Can mono- or di-butyltin chlorides produce tributyltin chloride at elevated temperatures? Implications for applications in chemical vapour deposition

Article abstract of DOI:10.1016/j.jorganchem.2006.05.006

The thermolysis of the butyltin chlorides at 200-300 °C in the liquid phase has been investigated by ¹H, ¹³C, and ¹¹⁹Sn NMR spectroscopy. The stabilities follow the order: Bu₂SnCl₂ > Bu₃SnC

Full text of DOI:10.1016/j.jorganchem.2006.05.006

Journal of Organometallic Chemistry 691 (2006) 3556–3561
www.elsevier.com/locate/jorganchem
Can mono- or di-butyltin chlorides produce tributyltin chloride
at elevated temperatures? Implications for applications in
chemical vapour deposition
*
Alwyn G. Davies, Andrea Sella , Rajaveen Sivasubramaniam
Department of Chemistry, Christopher Ingold Laboratories, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom
Received 11 April 2006; received in revised form 2 May 2006; accepted 2 May 2006
Available online 11 May 2006
Abstract
1
The thermolysis of the butyltin chlorides at 200–300 ꢀC in the liquid phase has been investigated by H, 13C, and 119Sn NMR spec-
troscopy. The stabilities follow the order: Bu2SnCl2 > Bu3SnCl > BuSnCl3. Only tributyltin chloride showed any evidence of redistribu-
tion, giving dibutyltin dichloride, together with metallic tin, butane, and but-1-ene, which would be formed by decomposition of
tetrabutyltin. Dibutyltin dichloride decomposed to give mainly butane with no other apparent liquid organotin compound. Butyltin tri-
chloride gave butane, some butene, and metallic tin, and showed no evidence of forming tributyltin chloride by the redistribution reac-
tion, which would have environmental implications for its use in the CVD coating of glass.
ꢁ 2006 Elsevier B.V. All rights reserved.
Keywords: Butyltin chlorides; Thermolysis; Redistribution; CVD
1. Introduction
toxicity of dibutyltin dichloride in environmental studies
[7]. If, therefore, tributyltin chloride could be formed under
CVD conditions by the redistribution of alkyl and chloride
groups of the precursor, the deposition process might pres-
ent a significant environmental hazard. In view of this,
some regulatory authorities have questioned whether the
process should be permitted.
Examples of the redistribution of alkyl and halogen
groups bonded to tin have been known since the early days
of organotin chemistry [8–10], but the reaction is usually
named after Kocheshkov who, from 1926 onwards,
exploited it as a route to organotin halides that could not
be prepared directly by the Grignard reaction (e.g. Eqs.
(1) and (2)) [11–15].
Organotin halides and their derivatives find a number of
important applications in industry and agriculture [1,2],
and some of these applications involve high temperatures.
In particular, to strengthen it, glass is coated with SnO2
by treating it with BuSnCl3 at about 600 ꢀC in the presence
of air (atmospheric pressure chemical vapour deposition,
APCVD) [3]. This raises a question over the use of organo-
tin chlorides, particularly butyltin trichloride, in the CVD
process, where the spent gases are exhausted to air.
In the press one often sees the statement made that tri-
butyltin chloride and its derivatives are ‘‘highly toxic’’.
Although this is true for molluscs, the risks have been often
overstated for mammals [2,4–6]. It has been suggested that
the spontaneous formation of even 0.1% tributyltin chlo-
ride (and tetrabutyltin) may be responsible for the apparent
4EtMgBr + SnCl4 ! Et4Sn
ð1Þ
ð2Þ
210 ꢀC
3Et4Sn þ SnCl4 ! 4Et3SnCl
*
The reaction is general in organometallic chemistry, and
is not confined to organic and halogeno groups. A review
Corresponding author. Tel.: +44 20 7679 4687; fax: +44 20 7679 7463.
E-mail address: a.sella@ucl.ac.uk (A. Sella).
