Reactivity of triethylborane towards di(alkyn-1-yl)(chloro)silanes. Competition between 1,1-organoboration and 1,2-hydroboration

Article abstract of DOI:10.1515/znb-2009-0107

Reactions of di(alkyn-1-yl)(chloro)silanes, HSi(Cl)(C≡C-R) ₂, R¹Si(Cl)(C≡C-R)2 or HSi(Cl)-(C≡C-R) C≡C-R′, with an excess of triethylborane, BEt₃, proceed slowly (several days) at 100 - 120 °C. Twofold 1,1-organoboration of

Full text of DOI:10.1515/znb-2009-0107

Reactivity of Triethylborane towards Di(alkyn-1-yl)(chloro)silanes.
Competition between 1,1-Organoboration and 1,2-Hydroboration
Ezzat Khan, Stefan Bayer, and Bernd Wrackmeyer
Anorganische Chemie II, Universita¨t Bayreuth, D-95440 Bayreuth, Germany
Reprint requests to Prof. Dr. B. Wrackmeyer. E-mail: b.wrack@uni-bayreuth.de
Z. Naturforsch. 2009, 64b, 47 – 57; received October 28, 2008
Dedicated to Professor Otto J. Scherer on the occasion of his 75th birthday
Reactions of di(alkyn-1-yl)(chloro)silanes, HSi(Cl)(C≡C-R)2, R1Si(Cl)(C≡C-R)2 or HSi(Cl)-
(C≡C-R)C≡C-Rꢀ, with an excess of triethylborane, BEt3, proceed slowly (several days) at 100 –
120 ◦C. Twofold 1,1-organoboration of HSi(Cl)(C≡C-R)2 or HSi(Cl)(C≡C-R)C≡C-Rꢀ leads to
siloles, independent of R = nBu, tBu, SiMe3. This provides the most straightforward way to siloles
bearing both a hydrogen and a chlorine at the silicon atom. However, in the cases of R = Ph, BEt3 acts
as 1,2-hydroborating reagent in the intermolecular first step of the reaction, leading to 1-silacyclo-
butene derivatives. All siloles and 1-silacyclobutene derivatives were characterized by multinuclear
NMR spectroscopy (1H, 11B, 13C and 29Si). Comparable 1-silacyclobutene derivatives were formed
using 9-borabicyclo[3.3.1]nonane, 9-BBN, as a well established 1,2- hydroborating reagent.
Key words: Triethylborane, Siloles, Silacyclobutene, Hydroboration, Organoboration, NMR
Introduction
Triethylborane, BEt3, is a commercial reagent and
has found widespread applications [1]. In our stud-
ies on 1,1-organoboration [2], BEt3 has been exten-
sively used for 1,1-ethylboration reactions of alkyn-
1-yl metal derivatives to form new C–C bonds, both
for the synthesis of non-cyclic and cyclic compounds.
Among the latter, a variety of siloles [2 – 6] became
readily accessible [Scheme 1(a)], circumventing other
much more tedious synthetic procedures. These par-
ticular 1,1-organoboration reactions require prolonged
periods (several days) of heating at elevated temper-
Scheme 1. Formation of silole (a) or 1-silacyclobutene
derivatives (b) using BEt3.
◦
ature (100– 120 C) and proceed in two steps. The
of alkenes expected for 1,1-ethylboration. Moreover,
di(alkyn-1-yl)(dichloro)silanes react with BEt3 to give
1-silacyclobutene derivatives [13] as the result of con-
secutive 1,2-hydroborationand intramolecular 1,1-vin-
ylboration [Scheme 1(b)].
first step involves intermolecular 1,1-ethylboration,
followed in the second step by intramolecular 1,1-vin-
ylboration. Triethylborane, BEt3, has been considered
as thermally stable [7 – 12], and 1,2-dehydroboration,
leading to the in situ formation of Et2BH and elim-
ination of ethene, has never been observed, in con-
In this work, we report on the reactivity of di(alkyn-
trast with many other trialkylboranes [7, 11, 12]. Re- 1-yl)(chloro)silanes (Scheme 2) towards BEt3 to study
cently we have explored the influence of Si–Cl func- the potential competition between 1,1-ethylboration
tions in alkyn-1-yl(chloro)silanes on the course of and 1,2-hydroboration. This study was expected to
1,1-ethylboration reactions. It has been shown that open the way to silole derivatives with hitherto un-
reactions of BEt3 with some alkyn-1-yl(trichloro)- known substituent patterns, and also to shed some light
silanes [13] and alkyn-1-yl(dichloro)silanes [14] af- on mechanistic implications. The potential 1,2-hydro-
ford exclusively alkenes via 1,2-hydroboration instead boration activity of BEt3 was confirmed by compar-
c
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48
E. Khan et al. · Reactivity of Triethylborane towards Di(alkyn-1-yl)(chloro)silanes
Table 1. 13C and 29Si NMR dataa of di(alkyn-1-yl)(chloro)-
silanes 1 – 6.
δ
13C(≡C)
δ
13C(Si–C≡)
δ
29Si
1ab 112.5 [25.9]
77.4 [125.8]
75.6 [125.4]
−57.5
1bc 120.1 [25.1]
−56.5
1cd 120.4 [20.0] [71.5]
103.3 [114.0] [11.5]
−60.1,
−16.3 {2.1}
−55.4
l
1de 109.5 [25.5]
2af 110.8 [24.9]
2cg 108.1 [24.5]
3ch 109.6 [25.2]
4ai 112.6 [26.3, β],
119.8 [24.7, β]
85.5 [124.3]
80.1 [122.8]
88.3 [121.3]
87.2 [126.1]
77.4 [126.3, α],
75.5 [125.2, α]
76.7 [126.8, α],
−34.9
−32.7
−42.0
−57.1
5cj 113.4 [26.1, β],
−58.8, −16.4
Scheme 2. Syntheses of di(alkyn-1-yl)(chloro)silanes as
starting materials.
