The preparation of a new kind of carbosilane dendrimer with 4-(naphthalen-1-yl)phenyl core - An application of Suzuki coupling reaction

Article abstract of DOI:10.1002/jccs.200500132

Using the divergent method, carbosilane dendrimers with p-bromophenyl core were synthesized by using alternating Grignard and hydrosilylation reactions. And then, α-naphthalenyl was connected to the core by using Suzuki coupling reaction. This gave a new carbosilane dendrimer with a 4-(naphthalen-1-yl)phenyl core. All the products were characterized by IR, ¹HNMR, ¹³CNMR, ²⁹SiNMR, and MS. The study shows that Suzuki Coupling reaction is an effective and powerful core- functionalization method and a satisfactory result can be achieved through prolonging the reaction time.

Full text of DOI:10.1002/jccs.200500132

Journal of the Chinese Chemical Society, 2005, 52, 947-952
947
The Preparation of a New Kind of Carbosilane Dendrimer with
4-(Naphthalen-1-yl)phenyl Core – An Application of Suzuki Coupling
Reaction
Chuan-Jian Zhoua,c* (
), Rui-Fang Guanb (
), Sheng-Yu Fengc (
),
David J. Bergd and Stephen R. Stobartd
aSchool of Materials Science and Engineering, Shandong University, Ji’nan, Shandong 250061, P. R. China
bSchool of Materials Science and Engineering, Ji’nan University, Ji’nan, Shandong 250022, P. R. China
cSchool of Chemistry and Chemical Engineering, Shandong University, Ji’nan, Shandong 250100, P. R. China
dDepartment of Chemistry, University of Victoria, P.O. 3065, Victoria, B.C., Canada V8W 3P6
Using the divergent method, carbosilane dendrimers with p-bromophenyl core were synthesized by using
alternating Grignard and hydrosilylation reactions. And then, a-naphthalenyl was connected to the core by
using Suzuki coupling reaction. This gave a new carbosilane dendrimer with a 4-(naphthalen-1-yl)phenyl
core. All the products were characterized by IR, 1H NMR, 13C NMR, 29Si NMR, and MS. The study shows that
Suzuki Coupling reaction is an effective and powerful core-functionalization method and a satisfactory result
can be achieved through prolonging the reaction time.
Keywords: Suzuki coupling reaction; Core functionalization; Carbosilane; Dendrimer; Naphthalene.
INTRODUCTION
Carbosilane dendrimers have aroused more and more
prepare than the other two ways; therefore, a lot of reports
have been published.3,4,5,6,7 However, for the core- (and fo-
cal-point-) functionalized dendrimers, the functional groups
could benefit from the site isolation that was created by the
dendritic environment; the site-isolation effects could show
some new characters.8 As a result, the study on the core-
functionalization is very important to develop the application
of carbosilane dendrimer. In the last paper, we reported a new
peripheral-functionalization method to prepare carbosilane
dendrimer with silcacyclohexane by using Grubb’s catalyst,9
and here we will report a new core-functionalization method
by using Suzuki coupling reaction.
