An electrostatically-anchored rhodium(I) catalyst for the hydroformylation and tandem hydroformylation/acetalization of biorenewable allyl benzenes

Article abstract of DOI:10.5935/0103-5053.20140254

A rhodium catalyst anchored in a commercial anion exchange resin (IRA900/TPPMS/Rh) was prepared straightforwardly through a simple protocol from readily available precursors. The material was used as a heterogeneous catalyst for the hydroformylation and tandem sequence hydroformylation/acetalization of eugenol and estragole under mild conditions. The regioselectivity for linear products was ca. 62percent, but for the allyl benzenes the branched isomer are also valuable. The performance of the anchored catalyst in hydroformylation was comparable to that of the conventional homogeneous rhodium system; however, its efficiency in the acetalization step was significantly higher. The material can be separated from the reaction solutions by decantation and re-used without a significant loss in activity and selectivity. This simple catalytic method represents an economically attractive route to commercially valuable fragrance compounds starting from the substrates easily available from natural bio-renewable sources.

Full text of DOI:10.5935/0103-5053.20140254

http://dx.doi.org/10.5935/0103-5053.20140254
J. Braz. Chem. Soc., Vol. 25, No. 12, 2370-2377, 2014.
Printed in Brazil - ©2014 Sociedade Brasileira de Química
0103 - 5053 $6.00+0.00
Article
A
An Electrostatically-Anchored Rhodium(I) Catalyst for the Hydroformylation and
Tandem Hydroformylation/Acetalization of Biorenewable Allyl Benzenes
Glenda A. Carvalho,a,b Elena V. Gusevskayaa and Eduardo N. dos Santos*,a
aDepartamento de Química - ICEx, Universidade Federal de Minas Gerais,
31270-901 Belo Horizonte-MG, Brazil
bCentro Federal de Educação Tecnológica de Minas Gerais, 37250-000 Contagem-MG, Brazil
Um catalisador de ródio ancorado em uma resina de troca iônica comercial (IRA900/TPPMS/Rh)
foi preparado de maneira direta, através de um protocolo simples, a partir de precursores prontamente
disponíveis. O material foi usado como um catalisador heterogêneo para a hidroformilação e a
sequência tandem hidroformilação/acetalização do eugenol e do estragol em condições brandas.A
regiosseletividade para os produtos lineares foi cerca de 62%, mas para os alil benzenos os produtos
ramificados são também valiosos. O desempenho do catalisador ancorado na hidroformilação
foi comparável aos catalisadores homogêneos de ródio convencionais, entretanto, sua eficiência
na etapa de acetalização foi significativamente mais elevada. O material pode ser separado da
solução reacional por decantação e pode ser reutilizado sem perda significativa de atividade ou
seletividade. Este método catalítico simples representa uma rota alternativa economicamente
atrativa para compostos de valor comercial como fragrâncias partindo de substratos prontamente
disponíveis de fontes bio-renováveis.
A rhodium catalyst anchored in a commercial anion exchange resin (IRA900/TPPMS/Rh)
was prepared straightforwardly through a simple protocol from readily available precursors. The
material was used as a heterogeneous catalyst for the hydroformylation and tandem sequence
hydroformylation/acetalization of eugenol and estragole under mild conditions. The regioselectivity
for linear products was ca. 62%, but for the allyl benzenes the branched isomer are also valuable.
The performance of the anchored catalyst in hydroformylation was comparable to that of the
conventional homogeneous rhodium system; however, its efficiency in the acetalization step was
significantly higher. The material can be separated from the reaction solutions by decantation and
re-used without a significant loss in activity and selectivity. This simple catalytic method represents
an economically attractive route to commercially valuable fragrance compounds starting from the
substrates easily available from natural bio-renewable sources.
