Quinolyl-functionalised Cp-chromium polymerisation catalysts: Synthesis and crystal structures of alkylation products

Article abstract of DOI:10.1016/j.jorganchem.2003.07.017

The quinolyl-functionalised Cp-chromium(III) complexes 1 and 2, which serve as precursors for highly active olefin polymerisation catalysts, were alkylated with benzylmagnesium chloride. From these reactions, the new metal complexes 4, 5 and 6 were obtained and structurally characterised. The expected alkylchromium compound 4 is formed together with complex 5, where the nucleophile replaced a hydrogen atom at the quinoline substituent. The dinuclear complex 6 is formed by nucleophile addition, rearrangement and dimerisation.

Full text of DOI:10.1016/j.jorganchem.2003.07.017

Journal of Organometallic Chemistry 687 (2003) 125Á130
/
www.elsevier.com/locate/jorganchem
Quinolyl-functionalised CpÁ
/
chromium polymerisation catalysts:
synthesis and crystal structures of alkylation products
Markus Enders a,*, Pablo Ferna´ndez a, Shahram Mihan b, Hans Pritzkow a
a Anorganisch-Chemisches Institut der Universitat, im Neuenheimer Feld 270, 69120 Heidelberg, Germany
¨
b Basell Polyolefins GmbH, Research Laboratory, Basell-M505, D-67056 Ludwigshafen, Germany
Received 26 June 2002; received in revised form 24 July 2003; accepted 24 July 2003
Abstract
The quinolyl-functionalised CpÁ
/
chromium(III) complexes 1 and 2, which serve as precursors for highly active olefin
polymerisation catalysts, were alkylated with benzylmagnesium chloride. From these reactions, the new metal complexes 4, 5
and 6 were obtained and structurally characterised. The expected alkylchromium compound 4 is formed together with complex 5,
where the nucleophile replaced a hydrogen atom at the quinoline substituent. The dinuclear complex 6 is formed by nucleophile
addition, rearrangement and dimerisation.
# 2003 Published by Elsevier B.V.
Keywords: Chromium; Donor-functionalised Cp-ligands; Olefin polymerisation; Catalyst activation
1. Introduction
Beside titanium-based ZieglerÁ
[5]. These compounds show advantageous catalytic
behaviour like very high activity and temperature
stability. In addition, they are able to incorporate a lot
of comonomer into high molecular weight polymers.
These properties make them attractive for industrial
application [6] (Fig. 1).
/
Natta catalysts, chro-
mium compounds play a significant role in coordination
polymerisation of a-olefins. Heterogeneous, silica sup-
ported systems such as Phillips [1] or Union Carbide [2]
catalysts are among the most important catalysts for the
production of polyolefins and have been put to wide-
spread commercial use. Homogeneous metallocene
catalysts have revolutionised olefin polymerisation and
many highly active systems with other transition metals
have been developed [3].
Despite the importance of chromium in the field of
olefin polymerisation, homogeneous chromium catalysts
have been investigated by a few groups only. The most
promising single-site systems consist of amino-functio-
nalised cyclopentadienyl ligands coordinated to a chro-
mium(III) centre [4].
In order to activate compounds like 1Á3, an alkyla-
/
tion at the chromium atom followed by abstraction of a
negatively charged ligand is necessary. These two
reactions can be achieved in one step by an excess of
methylaluminoxane (MAO). For a two step activation,
the catalyst precursors must first be alkylated. The
synthesis of dialkylated CpÁ
been demonstrated by several groups [4,7,8]. In princi-
ple, from such dialkyl-CpÁchromium compounds an
alkyl group can be abstracted by a Lewis acid (e.g.
MAO, B(C6F5)3) or by a proton source (e.g. DMABꢀ
dimethylanilinium tetrakispentafluorophenylborate),
leading to active catalysts of the type [CpCr(L)R]ꢁ. In
the case of compounds 1Á3, activation with MAO as
/
chromium compounds have
/
/
We have developed similar systems (1, 2, 3) where the
spacer group which connects the nitrogen donor with
/
well as activation with AlR3/DMAB leads to highly
active catalyst systems. However, nucleophiles like
Grignard- or organolithium reagents are known to
attack pyridine derivatives in 2-position relative to the
nitrogen atom, a reaction which is known as Ziegler-
alkylation [9]. Recently alkylation reactions on diimi-
the CpÁligand is incorporated into an aromatic system
/
* Corresponding author. Tel.: ꢁ
/
49-6221-562-452; fax: ꢁ49-6221-
/
564-197.
