화학공학소재연구정보센터
Inorganic Chemistry, Vol.59, No.7, 4741-4752, 2020
Theoretical Insight into Palladium(II)-Counterion-Ligand Cooperative Regiodivergent Syntheses of Indolo[3,2-c]coumarins and Benzofuro[3,2-c]quinolinones from Diphenylethyne Derivatives
With two distinct active sites, 2-hydroxy-2'-aminodiphenylethyne derivatives can offer benzofuro[3,2-dquinolinones via the O-attack/N-carbonylation cyclization or indolo [3,2-c]-coumarins via the N-attack/O-carbonylation cyclization. This work presents a density functional theory-based computational study to understand the mechanism and origin of the palladium(II)-catalyzed regiodivergent reactivity of diphenylethyne derivatives. It is indicated that the reaction features a palladium (II)-counterion-ligand cooperative catalysis. The O-attack/N-carbonylation cyclization mainly benefits from the inductive effect of the rigid electronwithdrawing bidentate nitrogen ligand and the stabilization of the 3c-4e bond between the trifluoroacetate (TFA) anion and the hydroxyl group in the substrate for the precursor and transition state, while the viability of the N-attack/O-carbonylation cyclization stems intrinsically from the stronger nucleophilicity of the N atom as well as the important pi-pi interaction between the flexible electron-rich bidentate phosphine ligand and the substrate. Moreover, these calculations propose an unconventional reductive elimination mechanism for the transformation from Pd(II) to Pd(0), where the intramolecular nucleophilic attack of the N/O atom on the carbonyl C atom results in the formal reductive elimination product. The calculated overall barriers of 14.8 kcal/mol for Pd(TFA)(2) with the bidentate nitrogen ligand and 23.9 kcal/mol for Pd(OTf)(2) with the bidentate phosphine ligand are qualitatively consistent with the mild experimental conditions.