1,2-Hydroboration of alkyn-1-yl(chloro)silanes: Alkenes bearing chlorosilyl and dialkylboryl groups in geminal positions

Article abstract of DOI:10.1515/znb-2007-0111

The 1,2-hydroboration of various alkyn-1-yl(chloro)silanes (3-7), derived from 1-hexyne (a) and ethynylbenzene (b),using 9-borabicyclo[3.3.1]nonane, 9-BBN, affords selectively alkene derivatives in which the dialkylboryl and chlorosilyl groups are in gemi

Full text of DOI:10.1515/znb-2007-0111

1,2-Hydroboration of Alkyn-1-yl(chloro)silanes: Alkenes Bearing
Chlorosilyl and Dialkylboryl Groups in Geminal Positions
Bernd Wrackmeyer, Ezzat Khan, and Rhett Kempe
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. 2007, 62b, 75 – 81; received September 11, 2006
The 1,2-hydroboration of various alkyn-1-yl(chloro)silanes (3 – 7), derived from 1-hexyne (a) and
ethynylbenzene (b), using 9-borabicyclo[3.3.1]nonane, 9-BBN, affords selectively alkene derivatives
in which the dialkylboryl and chlorosilyl groups are in geminal positions at the C=C bond. The
molecular structure of (Z)-α-(9-borabicyclo[3.3.1]non-9-yl)-α-dichloro(phenyl)silyl-styrene (11b)
was determined by X-ray diffraction. All alkenes were characterised by a consistent set of NMR
spectroscopic data (1H, 11B, 13C, 29Si NMR).
Key words: Alkynes, Alkenes, Boranes, Silanes, Hydroboration, NMR
Introduction
There is considerable interest in the synthesis of
alkenes bearing both boryl and silyl groups [1 – 9].
Among these, alkenes with silyl and boryl groups
in geminal positions with functional group(s) at sil-
icon would be highly welcome synthons for various
transformations [7 – 9]. 1,2-Hydroboration of alkyn-
1-ylsilanes appears to be an attractive route to such
alkenes, if the 1,2-hydroboration proceeds in a re-
giospecific way. This has been shown for alkyn-1-
yl(chloro)silanes of type 1 which react with 9-BBN to
give 2 [8] (Scheme 1).
Scheme 1. Previous results [8] for 1,2-hydroboration of
alkyn-1-yl(chloro)silanes using 9-BBN.
by using a large excess of the starting chlorosilane.
These mixtures can be separated by distillation to give
the pure alkyn-1-yl(chloro)silanes 3 – 7 (see for exam-
ple the 13C NMR spectrum of 4a in Fig. 1).
The 1,2-hydroboration of the alkyn-1-yl(chloro)-
silanes 3 – 7 (Scheme 2) is straightforward in most
cases, as shown, and the alkenes 10 have already been
used for further reactions [9].
The regioselectivity of the 1,2-hydroboration fol-
lows from a consistent set of NMR parameters (Ta-
ble 1 and Experimental Section; vide infra). In
the solid state, this stereochemistry is confirmed by
an X-ray structure determination of the crystalline
derivative 11b (vide infra). Except for 9b and 11b,
the alkenes 8 – 12 are colourless, air- and moisture-
sensitive oils or waxy solids.
In the present work, analogous results were ex-
pected for a greater variety of substituents at silicon
in the alkyn-1-yl(chloro)silanes 3 – 7, including up to
three Si–Cl functions as in 7. One further goal was to
obtain direct structural evidence for such alkenes re-
lated to 2. Therefore, phenyl groups at both silicon and
the C≡C bond have been introduced in order to obtain
suitable crystalline products.
