Synthesis of carbosilane dendrimers based on tetrakis(phenylethynyl)silane

Article abstract of DOI:10.1016/S0022-328X(98)00562-2

Carbosilane dendrimers of first to third generation were synthesized, using alkynylation/hydrosilation cycles with lithium phenylacetylide and dichloromethylsilane as building blocks and tetrakis(phenylethynyl)silane as a core molecule. The analysis of th

Full text of DOI:10.1016/S0022-328X(98)00562-2

Journal of Organometallic Chemistry 563 (1998) 43–51
Synthesis of carbosilane dendrimers based on
tetrakis(phenylethynyl)silane
Chungkyun Kim *, Moon Kim
Department of Chemistry, Dong-A Uni6ersity, Pusan, 604-714, South Korea
Received 26 November 1997; received in revised form 17 March 1998
Abstract
Carbosilane dendrimers of first to third generation were synthesized, using alkynylation/hydrosilation cycles with lithium
phenylacetylide and dichloromethylsilane as building blocks and tetrakis(phenylethynyl)silane as a core molecule. The analysis of
1
13
the H- and C-NMR, MALDI mass spectra and elemental analysis made it possible to obtain pure and unified dendrimers.
1998 Elsevier Science S.A. All rights reserved.
©
1. Introduction
with hexaallylethylenedisilane and siloxane tetramer
1,15]. The repeating of these cycles with hexaal-
[
From the beginning, due to their intriguing
lylethylenedisilane as a core molecule and dichlomethyl-
silane and allylmagnesium bromide as building blocks
resulted in G3 with 48 allylic end groups in excellent
yields ([15]b). The dendritic generations with alkynyl
end groups with organic rest have been synthesized [16].
In this paper, we wish to report our results on the
synthesis and identification of dendritic macromolecules
supramolecular properties, dendritic macromolecules
have received increasing attention [1,2]. Since the spear-
head reports on dendritic macromolecules by V o¨ gtle [3],
Denkewalter [4], Newkome [5] and Tomalia et al. [6]
have developed several synthetic pathways. The appli-
cation of dendrimers includes nanoscale catalysts, mi-
celle mimics, immunodiagnostics, agents for delivering
drugs, chemical sensors, high performance polymers
and liquid crystals [7–12].
The first preparation of the carbosilane dendrimers
introduced by van der Made was performed by repeti-
tive alkenylation–hydrosilation cycles using allylmag-
nesium bromide and trichlorosilane as building blocks
and tetraallylsilane as a core molecule [13]. Seyferth
and coworkers prepared the carbosilane dendrimers
that contain ethynyl-groups on their periphery ([14]a
and b). Meanwhile, numerous reports have also ap-
peared on the syntheses and properties of dendritic
carbosilane ([14]c and d). In the previous paper, we
described a preparation of carbosilane dendrimers
based on quantitative hydrosilation–alkenylation cycles
based on tetrakis(phenylethynyl)silane as
a core
molecule and bis(phenylethynyl)methylsilyl groups as a
repeat unit on its periphery. We reported the regioselec-
tive addition of hydrosilane to phenylalkynyl groups in
the presence of Pt/C as a heterogeneous catalyst [1,15].
Identification of prepared silane dendrimers can be
1
13
obtained by H- and C-NMR, MALDI mass, UV
spectroscopic attachments as well as elemental analysis.
2. Results and discussion
The synthesis of carbosilane dendrimers (G0–G3 and
G1P–G3P) is based on the complete hydrosilation and
alkynylation of alkynylsilane and chlorosilane as shown
in Scheme 1. The hyperbranched dendrimers, based on
tetrakis(phenylethynyl)silane ((PhCꢀC) Si; N =4) as a
*
Corresponding author. Fax: +82 51 2007259; e-mail: ck-
4
c
kim@.seunghak.donga.ac.kr
core molecule with bis(phenylethynyl)methylsilyl end
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00562-2

