MVS-derived palladium nanoparticles deposited on polydimethylphosphazene as recyclable catalysts for Heck-type reactions: preparation, structural study, and catalytic activity

Palladium nanoparticles, obtained by the metal vapor synthesis (MVS) technique, were deposited on polydimethylphosphazene (PDMP). The Pd/PDMP system showed high catalytic activity in the Heck C–C coupling of iodobenzene and methyl acrylate, with greater activity than com- mercially available catalysts such as Pd(OAc)2 and Pd on carbon. The Pd/PDMP is soluble in the reaction solvent, 1-methyl-2-pyrrolidinone, and can be quantitatively recovered at the end of the reaction by precipitation without loss of metal. When reused, the recovered Pd/PDMP retains its catalytic activity. A multinuclear (31P, 13C, 15N) solid-state NMR study identified and characterized the strong structural and dynamic mod- ifications induced by Pd nanoparticles on PDMP. Moreover, solid-state NMR studies and HRTEM analyses, performed on the pristine catalyst and on the catalyst recovered after the reaction, highlighted the almost complete structural invariability of the Pd/PDMP, pointing out the high stability toward agglomeration of the palladium nanoparticles in such a system. Pd/PDMP in the presence of triphenylphosphine was also active in the alkylative cyclization of 7-octen-1-ynes, an important C–C coupling reaction to obtain substituted 1,2-bis(alkylidene)cyclohexanes, which are valuable building blocks in fine chemistry.