Rhodium-sulfonated diphosphine catalysts in aqueous hydroformylation of vinyl arenes: High-pressure NMR and IR studies

Article abstract of DOI:10.1016/S1381-1169(02)00544-7

Hydroformylation of vinyl arenes (p-methoxystyrene andp-fluorostyrene) was performed in aqueous solutions using as catalyst precursor [Rh(μ-OMe)(cod)]₂ (cod = 1,5-cyclooctadiene) associated with the sulfonated 1,3-diarylphosphines (tetrasulfona

Full text of DOI:10.1016/S1381-1169(02)00544-7

Journal of Molecular Catalysis A: Chemical 195 (2003) 113–124
Rhodium-sulfonated diphosphine catalysts in aqueous
hydroformylation of vinyl arenes: high-pressure
NMR and IR studies
Ali Aghmiza, Arantxa Orejóna , Montserrat Diégueza, Maria Dolors Miquel-Serranoa,
Carmen Clavera, Anna M. Masdeu-Bultóa,∗ , Denis Sinoub,1, Gábor Laurenczyc,2
a
Departament de Qu´ımica F´ısica i Inorgànica, Universitat Rovira i Virgili, Pl. Imperial Tàrraco1, 43005 Tarragona, Spain
b
Laboratoire de Synthèse Asymétrique Associé au CNRS, CPE Lyon, Université Claude Bernard Lyon I,
43 Boulevard du 11 Novembre 1918, 69622 Villeurbanne Cédex, France
Ecole Polytechnique Fédérale de Lausanne, Faculté des Sciences de Base, Institut de Chimie Moléculaire et Biologique,
c
EPFL-BCH, CH-1015 Lausanne, Switzerland
Received 17 July 2002; accepted 18 September 2002
Abstract
Hydroformylation of vinyl arenes (p-methoxystyrene and p-fluorostyrene) was performed in aqueous solutions using as cat-
alyst precursor [Rh(␮-OMe)(cod)]2 (cod = 1,5-cyclooctadiene) associated with the sulfonated 1,3-diarylphosphines (tetra-
sulfonated 1,3-bis(diphenylphosphino)propane (dpppts)) and the chiral (S,S)-bdppts (2,4-bis(diphenylphosphino)pentane).
The influence of pH on the reaction rate was studied. After 24 h conversion was practically total with the achiral system in
basic medium for the substituted styrene substrates. Selectivities in aldehydes were >85%. At neutral pH, the asymmetric
hydroformylation of p-substituted styrenes using the rhodium–bdppts systems provides low conversion but the enantios-
electivities were as high as 66%, the highest reported so far for this kind of substrates in aqueous systems. Comparison
experiments using rhodium precursors with the non-sulfonated bdpp in organic solvents indicated that the enantioselectivity
was higher in aqueous solutions for the p-methoxystyrene derivative and slightly lower for p-fluorostyrene. However, in both
the cases the conversions in aqueous systems were low. High-pressure NMR and IR experiments in water/methanol indicate
that [RhH(CO)2(sulfonated diphosphine)] species form under catalytic conditions in basic medium. At neutral pH, the main
species observed in the case of the bdppts ligand is [Rh(bdppts)2]+ which may account for the low conversion in this medium.
© 2002 Elsevier Science B.V. All rights reserved.
Keywords: Rhodium; Hydroformylation; Sulfonated diphosphines; Aqueous systems; Asymmetric catalysis
1. Introduction
∗
Since the water soluble rhodium–tppts system
(tppts = P(C6H4-m-SO3Na)3) [1,2] was first applied
to the industrial hydroformylation of propene by
Corresponding author. Tel.: +34-977-559572;
fax: +34-977-559563.
E-mail addresses: masdeu@quimica.urv.es (A.M. Masdeu-Bulto´),
sinou@univ-lyon1.fr (D. Sinou), gabor.laurenczy@epfl.ch
(G. Laurenczy).
ˆ
Rhone-Poulenc/Ruhr-Chemie in 1984 [3,4], research
1
in the area of biphasic catalysis has become very
active [5]. Although other water-soluble ligands have
Fax: +33-4-72448160.
2
Fax: +41-216-939865.
1381-1169/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S1381-1169(02)00544-7

