Synthesis and reactions of palladium and platinum complexes bearing diphosphinidenecyclobutene ligands: A thermally stable catalyst for ethylene polymerization

Article abstract of DOI:10.1002/1521-3773(20001215)39:24<4512::AID-ANIE4512>3.0.CO;2-I

A cationic methylpalladium complex bearing a diphosphinidenecyclobutene ligand generated by the treatment of the corresponding dimethyl complex 1 with H (OEt₂)₂[BAr₄] (Ar = 3,5-(CF₃)₂C₆H₃), exhibits good catalytic activity for ethylene polymerization in soluton (up to 128 kgh^-1 (molcat.)^-1). The catalyst is thermally stable and promotes the polymerization even at 100°C without notable decomposition.

Full text of DOI:10.1002/1521-3773(20001215)39:24<4512::AID-ANIE4512>3.0.CO;2-I

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Complexes 1 and 2 were prepared by ligand displacement
of [PdMe2Ctmeda)] Ctmeda ˆ tetramethylethylenediamine)
with phenyl- and trimethylsilyl-substituted ligands in Et2O
and isolated as orange crystals in 94% and 63% yields,
respectively. Complex 3 was not obtained by this method but
prepared in 60% yield by using [PdMe2Ccod)] Ccod ˆ cy-
clooctadiene) in place of [PdMe2Ctmeda)]. The platinum
complex 4 was synthesized from [Pt2Me4CSMe2)2] in 89%
yield. All complexes were characterized by NMR spectros-
copy and elemental analysis Csee Supporting information).
The X-ray structure of 4,[7] which clearly shows chelate
coordination of the diphosphinidenecyclobutene ligand CFig-
ure 1). The two aryl rings on the phosphorus atoms are almost
Synthesis and Reactions of Palladium and
Platinum Complexes Bearing
Diphosphinidenecyclobutene Ligands:
A Thermally Stable Catalyst for Ethylene
Polymerization**
Shintaro Ikeda, Fumie Ohhata, Masaki Miyoshi,
Rika Tanaka, Tatsuya Minami, Fumiyuki Ozawa,* and
Masaaki Yoshifuji*
Diphosphaalkenes are phosphorus analogues of diimines
and form stable chelate rings with transition metal species.[1±3]
The coordination structures resemble those of diimine com-
plexes. However, owing to the unique electronic nature of
ˆ
P C bonds, diphosphaalkene complexes are expected to
possess rather intriguing chemical properties, significantly
different from the diimine analogues. Thus, we have been
interested in the reaction chemistry of diphosphaalkene
complexes, particularly in catalytic systems; data for such
systems is extremely limited.[2]
Herein we examine the synthesis, structures, and catalytic
properties of some methylpalladium and platinum complexes
C1 ± 4) coordinated with 3,4-bis[C2,4,6-tri-tert-butylphenyl)-
phosphinidene]cyclobutene derivatives.[4] A cationic mono-
methylpalladium complex derived from 1 exhibits good
catalytic activity for ethylene polymerization.
Figure 1. Molecular structure of 4. Hydrogen atoms are omitted for clarity.
Selected bond lengths [Š] and angles [8]: Pt-CC1) 2.093C3), Pt-P 2.2909C8),
P-CC2) 1.669C3), P-CC10) 1.829C3), CC2)-CC2)* 1.498C5), CC2)-CC3) 1.480C4),
CC3)-CC3)* 1.410C6), CC3)-CC4) 1.449C4); P-Pt-P* 82.85C4), CC1)-Pt-CC1)*
