3 research outputs found
Gold–Ligand-Catalyzed Selective Hydrogenation of Alkynes into <i>cis</i>-Alkenes via H<sub>2</sub> 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 H<sub>2</sub> 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 H<sub>2</sub> 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)<sub>2</sub>, over silica-coated magnetite (Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub>). 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<sup>II</sup> synthetic
hydrolase [Ni<sub>2</sub>(HBPPAMFF)(μ-OAc)<sub>2</sub>(H<sub>2</sub>O)]BPh<sub>4</sub> (<b>1</b>) (H<sub>2</sub>BPPAMFF
= 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 (H<sub>2</sub>BPPAMFF)
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<sup>II</sup> complex covalently attached to the silica surfaces
was fully characterized by different techniques. The catalytic turnover
number (<i>k</i><sub>cat</sub>) of the immobilized Ni<sup>II</sup>Ni<sup>II</sup> 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><sub>cat</sub>/<i>K</i><sub>M</sub>) and the
supported catalyst can be reused for subsequent diester hydrolysis
reactions