New non-hydrolysing poly(oxyethylene) silicon compounds as ligands for phase-transfer catalysis

Article abstract of DOI:10.1016/j.mencom.2008.03.007

The non-hydrolysing silicon-containing ligands have been synthesised via hydrosilylation and studied as catalysts for liquid-liquid and solid-liquid phase-transfer catalysis.

Full text of DOI:10.1016/j.mencom.2008.03.007

Mendeleev
Communications
Mendeleev Commun., 2008, 18, 78–79
New non-hydrolysing poly(oxyethylene) silicon
compounds as ligands for phase-transfer catalysis
·
Blazej Gierczyk* and Grzegorz Schroeder
Faculty of Chemistry, Adam Mickiewicz University, 60-780 Poznan´, Poland. Fax: +48 61 829 1505;
e-mail: hanuman@amu.edu.pl
DOI: 10.1016/j.mencom.2008.03.007
The non-hydrolysing silicon-containing ligands have been synthesised via hydrosilylation and studied as catalysts for liquid–
liquid and solid–liquid phase-transfer catalysis.
Podands are interesting ligands showing unique properties.1,2
Previously, we characterised the complex forming abilities of
podands being inorganic esters of poly(ethylene glycol) mono-
alkyl ethers.3,4 The compounds were also tested in phase-
transfer catalysis (PTC).5–7 Unfortunately, most of them are
hydrolytically unstable, so that their applicability to liquid–
liquid PTC (LL-PTC) is strongly limited. Their excellent
catalytic activity in solid–liquid PTC (SL-PTC) has inspired
the synthesis of water-resistant podands containing Si–C bonds,
differing in the number of poly(oxyethylene) chains, their length
and the structure of the binding centre.
from organic to aqueous layer, the ion exchange and the back
transfer (‘extraction’ mechanism), there are many premises
indicating that the LL-PTC does not require the concomitant
transfer of the organic (or a supramolecular complex) cation
(‘interfacial’ mechanism). In the case of SL-PTC, differences
between the mechanisms proposed are significantly more pro-
nounced. Two basic mechanisms, proposed in literature, are the
homogeneous solubilization (requires some finite solubility of
the solid reagent in the organic phase) and the heterogeneous
solubilization (involves the transfer of an anion from the surface
of the solid reagent directly to the organic phase by the PT
catalyst).
The test compounds were prepared using a hydrosilylation
reaction (Scheme 1).† The starting hydrosilane (1 mmol) was
dissolved in dry benzene (150 ml) and a stoichiometric amount
of allyl 2-methoxyethyl ether (n = 1, a) or triethylene glycol allyl