researchers’ interest not only because of their chemical and
thermal stability, but also because of their inert activity and
biocompatibility. Another advantage of this kind of den-
drimer is that they are fluid even at high molecular weight (in
other words, at high generation), which makes it possible to
synthesize high generation carbosilane dendrimers.1 The
flexible main chain, less intermolecular force, and high bond
energy play very important roles in these characters. Carbo-
silane dendrimers also have diverse structures, which is be-
cause silane monomers have multifunctional groups and
moderate reactivity. From the view of study, the research of
carbosilane dendrimers has stepped from their synthesis into
functionalization. The functionalized dendrimers can be used
as catalyst supporters, medicine control-released materials,
and photoelectric devices.2 The potential applications of the
functionalized dendrimers mainly depend on the functional-
groups. From the functional sites of dendrimers, they can be
divided into three categories: surface-functionalization, core-
functionalization, and focal-point functionalization. For the
carbosilane dendrimer, due to the diversity of carbosilane
monomers, the surface-functionalization is much easier to
Suzuki coupling reaction, which is a palladium-cata-
lyzed cross-coupling reaction between organoboronic acids
and aryl halides, is a powerful synthetic tool. It represents
one of the most valuable methods for carbon-carbon bond
formation, not least because of its tolerance of a broad range
of functional groups and its non-toxic byproducts. Boronic
acid is also thermally stable and inert to air and water which
allows easy handling without special precautions,10,11,12 The
project consists in developing a novel asymmetric Suzuki
coupling protocol for carbosilane dendrimers’ functionaliza-
tion which can introduce some molecules with big p-conju-
gated structures to the core of a dendrimer and these com-
* Corresponding author. E-mail: zhouchuanjian@sdu.edu.cn

948 J. Chin. Chem. Soc., Vol. 52, No. 5, 2005
Zhou et al.
pounds might show not only some bioactivities, but also
some special optical, electric or magnetic properties.13
G1(Br), G2(Br) was studied separately, and the satisfactory
results were also achieved.
However, the coupling reaction became more and more
difficult with the increasing of generation (from G0 to G2),
and a good result could be gotten only when the reaction time
was sufficiently prolonged. From the view of space hin-
drance, the core was entrapped in the center of branches,
which blocked up the attack of naphthalenyl boronate acid.
On the other hand, because the branches were hydrophobic
and the reaction was a heterogeneous reaction, with increas-
ing of generation, it became more and more difficult for the
inorganic base to diffuse into the center of the dendrimer. In
other words, the concentration of the base in organic phase
decreased. All these factors would affect the reaction rate.
Therefore, in order to get good yield, a longer reaction time
was requisite.
RESULTS AND DISCUSSION
The preparation of the carbosilane dendrimer with a
p-bromophenyl core
Using the divergent method, carbosilane dendrimers
with p-bromophenyl cores can be easily synthesized by alter-
nately using Grignard and hydrosilylation reactions.8 All the
carbosilane dendrimers were characterized by IR, H, 13C,
1
29Si NMR and MS. The 1H NMR of compounds 1, 2, 3 were
similar except for their integral values, but all integrals ac-
corded very well with the number of protons. The signal-
overlap of protons increased with the generation and the car-
bon signals in the high field increased too, which were related
to the carbon atoms of methyl and methylene connecting with
The structure analysis of dendrimer G0(Naph)-G2(Naph)
(Compound 5-7)
1
silicon atoms. In the H NMR, because of the slight differ-
1
ence among the chemical environments of different genera-
tions, the carbon signals of Si-CH3 had a slight difference but
all of them appeared at around d -5 ppm; and the numbers
were same as the generation numbers of dendrimers. The
number of 29Si signals showed the same result too; namely,
they had the right kinds according to the generation. From the
above information, it could be determined on a preliminary
basis that the structures of dendrimers were perfect. And
then, the MS spectrum confirmed their structure further: all
these dendrimers had molecular ion peaks and they became
weaker and weaker with the increasing of generation, which
indicated the stability of molecular ions decreased with the
increasing of generation. In addition, all the isotope peaks of
bromine-containing fragments were almost 1:1, and other
fragments had reasonable break-up paths.
The H-NMR and 13C-NMR spectrums are shown in
1
Scheme I. Compared with G0(Br)-G2(Br), the H NMR of
G0(Naph)-G2(Naph) had more aryl proton signals which di-
vided into three groups at around d 8.0-7.0 ppm, and the rate
of integral value was about 3:6:2, which was coincident with
the structure of dendrimers. The proton signals of naphtha-
lene divided into two groups and overlapped with each
other’s and the signals of phenyl. From the 1H NMR, it could
be learned that the naphthalene group did connect with the
dendrimers G0(Br)-G2(Br). In the 13C NMR, all changes were
related to the naphthalenyl-group; for example, the signals at
low field of about d 120 ppm increased, and the DEPT spec-
trum showed most of them were methylene carbon signals. In
a word, all the spectrums’ data were in accord with the target
structures. The MS confirmed the result further, too. All
dendrimers, from G0(Naph) to G2(Naph), had molecular ion
peaks and which became weaker and weaker. Other frag-
ments had reasonable sources.
