Iridium-PPh3 Catalysts for Conversion of Amides to Enamines

摘要

Studies on the deactivation mechanism of the reaction of N,N-dialkylamides with TMDS catalyzed by Vaska's complex, IrCl(CO)(PPh3)(2) (la), triggered the discovery of highly active Ir-PPh3 catalysts: photochemically activated la and thermally activated IrCl(PPh3)(3) (8). Both catalysts showed excellent activity toward the selective conversion of a variety of N,N-dialkyl-, N-alkyl-N-aryl-, and N,N-diarylamides to the corresponding enamines with low catalyst loadings. The 14-electron species "ClIr(PPh3)(2)", which is stabilized by solvents or reactants in the actual catalytic reactions, could be involved in the catalysis, which produces "HIr(PPh3)(2)" and "SiIr(PPh3)(2)" (Si = Me2HSiOMe2Si-) species in the catalytic cycle. An in situ generation method for the "ClIrL2" species was established by simply mixing [IrCl(eta(4)-COD)](2) with PPh3 or other phosphorus ligands, which realized the facile large-scale syntheses of enamines.