Synthesis and characterization of 1-methyl-1-silaindane and 1-methyl-1-germaindane

Article abstract of DOI:10.1016/j.jorganchem.2007.10.034

New synthetic routes to 1-methyl-1-silaindane (1b) and 1-methyl-1-germaindane (1b) were developed and the desired products were obtained in good isolated yield. Compounds 1a and 1b were fully characterized by mass spectroscopy, ¹H and ¹³

Full text of DOI:10.1016/j.jorganchem.2007.10.034

Available online at www.sciencedirect.com
Journal of Organometallic Chemistry 693 (2008) 169–172
www.elsevier.com/locate/jorganchem
Note
Synthesis and characterization of 1-methyl-1-silaindane
and 1-methyl-1-germaindane
b,
a,
*
Daniel A. Ruddy a,1, Donald H. Berry *, Chip Nataro
a
Department of Chemistry, Lafayette College, Easton, PA 18045, United States
Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, United States
b
Received 17 August 2007; received in revised form 11 October 2007; accepted 15 October 2007
Available online 26 October 2007
Abstract
New synthetic routes to 1-methyl-1-silaindane (1b) and 1-methyl-1-germaindane (1b) were developed and the desired products were
obtained in good isolated yield. Compounds 1a and 1b were fully characterized by mass spectroscopy, 1H and 13C{1H} NMR, and infra-
red spectroscopy.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Silaindane; Germaindane
1. Introduction
inorganic materials with applications in surface organome-
tallic chemistry and catalysis [7].
The importance of organosilicon and organogermanium
compounds to molecular and materials chemistry cannot
be understated. A variety of silanes have been developed
for use in organic synthesis as protecting groups, as well
as for C–C bond formation and functional group transfer
reactions [1]. Optically active sila-pharmaceuticals have
been prepared that display antimuscarinic properties [2].
Studies of Si–Si, Ge–Ge, and transition metal–Si/Ge bond-
ing have lead to new structures with intriguing, non-classi-
cal bonding geometries and coordination environments [3–
5]. Polysilanes and polygermanes represent materials with
interesting electronic and physical properties due to the
phenomenon of r-conjugation associated with the polymer
chain. These have been prepared catalytically via dehy-
drogenative and demethanative coupling [6]. Furthermore,
organosilanes have been utilized to create hybrid organic–
In many cases, the desired organosilane or organoger-
mane can be purchased or easily synthesized via salt
metathesis beginning with a halide derivative. However,
producing asymmetric cyclic compounds, such as those in
Fig. 1, has proven to be more difficult. The bicyclic indane
structure is particularly appealing for numerous applica-
tions alluded to above, and control over the R and R0
groups could tailor the system for the particular purpose.
A few silaindanes have been reported, most of which are
symmetrically substituted at Si [8–11]. The only germain-
dane reported is the symmetric 1,1-dimethyl-1-germain-
dane [12,13].
Early researchers in this field effected an intramolecular
ring-closing of a pendant silyl group with an aryl chloride
upon treatment with sodium in refluxing toluene [9]. This
method of cyclization typically results in low yields of the
desired silaindane. Recently, a catalytic dehydrogenative
process was reported to cyclize pendant silyl groups via
C–H activation of the aryl ring with good yields [8]. How-
ever, this process is not tolerant to chlorosilanes for further
derivation and requires a Pt catalyst with harsh reaction
conditions. Thus, a general one-step route to the synthesis
of cyclic silanes and germanes with mild conditions is
*
Corresponding authors. Fax: +1 610 330 5714 (C. Nataro), +1 215 573
2112 (D.H. Berry).
E-mail addresses: dberry@sas.upenn.edu (D.H. Berry), nataroc@
lafayette.edu (C. Nataro).
1
Current address: Department of Chemistry, University of California,
Berkeley, CA 94720, United States.
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.10.034

