Preparation of silica-supported bis(imino)pyridyl iron(II) and cobalt(II) catalysts for ethylene polymerization

Article abstract of DOI:10.1021/ma0347060

A new heterogeneous silica-supported Fe(II) and Co(II) catalysts with a bis(imino)-pyridyl group containing silicon ethoxide functionality onthe pyridine ring was reported. By reaction of this functionality with activated silica, the catalysts were covale

Full text of DOI:10.1021/ma0347060

Volume 36, Number 18
September 9, 2003
© Copyright 2003 by the American Chemical Society
Communications to the Editor
hydrolyzed trimethylaluminum on silica gel and were
P r ep a r a tion of Silica -Su p p or ted
Bis(im in o)p yr id yl Ir on (II) a n d Coba lt(II)
Ca ta lysts for Eth ylen e P olym er iza tion
used for ethylene polymerization.11
Herein we report a versatile heterogenization tech-
nique to covalently immobilize bis(imino)pyridyl Co(II)
and Fe(II) complexes onto silica gel, which exhibit high
activity in ethylene polymerization after activation with
methylaluminoxane (MAO).
Il Kim ,* Byeon g Heu i Ha n , Ch a n g-Sik Ha ,
J a e-Kon Kim , a n d Hon gsu k Su h
Department of Polymer Science and Engineering,
Department of Chemistry and Chemistry Institute for
Functional Materials, Pusan National University,
J angjeon-dong, Geumjeong-gu, Busan 609-735, Korea
The synthetic route of a new supported 2,6-bis(imino)-
pyridyl ligand is shown in Scheme 1. Cheldamic acid 1
was esterified in ethanol in the presence of sulfuric acid
as catalyst to give the diethyl ester 2 in 71% yield and
then alkylated with allyl bromide in the presence of K2-
CO3 in acetone to obtain 3 (81%). Ester compound 3 was
hydrolyzed with aqueous 5 N NaOH in tetrahydrofuran
(THF) to give the desired carboxylic acid 4. Carboxylic
acid 4 was treated with SOCl2, which was converted to
the diacetylpyridine 5 using CuI(I) and methyllithium
in 47% yield. The pyridyl diimine 6 was prepared by
the Schiff-base condensation with 2,6-dimethylaniline
and 4-(allyloxy)-2,6-diacetylpyridine (5) in 51% yield.
Utilizing the known methodology of chiral stationary
phase formation,12 pyridyl diimine 6 was reacted with
chlorodimethylsilane in the presence of H2PtCl6‚6H2O
as a catalyst in methylene chloride and then treated
with the mixed solvent of ethanol-triethylamine (1:1,
v/ v) to afford hydrosilylated compound 7 in 48% yield.
The resulting hydrosilyl compound 7 was refluxed for
72 h with toluene and 5 µm silica gel in a flask equipped
with Dean-stark trap and then was filtered and washed
with toluene, ethyl acetate, methanol, acetone, diethyl
ether, and hexane to afford 8. Elemental analysis of 8
(C, 6.95%; H, 0.79%) showed a loading of 0.199 mmol
(based on C) of 7 per gram of 8. Exact standard
procedures are described in the Supporting Information.
The supported iron(II) and cobalt(II) catalyst precursors
9 and 10 were synthesized by treating silica gel sup-
ported bis(imino)pyridyl compound 8 with FeCl2‚4H2O
(or CoCl2‚4H2O) in THF.
Received May 27, 2003
Revised Manuscript Received J uly 23, 2003
Recently, it was shown that a series of pyridyl bis-
(imide) complexes of cobalt(II) and iron(II) exhibit very
high activities for ethylene polymerization.1-4 The
protective bulk of the ortho substituents above and
below the metal center is critical to the molecular of the
resulting polyethylenes.2-5 In contrast to the nickel and
palladium systems, there is no chain walking and the
polyethylene is strictly linear with very high density.5
Regardless of the virtues these homogeneous new
catalysts possess, it is required to support these cata-
lysts on inorganic support materials if they can be
adapted to run in commercial polymerization processes.
