Iridium-PPh3 Catalysts for Conversion of Amides to Enamines

Studies on the deactivation mechanism of the reaction of N,N-dialkylamides with TMDS catalyzed by Vaska’s complex, IrCl­(CO)­(PPh3)2 (1a), triggered the discovery of highly active Ir-PPh3 catalysts: photochemically activated 1a 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(η4-COD)]2 with PPh3 or other phosphorus ligands, which realized the facile large-scale syntheses of enamines.