1,1-Organoboration of tetraynes - Routes to new siloles, stannoles and fused heterocycles

Article abstract of DOI:10.1016/S0022-328X(98)01029-8

The tetraynes R¹C≡C-SiMe₂-C≡C-SiMe ₂-C≡C...SiMe₂-C≡CR² [R¹ = R² = H (1a), SnMe₃ (1b), R¹ = SiMe₃, R² = H (2a), R² = SnMe

Full text of DOI:10.1016/S0022-328X(98)01029-8

Journal of Organometallic Chemistry 577 (1999) 82–92
1,1-Organoboration of tetraynes—routes to new siloles, stannoles and
fused heterocycles
Bernd Wrackmeyer *, Gerald Kehr, Ju¨rgen Su¨ß, Elias Molla 1
Laboratorium fu¨r Anorganische Chemie der Uni6ersita¨t Bayreuth, D-95440 Bayreuth, Germany
Received 4 August 1998
Abstract
The tetraynes R1CꢀC–SiMe2–CꢀC–SiMe2–CꢀC···SiMe2–CꢀCR2 [R1=R2=H (1a), SnMe3 (1b), R1=SiMe3, R2=H (2a),
t
i
R2=SnMe3 (2b)] and R1CꢀC–SiMe2–CꢀC–SnMe2–CꢀC–SiMe2–CꢀCR1 [R1=H (3a), nBu (3b), Bu (3c), Pent (3d), Ph (3e),
SiMe3 (3f)] were prepared, and their reactivity towards triethylborane Et3B 4 was studied. In the cases of 1a and 2a,
decomposition was observed whereas the reaction of the other tetraynes with Et3B affords siloles, 1,6-dihydro-1,6-disilapentalenes,
1,6-dihydro-1,6-stannasilapentalenes, and tricyclic heterocycles. In several cases it proved possible to show the stepwise proceeding
of the intramolecular 1,1-vinylboration, once the reaction had started with an intermolecular 1,1-ethylboration. Zwitterionic
intermediates were detected in the case of the reaction of 3 with Et3B. Characterisation of the products and intermediates was
achieved by multinuclear NMR spectroscopy (1H-, 13C-, 11B-, 13C-, 29Si-, 119Sn-NMR). © 1999 Elsevier Science S.A. All rights
reserved.
Keywords: Silicon; Boron; Alkynes; 1,1-Organoboration; Siloles; Pentalenes; NMR
1. Introduction
(1)
1,1-Organoboration of 1-alkynylsilanes or 1-alkynyl-
stannanes has proved useful in the syntheses of numer-
ous novel heterocyclic systems, not readily available
by other methods [1]. Recently, we have shown that
the 1,1-organoboration of certain triynes, in which
Since it was known that the 1,1-organoboration of
diynes of the type Me2M(CꢀCR1)2 can lead to metal-
the CꢀC bonds are separated by Me2Si moieties
leads to 1,6-dihydro-1,6-disilapentalene derivatives A
(Eq. (1)) [2]. The proposed intermediates were siloles
and zwitterionic borate-like species, which however
could not be isolated or detected by NMR spec-
troscopy.
loles [3] (M=Si [4], Ge [5], Sn [6], Pb [7]), the tetraynes
of the type 1–3 appeared to be attractive starting
materials for 1,1-organoboration reactions. Here we
report on the synthesis of 1–3, and on their reactivity
towards triethylborane Et3B 4.
* Corresponding author. Tel.: +49-921-552542; fax: +49-921-
552157; e-mail: b.wrack@uni-bayreuth.de
1 Alexander-von-Humboldt fellow; on leave from Jahangirnagar
University, Department of Chemistry, Savar, Dhaka, Bangladesh.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(98)01029-8

B. Wrackmeyer et al. / Journal of Organometallic Chemistry 577 (1999) 82–92
83
Scheme 3.
The synthesis of 2 starts with the silane 6 which can
be prepared readily by two routes as shown in Scheme
2. The silane 7 is obtained from 6 via its Grignard
reagent, treated with an excess of Me2SiCl2. The triyne
2a can then be obtained from the reaction of 7 with the
mono-Grignard reagent prepared from Me2Si(CꢀCH)2.
Treatment of 2a with one equivalent of Me3Sn–NEt2
affords 2b in quantitative yield.
Scheme 1.
2. Results and discussion
All compounds 3 are prepared, again in quantitative
yield, from the reaction of two equivalents of the
silanes 6 and 8 [2] with bis(diethylamino)dimethyltin
(Scheme 3). The compounds 1a, 2a, 6 and 8 are stable
towards air and water, whereas the tin compounds 1b,
2b, 3 and the silane 7 are sensitive to moisture.
2.1. Synthesis of the tetraynes 1–3
The most convenient route to the tetraynes 1a and 1b
is shown in Scheme 1. The use of Grignard-derivatives
is advisable [8] since we found that lithiation of the
terminal alkynes was accompanied by numerous side
reactions as a consequence of cleavage of Si–Cꢀ bonds.
