Synthesis of stannaindenyl anions and a dianion

Article abstract of DOI:10.1021/om050879x

Reduction of 1,1-diphenylstannaindene with excess lithium gave the intermediary 1-phenyl-1-stannaindenyl anion, which was further reduced to provide the 1-stannaindenyl dianion. The remarkable upfield ⁷Li NMR resonance in the dianion and the theoretical calculation suggest that the 1-stannaindenyl dianion has considerable aromatic character, as was observed in the sila- and germaindenyl dianions. Reaction of the 1-stannaindenyl dianion with tert-butyl chloride gave the 1-tert-butyl-1-stannaindenyl anion, as evidenced by NMR detection as well as a trapping experiment.

Full text of DOI:10.1021/om050879x

Organometallics 2006, 25, 2967-2971
2967
Synthesis of Stannaindenyl Anions and a Dianion
Masaichi Saito,*,† Masakazu Shimosawa,† Michikazu Yoshioka,† Kazuya Ishimura,‡ and
Shigeru Nagase‡
Department of Chemistry, Faculty of Science, Saitama UniVersity, Shimo-okubo,
Saitama City, Saitama, 338-8570 Japan, and Department of Theoretical Molecular Science,
Institute for Molecular Science, Myodaiji, Okazaki, Aichi, 444-8585 Japan
ReceiVed October 12, 2005
Reduction of 1,1-diphenylstannaindene with excess lithium gave the intermediary 1-phenyl-1-
stannaindenyl anion, which was further reduced to provide the 1-stannaindenyl dianion. The remarkable
upfield 7Li NMR resonance in the dianion and the theoretical calculation suggest that the 1-stannaindenyl
dianion has considerable aromatic character, as was observed in the sila- and germaindenyl dianions.
Reaction of the 1-stannaindenyl dianion with tert-butyl chloride gave the 1-tert-butyl-1-stannaindenyl
anion, as evidenced by NMR detection as well as a trapping experiment.
well-investigated mono- and dianions of siloles and germoles,
neither mono- nor dianions of stannole had been reported before
the start of our project to investigate stannole mono- and
dianions. Very recently, we have reported the first synthesis
and characterization of mono- and dianions of stannoles.8,9 In
the course of our studies on tin-containing aromatic compounds,
we report herein the synthesis of 1-stannaindenyl anions and a
dianion and their structural analysis by NMR spectra and
theoretical calculations.
Introduction
Recently, much attention has been focused on the anions and
dianions of siloles1 and germoles,1f,2 heavier congeners of the
cyclopentadienyl anion.3 The structural and chemical properties
of these species are of interest because these species, having a
novel π-electron system, may possess some degree of aroma-
ticity, as predicted by theoretical calculations.4 After consider-
able work on anions and dianions of group 14 metalloles,1-3
attention was next focused on the effect of benzannulation of
metallole anions and dianions on aromaticity. The five-
membered ring in the silaindenyl anion has a diene character
with C-C bond alternation, and hence, the silole ring is
essentially nonaromatic.5 The six-membered rings in both
silaindenyl and germaindenyl dianions have a diene property,
while the five-membered ring of each has considerable aromatic
character with no C-C bond alternation.6,7 In contrast to the
Results and Discussion
(a) Synthesis of 1,1-Diphenylstannaindene 1. Reductive
cleavage of phenyl groups on the tin in the reduction of a
stannole8b,c prompted us to choose 1,1-diphenylstannaindene 1
as a precursor of 1-stannaindenyl dianion 2. The dilithium
intermediate 3 prepared by the reaction of diphenylacetylene
with butyllithium reacted with dichlorodiphenylstannane to give
1,1-diphenylstannaindene 1 (57%).10
(b) Reduction of 1,1-Diphenylstannaindene 1. Reaction of
1 with 2.5 equiv of lithium in ether at room temperature gave
a deep red solution, suggesting the formation of an anionic
species. Treatment of the reaction mixture with methyl iodide
afforded 1-methyl-1-phenylstannaindene 4 (45%) as well as 1,1-
dimethylstannaindene 5 (15%),11 implying the formation of
intermediary 1-stannaindenyl anion 6 and dianion 2, respec-
tively. When an ether solution of 1 in the presence of excess
lithium was refluxed12 and then the reaction mixture was treated
* To whom correspondence should be addressed. E-mail:
masaichi@chem.saitama-u.ac.jp.
† Saitama University.
‡ Institute for Molecular Science.
(1) (a) Joo, W.-C.; Hong, J.-H.; Choi, S.-B.; Son, H.-E.; Kim, C. H. J.
Organomet. Chem. 1990, 391, 27. (b) Hong, J.-H.; Boudjouk, P. J. Am.
Chem. Soc. 1993, 115, 5883. (c) Hong, J.-H.; Boudjouk, P.; Castellino, S.
