Asymmetric hydroformylation of olefins in a highly cross-linked polymer matrix [19]

Full text of DOI:10.1021/ja973408d

J. Am. Chem. Soc. 1998, 120, 4051-4052
4051
Asymmetric Hydroformylation of Olefins in a Highly
Cross-Linked Polymer Matrix
Kyoko Nozaki,* Yohei Itoi, Fumitoshi Shibahara,
†
‡
Eiji Shirakawa, Tetsuo Ohta, Hidemasa Takaya, and
Tamejiro Hiyama
Department of Material Chemistry
Graduate School of Engineering
Kyoto UniVersity, Yoshida, Kyoto 606-8501, Japan
zene and 3- and 4-ethylstyrene. In this work, divinylbenzenes of
ReceiVed September 30, 1997
5
2
1
5% content were used without further purification. Initiated by
,2′-azobis(2,4-dimethylpentanenitrile) (V-65), a 3:97 mixture of
During the past two decades, intensive efforts have been
devoted to develop polymer-supported chiral catalysts in order
to introduce the advantages of heterogeneous catalysts, such as
easy separation from the products and facile recovery for
recycling, into homogeneous catalyst systems.1-3 Immobilization
of catalysts on polymer-supports often causes significant decrease
of catalytic activity or selectivity of the reactions due to the slower
diffusion of substrates in the polymer matrix.4 Further decrease
of catalytic activity or selectivity is expected to arise from utilizing
a higher degree of cross-linking of the polymer-supports, although
it is desirable to facilitate the treatments. Here, we report
asymmetric hydroformylation of olefins using polymer-im-
mobilized chiral phosphine-phosphite-Rh(I) complexes. Even
in a highly cross-linked polymer matrix, the highest levels of
catalytic activity and selectivity of the reaction were maintained.
We recently developed homogeneous asymmetric hydroformy-
lation of a wide variety of substrates catalyzed by Rh(I) complexes
of chiral phosphine-phosphite, (R,S)-BINAPHOS (1a).5 This
system serves as the first example of the truly efficient catalysts
of asymmetric hydroformylation for practical use. In this study,
a vinyl group is introduced to 1a so that the resulting ligand can
be copolymerized with styrene derivatives. Thus, ligands 1b-d
have been prepared in which one, two, and three vinyl groups,
respectively, are incorporated into 1a.6
b and the divinylbenzenes was copolymerized in toluene
7
(Scheme 1). Hereafter, this polymer is abbreviated as PS-1b.
This is a polymer with an extremely high degree of cross-linking,
compared to polystyrene with less than 10% of cross-linking that
1,3a-f
is employed in most conventional studies.
Other vinyl-BIN-
APHOSs were copolymerized in the same manner. The polymer-
supported ligands were dispersed in benzene in the presence of
Rh(acac)(CO) , and the mixtures were dried in vacuo. The result-
2
ing yellow solids, (PS-1b-d)-Rh(acac), were used as catalysts.
Asymmetric hydroformylation of styrene was examined under
carbon monoxide and hydrogen (total pressure of 20 atm, CO/H
2
)
1:1) employing the (PS-ligand)-Rh(acac) complexes as
catalysts in benzene at 60 °C (eq 1). The representative results
are summarized in Table 1. All runs were repeated at least three
times to ensure the reproducibility of the data. The reaction was
completed after 12 h in all runs and the range of error for both
the i-/n- ratio and enantiomeric excess (ee) was estimated to be
(<5%. Thus, with (PS-1b)-Rh(acac), 2-phenylpropanal and
3-phenylpropanal were obtained in an 84:16 ratio and the
enantiomeric excess of the iso-aldehyde was 89% (R) (run 2).
The highest level of catalytic activity, i.e., quantitative conversion
to aldehydes with substrate/catalyst ratio of 2000, is maintained.
