Carbosilane dendrons functionalized at their focal point

Article abstract of DOI:10.1002/ejic.200500182

The Si-Ph bond of PhSi[(CH₂)₃SiMe₂Bz] ₃ (5) is cleaved with triflic acid to give TfOSi[(CH ₂)₃SiMe₂Bz]₃, which, in turn, reacts with triethylammonium chloride or potas

Full text of DOI:10.1002/ejic.200500182

FULL PAPER
Carbosilane Dendrons Functionalized at Their Focal Point
Román Andrés,*[a] Ernesto de Jesús,*[a] F. Javier de la Mata,[a] Juan C. Flores,[a] and
Rafael Gómez[a]
Keywords: Dendrimers / Metallocenes / Silanes / Titanium / Zirconium
The Si–Ph bond of PhSi[(CH2)3SiMe2Bz]3 (5) is cleaved with
triflic acid to give TfOSi[(CH2)3SiMe2Bz]3, which, in turn, re-
x = 27, 12) have been obtained starting from Ph-Gn-[(CH2)3-
SiMe2Bz]x (6, 7). The metallocenes [{(BzMe2SiCH2CH2CH2)3-
acts with triethylammonium chloride or potassium cyclopen- SiC5H4}2MCl2] (M = Ti, 14; Zr, 15) have also been obtained
tadienide to give, respectively, ClSi[(CH2)3SiMe2Bz]3 (8) and
(C5H5)Si[(CH2)3SiMe2Bz]3 (10). This strategy can be applied
to the post-growth incorporation of nucleophiles to the focal
point of carbosilane dendritic wedges. In this way, cyclopen-
tadiene-functionalized dendritic wedges of second and third
from 10 and their catalytic behavior in ethylene and propyl-
ene polymerization, using MAO as a cocatalyst, has been
studied and compared to that of related non-dendritic com-
plexes.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
generation C5H5-Gn-[(CH2)3SiMe2Bz]x (n = 2, x = 9, 11; n = 3, Germany, 2005)
Introduction
The large number of dendrimers synthesized nowadays
from a diversity of cores, repetitive units, and peripheral
groups allows the design of macromolecules with tailored
properties through the incorporation of suitable functions
at the appropriate site of the dendritic molecule (i.e. core,
framework, or periphery).[1] Transition metal catalysts are
a good example of the relevance of the location of the func-
tional group in the dendritic structure because of the dif-
ferent accessibility of the metal center to the substrate in
core- and periphery-functionalized dendrimers.[2,3] In the
Scheme 1.
vast majority of metal-functionalized carbosilane dendri-
mers the metal complexes reside in the periphery.[4] Some
We have previously reported the synthesis of group 4
of the exceptions are represented by the metal complexes
that van Leeuwen and al. have synthesized from phosphane
ligands [triphenylphosphane, bis(diphenylphosphanyl)ferro-
cene (dppf), bis(diphenylphosphanyl)xanthene (xantphos),
or o-(diphenylphosphanyl)phenol] located in the core of
carbosilane dendrimers.[5] All these phosphanes have been
obtained from a family of dendritic wedges whose first gen-
eration, A, is represented in Scheme 1 and which are grown
from p-bromostyrene by the usual divergent methodology
that alternates hydrosilylation and alkylation steps using
HSiCl3 and allylmagnesium bromide, respectively.[6] In the
aforementioned dendritic phosphanes, prepared from the
lithium derivative of A, a styrene spacer separates the phos-
phorus and the core silicon atoms.
metallocenes derived from the first-generation dendron B
that possesses a cyclopentadienide anion (Cp–) directly
linked to its focal point.[7] In contrast to the aryl bromide
in A, the Cp group is not compatible with the hydro-
silylation and alkylation steps and cannot be incorporated
before the growth of the dendrimer. Here we describe a
strategy for the post-synthetic modification of the focal
point of a carbosilane dendritic wedge.
Results and Discussion
Fréchet introduced the term “dendritic wedge” in the de-
scription of the convergent strategy for the growth of den-
drimers.[8] In this strategy, the dendrimer is assembled from
the periphery and each successive generation is synthesized
from a single reactive group located at the focal point of a
dendritic wedge. The final reaction involves the attachment
of the dendritic wedges to a core molecule. For this reason,
[a] Departamento de Química Inorgánica, Universidad de Alcalá,
Campus Universitario, 28871 Alcalá de Henares, Madrid, Spain
Fax: +34-91-885-4683
E-mail: ernesto.dejesus@uah.es
3742
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/ejic.200500182
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Carbosilane Dendrons Functionalized at Their Focal Point
FULL PAPER
Scheme 2.
the convergent approach has been largely applied to the ated at the end of the growing process. In the case of a
synthesis of core- or focal-point functionalized dendrimers. carbosilane dendrimer, the phenyl group fulfills the main
Carbosilane dendrimers are, in general, synthesized diver- requirements of a silicon-core protector: it is inert towards
gently by a repetitive sequence of hydrosilylation and alky- hydrosilylation and alkylation, but forms bonds with silicon
lation steps.[6,9] The sequence of reactions depicted in that can undergo protolysis to give a by-product that is eas-
Scheme 2 illustrates a possible route for the convergent ily separable from the dendrimer. Thus, G0, G1, and G2
preparation of carbosilane dendrimers in which the Si–Cl compounds Ph-Gn-(CH2CHCH2)x (2–4, respectively) with
bond is reduced to Si–H instead of being alkylated as in a 3, 9, and 27 allyl end-groups, respectively, were synthesized
divergent synthesis. Thus, the carbosilane Cl-G1-[(CH2)3- from PhSiCl3 by successive allylation and hydrosilylation
1
SiMePh2]3 was prepared by hydrosilylation of chlorotrivin- steps (Scheme 3).[11] The H NMR olefinic resonances at
ylsilane with methyldiphenylsilane,[7] and reacted with lith- around δ = 4.8 and 5.7 ppm were used to follow the pro-
ium tetrahydridoaluminate to give H-G1-[(CH2)3SiMePh2]3 gress of the critical hydrosilylation steps in order to deter-
(1), the first-generation analog of the starting methyldi- mine their completion and, therefore, the absence of defects
phenylsilane, quantitatively. The presence of a Si–H bond in the branches of the final products. The growth was ter-
in 1 was confirmed by the septuplet observed in the 1H minated at the desired generation by using benzyldimethyl-
NMR spectrum at δ = 3.64 ppm (3JH,H = 2.9 Hz). Unfortu- silane instead of trichlorosilane as the hydrosilylating agent
nately, hydrosilylation of chlorotrivinylsilane with 1 always to give Ph-Gn-[(CH2)3SiMe2Bz]x (Bz = CH2C6H5, 5–7).