The step from 1a to 1b is a quantitative reaction, as for
most terminal alkynes [9].
2.2. 1,1-Organoboration of the tetraynes 1 and 2
It is well known that alkynylsilanes react with Et3B 4
only after prolonged heating at \100°C [1,2,4]. A
reaction between 1a and 4 or 2a and 4 started after
some hours in boiling toluene, but led to a complex
mixture of unidentified compounds, as had been ob-
served previously for similar alkynes [2]. However, the
Sn–Cꢀ bonds in 1b, 2b and 3 proved to be sufficiently
reactive in order to start the intermolecular 1,1-ethylbo-
ration under mild reaction conditions. In the case of 1b,
the reaction with an excess of 4 was complete after
warming to room temperature, and the bis(silolyl)silane
9 is formed selectively and quantitatively. The 1:1 reac-
tion gave the same result, and the starting material 1b
was left. Therefore, Et3B must have attacked 1b more
or less synchronously at both terminal Sn–Cꢀ bonds
(Scheme 4).
Scheme 2.
Scheme 4.

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B. Wrackmeyer et al. / Journal of Organometallic Chemistry 577 (1999) 82–92
Since the tetrayne 2b possesses only one reactive
Sn–Cꢀ bond, other products can be expected from its
reaction with Et3B 4, as shown in Scheme 5. It is
suggested that at first a mixture of non-cyclic products
10 is formed of which the Z-isomer (Z-10) cannot be
detected, since it undergoes fast intramolecular 1,1-
vinylboration to give the silole 11. In contrast, the
isomer E-10 does not have the correct stereochemistry
for intramolecular 1,1-vinylborations, and it has to
rearrange by repeated steps of deorganoboration and
organoboration to Z-10. The silole 11 can rearrange
to the 1,6-dihydro-1,6-disilapentalene derivative 12, as
it has been reported for the 1,1-organoboration of
triynes [2]. The 29Si- and 119Sn-NMR spectra of the
reaction mixture show typical signals for the com-
pounds E-10 and 11 together with those for 12 (Fig.
1). This type of rearrangement is complete after 20 h
at room temperature and pure 12 can be isolated by
removing all volatile material at room temperature.
The stereochemistry of 12 should be ideal for further
intramolecular 1,1-organoboration reactions. However,
it proved necessary to heat the sample for 72 h at
110°C in toluene in order to induce further reactions.
These lead to a mixture of the new fused heterocycles
13 and 14, in an approximately 3:2 ratio. The rather
harsh reaction conditions are most likely due to steric
repulsion between the ethyl and the diethylboryl group
in 13. The somewhat unexpected alternative formation
of 14 (treatment of bis(1-alkynyl)silanes with Et3B in
general gives siloles [1,2,4]) can be explained in the
same way, since steric repulsion is reduced for the
six-membered ring which, according to its NMR data,
is not planar.
Scheme 5.
Fig. 1. 49.7 MHz 29Si (refocused INEPT, 1H decoupled) and 93.3 MHz 119Sn{1H-inverse gated} NMR spectra of the reaction mixture containing
E-10, 11 and 12. The assignment are indicated, based on changes of the intensities as the reaction proceeds towards 12.

B. Wrackmeyer et al. / Journal of Organometallic Chemistry 577 (1999) 82–92
85
Scheme 6.
2.3. 1,1-Organoboration of the tetraynes 3
requires prolonged heating at \140°C and is accompa-
nied by decomposition of 15 as well as of 16. However,
17b, d, f could be identified with certainty by their
typical NMR data (see also Fig. 2 for 29Si- and 119Sn-
NMR spectra).
By monitoring the progress of the reactions of 3 with
Et3B 4 by 29Si- and 119Sn-NMR, it proved possible to
identify various intermediates. Scheme 7 shows two
routes to the bis(2-silolyl)tin derivatives 15. NMR spec-
tra indicate that the route via compounds 21–23 is
preferred, since characteristic 29Si- and 119Sn-NMR sig-
nals of these intermediates could be observed (Fig. 3).
Scheme 6 summarises the results of the 1,1-organob-
oration of the tetraynes 3. After warming to room
temperature, the reaction mixtures contain two new
compounds 15 and 16 (approximate ratios: 15a/16a=
1/3; 15b/16b=1/3; 15c/16c=1:2; 15d/16d=1:1; 15e/
16e=1:2; 15f/16f=3:1). In the case of the stannoles 16,
intramolecular 1,1-vinylboration should lead to the 1,6-
dihydro-1-stanna-6-sila-pentalene derivatives 17. In
contrast to the formation of 12 and other comparable
1,6-dihydro-1,6-disila-pentalenes [2], this rearrangement
Fig. 2. 49.7 MHz 29Si (refocused INEPT, 1H decoupled) and 93.3 MHz 119Sn{1H-inversegated} NMR spectra of the reaction mixture containing
15, 16 and 17. The indicated assignments are based on the changes in signal intensities upon heating of the initial reaction mixture. Note the
enormous range of l119Sn for the tin atoms in apparently similar surroundings.

