1,6-Dihydro-1,6-disilapentalene derivatives by 1,1-organoboration of triynes

Article abstract of DOI:10.1016/S0022-328X(98)00529-4

The triynes R¹CC-SiMe₂-CC-SiMe₂-CCR ¹ [R¹=H (3), SiMe₃ (4) SnMe₃ (5)] were prepared, and their reactivity towards triorganoboranes R₃B 6 [R=Et (a), CH₂Ph (b), Ph (c), 2-thienyl (d)] was studied. In the case of 3, decomposition was observed whereas the reaction of 4 and 5 with 6 affords the 1,6-dihydro-1,6-disilapentalene derivatives 7a-d (from 4) and 9a, c (from 5) in almost quantitative yield. This is the result of stereo- and regioselective intermolecular 1,1-organoboration in the first step of the reaction, followed by two consecutive intramolecular 1,1-vinyloborations. The products were characterised by their ¹H-, ¹¹B-, ¹³C-, ²⁹Si- and ¹¹⁹Sn-NMR data.

Full text of DOI:10.1016/S0022-328X(98)00529-4

Journal of Organometallic Chemistry 562 (1998) 207–215
1,6-Dihydro-1,6-disilapentalene derivatives by 1,1-organoboration of
triynes
Dedicated to: Professor Peter Jutzi on the occasion of his 60th birthday.
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 11 February 1998
Abstract
The triynes R1CꢀC–SiMe2–CꢀC–SiMe2–CꢀCR1 [R1=H (3), SiMe3 (4) SnMe3 (5)] were prepared, and their reactivity towards
triorganoboranes R3B 6 [R=Et (a), CH2Ph (b), Ph (c), 2-thienyl (d)] was studied. In the case of 3, decomposition was observed
whereas the reaction of 4 and 5 with 6 affords the 1,6-dihydro-1,6-disilapentalene derivatives 7a–d (from 4) and 9a, c (from 5)
in almost quantitative yield. This is the result of stereo- and regioselective intermolecular 1,1-organoboration in the first step of
1
the reaction, followed by two consecutive intramolecular 1,1-vinyloborations. The products were characterised by their H-, 11B-,
13C-, 29Si- and 119Sn-NMR data. © 1998 Elsevier Science S.A. All rights reserved.
Keywords: Silicon; Boron; Alkynes; 1,1-Organoboration; Pentalenes; NMR
1. Introduction
In the case of M=Sn [7] and Pb [8], the crucial
zwitterionic intermediates of type B have been isolated
and fully characterised. We have now started to study
the reactivity of cyclic and non-cyclic polyynes, with
CꢀC bonds separated by Me2Si moieties, towards vari-
ous triorganoboranes. The corresponding tin and lead
compounds would also be of interest; however, these
are much less stable owing to exchange reactions at the
M–Cꢀ bonds. In this work, we report on the synthesis
of the triynes 3-5 (Scheme 1) and their reactivity to-
wards the triorganoboranes R3B 6 [R=Et (a), CH2Ph
(b), Ph (c), 2-thienyl (d)].
Metalloles are attractive compounds for both
organometallic and organic syntheses [1]. We have
shown that numerous siloles [2], germoles [3], stannoles
[4] or plumboles [5] of type A can be prepared by
1,1-organoboration [6] of diynes, in which the CꢀC
bonds are separated by Me2M moieties (M=Si, Ge,
Sn, Pb) as shown in Eq. (1).
2. Results and discussion
2.1. Synthesis of the triynes 3–5
* Corresponding author. Tel.: +49 921 552542; fax: +49 921
552157.
1 Alexander-von-Humboldt fellow; on leave from Jahangirnagar
University, Department of Chemistry, Savar, Dhaka, Bangladesh.
