Ring-closing metathesis on an allyl-terminated carbosilane dendrimer

Article abstract of DOI:10.1002/jccs.200500017

Grubbs' catalyst was used to prepare a series of carbosilane dendrimers with silacyclopentene peripheral groups, suitable for further elaboration to functional dendrimers. The efficiency of the ring closing metathesis reaction was found to be strongly dep

Full text of DOI:10.1002/jccs.200500017

Journal of the Chinese Chemical Society, 2005, 52, 113-118
113
Ring-Closing Metathesis on an Allyl-Terminated Carbosilane Dendrimer
Ruifang Guana (
), Chuanjian Zhoub,c* (
), Shengyu Fengc (
),
David J. Bergd and Stephen R. Stobartd
aSchool of Materials Science and Engineering, Ji’nan University,
Ji’nan, Shandong 250022, P. R. China
bSchool of Materials Science and Engineering, Shandong University,
Ji’nan, Shandong 250061, 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
Grubbs’ catalyst was used to prepare a series of carbosilane dendrimers with silacyclopentene peripheral
groups, suitable for further elaboration to functional dendrimers. The efficiency of the ring closing metathesis
reaction was found to be strongly dependent on the reaction temperature and the amount of catalyst used, as
shown by 1H NMR monitoring.
Keywords: Grubbs’ catalyst; Ring-closing metathesis; Carbosilane; Dendrimer; Silacyclopenten.
INTRODUCTION
Grubbs’ catalyst has been extensively used in coupling
though cross metathesis proved difficult to achieve, ring-
closing metathesis of the allyl-terminated carbosilane den-
drimers resulted in a new kind of silacyclopentene terminated
dendrimers in high yield using Grubbs’ catalyst.
reactions of olefins such as ring-closing metathesis,1-4 cross-
metathesis,5 and ring-opening metathesis.6 Although the ac-
tivity of Grubbs’ catalyst is lower than that of Schrock’s mo-
lybdenum alkylidenes, it displays superior stability towards
oxygen, water, and minor impurities in the solvents. As a re-
sult, Grubbs’ catalyst has enjoyed widespread application in
organic and polymer chemistry7 as summarized in several re-
view articles.8-12 Most literature reports concentrate on the
synthesis of natural products with large ring structures,13-15
especially systems containing eight-membered rings that are
unstable from a kinetic and thermodynamic point of view.16
In short, Grubbs’ catalyst offers a powerful method for the
creation of chemical diversity, especially the cross-metath-
esis reaction that provides access to alkenes bearing a wide
range of functional groups.17-21
RESULTS AND DISCUSSION
Using the divergent method, carbosilane dendrimers
with allyl terminal groups (2, 5 and 7) can be easily synthe-
sized using alternating Grignard reagent and hydrosilylation
reactions (Scheme I).24,25 It was expected that reaction of
carbosilane dendrimers 2 or 5 with allyl phenol 3 or allyl
oxazoline X using Grubbs’ catalyst would produce the cross
metathesis target dendrimers (11 or 12), especially in the
presence of excess 3 or X.
However, no reaction was observed when 2 or 5 were
stirred with a fourfold excess of 3 and Grubbs’ catalyst at
room temperature for several days. But, increasing the tem-
perature of the reaction mixture and the amount of the cata-
lyst resulted in formation of the ring-closing products 4 and 6
in > 90% yield. And in the same time, reaction of 3 with
Grubbs’ catalyst on its own under the same conditions re-
sulted in self-metathesis to produce 9,26 so it is clear that
intramolecular metathesis reactions of carbon silane den-
Our initial goal in this research was to use cross-me-
tathesis methods to attach different chelating functionalities
to the periphery of a carbosilane dendrimer framework so that
lanthanide ions could be bound at the dendrimer exterior. The
high catalytic activity of lanthanide ions in Lewis acid cata-
lyzed transformations, as well as some oxidations and reduc-
tions, make these metals attractive reaction centers.22,23 Al-
* Corresponding author. E-mail: zhouchuanjian@sdu.edu.cn

114 J. Chin. Chem. Soc., Vol. 52, No. 1, 2005
Guan et al.
