MVS-derived palladium nanoparticles deposited on polydimethylphosphazene as recyclabe 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 commercially 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 modifications 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.