Chiral rhodium(I)-(polyether-phosphite) complexes for the enantioselective hydroformylation of styrene: Homogeneous and thermoregulated phase-transfer catalysis

Article abstract of DOI:10.1016/S0022-328X(00)00526-X

Chiral polyether-phosphite ligands derived from (S)-binaphtol were prepared and combined with [Rh(cod)₂]BF₄ complex. These systems showed high activity, chemo- and regioselectivity, for the catalytic enantioselective hydroformylation of styrene in thermoregulated phase-transfer conditions. ee Values of up to 25% were obtained and recycling was possible, without loss of enantioselectivity. Catalytic activity of the organic and aqueous phases was studied.

Full text of DOI:10.1016/S0022-328X(00)00526-X

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Journal of Organometallic Chemistry 616 (2000) 37–43
Chiral rhodium(I)–(polyether-phosphite) complexes for the
enantioselective hydroformylation of styrene: homogeneous and
thermoregulated phase-transfer catalysis
Je´re´my A.J. Breuzard, M. Lorraine Tommasino, Michel C. Bonnet, Marc Lemaire *
Laboratoire de Catalyse et Synthe`se Organique, UMR 5622, CPE, Uni6ersite´ Claude Bernard-Lyon I, 43, Bd du 11 No6embre 1918,
69622 Villeurbanne Cedex, France
Received 18 May 2000; accepted 25 July 2000
Abstract
Chiral polyether-phosphite ligands derived from (S)-binaphtol were prepared and combined with [Rh(cod)2]BF4 complex. These
systems showed high activity, chemo- and regioselectivity, for the catalytic enantioselective hydroformylation of styrene in
thermoregulated phase-transfer conditions. ee Values of up to 25% were obtained and recycling was possible, without loss of
enantioselectivity. Catalytic activity of the organic and aqueous phases was studied. © 2000 Elsevier Science B.V. All rights
reserved.
Keywords: Water-soluble phosphite; Two-phase hydroformylation; Asymmetric catalysis; Rhodium(I) complexes; Styrene; Thermoregulated
phase-transfer catalysis
lytic activity as a function of temperature: the catalyst
is soluble in the aqueous phase at temperatures lower
than a critical solution temperature called ‘cloud point
(Tp)’ [2,3] and can transfer into the organic phase at
higher temperatures. Such a ‘thermoregulated phase-
transfer catalyst’ should be a convenient system for
performing the reaction either in aqueous or organic
phase, as well as for the recovery of the catalyst.
Thermoregulated phase-transfer catalysis has already
been successfully applied to the aqueous/organic two-
phase hydroformylation of olefins [3]. Jin et al. de-
scribed a polyether-phosphite molecule derived from
catechol as a ‘thermoregulated phase-transfer’ ligand.
Its rhodium complex showed high catalytic activity,
chemo- and regioselectivity in the hydroformylation of
styrene [4].
Hydroformylation of functionalized vinylarenes fol-
lowed by oxidation of the resulting aldehydes can give
2-arylpropionic acids, which represent an important
class of analgesics [5,6]. Since only one enantiomer is
responsible for the biological activity, the preparation
of optically pure product is desired [7–10]. Takaya and
co-workers published the results of a highly enantiose-
lective hydroformylation of functionalized alkenes with
1. Introduction
Hydroformylation of propylene in biphasic condi-
tions (Ruhrchemie/Rhoˆne-Poulenc’s process) has pro-
duced approximately 3 million tons of n-butanal in 10
years, which proves the importance of the aqueous
phase catalysis [1]. In this process, the Wilkinson cata-
lyst HRh(CO)(PPh3)3 is modified with the water-soluble
ligand TPPTS [tris(3-sulfonatophenyl)-phosphine] as
sodium salt. However, the use of water as the second
phase suffers from drawbacks: severe mass-transfer lim-
itations appear for substrates with low water-solubility,
and a large excess of ligand are sometimes necessary to
maintain high activity and selectivity [1].
Bergbreiter et al. previously reported a catalytic sys-
tem based on nonionic water-soluble phosphine–
rhodium complexes [2]. With polyoxoethylene-chains as
the hydrophilic group, the complex exhibits a special
property of inverse temperature-dependent water-solu-
bility [2]. These ‘smart ligands’ should control the cata-
* Corresponding author. Tel.: +33-4-72431407; fax: +33-4-
72431408.
