Supported Metal Nanoparticles Assisted Catalysis: A Broad Concept in Functionalization of Ubiquitous C−H Bonds

Abstract

Supported metal nanoparticles (NPs) catalysed chemical transformations have been a vital area of research over the last few decades. Catalysis by supported NPs not only plays a pivotal role in the production of fine chemicals such as coupling products, heterocycles, alcohols, carbonyl compounds, acids, etc. but also provides sustainable chemical processes. The use of supported metal NPs provides a much prosperous basis than conventional homogeneous and heterogeneous catalysts for tuning reactivity, recyclability, high productivity and environment benevolent alternative for C−H functionalization. Consequently, as evidenced in the literature, various support materials such as silica, metal oxides, zeolites, carbon‐based materials, bio‐materials, magnetic materials, and MOFs have been moderately investigated in order to exploit their benefit in supported metal NPs catalyzed various C−H functionalizations. This review aims to summarize recent advances in the development of new support materials or novel supported NPs catalytic systems for functionalization of the challenging C−H bond under heterogeneous conditions. Furthermore, a deep scientific understanding of the mechanisms, active species, role of base and oxidants for these systems are also discussed to gain insight into the advance in the rational design of efficient catalytic systems, which may serve as an inspiration to researchers in their future work.

Nanoceria as an Electron Reservoir: Spontaneous Deposition of Metal Nanoparticles on Oxides and Their Anti-inflammatory Activities

“…Noble metal nanostructures exhibit fascinating catalytic properties for a wide range of reactions important in the chemical and pharmaceutical industries, but the downside is that during the synthesis or under catalytic operating conditions, sintering or coalescence invariably deteriorates the quality of metal nanoparticles (NPs) because of the thermodynamically unstable nature. − Deposition of noble metal catalysts onto metal oxide supports has been proven to be one of the most effective strategies to stabilize the NPs. Supported NPs display improved activities compared to their nonsupported counterparts due to the synergetic effects originated at the metal–metal oxide heterojunction via altered electronic structures. − A range of precious metal catalysts have been so far loaded on different transition or nontransition metals oxides with the purpose of improving stability and attaining enhanced activity. − The incipient impregnation, chemical vapor deposition, laser ablation, and electrochemical deposition approaches have been adopted for deposition of metal NPs. − Alternatively, high-quality monodispersed metal NPs with a narrow particle size distribution are synthesized under the protection of stabilizers (i.e., polymer or surfactant) prior to loading on supports, but the presence of the stabilizers at the interface between the metal NPs and the support minimizes the direct contact or electronic communication between metals and supports. − Naked NPs with maximum active surface areas are mostly the desired product; there have been few reports where bare metal NPs were in situ grown outside or inside metal oxides structures. − For instance, MnO nanocrystals were used as a reactive template to electrolessly deposit platinum NPs onto the surface via the galvanic replacement reaction. , In other reports, noble metal NPs were deposited on WO 2 nanowires and TiO 2 NPs. − There have been reports wherein metal core cerium oxide shelled based nanostructures were produced using wet chemical reaction systems. − In this study, we report as-synthesized hollow CeO 2 nanospheres as an electron reservoir to reduce the metal salts into metal NPs under optimized synthetic conditions, in contrast to previous reports wherein CeO 2 shells were formed on metal NPs. In this study, metal N...…”

Transition-metal-catalyzed C–H bond alkylation using olefins: recent advances and mechanistic aspects

“…In the past few decades, the development of C-H functionalization reactions that enable the construction of fundamentally important C-C and C-X bonds has witnessed tremendous upsurge. [1][2][3][4][5][6][7][8][9][10][11] Within the domain, transition metal catalysis forms the largest, ever expanding subset contributing to the broad spectrum of applications that ranges from organic synthesis to petrochemical processing. [12][13][14][15][16][17][18][19][20] In this context, the development of novel methods to access arylation, [21][22][23][24] alkenylation [25][26][27] and alkynylation of C-H bonds 28 has gained tremendous attention.…”

C–H Bond Activation Mechanism by a Pd(II)–(μ-O)–Au(0) Structure Unique to Heterogeneous Catalysts

“… 15 − 19 Thus, supported metal nanoparticle catalysts have the potential to create novel active site structures for efficient C–H bond activation via unique mechanisms. 20 However, the reaction mechanism with supported metal nanoparticle catalysts and the structure of the catalytically active sites are not well understood at the elementary reaction level, which makes developing general heterogeneous catalyst design strategies extremely difficult.…”

“…Supported metal nanoparticle catalysts are easy to separate and reuse, which is an attractive feature for green chemistry. In addition, supported metal nanoparticle catalysts can create unique active site structures different from those of homogeneous complex catalysts and sometimes outperform homogeneous catalysts by utilizing their specific systems, such as the ensemble effect, ligand effect, concerted catalysis, and geometric structures (e.g., core–shell, cluster-in-cluster, and alloy structures). − Thus, supported metal nanoparticle catalysts have the potential to create novel active site structures for efficient C–H bond activation via unique mechanisms . However, the reaction mechanism with supported metal nanoparticle catalysts and the structure of the catalytically active sites are not well understood at the elementary reaction level, which makes developing general heterogeneous catalyst design strategies extremely difficult.…”