Solid–state Synthesis of Polyhedral Oligomeric Silsesquioxane‐Supported N‐Heterocyclic Carbenes/Imidazolium salts on Palladium Nanoparticles: Highly Active and Recyclable Catalyst

We describe a novel and green synthetic methodology for the fabrication of polyhedral oligomeric silsesquioxane-supported N-heterocyclic carbenes/imidazolium salts on palladium(II) complexes; Pd(II)-MPIm-POSS (1) composite by solid-state annealing between Pd(OAc)2 and octakis(3-(1-methylimidazolium)propyl) octasilsesquioxane without added base. Subsequently, arylboronic acid based in situ or ex situ reduction of 1 in aqueous ethanol produces polyhedral oligomeric silsesquioxane-supported N-heterocyclic carbenes/imidazolium salts on palladium nanoparticles; Pd(0)-nano-POSS (2) composite, consisting of monodispersed and N-heterocyclic carbene (NHC) stabilized Pd nanoparticles of very small size (3.0 ± 1.5 nm). Nanocatalyst 2 is a highly efficient and easily recyclable homogeneous catalyst for Suzuki-Miyaura cross-coupling reactions with TOF up to 1670 h−1.