gave mixtures of the second-generation wedge Cl-G2- The reaction of allyl-terminated dendrimers with trichloros-
[(CH2)3SiMePh2]3 with partially hydrosilylated compounds, ilane in the presence of H2PtCl6 as a catalyst occurred
in spite of the variety of solvents, temperatures, and Pt cata- smoothly at room temperature, whereas the reaction mix-
lysts (Speier, Karstedt, and Pt/C) tested. This result was not ture had to be gently heated for the activation of the trialk-
completely unexpected because it is known that both bulky ylsilane HSiMe2Bz (1H NMR monitoring). Dendrimers 5–
and electron-donating substituents decrease the reactivity 7 were obtained as colorless oils after removal of the vola-
of silanes in the platinum-catalyzed hydrosilylation of ole- tiles in vacuo and were purified by chromatography on a
fins.[10] Both characteristics are combined in the silane 1 silica-gel column prior to subsequent use. After isolation,
and in its progressively bulkier higher-generation analogs the yields ranged from 93 to 96% for allyl-terminated den-
H-Gn-[(CH2)3SiMePh2]3, which are required for this con- drimers 2–4 (for 3 and 4 the values correspond to overall
vergent strategy, in contrast to the divergent growth that yields from the allyl dendrimer of the previous generation)
uses activated silanes with electron-withdrawing chloro sub- and 82–83% for 5–7.
stituents.
Acid-induced cleavage of the Ph–Si bond was attempted
The desired focal-point functionalization can also be with boron trichloride in hexane,[12] HCl and catalytic
achieved by an approach in which a protecting group is amounts of aluminum trichloride in diethyl ether,[13] or
linked to the core before the dendrimer growth and elimin- triflic acid (trifluoromethanesulfonic acid, TfOH) in chloro-
Scheme 3. Synthesis of carbosilane dendritic wedges 2–7 with a phenyl group attached to their focal point. Conditions: (i) diethyl ether,
room temperature, overnight; (ii) solvent-free reaction, H2PtCl6 in 2-propanol, room temperature, 4 h; (iii) solvent-free reaction, H2PtCl6
in 2-propanol; see Exp. Sect. for details.
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R. Andrés, E. De Jesús, F. Javier de la Mata, J. C. Flores, R. Gómez
FULL PAPER
form.[14] Boron trichloride failed to react with both allyl- the cyclopentadiene with a C(sp3)–Si bond (Scheme 5) and
and benzyldimethylsilyl-terminated compounds 2 and 5 at gives a broad resonance at δ = 3.4 ppm, whereas the minor
room temperature, and protic acids such as HCl or TfOH isomers show resonances at around δ = 3.0 ppm which are
reacted at the same time with the terminal allyl groups of sharper at room temperature. The usefulness of the de-
dendrimers Ph-Gn-(CH2CH=CH2)x (2–4).[15] Cleavage of scribed methodology for the synthesis of higher-generation
the Si–Ph bond with HCl was slow in diethyl ether at room dendritic wedges has been demonstrated by the synthesis of
temperature (1H NMR evidence), whereas the Si–Ph bond the G2 and G3 cyclopentadienes 11 and 12 (Scheme 5).
of dendrimers Ph-Gn-[(CH2)3SiMe2Bz]x (5–7) was cleanly They were obtained as yellow oils in the same conditions
and readily cleaved with triflic acid at 0 °C in chloroform described above for 10, starting from the corresponding
(Scheme 4), with the advantage that the triflate anion TfO– triflate TfO-Gn-[(CH2)3SiMe2Bz]x. The 1H NMR reso-
is a good leaving-group in silyl triflates, undergoing ex- nances in the cyclopentadiene sp3 region are similar to those
change with a wide range of nucleophiles.[16] For the reac- described above for 10, although they are accompanied by
tions described below, compounds TfO-Gn-[(CH2)3Si- the general broadening of resonances that the restricted
Me2Bz]x were used without isolation. As shown in mobility of protons causes in higher generations.
Scheme 4, the reaction of TfOSi[(CH2)3SiMe2Bz]3 with tri-
ethylammonium chloride in dimethoxyethane (DME) gave
ClSi[(CH2)3SiMe2Bz]3 (8). Other nucleophiles can be intro-
duced at the focal-point position either from the chlorosi-
lane or directly from the silyl triflate, as exemplified by the
preparation of the silanol HOSi[(CH2)3SiMe2Bz]3 (9) or the
cyclopentadiene (C5H5)Si[(CH2)3SiMe2Bz]3 (10). The 1H
NMR spectrum of 10 shows, at room temperature, broad-
ened temperature-dependent resonances for both types of
cyclopentadiene protons, those bonded to sp2 (δ = 6.4–
6.7 ppm) and those bonded to sp3 carbons (δ = 2.9–
3.5 ppm). The related trimethylsilylcyclopentadiene
(C5H5SiMe3), which is present as a mixture of the three
possible isomers, also shows broadened temperature-de-
1
pendent H resonances, which are ascribed to the intercon-
version of ring protons and isomers by sigmatropic SiMe3
and proton shifts.[17] The 1H NMR behavior of 10 is clearly
similar to that of C5H5SiMe3, especially in the distribution
and temperature dependence of the C(sp3)–H resonances.
Thus, the major isomer of 10 (ca. 70–75%) corresponds to
Scheme 5. Cyclopentadienes with carbosilane dendritic wedges of
first (10), second (11), and third generation (12). Only the major
isomers are represented.
