Siloles bearing Si-Vinyl and Si-Allyl functions. 1,1-organoboration and protodeborylation

Article abstract of DOI:10.1515/znb-2009-1002

1,1-Organoboration of dialkyn-1-yl(divinyl)silanes, dialkyn-1-yl(organo) (vinyl)silanes and dialkyn- 1-yl(allyl)(methyl)silane using triethylborane, BEt₃, or 9-ethyl-9-borabicyclo[3.3.1]nonane, Et-9- BBN, afforded selectively silole derivatives

Full text of DOI:10.1515/znb-2009-1002

Siloles Bearing Si-Vinyl and Si-Allyl Functions. 1,1-Organoboration
and Protodeborylation
Ezzat Khana,b and Bernd Wrackmeyera
a Anorganische Chemie II, Universita¨t Bayreuth, 95440 Bayreuth, Germany
b Department of Chemistry, University of Malakand, Chakdara, Dir(Lower), N. W. F. P., Pakistan
Reprint requests to Prof. Dr. B. Wrackmeyer. E-mail: b.wrack@uni-bayreuth.de
Z. Naturforsch. 2009, 64b, 1098 – 1106; received September 14, 2009
1,1-Organoboration of dialkyn-1-yl(divinyl)silanes, dialkyn-1-yl(organo)(vinyl)silanes and dialk-
yn-1-yl(allyl)(methyl)silane using triethylborane, BEt3, or 9-ethyl-9-borabicyclo[3.3.1]nonane, Et-9-
BBN, afforded selectively silole derivatives with Si-vinyl and Si-allyl functions, respectively, bearing
the dialkylboryl group in 3-position. The siloles are formed via intermolecular 1,1-alkylboration, fol-
lowed by intramolecular 1,1-vinylboration. In the cases of several 3-diethylboryl-substituted siloles,
smooth and essentially quantitative protodeborylation could be achieved by the reaction of the siloles
with an excess of acetic acid at ambient temperature. All new siloles were characterized in solution
by multinuclear magnetic resonance spectroscopy (1H, 13C, 11B and 29Si NMR).
Key words: Alkynylsilanes, Siloles, Organoboration, Triethylborane, Protodeborylation, NMR
Introduction
from dialkyn-1-ylsilanes, with vinyl group(s) or an al-
lyl group at silicon. This can be useful for further trans-
formation of the siloles and also for incorporating the
siloles into polymers.
Siloles [1] attract increasing interest owing to their
photophysical properties [2, 3] which depend on the
substituents at the silicon and the ring carbon atoms.
A versatile synthesis of siloles aiming for the intro-
duction of different substituents at all ring positions
has been developed, taking advantage of 1,1-organo-
boration [4, 5] of dialkyn-1-ylsilanes. For this purpose,
thermally robust triorganoboranes such as triethylbor-
ane, BEt3, or 9-ethyl-9-borabicyclo[3.3.1]nonane, Et-
9-BBN, have to be used [5 – 7]. Alternatively, triaryl-
boranes [8] or the extremely Lewis-acidic tris(penta-
fluorophenyl)borane, B(C6F5)3, have also proved use-
ful [9]. So far we have accomplished the straightfor-
ward synthesis of numerous siloles of type A and B,
some of which could readily be protodeborylated to
give the siloles C (Scheme 1).
Results and Discussion
1,1-Organoboration
The reactions of the respective alkynyllithium
reagents with diorganosilicon dichlorides [10, 11] led
to the dialkyn-1-ylsilanes 1 – 5 (Schemes 2 – 5), of
which 5 was obtained by consecutive reactions of
dichloro(divinyl)silane in the first step with hexyn-1-
yllithium nBu-C≡C–Li, and in the second step with 4-
tBu-C6H4-C≡C–Li. The dialkyn-1-ylsilanes were pu-
rified by distillation and characterized by NMR spec-
troscopy (e. g. Fig. 1). The NMR data of these starting
alkynes will be described elsewhere [12].
In the present work, we report on the first examples
Treatment of the dialkyn-1-yl(organo)vinylsilanes
of siloles, obtained via 1,1-organoboration starting 1 and 2 with an excess of BEt3 at 100– 120 ◦C
Scheme 1. Some silole derivatives bearing vari-
ous substituents at different positions, prepared
by 1,1-organoboration (A, B), followed by pro-
todeborylation (C), reported so far.
c
0932–0776 / 09 / 1000–1098 $ 06.00 ꢀ 2009 Verlag der Zeitschrift fu¨r Naturforschung, Tu¨bingen · http://znaturforsch.com
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E. Khan – B. Wrackmeyer · Siloles Bearing Si-Vinyl and Si-Allyl Functions
1099
Fig. 1. 100.5 MHz
1
13C{ H} and 59.6 MHz
1
29Si{ H} (upper insert)
NMR spectra of dihexyn-
1-yldivinylsilane
(4a)
◦
(in C6D6, 23 C). Satel-
lite signals marked by
asterisks correspond to
J(29Si, 13C).
