Olefin polymerization behavior of the cyclopentadienyl cobalt complexes bearing pendant sulfur or oxygen ligands

Article abstract of DOI:10.1016/j.inoche.2006.01.010

Four half-sandwich cobalt complexes bearing pendant sulfur or oxygen ligands have been reported and tested as catalysts for olefin polymerization in the presence of MAO. The molecular structure of complexes 1 has been determined by X-ray crystallographic

Full text of DOI:10.1016/j.inoche.2006.01.010

Inorganic Chemistry Communications 9 (2006) 423–425
www.elsevier.com/locate/inoche
Olefin polymerization behavior of the cyclopentadienyl
cobalt complexes bearing pendant sulfur or oxygen ligands
*
Xiu-Feng Hou, Yin-Qiang Cheng, Peng-Cheng Zhang, Guo-Xin Jin
Shanghai Key Laboratory of Molecular Catalysis Innovative Material, Department of Chemistry, Fudan University, Shanghai 200433, China
Received 22 December 2005; accepted 22 January 2006
Available online 13 March 2006
Abstract
Four half-sandwich cobalt complexes bearing pendant sulfur or oxygen ligands have been reported and tested as catalysts for olefin
polymerization in the presence of MAO. The molecular structure of complexes 1 has been determined by X-ray crystallographic analysis.
Complexes 1 and 2 exhibited high activities of up to 106 g PE molÀ1Co hÀ1 with moderate molecular weight (Mw ꢀ 104 g molÀ1) of poly-
ethylene in the ethylene polymerization.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Cobalt; Functional cyclopentadienyl group; Ethylene polymerization; Molecular structure
g5-Cyclopentadienyl derivatives of transition metals are
undoubtedly one of the most important classes of organo-
metallic compounds [1]. The half-sandwich complexes con-
taining one cyclopentadienyl ligand with a functionalized
side chain have received much attention by numerous
research groups [2]. With the functionalized side chain tem-
porarily and reversibly coordinated to the metal center, the
cyclopentadienyl ligand becomes a bidendate ligand with a
hemilabile binding structure [3]. Thus they are prone to
selective reactions and invaluable for catalytic purposes.
The constrained geometry catalysts (CGC) with the famil-
iar bridged Cp-amide ligand have showed great catalysis
activity in the ethylene polymerization [4]. Functionalized
silane as a side chain exemplifies the possibility of immobi-
lizing catalytically active complexes on the surface [5].
In comparison to related N-functionalized cyclopenta-
dienyl complexes, where catalytic applications of such spe-
cies have been remarkably successful (especially in olefin
polymerization) [6], the use of O- and S-functionalized
compounds in catalysis seems still underdeveloped. Our
previous work indicated that O- and S-functionalized rho-
dium complexes showed high activities for ethylene poly-
merization [7]. In this study, we introduce two different
functional ligands to cobalt complexes and make further
investigations into the effects of the donor ligands and
O- and S-functionalized substituents on cyclopentadienyl
as a weak coordination system. Here we report the use of
the four cobalt halides with cyclopentadienes bearing sul-
fur or oxygen functionalized side chains as catalysts for ole-
fin polymerization in the presence of methylaluminoxane as
a co-catalyst.
The complexes were prepared as shown in Scheme 1.
The starting materials, [g5-C5H4(CH2)2SCH2CH3]Co
(CO)2, [g5-C5H4(CH2)2OCH3]Co(CO)I2 (2) were prepared
by slightly modified literature procedures [8,9]. Complex
[g5-C5H4(CH2)2SCH2CH3]Co(CO)2 can be oxidized with
elemental iodine in diethyl ether solutions to give the air-
stable diiodocobalt(III) complexes [g5-C5H4(CH2)2SCH2-
CH3]CoI2 (1). Complex 1 is a black-purple crystalline solid.
In IR spectrum, the carbonyl absorption is absent. Reac-
5
tion of [g -C5H4(CH2)2OCH3]Co(CO)I2 (2) with equimo-
lar amount of pyridine or triphenyl phosphane in ether
leads to the formation of 3 and 4 as black-green, crystalline
solids in good yields. All complexes were characterized by
*
Corresponding author. Tel.: +86 21 65643776; fax: +86 21 65641740.
1
EA, IR and H NMR [10].
E-mail address: gxjin@fudan.edu.cn (G.-X. Jin).
1387-7003/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2006.01.010