Dendrimers 2–12 were characterized by elemental analy-
sis and 1H, 13C{1H}, and 29Si{1H} NMR spectroscopy.
Scheme 4.
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Three groups of methylene resonances are observed for the
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Carbosilane Dendrons Functionalized at Their Focal Point
FULL PAPER
SiCH2CH2CH2Si repeating unit in phenyl-protected dendri- here. In polymerization of propylene (Table 1), the zirco-
mers 5–7, at δ Ϸ 0.8 ppm for the methylene bonded to the nium complex 15 displays a similar activity to that observed
core silicon, δ = 1.2–1.3 ppm for the middle CH2 groups, for [(C5H5)2ZrCl2]. Some degree of stereocontrol in the po-
and δ Ϸ 0.5 ppm for the rest. Only the core SiCH2 reso- lymerization of α-olefins with metallocenes is, in principle,
nance is affected by the modification of the focal-point possible by restricting the rotation of the Cp ligand, for
group, and is progressively shifted to high field when Ph is example by means of sterically demanding substituents.[19]
replaced by Cl, OH, and C5H5. In the 29Si{1H} NMR spec- The polypropylene obtained with 15, at both 20 °C and
tra, a singlet is observed for every type of silicon atom pres- –30 °C, shows the distribution of 13C NMR resonances of
ent in the corresponding molecule. Mass spectra were ob- a mainly atactic polymer,[20] similar to that obtained with
tained by ESI or APCI techniques for all the first-genera- [(C5H5)2ZrCl2].
tion post-functionalized dendrimers 8–10. Attempts to re-
cord MALDI-TOF mass spectra of second- and third-gen-
eration cyclopentadiene dendrimers 11 and 12 failed. The
purity of phenyl-protected dendrimers 5–7, as well as that
of the post-modified cyclopentadienes 10–12, was routinely
checked by GPC chromatography in THF. Every chromato-
gram showed a unique peak with typical polydispersity val-
ues of about 1.02–1.03, according to the monodisperse na-
ture of these molecules. As expected, the elution time of
the dendrimers increases with the molecular weight. The
molecular weights obtained after calibration with a stan-
dard of polystyrene were not in good agreement with the
theoretical values because of the globular nature of dendri-
mers. However, a good linear relationship was shown be-
tween the logarithm of the theoretical molecular weights
and the elution times on GPC traces (R2 = 0.984).[18]
The first-generation cyclopentadienide 13 was synthe-
sized as a potassium salt by reaction of 10 with KH in
DME. Dendritic metallocenes 14 (Ti) and 15 (Zr) were sub-
sequently obtained by reaction of two equivalents of cyclo-
pentadienide 13 with TiCl4 or ZrCl4·2THF in toluene
(Scheme 6). These products were isolated as red (Ti) or col-
orless (Zr) oils that were rather stable upon exposure to
air. Upon activation with an excess of methylaluminoxane
(MAO), complexes 14 and 15 catalyze the polymerization
of ethylene. The results are summarized in Table 1 and com-
pared with those of simple metallocenes [(C5H5)2MCl2] (M
= Ti, Zr) obtained under the same conditions. The activity
is lowered by one order by the dendritic substituents in the
Scheme 6.
In view of these results, we tried the preparation of the
titanocene catalyst, but noticeably there is no such decrease second- and third-generation analogs of metallocenes 14
in the zirconocene case. We have previously reported a sim- and 15. Somewhat surprisingly, no reaction was observed
ilar result with vinyl-type carbosilanes [{(Ph2MeSiCH2CH2)3- between 11 or 12 and KH under the same conditions used
SiC5H4}2MCl2] (M = Ti, Zr), although in this example a for 10. When n-buyllithium was employed instead as a de-
1
small but significant decrease of 30% was observed for the protonating agent, the H NMR spectra in C6D6 showed
zirconocene compound.[7] These results can be interpreted the disappearance of the resonances due to the C(sp3) pro-
in steric terms by taking into account the bigger size of tons, as expected for the formation of the lithium cyclopen-
the zirconium atom, and the larger hindrance of vinyl-type tadienides. However, the formation of either mono- or bis-
carbosilanes when compared with the allyl type reported cyclopentadienyl complexes was never observed when these
Table 1. Ethylene and propylene polymerization results with complexes 14 and 15.[a]
Precatalyst
Ethylene
Yield [g]
Propylene
Yield [g]
Activity [kgPE/molM h]
Activity [kgPP/molM h]
[Cp2TiCl2]
14
[Cp2ZrCl2]
15
1.150
0.100
2.459
2.549
5520
480
11803
12235
–
–
–
–
0.446
0.311
2141
1493
[a] Conditions: MAO cocatalyst, Al/M = 1700, 1.25 mmol of catalyst dissolved in 50 mL of toluene, 10 min, 293 K, 1 bar of constant
monomer pressure.
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R. Andrés, E. De Jesús, F. Javier de la Mata, J. C. Flores, R. Gómez
FULL PAPER
Synthesis of Ph-Gn-(allyl)x (2–4): These compounds have been re-
ported previously but complete preparative details were not
given.[11] Here, the preparation of Ph-G2-(allyl)27 (4) is described
as representative. Ph-G1-(allyl)9 (3; 3.7 g, 5.4 mmol) was added to
an excess of trichlorosilane (10 mL, 99 mmol) in the presence of a
2×10–3  solution of H2PtCl6 in 2-propanol (0.080 mL, 0.16 µmol)
as catalyst. The solution was stirred for 4 h at room temperature
and, after verification of the complete hydrosilylation of 3 by 1H
NMR spectroscopy, the excess of silane and other volatiles were
removed under vacuum. Subsequently, the crude product was dis-
solved in diethyl ether (25 mL) and added dropwise (30 min) to an
ice-cooled solution of allylmagnesium bromide (180 mmol) in di-
ethyl ether (300 mL). When the addition was finished, the reaction
mixture was allowed to warm to room temperature and the stirring
was continued overnight. The excess of allylmagnesium bromide
was then hydrolyzed with a concentrated aqueous solution of
NH4Cl (100 mL). The organic phase was separated by decantation
and the aqueous solution was extracted again with diethyl ether
(2×100 mL). The combined organic phase were dried with anhy-
drous MgSO4, filtered, and the solvents evaporated in vacuo to
yield 4 (10.7 g, 96%) as a colorless liquid that was pure by 1H
NMR spectroscopy.
solutions were reacted with TiCl4 or ZrCl4 in the usual sol-
vents (toluene or THF for zirconium), with reaction times
of up to two days and temperatures up to 50 °C. The reason
for this failure − steric hindrance or inappropriate reaction
conditions − is not clear to us at this stage.