E-mail address: marc.lemaire@univ-lyon1.fr (M. Lemaire).
0022-328X/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00526-X

38
J.A.J. Breuzard et al. / Journal of Organometallic Chemistry 616 (2000) 37–43
a rhodium–(phosphine–phosphite) catalyst (94% ee)
[11–13]. At the same time, Babin et al. reported asym-
metric hydroformylation of various alkenes with ee
values of up to 90% using a rhodium-diphosphite cata-
lyst based on (2R,4R)-pentane-diol [14,15].
That prompted us to extend the ‘thermoregulated
phase-transfer’ concept to the enantioselective hydro-
formylation of styrene. The catalytic activity and the
enantioselectivity of rhodium complexes of chiral
polyether-phosphite ligands derived from (S)-binaphtol
have been examined. This paper describes the synthesis
of new chiral water-soluble phosphite ligands and their
properties for the catalytic aqueous/organic two-phase
hydroformylation of styrene using Rh(I) complexes.
ligands, illustrated in Scheme 1, were prepared through
conversion of (S)-binaphtol to the corresponding phos-
phochloridite [16]. Slow addition of polyether and tri-
ethylamine (THF solution) followed. Filtration of the
ammonium chloride and evaporation of the solvent
give a foam, which is stripped with dry ether. Separa-
tion of the ether phase gives 1 or 2, as raw products,
still containing polyether molecules.
Complex 1 was obtained as an orange viscous liquid.
The estimated cloud point (Tp [2–4]) of the ligand is
100°C [2% (w/w) in water solution]. The yield was
corrected to 70% according to the elemental analysis
(Calc.
for
70%
C53.6H80.3O19.3
P
and
30%
C33.6H69.3O17.3): C, 58.05 (58.93); H, 7.80 (8.00); P,
2.27% (2.23%). Characteristics of chiral monophosphite
([h]D= +67 (c=1.05; THF)), with different chain-
lengths was assessed by NMR and FAB-MS analysis:
31P{1H}: 143.2–143.1. 13C{1H}: 152.5–133.5–130.0–
129.7–128.6–127.9–127.8–127.6–126.4–126.2–125.8–
124.6–124.4–124.2–122.8–121.3–118.1 (arom.); 72.3–
2. Experimental
2.1. General
1
71.4–70.0–67.8–65.3 (CH2O); 58.5 (CH3). H: 8.0–7.0
All operations were performed under argon atmo-
sphere, using standard Schlenk flask techniques. Sol-
vents were dried and distilled before use.
(m, 12H, arom.); 4.1–3.4 (m, 65H); 3.35 (s, 3H, OMe).
FAB (NBA) (M+Na)+: 853.1–895.0–939.2–983.2–
1027.6–1073.6–1116.0–1159.9–1204.1. IR: w (cm−1)=
3449 (OH-PEG); 3050 (arom.); 2958; 2870; 1619; 1589;
1507; 1464; 1433; 1384; 1354; 1324; 1213; 1083; 818;
774; 749; 695.
Melting points (m.p.), noncorrected, were determined
with a Kofler apparatus. Elemental analysis (C, H, P)
were obtained from the Service Central d’Analyse of
the CNRS (Solaize). IR spectra were recorded on a FT
Bruker Vektor 22 spectrometer. 31P-, 1H- and 13C-
NMR spectra were obtained with a Bruker AC-200
instrument (31P 81.015 MHz; 1H 200.132 MHz; 13C
50.323 MHz; l (ppm); J (Hz); s, singlet; d, doublet; t,
triplet; q, quadruplet; m, multiplet; br, broad). Analyti-
cal GLC was carried out with a Shimadzu chro-
matograph fitted with a 15 m EC-5 (SE-54) capillary
column or a 30 m b-Dex-225 chiral column (Aldrich,
i.d. 0.25 mm). Absolute configuration was determined
after reduction with LiAlH4 [15] and comparison with
an authentic sample (ACROS). Rotatory power were
determined with a Perkin–Elmer 241 polarimeter (l=1
dm; 25°C; concentration in g dm−3).
Complex 2 was obtained as an orange viscous liquid.
Yield was corrected to 53% according to the elemental
analysis (Calc. for 62% C48.3H40.6O9.1P2 and 38%
C8.3H18.6O5.1): C, 68.08 (67.41); H, 5.50 (5.51); P, 6.47%
(6.51%). Characteristics of chiral diphosphite ([h]D=
+57 (c=1.02; CDCl3)), with different chain-lengths
was assessed by NMR analysis: 31P{1H}: 140.2–140.1.
