Synthesis, crystal structure and catalytic activity of some new chiral ansa-metallocenes of yttrium, lanthanum, samarium, lutetium and of zirconium

Article abstract of DOI:10.1016/S0022-328X(98)00729-3

Chiral silicon bridged yttrio- and lanthanidocene chlorides [MeRSi(C₅H₄)(C₅Me₄)LnCl]₂ (R=Et (a), Ph (b); Ln=Y (4a, b), La (5a, b), Sm (6a, b), Lu (7a, b)) and zirconocene dichlorides [MeRSi(C₅H₄)(C₅Me₄)ZrCl₂] (R=Et (8a), Ph (8b)) were synthesized. Compounds 4-7 react with sodium acetate yielding the corresponding monomeric acetates [MeRSi(C₅H₄)(C₅Me₄)LnO₂CMe] (R=Et (a), Ph (b); Ln=Y (9a, b), La (10a, b), Sm (11a, b), Lu (12a, b)). All compounds were characterized by elemental analysis, ¹H and ¹³C{¹H}-NMR spectroscopy, and by mass spectrometry. Single crystal X-ray structure determinations show a dimer for 6a and a monomer for 8a. The zirconocenes 8a, b are active catalysts for the polymerization of ethylene and propylene in the presence of methylalumoxane (MAO).

Full text of DOI:10.1016/S0022-328X(98)00729-3

Journal of Organometallic Chemistry 574 (1999) 228–240
Synthesis, crystal structure and catalytic activity of some new chiral
ansa-metallocenes of yttrium, lanthanum, samarium, lutetium and of
zirconium1
Herbert Schumann a,*, Kerstin Zietzke a, Roman Weimann a, Jo¨rg Demtschuk a,
Walter Kaminsky b, Anne-Meike Schauwienold b
a Institut fu¨r Anorganische und Analytische Chemie der Technischen Uni6ersita¨t Berlin, Straße des 17. Juni 135, D-10623 Berlin, Germany
b Institut fu¨r Technische und Makromolekulare Chemie, Uni6ersita¨t Hamburg, Bundesstraße 45, D-20146 Hamburg, Germany
Received 17 February 1998
Abstract
Chiral silicon bridged yttrio- and lanthanidocene chlorides [MeRSi(C5H4)(C5Me4)LnCl]2 (R=Et (a), Ph (b); Ln=Y (4a, b), La
(5a, b), Sm (6a, b), Lu (7a, b)) and zirconocene dichlorides [MeRSi(C5H4)(C5Me4)ZrCl2] (R=Et (8a), Ph (8b)) were synthesized.
Compounds 4–7 react with sodium acetate yielding the corresponding monomeric acetates [MeRSi(C5H4)(C5Me4)LnO2CMe]
(R=Et (a), Ph (b); Ln=Y (9a, b), La (10a, b), Sm (11a, b), Lu (12a, b)). All compounds were characterized by elemental analysis,
1H and 13C{1H}-NMR spectroscopy, and by mass spectrometry. Single crystal X-ray structure determinations show a dimer for
6a and a monomer for 8a. The zirconocenes 8a, b are active catalysts for the polymerization of ethylene and propylene in the
presence of methylalumoxane (MAO). © 1999 Elsevier Science S.A. All rights reserved.
Keywords: ansa-Metallocenes; Bridged cyclopentadienyl compounds; Organolanthanide compounds; Polymerizations; Zir-
conocenes
bridged zirconocenes [14] and lanthanidocenes [15] were
tested as catalysts for olefin polymerization. The first
1. Introduction
ansa-cyclopentadienyl compound with two different
substituents at the bridging silicon atom, [Me(H)Si-
Organometallic complexes containing two cyclopen-
tadienyl or two tetramethylcyclopentadienyl ligands
(C5H4)2TiCl2], was prepared by Ko¨pf et al. in 1983 [16].
bridged by Me2Si or Et2Si units are known of several
Chirality can be generated in such ansa-silylene com-
transition metals including zirconium [2,3] and of some
lanthanide metals [4–11]. Also asymmetric complexes
of zirconium [12,13] and of some lanthanides [4,7]
plexes if also the two cyclopentadienyl moieties differ
from each other. Whereas chiral ansa-metallocenes
bridged by CRR% units were already synthesized [17],
containing one unsubstituted cyclopentadienyl and one
corresponding silylene bridged compounds were un-
tetramethylcyclopentadienyl ligand bridged by the
known up to now.
Me2Si group were already reported. Several symmetri-
In this context we were interested in synthesizing and
cally and asymmetrically substituted dimethylsilylene
characterizing chiral ansa-lanthanidocenes and zir-
conocenes with silicon as the chiral center surrounded
by two differently substituted cyclopentadienyl ligands
and two different alkyl or aryl groups. Furthermore, we
wanted to study the influence of the chiral silicon
bridge on the catalytic properties of these compounds.
* Corresponding author. Tel.: +49 30 31423984; fax: +49 30
31422168; e-mail: Schumann@chem.zrz.tu-berlin.de
1 Part 125 of the series Organometallic Compounds of the Lan-
thanides. For Part 124 see Ref. [1]. Dedicated to Professor Dr Peter
Jutzi on the occasion of his 60th birthday with gratitude.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00729-3

H. Schumann et al. / Journal of Organometallic Chemistry 574 (1999) 228–240
229
Scheme 1.
2. Synthesis and properties
Like dicyclopentadienyl lanthanide chlorides in gen-
eral, 4a, b to 7a, b are very sensitive towards air and
moisture. Compounds 4b–7b containing the phenyl
substituted silicon bridge are moderately soluble in
saturated and unsaturated hydrocarbons like hexane,
benzene or toluene whereas the complexes 4a–7a with
the ethyl group at the silicon bridge are only slightly
soluble in toluene and benzene. All compounds are
soluble in donor solvents like diethylether or
tetrahydrofuran.
The way of preparing the ligands CpCp*SiRR% dif-
fers somewhat from the method given in the literature
[7]. Dichloroethylmethylsilane or dichloromethylpheny-
lsilane reacted with equimolar amounts of sodium te-
tramethylcyclopentadienide in THF giving the monote-
tramethylcyclopentadienyl substituted silanes 1a or 1b
as pale yellow liquids. Treatment of 1a or 1b with
sodium cyclopentadienide produced orange or dark
yellow colored, oily cylopentadienyl(ethyl)(methyl)
(tetramethylcyclopentadienyl)silane (2a) or cyclopenta-
dienyl(methyl)(phenyl)(tetramethylcyclopentadienyl)sil-
ane (2b), respectively. The compounds 2a and 2b were
reacted without further purification with sodium amide
yielding the corresponding disodium salts 3a and 3b.
Like the intermediate products 1a, b and 2a, b, the
disodium salts are sensitive towards air and moisture.
In contrast to 1a, b and 2a, b which are soluble in
common organic solvents, 3a, b are only soluble in
THF.
1
The H-NMR spectra of 7a, 5b, 6b and 7b in d5-py-
ridine and an X-ray structural analysis of poor quality
crystals of 7a [18] indicate that monomeric, THF con-
taining complexes of the type MeRSi(C5H4)(C5Me4)-
LnCl(THF) are the primary products which on vacuum
drying lose their THF with formation of dimers. In
accordance with this fact, no evidence is found for
coordinated THF performing elemental analysis of the
dried complexes. 4a, b to 7a, b have two possibilities to
dimerize, either with two equal or with two different
cyclopentadienyl ligands at the same site of the lan-
thanide atoms. For each of these isomers two racemic
homochiral and one meso heterochiral isomer can exist.
Me(R)SiCl2+Na(C5Me4H)
“Me(R)Si(C5Me4H)Cl+NaCl
1a, b
1
The H- and 13C{1H}-NMR solution spectra of 5a, b
and 6a, b which show two signals with an intensity ratio
of 2:1 for the CH3 group attached to each bridging
silicon atom indicate the presence of two isomers with
different rings on the same site of the lanthanide atoms.
In the mass spectra of 4a, b to 7a, b the peak for the ion
of the dimeric molecules is the peak of highest mass.
The single crystal X-ray structure determination of
crystals of 6a obtained by recrystallization from ether-
THF shows the dinuclear complex with two molecules
of THF completing the coordination sphere around the
samarium atoms (Fig. 1). These solvent molecules are
removed by vacuum drying of the complex. The vac-
uum dried, solvent-free dinuclear lanthanidocene chlo-
rides are less soluble in hydrocarbons and diethyl ether
than the complexes crystallized from THF.
Me(R)Si(C5Me4H)Cl+Na(C5H5)
“Me(R)Si(C5Me4H)(C5H5)+NaCl
2a, b
Me(R)Si(C5Me4H)(C5H5)+2NaNH2
“Na2[Me(R)Si(C5Me4)(C5H4)]+2NH3
3a, b
R=Et (1a, 2a, 3a), Ph (1b, 2b, 3b)
The trichlorides of yttrium, lanthanum, samarium
and lutetium react with 3a and 3b in THF with forma-
tion of the dimeric lanthanidocene chlorides 4a, b to 7a,
b (Scheme 1).
Zirconiumtetrachloride reacts with 3a and 3b to give
the zirconocene dichlorides 8a and 8b (Scheme 2).

