Gallium and indium complexes for ring-opening polymerization of cyclic ethers, esters and carbonates

International audienceOver the past five years, Ga(III) and most notably In(III) precursors have attracted a growing interest for application in ROP catalysis of cyclic esters, primarily lactide, and may now be considered as potentially efficient ROP initiators of cyclic esters/carbonates. Despite their higher cost (vs. Al), Ga and In derivatives exhibit key attractive features including: (i) Ga(III) and In(III) are biocompatible metal centers and (ii) their precursors are typically more stable than organoaluminum species in polar media. The present contribution reviews discrete Ga(III) and In(III) compounds thus far developed as ROP initiators of cyclic esters/carbonates. The very few reports on Ga(III)-mediated ROPs of cyclic ethers are also included. In addition to the ROP performances of such species, the synthesis and structural characterization of these initiators are also provided and thoroughly discussed with, whenever appropriate, the establishment of structure/reactivity relationships and mechanistic pathways

Combining NHC bis-Phenolate Ligands with Oxophilic Metal Centers: A Powerful Approach for the Development of Robust and Highly Effective Organometallic Catalysts:

The present paper describes an overview of a novel family of tridentate NHC pincer ligand in which two phenoxide moieties are directly connected to the nitrogen atoms of a central N-heterocyclic carbene. It was envisioned that such a structure might be suitable for coordination to a variety of metal centers across the periodic table, including oxophilic metals. Various metal complexes bearing such ligand are indeed readily accessible in high yields via straightforward routes. Interestingly, a robust zirconium-NHC complex was found to polymerize rac-lactide in a highly controlled, living and stereoselective manner to afford heterotactic PLA

Synthèse et réactivité de nouveaux complexes des métaux du groupe 13 portés par des ligands carbènes N-hétérocycliques

Au début de ces travaux, peu d études avaient été faites sur la complexation des carbènes N-hétérocycliques avec des métaux oxophiles, électropositifs et à hauts degrés d oxydation tel que les métaux du groupe 13. L optimisation de voies de synthèse a permis d étendre le nombre de complexes de types NHC-MIII (M = aluminium, gallium et indium), ainsi qu à des complexes cationiques. L association de ces précurseurs avec des NHCs plus encombrés a permis l observation de réactivités sans précédent (complexes anormaux, paires de Lewis frustrées, dicarbènes N-hétérocycliques). Dans un second temps, la réactivité inhabituelle des ligands NHCs a permis l isolation d analogue au réactif de Tebbe, très actifs en méthylénation de dérivés carbonyles.At the beginning of this work, few studies had been performed on the complexation of N-heterocyclic carbenes with oxophilic metals, in high oxidation states such as group 13 metals. The synthetic routes optimization has extended the number of complexes-type NHC-MIII (M = aluminum, gallium and indium), and the corresponding cationic complexes. The combination of these precursors with sterically congested NHCs allowed the observation of unprecedented reactivities (abnormal complexes, Frustrated Lewis Pairs, N-heterocyclic dicarbenes). In a second step, the unusual reactivity of NHC ligands has allowed the isolation of analogues of the Tebbe s reagent, formed to be very active in the methylenation of carbonyl compounds.STRASBOURG-Bib.electronique 063 (674829902) / SudocSudocFranceF

Synthèse de polyesters et polycarbonates (polymérisation en milieu homogène en vue d'une utilisation en milieu hétérogène permettant le recyclage de l'initiateur de polymérisation)

