600 Catal. Sci. Technol., 2013, 3, 600--605 This journal is cThe Royal Society of Chemistry 2013
Cite this: Catal. Sci. Technol., 2013,
3, 600
Comparison of phase transfer agents in the aqueous
biphasic hydroformylation of higher alkenes
Henriette Nowothnick,
a
Anke Rost,
b
Tobias Hamerla,
b
Reinhard Schoma
¨cker,*
b
Christian Mu
¨ller
c
and Dieter Vogt*
a
The Rh-catalyzed aqueous biphasic hydroformylation with the bidentate ligand SulfoXantPhos was
investigated for different phase transfer agents (PTA). As such, polymer latices and microemulsions
formed by non-ionic surfactants were used. In general, a higher PTA concentration enhances the
reaction progress. The feasibility of catalyst recycling by simple phase separation is shown in principle.
The Rh losses are low in the surfactant system and promising for a technical approach.
Introduction
The Ruhrchemie–Rho
ˆne–Poulenc process from 1984 is the most
successful industrial catalytic process performed in an aqueous
biphasic reaction medium, which has undoubted economic and
environmental benefits. In this process propene is converted in
water to butyraldehyde (800000 tonnes per annum),
1
without
addition of any phase mediator because of the sufficient water
solubility of propene. Due to their extremely low solubility in water,
the hydroformylation of higher olefins ( ZC6) following the example
of the Rho
ˆne–Poulenc process is not applicable. Yet, due to the
clear economic benefit of a biphasic reaction mixture based on the
ease of separation of the product and the catalyst phase and easy
catalyst recycling, this is still a very challenging topic. To overcome
problems like low space time yields and mass transport inhibition
by applying (aqueous) two phase catalysis for higher olefins,
different concepts exist in the literature. For instance, fluorous
solvent systems, with specific synthesized fluorous phosphine
ligands, have been investigated in biphasic hydroformylation of
higher alkenes
2
even in continuous mode.
3
Herein, monodentate
ligands perform much better than bidentates e.g. the XantPhos
derivatives show less solubility in the fluorous solvent and there-
fore the organic phase contained high amounts of Rh as well.
4
Besides the fluorous solvents, hydroformylation reactions
have been carried out in all so-called green solvents, such as
ionic liquids
5
and supercritical CO
2
,
6
or even in solvent
combinations like IL or fluorous and scCO
27
and with a solid
support.
8–11
In all these reaction media a single phase is
formed at reaction temperature and phase separation is accom-
plished by a change of temperature in order to isolate the
product and to recycle the catalyst. Microemulsions
12,13
and
polymers as a phase mediator
14
and as a catalyst support
15
have
already been applied for the hydroformylation of short alkenes
and higher alkenes, but with monodentate ligand-based water
soluble catalyst complexes only.
16,17
Monodentate ligands have a
drawback of producing a low linear to branched (l/b) selectivity.
There exist a lot of papers well describing the advantageous
concept of biphasic catalysis in hydroformylation, but without
showing results of recycling experiments and the question of Rh
losses into the organic phase remains open sometimes.
In this paper we investigate the aqueous biphasic hydro-
formylation of 1-octene and 1-dodecene in polymer latices and
in microemulsions, respectively. These two different phase
transfer methods to increase the interface between water and
the organic phase will be discussed for their advantageous as
well as disadvantageous aspects in catalysis, phase separation
and reuse of the catalyst. The rhodium and phosphor losses
were also determined. The hydroformylation experiments were
all carried out with Rh(acac)(CO)
2
and SulfoXantPhos as a
bidentate ligand (Scheme 1).
Phase transfer agents
(a) Polymer latices
The polymer latex was synthesized by microemulsion polymeri-
zation in water with different monomers such as styrene, a cationic
styrene salt, a polyethylene glycol styrene and divinylbenzene
as a crosslinker. This procedure was already described in an
earlier contribution (Fig. 1).
