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International audience; The antioxidant 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) group was covalently introduced into polydicyclopentadiene (PDCPD) through ring-opening metathesis polymerization (ROMP) copolymerization of dicyclopentadiene (DCPD) with a TEMPO-derived norbornene comonomer. The thermal oxidation of the resulting thin films was monitored by ThermoGravimetric Analyses (TGA) and Fourier-Transform Infra-Red spectroscopy (FT-IR). This new PDCPD stabilized by immobilization of the TEMPO antioxidant shows a better thermo-oxidative stability at 60 °C under air than an industrial formulation of PDCPD stabilized with 2,6-di‑tert‑butyl‑4-methylphenol (BHT). Impact of thermal oxidation on mechanical behaviour of both formulations have been studied by tensile tests and fracture tests, based on the essential work of fracture (EWF) concept. The TEMPO-functionalized PDCPD offers a promising alternative to BHT-stabilized PDCPD with comparable ductility but slower decay and better cracking resistance, confirming the benefit of the TEMPO antioxidant in PDCPD formulation when chemically bound to the matrix.

A series of new norbornene monomers containing sterically hindered phenol groups have been synthesized and polymerized via ring-opening metathesis polymerization (ROMP) using the Grubbs 3rd generation catalyst (G3’). ROMPs exhibit first-order kinetics and molar masses increase linearly with monomer conversion and well-controlled phenol hindered-functionalized polynorbornenes were obtained with a monomer to initiator ratio up to 1 000. The first-order rate constants show that the ROMP activity is closely associated with the norbornene monomer steric congestion. The antioxidant behavior of these hindered phenol-containing polynorbornenes with different para-bridged side groups in polypropylene (PP) was estimated by onset oxidation temperature (OOT) measurements. The ability of these hindered phenol-containing norbornenes to copolymerize by ROMP with dicyclopentadiene (DCPD) was used to bound covalently the antioxidant moiety onto a polydicyclopentadiene (PDCPD) resin whose thermal ageing has been investigated. We thank Mireille Barthe and Alexandre Bénard for SEC analyses and Sullivan Bricaud for NMR analyses. We acknowledge finan- cial support from Le Mans University, CNRS, and the French National Research Agency (VRPOM project, ANR-15-CE08-0025).

Polydicyclopentadiene (PDCPD) is a thermoset polymer synthetized from Ring Opening Metathesis Polymerization and produced by Reaction Injection Moulding process. Due to its interesting properties, like short processing times (less than 5 min) and high toughness, this polymer is widely used in commercial and industrial applications. This chapter reports chemical changes that occur in PDCPD during thermal oxidation. A particular attention was paid to the double bond consumption since these latter are associated with crosslinking and subsequent changes in mechanical properties. The final objective of this work is to establish a nonempirical kinetic model for lifetime prediction of PDCPD. For these purposes the thermal degradation of unstabilized PDCPD in the thin film has been investigated in severe conditions (temperatures: 50–120°C; oxygen pressures: 0.02–1 MPa) by FTIR and DSC. These experiments aim at determining the kinetic parameters used in kinetic model. • The initiation rate constants have been identified especially by means of hydroperoxide decomposition. • The termination rate constants have been obtained by specific experiments under various oxygen pressures.

International audience; Thin unstabilized PDCPD film were thermally oxidized in ovens at several temperatures ranging from 50 °C to 120 °C. Hydroperoxide concentration was monitored by DSC. It was observed that hydroperoxides concentration reaches a plateau with short induction times, for example around 8 h at 50 °C. This plateau occurs at very high concentration, around about 1 mol l−1 at 50 °C. In order to study both the chemical mechanisms and the kinetics of hydroperoxides decomposition, oxidized samples were thermally aged in an inert atmosphere to destroy hydroperoxides. For initially high concentrations corresponding to the plateau, it was shown that hydroperoxides decompose following a bimolecular process, the rate constant of which being calculated from the hydroperoxide depletion curves. The comparison of samples containing different polymerization catalyst amounts suggested the co-existence of an unimolecular process. This process mainly occurs at low hydroperoxides concentrations and slightly influences the overall oxidation process.

