Hexakis(2,4,6-triisopropylphenyl)cyclotristannoxane -A molecular diorganotin oxide with kinetically inert Sn-O bonds1

Article abstract of DOI:10.1002/1521-3749(200110)627:10<2413::AID-ZAAC2413>3.0.CO;2-H

The single-crystal X-ray structure analysis of hexakis(2,4,6-triisopropylphenyl)cyclotristannoxane, cyclo-[(2,4,6-i-Pr₃-C₆H₂)₂SnO] ₃ (1), is reported and reveals this compound to contain an almost planar six-membered ring. Redistribution reactions of 1 with cyclo-(t-Bu₂SnO)₃ and t-Bu₂SiCl₂, respectively, failed and indicate an unusual kinetic inertness of the Sn-O bonds in 1 as compared to related mo-lecular diorganotin oxides containing less bulkier substituents. The redistribution reaction of cyclo-(t-Bu₂SnO)₃ with cyclo-(t-Bu₂SnS)₂ leads to an equilibrium involving the trimeric diorganotin oxysulphides cyclo-t-Bu₂Sn(OSnt-Bu₂)₂S (2a) and cyclo-t-Bu₂Sn(SSnt-Bu₂)₂O (2b). WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001.

Full text of DOI:10.1002/1521-3749(200110)627:10<2413::AID-ZAAC2413>3.0.CO;2-H

Hexakisꢀ2,4,6-triisopropylphenyl)cyclotristannoxane ±
a Molecular Diorganotin Oxide with Kinetically Inert Sn±O Bonds1)
Jens Beckmann, Klaus Jurkschat*, Stephanie Rabe, and Markus SchuÈrmann
Dortmund, Lehrstuhl fuÈr Anorganische Chemie II der UniversitaÈt
Received March 27th, 2001.
Abstract. The single-crystal X-ray structure analysis of hexa-
kis(2,4,6-triisopropylphenyl)cyclotristannoxane, cyclo-[(2,4,6-
i-Pr3-C6H2)2SnO]3 (1), is reported and reveals this com-
pound to contain an almost planar six-membered ring.
Redistribution reactions of 1 with cyclo-(t-Bu2SnO)3 and t-
Bu2SiCl2, respectively, failed and indicate an unusual kinetic
inertness of the Sn±O bonds in 1 as compared to related mo-
lecular diorganotin oxides containing less bulkier substi-
tuents. The redistribution reaction of cyclo-(t-Bu2SnO)3 with
cyclo-(t-Bu2SnS)2 leads to an equilibrium involving the tri-
meric diorganotin oxysulphides cyclo-t-Bu2Sn(OSnt-Bu2)2S
(2 a) and cyclo-t-Bu2Sn(SSnt-Bu2)2O (2 b).
Keywords: Tin; Oxide; Sulphide; X-ray structure; NMR
Hexakisꢀ2,4,6-triisopropylphenyl)cyclotristannoxan ±
Ein molekulares Diorganozinnoxid mit kinetisch stabilen Sn±O Bindungen1)
InhaltsuÈbersicht. Es wird die EinkristallroÈntgenstrukturana-
lyse von Hexakis(2,4,6-triisopropylphenyl)cyclotristannoxan
cyclo-[(2,4,6-i-Pr3-C6H2)2SnO]3 (1) vorgestellt. Die Verbin-
dung liegt als nahezu planarer sechsgliedriger Ring vor. Das
Diorganozinnoxid 1 reagiert nicht mit cyclo-(t-Bu2SnO)3
bzw. t-Bu2SiCl2, was auf die ungewoÈhnliche kinetische Stabi-
litaÈt der Sn±O Bindungen in 1 im Vergleich zu aÈhnlichen
molekularen Diorganozinnoxiden mit sterisch weniger an-
spruchsvollen Substituenten hinweist. Die Redistributions-
reaktion von cyclo-(t-Bu2SnO)3 mit cyclo-(t-Bu2SnS)2 fuÈhrt
zu einem Gleichgewicht mit den trimeren Diorganozinn-
oxysulphiden cyclo-t-Bu2Sn(OSnt-Bu2)2S (2 a) and cyclo-
t-Bu2Sn(SSnt-Bu2)2O (2 b).