86
B. Wrackmeyer et al. / Journal of Organometallic Chemistry 577 (1999) 82–92
Scheme 7.
The route to the stannoles 16 is depicted in Scheme 8.
2.4. NMR spectroscopic results
Although the intermediates 24 were not detected by
NMR, the typical signals (e.g. at high frequency in the
119Sn-NMR spectrum with l119Sn 188.8, and large
The NMR data given in the Tables 1–6 are fully
consistent with the proposed structures of the tetraynes
and their 1,1-organoboration products. The advanta-
geous application of NMR spectroscopy is documented
also in the Figs. 1–4. Fig. 4 shows typical examples of
2D heteronuclear shift correlations (HETCOR), in this
2
magnitude of ꢀ J(119Sn, 29Si)ꢀ=217.1 Hz; see Fig. 3;
l11B values around −10, typical of four-coordinate
boron atoms [11]) for the zwitterionic intermediates
25a, 25b and 25f were strong at −50°C. At room
temperature these intermediates rearrange irreversibly
to the stannoles 16, in the same way as has been
described previously [5,10].
1
case by H detection, which help to establish the con-
nectivity of 1H, 13C, 29Si, and 119Sn nuclei in the starting
materials as well as in the products. As in previous
1
Fig. 3. 59.5 MHz 29Si (refocused INEPT, H decoupled) and 111.9 MHz 119Sn{1H-inversegated} NMR spectra of the reaction mixture containing
various intermediates of the reaction of 3f with Et3B. The indicated assignments are based on intensity changes as the reaction proceeds as well
as on 13C-NMR data, measured from parallel measurements.

B. Wrackmeyer et al. / Journal of Organometallic Chemistry 577 (1999) 82–92
87
helpful for structural assignments. In the case of 13C-
NMR spectra, the refocused INEPT pulse sequence
[14], based on coupling constants 3J(13C, 1H(MeSi)),
proved very useful, since it was possible to identify the
relevant 13C signals of quaternary carbon atoms to-
gether with satellite signals, and to circumvent the
problem of long relaxation times. The sensitivity of 29Si
nuclear shielding to the ring size [15] is demonstrated in
the cases of the compounds 13 and 14: in the six-mem-
bered ring in 14, the 29Si nuclear shielding is increased
by 32.4 ppm with respect to the five-membered ring in
13.
Scheme 8.
work in this field [1], the measurement of coupling
constants J(29Si, 13C), J(119Sn, 13C) from the corre-
sponding satellites in the 13C-NMR spectra, and the
observation of broadened 13C-NMR signals, typical of
boron-bonded carbon atoms [12,13], are particularly
3. Conclusions
1,1-Organoboration reactions of tetraynes with
SiMe2 or SnMe2 moieties separating the CꢀC bonds
Table 1
13C, 29Si and 119Sn NMR dataa of the tetraynes 1 and 2
1a (CDCl3) R1=R2=H 1b (CDCl3) R1=R2=SnMe3 2a (CDCl3) R1=SiMe3; R2=H 2b (C7D8) R1=SiMe3, R2=SnMe3
l
l
l
l
l
l
l
l
l
13C C(1)
13C C(2)
13C C(4)
13C C(5)
13C C(7)
13C C(8)
13C C(10)
13C C(11)
94.8 (19.0)
86.4 (94.3)
115.9 (13.4) [359.4]
112.8 (89.1) [55.8]
111.7 (87.3) (15.0) [2.3]
110.4 (89.0) (14.5)
110.4 (89.0) (14.5)
111.7 (87.3) (15.0) [2.3]
112.8 (89.1) [55.8]
115.9 (13.4) [359.4]
0.5, 0.1, 0.5 (61.5) (62.0)
(61.5)
115.6 (15.0) (75.3)
109.2 (89.0) (12.5)
111.5 (88.0) (14.0)
110.4 (88.7) (14.8)
111.2 (88.0) (15.0)
110.4 (88.5) (14.8)
86.4 (93.7)
94.4 (18.3)
0.0, 0.1, 0.2 (62.0) (82.0)
(61.5)
115.6 (15.5) (76.0)
109.7 (90.4) (12.3)
111.5 (88.8) (14.8) [2.0]
111.1 (88.9) (15.0)
110.5 (89.6) (14.7)
112.3 (87.9) (15.0) [2.5]
113.0 (90.6) [60.2]
115.8 (13.7) [377.3]
0.0, −0.2, 0.4 (61.8) (63.0)
(62.0)
−8.4 [402.0]
−41.9, −41.4, −43.2 (2.0) (2.0)
[14.3]
−74.2
−18.5 (2.0)
110.8 (89.3, 15.0)
111.0 (88.8, 15.0)
111.0 (88.8, 15.0)
110.8 (89.3, 15.0)
86.4 (94.3)
94.8 (19.0)
13C Me(3,6,9) 0.0, −0.1, 0.0 (62.0)
(62.8) (62.0)
l
l
13C R1, R2
−7.6 [402.5]
−43.0, −41.3, −43.0
[11.2]
0.24 (56.0)
−41.7, −41.0, −39.9 (2.0)
(2.0) (2.0)
29Si Si(3,6,9) −40.0, −41.0, −40.0
l
l
119Sn (R1,2
29Si(R1)
)
−70.9
−18.0 (2.0)
a Samples with 15–40% (v/v) at 25°C; nJ(29Si, 13C) (90.3 Hz) are given in parentheses; nJ(119Sn, X) (X=29Si, 13C) [90.5 Hz] are given in
brackets.
