Synthesis Of N - Heterocyclic Carbene Compounds And Aldehyde Catalytic Oxidation

In recent years, the study of organic catalytic reactions have drawn thewidespread attention. Organic catalysts have the advantage of lower cost, lowerloading and friendly-environmental impact, which is compared with metal organiccatalysts.Since unexpected catalytic action of N-heterocyclic carbenes (NHCs)resulted from the benzoin condensation reaction, the study of N-heterocycliccarbeneshas a long-term development with perspectives of synthesis ofN-heterocyclic carbenes, their intrinsic properties and catalytic application.N-heterocyclic carbenes serve as a kind of reaction intermediates, have high reactivityfor their unique nature like strong nucleophilicity and basicity. So as the organiccatalysts, N-heterocyclic carbenes are also widely used in many organic reactions,such as benzoin condensation reaction, Setter reaction, nucleophilic substitutionreaction and so on. The research of N-heterocyclic carbenes in the application oforganic catalytic reaction has achieved tremendous results. Furthermore, study onsynthesis of noble N-heterocyclic carbenes and its application in organic catalyticreaction is very meaningful.This paper focuses on two parts, for the first part, bis-NHC complexes aresynthetisedand applied to the catalytic oxidation of aldehydes. For the second part,We introduced poly-pyridine ruthenium complexes to modify the1,3-substituents ofN-heterocyclic carbine, and the corresponding compounds were characterized. Detailsof the study is shown below:Firstly, three bis-NHC complexes have been designed and synthesized, andcharacterizedwith method of NMR, electrospray ionization mass spectrometry(ESI-MS) and checked their constructure by X-ray diffraction analysis by single crystal cultivation. The catalytic activities of bis-NHC complexes in transformation ofaryladehydes to the corresponding carboxylic acids were tested. The experimentalconditions were optimized, including the length of the alky chain spacer in thecatalyst, the type of bases, solvents and temperature. The substrate scope of reactionwas checked under the condition that4.0equivalents of K2CO3were employed asbase, DMSO as solvent,5mol%catalyst effectively catalyzed the oxidation ofbenzaldehyde to benzoic acid in91%yield by1equivalent of H2O in the air at60oC,and theykept reactingfor36h. This study found that thecatalyst system is tolerant tomany functional groups, such as methyl, methoxyl, halide, and nitro groups etc.Especially the moderate catalytic action was been done by this catalyst system.Heteroaryl aldehydes were also analyzed and the oxidation of the furan and thiophenealdehydes afforded the corresponding acids in68and83%yields, respectively.Secondly, we designed and synthesized four new ruthenium pyridine derivativesof the N-heterocyclic carbenes. These compounds have been characterized by NMR,ESI-MS and UV visible spectrum andelectrochemical studies.And structure theorycalculation and catalytic properties are next step of my research.