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1. Catalyst carbonylation: a hidden, but essential, step in reaction initiation

   https://doi.org/10.1039/D1CY00322D  

   Alfonso, Nicolas; Do, Van K.; Chavez, Anthony J.; Chen, Yuhao; Williams, Travis J. (April 2021, Catalysis Science & Technology)

   null (Ed.)

   The proliferation of increasingly useful reactions for hydrogen transfer in organic synthesis has included the introduction of many new homogeneous catalysts into the organic synthesis lexicon. Unlike the proliferation of palladium-based cross-coupling reactions in which the mechanism is generally conserved, we are learning that these emerging hydrogen transfer catalysts have a rich diversity of mechanisms for catalyst activation, speciation, C–H bond cleavage and formation, and ultimately deactivation. We find that an underappreciated commonality in the catalytic activation for some of these systems is the generation of a (carbonyl)metal group, which dominates the downstream speciation of the catalyst system. In this mini-review we highlight a few well-documented cases of this phenomenon as food for thought for those who are designing new catalytic systems to introduce into this dynamic and impactful area. 

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2. Network-Supported, Metal-Mediated Catalysis: Progress and Perspective

   https://doi.org/10.1039/D0RE00229A  

   Bennett, Jeffrey A; Davis, Bradley; Efimenko, Kirill; Genzer, Jan; Abolhasani, Milad (January 2020, Reaction Chemistry & Engineering)

   Metal-mediated chemical reactions have been a vital area of research for over a century. Recently, there has been increasing effort to improve the performance of metal-mediated catalysis by optimizing the structure and chemical environment of active catalytic species towards process intensification and sustainability. Network-supported catalysts use a solid (rigid or flexible) support with embedded metal catalysts, ideally allowing for efficient precursor access to the catalytic sites and simultaneously not requiring a catalyst separation step following the reaction with minimal catalyst leaching. This minireview focuses on recent developments of network-supported catalysts to improve the performance of a wide range of metal-mediated catalytic reactions. We discuss in detail the different strategies to realize the combined benefits of homogeneous and heterogeneous catalysis in a metal catalyst support. We outline the unique versatility, tunability, properties, and activity of such hybrid catalysts in batch and continuous flow configurations. Furthermore, we present potential future directions to address some of the challenges and shortcomings of current flexible network-supported catalysts. 

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3. Recent advances in oxidative allylic C–H functionalization via group IX-metal catalysis

   https://doi.org/10.1039/D0CC05554A  

   Kazerouni, Amaan M.; McKoy, Quincy A.; Blakey, Simon B. (November 2020, Chemical Communications)

   null (Ed.)

   Allylic substitution, pioneered by the work of Tsuji and Trost, has been an invaluable tool in the synthesis of complex molecules for decades. An attractive alternative to allylic substitution is the direct functionalization of allylic C–H bonds of unactivated alkenes, thereby avoiding the need for prefunctionalization. Significant early advances in allylic C–H functionalization were made using palladium catalysis. However, Pd-catalyzed reactions are generally limited to the functionalization of terminal olefins with stabilized nucleophiles. Insights from Li, Cossy, and Tanaka demonstrated the utility of RhCp x catalysts for allylic functionalization. Since these initial reports, a number of key intermolecular Co-, Rh-, and Ir-catalyzed allylic C–H functionalization reactions have been reported, offering significant complementarity to the Pd-catalyzed reactions. Herein, we report a summary of recent advances in intermolecular allylic C–H functionalization via group IX-metal π-allyl complexes. Mechanism-driven development of new catalysts is highlighted, and the potential for future developments is discussed. 

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4. Highly selective transition-metal-free transamidation of amides and amidation of esters at room temperature

   https://doi.org/10.1038/s41467-018-06623-1  

   Li, Guangchen; Szostak, Michal (October 2018, Nature Communications)

   Abstract Amide chemistry has an essential role in the synthesis of high value molecules, such as pharmaceuticals, natural products, and fine chemicals. Over the past years, several examples of transamidation reactions have been reported. In general, transition-metal-based catalysts or harsh conditions are employed for these transformations due to unfavorable kinetics and thermodynamics of the process. Herein, we report a significant advance in this area and present the general method for transition-metal-free transamidation of amides and amidation of esters by highly selective acyl cleavage with non-nucleophilic amines at room temperature. In contrast to metal-catalyzed protocols, the method is operationally-simple, environmentally-friendly, and operates under exceedingly mild conditions. The practical value is highlighted by the synthesis of valuable amides in high yields. Considering the key role of amides in various branches of chemical science, we envision that this broadly applicable method will be of great interest in organic synthesis, drug discovery, and biochemistry. 

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5. Guiding Principles for Designing Highly Efficient Metal‐Free Carbon Catalysts

   https://doi.org/10.1002/adma.201805252  

   Zhang, Lipeng; Lin, Chun‐Yu; Zhang, Detao; Gong, Lele; Zhu, Yonghao; Zhao, Zhenghang; Xu, Quan; Li, Hejun; Xia, Zhenhai (December 2018, Advanced Materials)

   Abstract Carbon nanomaterials are promising metal‐free catalysts for energy conversion and storage, but the catalysts are usually developed via traditional trial‐and‐error methods. To rationally design and accelerate the search for the highly efficient catalysts, it is necessary to establish design principles for the carbon‐based catalysts. Here, theoretical analysis and material design of metal‐free carbon nanomaterials as efficient photo‐/electrocatalysts to facilitate the critical chemical reactions in clean and sustainable energy technologies are reviewed. These reactions include the oxygen reduction reaction in fuel cells, the oxygen evolution reaction in metal–air batteries, the iodine reduction reaction in dye‐sensitized solar cells, the hydrogen evolution reaction in water splitting, and the carbon dioxide reduction in artificial photosynthesis. Basic catalytic principles, computationally guided design approaches and intrinsic descriptors, catalytic material design strategies, and future directions are discussed for the rational design and synthesis of highly efficient carbon‐based catalysts for clean energy technologies. 

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