Formation of the first monoanion and dianion of stannole

Article abstract of DOI:10.1039/b200238h

The first syntheses of mono- and dianions of stannole were accomplished by transmetallation or reduction of the novel bi(1,1-stannole).

Full text of DOI:10.1039/b200238h

Formation of the first monoanion and dianion of stannole†
Masaichi Saito,* Ryuta Haga and Michikazu Yoshioka
Department of Chemistry, Faculty of Science, Saitama University, Shimo-okubo, Saitama-city, Saitama
338-8570, Japan. E-mail: masaichi@chem.saitama-u.ac.jp
Received 8th January 2002, Accepted 18th March 2002
First published as an Advance Article on the web 8th April 2002
The first syntheses of mono- and dianions of stannole were
accomplished by transmetallation or reduction of the novel
bi(1,1-stannole).
Recently, much attention has been focused on the anions and
1
1f,2
dianions of siloles and germoles, heavier congeners of the
3
cyclopentadienyl anion. The structural and chemical properties
of these species are of interest because these species having a
novel p-electron system may possess some degree of ar-
4
omaticity as predicted by theoretical calculations. The degree
of aromaticity of silolyl anions depends on the substituent on the
silicon,1 while the germolyl anions do not show aromaticity
because the negative charge localizes on the germanium.1
By contrast, the negative charges in the dianions of siloles and
b,f
f,2a,c
germoles significantly delocalize in the C
4
M (M = Si, Ge)
ring.1
d–f,2b,d,e
With regard to polymer chemistry, the silole
Fig. 1 ORTEP drawing of 2 with thermal ellipsoids plots (40% probability
for non-hydrogen atoms). Selected bond lengths (Å) and angles (°): Sn(1)–
Sn(1) 2.7844(7), Sn(1)–C(1) 2.152(7), C(1)–C(2) 1.34(1), C(2)–C(3)
dianions were reported to be useful precursors for the synthesis
of poly(1,1-silole)s having unique electronic characteristics. In
5
contrast to the well-investigated mono- and dianions of siloles
and germoles, neither mono- nor dianions of stannole has been
reported. We have already reported that reaction of
1
8
.50(1), C(3)–C(4) 1.38(1), C(4)–Sn(1) 2.146(8); C(1)–Sn(1)–C(4),
3.3(3).
1,1,2,3,4,5-hexaphenylstannole with bromine gave 1 through
8
is normal, 2.7844(7) Å. The stannole ring has nearly a planar
structure. The formation of 2 is noteworthy from the standpoint
of being the first example of a bi(1,1-stannole).
the cleavage of a Sn–C(vinyl) bond followed by the elimination
6
of a phenyl group (Scheme 1). We report herein the first
formation of stable mono- and dianions of stannole in solution
Since bi(1,1-metallole)s are known to be good precursors for
at room temperature from the bi(1,1-stannole) obtained by
metalloyl anions,1
a,e,f
the formation of a stannole monoanion
debrominative dimerization of 1.7
from 2 was examined. Reaction of 2 with butyllithium gave a
red solution, suggesting the formation of a stannole monoanion.
This color remained unchanged at room temperature, but
immediately changed to yellow upon the addition of methyl
iodide to the solution at room temperature. After usual workup,
the residual mixture was chromatographed to afford 1-methyl-
1
4
-phenylstannole 4 in 42% yield (Scheme 3). The formation of
could be reasonably interpreted in terms of the methylation of
Scheme 1
the initially formed stannole monoanion 5. To the best of our
knowledge, the formation of 4 provides the first evidence for the
formation of a stannole monoanion. Since stannole derivatives
are relatively unstable on silica gel or alumina, compound 4 is
likely to be isolated by chromatography in lower yield than the
true yield. Compound 2 was treated with tert-butyllithium
instead of butyllithium at low temperature and then methyl
First, we examined the synthesis of a stannole skeleton by the
debrominative cyclization of 1. Treatment of 1 with 2 equiv of
tert-butyllithium in THF at 290 °C gave a yellow solution.
After usual workup, the mixture was chromatographed to gave
bi(1,1-stannole) (58%) as yellow crystals together with stannole
3
(7%) (Scheme 2). Compound 2 was proved to have a
1
iodide was added to the reaction mixture. The H NMR analysis
13
symmetrical structure by its C NMR, and its structure was
finally established by X-ray structural analysis (Fig. 1).‡
Because of the symmetric structure of 2 with respect to the Sn–
Sn bond, a half moiety was refined. The length of Sn–Sn bond
of the reaction mixture using p-dimethoxybenzene as an internal
standard revealed the true yields of 3 and 4 to be 76 and 86%,
Scheme 2
†
Electronic supplementary information (ESI) available: experimental
details. See http://www.rsc.org/suppdata/cc/b2/b200238h/
Scheme 3
1
002
CHEM. COMMUN., 2002, 1002–1003
This journal is © The Royal Society of Chemistry 2002