Scheme 2. Synthesis of 1,1-organo(vinyl)siloles
and hydroboration of the Si–CH=CH2 function.
(Scheme 2a) afforded the siloles 6 and 7 in essen-
tially quantitative yield. The progress of the reaction
was monitored by NMR spectroscopy. In the case of
1, the reaction proceeded further, if heating was un-
necessarily continued for prolonged periods of time.
Then, BEt3 turned out to act as a hydroboratingreagent
[13, 14], and in repeated experiments variable amounts
of the siloles 6 were converted into siloles 8 via hy-
droboration of the Si–CH=CH2 group (see Fig. 2
for relevant 13C NMR spectra). This was confirmed
(Scheme 2b) by the quantitative hydroboration of 6a
using 9-BBN [15] as a common hydroboratingreagent.
The comparison of the NMR data sets of 8 and 9a was
conclusive.
Scheme 3. Synthesis of the 1-allyl substituted silole 10b.
and silole 10b was obtained without appreciable side
reactions.
Dialkyn-1-yl(divinyl)silanes 4 were treated with
BEt3 in excess (Scheme 4) in the same way as de-
scribed above. Three straightforward examples of 1,1-
divinylsiloles 11 were obtained in essentially quantita-
The successful syntheses of siloles bearing one tive yield (Scheme 4a). The dialkyn-1-yl(divinyl)silane
Si-vinyl function prompted us to study the case of 5 contains two different alkyn-1-yl groups. Apparently,
allyl(methyl)bis(phenylethynyl)silane 3b (Scheme 3), attack of the Si–C≡C-nBu was preferred over that
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1100
E. Khan – B. Wrackmeyer · Siloles Bearing Si-Vinyl and Si-Allyl Functions
1
Fig. 2. Part of the 100.5 MHz 13C{ H} NMR spectra of silole 6a, (bottom, after heating the mixture of 1a in BEt3 for 3 d at
◦
100 – 120 ◦C). The upper trace illustrates the result of the same reaction after 13 d at 100 – 120 C: 6a and 8a. 29Si satellite
n
signals marked by asterisks correspond to J(29Si, 13C) (n = 1,2), and J values are given in brackets. The typically broad
13C(3) NMR signal indicates the linkage C–B by partially relaxed 13C-11B spin-spin coupling [16].
Scheme 4. 1,1-Divinyl silole derivatives bear-
ing identical (11) or different substituents
(12) at 2- and 5-positions.
at the Si–C≡C-C6H4-4-tBu unit, leading to 12, and
only about 25 % of the other isomer 12ꢀ was formed
(Scheme 4b; see also Fig. 3 for relevant NMR spectra).
Similar to BEt3, 9-ethyl-9-borabicyclo[3.3.1]no-
nane [17], Et-9-BBN, is sufficiently stable to survive
the harsh reaction conditions required for the 1,1-
organoboration of many alkyn-1-ylsilanes. The reac-
Scheme 5. Synthesis of polycyclic siloles, using 9-Et-9-BBN
tion (Scheme 5) proceeds as described previously for
as organoborating reagent.
Me2Si(C≡C-Ph)2 [7a] by twofold expansion of the bi-
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E. Khan – B. Wrackmeyer · Siloles Bearing Si-Vinyl and Si-Allyl Functions
1101
1
Fig. 3. Part of the 100.5 MHz 13C{ H} NMR spectrum of the mixture of the siloles 12 and 12ꢀ. Expansions show 29Si satellites
(asterisks) corresponding to 1J(29Si, 13C) and 2J(29Si, 13C). Signals belonging to the isomer 12ꢀ are marked by filled circles
1
(see also Table 1 for details). Note the broad B-C(3) NMR signals [16]. The insert shows the 79.4 MHz 29Si{ H} NMR
spectrum with signals for both isomers 12 and 12ꢀ.
cyclic structure to give the polycyclic siloles 13 and 14
without any side products. The analogous silole with
R = Ph containing the Si(Ph)H unit has already been
characterized by X-ray diffration [7b].
