Allyl-end-grafted carbosilane dendrimers based on 1,4-phenylene units: Synthesis, reactivity, structure, and bonding motifs

Article abstract of DOI:10.1002/ejic.201201428

The synthesis of a series of carbosilanes of type 1-Br-C₆H ₄-4-SiMe_3-n(CH₂CH=CH₂)_n (n = 1, 2, 3), Si[C₆H₄-4-SiMe_3-n(CH ₂CH=CH₂)_n<

Full text of DOI:10.1002/ejic.201201428

FULL PAPER
DOI:10.1002/ejic.201201428
Allyl-End-Grafted Carbosilane Dendrimers Based on
1,4-Phenylene Units: Synthesis, Reactivity, Structure, and
Bonding Motifs
Zakariyya Ishtaiwi,[a] Tobias Rüffer,[a] Alexander Hildebrandt,[a]
Firas F. Awwadi,[b] Harald Hahn,[a] Akerke Abylaikhan,[a]
Deeb Taher,[b] Uwe Siegert,[a] Bernhard Walfort,[a] and
Heinrich Lang*[a]
Dedicated to Professor Dr. Jaroslav Holecˇek on the occasion of his 80th birthday[‡]
Keywords: Dendrimers / Self-assembly / Supramolecular chemistry / Pi interactions / NMR spectroscopy
The synthesis of a series of carbosilanes of type 1-Br–
along the crystallographic b axis with π–π contacts among
C6H4–4-SiMe3–n(CH2CH=CH2)n (n = 1, 2, 3), Si[C6H4–4-
the C6H4 groups of neighboring molecules, with the columns
interacting further by C–H···πCC arrangements. Two mole-
cules of 10a interdigitate in the solid state to form self-com-
plementary dimers that are stabilized by C–H···πCC and π–π
contacts. The structures of the monomer and the dimer were
optimized by using the MM+ force field as implemented in
HyperChem 4.02. In addition, the presence of self-comple-
mentary structures in solution is evidenced from 1H NMR
spectroscopy. In dichloromethane solely dimeric species ex-
ist, whereas in benzene monomers are observed. Calculated
electrostatic potentials were used to rationalize the supra-
molecular structures of these two carbosilane compounds.
SiMe3–n(CH2CH=CH2)n]4, 1-Br–C6H4-4-Si[C6H4–4-SiMe3–n
(CH2CH=CH2)n]3 (n = 0, 1, 2, 3), ClSi[C6H4–4-Si{C6H4–4-
SiMe3–n(CH2CH=CH2)n}3]3, Si[C6H4–4-Si{C6H4–4-SiMe3–n
-
-
(CH2CH=CH2)n}3]4 (n = 1, 2), and 1-Br–C6H4–4-Si[C6H4–4-
Si{C6H4–4-SiMe3–n(CH2CH=CH2)n}3]3 (n = 0, 1, 2, 3) is dis-
cussed. The structures of Si[C6H4–4-SiMe2(CH2CH=CH2)]4
(7b) and ClSi[C6H4–4-Si{C6H4–4-SiMe2(CH2CH=CH2)}3]3
(10a) in the solid state are reported. The crystal structures of
both dendrimers are based on C–H···πCC (πCC = double bond
of the CH=CH2 groups) and π–π interactions. The 3D net-
work structure observed for 7b is composed of three crystal-
lographically independent head-to-head stacking columns
functional groups.[1] Recent developments in this field of
chemistry have been focused on different applications.[2–7]
Depending on the nature of the dendrimer framework and
the functional groups present at the dendrimer core, shell,
or periphery, these molecules can be used as active compo-
nents in the field of homogeneous and heterogeneous catal-
ysis,[3] as liquid-crystalline materials,[4] as drug-delivery ve-
hicles,[5] as ionophores for chemical sensing in sensor tech-
nology,[6] as tectons for self-assembly with network forma-
tion,[7a] and as nonlinear optical materials.[7b] In addition,
dendrimers have found use in the synthesis and stabilization
of mainly monodisperse metallic nanoparticles.[7c] Among
them, much attention has been paid to the family of silicon-
containing dendrimers including silanes, carbosilanes, silox-
anes, carbosiloxanes, and silsesquioxanes.[8–13] The flexibil-
ity of aliphatic spacer units [(CH2)n; n = 2, 3] between the
silicon branching points, however, produces some limitation
in their application. Thus, in appropriate end-grafted palla-
dium-, platinum-, rhodium-, or ruthenium-supported
metallodendrimers not all the catalytic active centers are
Introduction
In general, dendrimers are three-dimensional, repetitively
branched molecules with a high degree of molecular uni-
formity, narrow molecular-weight distribution, and they
show specific size and shape characteristics. They can be
prepared by the divergent, convergent, or a combination of
these two synthetic methodologies to give highly function-
alized macromolecules that feature end-grafted and internal
[a] Department of Inorganic Chemistry,
Faculty of Natural Sciences, Institute of Chemistry,
Chemnitz University of Technology,
Strasse der Nationen 62, 09111 Chemnitz, Germany
Fax: +49-371-531-21219
E-mail: heinrich.lang@chemie.tu-chemnitz.de
Homepage: https://www.tu-chemnitz.de/chemie/anorg/
[b] Department of Chemistry,
The University of Jordan,
Amman 11942, Jordan
[‡] For his contribution to the chemistry of coordination and
organometallic compounds.
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201201428.
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accessible for the substrates. For this reason it is of interest less solids that are soluble in most common organic sol-
to synthesize shape-persistent carbosilane dendrimers by vents.
using rigid spacer units between the silicon atoms.
In this report, we focus on the convergent synthesis of
shape-persistent dendritic molecules with 1,4-phenylene
spacer units.
The first-generation dendrimers Si[C6H4–4-Si{C6H4–4-
SiMe3–n(CH2CH=CH2)n}3]4 (11a, n = 1; 11b, n = 2) are
accessible by subsequent treatment of 8b and 8c with tBuLi
and SiCl4/TMEDA (TMEDA = N,N,NЈ,NЈ-tetramethyleth-
ylenediamine; Scheme 2; see the Experimental Section), in
which TMEDA permits control of the selective formation
of 11a and 11b. Without TMEDA, only the chlorocarbosil-
anes 10a and 10b formed. This confirms the higher nucleo-
philicity of the lithiated species 9a and 9b in the presence
of TMEDA.[21]
Results and Discussion
A series of carbosilane dendrimers based on 1,4-substituted
phenylene units is accessible in a consecutive synthesis pro-
cedure by using the convergent growth method including
halide/lithium and lithium/silicon exchange reactions. The
synthesis of the key starting materials 1-Br–C6H4–4-Si-
Me3–nCln (3a,[14] n = 0; 3b,[15] n = 1; 3c,[15] n = 2; 3d,[16]
n = 3) and 1-Br–C6H4–4-SiMe3–n(CH2CH=CH2)n (5a,[17]
n = 1; 5b, n = 2; 5c,[18] n = 3) is depicted in Scheme 1. As a
suitable precursor, 1,4-dibromobenzene was used, which
was either monolithiated (synthesis of 3a) or transformed
into bromophenylmagnesium bromide (synthesis of 3b–3d)
As a starting material for the convergent synthesis of sec-
ond-generation dendrimers, the availability of first-genera-
tion dendrons 1-Br–C6H4–4-Si[C6H4–Si{C6H4–4-SiMe3–n
-
(CH2CH=CH2)n}3]3 (12a, n = 0; 12b, n = 1; 12c, n = 2; 12d,
n = 3) is required. These carbosilanes can be synthesized
from 8a–8d in a two-step synthesis procedure including
metalation of 8a–8d with tBuLi followed by addition of 1-
Br–C6H4–4-SiCl3 (3d) [Equation (1)]. However, all attempts
to synthesize 12a failed due to insolubility of the intermedi-
ate products. In contrast, 12b, 12c, and 12d are accessible
by using diethyl ether/tetrahydrofuran mixtures of ratio 1:3
(v/v). After appropriate workup, 12b–12d can be isolated
as colorless solids in a yield between 8 and 25% (see the
Experimental Section).
and subsequently treated with the chlorosilanes SiMe3–n
-
Cln+1 (2a, n = 0; 2b, n = 1; 2c, n = 2; 2d, n = 3) to obtain
compounds 3a–3d. Treatment of 3b–3d with allylmagne-
sium bromide gave 5a–5c. After appropriate workup, car-
bosilanes 3a–3d and 5a–5c could be isolated as colorless
liquids that dissolve in most common organic solvents.
All compounds were fully characterized by elemental
1
analysis as well as IR, H, 13C{1H}, and 29Si{1H} NMR
The zeroth-generation dendrimers Si[C6H4–4-SiMe3–n
-
(CH2CH=CH2)n]4 (7b,[19] n = 1; 7c, n = 2; 7d,[19] n = 3) were
prepared similarly to Si(C6H4–4-SiMe3)4 (7a)[20] by lithi-
ation of 5a–5c followed by addition of SiCl4 as depicted in
Scheme 1. The yield of isolated 7b–7d is 30–40% (see the
Experimental Section). When 1-Br–C6H4–4-SiCl3 (3d) is
spectroscopy. ESI-TOF mass spectrometry was additionally
used to characterize 7c and 8a–8d, whereas MALDI-TOF
studies were performed with 10a, 11a, and 12b, respectively.
