From surface-inspired oxovanadium
silsesquioxane models to active catalysts for
the oxidation of alcohols with O2 - the cinnamic
acid/metavanadate system
Christian Limberg
Institut für Chemie
Humboldt-Universität zu Berlin
CRC 546 „Transition metal oxide aggregates"
The oxidative dehydrogenation (ODH) with supported V2O5-catalysts
H2
C CH2 +
0.5 O 2
V2 O5/MO x
R
R
MeOH
+
0.5 O2
+ H 2O
V2 O5/MO x
H2C=O
+ H 2O
„The results of surface studies are the source of ideas for the molecular
chemist in the construction of new molecules, the development of new
reactions and, hopefully, the discovery of new catalysts.“
John A. Osborn, J. Mol. Catal. 1994, 86, 267
CRC 546 „Transition metal oxide aggregates"
Ligands for the simulation of an oxidic environment
R
O Si
OH
OH
R Si O Si
O
OH
R
R
O Si
OSi
R
O
O
O
Si
O Si
R
R
OH
OH
OH OH HO
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
CRC 546 „Transition metal oxide aggregates"
Active species?
O
O
O
O V O
O
O
O
O
O
O OV O OV O OV
O
O
O V
O
O V O V O V O
O
O
O V O V O
O
O
Active units?
O
O
O V O V O
O
O
O
O
O V O V O
O
O
O
O
O V O V O
O
O
S
S
S
S
S = Support
CRC 546 „Transition metal oxide aggregates"
1. Calixarene chemistry
R
O Si
OH
OH
R Si O Si
O
OH
R
O RSi
OSi
R
O
O
O
Si
O Si
R
R
OH
OH
OH OH HO
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
CRC 546 „Transition metal oxide aggregates"
Test of model function: Catalytic activity in the ODH
TOF/h
4 MeO
-1
O
100
O
O O
V
V
O O
OMe
2-
6
O
S
S OH
OH
S
80
S
3
40
O
V
O
O H
O O
O
V O
O
O
V
O
HO
S
S
S
S
2
O
V
O
O
O
O
O
RR'CHOH + 0.5 O2
Cat./80°C
9,10-H-Dihydroanthracene
1
9-Fluorenol
1-Phenyl-1-propanol
1-Phenyl-1-propargylic alcohol
2
Crotyl alcohol
Cinnamyl alcohol
3
Benzyl alcohol
0
O
O
HO
4
V
O
O
O
6
5
VO(acac) 2
O
O
60
20
O
RR'C=O
+ H
2O
CRC
546
O
1
5
V
O
O
O
O
S
O Cl Cl
V
OH O
OH
O
S
S
S
„Transition metal oxide aggregates"
Proposal of a catalytic cycle
2 PPh 4
S
2 PPh 4
S
OH
OH
S
OH
O
O
S
V
O
S
O
O
V
V
O
S
V
S
S
HO
S
O
O
O
V
V
S
O
O
HO
S
R
ROH
O
S
HO
O
OH
O
V
V
S
O
S
HO
O
HO
S
S
O
+ H2 O
S
80 °C
O2
2 PPh 4
2 PPh 4
S
OH
OH
S
OH
O H
O
O
IV
V
S
O
O
H
S
S
S
O
V
IV
S
ROH
HO
H
O
S
O
S
HO
O
OH
OH
O
IV
O
S
S
O
S
H
O
O
V
O
O
H
V
IV
O
S
O
S
HO
HO
S
+ H2 O
ROH =
E. Hoppe, C. Limberg, Chem. Eur. J. 2007, 13, 7006
CRC 546 „Transition metal oxide aggregates"
Addressing mechanistic questions
2 PPh4
2 PPh4
S
OH
S
OH
O
S
O
O
V
V
S
O
O
V
O
V
S
O
O
S
S
O
HO
O
O
S
HO
V
O
O
V
V
O
V
O
O
S
S
2 PPh4
O
O
O
V
S
V
OH
S
2 PPh4[O2VCl2], 2NEt3
O
O
V
O
S
tBu
2
V
O
But
OH
O
- 2 [NEt3H]Cl
tBu
tBu
CRC 546 „Transition metal oxide aggregates"
2 PPh 4
S
2 PPh 4
S
OH
OH
S
OH
O
O
S
V
O
S
O
O
V
V
O
S
V
S
S
ROH
O
S
HO
O
HO
OH
O
O
S
V
S
V
O
O
O
O
HO
S
R
VV
S
O
S
HO
O
HO
S
S
O
+ H2 O
S
80 °C
