Bio-inspired asymmetric Zn-N2O2 single-atom catalysts via natural skeleton for efficient N-alkylation of nitroarenes
Yu Huang1, Yan Li2, Xiaogang Yin3
1School of Chemistry and Materials Science, Guizhou Normal University, Guiyang, China.
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.
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