Boryl-substituted zirconocene dichloride complexes as catalyst precursors for homogeneous ethylene polymerization

Article abstract of DOI:10.1515/znb-2007-0303

The synthesis and characterization of 16 new boryl-substituted zirconocene dichloride complexes are reported. After activation with methyl aluminoxane (MAO) these complexes are catalysts for homogeneous ethylene polymerization. The combination of these co

Full text of DOI:10.1515/znb-2007-0303

Boryl-substituted Zirconocene Dichloride Complexes as Catalyst
Precursors for Homogeneous Ethylene Polymerization
Alexandra Kestel-Jakob and Helmut G. Alt
Laboratorium fu¨r Anorganische Chemie, Universita¨t Bayreuth, D-95440 Bayreuth, Germany
Reprint requests to Prof. Dr. H. G. Alt. Fax: +49-921-55-2044. E-mail: helmut.alt@uni-bayreuth.de
Z. Naturforsch. 2007, 62b, 314 – 322; received December 11, 2006
Dedicated to Professor Helgard G. Raubenheimer on the occasion of his 65th birthday
The synthesis and characterization of 16 new boryl-substituted zirconocene dichloride complexes
are reported. After activation with methyl aluminoxane (MAO) these complexes are catalysts for
homogeneous ethylene polymerization. The combination of these complexes with nickel catalysts
containing Lewis basic substituents produces polymers with bimodal molecular weight distributions.
Key words: Zirconium, Ethylene Polymerization, Donor-Acceptor Catalysts, Bimodal Molecular
Weight Distributions
Introduction
Only few metallocene catalysts carrying boryl-
substituted cyclopentadienyl derivatives are known in
the literature [1, 2]. Complexes with boryl-substituted
indenyl ligands are still unkown. The preparation of
boryl-substituted metallocene complexes via hydro-
boration of allyl complexes has been considered very
promising [3 – 6].
Scheme 1. Hydroboration of ω-alkenyl-substituted zircono-
cene complexes.
Cyclopentadienyl complexes with Lewis acidic
boryl substituents are of growing interest as self-
activating alkene polymerization catalysts [7, 8]. Fur-
ther potential arises from the connection of Lewis
acidic boryl-substituted metallocene complexes with
catalyst compounds containing a Lewis base func-
tion like an (α-diimine)nickel complex. These nickel
complexes have been known for a long time and
were applied by Brookhart as polymerization catalysts
[9 – 18].
Our aim was to produce polymers with bimodal
molecular weight distributions based on the features
of these two complex types. In the literature, re-
lated donor-acceptor-complexes are already known
[19 – 23]. The idea was to prepare dinuclear complexes
by donor-acceptor coupling.
conocene complex [24, 25] with 9-BBN (9-H-bora-
◦
bicyclo[3.3.1]nonane) at −70 C in THF (Scheme 1).
The obtained complexes were characterized by NMR
spectroscopy (Table 1). Fig. 1 gives a survey of the
synthesized zirconocene dichloride complexes.
Polymerization of ethylene
The synthesized complexes were activated with
MAO (Al : Zr = 2 500: 1) and used for the homoge-
neous polymerization of ethylene. The polymerization
activity of the zirconocene complexes with boryl sub-
stituents showed a dependence on the distance between
the ring systems and the 9-BBN group. The highest ac-
tivity was observed with the cyclopentadienyl-indenyl
systems. These complexes were substituted with one or
two boryl moieties. Complex 6 was the most active one
showing an activity of 68 300 [kg(prod)/mol(Zr)· h].
Results and Discussion
Synthesis of the boryl-substituted zirconocene dichlo-
ride complexes 1 – 16
The metallocene complexes 9 – 11 show an increas-
Boryl-substituted zirconocene complexes can be ing catalytic activity with an increasing number of car-
synthesized by the reaction of an ω-alkenyl zir- bon atoms between the 9-BBN group and the rings due
0932–0776 / 07 / 0300–0314 $ 06.00 © 2007 Verlag der Zeitschrift fu¨r Naturforschung, Tu¨bingen · http://znaturforsch.com
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A. Kestel-Jakob – H. G. Alt · Boryl-substituted Zirconocene Dichloride Complexes as Catalyst Precursors
Table 1. NMR data of compounds 1 – 16a.