44
C. Kim, M. Kim / Journal of Organometallic Chemistry 563 (1998) 43–51
Scheme 1. Synthetic way of dendritic carbosilane.
groups as a building block, to G3 (l=2, N =2) have
carbon) with quantitative yields. The silylated genera-
b
been synthesized by the use of hydrosilation-alkynyla-
tion sequences Scheme 2. The dichloromethylsilyl-
capped dendrimers (G1P–G3P) were produced by the
hydrosilation of alkynyl groups in Gn-1 generation with
dichloromethylsilane in the presence of a platinum cata-
lyst [17] (Pt/C; 10% platinum content on activated
tions (Cl MeSi-: GnP) were converted to the corre-
2
sponding dendritic carbosilanes containing pheny-
lethynyl groups by the treatment with lithium pheny-
lacetylide in THF. Carbosilane dendrimers with 8 (G1),
16 (G2), and 32 (G3 and G4P–1PA) alkynyl end
groups were obtained by using this synthetic approach.

C. Kim, M. Kim / Journal of Organometallic Chemistry 563 (1998) 43–51
45
Table 1
NMR spectroscopic data of Gn type dendrimers
Compounds
MeSi
CꢁCH
CꢀC
Ph (ppm)
6.97–7.05, 7.26–7.30
1
1
G0
H
C
—
—
—
—
—
3
86.03
06.57
128.22 (m), 129.45 (o)
132.49 (p), 122.01 (q)
1
1
1
G1
H
C
0.31 (s, 12H)
−0.93
6.10 (s, 4H)
147.14
56.18
7.19–7.25, 7.39–7.40
127.82 (o, G0),
128.14 (o, G1)
3
89.47
107.21
1
1
1
1
1
1
1
28.30 (m, G0),
32.01 (m, G1)
26.61 (p, G0),
28.69 (p, G1)
43.25 (q, G0),
22.81 (q, G1)
G2
1H
−0.91
5.53
(s, 4H, G1)
6.42
(s, 8H, G2)
157.47 (G1)
160.82 (G1)
07.43 (G2)
26.37 (G2)
7.30–7.40 (m, 20H, G0)
7.11–7.25 (m, 80H, G2)
6.86–7.07(m, 80H, G2)
(
s, 12H, G1)
.32
s, 24H, G2)
0
(
13C
−3.08 (G1)
0.91 (G2)
89.42
107.35
145.69 (m, G0),142.92
(o, G0), 144.97 (p, G0),
144.57 (q, G0), 128.05
(o, G1), 128.16 (o, G2),
−
1
1
1
(
1
26.37 (p, G1), 127.87
p, G2), 127.59 (q, G1),
22.72 (q, G2)
G3
1H
−0.92
5.78
6.68–7.50
(
s, 12H, G1)
.35
s, 24H, G2)
.29
(s, 4H, G1)
6.40
(s, 8H, G2)
6.52
(m, 300H, G1–G3)
0
(
0
(
48H, G3)
−1.96 (G1)
(s, 16H, G3)
107.39 (G3)
89.18 (G3)
13C
89.32
132.01 (m, G3), 128.17
−
−
3.28 (G2)
0.91 (G3)
107.48
(o, G3), 127.56 (p, G3)
122.62 (q, G3), 89.32,
1
1
1
1
1
29.00, 145.56, 107.39,
42.64, 157.71, 126.35,
42.77, 157.99, 128.01,
44.51, 161.07, 128.80,
45.25, 162.96
G4P–1PA
1H
−0.97
s, 12H, G1)
0.75
s, 72H, G2–G3)
.12
s, 192H, G4)
5.36
(s, 4H, G1)
5.63
(s, 8H, G2)
6.06
(s, 16H, G3)
6.61–7.36 (m, G0–G4)
(
−
(
0
(
6
.14
(
s, 32H, G4)
13C
−1.57 (G4)
2.63 (G1–G3)
92.51
131.83 (m, G4), 128.20
(o, G4), 127.63 (p, G4),
123.13 (q, G4),
−
(G4)
06.69
G4)
1
(
77.20, 132.11, 144.62,
1
1
1
25.99, 142.80, 145.06,
28.47, 143.71, 161.29,
28.85, 143.93
The subsequent generation G4P with 64 Si–Cl groups
did not make a unified form by the hydrosilation step.
But, the formation of G4P–1Cl by the reaction of G3
spectroscopic views. This result means that dendritic
growth has been limited [1,15]. Eventually, synthesis of
G4P with 64 Si–Cl bonds will result in surface satura-
tion, which will prevent further growth from all branch
and HSiMe Cl was unified as announced by NMR
2