respectively, indicating quite high efficiency for the generation
In summary, the first stannole mono- and dianions stable in
solution were successfully synthesized from the bi(1,1-stan-
nole). These anions reacted with methyl iodide to afford the
corresponding methylated stannoles. 1 Sn NMR studies sug-
gest a partial delocalization of negative charge in the mono-
anion and strong participation of a resonance form with
stannylene character in the dianion. Further investigation on
their structural analysis and application to novel tin-containing
polymers are currently in progress.
of 5 (Scheme 4).
19
Scheme 4
This work was partially supported by Grant-in-Aids for
Encouragement of Young Scientists, Nos. 10740288 (M. S.)
and 13740349 (M. S.) from the Ministry of Education, Science,
Sports and Culture, Japan and from Japan Society for the
promotion of Science, respectively.
Reductive formation of 5 from 2 was also investigated.
Treatment of 2 with an excess of lithium in THF at room
temperature gave a dark red solution. Upon the addition of
methyl iodide to this solution, the color of the reaction mixture
immediately changed to yellow. After chromatography, com-
pound 4 was obtained in 58% yield together with 1,1-dimethyl-
Notes and references
9
stannole 6 (6%). Thus, the reduction of 2 by lithium revealed
‡
Crystallographic data for 2: C34
H25Sn, M = 552.264, 0.1 3 0.1 3 0.1
evidence not only for the formation of the stannole monoanion
mm, monoclinic, space group P2 /c, a = 10.8790(5), b = 9.7350(5), c =
1
5
but also for the formation of the stannole dianion 7. The
3
2
1
c
6.2920(13) Å, b = 109.642(2)°, V = 2622.5(2) Å , T = 298 K, D =
formation of 6 prompted us to investigate exhaustive reduction
of 2. When a THF solution of 2 in the presence of excess lithium
was refluxed and then the reaction mixture was treated with
methyl iodide at room temperature, 1,1-dimethylstannole 6 was
formed as a main product. Recrystallization of the crude
mixture from hexane gave 6 in 23% yield (Scheme 3). The
formation of 6 could be interpreted in terms of the methylation
of the intermediary stannole dianion 7 resulting from the further
reduction of 5. The silole monoanion is known to be reduced to
the silole dianion by lithium via the tetraanion.10 To the best of
our knowledge, the formation of 6 is the first evidence for the
formation of a stannole dianion.
23
.3995 g cm , Z = 4, Mo-Ka radiation (l = 0.71073 Å), Weisenberg
scans. The non-hydrogen atoms were refined anisotropically and all the
hydrogen atoms were placed at calculated positions (d(C–H) = 0.93 Å).
The final cycle of full-matrix least-squares refinement was based on 3413
w
observed reflections [I > 2.00s(I)] and 316 variable parameters with R (R )
= 0.056 (0.111). CCDC reference number 170708. See http://www.rsc.org/
suppdata/cc/b2/b200238h/ for crystallographic data in CIF or other
electronic format.
1
(a) W.-C. Joo, J.-H. Hong, S.-B. Choi, H.-E. Son and C. H. Kim, J.
Organomet. Chem., 1990, 391, 27; (b) J.-H. Hong and P. Boudjouk, J.
Am. Chem. Soc., 1993, 115, 5883; (c) J.-H. Hong, P. Boudjouk and S.
Castellino, Organometallics, 1994, 13, 3387; (d) U. Bankwitz, H. Sohn,
D. R. Powell and R. West, J. Organomet. Chem., 1995, 499, C7; (e) R.
West, H. Sohn, U. Bankwitz, J. Calabrese, Y. Apeloig and T. Mueller,
J. Am. Chem. Soc., 1995, 117, 11608; (f) W. P. Freeman, T. D. Tilley,
G. P. A. Yap and A. L. Rheingold, Angew. Chem., Int. Ed. Engl., 1996,
The reaction of 2 with lithium was monitored by 119Sn NMR.
Compound 2 (50 mg, 0.045 mmol) and lithium (20 mg, 2.88
mmol) in THF were placed in an NMR tube with C D (as NMR
6 6
lock). The color of the solution changed to dark red. The Sn
119
3
5, 882; (g) W. P. Freeman, T. D. Tilley, L. M. Liable-Sands and A. L.
NMR signal attributable to stannole monoanion 5 (230.3 ppm)
