Demethylation of the [Me3Sn(PhN2O2)] 4 tetramer into dimeric [Me2Sn(PhN2O 2)2]2: A thermally induced methyl-transfer between supramolecules

Article abstract of DOI:10.1039/b506728f

The single crystals of tetrameric [Me₃Sn(PhN₂O ₂)]₄ (1) supramolecule demethylates into single crystals of [Me₂Sn(PbN₂O₂)₂]₂ dimer (2) and volatile Me₄Sn, as a result of a crystal-to-crystal supramolecular structural transformation, which occurs upon heating and it is accompanied by a significant change of the molecular and crystal structures. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b506728f

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COMMUNICATION
www.rsc.org/chemcomm | ChemComm
Demethylation of the [Me3Sn(PhN2O2)]4 tetramer into dimeric
[Me2Sn(PhN2O2)2]2: a thermally induced methyl-transfer between
supramolecules{{
Andrea Dea´k* and Ga´bor Ta´rka´nyi
Received (in Cambridge, UK) 12th May 2005, Accepted 14th June 2005
First published as an Advance Article on the web 15th July 2005
DOI: 10.1039/b506728f
The single crystals of tetrameric [Me3Sn(PhN2O2)]4 (1) supra-
molecule demethylates into single crystals of [Me2Sn-
(PhN2O2)2]2 dimer (2) and volatile Me4Sn, as a result of a
crystal-to-crystal supramolecular structural transformation,
which occurs upon heating and it is accompanied by a
significant change of the molecular and crystal structures.
A classical solid-state reaction can be photochemically1 and/or
thermally2 induced and proceed either by topochemical or non-
topochemical mechanism.3 The thermally induced methyl migra-
tion of organic compounds in the solid-state is of particular
structural interest since they are all methyl-transfer isomerisation
(rearrangement) reactions.4 Interestingly, in contrast to thermally
Fig. 1 Thermally induced crystal-to-crystal supramolecular structural
transformation of
a
[Me3Sn(PhN2O2)]4 (1) tetramer into
induced solid-state methyl migrations in organic molecules which
have been the subject of extensive investigations,4 the solid-state
methyl transfer phenomenon in organometallic complexes have
not been exploited. The methyl migrational dismutation of
triorganotins has been detected in the environment, and the alkyl
group removal has been attributed to the action of UV light,
chemical cleavage and biological degradation by bacteria, although
its chemistry has never been elucidated.5 In addition, toxic
organotins are progressively dealkylated to inorganic Sn(IV) in
mammalian organs, and recently it was shown that a linear peptide
derived from the membrane protein stannine is able to dealkylate
the trimethyltins.6 Interestingly, no cases of demethylation
processes occurring in the solid state have been published
previously for triorganotin(IV) derivatives.
[Me2Sn(PhN2O2)2]2 dimer (2) via methyl-transfer process.
of the sample. However, crystals of 1 stored at room temperature
were stable for several weeks as confirmed by liquid phase NMR
spectroscopic measurements in non-coordinating solvents
(e.g. CDCl3).9
To gain further insight into this process, the 1 A 2 + Me4Sn
methyl-transfer was carried out in open-end vials at different
temperatures (viz. 70, 86 and in the melt at 100 uC). Typically after
7 hours of heating the single crystals of 2 began to crystallize from
the melt at 100 uC (Fig. 2).
The X-ray structure determination of a well formed crystal
confirmed the formation of a dimer 2,§ and thus, the demethyl-
ation of tetramer 1. Accordingly, the 20-membered Sn4O8N8
macrocyclic ring system of 1 transforms into five-membered
inorganic SnO2N2 chelate rings, which are chelated to a
stannoxanic Sn2O2 dimerized supramolecule 2. This supramole-
cular structural transformation proceeds with the disruption of the
In this Communication, we report the first thermally accelerated
crystal-to-crystal supramolecular structural transformation of a
[Me3Sn(PhN2O2)]4 (1) tetramer into self-assembled [Me2Sn-
(PhN2O2)2]2 dimer (2) via methyl-transfer process (Fig. 1).7
During the X-ray diffraction measurements of 1 a significant
28% decay and a shrinkage (before: 0.55 6 0.30 6 0.25 mm; after:
0.45 6 0.25 6 0.24 mm) of the single crystal was observed,8
indicating radiation-induced crystal decay and thermal sensitivity
Institute of Structural Chemistry, Chemical Research Center, Hungarian
Academy of Sciences, P. O. Box 17, H-1525, Budapest, Hungary.
