Chemically induced magnetic isotope effect on the tin nuclei during the photolysis of (1-fluorenyl)trimethyltin

Article abstract of DOI:10.1134/S003602440606032X

A magnetic isotope effect on the ¹¹⁷Sn and ¹¹⁹Sn nuclei, accompanied by the fractionation of magnetic and nonmagnetic tin isotopes, was observed during the photolysis of (9-fluorenyl)trimethyltin. The magnetic and nonmagnetic isotopes were accumulated, respectively, in the initial compound and a photolysis product (hexamethyldistannane). Nauka/Interperiodica 2006.

Full text of DOI:10.1134/S003602440606032X

ISSN 0036-0244, Russian Journal of Physical Chemistry, 2006, Vol. 80, No. 6, pp. 1009–1010. © Pleiades Publishing, Inc., 2006.
Original Russian Text © A.L. Buchachenko, V.A. Roznyatovskii, V.L. Ivanov, Yu.A. Ustynyuk, 2006, published in Zhurnal Fizicheskoi Khimii, 2006, Vol. 80, No. 6, pp. 1150–1152.
SHORT
COMMUNICATIONS
Chemically Induced Magnetic Isotope Effect on the Tin Nuclei
during the Photolysis of (1-Fluorenyl)Trimethyltin
A. L. Buchachenkoa, V. A. Roznyatovskiib, V. L. Ivanova, and Yu. A. Ustynyuka
a Faculty of Chemistry, Moscow State University, Leninskie gory, Moscow, 119992 Russia
b Center of Magnetic Resonance and Spectroscopy, Moscow State University, Leninskie gory, Moscow, 119992 Russia
E-mail: ivanov@photo.chem.msu.ru
Received November 11, 2005
Abstract—A magnetic isotope effect on the 117Sn and 119Sn nuclei, accompanied by the fractionation of mag-
netic and nonmagnetic tin isotopes, was observed during the photolysis of (9-fluorenyl)trimethyltin. The mag-
netic and nonmagnetic isotopes were accumulated, respectively, in the initial compound and a photolysis prod-
uct (hexamethyldistannane).
DOI: 10.1134/S003602440606032X
The magnetic isotope effect, the dependence of the troscopy on a Bruker Avance-600 spectrometer as
rate of chemical reactions on the nuclear spin and mag- described in [7, 8].
netic moment of the reagents, is observed in spin-selec-
tive reactions of paramagnetic species (atoms, radicals,
metal ions, and molecules in triplet and high-spin
states); it leads to the fractionation of isotopes accord-
ing to their magnetic moments. This effect was discov-
ered in 1976 for the carbon isotopes and since then it
has been observed for many other isotope pairs and tri-
ads: 12ë/13C, 16O/17O/18O, 28Si/29Si/30Si, 32S/33S/34S,
72Ge/73Ge, 199, 201Hg/200, 202Hg, 24Mg/25Mg/26Mg, and
235U/238U [2–4].
RESULTS AND DISCUSSION
When (9-fluorenyl)trimethyltin (1) was photolyzed
up to a ~60% conversion, only hexamethyldistannane
(2), fluorene (3) and 9,9'-difluorenyl (4) were
observed as products. Fluorene was formed via the
abstraction of a hydrogen (deuterium) atom from a
solvent molecule by a fluorenyl radical. 9,9'-Difluore-
nyl is formed due to the recombination of fluorenyl
radicals. At the initial stages of the photolysis, both
these products are formed in nearly equal amounts. At
higher conversions, the concentration of 4 increases
faster than that of 3. This suggests that 3 can also be
formed by the photoinduced protolysis of 1 by water,
trace amounts of which were initially present in the
solvent as an admixture:
In studying the photolysis of (1-naphthylmethyl)tri-
methyltin [5], we revealed the magnetic isotope effect
for the tin nuclei [5], an effect accompanied by the frac-
tionation of magnetic and nonmagnetic tin isotopes. In
the present work, we studied the separation of tin iso-
topes during the photolysis of (9-fluorenyl)trimethyltin
in order to make sure that the nuclear-spin selectivity
effect on the tin nuclei is of universal character.
C13H9SnMe3 (1)
EXPERIMENTAL
hν
.
.
(9-Fluorenyl)trimethyltin (1) was synthesized and
purified as described in [6]. Photolysis of 1 in THF-d8
(0.1 M) was conducted in evacuated Pyrex ampoules
(5 mm in diameter) at room temperature under irradia-
tion with the 313- and 333-nm lines of a DRSh-250
mercury lamp, which were selected with a ZhZS-18 fil-
ter. The ampoule was placed into a quartz cell filled
with water and rotated in the light beam at 2 rpm. The
efficiency of irradiation was controlled by recording
absorption spectra. THF-d8 solvent (Merck) with a
99.95% degree of deuteration was used without prelim-
RH
C13H10
C13H9 + SnMe3
.
.
C13H9
SnMe3
(3)
C26H18 Sn2Me6
(4) (2)
The figure shows the isotope composition of tin in 1
and 2 as a function of the extent of conversion. We
observed, as in the case of the photolysis of (1-naphth-
inary purification. In the course of photolysis, the reac- ylmethyl)trimethyltin, the fractionation of isotopes: the
tive medium was analyzed by H and C NMR spec- 119Sn and 117Sn magnetic isotopes are predominantly
1
13
1009