Table 2
13C-, 29Si- and 119Sn-NMR dataa of the tetraynes 3a–f
3a
H
3b
Bu
3c
3d
3e
Ph
3f
SiMe3
R1=
tBu
iPent
l
l
l
13C C(1, 11)
94.9 (19.7)
86.7 (94.3)
114.4 (88.6)
[88.5]
108.5 (20.7)
86.7(94.3)
115.5 (88.5) [88.4]
116.9 (18.9)
79.5 (99.9)
115.7 (88.0)
[88.0]
109.0 (20.2)
81.5 (100.3)
115.8 (87.7) [91.8] 114.9 (87.6) [87.6]
106.5 (19.5)
91.0 (97.1)
114.8 (78.0) (13.9)
110.3 (89.8) (12.2)
115.2 (88.5) [88.0]
13C C(2, 10)
13C C(4, 8)
l
l
l
13C C(5, 7)
13C Me(3,6,9)
13C R1, R2
111.7 (13.8)
[525.7]
(62.0) −8.9
[491.2]
110.0 (13.6) [540.2] 110.7 (13.0)
[536.4]
110.3 (13.6)
[548.8]
(62.2) −6.6
[490.4]
18.3, 37.7, 27.6,
22.5
−42,5 [13.9]
−166.0
111.4 (13.6) [529.0]
112.8 (13.6) [528.3]
0.8 (62.2)−6.7
(62.1) −6.9
(62.1) −6.7 [490.0]
0.8 (61.4) −6.7
[490.6]
−0.2 (56.2)
[499.5]
[490.5]
23.4, 32., 21.1, 15.2 28.3, 30.7
123.0, 132.2, 129.0,
128.5
−41.1 [13.2]
−164.8
l
l
29Si Si(3,9)
119Sn Sn(6)
−40.9 [13.2]
−164.5
−42.9 [14.6]
−166.4
−41.2 [13.2]
−165.4
−43.0 [12.5]
−164.1
n
n
a In C6D6, 15–40% (v/v) at 25°C; J(29Si, 13C) (90.3 Hz) are given in parentheses; J(119Sn, X) (X=29Si, 13C) [90.5 Hz] are given in brackets.

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B. Wrackmeyer et al. / Journal of Organometallic Chemistry 577 (1999) 82–92
Table 3
119Sn-, 29Si- and 13C-NMR dataa of the bis[2-sillolyl]dimethylstannanes 15a–f and the bis[2-silolyl]dimethylsilane 9
l
13C
l
29Si
l
119Sn
C(2)
C(3)
C(4)
C(5)
Si(1)
15ab
137.1
[385.2]
(53.1)
135.1
[401.5]
(53.8)
135.6
[395.6]
(52.3)
135.0
[401.9]
(54.0)
137.9
[374.9]
(51.9)
142.1
[382.9]
(50.3)
146.5
[14.0]
(44.0)
(64.5)
171.2
181.0
Broad
135.5
[17.8]
(60.1)
150.0
[21.5]
(59.6)
160.0
[19.1]
(59.9)
149.9
[22.0]
(59.4)
152.0
[22.9]
(59.9)
146.8
[14.8]
(60.8)
141.2
[381.5]
(51.3)
16.4
[104.9]
−103.4
−105.0
−106.2
−104.8
−104.3
−102.6
−50.0
R1=H
15bc
171.1
[7.3]
166.3
Broad
13.3
[106.9]
R1=Bu
15cd
169.9
[8.7]
162.4
Broad
13.2
[106.9]
R1=tBu
15de
170.9
[8.0]
166.0
Broad
13.4
[107.7]
R1=iPent
15ef
171.5
[6.5]
168.0
Broad
14.4
[104.4]
R1=Ph
15fg
170.6
[3.9]
(11.8)
183.8
[7292]
Broad
184.1
Broad
25.7
R1=SiMe3
[110.6]
(10.9)
25.0i
[107.0]
(10.0)
9h
169.9
[3.7]
(8.9)
(11.7)
a In C6D6, 9 in C7D8, 15–40% (v/v) at 25°C; nJ(29Si, 13C) (90.3 Hz) are given in parentheses; nJ(119Sn, X) (X=29Si, 13C) [90.5 Hz] are given
in brackets; broad denotes broad signals due to partiallyrelaxed scalar 13C–11B coupling. l11B(C6D6)=87.090.5.
b l13C(15a)=33.4 [50.0], 14.6 [9.0] (Et); 22.8 broad, 9.2 (BEt2); −3.6 (47.2) (SiMe2), −7.5 [340.2] (SnMe2).