46
C. Kim, M. Kim / Journal of Organometallic Chemistry 563 (1998) 43–51
each alkynylation step. Carbosilane dendrimers with 8
G1), 16 (G2), 32 (G3), and 32 (G4P–1PA)
(
phenylethynyl end groups were obtained using this
synthetic approach.
The prepared dendrimers were structurally character-
1
13
ized by H- and C-NMR spectroscopy (Tables 1 and
, and Fig. 1), elemental analyses (Table 3), MALDI
mass (Fig. 3), IR (Table 4), and UV–VIS spectroscopy
Table 5 and Fig. 2). Firstly, both reactions to G4P–
PA generations seem to be free of side reaction by the
2
(
1
1
13
1
NMR spectroscopic observations ( H and C). The H-
and C-NMR spectroscopic analyses of G0–G3 as well
13
as G0P–G3P in CDCl show perfect building of den-
3
drimers. The NMR spectra reflect the transformation
from Gn-type dendrimers with phenylethynyl end
groups to GnP-type dendrimers with SiMeCl2 end
1
groups and the transition from GnP to Gn. By H-
NMR spectroscopic attachment, the formation of
alkenyl bonds (ꢁC–H) showed 6.10 ppm (for G1), 5.53
and 6.42 ppm (G2), 5.78, 6.40 and 6.52 ppm (G3) with
single signals consistent with 1:2 for G2 and 1:2:4 (G3)
of area ratio. The formation of methylsilyl groups
(MeSi) showed 0.31 ppm (for G1), −0.91 and 0.32
ppm (G2), −0.92, −0.35 and 0.29 ppm (G3) with
single signals consistent with 1:2 for G2 and 1:2:4 (G3)
Scheme 2. Planar view of third generation (G3) with 32phenylethynyl
groups (N =4, N =2 and M =7331).
c
b
w
points so that the dendrimer will no longer be unified.
But the other synthetic pathways of lower generations
(
G0–G3 and G1P–G3P and G4P–1Cl) produced
13
quantitative and unified dendrimers.
Purification of the dendrimers was performed by
chromatography with a freshly prepared column after
of area ratio. The C-NMR spectra of Gn-type den-
drimers show resonance at −0.93 ppm (G1), −3.08
and −0.91 ppm (G2), and −1.96, −3.28 and −0.91
Table 2
NMR spectroscopic data of GnP-type dendrimers
Compounds
MeSi
CꢁCH
Ph
1
1
G1P
H
C
0.62
4.53
5.89
146.48
56.56
6.94–6.99, 7.29–7.32
128.49 (o), 127.97 (p), 128.14 (m)
140.26 (q)
3
1
G2P
1H
−0.39 (G1)
6.16 (G1)
6.87 (G2)
126.65 (G1)
129.00 (G1)
56.84 (G2P)
57.80 (G2P)
7.22–7.27 (G1)
7.67–7.77 (G2P)
128.03 (o, G1), 146.33 (o, G2P),
127.80 (p, G1), 144.07 (p, G2P)
127.3 (m, G1), 139.92 (m, G2P),
125.25 (q, G1), 144.26 (q, G2P)
1
.13 (G2P)
−3.32 (G1)
.44 (G2P)
13C
4
1
1
G3P
1H
−0.82 (G1)
0.32 (G2)
.62 (G3P)
−2.03 (G1)
3.49 (G2)
.49 (G3)
158.38 (G1)
5.89 (G2)
6.38 (G3P)
139.92, 143.69
145.34, 146.15
157.28, 161.63
6.57–6.77, 7.03–7.30 (G1–G3P)
−
0
13C
128.05 (o, G3P), 127.85 (p, G3P)
129.41 (m, G3P), 129.04 (q, G3P)
127.66, 126.35, 125.29
−
4
G4P–1Cl
1H
−0.90 (G1)
0.72 (G2–G3)
5.30 (G1)
5.44 (G2)
6.07 (G3)
6.16–7.25 (G1–G4P)
−
0.29 (G4P)
6
.16(G4P)
13C
−2.77
137.86, 142.28
142.45, 143.65,
161.05
125.29, 126.04, 126.55, 127.71,
128.21, 128.34, 129.04
(
G1–G3)
.45(G4P)
1

