A bulky phosphite modified rhodium catalyst for efficient hydroformylation of disubstituted alkenes and macromonomers in supercritical carbon dioxide

Article abstract of DOI:10.1039/c2cy20867a

The hydroformylation of disubstituted alkenes and related macromonomers in supercritical CO₂ is demonstrated. Higher turnover frequencies were observed for the 1,2-disubstituted alkenes than for the 1,1-disubstituted alkenes. The turnover frequency for poly(styrene) macromonomer hydroformylation compares well with that observed for cyclohexene. The turnover frequency observed for poly(methyl methacrylate) macromonomer hydroformylation is considerably lower than that observed for methyl methacrylate. Unprecedented turnover frequencies are observed in comparison with previous studies where CO₂ has been applied as a solvent. This is achieved using rhodium modified with a readily available bulky phosphite ligand without the need of ligand modification to improve solubility in supercritical CO₂.

Full text of DOI:10.1039/c2cy20867a

Catalysis
Science & Technology
View Article Online
View Journal
PAPER
A bulky phosphite modified rhodium catalyst for
efficient hydroformylation of disubstituted alkenes
Cite this: DOI: 10.1039/c2cy20867a
and macromonomers in supercritical carbon dioxide†
Ard C. J. Koeken*z and Niels M. B. Smeetsy
The hydroformylation of disubstituted alkenes and related macromonomers in supercritical CO2 is
demonstrated. Higher turnover frequencies were observed for the 1,2-disubstituted alkenes than for
the 1,1-disubstituted alkenes. The turnover frequency for poly(styrene) macromonomer
hydroformylation compares well with that observed for cyclohexene. The turnover frequency observed
for poly(methyl methacrylate) macromonomer hydroformylation is considerably lower than that
observed for methyl methacrylate. Unprecedented turnover frequencies are observed in comparison
with previous studies where CO2 has been applied as a solvent. This is achieved using rhodium modified
with a readily available bulky phosphite ligand without the need of ligand modification to improve
solubility in supercritical CO2.
Received 11th September 2012,
Accepted 19th December 2012
DOI: 10.1039/c2cy20867a
www.rsc.org/catalysis
material,11 to apply a supported liquid phase (SPLC),12 or to
use membranes13 to achieve catalyst recovery.
Introduction
Hydroformylation, which is the conversion of an alkene, hydrogen,
and carbon monoxide into an aldehyde, is a reaction of significant
interest for academia as well as industry.1 Current research on
hydroformylation reactions focuses mostly on the application of
rhodium, cobalt, iridium and platinum catalysts.2 Generally, the
use of rhodium modified with a phosphorus ligand yields the
highest reaction rates and selectivity in hydroformylation
reactions.3 However, as rhodium is an expensive transition metal
a significant research effort is dedicated to maximizing catalyst
efficiency and improving recovery methods.
A promising approach to enhance catalyst recovery is to use
multiphase systems employing fluorous solvents,4 water,5 ionic
liquids,6 or supercritical fluids (SCF)7 in which a modified
homogeneous catalyst preferentially dissolves while the
product preferentially partitions into a second liquid phase.8,9
Other approaches include immobilizing the homogeneous
catalyst onto either a soluble10 or an insoluble support
Carbon dioxide, which has low toxicity and is inflammable,
can be applied as a solvent for homogeneous catalysis and it
allows for the creation of a single homogeneous supercritical
reaction system.14,15 A supercritical fluid has liquid like
densities in combination with gas like diffusivities, and permanent
gases (e.g. H2 or CO) can be dissolved in high concentrations in
such a phase, which counteracts possible mass transfer limita-
tions.14 Therefore, as a result of its characteristics supercritical
carbon dioxide (scCO2) can have a beneficial effect on catalyst
activity and has received much attention as a solvent for homo-
geneously catalysed hydroformylation.16 However, the application
of scCO2 as a solvent for homogeneous catalysis is limited by the
poor solubility of many catalysts in carbon dioxide-rich reaction
mixtures.17 The phosphorus ligands of a catalyst can be chemically
modified in order to improve catalyst solubility.18–22 In particular,
attaching perfluoroalkyl groups on the ligands of a catalyst appears
to be an effective means to ensure sufficient catalyst solubility in a
carbon dioxide rich reaction medium.23–31
Recently, it has been demonstrated that under certain reaction
conditions monodentate phosphorus ligand modified rhodium
Eindhoven University of Technology, Department of Chemical Engineering and
Chemistry, Den Dolech 2, Postbus 513, 5600 MB Eindhoven, The Netherlands
† Electronic supplementary information (ESI) available. See DOI: 10.1039/ catalysts can be used in scCO2 without the need for additional
catalyst modification.32 The apparent turnover frequency (TOF)
obtained using the tri(2,4-di-tert-butylphenyl) phosphite (L1)
c2cy20867a
‡ Current address: Dow Benelux BV, Herbert H. Dowweg 5, 4542 NM Hoek,
Netherlands. E-mail: ackoeken@dow.com
modified catalyst was considerably higher than that obtained using
§ Current address: McMaster University, Department of Chemical Engineering,
unmodified
or
tris(3,5-bis[trifluoromethyl]phenyl)phosphine
1280
Main
Street
West,
Hamilton,
Ontario,
Canada.
E-mail:
nmbsmeets@gmail.com
modified rhodium.32 The high activity of the L1 modified catalyst
c
This journal is The Royal Society of Chemistry 2013
Catal. Sci. Technol.

View Article Online
Paper
Catalysis Science & Technology
makes this rhodium complex a promising alternative for the 1,1- or 1,2-disubstituted CQC double bond. The disubstituted
hydroformylation of more sterically hindered double bonds. CQC double bond, which is formed through the CCTP-mediated
Recently, this has been successfully demonstrated in the free-radical polymerization of monomers such as styrenics and
hydroformylation of poly(styrene) and poly(methyl methacrylate) methacrylates, can also be converted into an aldehyde by hydro-
macromonomers performed in scCO2.33 scCO2 swells the macro- formylation.33 The aldehyde functional group allows for a number
monomer phase, reduces its viscosity and thus facilitates a good of further transformations including reduction to alcohols, oxida-
contact between the CQC double bonds in the macromonomer, tion to carboxylic acids, and reductive amination.48
the rhodium catalyst, CO and H2. Furthermore, although this is
In this paper we report the hydroformylation of sterically
outside the scope of the current paper, scCO2 can be used to extract hindered alkenes and macromonomers in the presence of
the catalyst and other possible solvent impurities from the supercritical carbon dioxide. We make a comparison of the
macromonomer phase.
