Synthesis and molecular structure of silole derivatives bearing functional groups on silicon: 1,1-organoboration of dialkynylsilanes

Article abstract of DOI:10.1002/ejic.200900697

Various dialkynylsilanes bearing Si-H or SiCl functions in addition to the alkynyl groups react with an excess of triethylborane after heating at 100-110 °C for several days via slow intermolecular 1,1-ethylboration followed by fast intramolecular 1,1-vin

Full text of DOI:10.1002/ejic.200900697

FULL PAPER
DOI: 10.1002/ejic.200900697
Synthesis and Molecular Structure of Silole Derivatives Bearing Functional
Groups on Silicon: 1,1-Organoboration of Dialkynylsilanes
Ezzat Khan,[a,b] Stefan Bayer,[a] Rhett Kempe,[a] and Bernd Wrackmeyer*[a]
Keywords: Main group elements / Silicon / Boron / Alkynes / Heterocyclic compounds
Various dialkynylsilanes bearing Si–H or SiCl functions in
addition to the alkynyl groups react with an excess of trieth-
ylborane after heating at 100–110 °C for several days via
slow intermolecular 1,1-ethylboration followed by fast intra-
molecular 1,1-vinylboration to give Si-functional substituted
siloles. Similarly, the reactions with 9-ethyl-9-borabicy-
clo[3.3.1]nonane afford polycyclic compounds containing the
silole ring. Protodeborylaton with an excess of acetic acid
leads to simultaneous substitution of BEt2 and Si–H functions
to give 1-acetoxysiloles. All new siloles were characterized
by NMR spectroscopy in solution (1H, 11B, 13C, 29Si NMR),
and for one example of a polycyclic silole derivative the mo-
lecular structure was determined by X-ray analysis.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
In the present work, we report on attempts to use appro-
priate dialkynylsilanes in 1,1-organoboration reactions to
synthesize siloles bearing one or two functional groups, in
particular hydrogen and chlorine, at the silicon atom.
Clearly, such siloles invite for further transformation taking
advantage of the reactive Si–H and/or Si–Cl bonds. The
reaction conditions (Scheme 1) require thermally fairly ro-
bust triorganoboranes, and for this purpose we have se-
lected triethylborane (BEt3) and 9-ethyl-9-borabicyclo[3.3.1]-
nonane (Et-9BBN).
Introduction
Siloles attract increasingly attention owing to their
photo-physical properties.[1–4] Various synthetic procedures
have become available,[5] most of which are multistep pro-
cedures, not generally applicable to introduce a wide range
of different substituents at the silicon or the ring carbon
atoms. In this context 1,1-organoboration[6] has paved a
convenient way to siloles bearing numerous different sub-
stituents in the 2–5 positions.[7] Recently, it was shown that
siloles bearing various organyl groups at silicon can be eas-
ily prepared via 1,1-organoboration (Scheme 1),[8,9] and the
mechanism of this reaction is fairly well understood. The
reaction proceeds in the first step via intermolecular 1,1-
ethylboration, followed in the second step by intramolecu-
lar 1,1-vinylboration.[6–9]
Results and Discussion
The dialkynylsilanes 1–5 (Scheme 2) were prepared by
the reaction of trichlorosilane or tetrachlorosilane with the
respective alkynllithium reagent. In general, these reactions
afforded mixtures of alkynylsilanes, in which less or more
than two Si–Cl were replaced by the Si–CϵC–R func-
tions.[9a] These mixtures were separated by distillation in
order to use the pure dialkynylsilanes for the 1,1-organo-
boration reactions (Scheme 2).
The siloles 6–10 were obtained in Ͼ 90% yield and high
purity in most cases as colorless or yellowish air- and moist-
ure sensitive oils. In the case of siloles containing the SiCl2
unit, the successful 1,1-organoboration reaction was found
to be restricted to 5d leading to 10d (Scheme 2, b). With
substituents (R = alkyl or aryl) other than R = SiMe3, the
products were silacyclobutene derivatives[9a,10] or complex
mixtures of these heterocycles with siloles and other un-
identified products.[9a]
Scheme 1. 1,1-Organoboration of dialkynyldiorganosilanes leading
in high yield to siloles.
[a] Anorganische Chemie II, Universität Bayreuth,
95440 Bayreuth, Germany
Fax: +49-921-552157
E-mail: b.wrack@uni-bayreuth.de
[b] Department of Chemistry, University of Malakand,
Chakdara, Dir (Lower), North West Frontier Province, Paki-
stan
The alkynylsilanes 1a and 1d, precursors of the siloles
6a,d, were most conveniently prepared by the reaction of
the respective chlorosilanes Cl(H)Si(CϵC–R)2 with Li-
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1,1-Organoboration of Dialkynylsilanes
(Scheme 4). The reactions with tBuLi and PhLi afforded
the siloles 12a,d and 8a, respectively, along with minor
amounts of side products. The major side reaction, in the
cases of nBuLi and PhLi, concerned the formation of tetra-
organoborates, e.g. 13d (ca. 10 –20% in repeated experi-
ments), which could not be competely suppressed. Expect-
edly, this was not a problem with the more bulky tert-butyl
group (12a,d), although the reaction of 9d with tBuLi pro-
ceeded rather slowly, and the conditions have not been opti-
mized as yet.
All siloles 6–12 were characterised in solution by their
typical NMR spectroscopic data (Table 1). Most note-
worthy in this respect were the 29Si NMR spectra which
were recorded in many cases with a signal-to-noise ratio to
show the 13C satellites owing to 29Si-13C spin spin coupling
(e.g. Figure 1). Similarly, the 13C NMR spectra (e.g. Fig-
ure 2), are valuable in particular for the olefinic range,
showing the typical pattern of one broad [13C(B-C3=)] and
three sharp [13C(C2,4,5)] NMR signals with the 29Si satellites
Scheme 2. Synthesis of Si-functionally substituted silole derivatives
via 1,1-organoboration reactions.
n
for the determination of J(29Si,13C) (n = 1,2). The latter
AlH4. Alternatively, the siloles 9a,d containing the Si(H)Cl
or the silole 10d were converted into 6a or 6d, respectively,
by treatment with LiAlH4 (Scheme 3).
coupling constants serve for assignments as conclusive in-
formation complementary to the 29Si NMR spectra.
