Molecular Dynamics within Diorganotin Systems: Solution and Solid State Studies of New Mixed Distannoxane Dimers [tBu2(Cl)SnOSn(Cl)R2]2

Article abstract of DOI:10.1021/ic9611608

Di-tert-butyltin oxide, (^tBu₂SnO)₃, reacts with R₂SnCl₂ to give mixed distannoxanes [^tBu₂(Cl)SnOSn(Cl)R₂]₂ (1, R = Me; 2, R = Et; 3, R = ⁱPr; 4, ⁿBu) whereas di-tert-butyltin hydroxide chloride, [^tBu₂Sn(OH)Cl]₂, reacts with [ⁿBu₂SnO]_n to give the chlorohydroxydistannoxane [^tBu₂(OH)SnOSn(Cl)ⁿBu₂]₂, 5; the dimeric nature of these tetraorganodistannoxanes was confirmed by crystal structure determinations of 1 and 4. Although stable in the solid state, compounds 1-4 rearrange to give a number of distannoxanes in solution. Addition of R₂SnCl₂ (R = Me, ⁱPr, ⁿBu) to solutions of 1, 3, and 4, respectively, causes displacement of ^tBu₂SnCl₂ with concomitant formation of [(^tBu₂SnCl₂)(R₂SnO) ₂(R₂SnCl₂)] and [(R₂SnCl₂)(R₂SnO)₂(R ₂SnCl₂)]. Thus 1-4 can be regarded as (R₂SnO)₂ units which are stabilized by two ^tBu₂SnCl₂ molecules. NMR data indicate that reaction between (¹Bu₂SnO)₃ and ^tBu₂SnCl₂ gives rise to an equilibrium involving linear [^tBu₂Sn(Cl)OSn(Cl)^tBu₂] and the novel three-quarter ladder compound [^tBu₂SnCl₂][^tBu₂SnO] ₂. Formation of trinuclear tin species is also evident from electrospray mass spectrometric studies.

Full text of DOI:10.1021/ic9611608

Inorg. Chem. 1997, 36, 2023-2029
2023
Molecular Dynamics within Diorganotin Systems: Solution and Solid State Studies of New
Mixed Distannoxane Dimers [tBu2(Cl)SnOSn(Cl)R2]2
†
Dainis Dakternieks,* Klaus Jurkschat,*,‡ and Serena van Dreumel
School of Biological and Chemical Sciences, Deakin University, Geelong, Victoria 3217, Australia
Edward R. T. Tiekink
Department of Chemistry, University of Adelaide, Adelaide, South Australia 5005, Australia
ReceiVed September 18, 1996X
Di-tert-butyltin oxide, (tBu2SnO)3, reacts with R2SnCl2 to give mixed distannoxanes [tBu2(Cl)SnOSn(Cl)R2]2 (1,
R ) Me; 2, R ) Et; 3, R ) iPr; 4, nBu) whereas di-tert-butyltin hydroxide chloride, [tBu2Sn(OH)Cl]2, reacts with
[nBu2SnO]n to give the chlorohydroxydistannoxane [tBu2(OH)SnOSn(Cl)nBu2]2, 5; the dimeric nature of these
tetraorganodistannoxanes was confirmed by crystal structure determinations of 1 and 4. Although stable in the
solid state, compounds 1-4 rearrange to give a number of distannoxanes in solution. Addition of R2SnCl2 (R )
Me, iPr, nBu) to solutions of 1, 3, and 4, respectively, causes displacement of tBu2SnCl2 with concomitant formation
of [(tBu2SnCl2)(R2SnO)2(R2SnCl2)] and [(R2SnCl2)(R2SnO)2(R2SnCl2)]. Thus 1-4 can be regarded as (R2SnO)2
units which are stabilized by two tBu2SnCl2 molecules. NMR data indicate that reaction between (tBu2SnO)3 and
tBu2SnCl2 gives rise to an equilibrium involving linear [tBu2Sn(Cl)OSn(Cl)tBu2] and the novel three-quarter ladder
compound [tBu2SnCl2][tBu2SnO]2. Formation of trinuclear tin species is also evident from electrospray mass
spectrometric studies.
Introduction
of these compounds in solution. These equilibria were rapid
on the preparative time scale but slow on the NMR time scale.
Although formation of monomeric species R2(X)SnOSn(X)R2
have been postulated,11 to date structural details have appeared
only for the compound (Rf)2(Cl)SnOSn(Cl)(Rf)2, which resulted
from the fortuitous oxidation and hydrolysis of (Rf)2Sn (Rf )
2,4,6-tris(trifluoromethyl)phenyl).12
Tetraorganodistannoxanes of the types R2(X)SnOSn(X)R2 and
R2(OH)SnOSn(X)R2 (R ) alkyl, Ph; X ) halide, OAc, NCS,
OR) have been known for some years.1 Derivatives with X )
halide are usually prepared by the controlled hydrolysis of
diorganotin dihalides2,3 or from reaction between equimolar
amounts of diorganotin oxide and diorganotin dihalide.1 Only
symmetrically substituted compounds have been fully charac-
terised so far3-7 although there is one early report of the
synthesis of the nonsymmetric tetraorganodistannoxane Et2(Br)-
SnOSn(Br)Pr2.8 A characteristic feature of symmetric tetraor-
ganodistannoxanes in the solid state is their dimerization which
results in the so-called ladder-type arrangement which contains
a central planar Sn2O2 four-membered ring; tin-119 NMR
investigations favor retention of this structure in solution.9
Asymmetric distannoxanes in the ladder configuration, where
the anionic X groups provide the asymmetry, were reported
recently.10 There was evidence for monomer-dimer equilibria
The trimer (tBu2SnO)3 has been well characterized structur-
ally,13 and its use as a convenient oxide transfer reagent was
recently described.14 We now report NMR and electrospray
mass spectrometric studies of reactions of (tBu2SnO)3 with a
i
number of diorganotin dihalides, R2SnCl2 (R ) Me, Et, Pr,
t
nBu, Bu) as well as the reaction of [tBu2Sn(OH)Cl]2 with
[nBu2SnO]n. We also report the crystal structures of [tBu2(Cl)-
n
SnOSn(Cl)R2]2 for R ) Me (1) and R ) Bu (4).
Experimental Section
General Methods. All solvents were dried by standard methods.