230
H. Schumann et al. / Journal of Organometallic Chemistry 574 (1999) 228–240
˚
Fig. 1. ORTEP plot [19] of 6a. Selected bond distances [A] and angles [°] (estimated standard deviations in parentheses; Cp and Cp* define the
centroids of the ring atoms C(1)–C(5) and C(13)–C(17), respectively: Sm–Cl 2.7793(14), Sm–Cl% 2.8169(9), Sm–O 2.614(2), Sm-Cp* 2.446(2),
Sm–Cp 2.458(2), Si–C(10) 1.891(4), Si–C(12) 1.875(4), Si–C(1) 1.867(3), Si–C(13) 1.861(3); Cl–Sm–O 71.71(6), O–Sm–Cp* 102.31(7),
Cp*–Sm–Cl 122.79(4), Cp–Sm–Cl% 95.75(3), Cp*–Sm–Cp 118.60(5), C(1)–Si–C(13) 100.29(13), C(10)–Si–C(12) 107.0(2).
Both zirconocenes are air and moisture sensitive.
Compound 8b is better soluble in saturated and unsatu-
rated hydrocarbons and in donor solvents than 8a.
NMR and mass spectra show the expected patterns.
The molecular structure of 8a could be proved by single
crystal X-ray structure determination (Fig. 2).
The new lanthanidocene chlorides react with sodium
acetate forming the corresponding lanthanidocene ac-
etates with 80–90% yield (Scheme 3).
characteristic of monomeric complexes containing only
one stereocenter, thus giving rise for the formation of
only one pair of enantiomers. In the case of 11a, b and
12b, the monomeric structure was confirmed by
cryoscopic molecular weight determinations in benzene.
The mass spectra show the parent ion and the fragmen-
tation pattern expected for the monomeric compounds,
but also fragments which must be assigned to the
dimeric molecular ion. Therefore, a dimeric structure of
the complexes in the solid state can not be excluded.
Compared to the corresponding chlorides, the ac-
etates are more stable against air and moisture, better
soluble in unpolar solvents like hexane, benzene or
toluene and much better in polar solvents like THF or
3. Molecular structures of 6a and 8a
1
diethyl ether. The H and 13C{1H}-NMR spectra (d5-
pyridine, 20 and −40°C) show patterns which are
The molecular structures of 6a and 8a were deter-
mined by single crystal X-ray diffraction. The crystal
data and refinement parameters are given in Table 1.
Fig. 1 shows an ORTEP plot [19] of 6a with the
atomic numbering scheme. Compound 6a crystallizes as
a dimer with one tetrahydrofuran molecule coordinated
to each samarium resulting in nine coordinate Sm3+
centers. Tetrahydrofuran solvated structures were also
found in some other biscyclopentadienylsamarium chlo-
rides such as [(C5H4Me)2Sm(THF)Cl]2 [20]. The coordi-
nation pattern around the samarium centers of 6a is of
the (C5R5)2MX ‘bent-sandwich’ type and is roughly
similar to that of other crystallographically character-
Scheme 2.

H. Schumann et al. / Journal of Organometallic Chemistry 574 (1999) 228–240
231
˚
(1.85 and 1.87 A) with R*=neomenthyl [25]. All other
bond lengths and angles are comparable to those found
in samarocene chloride complexes like [(C5H4Me)2Sm
(THF)Cl]2 [20], (C5Me5)2Sm(THF)Cl [22], and (C5H5)2
Sm(Cl)(THF)2(v-Cl)2Sm(Cl)2(THF)3 [26].
Solution of the X-ray diffraction data of 8a gener-
ated the structure shown in Fig. 2. The crystal consists
of monomeric molecules in a racemic 1:1 mixture with
regard to the ethyl and methyl group at the bridging
silicon atom. The angle ring centroid–Zr–ring centroid
of 126.70(4)° and the angle C(1)–Si–C(8) of 93.88(14)°
are similar to those in Me2Si(C5H4)2ZrCl2 (125.40°/
93.2°) [2], Me2Si(1-C5H2-3-tBu-5-Me)2ZrCl2 (126.7°/
94.3°) [14]b and rac-Me2Si(1-C5H2-2-Me-4-Ph)2ZrCl2
(126.0°/93.3°) [14]e. The angle Cl–Zr–Cl% (101.17(5)°) is
larger than that in comparable compounds like
Me2Si(C5H4)2ZrCl2 (97.98°) [2], Me2Si(1-C5H2-3-tBu-5-
Me)2ZrCl2 (97.6°) [14]a or rac-Me2Si(1-C5H2-2-Me-4-
Ph)2-ZrCl2 (98.8°) [14]e. All other bond distances and
angles are similar to those found in Me2Si(C5H5)2ZrCl2
[2], Me2Si(1-C5H2-3-tBu-5-Me)2ZrCl2 [14]a and rac-
Me2Si(1-C5H2-2-Me-4-Ph)2ZrCl2 [14]e.
˚
Fig. 2. ORTEP plot [19] of 8a. Selected bond distances [A] and angles
[°] (estimated standard deviations in parentheses; Cp and Cp* define
the centroids of the ring atoms C(1), C(2), C(3), C(3%), C(2%) and C(8),
C(9) C(10), C(10%), C(9%), respectively: Zr–Cl 2.4336(8), Zr–Cp*
2.218(2), Zr–Cp 2.219(2), Si–C(6) 1.856(3), Si–C(1) 1.875(3), Si–
C(8) 1.876(3); Cl–Zr–Cl% 101.17(5), Cp*–Zr–Cl% 106.32(3), Cp–Zr–
Cl 106.77(6), Cp*–Zr–Cp 126.70(4), C(1)–Si–C(8) 93.82(14),
C(6)–Si–C(6%) 107.0(2).
In accordance with the larger ionic radius of samar-
ium compared to zirconium, the bond distances M–
(C5H4) and M–(C5Me4) decrease in the order 6a
˚
˚
(2.458(2), 2.446(2) A) to 8a (2.219(2), 2.218(2) A) just
as do the angles C(1)–Si–C(13) and C(1)–Si–C(8) (6a
(100.29(13)°, 8a (93.82(14)°), whereas the angles ring
centroid–M–ring centroid increase in the same order
(6a 118.60(5)°, 8a 126.70(4)°).
ized lanthanidocenes with Cl and THF ligation. The
principal structural change that arises when the cy-
clopentadienyl rings are linked by a dialkylsilyl group,
is a decrease of the ring centroid–Sm–ring centroid
angle compared to samarocenes with unbridged cy-
clopentadienyl rings. The angle of 118.60(5)° in 6a is in
the same range as in [Me4C2(C5H4)2SmCl(THF)]2
(115.4 and 115.8°) [21], but smaller than in
(C5Me5)2SmCl(THF) (133(1)°) [22], [(C5H4Me)2Sm
(THF)(v-Cl)]2 (126.4°) [20] and in the Me2Ge-brid-
ged samarocene Me2Ge(C5Me4)2Sm(v-Cl)2Li(THF)2
(124.5°) [23]. This effect also could be observed for 8a.
Structure refinement of 6a shows the terminal carbon
atom of the ethyl substituent to be disordered racemi-
cally (50:50%) between the positions C(11) and C(11%).
The bond lengths Sm–Cl and Sm–Cl% are not equiva-
lent (2.7793(14) and 2.8169(9) A), a situation which was
also found for the Sm–Cl distances in [(C5H4Me)2
Sm(THF)Cl]2 (2.759 and 2.819 A) [20]. Bridging Sm–Cl
distances are usually longer than terminal Sm–Cl dis-
tances as e.g. in [(C5Me5)2Sm(THF)Cl] (2.709 A) [22].
The bond length Sm–O (2.614(2) A) is slightly longer
than that in [(C5H4Me)2Sm(THF)Cl]2 (2.563 A) [20]
4. Catalytic activity of 8a, 8b and
[(C5H5)(C5Me5)ZrCl2] (13)
The polymerization of ethylene and propylene was
conducted at 30°C in the presence of 8a/MAO, 8b/
MAO and the unbridged system [(C5H5)(C5Me5)ZrCl2]
(13)/MAO. The results of the experiments are given in
Table 2.
Besides the electronic and steric influence of the
silylene bridge itself, the linkage of the two cyclopenta-
dienyl ligands changes structure and energy of the
metal orbitals [27] and the angle between the ring
planes, the last fact influencing the space available for
reactions at the metal center. Different reactivities in
ethylene and propylene polymerizations should be the
consequence.
The results of the polymerization experiments using
the zirconocene complexes 8a and 13 as catalysts
demonstrate that, compared to the unbridged complex
13, the silyl-bridged complex 8a shows a notable de-
crease in ethylene polymerization activity, but a strong
increase in propylene polymerization activity. A similar
trend is observed for the molecular weights of the
polymers obtained, though that of polyethylene is much
˚
˚
˚
˚
˚
and very similar to that in [(C5Me5)2Sm(THF)2] (2.63
˚
˚
A) [24]. The distance Si–C(10) (1.881(4) A) is only
˚
slightly longer than the distance Si–C(12) (1.875(4) A).
They correspond to the bond lengths found in
[Me2Si(C5H3R*)(C5Me4)SmCH(SiMe3)2] (1.848 and
˚
1.861 A) or in [Me2Si(C5H3R*)(C5Me4)SmN(SiMe3)2]

