Nickel Complexes of New Electron-Rich, Sterically-Hindered PNP Pincer Ligands

This thesis describes the synthesis, characterization and reactivity studies of nickel complexes of a new family of electron-rich, bulky PNP pincer ligands (PNP = 2,6-{R2PC(CH3)2}2-pyridine). The first chapter introduces the literature review of pincer complexes with a focus on nickel complexes and their applications. The second chapter introduces a new family of pyridine-based PNP pincer ligands that are based on the classic PNP framework, explores how the modified ligand influences the behavior of nickel complexes, and describes examples of mostly metal-based reactivity. This chapter mainly focuses on how this new family of PNP ligands can remain unreactive under specific reductive conditions, which allows the stabilization of complexes having unusual oxidation state of the metal center. The third chapter explores how it is possible to induce new types of ligand-based reactivity on the PNP pincer framework by blocking classical modes of metal-ligand cooperation, and how changes in the electronics and steric properties of the complex can lead to switching from metal-based reactivity to ligand-based reactivity.Okinawa Institute of Science and Technology Graduate Universit

Complexes cationiques POCOP de nickel : synthèse, caractérisation, réactivité et étude catalytique

Ce mémoire traite de la chimie des complexes pinceurs de nickel (II) cationiques ayant un ligand de type POCOP. Elle se divise en deux parties. La première traite de la synthèse, de la caractérisation et de la réactivité des complexes cationiques pinceurs de Ni(II) de type POCOP (POCOP = 1,3-bis(phosphinitobenzene), où C fait partie d’un cycle benzénique et est lié au métal, et P est un ligand phosphoré aussi lié au métal). Ces complexes ont un ligand acétonitrile coordonné au centre métallique et sont du type [(R-POCOPR’)Ni(NCMe)][OSO2CF3], où R est un substituant du cycle benzénique et R’ est un substituant sur le ligand phosphoré (R’ = iPr: R = H (1), p-Me(2), p-OMe(3), p-CO2Me(4), p-Br(5), m,m-tBu2(6), m-OMe(7), m-CO2Me(8); R’ = t-Bu : R = H (9), p-CO2Me(10)). Les complexes cationiques sont préparés en faisant réagir le dérivé Ni(II) neutre correspondant R-(POCOPR’)Ni-Br avec Ag(OSO2CF3¬) dans l’acétonitrile à température ambiante. L’impact des groupements R et R’ du ligand POCOP sur la structure et sur les propriétées électroniques du complexe a été étudié par spectroscopies RMN, UV-VIS et IR, analyse électrochimique, et diffraction des rayons X. Les valeurs de fréquence du lien C≡N (ν(C≡N)) augmentent avec le caractère électroattracteur du complexe, dans l’ordre 7 < 3 ~ 2 ~ 6 < 1 < 5 ~ 8 < 4 et 9 < 10. Ces résultats sont en accord avec le fait qu’une augmentation du caractère électrophile du centre métallique devrait résulter en une augmentation de la donation σ MeCN→Ni. De plus, les complexes cationiques montrent tous un potentiel d’oxydation Ni(II)/Ni(III) plus élevé que leurs analogues neutres Ni-Br. Ensuite, une étude d’équilibre entre un complexe neutre (R-POCOPR’)NiBr et un complexe cationique [(R-POCOPR’)Ni(NCMe)][OSO2CF3] démontre l’échange facile des ligands MeCN et Br. La deuxième partie de ce mémoire consiste en deux chapitres. Le premier (Chapitre 3) est une étude structurelle permettant une meilleure compréhension du mécanisme d’hydroamination des oléfines activées promue par les complexes présentés au chapitre 1, suivi de tentatives de synthèse de nouveaux composés POCOP cationiques comportant un ligand amine et nitrile, et de déplacement du groupement amine par un groupement nitrile. Le deuxième chapitre (4) décrit la réactivité et la cinétique de la réaction d’hydroamination et d’hydroalkoxylation d’oléfines activées, qui permet ainsi de mieux comprendre l’impact des différentes variables du système (groupements R et R’, température, substrats, solvent, etc.) sur la réactivité catalytique.This thesis describes the chemistry of nickel (II) cationic pincer complexes bearing a POCOP ligand. The content is divided into two parts. The first part (chapter 2) concerns the synthesis, characterization and reactivities of nickel (II) cationic POCOP pincer complexes with an acetonitrile ligand coordinated to the metal center via the nitrile moiety, [(R-POCOPR’)Ni(NCMe)][OSO2CF3] where R is a ring substituent and R’ is a P-substituent (R’ = iPr : R = H (1), p-Me(2), p-OMe(3), p-CO2Me(4), p-Br(5), m,m-tBu2(6), m-OMe(7), m-CO2Me(8); R’ = t-Bu : R = H (9), p-CO2Me(10)). The cationic complexes are synthetized by reacting the neutral nickel (II) bromide derivatives R-(POCOPR’)Ni-Br with Ag(OSO2CF3) in acetonitrile at room temperature. The impact of R and R’ groups of the POCOP ligand on the structure and electronic proprieties of the complexes has been studied by NMR, UV-Vis and IR spectroscopy, as well as by single crystal x-ray diffraction studies and cyclic voltammetry measurements. The observed ν(C≡N) values were found to increase with the increasing electron-withdrawing nature of R, i.e., in the order 7 < 3 ~ 2 ~ 6 < 1 < 5 ~ 8 < 4 and 9 < 10. This trend is consistent with the anticipation that enhanced electrophilicity of the nickel center should result in an increase in net MeCN→Ni σ-donation. It is also interesting to note that all cationic complexes show a much higher Ni(II)/Ni(III) oxidation potential than their neutral Ni-Br analogues. Following this, an equilibrium study is presented that shows the facile exchange of the MeCN/Br ligands between the charge-neutral and cationic complexes (R-POCOPR’)NiBr and [(R-POCOPR’)Ni(NCMe)][OSO2CF3]. The second part of this thesis consists of two chapters describing, respectively, structural studies that are relevant to our understanding of the mechanism of hydroamination reactions promoted by the title complexes (chapter 3), and reactivity and kinetic studies aimed at understanding the impact of different variables (R and R’; temperature; substrates; solvent; etc.) on the Michael-type hydroamination and hydroalkoxylation of acrylonitrile and its substituted derivatives (chapter 4). Chapter 3 will also discuss the attempted synthesis of new amine and nitrile POCOP cationic and neutral complexes, as well as the facile displacement of the amine moiety by a nitrile

