Synthesis and NMR characterization of 2,5-bis(trimethylsilyl)-3,4-diphenyl-1-silacyclopentadienyl dianion

Article abstract of DOI:10.1080/10426507.2014.905574

Two new silyl-substituted silolide dianions (11a, 11b) have been synthesized and characterized spectroscopically. Their ¹H, ²⁹Si, and ¹³C NMR spectra show similarities to the known phenyl-and alkyl-substituted analogues. R

Full text of DOI:10.1080/10426507.2014.905574

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Phosphorus, Sulfur, and Silicon and the
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Synthesis and NMR Characterization of
2,5-Bis(Trimethylsilyl)-3,4-Diphenyl-1-
Silacyclopentadienyl Dianion
Csaba Feketea, László Nyulászia & Ilona Kovácsa
a Department of Inorganic and Analytical Chemistry, Budapest
University of Technology and Economics, Budapest, H-1111, Hungary
Accepted author version posted online: 14 May 2014.Published
online: 04 Aug 2014.
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To cite this article: Csaba Fekete, László Nyulászi & Ilona Kovács (2014) Synthesis and NMR
Characterization of 2,5-Bis(Trimethylsilyl)-3,4-Diphenyl-1-Silacyclopentadienyl Dianion,
Phosphorus, Sulfur, and Silicon and the Related Elements, 189:7-8, 1076-1083, DOI:
10.1080/10426507.2014.905574
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Phosphorus, Sulfur, and Silicon, 189:1076–1083, 2014
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2014.905574
SYNTHESIS AND NMR CHARACTERIZATION
OF 2,5-BIS(TRIMETHYLSILYL)-3,4-DIPHENYL-1-
SILACYCLOPENTADIENYL DIANION
Csaba Fekete, La´szlo´ Nyula´szi, and Ilona Kova´cs
Department of Inorganic and Analytical Chemistry, Budapest University
of Technology and Economics, Budapest, H-1111, Hungary
GRAPHICAL ABSTRACT
Abstract Two new silyl-substituted silolide dianions (11a, 11b) have been synthesized and
characterized spectroscopically. Their 1H, 29Si, and 13C NMR spectra show similarities to the
known phenyl- and alkyl-substituted analogues. Reaction with ethyl bromide gave the expected
diethylsilol. B3LYP/6-31 + G∗ geometry optimization revealed equalized CC distances, and
also NICS values indicate significant aromaticity.
Figures S1—S5 are available online in Supplemental Materials.
Keywords Aromacity; silolyl dianion; density functional calculation
INTRODUCTION
Silacyclopentadienyl anions—in contrast to the cyclopentadienyl anion—in general
exhibit small aromaticity, due to the pyramidality of the silyl anion,1 similarly to the
isoelectronic phospholes.2 Silacyclopentadienyl dianions do not suffer from the planarity
problem and are considered highly aromatic,3 likewise phospholide anions.4 Recently,
we have shown5 that α-silyl substitution enhances the aromaticity of the monoanion, by
increasing the weight of the b resonance form (Scheme 1). Having this in mind, we have
decided to investigate the aromaticity of the α-substituted silolid dianion as well, in a
combined synthetic/theoretical study.
Received 14 February 2014; accepted 6 March 2014.
Dedicated to Professor Louis D. Quin on the occasion of his 86th birthday.
Address correspondence to Ilona Kova´cs, Department of Inorganic and Analytical Chemistry, Budapest
University of Technology and Economics, Szt. Gelle´rt te´r 4. Budapest, H-1111, Hungary. E-mail: iko-
vacs@mail.bme.hu
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gpss.
1076

