Dissociation of the disilatricyclic diallylic dianion [(C 4Ph4SiMe)2]-2 to the silole anion [MeSiC4Ph4]- by halide ion coordination or halide ion nucleophilic substitution at the silicon atom

Article abstract of DOI:10.3390/molecules16108451

The reductive cleavage of the Si-Si bond in 1,1-bis(1-methyl-2,3,4,5- tetraphenyl-1-silacyclopentadiene) [(C₄Ph₄SiMe) ₂] (1) with either Li or Na in THF gives the silole anion [MeSiC ₄Ph₄]^- (2). The head-to-tail dimerization of the silole anion 2 gives crystals of the disilatricyclic diallylic dianion [(C₄Ph₄SiMe)₂]^-2 (3). The derivatization of 3 (crystals) with bromoethane (gas) under reduced pressure provides [(MeSiC₄Ph₄Et)₂] (4) quantitatively. The reverse addition of 3 in THF to trimethylsilyl chloride, hydrogen chloride, and bromoethane in THF gives 1-methyl-1-trimethylsilyl-1-silole [Me ₃SiMeSiC₄Ph₄] (6), 1-methyl-2,3,4,5- tetraphenyl-1-silacyclo-3-pentenyl-1-methyl-1-silole [C₄Ph ₄H₂SiMe-MeSiC₄Ph₄] (7), and 1-methyl-2,5-diethyl-2,3,4,5-tetraphenyl-1-silacyclo-3-pentenyl-1-methyl-1- silole [C₄Ph₄Et₂SiMe-MeSiC₄Ph ₄] (8), respectively. The reaction products unambiguously suggest that the silole anion [MeSiC₄Ph₄]^- is generated by coordination of the chloride ion at the silicon atom in 3 or by the nucleophilic substitution of either chloride or bromide ion at one of two silicon atoms in 3. The quenching reaction of 3 dissolved in THF with water gives 1,2,3,4-tetraphenyl-2-butene, the disiloxane of 1-methyl-2,3,4,5- tetraphenyl-1-silacyclo-3-pentenyl [O(MeSiC₄Ph₄) ₂] (10) and methyl silicate.

Full text of DOI:10.3390/molecules16108451

Molecules 2011, 16, 8451-8462; doi:10.3390/molecules16108451
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Dissociation of the Disilatricyclic Diallylic Dianion
[(C4Ph4SiMe)2]−2 to the Silole Anion [MeSiC4Ph4]− by Halide Ion
Coordination or Halide Ion Nucleophilic Substitution at the
Silicon Atom
Jang-Hwan Hong
Department of Nanopolymer Material Engineering, Pai Chai University, 155-40 Baejae-ro (Doma-
Dong), Seo-Gu, Daejon, 302-735, South Korea; E-Mail: jhong@pcu.ac.kr; Tel.: +82-42-520-5755;
Fax: +82-42-520-5798
Received: 26 August 2011; in revised form: 1 October 2011 / Accepted: 1 October 2011 /
Published: 10 October 2011
Abstract: The reductive cleavage of the Si-Si bond in 1,1-bis(1-methyl-2,3,4,5-
tetraphenyl-1-silacyclopentadiene) [(C4Ph4SiMe)2] (1) with either Li or Na in THF gives
the silole anion [MeSiC4Ph4]− (2). The head-to-tail dimerization of the silole anion 2 gives
crystals of the disilatricyclic diallylic dianion [(C4Ph4SiMe)2]−2 (3). The derivatization of 3
(crystals) with bromoethane (gas) under reduced pressure provides [(MeSiC4Ph4Et)2] (4)
quantitatively. The reverse addition of 3 in THF to trimethylsilyl chloride, hydrogen
chloride, and bromoethane in THF gives 1-methyl-1-trimethylsilyl-1-silole
[Me3SiMeSiC4Ph4] (6), 1-methyl-2,3,4,5-tetraphenyl-1-silacyclo-3-pentenyl-1-methyl-1-
silole [C4Ph4H2SiMe-MeSiC4Ph4] (7), and 1-methyl-2,5-diethyl-2,3,4,5-tetraphenyl-1-
silacyclo-3-pentenyl-1-methyl-1-silole [C4Ph4Et2SiMe-MeSiC4Ph4] (8), respectively. The
reaction products unambiguously suggest that the silole anion [MeSiC4Ph4]− is generated
by coordination of the chloride ion at the silicon atom in 3 or by the nucleophilic
substitution of either chloride or bromide ion at one of two silicon atoms in 3. The
quenching reaction of 3 dissolved in THF with water gives 1,2,3,4-tetraphenyl-2-butene,
the disiloxane of 1-methyl-2,3,4,5-tetraphenyl-1-silacyclo-3-pentenyl [O(MeSiC4Ph4)2]
(10) and methyl silicate.
