Study On Nanoporous Metal-Catalyzed Reduction Of Aryl Bromides,Amides And Nitro Compounds

Nanoporous metal have attracted increasing attention in the field of nanomaterial and heterogeneous catalysis owing to their unique three-dimensional nanopore structural features and catalytic performances.Compared with traditional nanoparticles,the nanoporous material was fabricated through a simple chemical dealloying process without any ligands or additives,thus residual organic or ions was avoided.The existence of high density of low-coordination atoms on the topmost surface of the nanoporous material renders the nanoporous metal higher catalytic activity than the traditional nanoparticle metal catalysts.The above features make the nanoporous metal to be a promising heterogeneous catalyst.In the first part,the selective hydrodebromination of aryl bromines was achieved by using nanoporous gold(AuNPore)as a catalyst.The hydrodebromination of various aromatic bromides proceeded smoothly in the presence of AuNPore to afford the corresponding products in 70%-93%yields.This protocol shows good functional group tolerance,such as acyl,carboxyl and a protected aldehyde,and the selective hydrodebromination reaction occurred exclusively in the coexistence of chlorine atom.The developed method can be practically applied for the degradation of bromine-containing herbicide,insecticide,and fire retardant,and the developed method can also be used as a promising deprotection strategy in organic synthesis.Leaching experiment indicated there was no gold atom leaching during the reaction process.The heterolytic cleavage of the H-H bonds occurred on AuNPore surface was verified through the deuterium-hydrogen exchange reaction.Control experiment indicated that the solvent MeOH also acted as a hydrogen donor in the hydrodebromination reaction.In the second part,a green and highly efficient heterogeneous catalyst system for the reduction of amides to amines using AuNPore as a catalyst was successful developed.Under optimized condtions,the reduction of various amides proceeded smoothly in the presence of AuNPore to afford the corresponding amines in 55%-94%yields.The substrates with electron-withdrawing groups on the nitrogen atom were unfavorable for this reaction,and the influence of the electronic properties of substituents around carbonyl group was not obvious.AuNPore catalyst can be simple recovered by filtration and reused for eleven times without any loss of the catalytic activity.The system was also successfully applied for the reduction of sulfoxide and N-oxide compounds.In the last part,the selective hydrogenation of nitro compounds catalyzed by nanoporous palladium(PdNPore)was developed and the relevance between catalytic activity and nanoporous structure was investigated.The order of the catalytic activity of the six PdNPore catalysts produced nearly coincided with the order of their specific surface area.Among the other cataylsts synthesized in this study,the PdNPore catalyst(Pd86Al14)with a specific surface area of 40.8 m2/g exhibited relatively high activity.The hydrogenation reactions of various nitro compounds proceeded smoothly with good functional group tolerance(acyl,ester,aminde and cyano)in the presence of this catalyst.Moreover,the nanoporous palladium is more useful for industrial applications than commercially available Pd/C and Raney-Ni catalysts because of its unique features,which include high stability and no palladium atom leaching during the hydrogenation reactions.