133 research outputs found
Insight into the mechanism of decarbonylation of methanol by ruthenium complexes; a deuterium labelling study
The authors thank Lucite international for funding.In the reaction of [RuHClP3] (P = PPh3) with NaOMe in methanol, the product is [RuH2(CO)P3]. Short reaction times show that the final product is formed through [RuH4P3] as the major intermediate. Using NaOCD3 in CD3OD, the first formed product is [RuH4P'3] (P' is PPh3 partially deuterated in the ortho positions of the aromatic rings). Further reaction leads to a mixture of [RuHnD2-n(CO)P3] (n = 0, 22 %; n = 1, 2 isomers each 28 %; n = 2, 22 %). Mechanistic aspects of both steps of the reaction are explored and, together with previously published calculations, they provide definitive mechanisms for both dehydrogenation and decarbonylation in these interesting systems.PostprintPeer reviewe
Parameterization and optimization of the menthol force field for molecular dynamics simulations
Experimental and Theoretical Mechanistic Investigation of the Iridium-Catalyzed Dehydrogenative Decarbonylation of Primary Alcohols
DFT studies on thiophene acetylide Ru(II) complexes for nonlinear optics: Structureâfunction relationships and solvent effects
On the importance of decarbonylation as a side-reaction in the ruthenium-catalysed dehydrogenation of alcohols : a combined experimental and density functional study
We report a density functional study (B97-D2 level) of the mechanism(s) operating in the alcohol decarbonylation that occurs as an important side-reaction during dehydrogenation catalysed by [RuH2(H2)(PPh3)3]. By using MeOH as the substrate, three distinct pathways have been fully characterised involving either neutral tris- or bis-phosphines or anionic bis-phosphine complexes after deprotonation. α-Agostic formaldehyde and formyl complexes are key intermediates, and the computed rate-limiting barriers are similar between the various decarbonylation and dehydrogenation paths. The key steps have also been studied for reactions involving EtOH and iPrOH as substrates, rationalising the known resistance of the latter towards decarbonylation. Kinetic isotope effects (KIEs) were predicted computationally for all pathways and studied experimentally for one specific decarbonylation path designed to start from [RuH(OCH3)(PPh3)3]. From the good agreement between computed and experimental KIEs (observed kH/kD=4), the rate-limiting step for methanol decarbonylation has been ascribed to the formation of the first agostic intermediate from a transient formaldehyde complex.PostprintPeer reviewe
Vibrofonçage à fréquence élevée
Cet article traite du vibrofonçage des pieux et des pal-planches Ă frĂ©quences Ă©levĂ©es (1 500 Ă 3 000 Hz). AprĂšs avoir prĂ©sentĂ© les principaux rĂ©sultats obtenus au cours d'essais systĂ©matiques sur modĂšle dans du sable sec, l'auteur propose une mise en Ă©quation du problĂšme utilisant en particulier l'hypothĂšse d'un frottement latĂ©ral du type frottement sec. Des essais spĂ©cifiques ont Ă©tĂ© rĂ©alisĂ©s pour vĂ©rifier les rĂ©sultats analytiques. Dans l'ensemble, l'expĂ©rimentation confirme les conclusions tirĂ©es de la thĂ©orie et permet entre autre de mettre en relief l'efficacitĂ© du fonçage liĂ© Ă l'existence d'un ventre de vibration en tĂȘte du pieu
Ătude de l'effet d'Ă©chelle de pieux battus en cours de centrifugation
L'objectif de cette contribution est de faire le point sur la validitĂ© des lois de la similitude dans le cas du battage en cours de centrifugation. Deux sĂ©ries d'essais ont Ă©tĂ© rĂ©alisĂ©es dans des conditions trĂšs particuliĂšres. Dans le premier cas. le mĂȘme pieu-modĂšle a Ă©tĂ© soumis Ă trois niveaux d'accĂ©lĂ©ration : les trois essais correspondent donc Ă trois pieux-prototypes diffĂ©rents. Dans le deuxiĂšme cas. on a utilisĂ© quatre pieux-modĂšles de dimensions proportionnelles, et respectivement soumis Ă des niveaux dâaccĂ©lĂ©ration tels qu'ils reprĂ©sentent tous les quatre le mĂȘme pieu-prototype. Dans les deux cas, on montre que les lois de similitude sont globalement vĂ©rifiĂ©es, ce qui justifie le dĂ©veloppement des Ă©tudes en centrifugeuse sur le comportement des pieux battus
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