Keywords: silole anion; silacyclopentadiene; aromaticity; dimer; tricyclic diallylic dianion

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1. Introduction
Since the first silacyclopentadienide anion, 5-methylbenzosilole anion, was prepared in 1958 by
Gilman [1], the chemistry of group 14 metalloles has developed enormously [2-7], in particular the
chemistry of silole and germole dianion [8]. Among the pioneering work reported are the first
synthesis of silole dianion [9] and germole dianion [10], including synthesis and trapping reactions
with halides, the NMR-characterization of the aromaticity in the silole/germole dianions [10-12], the
X-ray crystallography of the silole/germole dianions [13-22], and their computational theoretical study
[23,24]. All of the silole dianion and germole dianions are reported as highly delocalized systems,
regardless of their C-substituents [8]. In contrast, there have been few reports of delocalized silole
anions since NMR studies of [t-Bu-SiC4Ph4]− were reported [25]. For example, the NMR data of the
transition metal complex (η5-C5Me5)Ru[η5-(Me3Si)3SiSiC4Me4] [26] and X-ray crystallography of the
transition metal complex, (η5-C5Me5)MCl2[η5-(Me3Si)3SiEC4Me4] (E=Si, Ge, M = Hf, Zr) [27,28],
dimerization of [MeSiC4Ph4]− to the disilatricyclic diallylic dianion [29], and the theoretical study of
the silole anion [C4H4SiH]− [30-33]. Years ago, even the heavy analogue of CpLi, 1,2-disila-3-
germacyclopentadienide anion, has been reported [34]. Meanwhile there has been no additional
information concerning the dimerization of the silole anion and the reactivity of this anion and its
dimer. Here we report the novel generation of the silole anion [MeSiC4Ph4]− from the disilatricyclic
diallylic dianion [(MeSiC4Ph4)2]2−.
2. Results and Discussion
The reductive cleavage in THF of the Si-Si bond in 1,1-bis(1-methyl-2,3,4,5-tetraphenyl-1-
silacyclopentadiene) [(MeSiC4Ph4)2] (1) by either lithium or sodium gives silole anion [C4Ph4SiMe] (2,
Scheme 1) . Upon standing at r.t. the dark blue solution of 2 gives black crystals of the respective silole
anion dimer [(MeSiC4Ph4)2]2− (3) whose unique disilatricyclic diallylic dianion structure has been
determined by x-ray crystallography [29]. The tricyclic structure of 3 is maintained during the
derivatization of 3 (crystals) with bromoethane (gas) under reduced pressure, whereupon the derivative
[(MeSiC4Ph4Et)2] (4) is obtained quantitatively. In the case of iodomethane (gas) the analogous
derivative [(MeSiC4Ph4Me)2] (5) is also obtained quantitatively (Scheme 1).
Scheme 1. Synthesis of 3 and its derivatization with RX (EtBr, MeI).
