Nouveaux complexes salen chiraux polymérisés pour la catalyse asymétrique hétérogène

Nous avons développé une méthode originale d insolubilisation de complexes de type salen chiraux basée sur leur polymérisation par oxydation électrochimique. Ces nouveaux complexes ont été préparés puis électropolymérisés grâce à l introduction de substituants thiophènes sur les positions 5,5 du salen. Les polymères insolubles obtenus ont été testés en tant que catalyseurs asymétriques hétérogènes dans différentes réactions de formation de liaisons carbone-carbone ou carbone-hétéroatome catalysé par des complexes de chrome notamment les réactions d hétéro Diels-Alder, de Henry, d ouverture d époxydes et d addition de diméthylzinc. Ces nouveaux catalyseurs ont conduit à la synthèse des composés ciblés avec de très bons rendements et excès énantiomériques. Ils ont été recyclés jusqu à 20 fois sans perte ni d activité ni d énantiosélectivité prouvant ainsi leur efficacité pour le transfert de chiralité. Deux procédures de recyclage très originales rarement décrites dans la bibliographie ont été testées. L une consiste à modifier le substrat d une même réaction à chaque cycle pour une procédure multi-substrats, l autre consiste à changer de réaction à chaque cycle (procédure multi-réactions). Cette dernière nous a permis de démontrer la robustesse de nos catalyseurs hétérogènes. Nous avons également envisagé la synthèse d analogues obtenus par polycondensation pour laquelle un mélange d oligomères cycliques, de type Calix-Salen a été obtenus. Ces nouveaux catalyseurs ont permis d améliorer l énantiosélectivité des réactions ciblées notamment pour l ouverture des époxydes et confirmé l importance de la morphologie des matériaux et des conditions de polymérisation.The aim of this work was to develop an original methodology to insolubilize chiral salen type chromium complexes based on an oxidative electrochemical polymerization. New complexes were prepared and succesfully electropolymerized thanks to the introduction of thiophen substituents on the 5,5 -positions of the salen moiety. The insoluble polymers obtained as powder by this electrochemical procedure were tested as heterogeneous asymmetric catalysts to promote the formation of different carbon-carbon or carbon-heteroatom bonds by reactions such as hetero Diels-Alder reactions, Henry reactions, ring opening of epoxides and dimethylzinc additions. The targeted products were synthesized with good yields and enantiomeric excesses. It could be recycled more than 20 times without any loss of activity or enantioselectivity. The results proved an efficient transfer of chirality from the catalysts to the products. We also implement original recycling procedures with the same catalyst batch rarely described in the litterature. One involves a change of the substrate structure at each run (multi-substrate procedure), the other one consists in varying the reaction at each recycling run (multi-reaction procedure). This last methodology demonstrates the robustness of the heterogeneous catalyst but also highlighted some mechanistic considerations for transformations. The synthesis of analogous polymeric salen structures was also performed by polycondensation. A mixture of cyclic oligomers of type calixsalen was isolated. Corresponding chromium complexes induced an improved enantioselectivity especially in the ring opening of epoxides and confirmed thus the importance of the morphology of the polymers towards their efficiency.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Chiral salen complexes in polymeric main-chains for heterogeneous asymmetric catalysis - a brief account

International audienceThis brief account summarizes our contribution to the field of heterogeneous asymmetric catalysis with salen complexes. We have developed two different procedures to immobilize these highly efficient catalysts in polymeric main chains for multiple reasons. These heterogenized structures possess indeed solubility properties allowing their easy recovery by simple filtration. Furthermore, by avoiding the use of large either organic or inorganic supports, the introduced catalytic mass does not so much differ from the homogeneous one. Finally, catalytic sites location is precisely controlled, a parameter of major importance for some reactions in which bimetallic activation is needed. Their use and efficiency as insoluble catalysts is here described for the promotion of CO and CC bonds formation, with a specific emphasis on their reusability and cooperativity

Fluorophosphonylated Monomers for Dental Applications

International audienceThe synthesis of acrylate derivatives bearing a difluorophosphonic acid function has been realized by ring-opening reaction of oxacycles and alkylation of fluorinated carbanions. Their use in self-etch adhesives is reported. The resulting adhesives based on difluorophosphonic acid monomers provide significantly higher dentin shear bond strength (SBS) than the one based on phosphonic acid, mainly due to the presence of fluorine atoms

Synthesis and evaluation of new phosphonic, bisphosphonic and difluoromethylphosphonic acid monomers for dental application

International audienceSyntheses of novel 5-(methacryloyloxy)pentylphosphonic acid 1, 5-(methacryloyloxy)pentylidenebisphosphonic acid 2 and 1,1-difluoro-5-(methacryloyloxy)pentylphosphonic acid 3 are described. The ability of these monomers to adhere to hydroxyapatite was demonstrated using 31P CP-MAS NMR spectroscopy. Their copolymerization with N,N′-diethyl-1,3-bis(acrylamido)propane (DEBAAP) was investigated with photo differential scanning calorimetry. These mixtures exhibit a significantly higher reactivity than DEBAAP alone. Bisphosphonic acid 2 was shown to be significantly more reactive than monomers 1 and 3. Adhesive properties of these monomers were also studied. Adhesives based on bisphosphonic acid 2 and difluoromethylphosphonic acid 3 provide significantly higher dentin shear bond strength than the one based on phosphonic acid 1. // New acid monomers 1-3 were successfully prepared for dental applications. The capacity of these monomers to adhere to hydroxyapatite was investigated. Photopolymerization behaviors with N,N′-diethyl-1,3-bis(acrylamido)propane were studied. Bisphosphonic acid 2 exhibited the higher reactivity among the tested monomers. The adhesive properties of monomers 1-3 were evaluated. Primers based on these new monomers were able to generate a strong bond between the tooth substance and a composite. Bisphosphonic acid 2 and difluoromethylphosphonic acid 3 gave the most promising results

Constrained Cyclic β,γ-Diamino Acids from Glutamic Acid: Synthesis of Both Diastereomers and Unexpected Kinetic Resolution

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