O2
2 PPh 4
2 PPh 4
S
OH
OH
S
OH
O H
O
O
IV
V
S
O
O
H
S
S
S
O
V
IV
S
ROH
HO
H
O
S
O
S
HO
O
OH
OH
O
IV
O
S
S
O
S
H
O
O
V
O
O
H
V
IV
O
S
O
S
HO
HO
S
+ H2 O
ROH =
E. Hoppe, C. Limberg, Chem. Eur. J. 2007, 13, 7006
CRC 546 „Transition metal oxide aggregates"
Reoxidation via Peroxides
2 PPh4
2 PPh 4
OH
H
O
O
V
O
V
S
S
O
O
O
O
V
O
V
O
O
O
O
IV
O2
O
V
S
O
S
H
O
O
H
V
IV
O
O
-H2 O
+ H2 O
2 PPh4
O
O
H
OH
V
O
V
S
O
S
O
O
O
V
V
O
O
CRC 546 „Transition metal oxide aggregates"
2. Silsesquioxane chemistry
R
O Si
OH
OH
R Si O Si
O
OH
R
R
O Si
OSi
R
O
O
O
Si
O Si
R
R
OH
OH
OH OH HO
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
CRC 546 „Transition metal oxide aggregates"
A mononuclear vanadium(IV) model
R
OH
Si
O
OH
R
O
Si
Si OH
O
R
OR
Si O O Si R
O
O
Si
Si
O
R
R
TiX4
R
X
O
Si
Ti
O
O
R
O
Si
Si RO
O
R
O
Si O O Si R
O
O
Si
Si
O
R
R
X = OEt, OiPr, OiBu, CH 2Ph, NMe2
R
R
Cl
OH
O
Si
V
?
Si
O
OH
O
O
O
R
Si O
Si OH VCl4(thf)2 R Si O Si R
O
O
R
R
O Si
O Si
O R Si
O Si
exc. NEt3
R
R
O
O
O
O
- 3 [HNEt3]Cl
O
O
Si
Si
Si
Si
O
O
R
R
R
R
(a) Edelmann, F.T.; Gießmann,
S.; Fischer, A. J. Organomet.
Chem. 2001, 80-89. (b)
Duchateau, R.; Abbenhuis, H. C.
L.; van Santen, R. A.; Meetsma,
A.; Thiele, S. K.-H.; van Tol, M. F.
H. Organometallics 1998, 17,
5663-5673. (c) Crocker, M.;
Herold, R. H. M.; Orpen, A. G.
Chem. Commun. 1997, 24112412. (d) Viotti, O.; Seisenbaeva,
G. A.; Kessler, V. G. Inorg. Chem.
2009, 48, 9063-9065.
R = c-pentyl
CRC 546 „Transition metal oxide aggregates"
The contents of the red-brown solution
R
OH
Si
O
OH
R
O
Si
Si OH
O
R
OR
Si O O Si R
O
O
Si
Si
O
R
R
?
VCl4(thf)2
exc. NEt3
R
Cl
O
Si
V
O
O
R
O
Si
Si RO
O
OR
Si O O Si R
O
O
Si
Si
O
R
R
R = c-pentyl
51V
EPR spectrum of product in THF at 293 K
NMR: presence of Feher-Komplex
R
O
O
V
Si
O
O
O
R
Si O
Si RO
OR S i
O Si
R
O
O
O
Si
O Si
R
R
O
R
V
R O Si O
Si O
O
O
R
Si
O
R
0.5
R
O Si
O Si
O
R Si
O Si O
O
R
R
O Si
O
Si
Si
Si O
RO
O
O
Si
Si O R
O O
R
R Si
O
O
V
O
O
R
Feher, F. J.; Walzer,
J. F. Inorg. Chem.
1991, 30, 16891694.
R
CRC 546 „Transition metal oxide aggregates"
Precipitation of a trinuclear complex from a hexane solution
R
OH
Si
O
OH
R
O
Si
Si
O
OH
R
R
O
O Si
Si O
R
O
O
Si
O Si
R
R
R
?
thf / VCl 4(thf )2
ex c. NEt3
- 3 [HNEt3 ]Cl
V
O
O
Si R
O
O
OR
O Si
Si O
R
O
O
Si
Si
O
R
R
O
R
Si
Si
Cl
O
R
Si
- volatiles
blue crystals
+ hexane
R = c-pentyl
O
Si
R
O
V
O O
Si Si O V
R Si O
R
R
O
O
O
O
Si
Si
O
R thf
R
O
O O
R
R
O
Si
Si
O
O
O
O
Si Si O Si R
O
R
RO
O
O
O
V
Si
Si
O
O
R
R
thf
C. Ohde, C. Limberg, R. Stößer, S. Demeshko, Inorg. Chem. 2010, DOI: 10.1021/ic902392y
CRC 546 „Transition metal oxide aggregates"
The origin of the oxo ligands
R
Cl
O
Si
V
O
O
R
O
Si
Si R
O
O
R
O Si
O Si
R
O
O
O
Si
O Si
R
R
vs.