Dibutyltin oxide, dimethyltin dichloride, and dibutyltin dichloride were
purchased from Aldrich. Di-tert-butyltin dichloride15, di-tert-butyltin
oxide,13 and di-tert-butyltin hydroxide chloride16 were prepared by
published procedures. Elemental analyses were carried out by the
Microanalytical Laboratory of the Australian National University,
Canberra. Molecular weights were determined osmometrically using
a Hitachi Perkin-Elmer 115 molecular weight apparatus and a Knaur
osmometer (AO 280). Compounds 1 and 4 were measured at a
concentration of 0.660 g/100 g of CHCl3 solvent; compound 3 was
measured in the concentration range 0.200-0.400 g/100 g of CHCl3.
† Dedicated to Professor Max Herberhold on the occasion of his 60th
birthday.
‡ Present address: Institut fu¨r Anorganische Chemie, Fachbereich
Chemie, Universita¨t Dortmund, D-44221 Dortmund, Germany.
X Abstract published in AdVance ACS Abstracts, April 1, 1997.
(1) Alleston, D. L.; Davies, A. G.; Hancock, M.; White, R. F. M. J. Chem.
Soc. 1963, 5469.
(2) Chu, C. K.; Murray, J. D. J. Chem. Soc. A 1971, 360.
(3) Vollano, J. F.; Day, R. O.; Holmes, R. R. Organometallics 1984, 3,
745 and references cited therein.
(4) Okawara, R. Proc. Chem. Soc., London 1961, 383.
(5) Harrison, P. G.; Begley, M. J.; Molloy, K. C. J. Organomet. Chem.
1980, 186, 213.
(6) Puff, H.; Bung, I.; Friedrichs, E.; Jansen, A. J. Organomet. Chem.
1983, 254, 23.
(7) Parulekar, C. S.; Jain, V. K.; Das, T. K.; Gupta, A. R.; Hoskins, B.
F.; Tiekink, E. R. T. J. Organomet. Chem. 1989, 372, 193.
(8) Harada, T. Rep. Sci. Res. Inst., Tokyo 1948, 24, 177.
(9) Yano, T.; Nakashima, K.; Otera, J.; Okawara, R. Organometallics
1985, 4, 1501.
(11) Narula, S. P.; Bharadwaj, S. K.; Sharma, G.; Mairesse, P.; Barbier,
P.; Nowogrocki, G. J. Chem. Soc., Dalton Trans. 1988, 1719.
(12) Brooker, S.; Edelmann, F. T.; Stalke, D. Acta Crystallogr. 1991, C47,
2527.
(13) Puff, H.; Schuh, W.; Sievers, R.; Wald, W.; Zimmer, R. J. Organomet.
Chem. 1984, 260, 271.
(14) Dakternieks, D.; Jurkschat, K.; Schollmeyer, D.; Wu, H. Organome-
tallics 1994, 13, 4121.
(15) Kandil, S. A.; Allred, A. L. J. Chem. Soc. A, 1970, 2987.
(16) Puff, H.; Hevendehl, H.; Ho¨fer, K.; Reuter, H.; Schuh, W. J.
Organomet. Chem. 1985, 287, 163.
(10) Gross, D. C. Inorg. Chem. 1989, 28, 2355.
S0020-1669(96)01160-3 CCC: $14.00 © 1997 American Chemical Society

2024 Inorganic Chemistry, Vol. 36, No. 10, 1997
Dakternieks et al.
Table 1. Crystal Data and Refinement Details for 1 and 4
NMR Spectroscopy. Solution NMR spectra (typically of 0.5-1.0
M solutions) were recorded on either a 500 Varian Unity or a JEOL
GX 270 FT NMR spectrometer at 500 and 270.17 (1H), 125.697 and
67.84 (13C), and 186.409 and 100.75 (119Sn) MHz. The chemical shifts
are relative to external Me4Si (1H, 13C) and Me4Sn (119Sn). Solid-state
119Sn MAS (149.16 MHz) and 13C (100.44 MHz) CPMAS NMR spectra
were acquired on a Bruker MSL 400 spectrometer. For 119Sn NMR
1
4
formula
fw
cryst system
space group
a, Å
b, Å
c, Å
C20H48Cl4O2Sn4
937.1
monoclinic
C2/m,
8.306(1)
15.916(2)
12.810(1)
96.61(1)
1682.2
2 (tetramers)
1.850
C32H72Cl4O2Sn4
1105.5
monoclinic
P21/n
13.320(2)
10.813(1)
16.493(4)
101.38(1)
2328.8
2 (tetramers)
1.577
1
spectra, MAS high-power H decoupling and fast MAS (>10 kHz)
were used with a 4 mm double-bearing MAS probe. Spectra were
referenced to an external secondary standard of solid tetracyclohexyltin
at -97.4 ppm.
â, deg
V, Å3
Electrospray Mass Spectrometry. Solutions of the compounds
(approximately 2 × 10-4 M) were prepared in methanol/water (50:
50). Electrospray mass spectra were obtained using a VG Bio-Q triple
quadrupole mass spectrometer (VG BioTech, Altrincham, Cheshire,
U.K.) with a water/methanol (50:50) mobile phase. Solutions of the
compounds were injected directly into the spectrometer via a Rheodyne
injector equipped with a 10 µL loop. A Phoenix 20 micro LC syringe
pump delivered the solutions to the vaporization nozzle of the
electrospray ion source at a flow rate of 3 µL min-1. Nitrogen was
used both as a drying gas and for nebulization with flow rates of
approximately 3 L min-1 and 100 mL min-1, respectively. Pressure
in the mass analyzer region was about 3 × 10-5 Torr. Typically, about
20 signal-averaged spectra were required to give a good signal to
noise ratio. Measurements were made at a first-skimmer (B1) voltage
of 40 V.
Synthesis of [tBu2(Cl)SnOSn(Cl)Me2]2 (1). A mixture of (tBu2-
SnO)3 (7.59 mmol, 5.67 g) and Me2SnCl2 (22.70 mmol, 5.00 g) was
refluxed in toluene (100 mL) until the solution became clear. The
mixture was then left to cool slowly, and the colorless crystals which
formed were filtered off and dried in air to give 9.1 g (85%) of 1; mp
250 °C. Anal. Calcd for C20H48Cl4O2Sn4 (Mr ) 937.25): C, 25.64;
H, 5.18. Found: C, 25.32; H, 5.31.
