Chemistry Reference
In-Depth Information
SCHEME 16.11
The last example in the field of catalysis is at the border withmaterials. Phosphorus
dendrimers containing on their surfaces 15-membered azamacrocycles were synthe-
sized up to the fourth generation (dendrimers
36b-G
4
), and their
coordinating ability to palladium(0) atoms was tested. Depending mainly on the
amount of Pd(0) used, either discrete complexes or new nanoparticulated materials
were obtained, where nanoparticles are stabilized by the dendrimers of the zero, first,
or fourth generation. No reduction process of palladium(II) saltswas needed to prepare
nanoparticles of 2.5-7.9 nm diameter. These complexes and nanoparticles were used
for the Mizoroki-Heck reaction; in all cases, the catalyst could be recovered and
reused several times. The Pd-complex of
36a,b-G
0
,
36b-G
1
,
36a-G
0
displays constant catalytic activity
with recycling, whereas the Pd-nanoparticles stabilized with
36a-G
0
displays an
increasing catalytic efficiency with recycling; this could be related to a decrease in the
nanoparticles size, observed by electron microscopy (Scheme 16.11) [45].
16.4 PHOSPHORUS DENDRIMERS FOR THE ELABORATION
OR MODIFICATION OF (NANO)MATERIALS
The development of nanomaterials is presently one of the major challenges for
materials chemistry. In this perspective, nanosized molecules and particularly
dendrimers are attracting a considerable attention. Indeed, dendrimers can play a
key role in the chemical construction of periodic mesostructures synthesized by the
cooperative assembly and organization of organic and inorganic components. We
have already published twomain reviews in this field [46]; themost important findings
using phosphorus dendrimers will be highlighted in the next paragraphs.
