Combination of 1,2-hydroboration and 1,1-organoboration: A convenient route to 5-silaspiro[4,4]nona-1,6-diene derivatives

Article abstract of DOI:10.1002/ejic.200800790

Dialkyn-1-yl(divinyl)silanes were prepared and their reactions with 9-borabicyclo[3.3.1]nonane (9-BBN) were studied. 1,2-Hydroboration takes place selectively at the vinyl group, followed by intramolecular 1,1-organoboration to form a 1-silacyclopent-2-ene ring. Repetition of this sequence affords, in essentially quantitative yield, 5-silaspiro[4,4]nona-1,6-diene derivatives bearing substituents in the 1,6-positions and 9-borabicyclo[3.3.1]nonyl groups in the 2,7-positions. Protodeborylation with an excess amount of acetic acid gives the respective spirosilanes bearing substituents only in the 1,6-positions. All new compounds were characterized by NMR spectroscopy in solution (¹H, ¹¹B, ¹³C, ²⁹Si NMR) and for two examples of the spirosilanes by X-ray structural analysis in the solid state. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200800790

FULL PAPER
DOI: 10.1002/ejic.200800790
Combination of 1,2-Hydroboration and 1,1-Organoboration: A Convenient
Route to 5-Silaspiro[4,4]nona-1,6-diene Derivatives
Ezzat Khan,[a] Bernd Wrackmeyer,*[a] and Rhett Kempe[a]
Keywords: Silanes / Spiro compounds / Hydroboration / Organoboration / NMR spectroscopy
Dialkyn-1-yl(divinyl)silanes were prepared and their reac-
tions with 9-borabicyclo[3.3.1]nonane (9-BBN) were studied.
1,2-Hydroboration takes place selectively at the vinyl group,
followed by intramolecular 1,1-organoboration to form a 1-
silacyclopent-2-ene ring. Repetition of this sequence affords,
in essentially quantitative yield, 5-silaspiro[4,4]nona-1,6-
diene derivatives bearing substituents in the 1,6-positions
and 9-borabicyclo[3.3.1]nonyl groups in the 2,7-positions.
Protodeborylation with an excess amount of acetic acid gives
the respective spirosilanes bearing substituents only in the
1,6-positions. All new compounds were characterized by
NMR spectroscopy in solution (1H, 11B, 13C, 29Si NMR) and
for two examples of the spirosilanes by X-ray structural
analysis in the solid state.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
quires silanes, in which the silicon atom bears two vinyl and
two alkyn-1-yl groups, identical (1) or different (2). As
shown in Scheme 1, silanes 1 or 2 are readily accessible.
They are colorless liquids and stable towards air and moist-
ure, and they are characterized by their typical NMR spec-
troscopic data sets (Table 1 and Figure 1).
Introduction
In comparison to other tetraorganosilanes in general,[1,2]
those with silicon in the center of a spiro structure are much
less abundant.[3,4] There are few convenient routes towards
spirosilanes, in particular if the rings contain C=C bonds
or functional groups attached to carbon atoms. In addition
to numerous saturated spirosilanes and a few examples of
5-silaspiro[4,4]nona-2,7-dienes,[3,4] previous work has
shown that ethylboration of tetraalkyn-1-ylsilanes, Si(CϵC-
R)4, provides a straightforward route to 1,1-spirobisiloles
A.[5–7] Recently, we characterized the first spirosilanes con-
taining two four-membered rings B by using 1,2-hydrobor-
ation and 1,1-organoboration.[8] The combination of these
stereo- and regioselective reactions is attractive in synthe-
sis,[8–10] and in the present work further examples are given
that are aimed at the synthesis and first structural charac-
terization of the hitherto unknown 5-silaspiro[4,4]nona-1,6-
diene derivatives.
Scheme 1. Synthesis of the starting dialkyn-1-yl(divinyl)silanes.
