Siloxyaluminum alkyl cations: Syntheses, structures, and reactions related to activation of zirconocene catalysts on silica gel surfaces

Article abstract of DOI:10.1021/om0207515

Binuclear siloxyaluminum methyl complexes of the type Me₂Al(μ-OSiR₃)₂AlMe₂ react with protonated N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate, with release of CH₄, to form the dimethylaniline (DMA)-stabilized siloxyaluminum methyl cations Me₂Al(μ-OSiR₃)₂AlMe(NMe₂ (C₆H₅)⁺. These cations abstract a Cl^- ligand from (C₅H₅)₂ ZrCl₂, to give the dinuclear cation {(C₅H₅)₂ZrCl}₂(μ-Cl)⁺, and a CH₃^- ligand from (C₅H₅)₂Zr(CH₃)₂, to give by way of the DMA-stabilized cation (C₅H₅)₂Zr(CH₃)NMe₂(C ₆H₅)⁺ the CH-activation product (C₅H₅)₂ZrCH₂NMe(C₆ H₅)⁺; reaction with Me₂Si(ind)₂ ZrMe₂ in toluene solution yields a moderately active catalyst for ethene polymerization. This reactivity of siloxyaluminum methyl cations is qualitatively similar to, although substantially lower than, that of a silica gel surface treated with trimethylaluminum and a cationizing agent.

Full text of DOI:10.1021/om0207515

1320
Organometallics 2003, 22, 1320-1325
Siloxya lu m in u m Alk yl Ca tion s: Syn th eses, Str u ctu r es,
a n d Rea ction s Rela ted to Activa tion of Zir con ocen e
Ca ta lysts on Silica Gel Su r fa ces
Olaf Wrobel,† Frank Schaper,† Ulrich Wieser,† Heike Gregorius,‡ and
Hans H. Brintzinger*,†
Fachbereich Chemie, Universita¨t Konstanz, D-78457 Konstanz, Germany, and
Basell Polypropylen GmbH, D-67056 Ludwigshafen, Germany
Received September 11, 2002
Binuclear siloxyaluminum methyl complexes of the type Me2Al(µ-OSiR3)2AlMe2 react with
protonated N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate, with release of CH4,
to form the dimethylaniline (DMA)-stabilized siloxyaluminum methyl cations Me2Al(µ-
OSiR3)2AlMe(NMe2(C6H5)+. These cations abstract a Cl- ligand from (C5H5)2ZrCl2, to give
the dinuclear cation {(C5H5)2ZrCl}2(µ-Cl)+, and a CH3- ligand from (C5H5)2Zr(CH3)2, to give
by way of the DMA-stabilized cation (C5H5)2Zr(CH3)NMe2(C6H5)+ the CH-activation product
(C5H5)2ZrCH2NMe(C6H5)+; reaction with Me2Si(ind)2ZrMe2 in toluene solution yields a
moderately active catalyst for ethene polymerization. This reactivity of siloxyaluminum
methyl cations is qualitatively similar to, although substantially lower than, that of a silica
gel surface treated with trimethylaluminum and a cationizing agent.
In tr od u ction
Si-O-Al units.3 Simple silanols, R3SiOH, react with the
trialkylaluminum compounds AlR′3 to form siloxyalu-
minum alkyl compounds (siloxalanes) of the type [R3-
SiOAlR′2]2, which have been shown to be dimeric in the
solid state.4
To approach the question whether related surface-
bound species might participate in the activation of
supported metallocene catalysts, we have reacted the
easily accessible siloxyaluminum alkyl compounds 1a -c
with cationizing reagents and assessed the reactivity
of the resulting cations vis-a`-vis zirconocene chloride
and methyl complexes.
For practical applications, metallocene-based olefin-
polymerization catalysts are in general adsorbed on a
solid support, most frequently on a suitably modified
silica gel.1 Like their homogeneously dissolved ana-
logues, these supported metallocene catalysts are gener-
ally activated by use of methylalumoxane. Several
reports have dealt, however, also with their activation
by boron-based cocatalysts.2 In these cases, the silica
gel support is usually treated first with an aluminum
trialkyl compound and then with N,N-dimethylanilin-
ium tetrakis(pentafluorophenyl)borate (DMAB) and the
metallocene dialkyl or dichloride complex.
The mechanisms by which the zirconocene complexes
are activated for polymerization catalysis on silica gel
support materials have remained largely unexplored.
To identify intermediates and reaction steps which lead
to the formation of the active catalyst species, we have
sought to synthesize soluble, fully characterizable mod-
els for the alkylaluminum-treated silica surface. Silanol
groups, the most reactive species on silica gel surfaces,
are likely to react with an aluminum trialkyl reagent
under release of alkane and formation of surface-bound
Resu lts a n d Discu ssion
Syn th esis a n d Ca tion iza tion of Siloxya lu m in u m
* To whom correspondence should be addressed. E-mail:
Hans.Brintzinger@uni-konstanz.de.
Alk yl Com p ou n d s 1a -c. As previously described for
4a
compound 1a and for related representatives,4b-g the
† Universita¨t Konstanz.
‡ Basell Polypropylen GmbH.
siloxalanes 1a -c were prepared, in yields of 47-94%,
by reaction of the appropriate silanol precursors with 1
equiv of trimethylaluminum in toluene solution at room
(1) (a) Soga, K.; Park, J . R.; Shiono, T. Polym. Commun. 1991, 10,
310. (b) Kaminaka, M.; Soga, K. Makromol. Chem. Rapid Commun.
