Gold Particles Supported on Amino-Functionalized Silica Catalyze Transfer Hydrogenation of N-Heterocyclic Compounds

A Facile Strategy for Constructing a Carbon-Particle-Modified Metal-Organic Framework for Enhancing the Efficiency of CO2 Electroreduction into Formate

Electrocatalytic reduction of CO₂ by metal-organic frameworks (MOFs) has been widely investigated, but insufficient conductivity limits application. Herein, a porous 3D In-MOF {(Me₂ NH₂ )[In(BCP)]⋅2 DMF}_n (V11) with good stability was constructed with two types of channels (1.6 and 1.2 nm diameter). V11 exhibits moderate catalytic activity in CO₂ electroreduction with 76.0 % of Faradaic efficiency for formate (FE_HCOO- ). Methylene blue molecules of suitable size and pyrolysis temperature were introduced and transformed into carbon particles (CPs) after calcination. The performance of the obtained CPs@V11 is significantly improved both in FE_HCOO- (from 76.0 % to 90.1 %) and current density (2.2 times). Control experiments show that introduced CPs serve as accelerant to promote the charges and mass transfer in framework, and benefit to sufficiently expose active sites. This strategy can also work on other In-MOFs, demonstrating the universality of this method for electroreduction of CO₂ .

A decennary update on applications of metal nanoparticles (MNPs) in the synthesis of nitrogen- and oxygen-containing heterocyclic scaffolds

Heterocycles have been found to be of much importance as several nitrogen- and oxygen-containing heterocycle compounds exist amongst the various USFDA-approved drugs. Because of the advancement of nanotechnology, nanocatalysis has found abundant applications in the synthesis of heterocyclic compounds. Numerous nanoparticles (NPs) have been utilized for several organic transformations, which led us to make dedicated efforts for the complete coverage of applications of metal nanoparticles (MNPs) in the synthesis of heterocyclic scaffolds reported from 2010 to 2019. Our emphasize during the coverage of catalyzed reactions of the various MNPs such as Ag, Au, Co, Cu, Fe, Ni, Pd, Pt, Rh, Ru, Si, Ti, and Zn has not only been on nanoparticles catalyzed synthetic transformations for the synthesis of heterocyclic scaffolds, but also provide an inherent framework for the reader to select a suitable catalytic system of interest for the synthesis of desired heterocyclic scaffold.

General and Efficient Copper-Catalyzed Oxazaborolidine Complex in Transfer Hydrogenation of Isoquinolines under Mild Conditions

A general and efficient method for copper-catalyzed transfer hydrogenation of isoquinolines with an oxazaborolidine-BH₃ complex, under mild reaction conditions, is successfully developed. A broad range of isoquinolines has been reduced to the corresponding products with 61-85% yields. The method is applied to the synthesis of biologically active tetrahydrosioquinoline alkaloid (±)-norlaudanosine in 62% yield, which is the key precursor for the preparation of (±)-laudanosine, (±)-N-methyl-laudanosine, and (±)-xylopinine in one or two steps.

Cobalt-Polypyrrole/Melamine-Derived Co-N@NC Catalysts for Efficient Base-Free Formic Acid Dehydrogenation and Formylation of Quinolines through Transfer Hydrogenation

It is highly desired but remains a great challenge to develop non-noble metal heterogeneous catalysts to supersede noble metal catalysts for formic acid (FA) dehydrogenation and the corresponding transfer hydrogenation reactions. Herein, we developed a simple and feasible melamine-assisted pyrolysis strategy for the preparation of atomic cobalt-nitrogen (Co-N)-anchored mesoporous carbon with high metal loading (>6.8 wt %) and high specific surface area (750 m² g^-1). Systematic investigation reveals that both the organic carbon source polypyrrole and the nitrogen source melamine are crucial for the successful generation of such Co-N-based materials. The obtained samples (Co-N)_n@NC were demonstrated to be highly efficient and robust catalysts for FA dehydrogenation and formylation of quinolines through transfer hydrogenation, exhibiting a very high hydrogen production rate of 16 451 mL·g_Co^-1·h^-1 for FA dehydrogenation and affording excellent yields (up to 99%), selectivity (up to 98%), and stability for transfer hydrogenation. This work may provide a promising route for the fabrication of more low-cost metal-nitrogen catalysts for green fine chemical synthesis.

Iridium-Catalyzed Hydrogenation and Dehydrogenation of N-Heterocycles in Water under Mild Conditions

An efficient catalytic method is presented for the hydrogenation of N-heterocycles. The iridium-based catalyst operates under mild conditions in water without any co-catalyst or stoichiometric additives. The catalyst also promotes the reverse reaction of dehydrogenation of N-heterocycles, hence displaying appropriate characteristics for a future hydrogen economy based on liquid organic hydrogen carriers (LOHCs).

Heterolytic bond activation at gold: evidence for gold(iii) H-B, H-Si complexes, H-H and H-C cleavage

The coordinatively unsaturated gold(iii) chelate complex [(C^N-CH)Au(C6F5)]+ (1 +) reacts with main group hydrides H-BPin and H-SiEt3 in dichloromethane solution at -70 °C to form the corresponding σ-complexes, which were spectroscopically characterized (C^N-CH = 2-(C6H3Bu t )-6-(C6H4Bu t )pyridine anion; Pin = OCMe2CMe2O). In the presence of an external base such as diethyl ether, heterolytic cleavage of the silane H-Si bond leads to the gold hydrides [{(C^N-CH)AuC6F5}2(μ-H)]+ (2 +) and (C^N-CH)AuH(C6F5) (5), together with spectroscopically detected [Et3Si-OEt2]+. The activation of dihydrogen also involves heterolytic H-H bond cleavage but requires a higher temperature (-20 °C). H2 activation proceeds in two mechanistically distinct steps: the first leading to 2 plus [H(OEt2)2]+, the second to protonation of one of the C^N pyridine ligands and reductive elimination of C6F5H. By comparison, formation of gold hydrides by cleavage of suitably activated C-H bonds is very much more facile; e.g. the reaction of 1·OEt2 with Hantzsch ester is essentially instantaneous and quantitative at -30 °C. This is the first experimental observation of species involved in the initial steps of gold catalyzed hydroboration, hydrosilylation and hydrogenation and the first demonstration of the ability of organic C-H bonds to act as hydride donors towards gold.

Selective hydrogenation of quinolines into 1,2,3,4-tetrahydroquinolines over a nitrogen-doped carbon-supported Pd catalyst

In this study, we have prepared a nitrogen-doped carbon supported Pd catalyst with abundant porous structures (abbreviated as Pd/CN) for the hydrogenation of quinolines.