Scheme 1 summarises the most convenient route to
the triynes 3–5. At first, bis(dimethylsilyl)ethyne 1 is
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00529-4

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B. Wrackmeyer et al. / Journal of Organometallic Chemistry 562 (1998) 207–215
prepared [9] (step a) which is then treated with bromine
to give 2 (step b). The reaction of 2 either with ethynyl
magnesium bromide or trimethylsilylethynyl lithium
leads to 3 (step c) and 4 (step d), respectively. As usual
for terminal alkynes [10], the reaction of 3 with two
equivalents of trimethyltin diethylamide affords 5 in
almost quantitative yield. All compounds 1–5 are sta-
ble for years when kept under N2 or Ar in the
refrigerator.
2.2. 1,1-Organoboration of the triynes 3–5
There was no reaction of 3 with R3B 6a–d at r.t. or
in boiling hexane. The reaction started in boiling
toluene, leading to a complex mixture of compounds
which could not be identified so far. This is reminiscent
of the reaction of Me2Si(CꢀCH)2 with 6a where the
primarily formed silole is trapped, under the reaction
conditions (boiling triethylborane; ca. 100°C), by vari-
ous Diels–Alder cycloadditions [11].
The reaction of 4 with 6a–d started also in boiling
toluene and was complete after 48 h. The mixtures of
products consist to more than 85% of the 1,6-dihydro-
1,5-disilapentalene derivatives 7a–d and less than 15%
of the silole derivatives 8a–d, Eq. 2, as shown by
repeated experiments.
Scheme 1.
equilibrium between 10 and 10% (as the result of 1,1-de-
organoboration and 1,1-organoboration) is important,
since 10% cannot undergo further intramolecular 1,1-
organoboration reactions. The alternative attack of
R3B at Si–Cꢀ bonds marked by broken arrows leads to
the siloles 8 via the intermediates 12. This route corre-
sponds closely to that described previously [2] for the
In contrast, the analogous reaction of 5 with 6a,c starts
already below room temperature and is complete after
1 h at r.t.. It leads selectively to the 1,5-dihydro-1,5-dis-
ilapentalene derivatives 9a,c (Eq. 3).
The reaction mechanism of 1,1-organoboration is
well established [6]. In Scheme 2 it is shown that the
intermolecular 1,1-organoboration can start with the
cleavage of the Si–Cꢀ bonds in 4 in several places.
Cleavage of the Si–Cꢀ bonds indicated by drawn ar-
rows leads to intermediates 10, 10%, and 11, of which the
latter finally rearranges to the major product 7. The
Scheme 2.

B. Wrackmeyer et al. / Journal of Organometallic Chemistry 562 (1998) 207–215
209
119Sn-NMR data (Table 1). This is also true for the
siloles 8a–d (Table 2) which are formed as minor
products, and for which comparable sets of NMR data
already exist [2]. The 11B chemical shifts of the com-
pounds 7–9 (footnote ‘b’ in Tables 1 and 2) are not
particularly diagnostic, except for the fact that the data
are in agreement with boron atoms in trigonal planar
surroundings, typical of triorganoboranes [13].
29Si-NMR (Fig. 1), and in the case of the reactions of
5, also 119Sn-NMR spectroscopy proved extremely
valuable for monitoring the progress of the reactions.
As can be seen from the data in the Tables 1 and 2, the
formation of the new products is readily evident, since
there is no overlap with NMR signals of the starting
materials. There is little variation of the l29Si values of
7 and 9. The 29Si shielding is markedly increased with
respect to corresponding siloles (see Table 2), and the
29Si(1) nuclear shielding in the boryl-substituted ring is
8–9 ppm less than that of 29Si(6). Further evidence of
the ring formation comes from the observation of satel-
2
lites due to geminal coupling constants J(29Si,29Si) or
2J(119Sn,29Si). The 29Si(1)-NMR signal is broader than
that of Si(6) which is caused by unresolved 29Si(1)–11B
coupling across three bonds. This effect is much more
pronounced in the case of 119Sn-NMR signals as shown
for 9a in Fig. 1. The assignment of the 119Sn-NMR
signals is straightforward because of the different line
widths. The broader line belongs to the 2-SnMe3 group
because of a partially relaxed 119Sn–11B coupling
Scheme 3.
synthesis of siloles by 1,1-organoboration. It is evident
from the product distribution 7/8\4/1 that the cleav-
age of the Si–Cꢀ bonds marked by drawn arrows is
preferred not only for statistical reasons (2/1).