Introduction
cyclo-[(2,4,6-i-Pr±C6H2)2SnO]3 [16]. Furthermore, it
was claimed to appear from the oxidation of (2,4,6-i-
Pr±C6H2)2Sn as a kinetically labile dimer, cyclo-
[(2,4,6-i-Pr±C6H2)2SnO]2, which at room temperature
rearranges into the thermodynamically more stable
trimer within 24 h to a degree of more than 90% [15].
However, no experimental details on the preparation
as well as the rearrangement step were given and
spectroscopic data are available neither for the dimer
nor the trimer [13±17].
In addition to bis(2,4,6-triisopropylphenyl)tin oxide,
the closely related sulphide, cyclo-[(2,4,6-i-Pr±C6H2)2-
SnS]2 [18, 19] and oxysulphide cyclo-O[(2,4,6-i-
Pr±C6H2)2Sn]2S [19] were reported, which both repre-
sent four-membered rings in the solid state.
Various redistribution reactions of diorganotin chal-
cogenides, (R2SnX)n, (R = alkyl, aryl; X = O, S, Se, Te;
n = 2, 3) have demonstrated that the Sn±X bonds are
kinetically labile and that reactions involving cleavage
of these bonds are fast and proceed under mild condi-
tions [20±23]. In a recent conference contribution it
was pointed out that certain trimeric diaryltin sul-
phides, cyclo-(R2SnS)3 (R = Ph, o-Tol, m-Tol, p-Tol),
Diorganotin oxides (R2SnO)n have been known for
many years [1]. Depending on the steric demand of
the organic substituents they are either polymeric (I,
R = Me, Et, Bu, Vinyl, Ph) [1] or trimeric (II,
R = CH2SiMe3, [2] t-Bu, [3, 4] Me2EtC, [4] (Me3Si)3C/
Me, [5] 2,6-Me2±C6H3, [6] 2,6-Et2±C6H3, [7] 2,4,6-
(CF3)3±C6H2) [8]. While the six-membered ring struc-
ture of the latter compounds, (II), was established by
X-ray diffraction studies, the polymeric nature of the
former group, (I), was deduced from their virtual inso-
lubility in common organic solvents, 119Sn MoÈûbauer,
[9, 10] and 119Sn MAS NMR spectroscopy [11] reveal-
ing the presence of pentacoordinated tin atoms within
these compounds (Chart 1).
Furthermore, one example of a dimeric diorganotin
oxide containing extremely bulky substituents is known,
namely cyclo-{[(Me3Si)2CH]2SnO}2, (III) (Chart 1) [12].
Bis(2,4,6-triisopropylphenyl)tin oxide was prepared
by hydrolysis of (2,4,6-i-Pr±C6H2)2SnBr2 under basic
conditions [13±17] and it was reported to be a trimer,
* Prof. Dr. K. Jurkschat,
Lehrstuhl fuÈr Anorg. Chemie II der UniversitaÈt,
D-44221 Dortmund
1)
This work contains parts of the Ph.D. theses of J. B. and
E-mail: Kjur@platon.chemie.uni-dortmund.de
S. R., Dortmund University 1999.
Z. Anorg. Allg. Chem. 2001, 627, 2413±2419 Ó WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001 0044±2313/01/6272413±2419 $ 17.50+.50/0 2413

J. Beckmann, K. Jurkschat, S. Rabe, M. SchuÈrmann
and cyclo-[(2,4,6-i-Pr±C6H2)2SnO]2, or cyclo-[(2,4,6-i-
Pr±C6H2)2SnO]3.
Diorganotin oxides, such as cyclo-(t-Bu2SnO)3, find
synthetic applications as convenient proton free oxide
sources as was recently demonstrated in reactions with
spacer-bridged diorganotin dihalides [24], diphenyl-
dichlorosilane [25], diphenyldichlorogermane, and phe-
nylboron dichloride [26], respectively, and therefore a
thorough knowledge of the reactivity of this class of
compounds is highly desirable.
Results and Discussion
The hydrolysis of (2,4,6-i-Pr3±C6H2)2SnBr2 with aqu-
eous sodium hydroxide in toluene afforded cyclo-
[(2,4,6-i-Pr3±C6H2)2SnO]3 (1) in good yield (Eq. (1)).
