An efficient route to substituted 1-silacyclopent-2-enes and 1-silacyclohex-2-enes via consecutive 1,2-hydroboration and 1,1-organoboration

Article abstract of DOI:10.1016/j.ica.2005.03.016

The reaction of alkyn-1-yl(vinyl)silanes R₂Si(C≡CR ¹)CH=CH₂ [R = Me (1), Ph (2); R¹ = ^tBu (a), Ph (b), SiMe₃ (c)] with 9-borabicyclo[3.3.1] nonane in a 1:1 ratio affords the 1-silacyclopent-2-ene derivatives 4a-c (R = Me) and 5a-c (R = Ph) as a result of selective intermolecular 1,2-hydroboration of the vinyl group, followed by intramolecular 1,1-organoboration of the alkynyl substituent. The analogous reaction sequence converts the alkyn-1-yl(allyl) dimethylsilanes 3a,c into the 1-silacyclohex-2-ene derivatives 7a,c. All reactions were monitored by ²⁹Si NMR spectroscopy and the structural assignment of the final products was based on multinuclear magnetic resonance data (¹H, ¹¹B, ¹³C and ²⁹Si NMR). The molecular structure of 6a was determined by X-ray analysis.

Full text of DOI:10.1016/j.ica.2005.03.016

Inorganica Chimica Acta 358 (2005) 4183–4190
www.elsevier.com/locate/ica
An efficient route to substituted 1-silacyclopent-2-enes and
1-silacyclohex-2-enes via consecutive 1,2-hydroboration and
1,1-organoboration
*
Bernd Wrackmeyer , Oleg L. Tok, Rhett Kempe
Anorganische Chemie II, Universita¨t Bayreuth, D-95440 Bayreuth, Germany
Received 20 January 2005; accepted 6 March 2005
Available online 12 April 2005
Dedicated to Professor Hubert Schmidbaur on the occasion of his 70th birthday.
Abstract
The reaction of alkyn-1-yl(vinyl)silanes R2Si(C„CR1)CH@CH2 [R = Me (1), Ph (2); R1 = tBu (a), Ph (b), SiMe3 (c)] with 9-bora-
bicyclo[3.3.1]nonane in a 1:1 ratio affords the 1-silacyclopent-2-ene derivatives 4a–c (R = Me) and 5a–c (R = Ph) as a result of selec-
tive intermolecular 1,2-hydroboration of the vinyl group, followed by intramolecular 1,1-organoboration of the alkynyl substituent.
The analogous reaction sequence converts the alkyn-1-yl(allyl)dimethylsilanes 3a,c into the 1-silacyclohex-2-ene derivatives 7a,c. All
reactions were monitored by 29Si NMR spectroscopy and the structural assignment of the final products was based on multinuclear
magnetic resonance data (1H, 11B, 13C and 29Si NMR). The molecular structure of 6a was determined by X-ray analysis.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Silanes; Heterocycles; Hydroboration; Organoboration; NMR – multinuclear; X-Ray
1. Introduction
C„C bond [5,7]. It can be expected that this 1,2-hydrob-
oration will be followed by an intramolecular 1,1-orga-
noboration via cleavage of the Si–C„ bond to give
1-silacyclopent-2-enes [2,6,8] Therefore, we have studied
the reaction of the silanes 1–3 with 9-borabicy-
clo[3.3.1]nonane (9-BBN). Although, 1-silacyclopent-
enes have attracted some interest [9,10], there is no
convenient synthetic route available, in particular for
the isomer with the C@C bond in 2-position.
Alkyn-1-ylsilanes bearing a second functional group
at the silicon atom are attractive starting materials for
organometallic syntheses [1]. The second functionality
can be another alkyn-1-yl substituent [2], an amino group
[3], or an Si–Cl function [4] to name just a few examples.
For combining 1,2-hydroboration [5] and 1,1-organob-
oration [6], a vinyl group is of particular interest in this
context. We show that such alkyn-1-yl(vinyl)silanes
(e.g., 1, 2) are readily accessible by the reaction of
chloro(diorgano)(vinyl)silanes, some of which are com-
mercially available, with lithium alkynides. The regiose-
lective intermolecular 1,2-hydroboration of the C@C
bond should proceed much faster than that of the internal
Me2Si
R2Si
3
1
R
1
R
1,
2
a, b,
c
1
t
R = Me, Ph
R = Bu, Ph, SiMe3
Formulae 1-3
*
Corresponding author. Tel.: +49 921 55 2542; fax: +49 921 552157.
E-mail address: b.wrack@uni-bayreuth.de (B. Wrackmeyer).
0020-1693/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.03.016

4184
B. Wrackmeyer et al. / Inorganica Chimica Acta 358 (2005) 4183–4190
2. Results and discussion
Compounds of type 7 have already been obtained by
a completely different route, using the 1,1-allylboration
of bis(silyl)ethyne, which is followed by intramolecular
hydrosilylation and thermally induced ring contraction
to give 1-silacyclohex-3-enes such as 9 [14].
2.1. Hydroboration/organoboration of the alkenyl(alkyn-
1-yl)silanes 1–3 with 9-BBBN
The 1:1 reaction of 1 and 2 with 9-BBN (Scheme 1)
affords selectively the 1-silacyclopent-2-enes 4 and 5,
which could be isolated as colourless oils or a crystalline
solid (5a). The proposed intermediates 6 were not
observed.
