[4+2]Cycloadditions of organometallic-substituted siloles with dimethyl acetylenedicarboxylate and tetracyanoethylene

Article abstract of DOI:10.1016/S0022-328X(02)02114-9

1-Sila-2,4-cyclopentadienes (siloles) bearing five organyl groups and a diethylboryl group in 3-position (3), four organyl groups, a trimethylstannyl and a diethylboryl group in 2,4-positions (4), four organyl groups, a diethylboryl group in 3-position and a hydrido function at the silicon atom (5) react by [4+2]cycloaddition with dimethyl acetylenedicarboxylate, MeOC(O)-C≡C-C(O) OMe (1), and tetracycanoethylene, (NC)₂C=C (CN)₂ (2), to give 7-silanorbornadienes (6-8) and 7-silanorbornenes (10-12), respectively. The silole 5 is converted into isomers 8 and 8′, and 12 and 12′, in which the SiMe group in each major isomer (8 and 12) occupies the synposition with respect to the C(2)=C(3) bond. The molecular structure of 10a was determined by X-ray analysis. The 7-silanorbornadiene (7) rearranges into a benzene derivative by formation of an Si-O bond and 1,3-migration of the trimethylstannyl group. All products were characterised in solution by multinuclear magnetic resonance (¹H-, ¹¹B-, ¹³C-, ²⁹Si-, ¹¹⁹Sn-NMR spectroscopy). The geometries of 1,4,7,7-tetramethyl-7-silanorbornadiene, -7-silanobornene, and -7-silanorbornane were optimised by ab initio MO calculations (RHF/6-311+G(d,p) and chemical shifts δ²⁹Si were calculated (GIAO-RHF/6-311+G(d,p)).

Full text of DOI:10.1016/S0022-328X(02)02114-9

Journal of Organometallic Chemistry 665 (2003) 196ꢁ204
/
www.elsevier.com/locate/jorganchem
[4ꢀ
/
2]Cycloadditions of organometallic-substituted siloles with
dimethyl acetylenedicarboxylate and tetracyanoethylene
Bernd Wrackmeyer a,*, Wolfgang Milius a, Moazzam H. Bhatti a,b, Saqib Ali b
a Laboratorium fur Anorganische Chemie der Universitat, Bayreuth D-95440, Germany
¨
¨
b Department of Chemistry, Quaid-I-Azam University, Islamabad, Pakistan
Received 9 April 2002; accepted 20 August 2002
Abstract
1-Sila-2,4-cyclopentadienes (siloles) bearing five organyl groups and a diethylboryl group in 3-position (3), four organyl groups, a
trimethylstannyl and a diethylboryl group in 2,4-positions (4), four organyl groups, a diethylboryl group in 3-position and a hydrido
function at the silicon atom (5) react by [4ꢀ
and tetracycanoethylene, (NC)2CÄC(CN)2 (2), to give 7-silanorbornadienes (6ꢁ
silole 5 is converted into isomers 8 and 8?, and 12 and 12?, in which the SiMe group in each major isomer (8 and 12) occupies the syn-
position with respect to the C(2)ÄC(3) bond. The molecular structure of 10a was determined by X-ray analysis. The 7-
O bond and 1,3-migration of the trimethylstannyl
/
2]cycloaddition with dimethyl acetylenedicarboxylate, MeOC(O)Ã
/
CÅ
/
CÃ
/
C(O)OMe (1),
/
/
8) and 7-silanorbornenes (10ꢁ12), respectively. The
/
/
silanorbornadiene (7) rearranges into a benzene derivative by formation of an SiÃ
/
group. All products were characterised in solution by multinuclear magnetic resonance (1H-, 11B-, 13C-, 29Si-, 119Sn-NMR
spectroscopy). The geometries of 1,4,7,7-tetramethyl-7-silanorbornadiene, -7-silanobornene, and -7-silanorbornane were optimised
by ab initio MO calculations (RHF/6-311ꢀ
/
G(d,p) and chemical shifts d29Si were calculated (GIAO-RHF/6-311ꢀ
G(d,p)).
/
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Siloles; Cycloaddition; NMR; Multinuclear; X-ray
1. Introduction
products. In the case of the siloles 5, the silicon atom
bears a methyl group and a hydrido function, and
1-Sila-2,4-cyclopentadienes (siloles) are reactive
therefore, two different isomers can be formed by [4ꢀ
/
2]cycloaddition.
dienes [1] which readily undergo [4ꢀ2]cycloadditions
/
with activated alkynes or alkenes to give 7-silanorbor-
nadiene or 7-silanorbornene derivatives, respectively.
