Pd–Ni Alloy Nanoparticles as Effective Catalysts for Miyaura–Heck Coupling Reactions

In this work, Pd–Ni alloy nanoparticles (NPs) were produced by a facile and efficient one-pot synthetic strategy in the presence of oleylamine (OAm) and triphenylphosphine (TPP). Transmission electron microscopy (TEM), energy-dispersive spectrometry (EDS) mapping, inductively coupled plasma atomic emission spectroscopy (ICP-AES), and X-ray diffraction (XRD) were used to investigate the structure of Pd–Ni alloy NPs, which demonstrated that the as-prepared alloy NPs possessed uniform sizes and tunable compositions. Importantly, we found that TPP could affect the morphology of the Pd–Ni alloy. When TPP was absent from the reaction, the morphology of the Pd–Ni alloy was not uniform. In addition, the as-prepared Pd–Ni alloy NPs showed conspicuous composition-dependent catalytic activities for the Miyaura–Heck reaction. In the series of the Pd–Ni alloy NPs, Pd₁Ni₁ has an excellent effect for the Miyaura–Heck reactions. Furthermore, the Pd–Ni alloy NPs were also effective for different substrates in the Miyaura–Heck reactions. Compared to pure palladium, the Pd–Ni alloy NPs as the catalysts show better catalytic activity, selectivity, and stability

A Robust and Efficient Pd₃ Cluster Catalyst for the Suzuki Reaction and Its Odd Mechanism

The palladium-catalyzed Suzuki–Miyaura coupling reaction is one of the most versatile and powerful tools for constructing synthetically useful unsymmetrical aryl–aryl bonds. In designing a Pd cluster as a candidate for efficient catalysis and mechanistic investigations, it was envisaged to study a case intermediate between, although very different from, the “classic” Pd(0)­L<i>_n</i> and Pd nanoparticle families of catalysts. In this work, the cluster [Pd₃Cl­(PPh₂)₂(PPh₃)₃]⁺[SbF₆]⁻ (abbreviated <b>Pd</b>_<b>3</b><b>Cl</b>) was synthesized and fully characterized as a remarkably robust framework that is stable up to 170 °C and fully air-stable. <b>Pd</b>_<b>3</b><b>Cl</b> was found to catalyze the Suzuki–Miyaura C–C cross-coupling of a variety of aryl bromides and arylboronic acids under ambient aerobic conditions. The reaction proceeds while keeping the integrity of the cluster framework all along the catalytic cycle via the intermediate <b>Pd</b>_<b>3</b><b>Ar</b>, as evidenced by mass spectrometry and quick X-ray absorption fine structure. In the absence of the substrate under the reaction conditions, the <b>Pd</b>_<b>3</b><b>OH</b> species was detected by mass spectrometry, which strongly favors the “oxo-Pd” pathway for the transmetalation step involving substitution of the Cl ligand by OH followed by binding of the OH ligand with the arylboronic acid. The kinetics of the Suzuki–Miyaura reaction shows a lack of an induction period, consistent with the lack of cluster dissociation. This study may provide new perspectives for the catalytic mechanisms of C–C cross-coupling reactions catalyzed by metal clusters

Cobaltocene Reduction of Cu and Ag Salts and Catalytic Behavior of the Nanoparticles Formed

The modes of generation of nanoparticles (NPs) are of great interest for multiple applications in catalysis, optics, sensing, and nanomedicine. Here, fast reduction of CuSO₄·5H₂O and Ag salts by commercial cobaltocene yields small, stable, water-soluble Cu and Ag NPs with a narrow size distribution without any other ligand or support. The variation of the Ag salt counteranion (NO₃^–, F^–, BF₄^–) strongly influences both the plasmonic absorption of the AgNPs synthesized in this way and the high apparent rate constant of the AgNP-catalyzed reduction of 4-nitrophenol by NaBH₄, showing that the precursor counteranion binds to the AgNP surface. The CuNPs synthesized from CuSO₄ and cobaltocene are a recyclable catalyst for the Cu-catalyzed alkyne–azide cycloaddition reaction in water extended to various azides and alkynes, including functionalization of compounds of biomedical interest. Both CuNP and AgNP catalytic activities are also very promising signs for further extension to a variety of other truly efficient metal-NP-catalyzed reactions

Highly Selective and Sharp Volcano-type Synergistic Ni₂Pt@ZIF-8-Catalyzed Hydrogen Evolution from Ammonia Borane Hydrolysis

Ammonia borane hydrolysis is considered as a potential means of safe and fast method of H₂ production if it is efficiently catalyzed. Here a series of nearly monodispersed alloyed bimetallic nanoparticle catalysts are introduced, optimized among transition metals, and found to be extremely efficient and highly selective with sharp positive synergy between 2/3 Ni and 1/3 Pt embedded inside a zeolitic imidazolate framework (ZIF-8) support. These catalysts are much more efficient for H₂ release than either Ni or Pt analogues alone on this support, and for instance the best catalyst Ni₂Pt@ZiF-8 achieves a TOF of 600 mol_H₂·mol_catal^–1·min^–1 and 2222 mol_H₂·mol_Pt^–1·min^–1 under ambient conditions, which overtakes performances of previous Pt-base catalysts. The presence of NaOH boosts H₂ evolution that becomes 87 times faster than in its absence with Ni₂Pt@ZiF-8, whereas NaOH decreases H₂ evolution on the related Pt@ZiF-8 catalyst. The ZIF-8 support appears outstanding and much more efficient than other supports including graphene oxide, active carbon and SBA-15 with these nanoparticles. Mechanistic studies especially involving kinetic isotope effects using D₂O show that cleavage by oxidative addition of an O–H bond of water onto the catalyst surface is the rate-determining step of this reaction. The remarkable catalyst activity of Ni₂Pt@ZiF-8 has been exploited for successful tandem catalytic hydrogenation reactions using ammonia borane as H₂ source. In conclusion the selective and remarkable synergy disclosed here together with the mechanistic results should allow significant progress in catalyst design toward convenient H₂ generation from hydrogen-rich substrates in the close future