170
D.A. Ruddy et al. / Journal of Organometallic Chemistry 693 (2008) 169–172
3 h then stirred at room temperature overnight. The sol-
vent was evaporated under vacuum to yield a yellow oil,
which was triturated with hexanes and filtered through Cel-
ite. This solution was concentrated under vacuum and the
desired product eluted first through a column of silica gel
with hexanes as the eluent. Removal of the solvent yielded
a colorless oil (4.8 g, 88% yield). 1H NMR (CDCl3): d 7.55
E
R'
R
E = Si or Ge
R = H, alkyl, aryl
R' = alkyl, aryl
Fig. 1. Asymmetric sila- or germa-indanes.
3
(d, 1H, aryl, JH–H = 8.1 Hz), 7.26 (m, 2H, aryl), 7.13 (m,
3
1H, aryl), 3.74 (t, 2H, Cl–CH2, JH–H = 7.3 Hz), 3.20 (t,
3
welcome. Herein we report the synthesis and characteriza-
tion of two novel compounds, 1-methyl-1-silaindane (1a)
and 1-methyl-1-germaindane (1b). The compounds are pre-
pared in good yields via single-step cyclizations at room
temperature.
2H, aryl-CH2, JH–H = 7.3 Hz).
2.2.2. 1-Methyl-1-silaindane (1a)
A solution of 2 in THF was prepared in situ from 1-
bromo-2-(2-chloroethyl)benzene (1.00 g, 4.56 mmol). The
solution was added dropwise over 20 min via filter cannula
to a stirred solution of trichloromethylsilane (0.54 mL,
4.56 mmol) in THF (10 mL) at ꢀ78 ꢁC. The stirred solu-
tion was allowed to warm to room temperature overnight.
The reaction mixture was then added dropwise (10 min) via
cannula to a stirred suspension of lithium aluminum
hydride (0.26 g, 6.85 mmol) in THF (10 mL) at 0 ꢁC. After
30 min, the reaction was allowed to warm to room temper-
ature while stirring an additional 5 h. The reaction flask
was then immersed in an ice bath and a 10% aqueous
ammonium chloride solution (30 mL) was added dropwise
to destroy the excess lithium aluminum hydride. The solu-
tion was then filtered and 25 mL of diethyl ether were
added. The filtrate was washed with a 10% aqueous ammo-
nium chloride solution (3 · 30 mL), and then the organic
layer was dried over magnesium sulfate. The solution was
filtered and the solvent was removed in vacuo yielding a yel-
low oil (73% crude yield). Integration of the gas-chromato-
graph peaks shows that the crude product is >98% pure.
Vacuum distillation affords 0.340 g of a colorless oil,
(50% isolated yield, bp 27 ꢁC, 0.001 mmHg). Anal. Calc.
2. Experimental
2.1. General procedures
All manipulations were carried out in oven-dried glass-
ware under an argon atmosphere using standard Schlenk
techniques. Diethyl ether and THF were dried over potas-
sium benzophenone ketyl and distilled under argon prior to
use. Methylene chloride (CH2Cl2) and hexanes were dried
over calcium hydride and distilled. Triphenyl phosphine,
2-bromophenethyl alcohol, methyltrichlorosilane, carbon
tetrachloride, and magnesium turnings were purchased
from Aldrich. Trichloromethylgermane was provided by
Gelest, Inc. (Tulleytown, PA, USA). 1-Chloro-2-(2-bromo-
ethyl)benzene [14] and 1-bromomagensio-2-(2-(chloroma-
gensio)ethyl)benzene (2) [15] were prepared according to
the literature procedure.
The H and 13C{1H} NMR spectra were recorded at
1
400 MHzand100 MHz, respectively, onaJEOLEclipse+400
spectrometer at room temperature in chloroform-d (Aldrich)
or acetone-d6 (Acros). 1H NMR chemical shifts are reported
relative to tetramethylsilane (d = 0.00 ppm), and 13C NMR
shifts are reported relative to chloroform-d, (d = 77.0 ppm).
IR spectra were obtained on a Mattson FT-IR spectrometer
on NaCl plates. A Fisons Instruments GC8030 was used in
tandem with a Fisons MD800 mass spectrometer; the gas-
chromatograph employed an Alltech ECONO-CAP Faster
Fatty Acid Phase column, with phase SE-54, and dimensions
30 m · 0.25 mm ID · 0.25lm. UV–Vis absorbance spectra of
1 and 2 were obtained in dilute THF solution using a Chem
2000 spectrometer.
for C9H12Si: C, 72.90; H, 8.16. Found: C, 72.57; H,
3
8.38%. 1H NMR (acetone-d6): d 7.59 (d, 1H, JH–H
=
=
3
7.3 Hz, aryl), 7.27 (m, 2H, aryl), 7.18 (t, 1H, JH–H
3
7.2 Hz, aryl), 4.66 (q, 1H, JH–H = 3.5 Hz, Si–H), 3.08
(m, 2H, Ar-CH2), 1.24 (m, 1H, Si–CH), 0.95 (m, 1H, Si–
CH), 0.36 (d, 3H, JH–H = 3.7 Hz, Si–CH3). 13C{1H}
3
NMR (CDCl3): d 153.6 (s, C9), 136.8 (s, C4), 132.6 (s,
C5), 129.5 (s, C8), 125.7 (s, C6), 125.6 (s, C7), 32.3 (s,
C1), 8.7 (s, C2), ꢀ4.4 (s, C3). IR (neat, cmꢀ1): 3056,
2956, 2910, 2118 (Si–H), 1588, 1441. MS [m/z]: 148 (M+),
147 (MꢀH+), 133 (MꢀCH3+), 132 (MꢀCH4+), 120
(MꢀCH2CH2+), 105 (MꢀCH3–CH2CH2+). UV–Vis
(THF): k (nm) 268 (630 cmꢀ1 Mꢀ1), 275 (560 cmꢀ1 Mꢀ1).
2.2. Synthesis
2.2.1. 1-Bromo-2-(2-chloroethyl)benzene
2.2.3. 1-Methyl-1-germaindane (1b)
A solution of triphenyl phosphine (7.18 g, 27.4 mmol) in
CH2Cl2 (25 mL) was added dropwise (10 min) to a solution
of 2-bromophenethyl alcohol (5.00 g, 24.9 mmol) and car-
bon tetrachloride (4.00 mL, mmol) in CH2Cl2 (50 mL) at
0 ꢁC. After 15 min the ice bath was removed and the reac-
tion was refluxed for 4 h. Additional CCl4 was added
(1 mL) and the reaction was refluxed for an additional
A THF solution of 2 was prepared from 1-bromo-2-(2-
chloroethyl)benzene (2.0 g, 9.11 mmol) and transferred
dropwise over 20 min to a solution of trichloromethylger-
mane (1.77 g, 9.11 mmol) in THF (20 mL) at ꢀ78 ꢁC.
The stirred solution was allowed to warm to room temper-
ature overnight. The contents of this reaction were added
dropwise over 20 min to a suspension of lithium aluminum

