Intermetallic nickel silicide nanocatalyst—A non-noble metal–based general hydrogenation catalyst

Hydrogenation reactions are essential processes in the chemical industry, giving access to a variety of valuable compounds including fine chemicals, agrochemicals, and pharmachemicals. On an industrial scale, hydrogenations are typically performed with precious metal catalysts or with base metal catalysts, such as Raney nickel, which requires special handling due to its pyrophoric nature. We report a stable and highly active intermetallic nickel silicide catalyst that can be used for hydrogenations of a wide range of unsaturated compounds. The catalyst is prepared via a straightforward procedure using SiO2 as the silicon atom source. The process involves thermal reduction of Si–O bonds in the presence of Ni nanoparticles at temperatures below 1000°C. The presence of silicon as a secondary component in the nickel metal lattice plays the key role in its properties and is of crucial importance for improved catalytic activity. This novel catalyst allows for efficient reduction of nitroarenes, carbonyls, nitriles, N-containing heterocycles, and unsaturated carbon–carbon bonds. Moreover, the reported catalyst can be used for oxidation reactions in the presence of molecular oxygen and is capable of promoting acceptorless dehydrogenation of unsaturated N-containing heterocycles, opening avenues for H2 storage in organic compounds. The generality of the nickel silicide catalyst is demonstrated in the hydrogenation of over a hundred of structurally diverse unsaturated compounds. The wide application scope and high catalytic activity of this novel catalyst make it a nice alternative to known general hydrogenation catalysts, such as Raney nickel and noble metal–based catalysts

1-[2-(1H-Benzimidazol-2-yl)eth­yl]-1H-1,2,3-benzotriazole

In the title compound, C15H13N5, the N-containing heterocycles are linked by an ethyl­ene spacer in a gauche conformation, the N—C—C—C torsion angle along the linker being 60.1 (3)°. The dihedral angle between the terminal benzotriazole and benzimidazole rings is 39.02 (6)°. In the crystal, adjacent mol­ecules are connected by N—H⋯N hydrogen bonds, forming an infinite chain along the c axis. π–π stacking inter­actions [centroid–centroid distance = 3.8772 (7) Å] between the benzotriazole rings of neighbouring chains extend these chains into a supra­molecular sheet in the bc plane. Weak inter­molecular C—H⋯N inter­actions further stabilize the crystal structure

The synthesis of angular heteroarenochromones based on 7-hydroxy-8-carbonylchromones

The present review highlights advanced strategies to the synthesis of the chromones annulated with O- and N-containing heterocycles at C(7)-C(8) bond. Due to the prevalence of such motives in different kinds of natural flavonoids and some alkaloids, fused chromones have attracted a great deal of attention so far. On the other hand a wide range of biological activities is displayed by the compounds of this type both among naturally occurring flavonoids and their synthetic analogues. 8-Carbonyl-7-hydroxychromones proved to be versatile synthones for the synthesis of angular hetarenochromones via approach of annulation of a heterocycle to the chromone core. It also addresses the question of the biological activity of naturally occurring and fused synthetic hetarenochromones

Synthesis of 1-(pyridyl, quinolyl, and isoquinolyl)azulenes by Reissert-Henze type reaction

Azulene derivatives reacted with N-oxide of several heterocycles in the presence of trifluoromethanesultonic anhydride (Tf(2)O) to afford 1-(pyridyl, quinolyl, and isoquinolyl)azulenes in good yield, respectively. In the case of the reaction with the 1-azulenyl methyl sulfide (12), 1,1'-biazulene derivative 13 was obtained under the similar reaction conditions. The first synthesis of unsymmetrical 1,3-di(pyridyl)azulene derivative was also established via our new preparation method following the electrophilic pyriclinylation using the reaction with pyridine in the presence of Tf(2)O.ArticleTETRAHEDRON LETTERS. 51(39):5127-5130 (2010)journal articl

SYNTHESIS AND REACTIVITY OF N-CONTAINING HETEROCYCLES THROUGH CATALYTIC SYSTEMS.

