Ethylene polymerization and ethylene/styrene copolymerization with secondary phosphine-pendant and phosphide-pendant complexes of Zr and Hf

Article abstract of DOI:10.1016/j.molcata.2004.06.024

Ethylene and styrene polymerizations and ethylene/styrene copolymerization have been examined with a catalytic system obtained by a combination of zirconium or hafnium complexes bearing a secondary phosphine-pendant cyclopentadienyl ligand {η⁵ -C₅H₄(CH₂)₂P(H)R} (R = 2,4,6-trimethylphenyl (Mes), 2,4,6-tri(i-propyl)phenyl (Tip)) or a phosphide-pendant cyclopentadienyl ligand {η⁵ -C₅H₄(CH₂)₂PR-κP} with modified methylaluminoxane (MMAO) or a mixture of methylaluminoxane (MAO) and tri-i-butylaluminium (TIBA) as a cocatalyst. These systems show moderate activity in ethylene polymerization (8-316 g mmol^-1 h^-1) but show inactivity in styrene polymerization. In ethylene/styrene copolymerization, these systems afford ethylene/styrene copolymers with a relatively high styrene content (35-87%).

Full text of DOI:10.1016/j.molcata.2004.06.024

Journal of Molecular Catalysis A: Chemical 221 (2004) 41–45
Ethylene polymerization and ethylene/styrene copolymerization with
secondary phosphine-pendant and phosphide-pendant
complexes of Zr and Hf
Takeshi Ishiyamaa, Katsuhiko Miyoshia, Hiroshi Nakazawab,∗
a
Department of Chemistry, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
b
Department of Chemistry, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan
Received 29 December 2003; received in revised form 28 June 2004; accepted 29 June 2004
Available online 13 August 2004
Abstract
Ethylene and styrene polymerizations and ethylene/styrene copolymerization have been examined with a catalytic system obtained by a
combination of zirconium or hafnium complexes bearing a secondary phosphine-pendant cyclopentadienyl ligand {η5-C5H4(CH2)2P(H)R}
(R = 2,4,6-trimethylphenyl (Mes), 2,4,6-tri(i-propyl)phenyl (Tip)) or a phosphide-pendant cyclopentadienyl ligand {η5-C5H4(CH2)2PR-κP}
with modified methylaluminoxane (MMAO) or a mixture of methylaluminoxane (MAO) and tri-i-butylaluminium (TIBA) as a cocatalyst.
These systems show moderate activity in ethylene polymerization (8–316 g mmol−1 h−1) but show inactivity in styrene polymerization. In
ethylene/styrene copolymerization, these systems afford ethylene/styrene copolymers with a relatively high styrene content (35–87%).
© 2004 Elsevier B.V. All rights reserved.
Keywords: Catalysis; Olefin polymerization; Phosphorus-pendant Cp ligand; Zirconium; Hafnium
1. Introduction
due to preparative difficulties, the first report of preparation of
a phosphide-pendant Cp complex [19] was published about
10 years after the report of amide-pendant Cp complexes.
Several complexes with a phosphide-pendant Cp ligand have
been isolated and characterized to date [20–25]. However,
few studies have been reported on the catalytic activity in
olefin polymerization of the phosphide complexes. This
paper presents the results of ethylene and styrene polymer-
izations, and ethylene/styrene copolymerization promoted
by secondary phosphine-pendant and phosphide-pendant
complexes of Zr and Hf, which we recently reported. These
complexes are listed in Chart 1.
Since the discovery of the homogeneous zirconocene/
methylaluminoxane (MAO) catalyst system [1–4] achieved
a breakthrough in the heterogeneous Ziegler-Natta catalysts,
studies on homogeneous olefin polymerization catalysts
have been extended to a variety of non-metallocene com-
plexes, some of which have exhibited excellent catalytic
reactivities [5–18]. Among them, titanium complexes with
an amide-pendant cyclopentadienyl (Cp) ligand, [(η5-
C5Me4SiMe2NtBu-κN)TiL2] (L = Cl, alkyl group) called
constrained-geometry catalysts (CGC), have been reported
to be effective in olefin copolymerization [10–16]. The great
catalytic activity of group 4 transition-metal complexes
with the amide-pendant Cp ligand has been stimulating the
researchers to prepare analogous phosphide-pendant Cp
complexes and examine their catalytic activities. However,
2. Experimental
2.1. General remarks
∗
All experiments were performed under a nitrogen atmo-
sphere using Schlenk, glovebox, and vacuum line techniques.