114
A. Aghmiz et al. / Journal of Molecular Catalysis A: Chemical 195 (2003) 113–124
Fig. 1. Sulphonated diphosphines.
been used, most studies use the monodentate tppts
ligand.
Rh–tppts system. However, no optical induction was
observed. In the hydroformylation of styrene with wa-
ter/toluene as the solvents, no enantiomeric excesses
(e.e.) was observed when the chiral sulfonated deriva-
tive of biphlophos was used (Fig. 1) [14]. Neverthe-
less, the rhodium system with the chiral sulfonated
diphosphine (S)-binas6-Na, provided an enantioselec-
tivity as high as 18%, indicating that optical induction
can be obtained in aqueous systems [15].
In this context, we recently reported the asym-
metric hydroformylation of styrene using tetrasul-
fonated diphosphines (S,S)-bdppts ((tetrasulfonated
2,4-bis(diphenylphosphino)pentane) and (R,R)-cbdts
(cbdts: tetrasulfonated 1,2-bis(diphenylphosphinome-
thyl)cyclobutane) (Fig. 2) [16]. The enantioselectiv-
ities for rhodium–bdppts systems were in the same
range as those reported for binas-Na systems.
Although the activities and selectivities in the
hydroformylation of propene are better with sul-
fonated diphosphines such as bisbis [6] or binas-Na
[7] (Fig. 1) than with Rh–tppts very little can be
found in the literature about sulfonated diphosphines.
The Rh–dppets system (dppets: tetrasulfonated
1,2-bis(diphenylphosphino)ethane) [8] has been used
in the hydroformylation of 1-octene (conversion = 5–
25%) and the [Rh(acac)(CO)2]/dppbts system (dppbts:
tetrasulfonated 1,4-bis(diphenylphosphino)butane) in
the hydroformylation of methyl acrylate [9]. The
sulfonato group has also been incorporated into the
xantene backbone in the sulfonated xantphos (Fig. 1)
which has been used in the rhodium hydroformylation
of 1-hexene [10]. Chelating diphosphines with sul-
fonated pendant groups p-C6H4–(CH2)n–C6H4SO3Na
and a binaphtyl or biphenyl backbone [11,12] have
also been used in the hydroformylation of 1-octene.
There are few reports about the asymmetric hy-
droformylation of vinyl arene derivatives in aqueous
systems probably because the corresponding aldehy-
des are easy to racemize. Thus, the monophosphine
P(menthyl)[(CH2)8C6H4–p-SO3Na]2 associated with
rhodium complexes [13] gives higher conversion and
regioselectivity in the branched aldehyde than the
Fig. 2. Chiral sulphonated diphosphines.

A. Aghmiz et al. / Journal of Molecular Catalysis A: Chemical 195 (2003) 113–124
115
To avoid racemization of the 2-phenylpropanal
derivatives formed, the control of the pH is crucial
in aqueous systems. Nevertheless, the pH of the so-
lution affects the activity of the catalyst. It has been
reported that hydroformylation reactions of alkenes
are faster at basic pH [17–19]. Reactivity studies
concerning sulfonated monophosphines showed that
the chloro carbonyl complex [RhCl(CO)(tppms)2]
(tppms = PPh2(C6H4–m-SO3Na)) reacts with H2 to
form the species [RhH(CO)(tppms)3] only when the
pH is ≥5 [20] which explains the general observation
that activity increases as pH increases.
In this paper, we present our study on the hydro-
formylation of p-methoxystyrene and p-fluorostyrene
using rhodium catalysts with the 1,3-diphosphines
1,3-bis(diphenylphosphino)propane (dpppts) and the
ligands (S,S)-bdppts. We also compare our results with
the results provided by rhodium systems using the
non-sulfonated diphosphine bdpp in organic solvents.
Due to the importance of the reaction medium’s
pH for activity and selectivity since it controls the
species formed, we used high-pressure NMR and
IR techniques to analyse the Rh-sulfonated diphos-
phine solutions under CO and H2 as a function
of pH in order to identify the species present un-
der hydroformylation conditions. Although there
are many spectroscopic studies under hydroformy-
lation conditions with Rh–phosphine [21–23] and
Rh–diphosphine [24,25] systems in organic solvents,
the studies in aqueous solutions are very few [20].
for the separation of the chiral carboxylic acids. The
1H and 31P NMR spectra were registered on a Varian
300 MHz instrument and referenced in the usual way.
High-pressure NMR experiments (HP NMR) were
carried out in a 10 mm diameter sapphire tube with a
titanium cap [29]. High-pressure infrared experiments
(HP IR) were performed in an IR cell equipped with
a CaF2 window, sample holders built from PTFE and
mixing and heating facilities [30].
2.2. Catalysis
Hydroformylation experiments were carried out in
an autoclave equipped with magnetic stirrer. The reac-
tion mixtures were kept in a Teflon vessel and the inner
part of the autoclave’s cap was also Teflon-covered to
prevent the solution from coming into direct contact
with the stainless steel. An electric heating mantle kept
the temperature constant. The standard procedure for
the hydroformylation experiments in organic solvents
has been reported previously [31].
2.2.1. Standard hydroformylation experiment
The catalyst precursor [Rh(␮-OMe)(cod)]2 (0.015
mmol) and the sulfonated phosphorus compound
were stirred in the corresponding ratio for 1 h in the
corresponding solvent (6 ml) until they totally dis-
solved. The pH was adjusted to the desired value
using NaOH (0.25 M) or H2SO4 (0.25 M). The sub-
strate (15 mmol) was added and the whole mixture
placed in the evacuated autoclave. The gas mixture
was introduced and the heating started. When thermal
equilibrium was reached, more gas mixture was in-
troduced until the desired pressure. After the reaction
time, the autoclave was cooled to room temperature
and depressurized. The reaction mixture was extracted
with dichloromethane (3×5 ml) and the organic phase
was dried over magnesium sulfate and analyzed by
GC. Enantiomeric excesses were measured by GC
using a chiral column after the aldehydes had been
transformed into carboxylic acids in accordance with
described procedures [32].
2. Experimental
2.1. General methods
All syntheses of the rhodium catalyst precur-
sors were carried out using standard Schlenk tech-
niques under a nitrogen atmosphere. Solvents were
distilled and deoxygenated before use. All other
reagents were used as supplied. The complex
[Rh(␮-OMe)(cod)]2 [26] and the diphosphines dpppts
and (S,S)-bdppts were prepared as previously re-
ported [27,28]. Gas chromatography analyses were
performed in a Hewlett-Packard 5890A in an Ultra-2
(5% diphenylsilicone/95% dimethylsilicone) column
(25 m × 0.2 mm Ø) for the separation of the aldehy-
des and in a FS-cyclodex ␤-I/P (50 m × 0.25 mm Ø)
2.3. HP NMR experiments
In a typical experiment, the rhodium complex [Rh
(␮-OMe)(cod)]2 (0.04 mmol) and dpppts (0.16 mmol)
were dissolved in 2 ml of methanol-d4/D2O (3/1)