E-mail address: markus.enders@urz.uni-hd.de (M. Enders).
0022-328X/03/$ - see front matter # 2003 Published by Elsevier B.V.
doi:10.1016/j.jorganchem.2003.07.017

126
M. Enders et al. / Journal of Organometallic Chemistry 687 (2003) 125Á130
/
Fig. 1. Olefin polymerisation catalyst precursors 1Á3.
/
nopyridinium based catalysts have been reported to lead
also to ring alkylation [10]. In the case of quinolyl-
functionalised catalysts we have also observed, that
some alkylating agents react not only at the metal atom,
but also at the quinolyl moiety. In order to investigate
the catalyst activation, we now report about reactions of
1 and 2 with benzylmagnesium chloride.
Fig. 2. Molecular structure of 4.
nitrogen atom in the quinoline substituent) occurred in
the case of complex 5 (see Fig. 3) (Tables 1 and 2).
The coordination geometries around the chromium
atoms are similar to the geometry in 1 [5]. Complex 4
2. Results and discussion
crystallises in the monoclinic space group P21/n, 5 in the
¯
triclinic P1. The CrÁ
/
N distances lie in the expected
The chromium complex 1 was treated with one
equivalent of benzylmagnesium chloride. A mixture of
two products formed: the violet complex 4, well soluble
in toluene, and the green compound 5 with slightly
lower solubility. Due to this similar solubility behaviour
a complete separation of the two products was not
possible. The complete yield of this reaction is about
˚
range with 2.111 A (4) and 2.154 A (5) [4c,5]. The
˚
˚
distance between the metal atom and C19 in 4 (2.119 A)
is characteristic of carbonÁ
/
chromium s-bonds
[4c,12,13]. In 4 as well as in 5 the almost planar
˚
quinoline ring (max. deviation from planarity 0.02 A
˚
in 4 and 0.06 A in 5) and the Cp ring (max. deviation
˚
from planarity 0.01 A in both cases) are practically
80% with a ratio 4:5ꢀ
/
1:1.3. The UVÁVis spectrum of 5
/
possesses two significant bands in the same range as the
educt 1, characteristic of dichloro-chromium complexes
[11]. The MS-spectrum too shows the existence of two
chlorine atoms and also the presence of a benzyl group
incorporated into the ligand. The UVÁVis spectrum of
/
the other product (4) is typical for monoalkylated-
chromium(III) compounds [10]. The ratio of the two
products shows, that reaction of the Grignard reagent at
the ligand is faster than the chloride replacement at the
chromium atom. At lower temperatures even more of
complex 5 is obtained (Scheme 1).
Crystals of 4 and 5, suitable for X-ray diffraction,
were obtained from a mixture of toluene and hexane at
room temperature. The results of the structure analysis
reveal, that the carbon nucleophile have substituted a
chlorine atom in the case of 4 (see Fig. 2) whereas
reaction at the C3 atom (which is adjacent to the
Fig. 3. Molecular structure of 5.
Scheme 1. Formation of the compounds 4 and 5 by alkylation of 1.

M. Enders et al. / Journal of Organometallic Chemistry 687 (2003) 125Á
/130
127
Table 1
2 in THF did not lead to isolable products. Therefore
the reaction was performed with two equivalents of the
alkylating agent. By this procedure compound 6 was
isolated by extraction of the reaction mixture with
hexane (Scheme 2). The EI-mass spectrum shows the
presence of a dimeric compound with four benzyl
groups. The isotopic pattern proves that no chlorine
atoms are present.
Crystals of 6 precipitated from the solution at room
temperature. The result of the X-ray analysis is shown in
Fig. 4 (Table 3).
One benzyl group replaced a chlorine atom, and the
second one added to the heterocycle at the para position
(C5) relative to the nitrogen atom. This leads to an
activation of the CH3 group from which a hydrogen
atom is transferred to the neighbouring carbon atom.
