Fused silacarhacycles containing a silole unit: 1,2-hydroboration and n 1,1-organoboration of alkynyl(vinyl)silanes

Article abstract of DOI:10.1002/ejic.201000231

The reaction of various alkynyl(vinyl)silanes containing two alkynyl groups with 9-borabicyclo[3.3.1]nonane (9-BBN) proceeds by regloselective 1,2-hydroboration of the vinyl group in the first step, followed by two intramolecular 1,1-organoboration reacti

Full text of DOI:10.1002/ejic.201000231

FULL PAPER
DOI: 10.1002/ejic.201000231
Fused Silacarbacycles Containing a Silole Unit: 1,2-Hydroboration and
1,1-Organoboration of Alkynyl(vinyl)silanes
Bernd Wrackmeyer,*[a] Oleg L. Tok,[a] Elena V. Klimkina,[a] and Wolfgang Milius[b]
Keywords: Alkynylsilanes / Hydroboration / Organoboration / Siloles / NMR spectroscopy
The reaction of various alkynyl(vinyl)silanes containing two
alkynyl groups with 9-borabicyclo[3.3.1]nonane (9-BBN) pro-
ceeds by regioselective 1,2-hydroboration of the vinyl group
in the first step, followed by two intramolecular 1,1-organo-
boration reactions to afford 1,6-disilapentalene derivatives,
fused silacarbacycles with a silole unit. Similarly, the analo-
gous reaction of an alkynyl(allyl)silane gives a 1,7-disilaind-
ene derivative. The products were characterized by multi-
nuclear magnetic resonance (1H, 11B, 13C and 29Si NMR) in
solution and in two cases by X-ray structural analysis in the
solid state.
Introduction
Among silacarbacycles, the siloles[1] deserve particular
attention owing to the rich chemistry of their cyclic diene
system and, more recently, to their attractive photophysical
properties.[2–5] Although numerous synthetic procedures
have been developed for the synthesis of siloles,[1] many of
these methods are cumbersome multistep routes. Moreover,
fused ring systems containing the silole unit are scarce.[1,6]
It turned out that 1,1-organoboration reactions of dialk-
ynylsilanes provide a versatile route to siloles,[7,8] allowing
in principle to introduce numerous different substituents at
all ring positions.[9,10] This includes even functional groups
such as hydrogen and/or chlorine at silicon.[11] Previously,
we have shown that 1,1-organoboration of certain triynes
affords mainly 1,6-dihydro-1,6-disilapentalene derivatives[12]
(Scheme 1), along with side products, which could not be
separated. Similar results were obtained with comparable
tetraynes.[13] However, rather harsh conditions are required
in order to start the reactions in the case of alkynylsilanes
(100 °C, several hours), and ring closure appeared to be
slow and accompanied by side reactions. Molecular models
suggested that steric repulsion between the ethyl and dieth-
ylboryl groups prevents a clean intramolecular reaction.
Therefore, we have started a new approach, in which
intermolecular 1,2-hydroboration is combined with intra-
molecular 1,1-organoboration. This helps to introduce the
boryl group into the molecule under relatively mild condi-
tions, and it was hoped that the steric hindrance of further
intramolecular reactions would be less severe. As a conve-
nient and regioselective hydroborating reagent we have se-
Scheme 1. Synthesis of a 1,6-dihydro-1,5-disilapentalene derivative
by 1,1-organoboration of a 1,4,7,10-tetrasila-2,5,8-triyne.
lected 9-BBN [bis(9-borabicyclo[3.3.1]nonane)],[14] and
various alkynyl(vinyl)silanes 1–5 were used, all of which
contained two CϵC bonds (see Schemes 2 and 3).
Scheme 2. Reaction of 9-BBN with the alkynyl(vinyl)silanes 1. In
the structures of the intermediates (not detected), the interaction
of the electrophilic boron atom with the alkynyl carbon atom, indi-
cated by a dashed line, is followed by cleavage of the Si–C(alkyne)
bond, leading to a zwitterionic intermediate, which rearranges into
the 1,1-organoboration product.[7]
[a] Anorganische Chemie II, Universität Bayreuth,
95440 Bayreuth, Germany
Fax: +49-921-552157
E-mail: b.wrack@uni-bayreuth.de
[b] Anorganische Chemie I, Universität Bayreuth,
95440 Bayreuth, Germany
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Fused Silacarbacycles Containing a Silole Unit
cyclopent-2-enes,[16,17] and the reactions have been analyzed
by theoretical methods.[18] In the final step, this process is
repeated with the remaining Si–CϵC–R unit to give the
products 6 containing the silole unit [Scheme 2 (c)]. The
intramolecular activation of the Si–C(alkyne) bond
[Scheme 2 (b), (c)] allows to conduct the reactions fast un-
der milder conditions (100Ϯ10 °C; 2–5 min) than shown in
Scheme 1.
