Study On Catalytic Performance Of NHC-Cu Complexes In Oxidation Reactions

N-heterocyclic carbene（NHCs）have become ubiquitous ligands in organometallic chemistry.They can coordinate with various metals to form catalysts,and widely used in modern organic synthetic chemistry.The application of NHC-metal complexes in catalytic oxidation is a basic research topic in academia and industry,and the utilization of NHC-Cu in catalytic oxidation reaction has been occasionally reported.We designed and synthesized a series of new NHC-Cu complexes which were used in liquid phase oxidative carbonylation of methanol andα-H oxidation of unsaturated hydrocarbons.The aim of the topic was focused on opening up a wider application fields of NHC-Cu complexes.The first chapter introduced the discovery,features of electronic structure,different types and synthetic routes of NHCs,as well as the research progress of NHC-metal complexes in the field of catalytic oxidation.Finally,the research ideas,and significance of the topic were put forward.In chapter two,the synthesizing method of ten novel imidazole and benzimidazole NHC precursors and twelve NHC-Cu（I）complexes were described in detail.Using benzimidazole as raw material,different groups（such as carbonyl group,hydroxyl group,pyridyl group and hexyl group）were introduced into the branch chain to obtain NHC precursors.Using o-phenylenediamine and ethylenediamine as raw materials,NHC precursors containing phenolic hydroxyl groups were prepared by substitution,addition and cyclization reactions.The structures of all products were characterized by IR,¹H NMR,¹³C{¹H}NMR and MS.In the third chapter,twelve new NHC-Cu（I）complexes were used to catalyze the synthesis of DMC by liquid phase oxidative carbonylation of methanol.The reaction was detected by gas chromatography for 12 hours continuously.A lot of experimental data of catalytic performance were collected,detailed comparative analysis and summary were made.The experimental results show that the single-core catalyst（L9-Cu Cl）with double carbene coordination has the best comprehensive catalytic activity.When the reaction temperature is 120℃and the total pressure is 2.4 MPa(P_CO:P_O2=2:1),the conversion of methanol is 13.27%within 12 h,the average selectivity of DMC is over 96%,the highest space-time conversion is 1.57g·DMC/g·cat_*h,and the corrosion rate is 2.31 g/（m_*²h）for 316L stainless steel.The fourth chapter mainly described the synthesis of three NHC-Cu（II）complexes and their application in the oxidation ofα-H in unsaturated organic compounds.Three NHC-Cu（II）complexes were prepared by coordinating various NHC precursors with Cu Cl₂ after being treated with strong alkali.The structures of the complexes were characterized by UV-vis absorption spectrum,infrared spectrum,X-ray photoelectron spectroscopy and mass spectrometry respectively.Cyclohexene and derivatives of ethylbenzene were oxidized by tert-butyl hydroperoxide（TBHP）,the complexes being used as catalysts.The experimental results showed that the catalyst containing phenolic hydroxyl group NHC-Cu（Ⅱ）（L7-Cu Cl₂）had the best catalytic ability.When the reaction temperature was 353 K and the catalyst dosage was 1mol%,the conversion of ethylbenzene was 71%and the selectivity of acetophenone 92%.For extended oxidations of derivatives,the results showed that the conversion of substrates and the selectivity of corresponding ketones were increased,when electron-withdrawing substituents in the para-position of benzene.