NMR study of mono- and dilithium derivatives of alkyl and arylstannanes

Article abstract of DOI:10.1007/s11172-005-0122-x

Element-centered mono- and dianions of alkyl- and arylstannanes were studied by NMR spectroscopy. The ¹³C and ¹¹⁹Sn NMR chemical shifts for the dianions R₂SnLi₂ (R = Ph, Et) were measured for the first time.

Full text of DOI:10.1007/s11172-005-0122-x

Russian Chemical Bulletin, International Edition, Vol. 53, No. 10, pp. 2327—2329, October, 2004
2327
Brief Communications
NMR study of monoꢀ and dilithium derivatives
of alkyl and arylstannanes
ꢀ
P. A. Chugunov, N. A. Troitskii, K. S. Nosov, M. P. Egorov, and O. M. Nefedov
N.D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Elementꢀcentered monoꢀ and dianions of alkylꢀ and arylstannanes were studied by NMR
spectroscopy. The 13C and 119Sn NMR chemical shifts for the dianions R2SnLi2 (R = Ph, Et)
were measured for the first time.
Key words: anions, dianions, stannanes, 13C and 119Sn NMR.
Highꢀresolution NMR spectroscopy is an important
tool to study the structure of elementꢀcentered anions in
solutions. A number of recent publications1—4 are deꢀ
voted to 13C and 119Sn NMR studies of tinꢀcentered
monoanions; a communication5 reports measurement of
the 119Sn chemical shift of the stannol dianion. Nevertheꢀ
less, alkyl and arylꢀsubstituted tinꢀcentered geminal
dianions have not been studied by NMR as yet. The purꢀ
pose of our work was to study these anions by NMR
spectroscopy.
This procedure has long been known and used in clasꢀ
sical works to generate Me2SnNa2,6 Ph2SnNa2,7 and
Ph2SnLi2.8
The chemical shifts observed in the 119Sn and
13C NMR spectra of the compounds R3SnLi, R2SnLi2
and the starting halides are listed in Table 1. The assignꢀ
ment of the 13C NMR spectra of lithiumꢀ and halogenꢀ
substituted arylstannanes is based on the relative intensity
of the signals and on the spinꢀspin coupling constant
nJ(SnC) for the signal satellites, because the vicinal
spinꢀspin coupling constant is greater than the geminal
constant.
On passing from Et3SnCl to Et3SnLi and from
Et2SnCl2 to Et2SnLi2, the 119Sn signals shift upfield
(∆δ(119Sn) are –195 and –189, respectively). In both
cases, this attests to an increase in the negative charge
on the tin atom. In turn, on passing from Ph2SnCl2
Monoꢀ and dilithium derivatives of organylstannanes
were generated by reducing the corresponding haloꢀ
stannanes with metallic lithium under sonication directly
in an NMR tube.
n = 1, 2
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2229—2231, October, 2004.
1066ꢀ5285/04/5310ꢀ2327 © 2004 Springer Science+Business Media, Inc.