Another thermally fairly stable (with respect to 1,2-dehy-
droboration) trialkylborane is 9-ethyl-9-borabicyclo[3.3.1]-
nonane (Et-9-BBN).[11] The dialkynylsilanes 2 and 3 were
shown to react with Et-9-BBN selectively by twofold expan-
sion of the bicyclic ring system (Scheme 5) to give the poly-
cyclic silole derivatives 14 and 15, again in high yield and
purity as oils or crystalline solids (vide infra). The proposed
solution-state structures of the siloles 14 and 15 follow from
a consistent NMR spectroscopic data set (Table 2).
The molecular structure of the silole 15b (Figure 3) was
determined by X-ray analysis. Intermolecular interactions
appear to be negligible. The structural parameters of the
silole ring are typical.[5,12] Expectedly, the endocyclic bond
angle C1–Si1–C13 is small [92.3(2)°]. All atoms of the silole
Scheme 3. Three routes to siloles containing the SiH2 moiety.
The availability of the Si–Cl bond in siloles is an impor- ring are almost in the same plane (mean deviation 2.6 pm).
tant starting point to explore the chemistry of siloles.[5] The surroundings of the boron atom are trigonal planar,
Here, we report some preliminary first results for our new and the plane C7B1C20 forms an angle of 122.0° relative
siloles with respect to the introduction of various organyl to the silole ring. The phenyl groups C1–Ph and C13–Ph
substituents at silicon, starting from the siloles 9a,d are twisted by 119.5° and 25.7°, respectively, against the sil-
Scheme 4. Replacement of Si–Cl function in the siloles 9a,d by Si-alkyl or Si-Ph groups.
Eur. J. Inorg. Chem. 2009, 4416–4424
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E. Khan, S. Bayer, R. Kempe, B. Wrackmeyer
FULL PAPER
Table 1. 11B, 13C and 29Si NMR spectroscopic data[a] for the siloles 6–12.
δ
13C
δ
29Si
δ
11B
Si–R1
C2
C3
C4
C5
6a[b]
H
H
136.2 [65.2]
141.3 [45.3]
[63.8]
170.7br
157.7 [10.3]
174.1 [11.1]
132.6 [70.1]
133.7 [48.2]
[62.9]
–41.1
–19.9 {10.3};
–10.0, –10.4(SiMe3)
86.0
88.1
6d[c]
190.1br
7a[d]
7b[e]
7c[f]
7e[g]
8a[h]
8b[i]
8c[j]
8e[k]
9a[l]
9d[l]
Me
Me
Me
Me
Ph
Ph
Ph
Ph
Cl
139.4 [64.4]
143.9 [63.8]
143.6 [63.9]
135.4 [64.6]
138.7 [54.7]
142.3 [65.1]
142.0 [65.1]
133.9 [65.4]
135.3 [73.1]
139.9 [48.3]
[63.3]
168.2br
170.6br
169.8br
169.9br
169.8br
172.0br
171.3br
171.3br
169.1br
186.9br
155.7 [11.6]
158.1 [10.1]
157.8 [10.5]
157.4 [10.4]
157.4 [10.9]
159.6 [10.5]
159.3 [10.5]
158.9 [10.5]
157.2 [15.7]
173.3 [10.2]
[12.7]
135.2 [69.0]
138.1 [67.2]
137.6 [67.5]
130.3 [68.4]
134.9 [68.9]
137.1 [68.4]
136.7 [68.8]
129.2 [68.5]
131.7 [78.8]
132.3 [55.6]
[61.9]
–15.9
–12.2
–12.6
–11.8
–14.9
–12.9
–13.2
–11.9
87.0
87.2
87.1
86.9
86.4
86.8
86.8
86.8
89.7
87.1
–7.0
9.8:
Cl
–10.2, –9.8 (SiMe3)
36.0;
10d[m]
Cl2
145.2
186.4br
171.4
132.4
88.1
–9.2, –9.5 (SiMe3)
–12.8
10.0 {10.2}:
–10.7, –11.1(SiMe3)
–4.3
11a[n]
11d[o]
Bu
Bu
138.7
143.5 [42.8]
[62.9]
133.7 [63.4]
143.2
168.9br
187.7br
156.3
173.2 [10.7]
134.3
135.4 [48.1]
[62.0]
137.7 [62.0]
135.7
86.7
88.9
12a[p]
12d[q]
tBu
tBu
168.9br
188.6br
156.7 [10.2]
175.3
85.4
85.8
21.3:
–10.6, –10.9(SiMe3)
1
2
[a] Data measured at 23Ϯ1 °C as C6D6 solution (10–15% in 5 mm o.d. NMR tubes). Values in brackets are J(29Si,13C) and J(29Si,13C)
and those in braces belong to J(29Si,29Si). Superscript “br” means broad: 13C nuclei directly linked to 11B give broad signals as a result
2
of partially relaxed 13C-11B spin-spin coupling.[17] [b] Other 13C NMR spectroscopic data: δ = 22.6br, 9.2 (BEt2), 32.8, 13.9 (Et), 14.28,
14.30, 23.3, 23.4, 24.9, 28.9, 34.9, 35.4 (Bu) ppm. [c] Other 13C data: δ [J(29Si,13C)] = 22.4br, 9.4 (BEt2), 30.2, 15.2 (Et), 1.4 [52.0, SiMe3],
1.5 [51.6, SiMe3] ppm. [d] Data taken from ref. [9b]. [e] Other 13C NMR spectroscopic data: δ [J(29Si,13C)] = –6.8 [49.8, Si-Me], 22.3br,