Keywords: anchored rhodium catalyst, tandem, hydroformylation, acetalization
Introduction
such as monoterpenes2-10 and allyl benzenes.11 The
hydroformylation of allyl benzenes (1a-c) and propenyl
benzenes (2a-c) (Scheme 1) represents a potential route
to fragrance ingredients. In particular, aldehydes 5b and
5c are commercialized as valuable fragrance components
under the trade names of Chantoxal® (5b) and Helional®
or Tropional® (5c).12,13
For industrial processes involving rhodium complexes,
the recycling of the catalyst has to be guaranteed due to
the high price of this metal. Distillation is inconvenient or
even not viable for heavy products as it leads to the thermal
deactivation of the catalyst. Many strategies have been
investigated to recover the catalyst before the distillation
Hydroformylation (oxo synthesis) is an industrially
relevant reaction catalyzed by rhodium or cobalt
complexes in solutions. The word production of oxo
derivatives is in the order of 6 millions ton per year.
Rhodium-catalyzed hydroformylation is also employed
for fine chemicals syntheses,1 as showed in a recent
review.2 In the last years our group has been interested
in the hydroformylation of naturally occurring olefins,
*e-mail: nicolau@ufmg.br
Dedicated to Professor Roberto Fernando de Souza (in memoriam)

Vol. 25, No. 12, 2014
Carvalho et al.
2371
CHO
4a-c
R1
1a-c
R2
R1
CO/H2
R2
H2
CHO
5a-c
R1
R2
3a-c
H2
R1
CHO
R2
CO/H2
2a-c
R1
6a-c
R1
R2
R2
: R1 = -OH, R2 = -OCH3 : R1 = -OCH3 ,R2 = -H : R1-R2 = -OCH2-
a
b
c
Scheme 1. The hydroformylation products of allyl and propenyl benzenes.
step, such as the employment of biphasic systems14 or
anchoring the catalyst on a solid support.15 The latter
approach is more attractive from process viewpoint as
it allows catalyst separation by simple filtration or the
operation in fixed-bed continuous tubular reactors.Among
the drawbacks associated with this approach is the difficulty
to prepare suitable supports, which must have a functional
group capable to bind the catalyst through a chemical
bond. The preparation of these supports involves either
the synthesis of monomers containing functional groups
followed by polymerization or the chemical modification
of preformed polymers such as macroporous poly(styrene/
divinylbenzene) or silica gel.15
An alternative approach is to anchor the catalyst through
electrostatic interactions on a solid polyelectrolyte, such
as ion-exchange resins.16 Some grades of ion-exchange
resins are considerably cheap and are used in large scale,
e.g., for water purification or in agricultural formulations.
To be effective, the catalyst has to bear an electric charge
throughout the catalytic cycle and a way to fulfill this
requirement is to employ ligands with an ionic fragment
which binds the metal center of the catalysts.17-21 A great
variety of phosphines containing ionic moieties have
their synthetic routes well established.22 The most readily
synthesized one is 3-sulfonatophenyldiphenylphosphine,
monosodium salt (TPPMS), which has been anchored on
anion-exchange resins and used for the immobilization of
ruthenium18,23 and rhodium24 catalysts for the hydrogenation
of olefins.
Experimental
General procedures
The strongly basic anion-exchange resin IRA900
purchased from Fluka was alternately washed with solutions
of HCl (1 mol L–1), NaOH (1 mol L–1), HCl (1 mol L–1),
and finally, with deionized water. Eugenol and estragole
purchased from Aldrich were passed through a short
column of neutral alumina to remove peroxides. Hydrogen
(99.999%) and carbon monoxide (99%) were purchased from
Praxair. Bis[(m-methoxy)(1,5-cyclooctadiene)rhodium(I)]
([Rh(cod)(OMe)]2)25 and 3-sulfonatophenyldiphenyl-
prosphine monosodium salt (TPPMS)26 were prepared
according to published procedures. Manipulations under
argon were performed employing Schlenk techniques.
Toluene was refluxed with sodium/benzophenone for 8 h.
Methanol and anhydrous ethanol were refluxed with the
corresponding magnesium alkoxyde prepared in situ for 6 h.
Deionized water was refluxed under argon for 6 h. After the
treatment, all solvents were distilled and stored under argon.