1991, 12, 367. (c) Herrmann, H. F.; Bachmann, B.; Hierholzer, B.;
Spaleck, W. Eur. Pat. Appl. 563917 A1, 1993. (d) Hungenberg, K. D.;
Kerth, J .; Langhauser, F.; Marczinke, B.; Schlund, R. In Ziegler
Catalysts; Mu¨lhaupt, G., Fink, G., Brintzinger, H.-H., Eds.; Springer-
Verlag: Berlin, 1995; Chapter 20. (e) Hlatky, G. G. Chem. Rev. 2000,
100, 1347.
(2) (a) Chen, Y.-X.; Rausch, M. D.; Chien, J . C. W. J . Polym. Sci. A:
Polym. Chem. 1995, 33, 2093, (b) Hlatky, G. G.; Upton, D. J .
Macromolecules 1996, 29, 8019, (c) Kristen, M. O. Top. Catal. 1999, 7,
89.
(3) (a) Nesterov, G. A.; Zakharov, V. A.; Fink, G.; Fenzl, W. J . Mol.
Catal. 1991, 69, 129. (b) Bartram, M. E.; Michalske, T. A.; Rogers, J .
W. J . Phys. Chem. 1991, 95, 4453. (c) Van Looveren, L. K.; Geysen, D.
F.; Vercruysse, K. A.; Wouters, B. H.; Grobet, P. J .; J acobs, P. A. Angew.
Chem., Int. Ed. 1998, 37, 517. (d) Anwander, R.; Palm, C.; Groeger,
O.; Engelhardt, G. Organometallics 1998, 17, 2027. (e) Uusitalo, A.-
M.; Pakkanen, T. T.; Kro¨ger-Laukkanen, M.; Niinisto¨, L.; Hakala, K.;
Paavola, S.; Lo¨fgren, B. J . Mol. Catal. A: Chem. 2000, 160, 343.
10.1021/om0207515 CCC: $25.00 © 2003 American Chemical Society
Publication on Web 02/19/2003

Siloxyaluminum Alkyl Cations
Organometallics, Vol. 22, No. 6, 2003 1321
Sch em e 1
temperature. The products were obtained in the form
of colorless powders or crystals, after removal of solvent
(1a ), crystallization (1b), or sublimation (1c), and
characterized by their 1H, 13C, and 27Al NMR spectra
as well as by electron impact mass spectroscopy and
elemental analysis (see the Experimental Section). They
are thermally stable at room temperature and can be
kept under a dry dinitrogen atmosphere for several
months without noticeable decomposition.
Reactions of compounds 1a -c with 1 equiv of the
proton donor [Me2NHPh]+[B(C6F5)4]- in toluene solu-
tions led to the appearance of the 1H NMR signal of
methane in all three cases. Depending on the substit-
uents at the Si centers, different products were obtained,
however. With the tert-butoxy-substituted siloxalane 1a ,
methane evolution was observed immediately at room
1
temperature. After 1 h, all Al-Me H NMR signals had
completely disappeared, even though only 1 equiv of the
anilinium salt had been used. Concomitantly, changes
were observed in the 1H NMR regions at 0.9 and 1.6
ppm, typical for Si-bound alkyl groups, and a new,
unassigned signal appeared at 4.7 ppm. While we were
unable to isolate any products from the reaction mix-
ture, we conclude from these observations that a cationic
product, initially formed with release of methane, might
have undergone an exchange of methyl and tert-butoxy
substituents between Si and Al centers. Transfer of an
OtBu group from Si to Al might form a silylium cation;
subsequent transfer of Me from Al to Si would be
consistent with the observed spectral changes.
The siloxalanes 1b,c, on the other hand, required
elevated temperatures of ca. 75 °C to react with DMAB.
In both cases, evolution of methane and formation of a
new aluminum methyl species with three distinct Al-
Me signals were observed (Scheme 1). For the siloxy-
substituted siloxalane 1b, the reaction is complete after
ca. 20 h, while complete conversion of the alkyl-
substituted siloxalane 1c takes ca. 75 h. The reaction
products are isolated in yields of 28% (2b) and 88% (2c)
as colorless solids. The low yield of 2b is due to slow
decomposition of the neutral siloxalane precursor 1b at
the reaction temperature. Both compounds were char-
acterized as binuclear aluminum alkyl species with one
neutral and one cationic aluminum center by their NMR
spectra, by elemental analysis (see Experimental Sec-
tion), and by a crystal structure determination.
Ta ble 1. Selected Bon d Dista n ces (p m ) a n d An gles
(d eg) for Com p lexes 2b,c
2b
2c
Al1-N1
199.4(5)
194.0(6)
196.9(7)
195.3(7)
181.6(4)
183.0(4)
192.9(4)
201.5(3)
193.9(4)
195.3(4)
196.5(4)
180.1(3)
183.0(3)
Al1-C1
Al2-C2
Al2-C3
Al1-O1
Al1-O2
O1-Al2
Al2-O1
191.4(3)
191.4(3)
Al2-O2
191.9(4)
168.1(4)
Si1-O1
O1-Si1
172.5(3)
O2-Si5
167.9(4)
O2-Si2
171.4(3)
275.3(2)
87.7(1)
Al1-Al2
O1-Al1-O2
O2-Al2-O1
O1-Al2-O2
C1-Al1-N1
C3-Al2-C2
C2-Al2-C3
277.7(4)
86.0(2)
80.5(2)
82.1(1)
112.7(2)
114.7(2)
126.5(3)
120.7(2)
show that the planarity of the Al-O-Al-O ring, previ-
ously found in neutral siloxalanes,4 is not disturbed by
conversion of a neutral to a cationic Al center in these
complexes. Bond distances and angles of one of the Al
centers are affected by this cationization in the following
manner (Table 1).