The methyl groups at the silicon atom bearing the vinyl
group can be replaced by one or two phenyl groups, as
shown for the alkynyl(vinyl)silanes 2–4, which react readily
with 9-BBN to give the fused silacarbacycle 7–9 (Scheme 3).
The compounds 6–9 are obtained in essentially quantita-
tive yield as faintly yellow air-sensitive oils or solids, and
Scheme 3. Reactions of the alkynylsilanes 2–4 with 9-BBN.
1
the proposed structures are fully supported by H, 11B, 13C
Results and Discussion
and 29Si NMR spectroscopic data sets (Exp. Sect. and
Table 1). Furthermore, the molecular structure of 6c could
be determined by X-ray diffraction (vide infra). The pro-
gress of the reactions is most conveniently monitored by
29Si NMR spectroscopy, which, together with 13C NMR
spectroscopy, also serves to assign the structure of the final
products. In the 29Si NMR spectra, the signals typical of
alkynylsilanes at low frequency[15,19,20] are replaced by 29Si
The synthesis and spectroscopic properties of the alk-
ynyl(vinyl)silanes 1–5 used here have been reported else-
where.[15] In the course of the 1,2-hydroboration with 9-
BBN, the vinyl group is preferred over the alkynyl group
[Scheme 2 (a)]. In the next step, the neighbored Si–C(alk-
yne) bond is cleaved and 1,1-organoboration takes place
[Scheme 2 (b); the intermediates shown in brackets indicate
the mechanism of 1,1-orhganoboration[7]]. These first two NMR signals at much higher frequencies, typical of the cy-
steps have already been used to prepare numerous sila- clic structures.[20] Particularly helpful for the structural as-
Table 1. Selected 13C and 29Si NMR spectroscopic data[a] of disilapentalenes 6, 7, 8 and 9.
δ29Si(1)
δ29Si(6)
δ13C(2)
δ13C(3)
δ13C(3a)
δ13C(4)
δ13C(5)
δ13C(6a)
6a[b]
6b[c]
6c[d]
6d[e]
6e[f]
18.4
{13.6}
18.2
{13.1}
17.0
{13.4}
16.8
{10.8}
16.8
{13.6}
8.0
{13.6}
8.6
{13.1}
–3.4
{13.4}
16.7
{10.8}
19.0
{13.6}
{11.9}
19.5
{13.1}
17.4
{13.5}
{9.5}
18.9
13.3
[50.1]
13.6
[50.1]
13.8
[49.2]
14.2
[49.8]
14.2
[50.0]
35.2
[8.3]
36.9
[8.1]
38.0
[8.9]
36.4
[8.7]
36.9
[8.7]
181.8
[6.4], [6.1]
182.2
[6.1]
184.5
[6.4]
181.9
[11.7], [9.3], [7.0]
181.0
[13.7], [8.9], [7.2]
169.9
br.
163.8
br.
182.3
br.
181.3
br.
151.5
[58.4]
164.2
[57.9]
148.0
[63.9]
153.5
[62.1], [44.7]
151.9
137.6
2ϫ [58.8]
136.4
2ϫ [59.0]
137.6
2ϫ [60.4]
141.9
2ϫ [58.1]
144.0
2ϫ [57.0]
182.7
br.
[69.1], [44.3]
7[g]
8[h]
11.7
{13.1}
12.4
13.0
[51.9]
14.0
36.9
[8.3]
36.8
[8.6]
183.6
[13.8], [8.8], [7.5]
183.7
182.0
br.
179.0
br.
152.5
[68.8], [44.7]
158.4
139.6
[60.9], [57.5]
139.0
{13.5}
[50.8]
[11.1], [9.7], [7.2]
[61.5], [43.6]
[60.2], [57.2]
9[i]
12.1
{13.2}
13.8
[50.9]
37.1
[8.3]
182.2
[12.1], [9.4], [7.4]
184.5
br.
