Palladium-catalyzed dehydrostannylation of n-alkyltin trichlorides

Article abstract of DOI:10.1039/c1dt10330j

[Pd(PPh₃)₄] catalyzes the dehydrostannylation of n-alkyltin trichlorides into HSnCl₃(THF)_n and isomers of the corresponding alkene. The reaction mechanism involves oxidative addition of the Sn-C bond followed by β-H elimination from the resulting n-alkylpalladium trichlorostannyl species. Rate-determining reductive elimination of HSnCl₃ from cis-[PdH(SnCl₃)(PPh ₃)₂] completes the catalytic cycle. Organotin trichlorides without β-H atoms either do not react or undergo thermal disproportionation. These results are relevant to understand some of the problems associated with the use of monoalkyltin compounds as coupling partner in Stille-type cross-coupling reactions as well as with the catalytic hydrostannylation of 1-alkenes to monoalkyltin trichlorides. The Royal Society of Chemistry 2011.

Full text of DOI:10.1039/c1dt10330j

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PAPER
Palladium-catalyzed dehydrostannylation of n-alkyltin trichlorides†
Yves Cabon,a Robertus J. M. Klein Gebbinkb and Berth-Jan Deelman*a,b
Received 25th February 2011, Accepted 24th June 2011
DOI: 10.1039/c1dt10330j
[Pd(PPh3)4] catalyzes the dehydrostannylation of n-alkyltin trichlorides into HSnCl3(THF)n and
isomers of the corresponding alkene. The reaction mechanism involves oxidative addition of the Sn–C
bond followed by b-H elimination from the resulting n-alkylpalladium trichlorostannyl species.
Rate-determining reductive elimination of HSnCl3 from cis-[PdH(SnCl3)(PPh3)2] completes the
catalytic cycle. Organotin trichlorides without b-H atoms either do not react or undergo thermal
disproportionation. These results are relevant to understand some of the problems associated with the
use of monoalkyltin compounds as coupling partner in Stille-type cross-coupling reactions as well as
with the catalytic hydrostannylation of 1-alkenes to monoalkyltin trichlorides.
occurs if an excess of monoalkyltin trichloride is allowed to react
with [Pd(PPh3)4].
Introduction
Organotin compounds are important as reagents in the group 10
metal-catalyzed Stille-type cross-coupling reaction. Although this
reaction commonly uses tetraorganotins, there has been recent
interest in monoorganotins as alkylating reagents1–5 because their
tin tetrahalide by-products are less toxic than the triorganotin
halides which are generated by a tetraorganotin coupling partner.
However, if the alkyltin trihalide contains b-H atoms, this reaction
is limited to highly reactive aryl iodide coupling partners and
basic aqueous reaction conditions,4,5 with significant amounts of
homocoupling by-products being produced.5 A different type of
reaction, i.e the catalytic hydrostannylation of 1-alkenes using
[Pd(PPh3)4] as catalyst to produce n-alkyltin trihalides, also
appeared to face severe limitations. So far, only low conversions
could be achieved.6
Results and discussion
Reaction of nBuSnCl3 with a catalytic amount of [Pd(PPh3)4]
A study in a sealed NMR tube containing a THF-d8 solution of
nBuSnCl3 (0.6 M) did not exhibit any degradation of the alkyltin
compound during a 3 h period at 70 ◦C. The same tube, but with an
extra 1 mol% of [Pd(PPh3)4] added, did not show any significant
n
conversion of BuSnCl3 over a 3 h period at room temperature
either. However, when heated at 50 ◦C for 3 h, 1H NMR analysis
showed that 22% of the starting nBuSnCl3 reagent had been
converted into butene isomers. 1-Butene was initially formed as
the major product but, under these conditions, concomittant
isomerization led to its almost complete transformation into 2-
butene isomers (>95%) within 2 h.