0022-328X/$ - see front matter ꢁ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.05.006

A.G. Davies et al. / Journal of Organometallic Chemistry 691 (2006) 3556–3561
3557
by Moedritzer in 1971 on redistribution reactions listed
more than 1000 examples, 62 of which involved the
exchange of organic and halogen substituents on tin [16].
The redistribution reactions are, as a rule, reversible,
the equilibria usually favouring the compound with the
highest degree of shuffling of the ligands (comproportion-
ation), rather than the compounds with a lower degree of
shuffling (disproportionation). The rates of the redistribu-
tion reactions increase in the sequence I < Br < Cl, and
[23]. Although Grant and Van Wazer also reported equilib-
rium constants for the disproportionation of Me2SnCl2
into Me3SnCl and MeSnCl3 (K448 K = 1 · 10ꢁ4), and for
Me3SnCl into Me4Sn and SnCl4 (K448 K = 3 · 10ꢁ3), the
precise values are questionable since they are based on
imperfectly balanced equations. Nevertheless, these values
provide us with reasonable order of magnitude estimates.
The equilibria for the ethyltin halides lay almost entirely
on the left-hand side (Eq. (5), R = Et).
higher
alkyl < ethyl < methyl < vinyl < benzyl < phenyl.
2RSnCl3 ꢀ 2R2SnCl2 + SnCl4
ð5Þ
The mechanism of the reactions probably involves a 4-
centre transition state, with the nucleophilic power of
the halogen being dominant (Eq. (3)), consistent with
the reported rate trends.
Phenyltin trichloride reacts with tributylphosphine at
room temperature to give Ph2SnCl2 and SnCl4 as their
complexes with Bu3P [24,25].
In view of the commercial importance of the butyltin
chlorides, it is surprising that there appears to be no report
of a study of their thermal decomposition and dispropor-
tionation. However, Razuvaev et al. [26] reported that, at
400 ꢀC for 4 h in a sealed tube, tetrabutyltin gave metallic
tin, butane, mixed butenes, some octane, ethene, ethane,
and hydrogen. In a later FT-IR study, Harrison [27]
showed that, at 300 ꢀC for 22 min in the gas phase, it
underwent substantial decomposition to give a mixture of
but-1-ene and cis- and trans-but-2-ene, together with a
small amount of butane.
Cl
Cl
Sn
Sn
Sn
ð3Þ
Sn
R
R
The reactions involving organotin compounds are often
carried out in the absence of solvents, and Lewis acids,
such as AlCl3, can act as catalysts. However, in some cases
the presence of a Lewis acid may also lead to the formation
of alkyl chloride and tin(II) chloride, particularly from the
alkyltin trichlorides (when the alkyltin trichloride itself
may act as its own Lewis acid). Platinum(II) and palla-
dium(II) phosphine complexes catalyse the reaction of di-
butyltin dichloride with tin tetrachloride at 110 ꢀC during
10 h, to give butyltin trichloride in good yield [17]. At the
higher temperatures that may be needed in the absence of
a catalyst, the alkene and HCl, rather than the alkyl chlo-
ride, may be formed [18,19].
We report here a preliminary study of the effect of heat
on butyltin chlorides, BunSnCl4ꢁn, and on tetrabutyltin.
The principal techniques that we have used are 119Sn,
1
13C, and H NMR spectroscopy.
2. Experimental
High temperatures are not always needed, however.
There are a number of reports of observations of adventi-
tious disproportionation when organotin compounds were
being handled. For example, when triallyltin chloride was
treated with a sodium alkoxide, tetraallyltin and the diallyl-
tin dialkoxide were obtained [20]. There is also a very inter-
esting recent report of a disproportionation reaction in the
solid state. Cupferonatotrimethyltin, Me3SnON(N@O)Ph,
is a cyclic tetramer in the crystal. It is stable at room tem-
perature, but at 100 ꢀC in open vials it disproportionates
into crystalline Me2Sn[ON(N@O)Ph]2, which is a dimer,
and Me4Sn. At 100 ꢀC in the melt, the reaction is second
order in monomer with a rate constant of 1.6 · 10ꢁ4
6.9 · 10ꢁ6 l molꢁ1 sꢁ1 [21].