Z
D
calcd, g cm-3
F(000)
904
0.71073
30.31
0.511, 0.250
(h,+k,-l
293
1096
0.71073
21.96
n/a
(h,+k,-l
293
λ, Å
µ, cm-1
transm: max, min
hkl range
T, K
no. of data collcd
θ max, deg
no. of unique data
1654
25.0
1545
0.037
6823
27.5
5349
0.016
a
Ramal
no. of unique data
1311
2883
used with I g 2.5σ(I)
R
g
Rw
0.049
0.013
0.048
2.23
0.031
0.002
0.038
0.68
residual F, e Å-3
2
a Ramal ) {∑[N∑[w(Fmean - |Fo|)2]]/∑[(N - 1)∑(w|Fo| )]}1/2, where
the inner summation is over N equivalent reflections averaged to give
Fmean, the outer summation is over all unique reflections, and the weight,
w, is taken as [σ(Fo)]-2
.
Synthesis of [tBu2(Cl)SnOSn(Cl)Et2]2 (2). A mixture of (tBu2SnO)3
(0.45 mmol, 0.33 g) and Et2SnCl2 (1.33 mmol, 0.33 g) was refluxed
for 15 min in 10 mL of toluene. The reaction mixture was then filtered,
and the filtrate was stored at -5 °C for 5 days, after which the colorless
crystals that formed were filtered off and dried to give 0.46 g (70%)
of 2; mp 200 °C. Anal. Calcd for C24H56Cl4O2Sn4 (Mr ) 993.28): C,
29.02; H, 5.68; Cl, 14.28. Found: C, 29.33; H, 5.55; Cl, 14.45. δ-
crystal of 1 was 0.23 × 0.58 × 0.58 mm and that of the multifaceted
4 was approximately 0.5 mm in diameter. The net intensity values of
two standard reflections, monitored after every 7200 s of X-ray exposure
time, showed no change for 1 but indicated a linear decrease during
the course of the data collection for 4. At the conclusion of the latter
data collection, the intensity standards had decreased to 85% of their
original values and the data set was scaled accordingly. Lorentz
and polarization corrections17 were applied, and for 1, an analytical
absorption correction was applied.18 Crystal data are summarized in
Table 1.
Each structure was solved by direct methods19 and refined by full-
matrix least-squares procedures based on F.18 Anisotropic displacement
parameters were employed for all non-H atoms, and H atoms were
included in each model at their calculated positions. Disorder was noted
in the positions of the C atoms of the n-butyl groups in 4, and hence
these groups were refined with C-C bond distances constrained to
1.50(2) Å. A weighting scheme of the form w ) [σ2(F) + |g|F2]-1
was introduced, and the refinements were continued until convergence;
final refinement details are listed in Table 1. The analysis of variance
for each structure showed no special features, indicating that an
appropriate weighting scheme had been employed. The numbering
schemes employed are shown in Figure 1, which was drawn with the
ORTEP20 program at 25% probability ellipsoids. Scattering factors
for all atoms were those incorporated in SHELX76.18
(
119Sn) (major peaks in toluene): -152.9; -163.9 (2J(119SnO117/119Sn)
) 90 Hz, J(119Sn-C) ) 663 Hz).
Synthesis of [tBu2(Cl)SnOSn(Cl)iPr2]2 (3). A sample of iPr2SnCl2
(16.40 mmol, 4.54 g) was reacted with (tBu2SnO)3 (5.49 mmol,
4.09 g) in toluene in a manner analogous to that for 2. The color-
less solid 3 (5.0 g, 58%) precipitated from toluene: mp 175-189 °C.
Anal. Calcd for C28H64Cl4O2Sn4 (Mr ) 1049.46): C, 32.04, H,
6.15; Cl, 13.51. Found: C, 31.93; H, 6.18; Cl, 13.12. δ(119Sn) (major
peaks in CDCl3): -165.3 (2J(119SnO117/119Sn) ) 114 Hz); -180.2
(2J(119SnO117/119Sn) ) 98 Hz).
Synthesis of [tBu2(Cl)SnOSn(Cl)nBu2]2 (4). A sample of nBu2SnCl2
(16.46 mmol, 5.00 g) was reacted with (tBu2SnO3) (5.49 mmol, 4.09
g) in toluene in a manner analogous to that for 2. The colorless solid
4 (8.15 g, 90%) was recrystallized from toluene; mp 178-181 °C. Anal.
Calcd for C32H72Cl4O2Sn4 (Mr ) 1105.56): C, 34.78; H, 6.58. Found:
C, 35.74; H, 7.40. δ(119Sn) (major peaks in CDCl3): -150.7
(2J(119SnO117/119Sn) ) 81 Hz, J(119Sn-C) ) 517 Hz); -157.6
(2J(119SnO117/119Sn) ) 89 Hz, J(119Sn-C) ) 614 Hz).
Synthesis of [tBu2(OH)SnOSn(Cl)nBu2]2 (5). A mixture of 1/n
Results and Discussion
t
(Bu2SnO)n (1.39 mmol, 0.35 g) and Bu2Sn(OH)Cl (1.39 mmol, 0.40
Synthesis. Reaction of equimolar amounts of di-tert-butyltin
oxide (tBu2SnO)3 with diorganotin dichlorides R2SnCl2 (R )
g) was refluxed for 45 min in 15 mL of toluene. The solution was
filtered and the solvent evaporated in Vacuo. The residue was dissolved
in dichloromethane and the solution stored at -5 °C for 5 days to give
0.55 g (74%) of 5 as colorless crystals: mp 200-208 °C. Anal. Calcd
for C32H74Cl2O4Sn4 (Mr ) 1068.10): C, 35.97; H, 6.98; Cl, 6.64.
Found: C, 36.33; H, 7.21; Cl, 6.59. δ(119Sn) (in CDCl3): -181.7
(2J(119SnO117/119Sn) ) 38 and 222 Hz, J(119Sn-C) ) 625 Hz); -220.9
(2J(119SnO117/119Sn) ) 38 and 220 Hz, J(119Sn-C) ) 605 Hz).
Crystallography. Intensity data for transparent crystals of 1 and 4
were obtained at room temperature on an Enraf-Nonius CAD4F
diffractometer fitted with Mo KR radiation (graphite monochromator),
λ ) 0.7107 Å, employing the ω-2θ scan technique. The size of the
i
Me, Et, Pr, nBu) in dichloromethane or toluene results in
formation of clear solutions from which colorless crystals of
(17) PREABS and PROCES: Data Reduction Programs for the CAD4
Diffractometer. University of Melbourne, 1981.
(18) Sheldrick, G. M. SHELX76: Program for Crystal Structure Deter-
mination. University of Cambridge, England, 1976.