Silanes bearing a vinyl and an alkyn-1-yl group at the
silicon atom react with 9-borabicyco[3.3.1]nonane (9-BBN)
selectively by 1,2-hydroboration of the C=C bond, and the
boron atom becomes linked to the terminal carbon atom of
the vinyl group.[9] In comparison with other dialkylboranes,
this is a unique property of 9-BBN, which prefers the ter-
minal C=C bond over the CϵC bond.[11] The first interme-
Results and Discussion
The strategy of combining 1,2-hydroboration and 1,1-or- diates from the 1,2-hydroboration (not detected) possess a
ganoboration for the synthesis of the title compounds re- favorable arrangement for intramolecular 1,1-alkylboration
in the next step. The dashed line between boron and the
[a] Anorganische Chemie II, Universität Bayreuth,
alkynyl carbon atom (Scheme 2) indicates the interaction
95440 Bayreuth, Germany
leading to cleavage of the Si–Cϵ bond, formation of an
Fax: +49-921-552157
E-mail: b.wrack@uni-bayreuth.de
alkyn-1-ylborate, and 1,1-alkylboration.[12] The alternative
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E. Khan, B. Wrackmeyer, R. Kempe
FULL PAPER
Table 1. 13C and 29Si NMR spectroscopic data[a] of dialkyn-1-yl-
(divinyl)silanes 1a–c and 2a.
δ13C (Si-Cϵ) δ13C (ϵC) δ13C (Si–HC=) δ13C (=CH2) δ29Si
1a[b] 78.6 [107.1]
110.4 [20.4]
108.7 [20.0]
109.0 [20.3]
111.3 [20.3]
108.2 [20.0]
133.9 [81.2]
132.4 [82.1]
132.9 [81.8]
133.4 [81.7]
135.2
136.7
136.4
135.8
–54.6
–52.7
–52.8
–53.7
1b[c]
1c[d]
2a[e]
87.6 [105.1]
87.2 [105.4]
78.2 [108.1]
87.6 [104.3]
[a] Measured in C6D6 at 296Ϯ1 K, coupling constants [Hz] corre-
sponding to 1J(29Si,13C) and 2J(29Si,13C) are given in square brack-
ets. [b] Other 13C data: δ = 30.8, 22.2, 19.9, 13.8 (Bu) ppm. [c] Other
13C data: δ = 122.7, 132.4, 129.3, 128.5 (i, o, p, m, Ph) ppm.
[d] Other 13C data: δ = 120.1, 132.4, 125.5, 152.4, 34.7, 31.1 (i, o,
m, p, Ctert, Me3, 4-tBuC6H4) ppm. [e] See Figure 1; other 13C data:
δ = 13.7, 19.9, 22.1, 30.6 (Bu), 120.1, 132.3, 125.5, 152.3, 34.7, 31.2
(i, o, m, p, Ctert, Me3, 4-tBu-C6H4) ppm.
Scheme 2. Combination of 1,2-hydroboration and 1,1-organobor-
ation. The intermediates shown in brackets were not detected. 1-
Silacyclopent-2-enes 3a and 4a were identified in mixtures along
with the starting silanes and the spirosilanes (see Figure 2).
Table 2. 11B, 13C, and 29Si NMR spectroscopic data[a] for 1-silacy-
clopent-2-enes 3a and 4a.
δ13C (C-2) δ13C (C-3) δ13C (C-4) δ13C(C-5)
δ
29Si
δ
11B
3a[b] 146.8 [67.5] 169.2 (br.)
4a[c] 146.1 [69.4] 174.6 (br.)
34.1
35.0
10.4 [60.3] –11.8
10.9 [59.9] –10.9
85.6
86.0
[a] Measured in C6D6 at 23 °C, (br.) indicates that the 13C NMR
signal is broadened owing to partially relaxed 11B–13C spin–spin
1
coupling[20]; coupling constants [Hz] corresponding to J(13C,29Si)
are given in square brackets. [b] See Figure 3; other 13C data: δ
[J(29Si,13C)] = 136.3 [69.9, =CH], 134.3 (=CH2), 110.7 [16.3, Cϵ],
80.9 [89.6, Si–Cϵ], 31.0, 22.3, 20.1, 13.8 (ϵC-Bu), 33.7, 32.9, 23.5,
14.4 [(C-2)–Bu], 34.0, 34.0, 32.5 (br.), 23.6 (BBN) ppm. [c] See Fig-
ure 2 for the 29Si NMR spectrum; other 13C data: δ [J (29Si,13C)] =
34.5, 34.6, 32.5 (br.), 23.6 (BBN), 109.3 [16.2, ϵC], 90.4 [87.8, Si–
Cϵ] ppm; other carbon atoms are without assignment.
Figure 1. 100.5 MHz 13C{1H} NMR spectra of dialkyn-1-yl(divin-
yl)silane 2a as obtained (Scheme 1) without further purification.