Cr ysta l Str u ctu r es of Ca tion ic Siloxya lu m in u m
Alk yl Com p lexes 2b,c. Crystal structures of aniline-
stabilized cationic aluminum alkyl complexes or of
cationic siloxalanes have not been reported so far.5 The
structures of complexes 2b,c (Table 1 and Figure 1)
In the cations 2b,c, Al-C bond lengths for the cationic
Al centers (193 and 194 pm) are close to those for the
neutral Al centers (195-197 pm).6 Similarly, Si-O(Al)
bond distances in the cationic siloxalanes 2b,c (168-
172 pm) are close to those in neutral siloxalanes (167-
168 pm).4b,c Al-O bond distances and O-Al-O angles
adjacent to neutral and cationic Al centers, however,
differ significantly from each other: Al-O bond dis-
tances to cationic Al atoms are 8-11 pm shorter and
O-Al-O bond angles are 5-6° larger than those at
neutral Al centers. Al-N bond lengths in the cationic
(4) (a) Terry, K. W., Ganzel, P. K., Tilley, T. D. Chem. Mater. 1992,
4, 1290. (b) Schmidbaur, H. J . Organomet. Chem. 1963, 1, 28. (c)
Mu¨hlhaupt, R.; Calabrese, J .; Ittel, S. D. Organometallics 1991, 10, 0,
3403. (d) Apblett, A. W.; Barron, A. R. Organometallics 1990, 9, 2137.
(e) Rennekamp, C.; Wessel, H.; Roesky, H. W.; Mu¨ller, P.; Schmidt,
H.-G.; Noltemeyer, M.; Uson, I.; Barron, A. R. Inorg. Chem. 1999, 38,
5235. (f) McMahon, C. N.; Bott, S. G.; Alemany, L. B.; Roesky, H. W.,
Barron, A. R. Organometallics 1999, 18, 5395. (g) Similar products
have been obtained from a reaction of trimethylaluminum with a
silsesquioxane containing a monosilanol functionality: Skowronska-
Ptasinska, M. D.; Duchateau, R.; van Santen, R. A.; Yap, G. P. A.
Organometallics 2001, 20, 3519.
(5) Crystal structures of cationic aluminum alkyl complexes with
boron-based counteranions: (a) Cosledan, F.; Hitchcock, P. B.; Lappert,
M. F. Chem. Commun. 1999, 705. (b) Ihara, E.; Young, V. G., J r.;
J ordan, R. F. J . Am. Chem. Soc. 1998, 120, 8277. (c) Radzewich, C. E.;
Guzei, I. A.; J ordan, R. F. J . Am. Chem. Soc. 1999, 121, 8673.
(6) These bond lengths are comparable to values found in neutral
siloxalanes (193-196 pm).4

1322 Organometallics, Vol. 22, No. 6, 2003
Wrobel et al.
-
F igu r e 1. Structure of complexes 2b,c (B(C6F5)4 anions omitted for clarity).
Sch em e 2
complexes 2b,c are shorter by 5-20 pm than those
found for the coordination of a trialkylamine to neutral
siloxalane complexes (206-225 pm).7
indicates that binuclear zirconocene chloride cations8
arise from this reaction, as indicated in Scheme 2. Use
of more than 1 equiv of the siloxalane cations, 2b,c, per
2 equiv of the respective zirconocene dichloride complex
does not result in further halide abstraction from the
binuclear zirconocene cations. This is indicated by the
presence of equal amounts of the neutral siloxalane
product 3c and of the cation 2c after reaction of 2c with
1 equiv of (C5H5)2ZrCl2 or Me2Si(C5H4)2ZrCl2.
When the aluminum alkyl cations 2b,c are reacted
with a zirconocene dimethyl complex, abstraction of a
CH3 ligand from the zirconium center takes place with
formation of the neutral tetramethylsiloxalane species
1b,c (Scheme 3).9 1H NMR signals of the expected DMA-
stabilized zirconocene methyl cation cannot be detected
in these reaction mixtures, however. Instead, we observe
signals assignable to the respective C-H activation
product.10 Similar C-H activation products were ob-
served by J ordan and co-workers when THF-stabilized
R ea ct ion s of t h e Siloxa la n e Ca t ion s 2b,c w it h
Zir con ocen e Com p lexes. To explore possible reaction
pathways toward catalytically active zirconocene alkyl
cations, we have studied reactions of the aluminum
alkyl cations 2b ,c with different zirconocene species,
in particular with the dichloride and dimethyl deriva-
tives of (C5H5)2Zr, Me2Si(C5H4)2Zr, (MeC5H4)2Zr, and
(nBuC5H4)2Zr as model complexes.
In reactions of the aluminum alkyl cations 2b,c with
dicyclopentadienylzirconium dichloride derivatives, each
binuclear Al cation was found to consume 2 equiv of the
respective zirconocene complex. A neutral siloxalane
species with three methyl groups and one chloride
substituent is formed in these reactions. The isolated
1
siloxalane complexes are characterized by H, 13C, and
27Al NMR, by mass spectrometry, and by elemental
(8) Such binuclear complexes have been studied before by means of
low-temperature NMR spectroscopy ((a) Haselwander, T. Diplomarbeit,
Universita¨t Konstanz, 1993. (b) Haselwander, T.; Beck, S.; Brintzinger,
H.-H. In Ziegler Catalysts; Mu¨lhaupt, G., Fink, G., Brintzinger, H.-
H., Eds.; Springer-Verlag: Berlin, 1995; p 181.) but have not been
characterized by crystallography so far. Attempts to crystallize several
of the chloride-bridged cationic species yielded the neutral zirconocene
dichloride complexes in all cases.
analysis as 3b,c. The stoichiometry of this reaction
(7) (a) Hecht, E.; Gelbrich, T.; Thiele, K.-H.; Sieler, J . Z. Anorg. Allg.