In order to better understand the specific issues related to both
types of Pd-catalysis, we decided to have a closer look at the
interaction of [Pd(PPh3)4)] with several alkyltin trichlorides and
phenyltin trichloride. We have previously reported on the stoichio-
metric reactivity of monoorganotin trichlorides with [Pd(PPh3)4],
which involved oxidative addition of the Sn–C bond, followed by
The reaction mixture exhibited two broad 119Sn NMR signals at
d = -156 and -197 ppm. The first signal corresponds to unreacted
nBuSnCl3. The second is similar to the signal observed for an
independently prepared equimolar solution of SnCl2 and HCl in
THF-d8, a mixture that is described in the literature as giving
the “acidic complex” (HSnCl3)(solvent)n in donor solvents such
as Et2O, DMSO and pyridine.8 Accordingly, HSnCl3(THF)n was
identified as the coproduct of the butene isomers formation in
the reaction of nBuSnCl3 with a catalytic amount of [Pd(PPh3)4].
The overall reaction corresponds to a so far unprecedented
dehydrostannylation of monoalkyltin trichlorides catalyzed by
[Pd(PPh3)4] (eqn (1)). In the literature, only a non-catalytic version
of a dehydrostannylation reaction was previously observed by
Murai et al. in the specific case of b-trichlorostannyl ketones,
leading to the corresponding enones and HSnCl3(DMSO)n.9
n
rapid b-H elimination in the case of BuSnCl3.7 We now present
the discovery of a palladium-catalyzed dehydrostannylation that
aARKEMA Vlissingen B.V., P.O. Box 70, NL-4380, AB Vlissingen,
The Netherlands. E-mail: berth-jan.deelman@arkema.com; Fax: +31 113
612984; Tel: +31 113 617225
bOrganic Chemistry & Catalysis, Debye Institute for Nanomaterials Science,
Faculty of Science, Utrecht University, Universiteitsweg 99, NL-3584, CG
Utrecht, The Netherlands. E-mail: r.j.m.kleingebbink@uu.nl; Fax: +31
302523615; Tel: +31 302531996
† Electronic supplementary information (ESI) available: 1H and 13C NMR
spectra of nOctSnCl3. Van’t Hoff plot of the concentration at equilibrium
for the dehydrostannylation of nBuSnCl3. Conversion vs. time plots of
the kinetic studies of the dehydrostannylation of nOctSnCl3 for the
temperature-, nOctSnCl3-, catalysis-, 1-octene-, HSnCl3- and 2-octene-
dependent studies. See DOI: 10.1039/c1dt10330j
[Pd(PPh
1mol %
) ]
4
3
n BuSnCl
buteneisomers+(HSnCl )(THF)
3 n
(1)
ꢀꢀꢀꢀꢀꢀꢀꢁ
3 ꢂꢀꢀꢀꢀꢀꢀꢀ
THF, D
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The catalytic dehydrostannylation of nBuSnCl3 appeared to
be an equilibrium reaction. Not only has the reverse reaction
been claimed,6 but this also became apparent from experi-
ments at different temperatures in a sealed NMR tube. Within
can leave the system, drawing the dehydrostannylation reaction to
completion.
Reaction mechanism
◦
2 h at 50 C, the [butenes]/[nBuSnCl3] ratio returned to its
We previously reported on the stoichiometric reaction of nBuSnCl3
initial value ([butenes]/[nBuSnCl3] = 22/78) after the NMR
tube had been kept successively for 2 h at 60 ◦C ([butenes]/
[nBuSnCl3] = 29/71) and 70 ◦C ([butenes]/[nBuSnCl3] = 36/64). By
taking K = [butenes]2/[nBuSnCl3] (as a measure for K = [butenes]-
[HSnCl3]/[nBuSnCl3]), K values in the range 37 ¥ 10-3 to 121 ¥
10-3 M were obtained (50–70 ◦C). The thermodynamic parameters,
DH◦ = 55 kJ mol-1 and DS◦ = 125 J mol-1 K-1, were determined
from a Van’t Hoff plot and indicate that the dehydrostannylation
reaction is entropically driven.
