Highly effective Brønsted base/lewis acid cooperative catalysis: a new Cd metal–organic framework for the synthesis of Hantzsch 1,4-DHPs at ambient temperature

Abstract

A new 3D metal–organic framework {[Cd₃(BDC)₃(OPP)(DMF)₂]·2DMA}_n (TMU-33) has been synthesized using a novel V-shaped imine-functionalized ligand, N,N′-(oxybis(4,1-phenylene))bis(1-(pyridin-4-yl)methanimine) (OPP), terephthalic acid (H₂BDC), and Cd(NO₃)₂·4H₂O and has been fully characterized. The function of the imine moiety of the OPP ligand as a Brønsted base and open Cd site as a Lewis acid in this framework was investigated to determine the role of the cooperative catalyst in the synthesis of Hantzsch 1,4-dihydropyridines simultaneously and separately at ambient temperature. In addition, nanorods and nanoplates of TMU-33 were synthesized via a sonochemical reaction by the coordination modulation method, and the effect of the nanostructure on the relative accessibility of the catalytic site was studied. Moreover, the catalytic performance of TMU-33 with different morphologies was evaluated in this reaction. Efficient catalytic activity was observed for the nanoscale catalysts at ambient temperature, and the acidic sites in the cooperative catalyst were found to be more effective than the existing basic sites in the structure. TMU-33 can be reused by washing with ethanol at least four times with no significant degradation of the catalytic activity (less than 7%).