Synthesis and NMR-study of 1-trimethylsilyl substituted silole anion [Ph4C4

Article abstract of DOI:10.3390/molecules180910568

1-Trimethylsilyl, 1-R (R = Me, Et, i-Bu)-2,3,4,5-tetraphenyl-1- silacyclopentadiene [Ph₄C₄Si(SiMe₃)R] are synthesized from the reaction of 1-trimethylsilyl,1-lithio-2,3,4,5-tetraphenyl- 1-silacyclopentadienide anion [Ph

Full text of DOI:10.3390/molecules180910568

Molecules 2013, 18, 10568-10579; doi:10.3390/molecules180910568
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molecules
ISSN 1420-3049
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Article
Synthesis and NMR-Study of 1-Trimethylsilyl Substituted Silole
Anion [Ph4C4Si(SiMe3)]−•[Li]+ and 3-Silolenide 2,5-carbodianions
{[Ph4C4Si(n-Bu)2]−2•2[Li]+, [Ph4C4Si(t-Bu)2]−2•2[Li]+} via Silole
Dianion [Ph4C4Si]−2•2[Li]+
Jang-Hwan Hong †
Department of Nanopolymer Material Engineering, Pai Chai University, 155-40 Baejae-ro (Doma-Dong),
Seo-Gu, Daejon 302-735, Korea; E-Mail: jhong@pcu.ac.kr; Tel.: +82-42-520-5755;
Fax: +82-42-520-5798
†
Dedicated to Professor Wan-Chul Joo on the occasion of his 89th birthday.
Received: 24 July 2013; in revised form: 21 August 2013 / Accepted: 22 August 2013 /
Published: 30 August 2013
Abstract: 1-Trimethylsilyl, 1-R (R = Me, Et, i-Bu)-2,3,4,5-tetraphenyl-1-silacyclopentadiene
[Ph4C4Si(SiMe3)R] are synthesized from the reaction of 1-trimethylsilyl,1-lithio-2,3,4,5-
tetraphenyl-1-silacyclopentadienide anion [Ph4C4SiMe3]−•[Li]+ (3) with methyl iodide, ethyl
iodide, and i-butyl bromide. The versatile intermediate 3 is prepared by hemisilylation of the
1
silole dianion [Ph4C4Si]−2•2[Li]+ (2) with trimethylsilyl chloride and characterized by H-,
13C-, and 29Si-NMR spectroscopy. 1,1-bis(R)-2,3,4,5-tetraphenyl-1-silacyclopentadiene
[Ph4C4SiR2] {R = n-Bu (7); t-Bu (8)} are synthesized from the reaction of 2 with n-butyl
bromide and t-butyl bromide. Reduction of 7 and 8 with lithium under sonication
gives the respective 3-silolenide 2,5-carbodianions {[Ph4C4Si(n-Bu)2]−2•2[Li]+ (10) and
1
[Ph4C4Si(t-Bu)2]−2•2[Li]+ (11)}, which are characterized by H-, 13C-, and 29Si-NMR
spectroscopy. Polarization of phenyl groups in 3 is compared with those of silole
anion/dianion, germole anion/dianion, and 3-silolenide 2,5-carbodianions 10 and 11.
Keywords: silacyclopentadiene; silole; anion; dianion; silyation; 3-silolenide; aromaticity; NMR
1. Introduction
Cyclopentadienyl anion, the most representative aromatic compound, has for a long time played
important roles in organic and organometallic chemistry [1–3]. Therefore it has been a challenge

Molecules 2013, 18
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to synthesize the analogue framework [4–7], in which one of carbon atoms is replaced by a
heavier group 14 atom, and the ultimate question is to find out how its aromaticity changes
and is maintained [8–15]. Since the first silacyclopentadienide dianion was reported [16], the
aromaticity of sila- and germa-cyclopentadienide dianion has been suggested by NMR chemical shift
changes upon reduction [17,18]. Their aromatic structures [19,20] and the related structures
have been confirmed by X-ray crystallography [21–27]. Heavier metallic dianion equivalents, the
stannacyclopentadienide dianion [28–30] and plumbacyclopentadienide dianion [31], are also reported
to display aromaticity [32–37].