(19) Sheldrick, G. M. SHELXS86: Program for the Automatic Solution
of Crystal Structure. University of Go¨ttingen, Germany, 1986.
(20) Johnson, C. K. ORTEP; Report ORNL-5138; Oak Ridge National
Laboratory: Oak Ridge, TN, 1976.

Molecular Dynamics within Diorganotin Systems
Inorganic Chemistry, Vol. 36, No. 10, 1997 2025
Table 2. Selected Bond Distances (Å) and Angles (deg) for 1 and
4a
compd 1
compd 4
2.802(2) Sn(1)-Cl(1)′
Sn(1)-Cl(1)
2.907(2)
3.013(2)
2.075(3)
2.080(3)
2.107(6)
2.109(7)
2.598(2)
2.574(2)
2.034(3)
2.183(6)
2.177(7)
Sn(1)-Cl(2)
Sn(1)-O(1)
Sn(1)-O(1)′
Sn(1)-C(1)
Sn(1)-C(1)′′
Sn(2)-Cl(1)
Sn(2)-Cl(2)
Sn(2)-O(1)
Sn(2)-C(2)
Sn(2)-C(2)′′
3.126(2) Sn(1)-Cl(2)
2.074(5) Sn(1)-O(1)
2.104(5) Sn(1)-O(1)′
2.130(6) Sn(1)-C(11)
2.130(6) Sn(1)-C(15)
2.675(2) Sn(2)-Cl(1)
2.516(2) Sn(2)-Cl(2)
2.028(5) Sn(2)-O(1)
2.191(5) Sn(2)-C(21)
2.191(5) Sn(2)-C(25)
Cl(1)-Sn(1)-Cl(2)
Cl(1)-Sn(1)-O(1)
Cl(1)-Sn(1)-O(1)′
Cl(1)-Sn(1)-C(1)
158.8(1) Cl(1)′-Sn(1)-Cl(2)
144.8(1)
146.3(1)
72.1(2)
73.1(1)
Cl(1)′-Sn(1)-O(1)
148.4(1) Cl(1)′-Sn(1)-O(1)′
88.4(2)
Cl(1)′-Sn(1)-C(11) 84.0(2)
Cl(1)′-Sn(1)-C(15) 85.9(2)
Cl(1)-Sn(1)-C(1)′′ 88.4(2)
Cl(2)-Sn(1)-O(1)
Cl(2)-Sn(1)-O(1)′
Cl(2)-Sn(1)-C(1)
66.7(1)
Cl(2)-Sn(1)-O(1)
68.9(1)
144.0(1)
81.2(2)
84.3(2)
75.2(2)
108.7(2)
106.4(2)
106.2(3)
104.7(2)
142.3(1) Cl(2)-Sn(1)-O(1)′
81.8(2)
Cl(2)-Sn(1)-C(11)
Cl(2)-Sn(1)-C(15)
O(1)-Sn(1)-O(1)′
Cl(2)-Sn(1)-C(1)′′ 81.8(2)
O(1)-Sn(1)-O(1)′
O(1)-Sn(1)-C(1)
O(1)-Sn(1)-C(1)′′
O(1)′-Sn(1)-C(1)
75.4(1)
106.3(2) O(1)-Sn(1)-C(11)
106.3(2) O(1)-Sn(1)-C(15)
100.5(2) O(1)′-Sn(1)-C(11)
O(1)′-Sn(1)-C(1)′′ 100.5(2) O(1)′-Sn(1)-C(15)
C(1)-Sn(1)-C(1)′′
Cl(1)-Sn(2)-Cl(2)
Cl(1)-Sn(2)-O(1)
Cl(1)-Sn(2)-C(2)
144.7(2) C(11)-Sn(1)-C(15) 137.8(3)
158.8(1) Cl(1)-Sn(2)-Cl(2)
Figure 1. Molecular structures of 1 (upper) and 4 (lower).
158.6(1)
79.0(1)
95.3(2)
94.3(2)
79.7(1)
95.2(2)
94.9(2)
118.1(2)
117.1(2)
76.7(2)
92.6(2)
Cl(1)-Sn(2)-O(1)
Cl(1)-Sn(2)-C(21)
Cl(1)-Sn(2)-C(25)
Cl(2)-Sn(2)-O(1)
Cl(2)-Sn(2)-C(21)
Cl(2)-Sn(2)-C(25)
t
formulation Bu2(Cl)SnOSn(Cl)R2 were isolated (eq 1).
Cl(1)-Sn(2)-C(2)′′ 92.6(2)
1/3(tBu2SnO)3 +
Cl(2)-Sn(2)-O(1)
Cl(2)-Sn(2)-C(2)
82.1(2)
97.3(2)
CH2Cl2 or C7H8
R2SnCl2
8 tBu2(Cl)SnOSn(Cl)R2 (1)
Cl(2)-Sn(2)-C(2)′′ 97.3(2)
O(1)-Sn(2)-C(2)
O(1)-Sn(2)-C(2)′′
C(2)-Sn(2)-C(2)′′
Sn(1)-O(1)-Sn(2)
Sn(1)-O(1)-Sn(1)′
117.9(2) O(1)-Sn(2)-C(21)
117.9(2) O(1)-Sn(2)-C(25)
1: R ) Me
2: R ) Et
123.7(2) C(21)-Sn(2)-C(25) 124.8(3)
3: R ) iPr
4: R ) nBu
126.4(2) Sn(1)-O(1)-Sn(2)
104.6(2) Sn(1)-O(1)-Sn(1)′
126.5(2)
104.8(2)
Sn(2)-Cl(1)-Sn(1)′ 83.9(1)
Sn(1)′-Cl(2)-Sn(2) 82.0(1)
Sn(2)-Cl(1)-Sn(1)′ 83.4(1)
Sn(1)-Cl(2)-Sn(2)
82.8(1)
Interestingly, compound 4 can also be obtained by reaction of
di-tert-butyltin dichloride and di-n-butyltin oxide (eq 2).
a Primed atoms are related by a center of inversion, and doubly-
primed atoms are related by a mirror plane.
tBu2SnCl2 + (1/n)
is triply bridging; further links between the Sn atoms are
provided by the Cl atoms. In addition to the center of inversion,
1 has a crystallographic m symmetry such that the Sn4O2Cl4
atoms lie on this plane and the organic substituents are related
to each other across this plane. Although mirror symmetry is
not crystallographically imposed in 4, the Sn4O2Cl4 atoms are
planar to (0.034(2) Å.