Corresponding author. Tel.: +81 6 66053123; fax: +81 6 66052522.
E-mail address: nakazawa@sci.osaka-cu.ac.jp (H. Nakazawa).
1381-1169/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2004.06.024

42
T. Ishiyama et al. / Journal of Molecular Catalysis A: Chemical 221 (2004) 41–45
p-CHMe2 in Tip), 3.06–2.63 (m, 12H, 1,3-H in allyl and
CH2CH2), 1.42 (br, 12H, o-CHMe2 in Tip), 1.32–1.25 (m,
6H, p-CHMe2 in Tip). 13C{1H} NMR (75.5 MHz, C6D6): ␦
154.0 (d, JPC = 4.3 Hz, aromatic-C in Tip), 149.7 (d, JPC
=
1.8 Hz, aromatic-C in Tip), 137.5 (d, JPC = 8.7 Hz, aromatic-
C in Tip), 132.4 (d, JPC = 4.3 Hz, aromatic-C in Tip), 129.2
(m, 1-C in Cp), 121.7 (d, JPC = 5.6 Hz, 2-C in allyl), 103.4 (s,
2,5- or 3, 4-C in Cp), 101.1 (s, 2,5- or 3, 4-C in Cp), 62.9 (s, 1,
3-C in allyl), 39.7 (s, CpCH2), 34.7 (s, p-CHMe2 in Tip), 33.9
(d, JPC = 8.7 Hz, o-CHMe2 in Tip), 27.3 (d, JPC = 14.9 Hz,
PCH2), 25.6 (br-m, o-CHMe2 in Tip), 24.2 (s, p-CHMe2 in
Tip). 31P{1H} NMR (121.5 MHz, C6D6): ␦ 126.73 (s).
2.3. Synthesis of [␩5-CpHf(CH2Ph)3] (Hf-8)
The procedure followed is a modification of that for
[η5-CpZr(CH2Ph)3] [27,28]. A solution of (CH2Ph)MgCl
(1.17 mmol) in 7 mL of THF was added slowly to a solution
of [η5-CpHfCl3(dme)] [29] (0.17 g, 0.39 mmol) in 20 mL of
ether at room temperature. The reaction mixture was stirred
for 1 h, and then the volatile compounds were evaporated
in vacuo. The yellow residue obtained was extracted with
ether/hexane = 2/1 and then filtered. Removal of the solvents
gave yellow wax of Hf-8 (0.14 g, 71%). 1H NMR (300 MHz,
C6D6): ␦ 7.20–7.15 (m, 9H, Ph), 6.67–6.65 (m, 6H, Ph), 5.60
(s, 5H, Cp), 1.60 (s, 6H, CH2Ph). 13C{1H} NMR (75.5 MHz,
C6D6): ␦ 144.1 (s, Ph); 129.3 (s, Ph); 127.6 (s, Ph); 123.2 (s,
Ph); 113.0 (s, Cp); 77.2 (s, CH2Ph).
Chart 1.
All solvents used were dried over Na/K alloy or CaH2, and
distilled before use. Modified methylaluminoxane (MMAO),
which is an alkylaluminoxane containing mainly methyl
groups and partly i-butyl groups as alkyl groups, methyla-
luminoxane, and (Allyl)MgCl were obtained from common
commercial sources and used without further purification.
1H, 13C{1H}, and 31P{1H} NMR spectra were recorded on
a JEOL LA-300 or a JNM-AL400 multinuclear spectrome-
1
ter. H and 13C{1H} NMR data were referenced to SiMe4,
2.4. Ethylene polymerization
and 31P{1H} NMR data were referenced to 85% H3PO4.
The following complexes were synthesized according to lit-
erature methods: the trichloride complexes with secondary
phosphine-pendant ligands (Zr-1, Hf-1, Zr-6, Hf-6) [26], the
tribenzyl complexes having secondary phosphine-pendant
ligands (Zr-2, Hf-2) [25], the phosphide complexes (Zr-4,
Hf-4, Zr-5, Hf-5) [25], the monocyclopentadienyl tribenzyl
complex Zr-8 [27,28]. Zr-3 and Hf-3 were prepared via ther-
molysis of Zr-2 and Hf-2 in toluene, respectively [25], and
their toluene solutions were used directly without isolation
of products in the subsequent polymerization reactions.