methyl ether (n = 3, b) was added. To the vigorously stirred
mixture, the catalyst was added (0.2 mol% per mole of SiH
bonds). Tris(triphenylphosphine)rhodium(I) chloride (Wilkinson
Although the most popular mechanism of LL-PTC assumes
a transfer of the ion pair (onium salt, crown ether complex)
Ph
H
O
Si
+ 2
O
n
H
Ph
O
O
O
n
n
Ph
Ph
Si
1a: colourless liquid, bp 178–180 °C (0.1 mmHg), yield 85%. 1H NMR
O
†
(CDCl3) d: 1.08 (t, 2H, SiCH2), 1.77 (qu, 2H, CH2CH2CH2), 3.43 (t,
2H, CH2CH2CH2O), 3.51 (m, 4H, OCH2CH2O), 3.30 (s, 3H, OMe),
7.38 (m, 3H, ArH), 7.58 (m, 2H, ArH). Found (%): C, 69.38; H, 8.67.
Calc. for C24H36O4Si (%): C, 69.19; H, 8.71.
1b: colourless liquid, bp 245–248 °C (0.08 mmHg), yield 80%. 1H NMR
(CDCl3) d: 1.07 (t, 2H, SiCH2), 1.76 (qu, 2H, CH2CH2CH2), 3.35 (s,
3H, OMe), 3.43 (t, 2H, CH2CH2CH2O), 3.49 (m, 12H, OCH2CH2O),
7.38 (m, 3H, ArH), 7.58 (m, 2H, ArH). Found (%): C, 64.97; H, 9.00.
Calc. for C32H52O8Si (%): C, 64.83; H, 8.84.
1a,b
Si
O
Si
H
O
+ 2
O
n
H
O
O
Si
O
O
n
n
O
Si
2a: colourless liquid, bp 208–209 C (0.12 mmHg), yield 90%. 1H NMR
(CDCl3) d: –0.01 (s, 6H, SiMe), 0.47 (t, 2H, SiCH2), 1.54 (qu, 2H,
CH2CH2CH2), 3.29 (s, 3H, OMe), 3.51 (t, 2H, CH2CH2CH2O), 3.62 (m,
4H, OCH2CH2O). Found (%): C, 52.11; H, 10.44. Calc. for C16H38O5Si2
(%): C, 52.41; H, 10.45.
2a,b
H
Si
O
O
Si
O
O
H
+ 4
O
n
H
1
Si
2b: slightly yellow liquid, yield 95%. H NMR (CDCl3) d: –0.01 (s,
O
Si
H
6H, SiMe), 0.46 (t, 2H, SiCH2), 1.53 (qu, 2H, CH2CH2CH2), 3.37 (s, 3H,
OMe), 3.50 (t, 2H, CH2CH2CH2O), 3.60 (m, 12H, OCH2CH2O). Found
(%): C, 53.31; H, 10.08. Calc. for C24H54O9Si2 (%): C, 53.10; H, 10.03.
3a: slightly yellow viscous liquid, yield 95%, stochastic mixture of
stereoisomers. 1H NMR (CDCl3) d: 0.03 (br., 3H, SiMe), 0.41 (br., 2H,
SiCH2), 1.48 (br., 2H, CH2CH2CH2), 3.31 (br. s, 3H, OMe), 3.51 (br. t,
2H, CH2CH2CH2O), 3.60 (br., 4H, OCH2CH2O). Found (%): C, 47.77;
H, 9.29. Calc. for C28H64O12Si4 (%): C, 47.69; H, 9.15.
O
O
n
Si
O
O
O
O
Si
O
O
O
n
n
O
Si
Si
3b: slightly yellow viscous liquid, yield 92%, stochastic mixture of
stereoisomers. 1H NMR (CDCl3) d: 0.03 (br., 3H, SiMe), 0.40 (br., 2H,
SiCH2), 1.48 (br., 2H, CH2CH2CH2), 3.31 (br. s, 3H, OMe), 3.51 (br. t,
2H, CH2CH2CH2O), 3.61 (br., 12H, OCH2CH2O). Found (%): C, 50.13;
H, 9.33. Calc. for C44H96O20Si4 (%): C, 49.97; H, 9.15.
O
O
n
a n = 1
b n = 3
3a,b
Scheme 1 Synthesis of the test compounds.
– 78 –
© 2008 Mendeleev Communications. All rights reserved.