Me2Si
Me3Si
BAll2
9
In the same way, the reaction of 3 with 9-BBN pro-
ceeds to give the 1-silacyclohex-2-enes 7 without side
products (Scheme 2). In this case, the intermediate 8a
was detected by NMR measurements (vide infra) prior
to its intramolecular rearrangement into 7.
Formula 9
The heterocycles 4, 5 and 7 are fairly stable towards
common protodeborylation reactions. There is no reac-
tion with methanol at room temperature or after pro-
longed periods of heating. Similarly, they do not react
with acetic acid at room temperature. Only after heating
at 110 ꢁC in toluene, the reaction with acetic acid pro-
ceeds slowly to give 10a as shown for 5a in Scheme 3.
The initial 1,2-hydroboration works in the expected
way [5,7] to give selectively the proposed intermediates
6 and 8, respectively. The assumed intramolecular acti-
vation of the Si–C bonds by the electron-deficient boron
atom is indicated by dashed lines (Schemes 1 and 2). As
in other 1,1-organoboration reactions [8], cleavage of
the Si–C„ bond leads to alkynylborate-like intermedi-
ates A1 and A2, where the positively charged silicon
atom is side-on coordinated to the C„C bond. Zwitter-
ionic intermediates comparable with A1 or A2 have been
isolated and structurally characterised, when the silicon
is replaced by a tin [11] or lead atom [12,13] Finally, the
shift of an organyl group from boron to carbon together
with formation of the new Si–C@ bonds leads to the het-
erocycles 4, 5 and 7.
2.2. NMR spectroscopy
The proposed structures of the products 4, 5, 7 and 10
in solution follow from the consistent set of NMR data
(1H, 11B, 13C, 29Si NMR), as listed in Table 1 (see the
1
Section 3 for H NMR data).
AcOH, ∆
Ph2Si
tBu
Ph2Si
tBu
B
R2Si
Me3Si
R2Si
R1
B
B
H
A1
A2
5a
10a
Formulae A1 and A2
Scheme 3.
+
9-BBN
B
R2Si
R2Si
R2Si
B
a, b,
c
R1
R1
R1 = tBu, Ph, SiMe3
R1
6
4,
5
1,
2
R = Me, Ph
R = Me, Ph
Scheme 1.
+
9-BBN
Me2Si
Me2Si
R2Si
B
a,
c
R1
B
R1 = tBu, SiMe3
R1
tBu
8a
7
3
Scheme 2.

B. Wrackmeyer et al. / Inorganica Chimica Acta 358 (2005) 4183–4190
4185
Table 1
13C and 29Si NMR dataa1-silacyclopent-2-enes (4a–c, 5a,c, 10a) and 1-silacyclohex-2-enes (7a,c)
d29Si
d13C(C-2)
d13C(C-3)
d13C(C-4)
d13C(C-5)
d13C(C-6)
4ab
4bc
4cd
5ae
5cf
7ag
7ch
10ai
a
16.7
19.3
151.7 [63.5]
152.6 [60.6]
166.1 br
170.8 br
187.9 br
170.8 br
193.0 br
163.8 br
185.0 br
146.6 [11.2]
35.0
12.1 [53.3]
12.0 [53.3]
10.9 [51.5]
13.0 [55.1]
11.9 [ ]
35.1 [6.7]
40.2 [11.2], [6.8]
34.9
29.0 (11.4)
9.3
142.7 [61.5], [47.4]
149.3 [65.6]
20.7 (9.7)
À17.7
À15.6 (6.5)
7.6
138.9 [60.8], [49.5]
143.2 [64.0]
40.6 [12.1], [8.0]
32.6
22.9
22.3
15.9 [50.9]
15.0 [50.2], [5.0]
136.3 [56.9], [50.5]
152.8 [64.0]
36.0 [10.6], [4.9]
30.5
11.5 [55.0]
In C6D6, 297 K. Coupling constants J(29Si,13C) are given in brackets, J(29Si,29Si) in parentheses; (br) denotes a broad signal owing to partially
relaxed 13C–11B scalar coupling.
b
Other 13C NMR data: d = 1.7 {48.0] (Me2Si); 24.2 (BBN); 33.4 (br, BBN); 34.2 (tBu); 34.4 (tBu); 36.1 (BBN). 11B NMR data: d = 85.3.
c
Other 13C NMR data: d = À0.6 [49.2] (Me2Si); 24.2 (BBN); 33.0 (br, BBN); 34.9 (BBN); 126.6 (Ph); 128.4 (Ph); 128.8 (Ph); 144.4 (Ph). 11B NMR
data: d = 85.6.
d
Other 13C NMR data: d = 0.9 {48.0] (Me2Si); 2.7 [50.4] (Me3Si); 24.1 (BBN); 33.6 (br, BBN); 35.3 (BBN). 11B NMR data: d = 86.2. Other
29Si NMR data: d = À10.4 (11.4) (Me3Si).
e
Other 13C NMR data: d = 24.3 (BBN); 33.5 (BBN); 34.6 (tBu); 36.1 (BBN); 36.3 (tBu, 6.2); 128.7 [5.3] (m-Ph); 129.9 (p-Ph); 136.5 (o-Ph); 137.6
[65.5] (i-Ph). 11B NMR data: d = 83.2.