CH2Cl2 or C7H8
(nBu2SnO)n
8 t
Bu2(Cl)SnOSn(Cl)nBu2
(2)
4
In a similar manner, di-tert-butyltin hydroxide chloride reacts
with di-n-butyltin oxide to give 5 (eq 3).
1/2[tBu2Sn(OH)Cl]2 +
From an inspection of Table 2 it is clear that the Cl atoms
bridge the Sn atoms with relatively long and disparate Sn-Cl
bond distances so that assignment of coordination numbers to
the Sn atoms is ambiguous, in particular for the endocyclic Sn
atoms. For 1, the exocyclic Sn atom, Sn(2), is coordinated by
two organic substituents, the O(1) atom and two Cl atoms at
2.675(2) and 2.516(2) Å. The Sn(2)-Cl bond distances are
somewhat longer than the sum of the covalent radii of Sn and
Cl, at 2.39 Å, but are short enough to be considered as bonding
interactions, thereby leading to a distorted trigonal bipyramidal
geometry. The trigonal plane is defined by the O(1) atom and
CH2Cl2 or C7H8
(1/n)(nBu2SnO)n
8 t
Bu2(OH)SnOSn(Cl)nBu2
(3)
5
Compounds 1-5 have satisfactory elemental analyses; all are
colorless solids which are soluble in solvents such as dichlo-
romethane, chloroform, and toluene.
Molecular Structures of 1 and 4. The molecular structures
of 1 and 4 are shown in Figure 1, and selected interatomic
parameters for these compounds are given in Table 2. The
structures are essentially molecular although in 1 there is a weak
intermolecular contact between the Sn(1) atom and a symmetry-
related Cl(1) atom (symmetry operation: -x, -y, 1 - z) of
3.597(3) Å. Both compounds feature centrosymmetric dimers
situated about a crystallographic center of inversion at (1/2, 0,
t
two C atoms of the Bu groups, and the Cl(1)-Sn(2)-Cl(2)
axial angle is 158.8(1)°. The deviation from the ideal axial angle
and the elongation of the Sn(2)-Cl bond distances may be due,
in part, to the interaction of the Cl atoms with the endocyclic
Sn atoms. The immediate geometry about the Sn(1) atom is
defined by the two O atoms of the Sn2O2 core and two C atoms
of the methyl substituents which define a distorted tetrahedral
1/2) for 1 and at (1/2, /2, /2) for 4. Connected to the central
1
1
Sn2O2 unit are two exocyclic tBu2Sn groups so that each O atom

2026 Inorganic Chemistry, Vol. 36, No. 10, 1997
Dakternieks et al.
Table 3. Sn-Cl Bond Distances (Å) in [(R2Sn(Cl)OSn(Cl)R′2]2
Table 4. 119Sn NMR Data (186.409 MHz) for 1 (Analytically Pure
Sample) in CDCl3 Solution at 25 °C
δ(119Sn),
ppm
2J(119SnO117/119Sn), 1J(119Sn-13C),
Hz (Hz)
integral
assigntb
54.5
-75.9
8
1
3
0.5
0.5
0.5
6.5
6
2.5
5
46
46
6
0.5
4
tBu2SnCl2
-81.8
br
175
610
B
-110.0
-112.4
-112.7
-120.0
-126.6
-134.1
-135.1
-138.3
-145.6
-163.6
-216.0
-220.4
-222.3
R
R′
a
b
c
d
ref
72, 188
67
br
Me Me 2.445(2) 2.789(2) 3.409(2) 2.702(2) 24
680
B′
B′′
iPr
Ph
iPr
Ph
2.462(6) 2.803(5) 3.473(3) 2.675(6)
5
2.430(1) 2.697(1) 3.355(2) 2.688(1) 26
br, ∼100
Me tBu 2.516(2) 2.675(2) 3.126(2) 2.802(2) this work
nBu tBu 2.574(2) 2.598(2) 3.013(2) 2.907(2) this work
79
693 (394)
708 (400)
A
A′
bra
br, 105
geometry. The Sn(1) atom also forms two close contacts with
the Cl atoms, Sn(1)-Cl(1) ) 2.802(2) and Sn(1)-Cl(2) )
3.126(2) Å, and while the former distance is indicative of some
bonding interaction, the latter is quite long but nevertheless
shorter than the sum of the van der Waals radii for these atoms
of 4.0 Å.21 The environment about the Sn(1) atom is thus best
described as being based on a skew-trapezoidal planar geometry
with the methyl groups lying over the weaker, i.e. Sn-Cl, bonds.
The different Sn(1)-Cl bond distances are reflected in the
associated Sn(2)-Cl bond distances. Thus, the more tightly
held Cl(2) atom (Sn(2)-Cl(2) ) 2.516(2) Å) forms the weaker
intramolecular contact to the Sn(1) atom (3.126(2) Å) and
conversely the less tightly held Cl(1) atom (2.675(2) Å) forms
a shorter contact to the Sn(1) atom of 2.802(2) Å. From these
variations it can be seen that the Cl(1) atom forms the more
symmetrical bridge between the Sn atoms.
The geometry about the Sn(2) atom in 4 is the same as that
in 1 and the axial Cl(1)-Sn(2)-Cl(2) angle is equivalent, at
158.6(1)°. As in 1, there are weak Sn(1)-Cl interactions of
2.907(7) and 3.013(3) Å for Sn(1)-Cl(1)′ and Sn(1)-Cl(2),
respectively. Consequently, the geometry about Sn(1) is as
described for the comparable atom in 1. In 4, where the same
trends in the Sn-Cl bond distances as above are found, the
disparity in the Sn(2)-Cl bond distances (2.574(2), 2.598(2)
Å) is much less and the difference between the Sn(1)-Cl
interactions (3.013(2) and 2.907(2) Å) reflects this fact.
The basic structural type found for 1 and 4 has been observed
previously in other [(R2SnX)2O]2 compounds, for example,
where X ) NCS22 and X ) O2CR′ 23 and, particularly relevant
to the present study, where X ) Cl;5,24-26 selected interatomic
parameters for the X ) Cl derivatives are listed in Table 3.
The structure of the [(Me2SnCl)2O]2 compound has been
determined on three occasions,5,24,26 and the most recent
parameters have been included in Table 3. In the [(R2SnX)2O]2
compounds that have been structurally characterized, the R
groups are the same for both the endo- and exocyclic Sn atoms,
and thus these may be termed symmetrical tetraorganodistan-
noxanes, whereas the present series are examples of asymmetric
tetraorganodistannoxanes.