232
H. Schumann et al. / Journal of Organometallic Chemistry 574 (1999) 228–240
Scheme 3.
more susceptible to changes in the ligand structure of
the catalyst compared to the results in propylene
polymerization where the increase in molecular weight
is rather small. Exchange of ethyl for phenyl as one
of the two substituents bound to the silylene bridge
leads to a decrease in polymerization activity for both
monomers. Interestingly, a strong increase in the
molecular weight of the polyethylene produced is ob-
served whereas virtually no influence is detected in
propylene polymerization.
No significant differences were observed in pentad
distribution between the simple and the bridged zir-
conocenes and also an exchange of the substituents
bound to the bridging silicon atom had no influence
on the microstructure of the polymer. All examined
crowded Cp*2 ZrCl2/MAO system [28] were not de-
tected.
5. Experimental details
5.1. General comments
All reactions were carried out in an atmosphere of
dry, oxygen free nitrogen using Schlenk techniques.
Solvents were dried over sodium/benzophenone and
distilled prior to use. The NMR spectra were
recorded on a Bruker ARX 200 or a Bruker ARX
400 spectrometer (1H: d5-pyridine, 20°C; 13C{1H}: d5-
pyridine, 20°C; l in ppm relative to the remaining
proton content of the solvent; unless otherwise spe-
cified). CH analyses were performed on a Perkin-
Elmer 240 C elemental analyser. Mass spectra were
determined on a Varian MAT 311 A spectrometer
using electron impact. Kryoscopic molecular weight
measurements were carried out in benzene. The ligand
precursors Na[C5Me4H] [29] and Na[C5H5] [30] as
well as the anhydrous LnCl3 [31] were prepared by
published procedures. Dichloro(ethyl)methyl- and
dichloro(methyl)phenylsilane (ABCR) were distilled
prior to use.
metallocenes
produce
atactic
polypropylene
(mm=19%, mr=50%, rr=31%). Only a very slight
preference for syndiotactic enchainment could be
detected that can be attributed to the different
size of the C5H5 and the C5Me5 ligands. Polymer
13C-NMR also revealed that for these metallocenes
i-hydrogen elimination is the single chain termination
mechanism. Vinyl or isopropyl chain ends represent-
ing i-methyl elimination which was found to be
the main termination pathway in the highly

H. Schumann et al. / Journal of Organometallic Chemistry 574 (1999) 228–240
233
5.2. Syntheses of the ligands
added into the reaction flask. The resulting mixture was
stirred for 10 min, filtered and the filtrate evaporated
until a yellow liquid remained. Fractional distillation
yielded a pale yellow liquid. Yield 5.22 g (76%) of 1a.
5.2.1. Chloro(ethyl)(methyl)(2,3,4,5-tetramethylcyclo-
pentadienyl)silane (1a)
1
A solution of 4.00 g (29.82 mmol) Na[C5Me4H] in 80
ml of THF was cooled to −78°C. 4.26 g (4.04 ml=
29.82 mmol) of dichloro(ethyl)(methyl)silane were
added over a period of 30 min. The reaction mixture
was warmed very slowly to room temperature (over 6
h) and stirred for another 12 h. The solvent was re-
moved under reduced pressure, and 80 ml of Et2O were
B.p.: 61–63°C/0.1 mbar. H-NMR (400 MHz, C6D6):
0.11 (s, 3H, SiMe), 0.51 (m, 1H, SiCH2CH3), 0.59 (m,
1H, SiCH2CH3), 0.92 (t, 3H, J(HH)=4 Hz),
SiCH2CH3), 1.71 (s, 6H, C5Me4), 1.93 (s, 6H, C5Me4),
2.95 (s, 1H, SiC5H). 13C{1H}-NMR (100.64 MHz,
C6D6): −1.64, 7.06, 8.59, 10.73, 15.34, 55.58, 131.46,
131.60, 137.83.
5.2.2. [(Cyclopentadienyl)(ethyl)(methyl)(2,3,4,5-tetra-
methylcyclopentadienyl)silyl]disodium (3a)
Table 1
Crystal data and structure refinement for 6a and 8a
Na[C5H5] (2.01 g, 22.80 mmol) was dissolved in 10
ml of THF and was added to a solution of 5.19 g (22.80
mmol) of 1a in 30 ml of THF at –78°C. The reaction
mixture was then allowed to warm up to ambient
temperature. After stirring for 12 h, the THF was
removed in vacuo, and the orange residue was extracted
with hexane. The hexane was evaporated under reduced
pressure to yield 4.83 g (82%) of (cyclopentadi-
enyl)(ethyl)(methyl)(tetramethylcyclopentadienyl)silane
(2a) as an orange oil, which was used without further
purification.
6a
8a
Empirical formula
Formula weight
C34H38Cl2Si2Sm2
(C4H8O)2
1018.69
C17H24Cl2SiZr
418.57
(g mol−1
)
Temperature (K)
Crystal system
Space group
240(2)
Triclinic
P1 (No. 2)
162(2)
Orthorhombic
Pnma (No. 62)
(
Unit cell dimensions
˚
a (A)
11.225(5)
11.6278(2)
9.116(2)
93.865(14)
113.57(2)
77.98(2)
1066.4(6)×10−30
2
13.417(2)
9.938(2)
13.486(4)
˚
b (A)
˚
NaNH2 (1.47 g, 37.39 mmol) was suspended in 60 ml
of THF, and 4.83 g (18.70 mmol) of 2a dissolved in 10
ml of THF were slowly added. The suspension was
stirred for 12 h, filtered, and the solvent was removed in
vacuo. The resulting pale brown residue was washed
several times with hexane to obtain a cream-colored
solid, which was dried in vacuo at 0.1 mbar. Yield 6.44
g (92%) of the adduct of 3a with 1 THF. Anal. Found:
c (A)
h (°)
i (°)
k (°)
Volume (m3)
1798.3(6)×10−30
4
1.546
Z
Density (calculated, mg
1.602
m−3
)
Absorption coefficient
(mm−1
F(000)
2.820
0.916
)
C, 66.73; H, 8.11. C21H32Na2OSi·(374.66 g mol−1
)
512
840
1
(3a). Calc.: C, 67.34; H, 8.61%. H-NMR (400 MHz):
0.92 (s, 3H, SiMe), 1.17 (m, 2H,SiCH2CH3), 1.41 (m,
3H, SiCH2CH3), 1.61 (m, 4H, THF), 2.25 (s, 6H,
C5Me4), 2.64 (s, 6H, C5Me4), 3.66 (m, 4H, THF), 6.65
(m, 2H, C5H4), 6.81 (m, 2H, C5H4). 13C{1H}-NMR
(100.64 MHz): 0.36, 9.21, 10.75, 12.28, 15.12, 25.43,
67.46, 103.43, 107.33, 109.25, 111.41, 114.36, 116.51.
Crystal size (mm)
Aperture (mm)
Scan angle (°)
Range of data collection
Index ranges
0.30×0.36×0.50
2.4
(0.86+0.35tan q)
4°B2qB55°
05h514, −155 05h517, 05k5
k515, −115l5
0.20×0.23×0.33
2.3
(0.68+0.35tan q)
2°B2qB55°
12, −175l517
11
5213
Reflections collected
Independent reflections
4202
2137 (R(int)=
4852 (R(int)
=
0.0163)
0.0203)
Refinement method
Full-matrix least-
Full-matrix least-
squares on F2
2106/0/106
squares on F2
5.2.3. Chloro(methyl)(phenyl)(2,3,4,5-tetramethylcyclo-
pentadienyl)silane (1b)
Data/restraints/parameters 4829/0/235
Goodness-of-fit on F2 c
1.060
1.086
The procedure described above for the synthesis of
1a was carried out with 4.45 g (30.87 mmol) of
Na[C5Me4H] and 5.89 g (5.03 ml=30.87 mmol) of
dichloromethyl-(phenyl)silane in 70 ml of THF.
Workup as described above and fractional distillation
of the resulting yellow oil yielded a pale yellow liquid.
Yield 4.65 g (55%) of 1b. B.p.: 94–96°C/0.1 mbar.
1H-NMR (C6D6, 200 MHz): 0.50 (s, 3H, SiMe), 1.67 (s,
3H, C5Me4), 1.68 (s, 3H, C5Me4), 1.72 (s, 3H, C5Me4),
Final R indices [I\2|(I)] Ra1=0.0284,
Ra1=0.0331,
wRb2 =0.0852
R1=0.0439,
wR2=0.1108
Max. 0.653, min.
−0.440
wRb2 =0.0786
R indices (all data)
R1=0.0295,
wR2=0.0856
Max. 1.280, min.
−1.044
Largest difference peak
−3
˚
and hole (e A
)
a R1=ꢀ(ꢁFoꢁ−ꢁFcꢁ)/ꢀꢁFoꢁ.
2 1/2
b wR2=[ꢀw(ꢁFoꢁ−ꢁFcꢁ)2/ꢀwꢁFoꢁ ]
.
.
c GOOF=[ꢀw(ꢁFoꢁ–ꢁFcꢁ)2/(n−p)]1/2