with [Pd(PPh3)4], which happens rapidly (<1 min) even at low
◦
temperature (-50 C).7 It was found that the Sn–C bond of
nBuSnCl3 was oxidatively added on the Pd(0) center (probably
present as a [Pd(PPh3)2] fragment) and that the resulting cis-
[Pd(nBu)(SnCl3)(PPh3)2] species was only transient in nature. This
species suffered immediate b-H elimination producing butenes and
a mixture of three palladium-hydride species that were in equi-
librium: cis-[PdH(SnCl3)(PPh3)2], trans-[PdH(SnCl3)(PPh3)2] and
trans-[PdH(Cl)(PPh3)2] (the latter species was explained through
deinsertion of SnCl2 from the SnCl3 ligand).7 It was proposed
-
Substrate scope of the reaction
that, among those Pd–H species, cis-[PdH(SnCl3)(PPh3)2] was
responsible for the isomerization of the initially formed 1-butene
into 2-butenes through a 2,1-insertion/b-H elimination sequence.7
Based on these previous observations and the new results
obtained, we propose a catalytic cycle for the dehydrostannylation
of n-alkyltin trichlorides (Scheme 1). The cycle starts with the
oxidative addition of the Sn–C bond of the substrate on a
[Pd(PPh3)2] fragment (step A), followed by a b-H elimination
from the transient cis-[Pd(n-alkyl)(SnCl3)(PPh3)2] intermediate
(step B). The main cycle is closed by the reductive elimination
of HSnCl3 (detected in the reaction mixture) from the cis-
[PdH(SnCl3)(PPh3)2] intermediate (step C), which also regenerates
the active [Pd(PPh3)2] fragment. A secondary cycle is present
(D), which leads to the formation of internal olefin isomers from
the initially-formed terminal alkene through a 2,1-insertion/b-H
elimination sequence catalyzed by cis-[PdH(SnCl3)(PPh3)2].
The first two steps of the cycle are rapid processes under
stoichiometric conditions, even at low temperature, whereas
the catalytic dehydrostannylation reaction requires heating for
multiple hours. The most likely candidate for the rate limiting
step is therefore the reductive elimination of the HSnCl3 fragment
from cis-[PdH(SnCl3)(PPh3)2]. Because this species itself could
To test the scope of the reaction with respect to the organotin
substrate, reactions were run with several RSnCl3 compounds
(R = Me, Ph, nBu and nOct). To this end, THF solutions of
RSnCl3 (0.6 M) in the presence of 1 mol% of [Pd(PPh3)4] were
heated at 50 ◦C for 3 h. After a workup procedure with EtMgBr
to convert the remaining RSnCl3 into less reactive RSnEt3, the
reaction mixture was analyzed by GC using undecane as an
internal standard. The results are presented in Table 1.
For R = nBu, the results were identical to the NMR tube
experiment with an observed conversion of 22%. The R = Oct
n
case is similar, with an observed conversion of 25% and the
presence of octene isomers in the resulting gas chromatogram.10
Both reactions required the presence of the [Pd(PPh3)4] catalyst,
as was demonstrated in blank experiments (Table 1, entry b). For
R = Me, no reaction was observed, irrespective of whether or not
[Pd(PPh3)4] was used.
The case R = Ph is substantially different. Although the
disappearance of 52% of the starting PhSnCl3 was observed, it
did not correspond to a dehydrostannylation reaction but rather
to a disproportionation into equimolar amounts of Ph2SnCl2 and
SnCl4 which were both detected in 26% yield. This reaction did not
require Pd as a catalyst, as was demonstrated in a blank experiment
(Table 1, entry b). Consequently, it can be concluded that the
observed disproportionation reaction is a thermal non-catalytic
process.11
It is worthwhile to note that the dehydrostannylation of
nBuSnCl3 and nOctSnCl3 can be made quantitative in 12 h at 50 ◦C
when a nitrogen purge was introduced across the reaction vessel.
