空气下无配体钯催化二苯胺和卤代芳烃的C-N偶联

Ligand-free Pd-Catalyzed C—N Coupling of Diphenylamine and Aryl Halides under Air

研究了空气下无配体Pd(OAc)2在弱碱碳酸钾存在下催化二苯胺和溴代芳烃的C—N偶联合成三苯胺类化合物.与传统合成方法相比,该反应可以在无配体存在下在空气和温和的条件下进行,即,无需无水无氧操作条件,操作特别方便.催化剂用量、碱、溶剂、反应温度、反应时间等因素对反应的影响均做了考察.优化的反应条件是:在Pd(OAc)2(3 mol%)和K2CO3(1.5 equiv.)存在下,二苯胺和溴代芳烃在DMSO中在空气下在90℃加热24 h.溴代芳烃上的吸电子基团和二苯胺上的给电子基团有利于该偶联反应的进行,其中4-硝基三苯胺的产率高达93%.

Triphenylamine derivatives are extensively used as a number of organic dyes,drugs,intermediates,dye-sensitized solar cells（DSSCs） and organic electroluminescence materials.It is valuable to discover a new synthetic method of triphenylamines with mild reaction conditions,easy-operation,and cheap starting materials.During our research of C—H bond activation,accidentally we found palladium acetate accomplished the C—N cross coupling of diphenylamine and 4-nitrobromobenzene under air.This discovery meets one of hot research topics of modern organic chemistry,that is,transition-metal-catalyzed reactions which must operate under inert atmosphere in the traditional procedures now can be performed under air.Consequently,ligand-free Pd（OAc）2-catalyzed C—N cross coupling of diphenylamines and aryl halides under air for synthesis of triphenylamines was studied in details.The effect of catalyst loading,base,additives,solvents and reaction time on this transformation was investigated.The optimized conditions were as follows： Pd（OAc）2（3 mol%）,K2CO3（1.5 equiv.）,heated at 90 ℃ in DMSO under air.Electron-withdrawing group of phenyl bromides and electron-donating group of diphenylamine benefit the coupling reaction,and among them,4-nitrotriphenylamine gave yield up to 93%.Compared with traditional methods,the reactions were conducted under air and mild conditions in absence of ligand,that is,anhydrous and oxygen-free conditions are not required,and operation is extremely easy.