Chem. 2000, 626, 180. (b) Robson, D. A.; Rees, L. H.; Mountford, P.;
Schroder, M. Chem. Commun. 2000, 1269. (c) Thiele, K.-H.; Hecht,
E.; Gelbrich, T.; Dumichen, U. J . Organomet. Chem. 1997, 540, 89.
(d) Healy, M. D.; Barron, A. R. J . Am. Chem. Soc. 1989, 111, 398.

Siloxyaluminum Alkyl Cations
Sch em e 3
Organometallics, Vol. 22, No. 6, 2003 1323
of a zirconocene dichloride complex such as (nBuC5H4)2-
ZrCl2 or Me2Si(C5H4)2ZrCl2 led, within 24 h at 75 °C, to
a methyl-chloride exchange similar to that observed
before with Al2Me6 in C6D6 solution.12 When 5 µmol of
(nBuC5H4)2ZrCl2 was reacted with 4.2 mg of the TMA-
treated silica gel in 500 µL of C6D6, (nBuC5H4)2Zr(Me)-
Cl was formed in the ratio Zr(Me)Cl:ZrCl2 ) 1:12; when
21 mg of the silica gel was used, the ratio Zr(Me)Cl:
ZrCl2 ) 1:5.5 was observed. Reactions under the same
conditions with Me2Si(C5H4)2ZrCl2 result in the ratios
Zr(Me)Cl:ZrCl2 ) 1:6.2 (4.2 mg of silica gel) and 1:3.1
(21 mg of silica gel), respectively. These reactions of
zirconocene dichlorides with the trimethylaluminum-
treated silica gel are comparable to the reactions with
trimethylaluminum solutions, which likewise lead to
partial formation of the zirconocene methyl chlorides.
As was found for Al2Me6 in homogeneous solutions, the
silica gel supported trimethylaluminum induces a higher
degree of methylation with a Me2Si-bridged complex
than with an unbridged, alkyl-substituted zirconocene
reaction system.12 Analogous reactions are not observed,
however, when the neutral tetramethylsiloxalanes 1b,c
are treated in C6D6 with one of the zirconocene dichlo-
rides in ratios from 1:5 to 5:1. Apparently, the tendency
of the alkylaluminum species to exchange one of its CH3
groups with a chloride ligand of a zirconocene dichloride
is strongly reduced when both µ-CH3 groups of Al2(CH3)6
are replaced by O-SiR3 in 1b,c.
Another comparison between model and silica-surface
reactions concerns their respective reactivities toward
the cationization reagent DMAB. These reactions were
followed by monitoring the evolution of methane. Meth-
zirconocene methyl cations were treated with 2,6-
lutidine.11 This supports the notion that dimethyl-
aniline-stabilized methyl cations are formed in a first
reaction step.
When a toluene solution of Me2Si(ind)2ZrMe2, satu-
rated with 2 bar of ethene, is treated with the siloxalane
cation 2c, polyethene is indeed formed with moderate
activity (see Experimental Section). An analogous reac-
tion of a zirconocene dimethyl complex with a siloxalane
cation formed on a silica surface by treatment with an
aluminum alkyl compound and a cationizing reagent
might thus similarly generate catalytically active zir-
conocene species.
Com p a r ison betw een Mod el a n d Silica -Su r fa ce
Rea ction s. To compare the reactivity of homogeneously
dissolved aluminum alkyl siloxalanes with that of alkyl-
aluminum treated silica surfaces, we have studied their
respective reactions with zirconocene dichloride com-
plexes and with the cation-generating activator DMAB.
Reactions of a trimethylaluminum-treated silica gel
(see the Experimental Section) with a benzene solution
1
ane evolution was observed instantaneously by the H
NMR signal at 0.15 ppm when the TMA-treated silica
gel was reacted with DMAB in a benzene suspension
at room temperature. Siloxalanes 2b,c, on the other
hand, needed several hours at 75 °C before methane
could be detected in the reaction mixture.
With regard to the generation of catalytically active
methyl-zirconocene cations, the siloxalane cations 2b,c
do not reach the reactivity of a TMA-treated, cationized
silica gel surface. While the latter produces active
catalyst species from Cpx ZrCl2,2c the siloxalane cations
2
2b,c require Cpx ZrMe2 as a precursor for the genera-
2
tion of alkyl zirconocene cations.
The lower reactivity of the siloxalanes as compared
to the TMA-treated silica gel surfaces is likely to be due
to the presence of two bridging oxygen ligands between
the Al centers of the binuclear siloxalane species. One
might thus speculate that isolated SiOH functionalities
on the silica gel surface might lead to Al complexes with
only one oxygen ligand and, hence, higher reactivities.
Efforts to model more reactive species of this type are
underway in our laboratory.
(9) Reaction of a zirconocene methyl chloride complex with 2c in
ratios of 1:5 to 5:1 leads to the abstraction of either a chloride or a
methyl ligand from the zirconocene complex. Both reaction modes are
indicated by the observation of the siloxalane products 1c and 3c. In
reaction mixtures containing 2c and excess of (C5H5)2Zr(Me)Cl or
(MeC5H4)2Zr(Me)Cl, the signal intensity for the chlorotrimethylsilox-
alane 3c goes through a maximum after ca. 3 h and then declines to
zero, while that of the tetramethylsiloxalane 1c increases steadily until
the reaction is complete. The initially formed chlorotrimethylsiloxalane
3c thus appears to undergo a chloro-methyl exchange with zirconocene
methyl species present. Zirconocene dimethyl complexes such as
(C5H5)2ZrMe2 and (MeC5H4)2ZrMe2 do indeed react with the neutral
chlorotrimethylsiloxalane 3c in C6D6 in a clean and complete 1:1
reaction within 10 days to form the respective zirconocene methyl
chloride complexes and the tetramethylsiloxalane 1c.