The principal heavier congener of the cyclopentadienide anion, 1-tert-butyl-2,3,4,5-tetraphenyl-1-
silacyclopentadienide anion, has been reported to have aromaticity according to NMR chemical shift
changes upon reduction [38]. Meanwhile 1-methyl-2,3,4,5-tetraphenyl-1-silacyclopentadienide anion was
synthesized and crystallized in THF as a [2+2] dimer of its Si = C bond in aromatic ring structures [39], the
dimer of which is dissociated to the original silole anions when it is reacted with alkyl halides or
trimethylchlorosilane in THF [40]. Even the analogue frameworks of trimetallic anion {[C2GeSi2]−,
[C2Si3]−} and divalent germanium containing anion {[C3NGe:]−}, in which more than one carbon atom
of the cyclopentadienyl anion are replaced by heavier group 14 atoms of Si and/or Ge, are synthesized
and characterized to have aromaticity [41–43], making it possible to form heavy analogues of
ferrocene with them [44,45].
In contrast spectroscopic and X-ray crystallographic data [22,23] for 1-trimethylsilyl-tetramethyl/ethyl-
1-silacyclopentadienide anions have revealed that they possess pyramidal silicon centers and bond
localization in their butadiene moieties. Nevertheless the heavy analogues of ferrocene are synthesized
with them [24,27,46,47]. Therefore it is interesting to study 1-trimethylsilyl-2,3,4,5-tetraphenyl-1-
silacyclopentadienide anion [Ph4C4Si(SiMe3)]− to compare it with other metallole anions [48].
There are several routes for silole syntheses, via 1,4-dilithio-butadienides by using
diphenylacetylene [16,17,49] and 1,4-dihalobutadienes [23,50,51], the intramolecular reductive cyclization
of diethynylsilanes [52,53], metallacyclic transfer reactions [54], and organoboration [55–58]. However
those synthetic methods are not applicable to synthesizing of various siloles derivatives at the Si atom,
especially for preparing 1-trimethylsilyl group substituted siloles due to the feasibility of the
nucleophilic attack on the Si-Si bond by carbanions [22,24,27,59,60] and silole anion [39]. Coversely
all metallole dianions are potential and useful intermediates for the synthesis of various di-substituted
metallole derivatives, polysiloles, and silole-containing polymers [61–66].
Herein we report that silole dianion is a versatile intermediate to synthesize [Ph4C4Si(SiMe3)(R)]
(R = Me, Et, i-Bu) via [Ph4C4Si(SiMe3)]−, which is prepared by hemisilylation of the silole dianion and
characterized by 1H-, 13C-, and 29Si-NMR spectroscopy, and [Ph4C4SiR2] (R = i-Bu, t-Bu).
2. Results and Discussion
2.1. Preparation of 1-Trimethylsilyl,1-lithio-2,3,4,5-tetraphenyl-1-silacyclopentadienide Anion (3) and
Its Reaction with Methyl Iodide, Ethyl Iodide and i-Butyl Bromide
1-Trimethylsilyl-2,3,4,5-tetraphenyl-1-silacyclopentadienide anion [Ph4C4Si(SiMe3)]−•[Li]+ (3) was
prepared from the reaction of the silole dianion [Ph4C4Si]−2•2[Li]+ (2) with one equivalent of

Molecules 2013, 18
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trimethylsilyl chloride. The silole dianion 2 was generated by the sonication of 1,1-dichloro-2,3,4,5-
tetraphenyl-1-silacyclopentadiene [Ph4C4SiCl2] (1) with lithium in THF [17]. Compound 3 in THF was
reacted with the alkyl halides of methyl iodide, ethyl iodide, and i-butyl bromide to provide
[Ph4C4Si(SiMe3)(R)] [R = Me (4) , Et (5), i-Bu (6)], respectively (Scheme 1).
Scheme 1. Synthesis and alkylation of 3 via silole dianion 2.
Ph4
Ph4
Si
Ph4
Si
Ph4
)))
RX
Me3SiCl
-LiCl
4Li/THF
[Li+]
[Li+]2
-2LiCl
-LiX
Si
Si
(RX = MeI, EtI,i-BuBr)
Cl
Cl
SiMe3
R
SiMe3
(1)
(2)
(3)
(4) (R = Me)
(5) (R = Et)
(6) (R = i-Bu)
Silylation of 2 with trimethylsilyl chloride is a novel reaction to synthesize 1-trimethylsilyl substituted
silole anion 3; the similar alkylation of stannole dianion with t-butyl chloride was reported to give 1-t-butyl
substituted stannole anion, oxidation of which in the air provided 1,1-bis(1-t-butyl-stannole) [67,68].