Depuis une soixantaine d années, les matières plastiques de types polyoléfines (par exemple le polystyrène, le polyéthylène, le polypropylène) ont connu un essor considérable, au point de devenir, avec près de 50 millions de tonnes produites en 2009 en Europe seulement (250 millions de tonnes dans le monde), les matériaux les plus utilisés actuellement. Les polyoléfines sont issues de ressources fossiles non renouvelables (d origine pétrochimique), de plus en plus rares et chères. De plus, ces matériaux posent un problème environnemental, principalement en ce qui concerne leur élimination après utilisation (stockage dans des décharges, pollutions ). En conséquence, les polymères biodégradables et biocompatibles peuvent constituer une alternative viable aux plastiques d origine pétrochimiques et sont déjà utilisés dans des domaines comme l emballage, les outils biomédicaux ou les nanotechnologies. L avantage de ces polymères est de limiter le recours aux énergies fossiles, puisqu ils peuvent être issus de ressources renouvelables (blé, soja, maïs ). Le cycle de vie de ces produits implique une restitution des ressources prélevées via leur biodégradation et les analyses de ce cycle de vie tendent à montrer un impact moindre sur différents facteurs environnementaux (réchauffement climatique, acidification des pluies, nitrification des sols, émission d ozone, etc. ) ainsi qu une utilisation d énergie et un rejet de CO2 inférieurs à ceux des matériaux habituellement utilisés. La faible part de marché de ces matériaux, quoiqu en forte augmentation, est en partie dûe à leur coût, qui reste de cinq à dix fois supérieur à celui des plastiques traditionnels, ainsi qu à leurs plus faibles propriétés de résistances thermique et mécanique. La problématique actuelle est donc de créer des matériaux bon marché aux propriétés physiques améliorées. Les polyesters et polycarbonates aliphatiques ont reçu une attention croissante ces dernières années. Les polyesters/polycarbonates biodégradables mentionnés précédemment peuvent être obtenus via différentes voies, mais la méthode de choix pour effectuer une polymérisation contrôlée (contrôle de la longueur de chaîne et de la tacticité du polymère) est la polymérisation par ouverture de cycle (ROP). Ce travail de thèse s est donc focalisé sur la synthèse de complexes bien définis du groupe 13 pour leur application en tant qu' amorceurs de la ROP contrôlée d esters et de carbonates cycliques.Over the last sixty years, polyolefin-based plastics (for instance polystyrene, polyethylene, polypropylene) have considerably been developed, to become, with nearly 50 millions of tons produced in Europe in 2009 (250 millions of tons in the world), the most used materials today. Polyolefins are made from non renewable fossil resources (petrochemical origin), more and more rare and expensive. Moreover, these materials pose an environmental problem, mostly concerning their elimination after their use (waste storage, pollution ). As a consequence, biodegradable and biocompatible polymers may be a viable alternative to petrochemical-based plastics and are already used in domains such as packaging, biomedical tools or nanotechnologies. The advantages of these polymers are to limit the use of fossil energies, as they may derive from renewable resources (wheat, soybean, corn ). The life cycle of these products involves a restitution of the withdrawn resources via their biodegradation and the analyses of this life cycle show a lower impact on the different environmental factors (global warming, rain acidification, ground nitrification, ozone emission, etc ) and a lower use of energy end CO2 emission than those of the usually used materials. The low use of these materials, although in high increase, is partially due to their cost, which is five to ten times higher to the one of traditional plastics, and to their weaker thermal and mechanical resistances. Today, the problematic is to create unexpensive materials possessing improved physical properties. Aliphatic polyesters and polycarbonates (poly(lactic acid) (PLA), poly(s-caprolactone) (PCL), poly(trimethylene carbonate) (PTMC)) have received increasing attention over the last years. They can be obtained via different ways, but the method of choice to allow a controlled polymerization (controlled chain length and tacticity of the polymer) is the ring-opening polymerization (ROP). This PhD work has focused on the synthesis of well-defined group 13 complexes for their application as initiators for the controlled ROP of cyclic esters and carbonates.STRASBOURG-Bib.electronique 063 (674829902) / SudocSudocFranceF

A Discrete N,O,N-Supported Gallium Amido Complex for the Intermolecular Hydroamination of Terminal Alkynes

The diamino-ether ligand {(C₅H₉)­NH-C₆H₄}₂O (<b>1</b>) was found to readily react with 0.5 equiv of Ga₂(NMe₂)₆ via an amine elimination route to afford the N,O,N-supported Ga amido species {η³-<i>N,O,N</i>-((C₅H₉)­N-C₆H₄)₂O}­GaNMe₂ (<b>2</b>) in a reasonable yield (51%). As determined by X-ray crystallography, the four-coordinate Ga center in <b>2</b> adopts an unusual trigonal-monopyramidal geometry. Compound <b>2</b> effectively catalyzes the hydroamination of terminal alkynes (such as 1-hexyne and phenylacetylene) in the presence of primary amines (aniline and butylamine). Kinetic studies on the latter catalytic reactions suggest that these proceed with a first-order rate dependence on alkyne and on species <b>2</b>. In preliminary studies aiming at the isolation of intermediates relevant to the present catalysis, the dimeric Ga complex [{η²-<i>N,N</i>-((C₅H₉)­N-C₆H₄)₂O}­Ga­(μ-NHPh)]₂ (<b>3</b>) was synthesized by an aminolysis reaction between compound <b>2</b> and aniline; its identity was confirmed by X-ray crystallographic analysis

A Discrete N,O,N-Supported Gallium Amido Complex for the Intermolecular Hydroamination of Terminal Alkynes

The diamino-ether ligand {(C₅H₉)­NH-C₆H₄}₂O (<b>1</b>) was found to readily react with 0.5 equiv of Ga₂(NMe₂)₆ via an amine elimination route to afford the N,O,N-supported Ga amido species {η³-<i>N,O,N</i>-((C₅H₉)­N-C₆H₄)₂O}­GaNMe₂ (<b>2</b>) in a reasonable yield (51%). As determined by X-ray crystallography, the four-coordinate Ga center in <b>2</b> adopts an unusual trigonal-monopyramidal geometry. Compound <b>2</b> effectively catalyzes the hydroamination of terminal alkynes (such as 1-hexyne and phenylacetylene) in the presence of primary amines (aniline and butylamine). Kinetic studies on the latter catalytic reactions suggest that these proceed with a first-order rate dependence on alkyne and on species <b>2</b>. In preliminary studies aiming at the isolation of intermediates relevant to the present catalysis, the dimeric Ga complex [{η²-<i>N,N</i>-((C₅H₉)­N-C₆H₄)₂O}­Ga­(μ-NHPh)]₂ (<b>3</b>) was synthesized by an aminolysis reaction between compound <b>2</b> and aniline; its identity was confirmed by X-ray crystallographic analysis

Metal Complexes as Catalysts/Moderators for Polymerization Reactions

International audienceThis article highlights the most representative results on the use of coordination compounds in polymerization reactions, since the version of the Comprehensive Coordination Chemistry II by Gibson and Marshall (2003). Noteworthy developments of more efficient catalysts and related significant advancements in coordination polymerization of olefins, radical polymerization, lactide and related cyclic esters polymerization and CO2/epoxides polymerization are discussed therei