The diorganotin oxide 1 is a colorless high-melting
crystalline solid. The molecular structure is shown in
Figure 1. Selected bond lengths and angles are listed
in Table 1. Crystal data are given in Table 2.
The molecular structure consists of an almost planar
central Sn3O3 ring with the largest deviation from the
Ê
plane being 0.0115 A. Notably, two tin atoms, Sn(2)
and Sn(2 a), are crystallographically equivalent while
the third one, Sn(1), is independent. However, the
119Sn MAS NMR spectrum showed only one signal at
Chart 1
can be reversibly converted to their corresponding di-
mers, (R2SnS)2, by simply heating them in a high-boil-
ing solvent [21, 22]. One possible explanation for this
observation is the assumption of an equilibrium be-
tween these oligomers, with the position of this equili-
brium being controlled by the entropy term of the
Gibbs-Helmholtz equation.
Herein, we revisit the synthesis of bis(2,4,6-triiso-
propylphenyl)tin oxide (1) and describe the single-
crystal X-ray structure analysis of the trimer. Variable
temperature 119Sn NMR spectroscopic studies show
no evidence for dimers or other related species. In-
stead, a remarkable kinetic inertness of the Sn±O
bonds is observed in reactions with cyclo-(t-Bu2SnO)3
and t-Bu2SiCl2. Moreover, the redistribution reaction
between cyclo-(t-Bu2SnO)3 and cyclo-(t-Bu2SnS)2,
which gives rise to an equilibrium of the former with
the oxysulphides, cyclo-t-Bu2Sn(OSnt-Bu2)2S and cy-
clo-t-Bu2Sn(SSnt-Bu2)2O, suggests that the fully char-
acterized oxysulphide cyclo-O[(2,4,6-i-Pr±C6H2)2Sn]2S
[19] is also kinetically stabilized rather than being
the thermodynamically favored alternative to a mix-
ture of the former with cyclo-[(2,4,6-i-Pr±C6H2)2SnS]2
Fig. 1 General view (SHELXTL-PLUS) of a molecule of 1
showing 30% probability displacement ellipsoids and the
atom numbering.
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Z. Anorg. Allg. Chem. 2001, 627, 2413±2419

Hexakis(2,4,6-triisopropylphenyl)cyclotristannoxane
a)
Ê
Table 1 Selected Bond Lengths/A and Angles/° for 1
(t-Bu2SnO)3 (119.5(4)°), [4] cyclo-[(EtMe2C)2SnO]3
(118.(2)°), [4] cyclo-[(Me3SiCH2)2SnO]3 (118.3(2)°),
[2] cyclo-{[(Me3Si)3C]MeSnO}3 (116.1(6)°), [5] and cy-
clo-{[(Me3Si)2CH]2SnO}2 (119.9(9)°) [12]. The mean
Sn±O±Sn angle in 1 amounts to 136.1(2)° which is
close to the Sn±O±Sn angles reported for cyclo-
(t-Bu2SnO)3 (133.1(3)°) [4], cyclo-[(EtMe2C)2SnO]3
Sn(1)±O(1)
Sn(2)±O(1)
Sn(2 a)±O(2)
Sn(1)±C(1 a)
Sn(2)±C(21)
1.956(2)
1.970(2)
1.969(1)
2.150(4)
2.160(4)
Sn(1)±O(1 a)
Sn(2)±O(2)
Sn(1)±C(1)
Sn(2)±C(11)
1.956(2)
1.969(1)
2.150(4)
2.162(4)
O(1)±Sn(1)±O(1 a) 105.1(1)
O(1 a)±Sn(1)±C(1) 117.3(2)
O(1 a)±Sn(1)±C(1 a) 104.1(1)
O(1)±Sn(1)±C(1)
O(1)±Sn(1)±C(1 a)
C(1)±Sn(1)±C(1 a)
O(1)±Sn(2)±C(11)
O(1)±Sn(2)±C(21)
104.1(1)
117.3(2)
109.5(2)
115.2(2)
101.4(1)
(134(1)°),
[4]
and
cyclo-{[(Me3Si)3C]MeSnO}3
(133.2(5)°), [5] but bigger than the angles found for
cyclo-[(2,6-Me2±C6H3)2SnO]3 (120.8°) [6] and cyclo-
[(Me3SiCH2)2SnO]3 (122.4(2)°) [2].