315
Compound
1HNMR
13C NMR
11B
NMR
[J(H,H) in Hz]
7.81 (d, 2H, Flu-H) [8.3], 7.69 (d, 2H, Flu-H) [7.8], Cq: 144.4, 143.5, 142.2, 142.1, 125.3; CH: 128.6, 88.7
7.33 – 7.19 (m, 4H, Ar-CH), 7.02 (m, 4H, Ar-CH), 128.2, 127.8, 127.1, 127.0, 127.0, 126.9, 120.6,
5.55 (m, 1H, Ind-H3), 5.05 (m, 1H, Ind-H2), 1.77 – 120.2, (Ar-CH), 99.6 (Ind-C22), 31.5 (B-CH, br);
1.25 (m, 20H; 9 CH2, 2 CH9−BBN
)
CH2: 36.9, 33.4, 27.7, 23.6; 25.3 (B-CH2, br)
7.70 (d, 2H, Flu-H) [6.1], 7.36 – 7.27 (m, 10H, Ar- Cq: 148.3, 144.8, 143.5, 142.1, 120.6; CH: 127.9, 88.2
CH), 6.81 (m, 1H, Ind-H3), 6.50 (m, 1H, Ind-H2), 127.0, 126.9, 126.8, 125.2, 125.1, 123.2, 121.4, 120.2
1.90 – 1.17 (m, 22H; 10 CH2, 2 CH9−BBN
)
(Ar-CH), 30.8 (B-CH, br); CH2: 36.9, 33.4, 31.7,
25.5, 23.6 25.6 (B-CH2, br)
7.63 (d, 2H, Flu-H) [7.2], 7.26 (d, 2H, Flu-H) [7.2], Cq: 143.5, 142.2, 139.8, 139.3, 120.6; CH: 128.1, 88.0
7.28 – 7.15 (m, 8H, Ar-CH), 6.43 (m, 1H, Ind-H3), 127.8, 127.5, 127.4, 127.0, 126.9, 125.3, 120.2 (Ar-
6.21 (m, 1H, Ind-H2), 2.14 – 1.19 (m, 24H; 11 CH2, CH), 33.4 (B-CH, br); CH2: 36.9, 34.5, 27.2, 21.4,
2 CH9−BBN
)
21.1, 20.7 25.8 (B-CH2, br)
7.50 (m, 2H, Ar-CH), 7.13 – 7.01 (m, 5H, Ar-CH), Cq: 140.3, 139.0, 120.1; CH: 131.3, 129.3, 126.6, 88.1
6.86 (d, 2H, Ar-CH) [3.2], 6.34 (d,2H, Cp) [3.2], 125.9, 125.6, 125.4, 124.4, 124.0, 121.5, 116.9 (Ar-
5.86 – 5.73 (m, 2H, Cp), 5.41 (m, 1H, Ind-H3), 5.40 CH), 113.2 (Cp-CH), 112.8 (Cp-CH), 96.7, (Ind-C2),
(m, 1H, Ind-H2), 3.34 (m, 1H, CH2-Phenyl), 3.12 (m, 31.3 (B-CH, br); CH2: 34.4, 33.5, 26.2, 23.6, 23.0;
1H, CH2-Phenyl), 2.64 (m, 2H, CH2-Cp), 1.80 – 1.29 25.7 (B-CH2, br)
(m, 18H; 8 CH2, 2 CH9−BBN
)
7.34 (m, 2H), 7.23 – 6.91 (m, 7H), 6.42 (m, 1H, Cp), Cq: 141.8, 137.7, 121.4; CH: 128.9, 126.3, 125.5, 85.2
6.38 (m, 1H, Cp), 6.29 (m, 1H, Cp), 6.07 (m, 1H, Cp), 124.9, 124.4, 124.2, 121.6, 119.1, 116.3 (Ar-CH),
5.96 (m, 1H, Ind-H3), 5.93 (m, 1H, Ind-H2), 3.25 (m, 113.7 (Cp-CH), 113.4 (Cp-CH), 97.5 (Ind-C2), 30.8
2H, CH2-Ind), 2.72 (m, 2H, CH2-Phenyl), 1.83 – 1.44 (B-CH, br); CH2: 33.7, 33.5, 30.4, 25.7, 23.5, 23.0;
(m, 20H)
28.0 (B-CH2, br)
7.36 – 7.33 (m, 2H, Ar-CH), 7.15 – 7.02 (m, 7H, Ar- Cq: 141.8, 135.5, 121.1; CH: 128.9, 128.7, 126.3, 87.2
CH), 6.58 (m, 1H, Cp), 6.36 (d, 1H, Cp) [3.3], 5.88 125.7, 125.5, 125.0, 124.5, 124.3, 117.9, 116.5 (Ar-
(m, 1H, Cp), 5.70 (d, 1H, Cp) [2.8], 5.49 (d, 1H, Ind- CH), 113.5 (Cp-CH), 112.8 (Cp-CH), 96.8 (Ind-C2),
H3) [2.8], 5.34 (d, 1H, Ind-H2) [2.8], 3.28 (m, 2H, 31.3 (B-CH, br); CH2: 36.3, 34.0, 33.6, 33.4, 30.5,
CH2-Ind), 2.85 (m, 2H, CH2-Phenyl), 2.64 (m, 2H, 30.4, 24.6, 23.6 28.3 (B-CH2, br)
CH2-Cp), 2.09 – 1.20 (m, 20H)
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A. Kestel-Jakob – H. G. Alt · Boryl-substituted Zirconocene Dichloride Complexes as Catalyst Precursors
Table 1 (continued).