SILACYCLOPENTADIENYL DIANION
1077
Me3Si
SiMe3
Me3Si
SiMe3
Me3Si
SiMe3
Si
H
Si
H
Si
H
a
b
c
Scheme 1 Mesomeric structures of silolide anion.
The first silacyclopentadienyl dianon 1b (1,1-disodio-2,3,4,5-tetraphenylsilacyclopen
tadienyl dianion) (Scheme 2) was synthetized by Joo and Hong in 1990.6 To estimate
the extent of aromaticity, 29Si-NMR chemical shifts were also studied in the case of the
dilithio-dianion (1a).7 In theory, delocalization should result a charge transfer from the
silicon toward the butadiene moiety, which is considered to result in a downfield effect on
29Si NMR, and an upfield effect on the ring carbons in 13C NMR signals as compared to
the signals of the neutral tetravalent synthetic precursors (e.g. dichlorosilols). This charge
transfer effect was related to the aromatic character of the dianion.7 The X-ray structure
was also obtained in the case of 1,1-dilithio-2,3,4,5-tetraphenylsilolide (1b) exhibiting
nearly equal CC distances in agreement with the high aromaticity.8 Interestingly, while in
the solid state η1− η5–coordinated silolyl dianion was formed, in THF solution 7Li-NMR
studies indicated η5− η5–coordination. Tilley’s research group was able to obtain the X-ray
structure of the crown ether-coordinated 1,1-dipotassio-2,3,4,5-tetramethylsilolide (2b).9
Theoretical calculations carried out by Schleyer et al. also approved the high aromaticity
of the silolyl dianions and other groups’ 14 metallocyclopentadienyl dianions.3,10 Some
aromatic germoyl dianions were also published during this period and the synthesis of
a stannacyclopentadienyl dianion was also reported.11−14 Altogether only five different
silolyl dianions (Scheme 2) were published due to the limited number of the available
dihalo precursors.15,16 Despite the limited availability of silolyl dianions, their interesting
and unusual chemistry is continuously studied.17,18
Ph
Ph
Ph
Ph
nBu
Ph
Me
Me
Me
Et
Et
Et
Me Et
Si
2M+
Si
2M+
Si
2M+
Si
2M+
Si
2M+
5a M=Li
4 M=K
3 M=Li
1a M=Li
1b M=Na
2a M=Li
2b M=K
5b M=Na
Scheme 2 Silol dianions, silafluorenyl dianion, silaindenyl dianions.
Tetraphenylsilolyl dianions (1a, 1b) were produced from 1,1-dichloro-2,3,4,
5-tetraphenylsilol that can be prepared by the reaction of SiCl4 and 1,4-dilithio-1,2,3,4-
tetraphenylbuta-1,3-diene.6 The latter compound can be obtained from diphenylacetylene
and lithium,19 this reaction, however, is limited to the aryl-substituted derivatives.
Tetramethylsilolyl dianions (2a, 2b) can be obtained from the direct reduction of
1,1-dibromo-2,3,4,5-tetramethylsilol or 1,1-dichloro-2,3,4,5-tetramethylsilol. While the
former precursor can be synthetized from Cp2ZrC4Me4 and SiBr4,9,20 1,1-dichloro-
2,3,4,5-tetramethylsilol is generated by the reaction of SiCl4 and 1,1-dilithio-1,2,3,4,-
tetramethylbuta-1,3-diene which in turn can be produced from the corresponding

1078
C. FEKETE ET AL.
Cp2ZrC4Me4.21 The tetraethyl derivative can also be produced by the zirconocene
route.22 Silaindenyl and silafluorenyl derivatives were also prepared.23,24 Here we report
the synthesis and an NMR study of the new 2,5-bis(trimethylsilyl)-substituted silolide
dianions.
RESULTS AND DISCUSSION
Synthesis of 1,1-dichloro-2,5-bis(trimethylsilyl)-3,4-diphenylsilol was performed by
the same route that was published by Tamao’s research group (Scheme 3).25 Reaction
between bis(diethylamino)dichlorosilane (6) and lithium-phenylacetylide in THF solution
provides bis(phenylethynyl)bis(diethylamino)silane (8). Addition of 8 to a THF solution of
lithium-naphtalide, then quenching the mixture with excess amount of trimethylchlorosi-
lane gives 1,1-bis(diethylamino)-2,5-bis(trimethylsilyl)-3,4-diphenylsilol (9) in high yield.
Transformation of the diethylamino- to a chlorine-function can be achieved by bubbling
HCl gas through the diethylether solution of the diaminolsilol (9).
Ph
Ph
Ph
Ph
i
ii
+
(NEt2)2SiCl2
Ph
C
CH
Me3Si
Et2N
SiMe3
NEt2
Si
Si
Et2N NEt2
6
7
8
9
iii
Ph
Ph
Me3Si
SiMe3
Si
Cl
Cl
10
Scheme 3 (i) 1 molar amount nBuli, THF, 0◦C; (ii) 4 molar amount Li/Np, THF, −78◦C, 1 h, then 4 molar
amount Me3SiCl, −78◦C to RT, 8 h; (iii) 10 molar amount dry HCl gas, Et2O, −78◦C, 1 h.
Ph
Ph
Ph
Ph
Ph
Ph
4eq M
2eq EtBr
dioxane
Me3Si
SiMe3
Me3Si
SiMe3
Me3Si
SiMe3
Si
Si
2M+
Si
dioxane
Cl
Et
Cl
Et
11a M=K
11b M=Na
10
12
Scheme 4 Synthesis of dianions and their reaction with EtBr.
10 reacts with sodium in dioxane giving a dark red solution after 12 h at reflux
temperature. Applying potassium instead of sodium, the reaction time is decreased to 4 h,
while with lithium no reaction occurred. After the filtration of the suspension, the dianion
(11a, b) can be isolated as a yellow pyrophoric powder. Both compounds are stable in