Under these conditions, the volatile products, i.e. the olefin and/or
HCl (from HSnCl3 that is in equilibrium with HCl + SnCl2)8
Table 1 Conversion of the RSnCl3 substrate as measured by GC (0.6 M
in THF, 1 mol% of catalyst, 50 ◦C, reaction time: 3 h)
Conversion of the RSnCl3 substrate (%)
Entry Catalyst
R = Me
R = Ph
R = nBu
R = nOct
a
b
[Pd(PPh3)4]
None
0
0
52a
53a
22 (100)b
0
25 (100)b
0
Scheme 1 Proposed mechanism for the Pd-catalyzed dehydrostannyla-
tion of alkyltin trichlorides. For clarity, steps A and C are not indicated as
such but should be considered as being reversible as well.
a Equimolar amounts of Ph2SnCl2 and SnCl4 were observed. b Conversion
after 12 h when a nitrogen purge was applied.
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Table 2 Results of the kinetic experiments for the determination of the
activation energy and kinetic orders by the initial rate methodology
Entry [nOctSnCl3]0/M
[Pd(PPh3)4]/M T/◦C
Initial rate/M s-1
a
b
c
d
e
f
g
h
i
j
k
l
m
n
0.60
0.60
0.60
0.60
0.60
0.10
0.20
0.30
1.20
0.60
0.60
0.60
0.60
0.60
0.0060
0.0060
0.0060
0.0060
0.0060
0.0060
0.0060
0.0060
0.0060
0.0006
0.0012
0.0030
0.012
30
40
50
60
70
60
60
60
60
60
60
60
60
60
11.7 ¥ 10-6
19.1 ¥ 10-6
27.6 ¥ 10-6
50.1 ¥ 10-6
121 ¥ 10-6
44.1 ¥ 10-6
44.9 ¥ 10-6
46.9 ¥ 10-6
48.7 ¥ 10-6
7.2 ¥ 10-6
13.5 ¥ 10-6
31.3 ¥ 10-6
63.1 ¥ 10-6
77.8 ¥ 10-6
Fig. 2 Determination of the kinetic order in [Pd(PPh3)4].
0.024
not be isolated in pure form,7 kinetic studies were undertaken
to investigate this in more detail.
Kinetic studies
Kinetic measurements were performed using the initial rate
methodology to further test the validity of the catalytic cycle
proposed in Scheme 1. The case of nOctSnCl3 over that of nBuSnCl3
was preferred for these studies as the generated octene isomers are
less volatile than the butene isomers. This reduced losses of alkenes
during sampling, therefore improving the reproducibility of the
experiments. The results of the kinetic experiments are reported in
Table 2.
Fig. 3 Determination of the activation energy (Arrhenius plot).
The reaction was found to be close to zero order in nOctSnCl3 in
the concentration range 0.1 to 1.2 M (Table 2; entries d, f, g, h and
i; Fig. 1). A catalyst concentration-dependent study, in the range
0.0006 to 0.024 M, indicated that the reaction is first order in
catalyst below 0.012 M (Table 2; entries d, j, k, l, m and n; Fig. 2).
At higher loadings, the catalyst stock solution was visually turbid,
which indicates an incomplete solubilization of [Pd(PPh3)4] and
could explain the observation of a kinetic order inferior to one
at these concentrations. Finally, a temperature-dependent study
to determine the activation energy (Ea) allowed to estimate Ea =
Table 3 Results of the kinetic experiments for the inhibition studies
([nOctSnCl3], 0.20 M; [Pd(PPh3)4], 0.006 M; T, 60 ◦C)
[1-octene]0
Entry (mol%)
[2-octene]0
(mol%)
[SnCl2]0
(mol%)
[HCl]0
(mol%)
Initial
rate/M s-1
a
b
c
d
e
f
g
h
0
0
0
0
0
0
0
0
50
0
0
0
0
10
20
50
0
0
0
0
0
10
20
50
0
44.9 ¥ 10-6
33.4 ¥ 10-6
30.3 ¥ 10-6
15.5 ¥ 10-6
32.2 ¥ 10-6
17.7 ¥ 10-6
12.8 ¥ 10-6
42.8 ¥ 10-6
10
20
50
0
0
0
◦
50 kJ mol-1 at 50 C through an Arrhenius plot (Table 2; entries
a, b, c, d and e; Fig. 3).
0
[PdH(SnCl3)(PPh3)2] is the rate limiting step of the dehydrostan-
nylation process. Indeed, the kinetically observed zero order in
nOctSnCl3 and the first order in catalyst indicate that only a single
n
palladium centre and no free OctSnCl3 are involved in the rate
limiting step.
