Kinetic Control in the Chiral Recognition of Three-Bladed Propellers

The ion pair of the stereolabile C3-symmetric, i+o proton complex [1⋅H]+ of diaza-macropentacycle 1 and the configurationally stable Δ-TRISPHAT ([Δ-3]−) anion exists in the form of two diastereomers, namely, [Δ-(1⋅H)][Δ-3] and [Λ-(1⋅H)][Δ-3], the ratio of which, in terms of diastereomeric excess (de) decreases in the order [D8]THF (28 %)>CD2Cl2 (22 %)>CDCl3 (20 %)>[D8]toluene (16 %)>C6D6 (7 %)>[D6]acetone (0 %) at thermodynamic equilibrium. Except in the case of [D6]acetone, the latter is reached after a period of time that increases from 1 h ([D8]THF) to 24 h (CDCl3). Moreover, the initial value of the de of [1⋅H][Δ-3] in CDCl3, before the thermodynamic equilibrium is reached, depends on the solvent in which the sample has been previously equilibrated (sample “history”). This property has been used to show that the crystals of [1⋅H][Δ-3] formed by slow evaporation of CH2Cl2/CH3OH mixtures had 100 % de, which indicates that [1⋅H][Δ-3] has enjoyed a crystallization-induced asymmetric transformation. Structural studies in solution (NMR spectroscopy) and in the gas phase by calculations at the semiempirical PM6 level of theory suggest that the optically active anion is docked on the i+ (endo) external side of the proton complex such that one of the aromatic rings of [Δ-3]− is inserted into a groove of [1⋅H]+, a second aromatic ring being placed astride the outside i+ pocket. Solvent polarity controls the thermodynamics of inversion of the [1⋅H]+ propeller. However, both polarity and basicity control its kinetics. Therefore, the rate-limiting steps correspond to the ion-pair separation/recombination and [1⋅H]+/1 deprotonation/protonation processes, rather than the inversion of [1⋅H]+, the latter being likely to take place in the deprotonated form (1)

Synthese et etude de complexes du cuivre (I) et du ruthenium (II) en vue de la separation intramoleculaire des charges photoinduites

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

The ins and outs of proton complexation

International audienc

Récepteurs macropolycycliques biomimétiques (synthèse, étude structurale et dynamique, réactivité et propriétés stéréochimiques)

La nitrogénase, enzyme présente dans des bactéries symbiotiques de plantes légumineuses, permet la fixation naturelle du diazote et catalyse sa réduction en ammoniac à température et pression ambiantes. Le site actif de l'enzyme est un cluster constitué essentiellement d'atomes de fer pontés par des atomes de soufre. Une partie du travail a consisté en la synthèse de récepteurs aminothiolates macropolycycliques afin de préparer de nouveaux complexes de Fe reprenant les caractéristiques structurales du site actif de la nitrogénase, l'objectif étant l'activation de N2 par ce type de complexes. L'accès à ces macropolycycles multisites élaborés nécessite la préparation de nombreux intermédiaires. Parmi ceux-ci, un dérivé de topologie macropentacyclique a fait l'objet d'une étude structurale et dynamique approfondie en solution et à l'état cristallin. Ce macropentacycle, achiral sous forme neutre, adopte une conformation en triple hélice, chirale, après protonation avec un équivalent d'acide.Nitrogenase, an enzyme produced by symbiotic bacteriae of leguminous plants, is involved in biological dinitrogen fixation process. This protein catalyses the reduction of N2 into a bioavailable form NH3 at room temperature and pressure. The active site of nitrogenase is a cofactor mainly made of iron centers bridged by sulfur atoms. A first part of the research work consisted in the synthesis of macropolycyclic aminothiolate receptors of iron ions, designed following structural features of this active site. The main goal was activation of N2 through coordination by this new complex. Several intermediates have been prepared along the multistep synthetic route to polyfonctionalized ligands. A detailed structural and dynamical study of one of them, a macropentacyclic cryptand, is exposed in a second part. Non chiral under its neutral form, this macropentacycle takes up a helically chiral conformation after reaction with one equivalent of acid.DIJON-BU Sciences Economie (212312102) / SudocSudocFranceF

Synthesis of a linear bis-porphyrin with a Ru(phen)(2)(2+)-complexed 2,2 '-bipyridine spacer

A linear bis-porphyrin bridged by a 5,5-diphenyl-2,2-bipyridine rod-like spacer complexing a [Ru(phen)2]2+ fragment has been synthesized in 7.4% yield by one-pot condensation of 3,5-di-tert-butylbenzaldehyde, 4,4-dimethyl-3,3-dihexyl-2,2-methylenedipyrrole and the [Ru(phen)2]2+ complex of 5,5-bis(p-formylphenyl)-2,2-bipyridine, followed by chloranil oxidation. The protected dialdehyde (5,5-bis[(5,5-dimethyl-1,3-dioxan-2-yl)phenyl]-2,2-bipyridine) was obtained in 80% yield by Suzuki coupling of 2-[4-(5,5-dimethyl-1,3-dioxan-2-yl)phenyl]-4,4,5,5-tetramethyl-1,3-dioxaborolane and 5,5-dibromo-2,2-bipyridine, using [Pd(PPh3)4] as catalyst. A new procedure is reported for the preparation of 5,5-dibromo-2,2-bipyridine, which is obtained in 80% yield by Stille homocoupling of 2,5-dibromopyridine in the presence of hexamethylditin

Synthesis and investigation of cyclic hydroxamate ligands derived from natural siderophores for selective complexation of actinides

Pas de résumé en françaisThe goal of this research was the synthesis and spectroscopic, structural andphysical-chemical characterization of cyclic 6- and 7-membered hydroxamicacids, a tetrahydroxamic calix[4]arene-based tetrapodal receptor, and their metalcomplexes with trivalent and tetravalent metal cations. They were characterizedby several techniques such as 1H and 13C NMR, IR, and mass spectroscopies,single crystal X-ray analysis, and potentiometry. Cyclic hydroxamic acids arefound in a few mix siderophores but their coordination properties were stillunknown. The structural features of metal complexes formed with Fe(III),Ga(III), Ce(IV), Zr(IV), Hf(IV), U(IV) and U(VI) have been investigated both inthe solid state and in solution. The synthesis and complexation studies of anoriginal calix[4]arene-based tetrapodal receptor is described. Reactionparameters for all key steps in the synthetic route have been optimized. Thesingle X-ray crystal analysis of benzyl-protected receptor was obtained.Complexation studies with zirconium(IV) and hafnium(IV) evidenced theformation of two metal two ligand complexes rather than 1:1 species, whichwere shown to interact in solution with a third alkali cationDIJON-BU Doc.électronique (212319901) / SudocSudocFranceF

Versatility and dynamics of the copper(I) coordination sphere in sterically hindering tris(pyrazolyl)methane-incorporating macrobicycles

International audienc

Dual emission of a bis(pyrene)-functionalized, perbenzylated beta-cyclodextrin

International audienc

Synthesis and functional group transformations of tris(pyrazol-1-yl)methane (Tpm) and -ethane (Tpe) derivatives for the preparation of sterically hindered chelating macrobicycles

International audienc