1,721,113 research outputs found
Regio- and Stereo-Selective Carbon-Carbon Bond Formation in Ionic Liquids
No full textIonic liquids, that is molten salts, may represent activating and stabilizing solvents for C–C coupling reactions. In particular, tetrabutylammonium
bromide (TBAB) is particularly suitable for Heck reactions as it enhances reaction rates. In the presence of tetrabutylammonium
acetate as base, palladium complex with benzothiazolidene as ligands as well palladium acetate are transformed to Pd-nanoparticles which
allow regio- and stereo-specific Heck reactions with very high TON and TOF. Beside this, TBAB enhances, by solvation, the formation and
reactivity of carbanions. A comparative study on effects exerted by different ionic liquids on catalyst stabilization, reaction rates and regioand
stereo-selectivity in the C–C coupling reactions is also reported
Pd–benzothiazol-2-ylidene complex in ionic liquids: Efficient catalyst for carbon–carbon coupling reactions
No full textPd-benzothiazol-2-ylidene complex 3 catalyzes efficiently the carbon–carbon coupling reactions in the ionic liquid tetrabutylammonium
bromide (TBAB) as solvent. The IL does exert a striking influence on the reactivity and the stability of the catalyst.
This is probably due to the formation, by reaction with TBAB, of an anionic and more nucleophilic complex surrounded by large
tetrabutylammonium cation that would impede, by imposing a Coulombic barrier for collision, the formation of clusters growing
further into catalytically inactive metal particles. On the contrary, ionic liquids with planar structures and poor nucleophilic anions
like the [bmims], that form tight ion pairs, are barely efficient in influencing the reactivity and stability of the catalyst
Effects of Ionic Liquids on Pd-Catalysed Carbon-Carbon Bond Formation
No full textA comparative study of the effects exerted by different ionic
liquids on catalyst stability, reaction rates and regio- and
stereoselectivity in carbon–carbon coupling reactions points
to the superiority of the quaternary ammonium halides over
pyridinium- and imidazolium-derived ionic liquids. The influence
of ionic liquids on the Heck and Suzuki reactions
emerges as being associated with the Coulombic interaction
between the cations and anions in ILs as well as the nucleophilicity
of the anions. In the tetraalkylammonium halides
and acetate, the bulkiness of tetrahedral tetraalkylammo-
Introduction
A problem has emerged in today’s environmentally conscious
world, namely that many of the solvents traditionally
used in organic reactions, such as chlorinated hydrocarbons,
acetonitrile, DMF, DMA and NMP, to name but a few, are
currently on the “environmental blacklist”. Furthermore,
toxic and air-sensitive phosphanes are commonly used as
ligands in transition-metal-catalysed reactions, therefore
most industrial organic syntheses need rethinking. An approach
to resolve these drawbacks may be the replacement
of traditional solvents with ionic liquids (ILs), together with
the discovery of new ligands for the metals. The advantages
of using ILs would be manifold: in addition to facilitating
recovery of the catalyst and reaction products, they exhibit
high thermal and air stability and have a negligible vapour
pressure. For these reasons, ILs are nowadays finding an
increasing use for different reactions.[1] However, few studies
have been dedicated to exploring the influence of different
ILs on the rate and selectivity of organic reactions.
The objective of our research concerns the study of the
effects exerted by ILs on the rate and selectivity of C–C
coupling reactions.
[a] Department of Chemistry, University of Bari,
Via Orabona 4, 70126 Bari, Italy
[b] Lab. for Repressione frodi alimentari,
Via Cavedone, 18, 41100 Modena, Italy
E-mail: [email protected]
MICROREVIEWS: This feature introduces the readers to the authors’ research through a concise overview of the
selected topic. Reference to important work from others in the field is included.
