Efficient N‐Heterocyclic Carbene/Ruthenium Catalytic Systems for the Alcohol Amidation with Amines: Involvement of Poly‐Carbene Complexes?

• DOI: 10.1002/cctc.201800945
• Publication Date: 2018-07-30T07:22:55Z
• Authors: Hua Cheng; Mao‐Qian Xiong; Ni Zhang; Hua‐Jing Wang; Yang Miao; Wei Su; Ye Yuan; Cheng Chen; Francis Verpoort
• Keywords: Amide; Benzimidazole; Catalytic efficiency

Abstract The atom‐economic direct amidation of alcohols with amines has been recently highlighted as an attractive and promising transformation. Among the versatile reported catalytic systems, in situ generated N‐heterocyclic carbene (NHC)/ruthenium (Ru) systems have demonstrated their advantages such easy operation use commercial Ru compounds. However, existing catalyst loadings are relatively high, additional insights for generation still not well‐documented. In this work, a variety benzimidazole‐based NHC precursors were initially synthesized. Through screening various other reaction conditions, active discovered efficient amide synthesis. Notably, loading is low 0.5 mol %. Furthermore, experiments performed to validate rationale superiority current over our previous system. It was observed that ligand structure one reasons higher activity. addition, ratio precursor/[Ru] another important factor improvement. Further HR‐MS analysis identified formation two mono‐NHC‐Ru species major bearing multiple ligands minor species. Hopefully, readily‐accessible herein could demonstrate great potential further practical applications.