A new solid acid catalyst: The first phosphonate and phosphonic acid functionalised microporous polysilsesquioxanes

Article abstract of DOI:10.1039/b008192m

A novel microporous solid acid, the phosphonic acid modified polysilsesquioxane [(HO)SiCH₂CHPO(OH)₂ CH₂CH₂SiO₂(OH)]_n P2, from the new single precursor compound [(EtO)₃SiCH₂ CHPO(OCH₂CH₃)₂CH₂ CH₂Si(OEt)₃] 1, is reported, along with the catalytic activity of P2 for the pinacol-pinacolone rearrangement.

Full text of DOI:10.1039/b008192m

A new solid acid catalyst: the first phosphonate and phosphonic acid
functionalised microporous polysilsesquioxanes†
Magdalena Jurado-Gonzalez, Duan Li Ou, Bradley Ormsby, Alice C. Sullivan and John R. H. Wilson
Department of Chemistry, Queen Mary and Westfield College, Mile End Road, London, UK E1 4NS.
E-mail: a.c.sullivan@qmw.ac.uk
Received (in Cambridge, UK) 10th October 2000, Accepted 17th November 2000
First published as an Advance Article on the web 14th December 2000
A novel microporous solid acid, the phosphonic acid
modified polysilsesquioxane [(HO)SiCH CHPO(OH)
CH CH SiO (OH)] P2, from the new single precursor
compound [(EtO) SiCH CHPO(OCH CH CH CH
Si(OEt)
hydrochloric acid gave the corresponding phosphonic acid
n
2
2
-
modified material P2.¶ The absence of any Q type resonances
in the 29Si CP MAS NMR of P2 indicates that the transforma-
tion from ester to acid occurred without any Si–C cleavage. The
decrease in C+P ratio and changes in the NMR spectra from P1
to P2 (in particular the disappearance of the signals due to the
2
2
2
n
3
2
2
3
)
2
2
2
-
3
] 1, is reported, along with the catalytic activity of
P2 for the pinacol–pinacolone rearrangement.
2 3 2
phosphonate ester group 2PO(OCH CH ) at 63 ppm, see
1
a,b
The development of functionalised porous silicas
and
Fig. 1), is consistent with the formation of the phosphonic acid
from the ester. Average formulae for these materials derived
polysilsesquioxane materials1
c,d
for various applications is
2
proceeding at great pace as evidenced by recent reviews and
reports on synthesis and applications in this area. Functional
groups or their precursors may be attached to silica via
from C+P ratios and based on predominantly T environments
(66% condensation) are [(HO)SiCH
2
CHPO(OEt)
2
CHPO(OH)
2
CH
CH
2
CH
CH
2
-
-
SiO
SiO
2
(OH)]
(OH)]
n
P1 and [(HO)SiCH
P2.
2
2
2
3 2 n
compounds (RO) Si(CH ) X where X may be further modified
2
n
if required. Such materials offer a wide spectrum of potential
applications for example as acid, base, or oxidation catalysts or
The material P2 was found to be microporous by nitrogen
sorption porosimetry with very narrow pore size distribution.
It is our intention initially to utilise the phosphonic acid
functionality in these and related materials we have prepared for
various catalytic transformations. Preliminary experiments
based on catalytic pinacol–pinacolone rearrangement and
dehydration of cyclohexanol were used to test the reactivity of
the phosphonic acid functionality in P2. A range of solid acid
catalysts have been reported to catalyse pinacol–pinacolone
rearrangements; examples include metal substituted alumino-
phosphates, lanthanide substituted zeolites,9 heteropoly-
tungstates,10 various SAPOs (silicoaluminophosphates) and
polyphosphoric acid.12
asymmetric carbon–carbon coupling catalysts, or as biocompat-
ible surface groups.1
a,b,2
In the context of the present report
efforts are also being directed towards the synthesis of
functionalised porous polysilsesquioxanes, where the func-
tional group is an integral part of a single framework precursor.