14
a
Eindhoven University of Technology, Den Dolech 2, 5600 MB Eindhoven,
b
Technische Universita
¨t Berlin, Straße des 17. Juni 124-126, Secr. TC 8,
Fax: +49 30 314 79522; Tel: +49 30 314 24973
c
Freie Universita
¨t Berlin, Institute of Chemistry and Biochemistry, Berlin, Germany.
E-mail: c.mueller@fu-berlin.de; Tel: +49 30 838 54004
Received 8th September 2012,
Accepted 5th November 2012
DOI: 10.1039/c2cy20629c
www.rsc.org/catalysis
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Science & Technology
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Thereby, normal micelles are created, which remain in the
aqueous phase even at reaction temperature. This means the
system is always biphasic with an excess alkene phase (1-octene).
This behavior was studied in a glass tube under reaction
temperature and stirring up to 600 rpm. The continuous water
phase contains polymer micelles with a hydrophobic core, which
allows for enclosing the substrate alkene. The reaction takes
place in the aqueous phase at the interface of the latex by
electrostatic interaction with the catalyst. In this case, the
substrate is ‘‘transferred’’ to the water soluble catalyst complex.
For the separation of product and reuse of catalyst, the system is
cooled to room temperature. Reaction and separation take place
in an autoclave in batch mode. In principle the separation can be
carried out at any temperature.
(b) Nonionic surfactant micelles
Nonionic surfactants that are commercially available were exten-
sively investigated in the hydroformylation of 1-dodecene. The
broad phase behavior of surfactant systems to form a micro-
emulsion with excess phases (Fig. 2) was used to (i) ensure a fast
reaction progress and (ii) for fast separation at room tempera-
ture. At first, the phase behavior was studied extensively in test
tubes with a substrate and also a product mixture with different
surfactant concentrations by variation of temperature but with-
out gas pressure. After reaching the desired temperature, stirring
was stopped to await phase separation. The hydroformylation
experiments were performed at temperatures in which a water-
in-oil microemulsion (inverse micelles) with excess water phase
(2 phase) or a bicontinuous system (3 phase) can be assumed
according to the behavior in the test tubes. These systems are
characterized as media with low viscosity, low surface tension
and strongly increased interfacial area of micelles, especially
reverse micelles enclosing the water soluble catalyst in a con-
tinuous alkene phase (1-dodecene). This means that under
reaction conditions the catalyst is ‘‘transferred’’ to the substrate.
The microemulsion systems are thermodynamically stable and
their formation is reversible at any gas pressure and stirring
speed. After the reaction time, the mixture is cooled to room
temperature to give a two-phase system, where normal micelles
are stabilized in the continuous water phase with excess alkene
phase, for separating the product. It is assumed that the active
catalyst complex is quantitatively in the aqueous phase.
Results
For both systems several screening experiments were per-
formed before the determination of kinetic parameters and
limitations in order to find out the optimal reaction conditions
for the recycling experiments later. Hydroformylation experi-
ments (a) were carried out mostly at a precursor to ligand ratio
(M/L) of 1/2, whereas the hydroformylation experiments (b) were
performed mostly at a ratio of 1/4 unless otherwise mentioned
(Table 1). Comparing the water soluble ligands TPPTS and
SulfoXantPhos in biphasic hydroformylation, it can be sum-
marized that reactions with SulfoXantPhos run better at higher
temperatures ( Z100 1C), compared to the monodentate TPPTS
ligand, where high conversion is obtained under milder conditions
(80 1C),
17
i.e. comparable TOFs for both can be obtained when
higher reaction temperatures are chosen with SulfoXantPhos as
the ligand. But the major advantage of the bidentate ligand is the
much higher selectivity. The organic/water volume ratio is 2 in
Scheme 1 The resting state of the water soluble Rh(SulfoXantPhos) catalyst
complex.
Fig. 1 Microemulsion polymerization of styrene monomers (left); hydrophilic
polymer latex in the aqueous phase (right).
Fig. 2 The nonionic surfactant Marlophen NP 9 (left); phase diagram of
nonionic surfactants at a constant water-oil ratio
18
(right).