f
Other 13C NMR data: d = 2.9 [50.8} (Me3Si); 24.0 (BBN); 33.7 (br, BBN); 35.4 (BBN); 128.6 [4.7] (m-Ph); 130.0 (p-Ph); 136.2 [3.4] (o-Ph); 137.7
[65.3] (i-Ph). 11B NMR data: d = 85.5. Other 29Si NMR data: d = À8.7 (9.7) (Me3Si).
g
Other 13C NMR data: d = 3.1 [49.6] (Me2Si); 24.3 (BBN); 33.0 (br, BBN); 34.4 (tBu); 36.2 (br, BBN); 38.1 (tBu, 4.2); 38.5 (br, BBN). 11B NMR
data: d = 82.9.
h
Other 13C NMR data: d = 1.4 [50.0] (Me2Si); 3.3 [49.7] (Me3Si); 24.0 (BBN); 33.2 (br, BBN); 36.6 (BBN). 11B NMR data: d = 86.6. Other
29Si NMR data: d = À9.2 (8.5) (Me3Si).
i
Other 13C NMR data: 32.6 (tBu); 35.7 (tBu, 4.9); 128.7 [5.1] (m-Ph); 130.0 (p-Ph); 136.3 [3.9] (o-Ph); 137.0 [66.2] (I-Ph).
In several cases, 13C NMR spectra were recorded
with a signal-to-noise ratio that allowed for the observa-
tion of 29Si and 13C satellites corresponding to coupling
constants J(29Si,13C) and J(13C,13C), respectively. The
latter data are given in Table 2. Representative 13C
NMR spectra are shown in Figs. 1 and 3. The 29Si
NMR spectra are similarly instructive (Fig. 2). The
application of refocused INEPT experiments [15] guar-
antees high resolution and a signal-to-noise ratio suffi-
cient for the detection of 29Si and 13C satellites. The
latter confirm the assignments of J(29Si,13C) values mea-
sured from 13C NMR spectra.
The assignment of the 13C NMR spectra is supported
by the typically broad 13C NMR signals for carbon
atoms linked to boron, as a result of partially relaxed
scalar 13C–11B spin–spin coupling [16,17]. Together with
the 29Si and 13C satellites the assignments are unambig-
uous. The preferred orientation of the 9-BBN fragment
with respect to the planes of the rings containing silicon
in 4, 5 or 7 is of interest. For steric reasons, the BC2
plane of the 9-BBN unit should be orthogonal to the
respective ring plane, and rotation about the C(3)–B
bond may be hindered. This is not the case, at least at
room temperature, for the compounds 4 and 5, whereas
in the case of the six-membered rings 7 the slow rotation
about the C(3)–B bond is indicated by the broad and
different 13C signals for the four CH2 groups of the 9-
BBN unit as marked for 7c in Fig. 3. The intermediate
8a is formed almost quantitatively prior to rearrange-
ment into 7a, and this is evident from the 13C NMR
spectrum shown in Fig. 3. Similar to 4, 5 and 7, the same
arguments apply for the unequivocal assignment of the
13C NMR signals.
The 11B NMR signals of the products are rather
broad (h1/2 > 500 Hz) and are found at high frequencies
in the typical range [18] for triorganoboranes. The 29Si
chemical shifts serve as a criterion for the assessment
of the ring size [19], since the 29Si nuclei in the five-mem-
bered rings are significantly deshielded when compared
with six-membered rings (see Table 1 and Fig. 2). The
influence of phenyl groups in comparison with methyl
groups at silicon is the same as usual [19].
Considering the preferred orientation of the boryl
group in 4, 5 and 7, hyperconjugation [20,21] should
be reflected by the magnitude of the coupling constants
1J(13C,13C) (Table 2) for the ring carbon atoms in the
positions 2 and 3, and 3 and 4, respectively. Recently,
it has been shown that this parameter is sensitive to
hyperconjugation [22]. The data in Table 2 show that
the presence of the tert-butyl group has a significant
influence on the magnitude of 1J(13C(2),13C(3)) and
Table 2
Coupling constants 1J (13C,13C) (in Hz) in 1-silacyclopent-2-enes 4a–c,
10a, and in the 1-silacyclohex-2-ene 7a
1J(13C(2),
13C(3))
1J(13C(3),
13C(4))
1J(13C(4),
13C(5))
1J(13C(5),
13C(6))
4a
4b
4c
42.3
49.8
45.3
55.7
36.9
28.1
28.6
29.0
41.6
30.7
30.4
29.3
30.7
29.7
33.5
10a
7a
29.5

4186
B. Wrackmeyer et al. / Inorganica Chimica Acta 358 (2005) 4183–4190
Fig. 1. 125.8 MHz 13C{1H}NMR spectrum of the 1-silacyclopent-2-ene 4c in C6D6 (10%). Note the broad 13C NMR signals of carbon atoms bonded
to boron. 29Si and 13C satellites are marked by rhombus and asterisks, respectively (for coupling constants see Tables 1 and 2).
Fig. 2. 99.6 MHz 29Si{1H}NMR spectra of 4c (lower trace) and 7c (upper trace), both recorded using the refocused INEPT pulse sequence [20] with
delays based on 2J(29Si,1HMe) = 7 Hz. Note the marked difference in 20Si nuclear shielding for the SiMe2 groups. 13C and 29Si satellites are marked by
asterisks and rhombus, respectively (for data see Table 1). The 29Si NMR signals of the SiMe2 groups are slightly broader than those of the SiMe3
groups, since the scalar 29Si–11B coupling is less well averaged for the larger coupling interaction typical for the trans positions of the nuclei [16].