C. Kim, M. Kim / Journal of Organometallic Chemistry 563 (1998) 43–51
47
Fig. 1. 13C-NMR spectroscopic view of G0–G3 measured in CDCl3.
ppm (G3) attributed to terminal MeSi groups, reso-
nance with 107–160 ppm, due to alkenyl carbon
environ 7.25 ppm for protons of characteristic phenyl
group for Gn and GnP molecules (while the forma-
tion of GnP makes the resonance attributed to Gn
disappear: Tables 1 and 2).
UV-VIS spectroscopy is used to examine the solu-
tion of Gn-type dendrimers (G0–G3 and G4P–1PA)
in toluene. The spectra of given compounds are simi-
lar and consist of a broad band with a maximum at
a wave length (umax) of about 288 nm. The molar
(
1
CꢁCH), and resonance with 86.03–89.40 ppm and
06.5–107.0 ppm, introducing alkynyl triple bonds on
1
the periphery of each Gn dendrimer. The H-NMR
spectra of GnP type dendrimers reflect the same evi-
dence of Gn generations, which show three main sig-
nals at the environs of zero ppm for MeSi groups,
5.50–6.50 ppm for CꢁC–H groups, and at multiple

48
C. Kim, M. Kim / Journal of Organometallic Chemistry 563 (1998) 43–51
Table 3
Table 4
Elemental analyses
FT–IR spectroscopic data
−
1
Com-
pounds
Formula
C (found/calcd.) H (found/calcd.)
Compounds
IRwCꢁC
wCꢁC cm
G0
G1
G2
G3
2163.5
2158.8
2157.9
2157.8
2157.4
G0
G1
G2
C32H20Si
C100H76Si5 83.85/84.70
C236H188Si13 83.29/83.64
88.00/88.85
4.64/4.66
5.58/5.40
5.78/5.57
1594.4
1594.7
1595.0
1596.3
G4P–1PA
G3
C508H412Si29 83.16/83.23
5.81/5.66
6.43/6.46
G4P–1PA C828H796Si61 78.75/79.84
MALDI mass spectroscopy has recently found appli-
cation in this area [18]. A method on laser desorption
of molecules dissolved in a suitable matrix. The poten-
tial of MALDI mass spectroscopy for direct analysis of
dendritic macromolecules is intensely explored at
present [2]j, [12]a. Thus, the MALDI mass spectroscopy
is a highly valuable method for the analysis of the
structural perfection of dendrimers. This is demon-
strated by the recent investigation of polyethynyl den-
drimers, polyesters and carbosilane based dendritic
polyols with excellent results [12]a. The MALDI mass
absorbities (‡max) of all phenylethynylsilyl-capped den-
drimers [G0 (4 alkynyl groups), G1 (8 alkynyl groups),
G2 (16 alkynyl groups), G3 (32 alkynyl groups), and
G4P–1PA (32 alkynyl groups)] are approximately in
proportion to the number of alkynyl groups. We expect
the possibility of determining molecular mass of these
types of dendrimers by the use of increasing phenom-
ena of molar absorbities of given compounds (Table 5
and Fig. 2).
spectrum of G3 (M =7331) mainly shows two signals
w
that are clearly due to the 32 phenylethynyl end groups
Table 5
UV spectroscopic data
−
1
cm−1
)
‡max×103
Compounds
Mw
432.60
1418.1
3389.2
7331

