Synthesis, structure and catalytic applications of amidoterephthalate copper complexes in the diastereoselective Henry reaction in aqueous medium

Abstract

Terephthalic acid derivatives bearing amide side functional groups, viz. 2-propionamidoterephthalic acid (H₂L1) and 2-acetamidoterephthalic acid (H₂L2), have been structurally characterized using X-ray crystallography. While H₂L1 is hydrogen bonded with DMF molecules forming a 1D hydrogen bonded network, H₂L2 constructs a 2D hydrogen bonded network. They have been used to synthesize two new isostructural mononuclear copper complexes, [Cu(L1)(H₂O)₄] (1) and [Cu(L2)(H₂O)₄] (2), also characterized using X-ray crystallography. In these structures the hydrogen bonded assemblies of carboxylate and coordinated water molecules form a distorted cubane type of hydrogen bonded network. Complexes 1 and 2 act as heterogeneous catalysts for the diastereoselective nitroaldol (Henry) reaction in aqueous medium, 1 providing high yields (up to 77%) and good diastereoselectivities under ambient conditions. These catalysts can be recycled without significant loss of activity, and the catalytic process is efficient, simple, easy to work-up and operates under ‘green’ conditions.