Protodeborylation of siloles bearing the diethylboryl
group in 3-position
We have previously shown that protodeborylation of
siloles [7, 18] works efficiently with acetic acid in ex-
cess at r. t. In the course of these reactions (Scheme 6),
in each case, the diethylboryl group is converted into
the bicyclic boron-oxygen compound 19 [18], and the
siloles 15 – 18 were obtained and readily characterized
by their consistent NMR data sets (Table 2) The vinyl
group(s) (see e. g. Fig. 4 for 13C NMR spectra of 11a)
or the allyl group (see Fig. 5 for the 29Si NMR spec-
trum of 18b) are left untouched, ready for further trans-
Scheme 6. Protodeborylation of some 1-vinyl-siloles and of
a 1-allyl-silole.
formations. The siloles 13 and 14 did not react with
acetic acid under these conditions.
shifts of 13C and 29Si nuclei. For the siloles bearing the
dialkylboryl group in 3-position, the δ11B data are typ-
ical of triorganoboranes without BC(pp) π interactions
[16a, 19]. This is in agreement with a preferred confor-
mation in which the ring plane and the C2B plane of the
dialkylboryl group are close to perpendicular. Thus, the
Chemical shifts δ11B, δ13C, δ29Si and coupling
constants 1J(29Si,13C)
The nature of the π system of the siloles is influ-
enced by the various substituents in positions 1 – 5, and
this should be reflected to some extent by the chemical
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E. Khan – B. Wrackmeyer · Siloles Bearing Si-Vinyl and Si-Allyl Functions
Table 1. 11B, 13C and 29Si NMR dataa for siloles 6 – 14.
δ
13C(2)
δ
13C(3)
δ
13C(4)
δ
13C(5)
δ
29Si
δ
11B
6ab
140.1 [65.0]
144.6 [64.3]
139.7 [65.9]
140.2 [62.4]
145.3 [64.4]
140.3 [62.7]
144.7 [63.2]
139.1 [66.3]
143.1 [65.7]
142.4 [66.4]
139.9 [66.9]
141.5 [65.7]
148.0 [64.3]
146.4 [65.9]
167.7 (br)
169.9 (br)
169.2 (br)
167.4 (br)
169.7 (br)
167.4 (br)
169.7 (br)
168.8 (br)
170.9 (br)
170.3 (br)
170.5 (br)
168.6 (br)
171.1 (br)
171.2 (br)
155.5 [11.2]
157.6 [10.1]
157.0 [11.1]
155.0 [8.8]
157.3 [9.2]
155.1 [10.1]
157.5 [9.7]
156.7 [11.0]
158.6 [10.2]
158.4 [10.3]
157.0 [10.7]
158.0 [10.5]
166.8 [9.0]
167.7 [9.2]
135.8 [69.5]
139.2 [68.0]
135.7 [62.6]
135.6 [67.1]
139.5 [65.1]
135.6 [67.1]
139.0 [66.5]
135.1 [70.6]
138.1 [69.2]
137.5 [69.6]
137.6 [69.8]
135.8 [n. o.]
136.0 [66.5]
134.4 [69.7]
−3.5
−1.1
−8.4
9.7
86.8
85.1
86.5
85.6
85.1
87.9
86.5
87.1
86.2
86.9
86.3
86.3
88.1
87.9
6bc
7ad
8ae
8bf
12.3
9.6
6.9
9ag
10bh
11ai
11bj
11ck
12l
−11.7
−10.0
−10.2
−10.8
−10.5
−1.6
12ꢀ m
13bn
14do
−10.8
a
Measured as C6D6 solution at 23 ◦C, coupling constants J(29Si, 13C) are given in brackets, br denotes broad 13C resonance signals owing
to partially relaxed scalar 13C-11B coupling [16], n. o. means not observed; other 13C NMR data: δ = −5.7 [49.3] (SiMe), 22.8 (br), 9.2