The in situ thermal oxidation of thin unstabilized polydicyclopentadiene was studied by TGA to monitor mass gain, and DSC to characterize hydroperoxides concentration. Results were discussed using kinetic analysis, which allowed the estimation of activation energies for key reactions of the oxidation process. Activation energy for termination was shown to be higher than in hydrocarbon liquids, which was discussed from the theory of diffusion controlled reactions, and a possible link with local motions associated with sub-glassy transition. Activation energy of thermal decomposition of hydroperoxides was found lower than for model hydroperoxides, suggesting an accelerating effect of organometallic catalysts. Despite those two results that indicate a poor thermal stability of thin pDCPD films, measurements of oxygen diffusivity at several temperatures show that oxidation remains confined in a relatively thin surface layer which would allow the pDCPD properties to be preserved. Projet Carnot "OsMoSe" (2013-2014) et ANR VRPOM (2016-2019)

Advances in design of latent ruthenium phenylindenylidene catalysts bearing salicylaldimine ligands for ring-opening metathesis polymerization are described. The presence of the substituents in ortho position in N-aryl ring of salicylaldimine ligand has been found to be the main factor determining the catalyst stability. The best of the studied catalysts after acid activation offers activity comparable to that of the dichloride systems in ring-opening metathesis polymerization of DCPD, while maintaining very high stability in the monomer solution.

A ruthenium Schiff base catalyst (5), bearing an N-heterocyclic carbene ligand, was found to be a latent catalyst for the ring-opening metathesis polymerization of cis,cis-1,5-cyclooctadiene and dicyclopentadiene and is activated efficiently on addition of hydrochloric acid. A benchmark study was performed using the Grubbs first (1), second (2), and third (3) generation catalyst. Results further illustrate that the catalyst can be stored in dicyclopentadiene at a monomer/catalyst ratio of 15,000/1 without any significant polymerization during at least 12 months. After activation of the catalyst with a Bronsted acid, no undesired loss of performance can be detected. This concept of activation can be easily adapted to a Reaction Injection Molding process, and reaction control is obtained via the in situ generation of the cocatalyst as the outcome of the reaction of alcohols with Lewis acids. Insight into the activation mechanism was gained through an in-depth nuclear magnetic resonance study, and a plausible mechanism is proposed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 302–310, 2010

Kinetics of ring-opening metathesis polymerization (ROMP) of exo , exo -5,6-di(methoxycarbonyl)-7-oxabicyclo[2.2.1]hept-2-ene, promoted by the Grubbs’ 1st generation precatalyst, has been effectively monitored by FT-Raman and NMR spectroscopy. Both techniques evidenced similar monomer conversions to be attained under the same reaction conditions. The present FT-Raman study provided information on the polymer steric configuration, the Raman bands at 1670 and 1677 cm −1 being specifically assigned to stretching vibrations of double bonds from the cis- and trans -polymer, respectively. The trans / cis ratio observed by FT-Raman parallels the corresponding result from 1 H NMR. For the first time, a comparison was made on application of these complementary methods on the same ROMP reaction, evidencing their assets and disadvantages and reliability of FT-Raman.

We here report on the stability and catalytic activity of new indenylidene-Schiff base-ruthenium complexes 3a–f through representative cross-metathesis (CM) and ring-closing metathesis (RCM) reactions. Excellent activity of the new complexes was found for the two selected RCM reactions; prominent conversion was obtained compared to the commercial Hoveyda–Grubbs catalyst 2. Moreover, excellent results were obtained for a standard CM reaction. Higher conversions were achieved with one of the indenylidene catalysts compared with Hoveyda–Grubbs catalyst. Unexpectedly, an isomerization reaction was observed during the CM reaction of allylbenzene. To the best of our knowledge, isomerization reactions in this model CM reaction in closed systems have never been described using first generation catalysts, including the Hoveyda–Grubbs catalyst. The first model CM reactions as well as the RCM reactions have been monitored using 1H NMR. The course of the CM reaction of 3-phenylprop-1-ene (8) and cis-1,4-diacetoxybut-2-ene (9) was monitored by GC. The isomerization reaction was studied by means of GC-mass spectrometry and in situ IR spectroscopy. All catalysts were structurally characterized by means of 1H, 13C, and 31P NMR spectroscopy.