9.7 (BEt2), 24.7, 14.3 (Et), 141.7 [6.6, C-i], 140.6 [6.0, C-i], 128.8, 128.8, 128.6, 128.0, 126.5 (C-p), 126.0 (C-p) (Ph) ppm. [f] Other 13C
NMR spectroscopic data: δ [J(29Si,13C)] = –6.6 [49.6, SiMe], 22.3br, 9.8 (BEt2), 24.8, 14.4 (Et), 138.9 [6.6, C-i], 137.7 [6.1, C-i], 129.6 (C-
o), 129.5 (C-o), 128.6 (C-m), 128.0 (C-m), 135.9 (C-p), 135.2 (C-p), 21.2 (Me), 21.1 (Me) (4-Me-C6H4) ppm. [g] Other 13C NMR spectro-
scopic data: δ [J(29Si,13C)] = –6.1 [49.4, Si-Me], 22.3br, 9.6 (BEt2), 25.7, 13.8 (Et), 142.3 [7.2], 139.9 [6.4], 128.9, 127.8, 126.2, 125.5, 121.0,
120.2 (3-thienyl) ppm. [h] Other 13C NMR spectroscopic data: δ [J(29Si,13C)] = 34.9, 34.3, 32.6, 28.8, 23.3, 23.3, 14.2, 14.2 (Bu), 22.9br,
9.4 (BEt2), 24.9, 14.1 (Et), 134.0 [63.5, C-i], 135.6 (C-o), 129.8 (C-p), 128.5 (C-m) (SiPh) ppm. [i] Other 13C NMR spectroscopic data: δ
[J(29Si,13C)] = 22.3br, 9.9 (BEt2), 24.9, 14.3 (Et) 141.4 [6.7, C-i], 140.2 [5.9, C-i], 128.72, 128.65, 128.64, 128.63, 126.6 (C-p), 126.1 (C-p)
(Ph), 131.9 [67.4, C-i], 135.7 (C-o), 128.3 (C-m), 128.7 (C-p) (SiPh) ppm. [j] Other 13C NMR spectroscopic data: δ [J(29Si,13C)] = 22.3br,
9.9 (BEt2); 24.9, 14.4 (Et), 138.6 [6.7, C-i], 137.3 (C-i), 129.6, 129.5, 128.7, 128.6, 136.1 (C-p), 135.4 (C-p), 21.0 (Me), 21.1 (Me) (4-Me-
C6H4), 132.2 [67.4, C-i], 135.8 (C-o) 128.2 (C-m), 130.3 (C-p) (SiPh). [k] Other 13C NMR spectroscopic data: δ [J(29Si,13C)] = 22.4br, 9.6
(BEt2), 25.9, 13.8 (Et), 132.3 [67.2, C-i], 135.7 (C-o), 128.7 (C-m), 130.4 (C-p) (SiPh), 142.0 [7.3], 139.6 [6.5], 129.2, 127.9, 126.2, 125.4,
121.4, 120.7 (3-thienyl) ppm. [l] Data taken from ref.[9a]. [m] Other 13C NMR spectroscopic data: δ [J(29Si,13C)] = 0.76 [53.4, SiMe3], 0.84
[54.2, SiMe3], 23.0br, 9.3 (BEt2), 30.7, 13.9 (Et). [n] Other 13C NMR spectroscopic data: δ = 11.2, 14.0, 24.7, 33.0 (SiBu), 14.31, 14.34,
23.3, 23.4, 26.5, 29.1, 34.5, 35.1 (Bu), 22.8br, 9.3 (BEt2), 27.2, 14.1 (Et). [o] Other 13C NMR spectroscopic data: δ [J(29Si,13C)] = 1.57
[51.6, SiMe3], 1.62 [51.8, SiMe3], 12.3 [48.1], 26.6 [6.5], 26.3, 15.4 (SiBu), 22.8br, 9.6, 9.5 (BEt2), 30.3, 14.0 (Et) ppm. [p] Other 13C NMR
spectroscopic data: δ [J(29Si,13C)] = 27.7, 17.6 [53.6] (tBu), 14.3, 14.4, 23.3, 23.4, 24.9, 29.5, 34.9, 35.5 (Bu), 22.7br, 22.8br, 9.2, 9.3 (BEt2),
33.6, 14.3 (Et) ppm. [q] Other 13C NMR spectroscopic data: δ [J(29Si,13C)] = 2.2, 2.3 [54.7, 53.2, SiMe3], 11.6 [49.9], 29.4 (tBu), 22.3br,
9.5 (BEt2), 32.0, 14.4 (Et) ppm.
Figure 1. Examples of 59.6 MHz 29Si{1H} NMR spectra refocused INEPT[16] of a dialkynylsilane (2c) and a silole (7b), showing the 13C
n
satellites corresponding to J(29Si,13C) as indicated by asterisks and arrows.
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1,1-Organoboration of Dialkynylsilanes
Figure 2. Parts of 100.5 MHz, 13C{1H} NMR spectra of the silole 7b (upper trace), and the 1-acetoxysilole 16b (lower trace); 29Si satellites
1
2
are marked by asterisks corresponding to J(29Si,13C) and J(29Si,13C) belonging to the silole ring. Note the broad and fairly weak 13C3
NMR signal for 7b, owing to partially relaxed scalar 13C-11B spin-spin coupling.[17] In 16b the satellite signals marked by black arrows
2
correspond to J[29Si,13C(Ph-i)].
ole ring. The bond lengths between the ring carbon atoms
are slightly elongated when compared with other siloles[5,12]
which in the case of C2–C12 [151.6(6) pm] and C12–C13
[137.3(6) pm], might be explained by hyperconjugative ef-
fects.[13] These can be stronger, if the diorganoboryl group
is allowed to adopt a perpendicular orientation of the BC2
plane with respect to the silole ring. So far only two other
examples of a 3-boryl-substituted silole have been structur-
Scheme 5. Reactions of dialkynylsilanes with Et-9-BBN.
Table 2. 11B, 13C and 29Si NMR spectroscopic data[a] for polycyclic siloles 14 and 15.