The resulting complex fragment dimerises to give the
complex 6. During this sequence, one double bond of
˚
Selected bond lengths (A) and bond angles (8) of 4
Bond lengths
Cr(1)Á
Cr(1)Á
Cr(1)Á
Cr(1)Á
Cr(1)Á
Cr(1)Á
Cr(1)Á
Cr(1)Á
C(10)Á
C(11)Á
C(12)Á
C(13)Á
C(14)Á
/
N(1)
2.111(2) C(19)Á
2.306(1) C(1)Á
2.119(3) C(1)Á
2.201(3) C(9)Á
2.256(3) C(8)Á
2.279(3) C(7)Á
2.277(3) C(6)Á
2.211(3) C(6)Á
1.418(4) C(5)Á
1.415(4) C(4)Á
1.419(4) C(3)Á
1.419(4) C(2)Á
1.439(4)
/
C(20)
1.469(4)
1.417(4)
1.381(4)
1.402(5)
1.351(5)
1.427(4)
1.414(4)
1.409(5)
1.357(5)
1.404(4)
1.325(4)
1.384(3)
/
Cl(1)
C(19)
C(10)
C(11)
C(12)
C(13)
C(14)
/
C(2)
C(9)
C(8)
C(7)
C(6)
C(2)
C(5)
C(4)
C(3)
N(1)
N(1)
/
/
/
/
/
/
/
/
/
/
/
/
/
C(11)
C(12)
C(13)
C(14)
C(10)
/
/
/
/
/
/
/
/
Bond angles
N(1)ÁCr(1)Á
N(1)ÁCr(1)Á
Cl(1)ÁCr(1)Á
C(2)ÁC(1)Á
C(2)ÁC(1)Á
C(9)ÁC(1)Á
Cr(1)Á
/
/
Cl(1)
98.3(1) Cr(1)Á
103.5(1) Cr(1)Á
94.9(1) C(2)ÁN(1)Á
118.9(3) C(1)ÁC(10)Á
116.8(2) C(1)ÁC(10)Á
124.3(3) C(11)Á
113.6(2)
/
N(1)Á
/
C(2)
C(3)
116.8(2)
125.4(2)
117.7(2)
124.5(2)
125.5(2)
108.7(2)
/
/C(19)
/
N(1)Á
/
/
/
C(19)
/
/C(3)
/
/
C(9)
/
/
C(11)
the quinoline is reduced leading to a CÁ
/
C single bond
C5 1.513 A). The molecular ion of 6 (m/zꢀ992) is
not visible in the mass spectrum, but an ion at m/zꢀ988
/
/
C(10)
C(10)
/
/
C(14)
˚
(C4Á
/
/
/
/
/
C(10)ÁC(14)
/
/
/C(19)Á
/C(20)
(6%). Consequently four hydrogen atoms are eliminated
during ionisation and the aromaticity of the two
quinoline systems is recovered.
Table 2
˚
Selected bond lengths (A) and bond angles (8) of 5
Bond lengths
3. Conclusion
Cr(1)Á
Cr(1)Á
Cr(1)Á
Cr(1)Á
Cr(1)Á
Cr(1)Á
Cr(1)Á
Cr(1)Á
C(10)Á
C(11)Á
C(12)Á
C(13)Á
C(14)Á
/
N(1)
2.154(4) C(3)Á
2.308(2) C(1)Á
2.309(2) C(1)Á
2.165(5) C(9)Á
2.203(5) C(8)Á
2.272(5) C(7)Á
2.273(5) C(6)Á
2.214(5) C(6)Á
1.429(7) C(5)Á
1.426(7) C(4)Á
1.401(7) C(3)Á
1.440(7) C(2)Á
1.404(7)
/
C(19)
C(2)
C(9)
C(8)
C(7)
C(6)
C(2)
C(5)
C(4)
C(3)
N(1)
N(1)
1.495(8)
1.413(7)
1.359(7)
1.410(8)
1.368(8)
1.402(7)
1.417(7)
1.410(7)
1.356(8)
1.424(7)
1.343(6)
1.394(6)
/
Cl(1)
Cl(2)
C(10)
C(11)
C(12)
C(13)
C(14)
/
At the beginning of the activation of catalyst pre-
cursors for olefin polymerisation an alkylation at the
metal centre is required. In a second step, a chloride or
Rꢂ is abstracted leading to cationic complexes which
are active catalysts. In the case of quinolyl-substituted
compounds, a side reaction may occur depending on the
alkylating agent. When MAO is used, no alkylation
reaction at the quinolyl moiety was observed. However,
organolithium reagents as well as Grignard reagents are
highly reactive for the substitution at the quinoline and
at the metal. Therefore, the quinolyl substituted product
5 as well as the benzyl chromium complex 4 were
isolated and the solid state structures were determined.
