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

Étude quantique de blindenes-1:1’ ; C

Nous présentons dans ce travail une étude quantique, au moyen des méthodes EHT-FMO et MNDO, de la structure électronique et de la stabilité de deux biindènes-1,1’,3,3’ (d,1 et méso). Le calcul des caractéristiques principales de l’état fondamental a permis une étude comparative détaillée de ces deux molécules et de leurs fragments. Les deux méthodes apparaissent qualitativement équivalentes et montrent le caractère déterminant du système Pi dans la réactivité chimique de ces composés. Les indices de Wiberg calculés au moyen des deux méthodes sont en excellent accord avec les longueurs de liaison déterminées par diffraction de rayons-X. Thermodynamiquement le composé, d, 1 apparaît plus stable que le composé méso, sa tendance à s’intracycliser et donc à se polymériser est plus élevée

A DFT investigation of some (formally) redox isomerization reactions of bis(pentalenyl)iron and bis(azulenyl)iron

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Interaction of molecular H

The interaction of molecular hydrogen with some d6-ML5 and d8-ML4 metal complexes is studied by means of Extended Huckel calculations. In a dissymétric ligand field (σ-donor and π-acceptor ligands), the structure of the complex is governed, for the d6-ML5 metal fragment, by the amplitude of electron transfer toward [math], which is maximum for H2 lying in the plane of σ-donors. On the other hand, the structure of the complex with the d8-ML4 metal fragment is governed by the four-electron repulsion between z2 and σH2 orbitals : the addition of H2 leading to the dihydride adduct is easier in the plane of the π-acceptor ligands which decrease this repulsion at the transition state

Haptotropic shifts in mononuclear complexes of substituted pentalenes: A DFT investigation of the [CpFe(C8H4R2)]q (R = H, Me, NH2, CF3, CN ; q = −1, 0, +1) series

International audienceThe haptotropic migration of Fe from the unsubstituted ring to the substituted one in the pentalenic complexes [CpFe(η5-1,3 C8H4R2)]q (q = +1, 0, −1) has been investigated by the means of DFT calculations in the case of R = H, CH3, NH2, CF3 and CN. The low energy pathway is a least-motion one-step process in the cationic case. In the anionic series, it is a two-step process involving an intermediate in which the metal moiety is η3-bonded in an exocyclic way to the pentalene ligand. The activation barriers and the preference for the Fe coordination on one ring rather on the other one is investigated with respect to the donor or acceptor abilities of R. The effect of changing q on the haptotropic situation is analyzed in terms of redox molecular switching

On the structure and fluxionality of mononuclear complexes of naphthalene: A DFT investigation of (naphthalene)MCp (M = Sc, V, Mn, Fe, Ni) and related complexes

International audienceThe coordination modes of naphthalene to a MCp metal moiety has been investigated in the series of first-row transition metals. Depending on the electron-richness of M, the coordination modes of naphthalene in the ground state configuration can be η2, η4 or η6. The η3 or η10 coordination mode are also possible in high-energy minima which are predicted to be reaction intermediates in haptotropic migration mechanisms interconverting degenerate ground state structures. Except for the M = Sc case, all the inter-ring haptotropic exchanges occur through a transition state or intermediate in which the metal moiety is bonded in an exocyclic way to the naphthalene ligand

Exploring the binding pocket for pyridopyrimidine ligands at the CCK1 receptor by molecular docking.

International audiencePyridopyrimidine-based analogues are among the most highly potent and selective antagonists of cholecystokinin receptor subtype-1 (CCK1R) described to date. To better understand the structural and chemical features responsible for the recognition mechanism, and to explore the binding pocket of these compounds, we performed automated molecular docking using GOLD2.2 software on some derivatives with structural diversity, and propose a putative binding conformation for each compound. The docking protocol was guided by the key role of the Asn333 residue, as revealed by site directed mutagenesis studies. The results suggest two putative binding modes located in the same pocket. Both are characterized by interaction with the main residues revealed by experiment, Asn333 and Arg336, and differ in the spatial position of the Boc-Trp moiety of these compounds. Hydrophobic contacts with residues Thr117, Phe107, Ile352 and Ile329 are also in agreement with experimental data. Despite the poor correlation obtained between the estimated binding energies and the experimental activity, the proposed models allow us to suggest a plausible explanation of the observed binding data in accordance with chemical characteristics of the compounds, and also to explain the observed diastereoselectivity of this family of antagonists towards CCK1R. The most reasonable selected binding conformations could be the starting point for future studies