Synthesis of allylnickel complexes with phosphine sulfonate ligands and their application for olefin polymerization without activators

Article abstract of DOI:10.1021/om800781b

Phosphine sulfonate nickel complexes [(o-Ar₂- PC ₆SO₃)Ni(allyl)] (Ar = Ph, o-MeOC₆H₄) are prepared and used as catalysts for ethylene polymerization. The products were low molecular weight polyethylen

Full text of DOI:10.1021/om800781b

656
Organometallics 2009, 28, 656–658
Synthesis of Allylnickel Complexes with Phosphine Sulfonate
Ligands and Their Application for Olefin Polymerization without
Activators
Shusuke Noda, Takuya Kochi, and Kyoko Nozaki*
Department of Chemistry and Biotechnology, Graduate School of Engineering, The UniVersity of Tokyo,
7-3-1 Hongo, Bunkyo-Ku, Tokyo 113-8656, Japan
ReceiVed August 14, 2008
fluoride,5b acrylamides, vinyl pyrrolidone,6 and acrylonitrile.7
However, improvements in catalytic activity and molecular
weight of produced polymers are still desired.
In contrast, several nickel catalysts have shown considerable
catalytic activity and heteroatom tolerance. For example,
Brookhart’s nickel/R-diimine catalysts display higher activity
and produce polymers with higher molecular weight and fewer
branches than the corresponding palladium catalysts. Grubbs
and co-workers reported considerably active nickel catalysts
bearing salicylaldiminato ligand for ethylene polymerization to
generate high molecular weight polymers.8
Summary: Phosphine sulfonate nickel complexes [(o-Ar2-
PC6H4SO3)Ni(allyl)] (Ar ) Ph, o-MeOC6H4) are prepared and
used as catalysts for ethylene polymerization. The products were
low molecular weight polyethylenes possessing only methyl
branches. The actiVity for ethylene polymerization with the
phenyl-substituted complex was comparable to that of o-
methoxyphenyl-substituted complex in the absence of actiVator.
Comparison with the corresponding allylpalladium complex
reVealed that the nickel catalysts produced polyethylenes with
lower molecular weight and more branches than the palladium
catalyst.
Nickel catalysts bearing phosphine sulfonate ligands can be
candidates for more desirable catalysts. Rieger and co-workers
have reported the corresponding phenyl nickel catalysts with
triphenylphosphine ligand and performed ethylene polymeri-
zation with or without activators, such as B(C6F5)3 or Ni(cod)2.4d,9
Although improvement in the activity is observed, molecular
weights of the polymers are lower than those produced by the
palladium catalysts. The possibility of triphenylphosphine or
Introduction
Transition-metal-catalyzed insertion polymerization of olefins
has been studied and used considerably due to its great ability
to control polymer microstructures. Particularly, early transition
metal catalysts, such as Ziegler-Natta catalysts, are most widely
utilized for olefin polymerization. Recent intensive studies have
also developed the use of late-transition metals as catalysts for
olefin polymerization.1 One of the most elegant examples is
Brookhart palladium/R-diimine catalysts used for copolymeri-
zation of ethylene with alkyl acrylates.2 The palladium/R-diimine
catalysts produce unique amorphous-like highly branched
polyethylenes with over 100 branches per 1000 carbon atoms
via chain-walking. The catalysts were also successfully applied
to copolymerization of ethylene/R-olefins with alkyl acrylates
for the first time. More recently, Drent and co-workers reported
copolymerization of ethylene with alkyl acrylates3a using in situ
generated palladium catalysts bearing phosphine sulfonate
ligands.3 Polymers produced by the catalysts have very few
branches and acrylate units are incorporated into the polymer
backbone. In recent years, the phosphine sulfonate palladium
catalysts have been extensively studied4-7 because linear
copolymers of ethylene and polar vinyl monomers may provide
control over important properties such as toughness and
adhesion. Studies by many researchers, including our group,
have revealed that in situ generated and isolated phosphine
sulfonate palladium catalysts also copolymerize ethylene with
other polar vinyl monomers, such as vinyl ethers,5a vinyl
(4) (a) Hearley, A. K.; Nowack, R. J.; Rieger, B. Organometallics 2005,
24, 2755–2763. (b) Schultz, T.; Pfaltz, A. Synthesis 2005, 1005–1011. (c)
Haras, A.; Michalak, A.; Rieger, B.; Ziegler, T. J. Am. Chem. Soc. 2005,
127, 8765–8774. (d) Nowack, R. J.; Hearley, A. K.; Rieger, B. Z. Anorg.
