236
A. Dhakshinamoorthy and H. Garcia
4-methoxy-1-bromobenzene and styrene, observing that the activity of Pd/MIXMIL-53(Al)-NH 2 is mostly maintained for five cycles, the yield decreasing slightly
from 81 to 76%. The TEM image of the five times reused catalyst revealed that
the mean diameter of the Pd NPs was 3.4 nm which is identical to that of the fresh
catalyst.
Pd/MIL-101 prepared by double-solvent method has also been reported as heterogeneous catalyst for the Heck cross-coupling reaction [38] between styrene and
iodobenzene in DMF as solvent under air atmosphere using potassium carbonate as
base, reaching a yield of 98% after 2 h. The catalyst also exhibited wide substrate
scope demonstrating a very high activity and practical applicability. The solid catalyst was also recovered and reused for five cycles with no appreciable decay in its
activity. These results clearly indicate that the entrapped Pd NPs within the pores of
structurally robust MIL-101 remain highly active and that the preparation method
also plays a vital role in determining the activity and stability of a solid catalyst.
The Brönsted basicity in activated MOF-808 (denoted as MOF-808a) was used
as support for the deposition of Pd NPs to obtain Pd/MOF-808a that was used as
catalyst for the Heck cross-coupling between iodobenzene and styrene under basefree conditions [45]. The existence of Brönsted basicity in MOF-808a was confirmed
by CO 2 -TPD-MS, in situ DRIFTS, and acid–base titration. Pd NPs were highly
dispersed over the basic MOF-808a solid with a diameter of 4 ± 2 nm, indicating
that the Pd NPs are mainly located on the external surface since the pore dimensions of
MOF-808a are smaller than 4 nm. Pd/MOF-808a as catalyst without any additional
base afforded in DMF at 130 °C 93.6% yield of diphenylethene. In contrast, no
catalytic activity was observed under identical conditions for MOF-808a due to the
lack of Pd NPs as active sites. Pd/MIL-101 and Pd/UiO-66 gave under identical
conditions without any base 12 and 10% yields of stilbene. These results clearly
establish the role of Brönsted basicity of MOF-808a cooperating to the Heck reaction.
Recycling experiment indicated that the yield of the Heck product decreases slightly
after the first run and then the yield remained identical up to 10
th cycle with a value
of 84%, which is not too far from the initial activity of the fresh material. Powder
XRD patterns revealed that Pd/MOF-808a solid maintains a good crystallinity with
no obvious deterioration of the structural integrity after the 10
th cycle. Overall, the
catalytic activity of Pd/MOF-808a is promising showing how the basic sites installed
within the framework of MOF can contribute to C–C bond forming reaction.
7.5 Alcohol Oxidation
Besides C–C bond formation, oxidation and reduction reactions are useful reactions
in organic synthesis. With respect to oxidations, one of the targets is to use oxygen
and air as oxidizing reagent.
Regarding aerobic oxidations, Au NPs have shown to exhibit catalytic activity
to promote reactions using molecular oxygen. In this context, Au NPs have been
incorporated within MOFs and the resulting materials used as heterogeneous catalysts
A. Dhakshinamoorthy and H. Garcia
4-methoxy-1-bromobenzene and styrene, observing that the activity of Pd/MIXMIL-53(Al)-NH 2 is mostly maintained for five cycles, the yield decreasing slightly
from 81 to 76%. The TEM image of the five times reused catalyst revealed that
the mean diameter of the Pd NPs was 3.4 nm which is identical to that of the fresh
catalyst.
Pd/MIL-101 prepared by double-solvent method has also been reported as heterogeneous catalyst for the Heck cross-coupling reaction [38] between styrene and
iodobenzene in DMF as solvent under air atmosphere using potassium carbonate as
base, reaching a yield of 98% after 2 h. The catalyst also exhibited wide substrate
scope demonstrating a very high activity and practical applicability. The solid catalyst was also recovered and reused for five cycles with no appreciable decay in its
activity. These results clearly indicate that the entrapped Pd NPs within the pores of
structurally robust MIL-101 remain highly active and that the preparation method
also plays a vital role in determining the activity and stability of a solid catalyst.
The Brönsted basicity in activated MOF-808 (denoted as MOF-808a) was used
as support for the deposition of Pd NPs to obtain Pd/MOF-808a that was used as
catalyst for the Heck cross-coupling between iodobenzene and styrene under basefree conditions [45]. The existence of Brönsted basicity in MOF-808a was confirmed
by CO 2 -TPD-MS, in situ DRIFTS, and acid–base titration. Pd NPs were highly
dispersed over the basic MOF-808a solid with a diameter of 4 ± 2 nm, indicating
that the Pd NPs are mainly located on the external surface since the pore dimensions of
MOF-808a are smaller than 4 nm. Pd/MOF-808a as catalyst without any additional
base afforded in DMF at 130 °C 93.6% yield of diphenylethene. In contrast, no
catalytic activity was observed under identical conditions for MOF-808a due to the
lack of Pd NPs as active sites. Pd/MIL-101 and Pd/UiO-66 gave under identical
conditions without any base 12 and 10% yields of stilbene. These results clearly
establish the role of Brönsted basicity of MOF-808a cooperating to the Heck reaction.
Recycling experiment indicated that the yield of the Heck product decreases slightly
after the first run and then the yield remained identical up to 10
th cycle with a value
of 84%, which is not too far from the initial activity of the fresh material. Powder
XRD patterns revealed that Pd/MOF-808a solid maintains a good crystallinity with
no obvious deterioration of the structural integrity after the 10
th cycle. Overall, the
catalytic activity of Pd/MOF-808a is promising showing how the basic sites installed
within the framework of MOF can contribute to C–C bond forming reaction.
7.5 Alcohol Oxidation
Besides C–C bond formation, oxidation and reduction reactions are useful reactions
in organic synthesis. With respect to oxidations, one of the targets is to use oxygen
and air as oxidizing reagent.
Regarding aerobic oxidations, Au NPs have shown to exhibit catalytic activity
to promote reactions using molecular oxygen. In this context, Au NPs have been
incorporated within MOFs and the resulting materials used as heterogeneous catalysts