Organometallics 1994, 13, 3387. (d) Bankwitz, U.; Sohn, H.; Powell, D.
R.; West, R. J. Organomet. Chem. 1995, 499, C7. (e) West, R.; Sohn, H.;
Bankwitz, U.; Calabrese, J.; Apeloig, Y.; Mueller, T. J. Am. Chem. Soc.
1995, 117, 11608. (f) Freeman, W. P.; Tilley, T. D.; Yap, G. P. A.;
Rheingold, A. L. Angew. Chem., Int. Ed. Engl. 1996, 35, 882. (g) Freeman,
W. P.; Tilley, T. D.; Liable-Sands, L. M.; Rheingold, A. L. J. Am. Chem.
Soc. 1996, 118, 10457.
(2) (a) Dufour, P.; Dubac, J.; Dartiguenave, M.; Dartiguenave, Y.
Organometallics 1990, 9, 3001. (b) Hong, J.-H.; Boudjouk, P. Bull. Soc.
Chim. Fr. 1995, 132, 495. (c) Freeman, W. P.; Tilley, T. D.; Arnold, F. P.;
Rheingold, A. L.; Gantzel, P. K. Angew. Chem., Int. Ed. Engl. 1995, 34,
1887. (d) West, R.; Sohn, H.; Powell, D. R.; Mu¨ller, T.; Apeloig, Y. Angew.
Chem., Int. Ed. Engl. 1996, 35, 1002. (e) Choi, S.-B.; Boudjouk, P.; Hong,
J.-H. Organometallics 1999, 18, 2919.
(3) For examples of reviews, see: (a) Colomer, E.; Corriu, R. J. P.;
Lheureux, M. Chem. ReV. 1990, 90, 265. (b) Dubac, J.; Gue´rin, C.; Meunier,
P. In The Chemistry of Organic Silicon Compounds; Rappoport, Z., Apeloig,
Y., Eds.; John Wiley and Sons: Chichester, 1998; p 1961. (c) Saito, M.;
Yoshioka, M. Coord. Chem. ReV. 2005, 249, 765.
(4) (a) Goldfuss, B.; Schleyer, P. v. R. Organometallics 1995, 14, 1553.
(b) Goldfuss, B.; Schleyer, P. v. R.; Hampel, F. Organometallics 1996, 15,
1755. (c) Goldfuss, B.; Schleyer, P. v. R. Organometallics 1997, 16, 1543.
(5) Choi, S.-B.; Boudjouk, P. J. Chem. Soc., Dalton Trans. 2000, 841.
(6) Choi, S.-B.; Boudjouk, P.; Wei, P. J. Am. Chem. Soc. 1998, 120,
5814.
(8) (a) Saito, M.; Haga, R.; Yoshioka, M. Chem. Commun. 2002, 1002.
(b) Saito, M.; Haga, R.; Yoshioka, M. Chem. Lett. 2003, 912. (c) Saito,
M.; Haga, R.; Yoshioka, M. Phosphorus, Sulfur Silicon Relat. Elem. 2004,
179, 703.
(9) Saito, M.; Haga, R.; Yoshioka, M.; Ishimura, K.; Nagase, S. Angew.
Chem., Int. Ed. 2005, 44, 6553.
(10) The general synthetic route to metallaindenes was developed by
Rausch and Klemann, see: Rausch, M. D.; Klemann, L. P. J. Am. Chem.
Soc. 1967, 89, 5732.
(11) Compound 5 was first reported by Rausch and co-workers, see:
Rausch, M. D.; Klemann, L. P.; Boon, W. H. Synth. React. Inorg. Met.-
Org. Chem. 1985, 15, 923. Although compound 5 could not be isolated in
the literature, a 1H signal due to Sn-Me protons was observed at 0.40 ppm
in CD2Cl2. However, neither other spectral data nor elemental analysis was
provided. We carried out independently the characterization of compound
5 (see, Experimental Section). We observed a 1H signal due to Sn-Me
protons at 0.46 ppm in CD2Cl2, suggesting that our compound 5 should be
probably identical to Rausch’s compound.
(7) Choi, S.-B.; Boudjouk, P.; Qin, K. Organometallics 2000, 19, 1806.
10.1021/om050879x CCC: $33.50 © 2006 American Chemical Society
Publication on Web 05/10/2006

2968 Organometallics, Vol. 25, No. 12, 2006
Saito et al.
Scheme 1
Scheme 3
Scheme 2
evidently caused by the strong shielding effect of the diatropic
ring current resulting from the 6π-electron system, and hence
1-stannaindenyl dianion 2 is concluded to have considerable
aromatic character, as was suggested in the sila- and germain-
denyl dianions.6,7,16
(d) Synthesis of Stannaindenyl Anion from the Dianion.