Allg. Chem. 2005, 631, 2775–2781. (e) Kochi, T.; Yoshimura, K.; Nozaki,
K. Dalton Trans. 2006, 25–27. (f) Haras, A.; Michalak, A.; Rieger, B.;
Ziegler, T Organometallics 2006, 25, 946–953. (g) Haras, A.; Anderson,
D. W. G.; Michalak, A.; Rieger, B.; Ziegler, T. Organometallics 2006, 25,
4491–4497. (h) Skupov, K. M.; Marella, P. M.; Hobbs, J. L.; McIntosh,
L. H.; Goodall, B. L.; Claverie, J. P. Macromolecules 2006, 39, 4279–
4281. (i) Kochi, T.; Nakamura, A.; Ida, H.; Nozaki, K. J. Am. Chem. Soc.
2007, 129, 7770–7771. (j) Liu, S.; Borkar, S.; Newsham, D.; Yennawar,
H.; Sen, A. Organometallics 2007, 26, 210–216. (k) Newsham, D. K.;
Borkar, S.; Sen, A.; Conner, D. M.; Goodall, B. L. Organometallics 2007,
26, 3636–3638. (l) Vela, J.; Lief, G. R.; Shen, Z.; Jordan, R. F.
Organometallics 2007, 26, 6624–6635. (m) Bettucci, L.; Bianchini, C.;
Claver, C.; Suarez, E. J. G.; Ruiz, A.; Meli, A.; Oberhauser, W. Dalton
Trans. 2007, 5590–5602. (n) Skupov, K. M.; Marella, P. R.; Simard, M.;
Yap, G. P. A.; Allen, N.; Conner, D.; Goodall, B. L.; Claverie, J. P.
Macromol. Rapid Commun. 2007, 28, 2033–2038. (o) Nakamura, A.;
Munakata, K.; Kochi, T.; Nozaki, K. J. Am. Chem. Soc. 2008, 130, 8128–
8129. (p) Borkar, S.; Newsham, D. K.; Sen, A. Organometallics 2008, 27,
3331–3334.
(5) (a) Luo, S.; Vela, J.; Lief, G. R.; Jordan, R. F. J. Am. Chem. Soc.
2007, 129, 8946–8947. (b) Weng, W.; Shen, Z.; Jordan, R. F. J. Am. Chem.
Soc. 2007, 129, 15450–15451.
(6) Skupov, K. M.; Piche, L.; Claverie, J. P. Macromolecules 2008, 41,
2309–2310.
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2007, 129, 8948–8949.
(8) (a) Wang, C.; Friedrich, S.; Younkin, T. R.; Li, R. T.; Bansleben,
D. A.; Day, M. W.; Grubbs, R. H. Organometallics 1998, 17, 3149–3151.
(b) Younkin, R. T.; Connor, F. E.; Henderson, I. J.; Friedrich, K. S.; Grubbs,
H. R.; Bansleben, A. D. Science 2000, 287, 460–462.
(9) Very recently, two groups reported Ni phosphine sulfonate catalyzed
ethylene polymerization independently. (a) Zhou, X.; Bontemps, S.; Jordan,
R. F. Organometallics 2008, 27, 4821–4824. (b) Guironnet, D.; Ru¨nzi, T.;
Go¨ttker-Schnetmann, I.; Mecking, S. Chem. Commun. 2008, ASAP.
* E-mail: nozaki@chembio.t.u-tokyo.ac.jp
(1) (a) Boffa, L. S.; Novak, B. M. Chem. ReV. 2000, 100, 1479–1493.
(b) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. ReV. 2000, 100, 1169–
1203. (c) Gibson, V. C.; Spitzmesser, S. K. Chem. ReV. 2003, 103, 283–
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(2) (a) Johnson, L. K.; Mecking, S.; Brookhart, M. J. Am. Chem. Soc.
1996, 118, 267–268. (b) Mecking, S.; Johnson, L. K.; Wang, L.; Brookhart,
M. J. Am. Chem. Soc. 1998, 120, 888–899.
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Chem. Commun. 2002, 744–745. (b) Drent, E.; van Dijk, R.; van Ginkel,
R.; van Oort, B.; Pugh, R. I. Chem. Commun. 2002, 964–965.