The identities of 7b and 10a in the solid state were con-
firmed by single-crystal X-ray diffraction studies.
used instead of SiCl4 then 1-Br–C6H4–4-Si[C6H4–4-SiMe3–n
-
Single crystals of 7b could be obtained by cooling a solu-
(CH2CH=CH2)n]3 (8a, n = 0; 8b, n = 1; 8c, n = 2; 8d, n = tion of 7b in n-pentane to –30 °C. Compound 7b crystallizes
3) was obtained (yield 40–70%; Scheme 1; see the Experi- in the non-centrosymmetric chiral monoclinic space group
mental Section). Carbosilanes 7b–7d and 8a–8d are color- I2. The asymmetric unit comprises two molecules of 7b that
Scheme 1. Synthesis of 3a–3d, 5a–5c, 7a–7d, and 8a–8d.
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Scheme 2. Synthesis of dendrimers 10a, 10b, 11a, and 11b.
possess C1 symmetry (7b-I, 7b-II) and half of a further mo- tallographically independent molecules of 7b (7b-I, 7b-II,
lecule that possesses crystallographically imposed C2 sym- 7b-III) as well as a packing diagram are illustrated in Fig-
metry (7b-III). The molecular structures of the three crys- ure 1. The crystal data and structure-refinement parameters
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Figure 1. Crystal structure of 7b: (a) ORTEP diagram (30% probability level) of the molecular structures of the three crystallographically
independent molecules of 7b (left side; top: 7b-I; middle: 7b-II; bottom: 7b-III) and atom-numbering scheme of 7b-I, 7b-II, and 7b-III.
(b) Space-filling model of the unit cell showing the arrangement of 7b-I to 7b-III in the solid state by formation of three crystallographi-
cally independent head-to-head stacking columns along the crystallographic b axis. Hydrogen atoms and disordered atoms have been
omitted for clarity. Selected bond lengths [Å] and bond angles [°]: Si1–Cl 1.893(6), Si1–C12 1.887(6), Si1–C23 1.888(6), Si1–C34 1.895(6);
C1–Si1–C12 112.7(3), C1–Si1–C23 109.1(3), C1–Si1–C34 106.1(3), C12–Si1–C23 108.6(3), C12–Si1–C34 109.1(3), C23–Si1–C34 111.3(3).
are provided in Table S1 (Supporting Information). Selected head stacking columns along the crystallographic b axis
bond lengths [Å] and bond angles [°] of 7b-I are summa- (Figure 1), in which the columns formed by 7b-I and 7b-II
rized in the caption of Figure 1. Related bond lengths and (Figure 2), are similar with respect to the pattern of the π
angles of the other crystallographically independent mole- contacts. Thus, all C6H4 building blocks of individual mole-
cules do not differ significantly from these data and are cules of 7b-I and 7b-II are involved in one π–π contact to
therefore not presented. The bond lengths and bond angles one phenylene ring of a neighboring molecule. The dis-
are characteristic of carbosilanes that feature Si–C6H4–Si
and SiMe2(CH2CH=CH2) units, and hence there is no need
to discuss these building blocks in more detail.[22]
The 3D network structure of 7b is set up by nonclassical
C–H···πCC hydrogen-bonding (πCC = double bond of the
CH=CH2 groups; Table S2 in the Supporting Information)
and π–π interactions,[23] whereby the centroids of the C=C
double bonds can be considered as proton acceptors, of
which two types exist: two proton donors–one acceptor
(Figure S1, bottom, in the Supporting Information) and
one proton donor–one acceptor (Figure S1, top). The 3D
network is further stabilized by π–π interactions. Molecules
and B refer to atoms that belong to the second and third molecule
of 7b form three crystallographically independent head-to- of 7b-I along the chain.
Figure 2. Head-to-head stacking of molecules 7b-I including π–π
interactions between C6H4 units of sequenced molecules. Labels A
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tances between the centroids of interacting C6H4 units and
The most striking feature of the molecular structure of
the interplanar angles (Table S3 in the Supporting Infor- 10a in the solid state is that two molecules of 10a interdigi-
mation) fall within the typically observed values for T- tate to form self-complementary dimers in the form of a
shaped benzene stackings.[23a,23b]
hexagram (Figure 5). Clearly, the geometric parameters of
One C6H4 unit of 7b-III is involved in two, whereas all the three crystallographically different arms of 10a are ar-
other phenylene rings are involved in only one π–π interac- ranged in a fashion that optimizes interactions of two mole-
tion between adjacent molecules (Figure 3). Geometrical cules of 10a. The dimeric structure is stabilized by π–π in-
details of these contacts (Table S3 in the Supporting Infor- teractions through four trimeric phenylene aggregates (Fig-
mation) are similar to those observed for the chains based ure 5, top), of which two (A and B; Figure 5, bottom) are
on 7b-I and 7b-II (Table S3).
crystallographically independent. In addition, C23–
H23···πCC hydrogen bonding participates in stabilizing the
dimeric structure (Table S4 in the Supporting Infor-
mation).[23c–23e] Type-A aggregates are set up from a ter-
minal C6H4 ring of one molecule of 10a inserted between
two terminal C6H4 units from another molecule of 10a,
whereas type-B aggregates are formed by one inner phenyl-
ene moiety of 10a inserted between two terminal C6H4 rings
of another molecule (Figure 5). Both aggregates correspond
to T-shaped benzene dimers (Figure 5).[23a,23b] The ten-
dency of 10a to form self-complementary dimers through
π–π interactions is also verified by the Si–CAr distances. Ac-
cording to the CCD database, only two examples are
known with Si–CAr distances longer than 2.0 Å.[24] In 10a,
the Si4–C67 [2.009(8) Å] and Si2–C19 [2.014(7) Å] distances
are elongated relative to the other Si2–CAr and Si4–CAr
bonds (Figure 4). In B, the Si–CAr bonds of the intercalat-
ing C6H4 rings are exceptionally lengthened relative to
those of type-A assemblies, which most clearly is attributed
to the optimization of π–π interactions between two mole-
cules of 10a. The hexagrams form stacks on the basis of
further cross-linkage by means of C–H···πCC arrangements
(one proton donor–one proton acceptor) to form the three-
dimensional structure (Table S4).
Figure 3. Head-to-head stacking of 7b-III including π–π contacts
between C6H4 rings of sequenced molecules. Labels A and B refer
to atoms that belong to the second and third molecule of 7b-III
along the chain. Label Ј refers to symmetry-generated atoms, due
to crystallographically imposed C2 symmetry.
Single crystals of 10a were obtained by vapor-phase dif-
fusion of n-pentane into a solution of 10a in dichlorometh-
ane at 25 °C. The structure of 10a in the solid state is de-
picted in Figure 4, and the crystal data and structure-refine-
ment parameters are summarized in Table S1 (Supporting
Information). For selected bond lengths [Å] and bond
angles [°], see Figure 4.
The electrostatic potentials of 7b and 10a (Figure 6) were
calculated by using the DFT/B3LYP theory with a 6-31g(d)
basis set on all atoms [(d) = d functions added to heavy
atoms].[25,26] In 7b, the most negative electrostatic potential
values are around the C=C double bonds, whereas the most
positive values are found around the hydrogen atoms (Fig-
ure 6A). The observed C–H···πCC contacts and the second-
most-negative electrostatic potential values around the aro-
matic π systems rationalize the π–π interactions. A similar
behavior is observed for 10a (Figure 6B and C). Also, the
electrostatic potential values around Cl indicate the pres-
ence of less negative potentials end-capped along the Si1–
Cl1 bond (green color, Figure 6C), whereas the potential
values are more negative in the π region of the atom. The
anisotropy of the electrostatic potential around covalently
bonded chlorine atoms is known in the literature.[25a,25b] On
the basis of electrostatic laws, these potential surfaces
render the formation of the reported weak intermolecular
interactions inanimate.
Figure 4. ORTEP diagram (30% probability level) and atom-num-
bering scheme of 10a. The hydrogen atoms are omitted for clarity.
Selected bond lengths [Å] and bond angles [°]: Si1–Cl1 2.059(3),
Si1–Cl 1.819(7), Si1–C7 2.005(7), Si1–C13 1.887(7), Si2–C4
1.856(7), Si2–C19 2.014(7), Si2–C25 1.892(8), Si2–C3l 1.877(7),
Si3–Cl0 2.003(7), Si3–C37 1.892(8), Si3–C43 1.853(8), Si3–C49
1.854(7), Si4–C16 1.892(8), Si4–C55 1.853(8), Si4–C61 1.854(8),
Si4–C67 2.009(8) Si5–C22 2.10(8); C1–Si1–C7 110.6(3), C1–Si1–
C13 106.8(3), C7–Si1–C13 116.0(3).