To synthesize a 1-stannaindenyl anion from the dianion 2, the
alkylation of 2 was studied. Since the reaction of 2 with methyl
iodide gave dimethylated compound 5, tert-butyl chloride was
chosen as a bulkier alkylating reagent than methyl iodide. When
tert-butyl chloride was added to an ether solution of 2 at room
temperature, the color of the solution turned from deep red to
bright red. By treatment of the reaction mixture with methyl
iodide, 1-tert-butyl-1-methylstannaindene 11 was obtained in
40% yield, suggesting the formation of 1-stannaindenyl anion
12 by alkylation of 2 (Scheme 3). The formation of 12 from 2
was reasonably explained in terms of an electron transfer
mechanism, as was proposed in the reaction of a stannole
dianion with tert-butyl chloride.8b
with methyl iodide at room temperature, 1,1-dimethylstannain-
dene 5 was isolated in 40% yield,13 suggesting the exclusive
formation of 1-stannaindenyl dianion 2.
(c) Monitoring the Reduction of 1,1-Diphenylstannaindene
1 by NMR. The reaction of 1 with excess lithium in ether-
C6D6 was monitored by NMR. Compound 1 (78 mg, 0.154
mmol) and lithium (11 mg, 1.51 mmol) in ether were placed in
an NMR tube with C6D6 for NMR lock. The color of the
solution changed to dark red. The 119Sn NMR spectrum showed
two major signals at -14.2 and -104.8 ppm, assigned to
1-stannaindenyl dianion 2 and 1-stannaindenyl anion 6, respec-
tively. The 119Sn signal attributable to 2 (-14.2 ppm) appeared
at lower field than that for 1 (-99.2 ppm in CDCl3), as was
observed in the stannole dianion.8a,b,9 On the contrary, the tin
atom of 6 (-104.8 ppm) resonated at higher field than that of
1, as was observed in the formation of the silaindenyl anion
(δ(29Si): -23.06) from the corresponding chloride (δ(29Si):
14.90).5 After standing at room temperature for several hours,
Monitoring the reaction of 2 with tert-butyl chloride by NMR
was also carried out. In 119Sn NMR there appeared a signal for
7
1-stannaindenyl anion 12 at -30.3 ppm. In Li NMR a single
resonance was observed at 1.04 ppm, suggesting the rapid
intermolecular exchange of lithium cations between 12 and
lithium chloride.
(e) Theoretical Calculations. To aid in understanding the
structure of 2, the geometry of unsolvated 2 was optimized with
the hybrid density functional theory at the B3LYP17 level using
Huzinaga’s (433321/43321/421) (DZP) basis set and a polariza-
tion d-function (ê ) 0.183) for Sn18 and 6-31G(d) for C,19,20
H,21 and Li.20,22,23 Six different dilithio complexes (2a-f) were
found to be minima (Figure 1). The most stable complex (2a)
has two lithium atoms η5-coordinated to the planar stannole ring.
The complex 2f, having an η1- and an η5-coordinated lithium
atom, is less stable than 2a by 16.3 kcal/mol, as was observed
in the calculation of the stannole dianion.9 To estimate the effect
1
the H and 13C NMR spectra of the reaction mixture showed
the signals due to dianion 2 and phenyllithium. The intermediary
1-stannaindenyl anion 6 was easily reduced to provide 1-stan-
naindenyl dianion 2 even at room temperature. After refluxing
the reaction solution overnight, phenyllithium completely
decomposed and we could assign NMR signals due to 2.12 In
the 13C NMR spectrum, the signals assignable to the R-car-
bons were observed at 176.16 and 193.24 ppm with large
1J(Sn-C)s of about 350 MHz. The remarkable downfield
resonance of the R-carbon in the stannole dianion was also
reported.8a Although detailed assignment of 13C NMR chemical
shifts of sila- and germaindenyl dianions was not reported in
the literature,6,7 the two most downfielded resonances (146.99
and 158.07 ppm for the silaindenyl dianion;6 167.94 and 174.87
ppm for the germaindenyl dianion)7 in the metallaindenyl
dianions shift to downfield as the atomic number of the group
(14) The two most downfield resonances in the sila- and germaindenyl
dianions can be probably assigned to the R-carbon atoms of each dianion.
(15) In the 7Li NMR spectrum, signals besides that for the dianion 2
were observed at 0.66 and 0.95 ppm due to products resulting from the
decomposition of phenyllithium. The assignment of these two signals was
evidenced by separate experiments. After an ether-C6D6 solution of
phenyllithium was refluxed, the 7Li NMR spectrum of the resulting mixture
showed signals at 0.56 and 0.91 ppm.