Second-generation catalysts of the general formula Cl2Ru(SIMes)(L)(3-phenylinden-1-ylidene), 3a (L = PCy3), 3b (L = PPh3), 3c (L = py), and Cl2Ru(SIMe)(L)(3-phenylinden-1-ylidene), 4a (L = PCy3), 4b (L = PPh3), 4c (L = py) were found to be of interest in various metathesis transformations. The catalysts containing SIMe ligands showed improved initiation compared to the more robust SIMes substituted catalysts. A strong temperature effect was noted on all of the reactions tested. Interestingly, complex 3a, showing the lowest initiation rate at room temperature, emerged as the most productive of all systems examined at elevated temperature. It is shown that complexes containing the SIMe ligand display higher initiation efficiency than their corresponding SIMes analogues. Since the higher initiation is related to the ease of phosphane dissociation while phosphane dissociation also promotes catalyst decomposition, complexes bearing the SIMe ligand decompose faster. The complete 1H, 13C and 31P resonance assignment and the procedure applied to obtain these from a combination of 1D and 2D NMR techniques, is also reported. Combined with the ROESY technique, these enabled to investigate several conformational processes involving rotations around N–phenyl and C–Ru bonds on the millisecond to second timescale. A clear correlation is demonstrated between the bulkiness of the axial ligand (L) and the rotational freedom of the SIMe(s) ligand. A qualitative analysis also suggests that the extra para-methyl of SIMes leads to additional steric interactions with the 3-phenylinden-1-ylidene ligand. The data reported in this paper demonstrates that substitution patterns of the N-aryl have a significant influence on the activity of the second-generation indenylidene catalysts for a given metathesis reaction.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The paper presents recent work conducted in our group on the synthesis of a novel class of homogeneous and immobilized Ru- complexes containing Schiff bases as O,N-bidentate ligands benefiting from a versatile, quite general and thoroughly exemplified two- step procedure. The new Ru-complexes with improved stability incorporate a variety of Schiff bases, associated with traditional inorganic and organic ligands such as chloride, phosphanes, arenes, cyclodienes, NHC etc., and different carbenes (alkylidene, vinylidene, allenylidene and indenylidene). By a proper choice of the Schiff base, useful physical and chemical properties of the derived Ru- complexes could be induced resulting in tunable catalytic activity for metathesis and related processes. A pertinent example is the latency of selected Schiff base Ru catalysts which by becoming active only under specific conditions (heat or acid activation) are ideal for industrial applications, e.g. reaction injection molding processes. The synthetic approaches that are critically discussed in this artcile have led to a diversity of Ru-complexes of which several members have risen to the rank of commercial catalysts.

[Cd2(phen)2(DPZDA)2(H2O)2] · 8H2O (1) and [Zn(phen)(DPZDA)(H2O)] · 2H2O (2) have been synthesized by reaction of Cd(NO3)2/Zn(NO3)2 with phen and DPZDA (where phen = 1,10-phenanthroline, H2DPZDA = 3,5-dimethyl-2,6-pyrazinedicarboxylic acid) in aqueous ethanol solution. Elemental analysis, IR spectra, thermal analyses and X-ray single crystal diffraction were carried out to determine the composition and crystal structure of 1 and 2. In 1, a 2D supramolecular network containing a novel metal-water decamer were formed by hydrogen bonds. In 2, a 2D supramolecular structure was constructed from hydrogen bonds and π·· · π interactions. Moreover, 1 and 2 displayed photoluminescent properties in the blue range at room temperature.

The synthesis of complexes of the general formula Cl2Ru(SIMes)(L)(3-phenylinden-1-ylidene) (5, L = PCy3; 6, L = py; and 7, L = PPh3) from Cl2Ru(PR3)2(3-phenylinden-1-ylidene) (2a, R = Ph; 2b, R = Cy) is reported. This family of olefin metathesis catalysts was fully characterized (1H, 13C and 31P NMR spectroscopy and elemental analysis) and provided excellent activity in the ring-opening metathesis polymerization of 1,5-cyclooctadiene and the ring-closing metathesis of diethyl diallylmalonate. Comparison with the corresponding benzylidene-containing catalysts, 1a,c and 8b, established the decisive role of the carbene ligand on the procedure of the reaction and led to the observation of an unusual catalytic phenomenon, here called “self-inhibition”.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

A ruthenium based benzylidene complex bearing an O,N-bidentate Schiff base ligand exhibits poor olefin metathesis activity but generates a highly active catalyst system when treated with acidic cocatalysts. Various Lewis acids were able to boost the ring opening metathesis polymerization (ROMP) of cycloocta-1,5-diene (COD). The best results were obtained with trichlorosilane (HSiCl3), which was also found to improve metathesis activity of the Grubbs second generation catalyst [RuCl2( CHPh)(H2IMes)(PCy3)] in the ROMP of COD and the ring closing metathesis (RCM) of diethyl diallylmalonate.