116
A. Aghmiz et al. / Journal of Molecular Catalysis A: Chemical 195 (2003) 113–124
under nitrogen. The solution was placed into the sap-
phire NMR tube (Ø = 10 mm) which was closed.
After the mixture had been pressurized with H2/CO,
the tube was shaken at 50 ◦C for 16 h, it was placed
in the NMR spectrometer and the spectra were
recorded.
In all the experiments a 1/1 mixture of water/metha-
nol was used since previous studies showed that these
conditions provide the best chemioselectivity and ac-
tivity [16]. In the experiments with the Rh–dpppts
systems (entries 1–3, Table 1) the pH of the solu-
tion was adjusted to 11. The p-methoxy and p-fluoro
substituted substrates 1a and b were hydroformylated
with the rhodium/sulfonated diphosphine dpppts sys-
tem and the total conversions were higher than styrene
1c although selectivity in aldehydes was slightly
lower. The regioselectivity of the reaction for both the
substrates 1a and 1b was similar to that of styrene 1c.
When the asymmetric hydroformylation of the
styrene derivatives was performed with the rhodium
precursors and bdppts as the chiral ligand, the initial
pH was adjusted to 7 to avoid racemization of the
chiral aldehyde because of the keto-enol tautomeriza-
tion. As reported in the literature on systems that use
the monophosphine tppts as the ligand, a decrease in
the pH means that the conversion into aldehydes is
lower than when dpppts is used as the ligand (entries
4–6, Table 1) [17].
2.4. HP IR experiments
In a typical experiment, the rhodium com-
plex [Rh(␮-OMe)(cod)]2 (0.02 mmol) and dpppts
(0.08 mmol) were dissolved in a 4 ml of wa-
ter/methanol mixture (1/1) under nitrogen. The so-
lution was placed in the HP IR cell and pressurized
with the H2/CO mixture. The cell was placed in the
IR spectrometer and the spectra were recorded.
3. Results and discussion
3.1. Catalytic studies
The enantioselectivities obtained with the Rh-bdppts
catalysts for 1a and 1b were higher than those ob-
tained in the hydroformylation of styrene 1c (entry 6,
Table 1). In the hydroformylation of the p-methoxy
derivative 1a with the Rh–bdppts system at 30 ◦C the
enantiomeric excess for 2a was 66% (entry 4, Table 1).
At higher temperatures polymerization took place.
It is important to note that the neutralization should
be done carefully in order to obtain repetitive results in
enantioselectivity. Results were similar when a buffer
solution (HPO42−/PO43−) was used.
The hydroformylation of styrene derivatives 1a–c
and vinyl-naphthalene 1d yields the corresponding
branched aldehydes (2a–d) and linear aldehydes
(3a–d) according to Eqs. (1) and (2). We previously
reported the results obtained in the hydroformyla-
tion of 1c in aqueous systems [16]. Table 1 shows
the results in the hydroformylation of 1a and 1b us-
ing [Rh(␮-OMe)(cod)]2 with the sulfonated diphos-
phines dpppts and (S,S)-bdppts as catalyst precursors
in aqueous systems and with Rh–bdpp in organic
solvents.
(1)
(2)