Compound
1HNMR
[J(H,H) in Hz]
13C NMR
11B
NMR
7.48 (m, 2H, Ar-CH), 7.15 – 6.85 (m, 7H, Ar-CH), Cq: 140.3, 135.4, 120.9; CH: 129.3, 128.6, 127.7, 87.7
6.32 (d, 1H) [3.3], 5.88 (m, 1H), 5.81 (d, 1H) [3.3], 125.9, 125.5, 125.4, 124.4, 117.6, 116.6 (Ar-CH),
5.72 (m, 1H), 5.51 (m, 1H), 5.47 (m, 1H), 2.63 (m, 113.2 (Cp-CH), 112.9 (Cp-CH), 111.9, 96.6 (Ind-C2),
2H, CH2-Phenyl), 1.86 – 1.32 (m, 22H)
31.4 (B-CH, br); CH2. 33.6, 33.3, 32.9, 30.9, 25.7,
24.6, 23.7; 27.7 (B-CH2, br)
7.30 (m, 2H, Ar-CH), 7.15 – 6.98 (m, 7H, Ar-CH), Cq: 141.8, 134.9, 124.9; CH: 128.9, 128.6, 126.3, 87.8
6.85 (m, 1H), 6.34 (m, 1H), 5.84 (m, 1H), 5.46 (m, 125.7, 125.0, 124.3, 121.1, 117.7, 116.4, 115.0 (Ar-
1H), 5.34 (m, 1H), 5.33 (m, 1H), 3.23 (m, 2H, CH2- CH), 113.6 (Cp-CH), 112.9 (Cp-CH), 96.8 (Ind-C2),
Ind), 2.83 (m, 2H, CH2-Phenyl), 2.48 (m, 2H, CH2- 30.3 (B-CH, br); CH2: 36.3, 34.9, 31.9, 29.8, 29.7,
Cp), 2.10 (m, 2H), 1.43 – 1.22 (m, 22H)
27.2, 25.6, 23.0 33.4 (B-CH2, br)
7.67 (m, 2H, Ar-CH), 7.32 – 7.16 (m, 2H, Ar-CH), Cq: 134.7, 122.1; CH: 127.1, 125.5, 125.1, 124.8, 88.7
6.98 (m, 1H, Ind-H3), 6.70 (d, 1H, Ind-H2) [3.4], 6.06 124.4, 117.9, 116.7 (Ar-CH), 113.5 (Cp-CH), 112.9
(m, 1H, Cp), 5.85 (m, 1H, Cp), 5.67 (m, 1H, Cp), 5.54 (Cp-CH), 97.2 (Ind-C2), 32.2 (B-CH, br); CH2: 34.5,
(m, 1H, Cp), 2.76 (m, 2H, CH2-Cp), 2.15 (m, 2H), 33.6, 33.4, 27.3, 25.7, 24.8, 23.6; 27.7 (B-CH2, br)
1.99 – 1.31 (m, 36H)
7.53 (m, 2H, Ar-CH), 7.24 – 7.15 (m, 1H, Ar-CH), Cq: 135.4, 122.2; CH: 125.6, 125.0, 124.7, 124.4, 87.7
6.89 (m, 1H), 6.56 (d, 1H, Ind-H3) [3.2], 5.98 (d, 122.1, 117.8, 116.4 Ar-CH), 113.6 (Cp-CH), 112.9
1H, Ind-H2) [3.1], 5.91 (m, 1H, Cp), 5.71 (m, 1H, (Cp-CH), 97.2 (Ind-C2), 31.4 (B-CH, br); CH2: 34.7,
Cp), 5.56 (m, 1H, Cp), 5.44 (m, 1H, Cp), 3.08 (m, 34.0, 33.4, 30.5, 25.7, 24.6, 23.6, 23.0; 27.7 (B-CH2,
2H, CH2-Ind), 2.64 (m, 2H, CH2-Cp), 2.08 (m, 2H), br)
1.82 – 1.16 (m, 34H)
7.53 (d, 2H, Ar-CH) [8.8], 7.22 – 7.15 (m, 2H, Ar- Cq: 135.4, 122.4; CH: 126.3, 125.6, 125.0, 124.6, 86.3
CH), 6.88 (m, 1H), 6,56 (d, 1H) [3.3], 5.94 (m, 1H), 124.4, 122.4, 117.8, 116.5 (Ar-CH), 113.5 (Cp-CH),
5.72 (d, 1H) [2.2], 5.54 (d, 1H) [2.2], 5.40 (d, 1H) 112.8 (Cp-CH), 96.9 (Ind-C2), 31.3 (B-CH, br); CH2:
[2.2], 3.08 (m, 2H, CH2-Ind), 2.65 (m, 2H, CH2-Cp), 36.3, 34.0, 33.6, 33.4, 30.4, 24.6, 23.6; 28.3 (B-CH2,
1.86 – 1.19 (m, 40 H)
br)
7.68 (m, 2H, Flu-H), 7.21 – 7.14 (m, 6H, Flu-H), 6.38 Cq: 145.8, 141.6, 141.2, 141.1; CH: 129.4, 129.2, 87.1