Scheme I The synthesis route of the preparation of the dendrimers and the ring-closing metathesis reaction under the
Grubbs’ catalyst
Me
Si
Me
Si
Me
Me
Si
Me
Si
Me
MeO
MeO
Si
MeO
MeO
Si
4
2
4
2
7
i) HSiMeCl2
ii) CH2CHCH2MgBr
8
OMe
Me
Si
Si
Me
Si
Si
MeO
MeO
OMe
1
Si
Grubbs cat.
MeO
Me
Si
Me
Me
5
MeO
i) HSiMeCl2
Me
6
ii) CH2CHCH2MgBr
MeO
MeO
Si
Me
HO
N
Me
HO
or
MeO
MeO
HO
Me
4
OH
Si
X
Me
O
OH
MeO
Si
Me
3
or
X
2
Me
Me
MeO
Grubbs cat.
HO
Si
Me
11
9
OH
O
OH O
OH
N
N
or
MeO
MeO
O
N
X
X
Me
N
O
12
10
OH
drimers are dominant even when a significant excess of 3 is
present. The fact that the ring-closing reaction produces a
highly favored 5-membered ring apparently precludes obser-
vation of the cross metathesis products.27,28
in 2 to d 18.07 ppm in 4 due to ring strain. Similarly, the
Si-Me resonance in the 13C{1H} NMR shifts from -5.60 ppm
in 2 to -3.61 ppm in 4. As expected, the 13C-DEPT spectrum
shows that the methylene carbon of the terminal double
bonds (d 113.34 ppm) is no longer present. The MS also sup-
ports the structure of 4 as shown below (Scheme II).
The assignment of 4 as the silacyclopentene is evident
from the NMR spectrum. In the 1H-NMR, the alkenyl signals
at d 5.4-5.7 and d 4.75 ppm for 2 are replaced by a new singlet
at d 5.70 ppm due to the silacyclopentene ring vinyl protons
of 4.
The progress of the ring-closing reaction can be conve-
niently followed by the integral of the d 5.4-5.7 (a) and d 4.75
ppm (b) resonances (Fig. 1). Reaction of 2 and 3 (1:4 molar
ratio) in the presence of 0.5 mol% Grubbs’ catalyst did not re-
Significantly, the 29Si resonance shifts from 0.92 ppm
Scheme II The mass spectrum of compound 4

Ring-Closing Metathesis on Carbosilane Dendrimer
J. Chin. Chem. Soc., Vol. 52, No. 1, 2005 115
sult in the formation of 4 after stirring for 24 h at room tem-
perature in toluene solution. Increasing the catalyst loading
to 5 mol% also failed to produce any 4 under these conditions
despite the fact that there are several reports indicating that
metathesis should proceed readily at room temperature.
However, heating the reaction mixture with 0.5 mol% Grubbs’
catalyst at 80 °C did result in a 25% conversion of 2 to 4 in 12
h (Table 1, No. 3 and Fig. 1, ii). Increasing the time to 60 h
and catalyst loading to 1 mol% increased the conversion to
65% (Table 1, No. 4 and Fig. 1, ii). Further increases in tem-
perature to 100 °C at 1 mol% catalyst and 130 °C at 5 mol%
catalyst resulted in 85 and > 99% conversion respectively
(Table 1, No. 5 and 6 and Fig. 1, iii, iv). The conversion ap-
pears to be primarily dependent on reaction temperature, al-
though increasing the catalyst loading also appeared to be
beneficial; perhaps indicating that catalyst degradation was
occurring under the reaction conditions employed.
