Low-valent homobimetallic Rh complexes: influence of ligands on the structure and the intramolecular reactivity of Rh–H intermediates

Supporting two metal binding sites by a tailored polydentate trop-based (trop - 5H-dibenzo[a,d] cyclohepten-5-yl) ligand yields highly unsymmetric homobimetallic rhodium(I) complexes. Their reaction with hydrogen rapidly forms Rh hydrides that undergo an intramolecular semihydrogenation of two C≡C bonds of the trop ligand. This reaction is chemoselective and converts C≡C bonds to a bridging carbene and an olefinic ligand in the first and the second semihydrogenation steps, respectively. Stabilization by a bridging diphosphine ligand allows characterization of a Rh hydride species by advanced NMR techniques and may provide insight into possible elementary steps of H₂ activation by interfacial sites of heterogeneous Rh/C catalysts

The coordination chemistry of 2,4,6-oxy functionalised 1,3,5-triphosphinines

A number of stable group 6 metal complexes bearing 2,4,6-oxy functionalised 1,3,5-triphosphinines, phosphorus containing heterocyclic ligands with a central C3P3 core, were synthesised such that a complete series of [M{P3C3(OX)3}(CO)3] compounds is obtained [M = Cr(0), Mo(0), W(0); X = H, SitBuPh2, B(ipc)2]. In all complexes, the triphosphinine coordinates in a η6-binding mode via the delocalized 6π-system of the ring. The ligand properties can be tuned by changing the substituent on the oxygen centre. The π-electron accepting properties of the ligand increases in the following order: P3C3(OH)3 < P3C3(OSitBuPh2)3 < P3C3(OB(ipc)2)3. This trend is reflected in the structures determined by X-ray crystallography, and the ν(CO) stretching frequencies determined by IR spectroscopy. The collected data raise questions with respect to the frequently made assumption that phosphinines act as stronger π-acceptors with respect to arenes and thereby deplete electron density at the metal centres. With P3C3(OH)3 as an η6-coordinated ligand further molecules can be coordinated in the second coordination sphere via hydrogen bonds, which may be of interest for the construction of coordination polymers.ISSN:1477-9226ISSN:1477-923

From 0 to II in one-electron steps: a series of ruthenium complexes supported by tropPPh2

We report the synthesis of a series of ruthenium complexes supported by the phosphine olefin ligand tropPPh2 (trop=5-H-dibenzo-[a,d]cyclohepten-5-yl) in the oxidation states 0, +I, and +II, formed via successive one-electron oxidization steps from Ru(0) (tropPPh2 )2 . The bidentate character of the tropPPh2 ligand and its steric hindrance force the complexes to adopt uncommon geometries, which were investigated by X-ray diffraction analysis. EPR data of the mononuclear Ru(I) complex reveal couplings of the unpaired spin with the ruthenium and two phosphorus nuclei, as well as the olefinic protons which show that the spin is mainly localized on the Ru(I) center

Penser l'art et la culture avec les sciences sociales

« À Pierre Bourdieu, la philosophie reconnaissante ». Préfacé par Jacques Bouveresse, professeur au Collège de France, ce livre réunit les travaux d’un séminaire dirigé par Eveline Pinto, professeur de philosophie à l’Université Paris I Panthéon-Sorbonne. Ils visent à mesurer l’apport des sciences sociales à la philosophie de l’art, et à expliquer pourquoi il est devenu impossible de penser les biens de culture autrement qu’avec les catégories construites par le sociologue brutalement disparu. Christophe Charle, professeur d’histoire à l’Université Paris I, rend hommage à celui dont il fut l’élève en ajoutant à l’ouvrage son premier exposé au séminaire du maître à l’ENS Ulm, sur Zola, de la figure du savant à celle du prophète. Il y a comme un effet de réverbération entre des textes (études théoriques et analyses de cas) qui partagent les mêmes orientations épistémologiques. Littérature et sciences, même visée ? Par une pratique qui unit la critique littéraire et la réflexivité critique, Pierre Bourdieu montre leur convergence jusqu’à un certain point (Eveline Pinto). Vues d’Allemagne, les études littéraires en France ont paru longtemps décalées, jusqu’au moment où, grâce à leurs liens avec les sciences sociales, elles ont comblé leur retard (Joseph Jurt). À propos de « l’économie temporelle de la représentation théâtrale », est analysée la relation entre spectateurs et acteurs en termes d’attentes réciproques (Emmanuel Bourdieu). De l’écrivain de l’État monarchique à l’intellectuel moderne, l’évolution de cette figure apparaît étroitement liée à l’histoire de l’autonomisation du champ littéraire (Gisèle Sapiro). Les cas étudiés sont tous empruntés à la modernité littéraire et artistique : la naissance d’Ibsen, écrivain européen (Pascale Casanova) ; Proust, sociologue du particulier, dans la confrontation de l’habitus bourgeois et aristocratique (Jacques Dubois) ; Mallarmé/Manet et le face-à-face de l’artiste et de son public à l’âge des foules (Pascal Durand) ; les usages politiques paradoxaux de la référence à Sade dans le champ littéraire de l’après 1945 (Anne Simonin) ; l’autonomie de l’artiste affirmée par Hans Haacke (Inès Champey)

Reduction of Nitrogen Oxides by Hydrogen with Rh(I)-Pt(II) Olefin Complexes as Catalysts

International audienceThe nitrogen oxides NO2, NO, and N2O are among the most potent air pollutants of the 21st century. A bimetallic Rh(I)-Pt(II) complex containing an especially designed multidentate phosphine olefin ligand is capable of catalytically detoxicate these nitrogen oxides in the presence of hydrogen to water and dinitrogen as benign products. The catalytic reactions were performed at room temperature and low pressures (3 - 4 bar for combined nitrogen oxides and hydrogen gases). A turnover number (TON) of 587 for the reduction of nitrous oxide (N2O) to water and N2 was recorded, making these Rh(I)-Pt(II) complexes the best homogeneous catalysts for this reaction to date. Lower TONs were achieved in the conversion of nitric oxide (NO, TON = 38) or nitrogen dioxide (NO2; TON of 8). These unprecedented homogeneously catalyzed hydrogenation reactions of NOx were investigated by a combination of multi-nuclear NMR techniques and DFT calculations, which provide insight into a possible reaction mechanism. The hydrogenation of NO2 proceeds stepwise, to first give NO and H2O, followed by the generation of N2O and H2O, which is then further converted to N2 and H2O. The nitrogen-nitrogen bond-forming step takes place in the conversion from NO to N2O and involves reductive dimerization of NO at a rhodium center to give a hyponitrite (N2O22-) complex, which was detected as intermediate