The IR spectra of the allyl-end-grafted carbosilanes 7, 8
and 10–12 show characteristic absorptions at approximately
1630 cm–1 for the νC=C vibrations. In the range of 800–
840 cm–1, bands for the Si–C units are found, which is in
agreement with allyl-functionalized carbosilanes. The Si–
CH3 moieties absorb at 1250 cm–1 (Si–CH3 bending).[27]
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Figure 5. Top: side view of the dimeric structure of 10a (left). The dimer viewed along the axis that connects the chlorine and its symmetry-
equivalent atom (right). The two molecules are colored by symmetry operation (inversion center). Bottom: structural details of the two
crystallographically different aggregates A and B formed by π–π interactions of dimeric 10a.
For NMR spectroscopic assignment, the atom-number-
ing scheme of the respective molecules is depicted in Fig-
1
ure S3 (Supporting Information). The H NMR spectra of
7a–7d and 8a–8d show well-resolved resonance signals, as
is expected for the respective organic groups (see the Exper-
1
imental Section). In contrast, the H NMR spectra of the
first-generation dendrimers 10–12 show additional signals
for each organic group with a strong dependence on con-
centration, solvent, and temperature [i.e., the SiCH3 moie-
ties of 12b in CDCl3 show that the ratio of the relative inte-
grals of the high- to low-field signals decreases with
Figure 6. Calculated electrostatic potential surfaces of (A) 7b and
decreasing concentration (Figure 7b) and increasing tem-
(B, C) 10a [in (B), the chlorine atom is directed away from the
perature (Figure 7c)]. This indicates that 12b forms a mix-
viewer; in (C), the chlorine atom is directed towards the viewer].
ture of monomeric and self-associated dimeric species in
The electron density contour isovalue is set to 0.005. Units of the
solution. As depicted in Figure 7b and c, the high-field sig-
colored scale are in atomic units.
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nal is related to self-associated species, whereas the down-
field signal can be assigned to the monomeric form. The
high-field shift of the resonance signals can be explained by
the presence of the respective signals in a more shielded
anisotropic environment inside the self-associated species
relative to the chloroform environment for the monomer.
Other organic groups in 12b show a behavior similar to the
SiCH3 groups, however, it is impossible to completely ana-
lyze them due to spectral multiplicity (see the Experimental
Section).
1
Figure 8. (a) H NMR spectrum of 12b in C6D6 with a concentra-
1
tion of 12 mm at 25 °C. (b) H NMR region for the methyl groups
from spectrum (a). (c) 1H NMR spectroscopic signals for the
methyl groups of 12b in CDCl3 (12 mm, 25 °C). (d) 1H NMR spec-
troscopic region for the methyl groups in C6D6 at 75 °C. Label M
refers to the monomer and D to the dimer.
(type A and B phenylene aggregates) as already observed
for 10a in the solid state (Figure 5). The estimated core-
silicon–core-silicon distance for the 12b dimer is 6.957 Å,
whereas for dimeric 10a it is 7.094 Å. The molecular me-
chanical optimization data fit very well with the obtained
solid-state self-complementary structure of 10a (core-sili-
con–core-silicon distance 6.572 Å; Figure 5).
Figure 7. (a) 1H NMR spectrum of 12b in CDCl3 with a concentra-
tion of 75 mm at 25 °C. (b) Concentration dependence of the SiCH3
region (25–75 mm) at 25 °C. (c) Temperature dependence of the
SiCH3 region in the range of 25–53 °C at 49 mm.
1
The H NMR spectroscopic measurements of 12b were
repeated in [D6]benzene, because it is supposed that an aro-
matic solvent will reduce the concentration of the self-asso-
ciated species through competition of π–π interactions (Fig-
ure 8).[28] It was found that the high-field signal for the self-
associated system (SiCH3) in CDCl3 (Figure 8c, signal lab-
eled with D) is reduced to a low-field shoulder in [D6]benz-
ene (Figure 8a and b), which supports π–π interactions for
Figure 9. Optimized structure of (a) monomeric carbosilane 12b
and (b) its self-complementary structure.
The proof for the self-complementary structure of 12b in
the self-associated species. As expected, upon decreasing the solution, suggested by MM+ calculations, is obtained from
concentration and increasing the temperature to 75 °C, the 1H NMR spectroscopic studies. Figure 10 shows the 1H
shoulder disappeared (Figure 8b, label D, Figure 8d). The NMR spectra of 12b at 75 °C in C6D6 and at –80 °C in
appearance of the self-associated system as a low-field CD2Cl2. It is expected that the monomeric species predomi-
shoulder relative to the signal of the monomeric form is nates at high temperature in benzene; it shows three dif-
attributed to a weaker aromatic shielding environment in- ferent signals for the phenylene groups (BrC6H4Si, inner
side the self-associated system than the aromatic shielding and outer SiC6H4Si) and only one type of methyl and allyl
environment of the benzene solvent around the monomer.
groups (see the Experimental Section). In the self-comple-
To determine the structure of the self-associated species, mentary structure (Figure 9b), rotational restrictions result
molecular mechanics calculations were performed with the in the splitting of the nine outer SiC6H4Si units: three of
MM+ force field as implemented in HyperChem 4.02. The them are directed towards the other complementary mole-
optimized structure of carbosilane 12b is shown in Fig- cule, whereas six SiC6H4Si groups are oriented away from
1
ure 9a and the dimer as self-complementary structure in it. The H NMR spectroscopic signals of these groups at
Figure 9b. The optimized dimeric structures for 10a, 10b, –80 °C have a ratio of 4:24:12:12 (Figure 10b), which fits
11a, 11b, and 12b–12d display the same π–π interactions with the self-complementary, dimeric structure (Figure 9b).
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Figure 10. 1H NMR spectra of 12b: (a) measured in C6D6 (12 mm)
at 75 °C and (b) in CD2Cl2 (12 mm) at –80 °C.
Similar to the outer SiC6H4Si units, the nine terminal –
Si(CH3)2(CH2CH=CH2) groups are split into two sets (Fig-
ure 9b). This analysis fits with the 1H NMR spectrum mea-
sured at –80 °C, which shows two types for the SiCH3 pro-
tons (ratio 36:18) and two arrays for the allyl SiCH2 protons
(ratio 12:6). The signals of the three terminal –Si(CH3)2-
(CH2CH=CH2) units inside the dimer are observed at
higher field than those of the six terminal Si(CH3)2-
(CH2CH=CH2) moieties (see the Experimental Section).
This can be explained by a shielding of the C6H4 rings in-
side the dimer relative to the CD2Cl2 environment at the
surface (Figures 9b and 10b).
Figure 11. Temperature dependence of the SiCH3 proton signals of
12b in the temperature range of –80 to 25 °C (CD2Cl2, c = 12 mm).
facing arrow) between δ = 0.25 and 0.27 ppm increases with
rising temperature and decreasing concentration as allo-
cated to the monomer. On the other hand, the methyl sig-
nals with a downward-facing arrow have a relative integra-
tion that decreases with increasing temperature and
decreasing concentration and can be assigned to the dimer.
1
In the H NMR spectrum of 12b, only the dimeric spe-
cies exists in CD2Cl2 at –80 °C. To understand the mono-
1
mer formation from the appropriate dimer, a series of H
NMR spectra were measured between –80 and 25 °C in
steps of 5 °C. For simplicity, only the signals of the SiCH3
protons are shown in Figure 11. At –80 °C, two well-sepa-
rated signals in a ratio of 2:1 as expected for the dimer
are observed (Figure 9a). Coalescence is observed at –30 °C
(Figure 11). Close to this temperature, a new signal at lower
field for the monomer appeared. The integration ratio of
the CH3 signals (monomer versus dimer) increases with ris-
ing temperature (Figure 11), which can be explained by the
number of the dimeric species that have sufficient kinetic
energy to separate into the monomers with freely rotating –
C6H4–4-Si(CH3)2(CH2CH=CH2) units at higher tempera-
ture. As the monomer concentration increases, the relative
integration of this signal relative to the dimer increases con-
Figure 12. Comparison of the behavior of the methyl signals for
11a, 11b, 12b, and 12c [up arrow (Ȇ): integration increases (mono-
mer formation); down arrow (ȇ): integration decreases (dimer)
with increasing temperature and decreasing concentration].
tinuously (Figure 11, –30 to +25 °C).