13C{1H}:
152.5–133.5–130.0–129.7–128.6–127.9–
127.8–127.6–126.4–126.2–125.8–124.6–124.4–124.2–
122.8–121.3–118.1 (arom.); 72.3–71.4–70.0–67.8–65.3
(CH2O). 1H: 8.0–7.0 (m, 24H, arom.); 3.8–3.4 (m,
16.5H). IR: w (cm−1)=3436 (OH-PEG); 3055 (arom.);
2953; 2870; 1620; 1589; 1505; 1462; 1432; 1398; 1328;
1273; 1212; 1069; 1043; 947; 820; 769; 748; 695.
2.2. Ligand synthesis
2.3. Hydrogenation of itaconic acid
Poly(ethylene glycol)-methyl ether (Mn ca. 750) or
poly(ethylene glycol) (Mn ca. 200) (Aldrich) were cho-
sen to obtain characterizable molecules, although the
polyether chain of average mass 200 is hardly long
enough to give a water-soluble molecule. The phosphite
According to the principle of cloud point of the
nonionic surfactants, thermoregulated phase separation
or precipitation occurs in aqueous system [3]. Increas-
ing molecular weight of a polyethylene glycol induces
an increase of the temperature of precipitation from
water. Jin et al. reported the cloud points of various
polyether-based ligands and of some of their rhodium
complexes [3,4]. The activity of the catalyst was mea-
sured at various temperatures until the precipitation
occurs and the reaction stops. This represents a conve-
nient method to determine the cloud point of a complex
[2–4].
Scheme 1.

J.A.J. Breuzard et al. / Journal of Organometallic Chemistry 616 (2000) 37–43
39
Fig. 1. General principle of thermoregulated phase-transfer catalysis with organometallic species.
The hydrogenation was carried out in a 250 ml
double-walled glass flask (Bu¨chi) connected to a Bu¨chi
pressflow gas controller. Itaconic acid (5.2 g, 40 mmol),
RhCl3·3H2O (5 mg, 0.02 mmol, acid/Rh=2000), ligand
and water (150 ml, [Rh]=1.5×10−4 M) were added to
the reactor under argon atmosphere. The system was
purged three times with H2, pressurized at 4 bar H2 and
checked for leaks. The reactor was then heated or
cooled at a precise reaction temperature and the H2
uptake was monitored. The total pressure was main-
tained at 4 bar during the reaction. After collecting the
experimental data, the aqueous solution was acidified
to pH 1 and extracted with ether. The organic layer was
washed with brine and dried over magnesium sulfate.
SOCl2–MeOH was added to the resulting organic layer
and the mixture was stirred for 3 h, washed with brine
and dried over magnesium sulfate. The resulting ester is
used to determine the enantiomeric excess.
system (18×10−6 mol Rh), water (4 ml) and styrene (2
ml), pressurised with CO–H2 (1:1) and heated. After a
selected reaction time (6–24 h), the autoclave was
cooled and depressurized. The reaction mixture looks
like a white emulsion. Pentane (ca. 8 ml) was used to
transfer the whole emulsion from the autoclave in a
Schlenk flask. The organic layer was then separated and
the aqueous phase was extracted with pentane (ca. 5
ml). The white aqueous phase was reintroduced into the
same autoclave filled with styrene (2 ml) for a further
run. The organic layer (ca. 15 ml) was analyzed as for
homogeneous experiments and a 2 ml sample was intro-
duced into another autoclave already filled with water
(4 ml) and styrene (2 ml) for a new run in biphasic
conditions.
3. Results and discussion
2.4. Hydroformylation
3.1. Cloud point of the catalysts
As the reaction proceeds both in aqueous and or-
ganic systems, the experiments were performed in ho-
mogeneous as well as in biphasic conditions.
According to Bergbreiter [2], ‘smart materials’ un-
dergo physical property changes in response to a stimu-
lus, for instance a phase change. Polyether containing
molecules are known to have inverse temperature-de-
pendent solubilities in water. Thermoregulated phase
separation or precipitation occurs in aqueous systems
on heating above the cloud point. Thus the cloud point
could be easily estimated [2–4] (Fig. 1).