Using the optimal conditions of No. 6 (in Table 1), we
Table 1. The condition and result of the ring closed reaction
No. Reactant
Product Temp. (°C) Catalyst (mol%) Time (hr) Yielda (%)
20 0.5 48
20 5.0 48
1
2
4
0
2
3
4
5
6
7
8
2
2
2
2
2
5
7
4
0
25
65
4
4
4
4
6
8
80
80
100
130
130
130
0.5
1.0
1.0
5.0
5.0
5.0
12
60
60
24
24
24
85
> 99
> 99
> 99
a Determined by integration of the product and substrate alkenyl 1H resonances.
a
b
a
b
ii): Temp: 80 °C, Cat%: 1%, Time: 60 h
i): Temp: 80 °C, Cat%: 0.5%, Time: 12 h
a
a
b
iv): Temp: 130 °C, Cat%: 5%, Time: 60 h
iii): Temp: 100 °C, Cat%: 1%, Time: 60 h
Fig. 1. The 1H-NMR of the alkeneyl region for the ring-closing reaction of 2.

116 J. Chin. Chem. Soc., Vol. 52, No. 1, 2005
Guan et al.
found that 5 and 7 also underwent smooth ring closing me-
tathesis to afford the bis(silacyclopentene) 6 and 8 in excel-
lent conversion (entry 7 and 8).
mL 30% NH4Cl solution was added slowly under ice-salt
bath. The organic layer was separated, and the water layer
was extracted with 3*20 mL ether. The combined organic lay
was dried over anhydrous MgSO4 overnight. After filtering,
the solvent was removed under decompression, and the low
boiling materials was got rid of under vacuum (100-140 °C/2
mmHg); then, the remainders were purified by column, Hex-
ane:Ether = 40:1, colorless odorous oil was given. 4.56 g,
yield 75.0%.
IR (cm-1): 3076 (CH), 1629 (C=C), 1253 (Si-CH2), 813
(Ph); NMR (d ppm) 1H: 6.82-6.79 (d, 1H, J = 8.5 Hz, ArH),
6.74-6.73 (d, 1H, J = 8.5 Hz, ArH), 6.71 (s, 1H, ArH), 5.82-
5.76 (m, 2H, Si-CH2CH=CH2), 4.89-4.83 (s, d, 4H, J = 9.9
Hz, Si-CH2CH=CH2), 3.89-3.88 (s, 6H, OCH3), 2.60-2.55 (t,
2H, J = 7.1 Hz, Ar-CH2CH2CH2Si), 1.57-1.55 (m, 6H, Si-
CH2CH=CH2 and Ar-CH2CH2CH2Si), 0.64-0.59 (t, 2H, J =
7.8 Hz, Ar-CH2CH2CH2Si), 0.00 (s, 3H, Si-CH3); 13C{1H}:
148.9, 147.3, 135.4, 134.9, 120.4, 113.3, 112.0, 111.4, 56.1,
56.0, 39.7, 26.2, 21.5, 13.1, -5.6; 29Si{1H}: 0.92; MS (EI):
m/z 304 (M+).
CONCLUSION
Grubbs’ catalyst was highly effective at ring closing
metathesis on diallylsilane-terminated dendrimers to afford
silacyclopentenes 4, 6, and 8 in extremely high conversions.
The ideal reaction conditions for the RCM reaction were 130
°C in toluene using 5 mol% catalyst. No evidence for cross
metathesis with allylphenol 3 or allyl oxazoline X was ob-
served under any conditions, including a large excess of com-
pound 3 or X.
EXPERIMENTAL
General Method
1
All H-NMR, 13C-NMR, 13C-DEPT spectra were re-
corded in CDCl3 as solvent on Bruker AC-200 spectrometer,
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 Spectrometer.
Silica gel (silica gel 60, 230-400 mesh, Merck) was used for
Column Chromatography and others reagents were pur-
chased from Aldrich Company and were used without further
purification.
