Table 1 Results from the hydroformylation of oct-1-ene at 80–100 °C and 50 bar CO–H2 (1+1).
Conversion
after 24 h
(%)
Linear to
branched
ratioc
Alkene
isomerisationc
(%)
Linear
aldehydec
(%)
Entry
Catalyst [cycle]a
TOFb
1
2
3
4
5
6
7
8
9
Rh(A) [1]
Rh(A) [2]
Rh(A) [3]e
Rh(A) [4]e
Rh(A) [5]e
Rh(A) [6]e
Rh(A) [7]e
Rh(A) [8]g
Rh(A) [9]g
Rh(A) [10]g
7
28d
14
14
12
10
24f
37
46
48
1
1
38
44
46
42
40
40
39
31
31
27
1.9
5.7
5.0
8.7
8.5
7.7
7.3
7.0
4.1
5.8
95.6
92.2
93.0
89.2
89.3
90.0
90.3
90.1
92.9
90.7
15
14
14
13
10
44
55
55
10
11
12
13
14
Rh(TPPTS) [1]
Rh(TPPTS) [2]e
Rh(TPPTS) [3]g
Rh(TPPTS) [4]g
20
3
17
90f
15
30
160
146
3
3
3
2
7.4
12.3
7.3
67.2
67.2
70.5
33.9
52.6
a
Ligand to rhodium ratio is 10 for Rh(A) and 20 for Rh(TPPTS), catalysis performed at 80 °C and 50 bar CO–H2 in 15 ml toluene as a co-solvent
using 1 ml of oct-1-ene. b Average turnover frequencies were calculated as (mol aldehyde/mol catalyst)21 h21 c Determined by means of GC analysis using
.
decane as an internal standard. d Conversion after 96 h. e Catalysis performed in 15 ml oct-1-ene at 80 °C. f Conversion after 72 h. g Catalysis performed in
15 ml oct-1-ene at 100 °C.
§ The recycling experiments were performed as follows. A stainless steel 50
The product/catalyst separation efficiency of the SAPCs was
ml autoclave, equipped with a mechanical stirrer, a substrate vessel, a
examined on performing recycling experiments (Table 1).
cooling spiral and a sample outlet, was charged with 1 g of SAPC containing
Rh(A)/SAPC could be recycled numerous times without
(1) 1 3 1024 mol A; (2) 1 3 1025 mol Rh(acac)(CO)2 and (3) 4% (m/m)
deterioration of the catalyst performance (entries 1–10). The
water on CGP-240 in 10 ml toluene. The suspension was incubated for 1 h
at 80 °C under 20 bar CO–H2 (1+1). A mixture of 1 ml oct-1-ene and 1 ml
decane in 3 ml toluene was added and the CO–H2 pressure was brought to
selectivity towards the linear aldehyde remained high during all
experiments and the decrease in rate of hydroformylation was
very small (at 100 °C we even observed a small increase in rate
in successive runs).¶ This indicates that ligand A retains the
rhodium quantitatively on the support which is confirmed by
rhodium analysis on the product by means of ICP-AES. No
traces of rhodium were detected in the product phase of any of
the SAPC experiments (detection limit 1 ppm). In contrast,
Rh(TPPTS)/SAPC showed a drop in catalyst performance after
three catalytic runs (Table 1, entries 11–14). In the fourth cycle,
over 50% of the oct-1-ene isomerised and the linear-to-
branched ratio decreased to 2. The Rh(A)/SAPC is thus far more
robust then the TPPTS based SAPC; Rh(A)/SAPC could be
recycled over at least three weeks, showing no deterioration of
the catalyst performance whereas under similar conditions
Rh(TPPTS)/SAPC showed a strong reduction in hydroformyla-
tion performance after three days.
Importantly, Rh(A)/SAPC is stable in the absence of
substrate as it can be transformed into the dimer [Rh(A)(m-
CO)(CO)]2 which is stable over weeks when properly stored
under 1 bar of CO. The reversible switching between the
catalytically active species 1 and the stable dimeric species 2 did
not influence the catalytic performance in at least four
consecutive runs.∑
We can conclude that the introduction of rigid bidentate
diphosphines with a large ‘natural’ bite angle in the supported
aqueous phase catalysis improves the regioselectivity towards
the linear aldehyde enormously compared to the SAPCs known
thus far. Moreover, the application of Sulfoxantphos in SAP
catalysed hydroformylation gives rise to a significant improve-
ment of the sustainability of the system. To the best of our
knowledge this supported aqueous phase catalyst is the first
example of an immobilised homogeneous catalyst that is highly
selective and robust and shows no metal leaching in numerous
consecutive catalytic runs.
50 bar. The mixture was stirred for 24 h. The autoclave was cooled to 15 °C
and the pressure was reduced to 2 bar. With the small overpressure the liquid
was slowly removed from the catalyst with a 1.2 mm syringe. After the
catalyst was washed with 5 ml toluene, 10 ml of toluene was added and the
pressure was brought to 20 bar. Finally the mixture was heated to 80 °C and
the next cycle was performed.
¶ We also observed this increase in rate of hydroformylation in successive
catalytic runs in the biphasic Rh(A) system (ref. 10). We suggest that at this
temperature the remaining catalytically inactive species are slowly
transformed into the active form (the inactive species is most probably the
carbonyl bridged rhodium dimer).
∑ The procedure described above is extended as follows. After a catalytic run
was performed the reaction medium was cooled to 90 °C the CO–H2 (1+1)
pressure was removed and 20 bar of CO was introduced. The mixture was
slowly cooled to 20 °C and stirred for 4 h. The liquid was subsequently
removed from the catalyst by means of a syringe. The catalyst was washed
with CO-saturated toluene and the next cycle proceeded after the reaction
mixture was pressurised with 50 bar of CO–H2.
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This work was sponsored by the Innovation Oriented
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Notes and references
‡ For more experimental details see Electronic Supplementary Information
(ESI).
Communication 9/03916C
1634
Chem. Commun., 1999, 1633–1634