In the case of 5, the greater reactivity of the Sn–Cꢀ
bond, as compared with the Si–Cꢀ bond, controls the
course of the reaction. This corresponds to the results
of 1,1-organoboration of diynes of the type
Me2Si(CꢀCSnMe3)CꢀCR1) (R1=alkyl, aryl, etc.) [12].
It is shown in Scheme 3 that the intermolecular 1,1-
organoboration starts exclusively by attack at one of
the Sn–Cꢀ bonds (drawn arrows) leading to the inter-
mediates 13 and 13% which are in equilibrium with each
other (in the same way as 10 and 10%). Two consecutive
intramolecular 1,1-vinyloborations lead selectively, via
the silole 14, to the 1,6-dihydro-1,6-disilapentalenes 9.
The structures of the final products leave no doubt
about the intermediacy of zwitterionic species such as
15 (analogous to B) shown in Scheme 4, the immediate
precursor to 14, which rearranges to 9 via a similar
intermediate 16. However, the lifetime of these species,
in which a formally positively charged tri-coordinate
silicon atom is stabilised by side-on coordination to the
CꢀC bond, is too short, in contrast with similar zwitter-
ionic tin and lead derivatives [7,8]
3
[ꢀ J(119Sn,11B)ꢀ 50–60 Hz], as the result of scalar relax-
ation of the second kind [14,15]. The broadening is
much smaller or negligible for the 119Sn-NMR signal of
5
the 5-SnMe3 group [ꢀ J(119Sn,11B)ꢀB10 Hz]. Compound
9a is also a good example for coupling across conju-
gated
y systems, considering the magnitude of
6
ꢀ J(119Sn,119Sn)ꢀ=56.0 Hz (Fig. 2).
2.3. NMR-Spectroscopic results
The NMR data of the 1-alkynylsilanes 1–5 are given
in the Section 3. The structures of the 1,6-dihydro-1,6-
disilapentalene derivatives 7a–d and 9a,c are proposed
1
on the consistent set of H (Section 3), 13C-, 29Si- and
Scheme 4.

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B. Wrackmeyer et al. / Journal of Organometallic Chemistry 562 (1998) 207–215
211
Table 2
13C- and 29Si-NMR dataa,b of the silole derivatives 8a–d
l
13C
l
29Si
ꢁC(2)
ꢁC(3)
ꢁC(4)
ꢁC(5)
Si(1)
28.2
27.7
2-Si
5-Si
SiMe3
−19.5
−19.4
8ac
147.5
(n.m.)
151.0
(43.9)
(61.7)
155.1
(n.m.)
155.8
(n.m.)
179.2
br.
182.5
br.
171.6
(n.o.)
167.0
(n.o.)
133.6
(n.m.)
138.6
(n.m.)
−11.4
−11.2
−30.9
−30.6
8bd
8ce
8df
181.5
br.
179.0
br.
171.4
(n.o.)
163.0
(n.o.)
(n.m.)
29.5
28.3
−9.8
−9.4
−29.6
−29.7
−19.5
−19.5
144.5
(n.m.)
a
15–40% (v/v) at 25°C in [D8] toluene; nJ(29Si,13C) in Hz (90.5 Hz) are given in parentheses; br., broad resonances due to 1J(13C,11B); n.o.,
not observed; n.m., not measured; n.a., not assigned.
b l11B(BEt2)=8791; l11B[B(CH2Ph)2]=8392; l11B(BPh2)=71.092 l11B[B(2-thienyl)2]=6092.
c l13C(8a)=114.5, 113.9 (CꢀC); 29.8, 15.1 (Et); 22.4 br., 9.2 (BEt2);. −0.1 (SiMe3); −1.8 (MeSi(1)).