234
H. Schumann et al. / Journal of Organometallic Chemistry 574 (1999) 228–240
Table 2
Polymerization results obtained with [(C5H5)(C5Me5)ZrCl2] (13) and [RR%Si(C5H4)(C5Me4)ZrCl2] (R=Me; R%=Et (8a), Ph (8b))a
Metallocene
Monomer
Activityb
Mp (g mol−1
)
Mw/Mp
Tm (°C)
13
8a
8b
13
8a
8b
Ethylene
Ethylene
Ethylene
Propylene
Propylene
Propylene
22500
6700
3600
600
2800
1150
2135000
439000
1029000
13900
16100
17500
n.d.c
n.d.c
n.d.c
2.0
2.1
1.9
136
134
137
ad
ad
ad
a
At 30°C, 2 bar monomer pressure, 200 ml toluene, [MAO]=2 g l−1, [Zr]=1×10−6 mol l−1 (ethylene) and 5×10−6 mol l−1 (propylene),
t
Pol=60 min.
b In kg Pol (mol Zr·h)−1
.
c n.d., not determined.
d a, amorphous.
2.06 (s, 3H, C5Me4), 3.42 (s, 1H, SiC5H), 7.43 (m, 3H,
C6H5), 7.64 (m, 2H, C6H5). 13C{1H}-NMR (CDCl3,
50.32 MHz): −2.58, 11.11, 11.13, 14.15, 14.38, 55.95,
127.49, 128.31, 130.13, 133.62, 133.65, 134.63, 138.24,
148.98.
5.3. Syntheses of metallocene chlorides with ethyl,
methyl substitution at the bridging silicon atom
5.3.1. [Bis(v-chloro)(cyclopentadienyl)(ethyl)(methyl)-
(2,3,4,5-tetramethylcyclopentadienyl)silyl]diyttrium (4a)
A 100 ml Schlenk flask was charged with 1.17 g (2.83
mmol) of YCl3(THF)3 and 1.06 g (2.83 mmol) of 3a. An
80 ml volume of THF was added and the reaction
mixture was stirred for 12 h at room temperature,
followed by refluxing with stirring for 12 h and additional
stirring for 12 h at ambient temperature. The THF was
removed in vacuo. The resulting yellow solid was first
washed with 60 ml of Et2O and the product was then
separated by soxhlet extraction with 80 ml of Et2O. The
pale yellow extract was concentrated to 25 ml and cooled
to −30°C. The resulting colourless microcrystalline
product was isolated by decantation and subsequent
vacuum drying at 0.1 mbar. Yield 0.39 g (36%) of 4a.
Anal. Found: C, 53.57; H, 6.40. C34H48Cl2Si2Y2 (761.73
g mol−1) (4a). Calc.: C, 53.62; H, 6.35%. 1H-NMR (400
MHz): 0.88 (s, 3H, SiMe), 1.33 (m, 5H, SiEt), 1.69 (br
s, 3H, C5Me4), 2.12 (s, 3H, C5Me4), 2.14 (s, 3H, C5Me4),
6,20 (m, 1H, C5H4), 6,21 (m, 1H, C5H4), 6,70 (m, 2H,
C5H4). 13C{1H}-NMR (100,64 MHz): −2.98, 7.07, 7.59,
10.86, 13.55, 13.82, 103.05, 113.05, 113.55, 114.20,
118.05, 118.46, 121.69, 122.59, 125.39. MS (220°C, 35Cl,
28Si, m/z (%)): 760 (35) [(MeEtSi(C5Me4)(C5H4)YCl)2ꢀ
D]+, 731 (81) [D–Et]+, 716 (18) [D–Et–Me]+, 380 (23)
[MeEtSi(C5Me4)(C5H4)YCl]+, 351 (44) [MeSi(C5Me4)
(C5H4)YCl]+, 345 (100) [MeEtSi(C5Me4)(C5H4)Y]+,
336 (40) [Si(C5Me4)(C5H4)YCl]+, 316 (40) [MeSi(C5Me4)
(C5H4)Y]+and other fragments.
5.2.4. [(Cyclopentadienyl)(methyl)(phenyl)(2,3,4,5-
tetramethylcyclopentadienyl)silyl]disodium (3b)
Compound 1b (4.60 g, 16.62 mmol) was dissolved in
60 ml of THF, and the solution was cooled to –78°C.
Then, 1.46 g (16.62 mmol) of Na[C5H5] dissolved in 10
ml of THF were added slowly. The reaction mixture
was allowed to warm up to room temperature very
slowly over a period of 6 h and was stirred for 12 h at
ambient temperature. The THF was evaporated in
vacuo and the remaining residue was extracted with
hexane. The solvent was removed under reduced pres-
sure to yield 3.78 (74%) of (cyclopentadienyl)(methyl)
(phenyl)(tetramethylcyclopentadienyl)silane (2b) as a
dark yellow oil, which was used without further purifi-
cation.
To a suspension of 0.95 g (24.68 mmol) of NaNH2 in
80 ml of THF were slowly added 3.78 g (12.34 mmol)
of 2b dissolved in 10 ml of THF. The reaction mixture
was stirred for 12 h, filtered and the THF was evapo-
rated under reduced pressure. The resulting pale brown
residue was washed several times with hexane to give a
cream-coloured solid, which was dried in vacuo at 0.1
mbar. Yield 3.59 g (83%) of 3b. Anal. Found: C, 70.99;
H, 6.50. C21H24Na2Si (350.56 g mol−1) (3b). Calc.: C,
71.97; H, 6.90%. 1H-NMR (200 MHz): 1.06 (s, 3H,
SiMe), 2.23 (s, 6H, C5Me4), 2.36 (s, 6H, C5Me4), 6.73
(m, 2H, C5H4), 6.99 (m, 2H, C5H4), 7.24 (m, 3H,
C6H5), 8.44 (m, 1H, C6H5), 8.47 (m, 1H, C6H5).
13C{1H}-NMR (50.32 MHz): 3.69, 12.19, 15.74, 102.28,
107.74, 110.75, 111.87, 113.98, 115.10, 126.76, 135.73,
148.71.
5.3.2. [Bis(v-chloro)(cyclopentadienyl)(ethyl)(methyl)-
(2,3,4,5-tetramethylcyclopentadienyl)silyl]dilanthanum
(5a)
The preceding described synthesis for 4a was carried
out with 1.84 g (5.79 mmol) of LaCl3(THF) and 2.17 g