Conclusions
The post-synthetic modification of the focal point of a
dendrimer is useful for the chemistry of dendrimers and
hyperbranched polymers because it permits the incorpora-
tion of more-reactive cores.[21] In this paper, we have dem-
onstrated a methodology for such a modification of carbos-
ilane dendrimers that is based on the protolysis of Si–Ph
bonds with triflic acid and allows the linking of functional
nucleophiles to the focal point of carbosilane wedges. In
this way, we have synthesized dendritic cyclopentadienes up
to the third generation. We are currently exploring the util-
ity of this strategy for the modification of a variety of li-
gands.
Ph-G0-(allyl)3 (2; 13.0 g, 96%) was obtained from PhSiCl3 (9.5 mL,
59 mmol) and allylmagnesium bromide (200 mmol). Ph-G1-(allyl)9
(3; 11.4 g, 93%) was obtained from Ph-G0-(allyl)3 (2; 4.10 g,
18.0 mmol), trichlorosilane (10 mL, 99 mmol), and allylmagnesium
bromide (190 mmol).
Experimental Section
Reagents and General Techniques: All operations were performed
under argon by using Schlenk or dry-box techniques. Solvents were
dried and distilled under argon as described elsewhere.[22] Unless
otherwise stated, reagents were obtained from commercial sources
and used as received. Na(C5H5) was prepared from freshly distilled
cyclopentadiene and NaH in THF. HSiMe2Bz was synthesized
from HSiMe2Cl and BzMgCl in diethyl ether. ClSi(CH2CH2Si-
MePh2)3 was prepared as previously reported.[7] 1H, 13C, and 29Si
NMR spectra were recorded on Varian Unity 300 or 500 Plus spec-
trometers. Chemical shifts (δ, ppm) are relative to SiMe4, and were
measured by internal referencing to the deuterated solvent (13C and
residual 1H resonances), or by the substitution method (29Si).
Coupling constants (J) are given in hertz. The Analytical Services
of the Universidad de Alcalá performed the C, and H analyses with
a Heraeus CHN–O-Rapid microanalyzer, and the mass spectra
with an Automass Multi, ThermoQuest. GPC analyses were car-
ried out with a Varian Inert 9012 and 9065 Polychrom chromato-
graph, and Polymer Laboratories PL-ELS 1000 Light Scattering
detector, using Polymer Laboratories Plgel columns and tetra-
hydrofuran (THF) as the eluent.
Ph-G0-(allyl)3 (2): C15H20Si (228.40): calcd. C 78.88, H 8.83; found
C 78.80, H 8.81. 1H NMR (CDCl3): δ = 7.52 (m, 2 H, Ph), 7.36
(m, 3 H, Ph), 5.80 (m, 3 H, CH2CH=CH2), 4.89 (m, 6 H,
CH2CH=CH2) 1.86 (m, 6 H, CH2CH=CH2) ppm. 13C{1H} NMR
(CDCl3): δ = 135.2 (ipso-Ph), 134.2 (CH2CH=CH2), 133.8 (ortho-
Ph), 129.3 (para-Ph), 127.7 (meta-Ph), 114.3 (CH2CH=CH2), 19.5
(CH2CH=CH2) ppm. 29Si{1H} NMR (CDCl3): δ = –7.90 ppm.
Ph-G1-(allyl)9 (3): C42H68Si4 (685.33): calcd. C 73.61, H 10.00;
1
found C 73.57, H 9.98. H NMR (CDCl3): δ = 7.44 (m, 2 H, Ph),
7.34, (m, 3 H, Ph), 5.74 (m, 9 H, CH2CH=CH2), 4.84 (m, 18 H,
CH2CH=CH2), 1.54 (m, 18 H, CH2CH=CH2), 1.37 (m, 6 H,
SiCH2CH2CH2Si), 0.84 (m, 6 H, PhSiCH2CH2CH2), 0.66 (m, 6 H,
PhSiCH2CH2CH2Si) ppm. 13C{1H} NMR (CDCl3): δ = 137.2
(ipso-Ph), 134.1 (CH2CH=CH2), 133.7 (ortho-Ph), 128.6 (para-Ph),
127.4 (meta-Ph), 113.3 (CH2CH=CH2), 19.9 (CH2CH=CH2), 18.4,
17.6, and 16.7 [Si(CH2)3Si] ppm. 29Si{1H} NMR (CDCl3): δ =
–1.14 (3 Si), –4.01 (1 Si) ppm.
