Addition and elimination reactions of \H2\ in ruthenaborane clusters: A computational study

International audienceRuthenaborane clusters have been modelled by performing density functional theory calculations using the \B3LYP\ functional. The calculations gain insights into hydrogen storage and the H-H bond activation by ruthenaboranes. To study the nature of the chemical bond of \H2\ molecules attached to ruthenaboranes, we carried out structural optimizations for different ruthenaborane clusters and determined transition state structures for their hydrogenation addition/elimination reactions. Calculations of the reaction pathways yielded different transition-state structures involving molecular hydrogen bonded to the cluster or formation of metal hydrides. The H-H bond of \H2\ seems to be activated by the ruthenaborane clusters as activation energies of 24-42 kcal/mol were calculated for the \H2\ addition reaction. The calculated Gibbs free energy for the \H2\ addition reaction is 14-27 kcal/mol. The calculated activation energies and the molecular structures of the [(C5Me5)Ru2B10H16], [(C5Me5)Ru2B8H14] and [(C5Me5)Ru2B8H12] clusters with different degree of hydrogenation are compared. The mechanisms of the \H2\ addition and elimination reactions of the studied clusters suggest that they might be useful as hydrogen storage materials due to their ability to activate the H-H bond. They also serve as an example of the ability of hypoelectronic metallaboranes to reversibly or irreversibly bind hydrogen

Substituent effect in unsymmetrical lutetium bisphthalocyanines: a DFT analysis

International audienceDFT calculations have been carried out on a series of unsymmetrical bisphthalocyanine lutetium complexes in which one of the ligands is substituted by 8 or 16 chlorine atoms. It is shown that their unpaired electron is predominantly localized on the non-substituted ligand. An orbital explanation is provided to rationalize this effect. A good agreement is found between the computed and experimental ionization potentials and electroaffinities and the redox potentials of a closely related series, as well as between their TDDFT-computed and experimental UV-visible transitions which are analysed

Étude théorique de complexes inorganiques et de clusters métalliques de taille nanométrique (interprétation de leurs structures et de leurs propriétés)

Les travaux décrits dans cette thèse ont porté sur l'application de méthodes de la chimie quantique à l'étude de différents types et familles de composés chimiques, à savoir, des clusters encapsulant des anions et des complexes inorganiques de métaux de transition. On s'est particulièrement intéressé à la structure géométrique, la structure électronique et aux relations structures-propriétés optiques de systèmes moléculaires stables et bien caractérisés.The work reported in this manuscript deals with the applications of quantum chemistry tools on several types and families of chemical compounds, i. e., clusters entrapping anions and transition metals inorganic complexes. We have mainly focused our attention on the geometrical structure, the electronic structure and on the relationship between structure and optical properties of stable molecules which have been synthesized and characterized.RENNES1-Bibl. électronique (352382106) / SudocSudocFranceF

Theoretical and electrochemical studies on organometallic symmetrical schiff base complexes of Zn(II), Cu(II), Ni(II) and Co(II).

International audienceThe electronic communication between two redox centres through a Schiff base complex has been investigated in a series of ethylenediimine-bis(1-ferrocenyl-1,3-butanedionate) complexes of Zn(II) 1, Cu(II) 2, Ni(II) 3 and Co(II) 4. Cyclic voltammetry experiments of 1 and 2 exhibit a unique two-electron reversible oxidation wave, whereas in the case of 3 and 4 two and three one-electron oxidation processes are, respectively, observed. These results suggest some electronic interaction between the iron atoms of the ferrocenyl groups. DFT calculations carried out on model complexes show that for all the studied compounds the removal of the first two electrons corresponds to the oxidation processes of the iron centres in the weakly coupled ferrocenyl termini. The electronic communication between the two iron centres increases on going from 1 to 4. Finally, a re-indexation of the bands observed in the UV-Visible spectra has been carried out using TDDFT calculations

Reaction Mechanisms of Transition-Metal-Catalyzed Azide-Alkyne Cycloaddition “Click” Reactions: A DFT Investigation

International audienceDFT calculations at the PBE0/LANL2DZ level have been performed on model compounds to investigate the reaction mechanism of two recently reported metal-catalyzed alkyne azide cycloaddition (MAAC). The first one, that involves a [Cu(tren)]+Br- catalyst, is shown not to proceed through a metal alkynyl intermediate, but, after precomplexation of the alkyne in an η2-mode, directly to the 1,4-disubstituted 1,2,3-triazole product, through a metallacyclic transition state. The other system, involving a rare-earth Ln[N(SiMe3)2]3 complex, is found to proceed through an alkynyl-azide complex which produces an η 2-coordinated heterocyclic ligand before protonation by an incoming alkyne molecule. Our results are discussed with respect to other computational data from the literatur

An eleven-vertex deltahedron with hexacapped trigonal bipyramidal geometry.

International audienceThe first elemental cluster with hexacapped trigonal bipyramidal geometry is revealed in the luminescent undecanuclear silver complex which is stabilized by nine dithiocarbamate ligands and has an interstitial hydride. The hydride position within the Ag(11) cage is confirmed by a DFT investigation

Electronic structure and metal-metal communication in (CpM)2(as-indacene) and (CpM)2(s-indacene) (M = Mn, Fe, Co, Ni) complexes: a DFT investigation

International audienceDFT calculations with full geometry optimization have been performed on the series (CpM)2(as-indacene) and (CpM)2(s-indacene) (M = Mn, Fe, Co, Ni), as well as on the cations of the Fe, Co and Ni complexes. The compounds where M = Fe and Ni (as-indacene series) and M = Mn, Fe and Co (s-indacene series) were found to possess closed-shell ground states. In the mixed-valent cations as well as in the other open-shell species, the degree of metal-metal communication and the participation of the ligand into the spin density were evaluated. In general, the larger the total electron number, the larger the metal-metal communication and ligand participation to the frontier orbitals

DFT study of dihydrogen addition to molybdenum π-heteroaromatic complexes: a prerequisite step for the catalytic hydrodenitrogenation process

International audienceThe range of molybdenum hydride complexes that are sought to participate in the important catalytic hydrodenitrogenation process (HDN) of nitrogen containing polycyclic aromatic hydrocarbons were evaluated by DFT studies. The previously synthesized stable (η6-quinoline)Mo(PMe3)3 complex 1N, in which molybdenum is bonded to the heterocyclic ring, was chosen as a model. The hydrogenation of the quinone heterocycle, which was postulated as the initial step in the overall HDN reaction, is found to occur via three consecutive steps of the oxidative addition of dihydrogen to Mo in 1N. Successive transfer of hydrogen atoms from the metal to the heterocycle leads to the ultimate formation of the tetrahydrido molybdenum intermediate Mo(PMe3)4H413 and 2,2,3,3-tetrahydroquinoline C9H11N 14. All the involved intermediates and transition states have been fully characterized by DFT. This computational modeling of the hydrogenation of quinoline, as a part of extended HDN catalytic processes, provides a fundamental understanding of such mechanism