Abstract
A series of Fe-NHC complexes (1-2)c of the fused bicyclic imidazo[1,5-a]pyridine framework of the type [CpFe(2-R-imidazo[1,5-a]pyridin-3-ylidene)(CO)(2)]BF4 {R = mesityl (1c), nPr (2c)} successfully carried out the synthesis of beta-enamino ketones (3-10) and (17-27) and beta-enamino esters (11-16) and (28-36) by the condensation of acyclic and cyclic 1,3-dicarbonyl compounds and various aliphatic and aromatic amines in the presence of light irradiation. Quite significantly, the catalytically relevant substrate adduct species of the type [CpFe(NHC)(acac)] (2e) and the product adduct species of the type [CpFe(NHC)(beta-enaminone)] (2f) of the Fe-NHC precatalyst (2c) have been detected by mass spectrometry study. The [CpFe(2-R-imidazo[1,5-a]pyridin-3-ylidene)(CO)(2)]BF4 {R = mesityl (1c), nPr (2c)} complexes were obtained from their respective N-heterocyclic carbene precursors namely, the 2-R-imidazo[1,5-a]pyridin-2-ium chloride {R = mesityl (1a), nPr (2a)} by the reaction with CpFe(CO)(2)I in the presence of KN(SiMe3)(2) followed by the salt metathesis reaction with AgBF4.