R O
R O
R
R
Si
Si
thf
O
V
Si
Si
O
O O
O O
O
O
O
O
V
O
Si
Si
R Si O R
R
Si Si O Si R
O
OO
O
O
R
R
OO
O
O
Si
Si
V
O
R thf
Si
Si
R
O
O
R
R
ligand decomposition + external traces of water
R
Si
R
OH
O
OH
O
R
Si O
Si OH
R
O R Si
O Si
R
O
O
O
Si
O Si
R
R
MS 4 Å, NEt3
- H2O
Si
O
O
R
O
Si O
Si R
OR
C. Ohde, C. Limberg, R.
Stößer, S. Demeshko,
Inorg. Chem. 2010, DOI:
10.1021/ic902392y
OH
Si O O Si R
O
O
Si
Si
O
R
R
Feher, F. J.; Rahimian, K.; Budzichowski, T. A.; Ziller,
J. W.; Organometallics 1995, 14, 3920-3926.
CRC 546 „Transition metal oxide aggregates"
A model for reduced trimers
R
O
O
R
R
R
O
V
Si
Si
O
O O
O
O
VI O
O
O
O
V
O
Si
Si
O
R Si
R
R
Si Si O Si R
O
O
O
O
O
R
RO
VI
O
O
O
Si
Si
V
O
thf
R
Si
Si
R
O
O
R
R
Si
Si
O
thf
VI
O
M
O
R O
Si
O
OR
O Si
R Si
O
Si
O
O
V
V
O
Si R
R
O
O
Si
O
Si O
R
R
O Si
O
Si
O
Si
R
Si O
R Si
RO
O
O
O Si
V
O Si O R
V
R
O
O O
IV
O
V
V
V
O
O
IV
O
M
M
Klose, F.; Wolff, T.; Lorenz, H.;
Seidel-Morgenstern, A.;
Suchorski, Y.; Piórkowska, M.;
Weiss, H. J. Catal. 2007, 247,
176-193.
O2
R
V
O
O
R
+
[VIV]
C. Ohde, C. Limberg, R. Stößer, S. Demeshko, Inorg. Chem. 2010, DOI: 10.1021/ic902392y
CRC 546 „Transition metal oxide aggregates"
Functional models?!
O
P Ph4
R
V
Si O
O
O
O
R
O
Si O
Si
O R'
R
OR S i
O Si
O
O
O R
Si
Si
O
R
R
R
R
O
Si
Si
O
O
O
O
R
O
Si O
Si R
V
O
O
OR
O Si
Si O
O
R
O
Si
O Si
R
R
R
Si
O
V O
O
O
O
Si O
Si
OH
R
R
O Si
O Si
O
O
O R
Si
Si
O
R
R
R
R' = H, SiMe 3, SiMePh 2
R = c-pentyl
PP h4
Ca t./80 °C
R''R'''CHO H + 0.5 O2
R''R'''C=O + H 2O
CRC 546 „Transition metal oxide aggregates"
Functional models?!
O
P Ph4
R
V O
Si O
O
O
R
O
Si O
Si
OH
R
OR S i
O Si
O
O
O R
Si
O Si
R
R
R
O
O
PPh 4
V O
Si
O
O
O
R
Si O
Si
O
R
O R Si
O Si
O
O
O R
Si
Si
O
R
R
O
Me
Si
Me
Me
R
V O
Si O
O
O
R
O
Si O
Si
O
R
OR S i
O Si
O
O
O R
Si
O Si
R
R
P Ph4
Me
Si
Ph
Ph
R = c-pentyl
R''R' ''CHOH + 0.5 O2
C a t./8 0° C
R''R'''C= O + H2 O
C. Ohde, C. Limberg, Chem.- Eur. J. 2010, accepted
CRC 546 „Transition metal oxide aggregates"
Test of model function: Catalytic activity in the ODH
SiMePh2
SiMe3
H
C. Ohde, C. Limberg, Chem.- Eur. J. 2010, accepted
The course of catalysis
2 mmol cinnamic alcohol, 0.02 mmol Cat. and 1 g molecular sieves (3 Å) in 4 mL MeCN were
heated to 80°C in an O2/Ar atmosphere.