d l13C(8b)=140.4, 129.2, 128.2, 124.9, 39.4 br. (B(Ph–CH2)2); 138.8, 129.4, 128.3, 126.9, 42.3 (Ph–CH2); 114.6, 114.1 (CꢀC); 2.0 (2-SiMe); 0.8
(5-SiMe). −0.3 (SiMe3); −2.6 (MeSi(1)).
e l13C(8c)=144.2, n.a.(Ph); 141.9 br., 138.1, 131.6, 127.7 (BPh2); 115.2, 114.3 (CꢀC); 2.0 (2-SiMe); 0.8 (5-SiMe). −0.3 (SiMe3); −2.6 (MeSi(1)).
f l13C(8d)=144.7 br., 141.8, 136.5, 129.0 (B(2-thienyl)); 144.7 br., 141.7, 137.1, 128.9 (B(2-thienyl)); 144.8, 127.3, 126.0, 124.7 (2-thienyl); 115.0,
114.5 (CC); 1.4 (5-SiMe); 0.9 (2-SiMe). −0.1 (55.4) (SiMe3); −2.0 (MeSi(1)).
Broad 13C-NMR signals owing to partially relaxed
13C–11B coupling across one bond help to assign the
13C-NMR spectra, together with 29Si and 119/117Sn satel-
lites (in 9). A typical example taking advantage of
13C–Si–C–1H coupling is shown in Fig. 3. Further
assignments are based on 2D 1H/1H COSY and 2D
13C/1H heteronuclear shift correlations, based either on
spectra: Perkin Elmer 983 G spectrometer. NMR mea-
surements: Bruker ARX 250 or DRX 500 [1H-, 11B-,
13C-, 29Si-NMR (refocused INEPT [19] based on
1
2J(29Si,1H)=7 Hz), 119Sn-NMR (inverse gated H de-
coupled or by refocused INEPT [19] 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
n
1J(13C,1H) and J(13C,1H) (n\1).
J(29Si)=19.867184
MHz],
J(11B)=32.083971 MHz], and Me4Sn [l119Sn=0 for J
119Sn)=37.290665 MHz].
BF3OEt2
[l11B=0;
2.4. Conclusions
(
1,1-Organoboration of polyynes appears to be a
promising method for the synthesis of novel fused
heterocyclic compounds, as shown here in the case of
triynes for the first time. The 1,6-dihydro-1,6-disilapen-
talene derivatives should be useful in further transfor-
mations. Their synthesis can be improved and the
substitution pattern can be modified by developing
stepwise procedures, taking advantage of the results
presented in this work.
3.1. Bis(dimethylsilyl)ethyne 1
A slow stream of acetylene was bubbled into a
solution of n-BuLi in hexane (250 ml, 1.6 M) at r.t. for
1 h. The excess of acetylene was removed from the
white suspension thus formed by heating at reflux for
15 min. Then the suspension was cooled to 0°C, and
Me2SiHCl (50 g, 530 mmol) was added dropwise during
1 h. The reaction mixture was heated at 70°C for 12 h,
and insoluble material was filtered off. Fractional distil-
lation gave 10.4 g (37%) of the product 1 as a colourless
liquid (b.p. 95°C /760 Torr). 1H-NMR (C6D6): l1H
(nJ(29Si,1H)) {nJ(1H,1H)}=0.09 (7.3) {3.8} d, 12H,
Me2Si, 4.24 (202.5) {3.8} sept, 2H, HSi; 13C-NMR
(C6D6): l13C (J(29Si,13C))= −3.2 (56.1) Me2Si, 112.8
(78.8, 12.6); 29Si-NMR (C6D6): l29Si= −38.4.