Oxidation of stannole dianion were reported to give bistannole-1,2-dianion or terstannole-1,3-dianion
[69,70]. But the silole anion 3 decomposes in the air to give the ring opening products of 1,2,3,4-
tetraphenylbutadiene and silicate. Preparation of 4 is interesting since addition of trimethylsilyl
chloride to the silole anion [Ph4C4Si(Me)]−•[M]+ (M = Li, Na) in THF has given 1,1-bi(1-methyl-
silole) [Ph4C4Si(Me)]2, but addition of the silole dianion to trimethylsilyl chloride in THF has provided
[Ph4C4Si(SiMe3)(Me)] (4) [40].
2.2. Synthesis of 1,1-Bis(n-butyl/t-butyl)-2,3,4,5-tetraphenyl-1-silacyclopentadiene and NMR-Study of
3-Silolenide-2,5-carbodianions
1,1-bis(n-Butyl/t-butyl)-2,3,4,5-tetraphenyl-1-silacyclopentadiene {[Ph4C4Si(n-Bu)2] (7) and [Ph4C4Si
(t-Bu)2] (8)} are prepared in good yield from the reactions of silole dianion 2, which is generated by
the sonication of 1 with lithium in THF, with n-bromobutane and t-butyl bromide. In the case of
t-butyl bromide, [Ph4C4Si(t-Bu)2] (8) is produced along with 1,1-bi[(t-Bu)SiC4Ph4] (9) in the ratio of 3
to 1 (Scheme 2). Until now there is one report of the synthesis of 1,1-bis(t-butyl)-substituted silole,
which has been prepared photochemically in low yield [71].
1,1-bis(n-Butyl/t-butyl)-2,3,4,5-tetraphenyl-1-silacyclopentadiene {[Ph4C4Si(n-Bu)2] (7) and
[Ph4C4Si(t-Bu)2] (8)} are sonicated in THF-d8 with lithium in the 5 mm NMR tube for 2 h. During this
time the color of the mixture becomes red and/or purple. The NMR study of the reduced species in
THF-d8 shows clearly that the only one species is formed and is assigned to the respective reduced
3-silolenes with 2,5-carbodianions {[Ph4C4Si(n-Bu)2]−2•2[Li]+ (10) and [Ph4C4Si(t-Bu)2]−2•2[Li]+ (11)}.
Each of their 13C-NMR spectra presents ten peaks, consistent with C2 symmetry, and the 29Si spectrum
1
of each compound shows only one resonance. The respective H-NMR spectrum of 10 and 11 shows
two kinds of protons, 20 phenyl protons and 18 butyl protons. Even if they are sonicated further, they
show the same peaks with no change.

Molecules 2013, 18
Scheme 2. Synthesis of 7 and 8 and their reduction to 10 and 11.
10571
Ph4
Ph4
Ph4
Ph4
R
RBr
Si
Si
+
2[Li+]
(R = n-Bu, t-Bu)
R
Si
Si
R
R
(7) (R = n-Bu)
(8) (R = t-Bu)
(2)
(9) (R = t-Bu) (8:9 =3:1)
Li/THF-d8
)))
Ph4
2[Li+]
Si
R
R
(10) (R = n-Bu)
(11) (R = t-Bu)
Both chemical shifts of the two tert-C− groups (73.18 ppm for (10), 78.12 ppm for (11)) are
consistent with those of the reported 3-silolenides with 2,5-carbodianions, [Ph4C4Si(R1)(R2)]−2
(77.4 ppm for R1 = R2 = Me [72], 76.42 ppm for R1 = Me, R2 = H [73]), and 1,1-R1,R2-2-lithio-2,3,4,5-
tetraphenyl-1-silacyclopenta-3-enide anion (77.78 ppm for R1 = R2 = H [74]). The 13C-NMR chemical
shifts of two Ciα, Ciβ and two Cpα, Cpβ show at 151.51, 147.68 ppm and 108.49, 120.80 ppm for 10 and
at 152.59, 147.36 ppm and 110.87, 120.25 ppm for 11 (Table 1). The localized carbanions polarize the
phenyl groups more than those of the aromatic silole/germole dianions and silole anions. The extent of
polarization [Sum(Ci-Cp)/2] in those species shows in narrow range: 3-silolenides 2,5-carbodianions
(34.42 to 35.00 ppm), silole/germole dianions [Ph4C4E]−2 [E = Si (2), Ge] (28.60 to 28.64 ppm), and
silole anion [Ph4C4Si(t-Bu)]− (24.65 ppm). In case of the phenyl group on germanium atom in the localized
germole anion [Me4C4GePh]−•[Li]+ [75], the extent of polarization {[Sum(Ci-Cp)/2] = 35.3 ppm} is very
close to those of the localized 3-silolenide 2,5-carbodianions (Tables 1 and 2).