Rheingold, J. Am. Chem. Soc., 1996, 118, 10457.
3
appeared at lower field than that for 2 (299.3 ppm in CDCl ).
2
3
(a) P. Dufour, J. Dubac, M. Dartiguenave and Y. Dartiguenave,
Organometallics, 1990, 9, 3001; (b) J.-H. Hong and P. Boudjouk, Bull.
Soc. Chim. Fr., 1995, 132, 495; (c) W. P. Freeman, T. D. Tilley, F. P.
Arnold, A. L. Rheingold and P. K. Gantzel, Angew. Chem., Int. Ed.
Engl., 1995, 34, 1887–1890; (d) R. West, H. Sohn, D. R. Powell, T.
Müller and Y. Apeloig, Angew. Chem., Int. Ed. Engl., 1996, 35, 1002;
(e) S.-B. Choi, P. Boudjouk and J.-H. Hong, Organometallics, 1999, 18,
The possible interpretation for the downfield shift of 5
2
+
11
compared to 2 and Ph
3
Sn Li (2106.7 ppm in THF) in the
119
Sn NMR may be a partial delocalization of the negative
charge into the ring as was observed in the silolyl anion.1 After
standing the tube overnight at room temperature, an additional
new small signal appeared downfield which grew gradually
with concommitant disappearance of the signal for 5. After 2
days, only the new signal assignable to stannole dianion 7 was
observed at 186.7 ppm. The remarkable downfield shift of the
b
2
919.
For examples of reviews, see: (a) E. Colomer, R. J. P. Corriu and M.
Lheureux, Chem. Rev., 1990, 90, 265; (b) J. Dubac, C. Guérin and P.
Meunier, in The Chemistry of Organic Silicon Compounds, ed. Z.
Rappoport and Y. Apeloig, John Wiley and Sons, Chichester, 1998, p.
119
Sn signal for 7 is reasonably interpreted in terms of strong
participation of a resonance form with stannylene character 8, as
was observed in the silole dianion showing silylene character.1
The central tin of the isolobal diaminostannylene 9 is known to
1
961.
e
4 (a) B. Goldfuss and P. v. R. Schleyer, Organometallics, 1995, 14, 1553;
(b) B. Goldfuss, P. v. R. Schleyer and F. Hampel, Organometallics,
1
1
996, 15, 1755; (c) B. Goldfuss and P. v. R. Schleyer, Organometallics,
997, 16, 1543.
5
(a) H. Sohn, R. R. Huddleston, D. R. Powell and R. West, J. Am. Chem.
Soc., 1999, 121, 2935; (b) S. Yamaguchi, R-Z. Jin and K. Tamao, J. Am.
Chem. Soc., 1999, 121, 2937.
6
7
M. Saito, R. Haga and M. Yoshioka, Heteroat. Chem., 2001, 15, 349.
R. West has also independently reported the formation of a stannole
dianion from 1,1-dichlorostannole in a manner different from us (10th
International Conference on the Coordination and Organometallic
Chemistry of Germanium, Tin and Lead, 2001).
resonate at 269 ppm.12 The 13C NMR spectrum of 7 was also
measured. Compound 2 and lithium in THF–C
6
D
6
was
8 K. M. Mackay, in The Chemistry of Organic Germanium, Tin and Lead
Compounds, ed. S. Patai, John Wiley and Sons, Chichester, 1995, p.
144.
13
ultrasonicated to directly afford a deep red solution of 7. In
C
NMR, the signal assignable to the a-carbon in the five-
9
J. Ferman, J. P. Kakareka, W. T. Klooster, J. L. Mullin, J. Quattrucci, J.
membered ring was observed at 184.58 ppm judging from a
n
13
n
119
13
S. Ricci, H. J. Tracy, W. J. Vining and S. Wallace, Inorg. Chem., 1999,
large J(Sn– C) of about 320 Hz, though J( Sn– C) and
3
8, 2464.
n
117
13
J( Sn– C) could not be unfortunately estimated because of
1
0 T. Wakahara and W. Ando, Chem. Lett., 1997, 1179.
broadening. The strong downfield resonance of the a-carbon in
1
1 U. Edlund, T. Lejon, T. P. Pyykkö, T. K. Venkatachalam and E. Buncel,
J. Am. Chem. Soc., 1987, 109, 5982.
the silole dianion was also predicted by calculation.4 The Li
NMR spectrum of the reaction mixture was also measured, but
the assignment of signals could not be achieved because of
broadening and complexity.
b
7
1
2 (a) H. Braunschweig, B. Gehrhus, P. B. Hitchcock and M. F. Lappert,
Z. Anorg. Allg. Chem., 1995, 621, 1922; (b) B. Gehrhus, P. B. Hitchcock
and M. F. Lappert, J. Chem. Soc., Dalton Trans., 2000, 3094.
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