A concise overview is given on mononuclear and dinuclear, bidentate Schiff base ruthenium complexes with different additional ligands and on their applications in various chemical transformations such as Kharasch addition, enol-ester synthesis, alkyne dimerization, olefin metathesis and atom transfer radical polymerization. These new ruthenium complexes, conveniently prepared from commonly available ruthenium compounds, are very stable, exhibit a good tolerance towards organic functionalities, air and moisture and display high activity and chemoselectivity in chemical transformations. Relevant features of coordination chemistry connected with the reaction mechanism and chemoselectivity are also fully described. Since the nature of Schiff bases can be changed in a variety of ways, appealing routes for designing and preparing novel ruthenium complexes can be foreseen in the future.

The synthesis of various Schiff base mononuclear and binuclear ruthenium complexes, whose additional ligands around the metal core have been selected from an array of motifs, is described. These types of ruthenium complexes, conveniently prepared from commonly available ruthenium sources, are rather stable, display good tolerance towards diverse organic functionalities and also to air and moisture. Remarkably, they exhibit a high activity and chemoselectivity in a variety of catalytic processes such as ring-closing metathesis (RCM), Kharasch addition, alkyne dimerization, enol ester synthesis, ring-opening metathesis polymerization (ROMP) and atom-transfer radical polymerization (ATRP). This review covers both homogeneous and heterogeneous hybrid Schiff base-ruthenium complexes.

Olefin metathesis is a versatile synthetic tool for the redistribution of alkylidene fragments at carbon-carbon double bonds. This field, and more specifically the development of task-specific, latent catalysts, attracts emerging industrial and academic interest. This tutorial review aims to provide the reader with a concise overview of early breakthroughs and recent key developments in the endeavor to develop latent olefin metathesis catalysts, and to illustrate their use by prominent examples from the literature.

Olefin metathesis is a versatile synthetic tool for the redistribution of alkylidene fragments at carbon–carbon double bonds. This field, and more specifically the development of task-specific, latent catalysts, attracts emerging industrial and academic interest. This tutorial review aims to provide the reader with a concise overview of early breakthroughs and recent key developments in the endeavor to develop latent olefin metathesis catalysts, and to illustrate their use by prominent examples from the literature.

The synthesis of complexes of the general formula Cl2Ru(SIMes)(L)(3-phenylinden-1-ylidene), 3a (L = PCy3), 3b (L = PPh3), 3c (L = py) and Cl2Ru(SIMe)(L)(3-phenylinden-1-ylidene), 4c (L = PCy3), 4b (L = PPh3), 4c (L = py) from commercially available Cl2Ru(PR3)2(3-phenylinden-1-ylidene), 2a (R = Cy), 2b (R = Ph), is reported, and the summed complexes proved to be useful catalysts for various ring-closing metathesis reactions. The catalytic data reported furthermore demonstrate that the substitution pattern of the N-aryl group has a definite influence on the activity of the second generation indenylidene catalysts for a given metathesis reaction, i.e. catalysts containing the SIMe-ligand showed improved initiation compared to the more robust SIMes substituted catalysts. A strong temperature effect was observed on all of the reactions tested. It is shown that complexes containing the SIMe-ligand display higher initiation efficiency then their corresponding SIMes analogues.