A detailed analysis of the dimerization process for 11a,
1
The H NMR spectrum of 12b in nonaromatic solvents 11b, 12b, and 12c was achieved by thermodynamic studies
(e.g., CDCl3) features two signal categories, one of which (Supporting Information). As expected, these processes are
corresponds to the monomer and the other to the dimer enthalpy-favored and entropy-opposed. According to the
(Figure 9). Figure 12 shows the analysis of the signal behav- structure analysis of 10a in the solid state, the favorable
ior for the methyl groups in terms of its dependence on enthalpy is provided by π–π interactions between 1,4-phen-
temperature and concentration for 11a, 11b, 12b, and 12c. ylene units. This is also supported by the effect of the aro-
As can be seen, the intensity of the methyl signals (upward- matic solvent (i.e., [D6]benzene). Aromatic solvents reduce
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the appropriate π–π interactions,[28] which consequently re- (CH2CH=CH2)n units are observed at δ = –3.7 (n = 0), –4.2
duces the dimer formation (e.g., 12b; Figures 8 and 10a). (n = 1), –5.6 (n = 2), and –7.8 ppm (n = 3), respectively.
The free-energy ΔG values for the dimerization of 11a, 11b, The 29Si{1H} NMR spectra of 10a and 10b in CDCl3 at
12b, and 12c are, at –0.9 to –3.7 kcalmol–1, small. In terms 298 K show three characteristic Si signals: Si(C6H4)4 at δ ≈
of experimental error, the binding enthalpies of all four –14.7 ppm,[29] SiMe3–n(CH2CH=CH2)n at δ = –4.6 (10a) or
compounds are similar. However, the obtained values indi- –5.8 ppm (10b) and SiCl(C6H4)3 at δ = –12.8 ppm. The
cate that the binding enthalpy is slightly smaller for 11a and 29Si{1H} NMR spectra of 12c and 12d were measured in
11b than 12b and 12c (Table S5 in the Supporting Infor- CDCl3 at 55 and 50 °C, respectively, whereas the 29Si{1H}
mation). This can be explained by the presence of Si[C6H4– NMR spectra of 12b (20 °C), 11a (75 °C), and 11b (75 °C)
4-Si(CH3)3–n(CH2CH=CH2)n]3 groups in 11a and 11b, were determined in C6D6. For the core and inner silicon
which produce larger steric repulsion with intercalated arms atoms two signals (12b, 12c, and 12d) or one broad reso-
from the second molecule (Figure 9b) than the bromo sub- nance (11a, 11b) are found in the range of δ = –14.8 to
stituent present in 12b and 12c, respectively. Nevertheless, –13.3 ppm, whereas the terminal SiMe3–n(CH2CH=CH2)n
the smaller entropic loss for 11a and 11b with respect to units show resonances at δ ≈ –5.0 ppm for 12b and 11a, at
12b and 12c is responsible for the large increase in the di- δ ≈ –6.0 ppm for 12c and 11b, and at δ = –8.0 ppm for 12d.
merization constant of 11a and 11b (Table S5). The highly
ESI-TOF mass spectrometric measurements for 7 and 8
ordered monomers of 11a and 11b relative to the monomers showed the respective molecular ion peaks [M + K]+, when
of 12b and 12c are responsible for the small entropy loss doped with K+. Carbosilanes 10a, 11a, and 12b were
for the dimerization of 11a and 11b.
studied by MALDI-TOF mass spectrometry. For dendri-
Distinctive resonance signals are also observed for all or- mers 11a and 12b, the molecular ion peaks [M + Ag]+ in a
ganic groups in the 13C{1H} NMR spectra (see the Experi- nitroanthracene matrix (promoted by [AgOTf]) were ob-
mental Section). The 13C{1H} NMR spectra of the first- served. For 10a with an [AgOTf] promoter in a 2,5-dihy-
generation carbosilanes 10–12 show characteristic features droxybenzoic acid matrix, an ion peak at m/z = 2069.7 was
through some signal splitting and broadening (see above). found that can be assigned to [M + (HO)2C6H4CO2H –
Due to dimerization processes, the analysis was achieved Cl]+.
by 13C-DEPT-135 experiments and a comparison with the
spectral interpretation of the zeroth-generation compounds
7 and 8 (see the Experimental Section). However, it was not
Conclusion
possible to assign all of the carbon signals due to complica-
In this work, 1,4-phenylene was used as a building block
tion of broadening and splitting that resulted from dimer- in the convergent synthesis of a new class of zeroth- and
ization processes. For 11b and 12c, the signal splitting is, first-generation carbosilane dendrimers with dense shell
however, only observed for the SiCH3 and =CH2 units (see structures. The rigidity of the phenylene group provides
the Experimental Section). The 13C{1H} NMR spectro- these molecules with some advantages over well-known car-
scopic signals for the SiCH3 and SiCH2CH=CH2 groups of bosilane dendrimers with flexible aliphatic units (i.e., in
the first-generation carbosilanes show similar chemical homogeneous catalysis). The crystal structures of two den-
shifts to those observed for the zeroth-generation com- dritic carbosilanes (7b, 10a) illustrate that self-assembly of
pounds.
these molecules is controlled by C–H···πCC (πCC = C=C
All carbosilanes show for the hydrogen-bearing carbon double bond of the CH=CH2 groups) and π–π interactions
atoms of the terminal SiC6H4Si units resonances at δ = between C6H4 units that interact with each other exclusively
133.2 and 135.5 ppm, respectively. In 11a, 11b, and 12c, in a T-shaped fashion.
they are split into two signals that are explained by the mo-
The zeroth-generation dendrimer 7b shows 1D head-to-
nomeric and dimeric form present in solution (see above). head stacked columns that are aggregated further to form
Moreover, the chemical shifts of the outer CSi carbon a 3D network structure. On the other hand, the π–π interac-
atoms of the terminal SiC6H4Si units are directly affected tions observed for 10a in the solid state induce the forma-
by the substituent attached to Si. For example, the respec- tion of a unique self-complementary six-pointed star dimer,
tive carbon atom resonates at δ = 142.2 ppm in carbosilanes which is stabilized by four trimeric C6H4 aggregates to re-
that have three methyl groups attached to the silicon atom, sult in a total of eight π–π interactions. The calculated elec-
for example, 8a. This signal undergoes a high-field shift, trostatic potential surfaces rationalize the formation of
when the methyl groups are subsequently replaced by allyl C–H···πCC as well as π–π interactions. Also, the calculated
units (i.e., 8d; see the Experimental Section). For 11a and electrostatic potential indicated that the double bond is a
12b, this resonance is split into two signals due to dimeriza- better proton acceptor than the aromatic π system, which
tion processes. On the contrary, the inner CSi carbon atoms agrees with the observed solid-state self-assembly of 7b and
of the terminal SiC6H4Si units have a similar chemical shift 10a. Additionally, molecular mechanics calculations
at δ ≈ 134.4 ppm (see the Experimental Section).
(MM+), which were performed for the first-generation
In the 29Si{1H} NMR spectra of the zeroth-generation carbosilanes 10–12, propose similar self-complementary di-
compounds, a resonance signal is found at δ ≈ –14.5 ppm meric structures. The formation of dimers was proven by
for the inner silicon atom, which is in accordance with tet- dynamic NMR spectroscopic studies. Geometries closer to
raphenylsilanes.[29] The Si atoms of the terminal SiMe3–n
-
the globular shape enhance the dimerization, whereas the
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H7), 4.87 (m, 2 H, H7), 1.80 (dt, J = 8.08, 1.15 Hz, 4 H, H5), 0.29
(s, 3 H, H8) ppm. 13C{1H} NMR (CDCl3): δ = 135.6 (1 C4), 135.5
(2 C3), 133.7 (2 C6), 130.9 (2 C2), 124.1 (1 C1), 114.2 (2 C7), 21.4
(2 C5), –5.9 (1 C8) ppm. 29Si{1H} NMR (CDCl3): δ = –5.3 (1 Si1)
replacement of methyl by larger allyl units inhibits it due to
steric effects.
Experimental Section
ppm. IR (NaCl): ν = 3076, 3050, 2993, 2971, 2905, 2885, 1630 (m,
˜
C=C), 1254 (m, CH3 bending), 820 (s, Si–C), 803 (s, Si–C) cm–1.
C13H17BrSi (281.26): calcd. C 55.51, H 6.09; found C 55.45, H 6.08.
General: All reactions were carried out under nitrogen by using
standard Schlenk techniques. Solvents and reagents were purified
and dried by distillation. Diethyl ether, n-hexane, n-pentane, and
tetrahydrofuran were heated to reflux with sodium/benzophenone
ketyl, distilled, and saturated with nitrogen. The chlorosilanes were
distilled from magnesium prior to use, and TMEDA was heated to
reflux with calcium hydride, distilled, and saturated with nitrogen.
All other chemicals were purchased from commercial suppliers and
were used as received. IR spectra were recorded with a Perkin–
Elmer FTIR 1000 spectrometer as films between NaCl plates or as
KBr discs. 1H, 13C{1H}, and 29Si{1H} NMR spectra were recorded
with a Bruker Avance 250 spectrometer operating in the Fourier
Tetrakis{4-[diallyl(methyl)silyl]phenyl}silane (7c): nBuLi (2.5 m,
11.85 mmol, 4.74 mL, n-hexane) was added dropwise to 5b
(11.85 mmol, 3.33 g) dissolved in diethyl ether (60 mL) at –30 °C.
