Gold–Ligand-Catalyzed Selective Hydrogenation of Alkynes into <i>cis</i>-Alkenes via H₂ Heterolytic Activation by Frustrated Lewis Pairs

The selective hydrogenation of alkynes to alkenes is an important synthetic process in the chemical industry. It is commonly accomplished using palladium catalysts that contain surface modifiers, such as lead and silver. Here we report that the adsorption of nitrogen-containing bases on gold nanoparticles results in a frustrated Lewis pair interface that activates H₂ heterolytically, allowing an unexpectedly high hydrogenation activity. The so-formed tight-ion pair can be selectively transferred to an alkyne, leading to a <i>cis</i> isomer; this behavior is controlled by electrostatic interactions. Activity correlates with H₂ dissociation energy, which depends on the basicity of the ligand and its reorganization on activation of hydrogen. High surface occupation and strong Au atom–ligand interactions might affect the accessibility and stability of the active site, making the activity prediction a multiparameter function. The promotional effect found for nitrogen-containing bases with two heteroatoms was mechanistically described as a strategy to boost gold activity

Direct Access to Oxidation-Resistant Nickel Catalysts through an Organometallic Precursor

The synthesis of nickel catalysts for industrial applications is relatively simple; however, nickel oxidation is usually difficult to avoid, which makes it challenging to optimize catalytic activities, metal loadings, and high-temperature activation steps. A robust, oxidation-resistant and very active nickel catalyst was prepared by controlled decomposition of the organometallic precursor [bis­(1,5-cyclooctadiene)­nickel(0)], Ni­(COD)₂, over silica-coated magnetite (Fe₃O₄@SiO₂). The sample is mostly Ni(0), and surface oxidized species formed after exposure to air are easily reduced in situ during hydrogenation of cyclohexene under mild conditions recovering the initial activity. This unique behavior may benefit several other reactions that are likely to proceed via Ni heterogeneous catalysis

Design of a Dinuclear Nickel(II) Bioinspired Hydrolase to Bind Covalently to Silica Surfaces: Synthesis, Magnetism, and Reactivity Studies

Presented herein is the design of a dinuclear Ni^II synthetic hydrolase [Ni₂(HBPPAMFF)­(μ-OAc)₂(H₂O)]­BPh₄ (<b>1</b>) (H₂BPPAMFF = 2-[(<i>N</i>-benzyl-<i>N</i>-2-pyridylmethylamine)]-4-methyl-6-[<i>N</i>-(2-pyridylmethyl)­aminomethyl)])-4-methyl-6-formylphenol) to be covalently attached to silica surfaces, while maintaining its catalytic activity. An aldehyde-containing ligand (H₂BPPAMFF) provides a reactive functional group that can serve as a cross-linking group to bind the complex to an organoalkoxysilane and later to the silica surfaces or directly to amino-modified surfaces. The dinuclear Ni^II complex covalently attached to the silica surfaces was fully characterized by different techniques. The catalytic turnover number (<i>k</i>_cat) of the immobilized Ni^IINi^II catalyst in the hydrolysis of 2,4-bis­(dinitrophenyl)­phosphate is comparable to the homogeneous reaction; however, the catalyst interaction with the support enhanced the substrate to complex association constant, and consequently, the catalytic efficiency (<i>E</i> = <i>k</i>_cat/<i>K</i>_M) and the supported catalyst can be reused for subsequent diester hydrolysis reactions