Leveraging Heterogeneous Metal on Nitrogen-doped Carbon Materials for Aerobic Oxidation Catalysis

Book excerpt: Chemical redox reactions serve as an important class of transformations for the modernchemist, and advancements in homogeneous and heterogeneous catalysis are ever expanding the synthetic toolbox. Nonprecious metal catalysts and "green" reagents are sought after for their economic and environmental advantages to synthetic chemistries, and bridging seemingly disparate fields can lead to intriguing insights and developments. For decades, first-row transition metals incorporated into nitrogen-doped carbon (MNCs) have been studied for electrochemical oxygen reduction as leading alternatives to platinum in fuel cells, and more recently, MNCs have been used as catalysts for aerobic oxidation reactions in the context of organic synthesis. In this approach, protons and electrons from chemical bonds in organic molecules are used to promote oxygen reduction as balanced redox half reactions. This body of work describes our recent developments with MNC materials and their applications in organic synthesis. Chapter 1 offers an overview of MNC synthesis and characterization followed by a synopsisof the application of MNC catalysts to thermal organic transformations. This provides important context for Chapter 2 wherein we disclose our recently developed protocol for the incorporation of atomically-dispersed iron sites into nitrogen-doped carbon frameworks. The resulting MNC materials are then characterized in a cross-laboratory study targeting the quantification of active sites on MNCs prepared via diverse synthetic protocols. Chapter 3 presents the development of catalytic conditions for the formation of diazo compounds using oxygen as the terminal oxidant, initially by means of homogeneous copper catalysts. We then leveraged MNC catalysts for the same transformation and paired the formation of diazo compounds with enantioselective carbene transfer to achieve C-H insertion and cyclopropanation. This new MNC reactivity is further showcased in a flow reactor with gram-scale synthesis of diazo compounds. Chapter 4 describes ongoing work seeking to understand MNC-catalyzed hydrazone oxidation, including mechanistic insights, structure-activity relationships, and broadening this reactivity to other transformations involving proton-coupled electron transfers.