The reaction mixture was stirred below –10 °C for 30 min, and then
SiCl4 (8.50 mmol, 1.444 g, 0.98 mL) was added in a single portion.
The reaction mixture was stirred at this temperature for 30 min and
then at 25 °C for 24 h. Afterwards, it was quenched with water
(100 mL), and the resulting mixture was extracted with diethyl
ether (100 mL). The organic layer was dried with magnesium sulf-
ate, and all volatile materials were removed in an oil-pump vacuum.
The crude product was purified by silica gel column chromatog-
raphy (n-hexane/20% dichloromethane/n-hexane; column size:
4ϫ25 cm) to give 7c (0.850 g, 1.020 mmol, 34%) as a colorless so-
1
transform mode. H NMR spectra were recorded at 250.130 MHz
[internal standard relative to CDCl3 (δ = 7.26 ppm) and C6D6,
(7.16 ppm)]; 13C{1H} NMR spectra were recorded at 62.902 MHz
[internal standard relative to CDCl3 (δ = 77.0 ppm) and C6D6
(128.4 ppm)]; 29Si{1H} NMR spectra were recorded at 49.692 MHz
[external standard relative to SiMe4 (δ = 0.0 ppm)]. The assignment
of 13C{1H} and 29Si{1H} NMR spectroscopic signals is mainly
based on 13C-DEPT-135 spectra and 2D-correlation spectra [gradi-
ent with sensitivity-enhanced heteronuclear multiple quantum cor-
relation (gs-HMQC) for carbon and silicon and gradient with sen-
sitivity-enhanced heteronuclear multiple bond correlation (gs-
HMBC) for carbon]. ESI-TOF mass spectra were recorded with a
Mariner Biospectrometry Workstation 4.0 (Applied Biosystems)
with dichloromethane as solvent and potassium thiocyanate for
doping. MALDI-TOF mass spectra were performed with a Voy-
ager-DE PRO Biospectrometry Workstation (Applied Biosystems)
with nitroanthracene as matrix (11a and 12b) or 2,5-dihydroxy-
benzoic acid (10a) and silver triflate as promoter. C and H micro-
analyses were performed with a Foss Heraeus Vario EL analyzer.
Melting points of pure samples were measured with a Gallenkamp
MFB 595 010 equipment. Molecular mechanics calculations were
performed with the MM+ force field as implemented in Hyper-
Chem 4.02. DFT/B3LYP calculations: the atomic coordinates of 7b
and 10a were taken from the crystal structure. Gaussian 03 was
used for electronic energy calculations.[26]
1
lid. M.p. 237 °C. H NMR (CDCl3): δ = 7.53 [m, 8 H (H2) + 8 H
(H3)], 5.79 (ddt, J = 16.86, 10.18, 8.06 Hz, 8 H, H6), 4.90 (ddt, J
= 16.86, 2.76, 1.50 Hz, 8 H, H7), 4.87 (ddt, J = 10.10, 2.76, 1.50 Hz,
8 H, H7), 1.82 (dt, J = 8.06, 1.50 Hz, 16 H, H5), 0.29 (s, 12 H, H8)
ppm. 13C{1H} NMR (CDCl3): δ = 138.6 (4 C4), 135.5 (8 C2), 134.9
(4 C1), 134.1 (8 C6), 133.2 (8 C3), 113.9 (8 C7), 21.5 (8 C5), –5.9 (4
C8) ppm. 29Si{1H} NMR (CDCl3): δ = –14.8 (1 Si1), –5.8 (4 Si2)
ppm. IR (KBr): ν = 3070, 3047, 2989, 2967, 2907, 2878, 1630 (s,
˜
C=C), 1252 (m, CH3 bending), 1132, 820 (s, Si–C), 805 (s, Si–C)
cm–1. ESI-TOF: m/z (%) = 871.39 (10) [M + K]+. C52H68Si5
(833.52): calcd. C 74.93, H 8.22; found C 74.85, H 8.24.
1-Bromo-4-{tris[4-(trimethylsilyl)phenyl]silyl}benzene (8a): nBuLi
(2.5 m, 25.2 mmol, 10.08 mL, n-hexane) was added dropwise to 3a
(25.2 mmol, 2.310 g) dissolved in diethyl ether (100 mL) at –30 °C.
The reaction mixture was stirred below –10 °C for 30 min, then
TMEDA (37.8 mmol, 4.393 g, 5.71 mL) was added, and stirring
was continued for 5 min. A solution of 3d (8.0 mmol, 2.324 g) in
diethyl ether (40 mL) was added, and the reaction mixture was
stirred at –10 °C for 30 min and at 25 °C for 24 h. The reaction
solution was quenched with water (50 mL), and the resulting mix-
ture was extracted with diethyl ether (100 mL). The organic layer
was dried with magnesium sulfate, and all volatiles were removed
in an oil-pump vacuum. The crude product was purified by silica
gel column chromatography (n-hexane; column size: 4ϫ35 cm) to
afford 8a (3.286 g, 5.20 mmol, 65%) as a colorless solid. M.p.
Synthesis of 1-Br–C6H4–4-SiMe3–n(CH2CH=CH2)n (5a,[17] n = 1;
5b, n = 2; 5c,[18] n = 3)
General Method: Allylmagnesium bromide was prepared by slow
addition of allyl bromide (nϫ1.00 mol, nϫ120.98 g) dissolved in
diethyl ether (nϫ1000 mL) to a suspension of magnesium turnings
(nϫ1.50 mol, nϫ36.45 g) in diethyl ether (120 mL) for 8 h. After
2 h of stirring, the allylmagnesium bromide was transferred with a
cannula from the excess amount of magnesium. 1-Br–C6H4–4-
SiMe3–nCln dissolved in diethyl ether (200 mL) was added dropwise
to this solution over 2 h. The obtained reaction mixture was heated
to reflux for 5 h and then quenched with a 10% aqueous HCl solu-
tion (250 mL). The organic layer was extracted with water
(200 mL), dried with magnesium sulfate, and concentrated in an
oil-pump vacuum to give crude 1-Br–4-[SiMe3–n(CH2CH=CH2)n]-
C6H4. See the literature for spectroscopic and analytical data for
5a[17] and 5c.[18]
1
221 °C. H NMR (CDCl3): δ = 7.53 [s, 6 H (H6) + 6 H (H7)], 7.52
(dt, J = 8.5, 1.75 Hz, 2 H, H2), 7.44 (dt, J = 8.5, 1.75 Hz, 2 H, H3),
0.28 (s, 27 H, H9) ppm. 13C{1H} NMR (CDCl3): δ = 142.2 (3 C8),
138.0 (2 C3), 135.5 (6 C3), 133.9 (3 C5), 133.3 (1 C4), 132.7 (6 C7),
131.0 (2 C2), 124.6 (1 C1), –1.2 (9 C9) ppm. 29Si{1H} NMR
(CDCl ): δ = –14.6 (1 Si1), –3.9 (3 Si2) ppm. IR (KBr): ν = 3050,
˜
3
2996, 2954, 2892, 1249 (s, CH3 bending), 1133, 839 (s, Si–C) cm–1.
ESI-TOF: m/z (%) = 669.13 (80) [M + K]+. C33H43BrSi4 (631.94):
calcd. C 62.72, H 6.86; found C 62.48, H 7.09.
1-Bromo-4-{tris[4-(allyldimethylsilyl)phenyl]silyl}benzene (8b): The
same procedure as in the preparation of 8a was used for the synthe-
sis of 8b: nBuLi (2.5 m, 27.02 mmol, 10.80 mL, n-hexane), 5a
(27.02 mmol, 6.890 g) in diethyl ether (100 mL), TMEDA
(40.53 mmol, 4.710 g, 6.101 mL), and 3d (8.58 mmol, 2.492 g) in
diethyl ether (40 mL). The crude product was purified by silica gel
column chromatography (n-hexane; column size: 4ϫ35 cm) to af-
Data for 5b: Purified by fractional vacuum distillation. Yield
(93.50 g, 0.33 mol, 33%) of a colorless liquid. B.p. 96 °C/0.5 Torr.
1H NMR (CDCl3): δ = 7.50 (dt, J = 8.20, 1.84 Hz, 2 H, H2), 7.37
(dt, J = 8.20, 1.84 Hz, 2 H, H3), 5.75 (m, 2 H, H6), 4.89 (m, 2 H, ford 8b (3.580 g, 5.04 mmol, 59%) as a colorless solid. M.p. 102 °C.