Since 1,1-organoboration of bis(1-alkynyl)silanes has
opened a convenient access to organometallic-substi-
2. Results and discussion
tuted siloles [2ꢁ
of such siloles towards the dienophiles dimethyl acet-
ylenedicarboxylate, MeOC(O)ÃCÅCÃC(O)OMe (1),
and tetracyanoethylene, (NC)2CÄC(CN)2 (2). The si-
loles 3ꢁ5 (Scheme 1) were used. In comparison with 3,
where the Et2B group is the sole organometallic
substituent, the silole 4 bears an additional trimethyl-
stannyl group in 2-position, and this may have an
/
4], we have now explored the reactivity
2.1. Reactions of the siloles 3ꢁ
C(O)OMe (1)
/
5 with MeO(O)CÃ
/
CÅ
/
CÃ
/
/
/
/
/
All siloles 3ꢁ
(1) at room temperature in benzene solution within
minutes to give [4ꢀ2]cycloaddition products, the 7-
silanorbornadiene derivatives 6ꢁ8, in quantitative yield
/
5 react with MeO(O)CÃ
/
CÅ
/
CÃ/C(O)OMe
/
/
/
(Scheme 1A). These compounds are colourless, air- and
moisture-sensitive oils which become waxy solids after
some time of storage. The proposed structures are based
influence on the stability of its [4ꢀ2]cycloaddition
/
1
on the H (experimental), 11B-, 13C-, 29Si- and 119Sn-
* Corresponding author. Tel.: ꢀ
2157
E-mail address: b.wrack@uni-bayreuth.de (B. Wrackmeyer).
/
49-921-55-2542; fax: ꢀ49-921-55-
/
NMR data (Table 1). In the case of 5, a mixture
containing the two isomers 8 and 8? in an ca. 8:1 molar
0022-328X/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 2 1 1 4 - 9

B. Wrackmeyer et al. / Journal of Organometallic Chemistry 665 (2003) 196ꢁ
/
204
197
Scheme 1.
ratio was obtained (see Fig. 1), the major isomer with
the SiMe group in syn-position with respect to the C(2)Ä
C(3) bond, in agreement with an approach of the
dienophile to the less hindered side of the silole 5 [5].
/
Table 1
11B-, 13C- and 29Si-NMR data
a,b
of the 7-silanorbornadienes (5ꢁ8)
/
c
6a
6b
7
8
8?
d
d
d
d
d
d
d
13C(1)
13C(2)
13C(3)
13C(4)
13C(5)
13C(6)
13C(SiMe)
57.0 (50.2)
150.2 (4.5)
148.9 (br)
56.9 (49.7)
145.3 (3.4)
145.6 (3.4)
62.7 (46.9)
149.4
49.2 (39.1) [402.2]
151.8 [2.5]
150.2 (br)
55.9 (51.0)
150.5 (4.9)
149.2 (br)
56.4 (51.3)
144.9
56.0
149.7
148.6 (br)
56.5
146.8 (br)
65.4 (46.9)
140.4
69.3 (43.4) [39.1]
140.2 [2.3]
155.3 [36.2]
145.0
145.6
147.9
145.7 (3.7)
ꢂ2.4 (43.1), ꢂ
/
/
1.7 (45.6)
ꢂ
/
4.2 (45.5), ꢂ
/2.5 (47.9)
ꢂ
/
2.4 (43.5), ꢂ
/
1.3
ꢂ
/
3.6 (39.7)
ꢂ/3.4
(48.1)
21.4 (br), 9.7
d
d
d
13C(Et2B)
13C(Et)
21.8 (br) 9.3
23.6, 15.5
21.2 (br), 9.7
24.0, 15.0
165.9, 167.7, 51.3, 51.5
22.0 (br), 9.4
23.4, 15.6
166.9 [9.5], 168.1 [6.3], 166.3, 166.6, 51.23,
21.8 (br) 9.3
23.5, 15.3
28.8 [22.1], 15.3
13C(CO2Me) 166.4, 166.8, 51.15,
51.18
166.2, 166.4, 51.18,
51.21
51.3, 51.9
5.5 [353.9] 138.4,
51.25
33.6, 33.3, 28.6, 26.5,
23.8, 23.7, 14.1, 14.1
d
13C(1-R, 4-
33.4, 33.5, 26.7, 29.2,
23.9, 24.0, 14.2, 14.2
139.0, 140.1, 130.3, 132.3,
127.2, 128.7, 125.6, 126.7
ꢂ
/
33.5, 33.4, 29.2, 26.2,
23.9, 23.8, 13.9, 13.9
50.6
R)
128.8, 127.9, 126.2
85.1 [14.7]
89.0
d
d
29Si
11B
77.1
88.0
81.3
85.0
52.8
83.0
83.0
a
See Scheme 1 for numbering; for better comparison, numbering in Tables, Figures and Schemes does not follow nomenclature in all cases.
