This study shows that a highly recyclable catalyst, composed of earth-abundant
materials, can be employed in a relatively mild, operationally straightforward C–H
bond arylation reaction involving industrially relevant aromatic heterocycles. This
work includes somewhat rare evidence of a release–capture catalytic manifold.
5.2 Case Study II) Direct C–H Acetoxylations,
Methoxylations, Halogenations and Arylations
of Heterocycles Catalysed by Pd
II
/MWCNT Carbon
Nanotubes
Ellis et al. have worked extensively on Pd
II nanoparticles supported on a multiwalled
carbon nanotube system (Pd
II /MWCNT) (Fig. 11) for application in various directed
C(sp
2 )–H bond functionalisation reactions. Acetoxylations, etherifications
(e.g. methoxylations, ethoxylations) halogenations [70] and arylations [71], directed
by ortho-substituted N-containing arene substrates (e.g. phenylpyridines and benzo
[h]quinolines), were successfully carried out using the Pd
II /MWCNT catalyst
(Scheme 8). Such transformations have been proposed to occur via a Pd
II /Pd
IV
catalytic cycle [72]. Fine control of synthesis of Pd/MWCNT by a ball mill-mediated
process allowed for selective embedding of Pd
II (over Pd
0 ) onto a multiwalled
carbon nanotube structure, thus allowing for a supported heterogeneous catalytic
system that could carry out these transformations [73].
Some differing reactivity from the Pd
II /MWCNT catalyst preparation was
observed when compared to Pd(OAc) 2 deployed under the same conditions.
Increased yields but lower substrate tolerance was observed in some acetoxylation
reactions. Reduced rates were observed in some alkoxylation reactions. However,
Fig. 11 TEM image
showing Pd
II NPs embedded
in a multiwalled carbon
nanotube (MWCNT)
structure, a supported
heterogeneous catalyst
which can be employed in a
range of synthetically useful
functionalisation reactions.
Reproduced from Ref. [73]
with permission from The
Royal Society of Chemistry
Pd Nanoparticles in C–H Activation and Cross-coupling Catalysis
189
materials, can be employed in a relatively mild, operationally straightforward C–H
bond arylation reaction involving industrially relevant aromatic heterocycles. This
work includes somewhat rare evidence of a release–capture catalytic manifold.
5.2 Case Study II) Direct C–H Acetoxylations,
Methoxylations, Halogenations and Arylations
of Heterocycles Catalysed by Pd
II
/MWCNT Carbon
Nanotubes
Ellis et al. have worked extensively on Pd
II nanoparticles supported on a multiwalled
carbon nanotube system (Pd
II /MWCNT) (Fig. 11) for application in various directed
C(sp
2 )–H bond functionalisation reactions. Acetoxylations, etherifications
(e.g. methoxylations, ethoxylations) halogenations [70] and arylations [71], directed
by ortho-substituted N-containing arene substrates (e.g. phenylpyridines and benzo
[h]quinolines), were successfully carried out using the Pd
II /MWCNT catalyst
(Scheme 8). Such transformations have been proposed to occur via a Pd
II /Pd
IV
catalytic cycle [72]. Fine control of synthesis of Pd/MWCNT by a ball mill-mediated
process allowed for selective embedding of Pd
II (over Pd
0 ) onto a multiwalled
carbon nanotube structure, thus allowing for a supported heterogeneous catalytic
system that could carry out these transformations [73].
Some differing reactivity from the Pd
II /MWCNT catalyst preparation was
observed when compared to Pd(OAc) 2 deployed under the same conditions.
Increased yields but lower substrate tolerance was observed in some acetoxylation
reactions. Reduced rates were observed in some alkoxylation reactions. However,
Fig. 11 TEM image
showing Pd
II NPs embedded
in a multiwalled carbon
nanotube (MWCNT)
structure, a supported
heterogeneous catalyst
which can be employed in a
range of synthetically useful
functionalisation reactions.
Reproduced from Ref. [73]
with permission from The
Royal Society of Chemistry
Pd Nanoparticles in C–H Activation and Cross-coupling Catalysis
189