SILACYCLOPENTADIENYL DIANION
1079
Table 1 13C NMR chemical shifts in ppm (reference external TMS) of 1b, 10, 11, and 13
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Me3Si
Ph
Ph
SiMe3
Ph
Me3Si
SiMe3
Si
Si
Si
Si
2Na+
2Na+
11b
Cl
Cl
Cl
Cl
13
10
1b
δ(CDCl3)
δ(THF-d8)
ꢀδ
δ(CDCl3)
δ(C6D6/THF)
ꢀδ
Cα
Cβ
154.7
132.3
153.2
130.7
−1.5
−1.6
169.8
136.2
149.2
140.2
−20.6
4.0
β-Ph
β-Ph
Cipso
Corto
Cmeta
Cpara
135.4
129.3
128.2
127.1
—
146.7
133.4
126.4
121.8
—
11.3
4.1
−1.8
−5.3
—
140.4
128.4
127.5
127.2
0.3
143.1
131.0
125.4
121.2
5.1
2.7
2.6
−1.9
−6.0
4.8
CSiMe3
nitrogen atmosphere for months, however, they react with air rapidly to form a white
powder. Adding EtBr to the THF solution of 11a or 11b gives the expected diethylsilol
(12) in 90% yields. (Scheme 4).
The 29Si NMR signal of the ring silicon of 11a (49.3 ppm), 11b (44.9 ppm) is shifted
downfield compared to 10 (19.3 ppm) and 12 (2.8 ppm), and is between the reported
chemical shift of 1a (68.5 ppm)7 and 2a (29.8 ppm).21 13C NMR chemical shifts of 10 and
11b together with that of the tetraphenyl derivatives 13 and 1b are given in Table 1 (11a
exhibits similar data—see experimental section). The direct metallation of 10 results in a
significant upfield effect on the Cα of 11, while the upfield effect on Cβ is small. However,
chemical shift changes on β-phenyl groups during the reduction are similar in 1b and 11b
(see Table 1). The 13C NMR signals of the trimethylsilyl groups in 11b with respect to 10
are downfielded (11b: 5.1 ppm; 10: 0.3 ppm). This is probably caused by the ring current of
the delocalization, as was already observed on the alkyl signals (1H, 13C) of 2a, 2b, and 3.
Interestingly, the 29Si NMR and 1H NMR signals of the trimetylsilyl group changed to the
1
opposite direction than expected (29Si NMR: 11b: −19.1 ppm, 10: −7.9 ppm; H NMR:
11b: −0.96 ppm, 10: 0.22 ppm).
Density functional calculations were carried out on 11 for understanding the effect
of the trimethylsilyl substituents on the aromaticity of the ring. The optimized structure
of 11 is shown in Figure 1. Geometry optimization and NBO calculations were carried
out at B3LYP/6-31+G∗, whereas for NMR calculations B3LYP/pcS-2 level was used. The
CC bond lengths in the silolide ring is nearly the same (CαCβ: 1.439 Å CβCβ: 1.436 Å).
Indeed CβCβ is shorter than CαCβ which means that the mesomeric structure is closer
to type b or c (Scheme 1). The phenyl groups exhibit a propeller like arrangement—as
an apparent consequence of steric congestion—and therefore the conjugation between the
silol ring and the phenyl groups should be decreased as already noted in the case of the
tetraphenyl silolides (1a, 1b).7,22 Interestingly, NICS values show a moderate aromatic
character (NICS(0): −5.9 ppm; NICS(1)πzz: −19.4 ppm) while the planar monoanion
(C4H4SiH−) has larger NICS (NICS(0): −14.0 ppm; NICS(1)πzz: −26.1 ppm) values.5

