The Denitrative C-N And C-C Crosscoupling Reactions Of Nitroarenes Catalyzed By Pd/NHC Complexes

The palladium-catalyzed denitrative coupling of nitroarenes represents a promising direction in the development of cross-coupling.Pd（acac）₂/biphenyl monophosphine was reported to be active,it suffers from high catalyst loading and limited substrate range.To overcome these problems,we designed and synthesized a number of sterically bulky and electron-rich N-heterocyclic carbene（NHC）ligands,and explored the applications of these NHC ligands in palladium-catalyzed nitroarenes cross-coupling.This thesis will be divided into four parts.Part Ⅰ:We designed and synthesized a number of imidazolium salts as the NHC precursors with large steric hindrance and L-shaped structure.Pd（acac）₂/5-（2,4,6-triisopropylphenyl）imidazolylidene[1,5-a]pyridines has been shown to be effective for the C-N coupling of nitro（hetero）arenes and aromatic/aliphatic amines.We investigated the effects of the ligand structure,palladium catalysts,bases,and solvents on the C-N coupling reactions.The results showed that our Pd/NHC system exhibits excellent compatibility with nitroaromatics,including those substituted by electron-donating and electron-withdrawing groups,as well as nitroheteroarenes,and the corresponding products were obtained in up 99%yields.Moreover,the catalytic system showed good compatibility with some aromatic/aliphatic amines,including those substituted by electron-donating groups,electron-withdrawing groups,and some biologically active groups,and the corresponding amines were afforded in up to 99%yields.Part Ⅱ:We studied Pd/NHC catalyzed reductive coupling of nitroarenes in a presence of a reducing agent leading to diarylamine compounds.We investigated the effects of various reducing agents,bases,solvents,and palladium catalysts on the catalytic system.Our results showed that some nitroaromatics substituted by cyclopropyl,trifluoromethyl,and ester groups can be converted into diarylamines in good yields,with the highest yield at 78%.We also isolated and characterized two complexes,[Pd（NHC）（acac）Cl]and[Pd（a NHC）（acac）Cl],by means of single crystal X-ray diffraction,nuclear magnetic resonance,and high-resolution mass spectrometry.Part Ⅲ:The palladium/NHC catalyzed coupling of nitroarenes and hydrazines were studied leading to arylhydrazine derivatives.Through screening of various conditions,we identified optimized palladium catalysts and ligands.The catalytic system exhibited excellent compatibility with nitro-containing heterocyclic and fused-ring compounds.A number of arylhydrazine derivatives were obtained in good to excellent yields.Part Ⅳ:Heterocyclic biaryls are a class of heterocyclic compounds with important applications,but the previous biaryl monophosphine ligands cannot effectively realize the palladium catalyzed C-C coupling of nitroarenes and heterocyclic boronic acids.We developed a[Pd（cin）Cl]₂/NHC catalyzed C-C coupling method of nitro（hetero）arenes and heterocyclic boronic esters.We examined the influenece of palladium catalysts,ligands,reaction solvents,and bases.The method can obtain products with the highest yield of 99%for trifluoromethyl,ester,amido and alkynyl substituted nitroaromatics.Some nitroheteroaromatics and halogenated heteroaromatics can give heterocyclic biaryls in the highest yield of 99%.We isolated[Pd（NHC）（cin）Cl]precatalyst and characterized it by single crystal X-ray diffraction,NMR and high-resolution mass spectrometry.