b
(BEt2), 24.7, 14.2 (Et), 34.2, 33.6, 32.8, 28.8, 23.5, 23.49, 14.4, 14.3 (nBu), 133.1 (=CH2), 137.2 [61.3] (Si–CH=); c other 13C NMR data:
δ = −6.5 [51.3] (SiMe), 22.3 (br), 9.8 (BEt2), 24.7, 14.5 (Et), 142.0 [6.5], 141.0 [6.0], 128.7, 128.7, 128.3, 127.7, 126.4, 125.9 (Ph), 135.3
(=CH2), 135.1 [63.7] (Si−CH=); d other 13C NMR data: δ = 22.8 (br), 9.4 (BEt2), 24.9, 14.1 (Et), 34.1, 33.5, 33.0, 29.0, 23.3, 14.1 (nBu),
135.2, 135.15, 128.3, 129.7, (SiPh), 135.0 (=CH2), 133.9 [63.8] (Si−CH=); e other 13C NMR data: δ = −3.9 [46.3] (SiMe), 34.2, 33.2, 29.1,
23.61, 23.6, 14.4 (nBu), 22.8 (br), 9.4 (BEt2), 23.7, 13.4 (Et), 19.5 (br), 8.5 (BEt2), 19.5 (br) (BCH2), 6.6 [49.1] (SiCH2); f other 13C NMR
data: δ = −4.8 [48.5] (SiMe), 22.4 (br), 10.0 (BEt2), 24.7, 14.7 (Et), 19.5 (br), 8.5 (BEt2), 6.1 [51.1] (SiCH2), 19.4 (br) (BCH2), 142.6 [6.4],
141.7 [5.8], 128.7, 128.8, 128.1, 127.5, 126.3, 125.8 (Ph); g other 13C NMR data: δ = −4.0 [46.1] (SiMe), 22.8 (br), 8.5 (BEt2), 24.7, 14.4
(Et), 6.5 [49.0] (SiCH2], 20.6 (br) (BCH2), 34.2, 33.7, 33.2, 29.2, 23.7, 23.6, 14.4, 14.4 (nBu), 33.7, 31.5 (br), 23.8 (9-BBN); other 13C
h
NMR data: δ = −5.4 [49.5] (SiMe), 22.3 (br), 9.8 (BEt2), 24.6, 14.5 (Et), 133.8 (=CH), 114.0 (H2C=), 21.2 [46.2] (SiCH2], 142.3 [6.7],
141.4 [5.9], 128.8, 128.7, 128.3, 127.6, 126.4, 125.9 (Ph); i other 13C NMR data: δ = 24.8, 14.1 (Et), 22.8 (br), 9.3 (BEt2), 34.3, 33.7, 32.9,
29.0, 23.5, 23.4, 14.3, 14.2 (nBu), 134.5 [63.8] (Si−CH=), 134.4 (=CH2); j other 13C NMR data: δ = 24.8, 14.4 (Et), 22.2 (br), 9.8 (BEt2),
k
132.6 [66.4] (Si–CH=), 136.7 (=CH2), 141.9 [6.4], 140.9 [5.8], 128.7, 128.7, 128.5, 128.0, 126.5, 125.0 (Ph); other 13C NMR data: δ =
24.9, 14.5 (Et), 22.2 (br), 9.9 (BEt2), 133.1 [66.1] (Si–CH=), 136.5 (=CH2), 149.0, 148.4, 138.9 [6.7], 138.0 [5.3], 128.4, 128.0, 125.6, 125.6,
34.5 (C), 34.5 (C), 31.6 (Me), 31.5 (Me) (4-t Bu-C6H4); l other 13C NMR data: δ = 24.6, 14.3 (Et), 22.1 (br), 9.8 (BEt2), 34.5, 29.2, 23.5,
m
14.3 (nBu), 134.0 [64.7] (Si–CH=), 135.5 (=CH2), 139.0, 128.0, 125.6, 148.5, 33.6 (C), 31.5 (Me) (4-t Bu-C6H4); other 13C NMR data:
δ = 25.3, 14.3 (Et), 22.8 (br), 9.4 (BEt2), 34.2, 31.2, 23.4, 14.3 (nBu), 133.6 [64.9] (Si–CH=), 135.6 (=CH), 138.2, 128.4, 125.5, 148.1, 33.0
(C), 31.6 (Me) (4-t Bu-C6H4); n other 13C NMR data:δ = −6.6 (SiMe), 11.2, 21.6, 23.2, 22.4, 30.5, 30.7, 33.3, 34.9, 35.0 (Et-BC8H14), 143.1
[6.6], 141.2 [5.9], 128.6, 128.2, 127.9, 126.7, 125.8 (Ph), 135.2 (H2C=), 134.9 (Si–CH=); o other 13C NMR data: δ = 11.3, 21.5 (br), 21.2,
30.7, 31.2 (br), 34.9, 35.2 (Et-BC8H14), 136.3 (H2C=), 132.9 (Si–CH=), 140.3 [5.6], 138.1, 137.0, 134.9, 129.34, 129.29, 128.4, 128.2, 21.2
(4-Me-C6H4).
Table 2. 13C and 29Si NMR dataa for protodeborylated siloles 15 – 18.
