Full text of DOI:10.1070/MC2002v012n04ABEH001601

Mendeleev Commun., 2002, 12(4), 125–126
Electrochemistry of 1,1,2,2,3,3-hexa(2,6-diethylphenyl)cyclotristannane.
The first examples of electrochemical generation of a stannylene radical anion
and a tristannane radical cation
Ivan S. Orlov,a Anna A. Moiseeva,b Kim P. Butin,b Lawrence R. Sita,c Mikhail P. Egorov*a and Oleg M. Nefedova
a N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 119991 Moscow, Russian Federation.
Fax: +7 095 135 5328
b Department of Chemistry, M. V. Lomonosov Moscow State University, 119992 Moscow, Russian Federation
c Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA
10.1070/MC2002v012n04ABEH001601
The radical anion of di(2,6-diethylphenyl)stannylene (Ar2Sn) has been generated by the electrochemical reduction of cyclotri-
stannane cyclo-(Ar2Sn)3, and the electrochemical oxidation of cyclo-(Ar2Sn)3 resulted in Sn–Sn bond cleavage with the formation
of the radical cation of tristannane.
Significant and exciting progress has been achieved in the chem-
istry of small rings containing the atoms of Group 14 elements.1
Data on the electrochemistry of cyclotrisilanes2 and cyclotri-
germanes3 are available, but this area is still poorly investigated.
Here, we report on the electrochemical and simultaneous electro-
chemical–electron spin resonance (SE–ESR) study of a cyclo-
tristannane [1,1,2,2,3,3-hexa(2,6-diethylphenyl)cyclotristannane
1] and the first example of the electrochemical generation of a
stannylene radical anion from 1.†
[g = 2.015, a(117,119Sn) = 151 G and t1/2 ~ 2 min] correspond to
those of stannylene radical anion 2.4 Radical anion 2 was
detected earlier during the chemical reduction of 1 by lithium.4
Thus, one can safely assign peak A' to the oxidation of stannylene
radical anion 2. The following mechanism of the electrochemical
reduction of 1 can be suggested:
The cyclic voltammogram (CV) of the reduction of compound
1 [20 °C, in THF, 0.1 M Bu4NClO4 as a supporting electrolyte,
glassy carbon electrode, all potentials are vs. Ag|AgCl|aq. KCl (sat.)]
exhibits one cathodic peak at –2.0 V (one electron, peak A) and
one anodic peak at –0.72 V (A') on the reverse scan (Figure 1).
A great difference between the forward, A, and reverse, A',
peak potentials implies that peak A' corresponds to the oxidation
of a secondary product arising from the fragmentation of the
primary radical anion of 1, formed at –2.0 V. The nature of
this product was revealed using the SE–ESR technique. Upon
the electrochemical reduction of 1 at –2.0 V (20 °C, in THF,
0.1 M Bu4NClO4 as a supporting electrolyte, Pt electrode) with
the simultaneous measurement of the ESR spectrum, a singlet
with a set of 117,119Sn sattelites was detected. Its parameters
2
The single oxidation peak at +0.54 V (one electron, peak B)
is observed in a CV curve for the oxidation of 1 when the
potential was scanned from E = 0 V to the anodic site. On a
reverse scan, there is a peak (B') at –0.69 V corresponding to
the reduction of the product of fragmentation of the radical
cation of cyclotristannane 1. The ESR spectrum of the products
of oxidation of 1 at +0.54 V (20 °C, in THF, 0.1 M Bu4NClO4 as
a supporting electrolyte, Pt electrode) reveals two singlets from
two paramagnectic species (Figure 2). One singlet [g = 2.020,
a1(117,119Sn) = 394 G, a2(117,119Sn) = 112 G] was assigned to radi-
cal cation 3, the open form of the radical cation of 1. Indeed,
there are two sets of satellites corresponding to the coupling of
an unpaired electron with terminal (a1) and central (a2) tin atoms.
