Search results for "Elimination"

Hydration/elimination reactions of trapped protonated fluoroalkyl triazines

2007

Electrochemical and DFT studies of the oxidative decomposition of the trihydride complexes Cp*M(dppe)H3 (M = Mo, W) in acetonitrile

2006

International audience; A detailed electrochemical study of the oxidative decomposition of the trihydride complexes Cp*M(dppe)H3 (M = Mo, W) in acetonitrile is presented. For the Mo complex, the decomposition occurs by four different pathways involving classical and non-classical tautomers, whereas only the classical form is accessible for the W derivative. Each of the decomposition pathways has been quantitatively assessed by analyses of the linear sweep voltammograms. In addition to the previously established (B. Pleune, D. Morales, R. Meunier-Prest, P. Richard, E. Collange, J. C. Fettinger and R. Poli, J. Am. Chem. Soc., 1999, 121, 2209–2225) deprotonation, disproportionation, and H2 red…

Generation, Characterization, and Electrochemical Behavior of the Palladium-Hydride Cluster [Pd3(dppm)3(3-CO)(3-H)]+ (dppm=Bis(diphenylphosphinometha…

2007

Addition of formate on the dicationic cluster [Pd(3)(dppm)(3)(mu(3)-CO)](2+) (dppm=bis(diphenylphosphinomethane) affords quantitatively the hydride cluster [Pd(3)(dppm)(3)(mu(3)-CO)(mu(3)-H)](+). This new palladium-hydride cluster has been characterised by (1)H NMR, (31)P NMR and UV/Vis spectroscopy and MALDI-TOF mass spectrometry. The unambiguous identification of the capping hydride was made from (2)H NMR spectroscopy by using DCO(2) (-) as starting material. The mechanism of the hydride complex formation was investigated by UV/Vis stopped-flow methods. The kinetic data are consistent with a two-step process involving: 1) host-guest interactions between HCO(2) (-) and [Pd(3)(dppm)(3)(mu(3…

An unprecedented, bridged dihydrogen complex of a cofacial metallodiporphyrin and its relevance to the bimolecular reductive elimination of hydrogen

1990

Recently, the authors characterized the first metalloporphyrin dihydrogen complex, Os(OEP)(H{sub 2}), and proposed that a similar ruthenium porphyrin dihydrogen complex, Ru(OEP)(H{sub 2}), is involved as an intermediate in the catalytic H/D isotopic exchange between water and hydrogen. They now report that treatment of a metal-metal-bonded cofacial ruthenium porphyrin dimer with a sterically bulky ligand in the presence of hydrogen gas has yielded the first known complex containing a dihydrogen ligand bound between two metals. Such a bridged dihydrogen complex is proposed as an intermediate in the bimolecular elimination of dihydrogen from two metalloporphyrin hydrides.

A study of the diels-alder reaction of 3-oxabicyclo[3.3.0]oct-1(5)-ene-2,4-dione with cyclopentadiene and some related dienes

1984

Abstract The reaction of 3-oxabicyclo[3.3.0]oct-l(5)ene-2,4-dione, 2, with cyclopentadiene, 3, 5,5-diethoxycyclopentadiene, 4, and 6,6-dimethylfulvene, 5, is studied. Reaction of 2 and 3 yields the expected endo-adduct, while reaction of 2 and 5 gives a mixture of the endo- and exo-adducts whose ratio is slightly dependent on the reaction conditions. Attractive electrostatic interactions in the transition state leading to the exo-adduct can explain the absence of endo stereoselectivity in the last reaction. Steric factors seem to be responsible for the absence of reaction between 2 and 4. The analysis of the 13C NMR spectra of these adducts and some derived compounds confirms the tentative …

Unique distal size selectivity with a digold catalyst during alkyne homocoupling

2015

Metal-catalysed chemical reactions are often controlled by steric hindrance around the metal atom and it is rare that substituents far away of the reaction site could be differentiated during reaction, particularly if they are simple alkyl groups. Here we show that a gold catalyst is able to discriminate between linear carbon alkynes with 10 or 12 atoms in the chain during the oxidative homocoupling of alkynes: the former is fully reactive and the latter is practically unreactive. We present experimental evidences, which support that the distal size selectivity occurs by the impossibility of transmetallating two long alkyl chains in an A-framed, mixed-valence digold (I, III) acetylide compl…

Cluster Algorithm Integrated with Modification of Gaussian Elimination to Solve a System of Linear Equations

2020

The data accumulation and their inhomogeneous distribution lead to the issue of large and sparse systems solving in various fields: industrials, emergency management, etc. Complex structure in the data error creates additional risk to obtain an adequate solution. To facilitate problem-solving, we describe the technique that is based on intellectual division of data with following application of cluster algorithm and the modification of Gaussian elimination to different portions of data. In this paper, we present results of developed technique that was applied to samples of synthetic and real data. We compare them with outcomes of other algorithms (intelligence and classical) by using of num…

Kemp elimination: a probe reaction to study ionic liquids properties.

2008

The amino induced elimination of benzisoxazole into the relevant o-cyanophenolate ion (Kemp elimination) has been studied in [bmim][BF 4] solution at 298 K. To have information about the interactions between reactants and ionic liquid, the reaction has been carried out at different temperatures (293-313 K). Several primary, secondary, and tertiary amines have been used to study the effect of amine structure on the reaction rate. The collected data show that the amine structure seems to have a crucial role in determining the reaction rate. Furthermore, as different cation or anion structures of an ionic liquid can significantly affect its properties, the title reaction has been performed in …

Phenylation of cationic allylpalladium(II) complexes by tetraphenylborate anion. A mechanistic study

1990

Abstract The mechanism of the reaction of allyl complexes [Pd(η3-2-R′C3H4)(NN′)]+ (NN′ = α-diimine ligand) wiht BPh4− in the presence of activated olefins (ol), yielding the products [Pd(η2-ol)(NN′)] and PhCH2C(R′)CH2, has been investigated. The results are interpreted in terms of extensive association between the cationic substrate and the BPh4− anion in a tight ion-pair, followed by rate-determining phenyl transfer to the palladium center and fast reductive elimination of allylbenzene.

La recente riforma della disciplina italiana del subappalto nella prospettiva del bid rigging

2023

L’articolo analizza in chiave critica la disciplina nazionale del subappalto nell’ambito delle gare pubbliche, così come recentemente riformata a seguito di diversi interventi normativi in ottemperanza alla procedura d’infrazione avviata dalla Commissione UE. Stando alla tesi dell’A., l’attuale quadro normativo – caratterizzato dalla quasi totale eliminazione delle limitazioni previgenti (probabilmente anche spingendosi oltre ciò che la Commissione UE ha richiesto) – difetta nel trovare un equo bilanciamento tra il principio della massima partecipazione alla gara, da un lato, e l’esigenza di prevenire e svelare potenziali condotte collusive, dall’altro. La suddetta conclusione, peraltro, ap…