Table 1 Temperature dependencies and impact of ligand amount
T
react
Hydrof_a (after 65 h) Hydrof_b (after 3 h)
M/L Conv./Sel. (l/b) M/L Conv./Sel. (l/b)
80 1C 1/2 0.11/100 1/4 0.08/49
80 1C — — 1/4 0.22/32
b
100 1C 1/2 0.45/42 — —
110 1C 1/4 0.72/45 1/4 0.32/49
110 1C 1/2 0.95/28 1/2 0.77/1.4
a
a
4 ml of water only.
b
Marlipal 24/70 as the surfactant. Hydrof_a: 11 ml
water, 1.8 wt% latex, 11 mg Rh(acac)(CO)
2
+ 67.8 mg SulfoXantPhos,
150 mmol 1-octene (16.8 g, 23.5 ml), S/M/L = 3500/1/2, 40 bar, 600 rpm.
Hydrof_b: 20 ml water, 5 g Marlophen NP 9 (9 wt% surfactant), 12.9 mg
Rh(acac)(CO)
2
+ 158 mg SulfoXantPhos, 180 mmol 1-dodecene (30.3 g,
40 ml) S/M/L = 3600/1/4, 40 bar, 1000 rpm.
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both hydroformylation systems for the temperature dependent
measurements (entries 1 to 4). In general, the higher the reaction
temperature, the faster is the reaction progress. For the Hydrof_b
two experiments were performed at 80 1C (entries 1 and 2)
whereas in the first case a low conversion of 8% is obtained.
Here, the reaction mixture is a two phase system at reaction
temperature which is characterized by micelles formed in the
aqueous phase with a hydrophobic core and an excess oil phase.
In the second case another nonionic surfactant was chosen.
With Marlipal 24/70 a three phase system is formed at reaction
temperature. This three phase system consists of excess water
and oil phases and a middle phase which comprises of dodecene,
water and a high concentration of the catalyst that allows for a
faster reaction progress. In fact, surfactants with a lower degree of
ethoxylation n(n= 7 for Marlipal 24/70, see Fig. 2 for comparison)
form three phase systems at lower temperatures so that the
hydroformylation reactions can be carried out with high rates
also at milder reaction temperatures. In the case of Hydrof_a
milder reaction conditions (see Table 1, column 3) lead to a
higher selectivity, although the reaction cannot be completed to
full conversion e.g. at 80 1C. When the reaction is carried out at
110 1C, the selectivity decreases in time, due to the isomerization
of 1-octene, more branched products are obtained. When we
compare both hydroformylation reactions at the same M/L and
temperature (entry 4), the calculated l/b ratios are similar but they
seem to decrease at high conversions. It should be considered
that lower l/b ratios could be the result of decoordination of one
phosphorus ligand, which could be proven by in situ NMR.
Surprisingly by comparing entry 5, a M/L ratio of 1/2 leads to a
dramatic decrease of the linear aldehyde but parallel to a very fast
reaction (especially for Hydrof_b), which shows that the ligand
was not strongly coordinated to the metal. The selectivity of 1.4
only is comparable to l/b ratios achieved with monodentate
ligands or without ligand. For low M/L ratios, preformation of
the catalyst is essential. The hydroformylation with polymer
latices results in higher selectivities because the catalyst was
preformed first (see Experimental). For hydrof_a it was observed
that under same conditions but higher excess of ligand
(M/L = 1/4), a TOF value of 65 h
1
was obtained instead of a
TOF = 126 h
1
at M/L = 1/2, which is about half the value
obtained in the first experiment, showing that the reactions are
not mass transport limited but kinetically controlled by the
catalyst. On the other hand, the l/b ratio can be increased to 45
by a higher excess of ligand, which can be increased further, when
takingintoaccountthatinindustryanexcessof60forthe
monodentate system Rh–TPPTS is used. Another reason for the
much higher excess in the industrial process is to keep the metal
quantitatively in the aqueous phase, which is an important
economical aspect for the recycling that will be discussed later.