Ph4
Ph4
R
Ph4
Ph4
Me
Me
2M/THF
Si
Si
RX(g)
-2X-
Si
Si
Ph4
Me
Me
(M=Li or Na)
Si
Si
Me
Si
Me
Me
Ph4
Ph4
R
3a (M=Li)
3b (M=Na)
2a (M=Li)
2b (M=Na)
4 (RX = EtBr)
5 (RX = MeI)
1
Surprisingly no product is obtained from the reaction of 3 (crystalline solid) with
trimethylchlorosilane (gas) under reduced pressure. This can be attributed to the bulkiness of the
trimethylsilyl group. It has been observed that even the smaller dimethylsilyl group exhibits hindered

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rotation about the bond to the ring carbon due to its steric hindrance when the dimethylsilyl group is
introduced into the similar allylic anion in 1-methyl-2-dimethylsilyl-2,3,4,5-tetraphenyl-1-silacyclo-2-
pentene [MeHSiC4Ph4H(SiHMe2)] [35].
Interestingly, the addition of the trimethylchlorosilane to 3 dissolved in THF provides only 1,1-
bis(1-methylsilole) [(MeSiC4Ph4)2] (1) along with hexamethyldisilane (Scheme 2). Moreover the
reverse addition of 3b in THF to trimethylchlorosilane in THF for an extended reaction time gives
[Me(Me3Si)SiC4Ph4] (6) in 65% yield (Scheme 2). These results indicate that the disilatricyclic
diallylic dianion 3b is dissociated into the silole anions 2 in THF solution. A similar dissociation of the
gallole dimer [(C4Me4Ga-t-Bu) 2] in benzene was previously reported [36].
Scheme 2. Reaction of 3 with trimethylcholorosilane.
Ph4
Ph4
Me
Me3SiCl/THF
Me3SiCl/THF
Si
Si
Ph4
1
Si
- Me3SiSiMe3
Reversed addition
Me
SiMe3
Me
6
3
Furthermore, reverse addition of 3 in THF to an excess of dry hydrogen chloride in THF affords
neither a disilatricyclic derivative or the silole [Me(H)SiC4Ph4], but instead only the disilane
[C4Ph4H2SiMe-MeSiC4Ph4] (7). This disilane 7 has a 1-methylsilole moiety [MeSiC4Ph4] and a 1-
methyl-1-silacyclo-3-pentene moiety [MeSiC4Ph4H2], which is the hydrogenated derivative at the
allylic 2 and 5-carboanions in the silole ring (Scheme 3).
Scheme 3. Reaction of 3 with hydrogen chloride.
Ph4
Me
3/THF
Si Si
HCl/THF
Me
Ph4
7
In the case of bromoethane the disilane derivative [C4Ph4Et2SiMe-MeSiC4Ph4] (8) was obtained in
65~75 % yield, along with a minor amount of the disilatricyclic derivative [(C4Ph4EtSiMe)2] (4). The
disilane 8 has a 1-methylsilole moiety [MeSiC4Ph4] and the ethylation derivative at the allylic 2 and 5-
carboanions in the silole ring such as 7 (Scheme 4).
Scheme 4. Reaction of 3 with bromoethane.
Et
Ph4
Me
3/THF
EtBr/THF
S
i
+
Si
4
Me
Ph4
Et
8

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The minor product 4 unambiguously indicates that some of the unique disilatricyclic structure in 3
is sustained during the reaction. However, the major products of the disilanes 7 and 8 clearly suggest
that in THF the silole anion 2 and the silyl halide [R2Ph4C4SiMeX] (R=H, X=Cl for 7, R=Et, X=Br for
8) are generated in a ratio of 1:1 from 3, as indicated in Scheme 5:
Scheme 5. Suggested mechanism for the formation of disilanes (7 and 8).