E-mail: deak@chemres.hu; Fax: 00-36-1-438-4141/201;
Tel: 00-36-1-325-7547
{ Dedicated to Professor Alajos Ka´lma´n on the occasion of his 70th
birthday.
{ Electronic supplementary information (ESI) available: Crystallographic
data of 2 along with the figure of the molecular structure. The [A]21 vs t
plot used for the estimation of the k rate constant, and the aliphatic region
of the 1H-NMR spectra used for the component analysis of 1 after 70, 86
and 100 uC heating the crystals in open vials for various durations. See
http://dx.doi.org/10.1039/b506728f
Fig. 2 The images of the (single) crystals of 1 before heating (A) and the
melt-crystallised crystals of 2 after 9 hours of heating at 100 uC (B) as
observed through a microscope. It can be seen that the supramolecular
structural transformation proceeds with complete morphology change.
4074 | Chem. Commun., 2005, 4074–4076
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together by weak C–H p interactions,14 and the stacking distance
…
¯
original crystal structure turning the initial space group P421/c (1)
¯
into P1 (2). In crystal lattice, the tetramers of 1 stack in columns
˚
of identically oriented hydrogen-bonded layers in 2 is 0.05 A
parallel to the tetragonal c axis and the shortest intermolecular
…
Sn C distance between neighbouring columns is 4.81 A, however,
shorter than that in 29. It is clear that this 180u turn of the
hydrogen bonding patterns must generate very similar unit cell
dimensions and very similar packing in the same space group to
maintain the initial crystal symmetry, otherwise defects would be
introduced and the collapse of the crystal lattice occurs. In other
words, an 180u turn of the molecules around a non-crystal-
lographic axis is allowed since the a and b axes are nearly equal
˚
…
˚
the shortest intramolecular Sn C distance is only 4.69 A. Both
distances are appropriate for a topochemically controlled methyl
migration process. Nevertheless, since the reaction proceeds faster
in the melt and includes a marked change in the molecular and
crystal structures a non-topochemical process is also conceivable.
Further studies are necessary to clarify the discrete mechanistic
details.
˚
˚
(Dab 5 0.041 A for 29 and 0.031 A for 2), therefore they are
interchangeable, as are the hydrogen bonding patterns with respect
to the original crystal symmetry. The interchange of the cell axes as
well as the turn of the whole hydrogen bonding pattern around a
non-crystallographic axis are generally mediated by solvents
and/or temperature, whereas most cases occur with the disruption
of the original crystal lattice.15 To the best of our knowledge, the
crystal structures of 2 and 29 represent the second example of
hydrogen-bonded isostructural polymorphs related by a non-
crystallographic turn with virtually the same unit cell.16 In our
case, however, the source of the polymorphs is different and
unprecedented: melt versus solution.
The single crystal of 2 has a slightly different unit cell than that
of 29 obtained from solution.10 The high isostructurality index11
(Ii(23) 5 93.7% ) and the high volumetric index12 (Iv 5 98.5% )
indicate that 2 and 29 are isostructural. A comparison of the unit
cell parameters show that the a and b axis of the crystals obtained
from the melt (2) are shorter than those of 29 (Da 5 0.009 and
˚
Db 5 0.019 A), and the a and b angles are interchanged.
Accordingly, the a and b axes must also be interchanged, which
…
can be rationalized by the C–H N hydrogen-bonded molecular
layers of 2 and 29 projected along their c axis in Fig. 3.14 It can be
seen that polymorphs 2 and 29 can be distinguished via the
different orientation of a given hydrogen bond with respect to the
shortest a axis (Fig. 3A) of the triclinic crystals.13 They are related
to each other by a non-crystallographic twofold C*2-axis lying on
the plane of the molecules tilted at ca. 45u to the respective b (29) or
a (2) axis. A turn of 180u around this C*2-axis of the molecule 29
interchanges the a and b axes, consequently the orientation of the c
axis is also changed, therefore the direction of the hydrogen
bonding pattern becomes identical with those of 2 (Fig. 3B).
