Supported Single Atom Catalysts for C−H Activation: Selective C−H Oxidations, Dehydrogenations and Oxidative C−H/C−H Couplings

Abstract

The activation of C−H bonds in hydrocarbons (saturated, unsaturated and aromatics) by single atom catalysts immobilized in a solid support is an active research front in catalysis. On the one hand, different examples of transition metal catalysts atomically dispersed on inorganic, organic and hybrid supports are constantly designed, synthesized and characterized using advanced microscopy and spectroscopic techniques. On the other hand, active, selective and stable single metal sites are recently developed as high performant heterogeneous catalysts for the C−H activation of organic molecules. This review covers recent examples of selective alkane and arene C−H oxidations, dehydrogenations of alkanes, as well as C−H/C−H oxidative couplings involving arenes, alkenes and alkynes, based on the use of supported single atom catalysts.

Metal–organic framework (MOF)-, covalent-organic framework (COF)-, and porous-organic polymers (POP)-catalyzed selective C–H bond activation and functionalization reactions

“…Finally, this species easily reacts with the cyanide source, giving rise to the desired product. 48 The oxidative alkenylation of aromatics is also called the Fujiwara-Moritani or oxidative Heck reaction. The major limitations of this reaction are the instability of the Pd(II) catalyst and the competitive activation of C-H bonds at different positions.…”

“…Thus, to overcome some of these issues, single-site heterogeneous catalysts (SSHCs) have been developed by some research groups. 48,[81][82][83]209 In 2019, Farha and collegues 81 anchored single-ion Pd(II) sites on the nodes of two post-synthetically acid-modified MOFs as heterogeneous supports via solution-phase solvothermal deposition (SIM), denoted as Pd@Hf-MOF-808-PO 4 and Pd@Hf-MOF-808-SO 4 . Remarkably, Pd(II) interacted and stabilized the acidfunctionalized sites on the Hf6-oxo nodes, significantly preventing their aggregation and deactivation to dark-brown Pd(0) nanoparticles (NPs), highlighting the role of single-site heterogeneous catalysts (SSHCs).…”

“…The main content of the review is organized according to the type C-X bond formation (or C-H bond functionalization) via C-H activation reactions promoted by porous materials. [47][48][49] energy. In addition, heterogeneous catalysts are becoming increasingly important because they provide alternative routes for reactions with a lower activation energy.…”

“…Recently, crystalline supports have exhibited great potential for the creation of single-atom catalysts (SACs) 136,361 at the nodes, linkers, and pores of MOFs by pyrolysis, showing excellent atom-utilization efficiency and unique properties in heterogeneous (photo)catalysis. 43,48,[362][363][364] Metal nanoparticles with different shapes be can effectively synthesized via the This journal is © The Royal Society of Chemistry 2022 pyrolysis of MOFs as sacrificial templates in air for catalysis and photocatalysis. Besides, upon higher temperature pyrolysis in an inert atmosphere, metal nanoparticle/metal single atom-supported porous carbon-based materials 346,365 (or MOFderived porous catalysts) 366 with a highly dispersed incorporated metal phase can be obtained, preventing the aggregation of the metal and fine-tuning the product selectivity.…”

Atomically Dispersed Cu Anchored on Nitrogen and Boron Codoped Carbon Nanosheets for Enhancing Catalytic Performance

“…Metal single-atom catalysts (SACs) have received great attention in recent years owing to their well-defined coordination structure and near-100% atomic utilization. − Moreover, SACs are generally dispersed on a heterogeneous support, inducing easy separation and relative robustness. So far, many research groups have constructed SACs for enhanced catalytic activity and selectivity. − Generally, the catalytic performance of SACs is modulated by the electronic structure of the metal centers, which is closely associated with the local atomic structure. − An efficient strategy to tailor the local atomic structure of SACs is the construction of atomic interfaces. − By introducing alien coordination atoms into the support, the newly formed atomic interface between the pristine single-atom structure and the alien atom breaks the structure and electronic symmetry of the single atoms and thus directly alters the interaction with reactants.…”