Examples include polysilsesquioxanes with built-in NLO and
3
a,b
4
luminescence chromophores,
built-in crown-ether or cy-
5
clam groups for ion sensing applications or ferrocenyl groups
for electrochemical applications.6
8
11
It occurred to us that phosphonic acid functionalised silicas
and polysilsesquioxanes might offer a new class of solid acid
materials with wide-ranging potential to act as catalysts, ion
exchange and separation materials. There were no examples of
such materials previously reported in the literature.
We report here on unique examples of the uniformly
modified phosphonate and phosphonic acid polysilsesquiox-
A reaction between P2 (0.2 g) and pinacol (6.0 g) at 140 °C
(no solvent) resulted in 80% conversion to pinacolone after
12 h. Control experiments∑ using mesoporous or microporous
silicas under the same conditions afforded no rearranged
product. Attempted dehydration reactions using P2 (0.25 g) and
3
anes [(HO)SiCH
and [(HO)SiCH CHPO(OH)
from the new precursor compound [(EtO)
PO(OCH CH CH CH Si(OEt) ], 1, 1,4-bis(triethoxysilyl)-
-(diethylphosphonato)butane. Compound 1 was formed‡ as
2
CHPO(OCH
2
CH
3
)
2
CH
2
CH
(OH)] P2 prepared
SiCH CH-
2
SiO
2
(OH)]
n
P1
cyclohexanol (25 cm ) (C
6
H
11OH+PO(OH) = 60+1) at 120 °C
2
1
2
2
CH
2
CH
2
SiO
2
resulted in about 15% conversion to cyclohexene ( H NMR of
the cooled reaction mixture) after 12 h. In control experiments
using mesoporous or microporous silica under the same
conditions no cyclohexene was produced. Industrial processes
for production of cyclohexene require high temperature and
pressure whereby cyclohexanol is fed to activated catalysts such
as silica, alumina or zinc aluminate at 380–450 °C (see ref. 13
for example). Neat phosphoric acid used in large excess is also
active between 160–170 °C. 14
3
2
2
3
)
2
2
2
3
2
2
shown in eqn. (1) by radical addition of HPO(OEt) to the ene
fragment in 1,4-bis(triethoxysilyl)but-2-ene7 and was fully
characterised by solution phase NMR, mass spectrometry and
elemental analysis.
HPO(OEt) +
2
t
t
A detailed systematic study of both reaction types will be
carried out to optimise the catalyst performance.
Bu OOBu
[(EtO) SiCH CHNCHCH Si(OEt) ] æææ ææ Æ
3 2 2 2
[
(EtO) SiCH CHPO(OCH CH ) CH CH Si(OEt) ]
3
2
2
3 2
2
2
3
(1)
1
P1 was obtained as a transparent monolith after acid-
13
catalysed sol–gel processing of 1 in THF.§ The solid state
C
CP MAS NMR spectrum of P1 had peaks close to those
observed for compound 1; the 29Si spectrum showed one broad
2
resonance at 263 ppm consistent with predominantly T type
silicon sites while the 31P NMR showed a single peak at 35 ppm
similar to that of 1. Treatment of P1 with concentrated
†
Electronic supplementary information (ESI) available: Fig. 2 nitrogen
sorption isotherm of P2 and Fig. 3 BJH pore size distribution of P2. See
http://www.rsc.org/suppdata/cc/b0/b008192m/
Fig. 1
DOI: 10.1039/b008192m
Chem. Commun., 2001, 67–68
This journal is © The Royal Society of Chemistry 2001
67

Our material P2 and related materials we have prepared15 are
also subjects for other studies including rearrangements,
condensations, ion exchange and binding of biological mole-
cules.
We thank EPSRC for a quota studentship to Bradley Ormsby,
and Grant GR/M78281; Greg Coumbarides (QMW), Peter
Haycock and Harold Toms of the ULIRS High Field NMR
Service at QMW, Abil Aliev ULIRS solid state NMR service at
University College London, for NMR. We also thank the
University of London Central Research Fund and the Faculty
Research Support Fund of Queen Mary and Westfield College
for support.