Results and Discussion
The alkyn-1-yl(chloro)silanes3 – 7 were prepared in
the usual way [10,11] from the respective chlorosilanes
and alkynyllithium reagents. In general, this route
Solely in the case of the reaction of 3a with 9-
leads to mixtures containing the desired products along BBN, a mixture of isomers 8a and 8aꢀ (see Fig. 2 for
with alkyn-1-ylsilanes, in which more than one Si–Cl the 29Si NMR spectrum) was obtained, independent
function is substituted by an alkyn-1-yl group. Appar- of various reaction conditions. This result can be ex-
ently, such side reactions cannot be suppressed, even plained considering a fast second hydroboration of the
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B. Wrackmeyer et al. · 1,2-Hydroboration of Alkyn-1-yl(chloro)silanes
Table 1. 11B, 13C and 29Si NMR dataa of the alkenes 8 – 16.
δ
13C Si(B)C= 13C R1C= 13C Ph(Si)/R2
δ
δ
δ
13C R1
35.3, 31.2, 21.9, 13.5
δ
13C BBN
δ
11B
δ
29Si
8ab
8aꢀ
8b
9a
143.0 (br) [65.1]
139.2 (br) [57.2]
142.3 (br)
161.7
166.8
159.9
161.5
135.3 (i) [74.1],
131.2 (o), 127.6 (m),
128.2 (p)
134.0 (i) [66.1],
130.3 (o), 128.1 (m),
133.9 (p)
134.2 (i) [76.9],
134.3 (o), 128.1 (m),
129.3 (p)
137.5 (i) [74.6],
133.5 (o), 127.9 (m),
129.9 (p),
33.4, 33.3, 30.5 (br), 81.4 −54.2
23.2
35.1, 31.1, 22.4, 13.9
33.9, 33.8, 30.3 (br), 81.4 −38.5
23.1
138.5 (i), 130.4 (o),
129.4 (m), 128.2 (p)
34.5, 34.2, 31.3 (br), 82.2 −12.0
23.4
144.0 (br)
35.3, 23.1, 22.4, 13.5
33.9, 33.8, 31.2 (br), 81.6
31.1
7.6
7.9
4.2 [58.9] (SiMe)
133.8 (i) [70.9],
134.0 (o), 129.2 (m),
130.4 (p),
9bb
148.3 (br)
156.1
138.0 (i), 130.2 (o),
129.0 (m), 128.2 (p)
34.7, 34.4, 31.9 (br), 82.2
23.5
3.7 [59.8] (SiMe)
136.0 (i) [77.8],
134.9 (o), 128.3 (m),
130.4 (p)
135.4 (i) [78.9],
134.5 (o), 127.8 (m),
128.7 (p)
135.3 (i) [90.7],
133.3 (o), 128.2 (m),
131.2 (p)
138.2 (i) [92.7],
133.3 (o), 128.0 (m),
128.2 (p)
10a
10b
11a
11b
142.9 (br)
163.3
157.9
164.8
158.6
35.9, 31.2, 22.6, 13.9
34.2, 31.6 (br), 23.4
34.2, 31.6 (br), 23.1
34.0, 31.2 (br), 23.0
34.3, 31.6 (br), 23.1
81.7
83.1
82.7
83.6
−5.7
−2.1
3.4
144.3 (br)
138.3 (i), 130.0 (o),
129.4 (m), 127.5 (p)
141.6 (br)
35.3, 30.9, 22.4, 13.9
143.9 (br) [79.2]
132.7 (i), 129.4 (o),
127.9 (m), 125.4 (p),
2.2
12ab 141.8 (br)
12bb 143.0 (br) [95.7]
167.0
160.8
–
35.4, 31.1, 22.8, 14.1
34.5, 31.6 (br), 23.4
34.7, 31.9 (br), 23.4
81.5
81.3
−3.9
−4.8
–
138.0 (i), 130.4 (o),
129.8 (m), 128.4 (p)
a
Measured in CDCl3at 23 ◦C; (br) indicates a broad NMR signal owing to partially relaxed13C-11B scalar coupling [15]; some coupling
constants 1J(29Si,13C) are given in brackets;
measured in C6D6.
b
1
Fig. 1. 75.8 MHz 13C{ H}
NMR spectrum of the alkyn-
1-yl(chloro)silane 4a in CDCl3
at 23 ◦C. Expansions are given
for the signals showing 29Si
satellites, marked by asterisks,
corresponding to 1J(29Si,13C)
and 2J(29Si,13C).