NMR spectra were run at room temperature (20 ꢀC) on
a Bruker AMX400 spectrometer, operating at 149.21 MHz
1
for 119Sn, 100.63 MHz for 13C, and 400.14 MHz for H.
1
The 13C spectra were all run in the H-decoupled, gated
decoupled, or DEPT mode.
Bulk metallic tin was identified by X-ray diffraction with
a Bruker AXS D8 diffractometer using unfiltered Cu Ka
radiation, with a collimated X-ray beam (0.5 mm collima-
tor) and a general area detector. Data were collected in
reflection geometry with a fixed 5ꢀ angle of incidence angle.
Bruker GADDS software was used for acquisition and Bru-
ker EVA software for data manipulation.
The butyltin chlorides, without solvent, were sealed
under vacuum in 5 mm NMR tubes. The samples were then
heated in an oven at ca. 200 ꢀC, or in a tube furnace at ca.
300 ꢀC; in the latter case, the tubes were enclosed in a cop-
per tube in case of explosion, which sometimes did occur.
heat
½Me3SnONðN@OÞPhꢂ4 !fMe2Sn½ONðN@OÞPhꢂ2g2 þMe4Sn
ð4Þ
1
The samples were then cooled, and the 119Sn,13C, and H
Grant and Van Wazer showed that, in a few days at
175 ꢀC, 35% of MeSnCl3 partially disproportionated into
Me2SnCl2 and SnCl4 (K448 K = 7 · 10ꢁ2) [22]. The reaction
is faster in polar solvents such as isopropyl alcohol or water
(where the reaction has been shown to be second order in
stannane), and in 4 days at 50 ꢀC, 26% of MeSnCl3 under-
goes disproportionation (K323 K = 1 · 10ꢁ2), and is cataly-
sed by stannophilic ligands such as Clꢁ or ClO4ꢁ (Eq. (2))
NMR spectra were recorded.
3. Results
The NMR data for the neat liquids for BunSnCl4ꢁn
,
n = 1 and 3, and for the solution in decalin when n = 2
(as dibutyltin dichloride is a solid, m.p. 39–41 ꢀC), are

3558
A.G. Davies et al. / Journal of Organometallic Chemistry 691 (2006) 3556–3561
given in Table 1. They are in accord with previous results in
the literature, which have usually been obtained on solu-
tions in CDCl3; they confirm the absence of any impurities
containing tin or organic groups, and, further, they indi-
cate that there is no significant difference in the structures
of the chlorides, n = 1 or 3, in solution or as the neat
liquids.
Tributyltin chloride was heated at 200 ꢀC for 48 h. The
119Sn NMR spectrum (Table 2) then showed signals for
Bu3SnCl at d 144.1, and a second signal for Bu2SnCl2 at
d 114.7, the identity of which was confirmed by the 13C
spectrum; the relative intensity of the two signals was
3.6:1. There was no signal for Bu4Sn (d119Sn ꢁ12), or for
any other tin species, but a black granular solid was depos-
ited in the tube, and, in some experiments, a mirror-like
film and a small amount of an off-white solid collected
on the upper parts of the tube.
When dibutyltin dichloride was heated at 200 ꢀC for two
days no significant change in the 13C or 119Sn NMR spec-
trum was observed, though a small amount of an off-white
solid was apparent, and the contents resolidified on cool-
ing. The tube was therefore heated at 300 ꢀC for two days,
when the sample remained liquid after cooling. The only
119Sn signal was still that for Bu2SnCl2 at d 119.3, but
the 13C spectrum was now dominated by peaks at d 24.3
and 12.7 corresponding to the CH2 and CH3 groups of
butane. The 13C spectra in Fig. 1 illustrate the presence
of the butane, and the surprising absence of butene, though
there is a small unidentified peak for a CH or CH3 group at
d13C 23.0.