10.1021/om800781b CCC: $40.75
2009 American Chemical Society
Publication on Web 12/18/2008

Notes
Organometallics, Vol. 28, No. 2, 2009 657
Scheme 2
the insoluble sodium salt of the ligand, which is difficult to
separate from excess NaH. Therefore, sodium carbonate was
used as an alternative weaker base. Sulfonic acid 5 was treated
with sodium carbonate in CH2Cl2, followed by the addition of
a toluene solution of [(allyl)NiBr]2 to give the corresponding
nickel complex 4, which was isolated in 74% yield after
recrystallization (Scheme 2). The structure of complex 5 was
also confirmed by X-ray diffraction analysis.
Figure 1. Molecular structure of 1. Selected bond distances (Å)
and angles (deg): Ni(1)sP(1), 2.1845 (16); Ni(1)sO(1), 1.9235
(18);Ni(1)sC(19),2.066(2);Ni(1)sC(20),1.9979(19);Ni(1)sC(21),
1.981 (2); C(19)sC(20), 1.399 (3); C(20)sC(21), 1.413 (3); and
C(19)sC(20)sC(21), 117.98 (16).
Ethylene polymerization by the allylnickel complexes 1 and
4 was examined, and the results are summarized in Table 1.
When the polymerization was performed at 80 °C, only a trace
amount of polyethylene was generated (Table 1, entries 1 and
4). However, raising the reaction temperature to 100 °C
led to formation of low molecular weight polymers (Mn
1400-1700) with activities of 7-9 g · mmol-1 · h-1() 2-3
g · mmol-1 · h-1 · MPa-1) and with relatively narrow polydisper-
sities (Mw/Mn ) 1.5-2.0) (entries 3 and 5). These results show
ethylene polymerization with the allylnickel complexes can be
performed in the absence of activators. The observed dramatic
increase in the activity indicates that a higher reaction temper-
ature is required for initiation than for propagation. Almost no
product was given by in a shorter reaction time (entry 2). It
indicates slow initiation with the allyl nickel complex. Rieger
and co-workers reported that in the presence of B(C6F5)3 as an
activator, phenylnickel/PPh3 complex of o-methoxyphenyl-
substituted 5 catalyzed ethylene polymerization with high
activities but that only a trace amount of polyethylene was
obtained with the phenyl-substituted ligand 2.4d The importance
of the o-methoxy group was emphasized. Therefore, it is
noteworthy that, here in this study, phenyl-substituted complex
1 actually catalyzes ethylene polymerization with activity
comparable to the methoxyphenyl-substituted catalyst 4, both
in the absence of activators. All obtained polymers had certain
branches with 8-13 branches per 1000 carbon atoms. The
number of branches is measured by 13C NMR using inverse-
gated decoupling.10 The generated polyethylenes possess only
methyl branches, and there are no longer side chains, such as
ethyl, propyl, or butyl groups. It indicates that ꢀ-hydride
elimination and reinsertion of the resulting olefin often occurs,
but it occurs mostly at the chain end, and chain-walking further
into the polymer chain does not proceed at a significant rate.
Copolymerization with methyl acrylate is also examined, but
as the result, only poly(methyl acrylate) is obtained.
Scheme 1
phosphine scavengers affecting polymerization lets us investigate
activator- and additional phosphine-free phosphine sulfonate
nickel catalysts. In this paper, we report the synthesis of
allylnickel catalysts bearing phosphine sulfonate ligands and
our examination on ethylene homopolymerization and copo-
lymerization with polar vinyl monomers without any activators.
Results and Discussion
First, preparation of allylnickel complex bearing a phosphine
sulfonate ligand (1) was examined (Scheme 1). When phenyl-
substituted phosphine 2 was treated with NaH in THF, depro-
tonation proceeded smoothly to afford the corresponding sodium
salt of the phosphine sulfonate ligand 3, which is soluble in
THF. A THF solution of 3 was obtained by filtration and directly
used to form a nickel complex. Addition of this THF solution
of 3 to a toluene solution of [(allyl)NiBr]2 gave allylnickel
complex 1, which was isolated in 81% yield. The structure of
complex 1 was confirmed by X-ray crystallography (Figure 1).
As expected, the phosphine sulfonate ligand is bound to the
nickel atom via one of the three oxygen atoms of the sulfonate
group and the phosphorus atom to form a six-membered chelate.