δ
13C
δ29Si
δ11B
Si–R1
C2
C3
C4
C5
Me
14b[b]
14c[c]
15b[d]
15c[e]
15e[f]
147.5[g]
171.6br
170.7br
173.3br
172.4br
172.5br
167.4 [8.8]
167.2 [9.4]
169.1 [9.1]
168.9 [9.1]
169.0 [9.3]
134.9 [67.4]
134.4 [68.2]
133.7 [67.2]
133.3 [68.9]
133.7[g]
–13.5[g]
–13.2[g]
–13.5[g]
–13.8[g]
–12.7[g]
88.0
87.8
88.1
88.1
88.0
147.3 [64.0][g]
145.9 [61.0]
142.6[g]
Ph
143.9[g]
1
2
br
[a] Measured in C6D6 at 23 °C, coupling constants J(29Si,13C) and J(29Si,13C) are listed in square brackets, denotes broadened 13C
NMR signals owing to 13C-11B scalar spin-spin coupling.[17] [b] Other 13C NMR spectroscopic data: δ [J(29Si,13C)] = –6.8[g] (SiMe), 11.2,
21.8, 22.3br, 23.2br, 30.5, 30.7, 34.8, 34.9br (Et-BC8H14), 142.9[g] (C-i), 140.9 [5.8, C-i], 128.8 (C-o), 128.7 (C-o), 128.5 (C-m), 128.0 (C-m),
126.8 (C-p), 125.9 (C-p) (Ph). [c] Other13C NMR spectroscopic data: δ [J(29Si,13C)] = –6.7[g] [49.4, SiMe], 30.7br, 34.9, 34.8, 30.5br, 21.7,
11.3 (Et-BC8H14), 140.1[g] [6.4, C-i], 137.9 [6.1, C-i], 136.2, 135.1, 129.5, 129.4, 128.5, 128.3, 21.2, 21.2 (4-Me-C6H4). [d] Also measured
at 40 °C and 60 °C (see e.g. Figure 4), other 13C NMR spectroscopic data: δ = 11.3, 21.7, 22.0,[g] 22.3,[g] 30.6, 34.9, 35.0br (Et-BC8H14),
140.5[g] (C-i), 137.5 (C-i), 135.8, 132.1[g] (C-i), 130.4, 128.7, 128.7, 128.6, 128.3, 126.9, 126.0 (Ph, SiPh). [e] Other 13C NMR spectroscopic
data: δ = 35.1br, 30.7, 23.7br, 23.6, 11.4 (Et-BC8H14), 145.8[g] (C-i), 139.9[g] (C-i), 129.5 (C-o), 129.4 (C-o), 128.6 (C-m), 128.6 (C-m), 136.5
(C-p), 135.2 (C-p), 21.0 (Me), 21.1 (Me) (4-Me-C6H4), 132.5[g] (C-i), 135.9 (C-o), 128.3 (C-m), 130.3 (C-p) (SiPh). [f] Other 13C NMR
dara: δ[29Si,13C] = 11.3, 2.15, 23.6br, 30.5, 30.9, 33.9, 35.0br, 35.3 (Et-BC8H14), 139.8 [6.6,], 138.8,. [g] 129.0, 128.0, 126.2, 125.3, 120.8,
120.5 (3-thienyl), 132.3[g] (C-i) 135.9 (C-o), 128.7 (C-m), 130.5 (C-p) (SiPh) ppm. [g] 13C and 29Si NMR signals are exchange broadened.
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E. Khan, S. Bayer, R. Kempe, B. Wrackmeyer
FULL PAPER
ally characterized, which were obtained by 1,1-organobor-
Prior to certain further applications of the new siloles, it
ation of dialkynyl-diorganosilanes with B(C6F5)3.[14] Ap- might be useful to remove the boryl group by protodeboryl-
parently, the B(C6F5)2 in 3- and the C6F5 groups in 4-posi- ation reactions. In the case of the diethylboryl-substituted
tion take no major influence on the distances and bond siloles, treatment with an excess of acetic acid serves for this
angles in the silole ring.
purpose,[15] as shown for the siloles 7 and 8 (Scheme 6). The
protodeborylation is accompanied by substitution of the
Si–H function. Apparently other carboxylic acids can also
be used. In the cases shown in Scheme 6, the bicyclic bo-
ron–oxygen compounds 19 and 20 are formed.[15] The sil-
oles 16–18 are readily charcterized by their NMR spectro-
scopic data (Table 3; see also Figure 2 and Figure 5).
Conclusions
Siloles bearing functional substituents at silicon can be
obtained in high yield by a straightforward one-step synthe-
sis via 1,1-organoboration of appropriate dialkynylsilanes.
These functionalities invite for numerous further transfor-
mations which may include novel silylium cations, silylenes
and also silole anions and silole dianions.
Experimental Section
General: All manipulations and preparative work with air and
moisture sensitive chemicals were carried out under dry argon at-
mosphere. Dialkynylsilanes were prepared and purified following
reported procedures,[9a,18] and were fully characterized by multinu-
clear NMR spectroscopy.[21] Other chemicals such as, n-butyllith-
ium (1.6  in Hexane), tert-butyllithium (1.7  in pentane), phen-
yllithium (1.8  in cyclohexane/diethyl ether), glacial acetic acid
and triethylborane (BEt3) were commercial products and were used
as received. Ethyl-9-borabicyclo[3.3.1]nonane was prepared accord-
ing to the literature procedure.[11] NMR spectra: Bruker ARX 250
or Varian Inova 300 and 400 spectrometers (23Ϯ1 °C), all
equipped with multinuclear units, using C6D6 solutions, if not men-
tioned other wise (ca. 10–15% v/v) in 5 mm o. d. tubes. Chemical
shifts are given relative to SiMe4 [δ1H (C6D5H) = 7.15, δ13C (C6D6)
= 128.0, δ29Si = 0 for SiMe4 with Ξ(29Si) = 19.867187 MHz], and
δ11B = 0 for BF3–OEt2 with Ξ(11B) = 32.083971 MHz. 29Si NMR
spectra were recorded using the refocused INEPT pulse sequence
with 1H decoupling[16] based on nJ[29Si,1H(Me/Ph)] ≈ 7 Hz (n =
2,3), 3J[29Si,1H(C4)] ≈ 20–25 Hz, and 1J(29Si,1H) ≈ 200 Hz (after
Figure 3. Molecular structure of the polycyclic silole 15b (ORTEP
plot, 40% probability, hydrogen atoms except Si–H are omitted for
clarity) Selected bond lengths [pm] and angles [°]: C1–C2 135.1(6),
C2–C12 151.6(6), C12–C13 137.3(6), C13–Si1 186.1(4), C1–Si1
185.4(4), C22–Si1 186.7(4), C1–C28 148.0(6), C2–C3 151.0(6),
C13–C14 147.1(6), C7–B1 157.7(7), B1–C12 157.0(7), B1–C20
158.3(6), C2–C1–Si1 108.3(3), C1–C2–C12 116.4(4), C13–C12–C2
113.9(4), C12–C13–Si1 108.6(3), C1–Si1–C13 92.3(2), C1–Si1–C22
112.6(2), C28–C1–Si1 125.2(3), C12–B1–C7 127.0(4), C12–B1–C20
115.1(4), C7–B1–C20 117.8(4).
In the case of 15b, the conformation of the two rings
with the bridge head atoms C3 and C7 are different. This
1
is noteworthy, since it explains the somewhat puzzling H,
13C and 29Si NMR spectra in solution (Figure 4).