This result is comparable to that obtained with the homogeneous
system, Rh(acac)(1a) (run 1). Reduction of the cross-linking
degree resulted in no significant change in the selectivities (run
The vinyl-BINAPHOSs, 1b-d, were subjected to a radical co-
polymerization with styrene derivatives. Divinylbenzene is com-
mercially available as a mixture of 1,2-, 1,3-, and 1,4-divinylben-
†
Present address: Department of Molecular Science and Technology,
Faculty of Engineering, Doshisha University, Tanabe, Kyoto 610-8580, Japan.
‡
Deceased on October 4, 1995.
(
1) Reviews of polymer-supported chiral catalysts: (a) Itsuno, S. In
Polymeric Materials Encyclopedia; S. Salamone, J. C., Ed.; CRC Press: Boca
Raton, FL, 1996; Vol. 10, p 8078. (b) Blossey, E. C.; Ford, W. T. In
ComprehensiVe Polymer Science. The Synthesis, Characterization, Reactions
and Applications of Polymers; Eastmond, G. C., Ed.; Pergamon Press: Oxford,
3). With (PS-1c)-Rh(acac), the regio- and enantioselectivities
1
989; Vol. 6, p 81. (c) Synthesis and Separations Using Functional Polymers;
of the reaction were essentially the same as with Rh(acac)(1a)
and (PS-1b)-Rh(acac) (run 7). In contrast, however, lower ee
was observed with (PS-1d)-Rh(acac) (run 8).
Sherrington, D. C., Hodge, P., Eds.; Wiley: Chichester, 1988. (d) Stille, J.
K. J. Macromol. Sci. 1984, A21, 1689. (e) Stille, J. K. Pure Appl. Chem.
1
982, 99, 54.
(
2) For recent examples of polymer-supported chiral catalysts, see: (a)
Canali, L.; Karjalainen, J. K.; Sherrington, D. C.; Hormi, O. Chem. Commun.
997, 123. (b) Song, C. E.; Yang, J. W.; Ha, H. J.; Lee, S. Tetrahedron:
Because the present polymer catalyst hardly swells in benzene
or hexane (run 4), easy handling and recovery-reuse have been
achieved as shown in Figure 1. After the reaction was completed
in a pressure bottle, the yellow polymer catalyst settled at the
bottom of the bottle. The colorless supernatant suggests that the
release of the Rh catalyst from the solids is negligible. The liquid
phase containing the products was simply removed via a syringe,
and the remaining solid catalyst was charged with an olefin
1
Asymmetry 1996, 645. (c) Han, H.; Janda K. D.; J. Am. Chem. Soc. 1996,
1
1
18, 7632. (d) Seebach, D.; Marti, R. E.; Hintermann, T. HelV. Chim. Acta
996, 1710. (e) Kamahori, K.; Ito, K.; Itsuno, S. J. Org. Chem. 1996, 61, 1.
(
3) For hydroformylation with polymer-supported chiral catalysts, see: (a)
Fritschel, S.; Ackerman, J.; Keyser, T.; Stille, J. K. J. Org. Chem. 1979, 44,
152. (b) Pittman, C. U., Jr.; Kawabata, Y.; Flowers, L. I. J. Chem. Soc. Chem.
3
Commun. 1982, 473. (c) Stille, J. K.; Parrinello, G. J. Mol. Catal. 1983, 21,
2
4
03. (d) Parrinello, G.; Deschenaux, R.; Stille, J. K. J. Org. Chem. 1986, 51,
189. (e) Parrinello, G. J. Am. Chem. Soc. 1987, 109, 7122. With achiral
2
solution and H /CO to give the aldehydes without any loss of
catalysts, see: (f) Pittman, C. U., Jr.; Honnick, W. D.; Yang, J. J. J. Org.
Chem. 1980, 45, 684. (g) Collman, J. P.; Belmont, J. A.; Brauman, J. I. J.
Am. Chem. Soc. 1983, 105, 7288. (h) Chenand, J.; Alper, H. J. Am. Chem.
Soc. 1997, 119, 893.
8
productivity or selectivity (run 5 and 6).
