) Sun, W.-H.; Hao, P.; Li, G.; Zhang, S.; Wang, W.; Yi, J.; Asma,
M.; Tang, N. J. Organomet. Chem. 2007, 692, 4506.
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Corresponding Author
*E-mail: ilkim@pusan.ac.kr. Tel: þ82-51-510-2399. Fax: þ82-
51-513-7720.
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The authors thank H. J. Lee of KBSI, Jeonju Center, and J. E.
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University, for assistance with X-ray crystallographic analysis.
This work was financially supported by the World Class
University Program (No. R32-2008-000-10174-0). The authors
are also grateful to the National Core Research Center Program
from MEST and KOSEF (R15-2006-022-01002-0).
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