Heterogenization is required to operate the continuous
process smoothly by avoiding fouling of the reactor,
overheating of the particle, and melting of the polymer,
which could result in the particles adhering to form
sheets on the reactor walls and agitator.
Homogeneous metallocene catalysts have been suc-
cessfully supported using numerous methods on many
different types of carriers.6,7 Also, they have been
studied toward the immobilization of late transition
metal catalysts. Covalently attaching Ni(II) diimine
complexes to the support was demonstrated to be an
effective method.8,9 Recently, covalently attached bis-
(imino)pyridyl Fe(II) catalysts to silica gel were used
successfully for ethylene polymerization.10 The bis-
(imino)pyridyl Fe(II) complexes were also activated and
heterogenized with a cocatalyst consisting of partially
The supported catalysts were tested in slurry poly-
merization runs at an atmospheric pressure of ethylene
in toluene at temperature between 10 and 50 °C. A poly-
10.1021/ma0347060 CCC: $25.00 © 2003 American Chemical Society
Published on Web 08/05/2003

6690 Communications to the Editor
Macromolecules, Vol. 36, No. 18, 2003
Sch em e 1. Syn th etic Rou te of New Su p p or ted 2,6-Bis(im in o)p yr id yl F e(II) a n d Co(II) Com p lexesa
a
(i) EtOH, concentrated H2SO4, 90 °C; (ii) K2CO3, allyl bromide, acetone, reflux; (iii) 5 N NaOH, THF, 50 °C; (iv) SOCl2, DMF,
90 °C; (v) CuI(I), MeLi, Et2O, THF, -78 °C; (vi) 6, 2,6-dimethylaniline EtOH, AcOH, reflux; (vii) (CH3)2SiHCl, H2PtCl6‚6H2O
(catalyst), CH2Cl2, EtOH:Et3N ) 1:1; reflux; (viii) 5 µm silica gel, toluene, 120 °C; FeCl2 or CoCl2 , THF.
Ta ble 1. Exp er im en ta l Resu lts for P olym er iza tion w ith Hom o- a n d Heter ogen eou s Ca ta lysts in Com bin a tion w ith MAOa
b
b
Rhp × 10-7
Rhp × 10-3
run
no.
loading
(µmol)
temp
(C)
(g of PE/
(g of PE/
c
d
d
cat.
(mol of Mt h bar))
(g of cat. h bar))
Mh v × 10-3
Tm (C)
∆Hf (J /g)
Xce (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
9
19.99
10
30f
30
30g
50
10
30
50
10
30
50
10
30
50
1.71
4.92
3.08
2.52
4.87
2.10
2.59
1.60
163.74
203.88
251.01
158.87
156.59
54.99
3.42
9.84
6.18
5.04
9.75
4.20
5.19
3.19
202.3
152.3
165.9
164.2
114.4
68.3
50.3
40.6
36.7
18.4
17.9
4.5
131.8
131.9
156.4
57.9
171.5
63.5
131.7
129.9
129.1
128.3
127.6
126.4
127.3
118.5
114.8
107.6
178.6
166.2
177.0
158.9
191.63
197.3
197.3
221.3
229.4
240.2
66.2
62
66
62
71
73
73
82
85
89
10
11
12
19.99
6.04
6.04
3296.5
4104.7
5054.7
3198.6
3152.6
1099.0
2.4
2.2
a
b
250 mL reactor, 80 mL of toluene, 30 min runs, atmospheric pressure, [MAO]/[M] ) 700 equiv. Average rate of polymerization for
0.7
d
the period of polymerization. c Viscosity-average molecular weights calculated from the equation13 [η] ) 6.2 × 10-4Mh v
.
