Etude théorique de la structure et de la réactivité de complexes organométalliques de lanthanides et d'actinides

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Etude théorique de la structure et de la réactivité des complexes organomatalliques de lanthanides et d'actinides

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Catalytic hydrosilylation of olefins with organolanthanide complexes: A DFT study. Part II: Influence of the substitution on olefin and silane

International audienceThe reaction mechanism of the catalytic hydrosilylation of olefins in the presence of the samarium hydride (η5-C5H5)2SmH has been investigated for several silanes and olefins with DFT calculations. For any substrate, the active species is the silyl complex, formed in situ from the reaction of the metal hydride with the silane. In agreement with the experimental data, the substitution of hydrogen by methyl groups in the silane decreases the catalytic turn-over. This result is shown to have electronic origins: the methyl group decreases the electron density on the silicon atom, which weakens the Sm–Si bond and decreases the ability for the silyl group to stabilise the positively charged group in a σ-bond metathesis transition state. Substituting hydrogen by alkyl groups on the olefin modifies mostly steric effects, and, depending on the position of the substituting group, it can result in an increase or a decrease of the catalytic yield

Catalytic hydrosilylation of olefins with organolanthanides: a DFT study. Part I: Hydrosilylation of propene by SiH₄

International audienceInvestigation of the catalytic hydrosilylation of propene by primary silane in the presence of Cp2SmH has been carried out using DFT calculations. Using SiH4 as a model, it is shown that a catalytic cycle based on the hydride complex is unlikely. The activation of silane after insertion of propene is not competitive compared to the allylic activation of propene or the silyl formation. An alternative catalytic cycle, based on a silyl complex, is proposed. This alternative pathway accounts for the experimental observation. The allylic activation of propene is shown to be one of the main routes for the catalyst deactivation

DFT studies of the methyl exchange reaction between Cp2M–CH3 or Cp*2M–CH3 (Cp = C5H5, Cp* = C5Me5, M = Y, Sc, Ln) and CH4. Does M ionic radius control the reaction?

The activation energies for the methyl exchange reactions between Cp2M–CH3 and H–CH3 have been calculated for M = Sc, Y and representative metals of the lanthanide family (La, Ce, Sm, Ho, Yb and Lu) with DFT(B3PW91) calculations with large-core pseudopotentials for M. The r-bond metathesis reactions are calculated to have lower activation energies for early lanthanides than for late lanthanides and any of group 3 metals. The relative activation barriers are analyzed using the NBO charge distributions in the reactant and in the transition states. It is shown that the methane needs to be polarized in the transition state as H(+d)–CH3 (−d) by the reactant, because this r-bond metathesis is best viewed as heterolytic cleavage of methane, leading to a proton transfer between two methyl groups in the field of an electropositive M metal. Early lanthanides, which are involved in strongly ionic metal–ligands bonds are thus associated with the lowest activation energies. The ionic radius and the steric effects influence the relative rates of reaction for the complexes of Sc, Y and Lu. In agreement with earlier works of Sherer et al., the experimental reactivity trends found by Tilley are reproduced best with Cp*2M–CH3 (Cp* = C5Me5) rather than Cp2M–CH3 (Cp = C5H5) because the steric bulk of C5Me5 deactivates most the complex where the metal has the smallest ionic radius (Sc). While the steric effects and the influence of the metal ionic radius cannot be neglected, these factors are not the only ones involved in determining the activation barriers of the r-bond metathesis reaction

Optical Properties of Complex Plasmonic Materials Studied with Extended Effective Medium Theories Combined with Rigorous Coupled Wave Analysis

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DFT Investigation of the Catalytic Hydromethylation of Olefins by Scandocenes. 2. Influence of the Ansa Ligand on Propene and Isobutene Hydromethylation

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A DFT study of the mechanism of the polymerization of Ε-caprolactone initiated by organolanthanide (boro)hydride complexes

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A DFT study of the mechanism of the polymerization of Ε-caprolactone initiated by organolanthanide (boro)hydride complexes

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XXXth Workshop on Rare Earth Elements

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