Exp er im en ta l Section
All reactions were performed under argon with Schlenk-
line techniques or under nitrogen in a glovebox. Solvents were
dried prior to use by reflux over and distillation from sodium
or calcium hydride. Deuterated solvents were dried over 4 Å
molecular sieves and used without further purification. Zir-
conocene dichloride, dimethyl and methyl chloride complexes
(10) This species was first observed by Horton (private communica-
tion).
(11) Guram, A. S.; J ordan, R. F.; Taylor, D. F. J . Am. Chem. Soc.
1991, 113, 1833.
(12) Beck, S.; Brintzinger, H.-H. Inorg. Chim. Acta 1998, 270(1,2),
376.

1324 Organometallics, Vol. 22, No. 6, 2003
Wrobel et al.
were synthesized according to literature reports.13,14 Other
chemicals were purchased from commercial suppliers and used
without further purification. Samples of [Me2NHPh]+-
[B(C6F5)4]-, (nBuC5H4)2ZrCl2, and alkylaluminum-treated sili-
cas15 were obtained as gifts from Targor GmbH.
X-ray structure determination were isolated from a concen-
trated solution of 2b in chlorobenzene into which pentane was
1
slowly allowed to diffuse at room temperature. H NMR (250
MHz, CDCl3, 7.24 ppm, 300 K): δ 7.5-7.4 (m, Ph) 7.4-7.3
t
(m, Ph), 3.14 (s, 6H, N-Me2), 0.18 (s, 54H, Bu), -0.47 (s, 3H,
Al-Me), -0.61 (s, 3H, Al-Me), -0.97 (s, 3H, Al-Me). 13C NMR
(250 MHz, CDCl3, 77.0 ppm, 300 K): δ 146.2 (B(C6F5)4), 138.2
(B(C6F5)4), 134.3 (B(C6F5)4), 130.8 (arom), 129.6 (arom), 120.6
(arom), 46.6 (N-Me), 1.8 (Si-Me), -7.0 (Al-Me), -9.7 (Al-
Me), -13.8 (Al-Me). 27Al NMR (400 MHz, C6H5F, 358 K): no
resolved signals detectable. Anal. Calcd for C53H74Al2BF20NO8-
Si8: C, 41.81; H, 4.90; N, 0.92. Found: C, 40.47; H, 4.94; N,
0.82.
[(tBu O)3SiOAlMe2]2 (1a ). To a solution of 1.96 g (7.4 mmol)
of (tBuO)3SiOH in 30 mL of toluene at -6 °C was added
dropwise a solution of 0.54 g (7.5 mmol) of AlMe3 in 20 mL of
toluene with stirring over a period of 1 h. After the evolution
of methane had ceased, the solution was stirred for 1 h at -6
°C before it was warmed to room temperature. After the
mixture was stirred for another 12 h and the solvent removed
in vacuo, 2.24 g (3.5 mmol, yield 94%) of 1a was obtained as
1
[(tBu Me2SiO)2Al2Me3NMe2P h ]+[B(C6F 5)4]- (2c). A 4.00
g portion (10.6 mmol) of 1c and 4.25 g (5.30 mmol, 0.5 equiv)
of [Me2NHPh]+[B(C6F5)4]- were dissolved in 400 mL of toluene
and heated to 65 °C for 90 h. Toluene was removed in vacuo
from the resulting biphasic system, and the remaining dark
green residue was washed several times with pentane under
treatment with ultrasound to remove excess 1c. A 5.43 g
portion (4.67 mmol, 88% yield) of 2c was obtained as a colorless
powder. Crystals suitable for X-ray structure determination
were isolated from a solution of 2c in chlorobenzene into which
pentane was slowly transferred by diffusion at room temper-
a colorless powder. H NMR (250 MHz, C6D6, 7.15 ppm, 300
t
K, cf. ref 4a): δ 1.40 (s, 54H, Bu), -0.12 (s, 12H, Al-Me2).
EI-MS: m/z m/z 625 (M+ - Me), 569 (M+ - Me, tBu), 553 (M+
t
t
- 2Me, tBu), 513 (M+ - Me, 2 Bu), 457 (M+ - Me, 3 Bu), 401
(M+ - Me, 4 Bu), 385 (M+ - 2 Me, 4 Bu), 369 (M+ - 3 Me, 4
t
t
tBu), 345, 329, 313, 289, 255, 237, 193, 135, 57.
[(Me3SiO)3SiOAlMe2]2 (1b). The synthesis was performed
in the same way as that of 1a with 3.36 g (10.7 mmol) of (Me3-
SiO)3SiOH and 0.80 g (11.1 mmol) of AlMe3 in 100 mL of
toluene. After removal of the solvent in vacuo and crystalliza-
tion from a pentane solution at -60 °C, 2.30 g (3.12 mmol,
58% yield) of 1b was isolated in form of colorless cubic crystals.
1H NMR (250 MHz, C6D6, 7.15 ppm, 300 K): δ 0.22 (s, 54H,
Si-Me), -0.25 (s, 12H, Al-Me2). 13C NMR (250 MHz, C6D6,
128 ppm, 300 K): δ 1.8 (Si-Me), -8.3 (Al-Me2). 27Al NMR (400
MHz, C6H5F, 358 K): δ 158.2, w1/2 ) ca. 5400 Hz. EI-MS: m/z
721 (M+ - Me), 353 (M/2+ - Me), 281 (M/2+ - Me, Me3Si),
191, 147, 73. Anal. Calcd for C22H66Al2O8Si8: C, 35.83; H, 9.02.