To our knowledge, radical cation 3 is the first radical cation of
a tristannane reported so far. Nevetheless, we can compare the
a1(117,119Sn) value in 3 with that reported for the radical cation
of Me3Sn–SnMe3 [a||(117,119Sn) = 238 G, a^(117,119Sn) = 100 G,
measured at 77 K in a CFCl3 matrix5]. Both values are of the
same order of magnitude.
A
20 µA
B'
A'
Another singlet [g = 2.022, a(117,119Sn) = 250 G] observed upon
the oxidation of 1 was tentatively assigned to stannylene radical
cation 4.
B
1.0
0.0
–1.0
E/V
–2.0
Figure 1 Cyclic voltammogram of cyclotristannane 1 (10–3 M) in THF, at
20 °C, 0.1 M Bu4NClO4 as a supporting electrolyte, glassy carbon electrode,
scan rate of 200 mV s–1
.
(a)
(b)
†
Cyclic voltammetry was performed on a PI-50-1.1 potentiostat or a
home-made potentiostat interfaced with an IBM PC. The working elec-
trode was a glassy carbon disk (Æ 1.8 mm); the reference electrode was
Ag|AgCl|KCl (aq., sat.). The measurements were carried out in THF in
the presence of 0.1 M Bu4NClO4 as a supporting electrolyte in an argon
atmosphere.
The electrochemical cell for SE–ESR was described elsewhere.7
The ESR spectra were recorded using a Bruker EMX 6-1 spectrometer.
Cyclotistannane 1 was synthesised according to the published pro-
cedure.8
Figure 2 (a) ESR spectrum of radical cations 3 and 4. Singlets corre-
sponding to sattelites of 3 are marked by , those of 4 are marked by . (b)
ESR spectrum of 3 and 4 at higher gain.
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Mendeleev Commun., 2002, 12(4), 125–126
The following oxidation mechanism of 1 can be suggested:
This work was supported by the Russian Foundation for Basic
Research (grant nos. 00-15-97387 and 02-03-32148), INTAS
(grant no. 97-30344), the Ministry of Science of the Russian
Federation and the Russian Academy of Sciences (grant no. 1-20).
References
1 T. Tsumuraya, S. A. Batcheller and S. Masamune, Angew. Chem., Int.
Ed. Engl., 1991, 30, 902.
2 H. Watanabe, K. Yoshizumi, T. Muraoka, M. Kato, Y. Nagai and T. Sato,
Chem. Lett., 1985, 1683.
2
3 T. Tsumuraya, S. Sato and W. Ando, Organometallics, 1990, 9, 2061.
4 L. R. Sita and I. Kinoshita, J. Am. Chem. Soc., 1992, 114, 7024.
5 M. C. R. Symons, J. Chem. Soc., Chem. Commun., 1981, 1251.
6 H. Watanabe, M. Kato, E. Tabei, H. Kuwabaram N. Hirai, T. Sato and
Y. Nagai, J. Chem. Soc., Chem. Commun., 1986, 1662.
7 A. V. Il’yasov and Yu. M. Kargin, Magn. Reson. Rev., 1993, 16, 135.
8 L. R. Sita and R. D. Bickerstaff, J. Am. Chem. Soc., 1989, 111, 6454.
Radical cations 3 and 4 are short-living species (lifetimes of
about 2 to 3 min); therefore, we were unable to detect spectro-
scopically the transformation of 3 into 4. In fact, the open form
of the radical cation of cyclotrisilane (similar to 3) is formed
during the chemical oxidation of cyclotrisilane with tetracyano-
ethylene, as proposed on the basis of its trapping by ethanol.6
Thus, using the SE–ESR technique, the radical anion of stan-
nylene 2 and the open form of the radical cation of cyclotri-
stannane were detected, and the formation of the radical cation
of stannylene (radical cation 4) upon the electrochemical oxida-
tion of 1 was suggested. This technique opens new opportunities
to the electrochemical generation and detection of radical ions
of Group 14 element derivatives.
Received: 29th April 2002; Com. 02/1927
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