Catalyst preparation and characterization
Under argon, TPPMS (0.364 g, 1.0 mmol) dissolved in
water (10.0 mL) was kept in contact with wet IRA900 (1.0g)
for 24 h with occasional stirring. The remaining solution
was filtered off and the resin was washed twice with water
(5 mL) and dried under vacuum (5 × 10−4 atm) at room
temperature for 5 h. The resulting solid was kept in contact
with a solution of [Rh(cod)(OMe)]2 (0.0488 g, 0.100 mmol)
in toluene (10.0 mL) at room temperature for 24 h with
occasional stirring. The remaining solution was filtered off
and the solid was washed twice with toluene (5 mL) and dried
In the present work we propose a straightforward
protocol to prepare an effective and recyclable anchored
rhodium catalyst for the hydroformylation as well as for
the tandem sequence hydroformylation/acetalization of
allyl benzenes.

2372
An Electrostatically-Anchored Rhodium(I) Catalyst for the Hydroformylation
J. Braz. Chem. Soc.
under vacuum (5 × 10−4 atm) at room temperature for 5 h. The
catalyst was analyzed by infrared (IR) spectrometry in KBr
pellets (4000-400 cm−1) in a Perking-Elmer GX apparatus.
The rhodium content of the catalyst was measured by X-ray
Kevex and inductively coupled plasma mass spectrometry
(ICP-MS), and showed the value of 0.90 wt.%. The
phosphorus content was determined by molecular absorption
spectrometry resulting in 1.1 wt.%.
Acetal 5’a (R’ = CH2CH3). EM (m/z rel. int.):
268 /4.3 (M+); 222/46.3 (M+-CH3CH2OH); 177/12; 137/100
(M+-CH3CH2CH(OCH2CH3)2).
Acetal 4’b (R’ = CH3). MS (m/z rel. int.): 224/1 (M+);
192/11 (M+-CH3OH); 161/24; 135/12; 134/100; 75/23.
Acetal 5’b (R’ = CH3). MS (m/z rel. int.): 224/2 (M+);
192/44 (M+-CH3OH); 161/26; 145/11; 121/91; 91/12;
77/11; 75/100; 47/13.
Catalytic runs
Results and Discussion
A mechanically stirred stainless steel Parr 4560 bomb
coupled with a 4282 control module with a PID temperature
controller and tachometer was employed as the reaction
vessel. The bomb was loaded with the solid catalyst and
three cycles of vacuum/argon were made. The solvent
(15 mL) and the substrate (5 mmol) were introduced with
a syringe through a valved port under argon. The vessel was
pressurized with carbon monoxide followed by hydrogen
up to the reported pressure. Stirring and heating were then
started, and the desired temperature was attained in about
5 min. At appropriate time intervals, stirring was stopped
and liquid samples were taken through a valved dip tube
after quick catalyst settling. Recycling experiments were
performed maintaining the catalyst in the vessel and
washing it with the same solvent employed in the reaction
before a new cycle to remove product residues.
Catalyst preparation and characterization
The aim of the present work was to provide a simple and
inexpensive protocol to prepare an anchored rhodium(I)/
arylphosphine catalyst and test the material in the
hydroformylation and hydroformylation/acetalization of
allyl benzenes. Thus, we have chosen [Rh(cod)(m-OMe)]2
as the catalyst precursor, which is prepared straightforwardly
in two steps from rhodium trichloride in a high yield.
This complex contains labile ligands that can be readily
exchanged by a phosphorus(III) ligand. TPPMS is also
readily prepared from triphenylphosphine by sulfonation
with fuming sulfuric acid (20% SO3). The macroporous
anion exchange resin IRA-900 is a commercial and
inexpensive material.
The IRA900/TPPMS/Rh catalyst was prepared
according to Scheme 2. The commercial, strongly basic
anion exchange resin IRA900 in its chloride form was let
in contact with an aqueous solution of TPPMS. The resin
containing TPPMS anchored by electrostatic interaction
(IRA900/TPPMS) was let in contact with a toluene solution
of [Rh(cod)(m-OMe)]2 ([RhLn]2). The rhodium complex was
absorbed by the resin, as it could be noticed by discoloring
the pale-yellow solution.