23.1, 33.6;
29Si CP MAS NMR d 266.2; 31P CP MAS NMR d 33.5;
2
Average formula based on
PO(OH) CH CH SiO (OH)]
P2·2H O C 16.3, H 5.1, P 10.5. Found C 14.2, H 4.3, P 10.5%; BET surface
area 354 m g ; micropore surface area 345 m g ; micropore volume
T
2
environments [(HO)SiCH CH-
2
2
2
2
n
C+P = 1.55, Found C+P = 1.35; Calculated
2
2
21
2
21
3
21
3
21
0
.192 cm g ; total pore volume 0.219 cm g
.
∑
Control experiments were carried out with microporous and mesoporous
silicas prepared by standard methods from TEOS and with samples of these
treated with concentrated HCl and washed in the manner described above
for P2.
1 (a) P. M. Price, J. H. Clark and D. J. Macquarrie, J. Chem. Soc., Dalton
Trans., 2000, 101; (b) J. H. Clark and D. Macquarrie, Chem. Commun.,
998, 853; (c) D. A. Loy and K. J. Shea, Chem. Rev., 1995, 95, 1431; (d)
R. J. P. Corriu and D. Leclercq, Angew. Chem., Int. Ed. Engl., 1996, 35,
420.
I. Rodriguez, S. Iborra, A. Corma, F. Rey and J. L. Jorda, J. Chem. Soc.,
Chem. Commun., 1999, 593; J. A. Elings, R. Ait-Meddour, J. H. Clark
and D. J. Macquarrie, J. Chem. Soc., Chem. Commun., 1998, 2707; R.
Ciriminna, J. Blum, D. Anvir and M. Pagliaro, J. Chem. Soc., Chem.
Commun., 2000, 1441; Y. Wang, T. Ju Su, R. Green, Y. Tangt, D.
Styrkas, T. N. Danks, R. Bolton and J. R. Lu, J. Chem. Soc., Chem.
Commun., 2000, 587; S. J. Bae, S.-Wook Kim, T. Hyeon and B. Moon
Kim, J. Chem. Soc., Chem. Commun., 2000, 31.
3 H. W. Oviatt, K. J. Shea, S. Kalluri, Y. Shi, W. H. Steier and L. R.
Dalton, Chem. Mater., 1995, 7, 493; A.-C. Franville, D. Zambon and R.
Mahiou, Chem. Mater., 2000, 12, 428.
4 S. Brandes, R. J. P. Corriu, F. Denat, G. Dubois, R. Guilard and C. Reye,
J. Chem. Soc., Chem. Commun., 1999, 2283.
5 C. Chuit, R. J. P. Corriu, G. Dubois and C. Reye, J. Chem. Soc., Chem.
Commun., 1999, 723.
6 P. Audebert, P. Calas, G. Cerveau, R. J. P. Corriu and N. Costa,
J. Electroanal. Chem., 1994, 372, 275.
7 R. J. P. Corriu, J. J. E. Moreau, P. Thepot and M. Wong Chi Man, Chem.
Mater., 1992, 4, 1217.
8 B. Y. Hsu and S. F. Cheng, Microporous Mesoporous Mater., 1998, 21,
505.
9 C. P. Bezouhanova and F. A. Jabur, J. Mol. Catal., 1994, 87, 39.
10 Y. Toyoshi, T. Nakato and T. Okuhara, Bull. Chem. Soc. Jpn., 1998, 71,
2817; Y. Toyoshi, T. Nakato, R. Tamura, H. Takahashi, H. Tsue, K.
Hirao and T. Okuhara, Chem. Lett., 1998, 135.
11 F. A. Jabur, V. J. Penchev and C. P. Bezoukhanova, J. Chem. Soc.,
Chem. Commun., 1994, 1591.