δ
13C(2)
δ
13C(3)
δ
13C(4)
δ
13C(5)
δ
29Si
15bb
16ac
16bd
17e
143.3 [63.1]
143.5 [65.3]
142.1 [65.7]
139.9 [66.7]
137.9
142.9 [8.3]
154.6 [8.9]
156.0 [7.8]
155.0 [8.4]
155.5
155.1 [7.8]
144.9 [9.4]
143.7 [8.1]
143.2 [8.9]
145.0
137.3 [67.5]
133.4 [69.6]
135.9 [69.1]
135.7 [69.7]
135.8
−1.9
−12.7
−10.4
−11.1
−11.7
6.1
17ꢀf
18bg
a
143.4 [63.0]
142.6 [≈7]
155.0 [7.5]
137.4 [66.5]
◦
13
b
In C6D6 at 23 1 C; coupling constants J(29Si, C) are given in brackets [ 0.3 Hz]; other 13C NMR data: δ = −6.4 [51.9] (SiMe),
24.8, 13.7 (Et), 134.6 [64.3], (Si–CH=), 135.6 (=CH2), 140.5 [6.0], 139.1 [6.2], 129.0, 128.7, 128.4, 126.9, 127.3, 126.1 (Ph); other 13C
c
data: δ = 23.9, 13.5 (Et), 33.6, 33.0, 32.6, 28.9, 23.3, 23.0, 14.2, 14.2 (nBu), 133.5 [64.9] (Si–CH=), 135.0 (H2C=); d other 13C NMR data:
δ = 13.4, 24.8 (Et), 140.4 [5.4], 138.9 [5.3], 129.0, 128.7, 128.6, 127.1, 127.4, 126.1 (Ph), 132.1 [66.5] (Si–CH=), 137.1 (H2C=); e other 13
C
NMR data: δ = 24.0, 13.6 (Et), 34.5, 29.1, 23.3, 14.2 (nBu), 136.5 [5.4], 126.8, 125.7, 149.7, 33.5 (C), 31.4 (Me) (4-t Bu-C6H4), 133.3 [65.5]
(Si–CH=), 135.9 (H2C=); f other 13C NMR data: δ = 24.8, 13.6 (Et), 34.5, 31.1, 23.0, 14.1 (nBu), 136.7, 128.4, 125.5, 148.3, 33.1 (C), 31.5
(Me) (4-tBu-C6H4), 132.7 (Si–CH=), 136.1 (H2C=); other 13C NMR data: δ = −5.4 [49.5] (SiMe), 24.6, 14.5 (Et), 133.8 (HC=), 114.0
g
(=CH2), 21.2 [46.2] (SiCH2), 142.3 [6.7], 141.4 [5.9], 128.8, 128.7, 128.3, 127.6, 126.4, 125.9, (Ph).
boryl group should not affect the silole π system. This
δ
29Si [20] in 3-diethylboryl-substituted siloles (Ta-
is mirrored by the virtually unchanged chemical shifts ble 1) and the corresponding protodeborylated siloles
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E. Khan – B. Wrackmeyer · Siloles Bearing Si-Vinyl and Si-Allyl Functions
1103
Fig.
4.
Parts
of
1
the 13C{ H} NMR
(100.5 MHz) spectrum
of 2,5-dibutyl-3-ethyl-
1,1-divinylsilole
11a.
29Si satellites (marked by
asterisks in expansions)
correspond to J(29Si,
13C). The upper insert
shows the J-modulated
spectrum for assignment
of C, CH and CH2
carbons.
protodeborylation does not induce significant changes.
This is also true for 1J(29Si,13C) of all organyl groups
exocyclicly attached to silicon.
Conclusions
Siloles bearing various substituents at the ring po-
sitions are readily available in high yield via 1,1-
organoboration reactions. It is shown that this route to
siloles also tolerates vinyl or allyl groups at the sili-
con atom. Furthermore, if triethylborane is used for
the organoboration, the diethylboryl group can be re-
moved by protodeborylation, and the diene system as
well as the substituents at silicon (vinyl or allyl) are not
affected. On the other hand, the hydroboration of the
exocyclic vinyl group of 6a indicates that much more
chemistry can be done without disturbing the π system
of the silole.
1
Fig. 5. 59.6 MHz 29Si{ H} NMR spectrum (refocused IN-
EPT) of 1-allylsilole 18b. The 13C satellites belonging to
1J(29Si, 13C) are marked by asterisks, and those marked
by arrows (close to the parent signal) may be assigned to
nJ(29Si, 13C) (n ≥ 2).
