Vapor-phase asymmetric hydroformylation

Article abstract of DOI:10.1246/cl.2000.694

Polystyrene-supported (R,S)-BINAPHOS-Rh complex was demonstrated to be applicable to the asymmetric hydroformylation of gaseous substrates in a non-solvent system: 3,3,3-trifluoropropene (2a) and (Z)-2-butene (2b) were converted into the corresponding branched aldehydes with 90% and 80%ee, respectively.

Full text of DOI:10.1246/cl.2000.694

694
Chemistry Letters 2000
Vapor-Phase Asymmetric Hydroformylation
Kyoko Nozaki,* Fumitoshi Shibahara, and Tamejiro Hiyama
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501
(Received March 24, 2000; CL-000281)
Polystyrene-supported (R,S)-BINAPHOS–Rh complex was
demonstrated to be applicable to the asymmetric hydroformyla-
tion of gaseous substrates in a non-solvent system: 3,3,3-triflu-
oropropene (2a) and (Z)-2-butene (2b) were converted into the
corresponding branched aldehydes with 90% and 80%ee,
respectively.
In general, heterogeneous catalysis is advantageous due to
its high activity, thermal stability, easy recovery and reuse, and
thus, vapor-phase reactions over heterogeneous catalysts are most
widely used in industrial processes. On the other hand, vapor-
phase asymmetric catalysis has no precedents thus far.
Substrates for asymmetric catalysis often have rather high boiling
points. Above the boiling points, finely tuned chiral catalysts are
not stable, in many cases. Furthermore, the use of solvents is
considered to be essential in order to keep the reaction conditions
uniform throughout by interacting with solutes, via coordination,
hydrogen bonding, or dipoles. In order to avoid the use of organ-
ic solvents, recent efforts are focused on asymmetric catalysis in
1
environmentally benign solvents, such as supercritical CO2 and
water.2 Here we report that the vapor-phase asymmetric catalysis
over a chiral transition metal complex can be carried out without
any solvents.3 Attachment of the complex to a polymer matrix4
is the key solution for the problematic issues that arise from the
absence of solvents.
Asymmetric hydroformylation of olefins is a direct route to
optically active aldehydes which are valuable precursors for a
variety of pharmaceuticals and agrochemicals. Previously, we
developed chiral Rh(I) complex 1a as the first example of a truly
efficient catalyst for asymmetric hydroformylation of various
kinds of olefins.5 Attachment of complex 1a to polystyrene
enabled the recovery and reuse of the catalyst.6 As is common to
the other asymmetric catalysis, the achievements were performed
in a homogeneous catalysis style. In this transformation, sub-
strates such as olefins, carbon monoxide, and hydrogen are of
high volatility. Thus, the idea that gaseous mixture of all the sub-
strates would be easily available at low temperatures prompted us
to examine the vapor-phase asymmetric hydroformylation using
a fixed bed illustrated in Figure 1 (apparatus A). Polystyrene-
supported catalyst 1b is placed at the center of a stainless auto-
clave without touching the liquid phase. As a reference, a homo-
geneous catalysis style apparatus B was also employed.
A volatile substrate, 3,3,3-trifluoropropene (2a, saturated
vapor pressure 8.5 atm at 40 °C),7 was first employed. It is well
known that aldehyde 3a is an important intermediate for the
synthesis of a fluorinated amino acid, a potential biologically
active compound.5 As the reaction proceeded, the polymer cat-
alyst became wet judged from visual observation. Analysis
revealed that 3a was produced with 114 h-1 turnover frequency,
93% regioselectivity, and 90%ee (run 1). Thus, asymmetric
hydroformylation was accomplished without any solvents. By
ICP emission spectrometry analysis, no Rh was detectable in
the product with the experimental error range being less than
0.8% of the initially loaded Rh. This sharply contrasts to the
fact that polymer-fragmentation was a significant problem to
cause the dissociation of powdery Rh-containing polymer in the
sink-in apparatus B.6b
So far as polymer-supported 1b was employed, the per-
formance was maintained in apparatus B, except for the prob-
lematic polymer-fragmentation (run 2). Accordingly, it is like-
ly that the reaction in run 1 took place in a maner similar to that
in run 2, as realized by adsorption of substrate 2a on the surface
of swollen polymer catalyst 1b. In contrast, however, drastic
loss of catalytic activity was observed with non-supported cata-
lyst 1a (run 3). Due to the poor solubility of catalyst 1a in fluo-
rinated substrate 2a, the catalyst stuck on the bottom of the
autoclave during the reaction, without any dispersion. The
Copyright © 2000 The Chemical Society of Japan