147.2
[67.8], [46.5]
141.9
[59.6], [56.0]
{13.2}
{9.9}
[a] In C6D6 or in CD2Cl2 (6a, 7, 8, 9) at 296 K. nJ(29Si,13C) coupling constants [Ϯ0.5 Hz] are given in brackets; 2J(29Si,29Si) coupling
constants {Ϯ0.3 Hz} are given in braces. [b] Other 13C NMR spectroscopic data: δ = –4.1 [50.2], –0.2 [50.2] (SiMe2); 23.7, 31.9 (br.), 34.4
(BBN) ppm. [c] Other 13C NMR spectroscopic data: δ = –3.9 [49.7], 0.4 [50.2] (SiMe2); 24.0, 33.6 (br.), 34.4 (BBN); 126.7, 127.9, 128.8,
144.0 [5.9] [1.8] (Ph) ppm. [d] Other 13C NMR spectroscopic data: δ = –3.7 [49.7], 0.5 [49.6] (SiMe2); 23.2 (br.), 24.0, 25.3, 31.7, 35.5
(BBN); 49.1 (NMe2); 69.1 (CH2N) ppm. [e] Other 13C NMR spectroscopic data: δ = –2.4 [48.5], –0.9 [51.3], 0.2 [50.2] (SiMe2); 24.2, 33.0
(br.), 34.1 (BBN) ppm. Other 29Si NMR spectroscopic data: δ = –25.6 (SiMe2H) {10.2} ppm. [f] Other 13C NMR spectroscopic data: δ
= –2.3 [49.6], –0.1 [50.7] (SiMe2); 7.7 [56.0] (SiMe2Br); 23.7, 33.0 (br.), 34.8 (BBN) ppm. Other 29Si NMR spectroscopic data: δ = 10.7
(SiMe2Br) {11.9} ppm. [g] Other 13C NMR spectroscopic data: δ = –2.2 [50.1] [Si(2)Me2]; 7.4 [56.0] (SiMe2Br); 23.4, 32.9 (br.), 34.7
(BBN); 128.3 [5.5], 129.8, 135.4, 137.1 [68.2] (Ph) ppm. Other 29Si NMR spectroscopic data: δ = 9.8 (SiMe2Br) {13.3} ppm. [h] Other
13C NMR spectroscopic data: δ = –2.7 [48.8] [Si(6)Me, trans to Ph]; –2.4 [49.1] [Si(6)Me, cis to Ph]; –2.2 [52.1] [Si(1)Me]; 2.9 [51.0]
(SiMe3); 23.6, 32.8 (br.), 34.5, 34.6 (BBN); 128.2 [5.1], 129.4, 134.4, 139.9 [65.5] (Ph) ppm. Other 29Si NMR spectroscopic data: δ = –11.6
(SiMe3) {9.3 Hz} [51.0] ppm. [i] Other 13C NMR spectroscopic data: δ = –3.3 [49.6] [Si(6)Me, trans to Si(1)Ph]; –3.0 [50.0] [Si(6)Me, cis
to Si(1)Ph]; –2.2 [52.2] [Si(1)Me]; 23.2, 32.6 (br.), 34.1 (BBN); 128.0 [5.4], 134.4, 137.1. 137.3 [68.4] (SiPh3); 128.1 [4.8], 129.8, 136.0,
139.7 [65.6] (SiPh) ppm. Other 29Si NMR spectroscopic data: δ = –21.7 (SiPh3) {9.9} ppm.
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B. Wrackmeyer, O. L. Tok, E. V. Klimkina, W. Milius
FULL PAPER
signment is the observation of 29Si satellites in the 29Si CB(pp)π interactions.[22] In the case of 6c, the intramolecu-
NMR spectra, corresponding to the coupling constants lar N–B coordination is clearly evident by δ11B = 8.9 ppm,
2J(29Si,29Si) (see Figure 1), as well as in the 13C NMR spec- in the range characteristic for tetracoordinate boron
tra, corresponding to nJ(29Si,13C) (n = 1,2; see Figures 1 atoms.[22]
and 2). In 13C NMR spectra, the broadened signals, owing
The synthetic method introduced here can be extended
to partially relaxed 13C-11B spin-spin coupling,[21] lend fur- to different ring sizes (Scheme 4). When an allyl group is
ther support to the assignment. The δ11B data are in the present at one silicon atom as in 5, the analogous reaction
typical region of triorganoboranes without significant sequence as for 1–4 leads to the fused silacarbacycle 10
Figure 1. Bottom: 99.4 MHz 29Si{1H} NMR spectrum (refocused INEPT; in C6D6 at 296 K) of the reaction solution containing the
2
bicyclic compound 6e. Coupling constants J(29Si,29Si) are given in braces. The phase distortion of the 29Si satellite signals is typical of
homonuclear coupling, since this magnetization is not refocused in the course of the pulse sequence. Top: 128.5 MHz 13C{1H} NMR
n
spectrum of the region for the olefinic carbon atoms showing expansions for the 29Si satellites [coupling constants J(29Si,13C) are given
in brackets]. In the case of 13C-6a, the 29Si satellites overlap. A signal from an impurity is marked by an asterisk.
