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.
基金
supported by the National Natural Science Foundation of China (20972148)
CAS
NECT (08-0519)