Some 29Si satellites are marked by asterisks, and the coupling con-
stants J(29Si,13C) are given in brackets. The insert shows the J-
modulated spectrum.
enlargement of the 9-borabicyclo[3.3.1]nonane ring sys-
tem[13] was not observed here. Usually, the intermolecular
1,1-organoboration of alkyn-1-ylsilanes requires harsh con-
ditions and long reaction times.[12,14] However, the intramo-
lecular 1,1-organoboration proceeds fast and more
smoothly, in most cases studied so far.[8–10,15] This is shown
by the reactions of 1 or 2 with 9-BBN either in an equi-
molar ratio or with two equivalents of 9-BBN (Scheme 2).
If an equimolar amount of 9-BBN is used, monitoring of
the reaction by 1H, 13C, and 29Si NMR spectroscopy
(Table 2, Figure 2) enables 1-silacyclopent-2-enes 3 or 4 to
be detected in mixtures with the respective starting silane 1
or 2 and spirosilanes 5 or 6.
Figure 2. 29Si{1H} NMR 59.6 MHz spectrum (refocused IN-
EPT[18]) of the reaction mixture containing the starting silane 2a,
1-silacyclopent-2-ene 4a and spiro-silane 5a.
1-Silacyclopent-2-enes 3 or 4 can be converted into the
title compounds by adding more 9-BBN, or the treatment
of 1 or 2 with two equivalents of 9-BBN leads directly to
the desired 5-silaspiro[4,4]nona-1,6-diene derivatives 5 or 6. data sets (Table 3) are in complete agreement with the pro-
These spirosilanes are air sensitive, oily liquids (5a, 5c) or posed structures. The structure in solution is confirmed by
crystalline compounds (5b, 6a) that are formed in essen- the molecular structure of 5b in the solid state, as shown by
tially quantitative yield. The consistent NMR spectroscopic X-ray analysis (vide infra).
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A Convenient Route to 5-Silaspiro[4,4]nona-1,6-diene Derivatives
excess amount of acetic acid can lead directly to bicyclic
boron–oxygen compounds.[16] Therefore, it was of interest
to prove this point in the case of spirosilanes 5 and 6
(Scheme 3).
Scheme 3. Protodeborylation of spirosilanes 5 and 6 by using an
excess amount of acetic acid.
Figure 3. Part of the 100.5 MHz 13C{1H} NMR spectrum of the
reaction mixture containing starting material 2a (marked by filled
circles), 1-silacyclopent-2-ene derivative 3a (marked by squares),
and spirosilane 5a (marked by circles). 29Si satellites are marked by
asterisks.
The protodeborylation of 5 and 6 affords 1,6-disubsti-
tuted 5-silaspiro[4,4]nona-1,6-dienes 7 and 8 in essentially
quantitative yield along with the bicyclic boron–oxygen
compound 9. The latter compound was characterized pre-
viously both in solution (NMR spectroscopy) and in the
solid state (X-ray structural analysis).[16] The NMR spectra
and melting point of 9 are identical to those already re-
ported. Spirosilanes 7 and 8 are obtained in pure state,
readily characterized by their NMR spectroscopic data
(Table 3; Figure 4) and in one case (7b) by X-ray structural
analysis (vide infra). The information from the 29Si NMR
spectrum on the coupling constants J(29Si,13C) (Figure 4) is
frequently more readily obtained and complementary to the
results from 13C NMR measurements (Table 3).
Table 3. 11B, 13C, and 29Si NMR spectroscopic data[a] for 5-sila-
[4,4]spironona-1,5-diene derivatives 5–8.
δ13
C
δ13
C
δ13
C
δ13
C
δ
29Si
δ
11B
(C-1, 6)
(C-2, 7)
(C-3, 8)
(C-4, 9)
5a[b] 149.1 [58.2]
5b[c] 149.7 [58.9]
5c[d] 149.6 [59.3]
6a[e] 150.0 [58.2]
148.8 [58.9]
168.5 (br.)
173.5 (br.)
173.0 (br.)
172.4 (br.)
169.0 (br.)