observed reaction rates and selectivities for the variety of
Macromonomers are relatively low molecular weight substituted CQC double bonds. To the best of our knowledge
polymers (B103 to 104 g molꢀ1) containing a polymerisable few reports exist on the hydroformylation of disubstituted
vinyl o-end group.34 Due to the vinyl unsaturation, macro- alkenes like methyl methacrylate, 2-octene, a-methylstyrene,
monomers can be (co)polymerised to synthesize diverse polymeric cyclohexene, or poly(styrene) and poly(methyl methacrylate)
structures, e.g. graft, brush and comb architectures.35–38 Alterna- macromonomers using carbon dioxide as a solvent.
tively, functionalization of the unsaturated end group enables
synthesis of supramolecular structures by, for example, click-
Results and discussion
chemistry.39 Catalytic chain transfer polymerization (CCTP) is an
efficient technique to synthesize well-defined macromonomers First, the hydroformylation of disubstituted alkenes is
using free-radical polymerization chemistry.40–47 The use of only discussed. In Scheme 1 the hydroformylation of styrene (1),
ppm levels of low-spin cobalt(II) complexes ensures good molecular a-methylstyrene (3), methyl methacrylate (5), cyclohexene (7),
weight control. Additionally, when using cobalt(II) complexes and 2-octene (9a) is presented. An overview of the hydroformylation
as chain transfer agents the resulting polymer product has a conditions and results in terms of the TOF, conversion and
Scheme 1 Hydroformylation of styrene, 1, a-methyl styrene, 3, methyl methacrylate, 5, cyclohexane, 7, and 2-octene, 9a.
c
Catal. Sci. Technol.
This journal is The Royal Society of Chemistry 2013

View Article Online
Catalysis Science & Technology
Paper
a
Table 1 Main results of hydroformylation of 1, 3, 5, 7, and 9a in scCO2
Amount
[mmol]
TOF
tr
[h]
Conversionb
[%]
Selectivityb
[%]
Substrate
[103 molaldehyde molRhꢀ1hꢀ1
]
2a
14
4a
96
6a
35
8a
99.6
10a
3
2b
85
4b
3
6b
50
8b
0.4
10b
52
2c
1
4c
1
6c
15
1c
3
54.4
54.3
58.8
55.7
55.7
27
1.0
100
99
0.13
0.88
0.40
6.6
24.0
5.0
6.0
2.0
5
99
7
96
10c
36
10d
8
9ad
100
a
Reaction conditions: 90 1C, Vreactor = 0.1083 L, CO2 = 1.4 mol, CO = 0.109 mol, H2 = 0.109 mol, [Rh(CO)2acac] = 5.3 ꢁ 10ꢀ5 mol (acac:
acetylacetonate), Ligand L1 = 5.3 ꢁ 10ꢀ4 mol. Conversion of substrate and the selectivity for the respective products were determined by
b
c
calibrated GC-analysis of the samples taken from the high pressure reactor. In the initial stage of the reaction the medium temperature increased
d
to 97 1C as a result of the high reaction rate in combination with the exothermic reaction enthalpy of hydroformylation. Selectivity towards
9c + 9d was 1%. The main isomerization product was 9c.
selectivity for the hydroformylation of 1, 3, 5, 7, and 9a are collected several orders of magnitude lower than the TOF found for the
in Table 1. For all the substrates collected in Table 1 the hydro- hydroformylation of 1.57 Indeed, the rate of conversion of 3 is
formylation proceeded to full conversion with a high chemo- approximately 2 orders of magnitude less than the TOF found
selectivity towards the respective hydroformylation products for 1. Approximately 24 h of reaction was needed to completely
without any induction phenomena. Although it could not be convert 3 into the corresponding aldehydes (Fig. 1b). On the
confirmed visually, the reaction mixtures were expected to be a other hand, for 3 the selectivity is 96% for the linear aldehyde
single phase based on the concentration of reactants and products product 4a, while for 1 the selectivity towards the linear
found in the samples.49 Furthermore, the conversion with time aldehyde 2a is only 14%. This difference in the reaction rate
profile coincided closely with the decrease in pressure over time. and selectivity between the hydroformylation of 1 and 3 has
Further discussion on the phase behaviour of the reaction mixtures also been found by Lazzaroni and coworkers in benzene (as the
is provided in the ESI.†
Table 1 shows that the hydroformylation of 1, which is the addition of any phosphorus ligands.58,59
least substituted alkene (R1 = H and R2 = Ph) in the series 1, 3, 5, 5 is also a 1,1-disubstituted alkene (R1 = Me and R2
solvent) and using [Rh4(CO)12] as the catalyst precursor without
=
7, and 9a, proceeded at the highest initial rate (TOF) of COOCH3), but it is, however, structurally quite different from 3.
approximately 2.7 ꢁ 104 molaldehyde molRh
h
ꢀ1. In Fig. 1 the It can be seen from Table 1 that the production distribution
ꢀ1
concentration–time profiles for the hydroformylation of 1, 3, 5, from the hydroformylation of 5 differs considerably from that
7, and 9a are shown. Fig. 1a shows that for 1 nearly complete of 3. Compared to 3, the selectivity has shifted from the linear
conversion and a selectivity of 85% were obtained for the to the branched aldehyde (50%) and a significant amount of
branched aldehyde product 2b after 3 minutes of reaction.
hydrogenation side-product is formed (15%). The formation of
Several researchers have investigated the hydroformylation the hydrogenation side-product was negligible in the hydro-
of 1 in CO2 as a solvent.25,50–56 For example, Pedros obtained a formylation of 1 and 3. Moreover, the initial TOF found for the
´
ꢀ1
TOF of approximately 45 molaldehyde molRh hꢀ1 at 80 1C and hydroformylation of 5 (879 molaldehyde molRhꢀ1 hꢀ1) is approxi-
20 MPa total pressure with a P(C6H4-4-OCH2C7F15)3 modified mately 7 times higher than the TOFꢀ1found for the hydro-
rhodium catalyst.56 This is significantly lower than the TOF formylation of 3 (126 molaldehyde molRh
h
ꢀ1).
obtained here (2.7 ꢁ 104 molaldehyde molRh
h
ꢀ1) for the L1
Few literature reports discuss the differences in reaction rate
ꢀ1
modified rhodium catalyst. Furthermore, the selectivity for the and selectivity between the rhodium catalyzed hydroformyla-
branched product we have obtained (85%) and the overall tion of 3 and 5. Similar to our results, Cornelissen found higher
selectivity for aldehydes with the L1-rhodium catalyst was conversions for the hydroformylation of 5 than for 3 when
significantly higher than found by Pedros et al. The initial using diphosphorus ligand modified rhodium catalysts.60 In
´
TOF reported here is unprecedentedly high in comparison with addition, it appears that the difference in the hydroformylation
TOFs reported by others for the hydroformylation of 1 in product distribution for 3 and 5 is comparable to the literature
supercritical carbon dioxide.
data. For 3 generally the linear product 4a is preferentially
Compared to 1 (styrene), 3 (a-methylstyrene) has an addi- formed under hydroformylation conditions,58 while for 5 the
tional methyl substituent on the carbon which also carries the selectivity towards the linear or branched aldehyde can
phenyl substituent. Compared to 1, 3 possesses a carbon atom vary significantly with varying temperature, pressure, or
that is di-substituted (R1 = Me and R2 = Ph). It is expected that catalyst precursors.61–63 However, it must be noted that the
due to the more sterically hindered 1,1-disubstituted double hydroformylation of 3 has not been as widely studied as the
bond a TOF obtained for the hydroformylation of 3 could be hydroformylation of 5.
c
This journal is The Royal Society of Chemistry 2013
Catal. Sci. Technol.

