The Sonogashira Coupling Reaction Of Terminal Alkyne Catalyzed By Silica-chitosan Supported Palladium

Recently, the research and application of organic polymer supporters are beingpaid more and more attention, which the advantages are not only the easy separationand reusable, thus reducing costs; In addition, scientists found that the precious metalcatalysts supported by organic polymer have higher efficiency and selectivity.The heterogeneous catalysts was prepared by loading the palladium chloride tosilica/chitosan composite, and the relationships were analyzed between the palladiumloading, reused times and yield by IR, SEM and UV. It was shown that the percentageof palladium was6.73%.Then the catalyst was applied in the Sonogashira cross-coupling reaction ofphenylacetylene with iodobenzene in EtOH-H₂O solution, with amine-free andcopper-free, which reactivity and mechanism were explored. By studying the effectabout productivity and selectivity of the reaction temperature, the volume ratio ofethanol and deionized water, the amount of K₂CO₃or catalyst, and the ratio ofsubstrates, the optimized system was found: iodobenzene4mmol, phenylacetylene6mmol, K₂CO₃0.3g, catalyst0.5g, in co-solvent of15ml ethanol and1ml deionizedwater with nitrogen protecting, in50℃for24h, and the yield was up to88%; And therelationships were analyzed among the productivity, the palladium loading and reusedtimes, which showed that the catalyst can be used5times with the yield at least70%,while the palladium decreased gradually; The more and more lower yields, on the onehand may be due to the larger particles of resued catalysts, which means thedecreasing of the specific surface area of the active intermediate; another hand, theloss of palladium chloride.Under the same condition, the Sonogashira coupling reaction of o-methyliodide,m-methyliodide, p-methyliodide or nitro-iodobenzene with phenylacetylene wascarried out, which the effect of donating groups as methyl and electron withdrawinggroups as nitro were explored. Because of the electrophobic methyl, the activity of the-I reduced, which made the yield decreased; while the electrophilice effect of nitro canenhance the activity of the-I, the yield increased. After that, the catalyst was used for4,3,4or6times separately and the yields were up to65%.