R
R
X
X
Ph4
Ph4
Me
Me
Si
Si
Ph4
Ph4
X
R
Si
Me
Si
Me
3
-X
R
R
X
Ph4
Ph4
Me
Ph4
Si Me
+
Si
-X
Ph4
R
Si
Me
R
Si
Me
7 (R = H)
8 (R = Et)
9
The coupling reaction of an allylic anion in one of two 5-membered rings with RX releases above
the C4Si ring the latter’s halide ion, which is easily associated with the vicinal silicon atom of the
silicon in 3. This association easily induces ring opening in the highly strained 1-3-disilacyclobutane
via a pentacoordinated state since the angles of the C-Si-C bonds in both C4Si ring and 1,3-
silacyclobutane ring are nearly 90 degrees [29]. The nucleophilic substitution at the silicon atom
produces a [Si=C] double bond in the other 5-membered ring to generate the novel silole anion
[C4Ph4SiMe]− (9) via a pentacordinated anionic intermediate, in which the methyl group and one Si-C
bond of the C4Si ring occupy pseudo-axial positions and two bonds of X-Si-C and the other Si-C bond
of the C4Si ring occupy pseudo-equatorial positions. Simultaneously the pushing of the electron pair in
the other Si-C bond of 1,3-disilacyclobutane ring to the Cα carbon produces an allylic carbanion, which
immediately reacts with RX. The just generated silole anion 9 is beneath the silicon atom of the C4Si
ring, so coordination of the double bond [Si=C] to the silicon atom above of the C4Si ring would be an
alternative mechanism involving a pseudo-pentacoordinated intermediate to stabilize the [Si=C]
moiety of the silole anion 9, such as in (η5-C5Me5)(PR3)RuH(η2-CH2=SiPh2) [37,38] and
H2(PMe3)3Ru(η2-CH2=SiMe2) [39]. However, the preferred mechanism is a coupling reaction of the
silole anion 9 with the halide. Then the nucelophilic substitution at the silicon provides the Si-Si bond
of 7 or 8 while the allylic anion is rearranged to form a C=C double bond in the other C4Si ring to lead
the silole moiety [MeSiC4Ph4].
Similar pseudo-pentacoordiated silole intermediates lacking highly electronegative atoms on the
silicon atom have been proposed, and are produced by the apical attack of methyl lithium,
diphenylmethylsilyl lithium [40,41], sodium bis(trimethylsilyl)amide [42], and potassium hydride [35]

Molecules 2011, 16
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on the less hindered SiC4 ring. Even the neutral pseudo-pentacoordinate silole [Me(Me2NNp)SiC4Ph4]
has been reported [44]. In those pentacordinated anionic intermediates it was suggested that the SiC4
ring occupies one axial and one equatorial position during its peudorotation and substitution
reactions [45].
For some reason the reverse addition of 3 in THF to an excess of trimethylchlorosilane in THF
produces chloride ion from the trimethylchlorosilane. Then, the association of the chloride ion to the
silicon atom of 3 induces ring opening dissociation in the highly strained 1,3-disilacyclobutane to form
[Si=C] bonds in two silole anions 9 via a pentacoordinated state, in which the methyl group and one
Si-C bond of the C4Si ring occupy pseudo-axial positions and two bonds of X-Si-C and the other Si-C
bond of the C4Si ring occupy pseudo-equatorial positions. Then the cation coordination enhances the
stability by the delocalization in the silole ring [32]. The silole anion 9 is not consumed instantly by the
reaction with trimethylchlorosilane to produce [Me(Me3Si)SiC4Ph4] (6) due to the bulkiness of
trimethlsilyl group [35]. Therefore, only from the reverse addition of 3 in THF to an excess of
trimethylsilylchloride for the extended reaction time 6 could be obtained (Scheme 6).
Scheme 6. Suggested mechanism for the formation of 1.