View Article Online
Paper
Catalysis Science & Technology
Fig. 1 Conversion–time profiles for the hydroformylation of 1 (a), 3 (b), 5 (c), 7 (d) and 9a (e) in scCO2.
The hydroformylation of cyclohexene (7), a 1,2-disubstituted isomerized into 9b to 9d. Consequently, a mixture of linear and
alkene, with L1-Rh resulteꢀd1in an initial hydroformylation rate branched aldehydes is expected for the hydroformylation of 9a.
of 403 molaldehyde molRh
hꢀ1 (Table 1) and the reaction 9a was hydroformylated at a considerably higher overꢀal1l rate
proceeded with a high chemoselectivity (>99%) for the only than 7, 6.6 ꢁ 103 compared to 403 molaldehyde molRh hꢀ1
,
hydroformylation product 8a. van Rooy et al. found a comparable respectively. In two hours reaction time 9a is completely con-
result for the hydroformylation of 7 in toluene using rhodium verted into the aldehydes 10a to 10d (Fig. 1e). The presence of
modified with tris(2-tert-butyl-4-methylphꢀen1 yl) phosphite.64 They 10a and 10d is a result of the hydroformylation of the isomer-
reported a TOF of 788 molaldehyde molRh hꢀ1 using an initial ization products 9b and 9c, respectively. Only traces of 9b were
concentration of 0.91 mol Lꢀ1 at 90 1C. If it is thus assumed that detected by GC analysis. Nevertheless a significant selectivity of
the hydroformylation kinetics are first order in 7, our results in 3% for the linear aldehyde 10a was obtained. 9c was the main
scCO2 (with an initial concentration of 0.5 mol Lꢀ1) then closely isomerization product of 9a, observed during hydroformylation
resemble the results reported by van Rooy et al. On the other (Table 1). In the literature hydroformylation of 9a to the linear
hand the TOF found for hydroformylation of 7 here in scCO2 was product 10a is often used to demonstrate the performance of
higher than the TOF found with toluene as solvent and L1-Rh as Rh modified with bidentate phosphorus ligands. For example,
ꢀ1).65
applying a Rh-diphosphorus catalyst for hydroformylation of 9a
ꢀ1
catalyst at 90 1C (TOF of 214 mol7 molRh
h
As a substrate 2-octene (9a) is similar to 7, in the sense that resulted in a selectivitꢀy1to 10a of approximately 56% at a TOF of
both 7 and 9 are 1,2-disubstituted alkenes. Both 7 and 9a 150 molaldehyde molRh hꢀ1 66
.
are subjected to isomerization under the hydroformylation
Generally, the hydroformylation rates of 1, 3, 5, 7, and 9a we
conditions used. However, whereas isomerization of 7 does have found using the L1-Rh catalyst in carbon dioxide compare
not change the substitution on the double bond, 9a can be favourably to the hydroformylation rates and conversions
c
Catal. Sci. Technol.
This journal is The Royal Society of Chemistry 2013

View Article Online
Catalysis Science & Technology
Paper
Scheme 2 Hydroformylation of CCTP derived macromonomers of styrene 11
and methyl methacrylate 13.
reported by others at similar reaction temperatures using
rhodium catalysts and either organic liquids or carbon dioxide
as a solvent. However, direct detailed comparisons of initial
reaction rates reported here for the L1-Rh catalyst in CO2 with
reaction rates or selectivity values found by others are often
difficult, because of the variation in rhodium catalysts used and
the differences in reactant concentrations and reaction condi-
tions. Nevertheless, here the effectiveness of the combination
of the L1-Rh catalyst and carbon dioxide as a solvent for the
hydroformylation of sterically hindered alkenes is illustrated.
Previously, it has been demonstrated that it is possible to
hydroformylate poly(styrene) 11 and poly(methyl methacrylate)
13 macromonomers with high conversion and selectivity
(Scheme 2).33 It is now interesting to take a closer look into
the kinetics of the hydroformylation of 11 and 13 and establish
how this compares to the hydroformylation rates of 3, 5, 7, or 9a.
Fig. 2 (a) Pressure–temperature history for hydroformylation of poly(styrene)
(11) in CO2. Conditions: 25.5 g macromonomer, 0.011 mol unsaturated end
groups, 52 mmol Rh, 0.52 mmol L1, 75 mmol CO, 73 mmol H2, 1.3 mol CO2.
Conversion = 100% (based on 1H-NMR), selectivity = 87% (based on estimation
by MALDI-ToF-MS); (b) pressure–temperature history for hydroformylation of
poly(methyl methacrylate), 13, in CO2. Conditions: 15.5
g macromonomer,
0.022 mol unsaturated end groups, 49 mmol Rh, 0.52 mmol L1, 78 mmol CO,
81 mmol H2, 1.4 mol CO2. Conversion = 85% (based on 1H-NMR), selectivity =
91% (based on estimation by MALDI-ToF-MS).
The macromonomers 11 and 13 are synthesized by the pressure–temperature histories including additional conditions
cobaloxime-mediated catalytic chain transfer polymerization and results of the hydroformylation of 11 (Fig. 2a) and 13
of styrene and methyl methacrylate. The number-average mole- (Fig. 2b) are given. It can be seen that in the case of 13 the
cular weight (Mn) of macromonomers 11 and 13 was deter- pressure change was greater than the pressure change for 11.
mined by size exclusion chromatography (SEC) to be 700 and This can be attributed to a greater number of CQC double
2400 g molꢀ1, which corresponds to approximately 7 and 23 bonds hydroformylated in the case of 13. The total pressure in
repeating units. Furthermore, the macromonomers possess a the hydroformylation of the macromonomers was set to approxi-
vinyl unsaturation at the o-end group as determined from mately 40 MPa. This pressure was close to the total pressure used
1H-NMR analysis. When compared to their low molecular for the hydroformylation of the other 1,2-disubstituted alkenes
weight analogues 1 and 5, the macromonomers differ structurally, in this study. Note, however, that due to the relatively high
both in terms of the number of repeating units and, in the case molecular weight of the macromonomers a single phase super-
of the poly(methyl methacrylate) macromonomer, the sub- critical reaction mixture was not anticipated.