H. Schumann et al. / Journal of Organometallic Chemistry 574 (1999) 228–240
235
(5.79 mmol) of 3a in 70 ml of THF to yield a pale
yellow solid. Yield 0.44 g (18%) of 5a. Anal. Found: C,
48.39; H, 5.85. C34H48Cl2La2Si2 (861.73 g mol−1) (5a).
(s, 3H, C5Me4), 2.13 (s, 3H, C5Me4), 3.64 (m, THF),
6,17 (m, 1H, C5H4), 6.21 (m, 1H, C5H4) 6,25 (m, 2H,
C5H4). 13C{1H}-NMR (100,64 MHz): −3.07, 7.05,
7.84, 10.74, 11.00, 13.61, 13.89, 25,42, 67.44, 102.94,
111.70, 112.34, 113.33, 118.15, 118.57, 124.90, 124.94,
130.55. MS (220°C, 35Cl, 28Si, m/z (%)): 932 (37)
[(MeEtSi(C5Me4)(C5H4)LuCl)2ꢀD]+, 903 (100) [D–
Et]+, 466 (17) [MeEtSi–(C5Me4)(C5H4)LuCl]+, 437
(23) [MeSi(C5Me4)(C5H4)LuCl]+, 431 (39) [MeEtSi
(C5Me4)–(C5H4)Lu]+, 401 (23) [MeEtSi(C5Me4)Lu-
Cl]+and other fragments.
1
Calc.: C, 47.39; H, 5.61%. H-NMR (400 MHz): 0.70
(s, 2H, SiMe), 0.73 (s, 1H, SiMe), 1.29 (m, 5H, SiEt),
1.99–2.17 (m, 12H, C5Me4), 6.18 (m, 1H, C5H4), 6.22
(m, 1H, C5H4), 6.59 (m, 2H, C5H4). 13C{1H}-NMR
(100,64 MHz): −3.97, −2.85, 7.41, 7.80, 11.06–13.74,
112.08, 113.23, 115.38, 116.06, 117.67, 120.88, 121.08,
139
121.61, 121.67, 121.98. MS (329°C, 35Cl, 28Si,
La,
m/z (%)): 860 (21) [(MeEtSi(C5Me4)(C5H4)LaCl)2ꢀD]+,
725 (15) [D–(C5H4)SiMeEt]+, 513 (37) [D–2(C5Me4)
SiMeEt]+, 430 (26) [MeEtSi(C5Me4)(C5H4)LaCl]+, 395
(100) [MeEtSi(C5Me4)(C5H4)La]+, 366 (18) [MeSi
(C5Me4)(C5H4)La]+and other fragments.
5.3.5. [(Cyclopentadienyl)(ethyl)(methyl)(2,3,4,5-tetra-
methylcyclopentadienyl)silyl]zirconiumdichloride (8a)
1.92 g (8.24 mmol) of ZrCl4 were carefully dissolved
in 40 ml of THF and 3.08 g (8.24 mmol) of 3a were
added. The suspension was stirred for 48 h at ambient
temperature. The solvent was removed in vacuo, and
the yellow residue was extracted twice with 40 ml of
Et2O. The yellow extracts were concentrated to 25 ml
and cooled to –30°C. The resulting pale yellow crystals
were isolated by decantation and subsequent vacuum
drying. Single crystals for X-ray structure determina-
tion were obtained by recrystallizing the product from
Et2O/THF (10:1) at 0°C. Yield 1.64 g (48%) of 8a. M.p.
(sealed): 195°C. Anal. Found: C, 48.68; H, 5.70.
C17H24Cl2SiZr (418.64 g mol−1) (8a). Calc.: C, 48.78;
5.3.3. [Bis(v-chloro)(cyclopentadienyl)(ethyl)(methyl)-
(2,3,4,5-tetramethylcyclopentadienyl)silyl]disamarium
(6a)
Compound 6a was prepared analogously to 4a from
0.97 g (3.78 mmol) of SmCl3 and 1.42 g (3.78 mmol) of
3a in 60 ml of THF as an orange microcrystalline solid,
which was recrystallized from Et2O/THF (10:1) at −
30°C to obtain single crystals for X-ray structure deter-
mination. Yield 0.89 g (53%) of 6a. Anal. Found: C,
46.52; H, 5.52. C34H48Cl2Si2Sm2 (884.75 g mol−1) (6a).
Calc.: C, 46.11; H, 5.46%. 1H-NMR (400 MHz): −0.35
(s, 2H, SiMe), −0.26 (s, 1H, SiMe), 0.73 (m, 3H,
SiCH2CH3), 1.13 (m, 1.25H, SiCH2CH3), 1.52 (m,
0.75H, SiCH2CH3), 1.83−2.11 (m, 12H, C5Me4), 5.57
(s, 0.66H, C5H4), 5.69 (s, 0.33H, C5H4), 9.05 (m, 1H,
C5H4), 9.72 (s, 0.66H, C5H4), 9.81 (s, 0.33H, C5H4),
12.78 (s, 0.66H, C5H4), 12.95 (s, 0.33H, C5H4).
13C{1H}-NMR (100,64 MHz): −0.39, −0.30, 5.01,
7.29, 8.22, 10.47, 11.55, 11.70, 14.50, 14.69, 18.79–
18.91, 95.39, 103.11, 105.10, 107.28, 108.01, 111,37,
1
H, 5.78%. H-NMR (400 MHz): 0.74 (s, 3H, SiMe),
1.18 (m, 5H, SiEt), 1.90 (s, 3H, C5Me4), 1.92 (s, 3H,
C5Me4), 2.05 (s, 6H, C5Me4), 5.85 (m, 1H, C5H4), 5.90
(m, 1H, C5H4), 7.09 (m, 2H, C5H4). 13C{1H}-NMR
(100.64 MHz): −4.13, 6.29, 6.49, 11.92, 11.95, 14.40,
14.65, 98.20, 107.04, 112.62, 113.34, 125.42, 126.27,
126.38, 127.01, 135.37, 135.41. MS (120°C, 35Cl, 90Zr,
28Si, m/z (%)): 416 (55) [MeEtSi(C5Me4)(C5H4)ZrCl2]+,
381 (100) [MeEtSi(C5Me4)(C5H4)ZrCl]+, 352 (58)
[MeEtSi(C5Me4)ZrCl2]+, 346 (6) [MeEtSi(C5Me4)(C5
H4)Zr]+, 331 (3) [EtSi(C5Me4)(C5H4)Zr]+, 317 (12)
[MeSi(C5Me4)(C5H4)Zr]+, 302 (5) [Si(C5Me4)(C5H4)
Zr]+, 296 (5) [MeEtSi(C5H4)ZrCl2]+, 282 (4) [Me-
EtSi(C5Me4)Zr]+, 274 (5) [(C5Me4)(C5H4)Zr]+, 226 (6)
[MeEtSi(C5H4)Zr]+and other fragments.
115.66, 117.09, 117.95, 118.55, 118.98, 119.43, 126.70,
152
131.01, 134.27. MS (220°C, 35Cl, 28Si,
Sm, m/z (%)):
886 (42) [(MeEtSi(C5Me4)(C5H4)SmCl)ꢀD]+, 857 (22)
[D–Et]+, 443 (23) [MeEtSi(C5Me4)(C5H4)SmCl]+, 408
(100) [MeEtSi(C5Me4)(C5H4)Sm]+, 399 (17) [Si(C5Me4)
(C5H4)SmCl]+, 379 (15) [MeSi(C5Me4)(C5H4)Sm]+and
other fragments.
5.4. Syntheses of metallocene chlorides with methyl,
phenyl substitution at the bridging silicon atom
5.3.4. [Bis(v-chloro)(cyclopentadienyl)(ethyl)(methyl)-
(2,3,4,5-tetramethylcyclopentadienyl)silyl]dilutetium (7a)
The procedure described above for the synthesis of
4a was followed with 1.13 g (4.01 mmol) of LuCl3 and
1.50 g (4.01 mmol) of 3a in 70 ml of THF to yield a
colorless microcrystalline solid, which was recrystallized
from Et2O/THF (10:1) to obtain single crystals for
X-ray structure determination. Yield 0.47 g (25%) of
7a. Anal. Found: C, 43.65; H, 4.84. C34H48Cl2Lu2Si2
(933.87 g mol−1) (7a). Calc.: C, 43.73; H, 5.18%.
1H-NMR (400 MHz): 0.86 (s, 3H, SiMe), 1.28-1.45 (m,
5H, SiEt), 1.60 (m, THF), 1.62 (br s, 6H, C5Me4), 2.11
5.4.1. [Bis(v-chloro)(cyclopentadienyl)(methyl)(phenyl)-
(2,3,4,5-tetramethylcyclopentadienyl)silyl]diyttrium (4b)
A 100 ml Schlenk flask was charged with 1.44 g (3.51
mmol) of YCl3(THF)3 and 1.23 g (3.51 mmol) of 3b. A
60 ml volume of THF were added, and after stirring
this mixture for 12 h at room temperature it was heated
to reflux for 12 h followed by stirring at ambient
temperature for additional 12 h. The THF was evapo-
rated in vacuo, and the resulting yellow solid was