Butyltin trichloride (dSn 0.31) was kept at 200 ꢀC for
two days. A large amount of black crystalline solid sepa-
The NMR spectra showed the presence of but-1-ene
[d13C 139.5 (@CH–), 112.6 (@CH2), 25.4 (CH2), and 12.6
(CH3); d1H 5.34 (@CH–), 4.42 (@CH2) and 1.58 (CH2)]
and of butane [d13C 24.4 (CH2) and 12.4 (CH3)] in approx-
imately equal amounts.
On further heating, the intensity of the spectra which we
ascribed to butane and butene increased, but, if anything,
that of the 119Sn signal for Bu2SnCl2 diminished.
The formation of dibutyltin dichloride suggests that dis-
proportionation does occur, but that the tetrabutyltin does
not survive the conditions of the thermolysis (Eqs. (6) and
(7)).
200 ꢀC
2Bu SnCl
Bu SnCl þ Bu Sn
ð6Þ
ð7Þ
ƒƒƒ!
3
2
2
4
200 ꢀC
Bu Sn
BuH þ Buð–HÞ þ Sn
ƒƒƒ!
4
A sample of tetrabutyltin was therefore heated under the
same conditions; again a granular black solid was depos-
ited, and this was identified, by powder X-ray diffraction,
to be metallic tin.
Fig. 1. 13C NMR spectra of the products of thermolysis of dibutyltin
dichloride, showing the formation of butane. Bottom: 1H decoupled; the
signals for the a, b, c, and d carbon atoms of the butyl groups in the
reactant are marked. Top: with gated decoupling.
Table 1
Reference NMR spectra of the butyltin chloridesa
d119Sn
d13Ca
d13Cb
d13Cc
d13Cd
Bu3SnCl
Bu2SnCl2
BuSnCl3
a
144.1
119.4
0.3
17.5 (329.8/345.0)
26.7 (427)
33.7 (613.7/642.0)
27.8 (24.1)
26.3 (34)
26.4 (61.7)
26.7 (63.1)
25.4 (104)
25.2 (115)
13.4
12.77
13.0
Values of nJ(13C117/119Sn) (Hz) (or an average if the pair of satellites in the 13C spectrum were not resolved) are given in parentheses.
Table 2
NMR spectra of the butyltin chlorides after heatinga
d119Sn
d13Ca
d13Cb
d13Cc
d13Cd
Bu3SnCl
144.1
114.7
119.3
3.2 ꢁ174.2
17.0
27.2
26.3
12.9
Bu2SnCl2
BuSnCl3
a
26.3
33.1 (632.0)
25.7
26.3 (59.9)
25.0
25.0
12.4
12.8
The average values of nJ(13C117Sn) and nJ(13C119Sn) (Hz) are given in parentheses.

A.G. Davies et al. / Journal of Organometallic Chemistry 691 (2006) 3556–3561
3559
rated, and a metallic mirror formed on the tube. The only
119Sn NMR signal was a strong peak at d ꢁ145.1, which we
assign to SnCl4; no signal for BuSnCl3 remained, and none
for Bu2SnCl2 appeared. The 13C and 1H spectra were com-
plex, but the 13C spectrum was dominated by strong peaks
that it could account for the decomposition of Bu4Sn under
our conditions. If the Bu–SnBu3 bond dissociation energy
is taken to be 257 kJ molꢁ1, and the pre-exponential factor
is of the order of 1015, the half life of the unimolecular
homolysis at 200 ꢀC would be expected to be of the order
of 1013 s. A more rapid reaction of course might occur on
the surface of the glass.
1
at d 24.0 and 13.1, corresponding to butane, and the H
spectrum indicated the presence of some alkene. When
the tube was opened, acrid acid fumes (HCl) were evolved.