188
0.5
a Sharpens at -55 °C; 2J(119SnO117/119Sn) ) 75 Hz. b A ) [(tBu2SnCl2)-
(Me2SnO)2(tBu2SnCl2)]; A′ ) [(tBu2SnCl2)(Me2SnO)2(tBu2SnCl2)]; B
) [(tBu2SnCl2)(Me2SnO)2(Me2SnCl2)]; B′ ) [(tBu2SnCl2)(Me2SnO)2-
(Me2SnCl2)]; B′′ ) [(tBu2SnCl2)(Me2SnO)2(Me2SnCl2)].
involved in weak, but significant, interactions with the endocy-
clic Sn atom, in the symmetric compounds one Cl atom forms
a symmetric bridge and the other is essentially terminal. This
has the consequence that in the symmetric [(R2SnX)2O]2 species
both Sn atoms are five-coordinate and trigonal bipyramidal.
NMR Studies. The solid state 119Sn NMR spectrum of 1
contains two resonances at -145.8 and -172.0 ppm. The 13
C
CPMAS NMR spectrum of 1 (same sample as 119Sn) shows
resonances at 17.9 ppm, 1J(119Sn-13C) ) 732 Hz (SnCH3), 32.0
ppm (CH3), and 45.6 ppm, 1J(119Sn-13C) ) 504 Hz (SnC). The
solid state 119Sn NMR spectrum of 4 shows two signals, of
nearly equal intensity, at -153.5 and -169.0 ppm.
The 119Sn NMR spectrum of an analytically pure sample
of 1 in CDCl3 at 25 °C (Table 4) contains two major reso-
2
nances at -138.3 and -145.6 ppm which show J(119Sn-O-
117/119Sn) satellites of 79 Hz. The resonance at -138.3 ppm
displays a J(119Sn-13C) coupling of 693 Hz. These two
resonances account for about 68% of the total integrated signal
intensity of the 119Sn spectrum. In addition, the 119Sn NMR
spectrum contains 14 weaker resonances between 55 and -220
ppm (Figure 2). These 14 resonances contribute approximately
32% toward the total signal intensity of the spectrum, and the
origin of these signals is discussed further below.
The 13C NMR spectrum of 1 in CDCl3 (the same solu-
tion 119Sn NMR) displays major resonances at 14.63 ppm,
1J(119Sn-13C) ) 693 Hz (SnCH3), 30.35 ppm (CH3), and 46.74
1
ppm, J(119Sn-13C) ) 504 Hz (SnC). Additional resonances
of low intensity appear in the methyl region (9.32, 11.57, 12.93,
and 14.09 ppm) and in the tert-butyl region (29.18, 30.03, 30.35,
and 30.63 ppm). The 13C NMR data allow assignment of the
119Sn resonance A (at -138.3 ppm) to the Me2Sn moiety and
t
the 119Sn resonance A′ (at -145.6 ppm) to the Bu2Sn moiety
There is a substantial difference between the structures found
for the symmetric and asymmetric [(R2SnCl)2O]2 compounds.
Whereas in the asymmetric compounds both Cl atoms are
of [tBu2(Cl)SnOSn(Cl)Me2]2 (Figure 1).
The proton NMR spectrum (500 MHz, CDCl3) of 1 displays
two major resonances with a 1:3 integral ratio (δ 1.30 ppm,
3
2J(119Sn-1H) ) 82 Hz; δ 1.44 ppm, J(119Sn-1H) ) 124 Hz)
(21) Bondi, A. J. Phys. Chem. 1964, 68, 441.
(22) Chow, Y. M. Inorg. Chem. 1971, 10, 673.
(23) Tiekink, E. R. T. Appl. Organomet. Chem. 1991, 5, 1. Tiekink, E. R.
T. Trends Organomet. Chem. 1994, 1, 71.
(24) Dakternieks, D.; Gable, R. W.; Hoskins, B. F. Inorg. Chim. Acta 1984,
85, L43.
(25) Puff, H.; Friedrichs, E.; Visel, F. Z. Anorg. Allg. Chem. 1981, 477,
50.
(26) Graziani, R.; Casellato, U.; Plazzogna, G. Acta Crystallogr. 1983, C39,
1188.
which are assigned to the methyl and tert-butyl groups,
respectively. There are additional low-intensity singlets at δ
2
1.00 ppm, J(119Sn-1H) ) 84 Hz, and δ 1.18, 1.34, 1.44, and
1.46 ppm. Solution NMR results for compounds 2-4 are
similar.
The major resonances in the 119Sn NMR solution spectra of
1-4 are assigned to the two different tin sites in the ladder

Molecular Dynamics within Diorganotin Systems
Inorganic Chemistry, Vol. 36, No. 10, 1997 2027
Table 5. 119Sn NMR Data for 1 + Additions of Me2SnCl2 (CDCl3
at 25 °C)
Scheme 1
δ(119Sn),
ppm
2J(119SnO117/119Sn), 1J(119Sn-13C),
Hz Hz
integral
assignta
1 + 1.04 equiv of Me2SnCl2
54.3
-61.9
46
26
26
23
50
23
12
11
tBu2SnCl2
C
B
C′
B′
B′′
A
56 (br)
58 (br)
58
626 (370)
-81.9
637 (406)
674 (393)
681 (394)
-116.9
-126.6
-134.1
-130.3
-145.6
67
76 (br)
81
691 (302)
76 (br)
A′
1 + 2.29 equiv of Me2SnCl2
142.0
54.5
11
88
82
9
77
15
6
Me2SnCl2
tBu2SnCl2
-61.7
-81.9
-116.9
-126.6
-134.1
br
br
56
67
br
648
674
C
B
C′
B′
B′′
a A ) [(tBu2SnCl2)(Me2SnO)2(tBu2SnCl2)]; A′ ) [(tBu2SnCl2)-
(Me2SnO)2(tBu2SnCl2)]; B ) [(tBu2SnCl2)(Me2SnO)2(Me2SnCl2)]; B′
) [(tBu2SnCl2)(Me2SnO)2(Me2SnCl2)]; B′′ ) [(tBu2SnCl2)(Me2SnO)2-
(Me2SnCl2)]; C ) [(Me2SnCl2)(Me2SnO)2(Me2SnCl2)]; C′ ) [(Me2SnCl2)-
(Me2SnO)2(Me2SnCl2)].