Figure 2. 125.8 MHz 13C{1H} NMR spectrum (296 K) of the bicyclic compound 6b. Coupling constants nJ(29Si,13C) are given in brackets
(the relative intensities of the 29Si satellites in the cases of C-3a, C-6a correspond to coupling with two 29Si nuclei).
2278
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Fused Silacarbacycles Containing a Silole Unit
(Scheme 4). Compound 10 possesses similar properties as X-ray Structural Analyses of the Fused Silacarbacycles 6c
6–9, is clearly identified by its NMR spectroscopic data set and 10
(Exp. Sect.), and its molecular structure was determined by
The molecular structures of the silacarbacycles 6c (Fig-
X-ray diffraction (vide infra).
ure 3) and 10 (Figure 4) show the almost planar silole ring
(major deviation from planarity 2.6 pm for 6c and 1.8 pm
for 10) fused to a saturated nonplanar five- and six-mem-
bered ring, respectively. In the case of 6c, another non-
planar ring is present due to N–B coordination, in agree-
ment with NMR spectroscopic data in solution. Intermo-
lecular interactions appear to be negligible for both, 6c and
Scheme 4.
10. The structural parameters are in close agreement with
First attempts to remove the boryl group by protode- those found for the few examples obtained by 1,1-organo-
borylation showed that all compounds 6–10 react only boration reactions,[8,11] although the C–C bond lengths ap-
slowly with methanol, in particular with the Me3Si group pear to be slightly elongated, when compared with data for
in neighborhood to the boryl group. However, the silole other siloles.[1,23] This can be caused by the various organo-
ring remains unchanged (Scheme 5), as indicated by the metallic substituents at the C=C bonds. Most notably are
NMR spectroscopic data for 11 (Exp. Sect.).
the typically acute endocyclic bond angles in the silole units
of 6c [91.3(1)°] and 10 [94.0(5)°]. In the half-saturated part
of the silacarbacycle of 6c, the endocyclic C4–Si2–C6 angle
is slightly wider [93.5(1)°],[24] and in 10, the endocyclic
angles at Si1 [94.0(5)°] and Si2 [104.2(6)°] are expectedly
quite different, since Si2 is part of a six-membered ring.
The surroundings of the boron atom in 6c correspond to a
distorted tetrahedron, whereas the boron atom in 10 pos-
Scheme 5. Slow methanolysis of 10.
Figure 3. Molecular structure (ORTEP plot with 40% probability;
hydrogen atoms have been omitted for clarity) of the disilapental-
ene derivative 6c. Selected bond lengths [pm] and angles [°]: Si1–
C4 185.3(3), Si1–C1 186.2(3), Si2–C4 185.6(3), Si2–C6 187.2(3), N–
Figure 4. Molecular structure (ORTEP plot with 40% probability;
hydrogen atoms have been omitted for clarity) of the disilaindene
C11 150.3(4), N–B 176.8(4), B–C14 161.8(4), B–C18 163.0(4), B– derivative 10. Selected bond lengths [pm] and angles [°]: Si1–C4
C2 167.2(4), C1–C2 135.8(4), C1–C11 149.0(4), C2–C3 152.8(4), 186.5(12), Si1–C1 188.4(12), Si2–C4 186.2(12), Si2–C7 187.5(11),
C3–C4 136.8(4), C3–C5 152.5(4), C5–C6 154.0(4); C4–Si1–C1
91.27(13), C7–Si1–C8 108.60(15), C4–Si2–C6 93.52(14), C9–Si2–
Si3–C1 185.2(13), B–C26 155.1(17), B–C2 155.2(16), B–C22