1J(13C(3),13C(4)), if the data for the 1-silacyclopent-2-
ene 10a serve for comparison. The magnitude of 1J
(13C(4),13C(5)) is almost identical in 4 and 10a, whereas
2.3. Crystal structure of the 1-silacyclopent-2-ene 5a
The molecular structure of 5a is shown in Fig. 4. The
five-membered ring is almost exactly planar (mean devi-
ation from plane 5.5 pm) and the endocyclic bond angle
at the silicon atom is expectedly small (93.66(8)ꢁ). The
the
magnitude
of
1J(13C(2),13C(3))
and
1J
(13C(3),13C(4)) for 4 is significantly reduced when com-
pared with 10a.

B. Wrackmeyer et al. / Inorganica Chimica Acta 358 (2005) 4183–4190
4187
Fig. 3. 125.8 MHz 13C{1H}NMR spectra of the 1-silacyclohex-2-ene 7a (upper trace) and its precursor, the intermediate 8a (slower trace). Note the
broad 13C NMR signals of carbon atoms bonded to boron. 29Si and 13C satellites are marked by rhombus and asterisks, respectively. The data for 1J
(
13C,13C) for the intermediate 8a are given in braces.
agreement with hyperconjugation [20] involving the
C–C r bonds and the empty pz orbital at the boron
atom [21].
3. Experimental
3.1. General
All syntheses and the handling of the samples were
carried out observing necessary precautions to exclude
traces of air and moisture. Carefully dried solvents
and oven-dried glassware were used throughout. Sol-
vents were distilled from Na metal in an atmosphere
of argon. The starting materials were prepared as
described above or were commercially available [n-
butyllithium (1.6 M in hexane), terminal alkynes,
chlorosilanes, 9-BBN] and used without further purifi-
cation. NMR measurements: Bruker ARX 250 and
Fig. 4. ORTEP plot (50%) of the molecular structure of the 1-
silacyclopent-2-ene 5a (hydrogen atoms have been omitted for clarity).
Selected bond lengths [pm] and angles [ꢁ]: Si1–C1, 186.8(2); Si1–C4,
1.87.8(2); Si1–C9, 188.0(2); Si1–C15, 188.7(2); C1–C2, 152.9(2); C2–
C3, 153.1(2); C3–C4, 135.0(2); C3–B1, 157.0(2); C4–C5, 152.7(2) and
C1–Si1–C4, 93.66(8); C1–Si1–C9, 111.29(10); C4–Si1–C9, 113.25(7);
C1–Si1–C15, 113.61(9); C4–Si1–C15, 116.00(8); C9–Si1–C15,
108.49(8); C2–C1–Si1, 106.23(12); C1–C2–C3, 112.15(14); C4–C3–
C2, 116.89(13); C4–C3–B1, 128.89(14); C2–C3–B1, 114.22(13); C3–
C4–C5, 123.40(13); C3–C4–Si1, 110.35(11); C5–C4–Si1, 126.23(11).
1
DRX 500: H, 13C 11B, 29Si NMR (refocused INEPT
[20] based on 2,3J(29Si,1H) = 7 Hz). Chemical shifts are
given with respect to Me4Si [d1H (C6D5H) = 7.15; d13C
(C6D6) = 128.0; d29Si = 0 for N(29Si) = 19.867184 MHz;
d11B = 0
for
external
BF3–OEt2
with
surroundings of the boron atom are trigonal planar
within the experimental error and the BC2 plane of the
9-BBN unit is oriented almost orthogonal to the SiC4
plane (96ꢁ). Most of the C–C bond lengths are in the ex-
pected range except of C2–C3 (153.1(2) pm) and C3–C4
(135.0(2) pm), both being slightly elongated. This is in
N(11B) = 32.083971 MHz]. EI-MS spectra: Finnigan
MAT 8500 spectrometer (ionisation energy 70 eV)
with direct inlet; the m/z data refer to the isotopes
1H, 12C, 11B and 28Si. The melting points (uncor-
rected) were determined using a Buchi 510 melting
¨
point apparatus.

4188
B. Wrackmeyer et al. / Inorganica Chimica Acta 358 (2005) 4183–4190
1
3.2. Preparation of alkyn-1-ylsilanes 1a–c, 2a,c and 3a,c
3a: b.p. = 52–56 ꢁC (15 Torr). H NMR: d = 0.24 (s,
t
6H, Me2Si), 1.26 (s, 9H, Bu), 1.70 (dt, 2H, CH2, 8.1
The solution of the respective freshly prepared lith-
ium alkynide in THF was cooled to 0 ꢁC, and the
equimolar amount of the dimethyl(vinyl)-, diphenyl(vi-
nyl)-chlorosilane or allyl(dimethyl)chlorosilane was
added at 0 ꢁC. After the mixture was kept stirring
for 1 h at room temperature, THF was removed in va-
cuo and the residual oil was dissolved in pentane.
Insoluble materials were filtered off, pentane was re-
moved in vacuo, and fractional distillation at reduced
pressure gave the silanes 1a–c, 2a,c and 3a,c as colour-
less liquids.