Remix, répétition, break : l'attitude et la méthode du D.J. comme modèle de création

Ce projet de recherche présente une réflexion sur le déplacement des méthodes de travail et de l'attitude du D.J. dans le contexte d'une pratique en arts visuels. Le processus s'est développé en deux phases distinctes. Dans un premier temps, les notions d'échantillonnage et d'assemblage sont abordées comme procédés de création artistique à la lumière du mixage, opération qui permet au D.J. de sélectionner et d'agencer des pièces musicale en direct lors de performances. Quelques œuvres réalisées en cours de recherche ont permis de faire avancer la réflexion sur les possibilités et les limites de cette intention de départ. Dans un deuxième temps, une réflexion sur les effets de ce déplacement mène à une utilisation plus précise de certains procédés et à la production de l'exposition finale. L'idée de boucle et la notion de rythme sont retenues pour les effets qu'ils peuvent produire sur notre perception du monde. Si les œuvres nées de cette recherche sont d'abord produites exclusivement à partir de produits culturels existants, le processus de création se libère progressivement de cette contrainte afin d'explorer les possibilités de l'approche D.J. appliquées à l'ensemble de l'expérience du quotidien. Ainsi, tout ce qui compose notre environnement culturel, social ou matériel peut potentiellement servir de matière première à des assemblages et des interventions qui en détournent ou reformulent le sens. En adoptant le D.J. comme modèle de création, nous verrons comment l'identification de motifs rythmiques, à travers le flux d'information qui caractérise notre expérience du quotidien, peut être un moyen, une piste pour en saisir des fragments et produire du sens.\ud ______________________________________________________________________________ \ud MOTS-CLÉS DE L’AUTEUR : Assemblage, Boucle, Échantillonnage, Mixage, Rythm

Stable Nickel(I) Complexes with Electron-Rich, Sterically-Hindered, Innocent PNP Pincer Ligands