5.74 molar equiv of Me2SnCl2 shows that the dominant ladder
species is now [Me2(Cl)SnOSn(Cl)Me2]2 with only traces of
[(tBu2SnCl2)(Me2SnO)2(Me2SnCl2)] remaining evident. These
assignments are supported by the analogous 13C NMR spec-
tra. By comparison, the 119Sn NMR spectrum of a solution
structure which has been confirmed in the solid state for 1 and
4. This assignment is further supported by the similarity of
the solution and solid state spectra of 1 (13C) and 4 (119Sn).
The exocyclic (tBu2Sn) tins are clearly pentacoordinate whereas
the endocyclic (R2Sn) tin sites may be considered as intermedi-
ate between penta- and hexacoordinated. The Me-Sn-Me
angle for 1 in solution calculated from the equation of Lockhart
and Manders27 is 138°, close to the 144.7(2)° observed in the
solid state (Table 2). The Bu-Sn-Bu angle of 136° calculated
from the equation of Holecek and Lycka28 is even closer to the
value of 137.8(3)° found by X-ray analysis (Table 2).
t
of 1 to which has been added 2.2 mole equiv of Bu2SnCl2 is
very simple and shows only signals A and A′ and a signal for
tBu2SnCl2.
The 119Sn NMR spectra of a solution of 3 to which various
i
quantities of Pr2SnCl2 have been added indicate replacement
t
i
n
of Bu2SnCl2 by Pr2SnCl2. Similarly, addition of Bu2SnCl2
t
to a solution made from 4 indicates replacement of Bu2SnCl2
n
by Bu2SnCl2.
These exchange experiments suggest that 1-4 can be viewed
as Lewis acid-base adducts in which diorganotin oxide dimers
(R2SnO)2 are stabilized by two tBu2SnCl2 units. The 1:2 adducts
(tBu2SnCl2)(R2SnO)2(tBu2SnCl2) are stable in the solid state,
but in solution they undergo appreciable dissociation, which
enables the exocyclic tBu2SnCl2 units to be exchanged by other
R2SnCl2 moieties (Scheme 1).
The origin of the minor 119Sn and 13C NMR signals observed
for solutions of 1-4 becomes clear from the following addition
experiments. The 119Sn NMR spectrum of a solution of 1 to
which a 1.04 molar equivalent of Me2SnCl2 has been added
contains only eight resonances (Table 5). There is an ap-
preciable increase in concentration of tBu2SnCl2 and a decrease
in concentration of 1 (signals A and A′). The 119Sn NMR spec-
trum also contains resonances for the known compound9 [Me2-
(Cl)SnOSn(Cl)Me2]2, 6 (signals C and C′). The three 119Sn
resonances at -81.9, -126.6, and -134.1 ppm (signals B, B′,
and B′′; relative intensities 1:2:1) are assigned to the asym-
metrical species [(tBu2SnCl2)(Me2SnO)2(Me2SnCl2)], 7. These
results indicate that although 1 is a dimer in the solid state,
there is in solution an equilibrium among [tBu2(Cl)SnOSn-
(Cl)Me2]2, [(tBu2SnCl2)(Me2SnO)2(Me2SnCl2)], [Me2(Cl)SnOSn-
(Cl)Me2]2, and tBu2SnCl2. Addition of Me2SnCl2 favors
The lability of 1, 3, and 4 in solution is reflected in their
molecular weight determinations, which show association fac-
tors of 1.3, 0.6, and 1.2 for [tBu2(Cl)SnOSn(Cl)Me2], [tBu2(Cl)-
SnOSn(Cl)iPr2], and [tBu2(Cl)SnOSn(Cl)nBu2], respectively, in
t
chloroform solution. The lower Lewis acidity of the Bu2Sn
i
n
moiety compared to R2Sn (R ) Me, Et, Pr, Bu) accounts for
its facile displacement in solution. It may also account for the
observation that both reactions 1 and 2 lead to the same
t
compound 4, in which the Bu2Sn groups are exocyclic and
pentacoordinate.
The solution 119Sn NMR spectrum of [tBu2(OH)SnOSn(Cl)n-
Bu2]2, 5, in CDCl3 is simpler than those of 1-3. It shows two
signals of equal intensity at -181.7 and -220.9 ppm which
have two sets of 2J(119Sn-O-117Sn) satellites as well as
1J(119Sn-13C). The relative simplicity of the 119Sn NMR
spectrum of 5 indicates a higher stability of the dimeric structure
because hydroxide is a better bridging group than chloride for
tin.16 The 119Sn CPMAS NMR spectrum of 5 shows two
resonances at -178.0 and -220.5 ppm, indicating similar
structures in the solid and in solution. The molecular weight
determination of 5 in chloroform shows an association factor
of 1.9, which indicates negligible dissociation of the dimer in
solution. Single crystals of 5 suitable for X-ray investigation
could not be obtained, but the crystal structure determination
t
displacement of Bu2SnCl2 from the ladder complex.
Increasing the amount of added Me2SnCl2 moves the equi-
t
librium toward further displacement of exocyclic Bu2SnCl2
from ladder complexes. The 119Sn NMR spectrum of a solu-
tion of 1 to which has been added 2.29 molar equiv of
Me2SnCl2 indicates the disappearance of 1 and a significant
decrease in the concentration of [(tBu2SnCl2)(Me2SnO)2-
(Me2SnCl2)]. The relative concentration of the species [Me2-
(Cl)SnOSn(Cl)Me2]2 has increased significantly (Table 5). The
119Sn NMR spectrum of a solution of 1 to which has been added
(27) Lockhart, T. P.; Manders, W. F. J. Am. Chem. Soc. 1987, 109,
7015.
(28) Holecek, J.; Lycka, A. Inorg. Chim. Acta 1986, 118, L15.