(16) The high-field 6,7Li chemical shift is diagnostic of aromatic ring
currents. For examples, see: (a) Cox, R. H.; Terry, H. W., Jr.; Harrison, L.
W. J. Am. Chem. Soc. 1971, 93, 3297. (b) Cox, R. H.; Terry, H. W., Jr. J.
Magn. Reson. 1974, 14, 317. (c) Paquette, L. A.; Bauer, W.; Sivik, M. R.;
Bu¨hl, M.; Feigel, M.; Schleyer, P. v. R. J. Am. Chem. Soc. 1990, 112, 8776.
(d) Sekiguchi, A.; Sugai, Y.; Ebata, K.; Kabuto, C.; Sakurai, H. J. Am.
Chem. Soc. 1993, 115, 1144.
(17) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.; Yang,
W.; Parr, R. G. Phys. ReV. B 1988, 37, 785.
(18) Huzinaga, S.; Andzelm, J.; Klobukowski, M.; Radzio-Andzelm, E.;
Sakai, Y.; Tatewaki, H. Gaussian Basis Sets for Molecular Calculations;
Elsevier: Amsterdam, 1984.
(19) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972, 56,
2257.
(20) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta 1973, 28, 213.
(21) Ditchfield, R.; Hehre, W. J.; Pople, J. A. J. Chem. Phys. 1971, 54,
724.
7
14 elements increases.14 The Li signal assignable to 2 was
observed at -5.8 ppm.15 This appreciable upfield resonance is
(12) The 1-stannaindenyl dianion 2 was formed without refluxing. Thus,
the reflux conditions are necessary only for the decomposition of phenyl-
lithium.
(13) Although the 1H NMR spectrum of the crude product revealed the
formation of 5 as a main product, the isolated yield of 5 became low because
5 gradually decomposed in solution during purification to give a complex
mixture.
(22) Dill, J. D.; Pople, J. A. J. Chem. Phys. 1975, 62, 2921.

Synthesis of Stannaindenyl Anions
Organometallics, Vol. 25, No. 12, 2006 2969
Figure 1. Optimized geometry and relative energy (kcal/mol) of unsolvated 2.
Table 1. Natural Population Analysis for 2a and 2g
2a
2g
C1
C2
C3
C4
-0.68
-0.27
-0.28
-0.68
-0.67
-0.25
-0.25
-0.67
Figure 2. Optimized geometry and relative energy (kcal/mol) of
solvated 2. Hydrogen atoms are omitted for clarity.
Chart 1
of solvation on the relative stability of the dianion, the geometry
of solvated 2, whose lithium atoms each are coordinated to an
ether molecule, was optimized. The complex (2g) having two
lithium atoms η5-coordinated to the stannole ring is more stable
than that (2h) having an η1- and an η5-coordinated lithium atom
by 15.5 kcal/mol (Figure 2). Thus, the solvation does not
remarkably affect the relative stability of the complexes 2. The
following discussion about the structure and NMR analysis of
the dianion is concentrated on the complexes 2a and 2g. The
calculated C-C distances within the ring of 2a are nearly equal
(1.428, 1.461, and 1.468 Å), suggesting the considerable
aromatic delocalization of the negative charges in 2a. The trend
is quite similar to that of 2g (1.427, 1.459, and 1.461 Å).
According to the natural population analysis (Table 1), the
R-carbons are considerably negatively charged (-0.68 for 2a
and -0.67 for 2g), suggesting the large contribution of a
resonance form with stannylene character (Chart 1).24 The
calculated 13C chemical shifts25 of the quaternary carbons are
in good agreement with the measured values (Table 2).26 The
low-field resonance due to the R-carbon could be explained by
paramagnetic contribution of a tin-carbon bond, as was
observed in the stannole dianion.8a,9 The nucleus-independent-
chemical-shifts (NICS) values calculated at 1.0 Å above each
(23) All calculations were performed using Gaussian98, revision A.
11.1: Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.;
Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A.
D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi,
M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.;
Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.;
Salvador, P.; Dannenberg, J. J.; Malick, D. K.; Rabuck, A. D.; Raghavachari,
K.; Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Baboul, A. G.; Stefanov,
B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.;
Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen,
W.; Wong, M. W.; Andres, J. L.; Gonzalez, C.; Head-Gordon, M.; Replogle,
E. S.; Pople, J. A. Gaussian98, revision A. 11.1; Gaussian, Inc.: Pittsburgh,
PA, 2001.
(24) The low-field shift of the 119Sn nuclei of the dianion 2 compared to
that of 1 is reflected in the strong contribution of a stannylene character,
although the chemical shift itself is in a higher region than those of cyclic
diaminostannylenes isoelectronic to the resonance form A.29
(25) The theoretical calculations were carried out at GIAO-B3LYP/
(4333111/433111/421) and two polarization d-functions (ê ) 0.253, 0.078)
(TZDP) for Sn18 and 6-311G(d) for C and H, and Li//B3LYP/DZP for Sn
and 6-31G(d) for C, H, and Li.