stitution on the double bond. When compared to 5, for
The corresponding yield–time histories were obtained based
poly(methyl methacrylate) macromonomers R2 is similar on the following assumptions: (1) that the maximum pressure
(R2 = COOCH3), but R1 differs. For poly(styrene) macro- corresponded to zero conversion and conversion is negligible
monomers R1 = H and R2 = Ph are the same as 1. The difference during heating and pressurizing the reactor, (2) that hydroge-
in the position of the double bond in the poly(styrene) and nation as a side reaction did not influence the pressure
poly(methyl methacrylate) macromonomers originates from significantly, (3) that the pressure correlates linearly to the
the CCT process.47
aldehyde yield67 and (4) that the pressure just before stopping
As a result of the relatively high viscosity of the products and the reaction by cooling corresponds to the yield calculated from
reactants, it was unpractical to sample from the reaction 1H-NMR and MALDI-ToF-MS analysis. The selectivity for the
mixture during hydroformylation as was done for the hydro- different aldehydes was estimated from MALDI-ToF-MS analysis.
formylation of 1, 3, 5, 7 and 9a. The experimental setup allows Note that this was an estimation as differences in ionization
for online monitoring of the pressure in the reactor, which efficiency between the hydrogenated and hydroformylated
allows for an estimate of the aldehyde yield.67 In Fig. 2 the macromonomers can be expected.68–70 Here, it was assumed
c
This journal is The Royal Society of Chemistry 2013
Catal. Sci. Technol.

View Article Online
Paper
Catalysis Science & Technology
Fig. 4 The TOF as a function of conversion for 3 (a-methylstyrene) n, 5 (methyl
methacrylate) &, 7 (cyclohexane) J, 9a (2-octene) x. For 9a the shown TOF
values are divided by 10.
Fig. 3 Yield–time history for the hydroformylation of 11 and 13.
that they were the same. Based on the above assumptions eqn (1)
(Experimental section) can be used to convert the reactor
pressure into aldehyde yield. Fig. 3 shows the yield–time histories
for the hydroformylation of 11 and 13.
Table 2 Comparison of the turnover frequencies (TOF)
The apparent initial TOFs for the hydroformylation of 11
and 13 were estimated by taking the average of the TOF values
Conversion Amount CO
Substrate [%]
H
Estimate TOFꢀ1
[mmol]a [mmol]a [mmol]2 [molald molRh hꢀ1
]
a
11b
3e
0–30
79.7
81
11c
11
11
11
11
22c
22
22
22
22
75
67
69
65
68
78
77
78
76
79
73
65
61
65
68
81
76
72
75
79
121d
49
184
121
1043
77d
up to
a conversion of 30%. For the poly(styrene) and
poly(methyl methacrylate) macromonomers a TOF of 121 and
77 molaldehyde molRhꢀ1 hꢀ1 was observed, respectively. Note that
these TOF values likely are conservative estimates. The rates for
heating and pressurizing the reactor were relatively high (see
the Experimental section) but it was likely that there was some
conversion of macromonomers before the desired reaction
temperature and pressure were reached.
5e
7e
80
9ae
13b
3e
80.3
0–30
59.5
62
60.5
60.5
85
5e
340
219
2701
7e
9ae
a
b
Comparing the TOFs observed for the hydroformylation of 3,
5, 7, and 9a with the TOFs found for the hydroformylation of 11
and 13 is not straightforward, because, based on a homo-
geneous reaction phase, the initial concentration of CQC
double bonds differs between the experiments with 3 to 9a
and 11 and 13. However, a useful comparison can be made by
considering the TOF–conversion plots given in Fig. 4 for the
hydroformylation of 3, 5, 7, and 9a which were derived for the
respective conversion–time plots (Fig. 1). In Table 2 the initial
TOFs found for the hydroformylation of 11 and 13 are compared
with the TOFs observed for 3, 5, 7, and 9a at the alkene reactant
concentrations comparable to the initial concentrations of 11
and 13. In this manner the most appropriate comparison of the
TOFs can be made.
Values at the conversion level shown in the second column. See
c
Fig. 2 for reaction conditions. The amount of unsaturated end groups
in mol calculated based on the number-average molecular weight of the
prepared macromonomer. Average values for the conversion range up
to 30%. See Table 1 for the reaction conditions.
d
e
h
ꢀ1) on the other are comparable.
ꢀ1
(B70 molaldehyde molRh
The substitution pattern on the double bond for 11 and 7 is
similar which can explain the similarity in the hydroformyla-
tion rate. The similarity in TOF between 13 and 3 is not
expected as these substrates are structurally quite different.
One would expect the TOF for 13 to be more similar to that of 5.
Likely, as a result of the additional steric hindrance the hydro-
formylation rate of 13 is significantly lower than that found for 5.
Generally, 1,2-disubstituted alkenes are hydroformylated
with a higher rate than 1,1-disubstituted alkenes which is in
accordance with the observed trend.57 Considering the TOFs
given in Tables 1 and 2 either for 5 or 7 this seems not to be the
case, because higher hydroformylation rates are found for 5
than for 7. This discrepancy can potentially be accounted to the
different substituent R2. For 5 the ester function group can have
such an effect that it increases the rate of reaction in compar-
ison with 3. The fact that 7 is a cyclic alkene can account for the
much lower hydroformylation rate of 7 than of 9a. It can be
observed that the hydroformylation rates found for 11 and 7
(B120 molaldehyde molRhꢀ1 hꢀ1) on the one hand and 13 and 3
Conclusion
The hydroformylation of 1,1- and 1,2-disubstituted alkenes in
supercritical CO2 is demonstrated. Generally, higher turnover
frequencies were observed for the 1,2-disubstituted alkenes
than for the 1,1-disubstituted alkenes. The turnover frequencies
for the hydroformylation of macromonomers were derived from
pressure measurements during the reaction. The turnover
frequency for poly(styrene) (11) compares well with that observed
for cyclohexene. The turnover frequency observed for poly(methyl
c
Catal. Sci. Technol.