161.8(17), C1–C2 138.0(15), C2–C3 152.5(15), C3–C4 137.7(13),
C10 108.83(17), C13–N–C12 107.7(3), C13–N–B 108.8(2), C12–N– C3–C5 151.1(13), C5–C6 151.4(14), C6–C7 153.2(16); C8–Si1–C9
B 122.1(2), C11–N–B 103.0(2), C14–B–C18 104.8(2), C14–B–C2
122.7(2), C18–B–C2 113.3(2), C14–B–N 111.3(2), C18–B–N
111.0(2), C2–B–N 93.4(2), C2–C1–C11 113.5(3), C2–C1–Si1
111.9(2), C11–C1–Si1 133.6(2), C1–C2–C3 110.7(2), C1–C2–B
108.6(6), C4–Si1–C1 94.0(5), C10–Si2–C16 108.1(5), C4–Si2–C7
104.2(5), C26–B–C2 127.1(11), C26–B–C22 107.8(10), C2–B–C22
125.0(11), C2–C1–Si3 131.4(10), C2–C1–Si1 106.4(9), Si3–C1–Si1
122.2(7), C1–C2–C3 116.1(10), C1–C2–B 126.5(11), C3–C2–B
111.3(2), C3–C2–B 138.0(2), C4–C3–C5 116.8(2), C4–C3–C2 117.5(10), C4–C3–C5 124.6(10), C4–C3–C2 116.3(10), C5–C3–C2
118.1(3), C5–C3–C2 125.1(2), C3–C4–Si1 107.6(2), C3–C4–Si2 119.1(9), C3–C4–Si2 120.7(8), C3–C4–Si1 107.0(8), Si2–C4–Si1
110.3(2), Si1–C4–Si2 142.05(17), C3–C5–C6 110.8(3), C5–C6–Si2 132.1(6), C3–C5–C6 116.4(8), C5–C6–C7 111.6(10), C6–C7–Si2
105.7(2), C1–C11–N 106.0(2); B–C2–C1–C11 144.3(2).
107.9(9).
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FULL PAPER
4-(9-Borabicyclo[3.3.1]non-9-yl)-1,1,6,6-tetramethyl-1H,2H,3H,6H-
1,6-disilapentalene (6a): 1H NMR (500.13 MHz, CD2Cl2, 296 K): δ
= 0.18 (s, 6 H, SiMe2), 0.21 (s, 6 H, SiMe2), 1.00 (m, 2 H, CH2Si),
1.35, 1.8–2.0 (m, 14 H, BBN), 2.80 (m, 2 H, CH2), 6.95 [s,
2J(29Si,1H) = 14.9 Hz, 1 H, =CH] ppm. 11B NMR (160.5 MHz): δ
= 80.6 ppm.
sesses trigonal-planar surroundings within the experimental
error. In 10, the BC2 plane of the BBN unit forms an angle
of 66.5° with the plane of the silole ring.
Conclusions
4-(9-Borabicyclo[3.3.1]non-9-yl)-1,1,6,6-tetramethyl-5-phenyl-
1H,2H,3H,6H-1,6-disilapentalene (6b): 1H NMR (500.13 MHz,
C6D6, 296 K): δ = 0.42 (s, 6 H, SiMe2), 0.47 (s, 6 H, SiMe2), 1.16
(m, 2 H, CH2Si), 1.4–2.1 (m, 14 H, BBN), 2.96 (m, 2 H, CH2),
7.14 (m, 1 H, Ph-p), 7.20 (m, 2 H, Ph-o), 7.25 (m, 2 H, Ph-m) ppm.
11B NMR (160.5 MHz): δ = 83.1 ppm. EI-MS for C24H35BSi2: m/z
1,2-Hydroboration followed by intramolecular 1,1-or-
ganoboration provides a useful route to fused silacarba-
cycles, containing a silole unit. The synthetic potential of
this method becomes evident by inspecting the range of po-
tential substituents at the CϵC bond in the starting alk-
ynyl(vinyl)silanes 1–4. This enables further transformations
of the bicyclic compounds reported here. Moreover, the alk-
ynyl(vinyl)silanes 1–4 can be modified to contain three, four
or more CϵC bonds separated by silicon atoms. As will be
reported in forthcoming publications, such alkynyl(vinyl)-
silanes can be converted by cascade reactions into fused
siloles containing two, three or more silole units, depending
on the number of CϵC bonds in the starting alkynyl(vinyl)-
silanes. The steric hindrance, which prevented such an ap-
proach in previous work,[13] appears to be of minor impor-
tance if the first step, 1,2-hydroboartion, leads to a silacy-
clopent-2-ene derivative.
(%) = 390 (4) [M+], 270 (45) [M+ – BBN(C8H14B)], 255 (100) [M+
BBN(C8H14B) – Me].
