P-Stereogenic Phosphines for the Stabilisation of Metal Nanoparticles. A Surface State Study

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.

Palladium Nanoparticles in Polyols: Synthesis, Catalytic Couplings, and Hydrogenations

“…In the absence of molecular hydrogen, the reaction With the aim of modifying the coordination mode of the ligand at the metal surface, cinchonabased alkaloids were also used as stabilizers ( Figure 9). 79 In contrast to the strong interactions between P-donor ligands and metal surface, 80 mainly by -dative Pd-P bonds, cinchona ligands can interact with the surface through both N-quinoline  bonding or by  interaction with the quinoline aromatic ring. 81,82 Using quinidine as stabilizer, small (1.…”

“…With the aim of modifying the coordination mode of the ligand at the metal surface, cinchona-based alkaloids were also used as stabilizers (Figure ). In contrast to the strong interactions between the P-donor ligands and the metal surface, mainly by σ-dative Pd–P bonds, cinchona ligands can interact with the surface through both N -quinoline σ bonding or by π interaction with the quinoline aromatic ring. , Using quinidine as stabilizer, small (1.4 ± 0.3 nm) and well-dispersed PdNPs were obtained; PXRD and HR-TEM analyses evidenced the formation of fcc PdNPs. XPS spectra in glycerol confirmed the exclusive presence of Pd(0); curiously, in the nitrogen region, two signals were observed in contrast to one signal observed for PdNPs at solid state (isolated by centrifugation) and for the free ligand.…”