# Bio-inspired asymmetric Zn-N2O2 single-atom catalysts via natural skeleton for efficient N-alkylation of nitroarenes with alcohols

## TL;DR

This study creates a new zinc-based catalyst using chitosan to efficiently produce amines from alcohols and nitroarenes under mild conditions.

## Contribution

The first bio-inspired Zn single-atom catalyst with asymmetric Zn-N2O2 sites for efficient N-alkylation of nitroarenes with alcohols.

## Key findings

- Zn/CS catalyst achieves the highest turnover frequency among reported heterogeneous catalysts.
- The catalyst shows excellent reusability and a broad substrate scope with 56 examples.
- Asymmetric Zn-N2O2 sites facilitate bond formation and transition state generation in the reaction.

## Abstract

Although significant developments are made in non-noble metal catalysts for N-alkylation of nitroarenes with alcohols via borrowing hydrogen strategy, obtaining catalysts with superior activity, reusability and broad substrate scope under mild reaction conditions remains challenging. Single-atom catalysts (SACs) hold unique coordination/electron structures, to be the potential candidates for this reaction. In this study, we firstly and creatively fabricate bio-inspired Zn SACs with asymmetric Zn-N2O2 sites by utilizing the natural skeleton of biomass chitosan (denoted as Zn/CS), and achieve the first instance of heterogeneous Zn SACs in borrowing hydrogen reaction between nitroarenes and alcohols. The results reveal that the asymmetric Zn-N2O2 sites induced by natural skeleton (like ligands) and nanoporous structure of Zn/CS significantly promote the N-alkylation efficiency of nitroarenes with alcohols. Notably, the Zn/CS exhibits the highest turnover frequency (TOF) among the reported heterogeneous catalysts, as well as wide substrate scope (56 examples) and excellent reusability. Furthermore, the catalytic pathway/mechanism is investigated by combing theoretical calculations, which reveals that the asymmetric Zn-N2O2 sites with electron-deficient character can facilitate the formation of Zn-H and Zn-O bonds between Zn/CS and Ph-CH2O−, thus easily generating the transition state Ph-CH2O* and driving the whole reaction.

Making amines from alcohols and nitroarenes efficiently under mild, reusable conditions remains challenging. This study designs chitosan-based single zinc atom catalysts that enhance N-alkylation and reveal how asymmetric sites promote activity.