Lengthening the polyether chains in a molecule is
known to increase its water solubility. The cloud point
is also dependent on the molecule concentration in the
water solution [2]. The exact cloud point of the
rhodium catalyst formed using 1 as the ligand is deter-
mined by itaconic acid hydrogenation experiments (Fig.
2).
2.4.1. Homogeneous phase experiments
In a typical experiment, a 25 ml stainless-steel auto-
clave was purged with argon, filled with the catalytic
system (4 to 30×10−6 mol Rh), dry dichloromethane
(4 ml) and styrene (2 ml), pressurized with CO–H2 (1:1)
and heated. After a selected reaction time (6–96 h), the
autoclave was cooled and depressurized. The reaction
mixture was analyzed by GC.
2.4.2. Biphasic experiments and recycling
In a typical experiment a 25 ml stainless-steel auto-
clave was purged with argon, filled with the catalytic

40
J.A.J. Breuzard et al. / Journal of Organometallic Chemistry 616 (2000) 37–43
Fig. 2. Hydrogenation of itaconic acid in aqueous system under 4 bar H2 using RhCl3·3H2O/1 as catalyst. Cloud point of the reactive solution
is 22°C; [Rh]: 1.5×10−4 M, P/Rh=10.
Catalytic hydrogenation of itaconic acid was per-
formed under a constant pressure of hydrogen (4 bar),
using a complex prepared in situ from RhCl3·3H2O and
ligand 1. The catalytic activities were observed at vari-
ous temperatures, according to the amount of H2
consumed.
rhodium–ligand 1 (Rh-1) catalytic system increases
with the molar ligand to metal ratio (from 1 to 10). A
total pressure of 20 bar seems to be better for the
enantioselectivity despite a decrease of the activity.
Increasing further the 1/Rh ratio (i.e. \10) should
decrease both the activity and the regioselectivity of this
system and hitherto its application as catalyst for the
hydroformylation of olefins.
Chen et al. have already observed that, under bipha-
sic conditions, the conversion and the yield of aldehyde
increase when the polyether-monophosphite to rhodium
(P/Rh) ratio goes from 1 to 20 [4]. In addition, the i/n
ratio of aldehyde slightly decreases with an increase of
the P/Rh ratio. At P/Rh=13, the maximum conversion
of styrene is reached. Under these conditions, the con-
version of styrene and the yield of aldehyde both
increase with temperature and total pressure. The i/n
ratio decreases sharply as temperature increases al-
though it remains constant when the total pressure
changes. Little effect on the catalytic results is observed
with different non-polar solvents (from toluene to n-
heptane), but rhodium leaching is reduced when n-hep-
tane is used [4].
Fig. 2 shows that when the reaction temperature is
below the cloud point of the catalyst, namely 22°C,
hydrogenation occurs (eeB5%). The solution is then
clear, while when the temperature is kept above the
cloud point (25–50°C), the reaction stops and the
reaction medium is cloudy. If the temperature is low-
ered under the cloud point, the reaction resumes and
the solution is clear again. The reaction rate indicates
that degradation does not occur. Similar phenomena
have already been reported [2–4]. If an extra organic
phase containing a water-immiscible substrate is added
to the reaction system, the catalyst is extracted from the
aqueous phase on heating above its Tp and is trans-
fered into the organic phase. The reaction would then
take place into the organic phase.
3.2. Thermoregulated phase-transfer enantioselecti6e
hydroformylation of styrene
In biphasic conditions (Table 1, entries 5–6), the
asymmetric induction of the Rh-1 catalytic system ap-
pears when the ratio equals 9, and reaches 17% ee for
13. Moreover, increasing the molar 1/Rh ratio makes
the system more active. However, this decreases the
regioselectivity.
Contrary to the rhodium–ligand 1 (Rh-1) catalytic
system, in homogeneous conditions, Rh-2 is more ac-
tive and enantioselective when the total pressure de-
creases (Table 2, entries 7–11). Moreover, the regio-
selectivity is less sensitive to pressure effects with this
Catalytic reactions were carried out both in homoge-
neous and biphasic conditions to give a mixture of the
branched (i, 2-phenylpropanal) and normal (n, 3-
phenylpropanal) regioisomers (Scheme 2). Only traces
of the hydrogenated product were observed (ethylben-
zene B1%) [7–10]. Babin et al. have already reported
that the monophosphite derived from (S)-binaphtol
and (2-tert-butyl-4-methoxy)phenol, when combined
with [Rh(acac)(CO)2], was able to induce 10% ee, with
high regioselectivity (i/n=86/14) in the enantioselective
hydroformylation of styrene (9 bar, 45°C) [14]. We have
carried out this reaction using [Rh(cod)2]BF4 as the
catalyst precursor and polyether-phosphite 1 (Table 1)
or 2 (Table 2) as the ligand.