Surprisingly, when the quinoline ring is already sub-
stituted, another side reaction was found. By this route,
the unprecedented dinuclear compound 6 was isolated
and structurally identified. These investigations are
/
/
/
/
/
/
/
/
/
/
/
/
/
C(11)
C(12)
C(13)
C(14)
C(10)
/
/
/
/
/
/
/
/
Bond angles
N(1)ÁCr(1)Á
N(1)ÁCr(1)Á
Cl(1)ÁCr(1)Á
C(2)ÁC(1)Á
C(2)ÁC(1)Á
C(9)ÁC(1)Á
/
/
Cl(1)
97.7(1) Cr(1)Á
101.0(1) Cr(1)Á
100.2(1) C(2)ÁN(1)Á
120.8(5) C(1)ÁC(10)Á
116.2(4) C(1)ÁC(10)Á
122.9(4) C(11)Á
/
N(1)Á
/
C(2)
114.5(3)
127.2(3)
118.2(4)
123.6(5)
125.5(4)
109.8(4)
/
/Cl(2)
/N(1)Á
/
C(3)
/
/
Cl(2)
/
/C(3)
/
/
C(9)
/
/
C(11)
C(14)
/
/
C(10)
C(10)
/
/
/
/
/
C(10)Á
/
C(14)
orthogonal. Consequently, the nitrogen donor atoms are
ideally positioned for an interaction with the metal
atoms. The angles around N1 sum up to 359.98 in both
cases, so that the lone pair at nitrogen points directly to
the metal centre.
In order to avoid substitution at the ligand, complex 2
was used where the reactive C3 position at the quinoline
substituent is blocked by a CH3 group. Addition of one
equivalent of benzylmagnesium chloride to a solution of
Scheme 2. Synthesis of the dinuclear compound 6 from addition of
BzMgCl to 2.

128
M. Enders et al. / Journal of Organometallic Chemistry 687 (2003) 125Á130
/
mium(III) (2) [15] were synthesized by literature
procedures.
4.1. Synthesis of benzylchloro-h5-[2,3,4,5-tetramethyl-1-
(8-quinolyl)cyclopentadienyl] chromium(III) (4) and
dichloro-h5-{2,3,4,5-tetramethyl-1-[8-(2-
benzyl)quinolyl] cyclopentadienyl}chromium(III) (5)
A 2.51 M solution of benzylmagnesium chloride in
diethylether (2.1 ml, 5.2 mmol) was added dropwise to a
green solution of 1.92 g (5.2 mmol) of dichloro-h5-
[2,3,4,5-tetramethyl-1-(8-quinolyl)cyclopentadie-
nyl]chromium(III) in 60 ml of THF. The colour changed
to purple and, after 2 h, four drops of 1,4-dioxane were
added to aid the precipitation of magnesium chloride.
The solvent was removed in vacuum and the solid was
extracted with 50 ml of toluene to obtain a violet
solution. Addition of another 100 ml of toluene afforded
a green coloured second fraction. The solvents were
removed in vacuum to obtain 0.82 g (1.9 mmol, 36%) of
a violet solid and 1.10 g (2.4 mmol, 46%) of a green
Fig. 4. Molecular structure of 6. Only H atoms at C4, C5 and C10 are
shown for clarity.
Table 3
˚
Selected bond lengths (A) and bond angles (8) of 6
powder, respectively. After 24 h in tolueneÁhexane at
/
Bond lengths
room temperature (r.t.) small crystals of the complexes 4
and 5, respectively were obtained from each fraction.
