A tautomeric ligand enables directed C‒H hydroxylation with molecular oxygen

Science ◽  
2021 ◽  
Vol 372 (6549) ◽  
pp. 1452-1457
Author(s):  
Zhen Li ◽  
Zhen Wang ◽  
Nikita Chekshin ◽  
Shaoqun Qian ◽  
Jennifer X. Qiao ◽  
...  
Keyword(s):  
Transition Metal ◽  
Hydrogen Bonds ◽  
Late Stage ◽  
Computational Analysis ◽  
Palladium Complex ◽  
Transition Metal Catalysts ◽  
X Ray ◽  
Site Selectivity ◽  
Hydroxylation Reaction

Hydroxylation of aryl carbon–hydrogen bonds with transition metal catalysts has proven challenging when oxygen is used as the oxidant. Here, we report a palladium complex bearing a bidentate pyridine/pyridone ligand that efficiently catalyzes this reaction at ring positions adjacent to carboxylic acids. Infrared, x-ray, and computational analysis support a possible role of ligand tautomerization from mono-anionic (L,X) to neutral (L,L) coordination in the catalytic cycle of aerobic carbon–hydrogen hydroxylation reaction. The conventional site selectivity dictated by heterocycles is overturned by this catalyst, thus allowing late-stage modification of compounds of pharmaceutical interest at previously inaccessible sites.

scholarly journals Graphene catalyzes the reversible formation of a C–C bond between two molecules

2018 ◽  
Vol 4 (12) ◽  
pp. eaau9366 ◽  
Author(s):  
J. J. Navarro ◽  
M. Pisarra ◽  
B. Nieto-Ortega ◽  
J. Villalva ◽  
C. G. Ayani ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Transition Metal ◽  
Chemical Reaction ◽  
Transition Metal Catalysts ◽  
Magnetic Switch ◽  
Kondo Resonance ◽  
Efficient Charge ◽  
Catalytic Role ◽  
Reversible Formation

Carbon deposits are well-known inhibitors of transition metal catalysts. In contrast to this undesirable behavior, here we show that epitaxial graphene grown on Ru(0001) promotes the reversible formation of a C–C bond between −CH2CN and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ). The catalytic role of graphene is multifaceted: First, it allows for an efficient charge transfer between the surface and the reactants, thus favoring changes in carbon hybridization; second, it holds the reactants in place and makes them reactive. The reaction is fully reversible by injecting electrons with an STM tip on the empty molecular orbitals of the product. The making and breaking of the C–C bond is accompanied by the switching off and on of a Kondo resonance, so that the system can be viewed as a reversible magnetic switch controlled by a chemical reaction.

1.12 Intermolecular Radical C—H Functionalization

2021 ◽  
Author(s):  
M. Bietti ◽  
F. Dénès
Keyword(s):  
Hydrogen Atom ◽  
Transition Metal ◽  
Bond Formation ◽  
Metal Catalysts ◽  
Hydrogen Atom Transfer ◽  
Transition Metal Catalysts ◽  
Radical Species ◽  
Significant Challenge ◽  
Site Selectivity ◽  
Selection Of

AbstractThe generation of carbon-centered radicals via intermolecular hydrogen-atom transfer (HAT) from C—H bonds to an abstracting species (HAT reagent) represents a significant challenge in terms of reactivity, site-selectivity and stereoselectivity. The radical species resulting from such a transfer can then engage in carbon—carbon or carbon—heteroatom bond formation, possibly through the intervention of transition-metal catalysts, leading to a variety of functionalized products. This chapter aims to provide the reader with useful guidelines to understand, predict, and design selective radical transformations based upon initial HAT from a C—H bond coupled to different radical-capture strategies. A selection of examples that illustrate different approaches to implement HAT reactions in synthetically useful procedures are presented.

