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Design of mixed iminophosphorane and phosphine ligand systems for coordination chemistry and catalysis.
No full textLe contexte d’épuisement général des ressources naturelles rend nécessaire le développement de réactions chimiques à faible coût économique et environnemental. Cela suppose la mise au point de procédés efficaces et sélectifs. La catalyse organométallique a permis des avancées majeures en ce domaine.Néanmoins, le développement de nouveaux catalyseurs plus résistants, plus performants, utilisant des métaux plus abondants, capables de réaliser de nouvelles réactions économes en atome reste un enjeu important. Cela suppose un important travail de conception et d’élaboration de ligands. Au‐delà du fait que ce sont leurspropriétés stéréo‐électroniques qui déterminent celles des systèmes organométalliques, et donc leurs performances en catalyse, il a été montré ces dernières années que la mise au point de ligands non innocentspouvait permettre de développer des réactivités inédites. Dans ce cas‐là le ligand n’est plus spectateur de la réaction mais y participe directement en acceptant ou en donnant un électron ou un proton.1Au laboratoire de Chimie Moléculaire de l’Ecole polytechnique nous sommesspécialisés dans la synthèse de ligands originaux associant différant hétéro‐atomes, en particulier le phosphore mais aussi l’azote. Nous nous intéressons particulièrement à des ligands comportant la fonction iminophosphorane (P=N), riche en électrons. Des exemples de ligands développés ces dernières années sont présentés ci‐après.2 Nous avons, par exemple, développé l’analogue phosphoré des salen appelésphosphasalen 3 qui a été utilisé entre autres pour mettre au point d’excellentinitiateurs de polymérisation par ouverture de cycle.4L’objectif de ce projet de thèse est de développer de nouveaux ligands, d’étendre les familles de ligands dont nous disposons afin de préparer des complexes inédits et d’en étudier la réactivité. Nous nous focaliserons sur des métaux abondants comme le cuivre, le fer, le cobalt ou le manganèse dans un souci de développement durable.En terme de domaines d’application nous viserons par exemple la catalyse d’oxydation avec des oxydants bénins comme l’eau oxygénée à l’aide de complexe à haut degré d’oxydation, ou le développement de catalyseurs cationiques pour la préparation de biopolymères. Des résultats prometteurs ont été obtenus danschacun de ces domaines. Ces deux types de complexes nécessitent d’être stabilisés par des ligands riches en électrons, tout l’enjeu est donc de parvenir à équilibrer stabilité et réactivité.Les complexes de métaux non nobles à ligands coopératifs sont également particulièrement intéressants dans le domaine de la catalyse par auto‐transfert d’H2. Dans ces procédés, le catalyseur, dans unepremière étape, déshydrogène le substrat, qui sous cette forme subit unetransformation suivie d’une l’hydrogénation permise par l’équivalent de H2stocké par le catalyseur. Cela a, ces dernières années, permis le développement de réactions inédites, efficaces avec peu de sous‐produits ou des sous‐produits bénins comme l’eau.Le sujet de thèse proposé est donc pluridisciplinaire associant chimie organique, chimie de coordination etcatalyse. Plusieurs de ces travaux seront menés en collaboration.1 J. van der Vlugt, Eur. J. Inorg. Chem., 2012, 363‐375 ; T. Zell and D. Milstein, Acc. Chem. Res., 2015, 48, 1979‐1994.2 T. Cheisson, L. Mazaud, A. Auffrant, Dalton Trans., 2018, 47, 14521‐ 14530 ; I. Mustieles Marin and A. Auffrant, Eur. J.Inorg. Chem., 2018, 1634‐1643.3 I. Mustieles Marin and A. Auffrant, Eur. J. Inorg. Chem., 2018, 1634‐1643.The exhaustion of resources calls for the development of chemical reactions at low economical and environmental cost. This requires developing new efficient and selective processes. Organometallic catalysis has allowed major breakthrough in that sense. However, elaboration of more robust, efficient catalysts incorporating abundant eco‐compatible metals allowing atom economical reactions remains achallenge. It supposes the design and synthesis of new ligand systems. Beyond the fact that their stereoelectronic properties govern that of the entire organometallic system, and therefore their catalytic performances, it was demonstrated, in the last few years that non‐innocent ligands associated to base metal could allow unprecedented reactivity. In such case, the ligand is not anymore spectator of the catalytic event but directly participates via the storage or the release of one electron or one proton.1 At the molecular chemistry laboratory (LCM), we are specialized in the synthesis of original ligand system associating various heteroatoms, and in particular phosphorus and/or nitrogen. We are particularly interested by ligands incorporating the electron rich iminophosphorane (P=N) function.Examples of some ligand systems developed in the past few years are shownhereinafter.2 For instance we synthesized the phosphorous analogues of the well‐known salen ligands,that we termed phosphasalen, and used them to prepare efficient ring opening polymerization catalysts.3The goal of this PhD project is to develop unprecedented ligands, as well as broaden and extend the family of ligands in our hands in order to prepare unprecedented complexes and study their reactivity.We will focus particularly on base metals such as copper, iron, cobalt, or manganese for sustainability reason.Possible applications are oxidation catalysis with benign oxidants such as hydrogen peroxide using high valent metal complexes or the synthesis of cationic initiators for the