Studies On Ligand-Promoted N-H Bond Insertion By Siliver Catalysis

C-N bonds are widely found in natural products,pharmaceutical molecules,and functional materials.Nitrogen-containing organic compounds such asα-Amino acids,alkaloids and nitrogen-containing heterocyclic compounds have a wide range of biological activities,so it is of great significance to develop efficient and convenient methods for the construction of C-N bonds.Given the mild conditions,good tolerance of functional groups,and easy availability of raw materials,transition metal-catalyzed carbene-mediated N-H insertion reaction is one of the most efficient methods to construct C-N bonds at present.To date,N-H insertion reactions of carbene catalyzed by copper,rhodium,iron,ruthenium,iridium,palladium,and gold have been developed.Although silver catalysis has become a cornerstone of modern synthetic organic chemistry,the examples of silver-catalyzed carbene insertion into the N-H bonds are limited to electron-poor aromatic amines and carbene precursors are limited to diazo compounds.The reaction mechanism also needs to be discussed.Herein,we report a ligand-enabled carbene insertion into the N-H bonds of amines under silver catalysis.The achievements include the first silver-catalyzed N-H insertion of aliphatic amines in the presence of tribromo（tripyrazolyl）borate(Tp^Br3)ligand and an efficient N-H insertion of electron-rich aromatic amines using the1,2-diaminocyclohexane（DACH）ligand.We have also extended the diazo precursor to sulfonylhydrazines,which can be prepared in grams.This strategy has the advantages of simple operation under air conditions,mild reaction conditions,wide range of substrates,modular and tolerant to a variety of functional groups.X-ray powder diffraction and electrochemical experiments confirmed that DACH reduces the oxidation-reduction potential of the silver centre through coordination,preventing the silver catalyst from being reduced to simple silver,thus stabilising the silver catalyst.Experimental investigations and DFT calculations showed that DACH stabilises the silver catalyst by reducing its redox potential and the amine may act as a proton shuttle during the reaction,thus revealing an unprecedented mechanism for the silver-catalyzed N-H insertion.