A. Aghmiz et al. / Journal of Molecular Catalysis A: Chemical 195 (2003) 113–124
117
Table 1
Hydroformylation of p-methoxystyrene (1a), p-fluorostyrene (1b), styrene (1c) and 2-vinylnaphthalene (1d) using [Rh(␮-OMe)(cod)]2/L as
catalyst precursorsa
Entry
L
Substrate
T (◦C)
t (h)
CT (%)b
Selectivity in
aldehyde (%)
2/3
91/9
e.e. (%)
1
2
3c
4
dpppts
dpppts
dpppts
(S,S)-bdppts
(S,S)-bdppts
(S,S)-bdppts
(S,S)-bdpp
(R,R)-bdpp
(R,R)-bdpp
(R,R)-bdpp
1a
1b
1c
1a
1b
1c
1a
1b
1c
1d
80
80
80
30
65
65
30
65
65
50
24
24
24
72
8
24
48
8
99
99
62
2
10
4
20
99
92
54
85
89
100
82
98
100
95
100
100
100
–
–
–
94/6
93/7
100/0
97/3
90/10
95/5
95/5
94/6
96/4
66 (+)
44 (R)
14 (R)
54 (+)
54 (S)
56 (S)
65 (S)
5
6c
7d
8d
9d,e
10d
7
14
L = dpppts, bdppts and bdpp.
a Reaction conditions: [Rh(␮-OMe)(cod)]2 = 5.10–3 M, [substrate]/[Rh] = 500, P/Rh = 4, solvent 3 ml H2O/3 ml MeOH, 14 atm
pressure (CO/H2 = 1/1), t = 24 h, initial pH = 11 for experiments 1–3; initial pH = 7 for experiments 4–6.
b Total conversion measured by GC integral ratio based on substrate.
c Ref. [16].
d Reaction conditions: solvent = THF; CO/H2 = 1/1; substrate/precursor = 200; pressure = 10 atm.
e Ref. [31].
For substrate 1b, when the same catalytic system
was used the enantioselectivity at 65 ◦C was 44% e.e.
(entry 5, Table 1).
When vinyl naphthalene was used as substrate in
aqueous solution no aldehydes were detected because
it is not very soluble in water.
Comparing the results obtained in aqueous sys-
tems with the ones obtained in THF (entries 4–6
compared to entries 7–10, Table 1) we observe that,
as expected, conversions are lower in aqueous me-
dia but regioselectivities are similar. The enantios-
electivity obtained with aqueous systems is higher
for substrate 1a under the same conditions. For
substrate 1b, the enantioselectivity in the aqueous
system (44% e.e.) is lower than the one observed
in THF (54% e.e.) but the value is still signifi-
cative.
Vinyl-naphthalene was hydroformylated at 50 ◦C
and the e.e. observed was 65% while in aqueous sys-
tems no conversion was detected.
In conclusion, the comparative study shows that it
is possible to obtain moderate enantioselectivities if
aqueous systems are used in the hydroformylation of
vinyl arenes.
Fig. 3. 31P NMR spectrum at 121.4 MHz in CD3OD/D2O of [Rh(␮-OMe)(cod)]2/dpppts (P/Rh = 4) under 7 atm of H2.

118
A. Aghmiz et al. / Journal of Molecular Catalysis A: Chemical 195 (2003) 113–124
Scheme 1.
3.2. High-pressure NMR and IR studies
The doublet at δ = 39.6 ppm (1JP,Rh = 177 Hz)
was attributed to the Rh(I) species with coordinated
methanol [Rh(dpppts)(CD3OD)2]+ (4; Scheme 1).
The P–Rh coupling constants reported for analo-
gous complexes [Rh(diphosphine)(CH3OH)2]+ were
190 Hz for dppp and 175 Hz for the diphosphine
(2S,3S)-bis(diphenylphosphino)butane [33].
The doublet at δ = 27.6 ppm with a high cou-
pling constant (1JP,Rh = 192 Hz) may correspond
to a dimeric species [Rh(␮-OMe)(dpppts)]2 (5)
since it correlates well with the values reported
We analyzed the high-pressure NMR and IR spectra
so that we could identify the species formed under
catalytic conditions with sulfonated diphosphines.
We used methanol-d4/D2O (3/1) as solvent at basic
pH to record the 31P-{1H} and 1H NMR spectra of so-
lutions of the catalyst precursor [Rh(␮-OMe)(cod)]2
associated with the corresponding sulfonated diphos-
phine. To facilitate the identification of the species,
H2 was first added (7 atm), subsequently, carbon
monoxide was introduced up to 14 atm of total pres-
sure (CO/H2 = 1/1) and, finally the substrate was
added and the spectra recorded after each step.
for [Rh(␮-Cl)(dppp)]2 (1JP,Rh
=
184 Hz) and
[Rh(␮-Cl)(diop)]2 (1JP,Rh = 191 Hz) [33].
In the 20–23 ppm region of the 31P NMR spec-
trum there was a group of broad signals among
which a doublet was detected at δ = 21.6 ppm
(1JP,Rh = 142 Hz). The hydride region of the 1H
NMR spectrum had a wide signal at δ = −10.4 ppm.
By comparison with published data for the anal-
ogous complex [RhH(dppp)2] [34], these signals
were attributed to [RhH(dpppts)2] (6), the P–Rh
coupling constant reported for [RhH(dppp)2] was
J = 142.5 Hz. The phosphorus and hydride sig-
The 31P-{1H} NMR spectrum of the solution of
[Rh(␮-OMe)(cod)]2/dpppts (P/Rh = 4) under 7 atm
of H2 at room temperature showed five groups of sig-
nals at δ = 39.6 (d), 27.6 (d), 21.6 (d), 21.0 (dt) and
6.5 (broad) ppm (Fig. 3). The signals corresponding
to the oxidized phosphine at ca 35 ppm were also ob-
1
served. The H NMR spectrum in the hydride region
showed three broad signals at δ = −10.4, −8.1 and
−8.6 ppm.