b
Coupling constants J(29Si,13C) are given in parentheses, and J(119Sn,13C) and 2J(119Sn,29Si) in brackets (9
/
0.2 Hz); the broad 13C-NMR signals
for carbon atoms linked to boron are indicated by (br).
119Sn ꢂ
33.5.
c
d
/

198
B. Wrackmeyer et al. / Journal of Organometallic Chemistry 665 (2003) 196ꢁ204
/
Fig. 1. 29Si{1H}-NMR (49.7 MHz) spectrum of the mixture of isomers 8 and 8? (C6D6, 239
/
1 8C), showing the 13C satellite signals for the major
isomer 8, corresponding to 29Si satellites in 13C-NMR spectra (see Table 1).
The assignment of the 13C-NMR spectra is greatly
aided by the observation of 29Si satellites for
1J(29Si,13C), and in turn the 29Si-NMR spectra can be
recorded to show the corresponding 13C satellites (see
Figs. 1 and 2). In the case of 7, 117/119Sn satellites in the
13C-NMR spectra and 13C satellites in the 119Sn-NMR
spectra (Fig. 3) provide additional information. The
unique electronic structure of 7-silanorbornadienes [6] is
reflected by typical 29Si nuclear deshielding [7,8] when
compared with other tetraorganosilanes [9]. The diag-
nostic value of 11B-NMR spectra is low in monitoring
the reactions of the siloles with the dienophiles. All
Fig. 2. 29Si{1H}-NMR (49.7 MHz) spectrum (recorded by using the refocused INEPT pulse sequence) of the 7-silanorbornadiene 7, showing 13C and
117/119Sn satellites (see Table 1 for 13C-NMR data).

B. Wrackmeyer et al. / Journal of Organometallic Chemistry 665 (2003) 196ꢁ
/
204
199
Fig. 3. 119Sn{1H}-NMR (93.3 MHz) spectrum (recorded by using the refocused INEPT pulse sequence) of the 7-silanorbornadiene 7 (C6D6, 239
/
1 8C), showing 13C and 29Si satellites (see Table 1 for 13C-NMR data).
products give rise to a broad 11B-NMR signal at d11B
several months. Their NMR spectra (1H-NMR in
experimental part; 13C-, 11B-, 29Si-, 119Sn-NMR in Table
3) are conclusive with respect to the 7-silanorbornene
structure in solution (see Figs. 4 and 5 for typical 13C-
NMR spectra), and the molecular structure of 10a in the
solid state could be determined by X-ray analysis (vide
infra). Again, in the case of 5, isomers 12 and 12?(molar
ratio ca. 4:1) are obtained (see Fig. 5), in which the SiMe
8693, in the same region as the siloles, typical of
/
triorganoboranes with insignificant CB(pp)p interac-
tions [10], since the CCB plane of the Et2B group is,
on average, oriented perpendicular to the plane BÃ
/
C(2)ÄC(3).
/
2.2. Isomerisation of the 7-silanorbornadiene derivative 7
into a benzene derivative 9
group in 12 is in syn-position with respect to the C(2)Ä
/
C(3) bond, as confirmed by 1H/1H NOE difference
experiments [irradiation of 1H(SiMe) transition and
observation of NOE effects on 1H(Et) and 1H(BEt2)
resonances]. The nuclear magnetic shielding of 29Si in
the 7-silanorbornenes is still reduced when compared
with other tetraorganosilanes [9]; however, the missing
When the compound 7 was stored either in solution or
in pure state, rearrangements took place within several
days, and the new set of NMR data (Table 2) indicates
that a benzene derivative 9 was formed (Scheme 2). We
propose that the labile SnÃ
the migration of the SnMe3 group is accompanied by
formation of the SiÃO bond leading selectively to 9.
