Cycloalkyl-based unsymmetrical unsaturated (U2)-NHC ligands : flexibility and dissymmetry in ruthenium-catalysed olefin metathesis.

International audienceAir-stable Ru-indenylidene and Hoveyda-type complexes bearing new unsymmetrical unsaturated N-heterocyclic carbene (U2-NHC) ligands combining a mesityl unit and a flexible cycloalkyl moiety as N-substituents were synthesised. Structural features, chemical stabilities and catalytic profiles in olefin metathesis of this new library of cycloalkyl-based U2-NHC Ru complexes were studied and compared with their unsymmetrical saturated NHC-Ru homologues as well as a set of commercially available Ru-catalysts bearing either symmetrical SIMes or IMes NHC ligands

New library of aminosulfonyl-tagged Hoveyda-Grubbs type complexes: Synthesis, kinetic studies and activity in olefin metathesis transformations.

International audienceSeven novel Hoveyda-Grubbs precatalysts bearing an aminosulfonyl function are reported. Kinetic studies indicate an activity enhancement compared to Hoveyda's precatalyst. A selection of these catalysts was investigated with various substrates in ring-closing metathesis of dienes or enynes and cross metathesis. The results demonstrate that these catalysts show a good tolerance to various chemical functions

Microwave-Assisted Ruthenium-Catalysed Olefin Metathesis in Fluorinated Aromatic Hydrocarbons: A Beneficial Combination

International audienceHigh conversions in ruthenium-based olefin metathesis of demanding substrates are commonly forced by using a high loading of a catalyst and conducting reactions at elevated temperature for extended times. However, in many cases this approach is not fully effective. In this article we present that fluorinated aromatic hydrocarbons (FAH) combined with microwave (MW) irradiation using a commercially available ruthenium-based pre-catalyst creates attractive reaction conditions for promoting challenging olefin metathesis transformations

Control of the light-response in supramolecular metallopolymeric gels by tuning the coordination metal

International audienceTwo novel supramolecular metallo-heteropolymers bearing a photo-isomerizable telechelic bis-terpyridine ligand and either Fe(II) or Co(II) coordination metal were synthesized. Both polymers induced gelation of organic solvents at a concentration as low as 0.12 wt% yielding thixotropic gels. Judicious choice of the electronic and photophysical properties of both ditopic ligand and metal ion enabled to achieve control over photomechanical response in supramolecular organogels upon UV light irradiation through molecular design

Terpenic Compounds as Renewable Sources of Raw Materials for Cross-Metathesis

International audienceDihydromyrcenol is used as a hydrated masked form of citronellene in olefin cross-metathesis reactions in order to solve the selectivity problem that results from the presence of two double bonds in many terpenes. Several ruthenium catalysts are evaluated, with the best, M71-SIPr, utilized in the cross-metathesis of dihydromyrcenol with various olefins affording the expected products in good yields. It is shown that the masked double bond can be regenerated via an acid-catalyzed elimination reaction and the product is then subjected to a further cross-metathesis reaction with a second olefin

Latent ruthenium–indenylidene catalysts bearing a N-heterocyclic carbene and a bidentate picolinate ligand

A silver-free methodology was developed for the synthesis of unprecedented N-heterocyclic carbene ruthenium indenylidene complexes bearing a bidentate picolinate ligand. The highly stable (SIPr)(picolinate)RuCl(indenylidene) complex 4a (SIPr = 1,3-bis(2-6-diisopropylphenyl)imidazolidin-2-ylidene) demonstrated excellent latent behaviour in ring closing metathesis (RCM) reaction and could be activated in the presence of a Brønsted acid. The versatility of the catalyst 4a was subsequently demonstrated in RCM, cross-metathesis (CM) and enyne metathesis reactions

Biopolymer-Supported Ionic-Liquid-Phase Ruthenium Catalysts for Olefin Metathesis

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A fast-initiating ionically tagged ruthenium complex: a robust supported pre-catalyst for batch-process and continuous-flow olefin metathesis.

International audienceIn this study, a new pyridinium-tagged Ru complex was designed and anchored onto sulfonated silica, thereby forming a robust and highly active supported olefin-metathesis pre-catalyst for applications under batch and continuous-flow conditions. The involvement of an oxazine-benzylidene ligand allowed the reactivity of the formed Ru pre-catalyst to be efficiently controlled through both steric and electronic activation. The oxazine scaffold facilitated the introduction of the pyridinium tag, thereby affording the corresponding cationic pre-catalyst in good yield. Excellent activities in ring-closing (RCM), cross (CM), and enyne metathesis were observed with only 0.5 mol % loading of the pre-catalyst. When this powerful pre-catalyst was immobilized onto a silica-based cationic-exchange resin, a versatile catalytically active material for batch reactions was generated that also served as fixed-bed material for flow reactors. This system could be reused at 1 mol % loading to afford metathesis products in high purity with very low ruthenium contamination under batch conditions (below 5 ppm). Scavenging procedures for both batch and flow processes were conducted, which led to a lowering of the ruthenium content to as little as one tenth of the original values