Carbon Dioxide, a Solvent and Synthon for Green Chemistry

Carbon dioxide is a renewable resource of carbon when we consider the reuse of existing CO2 as a carbon source for producing chemicals. The development of new applications is of major interest from the point of view of carbon dioxide sequestration and within the scope of green chemistry. For example, using CO2 instead of CO or COCl2 for chemical synthesis constitutes an attractive alternative avoiding hazardous and toxic reactants. However, it has the lowest chemical reactivity, which is a serious drawback for its transformation. Supercritical CO2 as a reaction medium offers the opportunity to replace conventional organic solvents. Its benign nature, easy handling and availability, non volatile emitting, and the relatively low critical point (Pc = 73.8 bar, Tc = 31 °C) are particularly interesting for catalytic applications in chemical synthesis, over a wide range of temperatures and pressures. The benefits of coupling catalysis and supercritical fluids are both environmental and commercial: less waste and VOCs emission, improved separation and recycling, and enhanced productivity and selectivity. The case study described in this paper concerns the reaction of carbon dioxide with alcohols to afford dialkyl carbonates with special emphasis on dimethyl carbonate. It is of significant interest because the industrial production of this class of compounds, including polycarbonates, carbamates, and polyurethanes, involves phosgene with strong concerns on environmental impact, transport, safety and waste elimination. The future of carbon dioxide in green chemistry, including supercritical applications, is highly linked to the development of basic knowledge, know-how, and tools for the design of catalyst precursors and reactors

EXAFS STUDY OF SOLUBLE DINITROSYL IRON AND COBALT COMPLEXES CATALYSING SPECIFIC TRANSFORMATIONS OF OLEFINS

La spectroscopie EXAFS a permis de caractériser en solution la structure des complexes cationiques dinitrosyles de fer/cobalt, utilisés comme catalyseurs de la polymérisation des oléfines. Les spectres EXAFS de leurs précurseurs neutres et ceux de composés modèles : Fe(NO)2[PΦ3]Cl, Fe(NO)2[PΦ3]2 ont aussi été enregistrés. Pour le complexe cationique de fer, les résultats suggèrent une coordination du fer de type bipyramide à base trigonale impliquant trois molécules non équivalentes de solvant. Dans ce système comme dans son précurseur, les groupes nitrosyles devraient être légèrement coudés.EXAFS spectroscopy has been used in order to characterize in solution the structure of dinitrosyl iron/cobalt cationic complexes catalysing the polymerisation of olefins. EXAFS spectra were also recorded on the inactive precursors of these systems and on relevant model compounds : Fe(NO)2[PΦ3]Cl, Fe(NO)2[PΦ3]2. For the cationic iron species, the results are quite consistent with a trigonal bipyramidal coordination of iron implying three non equivalent solvent molecules. In this system as in its precursor, the nitrosyl groups are found slightly bent

Complexes bi- et polymétalliques à base de palladium (synthèse, électrosynthèse et applications en catalyse)

Ce mémoire concerne la synthèse, l'électrosynthèse et les applications en catalyse de complexes bi- et polymétalliques à base de palladium. La première partie concerne la réactivité chimique et électrochimique de dérivés d8-d8 du type Pd2(dppm)2Me2X2 (X = Cl, I). La structure cristallographique du dérivé en livre ouvert Pd2(dppm)2Me2(m-I)+ a été résolue. La deuxième partie décrit les propriétés d'hydroge nation catalytiques du cluster Pd4(dppm)4H22+ en fonction des conditions expérimentales ainsi que le mécanisme proposé et les études cinétiques qui le confortent. Ce cluster est l'un des meilleurs catalyseurs reportés à ce jour. La troisième partie concerne les propriétés chimiques et électrochimiques du dérivé hétérobimétallique PdPt(dppm)2Cl2. Le mécanisme intime d'électroréduction a été établi. Plusieurs dérivés originaux, dont PdPt(dppm)3, ont été caractérisés, et deux structures cristallographiques ont été résolues.This report deals with the synthesis, electrosynthesis and catalytic applications of bi- and polymetallic complexes of palladium. The first part concerns the chemical and electrochemical behaviour of d8-d8 compounds of the type Pd2(dppm)2Me2X2 (X = Cl, I). The X-ray structure of the A-frame Pd2(dppm)2Me2(m-I)+ has been solved. The second part describes the catalytic hydrogenation properties of the Pd4(dppm)4H22+ cluster when varying experimental conditions. A mechanism supported by kinetic studies is proposed. This cluster is one of the best known catalysts. In the third part, the chemical and electrochemical properties of the heterobimetallic PdPt(dppm)2Cl2 complex are studied. The whole reduction process has been addressed. Some new heterobimetallic compounds have been prepared and characterized, e. g. PdPt(dppm)3, and two X-ray structures have been solved.DIJON-BU Sciences Economie (212312102) / SudocSudocFranceF

Isolation and structural determination of two derivatives of the elusive carbamic acid

ABSTRACT The dibenzyl-substituted carbamic acid (PhCH2)(2)NC(O)OH (1), its deprotonation product [(PhCH2)(2)NH2]- [(PhCH2)(2)NCO2] (2) and CoCl(NO)(2)[PhP(OCH2CH2)(2)NC(O)OH]. 2MeCOMe(3 . 2MeCOMe) are reported, the diffractometric study showing the carbamic acids 1 and 3 to be paired through hydrogen bonds

A bridge from CO2 to methanol : News and Views

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