alkene 8a leading to 1,1,1-diboryl(silyl)hexane or 1,2- in the 29Si NMR spectrum at δ = −43.7 and −54.0
diboryl-1-silylhexane (both were not detected) as in- which can be tentatively assigned to the isomers 8aꢀꢀ
termediates (Scheme 3), which upon dehydroboration and 8aꢀꢀꢀ (Fig. 2). The presence of 8aꢀ in the mixture is
afford mainly the mixture of the isomers 8a and 8aꢀ. readily shown by the set of NMR parameters (Fig. 2,
There are two additional signal of appreciable intensity Table 1 and Experimental Section).
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B. Wrackmeyer et al. · 1,2-Hydroboration of Alkyn-1-yl(chloro)silanes
77
Fig. 2. 79.47 MHz 29Si NMR
spectra (INEPT) of the mix-
ture of isomers 8a and 8aꢀ.
1
The upper trace shows the H
coupled spectrum, the middle
traces show expansions of the
1H decoupled 29Si NMR sig-
nals with 13C satellites, and
the lower trace shows the
full spectrum. Additional sig-
nals, marked with filled cir-
cles, are tentatively assigned
to the isomers 8aꢀꢀ and 8aꢀꢀꢀ
(δ29Si = −43.7, 1J(29Si,1H)
= 197.0 Hz; δ29Si = −54.0,
1J(29Si,1H) = 208.3 Hz); see
Scheme 3.
ence of a broad weak signal is typical for the B–C
bond [15]. The sharp signal for the other olefinic car-
bon atom does not show 29Si satellites (2J(29Si,13C)
< 3 Hz) which means that the silyl group is attached
to the same olefinic carbon atom as the boryl group.
In principle, this can be shown in 13C NMR spectra by
29Si satellites corresponding to 1J(29Si,13C). However,
these signals are weak and broad and therefore, it is
difficult to obtain the signal-to-noise ratio required for
this purpose. The most convenient access to these data
1J(29Si,13C) is provided by observing the 13C satellites
in the 29Si NMR spectra. This is shown in Fig. 2 and
also in Fig. 3. The presence of the boryl group at the
same olefinc carbon typically [16] reduces the mag-
1
nitude of J(29Si,13C) in the order of 10 to 15 Hz in
comparison with other alkenylsilanes.
The 11B chemical shifts [17] are characteristic for
alkenyl(dialkyl)boranes, in which a conformation is
preferred where the boryl group is significantly twisted
against the B–C=C plane. The 29Si chemical shifts
are in the expected range considering the various sub-
stituent effects [16]. The fairly large difference be-
tween the δ29Si values for 8a and 8aꢀ corresponds to
the trend known for δ 13C of alkyl substituents in (Z,E)-
alkenes [18].
Scheme 2. Present results for 1,2-hydroboration of alkyn-1-
yl(chloro)silanes with various substituents on silicon, using
9-BBN.
The stereochemistry proposed for the solution-state
structure of the alkenes 8 – 12 is in agreement with the
1
results of H NMR spectroscopy using 1H/1H-NOE
difference spectra [14]. The pattern of substituents at
the C=C bond can also be assigned unambiguously
on the basis of the 13C NMR data. An inspection
of Table 1 clearly indicates that the alkenes possess
analogous structures. In the olefinic range, the pres-
Structure determination of the alkene 11b
The molecular structure of the alkene 11b is shown
in Fig. 3, together with selected structural parame-
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78
B. Wrackmeyer et al. · 1,2-Hydroboration of Alkyn-1-yl(chloro)silanes
Scheme 3. Potential reason for
the loss of stereo- and re-
gioselectivity of the 1,2-hydro-
boration of chloro(hexyn-1-yl)-
(phenyl)silane 3a.
1
Fig. 3. 99.4 MHz (left) and 79.47 MHz (right) 29Si{ H} NMR spectra of the alkenyl(chloro)silanes 11b and 12b, respectively.