/C bond is responsible, and
CÄ
/
C bond in the framework leads to increased 29Si
nuclear shielding in comparison with the 7-silanorbor-
nadienes.
/
This is related to the isomerisation process proposed for
other 7-silanorbornadienes [11] which finally ends by
oxidation to give benzene derivatives and (Me2SiO)n.
This type of isomerisation was not observed in the case
of the other products 6 or 8.
2.4. Ab initio MO calculations of 1,4,7,7-tetramethyl-7-
silanorbornadiene, -7-silanorbornene, and -7-
silanorbornane
2.3. Reactions of the siloles 3ꢁ
(2)
/
5 with (NC)2CÄ
/
C(CN)2
The calculated geometries [12] of the 7-sila-norborna-
diene (13), 7-silanorbornene (14), and 7-silanorbornane
(15) (Table 4) are in agreement with expectations and
experimental parameters if available. The calculated
Similar to the behaviour of 1, there is also a smooth
reaction of 3ꢁ5 with 2, and the 7-silanorbornene
derivatives 10ꢁ12 (Scheme 1B) are formed without
side products. The compounds 10ꢁ12 are waxy or
/
[12ꢁ
14] 29Si chemical shifts (Table 4) follow closely the
/
/
trend of experimental data, the 29Si nucleus in the 7-
silanorbornadiene being most deshielded. The calculated
nuclear shielding tensors show that deshielding contri-
butions in 13 arise mainly from the magnetic shielding
/
crystalline (10a), colourless, air- and moisture-sensitive
solids which can be stored in the dark under argon for

200
B. Wrackmeyer et al. / Journal of Organometallic Chemistry 665 (2003) 196ꢁ204
/
Table 2
13C-, 29Si- and 119Sn-NMR data
a,b
of the benzene derivative 9
13C(3) 13C(4)
d
13C(1)
d
13C(2)
d
d
d
13C(5)
d
13C(6)
d
29Si
d
119Sn
133.4 (68.2) [10.6]
141.5 [7.2]
147.0 (br)
147.1 [5.8]
151.2 [38.6]
126.1 [7.5]
6-C-SnMe3, 115.6
170.5 [2.1], 51.4 [655.7], 50.6 (OMe), [39.1],
7.0 (SnMe3), [320.3]
21.8 [11.2]
ꢂ
/
6.1 [11.2]
1-SiMe2, 1.3 (59.3), 2-Et, 31.2, 17.1 3-Bet2, 22.0 (br), 4-Ph, 141.8, 129.1, 5-CO2Me,
1.5 (59.6)
23.6 (br), 9.7, 9.3 128.2, 127.8
ꢂ/
a
See formula 9 in Scheme 2 for numbering.
b
Coupling constants J(29Si,13C) are given in parentheses, and J(119Sn,13C) and 3J(119Sn,29Si) in brackets (9
/
0.2 Hz); the broad 13C-NMR signals
for carbon atoms linked to boron are indicated by (br).
Scheme 2.
Table 3
11B-, 13C- and 29Si-NMR data
a,b
of the 7-silanorbornenes 10ꢁ12
/
c
10a
10b
11
12
12?