3. Experimental
All compounds were handled in an atmosphere of
dry argon, and carefully dried solvents were used for
syntheses and preparation of the samples for NMR
measurements. Starting materials were either used as
commercial products without further purification
(Me2Si(H)Cl, n-butyl lithium 1.6 M in hexane, Et3B) or
prepared as described (HCꢀCMgBr in THF [16], Ph3B
[17], tri(2-thienyl)borane [18]). Electron impact (EI)
mass spectra: Finnigan MAT 8500 with direct inlet. IR
3.2. Bis(bromodimethylsilyl)ethyne 2(Br)
A solution of Br2 (19.36 g, 6.20 ml, 122.53 mmol) in
CH2Cl2 (25 cm3) was added dropwise to a cooled

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B. Wrackmeyer et al. / Journal of Organometallic Chemistry 562 (1998) 207–215
Fig. 1. Contourplot of the 49.7 MHz 2D 29Si/1H heteronuclear shift correlation of the reaction mixture containing 7d and 8d. The assignment of
the 29Si-NMR signals is indicated. The broad 1H(SiMe2) resonances are due to hindered rotation about the C(3)–B bond.
(10°C) solution of compound 1 (8.70 g, 61.26 mmol) in
CH2Cl2 (50 ml) until colour of Br2 did not disappear.
The reaction mixture was allowed to reach r.t. and
stirring was continued for 1 h. After removing of all
volatile material at 25°C/15 Torr an oily liquid was left.
Fractional distillation of this oil gave 11.55 g (63.5%) of
2(Br) (b.p. 100°C/15 Torr) as a colourless liquid which
solidifies after some time. 1H-NMR (C6D6): l1H
(nJ(29Si,1H))=0.46 (7.3) s, Me2Si); 13C-NMR (C6D6):
l13C (J(29Si,13C))=4.2 (64.1) Me2Si, 111.1 (89.6, 14.8)
CꢀC; 29Si-NMR (C6D6): l29Si= −7.9.
Me2Si; 13C-NMR (C6D6): l13C (J(29Si,13C))=3.2 (66.0)
Me2Si, 111.1 (91.6, 14.8) CꢀC; 29Si-NMR (C6D6):
l29Si= −0.4.
3.4. Bis(ethynyl-dimethylsilyl)ethyne 3
A solution of compound 2 (2.91 g, 9.77 mmol) in
tetrahydrofuran (10 ml) was added dropwise to a
freshly prepared solution of HCꢀCMgBr (29 mmol) in
tetrahydrofuran (75 ml) at 5°C. The reaction mixture
was allowed to attain r.t. and stirred overnight. The
reaction mixture was hydrolysed with an aqueous
NH4Cl solution (80 ml). The aqueous layer was ex-
tracted 10 times with 25 ml portions of pentane. The
pentane extracts were combined, dried over Na2SO4
and filtered. The solvent was removed at 15 Torr at r.t..
A colourless oil was left, identified as 3 (1.2 g, 64%). IR
(hexane): w(CꢀC)=2043 cm−1, w(ꢀC–H)=3278, 3295
cm−1; 1H-NMR (CDCl3): l1H (nJ(29Si,1H))=0.28 (7.5)
s, 12H, Me2Si, 2.42 s, 2H, ꢀCH; 13C-NMR (CDCl3):
l13C (J(29Si,13C))= −0.2 (62.2) MeSi, 110.6 (88.8,
3.3. Bis(chlorodimethylsilyl)ethyne 2(Cl)
A saturated solution of Cl2 in CCl4 (150 ml) was
added dropwise to a cooled solution 0°C) of compound
1 (6.39 g, 45 mmol) in CCl4 (50 ml) until a pale yellow
colour persisted. The reaction mixture was then stirred
at r.t. for 3 h. Fractional distillation gave 4.17 g (44%)
of 2(Cl) as a colourless liquid (b.p. 72°C/15 Torr).
u1H-NMR (C6D6): l1H (nJ(29Si,1H))=0.31 (7.7) s,

B. Wrackmeyer et al. / Journal of Organometallic Chemistry 562 (1998) 207–215
213
Fig. 2. 93.3 MHz 119Sn{1H}-NMR spectrum of 9a recorded by the refocused INEPT pulse sequence based on 2J(119Sn,1H)=52 Hz. The broad
119Sn(2-SnMe3)resonance is the result of partially relaxed scalar 119Sn–CꢀC–11B coupling (see text).
15.0) Si–CꢀC–Si, 94.6 (18.3) ꢀCH, 86.1 (94.3)
ꢀCSiMe2; 29Si-NMR (CDCl3): l29Si= −7.9.