The line widths of the 29Si NMR signals increase with the number of chlorine atoms linked to silicon owing to unresolved
scalar one-bond 35/37Cl–29Si spin-spin coupling, and there is also a contribution from unresolved scalar two-bond coupling
2J(29Si,11B). In the case of 11b, further 13C satellites are visible, close to the parent signal, which arise from nJ(29Si,13C)
(n ≥ 2).
ters. Intermolecular contacts are negligible. Silicon, bridge, at least in the solid state. In solution, however,
boron and the C=C unit are in the same plane, The the NMR data for compounds of type 2 indicate the ab-
CBC plane of the 9-BBN unit is twisted against this sence of such interactions. In the present work this is
plane by 18.3◦, the planes of the C–Ph and Si–Ph confirmed by the molecular structure of 11b, where the
rings by 33.1◦ and 64.6◦, respectively. The distances phenyl group is close to the boron atom, and Si–Cl–B
between Cl1 and Cl2 and the boron atom are long bridges can be clearly discarded.
(459.1 pm and 409.1 pm). All other bond lengths and
angles are well comparable with structural data al-
ready published for alkenes of type 2 [6]. In the lat-
Conclusions
ter, it appears that the Si–Cl group prefers an orienta-
tion towards the boryl group, and one was tempted to
propose a weak donor-acceptor interaction, a Si–Cl–B
1,2-Hydroboration of alkyn-1-ylsilanes bearing hy-
drogen, alkyl, phenyl and up to three chloro functions
on silicon proceeds regio- and stereoselectively in such
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B. Wrackmeyer et al. · 1,2-Hydroboration of Alkyn-1-yl(chloro)silanes
Synthesis of alkyn-1-yl(chloro)silanes
79
A freshly prepared suspension of the respective lithium
alkynide (19.5 mmol) was cooled to −78 ◦C, and the respec-
tive chlorosilane was slowly added in 2 – 6 fold excess with
constant stirring. The reaction mixture was warmed to r. t.
and kept stirring for 3 – 4 h. The solution was filtered and
volatiles were removed in vacuo. The colourless oily residue,
a mixture of silanes, was subjected to fractional distillation.
3a: B. p. 105 – 115 ◦C/0.375 Torr. – 1H NMR (300 MHz;
CDCl3): δ = 2.2, 1.5, 1.4, 0.9 (m, m, m, t, 9H, Bu), 4.8 (s,
1J (29Si, 1H) = 224.9 Hz, 1H, SiH), 7.3 – 7.7 (m, 5H, SiPh).
–
13C NMR (75.8 MHz; CDCl3): δ = 111.4 (J(29Si,13C) =
20.1 Hz, C≡), 76.8 (J(29Si,13C) = 105.5 Hz, ≡CSi), 134.5
(o-C), 131.8 (J(29Si,13C) = 81.6 Hz, i-C), 130.0 (p-C),
128.0 (m-C, SiPh), 30.3, 21.9, 19.8, 13.6 (Bu). – 29Si NMR
(59.6 MHz; CDCl3): δ = −65.8.
Fig. 4. Molecular structure of 11b (ORTEP, at the 50 % prob-
ability level; hydrogen atoms omitted for clarity). Selected
bond lengths (pm) and bond angles (deg): C1–Si1 185.2(2),
C7–C8 135.0(3), C7–B1 156.1(3), C7–Si1 184.2(2), C15–
C16 154.0(4), C15–C19 155.1(4), C15–B1 156.5(4), C16–
C17 151.2(4), C19–C20 151.8(4), C22–B1 155.9(4), Si1–
Cl1 204.86(9), Si1–Cl2 205.60(8); C8–C7–B1 116.5(2), C8–
C7–Si1 127.5(2), B1–C7–Si1 115.9(2), C7–C8–C9 130.7(2),
C22–B1–C15 111.4(2), C7–B1–C15 122.9(2), C7–Si1–C1
108.7(1), C7–Si1–Cl1 114.39(8), C1–Si1–Cl1 108.66(9),
C7–Si1–Cl2 111.92(8), C1–Si1–Cl2 106.49(8), Cl1–Si1–
Cl2 106.38(4).
