0
.1 1C, to a standardized solution (10 ml) of catalyst (0.1 M)
Conclusion
which had previously been stirred over solid NaI (25 mmol) for
h, to obtain the complex formation. Timing and stirring were
The results as a whole proved that polypodands 1–7 are
efficient catalysts in anion-promoted reactions under solid–
liquid PTC conditions. The high catalytic activity is mainly due
to the excellent complexing ability of these many-armed
ligands. As a result, silicon polypodands 1–7, that combine
low cost and ease of synthesis with high complexation extent
and good anion activation, can be considered a promising
alternative to the traditional, more expensive, macrocyclic
polyethers in a number of solid–liquid phase transfer catalyzed
reactions.
1
started. Aliquots of the organic phase were withdrawn (after
stopping the stirring for 30–60 s to allow adequate separation),
centrifuged, separated from any eventual solid precipitate
and analyzed by GLC (see General methods). The reaction
rates were measured by following the disappearance and/or
appearance of substrate and reaction product. The pseudo-first-
order rate constants (kobsd) were computer generated by plot-
ting log[substrate] vs. time and determining the slope of the
straight lines.
Experimental
Kinetics under homogeneous conditions
General methods
Standardized chlorobenzene solutions (5 ml) of substrates 13
or 15 (0.15–0.30 M) were added to a standardized solution
GLC data were obtained with a Hewlett-Packard 6890 by
using a HP-5.5% phenylmethylsiloxane column (30 m ꢄ 320
mm ꢄ 0.25 mm). Potentiometric titrations were carried out
with a Metrohm 751 GPD Titrino using a combined silver
electrode isolated with a potassium nitrate bridge. Karl Fisher
determinations were performed with a Metrohm 684 KF
coulometer. H and P NMR spectra were recorded on Bruker
AC 300 and AMX 300 spectrometers, using as external refer-
3 4
ences TMS and 85% H PO , respectively.
(
0.02–0.04 M) of complexed MI (15 ml) in a 30 ml flask
thermostatted at 60 ꢂ 0.1 1C. The solution of preformed
1
M
ꢀ
complex (Ligand )I was prepared as described above. Sam-
ples (2–5 ml), withdrawn periodically, were quenched in ice-
cold MeOH (50 ml) and the unreacted iodide was potentiome-
1
31
trically titrated with 0.01 M AgNO . The second-order rate
3
ꢀ1
ꢀ1
constants k (M
s
) were evaluated using a least squares
computer program from the equation: 1/([B ]ꢀ[A ]) ꢅ ln([BA ]/
0
0
0
[AB
vice versa. All rates involved at least 8 samplings and gave
0
]) ¼ kt, where A ¼ substrate and B ¼ complexed MI or
Materials and solvents
correlation coefficients of 0.997 or better.
Dry (Fluka) chlorobenzene (H
metal iodides were AnalaR grade commercial products, kept in
2
O r 20 ppm) was used. Alkali
a desiccator under vacuum. Silicon polypodands 1–7 were
1
1,12
Acknowledgements
prepared following a previously reported procedure.
1
Their
structures were also proved by H, C and Si NMR spectro-
13
29
The present work was realized in the framework of a NATO
Science Fellowship (37/J/2000) granted to B. L. and grant
KBN N1 T09A 096 20. Financial support of CNR and
MURST is also acknowledged.
1
scopy. Ligands 8–10 were utilized as purchased.
2
Dicyclohexano-18-crown-6 (DCH18C6) 11 was an AnalaR
grade commercial product (mixture of isomers, purity Z 97%)
and was used as such. Merck Kryptofix 222D ([2.2.2,C10]) 12
(
the organic solvent under vacuum.
50% toluene solution) was used as purchased after removal of
References
2
0
Octyl methanesulfonate 13, bp 92–94 1C at 0.03 mmHg, nD
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2
3
4
5
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13
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0
20
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6
7
Extent of complexation
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8
–11 was determined by stirring a standardized chlorobenzene
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6
0 1C. The system was magnetically stirred for 2–4 h, then kept
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0
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PM5 theoretical methods .
3
potentiometrically titrated with 0.01 M AgNO . Potentio-
1
1
ꢀ
metric titrations of cryptates (M C[2.2.2,C10])I were carried
out in acid medium in order to avoid the simultaneous titration
11
5
11
12
13
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of the free ligand.
Kinetic measurements under SL-PTC conditions
H. R. Williams and H. S. Mosher, J. Am. Chem. Soc., 1954, 76,
In a typical procedure a standardized chlorobenzene solution
(
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14 A. Carayon-Gentil, T. Nguyen Than, G. Gouzy and P. Chabrien,
Bull. Soc. Chim. Fr., 1967, 1616–1620.
10 ml) of methanesulfonate 13 (1 M) and internal standard
dodecane) (0.5 M) was added, in a flask thermostatted at 60 ꢂ
(
1
198
N e w J . C h e m . , 2 0 0 5 , 2 9 , 1 1 9 5 – 1 1 9 8