Pauvreté et paupérisation en milieu urbain. Une enquête préliminaire

Les mesures relatives à la mise en place du programme « de stabilisation et d'ajustement structurel » n'ont fait qu'accentuer la détérioration de la situation économique et sociale des classes laborieuses en Égypte, tandis qu'on assiste à une redistribution du revenu et des biens en faveur des détenteurs de capitaux et au détriment des salariés. La baisse de la part du facteur humain dans le revenu national est due au gel des salaires, à la hausse des prix, à la suppression de nombreuses subv..

La violence politique en Égypte

Le phénomène de la violence politique en Égypte a, sans aucun doute, augmenté de manière sensible depuis le début des années 70 et plus particulièrement encore en 1993. Ce phénomène est ainsi devenu l'un des principaux défis auxquels se trouvent confrontés l'État et la société, surtout au regard des transformations et des changements majeurs qui ont lieu sur le plan arabe et international. Le chercheur ayant déjà effectué cinq études traitant de la question de la violence politique en Égypte ..

Calculations on the non-classical β-hydride elimination observed in trans-(H)(OMe)-Ir(Ph)(PMe3)3: possible production and reaction of methyl formate

The octahedral trans hydrido-alkoxide complex trans-(H)(OMe)-Ir(Ph)(PMe3)3 (2-OCH3) was prepared by Milstein and coworkers by addition of methanol to Ir(Ph)(PMe3)3 (1). 2-OCH3 was discovered to undergo a methanol catalyzed outersphere carbonyl de-insertion in which a vacant coordination site is not required. The reaction yields the octahedral trans dihydride complex trans-(H)2-Ir(Ph)(PMe3)3 (2-H) as a kinetic product along with formaldehyde derivatives reported as [CH2=O]x. We investigate the mechanism and products of this reaction using density functional theory. The de-insertion transition state has an ion-pair character leading to a high barrier in benzene continuum: ΔG‡ = 27.9 kcal/mol. Adding one methanol molecule by H-bonding to the alkoxide of 2-OCH3 lowers the barrier to 22.7 kcal/mol. When the calculations are conducted in a methanol continuum, the barrier drops to 8.8 kcal/mol. However, the thermodynamics of de-insertion are endergonic by near 5 kcal/mol in both benzene and methanol. The calculations identify a low energy outer-sphere H/OMe metathesis pathway that transforms the formaldehyde and another 2-OCH3 molecule directly into a second 2-H complex and methyl formate. Likewise, a second H/OCH3 metathesis reaction interconverting methyl formate and 2-OCH3 into 2-H and dimethyl carbonate is computed to be exergonic and kinetically facile. These results imply that the production of methyl formate and dimethyl carbonate from 2-OCH3 is plausible in this system. The net transformation from the square planar 1 and methanol to 2-H and either methyl formate or dimethyl carbonate would represent a unique stoichiometric dehydrogenative coupling reaction taking place at room temperature by an outer-sphere mechanism.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Lewis Structures and the Bonding Classification of End-on Bridging Dinitrogen Transition Metal Complexes

The activation of dinitrogen by coordination to transition metal ions is a widely used and promising approach to the utilization of Earth’s most abundant nitrogen source for chemical synthesis. End-on bridging N2 complexes (µ-N2) are key species in nitrogen fixation chemistry, but a lack of consensus on the seemingly simple task of assigning a Lewis structure for such complexes has prevented application of valence electron counting and other tools for understanding and predicting reactivity trends. The Lewis structures have traditionally been determined by comparing the experimentally observed NN distance to the bond lengths of free N2, diazene, and hydrazine. We introduce an alternative approach here, and argue that the Lewis structure should be assigned based on the total π-bond order in the MNNM core (number of π-bonds), which derives from the character (bonding or antibonding) and occupancy of the delocalized π-symmetry molecular orbitals (π-MOs) in MNNM. To illustrate this approach, the end-on bridging N2 complexes cis,cis-[(iPr4PONOP)MCl2]2(µ-N2) (M = W, Re and Os) are examined in detail. Each complex is shown to have a different number of nitrogen–nitrogen and metal–nitrogen π-bonds, indicated as, respectively: WN–NW, Re=N=N=Re and Os–NN–Os. It follows that each of these Lewis structures represents a distinct class of complexes in which the µ-N2 ligand has a different electron donor number (total of 4e-, 6e-, or 8e-). We show how this classification can greatly aid in understanding and predicting the properties and reactivity patterns of µ-N2 complexes

A Metathesis Model for the Dehydrogenative Coupling of Amines with Alcohols and Esters into Carboxamides by Milstein’s [Ru(PNN)(CO)(H)] Catalysts

Milstein’s [Ru­(PNN)­(CO)­(H)] catalyst (<b>1</b>-Ru) is known to mediate the dehydrogenative coupling of alcohols into esters. When it is used in alcohol–amine mixtures it catalyzes carboxamide formation selectively over esters and imines. The given chemistry is generally accepted to follow metal–ligand cooperation (MLC) mechanisms involving hemiacetals and hemiaminals as intermediates. Using electronic structure DFT methods we investigate alternative, more direct OR/H and NHR/H metal/acyl metathesis routes to coupling that circumvent the intermediacy of the hemiacetal and the hemiaminal. The newly proposed mechanism involves formation of hemiacetaloxide and hemiaminaloxide ion-pairs by addition of an aldehyde (from metal-catalyzed alcohol dehydrogenation) to an octahedral ruthenium-alkoxide or ruthenium-amide intermediate (from alcohol or amine addition to <b>1</b>-Ru), followed by simple rearrangement (slippage) within the intact ion-pairs to transfer a hydride from the hemiacetaloxide or hemiaminaloxide to the metal. We show that the computed potential energy surfaces that are sometimes invoked to support the MLC mechanism correspond to indirect routes to metathesis. Both the ion-pair and the MLC routes predict the dehydrogenative coupling of ethanol and methanol into methyl acetate to be kinetically much more favored than the kinetics of formation of <i>N</i>-methylacetamide from ethanol and methylamine. However, the calculations provide evidence for the accessibility of a low energy NHR/OR metathesis path that would amidate the ester into the experimentally observed thermodynamically more favored carboxamide product. In fact, <b>1</b>-Ru is known to be a catalyst for ester amidation