119.4 [19.7] [70.8, β] 104.2 [114.7] [11.6, α]
6ck 109.4 [25.8, β],
85.2 [124.2, α], 103.4 −58.0,
l
−16.3 {2.3}
120.3 [20.0] [71.6, β] [114.4] [11.6, α]
Measured in C6D6; coupling constants J(13C,29Si) [ 0.4 Hz] are
ison with analogous reactions using the well estab-
lished 1,2-hydroborating reagent 9-borabicyclo[3.3.1]-
nonane, 9-BBN. Multinuclear NMR spectroscopy (1H,
11B, 13C and 29Si) served for monitoring all reactions
and characterization of the final products.
a
b
given in square brackets;
other 13C data: δ = 30.1, 22.1, 19.7,
c
d
13.6 (nBu);
other 13C data: δ = 30.1, 28.3 (tBu);
other 13C
data: δ [J(13C,29Si)] = −1.0 [56.6, SiMe3];
121.3, 128.5, 132.6, 130.1 (i, o, m, p, Ph);
other 13C data: δ =
other 13C data: δ
e
f
[1J(13C,29Si)] = 5.1 [73.7, Si-Me], 30.2, 22.1, 19.6, 13.6 (nBu);
g
other 13C data: δ [1J(13C,29Si)] = 4.6 [74.8, Si-Me], 121.8, 132.6,
other 13C data: δ [1J(13C,29Si)] =
Results and Discussion
h
128.5, 129.8 (i, o, m, p, Ph);
132.6 [99.7], 134.4, 128.7, 131.8 (i, o, m, p, Si-Ph), 121.5, 132.7,
Synthesis of di(alkyn-1-yl)(chloro)silanes 1 – 6
i
128.5, 130.0 (i, o, m, p, Ph);
other 13C data: δ = 13.6, 19.6, 22.0,
29.9 (nBu), 28.4, 30.1 (t Bu);
other 13C data: δ [J(29Si,13C)]=
j
−0.9 [56.6, SiMe3], 13.5, 19.6, 22.0, 29.8 (nBu);
other 13C data:
k
The di(alkyn-1-yl)(chloro)silanes bearing identical
[1 – 3; Scheme 2(a)] or different C≡C-R groups [4 – δ = −0.9 [56.6, SiMe3], 121.2, 128.5, 132.6, 130.1 (i, o, m, p, Ph);
l
J(29Si, 29Si).
6; Scheme 2(b)] were prepared by the reactions
of the respective trichlorosilane R1SiCl3 with the
alkynyl lithium reagents following the literature pro-
cedure [15]. Pure samples of silanes 1 – 6 were ob-
tained by fractional distillation. Although some of
the di(alkyn-1-yl)(chloro)silaneshave already been de-
scribed [16], fairly complete NMR data sets were miss-
ing. Therefore, the NMR data of 1 – 6 were collected
(Table 1 and Experimental Section).
Scheme 3. Synthesis of siloles via 1,1-ethylboration of
silanes 1 – 3.
Formation of siloles: Reactions of di(alkyn-1-yl)
and e. g. Fig. 2) revealed the formation of the siloles 8a
(chloro)silanes 1a – c, 2a, 4a, 5c, and 6c with BEt3
and 9a.
The reaction of the silane 1a with BEt3, carried out
The silanes 4 – 6 containing different alkyn-1-yl
at 110– 120 C, affords selectively the silole 7a. The groups [R = Rꢀ; Scheme 2(b)] were treated with BEt3
◦
◦
analogous products (7b and 7c) are observed for R = at 110– 120 C. In the case of 4a, 1,1-ethylbora-
tBu and SiMe3 (Scheme 3). The reaction of 1d with tion of the Si–C≡C-nBu group occurs more read-
BEt3 gives a mixture of products. The NMR data (Ta- ily than of the Si–C≡C-tBu unit (Fig. 3), and in
bles 2 and 3) indicate the presence of the silole 7d and the cases of 5c and 6c, 1,1-ethylboration of the
a 1-silacyclobutene (vide infra) as major components Si–C≡C–SiMe3 units is preferred over C≡C-nBu or
(40– 45% each) along with several unidentified side C≡C-Ph groups (Scheme 4). This finding is sup-
products (ca. 15 %). The same reactions were carried ported by additional NMR data sets which can
out under identical reaction conditions with 2a and 3a. be assigned to siloles 13aꢀ, 14cꢀ and 15cꢀ, present
The NMR spectra of the reaction solutions (Table 2 in minor quantities. In addition to the mixture of
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E. Khan et al. · Reactivity of Triethylborane towards Di(alkyn-1-yl)(chloro)silanes
Table 2. 11B, 13C and 29Si NMR dataa of siloles 7 – 9 and 13 – 15.
49
δ
13C (C-2)
δ
13C (C-3)
δ
13C (C-4)
δ
13C (C-5)
δ
29Si
δ
11B
7ab
135.3 [73.1]
145.7 [84.1]
139.9 [48.3] [63.3]
141.9 [79.5]
136.6 [72.5]
136.6 [73.6]
145.7 [72.0]
135.5
169.1 (br)
166.4 (br)
186.9 (br)
172.1 (br)
167.1 (br)
169.0 (br)
164.4 (br)
168.8 (br)
169.3 (br)
170.7 (br)
157.2 [15.7]
156.7 [16.9]
173.3 [10.2] [12.7]
159.7 [n. m.]
155.4 [15.1]
157.2 [15.0]
155.3 [16.9]
157.7
131.7 [78.8]
139.3 [76.9]
132.3 [55.6] [61.9]
136.2 [n. m.]
132.5 [78.1]
132.7 [79.4]
132.2 [79.1]
139.3
−7.0
89.7
87.5
87.1
86.7
86.1
86.8
89.0
89.0
88.3
88.5
7bc
−5.8
7cd
9.8, −10.2, −9.8
7de
−6.6
16.7
5.3
8af
9ag
13ah
13aꢀI
14aj
15ck
−7.4
−5.6
0.8
143.4 [69.2]
144.3 [70.2]
174.6 [10.7]
174.5 [11.4] [10.1]
126.6 [63.7]
138.7 [57.4] [60.7]
0.9
a
Measured in C6D6, coupling constants corresponding to 1J(13C,29Si) and 2J(13C,29Si) are given in square brackets, n. m. means not
measured, (br) indicates a broad 13C resonance signal of carbon linked to boron atom owing to partially relaxed 11B–13C spin-spin scalar
b
c
coupling [21];
other 13C data: δ = 14.2, 23.4, 27.7, 33.7, 34.2 (nBu), 9.0, 22.1 (br), 22.6 (br) (BEt2), 13.4, 31.4 (Et);
other 13C data:
δ = 32.5, 32.7, 26.7 (tBu), 9.9, 22.7 (br) (BEt2), 14.4, 30.3 (Et);
other 13C data: δ [J(13C,29Si)] = 1.2 [51.8, SiMe3], 1.3 [52.3, SiMe3],
d
e
9.3, 9.3, 22.4 (br), 23.6 (br) (BEt2), 14.8, 30.2 (Et);
other 13C data: δ = 9.0, 22.3 (BEt2), 13.7, 27.1 (Et), Ph carbons without assignment;
f
other 13C data: δ [J(13C,29Si)] = 0.8 [69.5, Si-Me], 14.2, 14.3, 23.4, 27.8, 31.6, 32.9, 33.4 (nBu), 22.6 (br), 9.1 (BEt2), 24.7, 13.6 (Et);
g
h
other 13C are not assigned due to the presence of some side products including 1-silacyclobutene;
other 13C data: δ = 14.2, 23.4, 24.9,
27.7, 33.6 (nBu), 26.8, 32.7 (t Bu), 9.8, 22.1, 22.6 (BEt2), 13.7, 35.5 (Et);
other 13C data: δ = 14.4, 23.5, 25.2, 27.0, 34.1 (nBu), 26.4,
i
32.4 (t Bu), 9.1, 22.2 (BEt2), 13.5, 34.5 (Et);
other 13C data: δ = 1.3 [52.9, SiMe3], 14.1, 24.8, 31.5, 34.0 (nBu), 22.6, 9.0 (BEt2), 14.1,
j
k
31.1 (Et);
other 13C data: δ = 1.2 [52.3, SiMe3], 9.5, 22.3 (BEt2), 14.4, 30.8 (Et), 128.1, 128.6, 127.9, 126.8 (i, o, m, p, Ph).