To avoid such extensive decomposition, a sample of
BuSnCl3 was kept at 200 ꢀC for one day. Again, a black
crystalline solid was formed. The Sn NMR spectrum
showed a strong peak for the starting material at d 3.2,
and a smaller signal (relative amplitudes 10.5:1) at d
ꢁ174. This latter signal probably corresponds to SnCl4 car-
rying a fifth ligand, probably HþSnCl5ꢁ; unfortunately, the
119Sn chemical shift of this compound appears not to have
been determined, but the upfield shift by 29 ppm from that
of SnCl4 would be characteristic of an increase in coordina-
tion from 4 to 5. Apart from the major peaks of the
BuSnCl3, the 13C NMR spectrum showed new small peaks
at d 60.0, 44.4, 34.0, 32.7, 24.3, 24.2, 22.6, 22.1, 21.7, 19.4,
13.3, and 10.5. Eight of these peaks might reasonably be
ascribed to 1-chloro- and 2-chloro-butane, but the groups
of peaks at d 24.2, 22.7, 22.1, and 21.7 (which the DEPT
spectrum showed to be CH or CH3), are not accounted
for. The absence of peaks at d 113.5 and 140.5 rule out
the presence of butene.
An alternative mechanism would involve alternating b-
elimination and reductive elimination (Eqs. (11) and
(12)); repetition would give BuSnH and thence metallic
tin (Eqs. (13) and (14)). Although there are no precise
precedents for these reactions, they appear to be reasonable
in view of related organotin chemistry [25].
Bu3SnCH2CH2CH2CH3 ! Bu3SnH + Bu(–H)
Bu3SnH ! Bu2Sn: + BuH
ð11Þ
ð12Þ
ð13Þ
ð14Þ
€
Bu2Sn : ! BuSnH þ Buð–HÞ
€
BuSnH ! Sn þ BuH
A referee has suggested that deuterium labelling experi-
ments might be used to probe these alternatives. However,
starting from (CH3CH2CD2CH2)4Sn, both mechanisms
would give CH3CH2CD@CH2 and CH3CH2CD2CH2D
making it impossible to distinguish between them.
Whatever the correct mechanism, it is noteworthy that
Bu2SnCl2 does not undergo this type of reaction, even at
300 ꢀC. The formation of butane, without butene, from
Bu2SnCl2 was surprising, but is unambiguous (Fig. 1). It
could be brought about by adventitious water in the
Bu2SnCl2, when the initial reactions would be those shown
in Eqs. (15) and (16), but the presence of enough water to
bring about such extensive dealkylation of the tin is most
unlikely, and the absence of an 119Sn NMR signal for
any other soluble tin compound [such as BuSnCl3 or
(ClBu2Sn)2O], and the absence of any substantial amount
of an insoluble oxygen-containing tin compound [such as
Bu2SnO, BuSnO(OH)], or metallic tin, leaves unanswered
questions.
4. Discussion
The differences in the thermal stability and the thermol-
ysis patterns of the three butyltin chlorides are striking and
do not follow the order of substitution. The general ther-
mal stability is in the sequence Bu2SnCl2 > Bu3SnCl >
BuSnCl3.
Our results indicate that Bu3SnCl undergoes redistribu-
tion to give Bu2SnCl2 and Bu4Sn (Eq. (6)); the former of
these is relatively stable at the temperature of the reaction,
but the latter decomposes into metallic tin, butene and
butane (Eq. (7)).
Two reasonable mechanisms can be suggested for the
decomposition of Bu4Sn. First, homolysis of the Sn–C
bond would give a butyl radical (Eq. (8)), which would
react with Bu4Sn to give butane and a b-stannylalkyl rad-
ical, and this in turn would eliminate butene. Repetition
of this process could give the observed products.