3b: B. p. 115 – 126 ◦C/0.375 Torr. – 1H NMR (300 MHz;
CDCl3): δ = 5.4 (s, 1J(29Si, 1H) = 257.6 Hz, 1H, SiH), 7.1 –
7.7 (m, 10H, SiPh, Ph). – 13C NMR (75.8 MHz; CDCl3):
δ = 121.2 (J(29Si,13C) = 21.9 Hz, C≡), 85.7 (J(29Si,13C) =
110.1 Hz, ≡CSi), 134.1(o-C), 133.2 (J(29Si,13C) = 88.7 Hz,
i-C), 129.4 (p-C), 128.3 (m-C, SiPh), 132.3 (o-C), 131.4 (p-
C), 128.3 (m-C), 121.3 (i-C, Ph). – 29Si NMR (59.6 MHz;
CDCl3): δ = −29.9.
◦
4a: B. p. 82 – 88 C/0.375 Torr. – 1H NMR (300 MHz;
a way that alkenylsilanes are formed, in which the
boryl group becomes attached to the olefinic carbon
atoms which already bear the silyl group. If the reac-
tion cannot be controlled to proceed solely to the first
step, stereoselectivity and to some extent regioselectiv-
ity are lost.
CDCl3): δ = 2.2, 1.4, 1.3, 0.7 (m, m, m, t, 9H, Bu),
0.6 (s, 3H, SiMe), 7.2 – 7.6 (m, 5H, SiPh). – 13C NMR
(75.8 MHz; CDCl3): δ = 112.3 (J(29Si,13C) = 21.3 Hz, C≡),
79.4 (J(29Si,13C) = 110.7 Hz, ≡CSi), 134.4 (J(29Si,13C) =
86.4, i-C), 133.5 (o-C), 130.8 (p-C), 128.2 (m-C, SiPh), 3.0
(J(29Si,13C) = 67.7 Hz, SiMe), 30.2, 21.9, 19.6, 13.5 (Bu). –
29Si NMR (59.6 MHz; CDCl3): δ = −10.4.
Experimental Section
◦
7a: B. p. 72 – 74 C/0.375 Torr. – 1H NMR (300 MHz;
All preparative work was carried out by observing neces-
sary precautions to exclude traces of oxygen and moisture.
The starting chlorosilanes, 1-hexyne, ethynylbenzene, butyl-
lithium in hexane (1.6 M) and 9-BBN were used as commer-
cial products without further purification. NMR spectra were
recorded at 23 ◦C on Bruker DRX 500 or Varian Inova 300
and 400 spectrometers, all equipped with multinuclear units,
using C6D6 or CDCl3 solutions (ca. 10 – 15 % v/v) in 5 mm
tubes. Chemical shifts are given with respect to Me4Si
[δ1H (C6D5H) = 7.15, δ1H (CDCl3/CHCl3) = 7.25; δ13C
(C6D6) = 128.0, δ13C (CDCl3) = 77.0], δ29Si = 0 for
C6D6): δ = 1.9, 1.2, 0.7 (m, m, t, 9H, Bu). – 13C NMR
(75.8 MHz; C6D6): δ = 114.1 (J(29Si,13C) = 35.5 Hz, C≡),
77.7 (J(29Si,13C) = 177.6; ≡CSi), 29.6, 22.1, 19.4, 13.6 (Bu).
–
29Si NMR (59.6 MHz; C6D6): δ = −32.0. – IR: ν(C≡C) =
2281.0 cm−1. – EI-MS: m/z (%) = 215 (8) [M+], 172 (62)
[M+ – C3H7], 135 (38), 81 (100), 43 (90), 41 (60), 39 (20).
Hydroboration of the alkyn-1-yl(chloro)silanes with 9-BBN.