–
4-(9-Borabicyclo[3.3.1]non-9-yl)-5-[(dimethylamino)methyl]-1,1,6,6-
tetramethyl-1H,2H,3H,6H-1,6-disilapentalene (6c): M.p. 54–58 °C.
1H NMR (500.13 MHz C6D6, 296 K): δ = 0.33 (s, 6 H, SiMe2),
0.38 (s, 6 H, SiMe2), 1.11 (br. s, 2 H, BBN), 1.17 (m, 2 H, CH2Si),
1.9–2.6 (m, 12 H, BBN), 2.19 (s, 6 H, NMe2), 3.13 (s, 2 H, CH2N),
3.28 (s, 2 H, CH2) ppm. 11B NMR (160.5 MHz): δ = 8.9 ppm. EI-
MS (70 eV) for C21H38BNSi2: m/z (%) = 371 (100) [M+].
C21H38BNSi2 (371.24): calcd. C 67.94, H 10.26, N 3.77; found C
65.95, H 10.48, N 3.70; formation of carbides leads to a low C
value.
4-(9-Borabicyclo[3.3.1]non-9-yl)-5-(dimethylsilyl)-1,1,6,6-tetrameth-
yl-1H,2H,3H,6H-1,6-disilapentalene (6d): 1H NMR (500.13 MHz,
3
C6D6, 296 K): δ = 0.33 (s, 6 H, SiMe2), 0.36 [d, J(H,H) = 3.6 Hz,
6 H, SiHMe2], 0.37 (s, 6 H, SiMe2), 1.15 (m, 2 H, CH2Si), 1.6–2.3
(m, 14 H, BBN), 2.82 (m, 2 H, CH2), 4.77 [sept, 3J(H,H) = 3.6,
1J(29Si,1H) = 182.8 Hz, 1 H, SiH] ppm. 11B NMR (160.5 MHz): δ
= 79.8 ppm. EI-MS (70 eV) for C20H37BSi3: m/z (%) = 372 (86)
[M+], 252 (100) [M+ – BBN(C8H14B)].
Experimental Section
General and Starting Materials: All compounds were handled un-
der dry argon to exclude air and moisture, and carefully dried sol-
vents and oven-dried glassware were used throughout. 9-BBN (Ald-
rich) was used as received. The synthesis of the alkynylsilanes 1–5
is described elsewhere.[15] NMR measurements at 23 °C in 5 mm
(o.d.) tubes in C6D6, if not mentioned otherwise (concentration 5–
10%): Bruker ARX 250, DRX 500 and Varian Inova 400 [1H, 11B,
13C, 29Si NMR (refocused INEPT[25] based on 2J(29Si,1HMe) ≈ 7 Hz
or 3J(29Si,1HPh) ≈ 4–5 Hz)]. Chemical shifts are given relative to
Me4Si [δ1H(C6D5H) = 7.15 ppm, δ1H(CHDCl2) = 5.33 (Ϯ 0.01)
ppm; δ13C(C6D6) = 128.0 ppm, δ13C(CD2Cl2) = 53.8 (Ϯ 0.05) ppm;
δ29Si = 0Ϯ0.01 ppm for Ξ(29Si) = 19.867184 MHz] and BF3–OEt2
[δ11B = 0Ϯ0.3 ppm for Ξ(11B) = 32.083971 MHz]. Assignments in
4-(9-Borabicyclo[3.3.1]non-9-yl)-5-(bromodimethylsilyl)-1,1,6,6-tetra-
1
methyl-1H,2H,3H,6H-1,6-disilapentalene (6e): M.p. 68–72 °C. H
NMR (500.13 MHz, C6D6, 296 K): δ = 0.32 (s, 6 H, SiMe2), 0.47
(s, 6 H, SiMe2), 0.83 (s, 6 H, SiBrMe2), 1.13 (m, 2 H, CH2Si), 1.61
(m, 2 H, BBN), 1.83 (2 H, BBN), 2.0–2.1 (m, 6 H, BBN), 2.23 (m,
4 H, BBN), 2.79 (m, 2 H, CH2) ppm. 11B NMR (160.5 MHz): δ =
87.4 ppm.