1080
C. FEKETE ET AL.
Figure 1 Optimized structure of 11 at B3LYP/6-31+G∗ level of theory.
To obtain the mesomeric distribution of 11, NBO calculations were carried out. The β-
phenyl groups were removed from the structure for the easier comparison of the mesomeric
distribution of 11 with that of the 2,5-disilylsilolide anion.5 It is noteworthy that in the
absence of the steric repulsion between the phenyl residues, the CβCβ distance decreases
(from 1.436 to 1.400 Å) while CαCβ and the NICS values did not change significantly (see
Supporting Information). As expected, the mesomeric distribution of 2,5-bis(trimetilsilyl)
dianion (a: 7%, b: 31%, c: 23%, see Scheme 1) is close to that of the planar 2,5-disilylsilolide
(a: 9%, b: 32%, c: 23%, see Scheme 1).5
EXPERIMENTAL
All reactions were carried out under dry nitrogen atmosphere using standard Schlenk
techniques. Dioxane and THF were distilled from sodium benzophenone under nitrogen.
Hexane was dried with LiAlH4 and distilled under nitrogen atmosphere. C6D6 was dried
over sodium benzophenone and were vacuum transferred to the NMR tube. NMR spectra
were recorded on Bruker Avance 300 and Bruker Avance DRX-500 spectrometers in
CDCl3 or C6D6/THF. GC-MS data were obtained on a SHIMADZU GC-MS QP2010
with GC-MS system equipped with ZB-5 capillary column (95% methylpolysiloxane and
5% diphenylpolysiloxane). Quantum chemical calculations carried out with Gaussian 0926
software package at B3LYP/6-31 + G∗ level of theory. This method was successfully
applied earlier to calculate anionic structures converging to wavefunctions with the SOMO
not being a spatially diffuse orbital.27 Investigation of the wavefunction of 11 at B3LYP/6-31
+ G∗, indeed, showed that no electron was placed on the diffuse orbitals. NICS values28, 29
were calculated with B3LYP/pcS-2 method. Selected NMR and mass spectra for 11a and
12 are presented in the Supplemental Materials (Figures S1–S5).
Synthesis of 1,1-dicloro-2,5-bis(trimethylsilyl)-3,4-diphenilsilol (10)
10 was prepared according to the Tamao’s procedure.25 Before use 10 was recrys-
1
tallized from hexane at −40◦C. Yield: 3.2 g (81%). H NMR (CDCl3) δH: 0.22 (s, 18H,
Si(CH3)3), 6.77−6.96 (m, 10H, Ph). 13C NMR (CDCl3) δC: 0.3 (Si(CH3)3), 127.2 (Ph-
Cp), 127.5 (Ph-Cm), 128.4 (Ph-Cp), 136.2 (Cβ), 140.4 (Ph-Ci), and 169.8 (Cα). 29Si NMR
(CDCl3) δSi: −7.9 (Si(CH3)3), 19.3 (SiC4).