Cl
Ph4
Ph4
Me
Si
Si
Ph4
Ph4
+
Me Si
Si
Me
9
3
Ph4
Me3Si
9
Me3SiCl/THF
-Cl
1
Si
Me
- Me3SiSiMe3
6
Meanwhile the weak Si-Si bond of 6 is easily attacked by the other silole anion 9 or one-electron
oxidation of 9 with trimethylsilylchloride to produce only 1,1-bis(1-methylsilole) [(MeSiC4Ph4)2] (1)
when trimethylsilylchloride is added to 3 in THF since the reaction rate of the silole anion 9 with
trimethylchlorosilane is much slower than that of the anion 9 with the Si-Si bond of 6. Alternatively,
the silole anion 9 is persistent in the solution for a while due to the lower reactivity of the bulky
trimethylsilylchloride. A similar result in the form of a radical reaction of 1,1-bis(1-phenylsilole)
[(PhSiC4Ph4)2] has been reported by Jutzi and Karl [46].
The quenching reaction of 3 dissolved in THF with water gives no 1,2,3,4-tetraphenyl-1,3-
butadiene, which should be obtained if 1-methyl-2,3,4,5-tetraphenyl-1-silacyclopentadienyl moiety
[MeSiC4Ph4] were present in the THF solution [47]. Instead, the disiloxane [O(MeSiC4Ph4H2)2] (10),
1,2,3,4-tetraphenyl-2-butene, and methylsilicate are obtained (Scheme 7).

Molecules 2011, 16
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Scheme 7. Hydrolysis reaction of 3.
Ph4
Me
Si O Si
HCl(aq)/THF
Ph4
+
+ Methylsilicate
3
Me
Ph4
10
The disiloxane 10 is the condensation product of 1-methyl-1-hydroxy-2,3,4,5-tetraphenyl-1-
silacyclo-3-pentene [MeHOSiC4Ph4H2] (11), which is produced from the protonation of the allylic
anions and the hydrolysis cleavages of two Si-C bonds in 1,3-disilacyclobutane ring of 3. 1,2,3,4-
Tetraphenyl-2-butene and methylsilicate are the hydrolysis products of 10 and/or 11. These reaction
products unambiguously indicate that there is no 1-methyl-2,3,4,5-tetraphenyl-1-silacyclopentadienyl
moiety, but rather the disilatricyclic diallylic dianion species in the THF solution of 3 and/or the silole
anion 9. However, the self dissociation of 3 in THF to the silole anion 9 is not plausible since there is
no derivatization at the silicon atom from the reaction of 3 with hydrogen chloride. Therefore it is
suggested that the disilatricyclic diallylic dianion of 3 is sustained in THF solutions of 3 without halide
ion to give its hydrolysis products (Scheme 8). An alternative mechanism would be involve a bent η2-
chloride bridge between two silicon atoms of 1,3-disiacyclobutane in 3 to lead the silole anion 9 [48].
Scheme 8. Suggested mechanism for the hydrolysis reaction of 3.
H
H
Ph4
OH
Si
OH
Ph4
Me
HO
Si
Me
H
Ph4
H
H
+
Ph4
10
H
Me
Si
Si
HO
Me
HO
H
OH
H
11
3
There are five resonance forms for the silole anion [C4Ph4SiMe]- (2). From the reaction products the
resonance form A (Scheme 9) can be proposed as a prominent contributor to the silole anion. The other
four resonance forms are reduced to two sets of the symmetric resonance forms (B and E, C and D),
which have the allyllic carbanion and silaethene moiety. The coordination of the cation, especially
lithium, to the silole anion 2 enhances the delocalization in the silole ring [32], then the negative
charge or electron density of the silicon atom moves to the carbons in the ring to induce some silicon-
carbon double character. Consequently, the silicon atom becomes more electrophilic or less
nucleophilic than that of the silyl anion A. It is reasoned that the the silole anion 2 has considerable
Si=C double bond character and it dimerizes by head-to-tail [2 + 2] cycloaddition, which is known as
silenes [49]. A t-Bu [25] or Si(SiMe3)3 [26] substituent on the silicon hinders the dimerization, in
addition the electronic effect of the substituents on the silicon and on the carbons may be critical for
the planarity of the silole anion to induce a stable 2-silaallylic anion in it (Scheme 9). It is noteworthy
that the novel silole anion 9 coincides with resonance forms B and D or E and C of the silole anion 2
and it is an analogue of 2H or 3H-silole.