147.7 [11.5]
148.0 [11.2]
148.3 [11.2]
148.2 [11.9]
147.7 [10.8]
34.3
35.2
34.5
34.6
34.9
30.4
29.8
31.2
31.0
30.6
9.4 [50.8]
9.3 [51.8]
9.3 [52.5]
10.4 [49.9]
8.8 [52.3]
8.5 [51.1]
6.6 [51.7]
8.0 [52.1]
8.4 [50.2]
8.2 [51.8]
34.9 85.6
33.2 86.0
35.8 87.0
35.6 86.4
7a[f]
143.3 [59.8]
28.5
29.9
29.8
29.2
–
–
–
–
7b[g] 141.0 [60.8]
7c[h] 142.3 [61.8]
8a[i]
143.8 [60.6]
141.7 [60.3]
[a] Measured in C6D6 at 23 °C, (br.) indicates that the 13C NMR
signal is broadened owing to partially relaxed 11B–13C spin–spin
coupling[20]
; coupling constants [Ϯ0.4 Hz] corresponding to
2
1J(29Si,13C) and J(29Si,13C) are given in square brackets. [b] Other
13C data: δ = 33.9, 33.9, 32.4 (br.), 23.7 (9-BBN), 33.8, 33.2, 23.7,
14.4 (Bu) ppm. [c] Other 13C data: δ [J(29Si,13C)] = 34.3, 34.8, 32.7
(br.), 23.7 (9-BBN), 143.7 [6.3], 128.4, 128.2, 126.4 (i, o, m, p, Ph)
ppm. [d] Other 13C data: δ [J(29Si,13C)] = 34.9, 34.4, 32.7 (br.), 23.8
(9-BBN), 140.9 [6.7], 128.2, 125.3, 149.1, 35.2, 31.5 (i, o, m, p, Ctert
,
Me3, 4-tBu-C6H4) ppm. [e] Other 13C data: δ [J(29Si,13C)] = 33.9,
33.8, 32.7 (br.), 32.5 (br.), 23.8, 23.7 (9-BBN), 34.6, 33.4, 23.9, 14.4
(Bu), 141.1 [6.3], 128.2, 125.1, 148.9, 34.1, 31.7 (i, o, m, p, Ctert
,
Me3, 4-tBu-C6H4) ppm. [f] See Figure 4 for the 29Si NMR spec-
trum; other 13C data: δ [J(29Si,13C)] = 31.9 [5.9], 25.3, 23.0, 14.2
(Bu) ppm. [g] Other 13C data: δ [J(13C,29Si)] = 138.9 [5.5], 127.5,
125.5, 125.5 (i, o, m, p, Ph) ppm. [h] Other 13C data: δ [J(29Si,13C)]
= 137.5 [5.3], 126.7, 125.9, 149.5, 34.4, 31.4 (i, o, m, p, Ctert, Me3,
4-tBu-C6H4) ppm. [i] Other 13C data: δ [J(29Si,13C)] = 32.2, 31.1,
23.0, 14.1 (Bu), 137.6 [5.2], 126.6, 125.7, 149.3, 32.9, 31.5 (i, o, m,
p, Ctert, Me3, 4-tBu-C6H4) ppm.
Figure 4. 59.6 MHz 29Si{1H} NMR spectrum (refocused IN-
EPT[18]) of 1,6-dibutyl-5-silaspiro[4.4]nona-1,6-diene 7a. Satellites
1
2
marked by asterisks correspond to J(13C,29Si) and J(13C,29Si).
X-ray Structure Analysis of Spirosilanes 5b and 7b
The molecular structures of 5-silaspiro[4.4]nona-1,6-
Because spirosilanes 5 and 6 possess reactive B–C bonds, diene derivatives 5b and 7b are shown in Figure 5 and 6,
they invite further transformations. The protodeborylation respectively. Selected structural parameters are given in
is a typical reaction that is frequently performed after gen- Table 4. All the bond lengths and angles are comparable to
erating the desired organic compound. In these cases, in those reported for simple 1-silacyclopent-2-enes.[9] The five-
general, little attention is paid to the fate of the boryl group. membered rings are almost planar [mean deviations for 5b:
We have shown that protodeborylation of diethyl(organo)- 9.3 (Si1, C1–4) and 1.8 pm (Si1, C11–14); for 7b: 5.1 pm].
boranes or 9-organo-9-borabicyclo[3.3.1]nonanes with an The planes of the five-membered rings are oriented almost
Eur. J. Inorg. Chem. 2008, 5367–5372
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5369

E. Khan, B. Wrackmeyer, R. Kempe
FULL PAPER
perpendicular to each other (5b: 84.9°; 7b: 94.1°). The CBC involves the pz orbital of the boron atom and C–C σ
planes of 9-BBN in 5b are twisted by 52.2° (C21–B1–C25) bonds.[17] Comparison of bond angles of 7b with those of
and 55.4° (C29–B2–C33) against the respective ring planes. 5b shows an increase of 3.8° in ЄC4–C3–C2 and a decrease
The surroundings of the boron atoms in 5b are trigonal in ЄC3–C2–C1 by 1.8°. Intermolecular interactions were
planar within the experimental error. Expectedly, the endo- negligible in both 5b and 7b.