This journal is The Royal Society of Chemistry 2013

View Article Online
Catalysis Science & Technology
Paper
methacrylate) (13) is considerably lower than that observed for elsewhere.33 Briefly, the required amounts of AIBN and COBF
MMA (5). were placed in a round-bottom flask and deoxygenized. An
Unprecedented turnover frequencies are observed in oxygen-free toluene–monomer mixture was added and the
comparison with previous studies where CO2 has been applied solution was heated at 80 1C for 4 hours. The polymer solution
as a solvent. This is achieved using rhodium modified with a was passed over a column of basic aluminium oxide and the
readily available bulky phosphite ligand without the need of solvent and remaining monomers were removed. Detailed
ligand modification to improve solubility in supercritical CO2. characterization of the macromonomers by 1H-NMR, GPC,
The use of CO2 improves mass transfer in the reaction and MALDI-ToF-MS is reported elsewhere.33
mixture and allows for a facile hydroformylation. Furthermore,
Hydroformylation of disubstituted alkenes
scCO2 can be used to extract the catalyst and impurities from
the macromonomer phase and upon depressurization CO2 will The general procedure for a hydroformylation experiment
not remain in the macromonomer. Therefore, particularly for started with conveying 53 mmol of Rh(CO)2acac and 0.53 mmol
the modification of macromonomers the use of CO2 as a of phosphite ligand into the reactor of 0.108 L volume. A
solvent offers opportunities.
detailed description of the reactor setup can be found in
ref. 67. After closing the reactor, the reactor volume was
carefully flushed with argon and evacuated three times. Next,
the stirrer was turned on with a revolution speed of 700 rpm
and the desired amounts of carbon monoxide and hydrogen
Experimental
Materials
Carbon dioxide (CO2), carbon monoxide (CO), and hydrogen gas were fed to the reactor at room temperature. A total
(H2), grade 5.0, 4.7, and 5.0, respectively, were obtained from pressure of 4.9 MPa was used to obtain a concentration of
Hoekloos (The Netherlands). Prior to use CO2 was passed over a 1 mol Lꢀ1 for both CO and H2. The amounts of CO and H2
Messer Oxisorb filter to remove oxygen and moisture. The charged into the reactor were confirmed with the calibrated
rhodium precursor rhodium(I) dicarbonyl acetylacetonate mass flow controllers used to feed these gases. The reactor
(Rh(CO)2acac, Fluka) and the ligand tris(2,4-di-tert-butyl- content was then heated to a temperature of 70 1C and sub-
phenyl) phosphite (L1, Aldrich, 98%) were stored under argon sequently CO2 was pumped into the reactor to a pressure of
prior to use. The catalytic chain transfer agent, bis[(difluoroboryl)- 28 MPa. The pump used for CO2 feeding (Thar Technologies)
dimethylglyoximato]cobalt(II) (COBF), was prepared according to allowed for determining the amount of CO2 based on volume,
71
ˇ
the method of Bakac et al. Styrene (99%, Aldrich) and methyl pressure and temperature measurements. These conditions
methacrylate (99%, Aldrich) were purified by passing over a column were maintained for at least half an hour before heating further
of inhibitor remover (Aldrich) and activated basic aluminium oxide to the desired reaction temperature. An hour in total, 30 min at
to remove the inhibitor and epoxides, dried with pre-treated 70 1C and 30 min at 90 1C, was considered sufficient to allow
molecular sieves 3 Å (Aldrich, 4–8 mesh), and stored under argon the active catalyst complexes to be formed in situ from the
at –24 1C prior to use. a-Methylstyrene (99%, Aldrich) was purified [Rh(CO)2(acac)] precursor and the phosphite ligand. The mono-
by passing over a column of activated basic aluminium oxide, dried mer in the feed pump was then compressed to a pressure just
with pre-treated molecular sieves 3 Å (Aldrich, 4–8 mesh), and above the pressure present in the reactor. The reaction was
stored under argon at 4 1C prior to use. 2-Octene (98%, ABCR) and subsequently initiated by opening the valve between the pump
cyclohexene (99%, Acros) were purified by passing over a column of and the reactor, causing a fast pressure equalization, and by
activated basic aluminium oxide, dried with pre-treated molecular consecutively pumping the desired volume of monomer into
sieves 3 Å (Aldrich, 4–8 mesh), and stored at room temperature the reactor, which as a rule did not take more than 30 s.
prior to use. 2,2-Azobis(2-methylpropionitrile) (AIBN) was re-crystal- Initially, high pressure samples were taken every 10–30 min.
lized from methanol and stored at ꢀ24 1C prior to use. The solvents Samples were mostly taken from the bottom part of the reactor.
toluene (Merck, analytical grade), the standard n-decane (Aldrich, At higher conversions the sampling frequency was reduced to
>99% purity), tetrahydrofuran (analytical grade, Merck) and the 1 per h. The content of the sample volume was carefully
substances involved in the reactions, ethylbenzene (99.80%, Acros), bubbled through a vial with a solution of n-decane in toluene,
3-phenyl propion aldehyde (95%, Acros), 2-phenylpropion aldehyde and after depressurization the sample volume was rinsed with
(98%, Acros), cyclohexane (analytical grade, Merck), cyclohexane additional toluene solution to collect the substrate and its
carboxaldehyde (98%, Acros), methylisobutyrate (99%, Aldrich), reaction products quantitatively. Subsequently the sample
1-octene (98%, Aldrich), 2-octene (98%, ABCR), n-octane (Aldrich, volume was dried by alternately applying an argon flow and
>99%), nonanal (>95%, Fluka), cumene (98%, Fluka), 3-phenyl vacuum. Generally, the molar amount of product liquid
butyraldehyde (97%, Aldrich), used for the GC analysis (gas retrieved from the reactor after depressurization was 75 to 90%
chromatography with flame ionization detection), were used as of the molar amount of liquid alkene pumped into the reactor.
received.
Hydroformylation of macromonomers
Synthesis of the macromonomers 11 and 13
The general procedure for a hydroformylation experiment was
A full description of the synthesis of the poly(styrene) 11 and started by charging the desired amounts of macromonomers,
poly(methyl methacrylate) 13 macromonomers can be found [Rh(CO)2acac] (0.013 g, 52 mmol) and the phosphite ligand
c
This journal is The Royal Society of Chemistry 2013
Catal. Sci. Technol.