The siloles bearing identical (7a – d, 8a, 9a) or dif-
ferent (13a, 14c, 15c) substituents at 2 and 5 positions
are oily, air and moisture sensitive compounds, and
their structures were proposed on the basis of consis-
tent sets of NMR data (Table 2 and Figs. 1, 2, 3).
Formation of 1-silacyclobutene derivatives: Reactions
of di(alkyn-1-yl)(chloro)silanes 1d, 2d and 3d with
BEt3
The reaction of 1d with BEt3 gives the silole 7d to-
gether with a second major compound, subsequently
identified as the 1-silacyclobutene derivative 16d. This
result shows that 1,1-ethylboration can be accompa-
nied by competitive reactions which, depending on
various substituents, may become dominant, offering
an attractive route to novel heterocycles, such as 1-
silacyclobutene derivatives. Therefore, the reactions
of 2d and 3d with BEt3 are of interest (Scheme 5).
NMR spectra of the reaction solutions indicate almost
Scheme 4. Reactions of di(alkyn-1-yl)(chloro)silanes
H(Cl)Si(C≡C-R)C≡C-Rꢀ 4 – 6 (R = Rꢀ) with BEt3 to afford
mixtures of the respective siloles.
quantitative formation of 1-silacyclobutene derivatives
(> 90 %) instead of siloles. In the light of our previous
siloles, small amounts of the side products 10 –
12 (Scheme 4) are formed. These products are un-
suitable to undergo ring closure via intramolecu-
lar 1,1-vinylboration. The desired siloles (13 – 15)
are the main components in the reaction mixtures,
identified unambiguously by their distinct NMR
data.
Scheme 5. Reactions of chlorodi(phenylethynyl)silanes 1d –
3d with BEt3 leading to 1-silacyclobutene derivatives.
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50
E. Khan et al. · Reactivity of Triethylborane towards Di(alkyn-1-yl)(chloro)silanes
Table 3. 11B, 13C and 29Si NMR dataa of alkenyl(alkyn-1-yl)silanes 19 and 20.
δ
13C (BC=)
δ
13C (=C)
δ
13C (Si–C≡)
δ
13C (≡C)
δ
11B
δ
29Si
−15.6
−14.6
−23.7
19ab
19dc
20dd
144.0 [73.4, br]
147.7 [73.7, br]
144.1 [75.5, br]
162.2
156.3
158.7
82.9 [104.9]
91.8 [103.9]
90.2 [109.0]
110.7 [21.1]
108.2 [20.5]
109.3 [21.3]
81.9
83.6
84.6
a Measured in C6D6, coupling constants J(13C,29Si) [ 0.4 Hz] are given in square brackets, (br) denotes a broad 13C resonance signal as the
b
result of partially relaxed scalar 11B–13C spin-spin coupling [21];
other 13C data: δ [J(13C,29Si)] = 6.2 [64.6, Si-Me], 35.2, 31.7, 22.2,
c
14.3 (=C-Bu), 30.5, 22.9, 19.9, 13.7 (≡C-Bu), 34.4, 34.5, 31.3 (br), 23.6 (9-BBN);
other 13C data: δ [J(13C,29Si)] = 5.1 [65.9, Si-Me],
d
34.7, 34.7, 31.7 (br), 23.7 (9-BBN), 140.0, 132.5, 129.9, 129.5, 129.4, 128.6, 128.5, 122.5 (Ph);
other 13C data: δ = 34.7, 34.6, 31.9 (br),
23.6 (9-BBN), 139.1, 135.5, 134.5, 134.3, 132.6, 132.4, 130.7, 130.3, 129.4, 129.0, 128.7, 122.3 (Ph, Si-Ph).
1
1
Fig. 1. 100.5 MHz 13C{ H} and 79.6 MHz 29Si{ H} (inserted) NMR spectra of 7c. In the 13C NMR spectrum, the 29Si
satellites, marked by asterisks, correpond to 1J(13C,29Si) and nJ(13C,29Si), n ≥ 2. Note the typically broad signal belonging
to the carbon atom bonded to boron [21]. In the 29Si NMR spectrum, the respective 13C satellites are marked by asterisks and
diamonds, while 29Si satellites, marked by arrows, correspond to 2J(29Si,29Si). The 29SiMe3 nuclei 2ꢀ and 5ꢀ are precisely
assigned based on these NMR data.
Fig. 2. Part of the 100.5 MHz
1
13C{ H} NMR spectrum of a crude
reaction mixture mainly contain-
ing 8a. Only 13C signals belong-
ing to the silole ring are shown.
The 29Si satellites, marked by as-
terisks, represent 1J(13C,29Si) and
2J(13C,29Si). Note the typically
broad signal belonging to the car-
bon atom bonded to boron [21].
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E. Khan et al. · Reactivity of Triethylborane towards Di(alkyn-1-yl)(chloro)silanes
Table 4. 11B, 13C and 29Si NMR dataa of 1-silacyclobutene derivatives 16 – 18, 21 and 22.
51
δ
13C (=CH)
δ
13C (C-2)
δ
13C (C-3)
δ
13C (C-4)
δ
29Si
δ
11B
16db
17dc
18dd
21ae
21df
22dg
n.a.
130.1
134.4
128.9 [12.2]
131.0
141.9 [n.o.]
147.2 [58.0]
146.2 [58.8]
147.1 [58.4]
147.8 [57.9]
146.9 [58.8]
173.3 (br)
179.9 (br)
182.8 (br)
175.9 (br)
177.8 (br)
180.6 (br)
159.4 [n.o.]