d
d
d
d
d
d
d
d
d
d
13C(1)
54.9 (49.2)
147.6
59.0 (48.9)
147.2
44.3 (36.5) [245.4]
150.0 [5.4]
154.2 (br)
55.57 (51.2)
147.6
55.1
148.6
13C(2)
13C(3)
152.1 (br)
55.3 (49.7)
52.8
150.4 (br)
59.1 (48.1)
52.0
150.4 (br)
55.63 (50.1)
53.2 (9.4)
54.1 (9.1)
152.1 (br)
55.3
53.7
13C(4)
62.0 (45.9) [28.6]
53.6
56.5 (11.6) [30.2]
13C(5)
13C(6)
53.9
55.6
53.8
13C(SiMe)
13C(Et2B)
13C(Et)
13C(CN)
ꢂ
/
4.2 (62.1), 2.1 (40.8)
ꢂ
/
3.1 (62.6), 4.5 (41.4)
ꢂ
/
4.7 (62.0), 5.3 (40.8)
ꢂ
/
8.7 (61.1)
0.6 (38.4)
22.4 (br) 9.5
23.6, 15.7
21.5 (br) 9.0
23.6, 15.5
22.0 (br), 8.8
25.9, 13.1
212.0 (br), 9.1
30.4 [18.0], 14.4
21.9 (br), 9.1
23.9, 15.6
113.8, 113.0, 112.9, 112.7 113.6, 113.1, 111.41, 111.37 114.8 [6.5], 114.5,
113.7 [6.3], 112.4
113.5, 113.2, 113.1, 112.8 113.5, 112.8, 112.52,
112.50
31.94, 31.88, 29.8, 27.9, 32.8, 32.2, 29.2, 27.3,
d
13C (1-R, 4- 31.9, 31.7, 29.6, 27.9,
134.2, 133.2, 131.8, 129.8,
23.39, 23.35, 13.77, 13.71 129.7, 129.5, 129.2, 129.1
ꢂ
/
6.3 [349.4], 135.3,
R)
129.8, 129.7, 129.4
41.6 [3.0]
89.0
23.4, 23.3, 13.72, 13.70
23.2, 23.0, 13.82, 13.75
d
d
29Si
11B
33.6
85.0
38.4
89.0
14.7
84.0
11.5
84.0
a
See Scheme 3 for numbering; for better comparison, numbering in Tables, Figures and Schemes does not follow nomenclature in all cases.
b
Coupling constants J(29Si,13C) are given in parentheses, and J(119Sn,13C) and 2J(119Sn,29Si) in brackets (9
/
0.2 Hz); the broad 13C-NMR signals
for carbon atoms linked to boron are indicated by (br).
c
d
119Sn 1.1.

B. Wrackmeyer et al. / Journal of Organometallic Chemistry 665 (2003) 196ꢁ
/
204
201
Fig. 4. 13C{1H}-NMR (62.9 MHz) spectrum of 11 (C6D6, 2391 8C), showing the 13C signals in the range for the saturated ring carbon atoms 1, 4, 5,
/
and 6 with 117/119Sn and 29Si satellites.
tensor in the z-axis which should pass through the
silicon atom and the middle of the plane of the four
or 7-germanorbornenes [16a]. Typical are the elongated
SiÃC(bridgehead) bonds (191.7(2), 191.8(3) pm), when
compared with the SiÃC(Me) distances (184.5(3),
185.9(3) pm), and the small (c.f. the angle C(1)ÃC(7)Ã
C(4)ꢃ948 in norbornadiene [16b]) endocyclic bond
/
olefinic carbon atoms. This indicates that the CÄ
/
C and
/
SiÃC bonds are involved in the deshielding.
/
/
/
/
angle at the silicon atom (82.32(11)8). The six-membered
ring is folded at the line connecting the bridgehead
carbon atoms (114.88), and the CCB plane of the BEt2
2.5. X-ray structural analysis of the 7-silanorbornene
derivative (10a)
group is twisted by 60.78 against the BÃ
/
CÄ
/
C plane. The
The molecular structure of 10a is shown in Fig. 6, and
selected bond lengths and angles are given in the legend.
The structural parameters are comparable with other 7-
silanorbornadiene and 7-silanorbornene derivatives [15]
angles CCB in the BEt2 group are markedly wider, by
almost 108, than the expected tetrahedral angle, appar-
ently a common feature of ethylboron compounds [17].
Fig. 5. 13C{1H}-NMR (62.9 MHz) spectrum of the mixture of isomers 12 and 12? (C6D6, 239
/
1 8C), showing the 13C signals in the range for the
saturated ring carbon atoms 1, 4, 5, and 6 with 29Si satellites for the major isomer 12.

202
B. Wrackmeyer et al. / Journal of Organometallic Chemistry 665 (2003) 196ꢁ204
/
Table 4
Calculated optimised a geometries [pm, 8] b and chemical shifts d29Si c,d of 1,4,7,7-tetramethyl-7-silanorbornadiene (13), -7-silanorbornene (14) and -
7-silanorbornane (15)
SiÃ
/
C(1,4)
SiÃ/C(Me)
CÃ/C
CÃ/C
C(1)SiC(4)
C(Me)SiC(Me)
d
29Si
13 194.1
14 191.9
15 190.9
188.7
188.4, 189.0
188.7
132.5 (2ꢁ
132.8 (CÄ
155.9 (2ꢁ3)
/
3)
152.7 (1ꢁ
152.1 (1ꢁ
154.9 (1ꢁ
/
2)
80.5
82.1
83.3
106.6
107.6
108.3
77.8
34.9
12.0
/C), 155.6 (5ꢁ
/6)
/
2), 156.2 (3ꢁ4)
2)
/
/
/
a
Computation of vibrational frequencies indicates that the structures represent potential energy minima.
b
c
RHF/6-311ꢀ
GIAO-RHF/6-311ꢀ
0.
