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B. M. Bhanage et al. / Tetrahedron Letters 44 (2003) 3505–3507
Table 1. Simultaneous hydrogenation of a mixture of 3-
becomes much less active by the presence of Ru–TPP,
although Ru–TPP is little affected by the presence of
Pd–TPP. These observations indicate a limitation of
using a mixture of homogeneous metal complex cata-
lysts due to negative interactions between them. Prelim-
inary NMR measurements for Pd species have
phenylpropionaldehyde and 1,2-diphenylethylenea
Entry
Catalyst
Yield (%)
3
4
1
indicated some differences in 31P and H spectra in the
Homogeneous
absence (corresponding to entry 2) and presence (entry
3) of Ru species but not for Ru species. The structure
of only Pd species may change by the presence of Ru
species, resulting in the disappearance of the activity as
observed (entry 3).
1
2
3
Ru–TPP
Pd–TPP
Ru–TPP+Pd–TPP
94.1
0.3
90.1
1.0
98.9
7.8
SLPC
4
5
6
7
8
Ru–SLPCb
89.8
1.7
92.5
87.2
84.4
2.2
88.0
2.8
64.0
76.6
Pd–SLPCb
(Ru+Pd)–SLPCc
Ru–SLPC+Pd–SLPC
Ru–SLPC+Pd–SLPCd
Instead of homogeneous Ru–TPP and Pd–TPP, SLPC
samples including ruthenium–triphenylphosphine trisul-
fonnate trisodium salt (Ru–TPPTS) and/or palladium–
TPPTS in water film on a silica gel were used.
Hereafter, these SLPC samples are designated as M–
SLPC (M=Ru, Pd, etc.). Ru–SLPC and Pd–SLPC
selectively hydrogenate the substrates 1 and 2, respec-
tively (entries 4 and 5). When Ru–TPPTS and Pd–
TPPTS are included in the same supported water film
(entry 6), the yield of 4 is low, similar to the homoge-
neous reaction using both Ru–TPP and Pd–TPP (entry
3). When a physical mixture of Ru–SLPC and Pd–
SLPC is used (entry 7), both the yields of 3 and 4 are
still high.
a Solvent (DMF for the homogeneous catalysts and toluene for
SLPC), 10 mL; H2, 4 MPa; phenylpropioaldehyde, 7.6 mmol;
stilbene, 2.5 mmol; temperature 70°C; time 3 h for the homogeneous
catalysts and 4 h for SLPC.
b Besides the SLPC sample, 0.5 g of silica containing 0.3 mL of water
was added before the reaction.
c The catalyst was prepared from an aqueous solution containing
both Ru–TPPTS and Pd–TPPTS. Water, 0.6 mL; silica, 1 g.
d The catalysts for entry 7 was recycled.
given in Table 1† and those in homogeneous reactions
are described first: with ruthenium–triphenylphosphine
(Ru–TPP) catalyst, the hydrogenation of 1 proceeds
selectively but the hydrogenation of 2 is not substantial
The results obtained show that a bifunctional catalytic
system can be achieved by using the SLPC technique.
After the reaction with SLPC, no metal leaching was
observed to occur and the catalysts were easily sepa-
rated by simple filtration. They were then recycled for
another run and retained their initial activity (entry 8).
There are differences in the yields between homoge-
neous and SLPC reactions. This is due to complicated
kinetics features of multiphase SLPC reactions. The
overall rate of SLPC reaction depends on several fac-
tors such as thickness of supporting liquid film, concen-
tration of active species in the film, solid (SLPC) to
solvent ratio, and so on, which are not needed to
consider in homogeneous reactions.5 The optimization
of those factors is necessary for practical applications.
(entry 1). In
a
reverse manner, palladium–
triphenylphosphine (Pd–TPP) catalyst is selectively
active for the hydrogenation of 2 (entry 2). When a
mixture of Ru–TPP and Pd–TPP is used (entry 3), the
yield of 3 is comparable to that obtained with Ru–TPP
alone, while the yield of 4 is very low as compared with
Pd–TPP alone (entry 2). This means that Pd–TPP
† Experimental:
Preparation of the catalysts: Ruthenium chloride, palladium acetate
(for the hydrogenation), palladium chloride (for the Heck reaction)
and Rh(CO)2(acac), (acac=acetylacetone) were used for the metal
precursors. The precursor (0.062 mmol) and TPPTS (0.25 mmol)
were dissolved in 0.3 mL of water (for the hydrogenation reactions)
or ethylene glycol (for Heck and hydroformylation reactions). The
solution was pre-treated at 70°C for 1 h under 2 MPa of H2
(Ru–TPPTS), ambient atmosphere (Pd–TPPTS), or 0.1 MPa of
CO/H2 (Rh–TPPTS). Then 0.5 g of a porous silica gel (Aldrich
Davisil grade 646) was added into the solution and mixed well to
obtain dry powder. For the SLPC samples containing two metal
complexes, the metal–TPPTS solutions were pre-treated separately
and then mixed before adding silica. Ru–TPP and Pd–TPP were
pre-treated in 2 mL of DMF under the same conditions for their
analogous TPPTS complexes. The reaction experiments were per-
formed using a 50 mL mechanically agitated autoclave. The catalyst
prepared, 20 mL of the solvent, and the liquid substrates were
charged into the reactor. After purging with H2, ethylene or CO/H2
several times, the reactor was heated to desired reaction tempera-
tures and the gaseous substrate was further introduced up to desired
pressures. For the sequential reactions of Heck and hydroformyla-
tion, the reactor was once cooled to room temperature after the
former reaction and ethylene remained in the reactor was purged
with CO/H2 before the latter reaction. After the reactions, the
substrates and the products in the liquid phases were analyzed by a
gas chromatograph with FID and mass spectrometer.
As the second example, sequential reactions involving
Heck reaction and hydroformylation (Scheme 2) have
been carried out with Pd–SLPC and Rh–SLPC. In the
Scheme 2. Sequential reactions of Heck coupling followed by
hydroformylation.