Construction Of Nitrogen-Containing Ruthenium/Nickel Catalysts And Applications In Acceptorless Alcohol Dehydrogenation To Carboxylic Acids

Carboxylic acids are a fundamental class of organic compounds which have important applications in chemical industries such as synthetic plastics and fibers,and they are also important chemical raw materials and pharmaceutical intermediates.Therefore,their synthesis methods have received extensive attention.The traditional method for synthesizing carboxylic acids is the direct oxidation of primary alcohols,which often requires stoichiometric amounts of oxidants or hydrogen acceptors so that toxic waste is generated,which is inconsistent with the principles of environmental friendliness and sustainable development.In recent years,acceptorless dehydrogenative coupling(ADC)of primary alcohols and water/hydroxides has been proven to be an attractive new method to afford carboxylic acids,which has become one of the research hotspots.This new method reveals potential application prospects since it evolves the dihydrogen gas as the sole byproduct,avoids the use of any hydrogen acceptor or additive,and has the characteristics of high atom economy.At present,homogeneous and heterogeneous catalytic systems using a transition metal such as Ru,Ir,Mn Co or Ni as the central metal have been most widely studied.However,the existing catalytic systems usually have some problems,such as simple ligand structures,high catalyst loadings,unsatisfactory catalytic performance and stability,narrow substrate scope and so on.Based on the above considerations,this dissertation designed and prepared ruthenium-based catalytic systems containing nitrogen ligands as well as nitrogen-doped nickel-based catalytic materials.Furthermore,these catalytic systems were applied as potential catalysts for the acceptorless dehydrogenation of alcohols to carboxylic acids.The specific research contents have been listed as follows:In view of the strong coordination ability and structural modifiability of N-heterocyclic carbene(NHC)ligands,a series of NHC precursors with structural diversity were designed and synthesized in this chapter.Various substituents were introduced on the N terminus,imidazole skeleton and phenyl ring of the ligands to regulate the steric and electronic properties of these ligands and the corresponding ruthenium complexes(NHC/Ru complexes).Moreover,the steric and electronic effects on the catalytic performance of this transformation was thoroughly studied.Further investigations demonstrated that a broad range of carboxylic acids were efficiently synthesized in gram scales at an ultralow ruthenium loading of 62.5 ppm,which showed promising application potential of these catalytic systems in industry production.In addition,the formation and transformation of ruthenium hydrides in the catalytic reactions were monitored by nuclear magnetic resonance(NMR)spectroscopy,and the catalytic mechanism of the whole reaction process was speculated.Finally,the evaluation of green metrics shows the greenness and sustainability of these NHC/Ru catalytic systems.In this chapter,nitrogen-rich melamine was used as the catalyst precursor,and the corresponding nitrogen-doped porous carbon materials were prepared by thermo pyrolysis.The direct synthesis method was used to interact melamine with nickel,and the catalytic performance was adjusted by varying the pyrolysis temperature(550℃,650 ℃,750℃).Finally,a practical and reusable nickel-based catalyst was obtained and labelled as Ni@NC-650.Notably,this catalyst has the advantages of simple preparation method,low cost and good tolerance of functional groups.Moreover,it can be recycled for at least 5 times without obvious decline in activity,showing good application potential.