c l13C(15b)=33.8, 32.6, 23.5, 14.2 (Bu); 33.6 [52.6], 14.8 [9.2] (Et); 22.7 broad, 9.2 (BEt2); −2.8 (47.8) (SiMe2); −7.1 [338.4] (SnMe2).
d l13C(15c)=36.4, 32.8 (tBu); 32.8 [49.7], 15.8 [8.7] (Et); 22.3 broad, 9.7 (BEt2); −1.1 (47.4) (SiMe2); −6.5 [339.0] (SnMe2).
e l13C(15d)=40.9, 30.6, 28.7, 22.9 (iPent); 33.5 [49.9], 14.8 [9.2] (Et); 22.6 broad, 9.3 (BEt2); −2.7 (47.8) (SiMe2); −7.9 [338.8] (SnMe2).
f l13C(15e)=142.4, 128.7, 127.5, 126.2 (Ph); 33.4 [47.9], 15.1 [8.8] (Et); 22.3 broad, 9.7 (BEt2); −2.8 (48.0) (SiMe2); −7.0 [342.8] (SnMe2).
g l13C(15f)=32.6 [48.2], 15.7 [8.8] (Et); 23.0 broad, 9.8 (BEt2); (51.2) (SiMe3); −2.2 (47.2) (SiMe2); −6.9 [344.6] (SnMe2).l29Si(SiMe3)=−
10.9.
h l13C(9)=31.5 [46.0], 15.5 [8.8] (Et); 22.1 broad, 7.8 (BEt2); 2.2 (50.5) (SiMe2); −2.2 [2.3] (47.6) (SiMe2 (silolyl)); −8.6 [338.2] (SnMe3).
i l29Si (SiMe2)=−21.4 (10.0).
proceed stepwise, and rather harsh reaction conditions
are required to make use of all four CꢀC bonds. In
several cases it was possible to identify intermediates,
even those with a zwitterionic structure, in which a
triorganostannyl cation is co-ordinated by an alkynyl
group belonging to an alkynylborate anion. It became
clear that the 1,1-organoboration of polyynes with
more than four CꢀC bonds will probably not lead to
pure products, since the 1,1-organoboration of the te-
trayne 2b afforded in the last step a mixture of two
fused heterocycles 13 and 14.
solvents were used for syntheses and preparation of the
samples for NMR measurements. Starting materials
were either available as commercial products and used
without further purification (chlorosilanes, n-butyl
lithium (1.6 M in hexane), Et3B) or prepared as de-
scribed (HCꢀCMgBr in THF [16], Me3Sn–NEt2,
Me2Sn(NEt2)2 [17]). Electron impact (EI) mass spectra:
Finnigan MAT 8500 with direct inlet. IR spectra:
Perkin Elmer 983 G spectrometer. NMR measure-
ments: Bruker ARX 250 or DRX 500 [1H-, 11B-, 13C-,
29Si-NMR (refocused INEPT [14] based on
1
2J(29Si, 1H)=7 Hz), 119Sn-NMR (inverse gated H de-
coupled or refocused INEPT [14] based on
2J(119Sn, 1H)=50–60 Hz)]. Chemical shifts are given
with respect to Me4Si [l1H (CHCl3/CDCl3)=7.24,
(C6D5H)=7.14, (C6D5CD2H)=2.03; l13C (CDCl3)=
77.0, (C6D6)=128.0, (C6D5CD3)=20.4; l29Si=0 for
4. Experimental
4.1. General
All compounds were handled in an atmosphere of
dry argon, observing all precautions to exclude oxygen
and moisture when boranes were used. Carefully dried
](29Si)=19.867184
MHz],
](11B)=32.083971 MHz], and Me4Sn [l119Sn=0 for ]
119Sn)=37.290665 MHz].
BF3OEt2
[l11B=0;
(

B. Wrackmeyer et al. / Journal of Organometallic Chemistry 577 (1999) 82–92
89
Table 4
119Sn-, 29Si- and 13C-NMR dataa of the stannole derivatives 16a–f
l
13C
l
29Si
l
119Sn
ꢁC(2)
ꢁC(3)
ꢁC(4)
ꢁC(5)
Si(2)
Si(5)
16ab
142.2
183.7
Broad
168.7
[86.5]
(11.8)
168.1
[89.5]
(12.7)
168.1
[87.8]
(13.1)
167.8
[89.5]
(13.0)
168.7
[94.8]
(11.6)
168.7
[87.6]
(12.8)
135.6
−26.9
[102.5]
−25.8
[107.5]
136.5
132.6
133.6
132.4
134.8
134.4
R1=H
[200.5]
(71.1)
143.7
[200.5]
(72.4)
143.1
[201.6]
(72.1)
143.5
[201.1]
(72.6)
143.1
[199.5]
(70.9)
142.6
[200.8]
(66.4)
[274.9]
(72.3)
137.9
[272.9]
(72.3)
137.7
[271.4]
(74.1)
137.7
[275.7]
(71.5)
137.4
[271.9]
(70.5)
137.3
[276.6]
(71.9)
16bc
183.1
Broad
−27.6
[104.7]
−28.4
[114.3]
R1=Bu
16cd
183.1
Broad
−27.6
[108.4]
−28.4
[112.8]
R1=tBu
16de
182.8
Broad
−27.7
[106.9]
−28.5
[117.2]
R1=iPent
16ef
183.7
Broad
−26.1
[108.4]
−27.2
[115.7]
R1=Ph
16fg
183.1
Broad
−27.3
[102.6]
−28.4
[112.8]
R1=SiMe3
n
n
a In C6D6, 15–40% (v/v) at 25°C; J(29Si, 13C) (90.3 Hz) are given in parentheses; J(119Sn, X) (X=29Si, 13C) [90.5 Hz] are given in brackets;
broad denotes broad signals due to partially relaxed scalar 13C–11B coupling. l11B=87.090.4.