View Article Online
Paper
Catalysis Science & Technology
(0.335 g, 0.52 mmol) into the empty reactor, which is then 410 differential refractometer. A set of two mixed bed columns
closed and flushed with argon and subsequently evacuated (Mixed-C, Polymer Laboratories, 30 cm) were used in series at
three times. The desired amount of carbon monoxide and 40 1C. THF, stabilised with 3,5-di-tert-butyl-4-hydroxytoluene,
hydrogen gas (1 : 1) was fed to the reactor at room temperature was used as the eluent at a flow rate of 1 mL minꢀ1, and
up to a pressure of 4.9 MPa. In this case the reactor was 0.103 L, the system was calibrated using narrow molecular weight
because a certain part of the sampling system of the reactor was polystyrene standards ranging from 600 to 7 ꢁ 106 g molꢀ1
.
excluded. Sampling of the high pressure mixture was not
Matrix-assisted laser desorption/ionization time-of-flight
attempted due to the high probability of two phases being mass spectroscopy (MALDI-ToF-MS) analysis was carried out
present under reaction conditions. The reactor contents were on a Voyager DE-STR from Applied Biosystems using trans-2-
heated to 90 1C and simultaneously the reactor was charged [3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile
with carbon dioxide up to a pressure of approximately 40 MPa (DCTB) as matrix material and potassium trifluoroacetate as an
at 90 1C. In the case of hydroformylation of 11 the heating rate ionization agent. All spectra were recorded in the reflector
and pressurizing rate were 2.5 1C and 1.1 MPa minꢀ1, respec- mode. Samples were prepared by dissolving approximately
tively. In the case of hydroformylation of 13 the heating rate 3 mg mLꢀ1 in THF. The ratio of polymer sample to matrix
and pressurizing rate were 3.0 1C and 1.3 MPa minꢀ1, respec- was 1 : 1 (w/w).
tively. The moment in time these reaction conditions were
Proton nuclear magnetic resonance (1H-NMR) spectroscopy
reached was taken as the starting point of the reaction. After was performed using a VARIAN 400 NMR at 20 1C. Samples
a reaction time of 20 h, the reactor was cooled to room were diluted in CDCl3 to 30–50 mg mlꢀ1
temperature and carefully depressurized. The reactor was
.
Calculation of reaction parameters and data analysis
opened and part of the hydroformylated macromonomer was
collected as a yellow to green coloured liquid (containing some
white coloured solid material). The product solids were allowed
to dissolve in the viscous product liquid. The resulting yellow to
green coloured viscous liquid was further analyzed by 1H-NMR,
GPC, and MALDI-ToF-MS. For 11 (polystyrene) approximately
1 g was recovered directly for further analysis, 84% by weight
was recovered by rinsing the reactor with 125 mL of tetrahy-
drofuran. For 13 (poly methylmethacrylate) 80% by weight (of
The pressure measured during the reaction combined with the
conversion and selectivity obtained by MALDI-ToF analysis was
used to calculate the yield (Y) as a function of time:
PðtÞ ꢀ Pmax
P20h ꢀ Pmax PðtÞ ꢀ Pmax
YðtÞ ¼
¼
ꢁ
Pfinal ꢀ Pmax Pfinal ꢀ Pmax P20h ꢀ Pmax
PðtÞ ꢀ Pmax
¼ Y20h
ꢁ
(1)
P20h ꢀ Pmax
the amount of macromonomer charged into the reactor) could where P(t) is the reactor pressure as a function of time, Pmax is
be recovered. Note that the recovered material contained the Rh the initial maximum pressure after all the reactant and solvent
catalyst, the bulky phosphite ligand, and impurities from the have been charged into the reactor and the desired temperature
macromonomer synthesis.33 The macromonomer 11 was much has been reached, Pfinal is the final pressure reached upon
more viscous than 13 and therefore, 11 was recovered by using completion of the reaction, Pfinal,20h is the pressure reached
tetrahydrofuran. See Fig. S4 (11) and 5 (13) in ESI† for further after 20 h reaction, Y20h is the aldehyde yield reached after 20 h
visuals of the hydroformylated macromonomers.
reaction. In ref. 67 a linear correlation between aldehyde yield
and reactor pressure as proposed by eqn (1) has been observed.
Analysis
The samples obtained from the hydroformylation of disub-
stituted alkenes were analysed off-line using a Fisons Instru-
ments gas chromatograph with a flame ionization detector
(GC-FID) equipped with a Restek Rtx-5 column (fused silica,
length 30 m, internal diameter 0.53 mm) with helium as the
carrier gas. Calibration was done for all the substrates and
reaction products. Calibration for the methyl methacrylate
hydroformylation products was performed using the toluene
solutions with different concentrations of the product mixture.
The composition of the product mixture was further elucidated
and confirmed using the characteristic chemical shifts of the
a-isomer (Q), b-isomer (L), and the hydrogenation product
Notes and references
1 C. D. Frohning, C. W. Kohlpaintner and H.-W. Bohnen, in Applied
Homogeneous Catalysis, ed. B. Cornils and W. A. Herrmann,
Wiley-VCH, Weinheim, 2nd edn, 2002, vol. 1, pp. 31–103.
2 (a) M. Beller, B. Cornils, C. D. Frohning and
C. W. Kohlpaintner, J. Mol. Catal. A: Chem., 1995, 104,
17–85; (b) P. W. N. M. van Leeuwen, in Rhodium Catalyzed
Hydroformylation, ed. P. W. N. M. van Leeuwen and C. Claver,
Kluwer Academic Publishers, Dordrecht, 2000, pp. 1–13.
3 P. W. N. M. van Leeuwen, in Rhodium Catalyzed Hydro-
formylation, ed. P. W. N. M. van Leeuwen and C. Claver,
Kluwer Academic Publishers, Dordrecht, 2000, pp. 1–13.
1
isobutyraldehyde obtained by H-NMR spectroscopy. a-Isomer
´
4 For example: (a) I. T. Horvath, G. Kiss, R. A. Cook, J. E. Bond,
(Q) d = 9.66 ppm (s, 1H: –C(CH3)COH), d = 1.35 ppm (br s, 6H,
(CH3)2), b-isomer (L) d = 9.76 ppm (br m, 1H: –CH2COH),
d = 1.16 ppm (br m, 3H (CH3)), isobutyraldehyde, d = 1.25 ppm
(br d, 6H, (CH3)2).
Size exclusion chromatography (SEC) was performed using a
Waters GPC equipped with a Waters model 510 pump and a model
´
P. A. Stevens, J. Ra and E. J. Mozeleski, J. Am. Chem. Soc.,
1998, 120, 3133; (b) B. Richter, A. L. Spek, G. van Koten and
B.-J. Deelman, J. Am. Chem. Soc., 2000, 122, 3945;
(c) E. G. Hope and A. M. Stuart, J. Fluorine Chem., 1999,
100, 75–83.
c
Catal. Sci. Technol.
This journal is The Royal Society of Chemistry 2013

View Article Online
Catalysis Science & Technology
Paper
5 For example: (a) C. W. Kohlpaintner, R. W. Fischer and 16 (a) W. Leitner, Acc. Chem. Res., 2002, 35, 746–756;
´
B. Cornils, Appl. Catal., A, 2001, 221, 219; (b) F. Joo and
(b) S. Bektesevic, A. M. Kleman, A. E. Marteel-Parrish and
M. A. Abraham, J. Supercrit. Fluids, 2006, 38, 232–241.
´
A. Katho, J. Mol. Catal. A: Chem., 1997, 116, 3–26;
(c) S. Tilloy, G. Crowyn, E. Monflier, P. W. N. M. van 17 (a) P. G. Jessop, T. Ikariya and R. Noyori, Chem. Rev., 1999,
Leeuwen and J. N. H. Reek, New J. Chem., 2006, 30, 377–383.