The electronic and steric properties of a new class of electron-rich and sterically hindered tertamethylated PNP pincer ligands (Me4PNPR = 2,6-bisRdialkylphosphino)propylipyridine with R = Pr-i, Bu-t) are discussed. Introducing the methyl groups on the pincer arm prevents dearomatization of the pincer framework and increases the bulkiness and electron-donating capacity of the ligand. Highly reactive Ni-I species are thus prevented from dimerizing and can be analyzed by a wide variety of spectroscopic methods. X-ray diffraction study shows that steric bulk has an important influence on the resulting geometric and spectroscopic properties of the Ni-I complexes. Complexes S and 6, which contain Pr-i groups on the phosphorus atoms, show a very rare seesaw geometry around the metal center, while Bu-t complexes 7 and 8 show a distorted square-planar geometry. Computational analysis reveals that the SOMO for all complexes has a d(x)(-y)(2)(2) character with the spin density mostly residing on the nickel

Probing the donor strength of yldiide ligands : synthesis, structure and reactivity of rhodium complexes with a PCylideN pincer ligand

Control of the metal ligand interaction by changes in the ligand protonation state is vital to many catalytic transformations based on metal–ligand cooperativity. Herein, we report on the coordination chemistry of a new PCy(H)N pincer ligand with a central ylide as donor site, which through deprotonation to the corresponding yldiide changes from a neutral L3-type ligand to an anionic L2X-type PCYN ligand. The isolation of a series of rhodium complexes showed that the strong donor ability of the neutral ylide PCY(H)N is further increased upon deprotonation, as evidenced by one of the lowest reported CO stretching frequencies in complex [(PCYN)Rh(CO)] (2) compared to other known rhodium carbonyl complexes. DFT calculations revealed that the high donor ability mostly results from the antibonding interaction of the pπ orbital at the ylide with the dxz orbital at rhodium, which enhances the backdonation into the π* orbital of the CO ligand. This unique interaction results in a rather long metal–carbon bond, but still a strong activation of the CO ligand in order to minimize repulsion between the filled orbitals at the rhodium and the ylide ligand. Accordingly, CO by phosphine replacement leads to a strong deviation from the square-planar geometry in the analogous phosphine complexes [(PCYN)Rh(PR3)] and an unusual reactivity with small alkyl halides, which upon oxidative addition add to the CO ligand, before inserting into the P–C bond in the pincer ligand. These results demonstrate the unique donor strength of yldiide ligands and their potential in the activation of strong bonds

A new device to track and identify people in a multi-residents context

In recent years, technologies for monitoring people inside a house lead to the development of smart home. However, the vast majority of works deals only in monitoring the activities of a single inhabitant. Nevertheless, most of the people in the current context of ageing population does not live alone. Recognizing the activities performed by each inhabitant in a house is an important challenge. A first step to achieve this is to be able to distinguish where each inhabitant is in the house. In this paper, we present a new device to track and identify people in a multi-residents context. Experiments have been conducted to validate the reliability and accuracy of the proposed device

Archives audiovisuelles : trois points de vue

Cet article a été développé sur la base des communications présentées au congrès annuel de l'Association des archivistes canadiens (7-10 juin 2017, Ottawa, ON).This article was developed on the basis of the papers presented at the annual conference of the Association of Canadian Archivists (June 7-10, 2017, Ottawa, ON).Même si les archives audiovisuelles sont devenues omniprésentes dans l'environnement numérique, le milieu archivistique n'a pas nécessairement saisi pour autant toute l'importance du phénomène. À partir de cette réflexion, trois étudiants gradués ont présenté leur point de vue et recherches sur le sujet lors du congrès annuel de l'Association des archivistes canadiens (7-10 juin 2017, Ottawa, ON). Cet article a été développé sur la base des communications présentées au congrès. Chacun, face à son objet d'étude, s'interroge à sa manière sur la discipline archivistique à travers les archives audiovisuelles et les institutions qui les conservent. Tout d'abord, il sera question des nouveaux usages, usagers et formes d'exploitation des documents d'archives audiovisuels numériques et des moyens d'améliorer leur organisation et leur diffusion sur le Web. Ensuite, les Prelinger Archives serviront de base pour l'analyse du déplacement des lieux d'archives tant sur le plan théorique qu'institutionnel ou structurel. Finalement, une étude de plusieurs initiatives d'archivage des films de famille mettra en lumière la valeur de ces documents souvent laissés de côté par les institutions traditionnelles et permettra de réfléchir au rôle de médiateur de l'archiviste. À travers ces trois points de vue, il s'agit de repenser l'archivistique depuis l'exploitation, représentant pour les archivistes une occasion sans pareille de renouvellement et, par conséquent, de développement dans l'environnement numérique.Even though audiovisual archives have become ubiquitous in the digital environment, the archival science field has not necessarily grasped the overall complexity of the phenomenon. Based on this reflection, three graduate students presented their perspectives and research on the subject at the annual conference of the Association of Canadian Archivists (June 7-10, 2017, Ottawa, ON). This article was developed on the basis of the papers presented at the conference. Each, faced with its object of study, interrogates in its own way on the archival science discipline through the audiovisual archives and the institutions which preserve them. First of all, it will be discussed new uses, users and forms of exploitation of digital audiovisual archive documents and ways of improving their organization and distribution on the Web. Then, the Prelinger Archives will serve as a basis for the analysis of the displacement of archival sites on the theoretical, institutional and structural levels. Finally, a study of several home movies archiving initiatives will highlight the value of these documents often left aside by traditional institutions and will help to reflect on the archivist's role as mediator. Through these three points of view, archival science will be thought from the exploitation, representing for the archivists an unparalleled opportunity of renewal and, consequently, of development in the digital environment