236
H. Schumann et al. / Journal of Organometallic Chemistry 574 (1999) 228–240
washed with 30 ml of Et2O and the residue was ex-
tracted three times with Et2O. The extracts were evap-
orated to dryness in vacuo and the product was
isolated by soxhlet extraction with 80 ml of hexane.
The pale yellow solution was evaporated to about 25
ml and cooled to −30°C to give a cream-coloured
solid, which was dried in vacuo at 0.1 mbar. Yield
0.69 g (46%) of 4b. Anal. Found: C, 58.13; H, 5.95.
C42H48Cl2Si2Y2 (857.82 g mol−1) (4b). Calc.: C, 58.81;
(980.84 g mol−1) (6b). Calc.: C, 51.42; H, 4.93%.
1H-NMR (200 MHz): 0.38 (s, 2H, SiMe), 0.58 (s, 1H,
SiMe), 1.65 (m, 8H, THF), 1.96–2.20 (m, 12H,
C5Me4), 3.68 (m, 8H, THF), 6.43 (m, 1H, C5H4), 6.91
(m, 1H, C5H4), 7.53 (m, 2H, C5H4), 7.64 (m, 3H,
C6H5), 8.05 (m, 1H, C6H5), 8.58 (m, 1H, C6H5).
13C{1H}-NMR (50.32 MHz): 1.93, 11.16, 17.99, 18.14,
19.20, 19.81, 94.06, 99.54, 107.96, 108.13, 115.49,
118.26, 120.06, 121.55, 127.40, 128.03, 129.25, 134.03,
134.24, 142.82. MS (280°C, 35Cl, 28Si, 152Sm, m/z (%)):
982 (26) [(MePhSi(C5Me4)(C5H4)SmCl)2ꢀD]+, 862 (8)
[D–SiMePh]+, 742 (1) [D–SiMePh(C5Me4)]+, 707 (5)
[D–SiMePh(C5Me4)-Cl]+, 643 (15) [MePhSi(C5Me4)
(C5H4)Sm2Cl]+, 491 (15) [MePhSi(C5Me4)(C5H4)
SmCl]+, 456 (15) [MePhSi(C5Me4)(C5H4)Sm]+, 399
(1) [Si(C5Me4)(C5H4)SmCl]+, 304 (10) [MePhSi(C5-
Me4)(C5H4)]+, 107 (100) [MeSi(C5H4)]+and other
fragments.
1
H, 5.64%. H-NMR (400 MHz): 0.73 (s, 3H, SiMe),
1.71 (s, 3H, C5Me4), 1.73 (s, 3H, C5Me4), 1.75 (s, 3H,
C5Me4), 1.75 (s, 3H, C5Me4), 6.65 (m, 1H, C5H4), 6.73
(m, 1H, C5H4), 6.98 (m, 2H, C5H4), 7.34 (m, 1H,
C6H5), 7.39 (m, 1H, C6H5), 7.61 (m, 1H, C6H5), 7.72
(m, 1H, C6H5), 7.79 (m, 1H, C6H5). 13C{1H}-NMR
(50.32 MHz): −7.78, 10.88, 11.00, 13.53, 13.99, 95.97,
98.69, 113.30, 115.58, 117.45, 118.61, 120.55, 127.18,
128.26, 131.41, 132.77, 134.42, 135.88, 144.83. MS
(240°C, 35Cl, 28Si, m/z (%)): 856 (1.5) [(MePhSi-
(C5Me4)(C5H4)YCl)2ꢀD]+, 736 (6) [D-SiMePh]+, 616
(28) [D–SiMePh(C5Me4)]+, 428 (11) [MePhSi(C5Me4)
(C5H4)YCl]+, 393 (5) [MePhSi(C5Me4)(C5H4)Y]+, 337
(100) [Si(C5Me4)(C5H4)YCl]+, 303 (29) [Si(C5Me4)-
(C5H4)Y]+and other fragments.
5.4.4. [Bis(v-chloro)(cyclopentadienyl)(methyl)(phenyl)-
(2,3,4,5-tetramethylcyclopentadienyl)silyl]dilutetium (7b)
Compound 7b was synthesized in a similar manner
to 4b from 1.01 g (3.59 mmol) of LuCl3 and 1.26 g
(3.59 mmol) of 3b in 70 ml THF to obtain a colorless
solid. Yield 0.41 g (22%) of 7b. Anal. Found: C,
5.4.2. [Bis(v-chloro)(cyclopentadienyl)(methyl)(phenyl)-
(2,3,4,5-tetramethylcyclopenta-dienyl)silyl]dilanthanum (5b)
This compound was prepared from 1.27 g (4.00
mmol) of LaCl3(THF) and 1.40 g (4.00 mmol) of 3b in
80 ml THF by the method described for 4b to give a
pale yellow solid. Yield 0.31 g (16%) of 5b. Anal.
Found: C, 51.72; H, 4.45. C42H48Cl2La2Si2 (957.82 g
48.12; H, 4.25. C42H48Cl2Lu2Si2 (1029.96 g mol−1
)
1
(7b). Calc.: C, 48.99; H, 4.70%. H-NMR (200 MHz):
1.00 (s, 3H, SiMe), 1.11 (t, 3H, Et2O), 1.59 (m, 4H,
THF), 1.62 (s, 3H, C5Me4), 1.96 (s, 3H, C5Me4), 2.13
(s, 3H, C5Me4), 2.21 (s, 3H, C5Me4), 3.33 (q, 4H,
Et2O), 3.63 (m, 4H, THF), 6.23 (m, 1H, C5H4), 6.39
(m, 1H, C5H4), 6.45 (m, 1H, C5H4), 6.80 (m, 1H,
C5H4), 7.40 (m, 3H, C6H5), 7.53 (m, 1H, C6H5), 8.18
(m, 1H, C6H5). 13C{1H}-NMR (50.32 MHz): 0.35,
10.81, 11.58, 14.19, 15.05, 25.35, 67.39, 101.60, 109.27,
111.20, 112.10, 112.32, 112.76, 117.74, 118.01, 118.48,
119.46, 128.26, 129.39, 134.33, 139.26. MS (210°C,
35Cl, 28Si, m/z (%)): 1028 (38) [(MePhSi(C5-
Me4)(C5H4)LuCl)2.D]+, 908 (17) [D–SiMePh]+, 788
(35) [D–SiMePh–(C5Me4)]+, 514 (84) [MePhSi(C5-
Me4)(C5H4)LuCl]+, 479 (74) [MePhSi(C5Me4)(C5-
H4)Lu]+, 422 (71) [Si(C5Me4)(C5H4)LuCl]+, 387 (10)
[Si(C5Me4)(C5H4)Lu]+, 395 (22) [MePhSi(C5H4)
LuCl]+, 335 (38) [PhSi(C5H4)Lu]+, 185 (100) [MePh-
Si(C5H4)]+and other fragments.
1
mol−1) (5b). Calc.: C, 52.67; H, 5.05%. H-NMR (200
MHz): 0.76 (s, 2H, SiMe), 1.01 (s, 1H, SiMe), 1.59 (m,
8H, THF), 2.14–2.75 (m, 12H, C5Me4), 3.64 (m, 8H,
THF), 6.07 (m, 1H, C5H4), 6.42 (m, 1H, C5H4), 6.73
(m, 1H, C5H4), 6.92 (m, 1H, C5H4), 7.44 (m, 3H,
C6H5), 8.01 (m, 1H, C6H5), 8.25 (m, 1H, C6H5).
13C{1H}-NMR (50.32 MHz): 0.59, 1.36, 10.94, 11.37,
13.71, 15.57, 25.36, 64.31, 98.14, 109.88, 114.95,
116.06, 118.07, 121.48, 122.94, 124.19, 124.91, 128.03,
129.69, 134.94, 140.99, 142.35. MS (240°C, 35Cl, 28Si,
m/z (%)): 956 (1.5) [(MePhSi(C5Me4)(C5H4)LaCl)2ꢀ
D]+, 836 (6) [D–SiMePh]+, 716 (28) [D–
SiMePh(C5Me4)]+, 478 (11) [MePhSi(C5Me4)(C5H4)
LaCl]+, 443 (5) [MePhSi(C5Me4)(C5H4)La]+, 387
(100) [Si(C5Me4)(C5H4)LaCl]+, 353 (29) [Si(C5Me4)
(C5H4)La]+and other fragments.
5.4.5. [(Cyclopentadienyl)(methyl)(phenyl)(2,3,4,5-
tetramethylcyclopentadienyl)silyl]zirconiumdichloride (8b)
ZrCl4 (2.06 g, 8.85 mmol) was dissolved carefully in
70 ml of THF, and 3.10 g (8.85 mmol) of 3b were
added. The suspension was stirred for 96 h at room
temperature, the solvent was removed under reduced
pressure and the remaining pale brown residue first was
washed with 20 ml of Et2O and then extracted two
times with 40 ml of Et2O. The yellow extracts were
5.4.3. [Bis(v-chloro)(cyclopentadienyl)(methyl)(phenyl)-
(2,3,4,5-tetramethylcyclopentadienyl)silyl]disamarium (6b)
This compound was prepared by using the method
described for 4b from 1.30 g (5.04 mmol) of SmCl3
and 1.77 g (5.04 mmol) of 3b in 50 ml THF to yield
an orange microcrystalline solid. Yield 0.59 g (24%) of
6b. Anal. Found: C, 51.52; H, 4.96. C42H48Cl2Si2Sm2

H. Schumann et al. / Journal of Organometallic Chemistry 574 (1999) 228–240
237
reduced in vacuo to 25 ml, and the solvent was cooled
to –78°C to give a pale yellow solid, which was sepa-
rated by decanting and subsequent drying of the solid
in vacuo. The remaining product was recrystallized
from Et2O/THF (10:1) to obtain a pale yellow micro-
crystalline solid, which was dried in vacuo at 0.1 mbar.
Yield 1.49 g (36%) of 8b. M.p.(sealed): 163°C. Anal.
Found: C, 54.17; H, 5.47. C21H24Cl2SiZr (466.78 g
Y]+, 258 (4) [MeEtSi(C5Me4)(C5H4)]+and other frag-
ments.
5.5.2. [(Cyclopentadienyl)(ethyl)(methyl)(2,3,4,5-tetra-
methylcyclopentadienyl)silyl]lanthanumacetate (10a)
Compound 10a was prepared from 0.69 g (0.80
mmol) of 5a und 0.13 g (1.60 mmol) of sodium acetate
in 35 ml THF by the same method described for 9a to
give a cream-coloured solid. Yield 0.64 g (88%) of 10a.
Anal. Found: C, 49.54; H, 5.15. C19H27LaO2Si (454.43
1
mol−1) (8b). Calc.: C, 54.05; H, 5.18%. H-NMR (200
MHz): 0.91 (s, 3H, SiMe), 1.45 (s, 3H; C5Me4), 1.98 (s,
3H, C5Me4), 2.01 (s, 3H, C5Me4), 2.09 (s, 3H, C5Me4),
5.85 (m, 2H, C5H4), 6.14 (m, 2H, C5H4), 7.14 (m, 1H,
C6H5), 7.20 (m, 1H, C6H5), 7.96 (m, 3H, C6H5).
13C{1H}-NMR (50.32 MHz): −0.35, 12.04, 12.49,
15.09, 15.30, 97.60, 105.65, 112.97, 115.00, 125.27,
125.50, 128.19, 129.13, 129.22, 130.88, 134.29, 134.81,
137.33, 142.21. MS (25°C, 35Cl, 90Zr, 28Si, m/z (%)): 464
1
g mol−1) (10a). Calc.: C, 50.22; H, 5.99%. H-NMR
(200 MHz): 0.94 (s, 3H, SiMe), 1.35 (m, 5H, SEt), 2.01
(br s, 9H, C5Me4), 2.57 (s, 3H, C5Me4), 2.61 (s, 3H,
C5Me4), 6.38 (m, 2H, C5H4), 6.59 (m, 2H, C5H4).
13C{1H}-NMR (50.32 MHz): −1.82, 7.74, 8.83, 11.38,
14.25, 14.56, 15.18, 25.01, 65.43, 102.37, 108.22, 114.31,
114.57, 115.05, 121.12, 121.33, 121.53, 122.18, 131.33,
182.17. MS (280°C, 28Si, m/z (%)): 908 (32)
[(MeEtSi(C5Me4)(C5H4)LaO2CCH3)2ꢀD]+, 836 (2) [D–
SiMeEt]+, 454 (36) [MeEtSi(C5Me4)(C5H4)LaO2-
CCH3]+, 425 (100) [MeSi(C5Me4)(C5H4)LaO2CCH3]+,
395 (53) [MeEtSi(C5Me4)(C5H4)La]+, 258 (27) [MeEtSi-
(C5Me4)(C5H4)]+and other fragments.
(49)
[MePhSi(C5Me4)(C5H4)ZrCl2]+,
429
(100)
[MePhSi(C5Me4)(C5H4)ZrCl]+, 414 (17) [PhSi(C5Me4)-
ZrCl]+, 400 (4) [MePhSi(C5Me4)ZrCl2]+, 394 (7) [Me-
PhSi(C5Me4)(C5H4)Zr]+, 379 (6) [PhSi(C5Me4)(C5H4)-
Zr]+, 344 (2) [MePhSi(C5H4)ZrCl2]+, 330 (3)
[MePhSi(C5Me4)Zr]+, 317 (2) [MeSi(C5Me4)(C5H4)-
Zr]+, 302 (2) [Si(C5Me4)(C5H4)Zr]+and other frag-
ments.
5.5.3. [(Cyclopentadienyl)(ethyl)(methyl)(2,3,4,5-tetra-
methylcyclopentadienyl)silyl]samariumacetate (11a)
The procedure described above for the synthesis of
9a was repeated with 0.36 g (0.41 mmol) of 6a and 0.07
g (0.82 mmol) of sodium acetate in 35 ml of THF to
yield an intensive yellow microcrystalline solid. Yield
0.31 g (81%) of 11a. Anal. Found: C, 47.99; H, 5.81.
C19H27O2SiSm (465.94 g mol−1) (11a). Calc.: C, 48.90;
5.5. Syntheses of organolanthanide acetates with ethyl,
methyl substitution at the bridging silicon atom
5.5.1. [(Cyclopentadienyl)(ethyl)(methyl)(2,3,4,5-tetra-
methylcyclopentadienyl)silyl]yttriumacetate (9a)
A 50 ml Schlenk flask was charged with 0.30 g (0.39
mmol) of 4a and 0.07 g (0.79 mmol) of sodium acetate.
35 ml of THF were added and the reaction mixture was
stirred for 48 h at room temperature. The THF was
removed in vacuo, and the product was separated by
soxhlet extraction with Et2O. The extract was reduced
in vacuo to 25 ml and cooled to −30°C to give a
colourless microcrystalline solid. The product was iso-
lated by decantation and dried in vacuo at 0.1 mbar.
Yield 0.25 g (78%) of 9a. Anal. Found: C, 56.42; H,
6.94. C19H27O2SiY (404.43 g mol−1) (9a). Calc.: C,
56.43; H, 6.73%. 1H-NMR (200 MHz): 0.90 (s, 3H,
SiMe), 1.33 (m, 3H, SiCH2CH3), 1.57 (m, 2H,
SCH2CH3), 1.85 (s, 6H, C5Me4), 2.11 (s, 3H, O2CCH3),
2.37, 2.38 (s, 6H, C5Me4), 6.30 (br m, 4H, C5H4).
13C{1H}-NMR (50.32 MHz): −2.45, 7.41, 8.07, 10.51,
13.99, 14.32, 23.94, 103.29, 104.02, 107.08, 112.78,
113.19, 119.66, 121.51, 122.04, 122.62, 180.61. MS
(305°C, 28Si, m/z (%)): 808 (33) [(MeEtSi(C5Me4)
(C5H4)YO2CCH3)2ꢀD]+, 779 (1) [D–Et]+, 736 (1) [D
–SiMeEt]+, 404 (100) [MeEtSi(C5Me4)(C5H4)YO2
CCH3]+, 375 (13) [MeSi(C5Me4)(C5H4)YO2CCH3]+,
345 (8) [MeEtSi(C5Me4)(C5H4)Y]+, 339 (19) [MeEtSi-
(C5Me4)YO2CCH3]+, 316 (9) [MeSi(C5Me4)(C5H4)-
H, 5.84%. Molecular mass (kryoscopic): 502 g mol−1
.
1H-NMR (200 MHz): 0.39–0.58 (m, 8H, SiMe, SiEt),
0.90, 0.94, 1.01, 1.62 (s, 12H, C5Me4), 3.13 (br s, 3H,
O2CCH3), 7.05 (s, 1H, C5H4), 9.72 (s br, 2H, C5H4),
12.29 (s, 1H, C5H4). 13C{1H}-NMR (100.64 MHz):
−0.78, 7.03, 9.97, 15.04, 15.42, 17.50, 17.60, 21.86,
93.77, 104.49, 105.30, 107.85, 108.44, 110.94, 111.59,
114.86, 115.79, 116.56, 183.47. MS (220°C, 28Si, 152Sm,
m/z (%)): 934 (24) [(MeEtSi(C5Me4)(C5H4)SmO2-
CCH3)2ꢀD]+, 890 (2) [D–Me–Et]+, 862 (2) [D–
SiMeEt]+, 678 (6) [D–(C5H4)(C5Me4)SiMeEt]+, 467
(100) [MeEtSi(C5Me4)(C5H4)–SmO2CCH3]+, 408 (96)
[MeEtSi(C5Me4)(C5H4)Sm]+, 379 (18) [MeSi(C5Me4)-
(C5H4)–Sm]+, 258 (23) [MeEtSi(C5Me4)(C5H4)]+and
other fragments.
5.5.4. [(Cyclopentadienyl)(ethyl)(methyl)(2,3,4,5-tetra-
methylcyclopentadienyl)silyl]lutetiumacetate (12a)
Compound 12a was prepared analogously to 9a from
0.51 g (0.55 mmol) of 7a and 0.09 g (1.10 mmol) of
sodium acetate in 40 ml of THF to give a colourless
microcrystalline solid. Yield 0.47 g (88%) 12a. Anal.
Found: C, 45.47; H, 5.28. C19H27LuO2Si (490.50 g