Me3SiCꢀCH (3.5 g; 5 ml; 35.71 mmol) in hexane (40
ml) at 0°C over 20 min. As soon as the white suspen-
sion had reached r.t. a solution of compound 2 (3.70 g,
12.41 mmol) in hexane (20 ml) was added and stirring
was continued for 15 min.. After heating at reflux for 5
h pentane (100 cm3) was added and insoluble material
was filtered off. Removal of all volatile material left a
colourless solid identified as the pure compound 4 (3.87
3.5. Bis(trimethylsilylethynyl-dimethylsilyl)ethyne 4
A solution of n-BuLi in hexane (1.6 M, 17 cm3, 27.2
mmol) was added dropwise to a stirred solution of
g; 93%). IR (hexane):=w(CꢀC)=2113 cm−1
;
1H-
NMR (C6D6): l1H (nJ(29Si,1H)=0.05 (7.2) s, 18H,
Me3Si, 0.24 (7.6) s, 12H, Me2Si; 13C-NMR (C6D6):
l13C (J(29Si,13C))=0.1 (61.0) Me2Si, −0.4 [56.1]
Me3Si, 111.6 (88.6, 14.8) Si–CꢀC–Si, 115.8 (75.8, 14.8)
ꢀCSiMe3, 109.8 (90.6, 11.8) ꢀCSiMe2; 29Si-NMR
(CDCl3): l29Si= −42.7 SiMe2, -18.2 SiMe3. EI MS (70
eV): m/z (%)=334 (40) [M+], 319 (40), 231 (55), 73
(100).
3.6. Bis(trimethylstannylethynyl-dimethylsilyl)ethyne 5
Me3SnNEt2 (0.57 g; 0.44 ml, 2.42 mmol) was added
to a solution of compound 3 (0.23 g; 1.20 mmol) in
hexane (10 ml) at r.t.. The reaction mixture was stirred
for 3 h, and after removal of all volatile material the
pure compound 5 (0.56 g; 90%) was left as colourless
solid. 1H-NMR ([D8]toluene): l1H (nJ(29Si,1H))
[nJ(119Sn,1H)]= −0.01 [59.8] s, 18H, Me3Sn, 0.17 (8.2)
s, 12H, Me2Si. 13C-NMR ([D8]toluene): l13C
Fig. 3. Part of the 125.8 MHz 13C{1H}-NMR spectrum of 7c
recorded by the refocused INEPT pulse sequence based on
3J(13C,Si,C,1H)=1.8 Hz. This selects the 13C(2,5,6a) resonances [29Si
satellites are marked by arrows: 1J(29Si(1), 13C(2))=60.9 Hz;
1J(29Si(2-Si), 13C(2))=43.7 Hz; 1J(29Si(6),13C(5))=60.9 Hz;
1J(29Si(5-Si))=45.4
Hz;
1J(29Si(1),13C(6a))=57.4
Hz;
1J(29Si(6),13C(6a))=57.4 Hz]. The complete assignment rests on cor-
responding 2D 13C/1H and 29Si/1H heteronuclear shift correlations.

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(J(29Si,13C)) [J(119Sn,13C]= −0.3 (61.4) Me2Si, −8.3
[402.2] Me3Sn, 111.3 (88.0, 14.6) [2.0] Si–CꢀC–Si,
115.3 (14.0) [379.9] ꢀCSnMe3, 113.0 (90.3) [60.7]
3.8. Preparation of the 1,6-dihydro-1,6-disilapentalenes
9a and 9c:1,1-organo-boration of 5 with Et3B or
Ph3B (general procedure)
ꢀCSiMe2;
29Si-NMR
([D8]Toluene):
l29Si
[J(119Sn,29Si]= −43.4 [11.4]; 119Sn-NMR ([D8]Toluene)
l119Sn= −74.5.