b l13C(16a)=32.0 [85.6], 16.6 [9.0] (Et); 23.1 broad, 9.9 (BEt2).
c l13C(16b)=31.9 [87.0], 16.1 [9.9] (Et); 22.9 broad, 9.7 (BEt2).
d l13C(16c)=31.8 [87.4], 16.2 [9.8] (Et); 22.8 broad, 10.1 (BEt2).
e l13C(16d)=31.8 [87.0], 16.2 [9.7] (Et); 22.6 broad, 9.7 (BEt2).
f l13C(16e)=32.0 [88.3], 16.2 [8.8] (Et); 22.9 broad, 9.8 (BEt2).
g l13C(16f)=32.1 [85.6], 16.1 [9.9] (Et); 23.2 broad, 9.6 (BEt2); l29Si (SiMe3)=−19.0, −19.1.
4.2. 3,6,9-Hexamethyl-3,6,9-trisila-undeca-
1,4,7,10-tetrayne 1a
The reaction mixture was stirred for 3 h. Removal of all
volatile material in vacuo left the pure compound 1b as
1
a colourless oil (0.63 g, 87%). H-NMR (CDCl3) l1H
[nJ(119Sn 1H)]: 0.27 [60.8] (s, 18H, SnMe3), 0.30 (s, 12H,
A solution of EtMgBr (19 mmol) in THF (20 ml) was
added to a saturated solution of acetylene in THF (50
ml) over a period of 40 min. The reaction mixture was
stirred for an additional 2 h at room temperature and
gave a solution of HCꢀCMgBr which was then cooled
to 5°C. A solution of compound 5 (1.89 g, 6.45 mmol)
in THF (10 ml) was added dropwise, and the reaction
mixture was allowed to warm up to room temperature
and was kept stirring for 10 h. The reaction mixture
was hydrolysed with an aqueous NH4Cl solution (80
ml). After repeated extraction of the aqueous phase
with pentane, the pentane extracts were combined and
dried with Na2SO4. Insoluble material was filtered off,
and the solvent was removed in vacuo and 1.69 g (98%)
of the pure compound 1a was left as a colourless solid.
IR (in hexane): w(CꢀC)=2043 cm−1, w(ꢀC–H)=3277,
SiMe2), 0.31 (s, 6H, SiMe2).
4.4. 3,6,9-Hexamethyl-11-trimethylsilyl-3,6,9-
trisila-undeca-1,4,7,10-tetrayne 2a
A solution of EtMgBr (4.16 mmol) in THF (5 ml)
was added dropwise to a solution of diethynyldimethyl-
silane, Me2Si(CꢀCH)2, (0.44 g; 4.04 mmol) in THF (5
ml) over a period of 50 min. The solution became
yellow and was stirred additionally for 1.5 h. This
solution was then added dropwise to a solution of
compound 7 (1.10 g; 4.04 mmol) in THF (5 ml) over
15 min. The reaction mixture was stirred overnight,
and then the solvent was removed, after which an
oily solid was left. The solid was extracted twice
with portions of pentane (30 ml) and filtered. Removal
of solvent in vacuo gave solid 2a (1.37 g, 98%).
IR (hexane): w(CꢀC)=2043 cm−1, w(ꢀC–H)=3296
3295 cm−1 1H-NMR (CDCl3): l1H=0.27 (s, 6H,
.
SiMe2), 0.28 (s, 12H, SiMe2), 2.42 (s, 2H, ꢀCH).
4.3. 3,6,9-Hexamethyl-1,11-bis(trimethylstannyl)-
3,6,9-trisila-undeca-1,4,7,10-tetrayne 1b
1
cm−1. H-NMR (CDCl3) l1H [nJ(29Si 1H)]: 0.15 (7.6)
(s, 9H, SiMe3), 0.30 (7.6) (s, 6H, SiMe2), 0.31 (s,
6H, SiMe2), 0.33 (7.0) (s, 6H, SiMe2), 2.43 (s, 1H,
ꢀCH).
Me3SnNEt2 (0.57 g; 2.42 mmol) was added to a
solution of 1a in hexane (10 ml) at room temperature.