D.A. Ruddy et al. / Journal of Organometallic Chemistry 693 (2008) 169–172
171
hydride (0.80 g, 21.1 mmol) in THF (15 mL) at 0 ꢁC. After
30 min, the ice bath was removed and the solution was stir-
red overnight at room temperature. The solution was fil-
tered via cannula, rinsed with dry diethyl ether
(3 · 10 mL), and the solvent was removed in vacuo, yielding
1.35 g of a faint yellow oil (77% crude yield). Integration of
the GC shows that the crude product is >95% pure. Vac-
uum distillation yields 0.880 g of a colorless oil (50% iso-
lated yield, bp 29 ꢁC, 0.001 mmHg). Anal. Calc. for
C9H12Ge: C, 56.07; H, 6.27. Found: C, 55.98; H, 6.39%.
1H NMR (acetone-d6): d 7.58 (d, 1H, 3JH–H = 7.3 Hz, aryl),
The third and most successful method of preparing 1a
(Scheme 1) was from a di-Grignard reagent, 2, that was
recently reported in the literature [15]. It was prepared
from 1-bromo-2-(2-chloroethyl)benzene, which is not com-
mercially available. A new synthetic route to 1-bromo-2-(2-
chloroethyl)benzene was developed with yields similar to
other routes that have been reported [15,16]. In preparing
the di-Grignard, the magnesium was activated with 1,2-
dibromoethane, and upon addition of 1-bromo-2-(2-chlo-
roethyl)benzene, yielded 2 which was not isolated. Com-
pound 2 reacted with trichloromethylsilane to generate 3a
in situ which was then reduced with lithium aluminum
hydride, giving 1a in good yield. Upon successful synthesis
of 1a, the germanium analogue, 1b, was prepared using a
similar series of reactions and trichloromethylgermane.
The products were purified via careful vacuum distillation
and the isolated yield was 50% for each.
Compounds 1a and 1b were initially characterized using
gas chromatography–mass spectroscopy. For both com-
pounds, there were five easily assignable peaks in the mass
spectrum: the molecular ion peak, loss of a hydrogen, loss
of the methyl, loss of the ethylene bridge, and loss of the
methyl and ethylene groups. Infrared spectra of the com-
pounds were also obtained. In addition to the distinctive
aryl bands, intense peaks in the characteristic regions
for Si–H (m = 2105–2165 cmꢀ1) and Ge–H (m = 2020–
2060 cmꢀ1) stretches assured the presence of the E–H bond
in each sample [17]. UV–Vis spectra were also obtained,
and the peaks were in the typical range for aryl p–p*
transitions.
4
7.23 (m, 2H, aryl), 7.16 (dt, 1H, aryl, JH–H = 2.3 Hz,
3JH–H = 6.7 Hz), 4.79 (m, 1H, Ge–H), 3.12 (m, 2H, Ar-
CH2), 1.45 (m, 1H, Ge–CH), 1.12 (m, 1H, Ge–CH), 0.52
(d, 3H, 3JH–H = 3.3 Hz, Ge–CH3). 13C{1H} NMR (CDCl3):
d 151.5 (s, C9), 138.9 (s, C4), 132.8 (s, C5), 128.7 (s, C8),
125.8 (s, C6), 125.7 (s, C7), 33.8 (s, C1), 10.0 (s, C2), ꢀ4.4
(s, C3). IR (neat, cmꢀ1): 3055, 2967, 2913, 2034 (Ge–H),
1589, 1441. MS [m/z]: 193 (M+), 192 (MꢀH+), 178
(MꢀCH3+), 177 (MꢀCH4+), 164 (MꢀHꢀCH2CH2+), 149
(MꢀHꢀCH3-CH2CH2+). UV–Vis (THF): k (nm) 262
(1133 Mꢀ1 cmꢀ1), 269 (1076 Mꢀ1 cmꢀ1).
3. Results and discussion
While a variety of substituted 1-silaindanes are known
(e.g. 1,1-dimethyl and 1,1-diphenyl) the parent, 1-silain-
dane, has not been reported. The only reported 1-silaindane
in which there is one hydrogen on the silicon is 1-phenyl-1-
silaindane [9]. Compound 1a was initially prepared in order
to determine an appropriate route for the synthesis of 1b.
The key step in the synthesis of the desired bicyclic struc-
tures was forming the correct Grignard reagent to close
the five-membered ring. Three methods were investigated
for producing compound 1a. The first method involved an
attempt to form the di-Grignard of 1-bromo-2-(2-bromo-
ethyl)benzene [9]. While this di-Grignard reacts with dichlo-
rodiphenylsilane to produce 1,1-diphenyl-1-silaindane [9],
compound 1a was not the major product in the reaction
of the di-Grignard with trichloromethylsilane followed by
treatment with lithium aluminum hydride.
In order to further characterize 1a and 1b extensive
NMR experiments were performed. Acetone-d6 and chlo-
roform-d were the solvents used for 1H and 13C{1H}
NMR spectra, respectively, to avoid overlap of solvent
1
peaks with sample peaks. In the H spectra, both com-
pounds displayed an upfield doublet corresponding to the
methyl group; the chemical shift and coupling constants
for 1a and 1b are similar to ethylmethylphenylsilane [18]
and (4-trifluorotolyl)dimethylgermane [19], respectively.
While the Si–H in 1a was a well resolved quartet, the cor-
responding Ge–H in 1b was not. This was not unexpected
The second method examined for the preparation of 1a
was the metalation of 1-chloro-2-(2-bromoethyl)benzene.
In diethyl ether, metalation of the ethyl-bromide was the
primary product, although some di-Grignard and intramo-
lecular coupling to yield 1,4-di-(2-chlorophenyl)butane also
occurred. Since there was significant formation of the
mono-Grignard, the addition of a terminal –SiHCH3Cl
group was performed and confirmed by GC–MS. Unfortu-
nately, the subsequent conversion of the product to a
Grignard followed by ring-closing was consistently unsuc-
cessful, leaving only the unreacted starting material. Cycli-
zation of the product was also attempted using lithium
aluminum hydride to convert the –SiHCH3Cl group into
a –SiH2CH3group followed by refluxing with sodium in
toluene to close the ring [9]. While the desired product
was verified by GC–MS, the yield was quite low.
Scheme 1. Synthetic route to compounds 1a and 1b.