To investigate the thermal induction of the methyl transfer a
series of identical crystals of 1 were placed in open-end vials and
heated to 70, 86 and 100 uC, respectively. The molar ratio of the
1
methyl-moieties was monitored by H-NMR spectroscopy."
The progress with the time is shown in Fig. 4; based on these
data it appears that the calculated monomeric [Me2Sn(PhN2O2)2]1/
[Me3Sn(PhN2O2)]1 ratio increased substantially with the tempera-
ture: more than nine times greater ratio was measured in the melt
at 100 uC than at 86 uC after 2 hours of heating. This indicates that
the melt state is providing more than just a high concentration
medium for the demethylation of 1: we suppose that bimolecular
collisions of the monomers dominate. To clarify this we further
characterized the kinetics of the 1 A 2 + Me4Sn methyl-transfer by
keeping the crystals melt at the characteristic temperature 100 uC
for various durations (20 minutes to 4 hours). The kinetics of the
transformation in the melt was also followed by liquid NMR
analysis (CDCl3) of the samples after cooling down the individual
vials at different times. The initial reaction rates at 100 uC indicated
a second order 2A A B + C type kinetics with the approximate
rate constant of k 5 1.61 E–4 ¡ 6.9 E–6 l?mol21?s21 (for details
see Supporting Information{).
…
Furthermore, the C–H N bonded layers of 2 are connected
The appearance of the volatile by-product Me4Sn became
evident when the reaction mixtures from sealed vial melt
Fig. 3 Section of the crystal structures of 2 and 29 showing the infinite
…
C–H N hydrogen-bonded layers. (A) It can be seen that the orientation
of hydrogen-bonds are different with respect to the shortest a axis of a
triclinic crystals of 2 and 29. (B) A turn of 180u around the non-
crystallographic C*2-axis of the molecule 29 interchanges the a and b axes,
consequently the orientation of the c axis is also changed, therefore, the
direction of the hydrogen bonding pattern becomes identical to those of 2.
Fig. 4 Time course of the 1 A 2 + Me4Sn methyl-transfer induced by
heating at different temperatures.
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M. Miyata, Chem. Commun., 2001, 2004.
experiments (86 uC) were analysed. In contrast to the open vial
experiments, however, our attempt to provide reproducible kinetic
data from sealed vial experiments has failed. We assume that this
difference between the outcome of the two types of experiments is
strongly related to the complete or partial removal of a weakly
coordinating Me4Sn species from the reaction mixture. When
Me4Sn is removed through heating in an open vial experiment the
nascent product 2 is stabilized by dimerization, whereas if Me4Sn
remains more abundant in the reaction mixture, the self-assembled
dimer is destabilized opening ways for other competitive degrada-
tion processes. To provide more evidence for this theory further
liquid state investigations of 2 in coordinating and non-coordinat-
ing solvents are desirable.
2 (a) I. C. Paul and D. Y. Curtin, Acc. Chem. Res., 1973, 6, 217; (b)
R. Sekiya, K. Kiyo-oka, T. Imakubo and K. Kobayashi, J. Am. Chem.
Soc., 2000, 122, 10282; (c) S. Nomura, T. Itoh, H. Nakasho, T. Uno,
M. Kubo, K. Sada, K. Inoue and M. Miyata, J. Am. Chem. Soc., 2004,
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M. Kato, Angew. Chem. Int. Ed., 1998, 37, 2724; (f) R. S. Bogadi,
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(g) B. V. Lotsch, J. Senker and W. Schnick, Inorg. Chem., 2004, 43, 895;
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Harris, B. M. Kariuki, S. J. Kitchin, R. R. Tykwinski, I. P. Swainson
and J. D. Dunitz, J. Am. Chem. Soc., 2003, 125, 14449.