Magnetic shielding tensors (note that s and d have opposite signs): 13: s(xx)ꢃ
366.2, s(zz)ꢃ333.5; 15: s(xx)ꢃ399.4, s(yy)ꢃ380.4, s(zz) 374.3.
/
G** [12ꢁ
/
14].
/
G** [13,14]; calculated isotropic shielding s(29Si)ꢃ
/
1/3[s(xx)ꢀ
/
s(yy)ꢀ
/
s(zz)] with s(xx)ꢃ
/
s(yy)ꢃ
/
s(zz)ꢃ
/
396.7 in
SiMe4; set to d29Siꢃ
/
d
/
388.7, s(yy)ꢃ
/
366.9, s(zz)ꢃ
/
200.6; 14: s(xx)ꢃ
/
385.9, s(yy)ꢃ
/
/
/
/
of which the small endocyclic bond angle C(1)SiC(4)
(82.32(11)8) is particularly noteworthy.
4. Experimental
4.1. General
The preparation and handling of all compounds were
carried out in an atmosphere of dry argon, and carefully
dried solvents and oven-dried glassware were used
throughout. Starting materials were commercially avail-
able (1 and 2) or were prepared as described (siloles 3
[2a], 4 [3a] and 5 [4]). NMR measurements in C6D6 with
Fig. 6. Molecular strucrure of the 7-silanorbornene 10a (hydrogen
atoms are omitted for clarity). Selected bond lengths [pm] and angles
samples in 5 mm tubes at 2391 8C: Bruker ARX 250
/
and Bruker DRX 500: H-, 11B-, 13C-NMR and 29Si-,
1
119Sn-NMR (refocused INEPT [18] based on 1J(29Si,1H)
[8]: SiÃ
184.5(3), C(1)Ã
C(2)ÃC(3) 153.0(4), C(3)Ã
158.8(4), BÃC(7) 155.9(4), BÃ
C(3)ÃC(13) 153.2(4), C(4)ÃC(17) 148.0(4), C(4)Ã
C(5)ÃC(19) 148.8(4), C(5)ÃC(20) 148.2(3), C(6)ÃC(21) 153.2(4), CÃ
N 113.5(3) (mean value); C(3)ÃSiÃC(6) 82.32(11), C(25)ÃSiÃC(26)
108.9(2), C(3)ÃSiÃC(25) 117.6 (2), C(3)ÃSiÃC(26) 113.9(1), C(6)ÃSiÃ
C(25) 117.6(1), C(8)ÃC(7)ÃB 119.0(3), C(10)ÃC(9)ÃB 119.6(3), C(13)Ã
C(3)ÃSi 122.8(2), C(21)ÃC(6)ÃSi 121.8(2).
/
C(3) 191.8(3), SiÃ
C(2) 135.1(3), C(1)Ã
C(4) 159.3(4), C(5)Ã
C(9) 157.6(5), C(2)Ã
C(18) 147.7(4),
/
C(6) 191.7(2), SiÃ
C(6) 154.2(3), C(4)Ã
C(6) 158.3(4), C(1)Ã
C(11) 150.8(4),
/
C(25) 185.9(3), SiÃ
C(5) 160.3(4),
B)
/
C(26)
/
/
/
2
2
ca. 185 Hz, J(29Si,1HMe) ca. 7 Hz, and J(119Sn,1HMe
)
/
/
/
/
ca. 52 Hz); chemical shifts are given with respect to
Me4Si [d1H (C6D5H)ꢃ7.15; d13C (C6D6)ꢃ
128.0;
d29Siꢃ for J(29Si)ꢃ
19.867184 MHz]; external
Me4Sn [d119Snꢃ0 for J(119Sn)ꢃ
37.290665 MHz]; ex-
ternal BF3Ã 32.083971
OEt2 [d11Bꢃ for J(11B)ꢃ
MHz].