Cr(1)Á
Cr(1)Á
Cr(1)Á
Cr(1)Á
Cr(1)Á
Cr(1)Á
Cr(1)Á
Cr(1)Á
C(11)Á
C(12)Á
C(13)Á
C(14)Á
C(15)Á
/
N(1)
2.112(2) C(3)Á
2.130(2) C(1)Á
2.186(2) C(1)Á
2.213(2) C(9)Á
2.251(2) C(8)Á
2.304(2) C(7)Á
2.319(2) C(6)Á
2.290(2) C(6)Á
1.428(3) C(5)Á
1.425(3) C(4)Á
1.417(3) C(3)Á
1.428(3) C(2)Á
1.418(3)
/
C(10)
C(2)
C(9)
C(8)
C(7)
C(6)
C(2)
C(5)
C(4)
C(3)
N(1)
N(1)
1.418(3)
1.397(3)
1.392(3)
1.384(4)
1.384(4)
1.396(3)
1.406(3)
1.505(3)
1.513(3)
1.515(3)
1.329(3)
1.435(3)
/
C(20)
C(10A)
C(11)
C(12)
C(13)
C(14)
C(15)
/
/
/
Complex 4: UVÁ
MS(EI): m/z (%)ꢀ
C7H8], 298 (16) [Mꢁ ꢂ
Complex 5: UVÁVis (THF), lmax (o): 474 (531); 682
(542) nm. MS(EI): m/z (%)ꢀ
460 (1) [Mꢁ], 424 (4)
[Mꢁ ꢂHCl], 388 (2) [Mꢁ ꢂ
2HCl], 339 (100) [ligand ꢁ
Hꢁ], 91 (82) [C7H7ꢁ].
/
Vis (THF), lmax (o): 520 (710) nm.
426 (1) [Mꢁ], 334 (100) [Mꢁ ꢂ
C7H8ꢂ
HCl], 91 (72) [C7H7ꢁ].
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
C(12)
C(13)
C(14)
C(15)
C(11)
/
/
/
/
/
/
/
/
/
/
4.2. Synthesis of the dinuclear compound 6
/
Bond angles
N(1)ÁCr(1)Á
N(1)ÁCr(1)Á
C(20)Á
C(2)ÁC(1)Á
C(2)ÁC(1)Á
C(9)ÁC(1)Á
N(1)ÁC(3)Á
A 2.51 M solution of benzylmagnesium chloride in
diethylether (1.42 ml, 3.6 mmol) was added dropwise to
a green solution of 1.39 g (3.6 mmol) of dichloro-h5-
{2,3,4,5-tetramethyl-1-[8-(2-methyl)quinolyl]cyclopenta-
dienyl}chromium(III) in 50 ml of THF. No change of
colour was observed. After 2 h at r.t., four drops of 1,4-
dioxane were added and the solvents were removed in
/
/
C(20)
106.8(1) Cr(1)Á
93.3(1) Cr(1)Á
99.8(1) C(2)ÁN(1)Á
120.1(2) C(1)ÁC(11)Á
117.5(2) C(1)ÁC(11)Á
122.3(2) C(12)Á
123.6(2) C(3)ÁC(10)Á
/
N(1)Á
/
C(2)
115.4(1)
126.4(1)
117.8(2)
123.2(2)
126.6(2)
109.4(2)
120.8(2)
/
/C(10A)
/N(1)Á
/
C(3)
/
Cr(1)Á
/C(10A)
/
/C(3)
/
/
C(9)
/
/
C(12)
C(15)
/
/
C(11)
C(11)
/
/
/
/
/
C(11)Á
/
C(15)
Cr(1A)
/
/
C(10)
/
/
vacuum. The product was extracted with hexane (3ꢃ50
/
ml) and crystallised in toluene/hexane at room tempera-
ture to obtain crystals of complex 6.
important for the understanding of different catalyst
behaviours depending on the activating agents used.
MS(EI): m/z (%)ꢀ
[Mꢁ ꢂC7H8], 806 (12) [Mꢁ ꢂ
[C26H25NCrꢁ], 349 (100) [C26H23Nꢁ].