Hz, 3.4 Hz, 2J(29Si,1H) = 8.5 Hz), 5.05 (m, 2H,
@CH2), 5.97 (ddt, 1H, @CH-, 17.5 Hz, 9.4 Hz, 8.1
Hz). 13C NMR: d [J(20Si,13C)] = À1.3 [56.8] (Me2Si),
25.1 [52.4] (CH2), 28.8 [3.4], 31.6 (tBu), 81.2 [88.3]
(„C–Si); 117.4 [16.0] („C–tBu), 114.3 (@CH2), 134.9
(@CH–). 29Si NMR: d = À18.2. 3c: b.p. = 59–62 ꢁC
1
(15 Torr). H NMR: d = 0.12 (s, 6H, Me2Si), 0.13 (s,
9H, Me3Si), 1.59 (dt, 2H, CH2, 8.0 Hz, 1.0 Hz,
2J(29Si,1H) = 8.1 Hz), 4.8–4.9 (m, 2H, @CH2), 5.76
(ddt, 1H, –CH@, 16.8 Hz, 10.2 Hz, 8.0 Hz). 13C
NMR: [J(29Si,13C)] = À2.3 [56.8] (Me2Si), À0.1 [56.1]
(Me3Si), 23.9 [52.4] (CH2), 112.0 [77.9, 12.2] („C–
SiMe2), 114.9 [76.1, 12.1] („C–SiMe3), 113.8
1a: b.p. = 49–54 ꢁC (15 Torr). 1H NMR: d = 0.16 (s, 6
H, Me2Si); 1.19 (s, 9 H, tBu), 5.80 (dd, 1 H, @CH2, 19.8
3
Hz, 4.2 Hz; J(29Si,1H) = 9.4 Hz), 5.94 (dd, 1H, @CH2,
(@CH2),
133.8
(@CH).
29Si
NMR:
d
3
14.5 Hz, 4.2 Hz, J(29Si,1H) = 16.7 Hz), 6.09 (dd, 1H,
(J(29Si,29Si)) = À19.1 (1.6) (Me2Si), À18.8 (1.6)
@CH, 19.8 Hz, 14.5 Hz, 2J(29Si,1H) = 14.7 Hz). 13C
NMR: d [J(29Si,13C)] = À1.1 [57.7] (Me2Si), 28.2 (tBu);
31.0 (tBu), 79.6 [90.7] („C–Si), 117.2 [16.6] („C–tBu),
132.4 {<2] (@CH2); 137.5 [71.3] (@CH). 29Si NMR:
d = À25.5. 1b: b.p. = 63–68 ꢁC (15 Torr). 1H NMR:
d = 0.47 (s, 6H, Me2Si), 6.09 (dd, 1H, @CH2, 20.0 Hz,
3.9 Hz, 3J (29Si,1H) = 9.6 Hz), 6.21 (dd, 1H, @CH2,
(Me3Si).
3.3. Reaction of silanes 1a–c, 2a,c and 3a,c, with
9-borabicyclo[3.3.1]nonane (9-BBN)
3.3.1. General procedure
3.3.1.1. Reaction in toluene. To the mixture of 9-BBN
(4–5 mmol) in 3 mL of toluene, the equimolar amount
of the respective silane was added and the mixture
was heated at reflux for 10 min. Then, the solvent
was removed in vacuo and the oily residue was dis-
tilled under reduced pressure to give colourless oils
(4a–c, 7a,c) or crystallised from hexane to give white
solids (5a,c).
3
14.4 Hz, 3.9 Hz, J(29Si,1H) = 17.4 Hz), 6.35 (dd, 1H,
2
@CH, 20.0 Hz, 14.4 Hz, J(29Si,1H) = 7.6 Hz), 7.4 (m,
3H, Ph), 7.6 (m, 2H, Ph). 13C NMR:
d [J
(20Si,13C)] = À1.5 [58.0] (Me2Si), 91.8 [87.3] („C–Si),
106.2 [16.4] (C–Ph), 123.0, 128.1, 128.5, 131.9 (Ph),
133.1 [<2] (@CH2), 136.4 [71.9] (@CH). 29Si NMR:
d = À24.4. 1c: b.p. = 52–57 ꢁC (15 Torr). 1H NMR:
d = 0.19 (s, 9H, Me3Si), 0.23 (s, 6H, Me2Si), 5.86 (dd,
1H, @CH2, 20.0 Hz, 3.9 Hz), 6.01 (dd, 1H, @CH2,
14.7 Hz, 3.9 Hz), 6.12 (dd, 1H, @CH, 20.0 Hz, 14.7
Hz). 13C NMR: d [J (29Si,13C)] = À1.5 [57.6] (Me2Si),
À0.1 [56.3] (Me3Si), 111.4 [80.6, 12.4] („C–Si). 115.1
[76.4, 12.7] (C–Si), 133.1 [<2] (@CH2), 136.4 [71.6]
3.3.1.2. Reaction in THF. To the solution of 9-BBN (4–5
mmol) in 5 mL of THF, the equimolar amount of the
respective silane (in 5 mL of THF) was added at 0 ꢁC.
The immediate exothermic reaction gave the 1-silacyclo-
pent-2-enes 4a–c and 5a,c and 1-silacyclohex-2-enes
7a,c. The work-up procedure is the same as described
above.
(@CH). 29Si NMR:
d
(J(29Si,29Si)) = À25.8 (1.7)
(Me2Si), À18.7 (1.7) (Me3Si).