MMAO (10.00 mmol) and ca. 180 mL of toluene were
placed in a 500 mL separable reactor under nitrogen atmo-
sphere, and then the reactor was saturated with ethylene.
A toluene solution containing transition-metal precatalyst
(0.01 mmol) was added to the reactor to give 200 mL of
toluene in total. The reaction mixture thus formed was stirred
at 40 ◦C for 1 h with the passage of ethylene (1000 mL/min)
underatmosphericpressure. Then, EtOHandHClwereadded
to terminate the polymerization.
2.5. Styrene polymerization
2.2. Synthesis of [{␩5-C5H4(CH2)2PTip-␬P}Hf(allyl)2]
(Hf-7)
MAO (2.00 mmol), tri-i-butylaluminium (TIBA)
(2.00 mmol), and 10 mL of styrene were placed in a
40 mL ampoule sealed with a septum cap under nitrogen
atmosphere in a glovebox. After the ampoule was warmed
up to a set temperature, a toluene solution containing
transition-metal precatalyst (0.01 mmol) was added to the
reaction mixture. The reaction mixture was stirred for 1 h,
and then polymerization was terminated by adding MeOH.
The synthetic procedure was similar to that for Hf-4 [25].
A solution of (allyl)MgCl (3.75 mmol) in 4 mL of THF was
added to a suspension of Hf-1 (0.88 g, 1.25 mmol) in 20 mL
of ether at room temperature. After stirring overnight, the
volatile compounds were evaporated in vacuo. The orange
residue obtained was extracted with ether/hexane = 2/1 and
then filtered. Removal of the solvents gave a brown pow-
1
der of Hf-7 (0.43 g, 59%). H NMR (300 MHz, C6D6): ␦
2.6. Ethylene/styrene copolymerization
7.23 (d, JHH = 2.0 Hz, 2H, m-H in tri(i-propyl)phenyl (Tip)),
5.57–5.49 (m, 2H, 2-H in allyl), 5.35 (m, 2H, Cp), 5.28
(m, 2H, Cp), 4.39 (m, 2H, o-CHMe2 in Tip), 3.28 (m, 1H,
TIBA (1.00 mmol), 200 mL of styrene, and toluene were
placed in a 1500 mL stainless steel autoclave reactor, and

T. Ishiyama et al. / Journal of Molecular Catalysis A: Chemical 221 (2004) 41–45
43
then the reactor was saturated with ethylene. A toluene solu-
tion containing transition-metal precatalyst (0.01 mmol) and
MAO (10.00 mmol) was added to the reactor to give 200 mL
of toluene in total. The reaction mixture was stirred at a set
temperature for 1 h under ethylene pressure at 3 bar. Then,
polymerization was terminated by adding MeOH.
Molecular weights (Mw and Mn) of polymers were deter-
mined by the GPC analysis using o-dichlorobenzene or 1,2,4-
trichlorobenzene as a solvent and polystyrene as a standard.
Thepercentageofstyrenecomponentsintheethylene/styrene
copolymer (St (%)) was determined by GPC/FTIR measure-
ment [30].
Scheme 1.
Table 2
Results of ethylene polymerization with phosphorus-pendant complexes
having a Tip group
Yield (g)
Activity
(g mmol−1 h−1
Mw ×
Mn ×
Mw/Mn
)
10−4
10−4
Zr-6
Hf-6
Hf-7
0.64
0.29
0.12
64
29
12
18.34
20.51
41.23
0.62
0.75
1.87
29.41
27.52
22.10
3. Results and discussion
The phosphorus-pendant cyclopentadienyl Zr and Hf
complexes in Chart 1 were inactive by themselves in the
polymerization of ethylene and styrene. However, these com-
plexes in combination with a cocatalyst such as an alkylalu-
minoxane exhibited catalytic activity towards ethylene poly-
merization and ethylene/styrene copolymerization, but al-
most none towards styrene polymerization. Modified methy-
laluminoxane is widely used as an olefin polymerization co-
catalyst, and has generally greater stability and greater sol-
ubility in a hydrocarbon solution than methylaluminoxane
[31]. Therefore, MMAO or a mixture of MAO and tri-i-
butylaluminium was used as a cocatalyst in this study.