2028 Inorganic Chemistry, Vol. 36, No. 10, 1997
Dakternieks et al.
of [tBu2(OH)SnOSn(Cl)(cyclohexyl)2]2 shows a ladder structure
t
with exocyclic Bu2Sn units.29
Reaction of (tBu2SnO)3 with tBu2SnCl2. Reaction between
t
(tBu2SnO)3 and Bu2SnCl2 does not appear to produce the
corresponding “ladder”, [tBu2(Cl)SnOSn(Cl)tBu2]2. The room-
temperature 119Sn NMR spectrum of a dichloromethane solution
t
prepared from a 1:3 molar ratio of (tBu2SnO)3 and Bu2SnCl2
contains a very broad resonance at 57 ppm and a sharper signal
at -27.3 ppm with satellites of 877 Hz. Also present is a very
weak resonance at -81.7 ppm with 2J(119Sn-O-117Sn) coupling
of 363 Hz, consistent with the presence of (tBu2SnO)3, and two
very broad resonances at -86.2 and -215 ppm. Lowering the
temperature causes the resonances to sharpen, and at -90 °C
the spectrum contains a resonance of 59.5 ppm, attributed to
tBu2SnCl2. Also present at -90 °C is a resonance at -22.8
Electrospray Mass Spectrometric Data. ESMS is particu-
larly suitable for the study of these labile organotin systems in
solution, and a detailed ESMS study of these systems will be
the focus of a future paper. The positive-ion spectrum of 1
dissolved in MeOH/water (50:50) is comparatively simple. The
dominant fragments (m/z 807 (30%), 723 (100%), 699 (20%),
639 (20%), 619 (40%)) contain three tin atoms, and the
assignments are shown in the following display. Fragments with
2
ppm which has J(119Sn-O-117Sn) coupling of 842 Hz. The
119Sn chemical shift position of this resonance is indicative of
four-coordinate tin. The large 2J(119Sn-O-117Sn) coupling is
similar to values found for compounds with almost linear
t
2
Sn-O-Sn angles (e.g., linear Bu3SnOSntBu3 has J(119Sn-
O-117Sn) ) 900 Hz30,31), and consequently this resonance is
tentatively assigned to the species [tBu2(Cl)SnOSn(Cl)tBu2], 7.
The remaining two resonances in the 119Sn NMR spectrum at
-90 °C, at -82.8 and -171.7 ppm, have relative intensities of
2:1 and each has what appear to be 117/119Sn satellites of 150
Hz. These resonances are tentatively assigned to the “three-
quarter” ladder species [tBu2SnCl2][tBu2SnO]2, 8. These data
are consistent with an equilibrium (eq 4) which implies at least
the transient existence of the dimeric species (tBu2SnO)2. There
are no further substantive changes in the spectrum on cooling
to -100 °C.
m/z 807 are also present (100% relative abundance) in the
positive spectra of solutions of 4 as well in solutions pre-
t
pared from a 2:3 ratio of (tBu2SnO)3 and Bu2SnCl2. Experi-
mental and calculated isotopic cluster patterns are in excellent
agreement.
These fragments apparently arise from reaction of 1 with the
solvent system and demonstrate again the lability of ladder
systems in solution. It may well be that species similar to these
contribute to the very low-intensity signals observed in the
119Sn NMR solution spectra of samples of 1-4. Nevertheless
the existence of these cationic clusters adds support for the
proposed neutral 1:1 adducts of (R2SnO)2 in Scheme 1 and for
species 8.
The anionic spectrum of 1 contains peaks at m/z 485 (100%)
and 569 (40%). The anionic spectrum of 4 shows a fragment
peak at m/z 485 in 100% relative abundance. The isotope
patterns associated with these peaks are totally consistent with
the formulations of the two anionic species
The 119Sn NMR spectrum of a solution prepared from a 1:2
molar ratio (tBu2SnO)3 and tBu2SnCl2 is identical to the above
with the exception that now there is no resonance observable
for tBu2SnCl2. The proportion of 7 and 8 changes as a function
of temperature. At room temperature, the resonance of 7
comprises about 50% of the total intensity in the 119Sn NMR
spectrum. At -90 °C, the relative intensity of 7 is only about
10%, with the remainder of the intensity being found in the
two resonances attributed to 8. The fact that coupling in 7 and
in (tBu2SnO)3 is seen at room temperature in the same solution
is consistent with exchange between 7 and (tBu2SnO)3, which
is slow on the NMR time scale.
It was recently reported32 that (tBu2SnO)3 reacts with BR-
t
(OH)2 (R ) 2,4,6-Me3C6H2) to give the tritin species Bu2Sn-
(OH)2[(tBu2SnO)2OBR], 8a, which was characterized in the
solid state. This compound exhibited 119Sn NMR chemical
shifts of -260.0 and -278.5 ppm (relative intensities 2:1) in
solution, but no 117/119Sn-117/119Sn coupling was reported.
which is indirect support for existence of species such as 7.
Conclusion. Ladder compounds containing tBu substituents
at tin may be isolated in the solid state as discrete molec-
ular species [tBu2(Cl)SnOSn(Cl)R2]2, which may be regarded
as 1:2 adducts, [(tBu2SnCl2)(R2SnO)2(tBu2SnCl2)]. In solu-
tion these adducts are labile and undergo some dissociation,
(29) Dakternieks, D.; Jurkschat, K.; Baumeister, U. Unpublished results.
(30) Wrackmeyer, B. Annu. Rep. NMR Spectrosc. 1985, 16, 73.
(31) Kerschl, S.; Wrackmeyer, B. Z. Naturforsch. 1987, 42B, 387.
(32) Brown, P.; Mahon, M. F.; Molloy, K. J. Chem. Soc., Dalton Trans.
1992, 3503.

Molecular Dynamics within Diorganotin Systems
Inorganic Chemistry, Vol. 36, No. 10, 1997 2029
the extent of dissociation being dependent on the nature of the
R group. Addition of R2SnCl2 to solutions of these ladders
causes replacement of the exocyclic Bu2SnCl2 groups by the
Acknowledgment. We are grateful to the Australian Re-
search Council (ARC) for financial assistance (D.D. and
E.R.T.T.) and to the Stifterverband fu¨r die Deutsche Wissen-
schaft for support (K.J.). We thank Dr. T. J. Bastow, CSIRO
Division of Materials Science and Technology, for recording
the solid-state 119Sn and 13C NMR spectra and Dr. R. Colton,
La Trobe University, for recording the ESMS spectra.
t
added R2SnCl2. Attempts at formation of a ladder species,
[(tBu2SnCl2)(tBu2SnO)2(tBu2SnCl2)], where all four tin atoms
t
carry Bu substituents were unsuccessful. Formation of a
ladder species [(tBu2SnCl2)(tBu2SnO)2(tBu2SnCl2)] would re-
quire the tin atoms in the central (tBu2SnO)2 to be able to
become six-coordinate. Apparently, the tBu groups reduce the
Lewis acidity at tin to such an extent that six-coordination is
not possible. Instead, there is evidence for the 1:1 adduct
(tBu2SnCl2)(tBu2SnO)2 in which the tin atoms are all five-
coordinate.
Supporting Information Available: Listings of fractional atomic
coordinates, thermal parameters, H atom parameters, and all bond
distances and angles (9 pages). Ordering information is given on any
current masthead page.
IC9611608