Abstract
Palladium and ruthenium nanoparticles have been prepared following the organometallic precursor decomposition methodology, under dihydrogen pressure and in the presence of borane protected P-stereogenic phosphines. NMR (Nuclear Magnetic Resonance) monitoring of the corresponding syntheses has permitted to determine the optimal metal/ligand ratio for leading to small and well-dispersed nanoparticles. Exchange ligand reactions of the as-prepared materials have proven the strong interaction of the phosphines with the metal surface; only oxidative treatment using hydrogen peroxide could release the phosphine-based stabiliser from the metal surface. Pd and Ru nanoparticles have been evaluated in hydrogenation reactions, confirming the robustness of the stabilisers, which selectively permitted the hydrogenation of exocyclic C=C bonds, preventing the coordination of the aromatic rings and as a result, their hydrogenation.
Highlights
Based on the literature [37,38,39], metal nanoparticles (MNPs) were by organometallic complex decomposition in the presence of the corresponding ligand
The NMR monitoring of the syntheses of MNPs together with the TEM analyses of the resulting colloidal solutions, allowed us knowing the appropriate amount of ligand-to-metal in order to get non agglomerated materials
The coordination strength of the stabilisers at the metal surface is crucial to understand their aptitude as catalysts
Summary
The stereoselective reactions mainly concern hydrogenations and C-C bond formation reactions based on the third mechanism [13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31] In this context, the optically pure ligand should be able to generate both a strong enough coordination at the metallic surface to stabilize MNPs and an asymmetric environment to efficiently lead to one of the expected stereoisomers during the organic transformation. P-stereogenic phosphines are well-known in Catalysts 2016, 6, 213; doi:10.3390/catal6120213 www.mdpi.com/journal/catalysts homogeneous catalysis using organometallic complexes as catalytic precursors, finding applications in hydrogenation, transfer hydrogenation, cyclopropanation, hydrovinylation, Diels Alder reactionsinand catalysis using organometallic complexes as catalytic precursors, finding applications allylic substitutionstransfer [32,33,34].hydrogenation, and cyclopropanation, to the best of our knowledge, no P-stereogenic phosphanes hydrogenation, hydrovinylation, Diels Alder reactions have been previously used as stabilisers of MNPs-based and allylic substitutions [32,33,34]
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