(26) The assignment of CH carbons could not be achieved by the aid of
theoretical calculations because all of the CH carbons resonated closely in
the range of error of the theoretical calculation.

2970 Organometallics, Vol. 25, No. 12, 2006
Saito et al.
Table 2. Observed (2) and Calculated (2a and 2g) 13C
Chemical Shifts
lation of the 1-stannaindenyl dianion 2 by tert-butyl chloride
gave the 1-stannaindenyl anion 12.
2
2a
2g
C1
C2
C3
C4
C5
193.24
123.57
135.62
176.16
152.29
213.02
126.34
136.91
187.89
157.13
209.74
123.76
137.70
188.78
158.74
Experimental Section
General Procedure. All reactions were carried out under argon.
THF and diethyl ether used in the synthesis were distilled from
sodium benzophenone ketyl under argon atmosphere before use.
1H (400 MHz) and 13C NMR (100 MHz) spectra were recorded on
a Bruker AM-400 or an ARX-400 spectrometer with tetramethyl-
silane as an internal standard. Although nJ(Sn-13C) couplings were
observed in the 13C NMR spectra as satellite signals, most of the
nJ(119Sn-13C)s and nJ(117Sn-13C)s could not be separately estimated
because of broadening. The multiplicities of signals in the 13C NMR
given in parentheses were deduced from DEPT spectra. 119Sn (149
MHz) and 7Li NMR (156 MHz) spectra were recorded on a Bruker
DRX-400 spectrometer with tetramethylstannane and lithium
chloride as external standards, respectively. Wet column chroma-
tography (WCC) was carried out with Merck Kieselgel 60 (SiO2).
Preparative gel permeation chromatography (GPC) was carried out
on LC-918 (Japan Analytical Ind. Co., Ltd.) with JAIGEL-1H and
-2H columns. All melting points were determined on a Mitamura
Riken Kogyo MEL-TEMP apparatus and are uncorrected. High-
resolution mass spectra were measured on a JEOL JMX700-AM.
Elemental analyses were carried out at the Microanalytical Labora-
tory of Chemical Analytical Center, Saitama University.
Table 3. NICS(1) Calculation in 7-10
Table 4. Observed (1, 4, 5, and 11) and Calculated (4) 13C
Chemical Shifts
1
4
5
11
4
C1
C2
C3
C4
C5
C6
142.80
153.18
150.35
137.61
144.48
138.36
143.75
152.34
150.25
139.14
144.80
139.49
144.82
150.90
149.71
140.69
145.08
145.07
151.90
150.49
140.82
145.78
155.48
162.70
158.06
145.53
153.28
146.63
Preparation of 3-Butyl-1,1,2-triphenyl-1-stannaindene (1). To
a hexane (8 mL) solution of diphenylacetylene (1.004 g, 5.63 mmol)
and TMEDA (1.8 mL, 12 mmol) was added butyllithium (1.58 M
in hexane; 8.0 mL, 12.6 mmol) at room temperature. After being
stirred for 3 h, to the resulting mixture was added a THF (8 mL)
solution of dichlorodiphenylstannane (4.610 g, 13.1 mmol). After
the mixture was heated under reflux overnight, volatile substances
were evaporated. The residue was subjected to WCC (SiO2,
hexane-ethyl acetate, 20:1) followed by GPC to afford 3-butyl-
1,1,2-triphenyl-1-stannaindene (1) (1.605 g, 57%). 1: mp 98-99
ring27 (nonweighted mean of the heavy atom coordinate) of non-
lithium-coordinated 7-10 are shown in Table 3. The five-
membered rings of all the dianions 7-10 have more negative
NICS values than the six-membered rings, suggesting greater
aromatic character for the five-membered ring, as was calcu-
lated in the sila- and germafluorenyl dianions28 and the parent
fluorenyl dianion (Table 3). The negative NICS(1) value of the
five-membered ring of 7 also suggests that the 1-stannaindenyl
dianion 2 should have an aromatic nature, although the degree
of aromaticity of 2 is smaller than those of the germanium and
silicon analogues, judging from the NICS(1) values of 8 and
9. The 13C signal of all the aromatic quaternary carbons of
1,1-disubstituted stannindenes, 1, 4, 5, and 11, could be assigned
by the aid of theoretical calculations and J(Sn-C) values
(Table 4).26
1
°C (recrystallized from hexane); H NMR (CDCl3) δ 0.84 (t, J )
7 Hz, 3H), 1.29-1.38 (m, 2H), 1.57-1.65 (m, 2H), 2.64-2.68 (m,
2H), 7.10-7.14 (m, 3H), 7.23-7.35 (m, 9H), 7.40-7.43 (m, 1H),
7.52-7.60 (m, 5H), 7.63-7.73 (m, 1H); 13C NMR (CDCl3) δ 13.86
(-CH2CH2CH2CH3), 22.96 (-CH2CH2CH2CH3), 28.87 (-CH2CH2-
CH2CH3CH2, J(Sn-C) ) 54 Hz), 32.22 (-CH2CH2CH2CH3CH2),
124.94 (CH), 125.15 (CH), 127.35 (CH), 127.43 (CH), 128.29 (CH),
128.77 (CH, J(Sn-C) ) 55 Hz), 129.33 (CH, J(Sn-C) ) 12 Hz),
135.77 (CH, J(Sn-C) ) 44 Hz), 137.08 (CH, J(Sn-C) ) 41 Hz),
137.61 (C4), 138.36 (C6), 142.80 (C1, J(Sn-C) ) 427, 447 Hz),
144.48 (C5, J(Sn-C) ) 44 Hz), 150.35 (C3, J(Sn-C) ) 95 Hz),
153.18 (C2, J(Sn-C) ) 61 Hz); 119Sn NMR (CDCl3) δ -99.2. Anal.