A. Aghmiz et al. / Journal of Molecular Catalysis A: Chemical 195 (2003) 113–124
119
Fig. 4. 31P NMR spectrum at 121.4 MHz in CD3OD/D2O of [Rh(␮-OMe)(cod)]2/dpppts (P/Rh = 4) under 14 atm of CO/H2 (1/1) at: (a)
20 ◦C, (b) −60 ◦C, (c) 50 ◦C.
nal could not be resolved by decreasing the tempe-
rature.
olution was found even at temperatures as low as
−60 ◦C.
In the same region, there was a doublet of triplets at
The solution was then pressurized up to 14 atm of
CO/H2 (1/1). The 31P NMR spectrum at room temper-
ature (Fig. 4a) showed signals at δ = 15.8, 10.0 and
δ = 21.0 ppm (1JP,Rh = 100 Hz and JP,P = 30 Hz)
2
correlating with a broad signal at δ = 6.5 ppm. The
hydride region showed two broad signals at δ = −8.1
and −8.4 ppm. These values agree with those reported
for the analogous dihydrido species [RhH2(dppp)2]+
1
−8.4 ppm and the H NMR showed a broad hydrido
signal at δ = −9 ppm. The doublet at δ = 15.8 ppm
(1JP,Rh = 112 Hz) and the hydrido signal at δ =
−9 ppm in the 1H NMR were assigned to the species
[RhH(CO)2(dpppts)] (8) by comparison with reported
data for similar complexes with dppp [25]. Cooling
the solution to −60 ◦C (Fig. 4b) enabled the doublet
at δ = 15.8 ppm to be resolved into a doublet of
1
2
(31P: δ = 19.96 ppm, JP,Rh = 99.6 Hz and JP,P
=
1
1
30 Hz; δ = 9.12 ppm, JP,Rh = 82.2.6 Hz; H (hy-
dride region): δ = −8.2 and −8.9 ppm, multiplets)
[25,34]. Therefore, we assigned these signals to the di-
hydride species [RhH2(dpppts)2]+ (7). No better res-