85.1C2), P-Pt-CC1) 178.5C1), P-Pt-CC1)* 96.1C1), Pt-P-CC2) 111.2C1), Pt-P-
CC10) 136.9C1), CC2)-P-CC10) 111.8C1), P-CC2)-CC2)* 117.3C1), P-CC2)-CC3)
154.4C2), CC2)*-CC2)-CC3) 88.3C2), CC2)-CC3)-CC3)* 91.7C2), CC2)-CC3)-CC4)
131.5C3), CC3)*-CC3)-CC4) 136.7C2).
R
R
P
tBu
tBu
tBu
P
tBu
M
tBu
Me
tBu
Me
perpendicular to the square planar coordination plane,
making a dihedral angle of 92.52C8)8. The distance between
1: M = Pd, R = Ph
2: M = Pd, R = SiMe3
3: M = Pd, R = H
4: M = Pt, R = Ph
À
platinum and the methyl carbon CPt CC1) ˆ 2.093C3) Š) is
slightly longer than that of the diimine analogues C2.05 ±
2.079 Š),[8] showing a trans-influence for the diphosphaalkene
ligand that is slightly higher than that of the diimine ligands.
Table 1 lists the results of the ethylene polymerization
catalyzed by the palladium complexes. Similar to the diimine
analogues, dimethylpalladium complexes 1 ± 3 were inactive,
while their monomethyl derivatives C5 ± 7), generated in situ
by the treatment of 1 ± 3 with HCOEt2)2BAr4 CArˆ 3,5-
CCF3)2C6H3),[9] catalyzed the polymerization.
The diphosphaalkene ligands in 1 ± 4 were chosen with
reference to findings reported by Brookhart et al. on nickel-
and palladium-based catalysts for ethylene polymeriza-
tion.[5, 6] There the key to high catalytic activity was the use
of a-diimine ligands having bulky aryl groups at the nitrogen
atoms. The diphosphinidenecyclobutene ligands possess sim-
ilar structural features.
[*] Prof. Dr. F. Ozawa, S. Ikeda, F. Ohhata, M. Miyoshi, R. Tanaka,
Dr. T. Minami
Department of Applied Chemistry, Faculty of Engineering
Osaka City University
Table 1. Ethylene polymerization catalyzed by diphosphinidenecyclobutene
complexes of palladium.
Sumiyoshi-ku, Osaka 558-8585 CJapan)
Fax : C‡81)6-6605-2978
Entry[a] Precursor Temperature Pressure Activity
complex [8C]
Mw CMw/Mn)[b]
[kgfcmÀ2] [kghÀ1 Cmolcat)À1] [kgmolÀ1
]
E-mail: ozawa@a-chem.eng.osaka-cu.ac.jp
1
2
3
4
5
6
7
8
1
1
1
1
1
1
2
3
60
70
70
70
80
100
70
70
10
5
86.3
54.3
128
121
123
90.728.6 C12.4)
4.1
2.6
13.9 C10.5)
21.2 C9.2)
18.7 C14.8)
4.2 C6.6)
Prof. Dr. M. Yoshifuji
Department of Chemistry, Graduate School of Science
Tohoku University
10
30
10
10
10
10
Aoba, Sendai 980-8578 CJapan)
Fax : C‡81)22-217-6562
28.9 C13.9)
E-mail: yoshifj@mail.cc.tohoku.ac.jp
33.1 C5.2)
11.8 C6.8)
[**] This work was supported by a Grant-in-Aid for Scientific Research on
Priority Area ªThe Chemistry of Inter-element Linkageº from the
Ministry of Education, Science, Sports, and Culture, Japan.
[a] Reactions were performed in chlorobenzene C20 mL) for 1 h using 10 mmol of
Supporting information for this article is available on the WWW under catalysts generated from the precursor complexes and HCOEt2)2BAr4 CArˆ 3,5-
http://www.wiley-vch.de/home/angewandte/ or from the author. CCF3)2C6H3). [b] Determined by GPC based on polyethylene standards.
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Angew. Chem. Int. Ed. 2000, 39, No. 24