preparation of biopolymers.Promising results have already been obtained in each of these areas. Such complexes need to be stabilized by an electron rich ligand, nevertheless the challenge is always to reach the right balance between stability and reactivity.Cooperative ligands incorporating base metals are also particularlyinteresting for hydrogen borrowing catalysis. In such process (see scheme)the catalyst takes the H2 from the substrate and re‐adds it to the product ofa reaction, which was impossible before dehydrogenation. This has led inthe last few years to new efficient reactions with few side products or onlybenign ones such as water.The present PhD proposal is therefore multidisciplinary associating organic synthesis, coordinationchemistry and catalysis. Some of the projects will be conducted in collaboration.1 J. van der Vlugt, Eur. J. Inorg. Chem., 2012, 363‐375 ; T. Zell and D. Milstein, Acc. Chem. Res., 2015, 48, 1979‐1994.2 T. Cheisson, L. Mazaud, A. Auffrant, Dalton Trans., 2018, 47, 14521‐ 14530 ; I. Mustieles Marin and A. Auffrant,Eur. J. Inorg. Chem., 2018, 1634‐1643.3 D. Myers, A. J. P. White, C. M. Forsyth, M. Bown and C. K. Williams, Angew. Chem. Int. Ed., 2017, 56, 5277‐5282; T.P. A. Cao, A. Buchard, X. F. Le Goff, A. Auffrant and C. K. Williams, Inorg. Chem., 2012, 51, 2157‐2169; C. Bakewell,T. P. A. Cao, N. Long, X. F. Le Goff, A. Auffrant and C. K. Williams, J. Am. Chem. Soc., 2012, 134, 20577‐20580
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Journées de la Division de Chimie de Coordination de la Société Française de Chimie, affiche
No full textPhosphasalen ligands: Coordination, reactivity and catalysis
No full textInternational audienceSalen ligands are widely used in numerous domains among which bioinorganic chemistry, catalysis, and material science. Their popularity stems from their convenient synthesis allowing facile structural variations and their ability to coordinate a wide range of metals with different oxidation states. However, among all the skeleton variations proposed, only few concerns the introduction of a heteroatom in place of the carbon in the imine function. In 2010, we became interested in replacing the imine in salen by iminophosphorane (P=N) function to generate the phosphasalen platform, as we termed it. Initial coordination study started with groups 10 metals and allowed us to point divergences compared to salen. Since then, phosphasalen (Psalen) has been proved to be able to coordinate a large variety of metals. In this presentation, we will show the performances of their group 3 and group 4 compIexes as initiator of ring opening polymerization of lactide, discuss the redox non-innocence of their Cu and Ni complexes, and present the reactivity of their Fe and Mn complexes. With these results we will try to underline the impact of the introduction of the phosphorus atom in the ligand skeleton
Phosphasalen ligands: Coordination, reactivity and catalysis
No full textInternational audienceSalen ligands are widely used in numerous domains among which bioinorganic chemistry, catalysis, and material science. Their popularity stems from their convenient synthesis allowing facile structural variations and their ability to coordinate a wide range of metals with different oxidation states. However, among all the skeleton variations proposed, only few concerns the introduction of a heteroatom in place of the carbon in the imine function. In 2010, we became interested in replacing the imine in salen by iminophosphorane (P=N) function to generate the phosphasalen platform, as we termed it. Initial coordination study started with groups 10 metals and allowed us to point divergences compared to salen. Since then, phosphasalen (Psalen) has been proved to be able to coordinate a large variety of metals. In this presentation, we will show the performances of their group 3 and group 4 compIexes as initiator of ring opening polymerization of lactide, discuss the redox non-innocence of their Cu and Ni complexes, and present the reactivity of their Fe and Mn complexes. With these results we will try to underline the impact of the introduction of the phosphorus atom in the ligand skeleton
Exemples de catalyseurs à ligands iminophosphoranes
No full textNational audienceLa catalyse homogène est un des moyens privilégiés pour développer une chimie plus respectueuse de l'environnement. Dans ce contexte, les catalyseurs organométalliques jouent un rôle de premier plan et la mise au point de catalyseurs efficaces nécessite toujours un important travail de conception des ligands. Cet article montre au travers de quelques exemples comment des ligands iminophosphoranes, très électrodonneurs, ont pu être synthétisés très facilement et ont permis la mise au point de catalyseurs utilisant des métaux non toxiques (fer) ou permettant la préparation de biopolymères
Exemples de catalyseurs à ligands iminophosphoranes
No full textNational audienceLa catalyse homogène est un des moyens privilégiés pour développer une chimie plus respectueuse de l'environnement. Dans ce contexte, les catalyseurs organométalliques jouent un rôle de premier plan et la mise au point de catalyseurs efficaces nécessite toujours un important travail de conception des ligands. Cet article montre au travers de quelques exemples comment des ligands iminophosphoranes, très électrodonneurs, ont pu être synthétisés très facilement et ont permis la mise au point de catalyseurs utilisant des métaux non toxiques (fer) ou permettant la préparation de biopolymères
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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