An amino acid@isopolyoxometalate nanoparticles catalyst containing aspartic acid and octamolybdate for the synthesis of functionalized spirochromenes

Abstract

Amino acid polyoxometalate nanoparticles-embedded microcapsules were in situ fabricated by layer-by-layer (LbL) self-assembly method [isopolyoxometalate, Mo8O26·nH2O; amino acid, aspartic acid (AFO)]. Aspartate functionalized γ-octamolybdate (AFO) [Co2(C4H6NO4)2(Mo8O26)(H2O)10]·4H2Owas employed as heterogeneous catalyst for efficient, diverse, and high yielding synthesis of spirochromenes via a three-component reaction involving isatins or acenaphthenequinone, malononitrile or ethyl cyanoacetate, and various 1,3-diketones (dimedone, barbituric acid, or ethyl acetoacetate) or 4-hydroxycoumarin/3-methyl-1H-pyrazol-5(4H)-one in water/ethanol under reflux. The AFO is characterized by some physico-chemical approaches such as elemental analysis, ICP, IR, and UV–Vis spectroscopies and PXRD analyses. Notably, the heterogeneous catalyst AFO, containing molybdenum atom as the basis and appropriate redox nature, reinforced with the organic metal fragment in its structure, showed effective catalytic activity, and could be recovered simply from the reaction mixture and reused at least three runs without significant loss of its catalytic activity. This prolific combination of amino acids and isopolyoxometalates inaugurates a powerful class of porous catalysts for the different chemical transformations, which overcomes key limitations of previously established salts and Lewis acidic metals based catalysts under low catalyst loading, the use of water scavengers, dry solvents, and additives for facilitating the specialized experimental setups commonly employed to the organic reactions.