The concept of supported ionic liquid catalysis (silc) has successfully been applied to hydrogenation reactions, which significantly reduced the required amounts of ionic liquid phase and enabled the usage of fixed-bed technology; the resulting catalysts exhibited high activity and outstanding stability.
The hydroformylation of decene-1 was studied in the presence of
the fluorous-soluble P[CH2CH2(CF2)5CF3]3
modified rhodium catalyst at 100 °C and 1.1 MPa of CO/H2
(1:1) in a 50/50 vol % toluene/C6F11CF3 solvent mixture, which
forms a homogeneous liquid phase at and above 100 °C.
P[CH2CH2(CF2)5CF3]3 was selected on the basis of a
semiempirical calculation of the electronic properties of
P[(CH2)
x
(CF2)
y
CF3]3
(x = 0, y = 2, 4 and x = 0−5,
y = 2) and prepared by the reaction of PH3
with
CH2CH(CF2)5CF3.
The
solution structure of
HRh(CO){P[CH2CH2(CF2)5CF3]3}3
(1) in C6F11CF3 is
similar to that of
HRh(CO)(PPh3)3
(2) in toluene and
HRh(CO){P(m-C6H4SO3Na)3}3
(3) in water. High-pressure NMR of 1 under
2.1−8.3 MPa
of CO/H2 (1:1) revealed that 1 is in equilibrium
with
HRh(CO)2{P[CH2CH2(CF2)5CF3]3}2
(4). Kinetic studies
show that the reaction is first order in both rhodium and decene-1.
While the reaction is inhibited by
P[CH2CH2(CF2)5CF3]3,
the normal/iso (n/i) ratio of the aldehyde increases with increasing
phosphine concentration.
The catalytic activity of the
Rh/P[CH2CH2(CF2)5CF3]3
catalyst is similar to that of the nonfluorous analogue
Rh/P[(CH2)7CH3]3
catalyst and is an order of magnitude lower than that of the
Rh/PPh3 catalyst. Surprisingly,
the n/i product selectivity of
Rh/P[CH2CH2(CF2)5CF3]3
is closer to the selectivity of the Rh/PPh3 catalyst
than
that of the
Rh/P[(CH2)7CH3]3
catalyst. The fluorous biphase catalyst recovery concept was
tested in a
semicontinuous hydroformylation of decene-1 with the
Rh/P[CH2CH2(CF2)5CF3]3
catalyst. During 9 consecutive
reaction/separation cycles, a total turnover of more than 35 000 was
achieved with a loss of 1.18 ppm of
Rh/mol of undecanals. The fluorous-soluble
Rh/P[CH2CH2(CF2)5CF3]3
catalyst was also tested for the
continuous hydroformylation of ethylene using the high-boiling fluorous
solvent FC-70, which allows continuous
removal of propanal at the reaction temperature of 110 °C. The
long-term stability of the
Rh/P[CH2CH2(CF2)5CF3]3 catalyst is better than that of the
Rh/PPh3 catalyst. Thus, the
Rh/P[CH2CH2(CF2)5CF3]3
catalyst is the
first catalyst system which can be used for the hydroformylation of
both low and high molecular weight olefins
and provides facile catalyst separation for both low and high molecular
weight aldehydes.
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