In a further study, the amount of phase transfer agent was varied
(seeFig.3and4).Alowamountofthelatexpolymerissufficient
to facilitate the reaction (Fig. 3), whereas the surfactant containing
approach requires higher concentrations. Micelles have to be
formed in order to obtain a noticeable reaction acceleration and
to allow phase separation after the reaction. Interestingly, in Fig. 4
there is no strong influence of surfactant concentration noticeable
for 8 and 10 wt% as soon as enough micelles are available for
the transfer of the catalyst to the alkene phase. For the recycling
experiments 1.1 wt% of the latex polymer (Fig. 5) was chosen
Fig. 3 Variation of latex concentration: 23.5 ml 1-octene, 11 ml water,
S/M/L = 3500/1/2, 40 bar, 1101C, 600 rpm.
Fig. 4 Variation of surfactant concentration: 40 ml 1-dodecene, 4 ml water,
S/M/L = 3600/1/4, 40 bar, 1101C, 1000 rpm.
Fig. 5 Recycling experiment with 23.5 ml 1-octene, 1.1 wt.-% polymer, 11 ml
water, M/L/S = 1/2/3500, 55 bar, 1101C.
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although the reaction progress is not the fastest but the lower
amount of the polymer will have advantages in separating the
phases. In the microemulsion approach (Fig. 6), 10 wt% of
nonionic surfactant and 11 wt% of aqueous phase was chosen,
although the reaction is much faster when 36 wt% of aqueous
phase is used (wt% referred to the reaction mixture). It is
important to mention that for the recycling experiments in
microemulsions, the temperature was adjusted again to 80 1C
for each run, after the reaction slowed down at 110 1C. With
this measure the advantageous three phase state of the reaction
mixture was maintained. Therefore, the graphs are twisty.
Furthermore, it should be mentioned that the dead time is just
the time overnight (not the time for separating the phases) in
which no reaction could be performed due to safety reasons.
At a first glance both graphs show that after 80 hours four
cycles were obtained for the use of the surfactant micelles
whereas in the case of the polymer latex the second cycle could
be finished at comparable conversions. The main reasons for
this are the different concepts of phase transfer. The catalyst
transferred to the alkene phase via reverse micelles experiences
a much higher local olefin concentration than the catalyst at
the latex particles which are only swollen with alkene. In general,
the TOFs for both series of experiments decrease from run to
run (Table 2). Thereby, it should be noted that all TOF values
are calculated at a conversion of 20%. The TOFs in the recycling
experiments of the latex polymer are lower than in the single
runs, because a lower amount of latex polymer was used
here. Comparing these values with literature data, where
CTAB and RhCl(CO)(TPPTS)2-BISBIS,
19
an ionic liquid with
Rh-SulfoXantPhos
20
or amphiphilic diphosphines
21
were applied,
our TOFs are comparable or even higher. Furthermore, the yield of
n-nonanal for Hydrof_a was determined only at the end of each
run, no sampling during the reaction was possible. Interestingly,
the selectivities for Hydrof_b did not change after the first run,
whereas in the case of Hydrof_a a significant decrease was
obtained. Both observations were made in the temperature depen-
dent experiments and they support the hypothesis that lower
selectivities are the result of the parallel isomerization which
provides more internal alkenes that react with branched aldehydes
when the hydroformylation leads to higher or complete conver-
sions. From this point of view it would be interesting to see if the
selectivities in Hydrof_b are similar at complete conversions.
Finally, the organic phases of the recycling experiments were
analyzed for Rh and P leaching by ICP. The results are summarized
in Table 3 with the concentration of rhodium and phosphorus in
the organic phase and the percentage of this concentration
referred to the initial content of the catalyst in the reaction
mixture. It can be seen that the hydroformylations with the
polymer latex as a phase transfer agent have much higher losses
than the hydroformylation reactions carried out with the nonionic
surfactant micelles formed from Marlophen NP 9. The value after
the first run of 130 ppb Rh only that leached into the product
phaseisverylowandwellintherange of technical feasibility.