The anchoring process was followed by infrared
spectrometry. Although the support and the catalyst have
been dried under vacuum (5 × 10−4 atm) at room temperature
for 5 h, a significant amount of water remained, as shown
by a strong and broad band with a maximum at 3450 cm−1.
This fact stresses the strongly hygroscopic character of
this support. The introduction of TPPMS in the IRA900
material causes the appearance of a strong absorption at
1196 cm−1, which is characteristic of the sulfonate group.
No significant change in the IR spectrum was observed
with the introduction of the rhodium complex.
The results of the elemental analysis allowed us to
calculate a molar ratio between the components in the final
IRA900/TPPMS/Rh material. The phosphorus analysis
gave the value of 1.1 wt.% for the phosphorus content.
Comparing this value with the nominal ion-exchange
Product analysis
The products were quantitatively analyzed by gas
chromatography (GC) using a Shimadzu 17B instrument
equipped with a split/splitless injection port and flame
ionization detector, fitted with a Restek Rtx-wax capillary
column (30m × 0.25 mm × 0.25 mm). Conversion
and product distribution were determined by GC.
Qualitative analysis was made by GC coupled with
mass spectrometry in a Shimadzu GC2010/QP2010-plus
instrument fitted with a Restek Rtx-5 MS capillary column
(30 m × 0.25 mm × 0.25 mm), operating at 70 eV.
Aldehydes 4a, 4b, 5a and 5b. These compounds were
described in our previous work.11
Acetal 4’a (R’ = CH3). MS (m/z rel.int.): 240/3 (M+);
208/6 (M+-CH3OH); 177/18; 151/11; 150/100; 135/14;
75/21; 44/10.
Acetal 5’a (R’ = CH3). MS (m/z rel. int.): 240/8 (M+);
208/41 (M+-CH3OH); 177/14; 161/13; 137/80; 75/100;
44/55.
Acetal 4’a (R’ = CH2CH3). EM (m/z rel. int.):
268 /0.55 (M+); 223/1.4 (M+- CH3CH2OH); 177/23; 150/100
(M+-CH2CH(OCH2CH3)2).

Vol. 25, No. 12, 2014
Carvalho et al.
2373
*
n
*
n
*
n
*
*
*
+ [RhLn]2
- L
+ TPPMS
- NaCl
-
N+(CH3)3TPPMS
N+(CH3)3Cl-
IRA900
N+(CH3)3TPPMS--RhLn-1
IRA900/TPPMS/Rh
IRA900/TPPMS
CH3
O
P
Rh
Rh
SO3Na
O
CH3
[RhLn]2
TPPMS
Scheme 2. Catalyst synthesis.
capacity of the IRA900 resin (1.5 meq g−1), it is possible
to estimate that only one chloride out of four has been
exchanged with TPPMS. Therefore, the TPPMS/chloride
molar ratio in the catalyst is about 1:3. The rhodium content
of 0.90 wt.% indicates a rhodium/TPPMS molar ratio of
1:3. Thus, the molar ratio of Rh:TPPMS–:Cl− in the catalyst
is 1:3:9.
substrate to rhodium molar ratio of ca. 550 (Table 1, runs 1
and 2).At 50 oC and 60 atm of equimolar mixture of CO/H2,
the reaction occurred slowly reaching 60% of conversion
in 24 h and showed a combined selectivity for aldehydes
of only 60% because of the extensive isomerization and
hydrogenation of the substrate. Expectedly, at the same
pressure, the reaction was significantly accelerated by the
increase in temperature and was completed in 15 h at 70 oC.
The reaction rates were calculated as turnover frequencies
(TOF) from the kinetic curves (conversion versus time) as
shown in Figure 1. The TOF were 14 h−1 at 50 oC and 63 h−1
at 70 oC. These data expressed by means of the Arrhenius
equation yielded for the activation energy a reasonable
value of ca. 70 kJ mol−1.