Ph-G2-(allyl)27 (4): C123H212Si13 (2056.1): calcd. C 71.85, H 10.39;
found C 71.81, H 10.36. 1H NMR (CDCl3): δ = 7.42 (m, 2 H, Ph),
7.30 (m, 3 H, Ph), 5.74 (m, 27 H, CH2CH=CH2), 4.85 (m, 54 H,
CH2CH=CH2), 1.55 (m, 54 H, CH2CH=CH2), 1.28 (m, 24 H,
SiCH2CH2CH2Si), 0.84 (m, 6 H, PhSiCH2CH2CH2), 0.54 (m, 42
H, PhSiCH2CH2CH2Si and SiCH2CH2CH2Si) ppm. 13C{1H}
NMR (CDCl3): δ = 137.5 (ipso-Ph), 134.3 (CH2CH=CH2), 133.9
Synthesis of HSi(CH2CH2SiMePh2)3 (1):
A
solution of
ClSi(CH2CH2SiMePh2)3 (1.00 g, 1.35 mmol) in 10 mL of diethyl
ether was added to a mixture of lithium aluminum hydride (25 mg,
0.67 mmol) in diethyl ether (25 mL). After stirring the mixture for
6 h at room temperature, the excess of lithium aluminum hydride
was hydrolyzed with a 5% solution of HCl in water, and the ethe-
real and aqueous phases were separated. The aqueous phase was
extracted with diethyl ether (2×10 mL) and the ethereal fractions
were collected and dried with anhydrous MgSO4. Then, the solvent
was removed in vacuo and the residue characterized as
HSi(CH2CH2SiMePh2)3 (0.85 g, 89%) as a colorless oil. C45H52Si4
(ortho-Ph),
128.6
(para-Ph),
127.6
(meta-Ph),
113.4
(CH2CH=CH2), 19.8 (CH2CH=CH2), 18.6, 18.2, and 16.5 [G1-
Si(CH2)3Si], 18.3, 17.6, and 16.7 [G2-Si(CH2)3Si] ppm. 29Si{1H}
NMR (CDCl3): δ = –4.21 (1 Si), 0.42 (3 Si), –1.02 (9 Si) ppm.
Synthesis of Ph-Gn-[(CH2)3SiMe2Bz]x (5–7): The preparation of
Ph-G3-[(CH2)3SiMe2Bz]27 (7) is given as representative. An excess
of benzyldimethylsilane (9.3 mL, 59 mmol) and a 2×10–3  solu-
tion of H2PtCl6 in 2-propanol (0.080 mL, 0.16 µmol) were added to
1
(705.24): calcd. C 76.64, H 7.43; found C 76.31, H 7.39. H NMR
(CDCl3): δ = 7.45 (m, 12 H, Ph), 7.32 (m, 18 H, Ph), 3.64 (sept,
3JH,H = 2.9, 1 H, SiH), 1.50 (s, 9 H, Me), 0.88 (m, 6 H, HSiCH2),
and 0.54 (m, 6 H, CH2SiMePh2) ppm. 13C{1H} NMR (CDCl3): δ 4 (4.00 g, 1.95 mmol). The mixture was gently heated until reaction
= 137.1 (ipso-Ph), 134.5 (meta-Ph), 129.1 (para-Ph), 127.8 (ortho- started (the solution became more viscous and turned slightly yel-
Ph), 7.3 and 2.5 [Si(CH2)2Si], –5.1 (Me) ppm.
low) and then allowed to recover room temperature. The volatiles
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Carbosilane Dendrons Functionalized at Their Focal Point
FULL PAPER
were evaporated under vacuum at room temperature and the resi-
due was purified by flash chromatography on a silica gel column
with hexane as eluent. Dendrimer 7 (9.86 g, 83%) was obtained as
a colorless liquid.
(CDCl3): δ = 140.3 (ipso-CH2Ph), 128.1 (ortho-CH2Ph), 128.0
(meta-CH2Ph), 123.9 (para-CH2Ph), 25.7 (CH2C6H5), 20.9, 19.1,
and 17.6 [Si(CH2)3Si], –3.5 (Me) ppm. 29Si{1H} NMR (CDCl3): δ
= 30.50 (1 Si), 1.65 (3 Si) ppm.
Ph-G1-[(CH2)3SiMe2Bz]3 (5; 4.89 g, 82%) was obtained from
Synthesis of HO-G1-[(CH2)3SiMe2Bz]3 (9): An excess of anhydrous
lithium hydroxide (50 mg, 2.1 mmol) was added to a solution of 8
(0.50 g, 0.78 mmol) in dimethoxyethane (10 mL). After stirring the
mixture for 3 h at room temperature, the solvent was removed in
vacuo, the residue was extracted with hexane (10 mL), the mixture
was filtered, and the solvent evaporated to yield 9 (0.41 g, 84%) as
a colorless oil. Alternatively, compound 9 can be synthesized by
hydrolysis of a solution of 8 in diethyl ether with several drops of
water in the presence of an excess of triethylamine. C36H58OSi4
(619.19): calcd. C 69.83, H 9.44; found C 69.43, H 9.43. MS
(APCI–): m/z = 650 (calcd. for MMeOH–: 650). 1H NMR (CDCl3):
δ = 7.19 (m, 6 H, CH2Ph), 7.04 (m, 3 H, CH2Ph), 6.99 (m, 6 H,
CH2Ph), 2.06 (s, 6 H, CH2C6H5), 1.33 (m, 6 H, SiCH2CH2CH2Si),
1.20 (s, 1 H, OH), 0.61 and 0.54 (m, 12 H, SiCH2CH2CH2Si),
–0.05 (s, 18 H, Me) ppm. 13C{1H} NMR (CDCl3): δ = 140.3 (ipso-
CH2Ph), 128.1 (ortho-CH2Ph), 128.0 (meta-CH2Ph), 123.8 (para-
CH2Ph), 25.8 (CH2C6H5), 20.0, 19.5, and 17.7 [Si(CH2)3Si], –3.4
(Me) ppm. 29Si{1H} NMR (CDCl3): δ = 15.49 (1 Si), 1.57 (3 Si)
ppm.
benzyldimethylsilane (5.0 mL, 31.6 mmol) and
2
(2.00 g,
8.76 mmol); Ph-G2-[(CH2)3SiMe2Bz]9 (6; 7.68 g, 83%) was ob-
tained from benzyldimethylsilane (7,0 mL, 44.2 mmol) and 3
(3.10 g, 4.53 mmol).
