Mesoionic N‐Heterocyclic Olefins, Imines, Thiones, Phosphinidenes and Their Application in Catalysis

Abstract

Abstract Transition metal compounds are widely known for their ability to activate small molecules and are excellent catalysts for a wide range of reactions. However, environmentally friendly and cost‐effective alternatives are highly desirable due to their toxicity and low abundance. In recent years, there has been a significant surge in the study of main‐group‐based species, mainly p‐block element‐derived compounds, which revealed reactivity resembling that of transition metal complexes. Recently, the mesoionic N‐heterocyclic carbenes (mNHCs) adducts of p‐block elements, containing exocyclic fragments such as ═CH 2 (mNHOs), ═NR (mNHIs), ═PR (mNHPs), and ═S (mNHTs), have evolved as ligands for coordination chemistry, reactive species for the activation of small molecules, as well as efficient metal‐free catalysts for various challenging organic transformations, driven by their strong nucleophilicity. This minireview documents recent breakthroughs in the synthesis, reactivity, and catalytic applications of mNHOs, mNHIs, mNHTs, and mNHPs.