157.2 [63.8]
156.3 [63.6]
165.3 [58.7]
161.0 [61.1]
160.2 [62.4]
−16.4
86.7
85.7
86.9
84.2
86.8
84.6
10.7
−1.2
11.7
11.0
−1.8
132.6
a
Measured in C6D6, coupling constants 1J(13C,29Si) and 2J(13C,29Si) are given in square brackets [ 0.4 Hz], (br) denotes a broad 13C
resonance signal as the result of partially relaxed scalar 11B–13C coupling [21];
other carbons were not assigned, as silole accompanied
b
by some other unknown side products are present; c other 13C data: δ [J(13C,29Si)] = 3.6 [52.0, Si-Me], 21.6 (br), 9.0 (BEt2), 139.0, 137.3,
d
129.3, 129.1, 128.9, 128.1, 127.9 (Ph);
other 13C data: δ [J(13C,29Si)] = 21.7 (br), 9.3 (BEt2), 138.4 [4.6], 136.9 [5.3], 134.3, 132.7,
e
132.5, 130.3, 129.3, 128.9, 128.9, 128.2, 128.0, 127.1 (Ph);
23.4 (9-BBN);
129.8, 129.1, 128.9, 128.1, 127.8 (Ph);
132.7 [71.1], 134.5, 131.8, 131.3, 130.0, 129.0, 128.9, 128.9, 128.6, 128.5 (Ph).
other 13C data: δ [J(13C,29Si)] = 3.4 [49.8, Si-Me], 34.4, 34.2, 32.2 (br),
f
other 13C data: δ [J(13C,29Si)] = 3.2 [51.8, Si-Me], 34.4, 34.2, 32.2 (br), 23.4 (9-BBN), 139.1 [5.3], 137.7 [4.6], 131.1,
g
other 13C data: δ [J(13C,29Si)] = 34.5, 34.3, 32.4 (br), 23.5 (9-BBN), 138.7 [5.3], 137.5 [4.6],
Fig. 3. 49.7 MHz 29Si NMR
spectrum (refocused INEPT) of
the reaction mixture indicating
starting silane 4a, alkeny(alkyn-1-
yl)silane 10a (as a side product) and
the desired siloles 13a and in minor
quantity 13aꢀ (see Scheme 4).
experience [13, 14], we propose that the first step of the sition state. The Si–Cl function increases the strength
reaction proceeds selectively via 1,2-hydroboration of of the Si–C≡ bond and hampers the cleavage of this
one of the alkyn-1-yl groups of these silanes. The in- bond as required in the course of 1,1-ethylboration.
termediate (not detected) bears the diethylboryl and the Monitoring of the reactions by 29Si NMR spectroscopy
silyl groups at the same olefinic carbon atom. This is an (Fig. 4) proved helpful, and the solution-state struc-
ideal geometry for the rearrangement via intramolecu- tures of the final products could be deduced from the
lar 1,1-vinylboration to give 1-silacyclobutene deriva- complete set of multinuclear NMR data (Table 4).
tives. Apparently, the presence of the phenyl group at
the C≡C bond, together with the Si–Cl function, opens
Formation of 1-silacyclobutene derivatives: Reactions
of di(alkyn-1-yl)(chloro)silanes 2a, d and 3d with
9-BBN
the way to 1,2-hydroboration instead of 1,1-ethylbora-
tion (Scheme 5).
We propose that this particular 1,2-hydroboration,
unusual for BEt3, proceeds via β-hydrogen trans-
Reactions of di(alkyn-1-yl)(chloro)silanes with
fer [14] rather than via 1,2-dehydroboration after inter- 9-BBN require less stringent reaction conditions (80 –
◦
mediate formation of Et2BH. The phenyl group linked 100 C, few hours or few days in some cases) using
to the C≡C bond is considered to stabilize a polar tran- toluene or benzene as solvents. The reactions proceed
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52
E. Khan et al. · Reactivity of Triethylborane towards Di(alkyn-1-yl)(chloro)silanes
Fig. 4. Monitoring of the reaction of 3d with BEt3
by 59.6 MHz 29Si NMR spectroscopy (A) af-
ter 3 d; (B) after 9 d; (C) after 15 d. The reaction
mixture contains only the starting silane 3d and
the 1-silacyclobutene derivative 18d (ca. 9 : 1).
No intermediate analogous to 19 and 20 were de-
tected.
1
Fig. 5. 59.6 MHz 29Si{ H} NMR spectrum (re-
focused INEPT) of the reaction mixture con-
taining the starting silane 2a and the intermedi-
ate 19a. Expansion is given for the signal be-
longing to 19a, showing 13C satellites, owing to
nJ(13C,29Si), n = 1, 2.
via 1,2-hydroboration of one Si–C≡C- bond to give
at first the alkenyl(alkyn-1-yl)silanes 19 and 20 as in-
termediates. These are fairly stable [17, 18] and were
fully characterized by multinuclear NMR spectroscopy
(Table 4; Fig. 5). On further heating 19 and 20 un-
dergo intramolecular 1,1-vinylboration affording the
1-silacyclobutene derivatives 21 and 22 (Scheme 6;
Fig. 6). The NMR data obtained for 21 and 22 com-
pare well with those reported previously for analogous
heterocycles [18]. The reactions shown in Scheme
Scheme 6. Reactions of di(alkyn-1-yl)(chloro)silanes 2a, d
and 3d with 9-BBN.
6 were carried out to support the data obtained for
the four-membered heterocycles 16 – 18 (Scheme 5),
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E. Khan et al. · Reactivity of Triethylborane towards Di(alkyn-1-yl)(chloro)silanes
53
1
Fig. 6. Part of the 100.5 MHz 13C{ H}
NMR spectrum of 21d (measured
at 23 ◦C, ca. 15 % (v/v) solution
in C6D6). Signals for 1-silacyclobutene
ring carbons (C-2 and C-4) are evident
from 29Si satellites for 1J(13C,29Si),
while that of C-3 linked to the boron
atom is typically broad [21].
Scheme 7. Two alternative reaction path-
ways leading either to siloles or 1-sila-
cyclobutene derivatives.
where BEt3 served unexpectedly as a hydroborating by β-hydrogen transfer and elimination of ethene. In-
reagent.
tramolecular rearrangement by 1,1-vinylboration, sim-
ilar to the formation of the siloles (from C), leads
from E towards the 1-silacyclobutene derivatives.
