Monodisperse nickel-nanoparticles for stereo- and chemoselective hydrogenation of alkynes to alkenes

Mesoporous α-Al2O3-supported PdCu bimetallic nanoparticle catalyst for the selective semi-hydrogenation of alkynes

The selective hydrogenation of alkynes to alkenes is widely applied in the chemical industry; nevertheless, achieving highly selective hydrogenation with high catalytic activity is considerably challenging. Herein, ultrafine PdCu bimetallic nanoparticles encapsulated by high-surface-area mesoporous α-Al2O3 were prepared by high-temperature calcination-reduction using a porous organic framework (POF) as the template. As-obtained PdCu@α-Al2O3 exhibited a high selectivity of 95% for the semi-hydrogenation of phenylacetylene as a probe reaction under mild reaction conditions. The separation of continuous Pd atoms and modification of the Pd electronic state by Cu atoms suppressed β-hydride formation and alkene adsorption, contributing to high selectivity for the catalytic hydrogenation of alkynes. The catalytic activity was maintained after 7 cycles due to the strong interaction between the PdCu bimetallic nanoparticles and α-Al2O3 as well as the encapsulation effect of mesoporous α-Al2O3. Thus, the current work provides a facile strategy for fabricating high-surface-area mesoporous α-Al2O3-supported catalysts for industrial catalysis applications.

Stereoselective Semi-Hydrogenations of Alkynes by First-Row (3d) Transition Metal Catalysts

The chemo- and stereoselective semi-hydrogenation of alkynes to alkenes is a fundamental transformation in synthetic chemistry, for which the use of precious 4d or 5d metal catalysts is well-established. In mankind's unwavering quest for sustainability, research focus has considerably veered towards the 3d metals. Given their high abundancy and availability as well as lower toxicity and noxiousness, they are undoubtedly attractive from both an economic and an environmental perspective. Herein, we wish to present noteworthy and groundbreaking examples for the use of 3d metal catalysts for diastereoselective alkyne semi-hydrogenation as we embark on a journey through the first-row transition metals.

Unraveling High Alkene Selectivity at Full Conversion in Alkyne Hydrogenation over Ni under Continuous Flow Conditions

Selective hydrogenation of alkynes into alkenes in continuous flow conditions over non-precious metal catalysts is an attractive prospect for the chemical industry, especially for the petrochemical and polymer industry. Achieving...

Chemoselective semihydrogenation of alkynes catalyzed by manganese(i)-PNP pincer complexes

A first homogeneous manganese catalyzed chemoselective semihydrogenation of alkynes to Z-olefins in the presence of molecular hydrogen is described.

Monodisperse nanoparticles for catalysis and nanomedicine

The growth and breadth of nanoparticle (NP) research now encompasses many scientific and technologic fields, which has driven the want to control NP dimensions, structures and properties. Recent advances in NP synthesis, especially in solution phase synthesis, and characterization have made it possible to tune NP sizes and shapes to optimize NP properties for various applications. In this review, we summarize the general concepts of using solution phase chemistry to control NP nucleation and growth for the formation of monodisperse NPs with polyhedral, cubic, octahedral, rod, or wire shapes and complex multicomponent heterostructures. Using some representative examples, we demonstrate how to use these monodisperse NPs to tune and optimize NP catalysis of some important energy conversion reactions, such as the oxygen reduction reaction, electrochemical carbon dioxide reduction, and cascade dehydrogenation/hydrogenation for the formation of functional organic compounds under greener chemical reaction conditions. Monodisperse NPs with controlled surface chemistry, morphologies and magnetic properties also show great potential for use in biomedicine. We highlight how monodisperse iron oxide NPs are made biocompatible and target-specific for biomedical imaging, sensing and therapeutic applications. We intend to provide readers some concrete evidence that monodisperse NPs have been established to serve as successful model systems for understanding structure-property relationships at the nanoscale and further to show great potential for advanced nanotechnological applications.

Nickel-Catalyzed Stereodivergent Synthesis of E- and Z-Alkenes by Hydrogenation of Alkynes

A convenient protocol for stereodivergent hydrogenation of alkynes to E- and Z-alkenes by using nickel catalysts was developed. Simple Ni(NO3 )2 ⋅6 H2 O as a catalyst precursor formed active nanoparticles, which were effective for the semihydrogenation of several alkynes with high selectivity for the Z-alkene (Z/E>99:1). Upon addition of specific multidentate ligands (triphos, tetraphos), the resulting molecular catalysts were highly selective for the E-alkene products (E/Z>99:1). Mechanistic studies revealed that the Z-alkene-selective catalyst was heterogeneous whereas the E-alkene-selective catalyst was homogeneous. In the latter case, the alkyne was first hydrogenated to a Z-alkene, which was subsequently isomerized to the E-alkene. This proposal was supported by density functional theory calculations. This synthetic methodology was shown to be generally applicable in >40 examples and scalable to multigram-scale experiments.