Ph-G1-[(CH2)3SiMe2Bz]3 (5): C42H62Si4 (679.28): calcd. C 74.26, H
1
9.20; found C 74.21, H 9.19. H NMR (CDCl3): δ = 7.44 (m, 2 H,
SiPh), 7.35 (m, 3 H, SiPh), 7.18 (m, 6 H, CH2Ph), 7.05 (m, 3 H,
CH2Ph), 6.95 (m, 6 H, CH2Ph), 2.04 (s, 6 H, CH2Ph), 1.33 (m, 6
H, CH2CH2CH2), 0.81 (m, 6 H, PhSiCH2CH2CH2Si), 0.57 (m, 6
H, PhSiCH2CH2CH2Si), –0.07 (s, 18 H, CH3) ppm. 13C{1H} NMR
(CDCl3): δ = 140.4 (ipso-CH2Ph), 137.9 (ipso-Ph), 134.0 (meta-Ph),
128.7 (para-Ph), 128.1 (ortho-CH2Ph), 128.0 (meta-CH2Ph), 127.6
(ortho-Ph), 123.8 (para-CH2Ph), 27.7 (CH2Ph), 19.6, 18.3, and 17.3
[Si(CH2)3Si], –3.51 (Me) ppm. 29Si{1H} NMR (CDCl3): δ = 1.53
(3 Si), –3.99 (1 Si) ppm.
Ph-G2-[(CH2)3SiMe2Bz]9 (6): C123H194Si13 (2038.0): calcd. C 72.49,
1
H 9.59; found C 72.47, H 9.55. H NMR (CDCl3): δ = 7.42 (m, 2
H, Ph), 7.26 (m, 3 H, Ph), 7.17 (m, 18 H, CH2Ph), 7.03 (m, 9 H,
CH2Ph), 6.95 (m, 18 H, CH2Ph), 2.04 (s, 18 H, CH2C6H5), 1.24
(m, 24 H, SiCH2CH2CH2Si), 0.82 (m, 6 H, PhSiCH2CH2CH2),
0.50 (m, 42 H, PhSiCH2CH2CH2Si and SiCH2CH2CH2Si), –0.07
(s, 54 H, Me) ppm. 13C{1H} NMR (CDCl3): δ = 140.4 (ipso-
CH2Ph), 137.8 (ipso-Ph), 134.0 (ortho-Ph), 128.7 (para-Ph), 128.1
(ortho-CH2Ph), 128.0 (meta-CH2Ph), 127.6 (meta-Ph), 123.8 (para-
CH2Ph), 25.8 (CH2Ph), 19.6, 18.4, and 17.4 [G2-Si(CH2)3Si], 18.6,
17.8, and 17.7 [G1-Si(CH2)3Si], –3.5 (Me) ppm. 29Si{1H} NMR
(CDCl3): δ = 1.45 (9 Si), 0.47 (3 Si), –4.13 (1 Si) ppm.
Synthesis of C5H5-Gn-[(CH2)3SiMe2Bz]x (10–12): The preparation
of C5H5-G3-[(CH2)3SiMe2Bz]27 (12) is given as representative.
Compound 7 (10.0 g, 1.63 mmol) was dissolved in a small volume
of chloroform (4 mL). Trifluoromethanesulfonic acid (0.245 g,
1.63 mmol) was added dropwise from a syringe to this solution
previously cooled to 0 °C. Stirring was continued for 1 h at room
temperature and then the solvent was removed in vacuo and the
residue dissolved in dimethoxyethane (50 mL). Subsequently, solid
NaC5H5 (0.144 g, 1.63 mmol) was added in a dry box. The reaction
mixture was stirred for 3 h, the volatiles removed in vacuo, and the
residue extracted with hexane (3×20 mL). After evaporation of the
solvent, compound 12 (8.5 g, 85%) was obtained as a dark-yellow
oil.
Ph-G3-[(CH2)3SiMe2Bz]27 (7): C366H590Si40 (6114.02): calcd. C
1
71.90, H 9,73; found C 71.60, H 8.75. H NMR (CDCl3): δ = 7.42
(m, 2 H, Ph), 7.20 (m, 3 H, Ph), 7.14 (m, 54 H, CH2Ph), 7.00 (m,
27 H, CH2Ph), 6.93 (m, 54 H, CH2Ph), 2.03 (s, 54 H, CH2C6H5),
C5H5-G1-[(CH2)3SiMe2Bz]3 (10; 8.6 g, 80%) was obtained from 5
(11.0 g, 16.2 mmol), trifluoromethanesulfonic acid (2.43 g,
16.2 mmol), and NaC5H5 (1.43 g, 16.2 mmol). C5H5-G2-[(CH2)3Si-
Me2Bz]9 (11; 2.0 g, 80%) was obtained from 6 (2.50 g, 1.23 mmol),
trifluoromethanesulfonic acid (0.184 g, 1.23 mmol), and NaC5H5
(0.108 g, 1.23 mmol).
1.24 (m, 78 H, SiCH2CH2CH2Si), 0.80 (m,
6
H,
PhSiCH2CH2CH2), 0.51 (m, 150 H, PhSiCH2CH2CH2Si and
SiCH2CH2CH2Si), –0.07 (s, 162 H, Me) ppm. 13C{1H} NMR
(CDCl3): δ = 140.3 (ipso-CH2Ph), 137.8 (ipso-Ph), 134.1 (ortho-Ph),
128.4 (para-Ph), 128.1 (ortho-CH2Ph), 128.0 (meta-CH2Ph), 127.6
(meta-Ph), 123.9 (para-CH2Ph), 25.8 (CH2Ph), 18.7, 18.1, and 17.8
[G2-Si(CH2)3Si], 19.9, 18.5 and 17.5 [G3-Si(CH2)3Si], –3.4 (Me)
ppm; [G1-Si(CH2)3Si] not found. 29Si{1H} NMR (CDCl3): δ = 1.45
(27 Si), 0.44 (3 Si), 0.40 (9 Si), –4.11 (1 Si) ppm.