Et3B (6a) (23 ml, 0.16 mmol) was added in one
portion to a solution of 5 (80 mg; 0.16 mmol) in toluene
(5 ml) and stirred for 3 h. Then the reaction mixture
was allowed to attain r.t.. The 29Si-NMR spectrum
showed the complete conversion of the starting material
to 9a. Removal of all volatile material left 9a as a
colourless oil in quantitative yield. A similar reaction of
the triyne 5 with Ph3B (6c) gave 9c as a colourless solid
contaminated by a small amount of Me3Sn–Ph as the
result of an exchange reaction.
3.7. Preparation of the 1,6-dihydro-1,6-disilapentalene
(7)/silole (8) mixtures:1,1-organoboration of 4 with
BEt3 (6a), B(CH2Ph)3 (6b), BPh3 (6c) or B(2-thienyl)3
(6d). (general procedure)
1
9a: H-NMR: l1H [J(119Sn,1H)]=2.09, 0.95 5H, 4-
To a solution of 4 (94 mg; 2.81 mmol) in toluene
(20 ml) Et3B (6a) (2.19 ml, 15 mmol) was added in
one portion at r.t., and the reaction mixture was
heated at 120°C for 90 h. The progress of the reac-
tion was monitored by 29Si-NMR spectroscopy.
After removal of the solvent and excess of 6a under
high vacuum a residual yellowish oil was left and
identified as a mixture containing 90% of 7a and 10%
of 8a. The mixtures of 7b/8b (120°C for 50 h; yellowish
oil), 7c/8c (120°C for 65 h; white solid), 7d/8d
(120°C for 96 h; white solid) were obtained in the
same way. In the case of 7c/8c, repeated recristallisa-
tion from pentane leads to pure samples of 7c (see Fig.
3).
Et; 1.43, 0.96 10H, BEt2; 0.25, 0.25 12H, Me2Si(1,6);
0.29 [53.2], 0.25 [53.2] 18H, 2,5-Me3Sn.
9c: 1H-NMR: l1H [J(119Sn,1H)]=7.41, 7.08, 6.99
10H, BPh2; 7.25, 7.08, 6.99 5H, 4-Ph); 0.47 6H,
Me2Si(6); 0.34 6H, Me2Si(1); −0.17 [53.5], −0.26
[53.5] 18H, 2,5-Me3Sn.
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. We thank
Professor R. Ko¨ster (Mu¨lheim a.d. Ruhr) for a sample
of tribenzylborane
1
7a: H-NMR: l1H=2.01, 0.88 5H, 4-Et; 1.37, 0.92
10H, BEt2; 0.22, 0.19 12H, Me2Si(1,6); 0.15, 0.11 18H,
2,5-Me3Si.
7b: 1H-NMR: l1H=7.22–6.89 4-CH2Ph and
B(CH2Ph)2; 3.62 2H, 4-CH2; 3.05, 2.71 (2J(1H,1H)=
17.0 Hz) 4H, BCH2; 0.36, 0.27 12H, Me2Si(1,6); 0.33,
0.06 18H, 2,5-Me3Si.
References
7c: 1H-NMR: l1H=7.66, 7.21, 7.12 10H, BPh2; 6.69,
6.68, 6.47 5H, 4-Ph; 0.56 6H, Me2Si(1); 0.48 6H,
Me2Si(6); −0.22 9H, 5-Me3Si; −0.27 9H, 2-Me3Si.
[1] J. Dubac, A. Laporterie, G. Manuel, Chem. Rev. 90 (1990) 215.
[2] R. Ko¨ster, G. Seidel, J. Su¨ß, B. Wrackmeyer, Chem. Ber. 126
(1993) 1107.
[3] B. Wrackmeyer, J. Organomet. Chem. 310 (1986) 151.
[4] (a) L. Killian, B. Wrackmeyer, J. Organomet. Chem. 132 (1977)
213. (b) L. Killian, B. Wrackmeyer, J. Organomet. Chem. 148
(1978) 137. (c) B. Wrackmeyer, J. Organomet. Chem. 364 (1989)
331. (d) B. Wrackmeyer, U. Klaus, W. Milius, E. Klaus, T.
Schaller, J. Organomet. Chem. 517 (1996) 235.