The preparation of carbonsilane dendrimer G1(OMe) (5)
Using the same method as above, the carbonsilane den-
drimer G1(OMe) was prepared at 60% yield. 3.04 (10 mmol)
G1(OMe) reacted with dichloromethylsilane and allylbro-
mine Grignard reagent successively, and 3.36 g product was
given after purification.
IR (cm-1): 3076 (CH), 1629 (C=C), 1252 (Si-CH2), 813
(Ph); NMR (d ppm) 1H: 6.80-6.77 (d, 1H, J = 8.5 Hz, ArH),
6.74-6.73 (d, 1H, J = 8.5 Hz, ArH), 6.69 (s, 1H, ArH), 5.86-
5.68 (m, 4H, Si-CH2CH=CH2), 4.90-4.83 (d, 8H, J = 9.9 Hz,
Si-CH2CH=CH2), 3.89-3.88 (s, 6H, O-CH3), 2.60-2.57 (t, 2H,
J = 7.1 Hz, Ar-CH2CH2CH2Si), 1.61-1.58 (d, 8H, J = 5.0 Hz,
Si-CH2CH=CH2), 1.42-1.28 (m, 4H, CH2), 0.98-0.96 (t, 2H,
2H, J = 7.8 Hz, CH2), 0.61-0.42 (m, 10H, Si-CH2), 0.00 (s,
9H, Si-CH3); 13C{1H}: 148.6, 146.9, 135.1, 134.6, 120.4,
113.1, 111.9, 111.0, 39.4, 25.99, 21.5, 18.6, 12.2, 17.9, 13.7,
-5.1, -5.7; 29Si{1H}: 1.71, 0.22; MS: m/z 556 (M+).
The preparation of carbonsilane dendrimer G0(OMe) (2)
3.56 g (20 mmol) 3-(1,2-methyoxylphenyl-4-)propyl-
ene and 5 mL dry hexane were added to a dry Kontes tube un-
der inert atmosphere, and 5d Speirs catalyst was added to the
solution. After 5.52 g (4.8 mL, 48 mmol) dichloromethyl-
silane was added; the tube was sealed and put in a 80 °C oil
bath, and kept stirring overnight. (The mixture was cooled to
room temperature (r.t.), and then the excess reagent and sol-
vent 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, after the ice-salt
bath was removed, the reaction solution was warmed to r.t.
slowly and kept stirring for 4 hr. At the end of the reaction, 50
The preparation of carbonsilane dendrimer G2(OMe) (7)
Using the same method as above, the carbonsilane
dendrimer G2(OMe) was prepared at 54% yield. 2.33 g (5
mmol) G1(OMe) reacted with dichloromethylsilane and
allylbromine Grignard reagent successively, and 2.86 g prod-
uct was given after purification.
IR (cm-1): 3076 (CH), 1629 (C=C), 1252 (Si-CH2), 813
(Ph); NMR (d ppm) 1H: 6.81-6.78 (d, 1H, J = 8.5 Hz, ArH),

Ring-Closing Metathesis on Carbosilane Dendrimer
J. Chin. Chem. Soc., Vol. 52, No. 1, 2005 117
6.74-6.73 (d, 1H, J = 8.5 Hz, ArH), 6.70 (s, 1H, ArH),
5.88-5.71 (m, 8H, Si-CH2CH=CH2), 4.95-4.80 (m, 16H, Si-
CH2CH=CH2), 3.88-3.87 (s, 6H, O-CH3), 2.61-2.57 (t, 2H, J
= 7.0 Hz, Ar-CH2CH2CH2Si), 1.64-1.53 (d, 16H, J = 5.1 Hz,
Si-CH2CH=CH2), 1.41-1.20 (m, 12H, CH2), 1.028-0.80 (m,
4H, CH2), 0.71-0.42 (m, 24H, Si-CH2), 0.00 (s, 21H, Si-CH3);
13C{1H}: 148.5, 146.9, 135.1, 134.7, 120.7, 113.3, 112.1,
111.0, 39.2, 26.01, 21.5, 18.5, 12.2, 17.9, 13.7, -5.0, -4.98;
29Si{1H}: 1.65, 0.98, 0.24; MS: m/z 1060 (M+).