1
Considering all measured aqueous phases the average can be
found at approx. 70 ppb only, which is in the range of the reported
ones (less than 1 ppm).
19
The higher leaching in the first run could
be caused by traces of XantPhos. But the losses of surfactant into
the organic phase should also be taken into account. Especially in
the first run a non-negligible amount could be detected. Proposals
for a solution are under investigation. Furthermore, the conversion
should be at least 90%, otherwise the substrate and the aldehyde
must be separated by distillation which is detrimental for the long
chain aldehydes due to thermal instabilities.
Conclusions
Two different methods of phase transfer were tested in the
biphasic hydroformylation of higher alkenes. In method a
(Fig. 7), the alkene is enclosed by the polymer micelles and is
transferred to the aqueous catalyst phase. In method b (Fig. 8),
the water soluble catalyst is enclosed by the micelles formed
by nonionic surfactants and is transferred to the alkene.
Fig. 6 Recycling experiment with 40 ml 1-dodecene, 4 g (10 wt.-%) Marlophen
NP 9, 4 ml water, M/L/S = 1/5/3600, 40 bar, 1101C.
Table 2 Comparison of recycling experiments
1st run 2nd run 3rd run 4th run
Hydrof_a l/b 50 24 12 12
Yield [%] 58 36 43 24
TOF [h
1
]65 37 38 25
Hydrof_b l/b 99 49 49 49
Yield [%] 42 34 34 29
TOF [h
1
] 266 192 173 152
Hydrof_a: yield and selectivities estimated after the reaction was
stopped. Hydrof_b: yield and selectivities estimated after 8 hours of
each cycle.
Table 3 Rhodium and phosphor losses in the organic phase
Hydrof_a (latex) Hydrof_b (surfactant)
Rh ppm/(%) P ppm/(%) Rh ppm/(%) P ppm/(%)
6.10/(3) 7.05/(3.1) 0.13/(0.10) 1.69/(0.43)
1.74/(1) 4.60/(2) 0.04/(0.03) 1.07/(0.27)
0.75/(0.4) 5.92/(2.6) 0.05/(0.04) 0.87/(0.22)
0.50/(0.3) 6.38/(2.8) 0.05/(0.04) 0.73/(0.19)
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The chosen reaction conditions for both systems are compar-
able, as well as the calculated selectivities and TOF values for
the single batches. The commercially available technical grade
surfactants perform well enough for biphasic hydroformyla-
tion, which means a fast reaction rate and easy phase separa-
tion, since the phase behavior was investigated very well. The
fast progress is observed because the water droplets, including
the catalyst, are stabilized in the organic phase, so that no mass
transfer limitation is assumed (Fig. 8). The hydroformylation
with polymer latices is also not mass transfer limited, but much
slower, because the alkene has to be enclosed by the latex
particles (Fig. 7) and transferred into the aqueous catalyst
phase which is assumed to result in a much lower alkene
concentration than in the alkene phase with the catalyst inside
the reverse micelles. In the recycling experiments we could
show that a similar reaction progress was obtained. In the case
of using surfactants as phase transfer agents also much lower
Rh and P losses were estimated by ICP because of the oil-in-
water microemulsion as the continuous phase that is obtained
for the separation of the organic product phase. By the use of
the polymer latex, higher values for Rh and P were detected in
the organic phase. It can be concluded that the polystyrene
latices are not stable especially against high temperatures and
therefore release catalyst and coagulated material into the
organic phase. The property of surfactants, especially their
thermodynamic stability and reversible broad phase behavior,
makes them an unprecedented material for biphasic catalysis.
One has to say that in biphasic hydroformylation with bidentate
ligands where higher temperatures are required, polymer
latices made of polystyrenes are not suitable as phase transfer
agents. However, there is potential for this approach with other
types of polymers, showing higher temperature and shear
resistance.
Experimental
(a) Hydroformylation with latex polymers as a phase mediator
The synthesis of polystyrene based latices by microemulsion
polymerization has been described in an earlier contribution.
