Multiple light-induced NO linkage isomers in the dinitrosyl complex [RuCl(NO)₂(PPh₃)₂]BF₄ nravelled by photocrystallographic and IR analysis

Multiple light-induced reversible metastable NO linkage isomers (PLIs) have been detected in the dinitrosyl compound [RuCl(NO)(2)(PPh3)(2)]BF4 by a combination of photocrystallographic and IR analysis. The IR signature of three PLI states has been clearly identified, with estimated populations of 59% (PLI-1), 8% (PLI-2) and 5% (PLI-3) for a total population of the metastable state of 72%. The structural configuration of the major component (PLI-1) has been derived by X-ray photocrystallography. In the ground state, the structure is characterized by a bent and a linear nitrosyl, the bent one being oriented towards the linear equatorial nitrosyl with an Ru-N-O angle of 133.88 (9)degrees. X-ray Fourier difference maps indicate a selectivity of the photo-isomerization process in PLI-1: only the bent NO ligand changes its position, while the linear NO is unaffected. After irradiation at 405 nm, the orientation is changed by rotation towards the Cl ligand opposite the linear NO, with an Ru-N-O angle in this new position of 109 (1)degrees. The photocrystallographic analysis provides evidence that, in the photo-induced metastable state, the bent NO group is attached to the Ru atom through the N atom (Ru-N-O),rather than in an isonitrosyl Ru-O-N binding mode. In the IR spectra, the asymmetric NO vibrational band shifts by -33 cm(-1) to a lower value, whereas the symmetric band splits and shifts by 5 cm(-1) to a higher value and by -8 cm(-1) to a lower value. The down shift is a clear indication of the structural change, and the small upward shift in response to the new electronic configuration of the metastable structure. Variable-temperature IR kinetic measurements in the range 80-114 K show that the decay of the PLI-1 state follows an Arrhenius behaviour with an activation energy of 0.22 eV

Structural dynamics by stationary and time-resolved photocrystallography : instrumental developments and applications to photoisomerizable molecular materials

Ce travail de thèse s’inscrit dans l’étude des matériaux moléculaires photo-commutables. L’objectif est le contrôle réversible et persistant des propriétés physiques de la matière par application d’un stimulus externe, tel qu’une excitation optique. Le travail de thèse est constitué de deux parties principales. La première partie traite de la photo-isomérisation des ligands NO dans les complexes de ruthénium di-nitrosyle. Une démarche expérimentale systématique a été effectuée sur trois complexes. La spectroscopie infrarouge et la diffraction des rayons-X ont été utilisées conjointement à basse température. De multiples isomères de liaison photo-induits (PLI) ont été détectés. Il a été montré qu’il est possible de photo-commuter chacun des deux ligands nitrosyles indépendamment. De plus, une double photo-isomérisation a été caractérisée. La deuxième partie présente le développement et la mise en œuvre d’une expérience de diffraction des rayons-X résolue en temps en laboratoire. Le dispositif est un diffractomètre prototype avec un détecteur à pixel hybride XPAD, permettant des mesures à l’échelle de la milliseconde. Un système pompe-sonde est couplé au diffractomètre permettant une excitation périodique de l’échantillon et une caractérisation in-situ de la photo-commutation. Cette expérience a été validée par la mesure de l’état métastable MSII du complexe nitrosyle Na2[Fe(CN)5NO].2H2O, d’une durée de vie de 12 ms à 150 KThis work is part of the study of photo-switchable molecular materials. The objective is the reversible and persistent control of the physical properties of matter by the application of an external stimulus, such as optical excitation. The thesis work consists of two main parts. The first part deals with the photoisomerization of NO ligands in ruthenium di-nitrosyl complexes. A systematic experimental approach was performed on three complexes. Infrared spectroscopy and X-ray diffraction were used together at low temperature. Multiple photoinduced linkage isomers (PLI) were detected. It has been shown that it is possible to photo-switch each of the two nitrosyl ligands independently. In addition, a double photoisomerization was characterized. The second part presents the development and implementation of an in-house time-resolved X-ray diffraction experiment. The device is a prototype diffractometer with a XPAD hybrid pixel detector, allowing measurements on a millisecond time-scale. A pump-probe system is coupled to the diffractometer allowing periodic excitation of the sample and an in-situ characterization of the photo-switching. This experiment was validated by measuring the metastable state MSII of the nitrosyl complex Na2[Fe(CN)5NO].2H2O, with a lifetime of 12 ms at 150