1010
logS
BUCHACHENKO et al.
1 – α
------------
α
⎛
⎝
⎞
logS =
log(1 – F),
(1)
⎠
0.04
119Sn
where S = [117, 119Sn]/[117, 119Sn]0 is the ratio of the cur-
rent to the initial isotope content in 1 and α is the coef-
ficient of isotope fractionation (the ratio of the reaction
rates for molecules containing magnetic and nonmag-
netic isotopes). This dependence is strictly fulfilled for
all magnetic isotope effects [2] except for that involving
tin, for which logS is a nonlinear function of log(1 – F)
with asymptotic growth. That this dependence is non-
linear can be explained by the exchange reactions
between 2 and 1, these reactions leading to leveling of
the isotope composition, partially counterbalancing the
effect of spin-selective fractionation. Most probably,
these exchange reactions are also of radical character, i.e.,
photoinduced. Exchange reactions can be suppressed by
adding radical scavengers to the generating system.
117Sn
0.2
0
–0.04
–0.08
0
0.4
–log(1 – F)
119Sn
117Sn
The isotope fractionation coefficient α estimated
from the initial segment of the logS versus log(1 – F)
dependence at low extent of conversion (figure) was
found to be 1.16, a value close to that obtained for
(1-naphthylmethyl)trimethyltin [15] (1.15). Note that
the magnetic isotope effect for the tin nuclei is substan-
Isotope composition S as a function of the extent of conver-
sion F in the coordinates of Eq. (1) for the initial molecule
(logS > 0) and hexamethyldistannane (logS < 0).
13
tially stronger than that for the C nucleus during the
photolysis of dibenzyl ketone [1].
present in the initial compound, 1, while 2 is depleted
in these isotopes.
Thus, the fractionation of the tin isotopes was
observed during the photolysis of (9-fluorenyl)trimethyl-
tin: the magnetic isotopes (117Sn,119Sn) are accumulated
in the initial molecule while the nonmagnetic isotopes
(118Sn,120Sn) are accumulated in the photolysis products.
Both the distribution of the isotopes and the compo-
sition of the products suggest that the primary stage of
the reaction is photodissociation:
.
.
hν
C13H9SnMe3
1[C13H9SnMe3]
117, 119Sn
3[C13H9SnMe3]
ACKNOWLEDGMENTS
.
.
Sn2Me6.
We are grateful to N.N. Zemlyanskii and I.V. Boris-
ova for providing (9-fluorenyl)trimethyltin and to
A.Kh. Vorob’ev for help in preparing the samples for
photolysis and spectrum recording.
118, 120Sn
The
spin-selective
nanoreactor
is
the
.
.
[C13H9SnMe3 ] radical pair in the triplet-spin state. The
This work was supported by the Russian Foundation
for Basic Research, project no. 03-03-32652.
spin-forbidden recombination of this pair can only
occur after spin conversion to a singlet state. Radical
pairs containing magnetic tin nuclei, due to the mag-
netic interaction of these nuclei with the unpaired elec-
tron, undergo a fast conversion to the singlet state and
recombine, regenerating the initial molecule, 1, and
bringing into it an excess amount of magnetic nuclei.
The spin conversion of radical pairs with nonmagnetic
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RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY Vol. 80 No. 6 2006