Heterogeneous Pd/POSS Nanocatalysts for C–C Cross‐Coupling Reactions

An insoluble solid support of N −heterocyclic imidazolium‐functionalized cage‐like silsesquioxane (SQ); Bim‐SQ, was synthesized by nucleophilic substitution of octakis(3‐chloropropyl)octasilsesquioxane with an excess bis‐(imidazol‐1‐yl)methane and investigated as a new organic‐inorganic hybrid support. In the presence of Bim‐SQ, Pd(II) from [PdCl 4 ] 2− can be stabilized via both electrostatic interactions and imidazole‐ N ‐coordination, giving an amorphous material of Pd(II)@Bim‐SQ. Subsequent in situ reduction of Pd(II)@Bim‐SQ during Suzuki−Miyaura cross‐coupling reactions afforded monodispersed Pd nanoparticles (2.33 ± 1.50 nm) stablized on Bim‐SQ support, PdNp@Bim‐SQ with Pd loading up to 14% w / w . Catalytic studies revealed that the pre‐catalyst Pd(II)@Bim‐SQ was active heterogeneous catalyst for Suzuki−Miyaura cross‐coupling reactions, having the maximum TOFs of 5400 h −1 under mild conditions and in aqueous ethanol medium. Furthermore, PdNp@Bim‐SQ was also shown to be an efficient catalyst for Heck reactions. Simple catalyst recovery and reusability of PdNp@Bim‐SQ for at least 5 catalytic cycles without loss of activity were also demonstrated.