Found: C, 35.77; H, 9.43.
1
ature. H NMR (250 MHz, CDCl3, 7.24 ppm, 300 K): δ 7.6-
7.5 (m, Ph) 7.4-7.3 (m, Ph), 3.16 (s, 6H, N-Me2), 0.94 (s, 18H,
tBu), 0.19 (s, 6H, Si-Me), -0.08 (s, 6H, Si-Me), -0.11 (s, 3H,
Al-Me), -0.42 (s, 3H, Al-Me), -0.48 (s, 3H, Al-Me). 13C NMR
(250 MHz, CDCl3, 77.0 ppm, 300 K): δ 146.2 (B(C6F5)4), 138.2
(B(C6F5)4), 134.3 (B(C6F5)4), 131.3 (arom), 130.1 (arom), 120.9
(arom), 47.9 (N-Me), 25.8 (Si-C(CH3)3), 18.8 (Si-C(CH3)3),
-1.8 (Si-Me), -2.2 (Si-Me), -2.8 (Al-Me), -4.3 (Al-Me),
-5.1 (Al-Me). 27Al NMR (400 MHz, C6H5F, 358 K): δ 165.2,
w1/2 ) ca. 7900 Hz; 117.6, w1/2 ) ca. 3600 Hz. Anal. Calcd for
[tBu Me2SiOAlMe2]2 (1c). The synthesis was performed in
the same way as that of 1a with 10.0 g (75.7 mmol) of tBuMe2-
SiOH and 5.50 g (76.3 mmol) of AlMe3 in 200 mL of toluene.
The solvent was removed in vacuo, and the glassy residue was
purified by two successive sublimations in vacuo at 60 °C to
afford 6.71 g (17.8 mmol, 47% yield) of pure 1c in form of a
C
47H50Al2BF20NO2Si2: C, 48.55; H, 4.34; N, 1.21. Found: C,
49.55; H, 4.69; N, 0.98.
Rea ction of 2b w ith Cp 2Zr Cl2. A 0.44 g portion (0.29
mmol) of 2b and 0.25 g (0.86 mmol) of Cp2ZrCl2 were dissolved
in 80 mL of toluene in a glovebox, and the solution was stirred
at room temperature for 4 days. A light green crystalline
residue of the cationic zirconocene complex precipitated from
the reaction mixture, and was separated from the liquid phase
by centrifugation. After removal of solvent, the resulting
residue was extracted with two 30 mL portions of pentane,
evaporation of which yielded 0.19 g (0.25 mmol, 87% yield) of
1
white powder. H NMR (250 MHz, C6D6, 7.15 ppm, 300 K): δ
t
0.88 (s, 18H, Bu), 0.14 (s, 12H, Si-Me2), -0.34 (s, 12H, Al-
Me2). 13C NMR (250 MHz, C6D6, 128 ppm, 300 K): δ 25.8
(C(CH3)3), 18.4 (C(CH3)3), -2.6 (Si-Me2), -6.3 (Al-Me2). 27Al
NMR (400 MHz, C6H5F, 358 K): δ 156.4; w1/2 ) ca. 1800 Hz.
EI-MS: m/z 361 (M+ - Me), 319 (M+ - tBu), 247 (M+ - Me, 2
t
tBu), 205 (M+ - AlMe2, BuMe2Si), 189 (M/2+), 173 (M/2+
-
1
Me), 131, 73. Anal. Calcd for C16H42Al2O2Si2: C, 51.02; H,
11.24. Found: C, 51.0; H, 11.13.
a colorless powder of [(Me3SiO)3SiO]2Al2Me3Cl (3b). H NMR
(250 MHz, C6D6, 7.15 ppm, 300 K): δ 0.23 (s, 54H, Si-Me),
-0.10 (s, 3H, Al-Me), -0.20 (s, 3H, Al-Me), -0.27 (s, 3H,
Al-Me). 13C NMR (250 MHz, C6D6, 128.0 ppm, 300 K): δ 25.7
(Si-Me), -8.6 (Al-Me). 27Al NMR (400 MHz, C6H5F, 358 K):
δ 123.2, w1/2 ) ca. 2900 Hz (Al-(Me)Cl) and, overlapping with
it, one broad signal at ca. 160 ppm, w1/2 ) ca. 17 000 Hz (Al-
Me2). EI-MS: m/z 741 (M+ - Me), 297, 281, 73. Anal. Calcd
for C21H63Al2ClO8Si8: C, 33.28; H, 8.38. Found: C, 33.51; H,
7.75.
[((Me3SiO)3SiO)2Al2Me3NMe2P h ]+[B(C6F5)4]- (2b). A 1.94
g portion (2.63 mmol) of 1b and 1.18 g (1.47 mmol, 0.56 equiv)
of [Me2NHPh]+[B(C6F5)4]- were dissolved in 70 mL of toluene
and heated to 65 °C for 20 h. Toluene was removed in vacuo,
and the remaining dark blue oil was washed twice with
pentane and then purified by redissolving in chlorobenzene
and precipitating a byproduct by addition of a small amount
of pentane. The supernatant liquid was evaporated to dryness.
The resulting colorless foam was washed once with pentane
and dried in vacuo to afford 0.64 g (0.42 mmol, 28% yield) of
2b in the form of a colorless powder. Crystals suitable for an
Rea ction of 2c w ith Cp 2Zr Cl2. A 0.80 g portion (0.68
mmol) of 2c and 0.51 g (1.73 mmol) of Cp2ZrCl2 were dissolved
in 150 mL of toluene in a glovebox and stirred at room
temperature for 24 h. A light green crystalline residue of the
binuclear cationic zirconocene complex precipitated from the
reaction mixture and was separated from the liquid phase by
centrifugation. After removal of the solvent, the resulting
colorless residue was extracted twice with 100 mL of pentane.