Upon lithiation of 8 to 11 the 29Si-NMR chemical shift of 11 is not changed much (16.49 ppm (8) to
13.69 ppm (11) since there is no change of its hybridization with the same substituents on the silicon
atom (Table 1).
2.3. NMR Study of 1-Trimethylsilyl,1-lithio-2,3,4,5-tetraphenyl-1-silacyclopentadienide Anion (3)
[Ph4C4SiCl2] (1) is sonicated in THF-d8 with lithium in a 5 mm NMR tube for 2 h, whereby the
color of the mixture becomes red and/or purple. NMR study of the species in THF-d8 clearly indicates
that only one species of silole dianion [Ph4C4Si]−2•2[Li]+ (2) is generated. Upon adding one equivalent
of trimethylsilyl chloride to 2 the 29Si-NMR chemical shift changes from 68.54 ppm (for 2) to
−13.22 ppm with another new resonance peak of the trimethylsilyl group at −15.54 ppm
13
{[Ph4C4Si(SiMe3)]−•[Li]+ (3)}. The C-NMR spectrum of 3 shows ten peaks in the aromatic region,
1
consistent with C2 symmetry, and one peak for the trimethylsilyl group (Table 1). In its H-NMR

Molecules 2013, 18
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spectrum of it there are two kinds of protons, 20 protons corresponding to four phenyl groups and 9
protons of one trimethylsilyl group.
Table 1. 13C/29Si-NMR chemical shifts of the localized 3-silolenides and germole anions.
3-Silenes 2,5-
carbanion
Cα
[Ph4C4SiMe2]−2•
2[Li]+
[Ph4C4SiMeH]−2• [Ph4C4Si(n-Bu)2]−2•2[Li]+
[Ph4C4Si(t-Bu)2]−2
•2[Li]+ (11)
78.12
[Me4C4GePh]−•
[Li]+
138.7
151.5
290.2
12.8
2[Li]+
(10)
73.18
77.4
76.42
Cβ
128.5
128.82
128.06
130.34
Sum (Cα + Cβ)
Sum (Cβ − Cα)
205.9
205.24
201.24
208.46
51.1
52.40
73.18
78.12
Ph
Ph
Ph
Ph
Ph
Ci
Co
150.6, 147.3
123.3, 125.8
126.5, 132.4
107.8, 120.5
69.6/2 = 34.8
−
150.33, 147.82
132.47, 126.62
123.05, 125.98
107.65, 120.53
69.97/2=35.00
-34.14
151.51, 147.68
132.88, 126.61
123.58, 126.61
108.49, 120.80
69.90/2 = 34.95
-0.27
152.59, 147.36
132.75, 127.75
125.77, 125.93
110.87, 120.25
68.83/2 = 34.42
13.69
159.6
136.4
127.3
124.3
35.3a
−
Cm
Cp
Sum (Ci − Cp)/2
29Si-Ring
CH3, tert-C
Reference
−
72 b
2.58
73 b
14.70, 18.88, 27.34, 29.08
This Work b
31.5, 33.3 (brd d)
This Work b
−
75 b
b In THF-d8, reference = 25.30 ppm.
Table 2. 13C/29Si-NMR chemical shifts of silole/germole dianions and silole anions.
