Key words
Sonogashira - heterogeneous catalysis - supported nanoparticles - aryl acetylenes
- palladium
Abhay Srivastava is currently pursuing his PhD at the Materials Research Centre, Indian Institute
of Science Bangalore. His research is focused on soft materials, biomimetics chemistry,
and catalysis. He graduated from University of Delhi in 2019 with a major in chemistry
and subsequently completed his postgraduate from Indian Institute of Technology Guwahati.
He is a recipient of the prestigious Prime Minister’s Research Fellowship and INSPIRE
(DST) fellowship.
Nishita Avasthi has graduated from Sri Venkateswara College, University of Delhi, and is currently
pursuing MSc from IIT (BHU) Varanasi.
Sharda Pasricha is currently working as a Professor in the Department of Chemistry, Sri Venkateswara
College, University of Delhi, India. She has published nearly 20 research articles
in journals of national and international repute. She was recipient of the prestigious
‘Distinguished Teacher Award’ from University of Delhi in 2009. She has authored two
books and several e-modules for UG students. Her current research interests include
green chemistry, heterogenous catalysis, and synthesis of biologically relevant heterocycles.
Sonogashira reaction is an important C–C cross-coupling reaction employed for the
synthesis of biologically active aryl or vinyl acetylenes using terminal acetylenes
and aryl or vinyl halides, in the presence of Pd/Cu salt or Pd metal catalysts.[1]
[2] Aryl and vinyl acetylenes are structural moieties in polymers, natural products,
agrochemicals, and pharmaceuticals. Their constant demand stimulates the upgrading
of their synthetic methodologies and the design of newer catalysts.[3]
Currently, the worldwide demand for palladium surpasses the supply, leading to the
excessive cost of the catalysts.[4] Therefore, sustainable use and recycling of Pd is vital. Nanocatalysis is a green
and benign approach, which is desirable for sustainability and economic viability.[5] These catalytic systems are cheap, ligand-free, and are generally stable to air
and moisture.[5] Nanoparticles (NPs) with controlled compositions, uniform and low particle sizes,
high number of surface atoms, large surface area, shape selectivity, zeta potential
values, and superior surface chemistry exhibit tailorable catalytic properties and
selectivity.[6] Selection of a suitable solid support for nanocatalysts is critical as it not only
controls the shape, size, and distribution of NPs on its surface but also eases a
cooperative and efficient pathway to achieve the target product through strong metal-support
interaction (SMSI), high surface area, a substantial number of participating active
sites, increased stability, decreased leaching and agglomeration of metal nanoparticles
and increased recyclability.[7]
[8] Solid-supported heterogenized Pd nanoparticles are now being explored as useful
catalysts for Sonogashira, Heck, Suzuki–Miyaura, and several other C–C cross-coupling
reactions.[9–11] The recent reports on the synthesis of heterogenized Pd nanoparticles with controlled
shapes, sizes, detailed structures, and choice of a plethora of nanostructured solid
supports has led to meaningful progression in the field.[8–11] This spotlight article lists some examples of solid supports used for tailoring Pd
nanoparticles (Figure [1], Table [1]) and their catalytic application in Sonogashira cross-coupling reaction (Table [1]).
Figure 1 Some solid supports for Pd nanoparticles
Table 1 Examples of Sonogashira Reaction Catalyzed by Solid-Supported Heterogenized Pd Nanoparticles
|
(A) Pd@MGO-D-NH2
[11]
– solid support: graphene oxide
– higher yields
– fast reaction
– simple operation
– easy catalyst separation
4 times
|
|
|
(B) Pd@COP
[12]
– solid support: covalent organic polymer
– excellent yield
– fast reaction
– electron-deficient aryl halides preferred
– mild conditions
8 times
|
|
|
(C) PdNPs@NCmw
[13]
– solid support: nanocellulose
– renewable source
– short reaction time
– size-controlled spherical NPs
– wide substrate scope, including heteroaryl halides
3 times
|
|
|
(D) Pd@TMU-3
[14]
– solid support: metal-organic framework
– facile preparation
– excellent yields
– high efficiency
– high purity
– fast reaction
– easy transfer
5 times
|
|
|
(E) Pd@Fe
3
O
4
/AMOCAA
[15]
– solid support: functionalized magnetite
– excellent yield
– fast reaction
– easy recovery
7 times
|
|
|
(F) Pd@SBA-Pr-imine-furan
[16]
– solid support: mesoporous organosilicate (SBA)
– excellent yield
– fast reaction
– stable catalyst
7 times
|
|
|
(G) Pd/PiNe
[17]
– solid support: biochar
– circular economy
– continuous-flow protocol
– high catalyst stability
– good yield
– low E-factor
5 times
|
|
|
(H) Pd@CS/Al-Fe-Mt
[18]
– solid support: chitosan
– well-encaged Pd NPs
– thermally stable
– high selectivity
– high TON, TOF
– high yields with ArI and ArBr
18 times
|
|
The data reviewed in this spotlight has revealed that nanomaterial-supported Pd NPs
have unveiled several opportunities for the accomplishment of economical, greener,
and sustainable Sonogashira cross-coupling transformations by preventing oxidation,
agglomeration, and promoting recycling of NPs. The future of supported Pd NPs will
depend on how well the scientific community can address challenges like low cost,
simple procedures for synthesis, leaching, falling-off of activity, regio- and chemoselectivity
in asymmetric transformations, utilization of biowaste materials for support. The
key to all pertinent issues probably lies in the design of superior heterogeneous
support systems using diverse material design philosophies.