6 For example: (a) H. Olivier, J. Mol. Catal. A: Chem., 1999, 146,
99, 475–493; (b) P. G. Jessop, J. Supercrit. Fluids, 2006, 38,
211–231.
285–289; (b) P. Wasserscheid and W. Keim, Angew. Chem., 18 Y. Hu, W. Chen, L. Xu and J. Xiao, Organometallics, 2001, 20,
Int. Ed., 2000, 39, 3772–3789; (c) T. Welton, Chem. Rev., 1999, 3206–3208.
99, 2071–2083; (d) R. D. Rogers and K. R. Seddon, Science, 19 M. F. Sellin, I. Bach, J. M. Webster, F. Montilla, V. Rosa,
´
2003, 302, 792–793; (e) J. F. Brennecke and E. J. Maginn,
AIChE J., 2001, 47, 2384–2389; ( f ) B. Hamers,
T. Aviles, M. Poliakoff and D. J. Cole-Hamilton, J. Chem.
Soc., Dalton Trans., 2002, 4569–4576.
¨
P. S. Bauerlein, C. Mu¨ller and D. Vogt, Adv. Synth. Catal., 20 C. D. Ablan, D. Sheppard, E. J. Beckman, M. M. Olmstead
2008, 350, 332–342; (g) R. Sheldon, Chem. Commun., 2001, and P. G. Jessop, Green Chem., 2005, 7, 590–594.
2399–2407; (h) S. M. Silva, R. P. J. Bronger, Z. Freixa, 21 A. Galia, A. Cipollina, G. Filardo, O. Scialdone, M. Ferreira
J. Dupont and P. W. N. M. van Leeuwen, New J. Chem.,
2003, 27, 1294–1296.
and E. Monflier, J. Supercrit. Fluids, 2008, 46, 63–70.
22 M. F. Sellin and D. J. Cole-Hamilton, J. Chem. Soc., Dalton
Trans., 2000, 1681–1683.
`
7 For example: (a) K. Burgemeister, G. Francio, V. H. Gego,
L. Greiner, H. Hugl and W. Leitner, Chem.–Eur. J., 2007, 13, 23 S. Kainz, D. Koch, W. Baumann and W. Leitner, Angew.
2798–2804; (b) M. Solinas, J. Jiang, O. Stelzer and W. Leitner, Chem., Int. Ed. Engl., 1997, 15, 1628–1630.
Angew. Chem., Int. Ed., 2005, 44, 2291–2295; (c) M. F. Sellin, 24 D. R. Palo and C. Erkey, Ind. Eng. Chem. Res., 1998, 37,
P. B. Webb and D. J. Cole-Hamilton, Chem. Commun., 2001,
4203–4206.
781–782.
25 D. Koch and W. Leitner, J. Am. Chem. Soc., 1998, 120,
´
8 B. Cornils, W. A. Herrmann, I. T. Horvath, W. Leitner,
13398–13404.
S. Mecking, H. Olivier-Bourbigou and D. Vogt, in Multiphase 26 A. M. Banet Osuna, W. Chen, E. G. Hope, R. D. W. Kemmitt,
Homogeneous Catalysis, ed. B. Cornils, W. A. Herrmann,
D. R. Paige, A. M. Stuart, J. Xiao and L. Xu, J. Chem. Soc.,
Dalton Trans., 2000, 4052–4055.
´
I. T. Horvath, W. Leitner, S. Mecking, H. Olivier-Bourbigou
and D. Vogt, Wiley-VCH, Weinheim, 2005, vol. 1, pp. 3–23. 27 D. R. Palo and C. Erkey, Organometallics, 2000, 19, 81–86.
9 D. J. Cole-Hamilton, Science, 2003, 299, 1702–1706.
10 For example: D. E. Bergbreiter, J. Tian and C. Hongfa, Chem.
Rev., 2009, 109, 530–582.
11 For example: B. M. L. Dioos, I. F. J. Vankelecom and
P. A. Jacobs, Adv. Synth. Catal., 2006, 348, 1413–1446.
28 K.-D. Wagner, N. Dahmen and E. Dinjus, J. Chem. Eng. Data,
2000, 45, 672–677.
29 Y. Shimoyama, M. Sonoda, K. Miyazaki, H. Higashi, Y. Iwai
and Y. Arai, J. Supercrit. Fluids, 2008, 44, 266–272.
´
´
30 C. T. Estorach, A. Orejon and A. M. Masdeu-Bulto, Green
´
12 For example: (a) U. J. Jauregui-Haza, M. Dessoudeix,
Chem., 2008, 10, 545–552.
Ph. Kalck, A. M. Wilhelm and H. Delmas, Catal. Today, 31 (a) A. C. J. Koeken, M. C. A. van Vliet, L. J. P. van den Broeke,
2001, 66, 297–302; (b) G. Fremy, E. Monflier,
J.-F. Carpentier, Y. Castanet and A. Mortreux, Angew. Chem.,
Int. Ed. Engl., 1995, 34, 1474–1476; (c) A. Riisager,
R. Fehrmann, S. Flicker, R. van Hal, M. Haumann and
B. J. Deelman and J. T. F. Keurentjes, Adv. Synth. Catal.,
2006, 348, 1553–1559; (b) A. C. J. Koeken, M. C. A. van Vliet,
L. J. P. van den Broeke, B. J. Deelman and J. T. F. Keurentjes,
Adv. Synth. Catal., 2008, 350, 179–188.
P. Wasserscheid, Angew. Chem., Int. Ed., 2005, 44, 32 A. C. J. Koeken, N. E. Benes, L. J. P. van den Broeke and J. T.
815–819. F. Keurentjes, Adv. Synth. Catal., 2009, 351, 1442–1450.
13 See for example: (a) T. Mu¨ller and H. Bahrmann, J. Mol. Catal. 33 N. M. B. Smeets, J. Meuldijk, J. P. A. Heuts and A. C.
A: Chem., 1997, 116, 39–42; (b) L. J. P. van den Broeke, E. L. J. Koeken, Polym. Chem., 2010, 1, 1102–1108.
V. Goetheer, A. W. Verkerk, E. de Wolf, B.-J. Deelman, G. Van 34 K. Ito, Prog. Polym. Sci., 1998, 23, 581–620.
Koten and J. T. F. Keurentjes, Angew. Chem., Int. Ed., 2001, 40, 35 D. M. Haddleton, C. Topping, D. Kukulj and D. Irvine,
4473–4474; N. J. Hovestad, E. B. Eggeling, H. J. Heidbu¨, J. T. B.
