Mechanism of palladium-catalyzed decarboxylative cross-coupling between cyanoacetate salts and aryl halides  

作　　者：JIANG YuanYe FU Yao LIU Lei 

机构地区：[1]Department of Chemistry,University of Science and Technology of China,Hefei 230026,China [2]Department of Chemistry,Tsinghua University,Beijing 100084,China

出　　处：《Science China Chemistry》2012年第10期2057-2062,共6页中国科学（化学英文版）

基　　金：supported by the National Natural Science Foundation of China (20972148);CAS;NECT (08-0519)

摘　　要：Recently we reported Pd-catalyzed decarboxylative cross-coupling of cyanoacetate salts with aryl halides and triflates. This reaction shows good functional group tolerance and is useful for the synthesis of-aryl nitriles. To elucidate the mechanism for this reaction, we now carry out a density functional theory study on the cross-coupling of potassium cyanoacetate with bromobenzene. Our results show that the decarboxylation transition state involving the interaction of Pd with the-carbon atom has a very high energy barrier of +34.5 kcal/mol and therefore, must be excluded. Decarboxylation of free ion (or tight-ion-pair) also causes a high energy increase and should be ruled out. Thus the most favored decarboxylation mechanism corresponds to a transition state in which Pd interacts with the cyano nitrogen. The energy profile of the whole catalytic cycle shows that decarboxylation is the rate-determining step. The total energy barrier is +27.5 kcal/mol, which is comprised of two parts, i.e. the energy barrier for decarboxylation and the energy cost for transmetallation.Recently we reported Pd-catalyzed decarboxylative cross-coupling of cyanoacetate salts with aryl halides and triflates. This reaction shows good functional group tolerance and is useful for the synthesis of-aryl nitriles. To elucidate the mechanism for this reaction, we now carry out a density functional theory study on the cross-coupling of potassium cyanoacetate with bromobenzene. Our results show that the decarboxylation transition state involving the interaction of Pd with the-carbon atom has a very high energy barrier of ＋34.5 kcal/mol and therefore, must be excluded. Decarboxylation of free ion （or tight-ion-pair） also causes a high energy increase and should be ruled out. Thus the most favored decarboxylation mechanism corresponds to a transition state in which Pd interacts with the cyano nitrogen. The energy profile of the whole catalytic cycle shows that decarboxylation is the rate-determining step. The total energy barrier is ＋27.5 kcal/mol, which is comprised of two parts, i.e. the energy barrier for decarboxylation and the energy cost for transmetallation.

关 键 词：PALLADIUM catalytic DECARBOXYLATION MECHANISM density functional theory 

分 类 号：O643.36[理学—物理化学] TQ613[理学—化学]