Two-phase hydroformylation of higher olefins using randomly methylated α-cyclodextrin as mass transfer promoter: A smart solution for preserving the intrinsic properties of the rhodium/trisulfonated triphenylphosphine catalytic system

Article abstract of DOI:10.1002/adsc.200404229

The two-phase hydroformylation of higher olefins with the rhodium/trisulfonated triphenylphosphine catalytic system in the presence of various chemically modified α-cyclodextrins has been investigated. These cyclodextrins allowed us to increase greatly the reaction rate and the chemoselectivity of the reaction but, contrary to what has been observed previously with the chemically modified β-cyclodextrins, the linear to branched aldehydes ratio was not affected by the presence of α-cyclodextrin derivatives. Indeed, the latter was found to be similar to that obtained without any mass transfer promoter, suggesting that the catalytic species are stable in the presence of α-cyclodextrin derivatives.

Full text of DOI:10.1002/adsc.200404229

COMMUNICATIONS
Two-Phase Hydroformylation of Higher Olefins Using Randomly
Methylated a-Cyclodextrin as Mass Transfer Promoter: A Smart
Solution for Preserving the Intrinsic Properties of the
Rhodium/Trisulfonated Triphenylphosphine Catalytic System
a
a
a
a
´
Loꢀc Leclercq, Mathieu Sauthier, Yves Castanet, Andre Mortreux,
b
b,
´
Herve Bricout, Eric Monflier *
a
Laboratoire de Catalyse de Lille, UMR 8010, ENSCL, B. P. 108, 59652 Villeneuve dꢁAscq, France
Universite dꢁArtois, Laboratoire de Physico-Chimie des Interfaces et Applications, FRE CNRS 2485, Rue Jean Souvraz,
b
´
´
SP 18, 62307 Lens Cedex, France
Fax: (þ33)-3-21-79-17-55, e-mail: monflier@univ-artois.fr
Received: July 16, 2004; Accepted: November 11, 2004
Abstract: The two-phase hydroformylation of higher
olefins with the rhodium/trisulfonated triphenyl-
phosphine catalytic system in the presence of various
chemically modified a-cyclodextrins has been inves-
tigated. These cyclodextrins allowed us to increase
greatly the reaction rate and the chemoselectivity
of the reaction but, contrary to what has been ob-
served previously with the chemically modified b-cy-
clodextrins, the linear to branched aldehydes ratio
was not affected by the presence of a-cyclodextrin
derivatives. Indeed, the latter was found to be similar
to that obtained without any mass transfer promoter,
suggesting that the catalytic species are stable in the
presence of a-cyclodextrin derivatives.
trin (RAME-b-CD) that is a cheap, non-toxic and bulk
commercially available compound allowed one to ach-
ieve the hydroformylation of 1-decene with an initial
turnover frequency and aldehyde selectivity of 300 hꢀ1
and 95%, respectively, while avoiding the formation of
an emulsion and the partition of therhodium catalystbe-
tween the organic and aqueous phases.[7] This outstand-
ing result was attributed to the complexing and surface
active properties of the RAME-b-CD. Indeed, this com-
pound forms host/guest complexes with the water-in-
soluble olefin at the liquid/liquid interface and transfers
the olefin into the aqueous phase where it reacts with the
water-soluble rhodium catalyst. After reaction, the
product is released in the organic phase and the transfer
cycle can go on (Figure 1).[8]
Keywords: cyclodextrins; hydroformylation; long-
chain olefins; phosphanes; rhodium
Unfortunately, it was found that the normal to
branched aldehydes ratio (l/b) is always lower than
that observed without the mass transfer promoter (1.8
vs. 2.8 without cyclodextrin).[8] This unexpected de-
crease in the l/b aldehydes ratio was until now the major
drawback of the cyclodextrin-based hydroformylation
Although olefins with variable chain lengths have been process as the linear aldehyde is the most desired prod-
successfully hydroformylated in aqueous two-phase me- uct. The origin of this decrease was recently attributed to
dium with rhodium complexes modified by the sodium the formation of inclusion complexes between RAME-
salt of the trisulfonated triphenylphosphine (TPPTS), b-CD and the TPPTS ligand. In fact, by trapping TPPTS,
a distinction is generally made between lower and high- RAME-b-CD induces a displacement of the equilibria
er olefins.[1] Indeed, lower olefins such as ethylene, pro- between the different catalytic species towards phos-
pene and butene have a solubility in the aqueous catalyt- phane low-coordinated rhodium species poorly selec-
ic phase high enough to assure chemical reaction with- tive toward the formation of the linear aldehyde.[9]
out mass transfer limitations.[2] In contrast, the solubility
As we have recently proved that chemically modified
of higher olefins (five or more carbon atoms) is too low a-cyclodextrin cannot interact with the TPPTS ligand[10]
for industrially important rates to be achieved and the or with the [RhH(CO)(TPPTS)3][9] complex (due to
presence of cosolvent,[3] surfactant,[3a,4] amphiphilic li- their smaller cavity than b-CD), it was of great interest
gands[5] or cyclodextrins[6–8] is required.