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[6] For review, see: a) S. D. Ittel, L. K. Johnson, M. Brookhart, Chem.
Rev. 2000, 100, 1169; b) G. J. P. Britovsek, V. C. Gibson, D. F. Wass,
Angew. Chem. 1999, 111, 448; Angew. Chem. Int. Ed. 1999, 38, 428.
[7] Crystallographic data for 4: C54H74P2Pt, Mr ˆ 980.22, orthorhombic,
space group Pbcn CNo. 60), a ˆ 17.9602C2), b ˆ 18.3428C2), c ˆ
A typical procedure for polymerization Centry 3) is as
follows. An orange solution of 5, which was prepared by the
reaction of 1 C9.30 mg, 10 mmol) with HCOEt2)2BAr4 C10.7mg,
10 mmol) in chlorobenzene C5 mL) at room temperature, was
transferred by cannula into a 150 mL pressure bottle and
diluted with chlorobenzene C15 mL). Ethylene gas was
charged, and the mixture was mechanically stirred at 708C
for 1 h under a constant pressure C10 kgfcmÀ2; 1 kgf ˆ 9.81 N).
At this stage, the reaction system was a clear orange solution
containing a small quantity of white precipitates. The mixture
was poured into MeOH C80 mL), and the resulting precip-
itates were collected by filtration and dried under vacuum to
give a white solid of polyethylene C1.34 g). The reaction could
be carried out in 1,2-dichloroethane in place of chlorobenzene
at almost the same catalytic activity C124 kghÀ1 Cmolcat)À1). In
this case, however, precipitation of polymer from the reaction
solution was considerable and the molecular weight was
lowered CMw ˆ 12.9 kgmolÀ1, Mw/Mn ˆ 7.1).
15.2851C2) Š,
Vˆ 5035.5C1) Š3,
Z ˆ 4,
rcalcd ˆ 1.293 gcmÀ3
,
mCMoKa) ˆ 28.71 cmÀ1, Tˆ 296 K, RCF 2) CRwCF 2)) ˆ 0.031 C0.042) for
3202 data with I > 3sCI). Crystallographic data Cexcluding structure
factors) for the structure reported in this paper have been deposited
with the Cambridge Crystallographic Data Centre as supplementary
publication no. CCDC-147540. Copies of the data can be obtained
free of charge on application to CCDC, 12 Union Road, Cambridge
CB21EZ, UK Cfax: C‡44)1223-336-033; e-mail: deposit@ccdc.cam.
ac.uk).
[8] K. Yang, R. J. Lachicotte, R. Eisenberg, Organometallics 1998, 17,
5102.
[9] The formation of 5 in solution was supported by NMR spectroscopy.
The monomethyl structure of 5 was further confirmed by using its
acetonitrile adduct which was isolated. 1H NMR C300 MHz, CD2Cl2):
d ˆ 1.39 Cdd, JP,H ˆ 9.3, 3.3 Hz, 3H; PdMe), 1.44, 1.45, 1.59, 1.60, 1.60,
1.61 Ceach s, each 9H; tBu), 2.30 Cs, 3H; MeCN), 6.78 Cd, JH,H ˆ 7.8 Hz,
2H; o-Ph), 6.84 Cd, JH,H ˆ 8.1 Hz, 2H; o-Ph), 6.97Ct, JH,H ˆ 8.1 Hz, 2H;
m-Ph), 6.98 Ct, JH,H ˆ 7.8 Hz, 2H; m-Ph), 7.24 Ct, JH,H ˆ 7.8 Hz, 2H; p-
As seen from entries 3, 7, and 8 in Table 1, the catalytic
activity was highly sensitive to the R groups of the diphos-
phinidenecyclobutene ligands; the phenyl-substituted catalyst
5 derived from 1 exhibited much higher activity than the
others. The activity thus observed is similar to the level of the
diimine-based palladium catalysts.[6] Higher pressure tends to
improve the catalytic activity but causes a drop in the
molecular weight Centries 2 ± 4). The activity reached the
maximum at around 708C Centry 3).
Noteworthy is that the present catalysts bearing diphosphi-
nidenecyclobutene ligands possess extremely high thermal
stability in the reaction solutions; no sign of decomposition
was observed even at 1008C Centry 6). This property is
remarkable when compared with the diimine analogues[10]
and may be attributed to good coordination ability of the
phosphorus-based ligands with a soft palladium center.
Ph), 7.57 Cs, 4H; BAr), 7.61 Cd,JP, H ˆ 2.7Hz, 2H; PAr), 7.71 Cd, JP, H
ˆ
4.2 Hz, 2H; PAr), 7.73 Cs, 8H; BAr);13C{1H} NMR C75 MHz, CD2Cl2):
d ˆ 3.4 Cs, MeCN), 14.5 Cdd, JC,P ˆ 94, 3 Hz, PdMe), 31.3, 31.5, 33.8,
33.8, 34.1, 34.1 Ceach s, CMe3), 35.8, 36.0, 38.7, 38.7, 39.8, 39.9 Ceach s,
CMe3), 122.7Cs, N CMe); 31P{1H} NMR C121 MHz, CD2Cl2): d ˆ 133.6,
159.9 Ceach d, JP, P ˆ 30 Hz); elementary analysis calcd C%) for
C87H86BF24NP2Pd: C 58.68, H 4.87, N 0.79, found: C 58.25, H 4.75, N
0.73.
ˆ
[10] It was found that the diimine complex [PdMe{Ar'N CCMe)-
CCMe) NAr'}] [BAr4] CAr' ˆ 2,6-CiPr)2C6H3)[5a] under the reaction
conditions of entry 3 in Table 1 immediately starts to decompose
giving metallic palladium and loses all catalytic activity within 15 min,
1.10 g of a sludgy, dark polymer was obtained using 10 mmol of the
catalyst.
‡
À
ˆ
Received: August 4, 2000 [Z15585]
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Derivatives Using Selenocarbene Complexes as
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Hiroyuki Katayama, Hideto Urushima,
Tsuneo Nishioka, Chikaya Wada, Masato Nagao, and
Fumiyuki Ozawa*
With the advent of well-defined alkylidene catalysts of
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[*] Prof. Dr. F. Ozawa, Dr. H. Katayama, H. Urushima, T. Nishioka,
C. Wada, M. Nagao
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Department of Applied Chemistry, Faculty of Engineering
Osaka City University
Sumiyoshi-ku, Osaka 558-8585 CJapan)
Fax : C‡81)6-6605-2978
E-mail: ozawa@a-chem.eng.osaka-cu.ac.jp
[**] This work was supported by a Grant-in-Aid for Scientific Research
from the Ministry of Education, Science, Sports, and Culture, Japan.
Supporting information for this article is available on the WWW under
http://www.wiley-vch.de/home/angewandte/ or from the author.
Angew. Chem. Int. Ed. 2000, 39, No. 24
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