An inorganic–organic hybrid material based on a Keggin‐type polyoxometalate@Dysprosium as an effective and green catalyst in the synthesis of 2‐amino‐4H‐chromenes via multicomponent reactions

A novel inorganic–organic hybrid, [Dy 4 (PDA) 4 (H 2 O) 11 (SiMo 12 O 40 )]·7H 2 O denoted as (POM@Dy‐PDA), based on a lanthanide cluster, a Keggin‐type polyoxomolybdate, and PDA (1,10‐phenanthroline‐2,9‐dicarboxylic acid) was prepared and fully characterized by elemental analysis, Fourier‐transform infrared and UV–Vis spectroscopies, thermogravimetric analysis, powder X‐ray diffraction (PXRD), and single‐crystal X‐ray diffraction. The structural analysis study showed that the [SiMo 12 O 40 ] 4− ions reside in the interspace between two cationic layers as discrete counterions and are not coordinated to the rare‐earth ions. Significantly, this hybrid catalyst is a rare case of an inorganic–organic hybrid polyoxometalate (POM) with a PDA ligand based on CSD search (CSD version 5.40/November2018). The hybrid catalyst was further characterized via powder X‐ray diffraction (PXRD) pattern at room temperature which indicated the good phase purity of the catalyst. BET and Langmuir surface area analysis indicate surface area of POM@Dy‐PDA 6.6 and 51.3 m2g‐1, respectively. The catalytic activity of the hybrid catalyst was successfully examined in the synthesis of 2‐amino‐4 H ‐chromene derivatives through a multicomponent reaction. A three‐component, one‐pot reaction involving differently substituted benzaldehydes, resorcinol/α‐naphthol/β‐naphthol/4‐hydroxycoumarin/3‐methyl‐4 H ‐pyrazole‐5(4 H )‐one, and malononitrile or ethyl cyanoacetate in the presence of a catalytic quantity of the aforementioned hybrid catalyst in EtOH/H 2 O under reflux condition gave the corresponding highly functionalized 2‐amino‐4 H ‐chromenes in satisfactory yields. The catalyst can be reused several times without appreciable loss in its catalytic activity.