cyclic bond angles are acute (e.g., in 5b: ЄC1–Si1–C4
93.00° and ЄC11–Si1–C14 93.4°) in contrast to the exocy-
clic bond angles (e.g., in 5b: ЄC1–Si1–C14 121.3°, ЄC1–
Si1–C11 111.5°, ЄC4–Si1–C14 119.3°, and ЄC4–Si1–C11
Table 4. Selected bond lengths [pm] and angles [°] for spirosilanes
5b and 7b.
5b
C1–C2
C2–C3
C3–C4
C1–C5
C1–Si1
135.8(2)
152.6(2)
154.2(2)
147.2(2)
186.7(1)
187.7(1)
155.8(2)
110.0(1)
116.6(1)
111.7(1)
104.90(9)
93.00(6)
111.5(1)
121.3(1)
C11–C12
C12–C13
C13–C14
C11–C15
C11–Si1
C14–Si1
C12–B2
Si1–C11–C12
C11–C12–C13 116.6(1)
C12–C13–C14 112.4(1)
C13–C14–Si1
C11–Si1–C14
C4–Si1–C14
C4–Si1–C11
135.2(2)
152.3(2)
153.9(2)
147.4(2)
187.2(1)
187.3(1)
156.0(2)
111.1(1)
120.5°). The structure of 7b compares well to that of its
immediate precursor 5b. The changes in most of the bond
lengths are either minor or negligible within experimental
error. The C2–C3 and C3–C4 bond lengths in 7b are slightly
shorter than the respective bonds in 5b by 2.4 and 1.8 pm, C4–Si1
C2–B1
Si1–C1–C2
respectively. Elongation of these bonds in 5b can be ex-
plained by invoking the concept of hyperconjugation, which
C1–C2–C3
C2–C3–C4
C3–C4–Si1
C1–Si1–C4
C1–Si1–C11
C1–Si1–C14
106.3(2)
93.4(1)
119.3(1)
120.5(1)
7b
C3–C4
C2–C3
C1–C2
Si1–C4–C3
C4–C3–C2
C3–C2–C1
C2–C1–Si1
C1–Si1–C4
134.0(2)
150.2(2)
154.4(2)
108.2(1)
120.4(1)
109.8(1)
105.6(1)
93.34(1)
C4–C5
C4–Si1
C1–Si1
C4–Si1–C4A
C4–Si1–C1A
C1–Si1–C1A
C1–Si1–C4A
147.6(2)
187.9(2)
187.3(2)
113.7(1)
120.4(1)
117.2(1)
120.4(1)
Figure 5. Molecular structure of 2,7-bis[9-(9-borabicyclo[3.3.1]-
nonyl)]-1,6-diphenyl-5-silaspiro[4.4]nona-1,6-diene (5b; ORTEP
plot, 40% probability level, hydrogen atoms are omitted for clar-
ity). Selected structural parameters are listed in Table 5.
Conclusions
The consecutive combination of 1,2-hydroboration and
1,1-organoboration has opened an efficient route to 5-sila-
spiro[4,4]nona-1,6-dienes and is promising for further appli-
cations. The new spirosilanes were characterized in solution
by multinuclear NMR and for two examples in the solid
state by X-ray structural analysis.