The functionalization of carbonsilane dendrimer by us-
ing Suzuki coupling reaction
Suzuki coupling reaction is one of the most common
methods for preparing compounds with several aryl groups,
especially in the total synthesis of some natural compounds
which show high selectivity and high yield. With the naph-
thalenyl boronate acid in hand, the coupling reaction with
5-bromo-2-hydroxy-3-methylbenzonitrile was tested firstly,
mainly because the pure carbosilane dendrimer was difficult
to get. The reaction indeed gave a satisfactory result (82%
yield) by using 5% Pd(PPh3)4 and Na2CO3 aqueous as
base.14,15 Based on the result, the reaction between naphtha-
lenyl boronate acid and dendrimer G0(Br) (compound 1) or
CONCLUSION
Using the divergent method, carbosilane dendrimers
with p-bromophenyl cores can be easily synthesized by alter-
nating using Grignard reagent and hydrosilylation reactions,
which have a potential functional site---aryl bromine atom.
And then, 1-naphthalenyl was connected to the core by using
Suzuki coupling reaction. A new carbosilane dendrimer was
given. All the products were characterized by IR, 1H NMR,

The Preparation Dendrimer Using Suzuki Reaction
J. Chin. Chem. Soc., Vol. 52, No. 5, 2005 949
Scheme I The spectrum of Dendrimers G0(Naph)-G2(Naph)

950 J. Chin. Chem. Soc., Vol. 52, No. 5, 2005
Zhou et al.
13C NMR, 29Si NMR, and MS. The study shows that Suzuki
Coupling reaction is an effective and powerful core-function-
alization method. The reaction became more and more diffi-
cult with the increasing of generation of dendrimers, and a
satisfatory result can be achieved through prolonging the re-
action time.
added, the tube was sealed and put in an 80 °C oil bath and
kept stirring overnight. The mixture was cooled to room tem-
perature (r.t.), and then the excess reagent and solvent were
removed carefully under vacuum; colorless oil was given.
The oil was dissolved in 20 mL dry ether and added slowly to
an ether solution containing allylbromine Grignard reagent
under ice-salt bath; then the reaction solution was warmed to
r.t. and kept stirring for 4 hr. At the end of the reaction, 50 mL
30% NH4Cl solution was added slowly under an ice-salt bath
firstly, then 20 mL water. The organic layer was separated
and the water layer was extracted with 3*20 mL ether. The
combined organic layer was dried over anhydrous MgSO4
overnight. After filtering, the solvent was removed under de-
compression, and the low boiling point substances were got-
ten ride of under vacuum (100-140 °C/2 mmHg). The remain-
der was purified by column chromatography (Hexane:Ether
= 40:1), and a colorless and smelly oil was produced. 5.21 g,
yield 81.2%.
IR (cm-1): 3076 (CH), 1630 (C=C), 1461 (CH2), 1252
(Si-CH2), 893 (=CH2), 810 (Ph); 1H-NMR (d ppm): 7.42-7.40
(d, J = 11 Hz, 2H), 7.08-7.05 (d, J = 11 Hz, 2H), 5.86-5.67 (m,
2H), 4.91-4.88 (d, J = 14 Hz, 2H), 4.82 (s, 2H), 2.62-2.57 (t, J
= 7 Hz, 2H), 1.58-1.56 (d, J = 14 Hz, 6H), 1.42-1.25 (m, 2H),
0.00 (s, 3H); 13C-NMR (d ppm): 141.3, 134.6(b), 131.3,
130.2, 119.4, 113.3, 39.2, 25.6, 21.3, 12.8, -5.8; 29Si-NMR (d
ppm): 0.94; MS (m/z): 322, 324(M+).
