Lanthanide derivatives comprising arylhydrazones of β-diketones: cooperative E/Z isomerization and catalytic activity in nitroaldol reaction

Abstract

Two complexes [KLa(HL¹)₂{(CH₃)₂NCHO}₂(H₂O)₃] (1) and [Sm(H₂O)₉](E-H₂L²)₃·2H₂O (2) were synthesized by the reaction of lanthanum(III) and samarium(III) nitrates with potassium 3-(2-(2,4-dioxopentan-3-ylidene)hydrazinyl)-2-hydroxy-5-nitrobenzenesulfonate (KH₂L¹) and potassium (E,Z)-5-chloro-3-(2-(1,3-dioxo-1-phenylbutan-2-ylidene)hydrazinyl)-2-hydroxybenzenesulfonate (KH₂L²), respectively. Both complexes were fully characterized by elemental analysis, IR, ¹H and ¹³C NMR spectroscopy, ESI-MS and single-crystal X-ray diffraction. Cooperative E,Z→E isomerization of KH₂L², induced by resonance assisted hydrogen bonding and ionic interactions, occurs upon the interaction with Sm(III). Catalytic activities of KH₂L^1,2 and their lanthanide derivatives were evaluated in the Henry reaction of nitroethane with a variety of aromatic and aliphatic aldehydes. Good yields (up to 91%) and diastereoselectivities (syn/anti 3 : 1) were observed in the reactions catalyzed by 1 in water.