Bu2SnCl2 + 2H2O ! ClBu2SnOSnBu2Cl + 2HCl
Bu2SnCl2 + HCl ! BuH + BuSnCl3
ð15Þ
ð16Þ
The decomposition of BuSnCl3 appears best to be
accounted for by reductive elimination of BuCl leaving
SnCl2 which may decompose in part to give SnCl4 and
metallic tin; t-BuSnCl3 has been reported to decompose
at room temperature to give SnCl2 and t-BuCl [36]. In
the higher range of temperature, the butyl chloride elimi-
nates HCl, which can react with the initial BuSnCl3 to give
butane and SnCl4. Alternatively, one can envisage retrode-
hydrostannation giving butane and HSnCl3, which decom-
poses into HCl and SnCl2. The SnCl4 does not appear to
arise from a disproportionation reaction, as the other prod-
uct would be Bu2SnCl2, which is not detected, and would
not be expected to decompose at the temperature of the
experiment.
Bu4Sn ! Bu3SnÅ + BuÅ
ð8Þ
Bu3SnCH2CH2CH2CH3 +BuÅ !Bu3SnCH2 CHCH2CH3 +BuH
Å
ð9Þ
ð10Þ
Å
Bu3SnCH2 CHCH2CH3 ! Bu3SnÅ + Bu(–H)
This first step would be similar to Paneth and Hofeditz’s
classic generation of alkyl radicals in the gas phase by the
thermolysis of R4Pb with an R–PbR3 bond dissociation
energy of about 205 kJ molꢁ1 [28], but it seems unlikely

3560
A.G. Davies et al. / Journal of Organometallic Chemistry 691 (2006) 3556–3561
2Me2SnCl2
DHf 2ðꢁ331:9Þ
DHꢀr þ 4:6 kJ molꢁ1
2Me3SnCl
! Me3SnCl þ MeSnCl3
With all three compounds of course, the NMR spectra
would not have detected the elements in the solids that
were observed. The black solid was identified as metallic
tin, and the white solid appears to be largely SnCl2 (as
reported by Neumann for the decomposition of EtSnCl3)
[18].
ꢁ212:5
ꢁ 446:7
ð19Þ
ð20Þ
K448 K ¼ 2:9 ꢄ 10ꢁ1
Me4Sn þ Me2SnCl2
!
DHf 2ðꢁ212:5Þ
ꢁ49:7
ꢁ 331:9
DHꢀr þ 43:4 kJ molꢁ1
K448 K ¼ 8:7 ꢄ 10ꢁ6
5. Thermochemical aspects of the exchange
The breakdown of the additivity principle, and the
resulting equilibration in favour of a maximum degree of
mixing of the ligands can be rationalised as follows. The
Snd+–Cldꢁ bond is strongly polar in the sense that is shown
in Scheme 1, whereas the Sn–R bond is relatively non-polar
(R = alkyl). If two or more Cl ligands are bound to one tin
atom, there will be a destabilising interaction between the
positive ends of the two dipoles. With two alkyl groups
on tin, any such destabilisation will be trivial. With one
alkyl and one chloro ligand, the alkyl group can induc-
tively, and perhaps hyperconjugatively, release electrons
to accommodate the demand of the positive centre at tin,
to produce a more stable system [33].
If an appropriate mechanism for the reaction is avail-
able, redistribution will therefore take place to minimise
the number of electronegative ligands on the tin.
This qualitative model is supported by the results of Del
Re calculations, which are designed to take account of the
interaction between sigma bonds.
It is informative to attempt to rationalise why these
redistribution reactions, at equilibrium, usually maximise
the degree of mixing of the alkyl and halogen groups.
The number of bonds of any one type does not change
during the redistribution reaction; for example, in reaction
(5), there are 2 SnMe bonds and 6 SnCl bonds on both
sides of the equation. If bond strengths were additive
within the molecules, a statistical distribution of the possi-
ble combinations of ligands should be reached at equilib-
rium, yet reaction (1) proceeds to give methyltin
trichloride in 90% yield. Why should the additivity princi-
ple break down to favour the mixed-ligand combination
MeSnCl3?
If the equilibrium lies in favour of comproportionation,
the free energy of formation of the comproportionated
products (such as MeSnCl3) must be greater than the free
energies of formation of the disproportionated pair of reac-
tants (such as Me2SnCl2 and SnCl4). Entropy contributions
to the reaction are likely to be very small, hence, to a good
approximation, Eq. (17) should hold.