14
The biphasic hydroformylation experiments of 1-octene were
performed in a stainless steel autoclave, equipped with a
gas-impeller stirrer and a dropping funnel. The precursor
Rh(acac)(CO)
2
(11 mg, 0.043 mmol) and SulfoXantPhos
(67.8 mg, 0.086 mmol), giving a catalyst/ligand ratio of 1 : 2,
was stirred in 5.5 ml water and 5.5 ml latex (containing 320 mg
solid content) for 1 h. The autoclave was charged with the
catalyst solution and preformed at reaction temperature and
40 bar syngas for 1 h at 600 rpm. After that, the substrate
1-octene (150 mmol, 16.8 g, 23.5 ml, 60 wt% organic phase) was
added by a dropping funnel (ratio catalyst/substrate of 1/3500)
and the conversion was measured by the gas uptake and via GC
analysis.
For the recycling experiments, the reaction was stopped at a
certain time by cooling to room temperature and venting the
system. Argon was purged through the reactor while the organic
phase was taken out (app. 20 ml) and analyzed via GC and ICP
measurements. To start a new cycle, fresh 1-octene was added
into the dropping funnel. After a short preformation time
under reaction conditions (10 minutes), the substrate was
released into the autoclave by opening the valve.
(b) Hydroformylation with nonionic surfactants
All hydroformylation experiments were carried out in a 100 ml
stainless steel autoclave from Premex connected to a 300 ml gas
reservoir. The syngas (1 : 1 mixture) was purchased from Air
liquide and dispersed by a gas dispersion stirrer. All basic
chemicals were purchased from Roth or Sigma Aldrich and
used without further purification. In a general experiment the
autoclave was filled with 1-dodecene (180 mmol, 30.3 g, 40 ml)
and the nonionic surfactant Marlophen NP 9 (4 g, 10 wt%).
Then the reaction mixture was deoxygenated by repeated
evacuation and nitrogen purging. Then the catalyst solution
(0.05 mmol, 12.9 mg Rh(acac)(CO)
2
and 0.25 mmol, 198 mg
SulfoXantPhos) in 4 ml water was added to the reaction mixture
(catalyst/ligand/substrate = 1/5/3600) under a nitrogen atmosphere
Fig. 7 Normal micelle enclosing the alkene.
Fig. 8 Inverse micelle enclosing the water-soluble catalyst.
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over a dosing valve. The autoclave was heated by an oil bath
from Huber (CC3) and stirred at 1000 rpm. The initial pressure
of syngas was adjusted to 40 bar. At this pressure the systems
contain initially 270 mmol of CO and H
2
each. During the
reaction the pressure decreases according to the conversion of
the syngas, at full conversion to 15 bar. Samples were taken at
several time intervals and analyzed by gas chromatography.
After the reaction was stopped the autoclave was cooled to room
temperature, depressurized and flushed with nitrogen. For a
next run, new 1-dodecene (40 ml) was filled into the 100 ml
stainless steel reactor, after separation of the organic phase
from the aqueous catalyst and surfactant containing phase.
A new run was started after heating to 110 1C and addition of
syngas up to 40 bar.
ICP-OES. The organic phases were analyzed for rhodium and
phosphor losses. Therefore, a certain amount of organic phase
has been made accessible for the ICP/OES machine by addition
of acids and the use of a microwave (from CEM). In the case of
the hydroformylation reactions that were carried out in micro-
emulsions, the whole organic phase was incinerated (for con-
centrating the Rh and P values) and then the residue was
dissolved in acids and pre-treated by a microwave before the
measurements.
Acknowledgements
This work has been funded by NANO-HOST (FP 7 programme)
(H.N.). We thank Ton Staring for technical support. A.R. and T.H.
thank the DFG (this work is part of the Sonderforschungsbereich/
Transregio 63), Umicore for the rhodium catalyst and Sasol for
the surfactants. The authors thank Astrid Mu
¨ller-Klauke for the
ICP measurements.
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