1
2a: b.p. = 142–148 ꢁC (0.5 Torr). H NMR: d = 1.58
4a: 91%; b.p. = 132–135 ꢁC (0.5 Torr). 1H NMR:
d = 0.43 (s, 6H, Me2Si), 0.92 (m, 2H, CH2Si), 1.26 (s,
9H, Bu), 1.65 (m, 2H, BBN), 1.81 (m, 2H, BBN), 2.15
t
(s, 9H, Bu); 6.24 (dd, 1H, @CH2, 20.0 Hz, 3.8 Hz);
t
6.48 (dd, 1H, @CH2, 14.4 Hz, 3.8 Hz); 6.69 (dd, 1H,
@CH, 20.0 Hz, 14.5 Hz); 7.6 (m, 6H, Ph); 7.9 (m, 4H,
Ph). 13C NMR: d {J(20Si,13C)] = 28.4, 30.8 (tBu), 76.2
[99.2] („C–Si), 120.7 [17.6] („C–tBu), 127.8, 129.6,
134.2 [75.0], 135.0 (Ph), 133.6 [74.6] (@CH), 136.2 [<2]
(@CH2). 29Si NMR: d = À32.2. 2c: b.p. = 151–155 ꢁC
(0.5 Torr). 1H NMR: d = 0.40 (s, 9H, Me3Si), 6.14
(dd, 1H, @CH2, 19.7 Hz, 4.1 Hz), 6.40 (dd, 1H,
@CH2, 14.3 Hz, 4.1 Hz), 6.59 (dd, 1H, @CH, 19.7 Hz,
14.3 Hz), 7.5 (m, 6H, Ph), 7.8 (m, 4H, Ph). 13C NMR:
d [J(20Si,13C)] = À0.1 [56.6] (Me3Si); 107.3 [88.3, 11.9]
(„C–SiPh2), 119.3 [75.1, 13.3] („C–SiMe3), 127.9,
129.8, 133-3 [76.9], 135.1(Ph), 132.8 [75.3] (CH@),
136.8 [<2] (@CH2). 29Si NMR: d (J(29Si,29Si)) = À31.9
(1.7) (Ph2Si), À16.7 (1.7) (Me3Si).
(m, 10H, BBN), 2.70 (m, 2H, CH2).
4b: 88%; b.p. = 139–142 ꢁC (0.5 Torr). 1H NMR:
d = 0.31 (s, 6H, Me2Si), 1.02 (m, 2H, CH2Si); 1.42 (m,
2H, BBN), 1.67 (m, 2H, BBN), 1.81 (m, 4H, BBN),
1.92 (m, 6H, BBN), 2.93 (m, 2H, CH2), 7.09 (m, 3H,
Ph), 7.21 (m, 2H, Ph).
4c: 86%; b.p. = 136–141 ꢁC (0.5 Torr). 1H NMR:
d = 0.32 (s, 9H, Me3Si), 0.38 (s, 6H, Me2Si), 0.82 (m,
2H, CH2Si), 1.58 (m, 2H, BBN), 1.86 (m, 2H, BBN),
2.10 (m, 10H, BBN), 2.88 (m, 2H, CH2).
1
5a: 84%; m.p. = 122–126 ꢁC. H NMR: d = 1.20 (s,
9H, tBu), 1.36 (m, 2H, CH2Si), 1.8–2.1 (m, 14H,
BBN), 2.78 (m, 2H, CH2), 7.4 (m, 6H, Ph), 7.9 (m,
4H, Ph).

B. Wrackmeyer et al. / Inorganica Chimica Acta 358 (2005) 4183–4190
4189
1
5c: H NMR: d = 0.22 (s, 9H, Me3Si), 1.26 (m, 2H,
CH2Si), 1.6–2.1 (m, 14H, BBN), 2.95 (m, 2H, CH2),
Reflections collected = 16938. Independent reflections =
4670 [R(int) = 0.0687]. Completeness to h = 26.02ꢁ:
99.7%. Data/restraints/parameters = 4670/0/272. Good-
ness-of-fit on F2: 1.032. Final R indices [I > 2r(I)]:
7.3 (m, 6H, Ph), 7.8 (m, 4H, Ph).
1
7a: H NMR: d = 0.45 (s, 6H, Me2Si), 0.87 (m, 2H,
CH2Si), 1.25 (s, 9H, tBu), 1.7–2.2 (m, 16H, BBN,
CH2B), 2.26 (m, 2H, CH2).
R1 = 0.0430; wR2 = 0.1136.
R
indices (all data):
R1 = 0.0589; wR2 = 0.1193. ÀL3argest difference peak and
1
˚
7c: H NMR: d = 0.22 (s, 9H, Me3Si), 0.27 (s, 6H,
hole: 0.298 and À0.272 e A
.
Me2Si), 0.73 (m, 2H, CH2Si), 1.56 (m, 2H, BBN), 1.71
(m, 2H, CH2), 1.82 (m, 2H, BBN), 2.08 (m, 10H,
BBN), 2.23 (m, 2H, CH2).
4. Supplementary information
3.4. Hydroboration of 3a with 9-BBN
Crystallographic data (excluding structure factors)
for the structure reported in this paper have been depos-
ited with the Cambridge Crystallographic Data Centre
as supplementary publications no. CCDC-260721 (5a).
Copies of the data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK [fax (internat.): +44 1223/336033; e-mail:
deposit@ccdc.cam.ac.uk].