EXPERIMENTAL
General Method
1
All H NMR, 13C NMR, and DEPT spectra were re-
corded in CDCl3 as solvent on a Bruker AC-200 spectrome-
ter, using 5 mm O.D. tubes at 303 K, no internal reference.
29Si spectra were recorded in CDCl3 as solvent on Bruker
AC-500 spectrometer, using 5 mm O.D. tubes at 303 K. IR
spectrum was obtained on Ni Cdet FT-IR 20SX spectrometer
(KBr disk, 4000-400 cm-1). Mass spectra were obtained by a
FAB (fast atom bombardment) VG-70-250S Mass Spectrom-
eter. Silica gel (silica gel 60, 230-400 mesh, Merck) was used
for column chromatography and all solvents were distilled
under argon; others reagents were purchased from Aldrich
Company and were used without further purification.
Compounds (1-7) were synthesized according to the
following route (Scheme II).
The preparation of carbonsilane dendrimer G0(Br) (1)9
3.93 g (20 mmol) 3-(p-bromophenyl)propylene and 5
mL dry hexane were added to a dry Kontes tube under inert
atmosphere; 5d Speirs catalyst were added to the solution.
After 5.52 g (4.8 mL, 48 mmol) dichloromethylsilane was
The preparation of carbosilane dendrimer G1(Br) (2)
Using the same method as above, the carbosilane den-
drimer G1(Br) was prepared at 60.1% yield. 3.23 g (10 mmol)
G0(Br) reacted with dichloromethylsilane and allylbromine
Scheme II The synthesis route of carbonsilane dendrimers and their functionalization
a) HSiMeCl2/[Pt]
a) HSiMeCl2/[Pt]
Br
SiMe
G (Br)
Br
MgBr
b)
MgBr
b)
Me
1
0
Si
Me
Si
Me
Si
Me
Si
Si
Si
Br
Si Me
G (Br)
Me
Me
Br
Si Me
G (Br)
Me
Si
2
Si
Me
1
3
2
Br
Mg / Ether
B(OMe)3
1.
2.
BOH2
Dendrimer G
[Pd]
Dendrimer G
G(Br)0 -G(Br)2
G0 -G2
Br
+
3. HCl
4
5,6,7
1,2,3

The Preparation Dendrimer Using Suzuki Reaction
J. Chin. Chem. Soc., Vol. 52, No. 5, 2005 951
Grignard reagent successively, and 3.36 g product was given
after purification.
IR (cm-1): 3243 (b, -OH); 1H NMR (d ppm): 8.57-8.54
(d, J = 6 Hz, 1H), 7.95-7.81 (m, 2H), 7.51-7.40 (m, 4H),
2.85-2.60 (d, J = 7 Hz, 2H); 13C NMR (d ppm): 137.5, 134.3,
134.5, 130.6, 129.7, 129.1, 126.4, 126.1, 125.8, 105.3; MS
(m/z): 170 (M-1).
IR (cm-1): 3076 (C-H), 1629 (C=C), 1455 (CH2), 1252
(Si-CH2), 893 (=CH2), 813 (Ph); 1H NMR (d ppm): 7.42-7.40
(d, J = 11 Hz, 2H), 7.08-7.05 (d, J = 11 Hz, 2H), 5.86-5.68 (m,
4H), 4.91-4.88 (d, J = 10 Hz, 4H), 4.83 (s, 4H), 2.60-2.57 (t, J
= 7 Hz, 2H), 1.61-1.58 (d, J = 13 Hz, 8H), 1.42-1.28 (m, 8H),
0.98-0.96 (t, J = 8 Hz, 2H), 0.61-0.42 (m, 8H), 0.00 (s, 9H);
13C NMR (d ppm): 141.5, 132.8, 131.2, 119.3, 113.1, 39.4,
25.99, 21.5, 18.6, 12.2, 17.9, 13.7, -5.1, -5.7; 29Si NMR (d
ppm): 1.71, 0.22; MS (m/z): 598, 600 (M+Na+).
