Search results for "catalysis"

Thermo-Chromium: A Contactless Optical Molecular Thermometer.

2017

The unparalleled excited-state potential-energy landscape of the chromium(III)-based dye [1]3+ ([Cr(ddpd)2 ]3+ ; ddpd=N,N'-dimethyl-N,N'-dipyridin-2-yl-pyridin-2,6-diamine) enables a strong dual emission in the near infrared region. The temperature dependence of this dual emission allows the use of [1]3+ as an unprecedented molecular ratiometric thermometer in the 210-373 K temperature range in organic and in aqueous media. Incorporation of [1]3+ in biocompatible nanocarriers, such as 100 nm-sized polystyrene nanoparticles and solutol micelles, provides nanodimensional thermometers operating under physiological conditions.

Gold-Catalyzed Povarov-Type Reaction of Fluorinated Imino Esters and Furans

2016

A gold-catalyzed Povarov-type reaction of fluorinated imino esters and furans is described. The process, which takes place in dichoromethane at room temperature, gives rise to novel fluorinated tetrahydrofuran-fused tetrahydroquinolines in good yields and moderate levels of diastereo-selectivity in a very simple manner. The reported examples expand the versatility of the Povarov reaction to unprecedented fluorinated substrates, generating scaffolds that contain quaternary alpha-amino acid units.

Mononuclear Rearrangement of the Z-Phenylhydrazones of Some 3-Acyl-1,2,4-oxadiazoles: Effect of Substituents on the Nucleophilic Character of the &gt…

2019

The reaction rates for the mononuclear rearrangement of the Z-phenylhydrazones of 3-acyl-1,2,4-oxadiazoles 3a-c into the relevant 2-phenyl-2 H-1,2,3-triazoles (4a-c) have been measured in dioxane/water at different temperatures in a large range of proton concentrations. The occurrence of two different reaction pathways (one uncatalyzed, water assisted, and the other general base catalyzed) has- been observed. The obtained results have been able to furnish information about the effects of the nature of the 3-acyl structure and of the 5-substituents in the 1,2,4-oxadiazole ring on the reactivity of the examined rearrangements: they are well in line with the previsions carried out considering …

A Strongly Luminescent Chromium(III) Complex Acid

2018

The synthesis, structure, reactivity, and photophysical properties of a novel acidic, luminescent chromium(III) complex [Cr(H2 tpda)2 ]3+ (23+ ) bearing the tridentate H2 tpda (2,6-bis(2-pyridylamino)pyridine) ligand are presented. Excitation of 23+ at 442 nm results in strong, long-lived NIR luminescence at 782 nm in water and in acetonitrile. X-ray diffraction analysis and IR spectroscopy reveal hydrogen-bonding interactions of the counter ions to the NH groups of 23+ in the solid state. Deprotonation of the NH groups of 23+ by using a non-nucleophilic Schwesinger base in CH3 CN switches off the luminescence. Re-protonation by using HClO4 restores the emission. In water, the pKa value of …

A Combined Experimental and Theoretical Study of the Ammonium Bifluoride Catalyzed Regioselective Synthesis of Quinoxalines and Pyrido[2,3-b]pyrazines

2015

International audience; Ammonium bifluoride was efficiently used (at a 0.5 mol % loading) to catalyze the cyclocondensation between 1,2-arylenediamines and 1,2-dicarbonyl compounds at room temperature in methanol-water, affording quinoxalines and pyrido[2,3-b]pyrazines in excellent yields. Importantly, 2,8-disubstituted quinoxalines and 3-substituted pyrido[2,3-b]pyrazines were regioselectively formed by reacting aryl glyoxals with 3-methyl-1,2-phenylenediamine and 2,3-diaminopyridine, respectively. Analysis of the DFT reactivity indices allowed to explain the catalytic role of ammonium bifluoride.

Organocatalytic enantioselective Strecker reaction with seven-membered cyclic imines

2018

[EN] A highly enantioselective Strecker reaction with dibenzo[b,f][1,4]oxazepines has been described using a dihydroquinine-derived thiourea as organocatalyst. The reaction affords chiral 10,11-dihydrodibenzo[b,f][1,4] oxazepine 11-carbonitrile derivatives in excellent yields (up to 99%) and excellent enantioselectivities (up to 98%) under mild reaction conditions.

Organocatalytic Oxidation of Secondary Alcohols Using 1,2-Di(1-naphthyl)-1,2-ethanediamine (NEDA) (Eur. J. Org. Chem. 28/2014)

2014

Exploring the Slow Relaxation of the Magnetization in CoIII -Decorated {DyIII 2 } Units

2016

We have prepared and structurally characterized a new member of the butterfly-like {CoIII 2DyIII 2} single-molecule magnets (SMMs) through further CoIIIdecoration, with the formula [CoIII 4DyIII 2(OH)2(teaH)2(tea)2(Piv)6] (teaH3=triethanolamine; Piv=trimethylacetate or pivalate). Direct current (DC) susceptibility and magnetization measurements were performed allowing the extraction of possible crystal-field parameters. A simple electrostatic modeling shows reasonable agreement with experimental data. Alternating current (AC) susceptibility measurements under a zero DC field and under small applied fields were performed at different frequencies (i.e., 10–1500 Hz) and at low temperatures (i.…

Protonation and Electrochemical Properties of Pyridyl- and Sulfonatophenyl-Substituted Porphyrins in Nonaqueous Media

2017

International audience; The protonation and electrochemical properties of positively charged and negatively charged porphyrins are reported in up to five different nonaqueous solvents. The positively charged porphyrins are represented by mono- and di-pyridyl derivatives having the formula Pyx(PhMe)4-xPM, where P=the dianion of the porphyrin macrocycle, PhMe is a meso-tolyl group, Py a meso-pyridyl group, x=1 or 2, and M=H2, NiII, CuII, ZnII, or CoII. The negatively charged porphyrins are comprised of meso-tetrasulfonato derivatives having the formula [(R)4(TPPS)H2]4−(X+)4, where [(TPPS)H2]4− represents the porphyrin with four SO3− groups on the meso-phenyl substituents of the macrocycle, R=…

Role of the Open-Shell Character on the Pressure-Induced Conductivity of an Organic Donor-Acceptor Radical Dyad

2018

Single‐component conductors based on neutral organic radicals have received a lot of attention due to the possibility that the unpaired electron can serve as a charge carrier without the need of a previous doping process. Although most of these systems are based on delocalized planar radicals, we present here a nonplanar and spin localized radical based on a tetrathiafulvalene (TTF) moiety, linked to a perchlorotriphenylmethyl (PTM) radical by a conjugated bridge, which exhibits a semiconducting behavior upon application of high pressure. The synthesis, electronic properties, and crystal structure of this neutral radical TTF‐Ph‐PTM derivative (1) are reported and implications of its crystal…