[Ph4C4Si]−2•2[Li]+ (2)
151.22, 129.71 a
Ph
[Ph4C4Ge]−2•2[Li]+
165.57, 129.92 a
Ph
[Ph4C4Si(t-Bu)]−•[Li]+
155.76, 139.51
Ph
[Ph4C4SiSiMe3]−•[Li]+ (3)
159.67, 139.30
Ph
Ring carbons
Ci
Co
151.67, 145.83
129.97, 133.43
126.38, 126.38
119.48, 121.83
56.19/2 = 28.10
−
152.17, 146.30
129.92, 133.49
126.38, 126.38
119.29, 121.91
57.27/2 = 28.64
−
149.29, 144.72
130.50, 132.56
126.40, 126.51
121.38, 123.34
49.29/2 = 24.65
32.78(CH3), 23.58(tert-C)
25.10
148.81, 145.72
129.81, 132.85
126.30, 126.46
120.86, 122.86
40.81/2 = 20.41
-0.23 [Si(CH3)3]
−13.22
Cm
Cp
Sum(Ci − Cp)/2
CH3, tert-C
29Si-Ring
68.54
−
Refenence
17 b
18 b
38 b
This Work b
a
b
The reported assignments were revised [76], the chemical shifts did not coincided with each other [77]. In THF-d8,
reference = 25.30 ppm.
Upon adding trimethylsilyl chloride to 2 the chemical shifts of Cα and Cβ in 2 are shifted far
downfield from 151.22 ppm and 129.71 ppm to 159.67 ppm and 139.30 ppm in 3. The chemical shifts
of Ciα and Ciβ in 3 are observed at 145.72 ppm and 148.81 ppm, while the chemical shifts of Cpα and
Cpβ in 3 are observed at 122.86 ppm and 120.86 ppm respectively. These carbon peaks of four phenyl
groups indicate that the phenyl groups of 3 are still polarized, and the average chemical shift difference
of Ci and Cp is 20.41 ppm [Sum(Ci − Cp)/2] (Table 2). Such polarizations of phenyl groups are
generally observed due to the absence of the significant π-conjugation between their phenyl groups and
5-membered ring because of their bulkiness and the congestion of four phenyl groups. The
average chemical shift difference of 20.41 ppm for 3 is smaller than those of the silole dianion
[Ph4C4Si]−2•2[Li]+ (2) (28.10 ppm) [17], [Ph4C4Si]−2•2[Na]+ (29.17 ppm) [16], the germole dianion

Molecules 2013, 18
10573
[Ph4C4Ge]−2•2[Li]+ (28.64 ppm) [18], and even the silole anion [Ph4C4Si(t-Bu)]−•[Li]+ (24.65 ppm) [38].
The difference is also significantly smaller than those of the localized 3-silolenes (the reduced siloles to
2,5-carbodianions); [Ph4C4SiMe2]−2•2[Li]+ (34.8 ppm) [72], [Ph4C4SiHMe]−2•2[Li]+ (35.00 ppm) [75],
[Ph4C4Si(n-Bu)2]−2•2[Li]+ (34.95 ppm) (10), [Ph4C4Si(t-Bu)2]−2•2[Li]+ (34.42 ppm) (11), and that of the
phenyl group in the localized germole anion [Me4C4GePh]−•[Li]+ (35.3 ppm) [75] (Table 1). This trend
implies that the electron density in the silole ring carbons of 3 is significantly lower than those in the
rings of the localized 3-silolenes, the high aromatic silole/germole dianions {[Ph4C4Si]−2, [Ph4C4Ge]−2} and
the silole anion [Ph4C4Si(t-Bu)]− due to its low aromaticity and/or sp3 hydridization character on Si
atom in 3.
X-ray crystallographic data for 1-trimethylsilyl-2,3,4,5-tetramethyl/ethyl-1-silacyclopentadienide
anion) [R4C4Si(SiMe3)]− (R = Me, Et) have revealed that the anionic rings possess a pyramidal silicon
center and bond localization in the butadiene moiety of the ring, the 29Si-NMR chemical shifts of these
pyramidal ring Si atoms in those anions are observed from −41 ppm to −54 ppm [23]. However in the
case of 3 the 29Si-NMR chemical shift is observed at −13.22 ppm, far downfield from those of the
pyramidal Si atoms in the localized silole anions and far upfield from those of silole dianions and silole
anion (Table 3).
Table 3. 29Si-NMR chemical shifts of silole anions and dianion.
