Construction Of Nanoclusters@Porphyrin MOFs Composite Photocatalytic System And Its Application In Organic Synthesis

The conversion of solar energy into chemical energy through photocatalytic system is expected for simultaneously solving the energy crisis and environmental pollution faced by human society.However,the development of high-efficiency photocatalysts is of great significance for photosynthesis of pharmaceutical molecules.Metal-organic framework materials(MOFs)are widely used in the field of photocatalysis because of their well-defined molecular structure,easy modification,porous and stable structure.In this thesis,both metal clusters and single catalytic active centers were confined in to porphyrin-based MOF(PCN-221 and PCN-222),which can be used for synergetic catalytic organic conversion.(1)The synthesis of quinolones and isoquinolones have attracted intense attention due to their potent on pharmaceutical industry.In view of this,a series of composite photocatalysts(Pt_x@PCN-221,x=0.9,1.6,2.2 and 3.0 nm)were prepared by in situ photoreduction strategy,which confined ultra-small Pt nanoclusters into porphyrin MOFs(PCN-221)with strong visible light absorption.Among them,Pt_0.9@PCN-221 exhibits extremely high catalytic activity and stability.Without any electronic sacrificial agents,the yield of quinolinone could reach more than 90.0%after 2 h of irradiation,and the catalytic activity did not change significantly after 10cycles of catalytic activity.In addition,the yield of 1-methyl-5-nitroisoquinolinone reaches 175.8 g·g^-1_catwithin 6 hours,which is more active than PCN-221 increased 22times.The experimental results show that the subnanometer composite material can significantly promote the electron-hole separation and the generation of ¹O₂,and achieve a synergistic effect in the photocatalytic system,thus improving the photocatalytic activity of the catalyst.This work provides a new strategy for realizing the photocatalytic synthesis of biologically active heterocyclic molecules from MOFs.(2)At present,carbonylation reaction generally takes CO as the C1 source,which requires harsh reaction conditions such as high temperature and high pressure.It is extremely challenging to realize the photocatalytic carbonylation reaction with CO₂as the C1 source.Based on this,a single point catalyst Co was introduced into the center of the porphyrin ligand,and then metal nanoclusters(CuPd NCs)were encapsulated into the channels of MOFs by double solvent method,successfully constructed CuPd_x@PCN-222(Co)(x=1.3,2.0,3.0 nm)composite photocatalyst.It is used in the photocatalytic carbonylation Suzuki/Sonogashira coupling reaction under mild conditions,using CO₂as the C1 source,and exhibiting excellent catalytic performance.With CuPd_1.3@PCN-222(Co)as the catalyst,the yield of benzophenone reached more than 90%in 5 h.In addition,the carbon in carbonylation is derived from the carbon in photocatalytic CO₂by ¹³CO₂labeling experiment.(3)Furthermore,CuPd_1.3@PCN-222(Co)was used as a catalyst to realize the one-pot visible light-driven Suzuki/Sonogashira carbonylation reaction for the first time in the atmosphere of CO₂.The catalytic performance and mechanism of MOF composites were systematically studied.As a result,the composite showed good substrate compatibility,the yield of most of the substrates can reach more than 80%,and the catalytic activity can still reach 90.0%after 5 cycles.In addition,we also studied the mechanism of the photocatalytic reaction of the composite.Upon irradiation,porphyrin ligands in CuPd_1.3@PCN-222(Co)can be excited for the electron-hole separation.Then,the electrons on LUMO can be concurrently transferred to the Co sites and CuPd NCs,while the holes on HOMO can be compensated by TEA.Under Ar,iodobenzene was transformed into the phenyl-Pd-I intermediate by an oxidation addition.After a transmetalation,the phenyl-Pd-I and phenylboronic acid was transformed into the species of phenyl-Pd-phenyl under alkaline environment.Under CO₂atmosphere,single site cobalt(II)can drive photoreduction of CO₂to CO,which was inserted into the phenyl-Pd-I intermediate to afford the species phenyl(CO)-Pd-I.Then benzophenone was obtained by the transmetalation process and reductive elimination.Therefore,the synergistic effects among single active sites(CO),CuPd NCs and porphyrin ligands in MOFs composites make them exhibit excellent catalytic activity and cycling stability in the photocatalytic system.This work highlights the synergy between single-site catalyst,metal nanoclusters and absorbent materials and provides a new direction for photocatalytic conversion of CO₂ to higher value-added chemicals.