Experimental Section
General: All preparative work as well as handling of the samples
was carried out by observing precautions to exclude trace amounts
of air and moisture. Carefully dried solvents and oven-dried glass-
ware were used throughout. BuLi in hexane (1.6 ), dichloro(divi-
nyl)silane, ethynylbenzene, 1-hexyne, 1-ethynyl-4-tert-butylbenzene,
glacial acetic acid, and 9-borabicyclo[3.3.1]nonane were used as
commercial products without further purification. Mass spectra:
FOCUS DSQ (Thermo) mass spectrometer; the m/z data refer to
1
the isotopes H, 11B, 12C, 28Si. NMR measurements in C6D6 (con-
centration ca. 5–10%) with samples in 5 mm tubes at 23Ϯ1 °C:
Varian Inova 300 and 400 MHz spectrometers for 1H, 11B, 13C, and
29Si NMR; chemical shifts are given relative to Me4Si [δ1H
(C6D5H) = 7.15 ppm; δ13C (C6D6) = 128.0 ppm; δ29Si = 0 ppm for
Ξ(29Si) = 19.867184 MHz]; external BF3·OEt2 [δ11B = 0 ppm for
Ξ(11B) = 32.083971 MHz]. Chemical shifts are given to Ϯ0.1 for
13C and 29Si, and Ϯ0.4 ppm for 11B; coupling constants are given
Ϯ0.4 Hz for J(29Si,13C). 29Si NMR spectra were measured by using
Figure 6. Molecular structure of 1,6-diphenyl-5-silaspiro[4.4]nona-
1,6-diene (7b; ORTEP plot, 50% probability; hydrogen atoms are
omitted for clarity). Selected structural parameters are listed in
Table 5.
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A Convenient Route to 5-Silaspiro[4,4]nona-1,6-diene Derivatives
the refocused INEPT pulse sequence,[18] based on 3J(29Si,1HHC=) =
20–25 Hz or 2,3J(29Si,1H) = 8–12 Hz after optimizing the delay
times in the pulse sequence. The melting points (uncorrected) were
determined by using a Büchi 510 melting point apparatus.
afforded a mixture of 1a (starting silane), 3a and 5a. A further
equivalent of 9-BBN (0.82 g, 6.6 mmol) was added by using the
same conditions to give pure 5a. The procedure for the preparation
of spirosilanes 5b, 5c, and 6a was exactly the same. The solvent
(THF) from spirosilane 5b was completely evaporated, and the re-
maining solid was dissolved in pentane (3 mL). The solution was
kept at room temperature. Single crystals suitable for X-ray struc-
ture analysis appeared within 1–2 h. All soluble impurities were
filtered off, and a single crystal of appropriate dimensions was se-
lected and studied by X-ray analysis at low temperature (133 K).
General Procedure for the Synthesis of Dialkyn-1-yl(divinyl)silanes
1a–c and 2a: To a freshly prepared suspension of hexyn-1-yllithium
(25 mmol) in hexane (50 mL) cooled to –78 °C was added dichloro-
(divinyl)silane (12.5 mmol, 2 mL) in one portion. The reaction mix-
ture was warmed to room temperature and stirring was continued
for 4–5 h. Insoluble materials were filtered off, and all readily vola-
tile materials were removed in vacuo. The colorless oily residue was
identified as the mixture of 1a and Si(CH=CH2)2(CϵC–Bu)Cl as
the side product. These compounds could be separated by frac-
tional distillation to give both pure 1a and the chlorosilane. The
latter, Si(CH=CH2)2(CϵC–Bu)Cl (3.8 g, 19.2 mmol), was added to
a freshly prepared suspension of 4-tert-butylphenylethynyllithium
(19.2· mmol) in hexane (60 mL), following identical reaction condi-
1
3a: H NMR (400 MHz): δ = 0.7, 0.8, 1.5, 2.0, 2.1 (t, t, m, t, t, 18
H, Bu), 6.0–6.2 (m, 3 H, CH=CH2) ppm. Other signals were not
assigned due to overlap with signals belonging to other compounds
in the mixture.
1
5a: H NMR (400 MHz): δ = 1.3–1.9 (m, 28 H, 9-BBN), 0.9, 1.3,
2.4 (t, m, t, 18 H, Bu), 0.9, 1.0 (m, m, 4 H, C4,9H2), 2.7 (m, 4 H,
C3,8H2) ppm.
1
tions, and silane 2a was obtained as an oil (Ͼ99% from H NMR;
5b: Yield (after recrystallization from pentane): 93%. M.p. 104–
see also Figure 1). The same preparative method was adopted for
the preparation of dialkyn-1-yl(divinyl)silanes 1b and 1c.
1
106 °C. H NMR (400 MHz): δ = 1.4–1.9 (m, 28 H, 9-BBN), 1.1
2
3
[ddd, J(1H,1H) = 15.5 Hz, J(1H,1H) = 5.3, 9.3 Hz, 1 H, C4,9H2],
1
1a: H NMR (400 MHz): δ = 0.7, 1.3, 2.0 (t, m, t, 18 H, Bu), 6.0
1.2 [ddd, 2J(1H,1H) = 15.5 Hz, 3J(1H,1H) = 3.7, 9.1 Hz, 1 H,
(m, 6 H, Si-vinyl) ppm.