In summary, we have observed an unprecedented supramole-
cular structural transformation which occurs upon heating
accompanied by a significant change of the molecular and crystal
structure. As a result, a unique (single) crystal phase of 2 is
produced with a hydrogen bond orientation different from that in
3 K. Tanaka and F. Toda, Chem. Rev., 2000, 1025.
4 (a) W. J. Kusto, M. Bertault and J. Even, J. Phys. Chem. B, 1999, 103,
10549; (b) D. Dolphin, T. Niem, R. H. Felton and I. Fujita, J. Am.
Chem. Soc., 1975, 97, 5290; (c) C. N. Sukenik, J. A. Bonapace,
N. S. Mandel, P.-Y. Lau, G. Wood and R. G. Bergman, J. Am. Chem.
Soc., 1977, 99, 851; (d) P. Venugopalan, K. Venkatesan, J. Klausen,
E. Novotny-Berger, C. Leumann, A. Eschenmoser and J. D. Dunitz,
Helv. Chim. Acta, 1991, 74, 662; (e) J. D. Dunitz, Acta Cryst. B, 1995,
B51, 619; (f) M. Dessolin and M. Golfier, J. Chem. Soc., Chem.
Commun., 1986, 38; (g) M. Dessolin, O. Eisenstein, M. Golfier, T. Prange´
and P. Sautet, J. Chem. Soc., Chem. Commun., 1992, 132; (h)
M. Greenberg, V. Shteiman and M. Kaftory, Acta Cryst. B, 2001,
B57, 428.
5 (a) H. E. Guard, A. B. Cobet and W. M. Coleman, III, Science, 1981,
213, 770; (b) L. E. Hallas, J. C. Means and J. J. Cooney, Science, 1982,
215, 1505.
6 (a) B. A. Buck, A. Mascioni, C. J. Cramer and G. Veglia, J. Am. Chem.
Soc., 2004, 126, 14400; (b) B. Buck, A. Mascioni, L. Que, Jr. and
G. Veglia, J. Am. Chem. Soc., 2003, 125, 13316.
solvent-grown crystals. The demethylation of
1 proceeded
considerably faster in the melt than in the solid state. It is still
unclear how far the elementary steps of the ligand exchange
reaction occur intra- or intermolecularly in the melt and whether
this thermal reaction is topochemically controlled or not in the
solid state. Additional investigations are in progress to explore and
clarify the assumptions concerning the validity of a bimolecular
2A A B + C mechanism found in the melt state. One may
tentatively assume that this thermally induced methyl-transfer
reaction is not uncommon for triorganotin(IV) complexes and
further studies are in progress to discover analogous systems.
7 PhN2O2 is the abbreviation of N-nitroso-N-phenyl-hydroxylaminato
(cupferronato) anion.
Notes and references
8 A. Dea´k, I. Haiduc, L. Pa´rka´nyi, M. Venter and A. Ka´lma´n, Eur. J.
Inorg. Chem., 1999, 1593.
9 A. Dea´k, L. Radics, A. Ka´lma´n, L. Pa´rka´nyi and I. Haiduc, Eur. J.
Inorg. Chem., 2001, 2849.
10 A. Dea´k, M. Venter, A. Ka´lma´n, L. Pa´rka´nyi, L. Radics and I. Haiduc,
Eur. J. Inorg. Chem., 2000, 127.
11 A. Ka´lma´n, L. Pa´rka´nyi and Gy. Argay, Acta Crystallogr. B, 1993, B49,
1039.
§ Crystal data for 2: C28H32N8O8Sn2, M 5 846.04, triclinic, colorless
˚
prisms, a 5 9.408(3), b 5 9.439(3), c 5 10.739(2) A; a 5 64.31(2),
3
˚
b 5 75.94(2), c 5 78.00(2)u; V 5 827.9(4) A , T 5 293(2) K, space group
P1 (no. 2), Z 5 1, m(Mo–Ka) 5 1.568 mm21, rcalcd 5 1.697 Mg m23
,
¯
˚
F(000) 5 420, l 5 0.71073 A, crystal size 0.55 6 0.40 6 0.20 mm.