Catalytic runs
In the present work, we propose the use of eugenol
as a convenient model substrate for hydroformylation, as
it is a cheap, non-toxic, naturally occurring olefin and is
readily available from commercial sources in high purity.
In addition, the hydroformylation of eugenol, as well as
related allyl benzenes, is a potential route to produce the
components of synthetic fragrances (Scheme 1).12 In many
previously reported studies, 1-hexene was used as a model
substrate for the catalytic hydroformylation of olefins.21
However, four double-bond isomers and three aldehydes
can be formed from 1-hexene and these products are
difficult to be separated by GC. Moreover, their GC peaks
may overlap with those of commonly used solvents, such
as toluene. On the other hand, the isomerization of eugenol
produces only two isomers (2a, Scheme 1), which are
difficult to be hydroformylated under mild conditions. The
hydrogenated product, double-bond isomers and aldehydes
derived from eugenol are easily separated under regular
GC conditions and their GC peaks do not overlap with
those of usual solvents. Therefore, the catalyst parameters
such as conversion, reaction rate, chemoselectivity and
regioselectivity can be easily and unequivocally determined
by GC.
The comparison of the product distribution in the
reactions performed at different temperatures revealed a
remarkable trend. At higher temperature, the reaction is
much more selective for the aldehydes, as they correspond
to 89% of the mass balance at 70 oC but only 60% at 50 oC.
These results would suggest to test the catalyst at a higher
temperature, but the stability of the support is limited to
o
o
77 C. Thus, we decided to keep 70 C as the standard
temperature for the following experiments.
In Table 1, runs 2-6, the effect of the total and partial
pressures of CO and H2 is shown. The TOF is rather
independent of the total pressure in the range of 40-80 atm
(CO/H2 = 1, runs 2, 3 and 4) indicating that the reaction
is not limited by the diffusion of the gases to the catalytic
site and is either independent of both the CO and H2
concentration or a positive dependence is compensated by
a negative one. For triarylphosphine-promoted rhodium
catalysts in solution, the rate of hydroformylation is usually
independent of the H2 concentration and presents a slightly
negative order in CO pressure under “standard” conditions.
However, it is important to stress out that the kinetics of
We first tested the performance of the anchored IRA900/
TPPMS/Rh catalyst at different temperatures using a

2374
An Electrostatically-Anchored Rhodium(I) Catalyst for the Hydroformylation
J. Braz. Chem. Soc.
Table 1. The hydroformylation of eugenol (1a) in toluene solutions catalyzed by the IRA900/TPPMS/Rh catalysta
Selectivityd / % for the products of
hydroformylation (4a and 5a) isomerization (2a)
Run
Pressure CO:H2 / atm
timeb / h
TOFc / h–1
1e
2
30:30
30:30
20:20
40:40
40:20
20:40
30:30
30:30
24f
15
15
15
24
7
14
63
68
68
42
174
50
55
60
94
82
95
89
90
92
91
22
5
3
12
5
4
5
10
9
6
7g
8g
17
15
7
8
aConditions: solvent: toluene (15 mL), catalyst (0.10 g: TPPMS = 3.6 × 10–2 mmol, Rh = 9.0 × 10–3 mmol), substrate (5.0 mmol), 70 oC. Conversion and
selectivity are based on the substrate reacted; breaction time required for nearly complete conversion; creaction rate (TOF - turnover frequency taken from
d
the linear part of conversion vs. time plots); the rest of the mass balance was due to the hydrogenation product 2a. The regioselectivity for the linear
product (4a) was ca. 62% in all runs; e50 oC; f60% conversion; gruns 7 and 8 were the second and the third use of the catalyst separated after run 2.
the hydroformylation reactions is extremely sensitive to
the experimental conditions.27
benzenes the branched isomers are even more valuable than
the linear ones.