O(1)±Sn(2)±O(2)
O(2)±Sn(2)±C(11)
O(2)±Sn(2)±C(21)
Sn(1)±O(1)±Sn(2)
103.6(1)
105.0(1)
115.9(1)
135.5(1)
C(11)±Sn(2)±C(21) 115.5(2)
Sn(2)±O(2)±Sn(2 a) 136.6(2)
The diaryltin oxide cyclo-[(2,4,6-i-Pr3±C6H2)2SnO]3
(1) is highly soluble in common organic solvents. Ac-
cording to a molecular weight determination in
chloroform, the six-membered ring structure is re-
tained in solution. The 119Sn NMR spectrum (CDCl3)
of 1 shows one signal at ±128.6 ppm being almost
identical to the 119Sn MAS NMR chemical shift
mentioned above and very close to the 119Sn NMR
chemical shift reported for cyclo-[(2,6-Et2±C6H3)2-
SnO]3 (±125.0ppm) [7]. Interestingly, the 2J(119Sn±
O±117Sn) coupling of 501 Hz is significantly bigger as
compared to the corresponding coupling in the closely
related diaryltin oxide cyclo-[(2,6-Me2±C6H3)2SnO]3
(320Hz), [27] as well as in cyclo-(t-Bu2SnO)3
(369 Hz), [4] cyclo-[(Me2EtC)2SnO]3 (394 Hz), [4] and
cyclo-[(Me3SiCH2)2SnO]3 (335 Hz) [2]. This differ-
ence, especially in comparison with cyclo-[(2,6-Me2±
C6H3)2SnO]3 having an almost identical substituent
pattern at tin, is likely to originate from the well
a) Symmetry transformation used to generate equivalent atoms:
a = ±x + 1, y, ±z + 0.5
Table 2 Crystallographic Data for 1
Compound number
1
Empirical formula
Formular weight
Crystal system
Space group
Cell constants/A and °
a
C90H138O3Sn3
1624.07
orthorhombic
Pbcn
Ê
24.577(1)
14.748(1)
24.246(1)
8788.2(8)
4
1.227
1.254(1)
0.890
b
c
3
Ê
Volume/A
Z
Density(calculated) (Mg/m3)
Density(measured) (Mg/m3)
Absorption coeffizient/mm±1
Crystal size/mm3
0.25 ´ 0.15 ´ 0.15
3.46 to 25.03
114791
Theta range for data collection
Reflections collected
2
established dependence of the J(119Sn±O±117Sn) cou-
Independent reflections
Data/restraints/parameters
Goodness±of±fit on F2
R indices [I > 2sigma(I)]
7742 [Rint = 0.076]
7742/0/454
0.756
R1 = 0.0346
wR2 = 0.0458
R1 = 0.1344
wR2 = 0.0552
0.250/±0.257
pling from the Sn±O±Sn bond angle [27, 28] and
suggests this angle in compound 1 and in cyclo-[(2,6-
Me2±C6H3)2SnO]3 to be even more different in solu-
tion than in the solid state.
R indices (all data)
3
119Sn NMR spectrum ([D8]toluene) of 1 at 80 °C
Ê
Largest diff. peak and hole (e/A )
A
shows no significant change to the one described be-
fore, i. e., there is no indication for the formation of a
dimer. A further interesting feature of compound 1 in
solution is the observation in its 13C NMR spectrum
(CDCl3) of six resonances for the aryl carbon atoms
and nine resonances for the isopropyl carbon atoms,
indicating rotation about the Sn±Ci bond to be slow
on the NMR time scale.
±128.6 ppm (m1/2 ~ 350Hz) rather than the expected
two signals in a ratio of 2 : 1. The mean Sn±O and
Sn±C bond distances amount to 1.963(2) and
Ê
2.156(4) A, respectively, and are comparable with
those of other trimeric diorganotin oxides [4±8]. As a
result of the bulky 2,4,6-triisopropyl ligands, the tin
atoms exhibit distorted tetrahedral geometries. The
mean O±Sn±O angle in 1 amounts to 104.4(1)°, which
is close to the corresponding angles in cyclo-
t-Bu2SnO)3 (106.9(2)°), [4] cyclo-[(EtMe2C)2SnO]3
(106.1(6)°), [4] cyclo-[(2,4-Me2±C6H3)2SnO]3 (101.4°),
[6] cyclo-[(Me3SiCH2)2SnO]3 (103.2(2)°), [2] and cy-
clo-{[(Me3Si)3C]MeSnO}3 (104.7(3)°) [5] whereas the
corresponding O±Sn±O angle in the dimer cyclo-
{[(Me3Si)2CH]2SnO}2 (82.5(6)°) [12] differs drastically.
