Fe-Based Metal-Organic Frameworks(MOFs) For Light-Induced Organic Syntheses

Photocatalysis is one of the best solutions to solve the problems of global energy shortage and environmental deterioration since it can utilize the abundant and ubiquitous solar light for chemical transformations.Aimed to developing renewable energy based processes,increasing interest is being paid to light-induced organic synthesis via photocatalysis.In addition to traditional semiconductor-based photocatalysts,metal-organic frameworks(MOFs),a class of micro-mesoporous hybrid materials,are recently emerging as a new type of promising photocatalysts for organic synthesis due to their unique composition and structural characteristics.Among all the MOFs,Fe-containing MOFs are extremely appealing in light-induced organic transformations since most of the Fe-based MOFs are visible light responsive due to the existence of extensive iron-oxo(Fe-O)clusters and Fe-containing complexes are commonly used in catalysis and photocatalysis.However,there is almost no article focusing on Fe-based MOFs for light-induced organic transformations although several reports on Fe-based MOFs in photocatalysis have already been publishedThis thesis focuses on the studies of light-induced organic transformations over several different Fe-containing MOFs and the details as well as the results of our research were summarized as follows.(a)The reaction between aromatic alcohols and active methylene compounds was studied over NH2-MIL-01(Fe).It was found that the oxidation of aromatic alcohols to aldehydes and the Knoevenagel condensation between as-formed aldehydes and active methylene compounds to form a,p-unsaturated compounds can be realized over NH2-MIL-101(Fe)under visible light irradiation via a successful coupling of the photo-oxidation of Fe-0 clusters and the base(-NH2)catalysis.(b)Photocatalytic benzene hydroxylation was inverstigated over MIL-100(Fe)and MIL-68(Fe)in the presence of H2O2 as oxidant.It was found that both Fe-based MOFs can selectively hydroxylate benzene to produce phenol under visible light irradiation via photocatalysis of Fe-0 clusters combined with Fenton-like route.However,MIL-100(Fe)showed superior photocatalytic performance to MIL-68(Fe)due to the existence of ?3-O in its framework,which can promote the transfer of the electron from the metal center to the substrate.(c)The oxidation condensation between alcohols and o-aminothiophenol was studied over MIL-100(Fe)and MIL-68(Fe)under visible light irradiation with O2 as oxidant.It was found that both Fe-based MOFs were found to be active for oxidative condensation between alcohols and o-aminothiophenols to form benzothiazoles under visible light irradiation via successful coupling of Fe-O cluster-based photocatalysis and Fe3+-based acidic catalysis.Transient absorption spectroscopy(TAS)studies showed that higher concentration of long-lived transition species with positive charges can be generated over MIL-100(Fe)than over MIL-68(Fe),which explained the superior catalytic performance of NMIL-100(Fe)to that of MIL-68(Fe).(d)Controllable growth of Pd nanoparticles in the cavity of MIL-100(Fe)to give Pd@MIL-100(Fe)nanocomposite was studied via double solvent impregation combined with photoreduction process.Coupling of MOF-based photocatalysis with Pd-based hydrogenation,Pd@MIL-100(Fe)showed efficient catalytic activity for N-alkylation of amines with alcohols under visible light.Kinetic studies revealed that the whole N-alkylation reaction was limited by the photocatalytic alcohol-to-aldehyde dehydrogenation reaction.Its performance can be further improved by modification of Pd@MIL-100(Fe)with Au,which can facilitate the dehydrogenation of alcohols to aldehydes.The original results in this thesis are as follows.(1)Fe-based MOFs were employed as multifunctional catalysts for several light-induced organic transformations through the successful coupling of MOF-based photocatalysis and other catalytically active sites in MOFs,highlighting the great potential of MOF-based photocatalysis and the photocatalyic reaction systems for organic syntheses.(2)The structural influence on photocatalytic activity was elucidated by the studies on Fe-based MOFs with different structures,providing some guidance for developing highly efficient MOF-based photocatalysis.