238
H. Schumann et al. / Journal of Organometallic Chemistry 574 (1999) 228–240
mol−1) (12a). Calc.: C, 46.53; H, 5.55%. H-NMR (200
MHz): 0.88 (s, 3H, SiMe), 1.38 (m, 5H, SiEt), 1.86 (s,
6H, C5Me4), 2.09 (s, 3H, C5Me4), 2.11 (s, 3H, C5Me4),
2.38 (s, 3H, O2CCH3), 6.21 (m, 2H, C5H4), 6.31 (m, 2H,
C5H4). 13C{1H}-NMR (50.32 MHz): −2.50, 7.27, 8.14,
10.59, 14.07, 14.96, 24.49, 103.36, 104.00, 107.07,
112.13, 113.39, 113.82, 114.08, 118.14, 119.49, 120.84,
183.63. MS (260°C, 28Si, m/z (%)): 980 (36) [(MeEt-
Si(C5Me4)(C5H4)LuO2CCH3)2ꢀD]+, 490 (100) [MeEtSi-
(C5Me4)(C5H4)LuO2C-CH3]+, 461 (16) [MeSi(C5Me4)-
(C5H4)LuO2CCH3]+, 431 (5) [MeEtSi(C5Me4)(C5H4)-
Lu]+, 418 (11) [(C5Me4)(C5H4)LuO2CCH3]+and other
fragments.
113.88, 116.04, 127.03, 127.68, 133.87, 143.87, 182.32.
MS (240°C, 28Si, m/z (%)): 1004 (2) [(MePhSi(C5Me4)-
(C5H4)LaO2CCH3)2ꢀD]+, 820 (6) [D–MePhSi(C5-
H4)]+, 764 (5) [D–SiMePh(C5Me4)]+, 502 (17) [MePh-
Si(C5Me4)(C5H4)–LaO2CCH3]+, 443 (41) [MePhSi(C5-
Me4)(C5H4)La]+, 351 (2) [Si(C5Me4)(C5H4)La]+, 185
(100) [MePhSi(C5H5)]+and other fragments.
1
5.6.3. [(Cyclopentadienyl)(methyl)(phenyl)(2,3,4,5-
tetramethylcyclopentadienyl)silyl]samariumacetate (11b)
The procedure described for 9a was performed with
0.37 g (0.38 mmol) of 6b and 0.07 g (0.76 mmol) of
sodium acetate in 40 ml of THF to obtain an intensive
yellow microcrystalline solid. Yield 0.31 g (79%) of 11b.
Anal. Found: C, 52.97; H, 4.95. C23H27O2SiSm (513.99
g mol−1) (11b). Calc.: C, 53.76; H, 5.30%. Molecular
5.6. Syntheses of organolanthanide acetates with
methyl, phenyl substitution at the bridging silicon atom
1
mass (kryoscopic): 589 g mol−1. H-NMR (200 MHz):
5.6.1. [(Cyclopentadienyl)(methyl)(phenyl)(2,3,4,5-
tetramethylcyclopentadienyl)silyl]yttriumacetate (9b)
Compound 9b was synthesized in a similar manner as
described for 9a from 0.56 g (0.65 mmol) of 4b and 0.11
g (1.30 mmol) of sodium acetate in 40 ml of THF to
obtain a colourless solid. Yield 0.54 g (92%) of 9b.
Anal. Found: C, 60.69; H, 5.85. C23H27O2SiY (452.48 g
0.51 (s, 3H, SiMe), 0.92 (br s, 6H, C5Me4), 1.56 (s br,
3H, O2CCH3), 2.35 (s br, 6H, C5Me4), 6.78 (m, 1H,
C5H4), 7.51 (m, 3H, C5H4), 7.82 (m, 1H, C6H5), 7.90
(m, 1H, C6H5), 8.43 (m, 3H, C6H5). 13C{1H}-NMR
(50.32 MHz): 2.53, 14.00, 14.05, 17.81, 19.12, 21.38,
92.98, 102.40,107.40, 110.20, 114.19, 116.23, 128.04,
128.91, 134.20, 143.63, 181.92. MS (288°C, 28Si, 152Sm,
m/z (%)): 1030 (59) [(MePhSi(C5Me4)(C5H4)Sm-
O2CCH3)2ꢀD]+, 910 (19) [D–SiMePh]+, 846 (39) [D–
MePhSi(C5H4)]+, 790 (19) [D–SiMePh(C5Me4)]+, 726
(11) [D–MePhSi(C5Me4)–(C5H4)]+, 515 (76) [MePhSi-
(C5Me4)(C5H4)SmO2CCH3]+, 456 (100) [MePhSi(C5-
Me4)–(C5H4)Sm]+, 438 (13) [MeSi(C5Me4)(C5H4)SmO2-
CCH3]+, 379 (14) [Si(C5Me4)–(C5H4)Sm]+and other
fragments.
1
mol−1) (9b). Calc.: C, 61.06; H, 6.01%. H-NMR (400
MHz): 0.26 (s, 3H, SiMe), 1.69 (s, 3H, C5Me4), 1.71 (s,
3H, C5Me4), 1.74 (s, 3H, C5Me4), 1.77 (s, 3H, C5Me4),
2.03 (s, 3H, O2CCH3), 6.78 (m, 1H, C5H4), 7.40 (m, 5H,
C6H5), 7.88 (m, 2H, C5H4), 7.95 (m, 1H, C5H4).
13C{1H}-NMR (50.32 MHz): 5.29, 10.80, 10.90, 14.15,
14.98, 26.53, 106.59, 120.19, 122.07, 125.20, 127.77,
128.35, 129.45, 132.86, 133.81, 136.26, 143.54, 179.51.
MS (288°C, 28Si, m/z (%)): 904 (1) [(Me-
PhSi(C5Me4)(C5H4)YO2CCH3)2ꢀD]+, 812 (6) [D–Me–
Ph]+, 784 (2) [D–SiMePh]+, 692 (2) [D–Me–Ph–
(C5Me4)]+, 664 (8) [D–SiMePh(C5Me4)]+, 452 (16)
[MePhSi(C5Me4)(C5H4)YO2CCH3]+, 393 (48) [MePhSi-
(C5Me4)(C5H4)Y]+, 375 (44) [MeSi(C5Me4)(C5H4)-
YO2CCH3]+, 315 (100) [MeSi(C5Me4)(C5H4)Y–H]+,
303 (28) [Si(C5Me4)(C5H4)Y]+, 255 (29) [MeSi–(C5H4)-
YO2CCH3]+and other fragments.
5.6.4. [(Cyclopentadienyl)(methyl)(phenyl)(2,3,4,5-
tetramethylcyclopentadienyl)silyl]lutetiumacetate (12b)
The preceding synthesis for 9a was carried out with
0.35 g (0.34 mmol) of 7b and 0.06 g (0.68 mmol) of
sodium acetate in 40 ml of THF to yield a colourless
microcrystalline solid. Yield 0.34 g (92%) of 12b. Anal.
Found: C, 50.71; H, 5.25. C23H27LuO2Si (538.55 g
mol−1) (12b). Calc.: C, 51.30; H, 5.05%. Molecular
1
mass (kryoscopic): 554 g mol−1. H-NMR (200 MHz):
5.6.2. [(Cyclopentadienyl)(methyl)(phenyl)(2,3,4,5-
0.40 (s, 3H, SiMe), 1.68 (s, 3H, C5Me4), 1.72 (m, 4H,
THF), 1.82 (s, 6H, C5Me4), 1.96 (s, 3H, C5H4), 2.21 (s,
3H, O2CCH3), 3.65 (m, 4H, THF), 6.79 (m, 2H, C5H4),
6.88 (m, 2H, C5H4), 7.29 (m, 3H, C6H5), 7.87 (m, 2H,
C6H5). 13C{1H}-NMR (50.32 MHz): −6.30, 11.11,
14.44, 14.61, 24.47, 25.42, 67.45, 104.07, 105.27, 107.65,
108.62, 113.54, 113.90, 121.08, 126.98, 127.53, 133.24,
134.49, 143.03, 184.99. MS (200°C, 28Si, m/z (%)): 1076
(3) [(MePhSi(C5Me4)(C5H4)LuO2CCH3)2ꢀD]+, 956 (2)
[D–SiMePh]+, 892 (3) [D–Me–Ph–C5H4]+, 836 (5)
[D–SiMePh(C5Me4)]+, 538 (10) [MePhSi(C5Me4)(C5-
H4)LuO2CCH3]+, 479 (33) [MePhSi(C5Me4)(C5H4)–
Lu]+, 387 (12) [Si(C5Me4)(C5H4)Lu]+, 185 (100) [Me-
PhSi(C5H5)]+and other fragments.
tetramethylcyclopentadienyl)silyl]lanthanumacetate (10b)
Compound 10b was prepared by using the same
method as described for 9a from 0.46 g (0.48 mmol) of
5b and 0.08 g (0.96 mmol) of sodium acetate in 40 ml of
THF to give a cream-coloured solid. Yield 0.45 g (94%)
of 10b. Anal. Found: C, 55.47; H, 5.34. C23H27LaO2Si
(502.48 g mol−1) (10b). Calc.: C, 54.98; H, 5.42%.
1H-NMR (200 MHz): 0.32 (s, 3H, SiMe), 1.70–1.85 (m,
12H, C5Me4), 1.92 (br s, 3H, O2CCH3), 6.43 (m, 1H,
C5H4), 6.58 (m, 1H, C5H4), 6.65 (m, 1H, C5H4), 6.73
(m, 1H, C5H4), 7.36 (m, 1H C6H5), 7.40 (m, 2H, C6H5),
7.64 (m, 2H, C6H5). 13C{1H}-NMR (50.32 MHz): 1.53,
10.91, 14.06, 15.15, 25.43, 99.97, 105.21, 107.62, 112.50,