120
A. Aghmiz et al. / Journal of Molecular Catalysis A: Chemical 195 (2003) 113–124
doublets (δ = 16.7 ppm, 1JP,Rh = 103 Hz and 2JP,P
=
ciated with the non-sulfonated ligand dppp in THF
showed strong absorptions at 1943 and 1985 cm−1
50 Hz), which correlate with a new doublet of dou-
blets now appearing at δ = 2.4 ppm (1JP,Rh = 132 Hz
and 2JP,P = 50 Hz). These signals may be assigned to
the axial and equatorial phosphorus of species 8, re-
spectively, in which the equilibrium was frozen at low
temperature. The average of both coupling constants
(J = 117 Hz) was in the range observed at room tem-
perature. Although these signals are not usually ob-
served, the polar solvent and the ionic nature of the
ligand may allow these signals to be resolved. When
the solution was heated to 50 ◦C (Fig. 3c), the doublet
at δ = 15.8 ppm was formed again.
.
These absorptions were attributed to the species
[RhH(CO)2(dppp)] in which the phosphorus atoms
are coordinated in the equatorial and axial posi-
tion [25]. For diphosphines with larger bite angles,
the complex [RhH(CO)2(diphosphine)] may exist
as mixtures of equatorial–axial and –equatorial iso-
mers. The infrared spectra observed in these cases
showed four absorptions in the carbonyl region
[24,25]. The band at 2034 cm−1 for the Rh–dpppts
system may correspond to the equatorial–equatorial
species or to a Rh–H stretching frequency. The
␯(CO) reported for the equatorial–equatorial complex
[RhH(CO)2(binas-Na)] were 2041 and 1981 cm−1
[15]. For species 8, we were unable to detect the
expected second absorption maybe because the res-
olution of the spectrum was low. No carbonyl fre-
quencies were detected in the region of the bridged
carbonyl stretching frequencies.
Two broad signals at δ = 15 and −8.4 ppm in the
31P-{1H} NMR spectra were assigned to the monocar-
bonyl species [Rh(CO)(dpppts)2]+ (9) by comparison
to published data [35,36]. These signals could not be
resolved in the range from −60 to +50 ◦C.
Finally, the broad doublet observed at δ = 10.0 ppm
in the 31P NMR spectrum at room temperature in-
creased in intensity and resolved at 50 ◦C (1J =
150 Hz; Fig. 4c). It was attributed to the dimeric
species [Rh(␮-CO)(CO)(dpppts)]2 (10) [37].
Finally, a solution containing the rhodium complex
[Rh(␮-OMe)(cod)]2 with ligand dpppts (P/Rh = 4)
and styrene as a model substrate (substrate/catalyst =
5) was pressurized at 14 atm CO/H2 (1/1) and the evo-
lution of the hydroformylation reaction was monitored
by NMR. The 31P NMR of this solution showed wide
signals in the 15–16, 10 and −7 ppm regions corre-
sponding to species 8, 9 and 10 and the 1H NMR
a broad signal at δ = −9 ppm. These signals could
not be resolved in the temperature range from +60 to
−40 ◦C.
We confirmed the presence of species 8 by carrying
out HP IR experiments in a solution of the complex
[Rh(␮-OMe)(cod)]2 with ligand dpppts (P/Rh = 4) in
a mixture of 1/1 of water/methanol at 14 atm CO/H2
(1/1). The IR spectrum of this solution after 1.5 h
of stirring at 50 ◦C showed three strong absorptions
at 1955, 1990 and 2034 cm−1 in the n(CO) stretch-
ing region (Fig. 5). A reference experiment under
the same conditions with [Rh(␮-OMe)(cod)]2 asso-
The rhodium catalyst precursor system with bdppts
was also studied by HPNMR at different pH values.
The 31P NMR spectrum of [Rh(␮-OMe)(cod)]2 with
the ligand bdppts (P/Rh = 4), 14 atm CO/H2 (1/1)
(Fig. 6a) and basic pH showed only a clean doublet at
δ = 29.8 ppm (1JP,Rh = 111.7 Hz) and a broad sig-
1
nal at δ = 23.8 ppm. In the hydride region of the H
NMR spectrum a doublet of triplets at δ = −9.4 ppm
(2JH,P = 56.4 Hz, JH,Rh = 11.7 Hz) was observed.
1
The signal at δ = 29.8 ppm and the hydride was
attributed to the complex [RhH(CO)2(bdppts)] (11)
(Scheme 2) by comparison with the reported data for
the analogous non-sulfonated bdpp complex [25]. The
intermediate values of the phosphorus–hydride cou-
pling constants indicate that there is an equilibrium
between the two equatorial–axial diastereomers of 11
in fast exchange in the NMR time scale [25]. When
Fig. 5. v(CO) stretching region of the IR spectra in MeOH/H2O
of [Rh(␮-OMe)(cod)]2/dpppts (P/Rh = 4) under 14 atm of CO/H2
(1/1).

A. Aghmiz et al. / Journal of Molecular Catalysis A: Chemical 195 (2003) 113–124
121
Fig. 6. 31P NMR spectra at 121.4 MHz in CD3OD/D2O of [Rh(␮-OMe)(cod)]2/bdppts (P/Rh = 4) under 14 atm of CO/H2 (1:1) at pH = 11
at: (a) 20 ◦C (300.0 MHz 1H NMR hydride region inserted), (b) 80 ◦C, (c) 80 ◦C with styrene (Rh/styrene = 1/5).
the sample was cooled to −40 ◦C, the signals became
less resolved.
under nitrogen24b but it disappeared under H2 or
H2/CO pressure. In our case, we attribute the signal at
δ 23.8 ppm to the analogous complex [Rh(bdpp)2]+
(12), which may be present even under CO/H2 pres-
sure because the gases are not very soluble in the
aqueous solution and the polar solvents favored its
When the solution was heated, the broad signal at
δ = 23.8 ppm was resolved into a doublet (Fig. 6b).
At 80 ◦C, the coupling constant observed for this dou-
blet was J = 131.8 Hz. A doublet at δ = 23.7 ppm
with a coupling constant of 130 Hz has been re-
ported for the bisphosphine species [Rh(bdpp)2]+
in THF-d8. This species was reported to form in a
solution of [Rh(␮-OMe)(cod)]2 with excess of bdpp
formation. The 31P and H signals corresponding to
1
species 11 were also observed at 80 ◦C. Cooling again
the solution to room temperature, the 31P spectra was
similar to the one presented in Fig. 6a.