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Scheme 9. Resonance structures of the silole anion (2).
Ph4
Ph4
Ph4
Ph4
Ph4
Si
Si
Si
Si
Si
Me
Me
Me
Me
Me
E
A
D
C
B
3. Experimental
General
All reactions were performed under a nitrogen atmosphere using standard Schlenk techniques. Air
sensitive reagents were transferred in a nitrogen-filled glove box. THF and diethyl ether were distilled
from sodium benzophenone ketyl under nitrogen. Pentane was stirred over concentrated H2SO4 and
distilled from CaH2. NMR spectra were recorded on Bruker WP SY and Bruker AM 200 FT-NMR
spectrometers. MS data were obtained on a mass spectrometer DMX 300. IR spectra were recorded as
KBR pellets on a Shimazu IR 440 and melting points were measured on a Wagner & Meunz Co.
capillary type apparatus. Elemental analyses were done using a Yanaco elemental analyzer at the
Analytic Center of College of Engineering, Seoul National University.
[(MeSiC4Ph4)2] (1): Stirring of 1-chloro-1-methyl-2,3,4,5-tetraphenyl-1-silacyclopentadiene
[MeClSiC4Ph4] (4.58 g, 10 mmol) and sodium (0.23 g, 10 mmol) in THF (170 mL) at room
temperature for 10 hrs produced a pale green precipitate. After evaporating THF from the mixture, the
remaining solid was treated with water and dichloromethane. Removal of dichloromethane under
reduced pressure from the organic suspension, gave a pale green solid. The solid was washed with
ether for purification. It was identified by the comparison of its analytical data with an authentic
sample [50]. Yield: 3.69 g (90%); mp 322-329 °C (lit. [50] mp > 300 °C), 13C-NMR (CDCl3, ref; ext.
77.00 ppm), −6.09 (SiMe), 154.49, 143.25, 139.76, 138.69 (Cβ, Cα and Ci of Cβ and Cα), 130.18,
129.34, 127.81, 127.28 (Co and Cm of Cβ and Cα), 126.16, 125.52 (Cp of Cβ and Cα).
Crystalization of 3: From the dark purple THF solution, the volume of the solution reduced to a half
under reduced pressure. After standing for a week it provided black crystals of 3a and 3b, respectively.
[(MeSiC4Ph4Et)2] (4): The silole anion crystals (1.42 g, 1.7 mmol for the lithium salt, 1.48 g, 1.70
mmol for the sodium salt) was exposed to ethyl bromide vapor for 2 hrs under reduced pressure. After
evacuating the unreacted bromoethane, the resulting yellow solid was extracted with dichloromethane.
Concentration and storage of the solution at −15 °C for a day gave yellow crystals of 4. Yield: 1.38 g
(95%) for the lithium salt, 1.38 g (95%) for the sodium salt, mp 296−300 °C; 1H-NMR (CDCl3, ref; ext.
TMS = 0.00 ppm), 0.65 (s, 6H, SiMe), 0.70 (brd t, 6H, Me, J = 6.96Hz), 2.23 (brd q, 4H, CH2, J =
6.96Hz), 6.6-7.1 (brd m, 40H, Ph).; 13C-NMR (CDCI3, ref; solvent = 77.00 ppm), –1.26 (SiMe3), 11.71
(Me), 32.48 (CH2), 46.33 (q-C-Ph), 43.12 (q-C-Et), 148.90, 145.01, 141.65, 141.43, 140.99, 140.62
(ethenyl C and Ci), 132.16, 131.44, 131.09, 130.28, 127.04, 126.93, 126.62, 126.32 (Co and Cm),

Molecules 2011, 16
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126.09, 125.86, 125.28, 123.06 (Cp).; IR (cm−1), δSi-Me = 1255.; MS (M+, relative abundance), 856 (M+
,65), 797 (M+−59, 10), 428 (M+/2, 95), 135 (100).; Anal. Calcd. for C62H56Si2: C, 86.88; H, 6.59,
Found: C, 86.86: H, 6.58.