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1H NMR (CDCl3): δ = 7.53 [s, 6 H (H6) + 6 H (H7)], 7.53 (dt, J
= 8.33, 1.74 Hz, 2 H, H2), 7.43 (dt, J = 8.33, 1.74 Hz, 2 H, H3),
5.79 (ddt, J = 16.65, 10.37, 8.06 Hz, 3 H, H10), 4.88 (ddt, J = 16.65,
2.69, 1.06 Hz, 3 H, H11), 4.86 (ddt, J = 10.37, 2.69, 1.06 Hz, 3 H,
H11), 1.77 (dt, J = 8.05, 1.06 Hz, 6 H, H9) 0.29 (s, 18 H, H12) ppm.
was then extracted with diethyl ether (100 mL). The organic layer
was dried with magnesium sulfate, and all volatiles were removed
in an oil-pump vacuum. The crude product was purified by dissolv-
ing it in dichloromethane/n-pentane of ratio (1:9, 50 mL) and cool-
ing it to –30 °C. Pure 10a could be isolated as a colorless solid
13C{1H} NMR (CDCl3): δ = 140.5 (3 C8), 137.9 (2 C3), 135.5 (6 (0.332 g, 0.170 mmol, 57%). M.p. 345 °C (decomp.). 1H NMR
C6), 134.5 (3 C10), 134.2 (3 C5), 133.1 (1 C4), 133.0 (6 C7), 131.1 (2
C2), 124.7 (1 C1), 113.5 (3 C11), 23.5 (3 C9), –3.6 (6 C12) ppm.
29Si{1H} NMR (CDCl3): δ = –14.6 (1 Si1), –4.6 (3 Si2) ppm. IR
(C6D6, 10 mm, 75 °C): δ = 7.72 [m, 6 H (H2) + 6 H (H3) + 18 H
(H7)], 7.45 (br. d, J = 7.50 Hz, 18 H, H6), 5.75 (m, 9 H, H10), 4.87
(m, 9 H, H11), 4.85 (m, 9 H, H11), 1.69 (br. d, J = 8.00 Hz, 18 H,
(KBr): ν = 3070, 3048, 2989, 2953, 2908, 2885, 1629 (m, C=C), H9), 0.21 (s, 54 H, H12) ppm. 13C{1H} NMR (CDCl3): δ = 140.2
˜
1249 (m, CH3 bending), 1133, 836 (s, Si–C), 802 (s, Si–C) cm–1.
ESI-TOF: m/z (%) = 749.19 (100) [M + K]+. C39H49BrSi4 (710.05):
calcd. C 65.97, H 6.96; found C 65.81, H 6.72.
(9 C8), 136.4 (3 C1), 136.1 (3 C4) 135.7 (6 C3), 135.5 (18 C6), 134.5
(9 C10), 134.4 (9 C5), 134.2 (6 C2), 132.9 (18 C7), 113.4 (9 C11), 23.5
(9 C9), –3.6 (18 C12) ppm. 29Si{1H} NMR (CDCl3): δ = –14.7 (3
Si2), –12.7 (1 Si1), –4.6 (9 Si3) ppm. IR (KBr): ν = 3070, 3050,
˜
1-Bromo-4-{tris[4-(diallylmethylsilyl)phenyl]silyl}benzene (8c): The
same procedure as in the preparation of 8a was used to prepare
8c: nBuLi (2.5 m, 40.5 mmol, 16.5 mL, n-hexane), 5b (40.46 mmol,
11.37 g) in diethyl ether (150 mL), TMEDA (60.75 mmol, 7.047 g,
9.13 mL), and 3d (12.85 mmol, 3.731 g) in diethyl ether (60 mL).
Silica gel column chromatography (n-hexane/20% dichlorometh-
ane/n-hexane; column size: 4ϫ45 cm) afforded 8c (7.150 g,
9.072 mmol, 71%) as a colorless solid. M.p. 99 °C. 1H NMR
(CDCl3): δ = 7.55 [s, 6 H (H6) + 6 H (H7)], 7.54 (dt, J = 8.18,
1.72 Hz, 2 H, H2), 7.44 (dt, J = 8.18, 1.72 Hz, 2 H, H3), 5.81 (ddt,
J = 16.86, 10.17, 8.05 Hz, 6 H, H10), 4.92 (ddt, J = 16.86, 2.22,
1.31 Hz, 6 H, H11), 4.90 (ddt, J = 10.17, 2.22, 1.31 Hz, 6 H, H11),
1.76 (dt, J = 8.05, 1.31 Hz, 12 H, H9), 0.32 (s, 9 H, H12) ppm.
13C{1H} NMR (CDCl3): δ = 138.9 (3 C8), 137.9 (2 C3), 135.4 (6
C6), 134.3 (3 C5), 134.0 (6 C10), 133.3 (6 H7), 133.0 (1 C4), 131.0
(2 C2), 124.8 (1 C1), 114.0 (6 C11), 21.5 (6 C9), –5.9 (3 C12) ppm.
29Si{1H} NMR (CDCl3): δ = –14.5 (1 Si1), –5.8 (3 Si2) ppm. IR
2996, 2955, 2908, 1629 (m, C=C), 1250 (m, CH3 bending), 1133,
837 (s, Si–C), 802 (s, Si–C) cm–1. MALDI-TOF MS: calcd. for
C124H152O4Si13 2069.9; found 2069.7. C117H147ClSi13 (1953.98):
calcd. C 71.92, H 7.58; found C 71.68, H 7.49.
Tris[4-(tris{4-[diallyl(methyl)silyl]phenyl}silyl)phenyl]silyl Chloride
(10b): The same procedure as discussed for the synthesis of 10a was
used in the preparation of 10b: tBuLi (1.7 m, 6.00 mmol, 3.53 mL,
n-pentane), 8c (3.00 mmol, 2.361 g) in diethyl ether (20 mL), THF
(170 mL), and SiCl4 in THF (0.0436 m, 0.75 mmol, 17.2 mL). The
obtained product was purified by dissolving it in a mixture of
dichloromethane/n-pentane in a ratio of 1:9 (100 mL) to give on
cooling to –30 °C pure 10b (0.808 g, 0.3690 mmol, 49%) as a color-
less solid. M.p. 340 °C (decomp). 1H NMR (C6D6, 9.5 mm, 75 °C):
δ = 7.72 [m, 6 H (H2) + 6 H (H3) + 18 H (H7)], 7.47 (m, 18 H,
H6), 5.75 (ddt, J = 17.32, 9.69, 7.83 Hz, 18 H, H10), 4.88 (ddt, J =
17.32, 2.25, 1.13 Hz, 18 H, H11), 4.85 (ddt, J = 9.69, 2.25, 1.13 Hz,
18 H, H11), 1.74 (dt, J = 7.83, 1.13 Hz, 18 H, H9), 0.23 (s, 27 H,
H12) ppm. 13C{1H} NMR (CDCl3): δ = 138.6 (9 C8), 136.4 (3 C1),
136.2 (3 C4), 135.7 (6 C3), 135.5 (18 C6), 134.6 (9 C5), 134.2 (6 C2),
134.1 (18 C10), 133.3 (18 C7), 113.7 (18 C11), 21.5 (18 C9), –5.9 (9
C12) ppm. 29Si{1H} NMR (CDCl3): δ = –14.7 (3 Si2), –12.8 (1 Si1),
(KBr): ν = 3070, 3047, 2989, 2970, 2907, 2878, 1630 (s, C=C), 1253
˜
(m, CH3 bending), 1132, 820 (s, Si–C), 808 (s, Si–C) cm–1. ESI-
TOF: m/z (%) = 827.23 (100) [M + K]+. C45H55BrSi4 (788.16):
calcd. C 68.57, H 7.03; found C 68.56, H 7.13.
–5.8 (9 Si3) ppm. IR (KBr): ν = 3070, 3052, 2996, 2967, 2908, 2878,
1-Bromo-4-{tris[4-(triallylsilyl)phenyl]silyl}benzene (8d): The same
procedure as in the preparation of 8a was used to prepare 8d:
nBuLi (2.5 m, 22.3 mmol, 8.95 mL, n-hexane), 5c (22.3 mmol,
6.84 g) in diethyl ether (100 mL), TMEDA (33.42 mmol, 3.883 g,
5 mL), and 3d (7.075 mmol, 2.055 g) in diethyl ether (40 mL). Silica
gel column chromatography (n-hexane/20% dichloromethane/n-
hexane; column size: 4ϫ35 cm) afforded 8d (2.350 g, 2.713 mmol,
38%) as a colorless solid. M.p. 69.0 °C. 1H NMR (CDCl3): δ =
7.53 [s, 6 H (H6) + 6 H (H7)], 7.53 (dt, J = 8.42, 1.82 Hz, 2 H, H2),
7.41 (dt, J = 8.42, 1.82 Hz, 2 H, H3), 5.81 (ddt, J = 16.93, 10.09,
8.02 Hz, 9 H, H10), 4.94 (ddt, J = 16.93, 2.81, 1.16 Hz, 9 H, H11),
4.92 (ddt, J = 10.09, 2.81, 1.16 Hz, 9 H, H11), 1.88 (dt, J = 8.02,
1.16 Hz, 18 H, H9) ppm. 13C{1H} NMR (CDCl3): δ = 137.9 (2 C3),
137.3 (3 C8), 135.4 (6 C6), 134.5 (3 C5), 133.7 (9 C10), 133.6 (6 C7),
132.9 (1 C4), 131.1 (2 C2), 124.8 (1 C1), 114.4 (9 C11), 19.5 (9 C9)
ppm. 29Si{1H} NMR (CDCl3): δ = –14.6 (1 Si1), –8.0 (3 Si2) ppm.