H. Jastrzebski, U. Kragl, W. Keim, D. Vogt and G. van Koten, 36 D. M. Haddleton, C. Topping, J. J. Hastings and
Angew. Chem., Int. Ed., 1999, 38, 1655–1658; (c) K. de Smet, K. G. Suddaby, Macromol. Chem. Phys., 1996, 197, 3027.
S. Aerts, E. Ceulemans, I. F. J. Vankelecom and P. A. Jacobs, 37 K. J. Abbey, D. L. Trumbo, G. M. Carlson, M. J. Masola and
Polymer, 1998, 39, 3119.
Chem. Commun., 2001, 597–598; (d) M. Janssen, C. Mu¨ller and
D. Vogt, Adv. Synth. Catal., 2009, 351, 313–318.
R. A. Zander, J. Polym. Sci., Part A: Polym. Chem., 1993,
31, 3417.
14 P. G. Jessop and W. Leitner, in Chemical Synthesis Using 38 P. Cacioli, D. G. Hawthorne, R. L. Laslett, E. Rizzardo and
Supercritical Fluids, ed. P. G. Jessop and W. Leitner, Wiley-
VCH, Weinheim, 1999, pp. 1–36.
D. H. Solomon, J. Macromol. Sci., Part A: Pure Appl. Chem.,
1986, 23, 839.
15 ‘‘Applying scCO2 as a solvent’’ most commonly implies that 39 See for example: D. Fournier, R. Hoogenboom and
the reaction mixture, reactants, products and CO2 were in a
supercritical single-phase state.
U. S. Schubert, Chem. Soc. Rev., 2007, 36, 1369–1380;
B. S. Summerlin and A. P. Vogt, Macromolecules, 2010, 43,
c
This journal is The Royal Society of Chemistry 2013
Catal. Sci. Technol.

View Article Online
Paper
Catalysis Science & Technology
1–13; A. Gregory and M. H. Stenzel, Prog. Polym. Sci., 2012, 57 B. Breit and W. Seiche, Synthesis, 2001, 1–36.
37, 38–105.
58 R. Lazzaroni, R. Settambolo, G. Uccello-Barretta, A. Caiazzo
and S. Scamuzzi, J. Mol. Catal. A: Chem., 1999, 143,
123–130.
59 R. Lazzaroni, A. Raffaelli, R. Settambolo, S. Bertozzi and
G. Vitulli, J. Mol. Catal., 1989, 50, 1–9.
60 L. L. J. M. Cornelissen, Metal-Catalyzed Asymmetric Hydro-
formylation: Towards the Understanding of Stereoselection
Processes, PhD thesis, Eindhoven University of Technology,
2009.
40 N. S. Enikolopyan, B. R. Smirnov, G. V. Ponomarev and
I. M. Belgovskii, J. Polym. Sci., Part A: Polym. Chem., 1981, 19,
879–889.
41 J. P. A. Heuts, G. E. Roberts and J. D. Biasutti, Aust. J. Chem.,
2002, 55, 381–398.
42 A. A. Gridnev and S. D. Ittel, Chem. Rev., 2001, 101, 3611–3659.
43 L. V. Karmilova, G. V. Ponomarev, B. R. Smirnov and
I. M. Belgovskii, Russ. Chem. Rev., 1984, 53, 223–235.
44 T. P. Davis, D. M. Haddleton and S. N. Richards, 61 M. L. Clarke and G. J. Roff, Chem.–Eur. J., 2006, 12,
J. Macromol. Sci., Rev. Macromol. Chem., 1994, 34, 234–324. 7978–7986.
45 T. P. Davis, D. Kukulj, D. M. Haddleton and D. R. Maloney, 62 C. U. Pittman Jr, W. D. Honnick and J. J. Yang, J. Org. Chem.,
Trends Polym. Sci., 1995, 3, 365–373. 1980, 45, 684–689.
46 A. A. Gridnev, J. Polym. Sci., Part A: Polym. Chem., 2000, 38, 63 H. K. Reinius and A. O. I. Krause, J. Mol. Catal. A: Chem.,
1753–1766. 2000, 158, 499–508.
47 J. P. A. Heuts and N. M. B. Smeets, Polym. Chem., 2011, 2, 64 A. van Rooy, E. N. Orij, P. C. J. Kamer and P. W. N. M. van
2407–2423. Leeuwen, Organometallics, 1995, 14, 34–43.
48 T. W. G. Solomons, Organic Chemistry, John Wiley & Sons, 65 B. Breit, R. Winde and K. Harms, J. Chem. Soc., Perkin Trans.
Inc., New York, 6th edn, 1996.
1, 1997, 2681–2682.
49 A. C. J. Koeken, L. J. P. van den Broeke, B.-J. Deelman and 66 R. P. J. Bronger, J. P. Bermon, J. Herwig, P. C. J. Kamer and
J. T. F. Keurentjes, J. Mol. Catal. A: Chem., 2011, 346, 1–11.
50 D. Bonafoux, Z. Hua, B. Wang and I. Ojima, J. Fluorine
Chem., 2001, 112, 101–108.
51 S. Kainz and W. Leitner, Catal. Lett., 1998, 55, 223–225.
52 B. Lin and A. Akgerman, Ind. Eng. Chem. Res., 2001, 40,
1113–1118.
53 I. Kani, R. Flores, J. P. Fackler Jr and A. Akgerman,
J. Supercrit. Fluids, 2004, 31, 287–294.
54 F. Shibahara, K. Nozaki and T. Hiyama, J. Am. Chem. Soc.,
2003, 125, 8555.
P. W. N. M. van Leeuwen, Adv. Synth. Catal., 2004, 346,
789–799.
67 A. C. J. Koeken, S. J. M. de Bakker, H. M. Costerus, L. J.
P. van den Broeke, B. J. Deelman and J. T. F. Keurentjes,
J. Supercrit. Fluids, 2008, 46, 47–56.
68 G. Montaudo, F. Samperi and M. S. Montaudo, Prog. Polym.
Sci., 2006, 31, 277.
69 G. Montaudo, M. S. Montaudo and F. Samperi, in Mass
Spectrometry of Polymers, ed. G. Montaudo and
R. P. Lattimer, CRC Press, Boca Raton, 2002, ch. 2 and 10.
55 A. M. Kleman and M. A. Abraham, Ind. Eng. Chem. Res., 70 F. J. Cox, M. V. Johnston and A. Dasgupta, J. Am. Soc. Mass
2006, 45, 1324–1330. Spectrom., 2003, 14, 648.
´
´
´
ˇ
56 M. Gimenez Pedros, A. M. Masdeu-Bulto, J. Bayardon and 71 A. Bakac, M. E. Brynildson and J. H. Espenson, Inorg. Chem.,
D. Sinou, Catal. Lett., 2006, 107, 205–208.
1986, 25, 4108.
c
This journal is The Royal Society of Chemistry 2013
Catal. Sci. Technol.