1
7d: H-NMR: l1H=7.62, 7.28, 7.20, 6.77, 6.74 6H,
B(2-thienyl)2; 6.41, 6.18, 5.97 4-(2-thienyl); 0.46 broad,
6H, Me2Si(1); 0.31 broad, 6H, Me2Si(6); −0.12 9H,
5-Me3Si; −0.14 9H, 2-Me3Si.
1
8a: H-NMR: l1H=2.25, 0.88 5H, 4-Et); 1.43, 0.92
10H, BEt2; 0.32, 0.29 12H, Me2Si(1) and 5-SiMe2; 0.08,
[5] B. Wrackmeyer, K. Horchler, J. Organomet. Chem. 399 (1990)
1.
[6] B. Wrackmeyer, Coord. Chem. Rev. 145 (1995) 125–156, and
literature cited therein.
[7] (a) B. Wrackmeyer, K. Horchler von Locquenghien, S. Kundler,
J. Organomet. Chem. 503 (1995) 289. (b) B. Wrackmeyer, S.
Kundler, R. Boese, Chem. Ber. 126 (1993) 1361.
[8] B. Wrackmeyer, K. Horchler, R. Boese, Angew. Chem. 101
(1989) 1563–1565; Angew. Chem. Int. Ed. Engl. 28 (1989)
1500–1501.
[9] R.P. Corriu, J.J.E. Moreau, H. Proet, Organometallics 8 (1989)
2779.
[10] K. Jones, M.F. Lappert, Organomet. Chem. Rev. 1 (1966) 67.
[11] B. Wrackmeyer, J. Su¨ß, unpublished results.
[12] B. Wrackmeyer, G. Kehr, J. Su¨ß, Chem. Ber. 126 (1993) 2221.
0.04 18H, 2-Me3Si and ꢀC–SiMe3.
8b:
1H-NMR:
l1H=7.22–6.89
4-CH2Ph,
B(CH2Ph)2; 3.72 2H, 4-CH2); 2.81, 2.42 (2J(1H,1H)=
15.8 Hz) 4H, BCH2; 0.52 6H, Me2Si(1); 0.28 6H, 5-
Me2Si; 0.22 9H, 2-Me3Si; 0.14 9H, ꢀC–SiMe3.
8c: 1H-NMR: l1H=7.60, 7.15, 7.09 10H, BPh2; 7.08,
6.61, 6.42 5H, 4-Ph; 0.74 6H, Me2Si(1); 0.25 6H, 5-
Me2Si; 0.18 9H, ꢀC–SiMe3; 0.00 9H, 2-Me3Si.
1
8d: H-NMR: l1H=7.75, 7.74, 7.39, 7.29, 6.96, 6.83
6H, B(2-thienyl)2; 6.49, 6.39, 6.22 4-(2-thienyl); 0.67
6H, Me2Si(1); 0.14 6H, 5-Me2Si; 0.13 9H, ꢀC-SiMe3;
−0.03 9H, 2-Me3Si.

B. Wrackmeyer et al. / Journal of Organometallic Chemistry 562 (1998) 207–215
215
[13] H. No¨th, B. Wrackmeyer, Nuclear magnetic resonance spec-
troscopy of boron compounds, in: P. Diehl, E. Fluck, R. Kosfeld
(Eds.), NMR-Basic Principles and Progress, vol. 14, Springer,
Berlin, 1978.
[14] A. Abragam, The Principles of Nuclear Magnetism, Oxford
University Press, Oxford, 1961, Chapter 8.
[16] E.R.H. Jones, L. Skattebol, M. Whiting, Org. Synth. 39 (1959)
56.
[17] R. Ko¨ster, P. Binger, W. Fenzl, Inorg. Synth. 15 (1974) 134.
[18] B. Wrackmeyer, H. No¨th, Chem. Ber. 109 (1976) 1075.
[19] (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) D.
P. Burum, R. R. Ernst, J. Magn. Reson. 39 (1980)163.
[15] B. Wrackmeyer, Polyhedron 5 (1986) 1709.
.
.