1
The H, 13C NMR spectra measured at room tempera-
ture of the siloles 14 and 15 reveal the expected signals, of
which however, some are unexpectedly broad, and the 29Si
1
NMR signals are severely broadened, similar to the H(Si–
H) resonances (see Figure 4). Since the silicon atom is a optimization of the respective refocusing delays). EI-MS spectra:
b
chiral center, there should be four signals for the 13C(CH2 )
Finnigan MAT 8500 spectrometer (ionisation energy 70 eV) with
direct inlet, the m/z data refer to the isotopes 1H, 12C, 11B, 28Si,
35Cl. Elemental analyses (C/H) were performed on a Vario Ele-
mentar EL III. Melting points (uncorrected) were determined by
using Büchi 510 melting point apparatus.
c
and two for the 13C(CH2 ) nuclei, all of which should be
sharp. These signals, however, are extremely broad, barely
visible at room temperature, and they become sharper at
1
60 °C. Similarly, both the H(Si–H) and 29Si NMR signals
Syntheses of 2,5-Bis(alkyl/aryl)-3-diethylboryl-4-ethylsiloles 6–10
via 1,1-Ethylboration of Dialkynylsilanes 1–5: Methylbis(phenyle-
thynyl)silane 2b (2.97 g; 12.1 mmol) was filled into a Schlenk tube
and triethylborane (5 mL) was added in excess. The reaction mix-
ture was heated to 100–110 °C for 2 d. All volatiles were removed
in vacuo, the yellow to brown oily liquid left was identified as silole
7b. This experimental procedure and the work up procedure were
identical for all other silole derivatives, except of sight differences
in temperature and reaction times. Thus, the reaction of dihexyn-
1-ylsilane 1a with triethylborane was carried out at 80 °C and was
found to be complete after 18 h to afford silole 6a. Other examples
become much sharper with increasing temparature. This be-
havior can be understood considering the solid-state molec-
ular structure, e.g. of 15b. In solution at room temperature,
the inversion of the two different rings containing carbon
atoms a, b1, c1, d and a, b2, c2, d, is slow relative to the
NMR time scale. At higher temperature, the rate of ring
inversion increases, and the rings adopt on average the
structure depicted schematically in Figure 4. As shown,
these dynamic processes also affect the line widths of some
of the 13C(phenyl) and of the 13C(C2) NMR signals.
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 4416–4424

1,1-Organoboration of Dialkynylsilanes
Figure 4. 1H, 13C (in part) and 29Si NMR spectra of the silole 15b measured at various temperatures. The 13C NMR signals most notably
broadened by dynamic processes are marked by arrows.
are 6d (18 h/80 °C), 7c (2 d/105 °C), 7e (ca. 70% after 2 d/110 °C),
8a,b,c,e (≈ 95% after 7 d/105 °C;), 10d (40% after 5 d/105 °C).
6a: Yield 90%. 1H NMR (250 MHz): δ = 0.75–0.95 (m, 12 H, CH3,
Bu, BEt2, Et), 1.25–1.45 (m, 12 H, Bu, BCH2), 2.05 [m, 2 H, (CH2)-
1
Et], 2.25 (m, 4 H, Bu), 4.36 [s, 2 H, J(29Si,1H) = 189.1 Hz, SiH2]
ppm. Calcd. (found): C 74.45 (74.21), H 12.15 (12.07).
6d: Yield 70%. 1H NMR (250 MHz): δ = 0.16, 0.25 (s, s, 18 H,
SiMe3), 0.93, 2.23 (t, q, 5 H, Et), 0.98, 1.35 [t (br), m, 10 H, BEt2],
1
4.78 [s, J(29Si,1H) = 189.8 Hz, 2 H, SiH2] ppm. Calcd. (found): C
62.38 (61.95), H 10.18 (10.22).
7b: 1H NMR (400 MHz): δ = 0.20 (d, 3J = 4.2 Hz, 3 H, SiMe),
0.95, 1.35 [t (br), br, 10 H, BEt2], 0.77, 2.14, 2.34 (t, m, m, 5 H,
3
1
Et), 5.03 [q, J = 4.2, J(29Si,1H) = 190.9 Hz, 1 H, SiH], 6.93–7.05,
7.14–7.22 (m, m, 10 H, Ph) ppm. 7c: 1H NMR (400 MHz): δ =
0.25 (d, J = 4.2 Hz, 3 H, SiMe), 1.04, 1.39 [t (br), br, 10 H, BEt2],
3
Scheme 6. Protodeborylation of the silole derivatives 7 and 8.
Eur. J. Inorg. Chem. 2009, 4416–4424
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4421

E. Khan, S. Bayer, R. Kempe, B. Wrackmeyer
Table 3. 13C and 29Si NMR spectroscopic data[a] for protodeborylated silole derivatives 21–23.