/
/
/
/
/
/
/
/
/
/
/
/
/0
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/0
/
/
/
/
/
/
/
/
/
3. Conclusions
4.2. Reaction of the siloles 3ꢁ5 with dimethyl
/
acetylenedicarboxylate 1 and tetracycanoethylene 2
(general procedure)
It appears that all types of siloles, accessible by 1,1-
organoboration of bis(1-alkynyl)silanes, undergo
smoothly [4ꢀ2]cycloadditions with suitable dienophiles,
/
The siloles (3 mmol) were dissolved in C6H6 (5 ml),
and equimolar amounts of 1 or 2 as solutions in C6H6
(10 ml) were added at room temperature (r.t.). The
usually activated alkynes and alkenes. Acetylene itself
does not react, and also reactions with propyne, 1-
hexyne, 3-hexyne, and ethynyl(trimethyl)silane (all be-
tween 20 and 80 8C) could not be induced. The stability
mixtures were kept stirring for 12ꢁ
materials were removed in vacuo. The residues were
dissolved in hexane and kept at low temperature (ꢂ70
to ꢂ90 8C) in order to obtain crystalline material. This
/
24 h; then volatile
of the 7-silanorbornadienes 5ꢁ8 is remarkable, although
/
/
in the case of 7 slow rearrangement to a new benzene
derivative 9 occurred. The molar ratios 8:1 and 4:1 of
the isomers 8/8?and 12/12?, respectively, indicate that the
/
was successful in the case of 10a. In all other cases,
colourless, or yellowish (7), air-sensitive oils were
isolated after hexane had been removed in vacuo; these
oils turned into waxy solids after several days of storage.
approach of MeO2CÃ
more stereoselective than that of (NC)2CÄ
molecular structure of 10a shows the expected features,
/
CÅ
/
CÃ
/
CO2Me to the silole ring is
/
C(CN)2. The
6a: 1H-NMR (250 MHz): d1Hꢃ
0.18, 0.23 (s, s, 3H, 3H,
/

B. Wrackmeyer et al. / Journal of Organometallic Chemistry 665 (2003) 196ꢁ
/
204
203
SiMe2), 3.43, 3.43 (s, s, 3H, 3H, OMe), overlapping
multiplets for 1-Bu, 4-Bu, 2-Et and 3-Et2B groups. 6b:
(lꢃ71.073 pm, graphite monochromator) at r.t. The
/
hydrogen atoms are in calculated positions. All non-
hydrogen atoms were refined with anisotropic tempera-
ture factors. The hydrogen atoms were refined applying
the riding model with fixed isotropic temperature
factors.
1H-NMR (250 MHz): d1Hꢃ
0.26, 0.39 (s, s, 3H, 3H,
SiMe2), 1.45, 1.30, 1.04 (m, m, t, 2H, 2H, 6H, BEt2),
2.16, 2.03, 0.66 (m, m, t, 1H, 1H, 3H, 2-Et), 3.31, 3.33 (s,
/
s, 3H. 3H, OMe), 6.88ꢁ
/
7.10, 7.20ꢁ
/
7.30 (m,m, 10H, 1-
0.36, 0.43 (s, s,
3H, 3H, SiMe2), 0.46 (s, J(119Sn,1HMe)ꢃ
53.0 Hz, 9H,
Ph,4-Ph). 7: 1H-NMR (250 MHz): d1Hꢃ
/
10a: C26H39BN4Si, colourless prism: 0.25ꢄ
0.16 mm3; it crystallises in the monoclinic space group
P2(1)/c; aꢃ 9.3308(7), bꢃ 13.4994(12), cꢃ21.9530(18)
96.316(5)8, Zꢃ4, mꢃ
0.105 mmꢂ1; 6250 reflec-
tions collected in the range 2ꢁ258 in q, 4795: reflections
independent (I ꢀ2s(I)); full-matrix least-squares refine-
/
0.20ꢄ
/
2
/
SnMe3), 1.44, 1.27, 1.10 (m, m, t, 2H, 2H, 6H, BEt2),
/
/
/
˚
2.49, 2.42, 1.00 (m, m, t, 1H, 1H, 3H, 2-Et), 3.41, 3.45 (s,
A, bꢃ
/
/
/
s, 3H, 3H, OMe), 7.00ꢁ
(250 MHz): d1Hꢃ0.24 (d, 3J(H,H)ꢃ
SiMe), 3.42, 3.43 (s, s, 3H, 3H, OMe), 4.72 (q,
3J(H,H)ꢃ2.5 Hz, 1J(29Si,1H,)ꢃ
197.1 Hz, 1H, SiH),
overlapping multiplets for 1-Bu, 4-Bu, 2-Et, and 3-BEt2
groups. 8?: 1H-NMR (250 MHz): d1Hꢃ
0.27 (d,
3J(H,H)ꢃ
2.6 Hz, 3H, SiMe), 3.30, 3.30(s, 6H, OMe),
4.76(q, 3J(H,H)ꢃ
2.6 Hz, 1H, SiH), and overlapping
multiplets for 1-Bu, 4-Bu, 2-Et, and 3-BEt2 groups. 10a
/
7.10 (m, 5H, 4-Ph). 8: 1H-NMR
/
/
/2.5 Hz, 3H,
/
ment with 290 parameters, R1/wR2-values 0.0604/0.1645,
/
/
no absorption correction; max./min. residual electron
0.202ꢄ .