˜
1630 (m, C=C), 1252 (m, CH3 bending), 1133, 820 (s, Si–C), 805
(s, Si–C) cm–1. C135H165ClSi13 (2188.32): calcd. C 74.10, H 7.60;
found C 73.96, H 7.51.
Tetrakis(4-{tris[4-(allyldimethylsilyl)phenyl]silyl}phenyl)silane (11a):
tBuLi (1.7 m, 16.2 mmol, 9.53 mL, n-pentane) was added dropwise
to 8b (8.1 mmol, 5.75 g) dissolved in diethyl ether (40 mL) at
–76 °C. The reaction solution was stirred at this temperature for
1 h, then TMEDA (8.5 mmol, 1.0 g, 1.3 mL) was added in a single
portion, and stirring was continued for 5 min. SiCl4 (2.0 mmol,
0.34 g, 0.23 mL) dissolved in THF (120 mL) was added dropwise,
and stirring was continued at –20 °C for 20 min and at 25 °C for
24 h. The reaction mixture was then treated with water (100 mL),
and the resulting mixture was extracted with diethyl ether
(150 mL). The organic layer was dried with magnesium sulfate, and
all volatile materials were removed in an oil-pump vacuum. The
crude product was purified by silica gel column chromatography
(n-hexane/20% dichloromethane/n-hexane; column size: 4ϫ45 cm)
to give 11a (2.1 g, 0.824 mmol, 41%) as a colorless solid. M.p.
IR (KBr): ν = 3070, 3047, 2996, 2966, 2908, 2878, 1630 (s, C=C),
˜
1132, 794 (m, Si–C) cm–1. ESI-TOF: m/z (%) = 905.24 (22) [M +
K]+. C51H61BrSi4 (866.28): calcd. C 70.71, H 7.10; found C 70.34,
H 6.98.
1
380 °C (decomp.). H NMR (C6D6, 75 °C, 7.8 mm): δ = 7.90–7.18
Tris(4-{tris[4-(allyldimethylsilyl)phenyl]silyl}phenyl)silyl
Chloride
[m, 8 H (H2) + 8 H (H3) + 24 H (H6) + 24 H (H7)], 5.74 (m, 12
H, H10), 4.86 (br. d, J = 17.00 Hz, 12 H, H11), 4.85 (br. d, J =
10.00 Hz, 12 H, H11), 1.69 (br. d, J = 7.75 Hz, 24 H, H9), 0.21 (br.
s, 72 H, H12) ppm. 13C{1H} NMR (CDCl3, 21.6 mm, 25 °C): δ =
140.3 (C8), 140.2 (C8), 139.6 (12 C5), 135.6 (C6), 135.5 (C6), 135.2
(4 C4), 134.7 (4 C1), 134.6 (8 C2), 134.3 (12 C10), 132.9 (C7), 132.8
(C7), 132.7 (8 C3), 113.5 (C11), 113.4 (C11), 23.6 (C9), 23.5 (C9),
–3.5 (C12), –3.6 (C12) ppm. 29Si{1H} NMR (C6D6, 75 °C, 10 mm):
(10a): tBuLi (1.7 m, 2.00 mmol, 1.18 mL, n-pentane) was added
dropwise to 8b (1.00 mmol, 0.710 g) dissolved in diethyl ether
(7 mL) at –76 °C. The reaction solution was stirred at this tempera-
ture for 1 h and then diluted with THF (60 mL). SiCl4 dissolved in
THF (0.0436 m, 0.30 mmol, 6.9 mL) was added dropwise, and stir-
ring was continued at this temperature for 20 min and then at 25 °C
for 24 h. The reaction mixture was treated with water (50 mL) and
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FULL PAPER
δ = –14.3 (br., 1 Si1 & 4 Si2), –5.0 (12 Si3) ppm. IR (KBr disc): ν
C123H151AgBrSi13 2181.7; found 2181.9. C123H151BrSi13 (2074.53):
calcd. C 71.21, H 7.34; found C 70.94, H 7.24.
˜
= 3070, 3050, 2996, 2955, 2909, 1629 (m, C=C), 1250 (m, CH3
bending), 1132, 836 (m, Si–C), 802 (m, Si–C) cm–1. MALDI-TOF
MS: calcd. for C156H196AgSi17 2656.1; found 2655.7. C156H196Si17
(2548.68): calcd. C 73.52, H 7.75; found C 73.83, H 7.80.
1-Bromo-4-{tris[4-(tris{4-[diallyl(methyl)silyl]phenyl}silyl)phenyl]-
silyl}benzene (12c): The same procedure as discussed for the prepa-
ration of 12b was used in the synthesis of 12c: tBuLi (1.7 m,
7.134 mmol, 4.2 mL, n-pentane), 8c (3.567 mmol, 2.81 g) in diethyl
ether (25 mL), and 3d (1.133 mmol, 0.33 g) in THF (85 mL). Silica
gel column chromatography (n-hexane/20% dichloromethane/n-
hexane; column size: 4ϫ25 cm) afforded 12c (0.69 g, 0.3 mmol,
26%) as a colorless solid. M.p. 355 °C (decomp.). 1H NMR (C6D6,
12 mm, 75 °C): δ = 7.73 (br. d, J = 7.52 Hz, 6 H, H7), 7.72 (br. d,
J = 7.90 Hz, 18 H, H11), 7.66 (br. d, J = 7.52 Hz, 6 H, H6), 7.46
(br. d, J = 7.90 Hz, 18 H, H10), 7.35 (br. d, J = 8.22 Hz, 2 H, H2),
7.24 (br. d, J = 8.22 Hz, 2 H, H3), 5.74 (ddt, J = 16.91, 10.12,
7.94 Hz, 18 H, H14), 4.87 (ddt, J = 16.91, 1.95, 1.10 Hz, 18 H, H15),
4.85 (ddt, J = 10.12, 1.95, 1.10 Hz, 18 H, H15), 1.74 (dt, J = 7.95,
1.10 Hz, 18 H, H13), 0.23 (s, 27 H, H16) ppm. 13C{1H} NMR
(CDCl3, 22 mm, 25 °C): δ = 138.6 (9 C12), 138.3 (3 C8), 138.0 (2
C3), 136.9 (1 C4), 135.7 (6 C6), 135.6 (C10), 135.5 (C10), 134.6 (9
C9), 134.3 (3 C5), 134.1 (18 C14), 133.8 (6 C7), 133.3 (C11), 133.1
(C11), 131.1 (2 C2), 124.9 (C1), 124.8 (C1), 114.0 (C15), 113.9 (C15),
21.5 (18 C13), –5.7 (C16), –5.9 (C16) ppm. 29Si{1H} NMR (CDCl3,
55 °C): δ = –14.8 (3 Si2), –13.4 (1 Si1), –5.9 (9 Si3) ppm. IR (KBr):
Tetrakis[4-(tris{4-[diallyl(methyl)silyl]phenyl}silyl)phenyl]silane (11b):
tBuLi (1.7 m, 2.64 mmol, 1.55 mL, n-pentane) was added dropwise
to 8c (1.32 mmol, 1.040 g) dissolved in diethyl ether (7 mL) at
–76 °C. The reaction solution was stirred at this temperature for
1 h, then TMEDA (1.98 mmol, 0.230 g, 0.30 mL) was added in a
single portion, and stirring was continued for 5 min. The resulting
reaction mixture was diluted with THF (15 mL), afterwards SiCl4
in THF (43.6 mm, 0.30 mmol, 6.88 mL) was added, and stirring
was continued at this temperature for 20 min and at 25 °C for 24 h.
The reaction mixture was quenched with water (50 mL) and was
then extracted with diethyl ether (100 mL). The organic layer was
dried with magnesium sulfate, and all volatiles were removed in
an oil-pump vacuum. The crude product was purified by column
chromatography (n-hexane/20% dichloromethane/n-hexane; col-
umn size: 4ϫ25 cm) to give 11b (0.173 g, 0.061 mmol, 20%) as
1
a colorless solid. M.p. 375 °C (decomp.). H NMR (C6D6, 75 °C,
3.8 mm): δ = 7.73 [m, 8 H (H2) + 8 H (H3)], 7.71 (br. d, J = 7.63 Hz,
24 H, H7), 7.45 (br. d, J = 7.63 Hz, 24 H, H6), 5.75 (m, 24 H, H10),
4.88 (br. d, J = 17.63 Hz, 24 H, H11), 4.86 (br. d, J = 9.63 Hz, 24
H, H11), 1.74 (br. d, J = 8.00 Hz, 48 H, H9), 0.23 (br. s, 36 H, H12)
ppm. 13C{1H} NMR (CDCl3, 19.2 mm): δ = 138.6 (12 C8), 138.2
(12 C5), 135.6 (C6), 135.5 (C6), 134.7 (4 C4), 134.4 (4 C1), 134.1 (24
C10),133.8 (8 C2), 133.3 (C7), 133.2 (C7), 133.1 (8 C3), 114.0 (C11),
113.9 (C11), 21.5 (24 C9), –5.8 (C12), –5.9 (C12) ppm. 29Si{1H}
NMR (C6D6, 75 °C, 8.7 mm): δ = –14.4 (br., 1 Si1 and 4 Si2), –6.0
ν = 3070, 3051, 2996, 2967, 2908, 2878, 1630 (m, C=C), 1252 (m,
˜
CH3 bending), 1133, 820 (s, Si–C), 805 (s, Si–C) cm– 1
.