As the dehydrostannylation process is an equilibrium, the
presence of a significant amount of the reaction products at the
beginning of an experiment is expected to lower the reaction rate
by favouring the backward reaction. Indeed, kinetic experiments
performed in the presence of an initial concentration (10, 20 or
50 mol%) of 1-octene or HSnCl3 (introduced as a HCl/SnCl2
mixture) resulted in a dramatic decrease of the initial reaction rate
(Table 3).
Fig. 1 Determination of the kinetic order in nOctSnCl3.
Furthermore, in the case of the experiments in which 1-octene
was added, we observed that the inverse of the initial rate correlates
linearly with the initial concentration of 1-octene (Fig. 4). This
These three observations are in line with our proposal that
the reductive elimination of a HSnCl3 fragment from cis-
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material in closed systems at a 0.6 M concentration. Kinetic data
combined with data obtained from previously reported stoichio-
metric studies suggest a catalytic cycle involving oxidative addition
of the Sn–C bond followed by b-H elimination and rate-limiting
reductive elimination of HSnCl3 from a cis-[PdH(SnCl3)(PPh3)2]
species.
Experimental section
All operations were performed in dry degassed solvents (including
the deuterated solvents) under a dinitrogen atmosphere using
standard Schlenk techniques. THF and n-hexane were obtained
from a solvent purification system MBraun SPS-800. THF-
d8 was distilled from sodium-benzophenone. All solvents were
degassed by three freeze-pump-thaw cycles. MeSnCl3, PhSnCl3,
nBuSnCl3, 1-octene, anhydrous SnCl2, HCl (1 M in Et2O),
undecane and EtMgBr (25% in THF) were purchased from Sigma-
Aldrich. nOctSnCl3 was obtained from ARKEMA Vlissingen
B.V. [Pd(PPh3)4] was prepared according to literature procedures.
NMR data were recorded on a Varian Oxford 300 MHz or Varian
Oxford AS 400 MHz spectrometers, chemical shifts are reported
relative to SiMe4 (1H, 13C) or SnMe4 (1 M in benzene, 119Sn).
Coupling constants are expressed in Hertz and coupling patterns
are described using the following abbreviations: s (singlet), d (dou-
blet), t (triplet), q (quartet) and m (multiplet). Gas chromatograms
were recorded on a Perkin Elmer Clarus 500 Gas Chromatograph
with a Alltech ECONO-CAP EC-5 column (length 30 m, diameter
0.32 mm, packing 0.25 mm).
Fig. 4 Effect of a concentration of 1-octene on the initial reaction rate.
behavior suggests the existence of a pre-equilibrium between
cis-[PdH(SnCl3)(PPh3)2] + 1-octene and [Pd(Oct)(SnCl3)(PPh3)2]
species (Scheme 1).12 Back insertion of 2-octene is apparently less
important as no inhibiting effect was observed when 2-octene was
added to the reaction mixture (entry h, Table 3).
Consequences for other Pd-catalyzed processes
The presently described [Pd(PPh3)4]-catalyzed dehydrostannyla-
tion of n-alkyltin trichlorides could explain the so far poor per-
formance of b-H-containing monoalkyltins as alkylating reagents
in Stille-type cross-coupling reactions. Indeed, our studies demon-
strate that, within the generally accepted mechanism for Stille-type
cross coupling reactions, the oxidative addition of the aryl halide
substrate on Pd(0) would be in competition with the oxidative
addition of the Sn–C bond of the monoalkyltin coupling partner,
which results in its catalytic degradation. This may explain why
only aryl iodide substrates, which react faster with Pd(0) than their
bromide and chloride analogues, have been successfully coupled
with monoalkyltins so far.
The limited conversions obtained in the [Pd(PPh3)4]-catalyzed
hydrostannylation of 1-alkenes can be explained by the existence
of the backward (dehydrostannylation) reaction. In this specific
case, concomitant alkene isomerisation is probably playing an
important role as well. Indeed, the previously described Pd-
catalyzed hydrostannylation reaction required an initial excess of
1-alkene, the role of which can now be interpreted as being required
to shift the equilibrium reaction towards the formation of the
alkyltin trichloride product. During the reaction the excess of 1-
alkene is rapidly converted into internal isomers, thereby resulting
in the loss of driving force for the hydrostannylation reaction.