FULL PAPER
Si–R1
δ
13C
δ
29Si
MeCO2
C-2
C-3
C-4
C-5
Me
16a[b]
16b[c]
16c[d]
17a[e]
17b[f]
17e[g]
18a[h]
171.3, 22.0
170.1, 22.0
170.0, 22.1
170.5, 22.1
169.6, 21.9
170.1, 22.1
171.9, 59.1
(Ph2HCCO2)
140.3 [79.2]
139.2 [74.4]
138.8 [74.4]
140.3 [75.4]
138.6 [76.2]
132.5 [76.2]
139.9 [75.1]
153.9 [11.3]
155.6 [10.4]
155.3 [10.5]
155.4 [11.6]
156.6 [10.6]
157.2 [10.6]
155.6 [11.8]
144.2 [11.9]
142.8 [10.9]
142.0 [10.3]
145.3 [11.8]
144.1 [10.8]
145.0 [10.5]
145.5 [12.2]
130.0 [79.8]
132.8 [79.0]
132.2 [79.3]
132.5 [76.6]
132.5 [80.5]
124.6
10.6
8.6
8.8
–2.9
–5.9
–5.1
–2.1
Ph
132.1 [76.8]
1
2
[a] Measured in C6D6 at 23 °C, coupling constants J(29Si,13C) and J(29Si,13C) are given in brackets. [b] Other 13C NMR spectroscopic
data: δ[J(29Si,13C)] = –3.7 [56.9, SiMe], 32.9, 32.5, 31.9, 28.2, 23.2, 23.0, 14.3, 14.2 (Bu), 23.7, 12.9 (Et) ppm. [c] Other 13C NMR
spectroscopic data: δ[J(29Si,13C)] = –3.6 [59.8, SiMe], 24.8, 13.1 (Et), 139.5 [5.9, C-i], 137.9 [5.9, C-i], 129.1, 128.7, 128.5, 127.1, 127.7 (C-
p), 126.4 (C-p) (Ph) ppm. [d] Other 13C NMR spectroscopic data: δ[J(29Si,13C)] = –3.4 [59.6, SiMe], 24.9, 13.2 (Et), 136.5 [5.9, C-i], 135.2
[5.9, C-i], 129.8 (C-o), 129.5 (C-o), 128.5 (C-m), 127.2 (C-m), 137.2 (C-p), 135.2 (C-p), 21.2 (Me), 21.3 (Me) (4-Me-C6H4) ppm. [e] Other
13C NMR spectroscopic data: δ[J(29Si,13C)] = 24.1, 13.0 (Et), 32.8, 32.4, 31.7, 28.3, 23.1, 22.9, 14.2, 14.1 (Bu), 135.1 (C-i), 134.3 (C-o),
128.4 (C-m), 130.5 (C-p) (SiPh) ppm. [f] Other 13C NMR spectroscopic data: δ[J(29Si,13C)] = 25.0, 13.2 (Et), 139.3 [5.9, C-i], 137.7 [5.6,
C-i], 134.8, 131.1, 129.0, 128.7, 128.6, 128.6, 127.7, 127.2, 126.4 (SiPh, Ph) ppm. [g] Other 13C NMR spectroscopic data: δ [29Si,13C] =
25.7, 12.8 (Et), 130.9 [80.4, C-i], 135.7 (C-o), 128.7 (C-m), 131.2 (C-p) (Si-Ph), 139.3 [6.2], 138.8 [6.3], 128.5, 126.1, 125.7, 125.4, 123.2,
121.8 (3-thienyl) ppm. [h] Other 13C NMR spectroscopic data: δ[J(29Si,13C)] = 24.1, 13.0 (Et), 14.11, 14.14, 22.9, 23.1, 28.3, 31.7, 32.3,
32.7 (Bu), 139.3, 139.3, 129.2, 128.8, 128.8, 128.5, 127.4, 127.4 (Ph2AcO), 132.2 [77.1, C-i], 134.3 (C-o), 129.2 (C-m), 130.6 (C-p) (SiPh)
ppm.
1
8e: H NMR (400 MHz): δ = 1.05, 1.49 (t, br, 10 H, BEt2), 0.95,
2.32 (t, m, 5 H, Et), 5.49 [s, 1J(29Si,1H) = 197.1 Hz, 1 H, SiH], 6.68,
6.73, 6.83, 6.94, 7.00 (m, m, m, m, m, 6 H, 3-thienyl), 7.08, 7.68
(m, m, 5 H, SiPh) ppm.
1
9a: Yield 86%; b. p. 120 °C/1.0ϫ10–3 Torr. H NMR (250 MHz):
δ = 0.8, 0.9, 1.3, 2.3 (t, t, m, t, 18 H, nBu), 0.9, 2.0 (t, m, 5 H, Et),
1
0.9, 1.6 (t, br, 10 H, BEt2), 5.5 [s, J(29Si,1H) = 237.4 Hz, 1 H, Si-
H] ppm. calcd. (found): C 66.36 (65.97), H 10.52 (10.43), Cl 10.88
(10.65).
1
9d: H NMR (400 MHz): δ = 0.2, 0.3 (s, s, 18 H, SiMe3), 0.9, 2.2
1
(t, m, 5 H, Et), 0.9, 1.0, 1.3 (t, t, m, 10 H, BEt2), 5.6 [s, J(29Si,1H)
= 222.4 Hz, 1 H, Si-H] ppm. EI-MS (70 eV): m/z (%) = 356 (62)
[M+], 341 (46) [M+ – CH3], 328 (100) [M+ – C2H2], 299 (19) [328 –
Figure 5. Expansion of 59.6 MHz, proton-decoupled 29Si NMR
C2H3], 283 (8) [M+ – SiMe3], 263 (14) [no Cl], 219 (31) [no Cl], 201
spectra of 17b (refocused INEPT[16]). The 13C satellites (asterisks)
(12) [no boron], 111 (50) [SiC6H11+], 97 (50) [Me3Si–CC+], 73 (99)
1
2
correspond to J(29Si,13C), (arrows) to J[29Si,13C(C3,C4)] (all val-
[SiMe3+], 59 (26) [SiC2H7+].
ues are in agreement with data taken from the 13C NMR spectrum),
and (open circles) to J(29Si,13C) (nՆ2).
n
10d: 1H NMR (250 MHz): δ = 0.2 [s (br), 18 H, SiMe3], 0.7–2.2
(m, 15 H, BEt2, Et) ppm. Calcd.(found): C 51.78 (51.12), H 8.47
(8.32), Cl 16.98 (16.76).
3
1
0.83, 2.19, 2.40 (t, m, m, 5 H, Et), 5.05 [q, J = 4.2, J(29Si,1H) =
190.0 Hz, 1 H, SiH], 2.05, 2.12, 6.89, 7.01, 7.15, (s, s, m, m, m, 14
H, 4-Me-C6H4) ppm.
Synthesis of Siloles 8, 11 and 12: Silole 9a (4.22 mg; 1.3 mmol) was
dissolved in hexane (5 mL), the solution was cooled to –78 °C, and
a slight excess of BuLi (0.9 mL; 1.4 mmol) was slowly added
through a syringe. The reaction mixture was allowed to reach r. t.
and was kept stirring for 12 h. Then the mixture was heated at
60 °C for 5 min. Solid materials were filtered off and all volatiles
were removed under reduced pressure (20 Torr). The light yellow
oily residue left was identified as 1,2,5-tributyl-3-diethylboryl-4-
ethylsilole (11a) (Ͼ 95% by NMR). The same synthetic procedure
was adopted for the preparation of silole 11b. Substitution of the
Si–Cl function in 9a by the tBu group using tBuLi was carried out
in a simillar way. The reaction afforded mainly the desired silole
12a (Ͼ 70%) accompanied by starting material 9a (ca. 10%). Low
yield was achieved in the case of 12d (ca. 40% by NMR), very low
for silole 8a (30%) and extremely low for 8d (5%).
7e: 1H NMR (400 MHz): δ = 0.28 (d, 2J = 4.1 Hz, 3 H, SiMe),
1.08, 1.42 [t (br), br, 10 H, BEt2], 0.91, 2.27 (t, m, 5 H, Et), 4.96
[q, 2J = 4.1, 1J(29Si,1H) = 190.5 Hz, 1 H, SiH], 6.61–6.69, 6.88–
6.93, 7.01 (m, m, m, 6 H, 3-thienyl) ppm.