[(MeSiC4Ph4Me)2] (5): Silole anion crystals (1.42 g, 1.7 mmol for the lithium salt, 1.48 g, 1.70 mmol
for the sodium salt) was exposed to methyl iodide vapor for 2 hrs under reduced pressure. After
evacuating the unreacted methyl iodide, the residual yellow solid was extracted with ether.
Concentration and storage at −15 °C for 1 day gave yellow crystals of 4. Yield: 0.85 g (60%) for 3a,
1.22 g (87%) for 3b; mp 334−338 °C (lit. [29] 336−339 °C). The NMR data of 5 agreed with those
reported earlier [30].
[Me(Me3Si)SiC4Ph4] (6): After all volatile reagents were removed under reduced pressure, the residue
was extracted with pentane. Several recrystalizations from pentane gave pure green crystals of 6 [51].
1
Yield; 1.15 g (65%) for the lithium salt and 1.13 g (64%) for the sodium salt, mp 130−132 °C; H-
NMR (CDCl3, ref.: solvent = 7.27 ppm,), 0.03 (s, 9H, SiMe3), 0.58 (s, 3H, SiMe), 6.80-7.15 (brd m,
20H, Ph); 13C-NMR (CDCI3, ref; solvent = 77.00 ppm), −7.43 (SiMe3), −1.88 (SiMe), 153.84 (Cβ),
143.62(Cα), 140.21 (Ci of Cβ), 139.26 (Ci of Cα), 130.12, 127.27, 127.39, 127.82 (Co and Cm), 126.05,
125.36 (Cp); 29Si-NMR (CDCI3, ref; ext. TMS=0.00), −8.13 (ring Si), −15.50 (SiMe3); MS (M+,
relative abundance), 474 (M++2, 21), 473 (M++1. 45), 472 (M+, 100), 457 (M+−15, 42), 400 (M+−73,
5), 379 (48), 279(25), 221 (47), 135 (21), 105 (61), 73 (27); Anal Calcd. for C32H32Si2: C, 81.32 : H,
6.83, Found: C 81.52: H, 6.84.
[C4Ph4H2SiMe-MeSiC4Ph4] (7): Addition with stirring at room temperature of the purple solution of 3
to THF saturated with dry HCl gave a yellow solution. After removing the THF, the residue is
extracted with pentane. Pentane was replaced with diethyl ether, and crystallization of the solution at
−10°C for 1 day gave green crystals. Yield: 0.88g (65%) for the lithium salt, 0.85g (63%) for the
1
sodium salt; mp 215−218 °C; H-NMR (CDCI3 ref.: ext. TMS = 0.00 ppm,), −0.07 (s, 3H, SiMe of
13
butene), 0.58 (s, 3H, SiMe of butadiene), 3.53(s, 2H, CH), 6.5−7.1 (brd m, 40H, Ph); C-NMR
(CDCI3,ref.: ext. 77.00 ppm), −7.69 (SiMe of butene), −2.71 (SiMe of butadiene), 48.41 (CH), 138.80,
140.89, 141.86, 143.01, 143.45, 155.22 (ethylene, Ci), 129.96, 129.27, 129.12, 129.00, 128.09, 127.94,
127.52, 127.10 (Co and Cm), 126.25, 125.98, 125.44, 124.69 (Cp); Anal Calcd for C58H48Si2: C,86.96;
H,6.04, Found: C, 86.60; H, 6.02.