Experimental Section
Starting materials and measurements
(Table 2). This comparison is more straightforward
than that of the δ13C(2,3,4,5) data because of the in-
trinsic substituent effect exerted by the Et2B group as
compared to hydrogen. Another diagnostic criterion
for potential changes of the π system is available in
The preparations and handling of all air- and moisture-
sensitive samples were carried out under an inert atmo-
sphere (Ar), and carefully oven-dried glassware and dry
solvents were used throughout. BuLi in hexane (1.6 M),
all chlorosilanes, 1-hexyne, phenylethyne, 1-ethynyl-4-tert-
butylbenzene, triethylborane BEt3, and glacial acetic acid
1
the coupling constants J(29Si,13C(2,5)) [20]. An in-
spection of these data in the Tables 1 and 2 shows that
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E. Khan – B. Wrackmeyer · Siloles Bearing Si-Vinyl and Si-Allyl Functions
were commercial products and were used as received. 9- Hydroborylation of the Si-vinyl group in silole 6a using
Ethyl-9-borabicyclo[3.3.1]nonane [17], Et-9-BBN, dialkyn- 9-BBN, synthesis of silole 9a
1-yldivinylsilanes 4 and 5 [21] were prepared as described.
A Schlenk tube was charged with the solution of silole 6a
Dialkyn-1-ylvinylsilanes were prepared according to analo-
(0.13 g, 0.39 mmol) in THF (5 mL), and one equivalent of
gous literature procedures [22]. Data related to their struc-
solid 9-BBN (0.05 g; 0.39 mmol) was added in one portion.
The reaction mixture was stirred at r. t. for 2 h. Then, the
solvent and all other volatiles were removed, leaving silole
9a as an oily liquid.
9a: 1H NMR (400 MHz): δ = 0.3 (s, 3H, SiMe), 0.9, 2.1,
2.3 (t, m, m, 5H, Et), 0.9 – 1.0, 1.2 – 1.8 (m, m, Bu, Si(CH2)2,
BEt2, 9-BBN).
tures will be published elsewhere [12]. NMR spectra (1H,
11B, 13C, 29Si) were recorded in C6D6 (concentration ca.
10 – 15 %, v/v) with samples in 5 mm o. d. tubes at 23
1
◦C using Varian Inova 300 MHz and 400 MHz spec-
trometers; chemical shifts are given relative to Me4Si [δ1H
(C6D5H) = 7.15; δ13C (C6D6) = 128.0; δ29Si = 0 for
Ξ(29Si) = 19.867184 MHz] and external BF3-OEt2 [δ11B =
0 for Ξ(11B) = 32.083971 MHz]. Chemical shifts δ1H are
given to 0.04 ppm, δ13C and δ29Si to 0.1 ppm, and δ11
B
Synthesis of silole derivatives 11 and 12
to 0.5 ppm. 29Si NMR spectra were measured by using the
refocused INEPT pulse sequence [23], based on 2/3J(29Si–
C1H=CH2) and 3J(29Si,1HC4) 20 – 25 Hz (after optimiza-
tion of the respective refocusing delays).
Reactions for the preparation of silole derivatives 11 and
12 were carried out under harsh reaction conditions as de-
scribed above. All these compounds were obtained as vis-
cous oils. The reaction times were different for these siloles:
11a (2 d), 11b (4 d), 11c (10 d) and 12a, 12aꢀ (5 d).
1,1-Ethylboration of alkyn-1-ylsilanes 1 – 3
11a: 1H NMR (400 MHz): δ = 1.0, 1.4 (t, m, 10H, BEt2),
0.8, 2.1 (t, q, 5H, Et), 0.9, 0.9, 1.4, 2.1, 2.3 (t, t, m, t, t, 18H,
nBu), 5.9 (dd, 2H, J(1H,1H) = 4.0, 20.1, =CH2), 6.0 (dd, 2H,
J(1H,1H) = 4.0, 14.6, =CH2), 6.3 (dd, 2H, J(1H,1H) = 14.6,
20.1, Si–CH=).
11b: 1H NMR (400 MHz): δ = 1.1, 1.5 (t, br, 10H, BEt2),
0.9, 2.3 (t, q, 5H, Et), 6.0 (dd, 2H, J(1H,1H) = 3.7, 20.0 Hz,
=CH2), 6.0 (dd, 2H, J(1H,1H) = 3.7, 14.8 Hz, =CH2), 6.3
(dd, 2H, J(1H,1H) = 14.8, 20.0 Hz, HC=), 7.1 – 7.2, 7.3, 7.3
(m, m, m, 10H, Ph).