1
1
Notes and references
1,4-Bis(triethoxysilyl)-2-(diethylphosphonato)butane 1: 1,4-bis(tri-
ethoxysilyl)but-2-ene (30.0 g, 78.8 mmol) and diethyl phosphite (21.8 g,
58 mmol, 20.3 ml) and di-tert-butyl peroxide (0.58 g, 3.9 mmol, 0.72 ml)
2
‡
1
were heated at 140 °C for 18 h under nitrogen. The resultant mixture was
distilled under reduced pressure to yield 1 (22.5 g, 55%) bp 147 °C, 0.4 mm
+
Hg; Calcd C 46.3, H 9.1. Found C 46.1, H 9.0; m/z 541.5 (M + Na) 519.5
+
+
(
2 3 2
M ), 473.4 (M 2 OCH CH ) ; Calcd for C20H48Si P 519.2574; Found
6
5
1
2
9
10
5
19.2569;
CH
ronments as appropriate H(CDCl
CH
t, 6 H, CH
CH
C (CDCl
Hz), 16.30, 16.39 (d, CH
NMR:
[( CH
3
CH
2
O)
3
Si CH
2
CH{PO(O CH
2
CH
3
)
2
}-
3
4
7
8CH
2
CH
2
Si(O CH
2
3 3
)
] superscripts indicate proton or carbon envi-
1
1
3
2
) d 0.51–1.03 (complex m, 4H, CH ,
4
8
3
6
3
2
), 1.05 (t, 9 H, CH
3
, JHH 8 Hz), 1.06 (t, 9 H, CH
, JHH 8 Hz), 1.56–1.91 (complex m, 3H, CH, CH
3
, JHH 8 Hz), 1.27
10
3
2
3
(
3
2
), 3.66 (q,
, JPH 10 Hz);
7
3
5
3
9
3
2
, JHH 8 Hz), 3.69 (q, CH
2
3
, JHH 8 Hz), 3.95 (m, CH
2
13
4
1
2
3
) d 8.17 (d, CH
2
2
, JPC 4 Hz ), 8.92, 9.01 (d, CH
2
, JPC 6.5
), 23.56 (s,
), 58.29
) d 245.65 (s,
) d 36.13 (s).
10
6
8
3
, JPC 6.5 Hz ), 18.10 (s, CH
, JPC 4 Hz), 32.16, 34.35 (d, CH, JPC 138 Hz), 58.09 (s, CH
3
, CH
3
3
2
2
5
CH
2
2
7
9
2
29
(
s, CH
2
), 61.16, 61.25 (d, CH
2
, JPC 6.5 Hz); Si (CDCl
3
4
1
3
31
C-Si), 247.66, 247.94 (d, C-Si, JPSi 40 Hz); P (CDCl
P1: Compound 1 (4.45 g, 8.58 mmol), THF (37 ml) and 1 M HCl (0.8 ml)
3
§
were stirred under dynamic nitrogen for 1 h and stored in a polythene bottle.
Gelation occurred after 11 d. The transparent monolithic gel obtained was
air dried for 1 week and then dried at 60 °C in an oven for 24 h. A transparent
monophasic crack-free glass was produced. This was powdered, washed
with water, ethanol and ether consecutively, and then dried under vacuum
1
3
29
at 120 °C for 24 h; C CP MAS d 14.3, 16.9, 23.2, 33.2, 63.1; Si CP MAS
31
2
d 263.5; P CP MAS d 34.5; Calculated average formula based on T
environments [(HO)SiCH CHPO(OEt) CH CH SiO (OH)] C+P = 3.1,
Found C/P = 2.8; Calculated for P1·3H O C, 26.2; H, 6.3, P 8.5. Found C
2
2
2
2
2
n
12 M. A. Kakimoto, T. Seri and Y. Imai, Bull. Chem., Soc. Jpn., 1988, 61,
2643.
2
2
¶
6.6, H 6.0, P 9.6%.
P2: Powdered P1 (1.00 g) and concentrated HCl (100 ml) were refluxed
13 T. K. Shioyama and O. K. Bartlesville, Phillips Petroleum Company,
US1980000113948 April 7, 1981.
for 24 h. The mixture was filtered through a fritted funnel and washed with
excess H O to remove all traces of HCl, followed by ethanol and ether. The
residue was dried under vacuum at 120 °C for 24 h; C CP MAS d 16.5,
14 W. M. Dehn and K. E. Jackson, J. Am. Chem., Soc., 1933, 55, 4285.
15 A. Aliev, D. Li Ou, B. Ormsby and A. C. Sullivan, J. Mat. Chem., 2000,
10, 2758.
2
13
68
Chem. Commun., 2001, 67–68