Copper(II) coordination polymers of arylhydrazone of 1H-indene-1,3(2H)-dione linked by 4,4′-bipyridineor hexamethylenetetramine: Evaluation of catalytic activity in Henry reaction

The 1D and the 2D copper(II) coordination polymers [{Cu(κN,OO′-L)}₂(μ-1κN:2κN′-bpy)₂]_n (1) and [{Cu(μ-1κN,OO′:2κO″-L)}₂(μ-1κN:2κN′-hmt)]_n (2), respectively, were synthesized from copper(II) nitrate and sodium 2-(2-(1,3-dioxo-1H-inden-2(3H)-ylidene) hydrazinyl)benzenesulfonate (NaHL), in the presence of 4,4′-bipyridine (4,4′-bpy) (for 1) or hexamethylenetetramine (hmt) (for 2). 1 and 2 are water soluble and are characterized by elemental analysis, IR spectroscopy, ESI-MS and single crystal X-ray diffraction. Depending on the neutral linkers, the dianionic ligand L²⁻ displays tri- (in 1) or tetradentate (in 2) binding modes. The Cu²⁺ in 1 adopts a distorted N₃O₂ square-pyramid coordination environment, while in 2 it displays a distorted N₂O₃ trigonal bipyramid geometry. The catalytic activity of 1 and 2 was evaluated in the diastereoselective Henry reaction of nitroethane with a variety of aromatic and aliphatic aldehydes, in water and in organic solvents. β-Hydroxy nitroalkanes were obtained in high yields (up to 92%), and moderate-to-good syn/anti diastereoselectivities (up to 79:21), in water at room temperature.