Under homogeneous conditions (CH2Cl2 as solvent,
Table 1, entries 1–3) the asymmetric induction of the
Scheme 2.

J.A.J. Breuzard et al. / Journal of Organometallic Chemistry 616 (2000) 37–43
41
Table 1
Rhodium catalyzed enantioselective hydroformylation of styrene with ligand 1 a
b
Entry
Solvent
1/Rh
S/Rh
P (bar)
t (h)
%Conversion b
i/n
%ee b
1
2
3
4
5
6
CH2Cl2
CH2Cl2
CH2Cl2
H2O
H2O
H2O
1.5
1.5
10
1.5
9
600
600
600
1000
1000
1000
40
20
20
40
40
40
6
6
48
6
24
18
43
17
43
5
65
71
93/7
91/9
83/17
92/8
92/8
76/24
1
3
8
0
3
13
17
a S, styrene=2 ml; solvent or water: 4 ml; H2: CO (1:1); Rh=[Rh(cod)2BF4]; T=40°C.
b See Section 2; the configuration of the aldehyde is (S).
Table 2
Rhodium catalyzed enantioselective hydroformylation of styrene with ligand 2 a
b
Entry
Solvent
2/Rh
S/Rh
P (bar)
t (h)
%Conversion b
i/n
%ee b
7
8
9
10
11
12
13
14
15
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
H2O
H2O
H2O
H2O
1.0
1.0
1.5
1.5
3.5
0.75
1.5
3.8
8.5
4000
4000
4000
4000
4000
1000
1000
1000
1000
10
20
20
40
40
40
40
40
40
24
48
96
96
96
24
24
24
24
26
70
51
25
18
74/26
80/20
80/20
80/20
80/20
85/15
84/16
83/17
83/17
17
14
27
25
25
4
16
19
25
98
\99
\99
\99
a S, styrene=2 ml; solvent or water 4 ml; H2: CO (1:1); Rh=[Rh(cod)2BF4]; T=40°C.
b See Table 1.
system, and an i/n ratio of 80/20 is obtained when
L/Rh=1.5. However, an optimum is reached for 20
bar and a molar 2/Rh ratio of 1.5 (Table 2, entry 9).
With Rh-2, the activity is very high in biphasic
conditions. It is now well established that HRh(CO)4
is a very efficient catalyst for the hydroformylation of
styrene [17]. Part of the activity should be assigned to
unmodified species, as observed for 2/Rh=0.75
(Table 2, entry 12). However, when 2/Rh=8.5, enan-
tioselectivity reaches up to 25%, which is nearly the
value obtained in homogeneous conditions.
In conclusion, the diphosphite 2 is a better ligand
for the cationic rhodium catalyst than the monophos-
phite 1. Moderate enantioselectivity (17–25% ee) has
been obtained in both cases. These molecules are ac-
tually acting as ligands. Pressure and ligand to
rhodium ratio have to be chosen in order to optimize
activity, regio- and enantio-selectivity. Our results
compare well with those of Herrmann et al. The au-
thors have obtained 18% ee with a sulfonated-Naphos
derivative as ligand in biphasic conditions, instead of
32% for the Naphos in homogenous conditions [18].
rhodium complexes in water and the rhodium leach-
ing. This allowed us to collect information on the
structure of the catalyst: nature of the complex, lig-
and to rhodium ratio, cloud point of the cationic
complex. Thus, the catalytic activity of the organic
(biphasic conditions) and aqueous phase were studied
(Table 3).
The cloud point of the catalyst obtained with
RhCl3 and ligand 1 is 22°C. The cloud point of the
cationic complex should be very near from this value
since the organic layer is slightly yellow after the first
run. However, such a cationic species should be more
soluble in water. Lower enantioselectivity and activity
are obtained for the recycled aqueous phase with lig-
and 1, but the organic phase is even less active and
enantioselective. The catalyst is retained into the
aqueous phase, with only a small amount extracted.
However, this system does not recycle with the same
enantioselectivity. The hydrogenation experiment (Fig.