1b: 1H NMR (400 MHz): δ = 6.0 [t, 3J(1H,1H) = 8.8 Hz, 2 H,
C4,9H2], 2.8 [ddd, J(1H,1H) = 18.2 Hz, J(1H,1H) = 5.3, 9.3 Hz, 1
H, C3,8H2], 2.9 [ddd, 2J(1H,1H) = 18.2 Hz, 3J(1H,1H) = 3.7, 9.1 Hz,
1 H, C3,8H2], 7.2, 7.1, 7.0 (m, m, m, 10 H, Ph) ppm.
2
3
=CH], 6.2 (d, 4 H, =CH2), 6.9, 7.3 (m, m, 10 H, Ph) ppm.
1
1
1c: H NMR (400 MHz): δ = 1.1, 7.1, 7.3 (s, m, m, 26 H, 4-tBu-
5c: H NMR (400 MHz): δ = 1.4–1.9 (m, 28 H, 9-BBN), 1.1 (m, 4
C6H4), 6.1 (dd, 2 H, =CH-Si), 6.3 (m, 4 H, H2C=) ppm.
H, C4,9H2), 2.8 (m, 4 H, C3,8H2), 1.2, 7.1, 7.2 (s, m, m, 26 H, 4-
tBu-C6H4) ppm.
2a: 1H NMR (400 MHz): δ = 0.6, 1.2, 1.9 (t, m, t, 9 H, Bu), 6.0
1
(dd, 2 H, =CH-Si), 6.2 (m, 4 H, H2C=), 1.0, 7.0, 7.3 (s, m, m, 13 6a: H NMR (400 MHz): δ = 1.3–1.9 (m, 28 H, 9-BBN), 0.8, 1.5,
H, 4-tBu-C6H4) ppm.
2.7 (t, m, t, 9 H, Bu), 1.3 (m, 4 H, C4,9H2), 2.9 (m, 4 H, C3,8H2),
1.2, 7.1, 7.2 (s, m, m, 13 H, 4-tBu-C6H4) ppm.
Bis[9-(9-borabicyclo[3.3.1]nonyl)]-1,6-(R,R1)-5-silaspiro[4.4]nona- Protodeborylation of Spirosilanes 5 and 6: A solution of 5a (1.2 g,
Syntheses of 1-Silacyclopent-2-ene Derivatives 3a and 4a and 2,7-
1,6-dienes 5a–c and 6a: To a Schlenk tube charged with a solution
of 1a (1.6 g, 6.6 mmol) was added 9-BBN (0.82 g, 6.6 mmol,
2.5 mmol) in pentane (10 mL) was mixed with an excess amount
of acetic acid (2.0 mL) at 23 °C. The reaction mixture was stirred
1 equiv.) in THF (10 mL). The reaction mixture was stirred at room for 40–60 min. Then, all the readily volatile materials were removed
temperature for 2–4 h, and all volatile materials were then removed
under reduced pressure. A small part of the oily residue was dis-
solved in C6D6 and analyzed by NMR spectroscopy. The reaction
under reduced pressure. The oily residue left was dissolved in pen-
tane, and the solution was kept at –35 °C. Boron–oxygen com-
pound 9 precipitated and was separated. Pure spirosilane 7a was
Table 5. Data pertinent to the crystal structure determinations of 5b and 7b.
5b
7b
Formula
Crystal
Dimensions [mm]
Crystal system
Space group
C36H46B2Si
C20H20Si
colorless prism
0.47ϫ0.36ϫ0.35
triclinic
colorless prism
1.08ϫ0.77ϫ0.61
monoclinic
C2/c
¯
P1
Lattice parameters
a [pm]
b [pm]
c [pm]
α [°]
β [°]
γ [°]
Z
996.9(9)
1248.3(9)
1369.0(10)
113.5(5)
104.9(6)
91.6(6)
2
2094.6(2)
572.3(10)
1552.5(2)
90.00
126.478(10)
90.00
4
Absorption coefficient µ [mm–1]
Diffractometer
Measuring range [°]
Reflections collected
Independent reflections [IϾ2σ(I)]
Absorption correction
Refined parameters
wR2/R1 [IϾ2σ(I)]
0.103
0.148
STOE IPDS II, Mo-Kα, λ = 71.069 pm, graphite monochromator
1.7–25.7
20118
4759
none
352
2.4–24.6
8274
1180
none
136
0.095/0.035
0.216/–0.387
0.110/0.040
Max./min. Residual electron density [epm–3 ϫ10–6] 0.380/–0.302
Eur. J. Inorg. Chem. 2008, 5367–5372
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5371

E. Khan, B. Wrackmeyer, R. Kempe
FULL PAPER
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obtained as a colorless oil. The protodeborylation of silanes 7b, 7c,
and 8a was carried out under the same reaction conditions except
that 9 was separated by different way. The mixture of respective
spirosilanes (7b, 7c, and 8a) and 9 was heated at 120 °C (oil bath)
under reduced pressure (10–2 Torr) for ca. 2 h. This led to the ac-
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into another Schlenk tube. Crystallization proceeded in the case of
7b (X-ray analysis) and 7c, and crystals suitable for single X-ray
crystal analysis were grown after 5 and 20 d, respectively.
