From Zn(II)-Carboxylate to Double-Walled Zn(II)-Carboxylato Phosphate MOF: Change in the Framework Topology, Capture and Conversion of CO2, and Catalysis of Strecker Reaction

The ligand H₂L has been built by linking an imidazole moiety to the 5-position of isophthalic acid. It forms two types of porous frameworks, {[Zn(L)]·2DMF·2H₂O}_n (1) and {[(CH₃)₂NH₂][Zn₂(L)(H₂O)PO₄]·2DMF}_n (2). 1 is a porous neutral framework and has rtl rutile 3,6-conn topology, while 2 is an organo-metallophosphate anionic porous framework with double-walled hexagonal channels. Framework 1' (desolvated) exhibits moderate CO₂ adsorption (58 cc g^-1 at 273 K, 1 bar), whereas 2' (desolvated) shows a microporous nature with a high adsorption of CO₂ (111.7 cc g^-1 or 22 wt % at 273 K, 1 bar). Interestingly, this adsorbed CO₂ could be converted very efficiently to cyclic carbonates under mild conditions using 2' as the catalyst in the presence of tetrabutylammonium bromide as the cocatalyst. The presence of open metal sites in 2' makes it an efficient heterogeneous catalyst for solvent-free three-component Strecker reaction using various aldehydes/ketones together with amines and trimethylsilyl cyanide in high yields at room temperature. The straightforward experimental and product isolation procedure along with easy recovery and reusability of the catalyst provided an attractive route for the synthesis of α-amino nitriles.