H. Schumann et al. / Journal of Organometallic Chemistry 574 (1999) 228–240
239
5.7. X-ray crystallographic analyses
propylene from Gerling, Holz and Co. and ethylene
from Linde. The gases were purified by passage through
columns with Cu catalyst (BASF R3-11) and a molecu-
An Enraf Nonius CAD-4 automatic diffractometer
˚
˚
(ꢀ–2q scan, u=0.71096 A, variable scan time 45 s)
lar sieve of 10 A. Toluene was refluxed over Na/K for
fitted with a liquid nitrogen low-temperature device was
used for the intensity measurements. The unit cell
parameters were obtained from the angles of 25 reflec-
tions in the range of 18.6°B2qB28.0° for 6a and
18.8°B2qB29.8° for 8a. Reflections were scanned
with variable scan time, depending on intensities, with
2/3 of the time used for scanning the peak and 1/6
measuring each the left and the right background. The
intensities of three check reflections monitored every 2
h showed only statistical fluctuations during the data
collection. The orientation of the crystal was checked
every 200 intensity measurements by scanning three
strong reflections well distributed in reciprocal space. A
new orientation matrix would have automatically been
calculated from a list of 25 recentered reflections, if the
angular change was larger than 0.1%. The raw data
were corrected for Lorentz, polarisation and absorption
effects [32]. The positions of the heavy atoms were
determined from a Patterson synthesis (SHELXS-86)
[33]. Structure solution and refinement was carried out
with the SHELXS-86 [33] and SHELXL-93 [34] soft-
ware respectively. The non-hydrogen atoms were
refined with anisotropic temperature factors. The C–H
several days prior to use. Polymerizations were per-
formed in a 1l type I Bu¨chi autoclave with an addi-
tional internal cooling loop. For a typical experiment
the reactor was evacuated at 95°C for 1 h, flushed
several times with argon and filled with 200 ml of
toluene and 400 mg of MAO. Propylene or ethylene
pressure of 2 bar was applied and the polymerization
started by injection of the metallocene. Monomer con-
sumption was monitored with a Peteric 3002 pressflow
controller and a Bu¨chi bds 488 data system. The poly-
merization was terminated by injection of 5 ml ethanol
and venting off the monomer. Polyethylenes were
stirred with ethanol/HCl overnight and filtered, washed
with NaHCO3 and water. The polypropylene solutions
were stirred with aqueous HCl followed by phase sepa-
ration, neutralization, washing and removal of toluene
on a rotatory evaporator. The polymer yields were
determined after drying for 48 h at 60°C in vacuo.
5.9. Polymer analyses
13C{1H}-NMR spectra were recorded at 373 K on a
Bruker MSL 300 spectrometer at 75 MHz. Samples
were prepared in 10 mm tubes as 10 wt. % solutions of
the polymer in perchlorobutadiene/tetrachloroethane-
d2. DSC-analyses were carried out on a Perkin-Elmer
DSC 4 with a heating rate of 20°C min−1. The results
of the second scan are reported. Gel permeation chro-
matography was performed on a Waters 150-C instru-
ment (135°C/trichlorobenzene) equipped with a PL 360
evaporation light scattering detector. Viscosimetry was
carried out in decahydronaphthalene at 135°C using a
Ubbelohde capillary 0a and a Lauda viscoboy. Mark-
Houwink constants were taken from literature [38].
hydrogen atoms were calculated in idealized positions
2
˚
˚
(C–H=0.96 A, Uiso=0.08 A ). Scattering factors were
taken from references [35–37]. The non-hydrogen
atoms of the solvent molecules were refined with
isotropic temperature factors. Data reduction was per-
formed using PC-software [32]. All other calculations
were performed with SHELXL-93 [34]. Molecular plots
were obtained with the program ZORTEP [19]. 6a:
During the refinement of the structure the terminal
atom of the ethyl substituent was found to be disor-
dered racemically between the positions C(11) and
C(11%). 8a: The normalized structure amplitudes indi-
cated the space group Pbn21 (No. 33, non standard
orientation). After structure refinement the absolute
structure could not be determined. The ethyl and
methyl substituents at the silicon atom are racemically
distributed (50:50). Therefore the structure was trans-
ferred to the centrosymmetric space group Pnma (No.
62) and refined with a disordered atom C(7). Further
details of the crystal structure investigation are avail-
able on request from the Fachinformationszentrum
Karlsruhe GmbH, D-76344 Eggenstein-Leopoldshafen
(FRG), on quoting the depository numbers CSD-
407288 (6a) and CSD-407287 (8a).
Acknowledgements
This work was financially supported by the Fonds
der Chemischen Industrie, the Deutsche Forschungsge-
meinschaft (Graduiertenkolleg ‘Synthetische, mechanis-
tische
und
reaktionstechnische
Aspekte
von
Metallkatalysatoren’) and the Bundesminister fu¨r Bil-
dung, Wissenschaft, Forschungs und Technologie
(BMBF 03D 0023 D3).
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