122
A. Aghmiz et al. / Journal of Molecular Catalysis A: Chemical 195 (2003) 113–124
Scheme 2.
Fig. 7. 31P NMR spectra at 121.4 MHz in CD3OD/D2O of [Rh(␮-OMe)(cod)]2/bdppts (P/Rh = 4) under 14 atm of CO/H2 (1/1) at neutral
pH after 1 h reaction at: (a) 20 ◦C, (b) 80 ◦C.

A. Aghmiz et al. / Journal of Molecular Catalysis A: Chemical 195 (2003) 113–124
123
Finally, this solution was depressurized, styrene was
added in a 5:1 molar ratio respect to Rh and the so-
lution was re-pressurized to 14 atm (CO/H2 = 1/1).
At 80 ◦C, the main signal observed in the 31P-{1H}
spectrum (Fig. 6c) was the doublet at δ = 30.6 ppm
(1JP,Rh = 111.6 Hz). The double triplet hydride sig-
nal at −9.4 ppm in the 1H spectrum confirmed the
formation of species 11. The spectrum also showed a
broad doublet at δ = 24.7 ppm (J = 122.6 Hz), which
probably corresponds to species 12. The variation of
the coupling constant and the broadening of the signal
are indicative of fluxionality, probably because of the
reaction with the substrate.
sions into aldehydes were low at neutral pH but some
of the enantioselectivities obtained with the chiral sys-
tems were higher than the ones obtained in organic
solvents.
High-pressure NMR and IR experiments in wa-
ter/methanol showed that [RhH(CO)2(sulfonated
diphosphine)] species, which are analogous to those
observed in organic systems, form under catalytic
conditions at basic pH. When the pH of the solution
was neutral the main species formed was the cationic
inactive bischelated [Rh(bdppts)2]+ which reacts with
H2 and CO only at basic pH so enabling this process
to be reversed.
To sum up, the spectroscopy studies showed
that, like in organic solvents, [RhH(CO)2(bdppts)]
is formed in basic aqueous solutions. The inactive
dimeric species [Rh(␮-CO)(CO)(bdpp)]2 was re-
ported to form also in organic solvents under CO/H2
pressure. In aqueous systems, however, we observed
cationic bisphosphine species 12. The formation of
this species together with the low solubility of the
substrates in aqueous solutions may account for the
lower activity observed in water/methanol solutions.
At neutral pH, the 31P NMR spectrum of
[Rh(␮-OMe)(cod)]2 with the bdppts ligand (P/Rh =
4) at 14 atm CO/H2 (1/1), 20 ◦C (Fig. 7a) and after 1 h
reaction time shows a broad doublet at δ = 24.5 ppm,
which resolves at 80 ◦C (δ = 24.9 ppm, J = 132.7 Hz;
Fig. 7b) and which is attributed to cationic species 12.
After a reaction time of 16 h a small doublet at δ =
30.1 ppm (J = 106.1 Hz) corresponding to species 11
was also detected. The formation of cationic species
12 as a major product explains the drastic decrease
in activity at neutral pH. When styrene was added to
this solution (styrene/Rh ratio = 5/1) the 31P NMR
spectra under 14 atm CO/H2 (1/1) were similar.
After aqueous sodium hydroxide had been added to
the solution containing species 12 and 11 and it had
been repressurized to 14 atm (CO/H2 = 1/1), the 31P
NMR spectra showed an increase in species 11. This
process could be reversed by changing the pH.
Acknowledgements
We thank the Ministerio de Educación y Cien-
cia, the Generalitat de Catalunya and the Commision
for the European Communities for financial sup-
port (PB97-0407-C05-01, “Accio´ integrada” ACI-96,
COST D10 Action 01). G. Laurenczy thanks the
Swiss National Science Foundation for financial sup-
port (Grant 2100-061653.01). We also thank Dr. L.
Nádasdi for useful help in the realization of the HP
IR experiments.
References
[1] E.G. Kuntz, Rhoˆne-Poulenc Recherche, Fr 2.314.910, 1975.
[2] E.G. Kuntz, Chemtech, 1987, 570.
[3] B. Cornils, E.G. Kuntz, J. Organomet. Chem. 502 (1995) 177.
[4] B. Cornils, E. Wiebus, Rec. Trav. Chim. Pays-Bas 115 (1996)
211.
[5] B. Cornils, W.A. Herrmann, Aqueous-Phase Organometallic
Catalysis, Wiley-WCH, Weinheim, 1998.
[6] W.A. Herrmann, C.W. Kohlpaintner, H. Bahrman, W. Konkol,
J. Mol. Catal. 73 (1992) 191.
[7] W.A. Herrmann, C.W. Kohlpaintner, R.B. Manetsberger, H.
Bahrman, H. Kottmann, J. Mol. Catal. A 97 (1995) 65.
[8] T. Bartik, B.B. Bunn, B. Bartik, B.E. Hanson, Inorg. Chem.
33 (1994) 164.
[9] G. Fremy, E. Monflier, J.-F. Carpentier, Y. Castanet, A.
Mortreux, Angew. Chem. Int. Ed. Engl. 34 (1995) 1474.
[10] M. Schrender Goedheijt, P.C.J. Kamer, P.W.N.M. van
Leeuwen, J. Mol. Catal. 134 (1998) 243.
4. Conclusions
[11] H. Ding, J. Kang, B.E. Hanson, C.W. Kohlpaintner, J. Mol.
Catal. A 124 (1997) 21.
[12] B.E. Hanson, H. Ding, C.W. Kohlpaintner, Catal. Today 42
(1998) 421.
We used the catalyst precursor [Rh(␮-OMe)(cod)]2
with sulfonated diphosphines in aqueous solutions to
perform the hydroformylation of vinyl arenes. Conver-