(m, 1H, Cp), 5.54 (m, 1H, Cp), 5.36 (m, 1H, Cp), 2.46 128.8, 127.3, 127.0, 126.5, 124.8, 120.4, 120.3, 29Si
(m, 2H, CH2-Cp), 1.87 – 1.16 (m, 18 H), 0.96 (t, 6H, 118,8, 111.1, 32.5 (B-CH, br); CH2: 33.9, 27.3 (B- NMR
CH3), 0.86 (m, 4H, Si-CH2)
CH2, br), 25.7, 24.8, 23.7, 3.8 (Si-CH2); CH3: 6.2
n. b.
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A. Kestel-Jakob – H. G. Alt · Boryl-substituted Zirconocene Dichloride Complexes as Catalyst Precursors
317
Table 1 (continued).
Compound
1HNMR
[J(H,H) in Hz]
13C NMR
11B
NMR
7.73 (d, 2H, Flu-H) [8.2], 7.30 (m, 6H, Flu-H), 6.49 Cq: 145.5, 145.3, 141.0, 140.9; CH: 126.2, 126.1, 89.8
(m, 1H, Cp), 6.15 (m, 1H, Cp), 5.82 (m, 1H, Cp), 126.0, 125.9, 125.9, 125.8, 125.7, 125.7, 125.6, 29Si
2.13 – 1.26 (m, 24H), 0.71 (s, 3H, Si-CH3), 0.74 (s, 124.6, 120.1, 28.7 (B-CH, br); CH2: 33.6, 32.2, NMR
3H, Si-CH3)
31.4, 27.7 (B-CH2, br), 25.6, 24.2, 23.6, 22.9; CH3: −1.1
−0.8
7.78 (d, 1H, Flu-H) [8.5], 7.31 – 7.48 (m, 2H), 7.15 – Cq: 145.9, 145.6, 145.5, 143.1, 141.1; CH: 129.1, 88.8
7.29 (m, 9H), 6.05 (s, 1H, Ind-H2), 2.63 (m, 2H, 127.8, 127.8, 126.6, 126.5, 125.9, 125.3, 124.6, 29Si
CH2-Ind), 2.08 – 2.17 (m, 2H), 1.87 – 1.22 (m, 16H), 124.5, 124.3, 123.4, 120.5, 119.7, 29.1 (B-CH, br); NMR
0.29 (s, 3H, Si-CH3), 0.08 (s, 3H, Si-CH3)
CH2: 34.4, 33.4, 32.3, 27.7 (B-CH2, br), 25.7, 24.9, 6.9
23.6; CH3: −8.0, −9.9
7.82 (m, 2H, Flu-H), 7.74 – 7.48 (m, 2H, Flu-H), Cq: 142.6, 142.6, 41.8; CH: 128.3, 127.9, 127.3, 86.0
7.33 – 6.92 (m, 4H, Flu-H), 5.81 (m, 1H, Cp), 5.48 127.2, 127.1, 126.9, 119.6, 32.5 (B-CH, br); CH2:
(m, 1H, Cp), 5.25 (m, 1H, Cp), 2.04 – 1.25 (m, 20H), 33.6, 27.3 br, 26.9, 25.7, 24.8; CH3: 25.6
1.12 (s, 3H, CH3), 1.15 (s, 3H, CH3)
7.88 (d, 2H, Flu-H) [8.4], 7.52 (m, 2H, Flu-H), 7.39 Cq: 145.8, 145.2, 142.6, 142.4, 45.3 (bridge); CH: 88.4
(m, 2H, Flu-H), 7.37 – 7.11 (m, 2H, Flu-H), 6.21 (m, 128.4, 127.3, 126.5, 126.4, 126.3, 125.3, 125.2,
1H, Cp), 5.95 (m, 1H, Cp), 5.55 (m, 1H, Cp), 5.46 125.1, 123.6, 123.5, 122.4, 119.3, 27.7 (B-CH, br);
(m, 1H, Cp), 2.12 – 1.25 (m, 22H), 1.99 (s, 3H, CH3) CH2: 33.3, 31.4, 36.9, 23.9, 23.4; CH3: 25.4
a
All spectra in [D6]benzene at 25 ◦C; δ (ppm) vs. internal solvent (1H, 13C), ext. BF3–Et2O (11B), or ext. TMS (29Si).
to the better access of ethylene to the catalytically ac-
The nickel complexes contain Lewis base functions