1
8a: H NMR (400 MHz): δ = 1.96–2.17, 1.10–1.38, 0.99 (m, m, t,
18 H, Bu), 1.28, 0.85 (m, t, 10 H, BEt2), 1.27, 0.68 (m, t, 5 H, Et),
5.16 [s, 1J(29Si,1H) = 189.6 Hz, 1 H, SiH], 7.15–7.56 (m, 5 H, SiPh)
ppm.
8b: 1H NMR (400 MHz): δ = 1.42, 1.02 [t (br), br, 10 H, BEt2],
1
0.86, 2.23, 2.36 (t, m, m, 5 H, Et), 5.52 [s, J(29Si,1H) = 197.4 Hz,
1 H, SiH], 6.92–7.07, 7.18, 7.60 (m, m, m, 15 H, SiPh, Ph) ppm.
8c: 1H NMR (300 MHz): δ = 1.11, 1.50 [t (br), br, 10 H, BEt2],
8d: 1H NMR (250 MHz): δ = 0.03, 0.14 (s, s, 18 H, SiMe3), 4.88 [s,
1
0.92, 2.33, 2.47 (t, m, m, 5 H, Et), 5.66 [s, J(29Si,1H) = 195.8 Hz, 1J(29Si,1H) = 185.2 Hz, 1 H, SiH], 6.9–7.4 (m, 5 H, SiPh) ppm. 13
C
1 H, SiH], 1.98, 2.06, 6.79–7.21, 7.71 (s, s, m, m, 14 H, 4-Me-C6H4)
ppm.
NMR (62.9 MHz): δ = 0.5, –0.6 (SiMe3), 22.9 br, 9.4 (BEt2) ppm.
29Si NMR (49.7 MHz): δ = 4.6, –10.2, –10.8 ppm.
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 4416–4424

1,1-Organoboration of Dialkynylsilanes
1
11a: H NMR (250 MHz): δ = 0.78, 0.88, 0.90, 1.35, 2.31 (t, t, t,
phenylacetic acid (1.22 g; 5.7 mmol; in slight excess) was carried
m, m, 27 H, SiBu, Bu), 0.93, 2.03 (t, m, 5 H, Et), 1.06, 1.4–1.6 [t
out at 80–100 °C for 3–4 h. Silole 18a was obtained along with a
(br), br, 10 H, BEt2], 4.78 [s, 1J(29Si,1H) = 179.5 Hz, 1 H, SiH] small amount of diphenylacetic acid which could not be completely
ppm.
separated.
11d: Yield 92%. 1H NMR (250 MHz): δ = 0.16, 0.26 (s, s, 18 H,
SiMe3), 0.84, 2.12 (t, m, 5 H, Et), 0.88, 0.93, 1.35–1.50 (t, t, m, 9
H, SiBu), 1.00, 1.35–1.50 [t (br), m, 10 H, BEt2], 4.91 [s, 1J(29Si,1H)
= 183.7 Hz, 1 H, Si-H] ppm.
16a: 1H NMR (400 MHz): δ = 0.46 (s, 3 H, SiMe), 0.86–0.94, 1.26–
1.56, 2.23–2.40 (m, m, m, 18 H, Bu), 1.19, 2.10 (t, m, 5 H, Et), 1.70
(s, 3 H, MeCO2), 6.38 [s, 3J(29Si,1H) = 17.1 Hz, 1 H, C4H] ppm.
16b. 1H NMR (400 MHz): δ = 0.54 (s, 3 H, SiMe), 0.91, 2.22 (t,
m, 5 H, Et), 1.50 (s, 3 H, MeCO2), 7.03 (t, 1 H, C4H), 7.17, 7.24,
7.53 (m, m, m, 10 H, Ph) ppm.
1
12a: H NMR (250 MHz): δ = 0.87, 1.33, 2.2–2.4 (t, m, m, 18 H,
Bu), 0.90, 2.03 (t, q, 5 H, Et), 1.05, 1.40–1.60 [t (br), m (br), 10 H,
1
BEt2], 1.11 (s, 9 H, tBu), 4.53 [s, J(29Si,1H) = 181.7 Hz, 1 H, SiH]
16c: 1H NMR (400 MHz): δ = 0.60 (s, 3 H, SiMe), 0.96, 2.28 (t,
3
m, 5 H, Et), 1.55 (s, 3 H, MeCO2), 7.10 [s, J(29Si,1H) = 15.6 Hz,
ppm.
1 H, C4H], 2.09, 2.10, 7.01, 7.19, 7.48 (s, s, m, m, m, 14 H, 4-Me-
1
12d: H NMR (250 MHz): δ = 0.19, 0.29 (s, s, 18 H, SiMe3), 0.8–
1
C6H4) ppm. 17a. H NMR (400 MHz): δ = 0.70–0.97, 1.13, 2.15,
1.0, 2.25 [m (br), q, 5 H, Et], 1.13 (s, 9 H, tBu), 0.8–1.0, 1.3–1.50
2.32 (overlapping multiplets, 23 H, Bu and Et), 1.46 (s, 3 H,
1
[m (br), m (br), 10 H, BEt2], 4.84 [s, J(29Si,1H) = 183.1 Hz, 1 H,
MeCO2), 6.48 (s, 1 H, C4H), 7.14, 7.61 (m, m, 5 H, SiPh) ppm.
SiH] ppm.
1
17b. H NMR (400 MHz): δ = 0.91, 2.29 (t, m, 5 H, Et), 1.51 (s, 3
1,1-Organoboration of Dialkynylsilanes Using 9-Ethyl-9-borabi-
cyclo[3.3.1]nonane: Silane 2b (3 g) was filled into a Schlenk tube
and mixed with an excess (5 mL) of 9-ethyl-9-borabicyclo[3.3.1]-
nonane. This mixture was heated at 120 °C (oil bath temperature).
The progress of the reaction was monitored by 29Si NMR spec-
troscopy. After 12 h the reaction was found to be complete, and all
readily volatile materials were removed in vacuo (ca. 10–1 Torr).