Evaporation of pentane resulted in a light yellow powder of
2c. The crude product thus obtained was purified by sublima-
tion at 100 °C over 3 h in vacuo to afford 0.19 g (0.48 mmol,
70% yield) of pure (tBuMe2SiO)2Al2Me3Cl (3c) in the form of a
colorless powder. 1H NMR (250 MHz, C6D6, 7.15 ppm, 300 K):
(13) (a) Heyn, B.; Hipler, B.; Kreisel, G.; Schreer, H.; Walther, D.
Anorganische Synthesechemie-Ein Integriertes Praktikum; Springer-
Verlag: Berlin, 1986; p 84. (b) J ordan, R. F.; LaPointe, R. E.; Bradley,
P. K.; Baenziger, N. Organometallics 1989, 8, 2892. (c) Klouras, N.;
Ko¨pf, H. Monatsh. Chem. 1981, 112, 887.
(14) (a) Samuel, E.; Rausch, M. D. J . Am. Chem. Soc. 1973, 95, 6263.
(b) Couturier, S.; Tainturier, G.; Gautheron, B. J . Organomet. Chem.
1980, 195, 291. (c) Wailes, P. C.; Weigold, H.; Bell, A. P. J . Organomet.
Chem. 1971, 33, 181.
(15) Alkylaluminum-treated silica gels were synthesized at Targor
GmbH by slowly adding a 2 M trimethylaluminum solution to a
suspension of silica gel in toluene, so that the temperature does not
rise above 25 °C. The silica gel is collected by filtration under an
atmosphere of dry nitrogen and washed several times with toluene to
completely remove any residual trimethylaluminum.
t
δ 0.89 (s, 18H, Bu), 0.21 (s, 6H, Si-Me), 0.15 (s, 6H, Si-Me),
-0.23 (s, 3H, Al-Me), -0.31 (s, 3H, Al-Me), -0.39 (s, 3H,
Al-Me). 13C NMR (250 MHz, C6D6, 128.0 ppm, 300 K): δ 25.7

Siloxyaluminum Alkyl Cations
Organometallics, Vol. 22, No. 6, 2003 1325
Ta ble 2. Cr ysta llogr a p h ic a n d Exp er im en ta l Da ta a
for Com p lexes 2b,c
(Si-C(CH3)3), 18.4 (Si-C(CH3)3), -2.7 (Al-Me), -2.8 (Al-Me),
-6.7 (Al-Me). 27Al NMR (400 MHz, C6H5F, 358 K): δ 122.7,
w1/2 ) ca. 2600 Hz (Al-(Me)Cl); 158.6, w1/2 ) ca. 1200 Hz (Al-
2b
2c
Me2). EI-MS: m/z 381 (M+ - Me), 339 (M+ - tBu), 205 (M+
-
formula
C
53H74Al2BF20
NO8Si8
-
C47H50Al2BF20
NO2Si2
-
tBuMe2Si, AlMeCl), 189 (M+ - Me2 BuSiO, AlMeCl), 131, 75.
Anal. Calcd for C15H39Al2ClO2Si2: C, 45.37; H, 9.90. Found:
C, 43.84; H, 9.27.
t
cryst color and form
cryst syst, space group
a (Å)
b (Å)
c (Å)
colorless prism
triclinic, P1h
14.206(21)
16.071(19)
18.036(25)
83.88(7)
colorless plate
triclinic, P1h
10.538(7)
15.501(15)
18.797(11)
91.84(5)
101.72(3)
94.03(5)
2; 2996(4)
0.2 × 0.4 × 0.5
248; 1.288
0.185; 1188
ω; 1.1-26
11 707
Rea ctivity Stu d ies on th e NMR Sca le. All reactivity
studies were performed in C6D6, since all compounds were
stable in that solvent. The reactions were followed by 1H NMR
spectroscopy at room temperature. The NMR tubes were dried
prior to use at 200 °C in vacuo for 48 h. Stock solutions of
the individual compounds were prepared in a glovebox and
mixed at room temperature at various ratios of the reac-
tants. The NMR tubes were sealed and kept at -80 °C until
the first measurement. When higher temperatures were
necessary to perform a reaction, the NMR tubes were heated
in an oil bath and cooled to room temperature before measur-
ing the spectra.
R (deg)
â (deg)
81.39(11)
71.80(9)
γ (deg)
Z; V (Å3)
2; 3860(9)
0.2 × 0.3 × 0.4
248; 1.310
0.254; 1572
ω; 1.1-26
12 576
crystal size (mm)
T (K); dcalcd (g/cm3)
µ (mm-1), F(000)
scan mode; θ range (deg)
no. of rflns collected
no. of indep rflns
10 987 (Rint
3.67%)
)
11 207 (Rint
2.94%)
)
Reactions of excess 2c with zirconocene dichloride complexes
at 300 K gave rise, besides signals of 3c described above, to
the following 1H NMR signals: [{(C5H5)2ZrCl}2-µ-Cl]+B-
(C6F5)4-, 5.89 (s, 20 Cp H); [{Me2Si(C5H4)2ZrCl}2-µ-Cl]+B-
(C6F5)4- , 5.71 (m, 8H, Cp H), 5.36 (m, 8H, Cp H), 0.16 (s, 12H,
Me-Si); [{(nBuC5H4)2ZrCl}2-µ-Cl]+B(C6F5)4-, 5.98 (broad, 8H,
Cp H), 5.90 (broad, 8H, Cp H), 2.33 (broad, 8H, CH2CH2CH2-
CH3), ca. 1.27 (broad, 8H, CH2CH2CH2CH3), 1.20 (m, 8H, CH2-
CH2CH2CH3), 0.85 (t, 12H, CH2CH2CH2CH3). Reactions with
the zirconocene dimethyl complex (C5H5)2ZrMe2 at 300 K
gave rise, besides the signals of 1c described above, to the
no. of obsd rflns
5518
6354
(I > 2σ(I))
no. of params; GOF
R(F), Rw(F2)a (obsd data)
R(F), Rw(F2)a (all data)
largest diff peak (e/Å3)
848; 1.009
6.26, 11.0%
15.4, 15.9%
0.384
676; 0.982
6.03, 14.4%
11.3, 16.3%
0.363
Weighting scheme: 2c, w-1 ) σ2(Fo2) + (0.079P)2; 2b: w-1
)
a
σ2(Fo2) + (0.036P)2 + 3.36P. P ) (Fo + 2Fc2)/3.