SILACYCLOPENTADIENYL DIANION
1081
Synthesis of 1,1-dipotassio-2,5-bis(trimethylsilyl)-3,4-diphenilsilol (11a)
1.50 g (3.35 mmol) 10 was dissolved in 5 mL dioxane and 0.66 g (16.8 mmol)
potassium was added to the solution under nitrogen. The mixutre was stirred for 8 h at
reflux temperature. The mixture became dark red and a thick precipitate formed. Dioxane
was removed at reduced pressure and THF (10 mL) was added to the residual. The THF
suspension was filtered to remove unreacted sodium. The filtrate was concentrated and
hexane (10 mL) was added to the solution. The precipitate was filtered and washed with
hexane until the precipitate become yellow. The yellow solid was dried under reduced
pressure. Yield: 1.30 g (85%). 1H NMR (C6D6/THF) δH: 0.23 (s, 18H, Si(CH3)3), 6.79−6.83
(m, 2H, p-Ph), 6.92−6.97 (m, 4H, m-Ph), 7.05−7.15 (m, 4H, o-Ph). 13C NMR (C6D6/THF)
δC: 6.3 (Si(CH3)3), 122.7 (Ph-Cp), 126.7 (Ph-Cm), 132.0 ppm (Ph-Co), 141.3 (Cβ), 145.0
(Ph-Ci), and 149.7 (Cα). 29Si NMR (C6D6/THF) δSi:−15.0 (Si(CH3)3), 49.3 (SiC4).
Synthesis of 1,1-disodio-2,5-bis(trimethylsilyl)-3,4-diphenilsilol (11b)
1.50 g (3.35 mmol) 10 was dissolved in dioxane (5 mL) and 0.39 g (16.8 mmol)
sodium was added to the solution under nitrogen. The mixture was stirred for 24 h on
reflux temperature. The work up process was carried out the same way as for 11a. Yield:
1
1.29 g (91%). H NMR (C6D6/THF) δH: −0.96 (s, 18H, Si(CH3)3), 6.61−6.63 (m, 2H,
p-Ph), 6.72−6.78 (m, 4H, m-Ph), 6.86−6.90 (m, 4H, o-Ph). 13C NMR (C6D6/THF) δC: 5.1
(Si(CH3)3), 121.2 (Ph-Cp), 125.4 (Ph-Cm), 131.0 (Ph-Co), 140.2 (Cβ), 143.1 (Ph-Ci), 149.2
(Cα). 29Si NMR (C6D6/THF) δSi:−19.1 (Si(CH3)3), 44.9 (SiC4).
Synthesis of 1,1-diethyl-2,5-bis(trimethylsilyl)-3,4-diphenilsilol (12)
130 mg (0.29 mmol) 11a was dissolved in THF (3 mL) and 0.05 mL (0.58 mmol) EtBr
was added to the solution. The dark red solution became light yellow after 1 h. The solvent
and the volatiles were removed under reduced pressure and the residual was dissolved
in hexane and was filtered. Hexane was removed by vacuum to give a yellow oil. Yield:
112 mg (93%). 1H NMR (CDCl3) δH: 0.39 (s, 18H, Si(CH3)3), 1.15 (q, 4H, CH2CH3), 1.25
(t, 6H, CH2CH3), and 6.95−7.03 (m, 10H, Ph). 13C NMR (CDCl3) δC: 1.7 (Si(CH3)3),
6.0 (CH2CH3), 8.0 (CH2CH3), 126.9 (Ph-Cp), 127.72 (Ph-Cm), 129.5 (Ph-Co), 142.4 (Cβ),
143.8 (Ph-Ci), 172.3 (Cα). 29Si NMR (CDCl3) δSi: −10.0 (Si(CH3)3), 2.8 (SiC4). EI-MS:
m/z (M+, relative abundance): 434.3 (18.7) [M]+, 419.1 (5.6) [M − CH3]+, 405.1 (7.0) [M
− C2H5]+, 361.1 (7.5) [M −2C2H5 − CH3]+, 231.1 (25.3) [M −2CH2CH3 −2Si(CH3)
+ H]+
.
CONCLUSION
Synthesis of 1,1-disodio-2,5-bis(trimethylsilyl)-3,4-diphenilsilol and 1,1-dipotassio-
2,5-bis(trimethylsilyl)-3,4-diphenilsilol has been carried out successfully. The reaction
with EtBr produced the expected 1,1-diethyl-2,5-bis(trimethylsilyl)-3,4-diphenilsilol. NMR
studies shows that these dianions (11a, 11b) have enhanced aromatic character due to the
charge transfer effect that can be observed in 29Si NMR and 13C NMR spectra. However, the-
oretical calculations showed that the aromaticity of the dianions is somehow lesser than the
monoanions based on different NICS aromaticity measures, while the optimized structure
showed bond length equalization. This indicates that the aromaticity of the silolide anions