4-(9-Borabicyclo[3.3.1]non-9-yl)-5-(bromodimethylsilyl)-6,6-dimeth-
yl-1,1-diphenyl-1H,2H,3H,6H-1,6-disilapentalene (7): 1H NMR
(500.13 MHz, CD2Cl2, 296 K): δ = 0.39 (s, 6 H, SiMe2), 0.86 (s, 6
H, SiBrMe2), 1.67 (m, 2 H, CH2Si), 1.7–2.3 (m, 14 H, BBN), 2.98
(m, 2 H, CH2), 7.45 (m, 6 H, Ph), 7.64 (m, 4 H, Ph) ppm. 11B
NMR (160.5 MHz): δ = 82.4 ppm.
1H and 13C NMR spectra were confirmed by 2D H/13C HSQC[26]
1
and in some cases by gradient-enhanced 1H-1H NOE difference
experiments.[27] 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, 14N, 28Si. Elemental analyses were performed
with a Vario Elementar EL III. Melting points (uncorrected) were
determined by using a Büchi 510 melting point apparatus.
4-(9-Borabicyclo[3.3.1]non-9-yl)-1,6,6-trimethyl-1-phenyl-5-(trimeth-
ylsilyl)-1H,2H,3H,6H-1,6-disilapentalene (8): 1 H NMR
(500.13 MHz, CD2Cl2, 296 K): δ = 0.10 [s, 3 H, Si(6)Me, cis to Ph],
0.15 (s, 9 H, SiMe3), 0.21 [s, 3 H, Si(6)Me, trans to Ph], 0.41 [s, 3
H, Si(1)Me], 1.14 (m, 1 H, CH2Si, trans to Ph), 1.23 (m, 1 H,
CH2Si, cis to Ph), 1.5–2.1 (m, 14 H, BBN), 2.72–2.79 (m, 2 H,
CH2), 7.24 (m, 3 H, Ph), 7.44 (m, 2 H, Ph) ppm. 11B NMR
(160.5 MHz): δ = 87.1 ppm.
Reaction of the Alkynylsilanes 1–5 with 9-BBN (General Procedure):
To a solution of the respective alkynylsilane 1a–e, 2, 4 or 5 (300–
500 mg, 1.5–2.0 mmol) in benzene or toluene (2–3 mL) an equi-
molar amount of 9-BBN was added in one portion, and the mix-
ture was rapidly heated up to 90–110 °C. After 2–5 min, when the
crystalline 9-BBN was dissolved, the reaction was complete. Vola-
tile materials were removed in vacuo to give slightly yellowish oils
or solids. The NMR spectroscopic analysis of the products thus
formed showed an almost quantitative transformation of the alk-
ynyl(vinyl)silanes into the fused silacarbacycles, and the products
were found to be pure (95–98%). The compounds 6c and 10 were
crystallized from hexane to yield single crystals suitable for X-ray
analysis.
4-(9-Borabicyclo[3.3.1]non-9-yl)-1,6,6-trimethyl-1-phenyl-5-(triphen-
ylsilyl)-1H,2H,3H,6H-1,6-disilapentalene (9): 1 H NMR
(500.13 MHz, CD2Cl2, 296 K): δ = –0.22 [s, 3 H, Si(6)Me, trans to
Ph], –0.09 [s, 3 H, Si(6)Me, cis to Ph], 0.55 [s, 3 H, Si(1)Me], 1.12
(m, 2 H, CH2Si), 1.3–1.9 (m, 14 H, BBN), 2.89 (m, 2 H, CH2),
7.36–7.48 (m, 11 H, Ph), 7.61 (m, 2 H, Ph), 7.73 (m, 7 H, Ph) ppm.
11B NMR (160.5 MHz): δ = 89.0 ppm.
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 2276–2282

Fused Silacarbacycles Containing a Silole Unit
Table 2. Crystallographic data for the bicyclic compounds 6c and 10.
6c
10
Empirical formula
Crystal
Size [mm]
Crystal system
C21H38BNSi2
C32H54BSi3
colorless prism
0.28ϫ 0.20ϫ 0.18
monoclinic
colorless prism
0.25ϫ 0.19ϫ 0.18
monoclinic
Space group
P21/n
P21/c
Lattice parameters
a [pm]
b [pm]
c [pm]
1106.0(2)
1287.7(3)
1673.1(3)
108.13(3)
4
1207.6(2)
1885.3(4)
2833.3(6)
99.18(3)
8
β [°]
Z
Absorption coefficient µ [mm–1]
Diffractometer
0.161
0.167
STOE IPDS I (Mo-Kα, λ = 71.073 pm), graphite monochromator
Measuring range θ [°]
Reflections collected
Independent reflections [IϾ2σ(I)]
Absorption correction[a]
Refined parameters
wR2/R1 [IϾ2σ(I)]
1.96–26.01
15521
2140
none
226
0.1182/0.0546
0.334/–0.149
2.02–26.11
42086
2343
none
649
0.1032/0.0488
0.209/–0.133
Max./min. residual electron density [10–6 epm–3]
[a] Absorption corrections did not improve the parameter set.