tive center. The polymerization results are summarized (NMe2 groups), while the zirconocene complex car-
in Table 2.
ries a Lewis acidic boryl substituent. The combina-
tion of these two systems by a Lewis acid-base re-
action (donor-acceptor principle) should result in di-
or multinuclear complexes that can produce polymers
with a bimodal or multimodal molecular weight dis-
tribution. Scheme 2 shows the proposed formation of
a trinuclear complex with two different active centers,
while Scheme 3 shows the different combination possi-
bilities.
Formation of di- or trinuclear complexes
The most active zirconocene dichloride complexes
were combined with the (α-diimine)nickel complex 17
(Fig. 2). This nickel complex was synthesized from the
corresponding diimine with (dimethoxyethane)nickel
dibromide in THF. The paramagnetic complex was
characterized by mass spectrometry. Its polymerization
data are given in Table 2.
For polymerization reactions, the donor and the ac-
ceptor catalyst precursor were mixed together in equi-
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A. Kestel-Jakob – H. G. Alt · Boryl-substituted Zirconocene Dichloride Complexes as Catalyst Precursors
Table 2. Polymerization data of complexes 1 – 16.
Complex
Activity
[kg(PE)/mol(M)·h]
16 000
HT-GPC polymer share
Mn [g/mol]
98 200
70 600
75 300
75 000
96 300
74 100
63 300
89 600
110 100
97 400
60 900
82 600
116 300
99 300
122 400
55 200
2 080
Mw [g/mol]
337 300
335 000
358 800
286 600
335 500
246 600
262 000
322 200
365 600
361 800
253 600
281 200
391 500
269 700
425 800
175 000
9 000
Mz [g/mol]
Mz+1 [g/mol]
1 303 800
1 349 800
1 472 400
816 900
MP [g/mol]
210 400
220 100
220 900
208 700
261 600
178 500
183 600
260 300
316 400
333 200
172 900
191 000
312 800
191 700
309 600
101 000
1 190
D (= Mw/Mn)
1
2
784 600
816 500
894 700
571 700
620 900
494 200
609 500
599 700
633 200
648 100
601 700
618 500
790 800
570 600
890 000
514 200
42 000
3.4
4.8
4.8
3.8
3.5
3.3
4.1
3.6
3.3
3.7
4.2
3.4
3.4
2.7
3.5
3.2
4.3
1 000
670
37 200
40 500
68 300
35 700
55 600
30 400
39 000
55 800
5 500
1 800
5 800
2 200
490
930
3
4
5
854 600
735 900
6
7
1 037 500
830 800
8
9
850 200
869 700
10
11
12
13
14
15
16
17
1 051 900
1 061 400
1 230 400
997 300
1 378 800
1 112 700
88 700
(polymer share 11 %)
α = 0.83
Polymerization conditions: Al:Zr = 2 500 : 1; polymerization in 250 mL of n-pentane, 60 ◦C, 1 L autoclave, 10 bar ethylene pressure, 60 min.