1082
C. FEKETE ET AL.
and dianions is a complex issue, and it depends strongly on the nature of the substituents
on the ring carbons.
FUNDING
Financial Support from OTKA K 105417, and COST CM1302 is gratefully acknowl-
edged. The authors appreciate the help of Jo´zsef Balla for the GC-MS measurements.
SUPPLEMENTAL MATERIAL
Supplementary data for this article can be accessed on the publisher’s website,
www.tandfonline.com/gpss
REFERENCES
1. Schleyer, P. V R.; Freeman, P. K.; Jiao, H.; Goldfuss, B. Angew. Chem. Int. Ed. Engl. 1995, 34,
337-340.
2. Quin, L. D. Phospholes. In: Katritzky, A. R.; Rees, C. W.; Scriven, E. F. V. (Eds.) Comprehensive
Heterocyclic Chemistry II, Elsevier, 1996.
3. Goldfuss, B.; Schleyer, P. V R.; Hampel, F. Organometallics 1996, 15, 1755-1757.
4. Benko˝, Z.; Nyula´szi L. Aromatic phosphorus heterocycles. In: T. M. Krygowski and M. K.
Cyransky (Vol. Eds.), Aromaticity in Heterocyclic Compounds, Vol. 19; In: R. R. Gupta (Series
Ed.), Topics in Heterocyclic Chemistry ; Springer: Heidelberg, 2009, pp. 27-83.
5. Fekete, C. S.; Kova´cs, I.; Ko¨nczo¨l, L.; Benko˝, Z.; Nyula´szi, L. Struct. Chem. 2014, 25, 377-387.
6. Joo, W.-C.; Hong, J.-H.; Choi, S.-B.; Son, H.-E. J. Organomet. Chem. 1990, 391, 27-36.
7. Hong, J.-H.; Boudjouk, P.; Castellino, S. Organometallics 1994, 13, 3387-3389.
8. West, R.; Sohn, H.; Bankwitz, U.; Calabrese, J.; Apeloig, T.; Mueller, T. J. Am. Chem. Soc. 1995,
117, 11608-11609.
9. Freeman, W. P.; Tilley, T. D.; Yap, G. P. A.; Rheingold A. L. Angew. Chem. Int. Ed. 1996, 35,
882-884.
10. Goldfuss, B.; Schleyer, P. V. R. Organometallics 1997, 16, 1543-1552.
11. Hong, J.-H.; Boudjouk, P. Bull. Soc. Chim. Fr. 1995, 132, 495-498.
12. West, R.; Sohn, H.; Powell, D. R.; Mueller, T.; Apeloig, Y. Angew. Chem. Int. Ed. 1996, 35,
1002-1004.
13. Saito, M.; Haga, R.; Yoshioka, M. Chem. Commun. 2002, 1002-1003.
14. Saito, M.; Haga, R.; Yoshioka, M.; Ishimura, K.; Nagase, S. Angew. Chem. Int. Ed. 2005, 44,
6553-6556.
15. Hissler, M.; Dyer, P. W.; Reau, R. Coord. Chem. Rev. 2003, 244, 1-44.
16. Kato, R.; Ichinohe, M.; Lee, V. Y.; Sekiguchi, A. J. Am. Chem. Soc. 2005, 127, 13142-13143.
17. Toulokhonova, I. R.; Friedrichsen D. R.; Hill J. N.; Mu¨ller, T.; West, R. Angew. Chem. Int. Ed.
2006, 45, 2578-2581.
18. Toulokhonova, I. S.; Guzei, I. A.; West, R. J. Am. Chem. Soc. 2004, 126, 5336-5337.
19. Smith, L. I.; Hoehn, H. H. J. Am. Chem. Soc. 1941, 63, 1184.
20. Fagan, P. J.; Nugent, W. A.; Calabrese, J. C. J. Am. Chem. Soc. 1994, 116, 1880.
21. Bankwitz, U.; Sohn, H.; Powell, D. R.; West, R. J. Organomet. Chem. 1995, 499, C7-C9.
22. Hong, J. H. Molecules 2011, 16, 8033-8040.
23. Choi, S.-B.; Boudjouk, P. Tetrahedron Lett. 2000, 41, 6685-6688.
24. Liu, Y. L.; Stringfellow, C.; Ballweg, D.; Guzei, I. A.; West, R. J. Am. Chem. Soc. 2002, 124,
49-57.
25. Jin, R.-Z.; Tamao, K. Organometallics 1997, 16, 2230-2232.

SILACYCLOPENTADIENYL DIANION
1083
26. Gaussian 09, Revision B.01, Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji,
H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg,
J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.;
Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A. Jr.; Peralta, J. E.; Ogliaro, F.;
Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Keith, T.; Kobayashi,
R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi,
M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli,
C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador,
P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.;
Cioslowski, J.; Fox, D. J. Gaussian, Inc., Wallingford CT, 2010.
27. Modelli, A.; Hajgato´, B.; Nixon, J. F.; Nyulaszi, L. J. Phys. Chem. A 2004, 108, 7440-7447.
28. Schleyer, P. v R.; Maerker, C.; Dransfeld, A.; Jiao, H.; Hommes, N. v E. J. Am. Chem. Soc. 1996,
118, 6317-6318.
29. Schleyer, P. v R.; Jiao, H.; Hommes, N. V. E.; Malkin; V. G.; Malkina, O. L. J. Am. Chem. Soc.
1997, 119, 12669-12670.