Assembling Porphyrins into Extended Network Structures by Employing Aromatic Dicarboxylates: Synthesis, Metal Exchange, and Heterogeneous Catalytic Studies.

Three new metal-organic porphyrinic framework compounds of zinc and 5,10,15,20-tetrakis(4-pyridyl)porphyrin (TPyP) have been synthesized under solvothermal conditions. The compounds [Zn5 (C40 H24 N8 )(C8 H4 O4 )2 (NO3 )6 (DMA)2 ] (DMA)3 (H2 O)8 (1; DMA=dimethylacetamide), [Zn3 (C40 H24 N8 )(C8 H4 O4 )2 (DMF)](DMF)5 (H2 O)12 (2), and [Zn3 (C40 H24 N8 )(C12 H6 O4 )2 (DMA)2 ](H2 O)7 (3) have two (1) and three dimensionally (2 and 3) extended structures. All the three structures contain porphyrinic units connected through the carboxylate linkers. The nitrates bind the metal centers and are not hydrogen bonded. The different binding modes of nitrate in the structure of 1 are observed for the first time in a porphyrin-based MOF. The openness of the structure allowed us to explore metal exchange through a room-temperature metathetic route. Compound 2 undergoes 100 % exchange with copper, whereas compound 3 exchanges 70 % with copper. The copper-exchanged compounds Cu∈2 and Cu∈3 were observed to be good heterogeneous catalysts for many important organic reactions. The chemo and regioselective enamination of β-ketoesters, preparation of propargylamine derivatives as well as regioselective cycloadditions of alkyne and azide (click reactions) have been carried out with good yields and selectivity. All the compounds have been characterized by PXRD, IR, UV/Vis, atomic absorption spectroscopy (AAS), and energy-dispersive X-ray spectroscopy (for Cu exchange).