umax (mm)
‡max×10 (mole
G0 (C32H20Si)
4
287
289
288
287
288
136
593
1498
3173
3572
34
74
94
99
112
G1 (C100H76Si5)
G2 (C236H188Si13
G3 (C508H412Si29
8
16
32
32
)
)
G4P–1PA (C828H796Si61
)
12 460

number of triple bonds.
Fig. 2. Plot of ‡max versus number of triple bonds in Gn (n=1–3) type dendrimers.

C. Kim, M. Kim / Journal of Organometallic Chemistry 563 (1998) 43–51
49
Fig. 3. MALDI mass spectroscopic view of dendritic silanes G1, G2 and G3.

50
C. Kim, M. Kim / Journal of Organometallic Chemistry 563 (1998) 43–51
containing dendrimers. The m/z value of the dominant
signal corresponds to the calculated value of m/z for
G3 dendrimer (Fig. 3). No signals are observed be-
tween these peaks, which clearly confirms that frag-
mentation of phenylethynyl groups on the molecular
surface does not affect the analysis.
3.3. Hydrosilation (G1P)
A mixture of 10 g (23.12 mmol) of G0, 18 g (157.47
mmol) of HSiMeCl and 0.10 g of a common hydrosi-
2
lation catalyst (e.g. 10% Pt content on activated car-
bon) in 50 ml toluene was refluxed for 48 h. When the
reaction was complete ( H-NMR), excess HSiMeCl
1
The glass transition (T ) temperature has been mea-
g
2
sured for a number of dendritic molecules. Whereas,
no crystallization was observed for terminated den-
was removed under vacuum. The platinum catalyst
was filtered off and the volatile components were re-
moved under reduced pressure, leaving 20.64 g of G1P
as a yellow solid. Further purification was not avail-
able because sensitivities against moisture. But, C-
NMR spectrum showed only one dendrimer. Yields:
drimers. All dendrimers were soluble in THF, Et O,
2
and toluene but practically insoluble in hydrocarbons
and alcohols.
1
3
2
0.00 g (97%) of G1P as a yellow solid. G1P–G3P
3
. Experimental
and G4P–1Cl were synthesized by this method. For
characterization of GnP-type dendrimers G1P to
G4P–1Cl see Tables 2–5.
3.1. General procedures
All reactions were carried out under a static pres-
sure of dried N2 atmosphere. Ether and THF were
dried by distillation from the blue solution of sodium-
benzophenone ketyl, while solvents, such as pentane,
toluene and benzene, were dried and distilled from Na
metal. A platinum catalyst (Pt on activated carbon,
Acknowledgements
This study is supported by the Korean Ministry of
Education through Research Fund (BSRI-97-3446)
and Dong-A University (1997).
10% Pt content) was used after vacuum dry at room
temperature. NMR spectra were recorded on Bruker
AC-200 Spectrometer in CDCl . NMR chemical shifts
References
3
refer to the signals of the solvents used. FT–IR spec-
tra were measured by IFS 55 (Bruker). UV spectra
were measured by HP 8452A Diode Array UV/Vis.
Spectrophotometer (HP). Elemental analysis and
MALDI mass spectroscopic attachments were per-
formed by the Pusan and Daejon Branch of the Ko-
rean Basic Science Institute.
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clear, yellow solid. Yield: 12.10 g (27.97 mmol, 80%)
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were synthesized by this method. For characterization
of Gn-type dendrimers G0 to G4P–PA, see Tables 1
and 3–5.
4
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