The mixture of the equimolar amounts of silane 3a
and 9-BBN (1–1.5 mmol) in 0.5 mL of C6D6 was sealed
in the NMR tube and heated at 110 ꢁC for 2–3 min.
According to the NMR data (see, e.g., Fig. 3) the solu-
tion contained only the hydroboration product 8a. Fur-
ther heating at 110 ꢁC for 10 min led to the quantitative
formation of 7a.
1
8a: H NMR: d = 0.34 (s, 6H, Me2Si), 0.86 (m, 2H,
t
CH2Si), 1.34 (s, 9H, Bu), 1.39 (m, 2H, CH2B), 1.69
Acknowledgement
(m, 2H, CH2), 1.8–2.1 (m, 14H, BBN). 13C NMR:
[J(29Si,13C)] = À0.4 [55.3] (Me2Si), 19.9 (CH2), 21.0
[57.0] (CH2Si), 28.9, 31.7 (tBu), 24.2. 31.8 (br), 34.0
(BBN), 33.1 (br, CH2B), 82.0 [86.3] („C–Si), 116.8
[15.9] („C–tBu). 11B NMR: d = 80.6. 29Si
NMR: = À17.7.
This work was supported by the Deutsche
Forschungsgemeinschaft.
References
3.5. Protodeborylation of 5a
[1] (a) H. Schmidbaur, J. Ebenho¨ch, G. Muller, Z. Naturforsch. Teil
¨
B 43 (1988) 49;
(b) Y. Nishihara, K. Ikegashira, K. Hirabayashi, J. Ando, A.
Mori, T. Hiyama, J. Org. Chem. 65 (2000) 1780;
(c) J.A. Marshall, H.R. Chobanian, M.M. Yanik, Org. Lett. 3
(2001) 4107;
To a solution of 0.507 g (1.23 mmol) of 5a in 2 mL of
toluene, 0.09 g (1.5 mmol) of AcOH was added. The
mixture was heated at reflux for 6 h, and then all volatile
materials were removed in vacuo, and the residue was
chromatographed with pentane on silica to give 0.276
g (77%) of 2-tert-butyl-1,1-diphenyl-1-silacyclopent-2-
ene 10a as a colourless oil.
10a: H NMR: d = 1.20 (s, 9H, Bu), 1.31 (m, 2H,
CH2Si), 2.59 (m, 2H, CH2), 6.76 (t, 1H, @CH, 2.8 Hz,
3J(29Si,1H) = 14.9 Hz), 7.3 (m, 6H, Ph), 7.8 (m, 4H, Ph).
(d) G.A. Molander, J.A.C. Romero, C.P. Corrette, J. Organomet.
Chem. 647 (2002) 225;
(e) H. Zhao, M. Cai, J. Chem. Res. (S) (2002) 608;
(f) N.N. Vlasova, G.Yu. Zhila, O.G. Yarosh, M.G. Voronkov, J.
Organomet. Chem. 577 (1999) 157.
1
t
[2] (a) R. Ko¨ster, G. Seidel, J. Su¨ß, B. Wrackmeyer, Chem. Ber. 126
(1993) 1107;
(b) R. Ko¨ster, G. Seidel, I. Klopp, C. Kruger, G. Kehr, J. Suß,
¨
¨
B. Wrackmeyer, Chem. Ber. 126 (1993) 1385;
(c) B. Wrackmeyer, G. Kehr, J. Suß, Chem. Ber. 126 (1993) 2221;
¨
(d) B. Wrackmeyer, H.E. Maisel, J. Suß, W. Milius, Z. Natur-
¨
3.6. X-Ray structural analysis of the 1-silacyclopent-2-ene
5a
forsch. Teil B 51 (1996) 1320;
(e) B. Wrackmeyer, G. Kehr, J. Suß, E. Molla, J. Organomet.
¨
X-Ray crystal structure analysis of 5a was performed
using a STOE IPDS II equipped with a low temperature unit.
Formula weight: 412.48. Temperature: 193(2) K.
Wavelength: 71.069 pm. Crystal system: triclinic.
Chem. 562 (1998) 207;
(f) B. Wrackmeyer, G. Kehr, J. Suß, E. Molla, J. Organomet.
¨
Chem. 577 (1999) 82;
(g) B. Wrackmeyer, J. Su¨ß, Z. Naturforsch. Teil B 57 (2002) 741.
[3] B. Wrackmeyer, J. Suß, W. Milius, Chem. Ber. 129 (1996) 147.
¨
[4] (a) B. Wrackmeyer, A. Badshah, E. Molla, A. Mottalib, J.
Organomet. Chem. 584 (1999) 98;
ꢀ
Space group: P1. Unit cell dimensions: a = 751.90(6)
pm, a = 82.704(6)ꢁ, b = 1042.94(8) pm, b = 87.291(6)ꢁ,
c = 1546.81(12) pm, c = 82.453(6)ꢁ. Volume: 1.19217
(b) B. Wrackmeyer, H. Maisel, W. Milius, A. Badshah, E. Molla,
A. Mottalib, J. Organomet. Chem. 602 (2000) 45;
(c) B. Wrackmeyer, K. Shahid, S. Ali, Appl. Organomet. Chem.
19 (2005) 377.
(16) nm3. Z = 2. Absorption coefficient = 0.111 mmÀ1
.