Eur. J. Org. Chem. 2006, 3791–3802 © 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 3791
nium cations, which forces the anions away from the cation,
renders these anions available for a good activity and stability
of the palladium catalysts. On the contrary, the planar
structures of imidazolium and pyridinium cations, due to a
strong Coulombic interaction that binds the anions tightly,
decrease their availability for stabilisation and activity of the
catalysts
Regional scenarios: an opportunity to refine the evaluation of environmental risk of pesticide water contamination
No full textBook of Abstracts and presentations pp 92-9
Pd-Nanoparticles-Catalyzed Ullmann-Reactions in Ionic Liquids Using Aldehydes as the Reductants: Scope and Mechanism
No full textAn efficient Ullmann-type
reductive homocoupling of aryl, vinyl
and heteroaryl halides can be promoted
by an aldehyde in tetraalkylammonium
ionic liquids under very mild reaction
conditions. This simple procedure
generates symmetrical biaryls
under relatively mild conditions. The
ionic liquid is crucial for this process
because it behaves simultaneously as a
base, ligand and reaction medium. The
role of the aldehyde is also discussed
and a general mechanism for this unusual
reaction is proposed. These results
open the way to a new efficient
method of Pd-catalysed dehydrogenation
of carbonyl compounds
Cyclic Carbonates Formation from Carbon Dioxide and Oxiranes in Tetrabutylammonium Halides as Solvents and Catalysts
No full textEpoxides dissolved in molten tetralkylammonium salts bearing halides as counterions are converted into cyclic carbonates under atmospheric pressure of carbon dioxide. The reaction rate depends on the nucleophilicity of the halide ion as well as the structure of the cation
Pd Nanoparticles Catalyzed Stereospecific Synthesis of beta-Aryl Cinnamic Esters in Ionic Liquids
No full textReaction of the catalyst 1 or Pd(OAc)2 with tetrabutylammonium acetate, dissolved in tetrabutylammonium
bromide, leads to a fast formation of Pd nanoparticles which efficiently catalyze the
stereospecific reaction of cinnamates with aryl halides to give â-aryl-substituted cinnamic esters.
The role of tetrabutylammonium acetate is crucial in determining the formation of nanoparticles
and stereospecificity of the C-C coupling process
Palladium-Catalyzed Cross-Coupling of Styrenes with Aryl Methyl Ketones in Ionic Liquids: Direct Access to Cyclopropanes
No full textThe combined use of Pd(OAc)2, Cu(OAc)2, and dioxygen in molten tetrabutylammonium acetate (TBAA) promotes an unusual cyclopropanation reaction between aryl methyl ketones and styrenes. The process is a dehydrogenative cyclizing coupling that involves a twofold CH activation at
the a-position of the ketone. The substrate scope highlights the flexibility of the catalyst; a reaction mechanism is also proposed
Arylation of Allylic Alcohols in Ionic Liquids by a Pd-Benzothiazole Carbene Complex
No full textThe reaction of aryl bromides with allylic alcohols catalysed by a Pd-benzothiazole carbene complex, in tetrabutylammonium
bromide as solvent, leads principally to β-arylated carbonyl compounds
Effects of A1 and A2A adenosine receptor ligands in mouse acute models of pain
No full textThe effects of selective A(1) and A(2A) adenosine receptor compounds in two mouse models of acute nociception were studied: acetic acid-induced writhing and the hot plate assays. Stimulation of A(1) receptors by 2-chloro-N(6)-cyclopentyl-adenosine (CCPA, 0.01-0.1 mg/kg, i.p.; A(1)K(i)=6 nM) or blockade of A(2A) receptors by 5-amino-7-(beta-phenylethyl)-2-(8-furyl)pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine (SCH58261, 1-10 mg/kg, i.p.; A(2)(A)K(i)=1.3 nM) produced anti-nociceptive effects. At the highest dose tested, CCPA and SCH58261 reduced the number of writhings by 79 and 99%, respectively. On the contrary, the A(1) antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) (A(1)K(i)=2.8 nM) and the A(2A) agonist 2-(4-[2-carboxyethyl])phenethylamino-5'-N-ethylcarboxamido-adenosine-hydrochloride (GGS21680) produced pro-nociceptive effects in both tests. These findings suggest for the first time that blockade of A(2A) adenosine receptors produces anti-nociceptive effects
- …