An NMR tube was filled with 1a (0.23 g: 0.99 mmol)
and BEt3 in excess. The NMR tube was sealed and kept at
◦
100 – 120 C (oil bath). After three days the NMR tube was
cooled in liquid nitrogen, opened under argon, and all read-
ily volatile materials were removed in a vacuum. The brown
oily liquid left was identified as silole 6a. A portion of silole
6a was mixed with BEt3 and kept under identical conditions
in a sealed NMR tube. After 13 d the NMR tube was opened,
all volatile materials were evaporated, and the oily liquid was
identified as mixture of silole 6a and 8a. The reaction con-
ditions for the synthesis of siloles 6b and 8b were similar,
except that heating lasted for 5 d and 23 d, respectively. Re-
actions in the case of silole derivatives 7a and 10b continued
for 8 d and 6 d, respectively.
11c: 1H NMR (400 MHz): δ = 0.9, 1.3 (t, m, 10H, BEt2),
0.7, 2.2 (t, q, 5H, Et), 6.2 (dd, 2H, Si–CH=), 5.8 (m, 4H,
=CH2), 1.0, 1.1, 6.9, 7.1 (s, s, m, m, 26H, 4-tBu-C6H4).
1
12a: H NMR (400 MHz): δ = 0.9, 1.2 – 1.4 (t, m, 10H,
6a: 1H NMR (300 MHz): δ = 0.3 (s, 3H, SiMe), 0.7, 0.7,
1.3, 2.1 (t, t, m, m, 18H, nBu), 1.1, 1.3 (t, m, 10H, BEt2),
0.9, 2.3 (t, m, 5H, Et), 6.0 (dd, 1H, J(1H,1H) = 4.0, 20.1 Hz,
=CH2), 6.1 (dd, 1H, J(1H,1H) = 4.0, 14.6 Hz, =CH2), 6.5
(dd, 1H, J(1H,1H) = 14.6, 20.1 Hz, Si–CH=).
BEt2), 0.8, 2.0 (t, m, 5H, Et), 0.8, 1.2 – 1.4, 2.3 (t, m, t, 9H,
nBu), 5.9 (dd, 2H, J(1H,1H) = 3.8, 14.8 Hz, =CH2), 5.9 (dd,
2H, J(1H,1H) = 3.8, 19.8 Hz, =CH2), 6.2 (dd, 2H, J(1H,1H) =
14.8, 19.8 Hz, Si–CH=), 1.1, 6.9, 7.1 (s, m, m, 13H, 4-tBu-
C6H4).
6b: 1H NMR (400 MHz): δ = 0.5 (s, 3H, SiMe), 1.1, 1.5
(t, m, 10H, BEt2), 0.9, 2.3, 2.4 (t, m, m, 5H, Et), 5.9 (dd, 1H,
J(1H,1H) = 3.6, 20.2 Hz, =CH2), 6.1 (dd, 1H, J(1H,1H) =
3.6, 14.4 Hz, =CH2), 6.4 (dd, 1H, J(1H,1H) = 14.4, 20.2 Hz,
Si–CH=), 7.2, 7.3 (m, m, 10H, Ph).
1,1-Organoboration of silanes 1b and 4d using
9-ethyl-9-borabicyclo[3.3.1]nonane
Silane 1b (1 g, 3.7 mmol) was filled together with an
excess (1 mL, 0.72 g, 5.6 mmol) of 9-ethyl-9-borabicyclo-
[3.3.1]nonane into an NMR tube. The NMR tube was sealed
and heated at 120 ◦C (oil bath). The progress of the reaction
was monitored by 29Si NMR spectroscopy. After 15 h the
reaction was found to be complete, and all readily volatile
materials were removed in vacuo (ca. 10−1 Torr). Final◦ly,
1
7a: H NMR (300 MHz): δ = 0.7, 0.8, 1.2, 1.4, 2.1 (t, t,
n
m, m, m, 18H, Bu), 1.1, 1.4 (t, m, 10H, BEt2), 0.9, 2.3 (t,
m, 5H, Et), 6.0 (dd, 1H, J(1H,1H) = 3.8, 20.3 Hz, =CH2),
6.1 (dd, 1H, J(1H,1H) = 3.8, 14.8 Hz, =CH2), 6.5 (dd, 1H,
J(1H,1H) = 14.8, 20.3 Hz, Si–CH=), 7.2, 7.7 (m, m, 5H,
SiPh).
10b: 1H NMR (400 MHz): δ = 0.3 (s, 3H, SiMe), 1.0, 1.3 excess of Et-9-BBN was removed by heating at 60 – 70 C
(t, m, 10H, BEt2), 0.8, 2.1, 2.2 (t, m, m, 5H, Et), 1.7, 4.8, 5.7 in vacuo. The remaining oily product was identified as pure
(d, m, m, 5H, All), 7.0 – 7.2 (m, 10H, Ph).