Melting
temperature (Tm) and heat of fusion (∆Hf) of the polymer determined by DSC. e Crystallinity calculated by (∆Hf/∆Hf) × 100 (∆Hf ) 269.9
J /g for folded-chain polyethylene14). f Polymerization run time of 3 min. Polymerization run time of 60 min.
g
merization run time was 30 min. Polymerizations of
ethylene were also carried out using nonsupported bis-
(imino)pyridyl complexes [(2,6-C6H3Me2NdC(Me))2C5-
H3N]MCl2 [M ) Fe (11); Co (12)] at the same conditions
for the comparison. The results are summarized in
Table 1. The iron(II) and cobalt(II) complexes covalently
attached to silica gel through silicon ethoxide function-
alized ligands show high activities in ethylene poly-
merization when activated with MAO. Supported iron
precatalyst 9 shows polymerization activity of 4.87 ×
107 g of PE/(mol of Fe h bar) at 50 °C and cobalt pre-
catalyst 10 1.60 × 107 g of PE/(mol of Co h bar) at the
same polymerization temperature. These supported
catalysts showed about 100-fold lower activity than
analogue homogeneous catalysts. This is widely ascribed
to diffusion limitation of monomer into the interior pores
of the supported catalyst, but may also be the result of
reduced active sites present in the heterogeneous vari-
ant. Catalyst sites could be deactivated when supported
or may not be generated in the metal-cocatalyst inter-
action. A similar supported catalyst prepared by im-
mobilization of alkenyl functionalized [(2,6-C6H3(iPr)2Nd
C(Me))2C5H3N]FeCl2 on modified silica via hydrosyla-
tion showed a polymerization activity of 4.53 × 106 g of
PE/(mol of Fe h bar) for 45 min of polymerization time.10
Peter and Brookhart reported supported catalysts pre-
pared by using aryl R-diimine Ni(II) complexes substi-
tuted with amino functionality and silica pretreated
with trimethylaluminum showing similar activities.9
The molecular weight (as Mh v) of the polyethylene
produced by supported catalysts was higher than that
of polyethylene by analogue homogeneous catalysts. In
addition, the molecular weight was observed not to be
run time dependent. The polymer obtained from a 3 min
run had an Mh v of 1.52 × 105 while the polymers from
30 and 60 min runs had Mh v of 1.66 × 105 and 1.64 ×
105. The higher molecular weight notwithstanding lower
activity of supported catalysts suggests that the lower
activity of the catalyst is due to a reduced number of
active sites; were the propagation rate lower for a
supported catalyst, the rate of termination would have
to be reduced proportionately or more for these molec-
ular weight observations to hold. The decrease of
catalytic activity and the increase of molecular weight

Macromolecules, Vol. 36, No. 18, 2003
Communications to the Editor 6691
by heterogenization were also observed in metallocene
catalysts.1,6 Tait and co-workers determined that 91%
of zirconocenes sites were activated by MAO in solution,
but when the metallocene was supported on silica, the
concentration of active sites generated by MAO was only
9% of the total zirconium supported.15 Table 1 shows
that the molecular weight of the polymer decreases as
the increase of polymerization temperature for both
supported and unsupported catalysts. In transition-
metal-catalyzed polymerizations, the chain termination
reaction has normal activation energy and therefore can
be controlled by temperature. Since the activation
energy for the termination is somewhat higher than that
for propagation, the molecular weight can be controlled
by temperature.
Ack n ow led gm en t. This research was supported by
the Korea Research Foundation (NONDIRECTED
FUND, 2001). I.K. is grateful to the center for Ultra-
microchemical Process Systems and to the Brain Korea
21 Project in 2003. C.-S. Ha is also grateful to the
National Research Laboratory Program.
Su p p or tin g In for m a tion Ava ila ble: Synthesis of com-
pounds 9 and 10, supporting procedures, and polymerization
details. This material is available free of charge via the
Internet at http://pubs.acs.org.