From a more general point of view, the dehydrostannylation
of monoalkyltins could be relevant for the development of new
processes. A possible application would concern the catalytic
breakdown of alkyltin contaminants in waste water streams or
the conversion of obsolete stocks of alkyltins back into useful
inorganic tin and olefinic starting materials.13
nOctSnCl3
1H NMR (CDCl3, 25 ◦C, 400 MHz): d 2.39 (t, 2H, 3JH-H = 7.5 Hz,
3
JH-Sn = 83.0 Hz), 1.93 (q, 2H, JH-H = 7.5 Hz, JH-Sn = 208.7 Hz),
1.48 (q, 2H, 3JH-H = 7.2 Hz), 1.41–1.22 (m, 8H), 0.89 (t, 3H, 3JH-H
=
=
◦
1
6.9 Hz). 13C NMR (CDCl3, 25 C, 101 MHz): d 33.5 (s, J
13 117
C-
Sn
1
2
622, J
= 651 Hz), 32.7 (s, J
= 109 Hz, the 117Sn
13 119
13 117/119
C-
Sn
C- Sn
and 119Sn satellites were not resolved), 31.9 (s), 29.1 (s), 29.0 (s),
25.1 (s, J
= 61 Hz, the 117Sn and 119Sn satellites were not
3
13 117/119
C-
Sn
resolved), 22.8 (s), 14.3 (s).
Dehydrostannylation of nBuSnCl3 in NMR tubes
[Pd(PPh3)4] (3.5 mg, 0.003 mmol) and nBuSnCl3 (50 mL, 84.6 mg,
0.30 mmol) were dissolved in THF-d8 (0.5 mL) in an NMR tube.
The tube was sealed to prevent butenes leakage. The relative
n
concentrations of BuSnCl3 and butene isomers were monitored
1
by H NMR by observing the integrals of the olefinic protons
of butene isomers (1-butene: d 5.90 (m, 1H), 5.02 (m, 1H), 4.93
(m, 1H); 2-butenes (Z and E mixture): d 5.46 (m, 2H)) and
n
of the Pr-CH2-SnCl3 signal (d 2.39). For the determination of
the temperature-dependance of the concentrations at equilibrium
(Van’t Hoff plot), the same tube was heated successively at 50, 60
and 70 ◦C and then back to 60 and 50 ◦C. For each temperature,
the concentrations were measured after a 2 h equilibration time.
Conclusions
Dehydrostannylation of RSnCl3 (R = Ph, Me, nBu, nOct) in
Schlenk tubes
In this article we demonstrate that monoalkyltin trichlorides
containing b-H atoms suffer a dehydrostannylation reaction in
the presence of catalytic amounts of [Pd(PPh3)4]. The reaction
is an equilibrium, which lies to the side of the alkyltin starting
Substrate screening experiments. RSnCl3 (12.0 mmol; R = Me:
n
n
2.88 g; R = Ph: 1.97 mL; R = Bu: 2.00 mL; R = Oct: 4.06 g)
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was dissolved in THF (18.0 mL) together with undecane (internal
standard, 5.00 mmol, 1.05 mL) and heated to 50 ◦C. A t = 0 min,
the catalyst was introduced as 1.0 mL of a stock solution in THF
([Pd(PPh3)4]: 1.0 mol%, 1.39 g in 10 mL; blank experiments: 1.0 mL
1.6 mmol, 20 mol%; 4.0 mL/758.5 mg, 4.0 mmol, 50 mol%).