2) has shown that degradation is not observed during
the phase transfer. Decomposition of the complex
may occur during the transfer from the autoclave into
the Schlenk flask, but the L/Rh ratio is also modified.
Since the asymmetric induction requires at least a L*/
Rh=9 (Table 1), it is not surprising to obtain a
lower enantioselectivity when recycling this system.
3.3. Recycling experiments
Recycling experiments were carried out in order to
appreciate both the stability of the phosphite–

42
J.A.J. Breuzard et al. / Journal of Organometallic Chemistry 616 (2000) 37–43
Table 3
Enantioselective hydroformylation of styrene: recycling experiments
b
Entry
Cycle
Ligand
L/Rh
t (h)
%Conversion b
i/n
%ee b
16
17
18
1 a
2 d
2 c
1
13
–
–
18
24
24
71
58
7
76/24
82/18
90/10
17
8
3
Aqueous phase
Organic phase
19
20
21
1 a
2 c
2 c
2
8.5
–
–
24
24
24
\99
35
65
83/17
83/17
86/14
25
25
12
Aqueous phase
Organic phase
a Reactions were carried out in degazed and deionized water (4 ml); [Rh=[Rh(cod)2BF4]: 18×10−6 mol; S, styrene (2 ml); S/Rh: 1000,
p(H2+CO)=40 bar; T=40°C].
b See Table 1.
c Recycling of the aqueous phase or the organic phase in biphasic conditions (extraction temperature: 25°C).
With ligand 2, recycling of the aqueous phase is
possible with the same regio- and enantio-selectivity,
but with a lower activity. The yellow organic phase also
contains catalyst because the polyether chains are too
short for a satisfactory water-solubility. The species in
the organic phase gives a higher activity but a lower
enantioselectivy. Actually, the ee value is close to the
one obtained with a 2/Rh ratio of 1. These results
suggest that the catalyst is partially extracted as species
containing mainly one diphosphite ligand per rhodium
atom. However, the complex retained into the aqueous
phase leads to the same enantioselectivity since it does
not require a large excess of ligand 2 (Table 2), unlike
1.
In conclusion, the rhodium–ligand 1 system is kept
into the aqueous phase, but it does not recycle with the
same enantioselectivity. Contrary to the rhodium–lig-
and 1 system, the catalyst–ligand 2 is extracted at room
temperature from the aqueous phase containing the
excess of ligand. When separated from this aqueous
phase, the species dissolved into the organic phase
affords lower asymmetric induction since it depends on
the ligand to rhodium ratio. Nevertheless, recycling of
the aqueous phase is possible with ligand 2, with the
same regio- and enantio-selectivity, but with a lower
activity. However, it is unlikely that the Rh-2 catalytic
system will give higher ee and a satisfactory re-usable
system for the hydroformylation of styrene. The choice
of the chain-lengths of the polyether moiety to obtain
rhodium complexes with controlled cloud points is
currently being examined. The enantioselectivity should
also be optimized by using one of the various chiral
These ligands, combined with [Rh(cod)2]BF4, exhibit
high catalytic activity in the enantioselective hydro-
formylation of styrene. Thermoregulated phase-transfer
catalysis gives branched aldehydes with high regioselec-
tivity and enantioselectivity of up to 25%, which is
exactly the same value that has been obtained in the
homogeneous way. Although this asymmetric induction
is modest, it is the highest ever obtained for the hydro-
formylation of styrene in biphasic conditions. Recycling
was possible, but with a lower activity since rhodium
leaching can not be avoided. Extraction of the rhodium
complexes does not occur at temperatures below the
cloud point of the catalyst. Thus, the recyclability
should be improved by increasing the chain-length of
the polyether moiety. The properties of the organic
phase suggest extraction of diphosphite rhodium species
for temperatures above the cloud point of the catalyst
rather than degradation of the catalyst. This paper
demonstrates for the first time the feasibility of enan-
tioselective thermoregulated phase-transfer hydro-
formylation. It also proves that the catalytic system
should be easily improved: firstly, by modifications of
the polyether part of the ligand to induce higher cloud
points, and secondly, by a proper design of the chiral
part of the ligand, which controls the asymmetric
induction.
Acknowledgements
We are grateful to Genevie`ve He´raud for skillful
technical assistance.
moiety
described
for
the
homogeneous
hydroformylation.
References
4. Conclusion
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