424
X.-F. Hou et al. / Inorganic Chemistry Communications 9 (2006) 423–425
Table 1
SCH2CH3
Polymerization of ethylene by 1–4 in toluenea
n(Al)/n(Co) Pressure (atm) Activityb Mw (104)
c
I2
/Et2O
Entry Cat
T
Co
S
Co
(ꢁC)
I
CH2CH3
OCH3
OC
CO
I
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
2
3
4
20
20
20
20
20
40
60
20
40
60
1000
2000
3000
4000
5000
4000
4000
4000
4000
4000
1
1
1
1
1
1
1
1
1
1
2.4
3.4
7.1
10.4
8.3
3.1
0.6
7.4
5.1
3.0
5.28
4.31
2.48
2.04
2.52
3.52
4.25
3.81
0.34
2.24
1
OCH3
L
Co
Co
CO
L
I
I
I
I
10
a
L= py (3)
, PPh3(4)
2
A 200 ml Schlenk-type glass reactor containing 50 ml toluene was
Scheme 1.
equilibrated with the ethylene monomer.
b
105g PE molÀ1Co hÀ1g molÀ1
.
c
The molecular weight of the polymer was measured by the Ubbelohde
The molecular structure of complex 1 was determined by
single crystal X-ray diffraction. Suitable crystal was
obtained by slow hexane diffusion into a dichloromethane
solution at low temperature. As depicted in Fig. 1 [11], it
possesses basically a tri-legged half-sandwich CpM struc-
ture. In which the sulfur atom was attached via an intermo-
lecular coordination with the cobalt center and form an
18-electron complex. Because of the pendant arm the bond
calibrated viscosimeter technique through the investigation of the intrinsic
viscosity.
molar ratio becomes higher. Higher Al/Co molar ratio
increases the chain transfer reaction with MAO as the
acceptor; this results in lower polymer molecular weight.
The effect of temperature is very obvious, activity actually
decrease a lot increasing the temperature. Obviously, the
high temperature may deactivate the active center and
decrease the solubility of ethylene in toluene. Furthermore,
increase in temperature results in the reduction of molecu-
lar weight. At higher temperatures, there is an increase in
the rate of chain transfer. When the rate of chain propaga-
tion is much slower than that of chain transfer, the molec-
ular weight of the polymer drops greatly.
For complexes 2–4, we set the best ratio of n(Al)/n(Co)
at 4000 the same condition when complex 1 reaches its
highest activity. The activities of ethylene polymerization
by complexes 2–4 with the same substituted cyclopentadie-
nyl group have slight differences for different ligand car-
bonyl, pyridine or triphenylphosphorine. The less bulky
and weak electron-donated ligand led to an increase in
activity.
˚
length of Co–C1 (2.055(7) A) is the shortest and it forms a
five membered ring between the cobalt atom, cyclopenta-
dienyl ligand and the pendant arm.
Initially the polymerization of ethylene was studied
using the combination of diiodide 1 with MAO as a co-cat-
alyst in toluene (Table 1). For complex 1 the activity rises
and falls with the increase of the n(Al)/n(Co) and reaches
its pick at 10.4 (105 g PE molÀ1Co hÀ1) when the n(Al)/
n(Co) stays at 4000:1. But more MAO may deactivate the
active center causing the decrease of the activity. Such
behavior is well explained by the influence of the aluminum
concentration on the termination of polymer chains [12].
The polymer molecular weight decreases when the Al/Co
Comparing complexes 1 and 2, we see that complex 1
containing S-functionalized side-arm exhibits higher activ-
ity than complex 2 containing O-functionalized side-arm.
The sulfur atom of side-arm coordinated to center cobalt
in complex 1 led to an increase in the activity, probably
due to its hemilabile binding structure. For all the com-
plexes, the activities of ethylene polymerization are from
10.3 to 3.0 · 105 g PE molÀ1Co hÀ1 [n(Al)/n(Co)=4000:1].
The results show that half-sandwich cobalt complexes have
large tolerance for changing electronic and steric effect in
their structures.
Although the detailed mechanism of the catalytic olefin
polymerization is not clear, we suggest that a cationic
methyl cobalt complex is formed in the presence of co-cat-
alyst (MAO) and that a vacant site (active site) for coordi-
nation of the olefin must be generated. Further
investigations of the olefin polymerization of such com-
plexes and of the polymerization mechanism are ongoing.
Fig. 1. ORTEP view of 1 in the crystal. The hydrogen atoms are not
shown for clarity. Selected lengths (A) and angles (ꢁ): I(1)–Co(1)
2.5755(13), I(2)–Co(1) 2.6004(13), Co(1)–S(1) 2.246(2), Co(1)–C(1)
2.055(7) and C(1)–Co(1)–S(1) 85.5(2), S(1)–Co(1)–I(1) 92.83(6), S(1)–
Co(1)–I(2) 90.43(6), I(1)–Co(1)–I(2) 96.25(4), C(8)–S(1)–Co(1) 109.6(3),
C(7)–S(1)–Co(1) 97.4(3).
˚