With an initial concentration of 2-octene (cis-/trans- mixture):
temperature 60 ◦C; [Pd(PPh3)4] (stock solution of 1.39 g in 10 mL
THF); OctSnCl3 (2.70 g, 8.00 mmol); EtMgBr (25% in THF;
0.66 mL, 1.20 mmol); 1-octene (0.50 mL, 4.0 mmol, 50 mol%).
n
◦
of THF) and the mixture was stirred at 50 C for 3 h. After this
time, a sample of the reaction mixture (2 mL) was evaporated
to dryness under vacuum. n-Hexane (20 mL) was added under
vigorous stirring resulting in a red precipitate which contained the
palladium catalyst and HSnCl3(THF)n. EtMgBr (25% in THF,
2.0 mL, 3.70 mmol) was slowly added and the mixture stirred for
10 min (to transform the remaining RSnCl3 into RSnEt3 for GC
analysis). The excess of Grignard reagent was then hydrolyzed by
diluted aqueous H2SO4 (5%, 10 mL). A sample of the organic
phase was passed through a plug of silica, diluted 20 times and
analyzed by GC.
GC method for analysis of the reaction mixture. Injection
temperature: 270 ◦C, Detector temperature: 270 ◦C. Oven tem-
◦
perature: ramp of 20 C min-1 from 50 ◦C to 280 ◦C, then
hold at 280 ◦C for 4 min. Detector type: FID. Retention
times: 2.41 to 2.54 min (octene isomers), 3.38 min (MeSnEt3),
4.45 min (undecane), 7.01 min (PhSnEt3), 9.41 min (Ph2SnEt2),
4.10 min (SnEt4), 5.28 min (nBuSnEt3) and 7.77 min (nOctSnEt3).
Conversions were calculated by comparing the area of the peak
corresponding to RSnEt3 with its value at t = 0 min using undecane
as internal standard.
n
Kinetic experiments with OctSnCl3. The desired amount of
nOctSnCl3 was dissolved in THF (36.0 mL) together with undecane
as internal standard (2.11 mL, 10.0 mmol) and an eventual
additive. The reaction mixture was then heated to the desired
temperature. A t = 0 min the desired amount of [Pd(PPh3)4] was
introduced as 2.0 mL of a stock solution in THF and the system
was stirred at the desired temperature. At t = 0, 15, 30, 60, 120
and 240 min a sample of the reaction mixture (2.0 mL) was
poured in hexane (20 mL) and treated under vigorous stirring
with three equivalents of EtMgBr for 10 min (to transform the
remaining nOctSnCl3 into nOctSnEt3 for GC analysis). The excess
of Grignard reagent was hydrolyzed by dilute aqueous H2SO4 (5%,
10 mL). A sample of the organic phase was passed through a plug
of silica, diluted 20 times and analyzed by GC. The derived initial
rate data are listed in Table 2 and Table 3. As a function of the
Acknowledgements
The authors thank the Dutch Ministry of Economic Affairs/
Agentschap NL for financial support (project KWR09005).
Notes and references
1 A. M. Echavarren, Angew. Chem., Int. Ed., 2005, 44, 3962.
2 A. Herve, A. L. Rodriguez and E. Fouquet, J. Org. Chem., 2005, 70,
1953.
3 D. A. Powell, T. Maki and G. C. Fu, J. Am. Chem. Soc., 2005, 127, 510.
4 R. Rai, K. B. Aubrecht and D. B. Collum, Tetrahedron Lett., 1995, 36,
3111.
5 A. I. Roshchin, N. A. Bumagin and I. P. Beletskaya, Tetrahedron Lett.,
1995, 36, 125.
6 M. D. K. Boele, B.-J. Deelman, G. van Koten and E. M. Wagner, 2007,
EP 1743898 A1, WO 2007/006783 A1.
7 Y. Cabon, I. Reboule, M. Lutz, R. J. M. Klein Gebbink and B.-J.
Deelman, Organometallics, 2010, 29, 5904.
8 L. A. Woodward and M. J Taylor, J. Chem. Soc. Dalton Trans., 1962,
406; R. E. Hutton, J. W. Burley and V. Oakes, J. Organomet. Chem.,
1978, 156, 369; A. Tzsachach, W. Uhlig and K. Kellner, J. Organomet.