Table 3 shows the partial charges, q, on the atoms H, C,
Sn, and Cl in the tetramethyltin, the methyltin halides, and
tin tetrachloride, as calculated by Gupta and Hughes by
DGꢀ ꢃ DHꢀ ¼ ꢁRT ln K
ð17Þ
1
the Del Re method [34], and the corresponding H and
13C NMR chemical shifts. In accord with the model in
Scheme 1, the negative charge on Cl is greatest in Me3SnCl
where three alkyl groups release electrons into one SnCl
bond, and conversely the negative charge on C is lowest,
and the positive charge on H is greatest in MeSnCl3 where
three SnCl dipoles combine to attract electrons from one
alkyl group.
Unfortunately, only a few relevant enthalpies of forma-
tion of organotin compounds are known, and none for the
butyltin chlorides. Selected values for the methyltin halides
[29–31], based largely on Skinner’s determination of the
heats of mixing of tetramethyltin with tin tetrachloride in
the liquid phase [32] are given in Eqs. (18)–(20), which lead
to the reaction enthalpies shown, and thence, by Eq. (17),
to the equilibrium constants, K, at 448 K, the temperature
of Grant and Van Wazer’s [23] equilibrium studies. These
derivations should be treated with caution, however, as
the enthalpies of formation are uncertain to the extent of
δ−
Cl
δ+ δ+ δ−
Sn Cl
δ+ δ−
Sn Cl
R
R
Sn
R
about 7 kJ molꢁ1
.
Destabilising dipole-
dipole interaction
Stabilising electron release
by the alkyl group
Relatively negligible
interaction
2MeSnCl3
!
Me2SnCl2 þ SnCl4
a
b
c
DHf 2ðꢁ446:7Þ
ꢁ331:9
ꢁ 545:4
ð18Þ
DHꢀr þ 16:1 kJ molꢁ1
K448 K ¼ 1:33 ꢄ 10ꢁ2
Scheme 1.
Table 3
Local partial charges, and NMR chemical shifts of MenSnCl4ꢁn, n = 0–4
Compound
qH
dH
qC
dC
qSn
qCl
Me4Sn
+0.030
+0.0330
+0.0364
+0.0405
–
0.05
0.59
1.19
1.66
–
ꢁ0.2500
ꢁ0.2053
ꢁ0.1537
ꢁ0.0935
–
ꢁ9.3
ꢁ0.8
7.5
10.8
–
+0.6400
+0.7066
+0.7654
+0.8142
+0.848
–
Me3SnCl
Me2SnCl2
MeSnCl3
SnCl4
ꢁ0.3868
ꢁ0.3379
ꢁ0.2807
ꢁ0.212

A.G. Davies et al. / Journal of Organometallic Chemistry 691 (2006) 3556–3561
3561
[8] G.B. Buckton, Ann. Chem. Pharm. 112 (1859) 220.
The NMR chemical shifts of carbon and hydrogen
(though not of tin) reflect the electron densities on the
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and qC do correlate with those of dH and dC respectively.
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6. Conclusion
Our results show that, as the neat liquids at 300 ꢀC, the
principal reaction of the BuSnCl3 and Bu2SnCl2 is that of
decomposition rather than of redistribution. Evidence for
disproportionation was found only for Bu3SnCl, giving
Bu2SnCl2 and Bu4Sn, which decomposed. In particular,
no detectable Bu3SnCl was formed from BuSnCl3. As such
disproportionation reactions would be second order, they
are even less likely to occur under the gas phase conditions
that are used in the CVD treatment of glass.
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Acknowledgements
We are grateful to Dr. D.A. Armitage (Kings College,
London) and Dr. Ulrich Stewen (Crompton GmbH) for
the gift of chemicals, and to Malcolm Cattley (Rockware
Glass) for useful discussion.
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