rate of propagation
rate of propagation+rate of chain transfer
k
B
B
α =
=
)
(Schulz-Flory constant)
(k +k
C
Fig. 1. Synthesized boryl-sub-
stituted zirconocene dichloride
complexes 1 – 16.
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A. Kestel-Jakob – H. G. Alt · Boryl-substituted Zirconocene Dichloride Complexes as Catalyst Precursors
319
Scheme 2. Proposed formation
of a trinuclear complex.
Table 3. Polymerization data of multinuclear complexes.
Complex
Activity
[kg(prod)/mol (ZrNi)·h]
3 600
Polymer share
[wt. %]
96.6
α
17/6
17/11
17/14
0.71
0.69
0.81
20 100
1 900
96.4
46.6
Polymerization conditions◦: Al : M = 2 500 : 1; polymerization in
250 mL of n-pentane, 60 C, 1 L autoclave, 10 bar ethylene pres-
sure, 60 min. Schulz-Flory constant α as in Table 2.
Scheme 3. Different combination possibilities of donor/
acceptor catalyst precursors.
a characterization by NMR spectroscopy could not be
performed. The precipitate was activated with a 2 500-
fold molar excess of MAO and used for the homoge-
neous polymerization of ethylene. The obtained poly-
mers were dried in vacuo. Table 3 shows the polymer-
ization results.
Fig. 2. (α-Diimine)nickel complex with p-di-
methylaminophenyl groups.
valent amounts, and the mixture was stirred at r. t. for
two hours. A precipitate was formed but it could not
be dissolved in a non-coordinating solvent. Therefore
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A. Kestel-Jakob – H. G. Alt · Boryl-substituted Zirconocene Dichloride Complexes as Catalyst Precursors
Fig. 5. GPC diagram of polyethylene produced with
17/14/MAO.
Fig. 3. GPC diagram of polyethylene produced with
17/MAO.
Fig. 6. GPC diagram of polyethylene produced with
17/11/MAO.
Fig. 4. GPC diagram of polyethylene produced with
14/MAO.
The catalytic polymerization of ethylene with di-
or trinuclear complexes produced polymers with a bi-
modal molecular weight distribution. The nickel com-
plex produced polymers with a lower molecular weight
than the individual zirconocene component (Figs. 3
and 4). The combination of the two systems resulted in
a combination of both molecular weight distributions.
The first maximum belongs to the polymer produced
by the nickel complex and the second to that produced
by the zirconocene complex (Fig. 5). The molecular
weight distribution of the polymer produced by the
metallocene catalyst is broader indicating some mul-
timodal behavior.
Fig. 7. GPC diagram of polyethylene produced with
17/6/MAO.
When both complexes were applied in equimolar
amounts (Fig. 6) the zirconocene component showed
higher productivity than expected. The nickel complex
produced a polymer together with an oligomer with a
share of 55.3% which has not been considered in the
diagram.
share is 96.6%. Only a small amount of oligomers was
produced from the nickel center.
In all cases the activity of the di- or trinuclear com-
plexes was lower than the sum of the single activities
of the complexes. This was a hint for the formation
For the system 17/6/MAO the first maximum of of a new species with several catalytically active cen-
molecular weight has increased (Fig. 7). The polymer ters. Obviously, in these multinuclear complexes ac-
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A. Kestel-Jakob – H. G. Alt · Boryl-substituted Zirconocene Dichloride Complexes as Catalyst Precursors
321
cess of olefin to the active centers is more complicated nickel dibromide was added. The mixture was stirred for 12 h
at r. t. For purification, the volume of the solvent was reduced
in vacuo and the complexes were precipitated by adding n-
pentane. After washing several times with n-pentane, the
solvent remained colorless and the product was dried in
vacuo. The complex was obtained as a brown powder. Yield:
85 %. The complex was identified by mass spectrometry:
m/z = 541 [M]+; other fragments: m/z = 461, 322, 161, 120,
105, 77.
not only because of steric reasons but also because of
the interactions of the cationic active centers with the
MAO anions.