N-containing heterocycles are the more represented in natural products and drugs. Our research has been focused on various aspects of heterocycles synthesis and reactivity. For this purpose we use transition metals catalysis, among which Pd has a central role due to the existence of different and easily and interconvertible oxidation states, Pd(0), Pd(II) and Pd(IV). For the arylation reaction electron poor aryl derivatives are problematic substrates, but we are successful in apply an intramolecular Pd(0) catalyzed reaction, in ligand free conditions, to synthesize azine and diazine polyheterocycles. Following our study on the reactivity and functionalization of indole derivatives we focus our attention on the amination reaction applied to the heterocycle indoline. The indoline skeleton is a ubiquitous scaffold found in many biologically active alkaloids and pharmaceutically active compounds, useful even as chiral auxiliary and for advanced materials. We selected the best conditions to functionalize this heterocycle at the nitrogen atom; then we find environmental friendly conditions using a solvent-free, microwaves assisted, reaction method and substantially reducing the catalyst load. Further to this we demonstrate the possibility of making Pd(0)-catalyzed amination reactions even in ligand-free conditions. In the third part we study a new synthesis of tetracyclic 1,4-Benzodiazepin-5-ones. The exploited reactions are Pd(0) catalyzed heterocyclization on imidazolidinones allenylamide followed by 1,3-dipolar cycloaddition. In the last step of the synthesis we obtain an unexpected total diasteroselectivity so we make a DFT and HF computational study that justify our results also thanks to the use of the recent QTAIM theory. In the last part we use Pd(II) and Au(III)-catalyzed reactions to realize C-H activation reaction. Starting from isoxazol-5-ones we obtain a solvent based regioselectivity in the alkenylation with acrylates or propiolates. The use of Pd(II)/O2 catalysis with acrylates lead to regioselectivity but with low yield; Au(III) catalysis with propiolates gives better yield and shows a complete regioselectivity

Catalytic asymmetric carbon-carbon bond forming methodologies for synthesis of chiral N-containing heterocycles and chiral carboxamides

In this thesis, we have developed several strategies that allow the Cu-catalyzed asymmetric conjugate addition of Grignard reagents to various heterocyclic substrates, such as 2- quinolones, 4-pyridone, 2,3-dihydro-4-pyridone, 2-quinolones and N-acylpyridinium salts. In addition, we have demonstrated that Lewis acids are highly beneficial for such reactions and can be successfully employed to activate the corresponding acceptors towards nucleophilic additions, as well as control the selectivities in these reactions

Nitrogen- and Fluorine-Doped Carbon Nanohorns as Efficient Metal-Free Oxygen Reduction Catalyst: Role of the Nitrogen Groups

The search of active, stable and low costs catalysts for the oxygen reduction reaction (ORR) is crucial for the extensive use of fuel cells and metal–air batteries. The development of metal-free catalysts, instead of platinum-based materials, can dramatically reduce the cost and increase the efficiency of these devices. In this work, carbon nanohorns (CNHs) have been covalently functionalized with N-containing heterocycles by the Tour reaction protocol and tested as metal-free ORR catalysts. The insertion of N-functionalities favored the complete reduction of oxygen to hydroxyl ions, while their absence favored the production of hydrogen peroxide. With the aim of determining the N-species responsible for the ORR activity of CNHs, photoemission and electrochemical measurements were combined. Results suggest that protonated N is the main species involved in the ORR process, facilitating the adsorption of oxygen, with their consequent reduction to neutral hydrogenated N species

Understanding the fate of nitrogen during catalytic hydrothermal liquefaction of sewage sludge

In this study, the fate of nitrogen during catalytic hydrothermal liquefaction (HTL) of sewage sludge (SS) is investigated using three different catalysts (CuNi/SiO$_2$, HCOOH, CuSO$_4$) with 5 wt% loading. The bio-crude yields obtained from HTL experiments catalyzed with CuNi/SiO$_2$ are similar to those obtained through non-catalyzed experiments. HCOOH slightly increases the bio-crude yields, while maximum yields of 24.5 wt% is obtained in the presence of CuSO$_4$, which also reduces the nitrogen content by 15 % and enhances the hydrocarbons compared to the non-catalyzed HTL. Mechanistic investigations regarding the interaction of amino acids and carbohydrates by Maillard reactions are carried out using model compounds, namely lysine and lactose. CuSO$_4$ effectively increases the yield with 50 % and reduces the nitrogen content by 24 % in the bio-crude during HTL of lysine alone. In the case of the model mixtures, bio-crude yields, nitrogen content, and Maillard reactions products behaved similarly both for catalytic and non-catalytic HTL, a slight reduction of amines was found in the presence of CuSO$_4$. Hydro-char and some organic compounds are assumed to act highly reductant during catalytic HTL. Coke deposition and adsorbed poisoning by Maillard reaction products are proposed as the main reasons for the deactivation of catalysts