General Procedure
Pure 3a (1.01 g, 4.51 mmol) was dissolved in toluene
Me4Si with Ξ(29Si) = 19.867187 MHz], and δ11B = 0 for (10 ml) and 9-BBN (0.56 g, 4.51 mmol) was added as a solid
BF3· OEt2 with Ξ(11B) = 32.083971 MHz. 29Si NMR spec- in one portion. The reaction mixture was heated to reflux for
tra were recorded using the refocused INEPT pulse sequence 30 min, the solvent was removed in vacuo, and the remain-
with 1H decoupling [19] based on 1J(29Si,1H) (ca. 200 Hz), ing colourless oil was identified as a mixture of 8a and 8a .
ꢀ
3
3
2J(29Si,1HMe), J(29Si,1HPh) (ca. 7 Hz) or J(29SiC=C1H) This reaction was also carried out with the same result at r. t.,
(ca. 20 Hz). Mass spectra (EI, 70 eV): Finnigan MAT 8500 when it was complete after 12 h in the same solvent. The pro-
with direct inlet (data for 12C, 1H, 11B, 35Cl, 28Si). The melt- cedure for the preparation of the other alkenylsilanes is the
ing points (uncorrected) were determined using a Bu¨chi 510 same, except for a heating period of 3 h for 10a, 2 h for 9a,
melting point apparatus.
1 h for 10b, 11b and 0.5 h for 8b, 9b, 11a and 12b. In case
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80
B. Wrackmeyer et al. · 1,2-Hydroboration of Alkyn-1-yl(chloro)silanes
of 12a, the reaction was carried out at the same temperature 9-BBN). – EI-MS: m/z (%) = 336 (28) [M+], 279 (7) [M+
–
in a sealed NMR tube using benzene as the solvent, and the C4H9], 266 (5), 135 (8), 110 (100), 82 (65). 12b: 1H NMR
reaction was complete after 1 h. The yield of the products (300 MHz; C6D6): δ = 1.3 – 2.0 (m, 14H, 9-BBN), 7.8 (s,
was essentially quantitative.
3J(29Si,1H) = 33.2 Hz, 1H, =CH), 6.9 – 7.2 (m, 5H, Ph). –
8a: 1H NMR (300 MHz; CDCl3): δ = 2.4, 1.3 – 1.6, EI-MS: m/z (%) = 256 (1) [M+], 236 (23) [M+ – C8H14B],
1.0 (m, m, t, 9H, Bu), 1.4 – 1.8 (m, 14H, 9-BBN), 5.1 (s, 103 (100), 110 (32), 82 (48).
1J(29Si,1H) = 205.3 Hz, 1H, SiH), 7.3 (t, 3J(1H,1H) = 7.1 Hz,
X-ray structure determination of the alkene 11b
1H, =CH), 7.4 – 7.8 (m, 5H, SiPh). 8aꢀ: 1H NMR (300 MHz;
CDCl3): δ = 2.5, 1.3 – 1.6, 0.9 (m, m, t, 9H, Bu), 1.4 – 1.8 (m,
The X-ray structure determination of 11b was carried out
at 191(2) K on a single crystal selected at r. t. in perfluori-
nated oil [20] using a STOE IPDS II system equipped with
14H, 9-BBN), 5.2 (s, 1J(29Si, 1H) = 189.6 Hz, 1H, SiH), 7.1
3
(t, J(1H,1H) = 7.1 Hz, 1H, =CH), 7.4 – 7.8 (m, 5H, SiPh).
8b: 1H NMR (300 MHz; CDCl3): δ = 1.5 – 1.9 (m, 14H, 9-
BBN), 5.5 (s, 1J(29Si, 1H) = 237.5 Hz, 1H, SiH) 7.2 – 7.6
(m, 10H, SiPh, Ph), 8.2 (s, 3J(29Si,1H) = 20.4 Hz, 1H, =CH).