90
B. Wrackmeyer et al. / Journal of Organometallic Chemistry 577 (1999) 82–92
Table 5
13C-, 29Si- and 119Sn-NMR dataa of the fused heterocycles 12–14
12b
13c
14d
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
13C(2)
147.8 (49.0) [378.8]
168.1
179.0 [82.9]
148.0 (49.0) [382.7]
168.0
174.2 [87.1]
147.4 (49.7) [382.2]
168.6 [10.3]
177.8 (8.6)(8.6) [88.8]
183.1 broad
13C(3)
13C(3a)
13C(3b)
175.6 [10.3]
13C(4)
181.9 broad
181.2 broad
13C(5)
143.9e (43.8)(69.7) [8.9]
153.4e (42.5) (61.6)
184.8 broad
148.4 (53.1)(53.1) [1.6]
13C(6)
13C(6a)
150.5e (56.1)(58.8) [11.8]
153.9 (57.0)(57.0) [8.4]
156.9 (56.5)(57.3) [11.0]
13C(7a)
163.7e (42.6)(56.9) [8.4]
149.3 (56.1)(59.9) [11.8]
−3.8 (50.0), −3.6 (50.0)
13C(8a)
13C(1-Me)
13C(6-Me)
13C(7-Me)
13C(8-Me)
13C(EtB)
13C(3-Et)
13C(5-Et)
13C(2-SnMe3)
29Si(1)
−3.6 (50.2) {2.6]
−2.6 (49.5)
−3.8 (50.0)
−2.6 (49.1)
−3.7 (50.0)
0.2 (51.7), 1.3 (50.0)
−2.9 (49.1), −2.8 (50.0)
20.8 broad, 9.7
30.8 [46.6], 16.7 [9.5]
32.2 (10.3)(10.3), 15.2
−8.2 [338.0]
22.1 broad, 9.8
31.3 [45.0], 16.7 [8.4]
18.0 broad, 9.7
32.6 [50.0], 15.7 [8.6]
−8.0 [337.2]
10.8 (13.6) [85.0]
19.4 (10.9)(13.6) [1.8]
−8.3 [338.0]
6.3 (11.7) [83.2]
Si(6): 12.9 (8.7)(13.2) [4.6]
Si(7):1.1 (11.7)(13.2) [2.8]
−53.8
9.9 (13.8) [88.0]
29Si(6,7,8)
Si(7):−19.5 (8.6)(8.6) [4.0]
Si(8): 16.4 (8.6)(13.8) [2.5]
−52.8
l
119Sn
−49.8
n
n
a In C7D8, 15–40% (v/v) at 25°C; J(29Si, 13C) (90.3 Hz) are given in parentheses; J(119Sn, X) (X=29Si, 13C) [90.5 Hz] are given in brackets;
broad denotes broad signals due to partially relaxed scalar 13C–11B coupling. The numbering scheme of 14 was selected for better comparison.
b l11B=86.5; l13C=2.3 (56.6) 5-SiMe2, 0.1 (56.1) Me3Si–Cꢀ, 114.8 (77.5) (12.3) ꢀC–SiMe2, 115.3 (77.8) (12.1) ꢀC–SiMe3; l29Si=−31.5 (10.9)
(1.6) [5.7] 6-SiMe2, −19.4 (1.6) Me3Si–Cꢀ.
c l11B=86.5.
d l11B=72.0.
e The larger value belongs to coupling with the exocyclic 29Si nucleus.
4.5. 3,6,9-Hexamethyl-1-trimethylstannyl-11-
trimethylsilyl-3,6,9-trisila-undeca-1,4,7,10-tetrayne 2b
was left as a colourless solid. IR (hexane): w(CꢀC)=
2037, 2041, 2092 cm−1, w(ꢀC–H)=3289 cm−1 1H-
.
NMR (C6D6) l1H (nJ(29Si 1H)) [nJ(119Sn 1H)]: 0.06
[69.0] (s, 6H, SnMe2), 0.18 (7.2) (s, 12H, SiMe2), 2.20 (s,
2H, ꢀCH). EI-MS: m/z (%)=363 (5) [M+], 348 (100),
255 (20), 225 (10), 165 (40), 135 (25), 43 (10).
As described for 1b, treatment of 2a with one equiva-
lent of Me3SnNEt2 afforded compound 2b in 89% yield
as
a
colourless solid. 1H-NMR(C7D8): l1H
[nJ(119Sn 1H)]: 0.00 [60.7] (s, 9H, SnMe3), 0.01 (s, 9H,
SiMe3), 0.11 (s, 6H, SiMe2), 0.17 (s, 6H, SiMe2), 0.22 (s,
6H, SiMe2).
