catalyst concentration but also working under neat conditions
, but did not
affect the selectivity of the reaction. The selectivity is somewhat
improved by lowering of the reaction temperature from 110 to
This work was financially supported by ATOFINA Vlissin-
gen B.V. and the Dutch Ministry of Economic Affairs
(SENTER/BTS).
resulted in a decrease of the yield of n-BuSnCl
3
8
5 °C or by taking n-octane as solvent. However, these
Notes and references
variations also lower the overall catalyst activity.
†
In a typical experiment, Bu
toluene (500 mL). Next, SnCl
3 2
mixture followed by PtCl (PPh )
2
SnCl
(215 g, 0.83 mol) was added to the reaction
(215 mg, 0.27 mmol). The reaction
2
(252 g, 0.83 mol) was dissolved in
Since eqn. (2) is usually the problematic step for driving eqn.
4
(
1) to completion, we decided to test the complete redistribution
2
of n-Bu
PtCl (PPh
affording n-BuSnCl
small amount of SnCl
Addition of extra triphenylphoshine to the reaction of n-
4
Sn with 3 equivalents of SnCl
.‡ It was found that this was indeed possible
(83% isolated yield) together with only a
(3.7%).
4
in the presence of cis-
mixture was stirred for 12 h at 110 °C. After cooling to room temperature,
the reaction mixture was filtered. After evaporating the solvent in vacuo,
butyltin trichloride (373 g, 80%) was obtained by a vacuum distillation
2
3 2
)
3
2
(90 °C/11 mmHg). The solid SnCl (44.5 g, 14%) obtained from filtration,
2
was washed with toluene (3 3 20 mL) and dried in vacuo to give an off-
Bu
2
SnCl
2
with SnCl
4
(entries 14, 15) resulted in a decrease of
white solid. Elemental analysis of SnCl
requires: Cl, 37.4%; Sn, 62.6%.
2 2
: Cl, 37.0%; Sn, 61.2%. SnCl
activity and selectivity of the catalyst. The former effect has also
‡
Conditions: 0.033 mol% of cis-PtCl
2
(PPh
3 2 4
) (relative to n-Bu Sn), T =
been observed for triphenylphosphine–palladium catalysed
6
110 °C, [n-Bu
4
Sn] = 1.0 M, toluene as solvent. After stirring the reaction
cross-coupling reactions. Replacement of two monodentate
mixture for 2 h at 110 °C, the catalyst was added. Stirring was continued for
3
PPh ligands by bidentate, 1,2-bis(diphenylphosphino)ethane
an additional 12 h at this temperature.
(
(
dppe), led to complete inactivity of the resulting complex
entry 16) suggesting that dissociation of a phosphine ligand is
§
This experiment was performed analogously to entry 5 (Table 1), but with
toluene-d as solvent. The amounts of but-1-ene and but-2-ene (cis/trans)
were found to be 1 and 3%, respectively (relative to the amount of n-
Bu SnCl ): R. K. Harris and B. R. Howes, J. Mol. Spectrosc., 1968, 28,
191.
8
a crucial mechanistic step in the platinum-catalysed redistribu-
tion process.
2
2
2
While the exact mechanism leading to SnCl formation
remains unknown, the fact that this product is formed for both
R = n-Bu and n-Hex but not for R = Me suggests that an
intermediate Pt–alkyl species, which has a strong tendency to
1
F. Diederic and P. J. Stang, Metal-catalyzed Cross-coupling Reactions,
Wiley-VCH, Verlag GmbH, 1998; P. J. Smith, Chemistry of Tin,
Chapman & Hall, London, 1998, pp. 310–317; E. W. Abel, F. G. A. Stone
and G. Wilkinson, Comprehensive Organometallic Chemistry II, Elsevier
Science Ltd., Amsterdam, 1995, vol. 11, ch. 8.
7
undergo b-H elimination is involved. In addition, in the
2 2 4
reaction of n-Bu SnCl with SnCl , the presence of the b-H
elimination products but-1-ene and but-2-ene could be detected
2 N. Flitcroft and H. D. Kaesz, J. Am. Chem. Soc., 1963, 85, 1377.
3 Vinyltins and a few aryltins excepted. D. Seyferth, C. Sarafidis and A. B.
Evnin, J. Organomet. Chem., 1964, 2, 417; H. Zimmer and H. W.
Sparmann, Chem. Ber., 1954, 87, 645.
1
by H NMR spectroscopy of the reaction mixture.§ The
consumption of reactants in the PtCl
2
(PPh
3
)
2
-catalyzed redis-
tribution reaction of n-Bu SnCl with SnCl
2
2
4
was monitored by
4
W. P. Neumann and G. Burkhardt, Liebigs Ann. Chem., 1963, 663, 11;
H. G. Langer, Tetrahedron Lett., 1967, 1, 43; T. G. Kugele and D. H.
Parker, US Pat., 3862198, 1975; M. Buschhoff, W. P. Neumann, US Pat.,
119
Sn NMR (T = 110 °C) and found to be first order in n-
2
4 21
Bu
SnCl
formation (kobs = 1.5 3 10
SnCl
2
SnCl
4
2
(kobs = 1.9 3 10
s ) and essentially zero order in
. Since the same rate law was observed for n-BuSnCl
3
4
604475, 1986.
2
4
21
s
), it can be concluded that
5 J. F. Almeida, H. Azzazian, C. Eaborn and A. Pidcock, J. Organomet.
Chem., 1981, 210, 121; G. Butler, C. Eaborn and A. Pidcock,
J. Organomet. Chem., 1979, 181, 47.
2
4
21
2
formation (kcalc = 0.4 3 10
s ) is a competitive
process which takes place after rate determining transmetalla-
tion of the (pre)-catalyst. No additional SnCl is formed after the
reactants have been consumed, which excludes occurrence of a
secondary reaction involving decomposition of n-BuSnCl (e.g.
under the influence of spent catalyst) as the source of SnCl
6
A. L. Casado, P. Espinet and A. M. Gallego, J. Am. Chem. Soc., 2000,
22, 11 771; C. Mateo, D. Cárdenas, C. Fernández-Rivas and A. M.
Echavarren, Chem. Eur. J., 1996, 12, 1596; V. Farina, Pure Appl. Chem.,
996, 68, 73.
2
1
3
1
2
.
7
G. Cavinato, G. De Munno, M. Lami, M. Marchionna, L. Toniolo and D.
Viterbo, J. Organomet. Chem., 1994, 466, 277; A. Scrivanti, A. Berton,
L. Toniolo and C. Botteghi, J. Organomet. Chem., 1986, 314, 369; G. M.
Whitesides, J. F. Gaash and E. R. Stedronsky, J. Am. Chem. Soc., 1972,
94, 5258.
A more extensive study on the mechanism of the platinum-
catalysed redistribution process and the influence of the nature
of the ligands on the catalytic activity and selectivity will be
presented in future publications.
Chem. Commun., 2001, 1840–1841
1841