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

## TL;DR

This paper reviews recent progress in using mesoionic N-heterocyclic compounds as metal-free catalysts for chemical reactions.

## Contribution

The paper highlights novel mesoionic ligands derived from p-block elements and their catalytic applications.

## Key findings

- Mesoionic N-heterocyclic compounds show reactivity similar to transition metal complexes.
- These compounds are effective as metal-free catalysts for organic transformations.
- Recent breakthroughs in their synthesis and catalytic uses are documented.

## 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 ═CH2 (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.

This minireview covers recent advances in the synthesis, reactivity, and metal‐free catalytic uses of mesoionic N‐heterocyclic olefins (mNHOs), imines (mNHIs), thiones (mNHTs), and phosphinidenes (mNHPs).