Polymerization conditions: polym. time, 1 h; amount of catalyst, 0.01 mmol;
amount of MMAO, 10.00 mmol; atmospheric pressure of ethylene; 200 mL
of toluene; temperature, 40 ◦C.
tained using [η5-CpM(CH2Ph)3] (Zr-8, Hf-8) are also listed
in Table 1.
For the Zr complexes, the catalytic activities of the sec-
ondary phosphine complexes (21, for Zr-1, 8 for Zr-2) and
those of the phosphide complexes (21 for Zr-3, 43 for Zr-
4, 30 for Zr-5) are almost the same and these values are
also close to that of the phosphorus-pendant free Zr-8 (35).
For the Hf complexes, the catalytic activities of the sec-
ondary phosphine complex (180 for Hf-1, 80 for Hf-2) and
those of the phosphide complexes (148 for Hf-3, 305 for
Hf-4, and 316 for Hf-5) are almost the same, but these
values are greater than those for the phosphorus-pendant
Zr complexes (8–43) and that for the phosphorus-pendant
free Hf-8 (29). Since the phosphide complex was reported
to be formed through alkylation of the secondary phos-
phine trichloride complex in our previous papers (Scheme 1)
[24,25], it is likely that the precursor secondary phosphine
complexes would be first converted into phosphide com-
3.1. Ethylene polymerization
Ethylene polymerization was conducted with the
phosphorus-pendant Zr and Hf complexes under atmospheric
pressure of ethylene at 40 ◦C. The results of the Zr and
Hf complexes having a 2,4,6-trimethylphenyl (Mes) group
are summarized in Table 1. For comparison, the results ob-
Table 1
Results of ethylene polymerization with phosphorus-pendant complexes
having a Mes group
Table 3
Yield (g)
Activity
(g mmol−1 h−1
Mw ×
Mn ×
Mw/Mn
)
10−4
10−4
Results of styrene polymerization
Temperature (◦C)
Yield (g)
Activity (g mmol−1h−1
)
Zr-1
Hf-1
Zr-2
Hf-2
Zr-3
Hf-3
Zr-4
Hf-4
Zr-5
Hf-5
Zr-8
Hf-8
0.21
1.80
0.08
0.80
0.21
1.48
0.43
3.05
0.30
3.16
0.35
0.29
21
180
8
80
21
148
43
305
30
316
35
29
31.87
7.76
112.88
2.95
22.66
2.94
20.48
6.17
0.65
1.18
1.69
0.62
0.77
0.57
0.63
0.76
0.55
1.06
0.61
0.59
48.95
6.60
66.89
4.75
29.34
5.14
32.31
8.12
18.66
8.39
13.82
9.17
Zr-2
Hf-2
Zr-3
Hf-3
Blank
50
80
0.01
0.13
1
13
50
80
0.04
0.03
4
3
50
80
trace
0.05
–
5
10.20
8.86
8.43
50
80
0.09
0.03
9
3
5.41
50
80
0.03
0.07
–
–
Polymerization conditions: polym. time, 1 h; amount of catalyst, 0.01 mmol;
amount of MMAO, 10.00 mmol; atmospheric pressure of ethylene; 200 mL
of toluene; temperature, 40 ◦C.
Polymerization conditions: polym. time, 1 h; amount of catalyst, 0.01 mmol;
amount of MAO, 2.00 mmol; amount of TIBA, 2.00 mmol; amount of
styrene, 10 mL.

44
T. Ishiyama et al. / Journal of Molecular Catalysis A: Chemical 221 (2004) 41–45
Table 4
Results of ethylene/styrene polymerization
Temperature (◦C)
Yield (g)
Activity (g mmol−1 h−1
)
Mw × 10−4
Mn × 10−4
Mw/Mn
St (%)
Zr-2
Hf-2
Zr-3
Hf-3
50
80
0.46
0.60
46
60
30.97
7.68
2.00
0.89
15.50
8.70
35
64
50
80
0.32
0.93
32
93
15.21
5.99
0.79
0.83
19.30
7.20
78
87
50
80
0.43
1.08
43
108
33.08
9.14
1.85
1.08
17.90
8.50
31
62
80
0.79
79
269
0.58
4.60
75
Polymerization conditions: polym. time, 1 h; amount of catalyst, 0.01 mmol; amount of MAO, 10.00 mmol; amount of TIBA, 1.00 mmol; ethylene pressure,
3 bar; amount of styrene, 200 mL; amount of toluene, 200 mL.