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D.A. Ruddy et al. / Journal of Organometallic Chemistry 693 (2008) 169–172
4. Summary
Hf
c8
Ha
Hf
Ha'
The reaction of the di-Grignard, 2, with either trichloro-
c7
c6
c9
c4
c1
c2
methylsilane or trichloromethylgermane followed by subse-
quent treatment with lithium aluminum hydride yields 1a
or 1b, respectively. The cyclization reaction proceeds with
high selectivity, and the products are obtained in good
yield after vacuum distillation. Both 1a and 1b were fully
Hb
Hb'
c5
E
He
c3
Hc
Hd
Fig. 2. Atom labeling assignments for 1a and 1b.
characterized and the H and 13C peaks were assigned.
1
Acknowledgements
as the Ge–H signal for (4-trifluorotolyl)dimethylgermane
was not well resolved [19].
The 13C{1H}and the remaining signals in the 1H spectra
were assigned (Fig. 2) using DEPT, 1H–13C HETCOR and
1H–1H COSY experiments. The two less intense aromatic
peaks had no matching peaks in the DEPT spectrum, cor-
responding to quaternary carbons. Based on similar com-
pounds [18], the quaternary carbon bonded to the
heteroatom in 1a and 1b can be assigned as the peak fur-
ther upfield (C4). Two of the three upfield peaks inverted,
indicative of methylene groups while the most upfield peak
remained unchanged, indicative of the methyl carbon (C3).
Since the Si/Ge atom is a stereocenter, the protons on C1
and C2 are diastereotopic. Three sets of multiplets were
Partial financial support for this project was provided
by the National Science Foundation through their Re-
search Experience for Undergraduates program. CN
and DAR thank the Kresge Foundation for the purchase
of the Jeol NMR. Gelest, Inc. is also gratefully acknowl-
edged for donating the trichloromethylgermane used in
this work.
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1
13
0
Ha . Finally, the H– C HETCOR spectrum confirmed the
0
0
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´
´
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