3-(9-Borabicyclo[3.3.1]non-9-yl)-1,1-dimethyl-7,7-diphenyl-2-(tri-
methylsilyl)-1H,4H,5H,6H,7H-1,7-disilaindene (10): M.p. 91–94 °C.
1H NMR (500.13 MHz, C6D6, 296 K): δ = 0.22 (s, 6 H, SiMe2),
0.39 (s, 9 H, SiMe3), 1.27 (m, 2 H, CH2-6), 1.67 (m, 2 H, CH2-5),
1.9–2.3 (m, 14 H, BBN), 2.71 (m, 2 H, CH2-4), 7.3 (m, 6 H, Ph),
7.7 (m, 4 H, Ph) ppm. 13C NMR (125.8 MHz): δ [nJ(29Si,13C)] =
–1.3 [48.2] (SiMe2), 3.6 [51.0] (SiMe3), 11.4 [53.2] (C-6), 22.7 (C-5),
23.8 (BBN), 33.1 (br., BBN), 34.9 (BBN), 39.4 [6.5] (C-4), 128.5
(Ph), 130.0 (Ph), 130.8 [61.4] [52.6] (C-7a), 136.4 [3.8] (Ph), 137.6
[68.7] (Ph), 153.9 [62.1] [43.1] (C-2), 174.4 [11.6] [7.8 Hz] (C-3a),
183.8 (br., C-3) ppm. 11B NMR (160.5 MHz): δ = 82.0 ppm. 29Si
NMR (99.6 MHz): δ [2J(29Si,29Si)] = –18.2 [9.0] (SiPh2), –11.7 [9.6]
(SiMe3), 27.6 [9.6] [9.0 Hz] (SiMe2) ppm.
Acknowledgments
Support of this work by the Deutsche Forschungsgemeinschaft is
gratefully acknowledged.
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Methanolysis of 10: To the solution of the disilaindene derivative
10 (0.26 g, 0.5 mmol) in C6D6 (0.7 mL) a tenfold excess of meth-
anol was added. The mixture was kept at room temp. for 10 h and
then heated at 60–70 °C for 8 h. All volatiles were removed in
vacuo, and pure (1H NMR) 11 was left as a yellowish oil.
1,1-Dimethyl-7,7-diphenyl-2-(trimethylsilyl)-1H,4H,5H,6H,7H-1,7-
disilaindene (11): 1H NMR (500.13 MHz, C6D6, 296 K): δ = 0.16
(s, 6 H, SiMe2), 0.29 (s, 9 H, SiMe3), 1.00 (m, 2 H, CH2-6), 1.6–
2.3 (m, 16 H, BBN, CH2-5), 2.48 (m, 2 H, CH2-4), 7.20 [s, 1 H,
CH, 3J(29Si,1H) = 17.7 Hz], 7.3 (m, 6 H, Ph), 7.8 (m, 4 H, Ph) ppm.
13C NMR (125.8 MHz): δ [nJ(29Si,13C)] = –2.2 [49.0] (SiMe2), 0.1
[51.9] (SiMe3), 11.0 [53.5] (C-6), 21.8 (C-5), 34.9 [7.8] (C-4), 128.5
(Ph), 130.0 (Ph), 131.4 [61.6] [53.2] (C-7a), 136.3 [3.8] (Ph), 137.7
[68.6] (Ph), 152.4 [60.1] [46.3] (C-2), 158.2 [8.5] [4.3] (C-3), 171.8
[9.4] [5.5 Hz] (C-3a) ppm. 29Si NMR (99.6 MHz): δ [2J(29Si,29Si)]
= –18.7 [8.5] (SiPh2), –7.4 [9.8] (SiMe3), 21.8 [9.8] [8.5 Hz] (SiMe2)
ppm.
Crystal Structure Determinations of the Silacarbacycle 6c and 10:
Structure solution and refinement were carried out with the pro-
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www.eurjic.org
2281

B. Wrackmeyer, O. L. Tok, E. V. Klimkina, W. Milius
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Published Online: April 20, 2010
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