323,265 research outputs found
New Chiral Nitrogen Ligands Based on Amines Derived from -Pinene
No full textThe number of applications of bis-imines as ligands in homogeneous catalysis has much increased in recent years. Derivatives of acenaphthenequinone (R-BIAN) are especially useful for their chemical stability and rigidity. Until recently only Ar-BIAN ligands in which the aryl group contained electrondonating or moderately electronwithdrawing groups were known. We have recently expanded the available range of derivatives to ligands where the aryl group bears strongly electronwithdrawing substituents,1 two different aryl groups are present,2 and even to Alkyl-BIAN compounds.3,4 The latest had never been isolated before because an isomerization reaction occurred leading to their decomposition. We identified the cause of the decomposition in the ring strain of the five-membered ring of the acenaphthene moiety, which is partly released upon isomerization of the C=N double bond. The problem could be solved by employing ring-strained amines, for which this isomerization is thermodinamically unfavorable.3,4 Here we report the synthesis of a chiral cyclopropylamine derived from enantiomerically pure -pinene. The amine was obtained in good yields in four diastereomers. These can be separated by column chromatography. Two isomers are most abundant. One of them was employed in the synthesis of the corresponding BIAN derivative.
[1] Gasperini, M.; Ragaini, F.; Cenini, S. Organometallics, 2002, 21, 2950.
[2] Gasperini, M.; Ragaini, F.; Gazzola, E.; Caselli, A.; Macchi, P. Dalton Trans., 2004, 3376.
[3] Ragaini, F. ; Gasperini, M.;. Gallo, E.; Macchi, P. Chem. Commun., 2005, 1031.
[4] Ragaini, F.; Gasperini, M.; Parma, P.; Gallo, E.; Casati, N.; Macchi, P. New J. Chem. 2006, 30, 1046
CuO based catalysts on modified acidic silica supports tested in the de-NOx reduction
No full textA series of dispersed CuO catalysts supported on modified silica supports with Al2O3 (SA), TiO2 (ST), and ZrO2 (SZ) were prepared optimising the adsorption method of copper deposition assisted by ultrasound treatment, already reported in a previous paper (S. Bennici, A. Gervasini, V. Ragaini, Ultrason. Sonochem. 10 (2003) 61). The obtained catalysts were characterized in their bulk (atomic absorption, x-ray diffraction, temperature programmed reduction) and surface (N2 adsorption, x-ray photoelectron spectroscopy, scanning electron microscopy) properties. The morphology of the finished materials was not deeply modified compared with that of the relevant supports. The employed complemented techniques evidenced a well dispersed CuO phase with a copper-support interaction on the most acidic supports (SA and SZ).
The catalyst performances were studied in the reaction of selective catalytic reduction of NOx with ethene in oxidizing atmosphere in a flow apparatus under variable times (0.360-0.072 s) and temperatures (200-450°C). The catalysts prepared on the most acidic supports (SA and SZ) were the most active and selective towards N2 formation. They showed a particular interesting activity in the reaction of NO2 reduction besides that of NO reduction
Amination of C-H Bonds by Metal Porphyrins Catalysed Nitrene Transfer Reaction
No full textThe biological and pharmaceutical activities of organonitrogen compounds prompted the scientific community to develop new methods for the direct and selective C-N bond formation, working within restricted financial parameters and environmentally friendly requirements.In the last few years we have reported on the catalytic activity of metal porphyrin complexes in a wide range of reactions, such as olefin epoxidation,1 hydrocarbon amination and olefin aziridination. For these last reactions arylazides, a versatile class of starting material, was employed as atom-efficient aminating agents.2 ArN3 generate a nitrene functionality “ArN” and the eco-friendly molecular nitrogen is the only side product.
The selective insertion of “ArN” into C–H bonds of benzylic substrates or olefins yields benzylic amines, benzylic imines or allylic amines. To clarify the mechanism of the C-H amination reactions, the ruthenium bis-imido porphyrin complex (1) was isolated and characterised by X-ray analysis.
The role of 1 in catalytic nitrene insertions into C H bonds was studied in the reaction of ArN3 with several hydrocarbons proving that 1 is an active reaction intermediate. It also appears to have equilibrium between stability and reactivity.3 To the best of our knowledge, complex 1 is the first structurally characterized bis-imido porphyrin complex that shows a good catalytic activity in this class of reactions.
