Thermo-Responsive Poly (N-isopropyl acrylamide-b-vinylimidazole)/Pd Catalyst: Catalytic Application of Suzuki–Miyaura Coupling Reaction in Water

Abstract

This study reports a facile procedure for synthesizing and characterizing a novel catalyst based on thermo-responsive poly (N-isopropyl acrylamide-b-vinylimidazole)/Pd catalyst (PNIPAM-b-PVIm/Pd). A well-structured diblock copolymer was prepared using RAFT-controlled strategy. Initially, PNIPAM was fabricated with a lower critical solution temperature (LCST) at around 32 °C. Within another step, PNIPAM as a macro-RAFT agent and vinylimidazole as a monomer were utilized for synthesizing PNIPAM-b-PVIm. The reaction of PNIPAM-b-PVIm with Pd(OAc)₂ for one day, taken after applying NaBH₄ as a reducing agent, led to the synthesizing of PNIPAM-b-PVIm supported Pd. This new catalyst was characterized by different methods, i.e., ICP, FT-IR, NMR, UV–Vis spectrophotometer, TGA, DLS, SEM, EDX, and SEC. This catalytic system was utilized to deliver an assortment of substituted biaryl compounds in water with good to excellent yields through the Suzuki coupling reaction. The greatest advantage of this catalytic platform is related to the reusability of the catalyst up to 7 times and non-use of organic solvent in coupling reactions. Simple purification of the coupling products due to the effortless recyclability of the catalysts is another characteristic of the method. This important characteristic is achieved by just adding diethyl ether to the reaction mixture to extract the biphenyls. The catalyst remains intact in aqueous phase and reused in other reaction runs without considerable loss of efficiency.