to evaluate the behaviour of a-cyclodextrin derivatives
Among the different approaches proposed to increase in biphasic rhodium-catalyzed hydroformylation. Here-
the solubility of higher olefins, the use of chemically in, we report the influence of the addition of these com-
modified b-cyclodextrins preserves some economical vi- pounds on the hydroformylation rate and the linear to
ability. Indeed, the randomly methylated-b-cyclodex- branched aldehydes ratio. These experiments were con-
Adv. Synth. Catal. 2005, 347, 55–59
DOI: 10.1002/adsc.200404229
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55

Loꢀc Leclercq et al.
COMMUNICATIONS
Figure 1. Principle of the cyclodextrin-based hydroformylation process.
ducted using a Rh(acac)(CO)2/TPPTS combination as
catalyst precursor and 1-octene, 1-decene or 1-dodecene
as higher olefins (Figure 2).
The more significant results are summarised in Ta-
ble 1. At first, control experiments were performed in
the absence of any phase-transfer promoter under
standard reaction conditions in order to determine pre-
cisely the influence of each cyclodextrin (entries 1–3).
As expected, the conversion was very low without cyclo-
dextrin and did not exceed 2 or 3% after 6 h. Moreover,
an important part of the starting olefin was isomerized
and the aldehyde selectivity varied between 33 to
67%. As already reported,[7] addition of RAME-b-CD
to the reaction medium greatly increased the reaction
rate since the conversion of 1-octene and 1-decene
reached 90 and 95%, respectively, after 6 hours with
an aldehyde selectivity up to 97%. Concomitantly, the
l/b aldehyde ratio dropped from 2.8 to 1.7 or 1.8.
Before discussing the effect of chemically modified a-
cyclodextrins on the hydroformylation rate and alde-
hyde selectivity, it is worth mentioning that some pre-
liminary experiments were performed with the native
a-cyclodextrin. As already reported by Anderson
et al.,[6c] the results were totally disappointing. Indeed,
large amounts of solid were recovered in the bottom
of the reactor at the end of the reaction and no increase
in the reaction rate was observed with this cyclodextrin.
NMR analyses indicated that the recovered solid was
composed of water-insoluble inclusion complexes
formed between the higher olefins and the unmodified
cyclodextrin. This experiment demonstrates clearly
Figure 2. Rhodium-catalyzed hydroformylation of long-chain
that native a-cyclodextrin cannot be used as a mass olefins in the presence of chemically modified cyclodextrins.
56
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Adv. Synth. Catal. 2005, 347, 55–59

Two-Phase Hydroformylation of Higher Olefins
Table 1. Hydroformylation of long-chain olefins in the presence of different chemically modified cyclodextrins.[a]
COMMUNICATIONS
Entry
Olefin
CD
CD/Rh ratio
Time [h]
Conversion [%][b]
Selectivity [%][c]
l/b ratio[d]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
C8H16
C10H20
C12H24
C8H16
C10H20
C8H16
C8H16
C10H20
C10H20
C10H20
C10H20
C10H20
C12H24
C8H16
C10H20
C10H20
C12H24
C12H24
(-)
(-)
(-)
(-)
(-)
(-)
12
12
12
12
12
12
6
24
48
12
12
12
12
12
12
6
6
6
6
6
6
24
6
24
6
6
6
6
6
6
24
6
24
3
3
2
33
59
67
97
98
97
98
88
88
74
88
89
84
99
91
92
92
93
2.8
2.8
2.8
1.7
1.8
2.9
2.9
3.0
3.0
3.0
3.0
3.0
2.9
3.0
2.8
2.8
2.8
2.8
RAME-b-CD
RAME-b-CD
HP-a-CD
HP-a-CD
HP-a-CD
HP-a-CD
HP-a-CD
HP-a-CD
HP-a-CD
HP-a-CD
RAME-a-CD
RAME-a-CD
RAME-a-CD
RAME-a-CD
RAME-a-CD
90
97
28
67
24
26
15
40
57
6
96
43
65
9
28
[a]
Experimental conditions: Rh(acac)(CO)2 (4.07ꢁ10ꢀ2 mmol), TPPTS (0.21 mmol), H2O (11.5 mL), olefin (20.35 mmol),
808C, CO/H2 (1/1): 50 atm.