A series of N-heterocyclic carbene (NHC) ligands bearing aliphatic amino side groups were synthesized and reacted with the Grubbs first generation catalyst. Reactions involving symmetrical, aliphatic NHCs did not allow the isolation of any pure NHC substituted complexes due to their instability. Unsymmetrical NHCs having a planar mesityl group on one amino side reacted with Grubbs catalyst in a favorable manner, and the resulting complexes were stable enough to be isolated. X-ray crystallographic analysis demonstrated that the mesityl group is co-planar with the phenyl ring of the benzylidene, which indicates that a π–π interaction between the mesityl arm and the benzylidene moiety might constitute an important structural element. Catalysts substituted with an NHC derived from a primary or secondary amino-group were found to surpass the parent-complex for the ROMP of cycloocta-1,5-diene. The catalyst substituted with an NHC derived from tBu-NH2 was considerably less metathesis active. Also new N-alkyl-N′-(2,6-diisopropylphenyl) heterocyclic carbenes were synthesized. These NHC ligands revealed a different reactivity towards Grubbs complexes than the hitherto reported imidazolinylidenes: (i) facile bis(NHC) coordination was found, and (ii) both NHCs on the bis(NHC) complexes can be exchanged with a phosphine, thereupon regenerating the Grubbs first generation complex. Furthermore, a comparison between the classical Hoveyda–Grubbs complexes and complexes substituted with N-alkyl-N′-(aryl) heterocyclic carbenes demonstrates that the introduction of one aliphatic group into the NHC framework does not improve the catalytic activity in any of the tested metathesis reactions. The introduction of two aliphatic amino side groups enhances the reactivity in the ROMP reaction while the increase of steric interactions lowers the CM activity. The lower activity of the N-alkyl-N′-(2,6-diisopropylphenyl) heterocyclic carbene complexes compared with the N-alkyl-N′-mesityl heterocyclic carbene complexes, may analogously be attributed to a more demanding steric environment. While small differences in donor capacities might cause a significantly different catalytic behavior, it is thus plausible that subtle steric differences exert a more determining influence on the activity of the catalysts. In addition, the obtained results confirm that the NHC's amino side groups play a pivotal role in determining the reactivity, selectivity as well as the stability of the corresponding catalysts.

The NMR conformational study of three asymmetric phenylindenylidene ruthenium complexes 4.1-4.3, is presented. Complete (1)H and (13)C assignments could be obtained for 4.1-4.3 in benzene solution from multiple 2D homonuclear and heteronuclear NMR techniques. Our NMR analysis shows that each complex exists as a 55:45 mixture of two rotational isomers in slow exchange on the NMR chemical shift timescale. They are shown to be related by a 180 degrees flip of the indenylidene ligand along the Ru=CR bond. Both rotational isomers can be discriminated by means of NOEs contacts between the various ligands coordinating to the Ru. By matching these stereospecific assignments to the chemical shift, a chemical shift based fingerprint of the isomers that may allow straightforward assignment of future asymmetric phenylindenylidene ruthenium complexes is proposed.

The paper presents recent work conducted in our group on the synthesis of a novel class of homogeneous and immobilized Ru- complexes containing Schiff bases as O,N-bidentate ligands benefiting from a versatile, quite general and thoroughly exemplified two- step procedure. The new Ru-complexes with improved stability incorporate a variety of Schiff bases, associated with traditional inorganic and organic ligands such as chloride, phosphanes, arenes, cyclodienes, NHC etc., and different carbenes (alkylidene, vinylidene, allenylidene and indenylidene). By a proper choice of the Schiff base, useful physical and chemical properties of the derived Ru- complexes could be induced resulting in tunable catalytic activity for metathesis and related processes. A pertinent example is the latency of selected Schiff base Ru catalysts which by becoming active only under specific conditions (heat or acid activation) are ideal for industrial applications, e.g. reaction injection molding processes. The synthetic approaches that are critically discussed in this artcile have led to a diversity of Ru-complexes of which several members have risen to the rank of commercial catalysts.

Convenient routes for synthesis of ruthenium vinylidene complexes have been described, the majority of which use alkynes along with a ruthenium source as the main starting materials. Their successful application as efficient precatalysts in synthesis of heterocyclic and carbocyclic compounds by ring-closing metathesis of alpha,omega-dienes and in the synthesis of polymers by ring-opening metathesis polymerization of cyclooctene, norbornene, 5-substituted norbornene and dicyclopentadiene are fully illustrated. Relevant aspects concerning the activity and stereoselectivity in metathesis reactions of this type of Ru complexes are highlighted

Herein we describe an improved ruthenium catalyst for the oxidative cyclization of 2-aminobenzylalcohol with ketones, leading to quinolines via a modified Friedlaender synthesis.

A short general introduction combined with some historical milestones in the field of olefin metathesis is presented followed by an overview of recent repre- contributions and overwhelming work invested in intelligent design and innovative synthesis in this area. Despites of recent advances there is still a great interest in the generation of new, better performing, and more environment friendly metathesis.

Herein we describe an improved ruthenium catalyst for the oxidative cyclization of 2-aminobenzylalcohol with ketones, leading to quinolines via a modified Friedlaender synthesis.