[Et4C4SiSiMe3]−•
[M]+
[Et4C4Si]−2•
2[M]+
[Ph4C4SiSiMe3]−•[M]+
Silole Anion
[Me4C4SiSiMe3]−•[M]+
Li
(3)
Li
M
K
Li
K
Li
29Si-Ring
29Si-Ring
with crown
ether
−45.38
−
−43.96
−42.70
−41.52
−53.12 c −47.38
24.96
−13.22
18-CE-
6
12-CE-4
−
12-CE-4
−
−
−
29Si-SiMe3
−12.47
22 a
−11.68
22 b
−12.44
22 a
−11.00
22 b
−14.27
22 c
−14.22
22 c
−
51 c
−15.54
This work c
Reference
a In CH2Cl2-d2. b In Benzene-d6. c In THF-d8.
The 13C-NMR and 29Si-NMR chemical shifts of 3 do not support its aromaticity, the introduction of
trimethylsilyl group on the silicon atom might decrease aromaticity of silole anion with the substituent
effect of the trimethylsilyl group enhancing the s-character of the lone pair on the silicon atom and
decreasing the s-character of the Si-Si bond in 3 [23,48].
3. Experimental
General Procedures
All reactions were performed under an inert nitrogen atmosphere using standard Schlenk
techniques. Air sensitive reagents were transferred in a nitrogen-filled glove box. THF and ether were
distilled from sodium benzophenone ketyl under nitrogen. Hexane and pentane were stirred over
concentrated H2SO4 and distilled from CaH2. NMR spectra were recorded on JEOL GSX270 and
GSX400 spectrometers. GC-MS and solid sample MS data were obtained on a Hewlett-Packard 5988A

Molecules 2013, 18
10574
GC-MS system equipped with a methyl silicon capillary column. Elemental analyses were done by
Desert Analytics (Tucson, AZ, USA).
[Ph4C4Si(SiMe3)(R)] (R = Me (4), Et (5), i-Bu (6)). [Ph4C4SiCl2] (1) (0.57 g, 1.25 mmol) was
sonicated in THF with an excess of lithium for 5 h. Then the remaining lithium was removed by
filtration to give a red-purple solution. The solution was added to methyl iodide in THF with stirring at
room temperature for 4 h to give a yellow solution. After removing the solvent under vacuum the
remaining yellow solid was extracted with hexane. The concentrated solution was kept in a refrigerator
for a couple of days to provide yellow crystals.
[Ph4C4Si(SiMe3)(Me)] (4). Yield: 0.38 g (65%); mp. 130–132 °C (lit. [40], mp. 130–132 °C).
1
[Ph4C4Si(SiMe3)(Et)] (5). Yield: 0.54 g (59%); mp. 100–102 °C, H-NMR (CDCl3, ref; ext.
13
TMS = 0.00 ppm), 0.05 (s, SiMe3, 9H), 1.0–1.2 (brd m, ethyl, 5H), 6.68–7.15 (m, 20H); C-NMR
(CDCl3, ref; solvent = 77.00 ppm), −1.40 (SiMe3), 3.06 (CH2), 8.64 (CH3); 29Si-NMR (CDCl3, ref; ext.
TMS = 0.00), −2.53 (ring Si), −16.15 (SiMe3); Anal. Calcd. for C33H34Si2: C, 81.42; H, 7.04, Found:
C, 81.59; H, 7.19.
1
[Ph4C4Si(SiMe3)(i-Bu)] (6). Yield: 0.44 g (68%); mp. 154–156 °C, H-NMR (CDCl3, ref; ext.
TMS = 0.00 ppm), 0.03 (s, SiMe3, 9H), 0.92 (d, CMe2, 6H), 1.16 (d, CH2, 2H), 1.85 (m, CH, 1H),
6.68–7.15 (m, 20H); 29Si-NMR (CDCl3, ref; ext. TMS = 0.00), −6.49 (ring Si), −15.88 (SiMe3); Anal.
Calcd. for C35H38Si2: C, 81.65; H, 7.44, Found: C, 81.76; H, 7.31.
[Ph4C4Si(n-Bu)2] (7). [Ph4C4SiCl2] (1) (0.57 g, 1.25 mmol) was sonicated with an excess of lithium for
5 h. Then the remaining lithium was removed by filtration to give a red-purple solution of the silole
dianion. The solution was added to a THF solution of 1-bromobutane with stirring at room temperature
for 10 h to give a yellow solution. After removing the solvent under vacuum the remaining yellow
solid was extracted with hexane. The concentrated solution was kept in a refrigerator for a couple of
days to provide yellow crystals. Yield: 0.56 g (90%); mp. 85 °C (lit. [78] mp. 81 °C).