References: [1] S. Fantauzzi, E. Gallo, E. Rose, N. Raoul, A. Caselli, S. Issa, F. Ragaini, S. Cenini, Organometallics , 2008, 27, 6143; [2] For a review see: S. Fantauzzi, A. Caselli and E. Gallo, Dalton Trans., 2009, 5434; [3] S. Fantauzzi, E. Gallo, A. Caselli, F. Ragaini, N. Casati, P. Macchi and S. Cenini Chem. Commun., 2009, 3952–395
Mechanistic studies of palladium-catalysed carbonylation reactions of nitro compounds to isocyanates, carbamates and ureas
No full textMany different palladium-based catalytic systems have been reported for the carbonylation reactions of organic nitro compounds to isocyanates, carbamates and ureas. Almost all of these can be roughly divided into three groups: (i) those containing a second (or even a third) metal (usually a Lewis acid or a metal oxo compound or both), (ii) those in which phenanthroline or similar chelating nitrogen ligands are used and (iii) those in which monodentate phosphines are employed as ligands. The systems in which chelating phosphines are used as ligands lie in between the last two groups. The reaction mechanisms for the catalytic systems in each group appear to be related. Most of the information available does not derive from strictly mechanistic studies, but rather from synthetic studies and it is here critically analysed and compared with the information obtained from other related fields
Mechanistic study of the Ru-3(CO)(12)/chloride catalyzed carbonylation reactions of nitroarenes to carbamates and ureas; the role of the alkylammonium cation
No full textThe effect of the chloride countercation on the mechanism of the Ru-3(CO)(12)/chloride catalyzed carbonylation of nitroarenes to carbamates has been investigated. The reason for the higher activity and selectivity obtained with tetraethylammonium chloride with respect to [PPN][Cl] is due to the higher igroscopicity of the former (only when no aniline is added) and to its ability do decompose to yield triethylamine. The role of this last compound is twofold. On one hand, it accelerates the alcoholysis of the intermediately formed diarylurea. On the other, it favors a reaction pathway that consumes aniline together with nitrobenzene, thus converting a by-product into the desired product. (C) 2000 Elsevier Science B.V. All rights reserved
Intermediate formation of anilines in the synthesis of Schiff bases from nitroarenes and aldehydes
No full textThe role of the intermediate formation of anilines in the synthesis of Schiff bases from nitroarenes, aldehydes and CO catalysed by metal complexes has been investigated. Contrary to earlier belief, the reaction does not proceed through the reaction of an intermediate nitrene with the carbonyl compound, but by reduction of the nitroarene by CO and traces of water to initially afford the aniline, which then reacts with the aldehyde to afford the Schiff base, regenerating the water necessary to reduce more nitroarene. (C) 1999 Elsevier Science B.V. All rights reserved
Homogeneous catalysis in water without charged ligands. Reduction of nitrobenzene to aniline by CO/H2O catalysed by [Rh(CO)(4)](-)
No full textWe report here that [Rh(CO)(4)](-) (either as a K+, Cs+ or PPN+ salt, PPN+ = (PPh(3)N+) is a very active catalyst for the reduction of nitrobenzene to aniline by CO/H2O in water as solvent. No other ligand, except for CO itself, has to be added. The addition of bases, both inorganic or organic, has a negative effect on the reaction. The experimental conditions have been partly optimised. The reaction is selective for the nitro group
Gaseous CO-Free Palladium-Catalyzed Reductive Cyclization Reactions of Nitroarenes: An Endless Story Manar ahmed fouad abdellatif, doaa reda mohamed Ramadan, Simone Galié, F. Ferretti, F. Ragaini
No full textRecent progresses on Gaseous CO-Free Palladium-Catalyzed Reductive Cyclization Reactions of Nitroarenes are discussed
REDUCTION OF NITROBENZENE TO ANILINE BY CO/H2O, CATALYZED BY RU3(CO)12 - STRONG ACTIVATING ABILITY OF RIGID ALPHA-DIIMINE LIGANDS
No full textALLYLIC AMINATION OF UNACTIVATED OLEFINS BY NITROARENES, CATALYZED BY RUTHENIUM COMPLEXES. A REACTION INVOLVING AN INTERMOLECULAR C-H FUNCTIONALIZATION
No full textORGANOMETALLIC
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