Synthesis Of Metal-Orianic Suspended Ion Catalysts And Their Catalytic Properties In Electroorganic Synthesis

Organic electrochemistry has emerged as an environmentally friendly,atom-economic and sustainable alternative to traditional synthetic methods,thanks to the use of clean redox power in place of stoichiometric amount of oxidants or reductants.The reactivity of electrochemical reactions is systematically tunable by changing the applied potentials,which make certain complex molecules easily accessed under mild conditions.2,2,6,6_tetramethylpiperidine-l-oxyl(TEMPO)and its derivatives are a kind of environmentally friendly electrochemical catalysts and widely used in electrochemical organic synthesis.TEMPO is oxidized in the anode to TEMPO+,which is a highly selective oxidant with high catalytic activity and has been widely used in electrochemical reactions such as alcohol oxidation,biomass oxidation and C-H bond activation.However,TEMPO+,generated in the process of anodic oxidation,is likely to undergo electrochemical degradation in the cathode and lose its catalytic activity,and thus to reduce the Faraday efficiency.Meanwhile,after electrocatalysis,TEMPO catalyst is difficultly to be recycled.Metal-organic frameworks(MOFs)are a class of porous materials constructed from multidentate organic ligands and metal ions/clusters,featuring high porosity,high surface areas,and tunable pore sizes and shapes.The tunable pore nature and constituents of MOFs endow systematically introduce different redox-active and auxiliary centers to tune the catalytic properties for highly efficient and selective catalysis.However,the inherent low conductivity of most MOFs heavily deteriorated their electrocatalytic properties,especially in electroorganic synthesis.We developed a practically applicable strategy by suspending ion electrocatalysts in charged MOFs,which could markedly improve the conductivity and selectivity of MOFs in electrocatalysis.Firstly,we prepared a hexane imidazolyl(HIM)cationic MOF MIL-101(Cr)-HIMBr by post-modification.Anionic TEMPO-SO3-electrocatalyst was subsequently introduced into the cationic pores of the MOF to result in a suspension ion electrocatalyst TEMPO-SO3@MIL-101(Cr)-HIM by ion exchange.The working electrode decorated with the suspended ion electrocatalyst demonstrates high catalytic efficiency and selectivity in electro-oxidative self-coupling of benzylamines.Secondly,we prepared ethane imidazolyl(EIM)cationic MOFs MIL-53(M)-EIMBr(M=Fe,Cr,Al)by post-modification,and further synthesized a series of suspension ion electrocatalysts,TEMPO-SO3@MIL-53(M)-EIM by ion exchange,which exhibited high catalytic selectivity in electrocatalytic oxidation of benzoin derivatives to form the corresponding benzoyl compounds,depending on the synergistic effect between TEMPO-SO3-and metal nodes.