Runs 7 and 8 are the second and third uses of the catalyst
first used in run 2. All three reactions were essentially
completed in 15-17 h, without a significant decrease in the
reaction rates on the stationary periods (TOF = 63 h−1, 50 h−1
and 55 h−1 in the first, second and third uses, respectively).
Thus, the anchored IRA900/TPPMS/Rh catalyst can be
separated from the reaction solutions and re-used without
a significant loss in activity and selectivity at least for
three times.
100
80
60
40
Tandem hydroformylation/acetalization
Run 1
Run 2
Run 6
20
0
For some applications, it is desirable to transform
aldehydes in acetals both for protection purposes and
because some acetals, instead of the corresponding
aldehydes, can be the desired products.28 Chaudhari et al.21
demonstrated that a rhodium catalyst containing the
tris(3-sulfonatophenyl)phosphine trisodium salt (TPPTS)
supported on the ion-exchange resin IRA93 transformed
the aldehydes primarily formed in the hydroformylation of
1-hexene into acetals when methanol or ethanol were used
as solvents. IRA 93 is a neutral polymer containing amine
groups that has to be treated with a strong acid such as HCl
in order to be converted into an anion-exchanger and thus
this catalyst has ammonium ions with an acidic proton,
which account for the acid-catalyzed acetalization of the
aldehydes. In the IRA900 resin, the exchanging groups are
trimethylarylammonium groups without acidic hydrogens
and, although the acetalyzation was not expected to be
efficient, we tested the catalyst for the tandem sequence
hydroformylation/acetalization of eugenol using alcohols
as solvents (Scheme 3). The results are presented in Table 2.
0
5
10
15
20
25
time / h
Figure 1. Kinetic curves for selected runs in the hydroformylation of 1a.
For conditions see Table 1.
The results obtained for the reactions performed with
different proportions between CO and H2 are shown in
runs 5 and 6. The total pressure of the equimolar gas
mixture had no significant effect on the hydroformylation
of eugenol, which could reflect a net result of the opposite
kinetic effects of the gas reagents. Really, a positive order
in hydrogen (run 6 vs. run 3) and negative order in carbon
monoxide (run 5 vs. run 3) were found for this reaction. It
should be mentioned that the variation of either the total
pressure or the partial pressures of CO or H2 does not affect
significantly the product distribution at high conversions
indicating that essentially the same catalytically active
species operate under those conditions. The regioselectivity
for the linear aldehyde (4a) is quite low (62%), but for allyl

Vol. 25, No. 12, 2014
Carvalho et al.
2375
OR
OR
ROH/H+
-H2O
CHO
R1
R1
R2
R2
4'a,b
4a,b
ROH/H+
-H2O
CHO
R1
R1
RO
OR
R2
R2
5a,b
5'a,b
4a, 5a, 4'a, 5'a
4b, 5b, 4'b, 5'b
: R1= -OH, R2 = -OCH3
: R1= -OCH3, R2 = -H
R = -CH3 or -CH2CH3
Scheme 3. The step of the aldehyde acetalization.
The rate of eugenol conversion at the stationary period
was nearly the same (ca. 60 h−1) in all solvents used, i.e.,
toluene, methanol, and ethanol, with the reactions being
nearly completed in 24 h (Table 2, runs 2, 9 and 10).
However, the reactions in alcohols gave corresponding
acetals as main products, whereas in toluene the main
products were the aldehydes. The total selectivity for the
hydroformylation products (aldehydes and acetals) was
nearly 95% in all solvents. The regioselectivity of the
hydroformylation was also similar in all solvents, with the
regioselectivity for the linear aldehydes and acetals (4 + 4’)
being nearly 62% in all runs. The relative amount of the
acetals increased with the reaction time indicating that
the acetalization of the aldehydes occurred at a lower rate
than their formation. At the end of the 24-hour reaction,
the acetals accounted for 77 and 91% of the mass balance
in ethanol and methanol, respectively.