Calcd for C30H28Sn: C, 71.03; H, 5.56. Found: C, 71.19; H, 5.63.
Conclusion
Reduction of 3-Butyl-1,1,2-triphenyl-1-stannaindene (1) with
Lithium (2.5 equiv). To a mixture of 1 (259 mg, 0.51 mmol) and
lithium (9 mg, 1.27 mmol) was added ether (6 mL) at room
temperature, and then the reaction mixture was stirred for 4 h. After
addition of methyl iodide (0.1 mL, 1.61 mmol) to the reaction
mixture, insoluble materials were filtered off. After removal of
volatile substances, the residue was subjected to GPC to afford
recovered 1 (45 mg, 18%), 3-butyl-1-methyl-1,2-diphenyl-1-stan-
naindene (4) (83 mg, conv 45%), and 3-butyl-1,1-dimethyl-2-
phenyl-1-stannaindene (5) (24 mg, conv 15%). 4: pale yellow oil;
1H NMR(CDCl3) δ 0.69 (s, J(Sn-H) ) 57, 59 Hz, 3H), 0.84 (t, J
) 7 Hz, 3H), 1.27-1.37 (m, 2H), 1.54-1.62 (m, 2H), 2.58-2.62
(m, 2H), 7.10-7.14 (m, 3H), 7.23-7.35 (m, 9H), 7.40-7.43 (m,
1H), 7.52-7.60 (m, 5H), 7.63-7.73 (m, 1H); 13C NMR (CDCl3)
δ -10.23 (Sn-CH3, 1J(Sn-C) ) 352, 368 Hz), 13.86 (-CH2CH2-
CH2CH3), 22.96 (-CH2CH2CH2CH3), 28.78 (-CH2CH2CH2CH3-
CH2, J(Sn-C) ) 50 Hz), 32.17 (-CH2CH2CH2CH3CH2), 124.66
(CH, J(Sn-C) ) 43 Hz), 124.99 (CH), 127.07 (CH), 127.21 (CH,
Reduction of 1,1-diphenylstannaindene with lithium gave the
1-phenyl-1-stannaindenyl anion, which is further reduced to
provide the 1-stannaindenyl dianion 2. The strong upfield
resonance due to the diatropic ring current by the 6π-electron
system was observed in the 7Li NMR of 2. Theoretical
calculations revealed the planar structure of 2 with no C-C
bond alternation within the ring, suggesting the considerable
aromatic delocalization of the negative charges. Thus, the
1-stannaindenyl dianion 2 is considerably aromatic. The alky-
(27) Schleyer, P. v. R.; Manoharan, M.; Wang, Z.-X.; Kiran, B.; Jiao,
H.; Puchta, R.; Hommes, N. J. R. v. E. Org. Lett. 2001, 3, 2465.
(28) Liu, Y.; Ballweg, D.; Mu¨ller, T.; Guzei, I. A.; Clark, R. W.; West,
R. J. Am. Chem. Soc. 2002, 124, 12174.
(29) (a) Braunschweig, H.; Gehrhus, B.; Hitchcock, P. B.; Lappert, M.
F. Z. Anorg. Allg. Chem. 1995, 621, 1922. (b) Gehrhus, B.; Hitchcock, P.
B.; Lappert, M. F. J. Chem. Soc., Dalton Trans. 2000, 3094. (c) Gans-
Eichler, T.; Gudat, D.; Nieger, M. Angew. Chem., Int. Ed. 2002, 41, 1888.