The preparation of dendrimer G0 (Naph) (5)16
A 50 mL two-neck round-bottom flask was equipped
with condenser and stirrer. Under inert atmosphere, G0(Br)
108 mg (0.33 mmol), 50 mg [Pd(0)], 10 mL toluene, and 0.50
mL 6 M K2CO3 solution was added to the flask and then
naphthalenyl boronate acid 0.172 g (1 mmol) in 2 mL metha-
nol was added. The mixture was cooled to room temperature
after refluxing for 24 hr and afterwards extracting with 20
mL*3 chloroform. The combined organic layer was washed
with saturated K2CO3 solution, followed by water, and dried
over anhydrous MgSO4. The dry solution was filtered and
evaporated to dryness. After purification by column chroma-
tography, the product, colorless oil, was given, 0.10 g, yield
81.0%.
IR (cm-1): 3057, 2969, 1629, 1504, 1394, 1251, 1156,
893, 799. 1H NMR (d ppm): 7.98-7.80 (m, 3H), 7.58-7.38 (m,
6H), 7.22-7.19 (m, 2H), 5.28-5.65 (m, 2H), 4.85-4.79 (t, J =
11 Hz, 4H), 2.72-2.63 (t, J = 6 Hz, 2H), 1.78-1.63 (m, 2H),
1.61-1.56 (d, J = 12 Hz, 4H), 0.72-0.61 (m, 2H), 0.02 (s, 3H);
29Si NMR (d ppm): 0.99; MS (m/z): 370 (M+).
The preparation of carbonsilane dendrimer G2(Br) (3)
Using the same method, the carbonsilane dendrimer
G2(Br) was prepared at 51.3% yield. 2.88 g (5 mmol) G1(Br)
reacted with dichloromethylsilane and allylbromine Grig-
nard reagent successively, and 2.74 g product was given after
purification.
IR (cm-1): 3076 (C-H), 1629 (C=C), 1455 (CH2), 1252
(Si-CH2), 893 (=CH2), 810 (Ph); 1H NMR (d ppm): 7.41-7.39
(d, J = 11 Hz, 2H), 7.10-7.03 (d, J = 11 Hz, 2H), 5.88-5.71 (m,
8H), 4.95-4.80 (m, 16H), 2.61-2.57 (t, J = 7 Hz, 2H), 1.64-
1.53 (d, J = 11 Hz, 16H), 1.41-1.20 (m, 16H), 1.028-0.80 (m,
4H), 0.71-0.42 (m, 16H), 0.00 (s, 18H); 13C NMR (d ppm):
132.6, 131.2, 130.2, 113.5, 39.4, 26.0, 21.5, 18.8, 18.3, 18.0,
-5.0, -4.9; 29Si NMR (d ppm): 1.65, 0.98, 0.24; MS (m/z):
1078, 1080 (M-1).
The preparation of dendrimer G1 (Naph) (6)
Using a similar method as above, 0.11 g (0.19 mmol)
compound 2 reacted with 0.086 g (0.5 mmol) compound 4 un-
der a catalytic amount of Pd[0]; G1 (Naph) was given as col-
orless oil, 0.08 g yield 67%.
The preparation of naphthalenyl boronate acid (4)10
0.36 g magnesium scraps and 20 mL degas ether were
added to a dry three-neck round bottom flask with reflux con-
denser under argon; 2.07 g (10 mmol) a-bromonaphthalene
was added through a drop-funnel and the reaction solvent was
kept slightly boiling. Then, the mixture was warmed to reflux
and kept refluxing for 2 hr. The mixture was cooled to room
temperature, and the solvent was filtered, and then trans-
ferred to another dry two-neck flask under the atmosphere of
argon. 2.06 g (20 mmol) triethyl boronate acid in 20 mL dry
and degas tetrahydrofuran was added to the flask in a period
of 3 hr under ice-cooling and stirring. After that, the mixture
was warmed to r.t. and kept for 4 hr, and then 20 mL 3.35 M
HCl in 30 mL water was added quickly under a salt-ice bath.
