Synthesis of a series of Cd(ii) furan-2-thiocarobxylates: unprecedented coordination geometry of a Cd(ii) complex exhibiting catalytic efficiency for the synthesis of 3,4-dihydropyrimidine-2(1H)-one derivatives

Abstract

A series of Cd(II) complexes, [(PPh₃)₂Cd(SCOf)₂] (1), [PPh₄]₂[Cd(SCOf)₂(μ-Br)]₂ (2), [(PPh₃)₂Ag(μ₂-SCOf)₂Cd(SCOf)] (3), Na₂[(PPh₃)Cd(MeOH)(SCOf)₃]₂ (4a) and Na₂[(PPh₃)Cd(SCOf)₃]₂.C₇H₈ (4b) (Where SCOf = furan-2-thiocarboxylate), have been synthesized and characterized by single crystal X-ray analysis and other spectroscopic techniques. Complexes 1 and 2 show distorted tetrahedral and distorted trigonal bipyramidal geometries around Cd(II), respectively. In the case of 3, Cd(II) exhibits a trigonal prismatic structure, whereas, Ag(I) is at the center of a distorted tetrahedron. Complex 4, has a trigonal pyramidal geometry, hitherto unknown for a Cd(II) center. The catalytic activities of complexes for the synthesis of dihydropyrimidinone have been investigated. Out of four complexes, complex 4 is the most efficient catalyst for the one-pot multicomponent Biginelli-type coupling toward the synthesis of dihydropyrimidinone. Excellent yields of the desired products were obtained with very low catalyst loadings (1 mol%). With a few examples, the versatility and scope of the method have also been demonstrated. The catalysts were also tested for their recyclability.