To compare the performance of the anchored rhodium
catalyst with the conventional homogeneous system,
we tested the [Rh(cod)(m-OMe)]2 complex dissolved
in methanol in the presence of TPPMS as the catalyst
precursor (Table 2, entry 11). The activity of the
homogeneous catalyst was expectedly higher and the
reaction was completed in 5 h. A possible explanation
could be a faster formation of catalytically active species
under the homogeneous conditions, although the diffusional
restrictions during the substrate transfer in the polymer
domain cannot be ruled out. The product distribution,
including regioselectivity, was quite similar considering
the aldehydes and corresponding acetals together. This
indicates that active organometallic species in the catalytic
cycle seems to be similar in both systems. However, in the
homogeneous system, the rate of the acetalization step was
remarkably lower, with corresponding acetals accounting
Table 2. The hydroformylation and hydroformylation/acetalization of eugenol (1a) and estragole (1b) in various solvents catalyzed by the IRA900/
TPPMS/Rh catalysta
Selectivity for hydroformylationb / %
Run
Substrate
Solvent
Conversion / %
Total
94
Aldehydes (4 and 5) Acetals (4’ and 5’)
2
1a
1a
1a
1a
1a
1a
1b
2a
toluene
ethanol
99
96
98
100
96
94
94
9
94
17
5
0
9
94
77
91
10
88
88
71
23
10
11c
12d
13d
14
15
methanol
methanol
methanol
methanol
methanol
methanol
96
95
85
9
97
97
9
99
21
41
18
aConditions: solvent (15 mL), catalyst (0.10 g: TPPMS = 3.6 × 10−2 mmol, Rh = 9.0 × 10−3 mmol), substrate (5.0 mmol), 60 atm (CO/H2 = 1/1), 70 oC,
24 h. Conversion and selectivity are based on the substrate reacted; bthe rest of the mass balance was due to the hydrogenation and isomerization products,
2 and 3, respectively. The regioselectivity for the linear products (4 + 4’) was ca. 62% in all runs; ccatalyst: [Rh(cod)(m-OMe)]2 (5.0 × 10−3 mmol) and
TPPMS (5.0 × 10−2 mmol) instead of IRA900/TPPMS/Rh. The reaction was nearly completed in 5 h; druns 12 and 13 were the first and the second re-using
of the catalyst separated after run 10.

2376
An Electrostatically-Anchored Rhodium(I) Catalyst for the Hydroformylation
J. Braz. Chem. Soc.
only for 10% of the mass balance at the end of the 24-hour
reaction.A possible explanation for this observation is that,
differently from the chloride-free homogeneous system,
in the anchored system HCl can be released during the
formation of catalytically active species from the rhodium
precursor and this acid will favor the acetalization step.
After run 10 the catalyst was recovered and used
two more times (Table 2, runs 12 and 13). In both
recycles, eugenol was completely transformed into the
hydroformylation products in 24 h (ca. 90% acetals) at
nearly the same rate and with similar selectivity as in the
original reaction.
The catalyst is also useful to other naturally occurring
allyl benzene, i.e., estragole 1b (Table 2, run 14). The
reaction was also nearly completed in 24 h giving
hydrofomylation products in 99% selectivity, albeit with
slightly lower relative amounts of the corresponding acetals
(71%).
Isoeugenol (2a) was also tested under the
hydroformylation conditions in methanol solutions
(Table 2, run 15). The rate of the conversion of this internal
olefin was very low: only 9% of the substrate was converted
in 24 h. Moreover, most of the converted substrate was
transformed into the terminal isomer, eugenol 1a. The
latter yielded aldehydes 4a and 5a and corresponding
acetals 4’a and 5’a. Aldehyde 6a (Scheme 1), one of
the expected product of the direct hydroformylation of
2a, was not observed at all. This result shows that the
catalyst can be used for the selective hydroformylation of
allyl benzenes, even in the presence of a large quantity of
propenyl benzenes.
Nacional de Desenvolvimento Científico e Tecnológico
(CNPq), INCT-Catálise are acknowledged.
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Submitted: August 20, 2014
Published online: November 4, 2014