C. Ohde, C. Limberg, Chem.- Eur. J. 2010, accepted
Cinammic acid generates the acive catalyst
Oxidation of cinnamic alcohol in the presence of 5 mol% of cinnamic acid and 0.25 mol% of Cat.
C. Ohde, C. Limberg, Chem.- Eur. J. 2010, accepted
The role of the cynnamic acid
O
R'
Si
O
PPh 4
V O
O
Me
O
O
Si O
Si
O Si Me
R'
R'
O Si
OSi
Me
O
O
R'
O
Si
Si
O
R'
or
R'
NBu 4VO3
R'
R‘ = c-pentyl
O
OH
+ 2
-
Ph
H2 SiMe 3c -C5H9 T7
or
- H2 O
O
R
O O
V
O
O
NBu 4
O
R
CH2
R=
Ph
C. Ohde, C. Limberg, Chem.- Eur. J.
2010, accepted
Catalytic activity of the vanadyl cinnamate
O
R
H
C. Ohde, C. Limberg, Chem.- Eur. J. 2010, accepted
O O
V
O
SiMePh2
SiMe3
O
NBu4
O
R
CH 2
R=
Ph
Loss of activity and regeneration
Oxidation of 9-hydroxyfluorene catalysed by the vanadylcinnamate; after 40 min 6 equivalents of
cinnamic acid were added
C. Ohde, C. Limberg, Chem.- Eur. J. 2010, accepted
The reduced species within the catalytic cycle
exc.
H
O
R
O O
V
O
O
OH
NBu4
O
R
The reduced catalyst contains vanadium(IV)
The rate-determining step within the catalytic cycle
O
H
OH
O
R
+ 0.5 O 2
O
D
R
+ 0.5 O 2
NBu4
O
O
R
O
+ H 2O
80°C
vs.
OH
O O
V
O O
V
O
NBu4
O
O
R
O
+ HDO
80°C
KIE: 3.9
H atom transfer and quite symmetric transition
state along the H-transfer coordinate, O···H···C
C. Ohde, C. Limberg, Chem.- Eur. J. 2010, accepted
The reoxidation step within the catalytic cycle
exc.
OH
H
O
R
O O
V
O
NBu4
O2
O
O
O O
V
O
R
O
NBu4
O
O
O
R
H
OH
R = t-butyl
- H2O
O
R
O O
V
O
O
NBu4
O
O
+
R
Reoxidation takes place via peroxides
O
R
R
NBu 4
O O
V
O
O
O
R
The complete catalytic cycle
OH
H
2
O
R
O O
V
O
NBu 4
HO O
NBu 4
2
V
O
O
O
O
R
R
O
O
O
R
O2
O
-H2 O
+ H2 O
O
H
OH
R
O O
V
O
O
NBu 4
O
R
R
O O
NBu 4
O
V
O
O
O
O
R
C. Ohde, C. Limberg, Chem.- Eur. J. 2010, accepted
Cooperations
Detlef Schröder: ESI-MS with oxovanda calixarenes
Thorsten Siebert: fs-UV/Vis with oxovanada silsequioxanes
Christian Hess: Characterisation of supported molybdenumoxide
catalysts by UV-Raman
CRC 546 „Transition metal oxide aggregates"
3. Neutral VxOy clusters in cryogenic matrices
Small VxOy aggregates:
- simplest models
Matrix isolation
of V O clusters
cationic/anionic species x y
- quantum chemical investigation
- neutral VxOy clusters
(structure, spectroscopic properties, reactivity)
CRC 546 „Transition metal oxide aggregates"
V4O10
CRC 546 „Transition metal oxide aggregates"
Monitoring evaporation by mass spectrometry
Synthesis of other VXOY-Aggregates : V4O8, V6O12, V6O14, V2O4, ...
Mass spectrometer:
• Generation of V4O8,
V6O14, … (from V2O5
or alkoxides)
• Increase of V4O10
evaporation ( more
Raman intensity for
reactivity studies)
• Minimization of O2,
CO2, CO formation
Monitoring evaporation by mass spectrometry
Thanks
Dr. Burkhard Ziemer
Petra Neubauer
Christian Ohde
Dr. Elke Hoppe
Gunnar Werncke
Dr. Christian Herwig