Synthesis Of Novel NHC And Chelating Carbene Ligands For Olefin Metathesis Ruthenium Catalysts

Sterically demanding olefin metathesis reactions catalyzed by ruthenium carbene complex is one of the unsolved problems in the study of olefin metathesis.Olefin metathesis could not be applied in some syntheses of natural products and biologically active complex organic molecules because of the influence of the steric hindrance of adjacent groups in substrates.In addition,even for established demanding reaction systems,there are still problems such as excessive decomposition of the catalyst,large catalyst loading,and difficulty in controlling stereochemistry.The development of ruthenium catalysts with high catalytic activity and stability is expected to achieve demanding olefin metathesis,and has good theoretical and application values.In this thesis,in order to improve the thermal stability of active catalytic species,we studied the ligand modification in HG-Ⅱ type ruthenium catalysts.First,we summarized the studies on ruthenium-catalyzed olefins metathesis in the past two decades,as well as the studies on the NHC ligands and chelating carbene ligands in the HG-Ⅱ type ruthenium catalysts.We then summarized our research progresses on synthesizing chelating carbene ligands and novel NHC ligands.The specific research work is as following:1.In the study of the synthesis of chelating benzylidene ligands,we designed electron-rich ligands with additional side-chain coordinating groups to increase their chelating ability.The synthetic routes were established,and several target compounds were prepared.2.In the study of the synthesis of NHC ligand precursors,imidazole-type and dihydroimidazole-type NHC ligands with substituted indole groups on the nitrogen atom were designed to enhance the protective effect to ruthenium atom.Synthetic routes for desired 4-bromoindoles were established,and various indole intermediates were prepared.