The mean C±Sn±C angle in 1 amounts to 112.5(2)°
which is close to the corresponding angle in cyclo-
[(2,4-Me2±C6H3)2SnO]3 (114.8°) [6] but somewhat
smaller than those values reported for cyclo-
Redistribution Reactions
The diorganotin oxides cyclo-[(Me3SiCH2)2SnO]3 and
cyclo-(t-Bu2SnO)3 are known to undergo a redistribu-
tion reaction under mild conditions and to form an
equilibrium with the mixed oxides cyclo-t-Bu2Sn-
[OSn(Me3SiCH2)2]2O and cyclo-(Me3SiCH2)2Sn(OSnt-
Bu2)2O [20]. The same holds for diorganotin sulphides
cyclo-(R2SnS)3 and cyclo-(R' SnS)3 (R, R' = Me, Bu,
2
Ph, o-Tol) which realize equilibria of the mixed su-
phides cyclo-R2Sn(SSnR' ) S and cyclo-R' Sn(SSnR2)2S
2 2
2
[21, 22]. Furthermore, dimethyltin chalcogenides cy-
Z. Anorg. Allg. Chem. 2001, 627, 2413±2419
2415

J. Beckmann, K. Jurkschat, S. Rabe, M. SchuÈrmann
clo-(Me2SnX)3 and cyclo-(Me2SnY)3 (X, Y = S, Se,
Te) react with each other to give the mixed chalco-
genides cyclo-Me2Sn(XSnMe2)2Y and cyclo-Me2Sn-
(YSnMe2)2X in situ [23]. These redistribution reac-
tions proceed under very mild conditions which can
be attributed to the high kinetic lability of the Sn±X
bonds (X = O, S, Se, Te). Surprisingly, equimolar
amounts of 1 and cyclo-(t-Bu2SnO)3 do not react,
even upon heating at reflux in [D8]toluene for 6 d
(Eq. (2)). The 119Sn NMR spectrum ([D8]toluene) of
the reaction mixture exclusively showed two signals at
±84.5 (2J(119Sn±O±117Sn) 369 Hz, cyclo-(t-Bu2SnO)3)
and ±128.4 (2J(119Sn±O±117Sn) 501 Hz, cyclo-[(2,4,6-i-
Pr3±C6H2)2SnO]3 (1)), demonstrating the coexistence
of the reactants in solution.
±42.4 ppm (cyclo-(Ph2SiO)4, identity confirmed by
addition of an authentic sample), ±43.0ppm, and
±46.8 ppm. Most of these signals could not be
assigned but they might belong to open-chain chloro-
siloxanes such as Ph2ClSiOSiClPh2, Ph2Si(OSiClPh2)2,
O(SiPh2OSiClPh2)2, and/or Ph2Si(OSiPh2OSiClPh2)2.
It is interesting to note that along the reaction (i) no
stannasiloxanes were detected and (ii) that only trace
amounts of cyclo-(Ph2SiO)4 are formed.
The inertness of cyclo-[2,4,6-i-Pr3±C6H2)2SnO]3 (1)
in its reaction with t-Bu2SiCl2 can be interpreted in
terms of an enhanced kinetic stability of the Sn±O
bonds. The synthesis and complete characterization of
the four-membered ring cyclo-O[(2,4,6-i-Pr3±C6H2)2-
Sn]2S [19] supports this interpretation as it is stable
and does not rearrange to give cyclo-[2,4,6-i-
Pr3±C6H2)2SnS]2 [18, 19] and cyclo-[2,4,6-i-Pr3-
C6H2)2SnO]3 (1).