Reaction mechanism
The proposed mechanisms for the formation of
siloles and 1-silacyclobutene derivatives are summa-
rized in Scheme 7. Clearly, the product distribution
NMR spectroscopic studies
The 11B, 13C and 29Si NMR data for siloles (7 – 9,
depends on the Si–Cl and C≡C-R/Rꢀ functions. The 13 – 15), alkenyl(alkyn-1-yl)silane intermediates (19,
silanes bearing R = Rꢀ = Ph open the way to 1- 20) and 1-silacyclobutene derivatives (16 – 18, 21,
silacyclobutene derivatives. We propose a transition 22) are summarized in Tables 2 – 4, respectively. The
state D, containing a six-membered cycle, and sug- 1H NMR data are listed in the Experimental Sec-
gests the ability of the C≡C-Ph group to delocalize tion. The data sets are in full agreement with the pro-
a positive charge plays an important role in its stabi- posed structures. Both siloles and 1-silacyclobutenes
lization. Starting from D, the intermediate E is formed can readily be identified by their characteristic NMR
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54
E. Khan et al. · Reactivity of Triethylborane towards Di(alkyn-1-yl)(chloro)silanes
parameters (for comparison see Figs. 1, 2 and 6). The spectra were recorded using the refocused INEPT pulse se-
quence with 1H decoupling [23], based either on 1J(29Si,1H)
≈ 280 Hz, 3J(29SiC=C1H) ≈ 30 – 35 Hz, 2J(29Si,1H(SiMe))
or 3J(29Si,1H(SiPh)) ≈ 7 Hz (after optimization of the re-
spective refocusing delays).
chemical shifts δ11B for intermediates (i. e. 19 and 20;
δ = 82 1) and all products were observed in the ex-
pected range typical of triorganoboranes without sig-
nificant BC(pp) π interactions [19, 20]. The siloles
and 1-silacyclobutenes possess well distinguishable
13C NMR data. Most 13C NMR signals could be read-
ily assigned by their 29Si satellites [1J(29Si,13C) and
2J(29Si,13C)] or by the typical increase in the line
widths owing to partially relaxed one-bond 13C–11B
spin-spin coupling [21]. Because of their simplicity
(Figs. 3, 4), 29Si NMR spectra are helpful in monitor-
ing the reactions, and δ29Si data are markedly different
for siloles and 1-silacyclobutene derivatives (Tables 2
and 3). In the 1H NMR spectra (e. g. 16d, 17d, 18d), a
singlet for an olefinic proton [C=CH(Ph)] and the ab-
sence of signals for the =C-Et group in the aliphatic
region clearly show that 1,2-hydroboration has taken
place.
Synthesis of di(alkyn-1-yl)(chloro)silanes 1 – 6
To a freshly prepared suspension of Li–C≡C-nBu
(61 mmol) in hexane (50 mL), trichlorosila◦ne HSiCl3
(1.9 mL, 19.3 mmol) was added slowly at −78 C. The re-
action mixture was allowed to reach r. t. Insoluble materials
were filtered off, and all readily volatile materials were re-
moved under reduced pressure (10−2 Torr). The oily residue
left was analyzed to contain a mixture of HCl2Si–C≡C-Ph,
HClSi(C≡C-Ph)2 (1a) and HSi(C≡C-Ph)3, and fractional
distillation gave pure 1a as a colorless oil. The same pro-
cedure was followed for the syntheses of the analogous
silanes 1b – d, 2a, d and 3d. A solution of HCl2Si–C≡C-tBu
(lighter fraction of the mixture containing 1b) in hexane
(10 mL) was added to a freshly prepared Li–C≡C-nBu sus-
pension at −78 ◦C. The reaction mixture was slowly warmed
to r. t. and was stirred for 1 h. The work-up procedure as
described above gave the pure silane 4a as a colorless oil
(yield 43.1 %). The same procedure was adopted for the syn-
thesis of silanes 5c (yield 49 %) and 6c (yield 37.3 %).
Conclusions
1,1-Ethylboration of di(alkyn-1-yl)(chloro)silanesis
an efficient method for the preparation of siloles bear-
ing substituents on the silicon atom such as Si–Cl and
Si–H. In comparison to other reported methods [22]
this process is fairly straightforward. In particular the
H(Cl)Si- group in the new siloles, almost without
precedent, is promising for further transformations.
The role of the Si–Cl function for the stability of the
Si–C≡ bond is evident from a series of reactions where
BEt3 acts as hydroborating reagent leading to 1-sila-
cyclobutene derivatives. In this context, the influence
of the phenyl group at the C≡C bond is striking.
1a: B. p. = 85 ◦C/2 × 10−2 Torr. – 1H NMR data
(250 MHz): δ = 0.7, 1.2, 1.9 (t, m, t, 18H, nBu), 5.2 (s,
1H, 1J(29Si,1H) = 276.1 Hz, Si–H). – IR (C6D6): v = 2185
(C≡C), 2147 (Si–H) cm−1
.
1b: B. p. = 47 ◦C/1.8×10−1 Torr. – 1H NMR (250 MHz):
δ = 1.0 (s, 18H, tBu), 5.3 (s, 1H, 1J(29Si,1H) = 274.2 Hz, Si–
H). – IR (C6D6): v = 2158 (C≡C), 2128 (Si–H) cm−1
.
1c: B. p. = 58 ◦C/8.3×10−2 Torr. – 1H NMR (250 MHz):
δ = −0.04 (s, 18H, SiMe3), 5.1 (s, 1H, 1J(29Si,1H) =
279.0 Hz, Si–H).
1d: B. p. = 112 ◦C/1.0 × 10−3 Torr. – 1H NMR
(250 MHz): δ = 5.4 (s, 1H, 1J(29Si,1H) = 280.9 Hz, Si–H),
6.8 – 7.0, 7.2 – 7.3 (m, m, 10H, Ph).
Experimental Section
All preparative work and handling of air-sensitive chemi-
cals were carried out by observing necessary precautions to
exclude traces of oxygen and moisture. Trichlorosilane, tri-
chloro(methyl)silane, trichloro(phenyl)silane, 1-hexyne, 3,3-
dimethyl-but-1-yne, ethynylbenzene, trimethylsilylethyne,
n-butyllithium in hexane (1.6 M), triethylborane (BEt3), 9-
borabicyclo[3.3.1]nonane (9-BBN) were commercial prod-
ucts and were used without further purification. NMR spec-
tra: Bruker ARX 250 MHz or Varian Inova 300 MHz and
400 MHz spectrometers (23 1 ◦C), all equipped with multi-
nuclear units, using C6D6 solutions (ca. 15 – 20 % v/v) in
5 mm tubes. Chemical shifts are given with respect to SiMe4
[δ1H (C6D5H) = 7.15, δ13C (C6D6) = 128.0, δ29Si = 0
2a: B. p. = 83 – 85 ◦C/2.8 × 10−2 Torr. – 1H NMR
(400 MHz): δ = 0.6 (s, 3H, 2J(29Si,1H) = 8.2 Hz, Si-Me),
0.5, 1.1, 1.7 (t, m, t, 18H, nBu).