[Ph4C4Si(t-Bu)2] (8). [Ph4C4SiCl2] (1) (0.55 g, 1.21 mmol) was sonicated with an excess of lithium in
THF for 5 h. Then the remaining lithium was removed by filtration to give a red-purple solution of 2.
The solution was added to a THF solution of t-butyl bromide with stirring at room temperature for 24 h
to give a yellow solution. After removing the solvent under vacuum the remaining yellow solid was
extracted with ether. The concentrated solution was kept in a refrigerator for a couple of days to provide
pale yellow crystals of bissilole 1,1-bi[(t-Bu)SiC4Ph4] [14]. The filtered solution was concentrated under
vacuum, then it was kept in a refrigerator for a couple of days to give yellow crystals of [Ph4C4Si(t-Bu)2]
1
(8). Yield: 0.33 g (54%); mp. 169-171 °C, H-NMR (CDCl3, ref; ext. TMS = 0.00 ppm), 1.16 (s, Me,
29
18H), 6.68–7.15 (m, 20H), Si-NMR (CDCI3, ref; ext. TMS=0.00), 16.49 (ring Si); Anal. Calcd. for
C36H38Si1: C,86.69; H,7,68, Found: C, 86.71; H, 7,75.
1,1-Bi[(t-Bu)SiC4Ph4] (9). Yield: 0.19 g (18%); mp. 295–307 °C (lit. [16] mp. 296-307 °C), 29Si-NMR
(THF-d8, ref; ext. TMS = 0.00), 3.62 (ring Si).

Molecules 2013, 18
10575
1,1-Bis(R)-2,5-dilithio-2,3,4,5-tetraphenyl-1-silacyclopenta-3-enide anion [R = n-Bu (10), R = t-Bu (11)].
The respective [Ph4C4Si(n-Bu)2] (7) (0.025 g, 0.05 mmol) and [Ph4C4Si(t-Bu)2] (8) (0.025 g,
0.05 mmol) was transferred into 5 mm NMR tube, they were sonicated with an excess of lithium
1
in THF-d8 for 2 h to give a red-purple solution. Then H-, 13C-, and 29Si-NMR spectroscopic study
was performed.
1
[Ph4C4Si(n-Bu)2]-2•2[Li]+ (10); H-NMR (THF-d8, ref; ext. TMS = 0.00 ppm), 0.83 (t, CH3, 6H),
0.90 (m, CH2, 4H), 1.36 (sept, CH2, 4H), 1.52 (m, CH2, 4H), 6.68–7.15 (m, 20H), 29Si-NMR (THF-d8,
1
ref; ext. TMS = 0.00), −0.27 (ring Si). [Ph4C4Si(t-Bu)2]-2•2[Li]+ (11); H-NMR (THF-d8, ref; ext.
TMS = 0.00 ppm), 1.21 (brd s, Me, 18H), 6.68-7.15 (m, 20H), 29Si-NMR (THF-d8, ref; ext.
TMS = 0.00), 13.69 (ring Si).
4. Conclusions
Silole dianion [Ph4C4Si]−2 (2) is a versatile intermediate to prepare symmetrically substituted siloles
of [Ph4C4SiR2] (R = n-Bu, t-Bu) and unsymmetrically substituted siloles of [Ph4C4Si(SiMe3)(R)]
(R = Me, Et, i-Bu). The formers are synthesized from the reaction of silole dianion 2 with the
+
corresponding alkyl bromides, while the latter are synthesized via [Ph4C4Si(SiMe3)]−•[Li] (3) by
hemsilylation of 2 with trimethylsilyl chloride and then by alkylation of 3 with the corresponding alkyl
halides. The silole anion 3 and the reduced 3-silolenide 2,5-carbodianions {[Ph4C4Si(n-Bu)2]−2•2[Li]+
(10) and [Ph4C4Si(t-Bu)2]−2•2[Li]+ (11)} are characterized by 1H-, 13C-, and 29Si-NMR spectroscopy.
Acknowledgments
This research was supported by Basic Science Research Program through the National Research
Foundation of Korea (NFR) funded by Ministry of Education. The author thanks Sung-Jun Cho
(Pai Chai University, Daejon S. Korea) for supporting with lab facilities.
Conflicts of Interest
The authors declare no conflict of interest.
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