Diorganotin oxysulphides other than cyclo-O[(2,4,6-
i-Pr3±C6H2)2Sn]2S are not known so far. However, the
six-membered rings cyclo-t-Bu2Sn(OSnt-Bu2)2S (2 a)
and cyclo-t-Bu2Sn(SSnt-Bu2)2O (2 b) were generated
in situ by heating at reflux for 12 h a mixture in
chloroform of cyclo-(t-Bu2SnO)3 and cyclo-(t-Bu2SnS)2
in a ratio of 2 : 3 (Eq. (3)).
The reaction of cyclo-(t-Bu2SnO)3 with various
amounts of t-Bu2SiCl2 provided a number of cyclic
and open-chain stannasiloxanes, such as cyclo-t-
Bu2Si(OSnt-Bu2)2O, cyclo-(t-Bu2SiOSnt-Bu2O)2, and
t-Bu2Si(OSnt-Bu2SnCl)2 [25]. This reaction is irrever-
sible with the thermodynamic driving force being the
formation of energetically favored Si±O bonds. In
contrast, the analogous reaction of 1 with t-Bu2SiCl2
in [D8]toluene after 6 d heating at reflux failed. No re-
action was observed even after prolonged heating of
the pure reactants at 220 °C for 6 d. The 119Sn and 29Si
NMR spectra ([D8]toluene) of the reaction mixtures
exclusively showed signals for the starting materials
at ±128.4 ppm (2J(119Sn±O±117Sn) 501 Hz; 1) and
35.6 ppm (t-Bu2SiCl2), respectively.
The reaction of 1 with the sterically less crowded
Ph2SiCl2 in [D8]toluene resulted indeed in oxide
transfer from the organotin oxide to the organosilicon
species. After 30min at 90 °C, the 119Sn NMR
spectrum displayed resonances at ±128.0ppm
(2J(119Sn±O±117Sn) 501 Hz, integral 84%) belonging
to the organotin oxide 1 and at ±66.6 ppm (integral
16%) assigned to (2,4,6-i-Pr3±C6H2)2SnCl2. The 29Si
NMR spectrum of the same reaction mixture dis-
played a major resonance at 6.1 ppm (integral 88%;
Ph2SiCl2) and two minor resonances at ±21.8 (integral
4%) and ±30.2 ppm (integral 7%). The oxide transfer
is almost complete after 115 h at 90 °C. The 119Sn
NMR spectrum displayed a major resonance at
±66.6 ppm (integral 97%) belonging to the diorganotin
dichloride and a minor resonance at ±128.0ppm (inte-
gral 3%) belonging to compound 1. The 29Si NMR
spectrum of this reaction mixture showed six major
resonances at 6.0ppm (integral 8%, Ph 2SiCl2),
±37.0ppm (integral 17%), ±37.3 ppm (integral 17%),
±45.0ppm (integral 30%), ±45.2 ppm (integral 11%),
and ±45.6 ppm (integral 6%), and five minor reso-
nances (total integral 11%) at ±21.8 ppm, ±35.2 ppm,
The 119Sn NMR spectrum (CHCl3, D2O-capillary)
showed six signals belonging to cyclo-(t-Bu2SnO)3
(d ±84.5, 2J(119Sn±O±117Sn) 365 Hz; integral 30%),
cyclo-(t-Bu2SnS)2 (d 123.9, 2J(119Sn±S±117Sn) 112 Hz;
integral 40%), cyclo-t-Bu2Sn(OSnt-Bu2)2S (2 a;
d
2
2
13.4, J(119Sn±O±119/117Sn) 520Hz, d ±99.5, J(119Sn±
O±119/117Sn); ratio 2 : 1; total integral 23%) and cyclo-
2
t-Bu2Sn(SSnt-Bu2)2O (2 b; d 86.2, J(119Sn±S±119/117Sn)
2
2
69 Hz, d ±6.0, J(119Sn±O±119/117Sn) 672 Hz, J(119Sn±
S±119/117Sn) 65 Hz; ratio 1 : 2; total integral 7%).