Finally traces of Et-9-BBN had to be removed by heating at 60–
70 °C in vacuo. The silole 14b was obtained in Ͼ 90% yield and
high purity (99%). The other siloles 14 and 15 were synthesized in
the same way. Silole 15b was dissolved in pentane, and after 4 d at
ambient temperature rather small crystals were growing which
could be isolated and used for X-ray structural analysis. Crystals,
again very small, of the same silole could also be obtained in ethyl
ether.
H, MeCO2), 6.93, 7.05, 7.23, 7.49, 7.78 (m, m, m, m, m, 15 H,
3
SiPh, Ph), 7.23 [t, J(29Si,1H) = 16.0 Hz, 1 H, C4H] ppm.
1
17e: H NMR (400 MHz): δ = 1.03, 2.42 (t, m, 5 H, Et), 1.68 (s, 3
H, MeCO2), 6.94–6.99, 7.06, 7.18, 7.23, 7.33, 7.78 (m, m, m, m, m,
m, SiPh, C4H, 3-thienyl) ppm.
1
18a: H NMR (400 MHz): δ = 0.68, 0.68, 1.12, 1.29, 2.10–2.30 (t,
t, m, m, m, 18 H, Bu), 0.89, 2.10–2.30 (t, m, 5 H, Et), 5.05 (s, 1 H,
3
Ph2CH), 6.50 [s, J(29Si,1H) = 17.1 Hz, 1 H, C4H], 6.92–7.07, 7.28,
7.54 (m, m, m, 15 H, SiPh, CPh2) ppm.
X-ray Structural Analysis of 15b:[20] The X-ray crystal structural
analysis of 15b was carried out for a single crystal (selected in per-
fluorinated oil[21] at room temperature) at 133(2) K using a STOE
IPDS II system (wavelength: λ = 0.71069 Å), equipped with an Ox-
ford Cryostream low-temperature unit. Formula weight: 458.50.
Crystal system: Monoclinic. Space group: P21/c. Unit cell dimen-
sions: a = 9.6160 (10) Å, b = 15.248 (2) Å, c = 18.083 (2) Å, β =
102.2°. V = 2591.2 (5) Å3, Z = 4. Absorption coefficient µ =
0.11 mm–1. F(000): 984. Crystal size: 0.35ϫ0.16ϫ0.15 mm3. Theta
range for data collection: 1.8–25.7°. Index ranges: –11Յ hՅ 11,
–15Յ kՅ 18, –21Յ lՅ 22. Reflections collected: 14705. Indepen-
dent reflections [IϾ2σ(I)]: 2825 [R(int) = 0.116]. Data/restraints/
parameters: 2825/0/447. Goodness-of-fit on F2: 1.16. Final R in-
dices [F2 Ͼ 2σ(F2)]: R1 = 0.089, wR2 = 0.157, R indices (all data):
R1 = 0.155, wR2 = 0.139. Largest difference peak and hole: 0.23
and –0.25 eÅ–3. Structure solutions and refinements were ac-
complished using SIR97,[22] SHELXL-97,[23] and WinGX.[24]
14b: Reaction time 10 h. 1H NMR (400 MHz): δ = 0.23 (d, 3J =
3.8 Hz, 3 H, SiMe), 0.82, 1.11, 1.48–2.06, 3.33 (t, br, m, m, 19 H,
Et-B C8H14), 5.06 [br., 1J(29Si,1H) = 190.2 Hz, 1 H, SiH], 6.96–7.20
(m, 10 H, Ph) ppm. 14c: Reaction time 12 h. 1H NMR (400 MHz):
3
δ = 0.27 (d, J = 3.8 Hz, 3 H, SiMe), 0.85, 1.16, 1.57–2.02, 3.46 (t,
br, m, m, 19 H, Et-BC8H14), 2.11, 2.17, 6.96, 7.06, 7.16 (s, s, m, m,
m, 14 H, 4-Me-C6H4), 5.15 [br., 1J(29Si,1H) = 190.2 Hz, Si-H] ppm.
15b: Reaction time 3 d; Yield after recrystallization from pentane
1
87%; m.p. 111–115 °C. H NMR (400 MHz): δ = 0.75, 1.05, 1.38,
1.57, 1.95, 3.27 [t, q (br), m, m, m, t, 19 H, Et-BC8H14], 5.32 [br.,
1J(29Si,1H) = 197.5 Hz, 1 H, SiH], 6.67–7.03, 7.48 (m, m, 15 H,
SiPh, Ph) ppm.
1
15c: Reaction time 3 d. H NMR (300 MHz): δ = 0.96, 1.34, 1.58–
1.85, 3.53 [t, q (br), m, m, 19 H, Et-BC8H14], 5.67 [br., J(29Si,1H)
1
Acknowledgments
= 198.2 Hz, 1 H, SiH], 2.01, 2.07, 6.82–7.14, 7.70 (s, s, m, m, 14
H, 4-Me-C6H4) ppm. 15e: Reaction time 4 d. 1H NMR (400 MHz):
δ = 1.21, 1.46, 1.86–2.14, 2.39, 3.86 (t, br, m, m, m, 19 H, Et-
BC8H14), 5.67 (br., 1 H, Si-H), 6.86, 6.93, 7.06, 7.15 (m, m, m, m,
6 H, 3-thienyl), 7.41, 7.93 (m, m, 5 H, SiPh) ppm.
E. K. is grateful to Deutscher Akademischer Austausch Dienst
(DAAD) and Higher Education Commission (Pakistan) for schol-
arship (Code A/04/30788). This work has been supported by the
Deutsche Forschungsgemeinschaft (DFG). We thank Germund
Glatz and Christian Döring for assistance with the X-ray structural
analysis.
Protodeborylation of Siloles 7 and 8 with Acetic Acid or Di-
phenylacetic Acid: A solution of silole 7a (1.2 g) in pentane (10 mL)
was prepared in a Schlenk tube and glacial acetic acid (3 mL) was
added in excess. The reaction mixture was stirred at room tempera-
ture for 40 min, and all readily volatile materials were removed un-
der reduced pressure (10–2 Torr). The oily product left contained
silole 16a and the bicyclic boron–oxygen compound 19. The experi-
mental procedure for the synthesis of silole 16b,c and 17a,b,e was
exactly the same. The compound 19 could be separated as de-
scribed.[15,19] The reaction of silole 7a (1.04 g; 2.82 mmol) and di-
[1] a) C. Booker, X. Wang, S. Haroun, J. Zhou, M. Jennings, B. L.
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Received: July 22, 2009
Published Online: September 17, 2009
4424
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