A Comparative Study of the Selective Oxidation of NH3 to N2 over Transition Metal Catalysts

2013 ◽  
Vol 798-799 ◽  
pp. 239-244
Author(s):  
Wen Qin Wang ◽  
Xiao Long Tang ◽  
Hong Hong Yi ◽  
Jing Li Hu
Keyword(s):  
Transition Metal ◽  
Catalytic Oxidation ◽  
Transition Metal Catalysts ◽  
Oxidation Catalyst ◽  
High Yield ◽  
Incipient Wetness Impregnation ◽  
Selective Catalytic Oxidation ◽  
Series Of Experiments ◽  
Incipient Wetness

Cu-Mn/Al2O3, Cu-Mn/TiO2and Cu-Mn/SBA-15 were prepared by incipient wetness impregnation. The activity of those catalysts for selective catalytic oxidation (SCO) of ammonia to nitrogen at low temperature (100°C~250°C) is not so satisfying. 5%Cu-5%Zr/TiO2has the highest NH3conversion and highest NO, NO2yield. 5%Cu-5%Mn/Al2O3is a promising NH3selective catalytic oxidation catalyst, but still needs further study. SBA-15 is a bad support for Cu-Mn. Al2O3-based catalysts and TiO2-based catalysts were also prepared by incipient wetness impregnation to sure the synergistic effect between transition metal. The results find the activity on Cu-Mn/Al2O3is better than Cu-Mn/TiO2, but NH3conversion on Cu-Zr/TiO2is rather well with high yield of NO. The role of supports and transition metals play in catalyst are discussed by a series of experiments. Key ward: SCO, NH3, transition metal, γ-Al2O3, TiO2, SBA-15

Role of Transition Metal Catalysts in Single-Walled Carbon Nanotube Growth in Chemical Vapor Deposition

2003 ◽  
Vol 107 (44) ◽  
pp. 12161-12164 ◽  
Author(s):  
Yoshikazu Homma ◽  
Yoshiro Kobayashi ◽  
Toshio Ogino ◽  
Daisuke Takagi ◽  
Roichi Ito ◽  
...  
Keyword(s):  
Chemical Vapor Deposition ◽  
Carbon Nanotube ◽  
Transition Metal ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Transition Metal Catalysts ◽  
Single Walled Carbon Nanotube ◽  
Carbon Nanotube Growth ◽  
Nanotube Growth

Role of the gauche effect and local 1,3-dipole–dipole interactions in stabilizing an unusual conformation of tartarodinitriles

2008 ◽  
Vol 64 (4) ◽  
pp. 497-503 ◽  
Author(s):  
Urszula Rychlewska ◽  
Natalia Waścinska ◽  
Beata Warżajtis ◽  
Jacek Gawroński
Keyword(s):  
Hydrogen Bonds ◽  
Tartaric Acid ◽  
Conformational Equilibrium ◽  
Carbon Chain ◽  
Dipolar Interactions ◽  
Nmr Studies ◽  
X Ray ◽  
Gauche Effect ◽  
Dipole Interactions

This paper reports the synthesis, X-ray and NMR investigations of chiral and meso dinitriles of tartaric acid (tartarodinitriles) and their O,O′-diacetyl and O,O′-dibenzoyl derivatives. While in chiral tartaric acid its esters and NH amides the four-atom carbon chain is overwhelmingly trans, it is gauche in chiral tartarodinitriles. Conversely, meso-tartaric acid, its esters and amides display a tendency for the gauche conformation, but meso-tartarodinitriles usually have the trans conformation. The NMR studies of tartarodinitriles reveal the presence of a conformational equilibrium in solution with a preference for those conformers found in crystals. The gauche conformation of meso-tartarodinitriles seems to be stabilized by local dipolar interactions, intramolecular C—H...O hydrogen bonds and by a tendency for maximization of the gauche effect, the latter effect also operating in chiral tartarodinitriles. Stabilization of the trans conformers of tartarodinitriles in the crystals seems to originate from specific intermolecular interactions.

scholarly journals Small angle X-ray scattering analysis of Cu2+-induced oligomers of the Alzheimer's amyloid β peptide

Metallomics ◽  
2015 ◽  
Vol 7 (3) ◽  
pp. 536-543 ◽  
Author(s):  
Timothy M. Ryan ◽  
Nigel Kirby ◽  
Haydyn D. T. Mertens ◽  
Blaine Roberts ◽  
Kevin J. Barnham ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Transition Metal ◽  
Small Angle ◽  
Amyloid Β ◽  
Amyloid Β Peptide ◽  
X Ray ◽  
X Ray Scattering ◽  
Ray Scattering

Research into causes of Alzheimer's disease and its treatment has produced a tantalising array of hypotheses about the role of transition metal dyshomeostasis, many of them on the interaction of these metals with the neurotoxic amyloid-β peptide (Aβ).

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