CoII, NiII and UO2II complexes with β-diketones and their arylhydrazone derivatives: Synthesis, structure and catalytic activity in Henry reaction

Abstract

The new uranyl, nickel and cobalt complexes, [UO2(L1)2(R)] (1), [Ni(L1)2((CH3)2SO)2] (2), [Co(H2O)4(HL2)2]·2H2O (3) and [UO2(H2O)2(HL2)2]·2H2O (4), were prepared by reaction of UO2(CH3COO)2·2H2O, Ni(CH3COO)2·4H2O or Co(CH3COO)2·4H2O with 1,3-diphenyl-propane-1,3-dione (H2L1) or 4-(2-(2,4-dioxopentan-3-ylidene)hydrazinyl)benzoic acid (H2L2) in the presence of N,N-diethylnicotinamide (R) (for 1). Complexes 1–4 were characterized by elemental analysis, IR spectroscopy, ESI-MS and single crystal X-ray diffraction technique. In both 1 and 2 the (L1)− coordinates in a bidentate chelating mode where the UO22+ in 1 exhibits a distorted pentagonal bipyramidal and Ni2+ in 2 a distorted octahedral geometries. In 3 and 4 a hydrazone moiety containing an intramolecular resonance assisted hydrogen bond, with N–H⋯O distances of 2.5469(18) and 2.549(7)Å, respectively, was found in the coordinated ligand (HL2)−. The supramolecular networks (packing diagrams) of 1–4 are constructed via hydrogen bonding, CH–π or π–π interactions. All the four complexes (1–4) act as a good catalyst towards the diastereoselective nitroaldol (Henry) reaction of aliphatic and aromatic aldehydes with nitroethane in different solvents such as acetonitrile, methanol or water. Complex 3 was found to be efficient catalyst for the Henry reaction in aqueous medium, providing β-nitroalcohols with good yields (68–91%) and diastereoselectivities (syn/anti 77:23–73:27).