(d, 16H, J = 6.3 Hz, Si-CH2CH=CH), 0.99-0.96 (t, 2H, J = 7.0
Hz, CH2), 0.63-0.41 (m, 26H, Si-CH2), 0.00 (s, 21H, SiCH3);
13C{1H}: 148.6, 143.7, 135.1, 120.4, 111.9, 111.0, 56.5, 56.4,
39.4, 25.99, 21.5, 18.6, 12.2, 17.9, 13.7, -3.59, -5.7; 29Si{1H}:
1.83, 19.68; MS: m/z 947 (M+-1).
ACKNOWLEDGMENT
The project was sponsored by the Scientific Research
Foundation of Shandong University.
The preparation of the dendrimers with silacyclopentene
terminal groups (4, 6, 8)
General method: 0.1 mmol allyl terminal carbonsilane
dendrimers 2, 5 or 7 and 0.5%-5% (based on the mol of allyl
groups) Grubbs’ catalyst 5 mL dry toluene were added to a
dry Kontes tube under inert atmosphere, and kept stirring for
several hours at the temperatures that are shown in Table 1.
After the reaction, the solvent was removed under vacuum
and then purified by column chromatography (Ether:Hexane
= 1:20).
Received January 30, 2004.
REFERENCES
1. Achermann, L.; Furstner, A.; Weskamp, T.; Kohl, F. J.;
Hermann, W. A. Tetrahedron lett. 1999, 40, 4787.
2. Weskamp, T.; Kohl, F. J.; Hieringer, W.; Gleich, D.;
Herrmann, W. A. Angew. Chem. Int. Ed. 1999, 38, 2416.
3. Weskamp, T.; Kohl, F. J.; Herrmann, W. A. J. Orga-
nometmet. Chem. 1999, 582, 362.
Spectroscopic data for compound 4
IR (cm-1): 3076 (CH), 1632 (C=C); NMR (d ppm) 1H:
6.65-6.55 (m, 3H, ArH), 5.70 (s, 2H, CH=CH), 3.65-3.64 (s,
6H, OCH3), 2.47-2.38 (t, 2H, J = 7.8 Hz, Ar-CH2CH2CH2-Si),
1.58-1.39 (m, 2H, Ar-CH2CH2CH2-Si), 1.15-1.05 (d, 4H, J =
6.4 Hz, CH2CH=CH), 0.61-0.49 (t, 2H, J = 7.1 Hz, Ar-
CH2CH2CH2-Si), 0.02 (s, 3H, SiCH3); 13C{1H}: 148.2, 142.3,
135.3, 131.1, 120.3, 111.9, 111.2, 55.9, 55.8, 39.25, 26.38,
16.48, 14.48, -3.61; 29Si{1H}: 18.07; MS: m/z 276 (M+).
4. Durstner, A.; Thiel, O.; Ackermann, R. L.; Schanz, H. J.;
Nolan, S. P. J. Org. Chem. 2000, 65, 2204.
5. Toste, F. D.; Chatterjee, A. K.; Grubbs, R. H. Pure Appl.
Chem. 2002, 74(1), 7.
6. Tallarico, J. A.; Bonitatebus, P. J.; Snapper, M. L. J. Am.
Chem. Soc. 1997, 119, 7157.
7. Strong, L. E.; Kiessling, L. L. J. Am. Chem. Soc. 1999, 121,
6193.
Spectroscopic data for 6
8. Furstner, A. Alkene Metathesis in Organic Synthesis;
Springer: Berlin, 1998.