Another preparative route to the polymer-supported catalyst is
the polymerization of a Rh(I) complex of the ligands. Thus, at
(
4) See refs 1-3. A few exceptions have been reported. (a) Corma, A.;
Iglesias, M.; del Pino, C.; S a´ nchez, F. J. Chem. Soc., Chem. Commun. 1991,
2
first, ligand 1b was treated with Rh(acac)(CO) to form Rh(acac)-
1
1
253. (b) Hodge, P.; Khoshdel, E.; Waterhouse, J. J. Chem. Soc., Perkin Trans.
(1b). Copolymerization of Rh(acac)(1b) with divinylbenzenes
1983, 2205. (c) Itsuno, S.; Kamahori, K.; Watanabe, K.; Koizumi, T.; Ito,
K. Tetrahedron: Asymmetry 1994, 5, 523.
(
5) Nozaki, K.; Sakai, N.; Nanno, T.; Higashijima, T.; Mano, S.; Horiuchi,
T.; Takaya, H. J. Am. Chem. Soc. 1997, 119, 4413 and references therein.
6) See Supporting Information for synthesis of vinyl-BINAPHOSs 1b-d
and copolymerization of these ligands with divinylbenzene (55% content).
(7) The polymeric ligands PS-1b-d and complexes (PS-1b-d)-Rh(acac)
and PS-[Rh(acac)(1b-d)] were all insoluble in organic solvents such as
benzene, THF, CH Cl , CHCl , DMSO, and DMF. For this reason, molecular
weight of the polymers could not be determined.
(
2
2
3
S0002-7863(97)03408-2 CCC: $15.00 © 1998 American Chemical Society
Published on Web 04/29/1998

4052 J. Am. Chem. Soc., Vol. 120, No. 16, 1998
Communications to the Editor
Scheme 1
Table 1. Asymmetric Hydroformylation of Styrene Catalyzed by
Polymer-Supported (R,S)-BINAPHOSsa
ee
ee
i-/n- (%)
run
catalyst
i-/n- (%) run
catalyst
1
2
Rh(acac)(1a)
89:11 92
7
8
9
(PS-1c)-Rh(acac) 89:11 89
(PS-1d)-Rh(acac) 88:12 68
PS-[Rh(acac)(1b)] 85:15 90
(PS-1b)-Rh(acac) 84:16 89
(PS-1b)-Rh(acac) 83:17 89
b
3
c
4
(PS-1b)-Rh(acac) 80:20 81 10 PS-[Rh(acac)(1c)] 90:10 87
(PS-1b)-Rh(acac) 84:16 89 11 PS-[Rh(acac)(1d)] 87:13 85
d
5
d
e
Figure 1. Left: The glass pressure-bottle when the asymmetric hydro-
formylation of styrene was completed using (PS-1b)-Rh(acac) (corre-
sponds to Table 1, run 5). During the reaction, slow stirring was carried
out with a magnetic stirring bar (shown as the white bar). The colorless
supernatant fluid suggests that the Rh(I) catalyst stays in the yellow solid
catalyst. Right: After removal of the product solution via a syringe in a
stream of Ar. The yellow polymer was reused (Table 1, run 6).
6
(PS-1b)-Rh(acac) 79:21 86
a
A solution of styrene (6.20 mmol) in benzene (0.35 mL) was treated
with carbon monoxide (10 atm) and hydrogen (10 atm) in the presence
-
3
of the polymer catalyst (3.1 × 10 mmol of Rh) at 60 °C for 12 h.
The conversion of styrene to aldehydes (>99% for all the runs), and
1
the i-/n- ratios were determined by H NMR. The enantiomeric excesses
were determined by GLC analysis (Chrompack Cp-Cyclodex â-236M,
2
1
35 °C, He 2.0 kg cm ) of the corresponding carboxylic acid derived
Table 2. Asymmetric Hydroformylatyion of Vinyl Acetate
a,b
by the Jones oxidation of the product aldehyde. The absolute config-
uration of the iso-aldehyde was determined to be R for all runs. b The
polymer ligand was prepared from a 3:87:10 mixture of 1b, styrene,
Catalyzed by Polymer-Supported (R,S)-BINAPHOS
run
catalyst
convn (%)
i-/n-
ee (%)
c
and divinylbenzenes (55% content). Hexane was used as the solvent.