C141H169BrSi13 (2308.87): calcd. C 73.35, H 7.38; found C 72.93,
H 7.33.
1-Bromo-4-[tris(4-{tris-[4-(triallylsilyl)phenyl]silyl}phenyl)silyl]-
benzene (12d): The same procedure as applied in the synthesis of
12b was used in the preparation of 12d: tBuLi (1.7 m, 3.96 mmol,
2.33 mL, n-pentane), 8d (1.982 mmol, 1.71 g) in diethyl ether
(20 mL), and 3d (0.654 mmol, 0.190 g) in THF (60 mL). Silica gel
column chromatography (n-hexane/20% dichloromethane/n-hex-
ane; column size: 2ϫ25 cm) to give 12d (0.140 g, 0.0550 mmol,
8.4%) as a colorless solid. M.p. 350 °C (decomp.). 1H NMR (C6D6,
55 °C, 10 mm): δ = 7.73 (br. d, J = 8.0 Hz, 18 H, H11), 7.72 (br. d,
J = 7.81 Hz, 6 H, H7), 7.62 (br. d, J = 7.81 Hz, 6 H, H6), 7.48 (br.
d, J = 8.0 Hz, 18 H, H10), 7.32 (br. d, J = 8.38 Hz, 2 H, H2), 7.22
(br. d, J = 8.38 Hz, 2 H, H3), 5.76 (ddt, J = 16.92, 10.07, 7.98 Hz,
27 H, H14), 4.91 (ddt, J = 16.92, 2.02, 1.16 Hz, 27 H, H15), 4.87
(ddt, J = 10.07, 2.02, 1.16 Hz, 27 H, H15), 1.79 (dt, J = 7.98,
1.16 Hz, 54 H, H13) ppm. 13C{1H} NMR (CDCl3, 25 °C, 30 mm):
δ = 138.0 (2 C3), 137.1 (9 C12), 135.8 (6 C6), 135.6 (6 C7), 135.5 (18
C10), 134.8 (9 C9), 134.4 (3 C8), 133.7 (27 C14), 133.6 (18 C11), 132.9
(1 C4), 132.7 (3 C5), 131.1 (2 C2), 124.9 (1 C1), 114.4 (27 C15), 19.5
(27 C13) ppm. 29Si{1H} NMR (CDCl3, 50 °C, 20 mm): δ = –14.7 (3
(12 Si3) ppm. IR (KBr): ν = 3070, 3052, 2996, 2967, 2915, 2878,
˜
1630 (m, C=C), 1252 (m, CH3 bending), 1132, 817 (s, Si–C), 806 (s,
Si–C) cm–1. C180H220Si17 (2861.13): calcd. C 75.56, H 7.75; found C
75.20, H 8.02.
1-Bromo-4-[tris(4-{tris[4-(allyldimethylsilyl)phenyl]silyl}phenyl)-
silyl]benzene (12b): tBuLi (1.7 m, 6.866 mmol, 4.04 mL, n-pentane)
was added dropwise to 8b (3.433 mmol, 2.44 g) in diethyl ether
(25 mL) at –76 °C. The reaction mixture was stirred at this tem-
perature for 1 h. Compound 3d (1.133 mmol, 0.33 g) dissolved in
THF (85 mL) was then added dropwise, and stirring was continued
at –20 °C for 20 min and then at 25 °C for 24 h. The reaction mix-
ture was afterwards treated with water (50 mL), and the resulting
mixture was extracted with diethyl ether (100 mL). The organic
layer was dried with magnesium sulfate, and all volatile materials
were removed in an oil-pump vacuum. The crude product was puri-
fied by silica gel column chromatography (n-hexane/20% dichloro-
methane/n-hexane; column size: 4ϫ25 cm) to give 12b (0.545 g,
Si2), –14.3 (1 Si1), –8.0 (9 Si3) ppm. IR (KBr): ν = 3070, 3048,
˜
1
0.263 mmol, 23%) as a colorless solid. M.p. 360 °C (decomp.). H
2996, 2967, 2915, 2878, 1630 (m, C=C), 1133, 798.2 (m, Si–C) cm–1.
C157H187BrSi13 (2543.20): calcd. C 75.09, H 7.41; found C 75.24,
H 7.13.
NMR (C6D6, 12 mm, 75 °C): δ = 7.75 (br. d, J = 7.64 Hz, 6 H, H7),
7.72 (br. d, J = 7.36 Hz, 18 H, H11), 7.67 (br. d, J = 7.64 Hz, 6 H,
H6), 7.45 (br. d, J = 7.36 Hz, 18 H, H10), 7.37 (br. d, J = 7.78 Hz,
2 H, H2), 7.25 (br. d, J = 7.78 Hz, 2 H, H2), 5.75 (ddt, J = 16.66, Crystal Structure Determination: Crystal data for 7b and 10a are
10.25, 7.99 Hz, 9 H, H14), 4.86 (br. d, J = 16.66 Hz, 9 H, H15), 4.85
presented in Table S1 (Supporting Information). The data for 7b
(br. d, J = 10.25 Hz, 9 H, H15), 1.69 (br. d, J = 7.99 Hz, 18 H, were collected with a Bruker Smart CCD 1k diffractometer at
H13), 0.31 (s, 54 H, H16) ppm. 13C{1H} NMR (CDCl3, 30 mm, 183 K and those of 10a with a Stoe IPDS-II/2T diffractometer,
25 °C): δ = 140.3 (C12), 139.7 (C12), 138.0 (2 C3), 136.0 (3 C8), 135.7 both with graphite-monochromated Mo-Kα (λ = 0.71073 Å) radia-
(6 C6), 135.5 (18 C10), 135.3 (C4), 134.6 (C9), 134.5 (9 C14), 134.4 tion. The structures were solved by direct methods using SHELXS-
(C9), 134.3 (C9), 134.2 (C5), 134.0 (C5), 132.9 (18 C11), 132.7 (6 C7),
131.1 (2 C2), 124.8 (1 C1), 113.4 (9 C15), 23.5 (9 C13), –3.6 (18 C16)
97[30] and refined by full-matrix least-squares procedures on F2
using SHELXL-97.[31] All non-hydrogen atoms were refined aniso-
ppm. 29Si{1H} NMR (C6D6, 30 mm, 25 °C): δ = –14.0 (3 Si2), –13.7 tropically, and a riding model was employed in the refinement of
(1 Si1), –4.9 (9 Si3) ppm. IR (KBr): ν = 3070, 3050, 2996, 2956,
the hydrogen-atom positions. In the case of 7b, the atoms C21/C22,
C32/C33, C54/C55, C87/C88, C109/C110, and C95/C96/C98/C99
were refined disordered on two positions with occupation factors
˜
2908, 2885, 1629 (m, C=C), 1250 (m, CH3 bending), 1133, 836 (s,
Si–C), 802 (s, Si–C) cm–1. MALDI-TOF MS: m/z calcd. for
Eur. J. Inorg. Chem. 2013, 2368–2381
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FULL PAPER
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of 0.71, 0.53, 0.70, 0.51, 0.70, and 0.66, respectively. In the case of
10a, the asymmetric unit comprises an n-pentane molecule with an
occupation factor of 0.5. The occupation factor was fixed after pre-
refinements gave values close to 0.5. The atoms C115–C117 were
refined disordered on two positions with an occupation factor of
0.47. During the measurements, although performed at 100 K, a
significant decrease in the intensities of the standard reflections was
observed. Together with this effect, a number of additional reflec-
tions appeared that did not belong to the unit cell mentioned here.
The same effect was observed when measuring other crystals. It
was thus concluded that the specific compound and/or its crystals
do show a phase transition at approximately 100 K or that the n-
pentane as packing solvent “evaporates” slowly, but thereby perma-
nently destroying the single-crystal property. The measurement was
thus optimized in the sense that the largest suitable crystal was
selected, and exposure times were set to minimum requirements.
Despite this, the completeness reached only 87% to θ = 24.4°.
CCDC-905944 (7b) and -905943 (10a) contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
[4]
Supporting Information (see footnote on the first page of this arti-
cle): Atom numbering scheme, crystal data and structure refinemnt
parameters, tables concerning hydrogen bonding interactions.
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Acknowledgments
We gratefully acknowledge generous financial support from the
Deutsche Forschungsgemeinschaft and the Fonds der Chemischen
Industrie.
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Published Online: February 28, 2013
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