[b]
[c]
[d]
Calculated with respect to the starting olefin.
(Mol. of aldehydes)/(mol. of converted olefins)ꢁ100. The side products were mainly isomeric olefins.
Ratio of linear to branched aldehyde product.
transfer promoter due to the water insolubility of the 6 and 7 and entries 8 and 9). This decay of the global ac-
olefin/a-cyclodextrin inclusion complexes. tivity of the system is not ascribable to the decomposi-
As indicated in Table 1, hydroxypropylated-a-cyclo- tion of the rhodium catalytic species since the
dextrin (HP-a-CD) was not such an efficient mass trans- [RhH(CO)(TPPTS)3] complex was stable under similar
fer promoter as RAME-b-CD under comparable reac- reaction conditions[9] and that the phenomenon seems
tion conditions (Table 1, entries 6, 8, 13). Nevertheless, not to occur with the 1-octene. A poisoning of the HP-
no solid product was formed during the reaction and a-CD by the reaction products is probably the origin
the conversion can be notably increased. For instance, of this phenomenon. In fact, the C11 aldehydes produced
in the case of 1-octene, the conversion after 6 hours during the reaction likely form more stable inclusion
was almost ten-fold higher than in the corresponding complexes with HP-a-CD than the C9 aldehydes. Thus,
control experiment (compare entries 1 and 6). On the the HP-a-CD cannot play its role of phase transfer agent
other hand the effect was less marked with 1-dodecene for the substrate when the aldehyde concentration is too
(6% conversion after 6 h instead of 2% without cyclo- high.
dextrin – entries 3 and 13). In the same way, the alde-
This problem can be easily overcome by using another
hyde selectivity was higher in the presence of HP-a- chemically modified a-cyclodextrin: the randomly me-
CD. The best aldehyde selectivity was observed with 1- thylated a-cyclodextrin (RAME-a-CD). Indeed, Ta-
octene (97%) and regularly decreased from C8 to C12 ole- ble 1 shows that the RAME-a-CD was much more effi-
fins (97%, 88% and 84% for the C8, C10 and C12 olefins, cient than HP-a-CD especially in the case of 1-octene.
respectively). Interestingly, the aldehyde selectivity was Actually, the conversion with 1-octene was even higher
always higher than that obtained without cyclodextrin. than the one observed with RAME-b-CD and reached
These promising results prompted further investigation 96% after 6 hours with an excellent aldehyde selectivity
to delineate the behaviour of this a-cyclodextrin in the of 99%. On the other hand, RAME-a-CD was less suit-
biphasic hydroformylation reaction. The effect of cyclo- able with 1-decene since the conversion after 6 hours
dextrin concentration was investigated with 1-decene as was only the half of that observed with RAME-b-CD
substrate (entries 8 and 10–12). The activity and selec- under the same conditions. Nevertheless, it must be
tivity increased with the HP-a-CD concentration pointed out that the conversion regularly increased
whereas the l/b ratio remained unchanged. It is also and there was no inhibition of the reaction (entries 15
noteworthy that the conversion regularly increased dur- and 16). In the same way, no inhibition of the reaction
ing the reaction in the case of 1-octene whereas with 1- was found with 1-dodecene although the efficiency of
decene the reaction practically stopped after 6 hours the system based on RAME-a-CD markedly decreased
that corresponds to 25% conversion (compare entries again (entries 17 and 18). Interestingly, whatever the
Adv. Synth. Catal. 2005, 347, 55–59
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Loꢀc Leclercq et al.