Cobalt Complexes of Bulky PNP Ligand: H2 Activation and Catalytic Two-Electron Reactivity in Hydrogenation of Alkenes and Alkynes

The reactivity of cobalt pincer complexes supported by the bulky tetramethylated PNP ligands Me4PNPR(R = iPr, tBu) has been investigated. In these ligands, the undesired H atom loss reactivity observed earlier in some classical CH2-arm PNP cobalt complexes is blocked, allowing them to be utilized for promoting two-electron catalytic transformations at the cobalt center. Accordingly, reaction of the formally CoIMe complex 3 with H2 under ambient pressure and temperature afforded the CoIII trihydride 4-H, in a reaction cascade reasoned to proceed by two-electron oxidative addition and reductive eliminations. This mechanistic proposal, alongside the observance of alkene insertion and ethane production upon sequential exposure of 3 to ethylene and H2, prompted an exploration into 3 as a catalyst for hydrogenation. Complex 4-H, formed in situ from 3 under H2, was found to be active in the catalytic hydrogenation of alkenes and alkynes. The proposed two-electron mechanism is reminiscent of the platinum group metals and demonstrates the utility of the bulky redox-innocent Me4PNPR ligand in the avoidance of one-electron reactivity, a concept that may show broad applicability in expanding the scope of earth-abundant first-row transition-metal catalysis.journal articl

Nickel(II) Complexes with Electron-Rich, Sterically Hindered PNP Pincer Ligands Enable Uncommon Modes of Ligand Dearomatization

We report the reactivity and characterization of hydride, methyl, and bromo Ni-II complexes with a new class of electron-rich and sterically hindered PNP pincer ligands, Me₄PNPR (R = Pr-i, Bu-t), in which a classical metal-ligand cooperative mode of reactivity via CH2 arm deprotonation is blocked by methylation. This enables new, uncommon modes of PNP ligand dearomatization that involve reactivity in the para position of the pyridine ring. In particular, the reduction of [(Me₄PNPiPr) (NiMe)-Me-II]B(Ar-F)(4) with KC₈ leads to the formation of a new C-C bond via dimerization of two complexes through the para position. This reactivity stands in sharp contrast to the previously reported bromo or chloro complexes, where stable Ni-I halogen moieties are formed. Computational analysis showed a greater propensity for ligand-centered radical formation for the presumed intermediate one-electron-reduced species. UV-induced homolysis of the Ni-II-Me bond in [(Me₄PNPiPr) (NiMe)-Me-II]B(Ar-F)(4) leads to the formation of a Me radical detected by radical traps and Ni(I )intermediates that can be trapped in the presence of halide ions to give previously characterized, stable Ni-I halogen complexes. In addition, treatment of the bromo complexes [(Me₄PNPR)(NiBr)-Br-II]BPh₄ with a powerful hydride source, LiBEt₃H, leads to the reduction of the pyridine ring and the formation of Ni-II complexes with an anionic amide donor reduced pincer ligand, although aromatic Ni-II hydride complexes could also be obtained with a weaker hydride source. We have observed that steric bulk at the phosphine donors controls the reactivity of the resulting Ni(II)H( )complexes. While t-Bu-substituted [(Me₄PNPtBu) (NiH)-H-II]Y(Y=BPh₄, B(Ar-F)(4)) does not react with O-2, the less sterically hindered Pr-i-substituted [(Me₄PNPiPr)(NiH)-H-II]Y reacts instantaneously to give an unstable superoxide adduct that can be observed by EPR