Room Temperature Reduction of Titanium Tetrachloride-Activated Nitriles to Primary Amines with Ammonia-Borane

The reduction of a variety of aromatic and aliphatic nitriles, activated by a molar equivalent of titanium tetrachloride, has been achieved at room temperature using ammonia borane as a safe reductant. The corresponding methanamines were isolated in good to excellent yields following a simple acid-base workup.

Chemoselective and Site-Selective Reductions Catalyzed by a Supramolecular Host and a Pyridine-Borane Cofactor

Supramolecular catalysts emulate the mechanism of enzymes to achieve large rate accelerations and precise selectivity under mild and aqueous conditions. While significant strides have been made in the supramolecular host-promoted synthesis of small molecules, applications of this reactivity to chemoselective and site-selective modification of complex biomolecules remain virtually unexplored. We report here a supramolecular system where coencapsulation of pyridine-borane with a variety of molecules including enones, ketones, aldehydes, oximes, hydrazones, and imines effects efficient reductions under basic aqueous conditions. Upon subjecting unprotected lysine to the host-mediated reductive amination conditions, we observed excellent ε-selectivity, indicating that differential guest binding within the same molecule is possible without sacrificing reactivity. Inspired by the post-translational modification of complex biomolecules by enzymatic systems, we then applied this supramolecular reaction to the site-selective labeling of a single lysine residue in an 11-amino acid peptide chain and human insulin.

Hydrogenation of nitriles and imines for hydrogen storage

This review focuses on the selective catalytic hydrogenation of nitriles to primary amines both homogeneously and heterogeneously with transition metal-based catalysts in the view of nitriles as hydrogen carriers. Nitriles can be reduced with two equivalents of H2 to primary amines, thus having a great potential to serve as liquid organic hydrogen carriers (LOHCs) for hydrogen storage. Imines are intermediates in the hydrogenation of nitriles to amines, thus they can also serve as potential LOHCs, however with a lower hydrogen storage capacity (HSC).

Synthesis of α-trifluoromethyl ethanone oximes via the three-component reaction of aryl-substituted ethylenes, tert-butyl nitrite, and the Langlois reagent

A three-component reaction of aryl-substituted ethylenes, tert-butyl nitrite, and the Langlois reagent to synthesize a-trifluoromethyl ethanone oximes was developed.

Study of the Lyase Activity of Human DNA Polymerase β Using Analogues of the Intermediate Schiff Base Complex

DNA polymerase β (Pol β) participates in mammalian base excision repair. The enzyme has a two-domain architecture, reflecting its dual functionality. The polymerase activity, which replaces damaged nucleosides removed during an initial excision process, is within the C-terminal 31 kDa domain, while the N-terminal 8 kDa domain participates in a lyase function, working to remove a 5'-deoxyribose phosphate (5'-dRP) moiety from the damaged DNA substrate. The currently accepted mechanism of the lyase reaction involves a transient covalent enzyme-DNA intermediate in the form of a Schiff base connecting Lys72 of the enzyme with the 5'-dRP moiety. The Schiff base intermediate is resolved via a β-elimination reaction, initiated by abstraction of a C2'-H atom from the 5'-dRP moiety. Presently, we describe the preparation of three Pol β enzymes modified at position 72 with aminooxy or hydrazinyl analogues of lysine. These enzymes form transient covalent bonds with the 5'-dRP moiety of the damaged DNA, in the form of an oxime or hydrazone, respectively. Both types of enzyme DNA intermediates are ultimately resolved by the lyase activities of each of the modified enzymes. Unsurprisingly, the formation and resolution of these E-S complexes proceed with diminished kinetics, and with an altered pH profile. The performed experiments provide additional support for Schiff base formation as an obligatory intermediate on the pathway to DNA repair, as well as for the proposed participation of Lys72 in effecting opening of the 5'-dRP ring via protonation of the ring oxygen atom, and for complex resolution via a β-elimination reaction.

Nitrile hydroboration reactions catalysed by simple nickel salts, bis(acetylacetonato)nickel(ii) and its derivatives

Simple nickel salts, bis(acetylacetonato)nickel(ii) and its derivatives, catalyzed the hydroboration reactions of aryl and alkyl nitriles with catechol borane.

Nano-K2CO3: preparation, characterization and evaluation of reactive activities

Nano-K₂CO₃ shows higher basicity and can replace sodium (potassium) alkoxide to carry out monoalkylation and oximation of active methylene compounds.

Fabrication and Characterization of Monodisperse Magnetic Porous Nickel Microspheres as Novel Catalysts

A facile and efficient hard-templating strategy is reported for the preparation of porous nickel microspheres with excellent uniformity and strong magnetism. The strategy involves impregnation of porous polymer microspheres with nickel precursors, calcination to remove the template, followed by thermal reduction. The morphology, structure, and the property of the Ni microspheres were characterized by scanning electron microscopy, X-ray powder diffraction, N2 adsorption-desorption isotherms, thermogravimetric analysis, and magnetic hysteresis measurement. The obtained porous nickel microspheres were monodispersed with a particle size of 0.91 μm and crystallite size of 52 nm. Their saturation magnetization was much higher than that of Ni nanoparticles. The unique porous nanostructured Ni microspheres possess catalytic activity and excellent recyclability, as demonstrated in the catalytic reduction of 4-nitrophenol to 4-aminophenol. The micropherical Ni catalysts could be easily separated either by an external magnetic field or by simple filtration.

Photocatalyzed site-selective C-H to C-C conversion of aliphatic nitriles

β- or γ-Site-selective C-H alkylation of aliphatic nitriles has been achieved using a decatungstate salt as the photocatalyst. The observed site selectivity was justified by a radical polar effect in transition states for hydrogen abstraction.

Mild and selective hydrogenation of aromatic and aliphatic (di)nitriles with a well-defined iron pincer complex

The catalytic hydrogenation of carboxylic acid derivatives represents an atom-efficient and clean reduction methodology in organic chemistry. More specifically, the selective hydrogenation of nitriles offers the possibility for a green synthesis of valuable primary amines. So far, this transformation lacks of useful, broadly applicable non-noble metal-based catalyst systems. In the present study, we describe a molecular-defined iron complex, which allows for the hydrogenation of aryl, alkyl, heterocyclic nitriles and dinitriles. By using an iron PNP pincer complex, we achieve very good functional group tolerance. Ester, ether, acetamido as well as amino substituents are not reduced in the presence of nitriles. Moreover, nitriles including an α,β-unsaturated double bond and halogenated derivatives are well tolerated in this reaction. Notably, our complex constitutes the first example of an homogeneous catalyst, which permits the selective hydrogenation of industrially important adipodinitrile to 1,6-hexamethylenediamine.