X.-F. Hou et al. / Inorganic Chemistry Communications 9 (2006) 423–425
425
[9] (a) P. Jutzi, M.O. Kristen, J. Dahlhaus, B. Neumann, H.–G.
Stammler, Organometallics 12 (1993) 2980;
Acknowledgments
(b) M. Enders, G. Ludwig, H. Pritzkow, Organometallics 20 (2001)
827 (and its references);
Financial support by the National Science Foundation
of China for Distinguished Young Scholars (20421303, and
20531020) and by the National Basic Research Program
of China (2005CB623800) is gratefully acknowledged.
(c) O. daugulis, M. Brookhart, Organometallics 22 (2003) 4699.
[10] [g5-C5H4(CH2)2SCH2CH3]CoI2 (1): Yield 72%. Anal. Calcd. for
C9H13CoSI2 (465.99 g/mol): C, 23.20; H, 2.81. Found: C, 23.38; H,
2.48. IR (film): m(CSC) 831 cmÀ1. 1H NMR (500 MHz, CDCl3, ppm):
d 5.22 (t, 2H, Cp), 5.08 (t, 2H, Cp), 3.99 (t, 2H, SCH2), 2.49 (t, 2H,
3
CH2), 2.96 (q, 2H, SCH2), 1.34 (t, 3H, CH3, JHH = 7.3 Hz). 13C
Appendix A. Supplementary data
NMR (125 MHz, CDCl3, ppm): d 113.7, 85.3, 83.7, 82.8, 81.6,
(C5H4), 35.7 (CH2CH2S), 30.3 (CpCH2), 25.4 (SCH2CH3), 13.6
(CH3). [g 5-C5H4(CH2)2OCH3]Co(py)I2 (3): Yield 65%. Anal. Found:
C 30.1%, H 3.15%, N 2.81% Calc. for C13H16ONCoI2: C 30.3%, H
3.13%, N 2.72%. 1H NMR (CDCl3, 500 MHz) d: 5.29 (t, 2H, Cp),
5.15 (t, 2H, Cp), 3.52 (t, 2H, OCH2), 3.27 (s, 3H, CH3), 2.46 (t, 2H,
CpCH2), 10.06, 7.78, 7.30 (m, 5H, py). 13C NMR (125 MHz, CDCl3,
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.inoche.2006.
01.010.
ppm):
d
144.4, 137.8, 124.9, (CHpy), 98.0, 85.2, 79.9, (C5H4),
References
70.3(CH2O), 58.4(OCH3), 28.3(CpCH2). IR (KBr) m (cmÀ1): 3428,
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C5H4(CH2)2OCH3]Co(PPh3)I2 (4): Yield 80%. Anal. Found: C 44.4%,
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(CpCH2). IR (KBr) m (cmÀ1): 3390, 2921, 1621,1480, 1433, 1089, 801,
749, 691.
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