[C4Ph4Et2SiMe-MeSiC4Ph4] (8): Yield: 0.87 g (60%) for the lithium salt and 1.02 g (70%) for the
1
sodium salt; mp 288−290 °C; H-NMR (CDCl3, ref.: solvent = 7.27 ppm,), 0.11 (s, 3H, SiMe of
butene), 0.16 (s, 6H, Me, J = 6.96Hz), 0.70 (s, 3H, SiMe of butadiene), 1.86 (brd q, 4H, CH2), 6.6−7.2
(brd m, 40H, Ph).; 13C-NMR (CDCI3, ref.: solvent = 77.00 ppm), −4.66 (SiMe of butene), 10.56 (Me),
27.75 (CH), 49.69 (q-C), 154.85, 147.59, 144.32, 142.52, 139.52, 139.32, 139.15 (three sp2 C and four
Ci), 130.78, 130.61, 130.31, 129.90, 127.42, 127.35, 126.59, 126.12 (four Co and four Cm), 125.61,
125.28, 125.21 (Cp).; IR (cm−1), δSi-Me = 1245; MS (M+, relative abundance), 856 (M+, 38), 457 (M+-
Me-silole, 100), 442 (65), 427 (35), 197 (70).; Anal Calcd for C62H56Si2: C, 86.88; H, 6.59, Found: C,
87.20; H, 6.60.

Molecules 2011, 16
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[(C4Ph4H2SiMe) 2O] (10): Aqueous HCl (0.10N) was added to a THF solution of 3 with stirring at
room temperature until the pH of the mixture reached neutrality. Filtration of the hydrolyzed mixture
gave a white solid, which was insoluble in organic solvents and water, did not melt when heated to
over 300 °C, and showed a broad band at 1000−1100 cm−1in the IR spectrum. After THF was removed
from the filtrate, the residue was extracted with diethyl ether. The concentrated ether solution was kept
at −20 °C for 1 day and pale green crystals of 10 were obtained. The mother solution was concentrated
and after standing at −20 °C for 1 day it yielded colorless crystals of 1,2,3,4,-tetraphenyl-2-butene
(yield: 0.72 g, 40%), whose spectral data agreed with those reported earlier [9]. Yield(10): 1.35 g
(33%) for 3a and 1.23 g (30%) for 3b; mp 292 °C; 1H-NMR (CDCI3 ref.: ext. TMS = 0.00 ppm), −0.45
(s, 6H, SiMe), 3.15 (s, 4H, CH), 6.8−7.3 (brd m, 40H, Ph); MS (M+, relative abundance), 818 (M+,
100), 650 (M+, 18), 537 (60), 460 (50), 445 (25), 383 (40), 382 (30); Anal Calcd for C58H50Si2O: C,
85.05; H, 6.16, Found: C, 84.82; H, 6.12.
4. Conclusions
The pathway for generation of the silole anion 9 is dependent on the reactivity of the alkyl halide
used. Two silole anions 9 are generated from the disilatricyclic diallylic dianion 3 in THF by the
coordination of the chloride ion to the silicon atom in it; the reaction of 9 with trimethylchlorosilane
provides [(MeSiC4Ph4Me)2] (5) or [Me(Me3Si)SiC4Ph4] (6) according to the method of the addition.
From the reverse addition of 3 in THF to bromoethane or hydrogen chloride in THF the silole anion 9
and the silyl halide [R2Ph4C4SiMeX] (R=H, X=Cl for 7, R=Et, X=Br for 8) are generated in a ratio of
1:1, then the coupling reaction of the two produces the corresponding disilane [C4Ph4R2SiMe-
MeSiC4Ph4] (R=H, X=Cl for 7, R=Et, X=Br for 8).
Acknowledgments
The author acknowledges the advice provided by Wan-Chul Joo (Sung Kyun Kwan University,
Seoul, Korea) and Professor Philip Boudjouk (North Dakota State University, Fargo, ND, US).
Conflict of Interest
The author declares no conflict of interest.
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Sample Availability: Samples of the derivatives of the silole anion [MeSiC4Ph4]- are available from the
author.
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