plexes in combination with MMAO, and then into a real
active species. Although it is hard, at present, to specify
the real active species in the catalytic system, we presume
that a cationic phosphide monoalkyl complex formulated as
[(η5-C5H4CH2CH2PMes-κP)MR]+ would serve as an active
species, because analogous cationic amide monoalkyl com-
plexes [(η5-C5Me4SiMe2NtBu-κN)MR]+ (M = Ti, Zr) have
been proposed as an active species in the polymerization re-
action [10,31–39]. One of the reasons for the low activity with
Zr catalyst may come from the short life time of the Zr activite
species, since complexes of the second row transition-metals
in the periodic table are less stable that those of the third row
transition-metals. The large polydispersity in the case of Zr
system may stem from the presence of a few active species
in this system.
Table 2 presents the results of ethylene polymerization
with the complexes having a 2,4,6-tri-i-propylphenyl group
under the same conditions. It is remarkable that the Tip Hf
complexes show much lower activities (29 for Hf-6 versus
180 for Hf-1 and 12 for Hf-7 versus 305 for Hf-4) and larger
Mw/Mn values (22.10–27.52) than the Mes Hf complexes
(6.60–8.12). It is highly probable that the bulky Tip group
would interfere with coordination of ethylene to the metal,
causing the low avtivities. The reason for the large Mw/Mn
values is not clear now.
Table 4 presents the results of ethylene/styrene copoly-
merization at 50 and 80 ◦C. These systems based on the
phosphorus-pendant Cp complexes showed activities. How-
ever, the activities were relatively low compared with those
reported to date [10,42,44]. The polymers obtained were an-
alyzed by GPC/FTIR measurement [30], which revealed that
the polymers contain styrene components. St (%) in Table 4
shows the percentage of styrene components in the poly-
mer. It should be noted that the polymers are not mixtures of
polyethylene and polystyrene but ethylene–styrene copoly-
mers, since these phosphorus-pendant complex systems did
not show activity in styrene polymerization (Table 3). At
higher temperature (80 ◦C), all phosphorus-pendant com-
plex systems exhibited higher activities and higher St (%)
values, which suggests the possibility that these catalysts
can control the ratio of the ethylene/styrene content in the
formed copolymer through thermal conditions. It should
be noted that the catalytic system obtained by combining
phosphorus-pendant complexes and alkylaluminium affords
ethylene/styrene copolymers with a high styrene content,
in contrast with CGC bearing an amide ligand; CGC-type
Ti complexes give the copolymers with styrene contents
limited to maximum 50% [10,44], and CGC-type Zr com-
plexesaffordnocopolymerbutpolyethyleneevenunderethy-
lene/styrene copolymerization conditions [16].
3.2. Ethylene/styrene copolymerization
4. Conclusions
Whether a catalyst has copolymerization activity or not is
one of the interesting subjects in the olefin polymerization
field [40–44]. Therefore, we examined catalytic activities
in ethylene/styrene copolymerization with the phosphorus-
pendant complexes.
The results of styrene polymerization are listed in Table 3.
For comparison, the results of a blank experiment are
also added in Table 3. On the basis of the results of the
blank experiment, it was found that the systems based on
these phosphorus-pendant complexes are almost inactive in
styrene single-polymerization, similarly in the case of [(η5-
C5Me4SiMe2NtBu-κN)ML2] (M = Ti, Zr; L = Cl, alkyl
group) [10,16].
Catalytic activities in the polymerization of ethylene and
styreneandcopolymerizationofethylene/styrenewereexam-
ined for the systems obtained by combination of secondary
phosphine-pendant and phosphide-pendant complexes of Zr
and Hf with alkylaluminium co-catalysts. The systems of
both Zr and Hf complexes exhibit activity in ethylene poly-
merization and catalysts based on the Hf complexes are more
active. In contrast, these systems are inactive in styrene poly-
merization. It should be noted that these systems are active
in the copolymerization of ethylene/styrene and the copoly-
mers obtained have a relatively high styrene content. Such
behavior has not been observed in copolymerizations with
the corresponding amido-pendant Cp complexes.

T. Ishiyama et al. / Journal of Molecular Catalysis A: Chemical 221 (2004) 41–45
45
Acknowledgments
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