Chem., 1984, 266, 17; J. Coddington and M. J. Taylor, J. Chem. Soc.,
Dalton Trans., 1989, 2223.
n
temperature: OctSnCl3 (8.12 g, 24.0 mmol); [Pd(PPh3)4] (stock
solution of 1.39 g in 10 mL of THF); EtMgBr (25% in THF,
2.0 mL, 3.7 mmol); temperatures of 30, 40, 50, 60 and 70 ◦C.
As a function of the substrate concentration: [Pd(PPh3)4] (stock
solution of 1.39 g in 10 mL THF); temperature 60 ◦C; nOctSnCl3
(1.35 g, 4.00 mmol; 2.71 g, 8.00 mmol; 4.06 g, 12.00 mmol,
8.10 g, 24.0 mmol and 16.2 g, 48.0 mmol); EtMgBr (25% in THF;
0.33 mL, 0.60 mmol; 0.99 mL, 1.8 mmol; 2.0 mL, 3.7 mmol;
4.0 mL, 7.3 mmol). As a function of the catalyst loading: nOctSnCl3
9 I. Ryu, S. Murai and N. Sonoda, J. Org. Chem., 1986, 51, 2389; H.
Nakahira, I. Ryu, M. Ikebe, Y. Oku, A. Ogawa, N. Kambe, N. Sonoda
and S. Murai, J. Org. Chem., 1992, 57, 17.
◦
(8.12 g, 24.0 mmol); temperature 60 C; EtMgBr (25% in THF;
10 As for the nBuSnCl3 case, the dehydrostannylation of nOctSnCl3 initially
leads mainly to the formation of the terminal olefin, in this case 1-
octene. But, under the conditions employed, the terminal olefin is
concomitantly isomerized into its internal isomers resulting in >95%
of internal isomers after 3 h of reaction.
2.0 mL, 3.7 mmol). [Pd(PPh3)4] (stock solution in 10 mL THF;
139 mg, 0.024 mmol, 0.1 mol%; 278 mg, 0.048 mmol, 0.2 mol%;
695 mg, 0.12 mmol, 0.5 mol%; 1.39 g, 0.24 mmol, 1 mol%;
2.78 g, 0.48 mmol, 2 mol%; 5.65 g, 0.96 mmol, 4 mol%). With an
initial concentration of 1-octene: temperature 60 ◦C; [Pd(PPh3)4]
(stock solution of 1.39 g in 10 mL THF); nOctSnCl3 (2.70 g,
8.00 mmol); EtMgBr (25% in THF; 0.66 mL, 1.20 mmol); 1-octene
(0.12 mL, 0.80 mmol, 10 mol%; 0.25 mL, 1.6 mmol, 20 mol%;
0.50 mL, 4.0 mmol, 50 mol%). With an initial concentration
of HSnCl3: temperature 60 ◦C; [Pd(PPh3)4] (stock solution of
11 For a general discussion of thermal disproportionation of organotins
see: S. H. L. Thoonen, B.-J. Deelman and G. van Koten, J. Organomet.
Chem., 2004, 689, 2145 and references therein.
12 Without any initial concentration of 1-octene, SnCl2 or HCl, the rate
law is written v = k[PdH(SnCl3)(PPh3)2] with [PdH(SnCl3)(PPh3)2] =
[Pd]tot. For example, in the presence of a pre-equilibrium K between
[PdH(SnCl3)(PPh3)2], octene and [Pd(Oct)(SnCl3)(PPh3)2], the concen-
tration of the key intermediate can be written as [PdH(SnCl3)(PPh3)] =
[Pd]tot/(1 + K[octene]). Thus, 1/v = A + B[octene] (A = 1/(k[Pd]tot); B =
KA).
n
1.39 g in 10 mL THF); OctSnCl3 (2.70 g, 8.00 mmol); EtMgBr
(25% in THF, 0.66 mL, 1.20 mmol); HCl (1 M in Et2O)/SnCl2
(0.80 mL/151.7 mg, 0.80 mmol, 10 mol%; 1.60 mL/303.4 mg,
13 For a review on the interest of degrading alkyltin pollutants see e.g. R.
De Carvalho Oliveira and R. E. Santelli, Talanta, 2010, 82, 9.
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The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 8651–8655 | 8655
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