Mendeleev Commun., 2008, 18, 78–79
The complex-forming abilities of the compounds were tested
Table 1 Complexation extent, complex stoichiometry and stability con-
stants of the test compounds.
by 23Na NMR titration experiments carried out at a constant
concentration of the sodium ion (1 mM) and changing the
ligand/metal ratio from 0.1 to 25. All of the 23Na NMR spectra
were measured at 293 K using [2H]3-acetonitrile as a solvent
and anhydrous NaClO4 as a sodium salt. The 23Na NMR acqui-
sition parameters were as follows: sfrq, 79.373 MHz; pw, 8.0 s;
pw90, 11.5 s; tpwr, 55 dB; at, 1.5 s; np, 16k; sw, 3000 Hz;
d1, 0.5 s; nt, 512. The stoichiometry and stability constants
of the complexes formed in solution were determined from
the fit to the titration curves using the WinEQNMR software.
Additionally, the complexation extent was determined by the
conductometric titration (argentometry) of a saturated solution
of sodium iodide in a 0.1 M solution of the test ligands in
anhydrous chlorobenzene (Table 1) (2 ml of the solution obtained
was dissolved in 50 ml of methanol and titrated with a 0.01 M
aqueous AgNO3 using an Eurosensor EPS-2 conductometric
probe). The reaction of n-octyl methanesulfonate with NaI in PhCl
was chosen for catalytic tests (SN2 nucleophilic substitution).
The results of these experiments are summarised in Table 2.
The ligands were stable up to 250 °C; ligands 1 and 2 were
hydrolytically stable, while compound 3 polymerised sponta-
neously in acidic media. After the reaction completion, the
podands were isolated and used again without a decrease in
the activity. No catalyst decomposition during the activity tests
was observed (1H NMR).
23Na NMR titration results
Complexation
Compound
extenta
Stoichiometry of
Stability constant
complexes observedb
1a
1b
0.76
1.1
1:1
1:1
2:1
120 10
200 30
40 10
2a
2b
0.69
0.93
1:1
1:1
2:1
65 5
130 20
10 5
3a
3b
0.73
1.21
1:1
1:1
2:1
150 30
300 30
100 25
aDefined as complexed NaI [mol]/ligand [mol]. bDefined as metals cation/
ligand ratio.
catalyst) was used for the synthesis of 1, while 1,3-divinyl-
1,1,3,3-tetramethyldisiloxane-platinium(0) complex (Karstedt
catalyst) was used for the synthesis of 2 and 3. The solution was
heated in an inert atmosphere at 50 °C until no allyl and SiH
hydrogen atoms were detected (1H NMR), which happened
after 60–100 h. Then, the reaction mixture was filtered thought
Celite and the solvent was evaporated in a vacuum. Compounds
1a,b and 2a were purified by vacuum distillation (final purity of
~98%, GC), while the other ones were used without purifi-
cation (purity of ~92–95%, NMR).
This work was supported by the Polish Ministry of Science
and Higher Education (grant no. R0501601, 2006–2008). B.G.
thanks the Foundation for Polish Science for the fellowship.
Table 2 Catalytic activity of the podands and reference compounds in the
reaction between n-octyl methanesulfonate with sodium iodide under SL-
and LL-PTC conditions.a
References
n-C8H17OSO2Me + NaIsolid ® n-C8H17I + MeSO3Na
n-C8H17OSO2Me + NaIsolution ® n-C8H17I + MeSO3Na
SL-PTC
LL-PTC
1
G. W. Gokel and O. Murillo, in Comprehensive Supramolecular Chemistry –
Molecular Recognition: Receptors for Cationic Guests, ed. G. W. Gokel,
Elsevier, Oxford, 1996, vol. 1, pp. 1–34.
Reaction timeb/h
2 D. Landini, A. Maia and M. Penso, in Comprehensive Supramolecular
Chemistry – Molecular Recognition: Receptors for Cationic Guests,
ed. G. W. Gokel, Elsevier, Oxford, 1996, vol. 1, pp. 417–464.
Compound
SL-PTC
LL-PTC
—
1a
1b
200
24.1
6.0
110
17.9
5.5
25.2
10.3
6.0
3.1
0.9
5.2
·
3 B. Gierczyk, G. Schroeder, G. Wojciechowski, B. Rózalski, B. Brzezinski
and G. Zundel, Phys. Chem. Chem. Phys., 1999, 20, 4897.
4 G. Schroeder, B. Gierczyk and B. Leska, J. Inclusion Phenom., 1999,
35, 327.
5 B. Leska, R. Pankiewicz, G. Schroeder and A. Maia, Tetrahedron Lett.,
2006, 47, 5673.
2a
2b
3a
30.5
15.0
6.8
3b
4.2
0.8
6.9
70
DCH18C6c
6 A. Maia, D. Landini, B. Leska and G. Schroeder, Tetrahedron Lett.,
2003, 44, 4149.
c
PEG400Me2c
7 A. Maia, D. Landini, C. Betti, B. Leska and G. Schroeder, New J. Chem.,
PEG150Me2
95
2005, 29, 1195.
aFor SL-PTC experiments: 1 cm3 of 1
M
solution of substrate (n-C8H17OSO2Me)
and 0.01 M of catalyst in chlorobenzene, 5 mmol of solid NaI; for LL-PTC
experiments: 1 cm3 of 1 M solution of substrate (n-C8H17OSO2Me) and
0.01 M of catalyst in chlorobenzene and 5 cm3 of 1 M aqueous solution of NaI.
0.1 mmol of n-dodecane, as internal standard, was added in both cases. Such
mixtures were vigorously stirred and thermostated to 333 K. bA conver-
c
sion equal to 90%, from GC measurements. DC18C6 is dicyclohexano-
18-crown-6; PEG400Me2 is nonaethylene glycol dimethyl ether; PEG150Me2
is triethylene glycol dimethyl ether.
Received: 14th September 2007; Com. 07/3014
– 79 –