IR (cm-1): 3076 (CH), 1633 (C=C), 1252 (Si-CH2);
1
9. Grubbs, R. H.; Chang, S. Tetrahedron 1998, 54, 4413.
10. Abell, A. D. Aldrichimica Acta 1999, 32, 75.
11. Pariya, C.; Jayaprakash, K. N.; Sarkar, A. Coord. Chem. Res.
1998, 168, 1.
NMR (d ppm) H: 6.68-6.56 (m, 3H, ArH), 5.72 (s, 4H,
CH=CH), 3.70-3.69 (s, 6H, OCH3), 2.58-2.56 (t, 2H, J = 7.8
Hz, Ar-CH2CH2CH2Si), 1.42-1.28 (m, 4H, CH2), 1.16-1.02
(d, 8H, J = 6.2 Hz, Si-CH2CH=CH), 0.98-0.96 (t, 2H, J = 7.1
Hz, CH2), 0.61-0.42 (m, 10H, Si-CH2), 0.00 (s, 9H, SiCH3);
13C{1H}: 148.6, 143.7, 135.1, 120.4, 111.9, 111.0, 56.5, 56.4,
39.4, 25.99, 21.5, 18.6, 12.2, 17.9, 13.7, -3.59, -5.7; 29Si{1H}:
1.83, 19.68; MS: m/z 501 (M++1).
12. Schuster, M.; Blechert, S. Angew. Chem. 1997, 109, 2124.
13. Furstner, A.; Langemann, T. J. Org. Chem. 1996, 61, 3942.
14. Furstner, A.; Langemann, T. Synthesis 1997, 792.
15. Crimmins, M. T.; Choy, A. L. J. Org. Chem. 1997, 62, 7548.
16. Papaioannou, N.; Evans, C. A.; Blank, J. T.; Miller, S. J.
Org. Lett. 2001, 3(18), 2879.
Spectroscopic data for 8
17. Choi, T. L.; Chatterjee, A. K.; Grubbs, R. H. Angew. Chem.
Int. Ed. 2001, 49, 1277.
IR (cm-1): 3076 (CH), 1633 (C=C), 1253 (Si-CH2);
1
NMR (d ppm) H: 6.69-6.56 (m, 3H, ArH), 5.71 (s, 8H,
18. Chatterjee, A. K.; Choi, T. L.; Grubbs, R. H. Synlett. 2000,
1034.
CH=CH), 3.71-3.70 (s, 6H, OCH3), 2.60-2.57 (t, 2H, J = 7.8
Hz, Ar-CH2CH2CH2Si), 1.44-1.27 (m, 12H, CH2), 1.18-1.04
19. Chatterjee, A. K.; Morgan, J. P.; Scholl, M.; Grubbs, R. H. J.

118 J. Chin. Chem. Soc., Vol. 52, No. 1, 2005
Guan et al.
Am. Chem. Soc. 2001, 123, 10903.
24. Van der Made, A. W.; van Leeuwen, P. W. N. M. Chem.
Commun. 1992, 1400.
20. Blackwell, H. E.; O’Leary, D. J.; Chatterjee, A. K.;
Washenfleder, R. A.; Bussman, D. A.; Grubbs, R. H. J. Am.
Chem. Soc. 2000, 122, 58.
25. Lorenz, K.; Mulhaupt, R.; Frey, H.; Rapp, U.; Mayer-Posner,
F. J. Macromolecules 1995, 28, 6657.
21. Chatterjee, A. K.; Grubbs, R. H. Org. Lett. 1999, 1, 1751.
22. Onozawa, S. Y.; Sakakura, T.; Tanaka, M. Chem. Lette.
1994, 531.
26. The details of the results will be published in another paper.
27. Furstner, A.; Gastner, T.; Weintritt, H. J. Org. Chem. 1999,
64, 2361.
23. Gun’ko, Y. K.; Hitchcock, P. B.; Lappert, M. F. Chem.
Commun. 1998, 1843.
28. Huang, K. S.; Wang, E. C. J. Chin. Chem. Soc. 2004, 51(2),
383.