Palladium-catalyzed Sonogashira Reaction: Activated Carbon-supported Palladium-copper Catalyst And Trace Palladium Catalysis

Transition-metal catalyzed cross-coupling reactions of carbon-carbon bond play a significant role in organic synthesis methodology.One of them was named Sonogashira coupling reaction,which can make the cross-coupling of Csp and Csp2,was catalyzed by Pd most of the time.And this well-known name-reaction was applied widely due to it's capacity for introducing the carbon-carbon multiple bond into a great many practical organic molecules.Despite many attempts to develop other transition-metal catalysts,the majority of today's cross-coupling reactions still rely on Pd.However,Pd is a toxic,precious metal and the demand of Pd is always large in traditional catalytic system.Therefore,the problems such as high cost,difficult-separation of product and the risk of heavy metal pollution limit the application of Sonogashira coupling reaction.Herein,we developed two strategies to make the reaction more convenient,greener and economical.One is synthesizing a heterogeneous bimetallic catalyst and another is realizing the trace-Pd catalysis.The specific research contents are as follows:(1)Activated Carbon supported Pd/Cu bimetallic catalyst:A facile solvothermal synthesis method has been selected to produce a heterogeneous bimetallic catalyst,Activated Carbon supported Pd/Cu(Pd/Cu@AC),during a one-pot procedure and the polyols were served as the solvent and reductant.Cat 5 produced by PEG-OMe 500 was confirmed as the most effective one.This catalyst showed great catalytic activity in Sonogashira cross coupling reactions under mild conditions and was compatible with diverse aryl iodides and bromides.Moreover,Pd/Cu@AC could be recycled at least nine times.All in all,Pd/Cu@AC,which was procedural simplicity,cheap,post-processing simple,high efficiency,long recycle-life,has been confirmed as a great heterogeneous catalyst and therefore solved the problem we mentioned to some extent.(2)a,P-Ynone accelerate trace-Pd catalytic system:Based on ?,?-Ynone ligand,we developed an efficient Phosphine-free trace-Pd catalytic system.A great deal of experiments proved that the 1-(4-methoxyphenyl)-3-phenylprop-2-yn-l-one(L2)was the most resultful ligand and the Sonogashira coupling reaction system involved in L2 could proceed with only 5ppm Pd.Furthermore,the coupling reaction could be applied in various substrates including electron poor or rich aryl halide and aromatic or heterocycle terminal alkyne in good to excellent yields.Refer to the classic catalytic mechanism,we presented that the crucial point of this reaction was the interaction between ?,?-ynone and Pd.A reductive-elimination proceeding procedure may take place via the coordination effect of ?,?-ynone's O atom and alkynyl and therefore the catalytic activity of Pd-species was increased efficiently.Additionally,the reaction could proceed under mild condition and EtOH could serve as solvent in this Phosphine-free trace-Pd catalytic system.