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chased from Strem Chemicals and Aldrich Chemicals in their
highest purity and used without further purification. Random-
ly methylated b-cyclodextrin (RAME-b-CD) was purchased
from Aldrich Chemicals. Randomly methylated a-cyclodex-
trin (RAME-a-CD) was prepared by adapting a procedure re-
ported by Kenichi et al.[15] These two cyclodextrins were parti-
ally methylated. Methylation occurred at positions 2, 3, or 6
and 1.8 OH groups per glucopyranose unit were statistically
modified. Hydroxypropylated a-cyclodextrin (HP-a-CD)
was obtained from Aldrich Chemicals. This cyclodextrin was
partially O-2-hydroxypropylated; statistically 0.6 OH groups
were modified per glucopyranose unit. Tris(3-sodium sulfona-
tophenyl)phosphine [TPPTS – P(m-C6H4SO3Na)3] was synthe-
sized as reported by Gꢃrtner et al.[16] The purity of the TPPTS
was carefully controlled. In particular, 31P solution NMR indi-
cated that the product was a mixture of phosphine (ca. 98%)
and its oxide (ca. 2%). Carbon monoxide/hydrogen mixtures
(1:1) were used directly from cylinders (>99.9% pure; Air
Liquide). Distilled deionized water was used in all experi-
ments. All catalytic reactions were performed under nitrogen
using standard Schlenk techniques. All solvents and liquid re-
agents were degassed by bubbling nitrogen for 15 min before
each use or by two freeze-pump-thaw cycles before use.
olefin, the aldehyde selectivities obtained with the
RAME-a-CD were higher than those obtained with
the HP-a-CD, confirming the beneficial effect of a-cy-
clodextrins on the aldehyde selectivity. Much more in-
teresting is the value of the l/b ratio obtained with this
cyclodextrin. Indeed, whatever the olefin, the l/b ratio
remained identical to the one observed in control ex-
periments, suggesting again that the behaviour of the
Rh/TPPTS catalytic system was not modified by the
presence of methylated a-cyclodextrins.
Two factors can likely account for the high reaction
rates observed with RAME-a-CD. The first is the sur-
face-active behaviour of this cyclodextrin[11] and, the
second, the lower stability of the RAME-a-CD/alde-
hydes inclusion complexes.[12] Indeed, the possibility to
form a stabilizing hydrogen bond between the aldehyde
group of the product and the OH group of the cyclodex-
trin is greatly reduced in such ahost compound. The high
aldehydes selectivities (up 99%) observed with the a-cy-
clodextrins result probably from the formation of inclu-
sion complexes. Indeed, when the olefin is inside the hy-
drophobic host cavity of the a-cyclodextrins, the forma-
tion of isomerizing species leading to internal olefins by
b-hydride elimination is prohibited by the steric hin-
drance. The very high selectivities (>91%) observed
with RAME-a-CD could be due to presence of a deep
hydrophobic host cavity. Indeed, attachment of 11–14
methyl groups to the a-CD greatly extends the cavity
of the a-CD. Thus, the RAME-a-CD has a much more
important lipophilic domain and cavity volume than
HP-a-CD or native a-CD due to the increase in the
height of the CD torus. This gives rise to CDs that wrap
more efficiently the hydrophobic olefins.[12] Finally, it is
noteworthy that we have also observed this remarkable
protective effect of complexation with chemically modi-
fied b-cyclodextrin during hydrocarboxylation[13] and
Wacker oxidation[14] of water-insoluble olefins.
In conclusion, contrary to modified b-cyclodextrins,
the use of modified a-cyclodextrins as mass transfer pro-
moter in the aqueous two-phase hydroformylation of
higher olefins allows us to preserve the intrinsic proper-
ties of the classical Rh/TPPTS catalytic system as no de-
crease in the l/b aldehyde ratio was observed. From a
point of view of reaction rate, the stability of the inclu-
sion complexes between the a-cyclodextrin derivatives
and the substrate or the product appears as a crucial
point. Work is underway to investigate quantitatively
this important aspect of the two-phase hydroformyla-
tion assisted by chemically modified a-cyclodextrins.
Catalytic Experiments
Rh(acac)(CO)2 (4.07ꢁ10ꢀ2 mmol), TPPTS (0.21 mmol) and
the required amount of chemically modified cyclodextrin
were dissolved in 11.5 mL of water. The resulting aqueous
phase and an organic phase composed of olefin (20.35 mmol)
and undecane (4 mmol – GC internal standard) were charged
under an atmosphere of N2 into the 50-mL reactor which was
heated at 808C. Mechanical stirring by means of a multipaddle
unit was then started (1500 rpm) and the autoclave was pres-
surized with 50 atm of CO/H2 (1/1) from a gas reservoir con-
nected to the reactor through a high pressure regulator valve
allowing us to keep constant the pressure in the reactor
throughout the whole reaction. The reaction medium was sam-
pled during the reaction for GC analyses of the organic phase
after decantation. For kinetic measurements the time corre-
sponding to the addition of CO/H2 was considered as the begin-
ning of the reaction.
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