2d: B. p. = 145 – 150 C/9.1 × 10−2 Torr. – 1H NMR
◦
(400 MHz): δ = 0.5 (s, 3H, 2J(29Si,1H) = 8.0 Hz, Si-Me),
6.6, 7.1 (m, m, 10H, Ph).
3d: B. p. = 192 – 196 ◦C/0.14 Torr. – 1H NMR
(400 MHz): δ = 6.8, 7.2, 8.0 (m, m, m, 15H, Si-Ph, Ph).
4a: B. p. = 44 ◦C/1×10−2 Torr. – 1H NMR (250 MHz):
n
t
δ = 0.7, 1.4, 1.8 (t, m, t, 9H, Bu), 1.0 (s, 9H, Bu), 5.2 (s,
1H, 1J(29Si,1H) = 273.5 Hz, Si–H).
5c: B. p. = 55 ◦C/1×10−2 Torr. – 1H NMR (250 MHz):
for SiMe4 with Ξ(29Si) = 19.867187 MHz], and δ11B = 0 δ = 0.00 (s, 9H, SiMe3), 0.6, 1.0 – 1.2, 1.8 (t, m, t, 9H, nBu),
for BF3–OEt2 with Ξ(11B) = 32.083971 MHz. 29Si NMR 5.2 (s, 1H, 1J(29Si,1H) = 275.8 Hz, Si–H).
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E. Khan et al. · Reactivity of Triethylborane towards Di(alkyn-1-yl)(chloro)silanes
55
6c: B. p. = 78 ◦C/1×10−2 Torr. – 1H NMR (250 MHz): 1J(29Si,1H) = 226.1 Hz, Si–H), 7.0 – 7.1, 7.4 – 7.6 (m, m, 5H,
δ = 0.01 (s, 9H, SiMe3), 6.8 – 7.0, 7.2 (m, 5H, Ph), 5.2 (s, Ph).
1H, 1J(29Si,1H) = 279.1 Hz, Si–H).
15cꢀ: 1H NMR (250 MHz): δ = 0.3 (s, 9H, SiMe3), 5.2
(s, 1H, Si–H).
1,1-Ethylboration of silanes 1 – 6, syntheses of siloles 7 – 9
and 13 – 15
Alkenyl(alkyn-1-yl)silanes 10a, 11c and 12c
General procedure: A Schlenk tube was charged with
the solution of the respective di(alkyn-1-yl)silane and tri-
ethylborane in large excess (as the reagent as well as t◦he sol-
vent). The reaction solution was heated at 100 – 120 C (oil
bath temperature). The reaction was monitored by 29Si NMR
spectroscopy. After it was complete, all volatile materials
were removed under reduced pressure, and the remaining
brown oily liquids (siloles) were studied by NMR spec-
troscopy. Except for the reaction time, the experimental pro-
cedure was the same for all siloles. Time required for reaction
completion was 1 d (7a), 7 d (7b, 8a), 4 h (7c), 10 d (7d) and
20 d (9a).
Silanes 10a, 11c and 12c were present as side products
accompanying the siloles 13 – 15.
10a: 1H NMR (250 MHz): δ = 5.6 (s, 1H, 1J(29Si,1H) =
248.6 Hz, Si–H).
–
13C NMR: δ = 82.9 (Si–C≡), 119.2
(≡C), 30.4 (tBu-Me3). – 29Si NMR: δ = −39.8.
11c: 29Si NMR: δ = −42.6 ppm, 1J(29Si,1H) = 246.6 Hz.
12c: 1H NMR (250 MHz): δ = 0.2 (s, 9H, SiMe3), 5.6
(s, 1H, 1J(29Si,1H) = 244.8 Hz, Si–H). – 13C NMR: δ =
1.3 (SiMe3), 89.9 (Si–C≡), 108.7 (≡C), 139.3 (=C), 191.6
(br, C=), 123.6, 128.5, 129.5, 132.3 (Ph). – 29Si NMR: δ =
−43.0, −5.1 (29SiMe3).
7a: B. p. = 120 ◦C/1.0 × 10−3 Torr. – 1H NMR
(250 MHz): δ = 0.8, 0.9, 1.3, 2.3 (t, t, m, t, 18H, nBu),
0.9, 2.0 (t, q, 5H, Et), 0.9, 1.6 (t, br, 10H, BEt2), 5.5 (s, 1H,
1J(29Si,1H) = 237.4 Hz, Si–H).
7b: B. p. = 100 ◦C/1.0 × 10−3 Torr. – 1H NMR
(250 MHz): δ = 1.1, 1.3 (s, s, 18H, tBu), 1.0, 2.1 (t, q, 5H,
Et), 1.1, 1.6 (t, br, 10H, BEt2), 5.4 (s, 1H, 1J(29Si,1H) =
222.6 Hz, Si–H).
7c: 1H NMR (400 MHz): δ = 0.2, 0.3 (s, s, 18H, SiMe3),
0.9, 2.2 (t, q, 5H, Et), 0.9, 1.0, 1.3 (t, t, m, 10H, BEt2), 5.6 (s,
1H, 1J(29Si,1H) = 222.4 Hz, Si–H).
7d: 1H NMR (250 MHz): δ = 0.9, 2.1 (t, q, 5H, Et),
1.1, 1.2 – 1.5 (t, m, 10H, BEt2), 5.6 (s, 1H, 1J(29Si,1H) =
234.9 Hz, Si–H), 6.8 – 7.0, 7.1 – 7.3 (m, m, 10H, Ph).
Hydroboration of di(alkyn-1-yl)(chloro)silanes 1 – 3 using
BEt as hydroborating reagent
3
A mixture of the silane MeSiCl(C≡C-Ph)2, 2d (0.5 g,
1.8 mmol) and BEt3 (1 mL, in slight◦excess) was sealed in
an NMR tube and kept at 100 – 120 C in an oil bath. The
progress of the reaction was monitored by 29Si NMR spec-
troscopy, and after 12 d the reaction was found to be com-
plete. The NMR tube was cooled in liquid N2 and opened.
Excess of BEt3 and other volatiles were removed under re-
duced pressure (10−2 Torr), and the oily residue was identi-
fied as 17d (ca. 90 % pure according to 1H NMR spectra).
The procedure for 18d was identical to 17d, except that heat-
ing lasted for 15 d and the reaction was complete only to
ca. 90 % (Fig. 4).