Synthesis of Stannaindenyl Anions
Organometallics, Vol. 25, No. 12, 2006 2971
J(Sn-C) ) 18 Hz), 128.23 (CH), 128.54 (CH), 129.03 (CH),
129.09 (CH), 135.58 (CH, J(Sn-C) ) 45 Hz), 136.43 (CH,
J(Sn-C) ) 41 Hz), 139.14 (C4), 139.49 (C6), 143.75 (C1,
1J(Sn-C) ) 432, 452 Hz), 144.80 (C5, J(Sn-C) ) 44 Hz), 150.25
(C3, J(Sn-C) ) 89, 93 Hz), 152.34 (C2, J(Sn-C) ) 59 Hz); 119Sn
NMR (CDCl3) δ -53.4; HRMS [M], calcd for C25H26120Sn
446.1057, found 446.1057. Anal. Calcd for C25H26Sn: C, 67.45;
125.13 (CH), 126.97 (CH), 127.02 (CH), 127.46 (CH), 136.14 (CH),
138.33 (CH), 147.31 (C), 151.81 (C), 154.98 (C), 157.53 (C),
164.44 (C), 168.51 (C); 119Sn NMR (Et2O-C6D6) δ -104.8. The
nJ(Sn-C)s could not be estimated because of low S/N ratios. The
1H signals due to 6 could not be assigned because of overlapping
of signals due to 6, 2, and a solvent.
Synthesis of 1-tert-Butylstannaindenyl Anion 12 by the
Reaction of 1-Stannaindenyl Dianion 2 with tert-Butyl Chloride.
To a mixture of 1 (251 mg, 0.49 mmol) and lithium (32 mg, 4.65
mmol) was added ether (5 mL), and the mixture was stirred for 21
h at room temperature. To the resulting solution of 2 was added
tert-butyl chloride (0.08 mL, 0.72 mmol) at room temperature. After
being stirred for 20 min, the resulting solution of 12 was treated
with methyl iodide (0.1 mL, 1.65 mmol). After removal of volatile
substances, the residue was subjected to GPC to afford 3-butyl-1-
tert-butyl-1-methyl-2-diphenyl-1-stannaindene (11) (83 mg, 40%).
1
H, 5.89. Found: C, 66.64; H, 5.79. 5: colorless oil; H NMR
(CDCl3) δ 0.45 (s, J(Sn-H) ) 56, 59 Hz, 6H), 0.83 (t, J ) 7 Hz,
3H), 1.25-1.34 (m, 2H), 1.49-1.55 (m, 2H), 2.51-2.55 (m, 2H),
7.07-7.09 (m, 2H), 7.15-7.21 (m, 1H), 7.22-7.40 (m, 4H), 7.46-
7.51 (m, 1H), 7.58-7.65 (m, 1H); 13C NMR (CDCl3) δ -8.93
(Sn-CH3, J(Sn-C) ) 332, 348 Hz), 13.63 (-CH2CH2CH2CH3),
22.73 (-CH2CH2CH2CH3), 28.45 (-CH2CH2CH2CH3CH2,
J (Sn-C) ) 48 Hz), 31.84 (-CH2CH2CH2CH3CH2), 124.20 (CH,
J(Sn-C) ) 41 Hz), 124.58 (CH), 126.46 (CH, J(Sn-C) ) 41 Hz),
126.71 (CH, J(Sn-C) ) 18 Hz), 127.99 (CH), 128.55 (CH), 135.08
(CH, J(Sn-C) ) 45 Hz), 140.69 (C4, J(Sn-C) ) 430, 450 Hz),
144.82 (C1, J(Sn-C) ) 413, 432 Hz), 145.08 (C5), 149.71 (C3,
J(Sn-C) ) 85, 89 Hz), 150.90 (C2, J(Sn-C) ) 55 Hz); 119Sn NMR
(CDCl3) δ -17.3; HRMS [M], calcd for C20H24120Sn 384.0900,
found 384.0902. Anal. Calcd for C20H24Sn: C, 62.70; H, 6.31.
Found: C, 62.14; H, 6.18.