2
were applied using ψ-scan data. One TMS group in 2b was
found to be disordered, with occupation factors refined to 0.7
and 0.3, respectively. Residual electron densities up to 3 e/Å3
without bonding contacts to the molecule were found in the
proximity of an inversion center in 2c. A void of 459 Å3 in the
elemental cell and 149 electrons in this solvent area were
reported by the SQUEEZE program,17 which is reasonably
close to the sum of 142 electrons expected for two pentane
molecules and one chlorobenzene molecule in the unit cell.
Since other attempts to fit the solvents used in the crystal-
lization process to the very diffuse electron densities failed and
geometrical parameters drastically improved by the applica-
tion of SQUEEZE (e.g. the variation in the four chemically
equivalent B-C distances was reduced from 30 to 4 pm), we
corrected the residual electron density in the structural void
with the SQUEEZE program as “diffuse solvent”.17 Crystal-
lographic data (excluding structure factors) have been depos-
ited with the Cambridge Crystallographic Data Centre as
supplementary publications CCDC 189032 and 189033. Copies
of the data can be obtained, free of charge, on application to
the CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. (fax,
+44 1223 336033; e-mail, deposit@ccdc.cam.ac.uk).
following 1H NMR signals: (C5H5)2ZrCH2NMe(C6H5)+B-
- 10
(C6F5)4
,
7.0-6.6 (m, 5H, C6H5), 5.41 (s, 5H, Cp H), 5.13 (s,
5H, Cp H), 2.79 (d, 1H, N-CH1-Zr), 2.29 (s, 3H, N-Me), 2.01
(d, 1H, N-CH2-Zr).
Rea ction s w ith Alk yla lu m in u m -Tr ea ted Silica Gels.
For these studies, samples of a spray-dried silica gel obtained
from W. R. Grace & Co., Columbia, MA 21044, with particle
size 70 µm, were used, which had been dried at 180 °C in vacuo
for 8 h, subsequently treated with Al2Me6, and dried again in
vacuo.15 An elemental analysis yielded values of 4.3 g of Al
and 38 g of Si per 100 g of silica gel. A defined quantity of the
alkylaluminum-treated silica gel was weighed directly into an
NMR tube, and a stock solution of the reactant in C6D6 was
added. The reaction mixture was stored at the temperature
indicated and shaken from time to time for a few minutes,
before 1H NMR spectra were taken.
Eth en e P olym er iza tion w ith 2c a s Activa tor . Since
addition of any alkylaluminum scavenger to the reaction
system would lead to complicating alkyl exchange reactions,
an excess of the dimethyl zirconocene complex was used to
eliminate impurities. To a solution of 20 mg (48 µmol) of Me2-
Si(ind)2ZrMe2 in 100 mL of toluene, saturated in a 250 mL
autoclave at 30 °C with 2 bar of ethene for 20 min, was added
5 mL of a toluene solution of 5.8 mg (5 µmol) of cation 2c by
way of a pressure-addition vessel. After 6 h, the reaction
mixture was poured into 200 mL of a mixture of methanol and
aqueous HCl. Collection and drying of the precipitate yielded
1.14 g of polyethene.
Ack n ow led gm en t. Financial support of this work
by BMBF and BASF AG and gifts of chemicals by
BASF AG and Targor GmbH are gratefully acknowl-
edged. We thank the state of Baden-Wu¨rttemberg for a
Landesgraduierten-Stipend to O.W. and Dr. Dmitrii
Babushkin (Boreskov Institute of Catalysis) for mea-
surements of 27Al NMR spectra.
Cr ysta l Str u ctu r e Deter m in a tion s. X-ray diffraction
analysis was carried out on a Siemens P4 four-circle diffrac-
tometer using Mo KR radiation (71.073 pm) and a graphite
monochromator (Table 2). Crystal decay was monitored by
measuring 3 standard reflections every 100 reflections. The
structures were solved using direct methods.16 Hydrogen atoms
were refined on calculated positions with fixed isotropic U
values, using riding model techniques.16 Absorption corrections
Su p p or tin g In for m a tion Ava ila ble: Full listings of
crystallographic data, atomic coordinates, bond lengths and
angles, and anisotropic displacement parameters for complexes
2b,c. This material is available free of charge via the Internet
at http://pubs.acs.org.
OM0207515
(16) Sheldrick, G. M. SHELXS-86; University of Go¨ttingen, Go¨ttin-
gen, Germany, 1990. Sheldrick, G. M. SHELXL-93; University of
Go¨ttingen, Go¨ttingen, Germany.
(17) Spek, A. L. Acta Crystallogr. 1990, A46, C-34.