Data for C5H5-G1-[(CH2)3SiMe2Bz]3 (10): C41H62Si4 (667.27):
calcd. C 73.80, H 9.37; found C 73.75, H 9.36. MS (ESI–): m/z =
1
666 (calcd. for M–H–: 666). H NMR (CDCl3): δ = 7.19 (m, 6 H,
CH2Ph), 7.04 (m, 3 H, CH2Ph), 6.96 (m, 6 H, CH2Ph), 6.57, 3.42,
and 2.96 (broad resonances, 5 H, C5H5), 2.05 (s, 6 H, CH2C6H5),
1.27 (m, 6 H, SiCH2CH2CH2Si), 0.53 and 0,46 (m, 12 H,
SiCH2CH2CH2Si), –0.06 (s, 18 H, Me) ppm. 13C{1H} NMR
(CDCl3): δ = 140.2 (ipso-CH2Ph), 133.1 (C5H5), 129.9 (C5H5),
128.0 (ortho-CH2Ph), 127.9 (meta-CH2Ph), 123.8 (para-CH2Ph),
49.7 (C5H5), 25.8 (CH2C6H5), 19.7, 18.8, and 17.5 [Si(CH2)3Si],
–3.3 (Me) ppm. 29Si{1H} NMR (CDCl3): δ = 2.71 (1 Si), 1.54 (3
Si) ppm.
Synthesis of Cl-G1-[(CH2)3SiMe2Bz]3 (8): Compound 5 (1.00 g,
1.47 mmol) was dissolved in a small volume of chloroform (1 mL).
Trifluoromethanesulfonic acid (0.14 mL, 1.6 mmol) was then added
dropwise from a syringe to this solution previously cooled to 0 °C.
Stirring was continued for 1 h at room temperature, the solvent was
removed in vacuo, the residue was dissolved in dimethoxyethane
(10 mL), and an excess of solid triethylammonium chloride (0.30 g,
2.2 mmol) was added. After stirring the reaction mixture for 2 h,
the volatiles were removed in vacuo and the residue was extracted
with hexane (10 mL), the mixture was filtered, and the solvent was
evaporated to yield 8 (0.81 g, 86%) as a colorless oil. C36H57ClSi4
Data for C5H5-G2-[(CH2)3SiMe2Bz]9 (11): C122H194Si13 (2026.0):
1
calcd. C 72.33, H 9.65; found C 71.86, H 9.27. H NMR (CDCl3):
(637.63): calcd. C 67.81, H 9.01; found C 67.35, H 9.10. MS
δ = 7.16 (m, 18 H, CH2Ph), 7.02 (m, 9 H, CH2Ph), 6.95 (m, 18 H,
1
(ESI–): m/z = 653 (calcd. for MOH–: 653). H NMR (CDCl3): δ = CH2Ph), 6.54, 3.40, and 2.97 (broad resonances, 5 H, C5H5), 2.04
7.19 (m, 6 H, CH2Ph), 7.04 (m, 3 H, CH2Ph), 6.98 (m, 6 H,
CH2Ph), 2.06 (s, 6 H, CH2C6H5), 1.37 (m, 6 H, SiCH2CH2CH2Si), H, SiCH2CH2CH2Si), –0.07 (s, 54 H, Me) ppm. 13C{1H} NMR
0.79 (m, H, ClSiCH2CH2CH2Si), 0.57 (m, H, (CDCl3): δ = 140.4 (ipso-CH2Ph), 132.9 (C5H5), 130.1 (C5H5),
ClSiCH2CH2CH2), –0.04 (s, 18 H, Me) ppm. 13C{1H} NMR 128.1 (ortho-CH2Ph), 128.0 (meta-CH2Ph), 123.9 (para-CH2Ph),
(s, 18 H, CH2C6H5), 1.26 (m, 24 H, SiCH2CH2CH2Si), 0.51 (m, 48
6
6
Eur. J. Inorg. Chem. 2005, 3742–3749
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3747

R. Andrés, E. De Jesús, F. Javier de la Mata, J. C. Flores, R. Gómez
FULL PAPER
49.9 (C5H5), 25.8 (CH2C6H5), 19.9, 18.5, and 17.5 [G2-Si(CH2)3Si], 6 H, C5H5SiCH2CH2CH2Si), –0.05 (s, 18 H, Me) ppm. 13C{1H}
18.9, 18.0 and, 17.9 [G1-Si(CH2)3Si], –3.4 (Me) ppm. 29Si{1H}
NMR (CDCl3): δ = 2.70 (1 Si), 1.58 (9 Si), 0.55 (3 Si) ppm.
NMR (CDCl3): δ = 140.1 (ipso-CH2Ph), 127.9 (ortho-CH2Ph),
125.5 (C5H4), 127.8 (meta-CH2Ph), 123.6 (para-CH2Ph), 115.5
(C5H4), 25.9 (CH2C6H5), 19.9, 18.8, and 18.3 [Si(CH2)3Si], –3.1
(Me) ppm; ipso-C5H4 not found. 29Si{1H} NMR (CDCl3): δ =
–6.34 (1 Si), 1.54 (3 Si) ppm.
Data for C5H5-G3-[(CH2)3SiMe2Bz]27 (12): C365H590Si40 (6102.0):
1
calcd. C 71.84, H 9.75; found C 71.15, H 9.44. H NMR (CDCl3):
δ = 7.14 (m, 54 H, CH2Ph), 7.02 (m, 27 H, CH2Ph), 6.92 (m, 54
H, CH2Ph), 6.50, 3.35, 2.93 (broad resonances, 5 H, C5H5), 2.01
(s, 54 H, CH2C6H5), 1.25 (m, 78 H, SiCH2CH2CH2Si), 0.51 (m, 156
H, SiCH2CH2CH2Si), –0.09 (s, 162 H, Me) ppm. 13C{1H} NMR
(CDCl3): δ = 140.2 (ipso-CH2Ph), 133.0 (C5H5), 130.1 (C5H5),
128.1 (ortho-CH2Ph), 127.9 (meta-CH2Ph), 123.8 (para-CH2Ph),
49.5 (C5H5), 25.8 (CH2C6H5), 19.9, 18.6, and 17.5 [G3-Si(CH2)3Si],
18.8, 18.3, and 17.9 [G2-Si(CH2)3Si], –3.3 (Me) ppm; [G1-Si(CH2)
3Si] not found. 29Si{1H} NMR (CDCl3): δ = 2.60 (1 Si), 1.48 (27
Si), 0.43 (9 Si), 0.38 (3 Si) ppm.