1
11: colorless oil; H NMR (CDCl3) δ 0.45 (s, J(Sn-H) ) 51, 54
Hz, 3H), 0.82 (t, J ) 7 Hz, 3H), 1.17 (J(Sn-H) ) 72, 75 Hz, 9H),
1.28-1.34 (m, 2H), 1.46-1.59 (m, 2H), 2.51-2.58 (m, 2H), 7.07-
7.09 (m, 2H), 7.13-7.16 (m, 1H), 7.22-7.27 (m, 1H), 7.29-7.37
(m, 4H), 7.46-7.50 (m, 1H), 7.52-7.62 (m, 1H); 13C NMR
1
(CDCl3) δ -11.64 (Sn-CH3, J(Sn-C) ) 274, 287 Hz), 13.87
(-CH2CH2CH2CH3), 22.93 (-CH2CH2CH2CH3), 28.45 (C(CH3)3),
28.74 (-CH2CH2CH2CH3CH2, J(Sn-C) ) 44 Hz), 30.56 (C(CH3)3),
32.20 (-CH2CH2CH2CH), 124.46 (CH, J(Sn-C) ) 37 Hz), 124.67
(CH), 126.52 (CH, J(Sn-C) ) 38 Hz), 127.04 (CH, J(Sn-C) )
16 Hz), 128.21 (CH), 128.62 (CH), 135.51 (CH, J(Sn-C) )
43 Hz), 140.82 (C4), 145.07 (C1), 145.78 (C5, J(Sn-C) ) 43
Hz), 150.49 (C3, J(Sn-C) ) 75, 78 Hz), 151.90 (C2, J(Sn-C) )
47 Hz); 119Sn NMR (CDCl3) δ -15.6; HRMS [M], calcd for
C23H30120Sn 426.1369, found 426.1368. Anal. Calcd for C23H30Sn:
C, 64.97; H, 7.11. Found: C, 65.19; H, 7.04.
Reduction of 3-Butyl-1,1,2-triphenyl-1-stannaindene (1) with
Lithium (Excess). To a mixture of 1 (247 mg, 0.49 mmol) and
lithium (26 mg, 3.72 mmol) was added ether (5 mL) at room
temperature, and the reaction mixture was stirred for 3 h. After
being refluxed for 14 h, the resulting mixture was treated with
methyl iodide (0.15 mL, 2.41 mmol). After removal of volatile
substances, the residue was subjected to GPC to afford 3-butyl-
1,1-dimethyl-2-phenyl-1-stannaindene (5) (75 mg, 40%).
Monitoring the Reduction of 3-Butyl-1,1,2-triphenyl-1-stan-
naindene (1) with Lithium by NMR. Compound 1 (78 mg, 0.154
mmol) and lithium (11 mg, 1.51 mmol) in ether were placed in
an NMR tube with C6D6 for NMR lock. The tube was degassed
by freeze-pump-thaw cycles and sealed, and the reaction
was monitored by NMR spectroscopy. After an ether solution
was refluxed overnight, we could assign NMR signals due to
1-stannaindenyl dianion 2. 2: 13C NMR (Et2O-C6D6) δ 14.06
(-CH2CH2CH2CH3), 23.67 (-CH2CH2CH2CH3), 30.27 (-CH2CH2-
CH2CH3CH2), 35.08 (-CH2CH2CH2CH3CH2), 112.50 (CH), 121.04
(CH), 122.26 (CH), 123.57 (C2), 127.01 (CH), 128.72 (CH,
J(Sn-C) ) 14 Hz), 135.62 (C3), 143.66 (CH, J(Sn-C) ) 40 Hz),
152.59 (C5, J(Sn-C) ) 37 Hz), 176.16 (C4, J(Sn-C) ) 357, 372
Hz), 193.24 (C1, J(Sn-C) ) 360 Hz); 119Sn NMR (Et2O-C6D6) δ
Monitoring the Reaction of 1-Stannaindenyl Dianion 2 with
tert-Butyl Chloride by NMR. To a mixture of 1 (404 mg, 0.80
mmol) and lithium (54 mg, 7.77 mmol) was added ether (4 mL),
and the mixture was heated under reflux for 12 h. To the resulting
solution of 2 was added tert-butyl chloride (0.09 mL, 0.82 mmol)
at room temperature. After being stirred for 2 h, an aliquot of the
solution was placed in an NMR tube with C6D6 (0.2 mL) for NMR
lock. The tube was degassed by freeze-pump-thaw cycles and
sealed, and the reaction was monitored by NMR spectroscopy. 12:
119Sn NMR(Et2O-C6D6) δ -30.3.
Acknowledgment. This work was partially supported by a
Grant-in-Aid for Encouragement of Young Scientists (B), No.
17750032 (M. Saito), and the Nanotechnology Support Project
from the Ministry of Education, Science, Sports and Culture,
Japan. M. Saito acknowledges a research grant from Toray
Science Foundation.
7
1
-9.2; Li NMR (Et2O-C6D6) δ -5.8. The H signals of 2 could
not be assigned because of overlapping of signals due to 2 and a
solvent. The 13C NMR signal due to 6 could be assigned by
subtracting the signals for 2 from those for the reaction mixture. 6:
13C NMR (Et2O-C6D6) δ 14.10 (-CH2CH2CH2CH3), 23.50
(-CH2CH2CH2CH3),29.76(-CH2CH2CH2CH3CH2),33.17(-CH2CH2-
CH2CH), 122.55 (CH), 123.76 (CH), 123.86 (CH), 125.05 (CH),
OM050879X