CYCLODEXTRINS: NEW OPPORTUNITIES FOR AQUEOUS CATALYSIS
Anne Ponchel, Sébastien Tilloy and Eric Monflier*
Université d’Artois, Laboratoire de Physico-Chimie des Interfaces – FRE CNRS 2485 – LENS – France
Phone: 00 33 (0)3 3 21 79 17 72; Fax: 00 33 (0)3 3 21 79 17 55; email: [email protected]
Biphasic aqueous catalysis
Chemically modified cyclodextrins in biphasic aqueous catalysis
Abbreviation Substituant Carbon bearing Average number
(Z)
the OCH3 group of OCH3 group
by CD (DS)
Hydrophilic
surface
H
(-)
(-)
β-CD
Main advantages of aqueous catalysis:
catalysis:
Substrate
- Catalyst is easily recovered by separation of the aqueous and organic
phase
- Water is non-toxic, nonflammable, inexpensive, and environmentally
friendly solvent
- Use of organic solvent can be avoided
Product
Hydrophobic
Cavity
OZ
OZ
O
O
ZO
Organic layer
RAME-β-CD H and CH3
7
2, 3 and 6
12.6 (DS: 1.8) or
5 (DS: 0.7)
(Z = CH3 or H)
Water
Main drawbacks of aqueous catalysis:
catalysis:
- Substrate or product must be stable in water
- Use of water soluble ligands or dispersing agents is required to maintain
catalyst in aqueous phase
- Substrate must be partially soluble in the aqueous phase to avoid mass
transfert limitation
catalyst
Cyclodextrins allow:
- to increase the rate and selectivity of reactions catalyzed by water-soluble organometallic catalysts.
- to stabilize catalytically active noble metal nanoparticles in water
- to favour the dispersion of the Pd/C particles in water
- to design new water soluble ligands for aqueous organometallic catalysis
Cyclodextrin as mass transfer promoter in aqueous organometallic
biphasic catalysis
Stabilization of metal nanoparticles in water
%
25
20
Organic Layer
Organic Layer
Product
Product
Substrate
Substrate
15
10
5
Water-soluble
organometallic
catalyst
Interfacial layer
Aqueous layer
The mechanism depends
on the water-solubility of
inclusion complexes.
Interfacial layer
NaBH4,
RAME-CD
H2O, RT
RuCl3. H2O
1,0
1,5
2,0
2,5
3,0
3,5
Transmission
Electron
micrograph
and
size
distribution
of
Ru(0)
nanoparticles stabilized by
RAME-β-CD (0.7) ; Mean
size: 1.5 nm
nm
Ru (0)
Water-soluble
organometallic catalyst
Aqueous layer
Aqueous layer
Inverse phase transfer catalysis
Interfacial catalysis
CDs stabilized Ru(0) nanoparticles were active in hydrogenation reaction
CDs increase the conversion and selectivity in hydroformylation reaction
RAME-CD / Ru(0)
CHO
Rh, Sulfoxanthphos
CH3 (CH2)7 CH CH2
CO / H2
NaO3S
SO3Na
40
100
Ph
O
H
Rh
P
80
P
RAME-α
α-CD (DS: 1.8): 100 % ethylbenzene
RAME-β
β -CD (DS: 1.8): 100 % ethylbenzene
RAME-β
β -CD (DS: 0.7): 100 % ethylcyclohexane
RAME-γγ-CD (DS: 1.8): 100 % ethylcyclohexane
Ph
CO
60
20
(%)
R
RAME-CD or HEA16 / Ru(0)
1 bar H2, RT, H2O
40
20
0
+
1 bar H2, RT, H2O
CH2 CHO (l) + CH3 (CH2)7 CH CH3 (b)
CH3 (CH2)7 CH2
Additional steric stress of the CD cavity compelled
the substrate to react preferentially by its terminal
carbon.
0
Conversion
l/b
Selectiviy
RAME-β-CD
(-)
HEA 16: t(100 %) = 15 h ; e.d. 50 %
RAME-β
β -CD (DS: 1.8): t(100 %) = 4 h ; e.d. 52 %
RAME-α
α-CD (DS: 1.8): t(100 %) = 6 h ; e.d. 74 %
E. Monflier et al. Organometallics 2005, 24, 2070
E. Monflier et A. Roucoux. Chem. Commun. 2006, 296-298.
E. Monflier et A. Roucoux. Dalton. Trans. 2007, in press,
CDs as efficient dispersing agent
of Pd/C in water and as mass transfer promoter
New Ligands for aqueous organometallic catalysis
Self-assembled supramolecular bidentate ligand
Bulky supramolecular monodentate ligand
Pd/C dispersion
NH2
Product
Substrate
+
+ M
Phase transfer
PtCl2
+= monoamino-β-CD
n
SO3Na
n
=
NH2
SO3Na
A
H
P
=
NH2
K2PtCl4
M
P
B
=
Hmonoamino-β-CD
=
P
Dispersion
HA
With β-CD
Without CD
Aqueous phase
Metal/Charcoal
2
SO3Na
2
HB
2
With RAME-β-CD
Active in hydrogenation reaction
Active in C-C coupling reaction
E. Monflier et al. Angew. Chem. Int. Ed. 2007, 46, 3040-42
E. Monflier et al. Adv. Synth. Catal. 2004, 346, 1449-1456.
Aqueous CD-Pd/C solutions were active in hydrodechloration, Suzuki and Heck reactions
O
Conclusion
Cyclodextrins, Pd/C
I
CH CH CO2Et + byproducts
OEt
+
H2O, N(Et)3
Z or E
Entry
Additive
Conv. (%)
Can CD also contribute to development of catalytic processes conducted in others green solvents
(scCO2, ionic liquid)? YES
Selectivity (%)
E-isomer
O
CD can contribute to the development of aqueous catalytic processes (Increase reaction rate,
chimio-, regio- and stereoselectivity and stability or availability of catalyst
Z-isomer
OC2 H5
OC 2H5
OAc
O
CDs increase the
conversion and
selectivity in Heck
reaction
O
O
AcO
1
-
33
45.5
0.4
33.2
20.9
2
β-CD
43
44.3
0.3
28.9
26.5
3
RAME-α-CD
57
75.9
0.1
12.7
11.3
4
RAME-β-CD
66
81.1
0.6
8.9
9.4
4
RAME-γ-CD
53
86.2
1.6
3.2
9.0
OAc
P
7
O
Rh
E. Monflier et al. Org. Lett. 2006, 8, 4823-4826,
E. Monflier et al. Catal. Comun. 2007, in press
scCO2 / CO / H2
H
E. Monflier et al. J. Phy.Chem. B.. 2007, 111, 2573-78