124
A. Aghmiz et al. / Journal of Molecular Catalysis A: Chemical 195 (2003) 113–124
[13] T. Bartik, H. Ding, B. Bartik, B.E. Hanson, J. Mol. Catal. A
98 (1995) 117.
[14] F.A. Rampf, M. Spiegler, W.A. Herrmann, J. Organomet.
Chem. 582 (1999) 204.
[15] R.W. Eckl, T. Priermeier, W.A. Herrmann, J. Organomet.
Chem. 532 (1997) 243.
[25] A. Castellanos-Páez, S. Castillón, C. Claver, P.W.N.M.
van Leeuwen, W.G.J. de Lange, Organometallics (1998)
2543.
[26] R. Usón, L.A. Oro, J. Cabeza, Inorg. Synth. 23 (1985) 126.
[27] Y. Amrani, L. Lecomte, D. Sinou, J. Bakos, I. Toth, B. Heil,
Organometallics 8 (1989) 542.
[16] M.D. Miquel-Serrano, A.M. Masdeu-Bultó, C. Claver, D.
Sinou, J. Mol. Catal. A 143 (1999) 49.
[28] L. Lecomte, D. Sinou, Phosphorus, Sulfur Silicon 53 (1990)
239.
[17] R.M. Deshpande, Purwanto, H. Delmas, R.V. Chaudhari, J.
Mol. Catal. A 126 (1997) 133.
[29] A. Cusanelli, U. Frey, D.T. Richens, A.E. Merbach, J. Am.
Chem. Soc. 118 (1996) 5265.
[18] R.T. Smith, R.K. Ungar, L.J. Sanderson, M.C. Baird,
Organometallics 2 (1983) 1138.
[30] G. Laurenczy, F. Lukács, R. Roulet, Anal. Chim. Acta 359
(1998) 275.
[19] E. Mieczynska, A.M. Trzeciak, J.J. Ziólkowski, J. Mol.
Catal. A 148 (1999) 59.
[20] F. Joó, J. Kovács, A.C. Bényei, L. Nádasdi, G. Laurenczy,
Chem. Eur. J. 7 (2001) 193.
[31] A.M. Masdeu-Bultó, A. Orejón, A. Castellanos-Páez, S.
Castillón, C. Claver, Tetrahedron Asymm. 7 (1996) 1829.
[32] A. Abiko, J.C. Roberts, T. Takemasa, S. Masamune,
Tetrahedron Lett. 27 (1986) 4537.
[21] A.A. Oswald, J.S. Merola, E.J. Mozeleski, R.V. Kastrup, J.C.
Reisch, Adv. Chem. Ser. 104 (1981) 503.
[33] D.A. Slack, I. Grevelin, M.C. Baird, Inorg. Chem. 18 (1979)
3125.
[22] I.T. Horváth, R.V. Kastrup, A.A. Oswald, E.J. Mozeleski,
Catal. Lett. 2 (1989) 85.
[23] C. Bianchini, H.M. Lee, A. Meli, F. Vizza, Organometallics
19 (2000) 849.
[24] L.A. Van der Veen, M.D.K. Boele, F.R. Bregman, P.C.J.
Kamer, P.W.N.M. Van Leeuwen, K. Goubitz, J. Fraanje, H.
Schenk, C. Bo, J. Am. Chem. Soc. 120 (1998) 11616.
[34] B.R. James, D. Mahajan, Can. J. Chem. 57 (1979) 180.
[35] F. Fache, P. Gamez, F. Nour, M. Lemaire, J. Mol. Catal. 85
(1993) 131.
[36] J.M. Brown, A.G. Kent, J. Chem. Soc., Perkin Trans. 2 (1987)
1597.
[37] B.R. James, D. Mahajan, S.J. Rettig, G.W. Williams,
Organometallics 2 (1983) 1452.