17d: 1H NMR (400 MHz): δ = 0.7 (s, 3H, Si-Me),
0.9, 1.4 (t, m, 10H, BEt2), 6.4 (s, 1H, 3J(1H,29Si) =
19.3 Hz, =CH), 6.9 – 7.4 (m, 10H, Ph, Ph).
18d: 1H NMR (400 MHz): δ = 1.0, 1.5 (t, m, 10H, BEt2),
6.5 (s, 1H, 3J (1H,29Si) = 21.4 Hz, =CH), 6.8 – 7.4 (m, 15H,
Si-Ph, Ph).
8a: 1H NMR (400 MHz): δ = 0.5 (s, 3H, Si-Me), 0.8, 0.8,
1.3, 2.2 (t, t, m, m, 18H, nBu), 1.0, 2.3 (t, m, 5H, Et), 0.9, 1.5
(t, m, 10H, BEt2).
9a: 1H NMR (400 MHz): δ = 0.6 – 1.4, 1.8 – 2.5 (over-
lapping multiplets of nBu, BEt2 and Et groups), 7.1, 7.7 (m,
m, 5H, Si-Ph).
13a: 1H NMR (250 MHz): δ = 0.7, 1.2 – 1.3, 1.9 (t, m, m,
9H, nBu), 1.1 (s, 9H, tBu), 1.1, 2.2 (m, q, 5H, Et), 1.1, 1.2 –
1
1.3 (m, m, 10H, BEt2), 5.3 (s, 1H, J(29Si,1H) = 221.9 Hz, Hydroboration of di(alkyn-1-yl)(chloro)silanes 2a, d and 3d
Si–H).
using 9-BBN
13aꢀ: 1H NMR (250 MHz): δ = 5.3 (s, 1H, Si–H).
A solution of silane 2a (0.74 g, 3.1 mmol) in C6D6
(1.5 mL) was mixed with the crystalline 9-BBN dimer
(0.387 g, 3.1 mmol). The mixture was heated to 80 ◦C
for 20 min. During this time 9-BBN was completely con-
sumed (monitored by 11B NMR spectroscopy). The NMR
data clearly indicated the formation of 19a. The 1,2-hydro-
boration of the silanes 2d and 3d was carried out in
14a: 1H NMR (250 MHz): δ = 0.3 (s, 9H, SiMe3), 0.8,
1.0 – 1.2, 2.2 (t, m, t, 9H, nBu), 0.9, 2.0 – 2.1 (t, m, 5H,
Et), 1.0, 1.3 (m, m, 10H, BEt2), 5.5 (s, 1H, 1J(29Si,1H) =
222.3 Hz, Si–H).
14aꢀ: 1H NMR (250 MHz): δ = 0.2 (s, 9H, SiMe3), 5.5
(s, 1H, Si–H).
15c: 1H NMR (250 MHz): δ = 0.3 (s, 9H, SiMe3), 1.0, the same way leading to alkenyl(alkyn-1-yl)silanes 19d
2.4 (t, q, 5H, Et), 0.9, 1.4 (t, q, 10H, BEt2), 5.5 (s, 1H, and 20d.
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56
E. Khan et al. · Reactivity of Triethylborane towards Di(alkyn-1-yl)(chloro)silanes
19a: 1H NMR (400 MHz): δ = 0.7 (s, 3H, 2J(29Si,1H) = intramolecular 1,1-vinylboration was 7 d (21a), 5 d (21d)
7.4 Hz, Si-Me), 0.7, 0.9, 1.2 – 1.3, 2.0, 2.5 (t, t, m, t, m, and 12 h (22d).
18H, nBu), 1.4, 1.8 – 2.0 (m, m, 14H, 9-BBN), 7.0 (t, 1H,
3J(1H,1H) = 7.3 Hz, 3J(29Si,1H) = 21.1 Hz, =CH).
19d: 1H NMR (400 MHz): δ = 0.3 (s, 3H, 2J(29Si,1H) =
7.7 Hz, Si-Me), 1.2, 1.6 – 2.1 (m, m, 14H, 9-BBN), 7.3, 7.1,
7.0, 6.7 – 6.8 (m, m, m, m, 10H, Ph), 7.9 (s, 1H, 3J(1H,29Si) =
21.7 Hz, =CH).
21a: 1H NMR (400 MHz): δ = 0.8 (s, 3H, Si-Me), 0.8,
1.3, 2.3 (t, m, m, 18H, nBu), 1.3, 1.8 – 1.9 (m, m, 14H,
9-BBN), 5.8 (t, 1H, 3J(1H,1H) = 6.9 Hz, 3J(29Si,1H) =
22.1 Hz, =CH).
21d: 1H NMR (400 MHz): δ = 0.4 (s, 3H, 2J(29Si,1H) =
7.1 Hz, Si-Me), 1.2 – 2.1 (m, 14H, 9-BBN), 6.6 – 7.2 (m,
11H, Ph, =CH).
20d: 1H NMR (400 MHz): δ = 1.4, 1.9 – 2.2 (m, m, 14H,
9-BBN), 7.9, 7.6, 6.9 – 7.3 (m, m, m, 15H, Si-Ph, Ph), 8.2 (s,
1H, 3J(29Si,1H) = 21.4 Hz, =CH).
22d: 1H NMR (400 MHz): δ = 1.4 – 2.0 (m, 14H,
9-BBN), 6.8 – 7.2, 7.4, 7.9 (m, m, m, 16H, Si-Ph, Ph, =CH).
Acknowledgements
Syntheses of 1-silacyclobutene derivatives 21a, d and 22d
Compounds 19 and 20 were heated at 80 ◦C to afford the
1-silacyclobutene derivatives 21a, 21d and 22d upon ring
closure. The time required for complete rearrangement via
We thank the Deutsche Forschungsgemeinschaft for sup-
porting this work. E. K. is grateful to DAAD and HEC (Pak-
istan) for a scholarship.
[1] a) K. Oshima, Bull. Chem. Soc. Japan 2008, 81, 1;
b) M. Kimura, Y. Tamaru, Topics Curr. Chem. 2007,
279, 173; c) Y. Tamaru, Organomet. News 2007, 12;
d) T. Ukon, T. Harada, Eur. J. Org. Chem. 2008, 4405;
e) D. S. Lim, S. C. Ngo, S. G. Lal, K. E. Minnich, J. T.
Welch, Tetrahedron Lett. 2008, 49, 5662; f) C. Bil-
laud, J.-P. Goddard, T. Le Gall, C. Mioskowski, Tetra-
hedron Lett. 2003, 44, 4451; g) J. F. Geisz, D. J. Fried-
man, S. Kurtz, R. C. Reedy, G. Barber, J. Electr. Mat.
2001, 30, 1387; h) S. Deprele, J.-C. Montchamp, J.