Ethylene and Propylene Polymerization: A 250-mL flask charged
with toluene (50 mL) and equipped with a magnetic stirrer was
evacuated and refilled with pre-dried ethylene or propylene gas four
times. Whilst keeping the flask pressurized with the corresponding
gas (1 bar) and stirring at room temperature, a toluene solution of
methylaluminoxane (PMAO-IP 13% Akzo Nobel, 0.50 mL) was
syringed through a septum. After 5 min, a toluene solution of the
catalyst (0.50 mL, 2.5 m) was injected into the flask with simulta-
neous starting of a stopwatch. The polymerization was quenched
10 min later by closing the gas feed, release of the overpressure,
and addition of acidified methanol (4% v/v HCl). The mixture was
stirred for 6 h and the polymer was filtered, washed with copious
amounts of methanol, and dried in an oven to constant weight.
Synthesis of KC5H4-G1-[(CH2)3SiMe2Bz]3 (13): In a dry box, solid
potassium hydride (0.60 g, 15 mmol) was added to a solution of 10
(10 g, 15 mmol) in dimethoxyethane (50 mL). The reaction mixture
was stirred overnight, filtered, and subsequently the solvent was
evaporated in vacuo. Washing the resulting dark-yellow oil, which
was insoluble in alkanes, with pentane (3×30 mL) yielded 8.7 g
(82%) of pure 13, which is stable enough to be characterized and
stored for months in a dry box. MS (ESI+): m/z = 705 (calcd. for
Acknowledgments
We gratefully acknowledge financial support from the DGI-Minis-
terio de Ciencia y Tecnología (Project BQU2001-1160 and Pro-
grama Ramón y Cajal), and the DGI-Comunidad de Madrid (Pro-
ject GR/MAT/0733/2004).
1
MH+: 705). H NMR (C6D6): δ = 7.24 (m, 6 H, CH2Ph), 7.09 (m,
9 H, CH2Ph), 6.01 (broad resonance, 4 H, C5H4), 2.20 (s, 6 H,
CH2C6H5), 1.64 (m,
6 H, CH2CH2CH2), 0.90 (m, 12 H,
CH2CH2CH2), 0.17 (s, 18 H, Me) ppm. 13C{1H} NMR (C6D6): δ
= 140.5 (ipso-CH2Ph), 128.7 (ortho-CH2Ph), 128.5 (meta-CH2Ph),
124.5 (para-CH2Ph), 114.0 (C5H5), 109.3 (C5H5), 26.6 (CH2C6H5),
21.0, 20.8, and 20.3 [Si(CH2)3Si], –2.5 (Me) ppm; ipso-C5H4 not
found. 29Si{1H} NMR (C6D6): δ = –12.03 (1 Si), 1.46 (3 Si) ppm.
[1] a) Dendrimers and Other Dendritic Polymers (Eds.: J. M. J. Fre-
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solution of TiCl4 in toluene (3.0 mL, 0.60 mmol) was added from a
syringe to a solution of the potassium cyclopentadienide 13 (0.85 g,
1.2 mmol) in toluene (20 mL). The mixture was stirred at room
temperature overnight. After filtration, the solution was evaporated
in vacuo to dryness. The crude red oil thus obtained was charac-
terized as 14 (0.79 g, 91%). C82H122Cl2Si8Ti (1451.3): calcd. C
1
67.86, H 8.47; found C 67.83, H 8.42. H NMR (CDCl3): δ = 7.17
[5] a) G. E. Oosterim, R. J. van Haaren, J. N. H. Reek, P. C. J.
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(m, 6 H, CH2Ph), 7.03 (m, 3 H, CH2Ph), 6.95 (m, 6 H, CH2Ph),
6.65 (pseudo t, AAЈ part of an AAЈBBЈ spin system, 2 H, C5H4),
6.49 (pseudo t, BBЈ part of an AAЈBBЈ spin system, 2 H, C5H4),
2.06 (s, 6 H, CH2C6H5), 1.30 (m, 6 H, SiCH2CH2CH2Si), 0.81 (m,
6
H,
C5H5SiCH2CH2CH2Si),
0.56
(m,
6
H,
C5H5SiCH2CH2CH2Si), –0.06 (s, 18 H, Me) ppm. 13C{1H} NMR
(CDCl3): δ = 140.1 (ipso-CH2Ph), 129.2 (C5H4), 127.9 (ortho-
CH2Ph), 127.8 (meta-CH2Ph), 123.6 (para-CH2Ph), 119.1 (C5H4),
25.9 (CH2C6H5), 20.0, 18.8, and 18.3, [Si(CH2)3Si], –3.1 (Me) ppm;
ipso-C5H4 not found. 29Si{1H} NMR (CDCl3): δ = –5.65 (1 Si),
1.53 (3 Si) ppm.
Synthesis of [{C5H4-G1-[(CH2)3SiMe2Bz]3}2ZrCl2] (15): Solid
ZrCl4·2THF (0.267 g, 0.71 mmol) was added, in a dry box, to a
solution of 13 (1.00 g, 1.42 mmol) in toluene. The reaction mixture
was stirred overnight, evaporated in vacuo, and extracted with hex-
ane (3×10 mL). After filtration, the solvent was evaporated in
vacuo to yield 15 (0.89 g, 84%) as a colorless oil. C82H122Cl2Si8Zr
(1494.66): calcd. C 65.89, H 8.23; found C 65.84, H 8.21. 1H NMR
(CDCl3): δ = 7.19 (m, 6 H, CH2Ph), 7.05 (m, 3 H, CH2Ph), 6.95
(m, 6 H, CH2Ph), 6.56 (pseudo t, AAЈ part of an AAЈBBЈ spin
system, 2 H, C5H4), 6.46 (pseudo t, BBЈ part of an AAЈBBЈ spin
system, 2 H, C5H4), 2.06 (s, 6 H, CH2C6H5), 1.32 (m, 6 H,
SiCH2CH2CH2Si), 0.85 (m, 6 H, C5H5SiCH2CH2CH2Si), 0.58 (m,
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3748
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Inorg. Chem. 2005, 3742–3749

Carbosilane Dendrons Functionalized at Their Focal Point
FULL PAPER
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Received: March 1, 2005
Published Online: August 4, 2005
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www.eurjic.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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