A novel nanomagnetic palladium (II) complex of bisimidazolium-based N–heterocyclic carbene; An efficient heterogeneous catalyst for A³ coupling reactions

Herein, a novel nanomagnetic NHC-Palladium complex was successfully prepared applying post-synthetic modification (PSM) condensation between Fe₃O₄-support imidazole and a synthetic bisamide moiety, carrying the alkyl halide functionalities at the end of its chain, followed by chelation of Pd ions to generate the corresponding complex. The [Fe₃O₄@bisimidazolium-Pd]^2Cl− complex gave the best catalytic performance in synthesizing propargylamines through A³ coupling of various substituted aromatic and cycloaliphatic aldehydes and secondary amines with aromatic and liner alkynes in PEG-400. Primary amines are inefficient to produce unknown byproducts; whereas, secondary amines react quickly. Significantly, alkynes having a high electron density reduce the conversion rate. Moreover, aromatic and aliphatic aldehydes are active, but the electron-drawing substituent on benzaldehyde decreases the rate of conversion. Furthermore, the [Fe₃O₄@bisimidazolium-Pd]^2Cl− catalyst can be reused seven times without metal leaching or losing its ability, which shows how stable it is when used in a reaction.