The allyl group binds to nickel in a η3 fashion. The two terminal
allyl carbons, the coordinating phosphorus and the oxygen, and
the nickel are all placed in a single plane. The distance between
the terminal carbon and the nickel is longer for the bond located
trans to the phosphorus from that trans to the oxygen, reflecting
the stronger trans influence of the phosphine than that of the
sulfonate.
Ethylene polymerization with the corresponding Pd complex
bearing a phosphine sulfonate ligand was also examined. The
use of allylpalladium complex [(o-Ar2PC6H4SO3)Pd(allyl)] (Ar
) o-MeOC6H4) (6)4j produced polyethylene with a higher
molecular weight (Mn ) 11500) and higher linearity (less than
1 branch per 1000 carbon atoms) but lower reactivity than nickel
complexes under the same conditions (entry 6). The higher
molecular weight and linearity indicate that allylpalladium
complex 6 bearing phosphine sulfonate ligand has less tendency
to undergo ꢀ-hydride elimination than the corresponding nickel
Synthesis of allylnickel complex with an o-methoxyphenyl-
substituted ligand (4) was then investigated. However, treatment
of sulfonic acid 5 with NaH in THF resulted in formation of
(10) (a) Guan, Z.; Cotts, P. M.; McCord, E. F.; McLain, S. J. Science
1999, 283, 2059–2062. (b) Cotts, P. M.; Guan, Z.; McCord, E.; McLain, S
Macromolecules 2000, 33, 6945–6952.

658 Organometallics, Vol. 28, No. 2, 2009
Notes
Table 1. Ethylene Polymerization with Phosphine-Sulfonate Allyl Complexesa
productivity
(g · mmol-1 · h-1 · MPa-1
temp
(°C)
time
(h)
yield
(g)
branches
(/1000C)
entry
catalyst
(g · mmol-1 · h-1
)
)
Mn
NDb
ND
1400
ND
1700
11600
Mw/Mn
1
2
3
4
5
6
1
1
1
4
4
6
80
100
100
80
100
100
15
1
15
15
15
15
trace
ND
1.3
trace
1.0
0.35
trace
ND
8.9
trace
6.8
trace
ND
2.9
trace
2.2
ND
ND
1.5
ND
2.0
2.3
ND
ND
8
ND
13
2.2
0.7
<1
a Conditions: 0.010 mmol of catalyst, ethylene pressure ) 3.0 MPa, 2.5 mL of toluene. b Not determined.
procedures.3b,4b Phosphine sulfonate palladium complex 6 was
prepared according to literature method.4j
complexes 1 and 4. It is of interest to compare the difference
between nickel complex 4 and palladium complex 6 in relation
to the Brookhart’s R-diimine complexes. The result that the
nickel/phosphine sulfonate complexes produce polyethylenes
with lower molecular weight and more branches than palladium/
phosphine sulfonate is in sharp contrast to that the nickel/R-
diimine complexes are considered to produce more linear
polyethylene with higher molecular weight than the correspond-
ing palladium complexes. The origin of the difference is not
clear at this moment.
The polymerization activity initiated by the allylpalladium 6
is lower than that by alkylpalladium complex: alkyl complex
(o-Ar2PC6H4SO3)PdCH3(2,6-lutidine) produced polyethylene
with 15.0 g · mmol-1 · h-1() 5.0 g · mmol-1Pd · h-1 · MPa-1), Mn
) 75 700, Mw/Mn 2.2, <1 branches over 1000 carbons at 80
°C.7 The lower activity with π-allyl complex 6 may originate
from the higher activation energy requested for the olefin
insertion into the Pd-C bond in the η3-complex when compared
to methylpalladium complex.4j
Preparation of [(o-Ph2PC6H4SO3)Ni(allyl)] (1). To a suspension
of 50 mg of sodium hydride (2.05 mmol) in 20 mL of THF was
added 205 mg of 2 (0.60 mmol), and the resulting mixture was
stirred for 1 h at rt. The mixture was filtered and slowly added to
a solution of 115 mg of [(allyl)NiBr]2 (0.32 mmol) in 10 mL of
toluene and stirred for 20 h at rt. The resulting mixture was filtered
through Celite and evaporated to dryness. The residue was extracted
with CH2Cl2. Slow diffusion of hexane into the concentrated CH2Cl2
solution afforded nickel complex 1 (128.3 mg, 0.29 mmol, 48%
1
yield). H NMR (CDCl3): δ 8.21-8.18 (m, 1H), 7.56-7.38 (m,
12H), 7.08 (t, J ) 8.4 Hz, 1H), 5.70-5.29 (m, 1H), 4.80-0.98 (br
m, 4H). 13C{1H} NMR (CDCl3, -50 °C): δ 48.8 (CH2, allyl), 116.2
(ArC), 119.7 (CH, allyl), 129.4, 129.8, 131.1, 131.9, 133.2, 135.3,
136.6, 148.7 (ArC, ArCH). 31P NMR (CDCl3): δ 8.6. Anal. Calcd
for C21H19NiO3PS: C, 57.18; H, 4.34. Found: C, 56.96; H, 4.48.