Dynamique structurale par photocristallographie stationnaire et résolue en temps : développements instrumentaux et applications aux matériaux moléculaires photoisomérisables

This work is part of the study of photo-switchable molecular materials. The objective is the reversible and persistent control of the physical properties of matter by the application of an external stimulus, such as optical excitation. The thesis work consists of two main parts. The first part deals with the photoisomerization of NO ligands in ruthenium di-nitrosyl complexes. A systematic experimental approach was performed on three complexes. Infrared spectroscopy and X-ray diffraction were used together at low temperature. Multiple photoinduced linkage isomers (PLI) were detected. It has been shown that it is possible to photo-switch each of the two nitrosyl ligands independently. In addition, a double photoisomerization was characterized. The second part presents the development and implementation of an in-house time-resolved X-ray diffraction experiment. The device is a prototype diffractometer with a XPAD hybrid pixel detector, allowing measurements on a millisecond time-scale. A pump-probe system is coupled to the diffractometer allowing periodic excitation of the sample and an in-situ characterization of the photo-switching. This experiment was validated by measuring the metastable state MSII of the nitrosyl complex Na2[Fe(CN)5NO].2H2O, with a lifetime of 12 ms at 150 KCe travail de thèse s’inscrit dans l’étude des matériaux moléculaires photo-commutables. L’objectif est le contrôle réversible et persistant des propriétés physiques de la matière par application d’un stimulus externe, tel qu’une excitation optique. Le travail de thèse est constitué de deux parties principales. La première partie traite de la photo-isomérisation des ligands NO dans les complexes de ruthénium di-nitrosyle. Une démarche expérimentale systématique a été effectuée sur trois complexes. La spectroscopie infrarouge et la diffraction des rayons-X ont été utilisées conjointement à basse température. De multiples isomères de liaison photo-induits (PLI) ont été détectés. Il a été montré qu’il est possible de photo-commuter chacun des deux ligands nitrosyles indépendamment. De plus, une double photo-isomérisation a été caractérisée. La deuxième partie présente le développement et la mise en œuvre d’une expérience de diffraction des rayons-X résolue en temps en laboratoire. Le dispositif est un diffractomètre prototype avec un détecteur à pixel hybride XPAD, permettant des mesures à l’échelle de la milliseconde. Un système pompe-sonde est couplé au diffractomètre permettant une excitation périodique de l’échantillon et une caractérisation in-situ de la photo-commutation. Cette expérience a été validée par la mesure de l’état métastable MSII du complexe nitrosyle Na2[Fe(CN)5NO].2H2O, d’une durée de vie de 12 ms à 150

A Modular Access to 1,2‐ and 1,3‐Disubstituted Cyclobutylboronic Esters by Consecutive Radical Additions.

International audienceA modular approach to substituted cyclobutylboronic esters is described. It proceeds by successive intermolecular radical additions of xanthates to pinacolato 1-cyclobutenylboronate and to pinacolato bicyclo[1.1.0]but-1-ylboronate. Success hinges on tuning the stability of the a-boryl radical by exploiting the stabilizing influence of the trivalent boronic ester and the slightly destabilizing cyclobutane, which increases the s-character of the radical. Reductive removal of the xanthate group finally provides a range of 1,2-and 1,3disubstituted cyclobutylboronic esters. The contrast with cyclopropylboronic esters is striking, since the strong destabilization by the highly strained cyclopropane ring allows the first radical addition to take place but not the second. Furthermore, the first adducts are geminal xanthyl boronic esters that can be converted into cyclobutanones. This chemistry furnishes cyclobutylboronic esters that would be quite difficult to obtain otherwise and thus complements existing methods

