1D Zn(II) Coordination Polymers as Effective Heterogeneous Catalysts in Microwave-Assisted Single-Pot Deacetalization-Knoevenagel Tandem Reactions in Solvent-Free Conditions

• Main Authors: Anup Paul, Anirban Karmakar, M. Fátima C. Guedes da Silva, Armando J. L. Pombeiro
• Format: Article
• Language: English
• Published: MDPI AG 2021-01-01
• Series: Catalysts
• Subjects: coordination polymers; heterogeneous catalyst; tandem reactions; microwave; solvent-free
• Online Access: https://www.mdpi.com/2073-4344/11/1/90

The new 1D CPs [Zn(L¹)(H₂O)₄]_n.nH₂O (<b>1</b>) and [Zn(L²)(H₂O)₂]_n (<b>2</b>) [L¹ = 1,1′-(ethane-1,2-diyl)bis(6-oxo-1,6-dihydropyridine-3-carboxylic acid); L² = 1,1′-(propane-1,3-diyl)bis(6-oxo-1,6-dihydropyridine-3-carboxylic acid)] were prepared from flexible dicarboxylate pro-ligands (<b>H₂L¹</b> and <b>H₂L²</b>). Both CPs <b>1</b> and <b>2</b> were characterized by elemental, FTIR, and powder X-ray diffraction analysis. Their geometry and the structural features were unveiled by single-crystal X-ray diffraction analysis. The underlying topology of the CPs was illustrated by the topological analysis of the H-bonded structure of CP <b>1</b>, which revealed a 3,4,6-connected trinodal net. On the other hand, topological analysis on the hydrogen-bonded network of CP <b>2</b> showed a 2,3,3,4,6,7-connected hexanodal net. The thermal stability of the CPs was investigated by thermogravimetric analysis. CPs <b>1</b> and <b>2</b> act as heterogeneous catalysts in one-pot tandem deacetalization–Knoevenagel condensation reactions under environmentally mild conditions. CPs <b>1</b> exhibits a yield of ca. 91% in a microwave-assisted solvent-free medium, whereas a slightly lower yield was obtained for CP <b>2</b> (87%) under the same experimental protocol. The recyclability of catalyst <b>1</b> was also assessed. To our knowledge, these are the first Zn(II)-based CPs to be applied as heterogeneous catalysts for the above tandem reactions under environmentally friendly conditions.