Synthesis Of Aromatic Triangular Palladium Complexes And Their Applications In C-I Selective Coupling Reactions

Aromatic triangular palladium clusters had been widely used in the fields of synthesis,coordination,catalysis and photochemistry.Since aromatic triangular palladium clusters had been prepared for the first time,their preparation and catalytic application had been the focus of many scientists.In terms of synthesis,the mixed platinum palladium cluster[Pd₂Pt]⁺,[Pd₂Pt]⁺and mixed ruthenium-palladium clusters[Pd₂Ru]⁺had been successfully synthesized;in coordination field,it could form pyramid structure with Ag⁺coordination.In the field of catalysis,it not only showed highly selectivity for the reduction of endoalkynes,but also could catalyzed the cyclization of 1,6-enylene efficiently.In the previous works,our group studied the photoelectric properties of[Pd₃]⁺and their preliminary catalytic behaviors in the Suzuki coupling reaction and realized the gram-scale synthesis for the analogues cyclooxygenase-2（COX-2）inhibitors with good yields.In order to further study the catalytic application of aromatic triangular palladium complex in coupling reaction.My work mainly explored Sonogashira coupling and Heck coupling reactions catalyzed by[Pd₃]^+,and actively explored the preparation of more different types of new triangular palladium complexes.Specifically,it includes the following three aspects:1.One pot method was used to prepare[Pd₃]⁺and its catalytic Sonogashira coupling reaction was successfully applied.The target product was prepared in gram-scale with a catalytic loading of 0.02 mol%and the use of copper salts as cocatalyst was avoided.Compared with ordinary palladium,it was found that the aromatic triangle palladium clusters showed specific selectivity for the activation of C（sp²）-I.The substrate scope of substituted aryl halides and phenylacetylenes was wide even including the halogenated fused rings and heteroaromatics（1-iodothiophene,2-iodothiophene,3-iodopyridine and2-iodopyrazine）.Under the optimized catalytic conditions,the yields could reach 71-95%.We monitored the entire catalytic process with HRMS and found that the catalyst maintained its integrity throughout the catalytic process.2.Aromatic triangular palladium clusters had been applied in Heck coupling reaction.Similar to the Suzuki coupling and Sonogashira coupling reactions,these[Pd₃]⁺clusters showed good catalytic activity and C-I selectivity for various iodinated aromatics and functionalized alkenes（ester group and amide group）.When the catalyst loading was 0.5mol%,the separation yield of the coupling reaction of gram Heck reached 92%under mild conditions.It was found that the aromatic triangular palladium clusters maintained their integrity during the whole catalytic process by HRMS.3.The preparation of aromatic triangular palladium complex with nitroheterocyclic carben as ligand was further studied by ligand exchange.The reaction conditions such as temperature,solvent and other conditions were screened,A triangular palladium cluster with phosphine ligands replaced by nitroheterocyclic carbens ligands was obtained by preliminary high-resolution characterization.