Refer en ces a n d Notes
(1) Ittel, S. D.; J ohnson, L. K.; Brookhart, M. Chem. Rev. 2000,
100, 1169 and references therein.
All of the catalysts reported converts ethylene to
highly linear polyethylene as determined by differential
scanning calorimetry (show only one Tm peak). The Tm
values of polymer increased by about 4 °C for iron
catalyst and over 10 °C for cobalt catalyst by hetero-
genization. The increase of melting temperature is
evidently ascribed to the increase of molecular weight.
Mathot and Pijpers studied with DSC the melting and
crystallilization behavior of polyethylene fractions of
widely varying molecular weight, concluding the melting
temperature increases with molecular weight of 20 000
up to an almost asymptotic value.16 The higher crys-
tallinities of lower molecular weight polymers obtained
by homogeneous catalysts (11 and 12 in Table 1)
demonstrate that at higher molecular weight the chains
are so large that parts of them can independently
crystallize due to a delaying effect of entanglement.
In summary, we report a new heterogeneous silica-
supported Fe(II) and Co(II) catalysts with a bis(imino)-
pyridyl group containing silicon ethoxide functionality
on the pyridine ring. By reaction of this functionality
with activated silica, the catalysts were covalently
bound to the support. These silica-supported catalysts
showed high activity (up to 4.87 × 107 g of PE/(mol of
Fe h bar)) and gave high molecular weight polymer (up
to Mh v ) 2.02 × 105). These new silica-supported late
transition metal catalysts are a new family of promising
catalysts for the polymerization of ethylene. The sup-
ported catalysts with different aryl ligands and detailed
kinetic studies using the said catalysts are under
investigation.
(2) Small, B. L.; Brookhart, M.; Bennet, A. M. A. J . Am. Chem.
Soc. 1998, 120, 4049.
(3) Britovsek, G. J . P.; Gibson, V. C.; Kimberly, B. S.; Maddox,
P. J .; McTavish, S. J .; Solan, G. A.; White, A. J . P.; Williams,
D. J . Chem. Commun. 1998, 849.
(4) Britovsek, G. J . P.; Gibson, V. C.; Wass, D. F. Angew. Chem.,
Int. Ed. 1999, 38, 428.
(5) Britovsek, G. J . P.; Bruce, M.; Gibson, V. C.; Kimberly, 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.
(6) Hlatky, G. G. Chem. Rev. 2000, 100, 1347 and references
therein.
(7) Fink, G.; Steinmetz, B.; Zechlin, J .; Przybyla, C.; Tesche,
B. Chem. Rev. 2000, 100, 1377.
(8) Boussie, T. R.; Murphy, V.; Hall, K. A.; Coutard, C.; Dales,
C.; Petro, M.; Carlson, E.; Turner, H. W.; Powers, T. S.
Tetrahedron 1999, 55, 11699.
(9) Peter, P.-P.; Brookhart, M. Macromolecules 2002, 35, 6074.
(10) Kaul, F. A. R.; Puchta, G. T.; Schneider, H.; Bielert, F.;
Mahalios, D.; Herrmann, W. A. Organometallics 2002, 21,
74.
(11) Schmidt, R.; Welch, M. B.; Palackal, S. J .; Alt, H. G. J . Mol.
Catal. 2002, 179, 155.
(12) Hyun, M. H.; Na, M. S.; J in, J . S. J . Chromatogr., A 1996,
77, 752.
(13) Chiang, R. J . Polym. Sci. 1957, 28, 235.
(14) Soga, K. Makromol. Chem. 1989, 190, 995.
(15) Tait, P. J . T.; Monterio, M. G. K.; Yang, M.; Richardson, J .
L. Proceedings of MetCon 1996, Houston, TX, 12-13 J une
1996.
(16) Mathot, V. B. F.; Pijpers, M. J . F. Polym. Bull. (Berlin) 1984,
11, 297.
MA0347060