Two Thiophene-Functionalized Co-MOFs as Green Heterogeneous Catalysts for the Biginelli Reaction

Two Co(II) metal-organic frameworks (Co-MOFs), namely, [Co(DMTDC)(bimb)]_<i>n</i> (<b>Co-MOF-1</b>) and {[Co(DPTDC)(bimb)(H₂O)]·2DMF}_<i>n</i> (<b>Co-MOF-2</b>) (H₂DMTDC = 3,4-dimethylthieno[2,3-<i>b</i>]thiophene-2,5-dicarboxylic acid, H₂DPTDC = 3,4-diphenylthieno[2,3-<i>b</i>]thiophene-2,5-dicarboxylic acid, bimb = 1,4-bis((1<i>H</i>-imidazol-1-yl)methyl)benzene), were obtained by the reaction of flexible N-containing ligand bimb and two structurally related thiophene-containing ligands H₂DMTDC and H₂DPTDC, respectively. These Co-MOFs displayed a 3D framework and porous structure, respectively. <b>Co-MOF-1</b> and the activated sample <b>Co-MOF-2'</b> could act as green heterogeneous catalysts for the one-pot multicomponent Biginelli reaction, specifically the dehydration condensation process involving aldehydes, acetoacetates, and urea to yield dihydropyrimidin-2(1<i>H</i>)-ones. The reaction has advantages such as solvent-free conditions, water as only byproduct, readily accessible starting materials, excellent functional group compatibility, and simple operation. Both catalysts exhibited a wide substrate scope and maintained significant catalytic activity over five cycles. The special catalytic performance may be ascribed to functional groups within the ligand.