F(000) = 448. Crystal size = 0.45 · 0.20 · 0.15 mm3. h
Range for data collection = 1.33–26.02ꢁ. Index
ranges = À8 6 h 6 9, À12 6 k 6 12, À19 6 l 6 19.
[5] H.C. Brown, Organic Syntheses via Boranes, Wiley-Interscience,
New York, 1975.

4190
B. Wrackmeyer et al. / Inorganica Chimica Acta 358 (2005) 4183–4190
[6] B. Wrackmeyer, Coord. Chem. Rev. 145 (1995) 125.
[7] (a) G. Zweifel, H.C. Brown, J. Am. Chem. Soc. 85 (1963) 2066;
(b) G. Zweifel, N.L. Polston, J. Am. Chem. Soc. 92 (1970) 4068.
[8] B. Wrackmeyer, H.E. Maisel, E. Molla, A. Mottalib, A. Badshah,
M.H. Bhatti, S. Ali, Appl. Organomet. Chem. 17 (2003) 465.
[9] (a) Y. Landais, C. Mahieux, K. Schenk, S.S. Surange, J. Org.
Chem. 68 (2003) 2779;
(c) B. Wrackmeyer, O.L. Tok, Yu.N. Bubnov, Appl. Organomet.
Chem. 18 (2004) 43.
[15] (a) G.A. Morris, R. Freeman, J. Am. Chem. Soc. 101 (1979) 760;
(b) G.A. Morris, J. Am. Chem. Soc. 102 (1980) 428;
(c) J. Schraml, in: Z. Rappoport, Y. Apeloig (Eds.), The
Chemistry of Organic Silicon Compounds, vol. 3, Wiley, Chich-
ester, 2001, p. 223.
(b) R. Boukherroub, G. Manuel, J. Organomet. Chem. 604 (2000)
141;
[16] B. Wrackmeyer, Polyhedron 5 (1986) 1709.
[17] B. Wrackmeyer, Progr. NMR Spectrosc. 12 (1979) 227.
[18] H. No¨th, B. Wrackmeyer, Nuclear magnetic resonance spectros-
copy of boron compounds, in: P. Diehl, E. Fluck, R. Kosfeld
(Eds.), NMR – Basic Principles and Progress, vol. 14, Springer,
Berlin, 1978.
(c) G. Manuel, P.W. Weber, R. Boukherroub, Main Group Met.
Chem. 19 (1996) 263;
(d) B. Wrackmeyer, H.E. Maisel, W. Milius, M.H. Bhatti, S. Ali,
Z. Naturforsch. Teil B 58 (2003) 543.
[10] (a) W.S. Palmer, K.A. Woerpel, Organometallics 16 (1997) 1097;
(b) D. Damour, M. Barreau, F. Dhaleine, G. Doerfinger, M.
Vuilhorgne, S. Mignani, Synlett (1996) 890.
[11] (a) B. Wrackmeyer, G. Kehr, R. Boese, Angew. Chem. 103 (1991)
1374;
[19] E. Kupce, E. Lukevics, in: E. Buncel, J.R. Jones (Eds.), Isotopes
in the Physical and Biomedical Sciences, vol. 2, Elsevier, Amster-
dam, 1991, p. 213.
[20] (a) M.J.S. Dewar, Hyperconjugation, Ronald Press, New York,
1962;
(b) B. Wrackmeyer, G. Kehr, R. Boese, Angew. Chem. Int. Ed.
30 (1991) 1370;
(b) G.A. Olah, J. Org. Chem. 66 (2001) 5943;
(c) V. Alabugin, T.A. Zeidan, J. Am. Chem. Soc. 124 (2002) 3175.
[21] (a) T. Laube, Acc. Chem. Res. 28 (1994) 399;
(b) A. Berndt, Angew. Chem. 105 (1993) 1034;
(c) A. Berndt, Angew. Chem. Int. Ed. 32 (1993) 985;
(d) J. Mo, H. Jiao, P.v.R. Schleyer, J. Org. Chem. 69 (2004)
3493;
(c) B. Wrackmeyer, S. Kundler, R. Boese, Chem. Ber. 126 (1993)
1361;
(d) B. Wrackmeyer, S. Kundler, W. Milius, R. Boese, Chem. Ber.
127 (1994) 333.
[12] B. Wrackmeyer, K. Horchler, R. Boese, Angew. Chem. 101
(1989) 1563.
(e) R. Boese, D. Blaeser, N. Niederprum, M. Nusse, W.A.
¨ ¨
[13] B. Wrackmeyer, K. Horchler, R. Boese, Angew. Chem. Int. Ed.
28 (1989) 1500.
Brett, P.v.R. Schleyer, M. Buehl, N.J.R. van Eikema Hommes,
Angew. Chem. 104 (1992) 356;
(f) R. Boese, D. Blaeser, N. Niederprum, M. Nusse, W.A. Brett,
¨ ¨
[14] (a) B. Wrackmeyer, O.L. Tok, Y.N. Bubnov, Angew. Chem. 111
(1999) 214;
P.v.R. Schleyer, M. Buehl, N.J.R. van Eikema Hommes, Angew.
Chem. Int. Ed. 31 (1992) 314.
[22] B. Wrackmeyer, O.L. Tok, Z. Naturforsch. Teil B 60 (2005) 259.
(b) B. Wrackmeyer, O.L. Tok, Yu.N. Bubnov, Angew. Chem.
Int. Ed. 38 (1999) 124;