Table 1 Fluorous biphase hydroformylation of olefins by soluble polymer
catalysts
model example. The other substrates and related products
should be easier to separate under the fluorous biphase
conditions as they are less miscible with the perfluoro solvent.
At 100 °C and 50 bar with olefin/Rh = 48 000, three
consecutive hydroformylation reactions were run, giving a
combined TON of 70 000 and an average aldehyde selectivity
of 99%. A 1 ppm loss of rhodium accompanied with a 6%
decrease in conversion in each recycle experiment was
measured. This loss in rhodium and in catalyst activity appears
to be largely due to the finite miscibility of the substrate/product
with the perfluorinated solvent. At the end of the third run, all
the perfluoromethylcyclohexane had leached to the product
phase, thus making the polymer catalyst partially soluble in the
product. By optimising the operating conditions, e.g. by varying
the organic solvent, the problem of rhodium leaching can be
minimised.
In conclusion, we have introduced a fluorous soluble polymer
ligand for FBC and shown the arylphosphine-containing ligand,
when combined with rhodium, to be highly active and selective
in the fluorous biphase hydroformylation of various olefins.
Given the easy availability of various vinyl monomers that can
be used for fluoropolymer synthesis and the variability in FBC
conditions, better performing soluble polymer catalysts coupled
with efficient phase separation could be envisioned not only for
FBC but also for fluorous combinatorial chemistry.
a
Conversion Selectivityb
Olefin
Polymer Olefin/Rh (%)
(%)
L/Bc
Dec-1-ene
Hexadec-1-ene
Styrene
1
2
1
2
1
2
1
2
2120
2120
2100
2100
3500
3500
2800
2800
97
90
78
59
85
80
100
100
99
99
98
4.8/1
5.9/1
4.8/1
5.0/1
1/6.2
1/5.4
99
> 99
> 99
> 99
> 99
d
n-Butyl acrylate
B
d
B
a
2 2
Reaction conditions: 5 mmol [Rh(CO) (acac)] (P/Rh = 6), 30 bar CO–H
(
1+1), 100 °C for dec-1-ene and hexadec-1-ene, 80 °C for styrene and n-
butyl acrylate, hexane–toluene–perfluoromethylcyclohexane 4+2+4
mL), 15 h reaction time. The products were analysed by H NMR and the
=
1
(
b
conversion and selectivity confirmed by GC. To aldehyde, olefin
isomerisation accounts for the product balance. Linear to branched
aldehyde ratio, determined by H NMR. The branched product was a 1+1
mixture of enol and aldehyde, the linear aldehyde was < 1%.
c
1
d
(
TOF) for the fluorous biphase hydroformylation of dec-1-ene
2
1
is 136 mol aldehyde h per mol of rhodium catalyst with an
aldehyde selectivity of 99%. In comparison, a rhodium catalyst
supported on the water soluble polymer poly(enolate-co-vinyl
alcohol-co-vinyl acetate) gave a TOF of 56 (100 °C, 41 bar)
with an aldehyde selectivity < 70% in the aqueous hydro-
formylation of oct-1-ene.13 As might be expected, ligand 1,
which has a higher phosphine loading, gave higher turnovers.
We are indebted to the EPSRC and the University of
Liverpool Graduates Association (Hong Kong) for postdoctoral
research fellowships (W. C. and L. X.).
Notes and references
(
ii) As with solid polymer-supported catalysts,10 the linear/
1
2
3
I. T. Horváth and J. Rábai, Science, 1994, 266, 72.
I. T. Horváth, Acc. Chem. Res., 1998, 31, 641.
E. de Wolf, G. van Koten and B. J. Deelman, Chem. Soc. Rev., 1999, 28,
37.
branched (L/B) ratio is markedly higher than achievable with
similar P/Rh ratios when using homogeneous rhodium phos-
phine catalysts, e.g. [RhH(CO)(PPh
ratio of 2.9 only in the presence of an excess of PPh
1
2
3
)
3
], which yielded a L/B
(P/Rh =
9) in the hydroformylation of pent-1-ene in benzene (100 °C,
7 bar).15 (iii) Smaller olefins appear to give higher turnovers,
3
4 I. T. Horváth, G. Kiss, R. A. Cook, J. E. Bond, P. A. Stevens, J. Rábai
and E. J. Mozeleski, J. Am. Chem. Soc., 1998, 120, 3133.
5 D. Rutherford, J. J. J. Juliette, C. Rocaboy, I. T. Horváth and J. A.
Gladysz, Catal. Today, 1998, 42, 381.
probably owing to better miscibility of the olefins with the
fluorous phase. In fact, when hex-1-ene was hydroformylated
under conditions identical to those for dec-1-ene, a conversion
of 70% with an aldehyde selectivity of 98% and a L/B ratio of
6
7
8
J. J. J. Juliette, D. Rutherford, I. T. Horváth and J. A. Gladysz, J. Am.
Chem. Soc., 1999, 121, 2696.
D. Sinou, G. Pozzi, E. G. Hope and A. M. Stuart, Tetrahedron Lett.,
1
999, 40, 849.
4.4 was obtained in 1 h reaction time, corresponding to a
D. E. Bergbreiter and J. G. Franchina, Chem. Commun., 1997, 1531.
remarkable TOF of 1454. Again, a low olefin isomerisation
selectivity of 1.7% was observed.
The activity and stability of the soluble fluoropolymer
catalysts may also be judged by the hydroformylation of hex-
9 M. Beller, B. Cornils, C. D. Frohning and C. W. Kohlpaintner, J. Mol.
Catal., 1995, 104, 17 and references therein.
10 F. R. Hartley, Supported Metal Complexes. A New Generation of
Catalysts, Reidel, Dordrecht, 1985.
1
1 T. Malmström, C. Andersson and J. Hjortkjaer, J. Mol. Catal., 1999,
39, 139.
1
1
-ene when the olefin/Rh ratio was increased to 200 000. At
00 °C and 50 bar syngas with polymer 1 as the supporting
1
1
1
1
2 A. N. Ajjou and H. Alper, J. Am. Chem. Soc., 1998, 120, 1466.
3 J. Chen and H. Alper, J. Am. Chem. Soc., 1997, 119, 893.
4 D. C. Sherrington, Chem. Commun., 1998, 2275 and references
therein.
ligand, the catalyst afforded a turnover number (TON, mole of
aldehyde per mol of rhodium) of ca. 140 000 with a 98%
selectivity to aldehyde (L/B = 4.4; 2% isomerisation) for 58 h
reaction time. We also examined the recyclability of the
fluoropolymer catalysts taking the reaction of hex-1-ene as a
15 C. U. Pittman, Jr. and R. M. Hanes, J. Am. Chem. Soc., 1976, 98,
5402.
840
Chem. Commun., 2000, 839–840