Catalytic Performance of a New 1D Cu(II) Coordination Polymer {Cu(NO3)(H2O)}(HTae)(4,40-Bpy) for Knoevenagel Condensation

Abstract

The {Cu(NO3)(H2O)}(HTae)(4,40-Bpy) (H2Tae = 1,1,2,2-tetraacetylethane, 4,40-Bpy = 4,40-Dipyridyl) 1D coordination polymer has been obtained by slow evaporation. The crystal structure consists of parallel and oblique {Cu(HTae)(4,40-Bpy)} zig-zag metal–organic chains stacked along the [100] crystallographic direction. Copper(II) ions are in octahedral coordination environment linked to two nitrogen atoms of two bridging 4,40-Bpy and to two oxygen atoms of one HTae molecule in the equatorial plane. The occupation of the axial positions varies from one copper atom to another, with different combinations of water molecules and nitrate anions, giving rise to a commensurate super-structure. By means of the thermal removal of water molecules, copper coordinatively unsaturated centres are obtained. These open metal sites could act as Lewis acid active sites in several heterogeneous catalytic reactions. The dehydrated compound, CuHTaeBpy_HT, has been tested as a heterogeneous recoverable catalyst for Knoevenagel condensation reactions. The catalyst is active and heterogeneous for the condensation of aldehydes with malononitrile at 60 ºC using a molar ratio catalyst:substrate of 3 % and toluene as solvent. The catalyst suffers a partial loss of activity when reusing it, but can be reused at least four times.