Intensity data of 12298 reflections were measured (2.49 ¡ H ¡ 32.04u) on
an Enraf-Nonius CAD-4 diffractometer (v-2H scans) of which 5723 were
independent (Rint 5 0.022). The intensities of the standard reflections
indicated a crystal decay of 2%, which was corrected. A semi-empirical (psi-
scan) absorption correction was also applied. The structure was solved by
direct methods (SHELXS-97)17 and refined by full-matrix least-squares
(SHELXL-97).17 5723 reflections were employed in the structure refine-
ment (210 parameters, 0 restraints). The final R values were R1 5 0.0543
(I . 2s(I)) and wR2 5 0.1396 (all data). All non-hydrogen atoms were
refined anisotropically. Hydrogen atomic positions were generated from
assumed geometries. A riding model refinement was applied for the
hydrogen atoms. CCDC 272081. See http://dx.doi.org/10.1039/b506728f for
crystallographic data in CIF or other electronic format.
12 L. Fa´bia´n and A. Ka´lma´n, Acta Crystallogr. B, 1999, B55, 1099.
13 For the better comparison between the cell parameters of 2 and 29
polymorphs, we have adopted the convention a , b , c for the unit cell
setting in triclinic crystal system.
…
14 The geometric parameters of C–H
N hydrogen-bonds are
i
H(6A) N(6A) 2.70 A, C(6A) N(6A) 3.403(6) A, C(6A)–
i
…
…
˚
˚
i
…
H(6A) N(6A) 133.0u; symmetry code: (i) 1 2 x, 2 2 y, 2 z for 2
i
and H(2A) N(2A) 2.70 A, C(2A) N(2A) 3.407(3) A, C(2A)–
i
…
…
˚
˚
i
…
H(2A) N(2A) 132.9u; symmetry code: 2 x, 1 2 y, 1 2 z for 29,
respectively. The geometric parameters of C–H p hydrogen-bond are
…
1
i
…
p
i
…
p
i
…
3.560(6) A, C(2B)–H(2B) p
˚
3.32 A, C(2B)
˚
" H-NMR spectra were recorded on a Varian-INOVA 400 MHz
H(2B)
97.5u;
spectrometer in CDCl3 (Merck Gmbh) at 25 uC. Chemical shifts were
referenced to the residual protons of the deuterated solvent. In open vial
reactions, 1 and 2 were the only detectable species and the
symmetry code: (i) 2 x, 2 2 y, 1 2 z for 2, where p is the centroid of the
C(1A)/C(2A)/C(3A)/C(4A)/C(5A)/C(6A) phenyl-ring.
15 (a) G. E. Hardy, W. C. Kaska, B. P. Chandra and J. I. Zink, J. Am.
Chem. Soc., 1981, 103, 1074; (b) L. Fa´bia´n, A. Ka´lma´n, Gy. Argay,
G. Berna´th and Zs. Gyarmati, Chem. Commun., 2004, 2114.
16 A. Ka´lma´n, L. Fa´bia´n, Gy. Argay, G. Berna´th and Zs. Gyarmati,
J. Am. Chem. Soc., 2003, 125, 34.
[Me2Sn(PhN2O2)2]1/[Me3Sn(PhN2O2)]1 molar ratio of the product and
starting material was usually measured by dissolving the reaction mixture in
CDCl3 and integrating their respective methyl resonances. The H-NMR
1
spectra of 2 and 29 were identical (CDCl3).
17 (a) G. M. Sheldrick, SHELXS-97, Program for solution of crystal
structures, University of Go¨ttingen, Germany, 1997; (b) G. M. Sheldrick,
SHELXL-97, Program for refinement of crystal structures, University of
Go¨ttingen, Germany, 1997.
1 (a) M. A. Garcia-Garibay, Acc. Chem. Res., 2003, 36, 491; (b)
D. Sampedro, A. Soldevilla, M. A. Rodriguez, P. J. Campos and
M. Olivucci, J. Am. Chem. Soc., 2005, 127, 441; (c) T. Devic, P. Batail
4076 | Chem. Commun., 2005, 4074–4076
This journal is ß The Royal Society of Chemistry 2005