9a: 1H NMR (300 MHz; CDCl3): δ = 0.6 (s, 3H, SiMe), 2.2,
1.4, 1.3, 0.7 (m, m, m, t, 9H, Bu), 1.5 – 1.8 (m, 14H, 9-BBN),
6.9 (t, 3J(1H,1H) = 7.2 Hz, 1H, =CH) and 7.2 – 7.6 (m, 5H,
SiPh). 9b: Yield after recrystalisation from pentane at r. t.
˚
an Oxford Cryostream low-temperature unit; λ = 0.71069 A,
Mr = 399.22, monoclinic, space group P21/n, a = 6.5500(4),
◦
˚
b = 22.9790(16), c = 13.8360(10) A, β = 95.305(5) , V =
2073.6(2) A , Z = 4, µ(Mo Kα) = 0.374 mm−1, F(000) =
3
˚
840 e, crystal size: 0.87×0.32×0.28 mm3, θ range for data
collection: 1.72 – 25.70◦, hkl ranges: −7 ≤ h ≤ 7, −27 ≤
k ≤ 27, −16 ≤ l ≤ 16, reflections collected: 26069, inde-
pendent reflections: 3096 (Rint = 0.0648), completeness to
θ = 25.70◦: 99.5 %, data/restraints/parameters: 3096/0/239.
Goodness-of-fit on F2: 1.001, final R indices (I ≥ 2σ(I)):
R1 = 0.0487, wR2 = 0.1277, R indices (all data): R1 = 0.0641,
wR2 = 0.1350, largest difference peak and hole in final dif-
◦
was 75 %; m. p. 58 – 60 C. – 1H NMR (300 MHz; C6D6)
δ = 0.3 (s, 3H, SiMe), 1.5 – 1.9 (m, 14H, 9-BBN), 8.0 (s,
3J(29Si, 1H) = 20.3 Hz, =CH), 7.0 – 7.4 (m, 10H, SiPh, Ph).
10a: 1H NMR (300 MHz; C6D6): δ = 2.2, 1.2, 1.0, 0.7 (m, m,
m, t, 9H, Bu), 1.3 – 1.9 (m, 14H, 9-BBN), 7.2 (t, 3J (1H,1H) =
7.4 Hz, 1H, =CH), 7.1 – 7.7 (m, 10H, SiPh2). 10b: 1H NMR
(300 MHz; CDCl3): δ = 8.1 (s, 3J(29Si,1H) = 20.5 Hz, =CH),
1.1 – 1.7 (m, 14H, 9-BBN) and 6.8 – 7.5 (m, 15H, SiPh2, Ph).
11a: 1H NMR (300 MHz; CDCl3): δ = 2.1, 1.1, 1.0, 0.5 (m,
m, m, t, 9H, Bu), 1.4 – 1.6 (m, 14H, 9-BBN), 6.9 (t, 1H, =CH
3J(1H,1H) = 7.5 Hz) and 7.1 – 7.5 (m, 5H, SiPh). 11b: Yield
after recrystalisation from hexane/chloroform (4 : 1) at r. t.
was 80 %; m. p. 74 – 75 ◦C. – 1H NMR (300 MHz; CDCl3):
δ = 7.8 (s, 3J(29Si,1H) = 25.7 Hz, =CH), 1.0 – 2.0 (m, 14H,
9.BBN) and 6.8 – 7.4 (m, 10H, SiPh, Ph). 12a: 1H NMR
(300 MHz; C6D6): δ = 2.5, 1.1 – 1.3, 0.8 (m, m, t, 9H, Bu),
7.0 (t, 3J(1H,1H) = 7.8 Hz, 1H, =CH), 1.3 – 1.9 (m, 14H,
ference map: 0.858/−0.319 e A−3. Structure solution and
˚
refinement were accomplished using SIR97 [21], SHELXL-
97 [22] and WinGX [23].
CCDC 617200 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre
via http://www.ccdc.cam.ac.uk/data request/cif.
Acknowledgements
This work was supported by the Deutsche Forschungs-
gemeinschaft. E. K. thanks the DAAD, Germany, and HEC,
Pakistan, for a scholarship.
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