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Russ.Chem.Bull., Int.Ed., Vol. 53, No. 10, October, 2004
Chugunov et al.
Table 1. 119Sn and 13C NMR chemical shifts of R3SnLi, R2SnLi2, and the starting halides
Comꢀ
pound
δ
J/Hz
119Sn
13C
Cα
Cβ
Cipso
Cortho
Cmeta
Cpara
Et3SnCl
+103
+9
10.38
10.37
1J(119Sn, 13Cα) = 300,
1J(117Sn, 13Cα) = 286,
2J(119Sn, 13Cβ) = 32
Et2SnCl2
22.58
10.02
1J(119Sn, 13Cα) = 586,
1J(117Sn, 13Cα) = 560,
2J(119Sn, 13Cβ) = 50,
1J(119Sn, 13Cipso) = 650
1J(117Sn, 13Cipso) = 682,
2J(119Sn, 13Cortho) = 47.6,
2J(119Sn, 13Cmeta) = 65.5,
4J(119Sn, 13Cpara) = 13.5,
2J(119Sn, 13Cortho) = 61
3J(119Sn, 13Cmeta) = 81,
4J(119Sn, 13Cpara) = 17,
1J(119Sn, 13Cα) = 124
2J(119Sn, 13Cβ) = 32
Ph3SnCl
Ph2SnI2
–105
–290
140.56
138.44
136.97 129.45
135.26 129.73
130.59
131.57
Et3SnLi
Et2SnLi2
Ph3SnLi
Ph2SnLi2
–92
–180
–105
–103
18.62
15.91
22.08
3.12
2J(119Sn, 13Cortho) = 50.3
1J(119Sn, 6Li) = 282
1J(119Sn, 13Cortho) = 52.9
166.87
140.74
137.94 125.83
139.11 126.45
122.93
123.79
Table 2. Changes in the 119Sn and 13C NMR chemical shifts upon the formation of
PhnSnLi4–n from the corresponding halides PhnSnCl4–n
PhnSnLi4–n
∆δ (RnSnCl4–n → RnSnLi4–n)
119Sn
13C
Cα
Cβ
Cipso
Cortho
Cmeta
Cpara
Et2SnLi2
Et3SnLi
Ph3SnLi
Ph2SnLi2
–189
–195
–0
8.24
–6.67
10.37
–6.9
2.3
26.31
3.85 –3.28
0.97 –3.62
–7.78
–7.66
–58а
a
δ
119Sn(Ph2SnCl2) = –45.10
(δ(119Sn) = –32 9) to the corresponding Ph2SnLi2 dianion,
the upfied shift of the 119Sn resonance is ∆δ = –58, whereas
upon the formation of the Ph3SnLi anion from the chloꢀ
ride Ph3SnCl, the tin chemical shift almost does not
change. The similarity of the 119Sn chemical shifts for
Ph3SnLi and Ph2SnLi2 may be indicative of the fact that
only one Sn—Li bond of the latter molecule dissociates in
a THF solution to give the Ph2SnLi– anion.
fully corresponds to these features. The changes in the
chemical shifts point to πꢀpolarization of the phenyl subꢀ
stituents and to the lack of resonance stabilization. Thus,
there is no significant negative charge delocalization over
the aryl substituents in Ph2SnLi2 or Ph3SnLi.
Experimental
It is known from published data1 that in the series of
arylꢀsubstituted organoelement compounds, transition
from haloꢀderivatives to compounds with the E—M bond
(M is an alkali metal) is accompanied by a decrease in the
shielding of the Cipso and Cortho atoms and an increase in
the shielding of the Cmeta and Cpara atoms. The change in
the 13C chemical shifts on going from Ph2SnI2 to Ph2SnLi2
All experiments were carried out under dry argon. Commerꢀ
cial chemicals purified additionally by distillation or recrystalliꢀ
zation were used. Diphenyldiiodostannane Ph2SnI2 was syntheꢀ
sized by a known procedure.11 Prior to use, THFꢀd8 was reꢀ
fluxed over sodium benzophenone ketyl and distilled over argon.
13C and 119Sn NMR spectra were recorded on Bruker WMꢀ250
and Bruker DRXꢀ500 spectrometers.

NMR study of anions of alkyl and arylstannanes
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 10, October, 2004
2329
Preparation of compounds RnSnLi4–n (n = 2, 3) (general
procedures). RnSnX4–n (n = 2, 3) (0.00022 mol) and finely cut
lithium (0.00053 mol; or 0.0011 mol for dianions) were placed
in an NMR tube and 0.5 mL of anhydrous THFꢀd8 was added.
The reaction mixture was sonicated for 10 h and then the NMR
spectrum was recorded.
4. U. Englich, U. Hermann, I. Prass, T. Schollmeier,
K. RuhlandtꢀSenge, and F. Uhlig, J. Organomet. Chem., 2002,
646, 271.
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This work was supported by the Russian Foundation
for Basic Research (Project No. 02ꢀ03ꢀ32148).
9. I. Wharf and M. G. Simard, J. Organomet. Chem.,
1997, 532, 1.
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Received September 14, 2004