Org. Chem. 2001, 66, 6745; i) K. Nakamura, T. Sasaki,
J. Solid State Chem. 2000, 154, 101; j) A. Shifman,
N. Palani, S. Hoz, Angew. Chem. 2000, 112, 974;
Angew. Chem. Int. Ed. 2000, 39, 944; k) R. Ko¨ster,
W. Schu¨ ssler, R. Boese, M. Herberhold, S. Gerst-
mann, B. Wrackmeyer, Chem. Ber. 1996, 129, 503;
l) P. Binger, R. Ko¨ster, Inorg. Synth. 1974, 15, 136;
m) R. Ko¨ster, W. Fenzl, Liebigs Ann. Chem. 1974, 69.
[2] R. Ko¨ster, G. Seidel, G. Su¨ß, B. Wrackmeyer, Chem.
Ber. 1993, 126, 1107.
[3] a) B. Wrackmeyer, Coord. Chem. Rev. 1995, 145, 125;
b) B. Wrackmeyer, Heteroatom Chem. 2006, 17, 188;
c) B. Wrackmeyer, O. L. Tok, Comprehensive Hete-
rocyclic Chemistry III, (Eds.: A. R. Katritzky, C. A.
Ramsden, E. F. V. Scriven, R. J. K. Taylor), Elsevier,
Oxford, 2008, pp. 1181 – 1223.
[4] a) B. Wrackmeyer, W. Milius, M. H. Bhatti, S. Ali,
J. Organomet. Chem. 2003, 665, 196; b) B. Wrack-
meyer, O. L. Tok, M. H. Bhatti, S. Ali, Coll. Czech.
Chem. Commun. 2002, 67, 822; c) B. Wrackmeyer,
O. L. Tok, K. Shahid, S. Ali, Inorg. Chim. Acta 2004,
357, 1103.
[6] a) B. Wrackmeyer, O. L. Tok, A. Khan, A. Badshah,
Z. Naturforsch. 2005, 60b, 251; b) B. Wrackmeyer,
O. L. Tok, A. Khan, A. Badshah, Appl. Organomet.
Chem, 2005, 19, 1249.
[7] A. Stock, F. Zeidler, Ber. Deutsch. Chem. Ges. 1921,
54B, 531.
[8] a) L. Rosenblum, J. Am. Chem. Soc. 1955, 77, 5016;
b) R. Ko¨ster, Liebigs Ann. Chem. 1958, 618, 31; c)
E. C. Ashby, J. Am. Chem. Soc. 1959, 81, 4791; d) P. F.
Winternitz, A. A. Carotti, J. Am. Chem. Soc. 1960, 82,
2430.
[9] R. Ko¨ster, G. Benedikt, W. Larbig, K. Reinert,
G. Rotermund, Angew. Chem. 1963, 75, 1079.
[10] R. Ko¨ster, W. Larbig, G. W. Rotermund, Liebigs Ann.
Chem. 1965, 682, 21.
[11] R. Ko¨ster in Houben-Weyl Methoden der Organischen
Chemie, Vol 13/3c, Ed.: R. Ko¨ster), Thieme Stuttgart,
1984, p. 217.
[12] E. Abuin, J. Grotewold, E. A. Lissi, M. C. Vara,
J. Chem. Soc. B 1968, 1044.
[13] B. Wrackmeyer, E. Khan, S. Bayer, K. Shahid, Z. Na-
turforsch. 2007, 62b, 1174.
[14] B. Wrackmeyer, E. Khan, W. Milius, Z. Naturforsch.
2008, 63b, 1267.
[15] a) W. E. Davidsohn, M. C. Henry, Chem. Rev. 1967, 67,
73; b) L. Brandsma, Preparative Acetylenic Chemistry,
(2nd ed.), Elsevier, Amsterdam, 1988; c) L. Brandsma,
Synthesis of Acetylenes, Allenes, Cumulenes – Methods
and Techniques, Elsevier, Amsterdam, 2004.
[16] a) H. Lang, U. Lay, L. Zsolnai, J. Organomet. Chem.
1991, 417, 377; b) C. K. Frisch, B. R. Young, J. Am.
Chem. Soc. 1952, 74, 4853; c) N. O. Florensova, A. B.
Sokolov, I. L. Volkova, Izvest. Akad. Nauk SSSR, Ser.
Khim. 1973, 1390.
[5] a) B. Wrackmeyer, G. Kehr, J. Su¨ß, Chem. Ber. 1993,
126, 2221; b) B. Wrackmeyer, J. Su¨ß, Z. Naturforsch.
2002, 57b, 741.
[17] B. Wrackmeyer, H. E. Maisel, E. Molla, A. Mot-
Unauthenticated
Download Date | 11/18/19 2:21 AM

E. Khan et al. · Reactivity of Triethylborane towards Di(alkyn-1-yl)(chloro)silanes
57
talib, A. Badshah, Appl. Organomet. Chem. 2003,
17, 465.
[18] B. Wrackmeyer, E. Khan, R. Kempe, Appl. Organomet.
Chem. 2007, 21, 39.
[19] a) B. Wrackmeyer, E. Khan, R. Kempe, Z. Natur-
forsch. 2007, 62b, 75; b) B. Wrackmeyer, A. Badshah,
E. Molla, A. Mottalib, J. Organomet. Chem. 1999,
98, 584; c) B. Wrackmeyer, K. Shahid, S. Ali, Appl.
Organomet. Chem. 2005, 19, 377; d) B. Wrackmeyer,
W. Milius, M. H. Bhatti, S. Ali, J. Organomet. Chem.
2003, 72, 669.
Basic Principles and Progress, Vol. 14, Eds.: P. Diehl,
E. Fluck, R. Kosfeld) Springer, Berlin, 1978.
[21] a) B. Wrackmeyer, Progr. NMR Spectrosc. 1979, 12,
227; b) B. Wrackmeyer, Annu. Rep. NMR Spectrosc.
1988, 20, 61.
[22] a) J. B.-Wilking, Y. Zhang, J. Y. Corey, N. P. Rath,
J. Organomet. Chem. 2008, 693, 1233; b) H. Sohn,
J. Organomet. Chem. 2004, 689, 134.
[23] a) G. A. Morris, R. Freeman, J. Am. Chem. Soc. 1979,
101, 760; b) G. A. Morris, J. Am. Chem. Soc. 1980,
102, 428; c) G. A. Morris, J. Magn. Reson. 1980, 41,
185; d) D. P. Burum, R. R. Ernst, J. Magn. Reson. 1980,
39, 163.
[20] H. No¨th, B. Wrackmeyer, Nuclear Magnetic Reso-
nance Spectroscopy of Boron Compounds in NMR –
Unauthenticated
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