A clear solution was given. 50 mL ether was added to the so-
lution and the aqueous layer was extracted with 3*20 mL
ether. The combined organic layer was washed with water to
neutral and dried over anhydrous MgSO4 overnight. White
crystal was given after removing the solvent and then recrys-
tallized from ethanol. 1.23 g, Mp: 117 °C, yield: 72.0%.
IR (cm-1): 3076, 1654, 1629, 1593, 1419, 1395, 1251,
1
1022, 991, 892, 798, 776. H NMR (d ppm): 8.00-7.82 (m,
3H), 7.58-7.38 (m, 6H), 7.33-7.21 (d, J = 11 Hz, 2H),
5.86-5.72 (m, 4H), 4.91-4.81 (t, J = 7 Hz, 8H), 2.78-2.64 (t, J
= 14 Hz, 2H), 1.79-1.62 (m, 2H), 1.61-1.53 (d, J = 11 Hz, 8H),
0.74-0.43 (m, 10H), 0.04 (s, 9H); 13C NMR (d ppm): 143.71,
142.63, 138.72, 134.85, 133.80, 129.95, 128.32, 128.23,
127.41, 126.90, 126.12, 125.88, 125.69, 125.39, 113.05,
45.72, 39.81, 26.07, 21.90, 21.49, 18.70, 18.25, 17.95, 14.11,
-4.79, -5.71; 29Si NMR (d ppm): 0.23, 0.98; MS (m/z): 622
(M+).
The preparation of dendrimer G2 (Naph) (7)
Using a similar method, 0.13 g (0.12 mmol) compound
3 reacted with 0.086 g (0.5 mmol) compound 4 under a cata-
lytic amount of Pd[0]; the dendrimer G2 (Naph) was given as

952 J. Chin. Chem. Soc., Vol. 52, No. 5, 2005
Zhou et al.
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colorless oil, 0.086 g, yield 64%.
IR (cm-1): 3076 (C-H), 1629 (C=C), 1455 (CH2), 1252
(Si-CH2), 893 (=CH2), 810 (Ph); 1H NMR (d ppm): 8.01-7.83
(m, 3H), 7.57-7.38 (m, 6H), 7.35-7.22 (d, J = 11 Hz, 2H),
5.87-5.70 (m, 8H), 4.94-4.80 (m, 16H), 2.62-2.57 (t, J = 8 Hz,
2H), 1.65-1.53 (d, J = 13 Hz, 16H), 1.40-1.20 (m, 16H),
1.03-0.80 (m, 4H), 0.72-0.43 (m, 16H), 0.00 (s, 18H); 13C
NMR (d ppm): 143.9, 142.7, 138.6, 135.0, 133.9, 129.9,
128.4, 128.3, 127.2, 127.1, 126.2, 125.9, 125.7, 125.5, 113.0,
39.7, 26.2, 22.5, 18.9, 18.2, 17.9, -5.1, -4.8; 29Si NMR (d
ppm): 1.72, 0.99, 0.22; MS (m/z): 1150 (M+Na+).
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ACKNOWLEDGMENT
The project was sponsored by the Scientific Research
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(-CN); 1H NMR (d ppm): 7.76-7.73 (m, 3H, Ar-H), 7.66-7.64
(s, 1H, Ar-H), 7.45-7.32 (m, 5H, Ar-H); 5.23 (b, 1H, Ar-
OH), 2.35 (s, 3H, Ar-CH3); 13C NMR (d ppm): 158.9, 139.3,
136.7, 136.5, 135.5, 131.9, 130.5, 128.6, 128.5, 128.4, 128.2,
127.9, 127.2, 126.2, 125.9, 115.9, 105.2, 13.9; MS (m/z): 258
(M+-1).
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