Further heating for 24 h did not change the integral
ratio indicating that the reaction mixture had reached
equilibrium. Slow evaporation of the solvent from the
reaction mixture afforded a microcrystalline solid
from which a 119Sn MAS NMR spectrum was re-
corded (Figure 2). It shows six center bands with ac-
2416
Z. Anorg. Allg. Chem. 2001, 627, 2413±2419

Hexakis(2,4,6-triisopropylphenyl)cyclotristannoxane
other trimeric diorganotin oxides. The six-membered
ring is retained in solution, and no evidence was
found for the formation of a dimer, cyclo-[(2,4,6-i-
Pr±C6H2)2SnO]2. Redistribution reactions with cyclo-
(t-Bu2SnO)3 and t-Bu2SiCl2 failed and reveal an en-
hanced kinetic inertness of the Sn±O bonds in 1 as
compared to other trimeric diorganotin oxides such as
cyclo-(t-Bu2SnO)3 which is attributed to the high
shielding capacity of the 2,4,6-isopropylphenyl ligands
[36]. The reaction of 1 with Ph2SiCl2 proceeds under
oxygen transfer to give a mixture of open-chain chlor-
osiloxanes, but only traces of cyclo-diphenylsiloxanes.
This is in contrast to the reaction in chloroform of
(t-Bu2SnO)3 with Ph2SiCl2 which proceeds at lower
temperature and gives cyclo-(Ph2SiO)n (n = 3, 4) as
major products [25].
Fig. 2 119Sn MAS NMR spectrum (149.21 MHz) of a reac-
tion mixture according Equation 4 (Spin frequency 9 KHz;
10000 transitions). Center bands are indicated by arrows.
Experimental Part
All operations were performed under a nitrogen atmosphere
using standard Schlenk techniques. Solvents were dried ac-
cording to standard procedures and freshly distilled prior to
use. (2,4,6-i-Pr±C6H2)2SnBr2, [37] cyclo-(t-Bu2SnO)3, [4] and
cyclo-(t-Bu2SnS)2 [31] were prepared according to literature
procedures. t-Bu2SiCl2 was commercially obtained (Fluka)
and used as supplied. Solution 1H, 13C{1H}, 29Si{1H}, and
companying sets of spinning sidebands, which are un-
ambiguously assigned to cyclo-(t-Bu2SnO)3 (d ±84.3;
integral 28%), [29] cyclo-(t-Bu2SnS)2 (d 126.1; integral
36%), cyclo-t-Bu2Sn(OSnt-Bu2)2S (2 a; d 14.7, ±99.5;
ratio 2 : 1; total integral 26%) and cyclo-t-Bu2Sn-
(SSnt-Bu2)2O (2 b; d 86.0, 5.6; ratio 1 : 2; total integral
10%). It is worth mentioning that the 119Sn MAS
NMR chemical shift measured for cyclo-(t-Bu2SnS)2
(d 126.1) differs from that previously reported by Har-
ris and Sebald (d 119.4, 117.3) [30] which is tentatively
attributed to the presence of different polymorphs. In-
deed, monoclinic (a-form) and triclinic (b-form) modi-
fications have been reported for (t-Bu2SnS)2 [31].
However, both 119Sn MAS chemical shifts are consis-
tent with the respective value of cyclo-(t-Bu2SnS)2 in
CDCl3 solution (d 124.1) [27]. The graphical integra-
tion of the signals was achieved by taking into account
the intensity of the center bands and all spinning side-
bands belonging to them. However, the integration
has to be considered as an estimate because errors
may arise from poor signal-to-noise ratio and dispa-
rate applying cross polarization. It is very likely that
cyclo-(t-Bu2SnO)3, 2 a, and 2 b realize mixed crystals
as the trimeric di-tert-butylelement oxides, cyclo-
(t-Bu2MO)3 (M = Si, Ge, Sn), [3, 4, 32, 33] cyclo-t-Bu2M-
(OSnt-Bu2)2O (M = Si, Ge), [2, 29] and di-tert-butyl-
element imines cyclo-(t-Bu2MNH)3 (M = Si, Sn) [34,
35] all crystallize in the trigonal space group R-3c.
119Sn{1H} NMR spectra were recorded on
a Bruker
DRX 400 instrument at 400.13 (1H), 100.31 (13C), 79.49
(29Si), and 149.20MHz ( 119Sn). 119Sn{1H} MAS NMR spec-
tra were obtained from a Bruker MSL 400 spectrometer at
149.20MHz using cross polarization and high power proton
decoupling. Three different spinning speeds were applied in
order to assign unambiguously the center bands. c-Hex4Sn
was used as a second reference (d ±97.35 ppm against
Me4Sn). The elemental analysis was determined on an
instrument from Carlo Erba Strumentazione (Model 1106).