1
7a: H NMR (400 MHz): δ = 1.0 (m, 4 H, C4,9 H2), 2.4 (m, 4 H,
C3,8H2), 0.9, 1.6, 2.2 (t, m, t, 18 H, Bu), 6.4 [m, 2 H, (C2,7H)] ppm.
7b: Yield (after recrystallization from hexane): 63%. M.p. 51–
52 °C. 1H NMR (400 MHz): δ = 0.8 [ddd, 2J(1H,1H) = 15.7 Hz,
3J(1H,1H) = 4.4, 9.5 Hz, 2 H, C4,9H2], 1.1 [ddd, 2J(1H,1H) =
[8] B. Wrackmeyer, E. Khan, R. Kempe, Appl. Organomet. Chem.
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3
2
15.7 Hz, J(1H,1H) = 4.1, 9.4 Hz, 2 H, C4,9H2], 2.4 [m, J(1H,1H)
= 19.0 Hz, 2 H, C3,8H2], 2.5 [m, 2J(1H,1H) = 19.0 Hz, 2 H, C3,8H2],
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6.9, 7.4 (m, m, 10 H, Ph), 7.1 (m, 2 H, C2,7H) ppm. GC–MS: tR
=
22.01 min; m/z (%) = 288.06 (41) [M]+, 134.3 (21) [M – C12H10]+,
132.2 (72) [M – C12H12]+, 158.0 (90) [M – C10H10]+, 105.0 (100)
[M – C12H14Si]+.
7c: Yield (recovered after recrystallization from pentane): 20%.
M.p. 64–65 °C. 1H NMR (400 MHz): δ = 0.9, 1.2 (m, m, 4 H,
C4,9H2), 2.5–2.6 (m, 4 H, C3,8H2), 7.1 [t, 3J(1H,1H) = 3.1 Hz,
3J(29Si,1H) = 13.9 Hz, 2 H, C2,7H], 1.2, 7.2, 7.5 (s, m, m, 26 H, 4-
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8a: 1H NMR (400 MHz): δ = 0.9 (m, 4 H, C4,9H2), 2.5 (m, 4 H,
C3,8H2), 0.8, 1.4, 2.3 (t, m, t, 9 H, Bu), 7.0 (t, 1 H, C2H), 6.5 (m,
1 H, C7H), 1.2, 7.2, 7.4 (s, m, m, 13 H, 4-tBu-C6H4). GC–MS: tR
= 26.2 min; m/z (%) = 400.11 (20) [M]+, 384.20 (13) [M – CH3]+,
343.20 (42) [M – C4H9]+, 287.01 (8) [M – C8H18]+, 56.99 (100)
[Si(CH2)2]+ or [C4H8]+.
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Crystal Structure Determination of Spirosilanes 5b and 6b: Details
pertinent to the crystal structure determinations are listed in
Table 5.[19] Crystals of appropriate size were selected (in perfluori-
nated oil[21] at room temperature), and the data collections were
carried out at 133 K by using a STOE IPDS II system equipped
with an Oxford Cryostream low-temperature unit. Structure solu-
tions and refinements were accomplished by using SIR97,[22]
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[19] CCDC-697108 (for 5b) and -697109 (for 7b) contain the sup-
plementary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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Acknowledgments
This work was supported by the Deutsche Forschungsgemein-
schaft, the DAAD, and HEC (Pakistan) (E. K.).
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Received: August 7, 2008
Published Online: October 29, 2008
5372
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 5367–5372