The reaction was carried out under CO (2.5 atm) and H (2.5 atm) in
2
1
2
3
4
5
6
7
Rh(acac)(1a)
98
75
54
61
67
83
78
84:16
85:15
90:10
87:13
87:13
90:10
90:10
92
91
92
78
92
93
89
d
(PS-1b)-Rh(acac)
(PS-1c)-Rh(acac)
(PS-1d)-Rh(acac)
PS-[Rh(acac)(1b)]
PS-[Rh(acac)(1c)]
PS-[Rh(acac)(1d)]
e
a glass pressure-bottle. The catalyst used in run 5 was reused.
55% content) afforded the corresponding polymer-supported
complex, PS-[Rh(acac)(1b)]. In the same procedure, PS-[Rh-
acac)(1c)] and PS-[Rh(acac)(1d)] were synthesized. Asymmetric
hydroformylation of styrene was examined with these PS-[Rh-
acac)(ligand)] catalysts, and the results are summarized in Table
, runs 9-11. Again, the activity and selectivity were comparable
to the results with the corresponding homogeneous system.
Noteworthy is that the use of PS-[Rh(acac)(1d)] showed higher
enantioselectivity than that with (PS-1d)-Rh(acac) (compare runs
(
(
a
The reactions were carried out in a manner similar to that for styrene
with the substrate/catalyst ratio of 500 and total pressure of 100 atm.
(
1
b
The absolute configuration of the iso-aldehyde was S for all runs. All
runs were repeated at least twice to confirm the reproducibility. The
i-/n- ratio and the ee were always reproducible, but the conversions in
runs 2-6 contained errors of (20%.
substrate because hydrogenated byproducts are produced under
lower pressure. The results are summarized in Table 2. When
8
and 11). The difference can be explained as follows. When
the polymerization is carried out in the absence of Rh(I), ligand
d is frozen as a matrix of various conformations, some of which
1
are not suitable to coordinate to Rh(I). This may result in the
formation of a less stable Rh(I) complex, for example, with
monodentate coordination. Existence of plural active species
could have caused the loss of selectivity. On the other hand, the
conformation of the ligand should be fixed to a suitable form for
the bidentate coordination to Rh(I), when 1d is complexed with
Rh(I) before polymerization. In this case, the catalyst can work
in a manner similar to a homogeneous catalyst. Such difference
is observed only with 1d in which both the phosphine site and
the phosphite site are attached to the polymer. With 1b,c, the
ligands keep their flexibility in the polymer matrix because only
one of the two binaphthyl groups is bound to the polymer chain.
Asymmetric hydroformylation of vinyl acetate was also
examined (eq 2). Total pressure of 100 atm is employed for this
the reaction was catalyzed by the polymer-supported catalysts,
conversion of the reaction was variable ((20% range of error),
but the i-/n- ratio and ee were sufficiently reproducible ((<5%)
with the values of 85:15 to 90:10 and 89-93% ee(S) (runs 2, 3
and 5-7), similar to those attained in the homogeneous system
(
run 1). Again, slightly lower ee was observed when (PS-1d)-
Rh(acac) was used as the catalyst (run 4).
Acknowledgment. We are grateful to Professor Kiitiro Utimoto
(Kyoto University) and Professor Shin-ichi Itsuno (Toyohashi University
of Technology) for helpful discussions. This work was partially supported
by Grant-in-Aid for Scientific Research on Priority Areas (no. 283,
“Innovative Synthetic Reactions”) from Monbusho.
(8) Itsuno has reported an easier process, a continuous flow system. (a)
Itsuno, S.; Ito, K.; Maruyama, T.; Kanda, N.; Hirao, A.; Nakahama, S. Bull.
Chem. Soc. Jpn. 1986, 59, 3329. (b) Itsuno, S.; Sakurai, Y.; Ito, K.; Maruyama,
T.; Nakahama, S.; Fr e´ chet, J. M. J. J. Org. Chem. 1990, 55, 304.
JA973408D