The molecular weight was measured on a Knauer os-
mometer.
Synthesis of Hexakisꢀ2,4,6-triisopropylphenyl)cyclotristann-
oxane ꢀ1). A solution of NaOH (0.85 g, 21.2 mmol) in water
(20mL) was slowly added to
a solution of (2,4,6- i-
Pr±C6H2)2SnBr2 (7.25 g, 10.5 mmol) in refluxing toluene
(300 mL). After 3 h the mixture was allowed to cool to
40 °C, then the layers were separated, and the organic layer
was dried over sodium sulphate. The solvent was reduced to
approx. 100 mL. The crude product that crystallizied after
12 h at ±10 °C was recrystallized from chloroform/hexane to
give 4.6 g (8.5 mmol, 81%) of colorless crystals of 1, mp.
> 360 °C.
Anal. Calcd for C90H138O3Sn3 (1624.3): C, 66.6; H, 8.6.
Found: C, 66.6; H, 9.2%.
1H NMR (CDCl3): d = 6.89 (4J(117/119Sn±1H) 30Hz, phenyl proton), 6.86
(4J(117/119Sn±1H) 28 Hz, phenyl proton), 3.72 (sept, 1 H, 3J(1H±1H) 7 Hz,
Me2CH), 3.01 (sept, 1 H, 3J(1H±1H) 7 Hz, Me2CH), 2.78 (sept, 1 H,
3J(1H±1H) 7 Hz, Me2CH), 1.32 (d, 3 H, 3J(1H±1H) 7 Hz, Me2CH), 1.17 (d,
3 H, 3J(1H±1H) 7 Hz, Me2CH), 0.92 (d, 6 H, 3J(1H±1H) 7 Hz, Me2CH)
0.57 (d, 3 H, 3J(1H±1H) 7 Hz, Me2CH), 0.30 (d, 3 H, 3J(1H±1H) 7 Hz,
Me2CH); 13C{1H} NMR (CDCl3): d = 155.1 (s, 2J(13C±117/119Sn) 51 Hz,
Co), 153.9 (s, 2J(13C±117/119Sn) 58 Hz, Co), 149.8 (s, Cp), 143.0(s,
1J(13C±119Sn) 809 Hz, Ci), 121.9 (s, 3J(13C±117/119Sn) 69 Hz, Cm), 121.0(s,
3J(13C±117/119Sn) 67 Hz, Cm), 37.4 (s, 3J(13C±119Sn) 46 Hz, Me2CH), 34.2
(s, Me2CH), 33.9 (s, 3J(13C±119Sn) 28 Hz, Me2CH), 25.8 (s, Me2CH), 25.3
Conclusion
Bis(2,4,6-triisopropylphenyl)tin oxide, cyclo-[(2,4,6-i-
Pr±C6H2)2SnO]3 (1), was prepared in high yield as a
cyclic trimer by the hydrolysis of (2,4,6-i-Pr±C6H2)2-
SnBr2 under basic conditions. The molecular structure
of 1 shows no significant difference from those of
Z. Anorg. Allg. Chem. 2001, 627, 2413±2419
2417

J. Beckmann, K. Jurkschat, S. Rabe, M. SchuÈrmann
(s, Me2CH), 25.1 (s, Me2CH), 24.4 (s, Me2CH), 24.0(s, Me2CH), 23.9
(s, Me2CH); 119Sn{1H} NMR (CDCl3): d = ±128.4 (s, 1J(119Sn±13Ci) 806 Hz,
2J(119Sn±117Sn) 501 Hz, 2J(119Sn±13Co) 51 Hz, 3J(119Sn±13Cm) 69 Hz);
119Sn{1H} MAS NMR: d = ±128.6. Molecular weight determination
tained, free of charge, on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK (Fax: + 44-(0)12 23-33 60 33
or e-mail: deposit@ccdc.cam.ac.uk).
(10mg ´ ml ±1, CHCl3): 1674 g ´ mol±1
.
References
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6 d. A 119Sn NMR spectrum was recorded which is discussed
in the text.
1
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Ê
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2418
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Z. Anorg. Allg. Chem. 2001, 627, 2413±2419
2419