Diastereo-and Enantioselective Palladium-Catalyzed Cycloadditions of 5-Vinyloxazolidine-2,4-diones with Electrophilic Imines

International audienceDespite the importance of the 4-imidazolidinone scaffold in bioactive compounds or organocatalysts, methodologies to access these nitrogenated heterocycles remain scarce. This manuscript describes a novel preparation of 4-imidazolidinones via a diastereo-and enantioselective (3+2) cycloaddition between 5-vinyloxazolidine-2,4-diones (VOxD) and electrophilic imines under palladium catalysis. This work supports the synthetic potential of VOxD as promising equivalents of the C-C(=O)-N synthon

Diastereo- and Enantioselective (3 + 2) Cycloaddition of a New Aza-π-Allylpalladium Zwitterionic Intermediate

International audienceCycloaddition of azaoxyallyl cations or other C-(C=O)-N synthon precursors is a well-established route towards lactams and other N-heterocycles but, despite the wide synthetic scope of this approach, enantioselective versions remain scarce. We herein report 5-vinyloxazolidine-2,4-diones (VOxD) as a suitable precursor of chiral palladium-aza-oxyallyl intermediates. In the presence of electrophilic alkenes, (3+2) γ-lactam cycloadducts could be formed with high level of diastero-and enantioselectivity

Diastereo- and Enantioselective (3+2) Cycloaddition of a New Palladium-Aza-Oxyallyl Intermediate

Cycloaddition of azaoxyallyl cations or other C-(C=O)-N synthon precursors is a well-established route towards lactams and other N-heterocycles but, despite the wide synthetic scope of this approach, enantioselective versions remain scarce. We herein report 5-vinyloxazolidine-2,4-diones (VOxD) as a suitable precursor of chiral palladium-aza-oxyallyl intermediates. In the presence of electrophilic alkenes, (3+2) -lactam cycloadducts could be formed with high level of diastero- and enantioselectivity

Vinylcyclopropanes as All-Carbon 1,5-Dipoles: A Reactivity Switch for Palladium-Catalyzed (5 + 4) Cycloadditions

International audienc

Bicyclic N -dihalocyclopropylamide derivatives as precursors of nitrogen-containing fused polycyclic systems

International audienceExamples of carbon–carbon bond-forming cyclisation reactions, involving allyl cations generated by the thermal ring-opening of halocyclopropanes, have been scarcely reported. In this contribution, we are describing the results of a study conducted with N-dihalocyclopropylamide substrates, designed as precursors of cyclic iminium intermediates that were aimed at participating in intramolecular reactions with electron-rich aromatic groups. Competitive side-reactions were identified, and access to the desired polycyclic products was carefully evaluated. The results were found to be strongly dependent on the substitution pattern of the nucleophilic aromatic moieties, as well as on the sizes of the rings of the target products. In spite of the rather moderate yields generally obtained, this approach represents a particularly short and inexpensive route to various interesting nitrogen-containing polycyclic systems, namely benzoindolizidine, benzoquinolizidine, piperidinobenzoazepane and azepanoisoquinoline compounds

Asymmetric synthesis of a stereopentade fragment toward latrunculins

International audienceLatrunculins are marine toxins used in cell biology to block actin polymerization. The development of new synthetic strategies and methods for their synthesis is thus important in order to improve, modulate or control this biological value. The total syntheses found in the literature all target similar disconnections, especially an aldol strategy involving a recurrent 4-acetyl-1,3-thiazolidin-2-one ketone partner. Herein, we describe an alternative disconnection and subsequent stereoselective transformations to construct a stereopentade amenable to latrunculin and analogue synthesis, starting from (+)-β-citronellene. Key stereoselective transformations involve an asymmetric Krische allylation, an aldol reaction under 1,5- anti stereocontrol, and a Tishchenko–Evans reduction accompanied by a peculiar ester transposition, allowing to install key stereogenic centers of the natural products