13b in > 95 % yield and high purity (99 %). The silole 14d
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E. Khan – B. Wrackmeyer · Siloles Bearing Si-Vinyl and Si-Allyl Functions
1105
was obtained in the same way. Silole derivatives 13b and 14d
were air- and moisture-sensitive oily liquids.
16b: 1H NMR (400 MHz): δ = 0.9, 2.3 (t, q, 5H, Et),
5.9 (dd, 2H, J(1H,1H) = 3.5, 20.1 Hz, =CH2), 5.9 (dd, 2H,
J(1H,1H) = 3.5, 14.9 Hz, =CH2), 6.2 (dd, 2H, J(1H,1H) =
14.8, 20.1 Hz, Si–CH=), 7.0 – 7.2, 7.3, 7.5 (m, m, m, 11H,
Ph, C4H).
13b: 1H NMR data (400 MHz): δ = 0.5 (s, 3H, SiMe),
0.8, 1.1, 1.5, 1.7, 2.0 – 2.1, 3.3 (t, m, m, m, m, m, 19H, Et-
BC8H14), 5.9 – 6.2 (m, 3H, Si-Vinyl), 6.9, 7.0 – 7.2, 7.3 (m,
m, m, 10H, Ph).
17: 1H NMR (400 MHz): δ = 0.9, 1.3, 2.4 (t, m, t, 9H,
nBu), 1.0, 2.3 (t, q, 5H, Et), 6.0 (dd, 2H, J(1H,1H) = 3.9, 19.9
Hz, =CH2), 6.1 (dd, 2H, J(1H,1H) = 3.9, 15.0 Hz, =CH2),
6.3 (dd, 2H, J(1H,1H) = 15.0, 19.9 Hz, Si–CH=), 7.2 (s, 1H,
3J(29Si,1H) = 13.3 Hz, C4H), 1.2, 7.3, 7.5 (s, m, m, 13H,
4-tBu-C6H4).
14d: 1H NMR data (300 MHz): δ = 1.1, 1.4, 1.4 – 1.8,
3.4 (t, q, m, m, 19H, Et-BC8H14), 5.9 – 6.1, 6.3 (m, m, 6H,
Si–CH=CH2), 2.1, 6.9 – 7.1 (s, m, m, 13H, 4-tBu-C6H4).
Protodeborylation of the silole derivatives 6, 10, 11,
and 12
1
17ꢀ: H NMR (400 MHz): δ = 6.6 (m, 1H, C4H), other
The protodeborylation of the silole derivatives was carried
out following literature procedures [18, 21].
protons were not assigned owing to overlap with signals be-
longing to silole 17a.
15b: 1H NMR (400 MHz): δ = 0.3 (s, 3H, SiMe), 0.8,
2.3 (t, m, 5H, Et), 5.8 (dd, 1H, J(1H,1H) = 3.5, 20.3 Hz,
=CH2), 5.9 (dd, 1H, J(1H,1H) = 3.5, 14.6 Hz, =CH2), 6.2
(dd, 1H, J(1H,1H) = 14.6, 20.3 Hz, Si–CH=), 7.0 – 7.2, 7.4
(m, m, 11H, C4H, Ph).
18b: 1H NMR (400 MHz): δ = 0.3 (s, 3H, SiMe), 1.0, 2.3
(t, m, 5H, Et), 1.7 (d, 2H, J(1H,1H) = 8.0 Hz, Si–CH2), 4.7
(m, 1H, =CH), 5.6 (m, 2H, =CH2), 7.1, 7.2, 7.4 (m, m, m,
11H, C4H, Ph).
16a: 1H NMR (400 MHz): δ = 0.8, 0.8, 1.2, 1.4, 2.2, 2.3
(t, t, m, m, t, t, 18H, nBu), 0.9, 2.1 (t, q, 5H, Et), 5.9 (dd, 2H,
J(1H,1H) = 4.1, 20.0 Hz, =CH2), 5.9 (dd, 2H, J(1H,1H) =
4.1, 14.8 Hz, =CH2), 6.1 (dd, 2H, J(1H,1H) = 14.8, 20.0 Hz,
Si–CH=), 6.4 (m, 1H, 3J(29Si,1H) = 13.8 Hz, C4H).
Acknowledgements
This work was supported by the Deutsche Forschungsge-
meinschaft. E. K. is grateful to DAAD and HEC (Pakistan)
for a scholarship.
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