Experimental Section
NMR Spectroscopic investigations◦were performed with
a Bruker ARX 250 instrument at 25 C. CDCl3 and C6D6
served as solvents. The chemical shifts (δ) in the NMR spec-
tra are referenced to the (residual) signal of the solvent (1H:
δ = 7.24 ppm for chloroform; δ = 7.15 ppm for benzene, 13C:
δ = 77.0 ppm for chloroform; δ = 128.0 ppm for benzene).
Mass spectra were recorded with a VARIAN MAT CH7 mass
spectrometer (direct inlet system, electron impact ionization,
70 eV). In addition, a Hewlett Packard 5971A mass spec-
trometer was routinely used in combination with a Hewlett
Packard Series II 5890 gas chromatograph to record GC/MS
spectra. Molecular weight determinations of the polyethy-
General procedure for the combination of donor and accep-
tor catalyst precursors
Equivalent amounts of the corresponding zirconocene
dichloride and the nickel complex were dissolved in toluene
and stirred at r. t. for 2 h. The solvent was removed in
vacuo and the activated catalyst suspended in 50 mL of
n-pentane.
lene samples were performed using HT-GPC equipment. Gas General procedure for the activation of the complexes
chromatograms were recorded using a Perkin Elmer Auto
An amount of 5 – 10 mg of the complex was suspended
System gas chromatograph with flame ionization detector
in toluene and activated with the corresponding amount of
(FID) and helium as carrier gas (5.7 mL min−1). The temper-
MAO (Al : Ni = 2 500 : 1). The solvent was removed in vacuo
ature program wa◦s as follows: starting phase: 3 min at 50 ◦C;
and the activated catalyst was suspended in 50 mL of n-
◦
heating phase: 4 C min−1 (15 min); plateau phase: 250 C
pentane. The catalyst suspension was used for ethylene poly-
merization.
(37 min). Methylaluminoxane was supplied by Witco GmbH,
Bergkamen, as a 30 % solution in toluene (average molecu-
lar weight 1100 g/mol, aluminum content: 13.1 %, 3.5 % as
trimethylaluminum).
Homogeneous polymerization of ethylene
n-Pentane (250 mL) was placed in a 1 L Bu¨chi labora-
General procedure for the synthesis of the boryl-substituted
complexes 1 – 16
tory autoclave, mixed with the catalyst solution and the auto-
◦
clave thermostated at 60 C. An ethylene pressure (99.98 %
ethylene) of 10 bar was applied after an inside temperature
of 50 C was reached. The mixture was stirred for 1 h at
1 mmol of the corresponding zirconocene d◦ichloride com-
plex was dissolved in mL of THF. At −78 C one or two
equivalents of 9-H-borabicyclo[3.3.1]nonane were dissolved
in 20 or 40 mL of THF, respectively. The two solutions were
combined and the reaction mixture was stirred at −78 ◦C for
1 h and at r. t. for 2 h. After removing the solvent in vacuo, the
residue was washed with n-hexane. The products remained as
yellow or orange solids. Yields: 80 – 95 %.
◦
60( 2) ◦C, and subsequently the reaction was terminated by
releasing the pressure in the reactor. For the separation of
the oligomers and the polymers, the mixture was filtered and
the remaining polymer was washed with half-concentrated
hydrochloric acid in order to remove excess MAO. After
that the polymer was dried in vacuo and weighed. The pen-
tane of the oligomer solution was removed by destillation
over a Vigreux column and the oligomers were analyzed
by GC.
All compounds were characterized by NMR spectroscopy
(Table 1).
General procedure for the synthesis of the nickel
complex 17
Acknowledgement
0.7 mmol of the respective diimine ligand was dissolved
in 50 mL of THF. Then 0.7 mmol of (dimethoxyethane)
We thank SABIC, Riyadh, Saudi Arabia, for the financial
support of the project.
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