Chemistry Letters 2000
695
existence of benzene improved the TOF only to some extent
(run 4). Hence, the difference between the results with poly-
mer-supported catalyst 1b (runs 1 and 2) and that with non-sup-
ported 1a (runs 3 and 4) suggests that the existence of the poly-
mer matrix is essential in providing a phase where the substrate
efficiently meets the active center of the catalyst,8 particularly
in the case that the catalyst is insoluble in the substrate.
Sports, and Culture. We are grateful to Professor Tetsuo Ohta
(Doshisha University) for helpful discussions. We thank Mr.
Yoshiji Honda (Kyoto University) for the ICP emission spec-
trometry in measuring the dissociation of Rh.
References and Notes
1
a) “Chemical Synthesis Using Supercritical Fluids,” ed. by
P.G. Jessop and W. Leitner, Wiley-VCH, Weinheim
(1999). b) G. Francià and W. Leitner, Chem. Commun.,
1999, 1663.
2
a) W. A. Herrmann and C. W. Kohlpaintner, Angew.
Chem., Int. Ed. Engl., 32, 1524 (1993). b) M. T. Reetz,
Top. Catal., 4, 187 (1998).
3
4
Solvent-free organic syntheses in general: J. O. Metzger,
Angew. Chem., Int. Ed. Engl., 37, 2975 (1998).
Polymer-supported chiral catalysts: a) S. Itsuno,
“Polymeric Materials Encyclopedia” ed by J. C. Salamone,
CRC Press, Boca Raton, FL, (1996), Vol. 10, p 8078. b) P.
J. Comina, A. K. Beck, and D. Seebach, Organic Research
& Development, 2, 18 (1998).
The catalyst system, namely 1b without solvents, was also
applicable to another low-boiling point substrate, (Z)-2-butene
(2b, saturated vapor pressure 9.1 atm at 60 °C)9 (run 5), the
results being comparable to the performance previously attained
under homogeneous conditions using 1a in benzene (run 8).
Even a less volatile olefin, styrene (2c, 0.092 atm at 60 °C), was
successfully hydroformylated by the present process although
the TOF was inferior to the homogeneous counterpart (runs 9
and 10).
5
6
K. Nozaki, H. Takaya, and T. Hiyama, Top. Catal., 4, 175
(1997), and references cited there in.
a) K. Nozaki, Y. Itoi, F. Shibahara, E. Shirakawa, T. Ohta,
H. Takaya, and T. Hiyama, J. Am. Chem. Soc., 120, 4051
(1998). b) K. Nozaki, F. Shibahara, Y. Itoi, E. Shirakawa,
T. Ohta, H. Takaya, and T. Hiyama, Bull. Chem. Soc. Jpn.,
72, 1911 (1999).
Thus, the solvent-free asymmetric hydroformylation
demonstrates the potential application of this catalyst to contin-
uous use in a flow system. The absence of mechanical breaking
of the polymer catalyst prevents the leaching of metals.
Meanwhile, the polymer matrixes are presented of potential use
as the substitute for organic solvents10 in asymmetric catalysis.
7
8
T. E. Daubert, J. W. Jalowka, and V. Goren, AIChE. Symp.
Ser., 83, 128 (1987).
Concept of "interphase" is proposed by Lindner and
Mayer. E. Lindner, T. Schneller, F. Auer, and H. A.
Mayer, Angew. Chem., Int. Ed. Engl., 38, 2154 (1999).
“Kagaku Binran, The Basic Part,” 3rd ed, ed. by The
Chemical Society of Japan, Maruzen, Tokyo, (1984).
9
This work was partially supported by Grant-in-Aid for
Scientific Research on Priority Areas (No. 283 , "Innovative
Synthetic Reactions") from the Ministry of Education, Science,
10 An example of the use of polymeric micelles as a "solvent"
for extraction: P. N. Hurter and T. A. Hatton, Langmuir, 8,
1291 (1992).