/
988 (6) [Mꢁ ꢂ
/
4H], 900 (38)
/
/
4Hꢂ
/
2Bz], 403 (32)
4. Experimental
4.3. X-ray crystal structure determinations of 4, 5 and 6
Crystal data were collected for 4, 5 and 6 with a
All manipulations were carried out under a nitrogen
atmosphere with anhydrous solvents saturated with
nitrogen. Glassware was heated under vacuum prior to
use. Benzylmagnesium chloride [14], dichloro-h5-
[2,3,4,5-tetramethyl-1-(8-quinolyl)cyclopentadie-
nyl]chromium(III) (1) [5] and dichloro-h5-[2,3,4,5-tetra-
methyl-1-(2-methyl-8-quinolyl)cyclopentadienyl]chro-
Bruker AXS area detector SMART 1000 (MoÁ
/
Ka
radiation, v-scan, Tꢀ 100 8C). The structures were
/
ꢂ
/
solved by direct methods and refined by full-matrix
least-squares against F2 with all reflections using the
SHELXTL-program system [16]. All non-hydrogen atoms

M. Enders et al. / Journal of Organometallic Chemistry 687 (2003) 125Á
/130
129
Table 4
Crystal data and structure refinement details for 4, 5 and 6
4
5
6
Empirical formula
Formula weight
Crystal system
C25H25ClCrN
426.91
C25H24Cl2CrN
507.42
Triclinic
C66H68Cr2N2
993.22
Triclinic
Monoclinic
P21/n
¯
P1
¯
P1
Space group
Unit cell dimensions
˚
a (A)
10.1365(9)
20.695(2)
11.095(1)
90
9.8385(6)
10.0094(7)
13.8402(9)
77.256(5)
71.560(5)
77.240(5)
1244.2(1)
2
10.9101(3)
11.3734(3)
12.4951(3)
67.848(2)
65.251(2)
87.142(2)
1293.3(1)
1
˚
b (A)
˚
c (A)
a (8)
b (8)
114.959(2)
90
g (8)
3
V (A )
˚
2110.0(3)
4
1.344
Z
Dcalc (g cmꢂ3
)
1.354
0.691
528
1.275
0.464
526
Absorption coefficient (mmꢂ1
F(000)
)
0.679
892
Crystal size (mm3)
0.52ꢃ
26.38
125h 5
l 513
/
0.07ꢃ
/
0.07
0.30ꢃ
1.57Á23.25
105h 5
l 515
/0.20ꢃ
/
0.04
0.30ꢃ
1.95Á28.38
135h 5
l 516
/0.20ꢃ
/
0.14
Theta range for data collection (8) 1.97Á
Index ranges
/
/
/
ꢂ/
/
/
11, 05
/
k 5
/
25, 05
/
ꢂ/
/
/
10, ꢂ
/
105
/
k 5
/
11, 05
/
ꢂ/
/
/
14, ꢂ
/
135
/
k 5
/
15, 05
/
/
/
/
Reflections collected
Independent reflections
Goodness-of-fit on F2
14419
4320
0.959
11652
3574
0.985
17532
6335
1.056
Final R indices [I ꢀ
R indices (all data)
Largest difference peak and hole (e 0.554 and ꢂ
/
2s(I)]
R1ꢀ
/
0.0431, wR2ꢀ
0.0667, wR2ꢀ
0.672
/
0.1045
R1ꢀ
R1ꢀ
1.561 and ꢂ
/
0.0601, wR2ꢀ
0.0872, wR2ꢀ
0.668
/
0.1462
R1ꢀ
R1ꢀ
0.846 and ꢂ
/
0.0548, wR2ꢀ
0.0762, wR2ꢀ
0.884
/
0.1428
R1ꢀ
/
/0.1150
/
/0.1595
/
/0.1601
/
/
/
ꢂ3
˚
A
)
[2] (a) G.L. Karapinka, US Patent 3709853 (1973).;
were refined anisotropically. Crystal data and experi-
mental details are listed in Table 4.
(b) F.J. Karol, G.L. Karapinka, C. Wu, A.W. Dow, R.N.
Johnson, W.L. Garrick, J. Polym. Sci. A 10 (1972) 2621.
[3] (a) G.J.P. Britovsek, M. Bruce, V.C. Gibson, B.S. Kimberley, P.J.
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Solan, S. Stromberg, A.J.P. White, D.J. Williams, J. Am. Chem.
¨
5. Supplementary material
Soc. 121 (1999) 8728;
(b) S.D. Ittel, L.K. Johnson, M. Brookhart, Chem. Rev. 100
(2000) 1169;
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
(c) G.G. Hlatky, Chem. Rev. 100 (2000) 1347;
(d) E. You-Xian Chen, T.J. Marks, Chem. Rev. 100 (2000) 1391;
(e) V.C. Gibson, S.K. Spitzmesser, Chem. Rev. 103 (2003) 283.
Data Centre, CCDC nos. 187968Á187970. Copies of this
/
information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge CB2 1EZ,
[4] (a) R. Emrich, O. Heinemann, P.W. Jolly, C. Kruger, G.P.J.
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Verhovnik, Organometallics 16 (1997) 1511;
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(b) S. Mihan, D. Lilge, G. Schweier, M. Enders, PCT Int. Appl.
WO 0112687 A1, (2001).
The authors gratefully acknowledge support from the
Anorganisch-Chemisches Institut der Universitat and
BASELL Polyolefine GmbH.
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