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

The new uranyl, nickel and cobalt complexes, [UO2(L-1)(2)(R)] (1), [Ni(L-1)(2)((CH3)(2)S=O)(2)] (2), [Co(H2O)(4)(HL2)(2)]center dot 2H(2)O (3) and [UO2(H2O)(2)(HL2)(2)]center dot 2H(2)O (4), were prepared by reaction of UO2(CH3COO)(2)center dot 2H(2)O, Ni(CH3COO)(2)center dot 4H(2)O or Co(CH3COO)(2)center dot 4H(2)O 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 (L-1)(-) 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 center dot center dot center dot O distances of 2.5469(18) and 2.549(7) angstrom, respectively, was found in the coordinated ligand (HL2)(-). The supramolecular networks (packing diagrams) of 1-4 are constructed via hydrogen bonding, CH-pi or pi-pi 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 beta-nitroalcohols with good yields (68-91%) and diastereoselectivities (synlann 77:23-73:27). Crown Copyright (C) 2015 Published by Elsevier Ltd. All rights reserved.