Preparation of [{(o-(o-MeOC6H4)2P)C6H4SO3}NiCH2CHCH2]
(4). To a solution of 436 mg of 5 (1.08 mmol) in 20 mL of CH2Cl2
was added 230 mg of sodium carbonate (2.17 mmol), and the
reaction mixture was stirred for 4 h at rt. Then a solution of 210
mg of allylnickel bromide (0.584 mmol) in 20 mL of CH2Cl2 was
added to the mixture and stirred for 3 h at rt. The resulting mixture
was filtered through Celite. Slow diffusion of hexane into the
concentrated CH2Cl2 solution afforded nickel complex 4 as a red-
brown powder (405 mg, 0.808 mmol, 74% yield). 1H NMR
(CDCl3): δ 8.20-8.17 (m, 1H), 7.52-7.46 (m, 3H), 7.30 (t, J )
7.4 Hz, 1H), 7.01-6.92 (m, 7H), 5.59-5.49 (m, 1H), 3.78 (s, 6H),
4.74-0.53 (br m, 4H). 31P NMR (CDCl3): δ 41.7. Anal. Calcd for
C23H23NiO5PS: C, 55.12; H, 4.63. Found: C, 54.96; H, 4.64.
Ethylene Polymerization. To a 50 mL autoclave containing
0.010 mmol of metal complex and a stir bar was transferred 2.5
mL of toluene under argon atmosphere. The mixture was stirred at
rt for 10 min and charged with 3.0 MPa of ethylene. The autoclave
was heated, and the mixture was stirred for 15 h. After the reaction,
MeOH was added to the cooled contents of the autoclave.
Precipitated materials were collected by filtration and washed
several times with MeOH. The remaining solid was dried under
vacuum at 80 °C to afford polyethylene, which was analyzed
without further purification.
Conclusion
Phosphine sulfonate nickel complexes are prepared and used
as catalysts for ethylene polymerization without addition of any
activator. Structures of the obtained low molecular weight
polyethylene were analyzed to detect only methyl branches. The
activity for ethylene polymerization with 1 was comparable to
that with 4. Comparison with the corresponding allylpalladium
complex 6 revealed that the nickel catalysts produced polyeth-
ylenes with lower molecular weight and more branches than
the palladium catalyst.
Experimental Section
General Methods. All manipulations were carried out using the
standard Schlenk technique under argon purified by passing through
1
a hot column packed with BASF catalyst R3-11. H (500 MHz),
13C (126 MHz), and 31P NMR (202 MHz) spectra were recorded
on a JEOL JNM-ECP-500 spectrometer. Elemental analysis was
performed by the Microanalytical Laboratory, Department of
Chemistry, Faculty of Science, the University of Tokyo. Size
exclusion chromatography analyses at 145 °C were carried out with
a Tosoh instrument (HLC-8121) equipped with three columns
(Tosoh TSKgel GMHhr-H(20)HT) by eluting the columns with
o-dichlorobenzene at 1 mL/min.
Acknowledgment. This work was supported by a Grant-
in-Aid for Scientific Research on Priority Areas “Advanced
Molecular Transformations of Carbon Resources” from the
Ministry of Education, Culture, Sports, Science and Technol-
ogy, Japan.
Dichloromethane, toluene, THF, and hexanes were purified by
the method of Pangborn et al.11 2-(Diphenylphosphino)benzene-
sulfonic acid (2) and 2-{di(2-methoxyphenyl)phosphino}ben-
zenesulfonic acid (5) were prepared according to literature
Supporting Information Available: X-ray crystallographic data
of 1 and 4 (CIF). This material is available free of charge via the
Internet at http://pubs.acs.org.
(11) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518–1520.
OM800781B