A study on the catalytic behaviour of Cd(II) and Sm(III) coordination complexes towards the four-component synthesis of quinoline-3-carboxylates

Abstract

We report the synthesis two 3-dimensional coordination complexes namely, [Cd(2,5-Pydc)2(H2O)2].H2O (1) [Sm(2,5-Pydc)(NO3)(H2O)].(H2O) (2) using 2,5-Pyridine dicarboxylic acid (2,5-Pydc) as ligand by simple hydrothermal method. Nitrogen and oxygen atoms of 2,5-Pydc provided more scope for the coordination of Cd(II) and Sm(III) ions to the ligand in both the complexes with high dimensionality. The 3D networks of complexes 1 and 2 possessed attractive structures of supramolecular assemblies with good rigidity and high thermal stability. The coordinatively unsaturated metal sites in both 1 and 2 upon activation process generate a Lewis acidic environment. The Lewis acidic nature of complexes 1 and 2 was promptly utilised in the synthesis of novel quinoline-3-carboxylate moieties from the four-component single-pot fusion. Both 1 and 2 showed impressive catalytic activity in the formation of the products in high yield (92–96%) and in a short interval of time (15–25 min). The complexes 1 and 2 catalysed the Knovenagel condensation between aldehyde and active methylene group, leading to the generation of the reaction intermediate and target products with high selectivity. Optimisation studies confirmed that compound 2 showed superior catalytic activity over 1 due to the strong Lewis-acidic character of Sm(II). The method has potential as a low-cost, high-performance, green protocol for futuristic catalytic applications.