4.7. 3,6,9-Hexamethyl-1,11-bis(trimethylsilyl)-3,9-
disila-6-stanna-undeca-1,4,7,10-tetrayne 3f
4.6. 3,6,9-Hexamethyl-3,9-disila-6-stanna-
undeca-1,4,7,10-tetrayne 3a
In the same way as described for 3a, the silane 6
reacted with Me2Sn(NEt2)2 in 2:1 molar ratio to give
compound 3f as a colourless solid in 95% yield. IR
1
Bis(diethylamino)dimethyltin, Me2Sn(NEt2)2 (0.48.g;
2.02 mmol) in diethylether (20 ml) was added to a
(hexane): w(CꢀC)=2037, 2092, 2110 cm−1; H-NMR
(C6D6) l1H (nJ(29Si 1H)) [nJ(119Sn 1H)]: 0.02 (6.8) (s,
18H, SiMe3), 0.05 [69.0] (s, 6H, SnMe2), 0.24 (7.0) (s,
12H, SiMe2). EI-MS: m/z (%)=508 (5) [M+], 493
(100), 327 (25), 297 (40), 181 (15), 135 (25), 73 (10), 43
(15). The compounds 3b–e were prepared in the same
dilute
solution
of
diethynyldimethylsilane,
Me2Si(CꢀCH)2, (0.44 g; 4.04 mmol) in diethylether (50
ml). After stirring the mixture for 2 h, all volatile
material was removed in vacuo. Compound 3a (91%)

B. Wrackmeyer et al. / Journal of Organometallic Chemistry 577 (1999) 82–92
91
Table 6
13C-, 29Si- and 119Sn-NMR dataa of the 1,6-dihydro-1-stanna-6-sila-pentalene derivatives 17b, d, f
17b (R1=nBu)
17d (R1=ipent)
17f (R1=SiMe3)
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
13C(2)
142.5 [274.8] (72.0)
166.7
177.8 [69.4]
163.6 broad
151.0 [10.0]
143.7 [322.8]
−8.0 [337.0]
−3.1
2.4
30.9, 16.8
22.3 broad, 9.3
85.6
142.4 [273.1] (71.7)
166.7
177.8
163.0 broad
150.9 [10.4]
143.6 [324.2] (60.0)
−8.0 [323.1]
−3.0
2.2
30.6, 17.0
22.4 broad, 9.3
85.5
142.2 [274.7] (70.7)
167.0
13C(3)
13C(3a)
178.3 [74.0]
181.8 broad [85.0]
146.7 [5.0]
152.3 [308.4] (57.8)
−8.2 [328.5]
−2.9 (47.4)
1.7
29.5, 17.0
22.7 broad, 9.5
113.7
13C(4)
13C(5)
13C(6a)
13C(Me2Sn(1))
13C(Me2Si(6))
13C(Me2Si-2)
13C(Et-3)
13C(Et2B)
13C(ꢀCSi)
13C(ꢀCR1)
13C(R1)
108.0
107.9
114.9
1.5, 1.4
22.3, 31.0, 20.1, 13.8; 32.7, 33,6, 23.5, 14.3
10.7
−28.5
42.3
18.4, 37.9, 27.5, 22.7; 28.8, 40.9, 28.6, 23.0
10.8
−28.5
42.1
29Si(Si(6))
29Si (2-Si)
119Sn (Sn(6))
21.8 [121.3] (9.4)b
−28.7 [83.6]
37.4
n
n
a In C6D6, 15–40% (v/v) at 25°C; J(29Si, 13C) (90.3 Hz) are given in parentheses; J(119Sn, X) (X=29Si, 13C) [90.5 Hz] are given in brackets;
broad denotes broad signals due to partially relaxed scalar 13C–11B coupling.
b l29Si(5-SiMe3)=−12.8 (9.4); l29Si (ꢀC–SiMe3)=−19.5.
Fig. 4. Contour plots of the 500 MHz 2D (HMQC) 1H/13C and 1H/29Si experiments for 2b which establish the connectivity of the respective
resonance signals as indicated.

92
B. Wrackmeyer et al. / Journal of Organometallic Chemistry 577 (1999) 82–92
way from the corresponding silanes [18] and were ob-
tained as colourless oily liquids.
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All reactions were carried out first on a small scale
(B1 mmol) in NMR tubes. The alkynes were dissolved
in benzene (C6D6) or toluene (C7D8), cooled at −78°C
and the desired amount (excess or stoichiometric
amount) of triethylborane was injected in one portion.
The progress of the reactions was monitored mainly by
29Si- and 119Sn-NMR (see Figs. 1–3). The same results
were obtained when the reactions were carried out on a
larger scale (\2 mmol) in order to attempt distillation
of the mixtures or to obtain products selectively by
thermally induced rearrangements. This did not give
pure products, and in many cases, decomposition oc-
curred, leading to even more complex mixtures. At-
tempts to separate the mixtures on silica or Al2O3 have
not been successful as yet, since the organoboration
products decomposed, and elution with various polar
and non-polar solvents did not give an appreciable
amount of defined products. The products 9 and 12
were obtained quantitatively in high purity (1H-NMR)
just by removing all volatile material. In the case of the
mixtures containing 15/16 all NMR spectra indicate
there are no further impurities.
Acknowledgements
We gratefully acknowledge support of this work by
the Deutsche Forschungsgemeinschaft and the Fonds
der Chemischen Industrie. E.M. thanks the Alexander-
von-Humboldt Stiftung for a fellowship.
.