10ꢂ6 e pmꢂ3
density 0.415/ꢂ
/
/
/
/
/
5. Supplementary material
1
(m.p. 95ꢁ
/
97 8C); H-NMR (250 MHz): d1Hꢃ
/
ꢂ0.12,
/
Crystallographic data (excluding structure factors) for
the structure reported in this paper have been deposited
with the Cambridge Crystallographic Data Centre as
supplementary publication no. CCDC-183250 (10a).
Copies of the data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge CB2
0.48 (s, s, 3H, 3H, SiMe2), overlapping multiplets for 1-
1
Bu, 4-Bu, 2-Et, and 3-BEt2 groups. 10b: H-NMR (250
MHz): d1Hꢃ
/
0.63, 1.02 (s, s, 3H, 3H, SiMe2), 1.16, 0.93
(m, t, 4H, 6H, BEt2), 2.18, 2.04, 0.49 (m, m, t, 1H, 1H,
3H, 2-Et), 7.30ꢁ
7.60 (m, 10H, 1-Ph, 4-Ph). 11: 1H-NMR
(250 MHz): d1Hꢃ
0.07, 0.76 (s, s, 3H, 3H, SiMe2), 0.38
(s, J(119Sn,1HMe)ꢃ
54.7 Hz, 9H, 1-SnMe3), 1.06, 0.83
(m, t, 4H, 6H, BEt2), 2.16, 1.81, 0.88 (m, m, t, 1H, 1H,
/
/
1EZ, UK [fax: ꢀ44-1223-336033; e-mail: deposit@
/
2
/
ccdc.cam.ac.uk; www: http://www.ccdc.cam.ac.uk].
1
3H, 2-Et), 7.00ꢁ
/
7.30 (m, 5H, 4-Ph). 12: H-NMR (250
2.7 Hz, 3H, SiMe),
2.7 Hz, J(29Si,1H)ꢃ
189.6 Hz, 1H,
SiH), overlapping multiplets for 1-Bu, 4-Bu, 2-Et and 3-
MHz): d1Hꢃ0.08 (d, 3J(H,H)ꢃ
/
/
3
1
Acknowledgements
4.98 (q, J(H,H)ꢃ
/
/
BEt2 groups. 12?: H-NMR (250 MHz): d1Hꢃ
/
0ꢁ
/
41 (d,
1
Support of this work by Volkswagen-Stiftung,
Deutsche Forschungsgemeinschaft, Fonds der Che-
mischen Industrie (B.W.), DAAD (M.H.B.), and the
Alexander-von-Humboldt Stiftung (S.A.) is gratefully
acknowledged.
3J(H,H)ꢃ3.7 Hz, 3H, SiMe), 3.67 (q, 3J(H,H)ꢃ
Hz, 1H, SiH), overlapping multiplets for 1-Bu, 4-Bu, 2-
Et, and 3-BEt2 groups.
/
/3.7
4.3. Rearrangement of 7 to 9
A solution of 7 (0.1 g, 0.17 mmol) in C6H6 (1 ml) was
kept for 5 days at r.t., and then NMR spectra indicated
complete rearrangement. After removing of the solvent
in vacuo, a yellowish oil was left which turned into a
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