Palladium Acetate and Pd Nanoparticles Loaded Hexamethylenetetramine Anchored Magnetically Retrievable Assemblies for Catalyzing Mizoroki-Heck Type Mono and Gem-Dicoupling Reactions

Fe₃O₄ nanoparticles have been covalently coated and chemically modified to anchor hexamethylenetetramine (Fe₃O₄@HMTA) for hosting Pd catalysts such as palladium acetate and palladium nanoparticles. Thus prepared nanocatalyst assemblies have been extensively characterized for their chemical, physical, thermal and magnetic properties. The turnover number and turnover frequency of these catalysts in a model Mizoroki-Heck coupling reaction involving 3-acrylomorpholine and iodobenzene with a base as solvent are found to be 186 and 46 h⁻¹, respectively, which are better than that reported in literature. This was attributed to synergistic effect of local basic environment of HMTA rich in tertiary nitrogen content. Gem-dicoupled products are formed when reactions are performed in the presence of 1 equivalent of acrylate and 2.1 equivalents of aryl iodide, and gem-hetero-dicoupled product is obtained when reaction is performed in sequential manner. The mechanisms of the formation of the gem-homo-dicoupled and gem-hetero-dicoupled products have been elucidated by using the results obtained from NMR and single crystal X-ray crystallography studies.