Synthesis Of N-(4-Indolyl) Heterocyclic Carbene Ligands And Their Application In Metal Catalysis

With their strong σ-donating ability,N-heterocyclic carbine(NHC)are similar to electronrich phosphine ligands.Comparing with phosphine ligands,NHC scaffold has a diversified structure and is easy to modify,and has a strong coordination ability to metals.The type and number of substituents on the NHC side chain can be changed.To change its steric effect and electronic effect,thereby changing the spatial configuration of the nitrogen heterocyclic carbene metal catalyst,and can induce chirality.Therefore,NHC ligands have a wide range of applications in transition metal catalysis.Developing new metal catalysts with high performance,good stability and wide range of substrates is one of the focuses in the field of homogeneous catalysis.The indole ring system is large,electron-rich and geometrically unique,and its benzene-fused five-membered ring can also generate steric effects different from that of a benzene ring.We thus envision that indole could be used as the side chain of NHC.This thesis mainly studies the synthesis and catalytic performance of N-(4-indolyl)NHC and its transition metal complexes,including the following two parts:1)The synthetic routes of indole-bearing NHC ligands and their transition metal complexes have been established.We have established synthetic routes of symmetric or unsymmetric NHC,and optimized previous synthetic routes of the established NHC precursors.Several series of symmetric or unsymmetric imidazole and dihydroimidazole NHC-Cu and NHC-Pd complexes containing 4-indolyl groups have been synthesized.2)The catalytic performance of the obtained indole-bearing NHC transition metal complexes have been tested in model reactions,and the structure-activity relationship of NHC ligands summarized.Indole-bearing NHC copper complexes were evaluated in aryl boronic acid carboxylation reactions,and palladium complex were evaluated in cross-coupling reaction such as Suzuki-Miyaura reaction.Among the new NHC ligands,several are found performed well in the reactions.Structurally,significant steric effects are found necessary for these ligands.Overall,these results support the concept of NHC ligand with indolyl side chain,demonstrating the promising application of these ligands in metal catalysis.