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CoII, NiII and UO2II complexes with β-diketones and their arylhydrazone derivatives: Synthesis, structure and catalytic activity in Henry reaction
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The new uranyl, nickel and cobalt complexes, [UO2(L1)2(R)] (1), [Ni(L1)2((CH3)2Sdouble bond; length as m-dashO)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 14 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 14 are constructed via hydrogen bonding, CH–π or π–π interactions. All the four complexes (14) 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).

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