Evidence of a type 1/type 2 dichotomy in the correlation between quasar optical polarization and host-galaxy/extended emission position angles

peer reviewedAims.For Seyfert galaxies, the AGN unification model provides a simple and well-established explanation of the type 1/type 2 dichotomy through orientation-based effects. The generalization of this unification model to the higher luminosity AGNs that quasars are remains a key question. The recent detection of type 2 radio-quiet quasars seems to support such an extension. We propose a further test of this scenario. Methods: On the basis of a compilation of quasar host-galaxy position angles consisting of previously published data and of new measurements performed using HST Archive images, we investigate the possible existence of a correlation between the linear polarization position angle and the host-galaxy/extended emission position angle of quasars. Results: We find that the orientation of the rest-frame UV/blue extended emission is correlated to the direction of the quasar polarization. For type 1 quasars, the polarization is aligned with the extended UV/blue emission, while these two quantities are perpendicular in type 2 objects. This result is independent of the quasar radio loudness. We interpret this (anti-)alignment effect in terms of scattering in a two-component polar+equatorial model that applies to both type 1 and type 2 objects. Moreover, the orientation of the polarization -and then of the UV/blue scattered light- does not appear correlated to the major axis of the stellar component of the host-galaxy measured from near-IR images

Two-Dimensional Controlled Syntheses of Polypeptide Molecular Brushes via N-Carboxyanhydride Ring-Opening Polymerization and Ring-Opening Metathesis Polymerization.

Well-defined molecular brushes bearing polypeptides as side chains were prepared by a "grafting through" synthetic strategy with two-dimensional control over the brush molecular architectures. By integrating N-carboxyanhydride ring-opening polymerizations (NCA ROPs) and ring-opening metathesis polymerizations (ROMPs), desirable segment lengths of polypeptide side chains and polynorbornene brush backbones were independently constructed in controlled manners. The N2 flow accelerated NCA ROP was utilized to prepare polypeptide macromonomers with different lengths initiated from a norbornene-based primary amine, and those macromonomers were then polymerized via ROMP. It was found that a mixture of dichloromethane and an ionic liquid were required as the solvent system to allow for construction of molecular brush polymers having densely-grafted peptide chains emanating from a polynorbornene backbone, poly(norbornene-graft-poly(β-benzyl-l-aspartate)) (P(NB-g-PBLA)). Highly efficient postpolymerization modification was achieved by aminolysis of PBLA side chains for facile installment of functional moieties onto the molecular brushes

Design and Synthesis of New Ruthenium Catalysts for the Formation of C – C Bonds

During the last decade, catalytic methods enabling the formation of single and multiple C–C bonds have sparked a major interest from the Chemists community. Among them, olefin metathesis has emerged as a powerful tool, opening unique routes to synthesize organic compounds and polymers. This is mainly due to the advent of well-defined ruthenium–benzylidene complexes first developed by Grubbs and co-workers in the early 1990’s. Since then, countless structural alterations have been made to these archetypal compounds in order to tailor their activity, stability, solubility, . . . However, the synthesis of these derivatives may be tedious and costly since it almost systematically requires the use of the Grubbs 1st generation catalyst as a starting material. Therefore, non-proprietary catalysts with high activity are still eagerly sought. This thesis is mainly focused on the design of straightforward and reliable syntheses of new complexes derived from the homobimetallic molecular scaffold (I) first reported by Severin in 2005. Our first aim was to enhance the catalytic activity of such compounds in olefin metathesis and in controlled radical reactions.formation de liaisons C–C simples et multiples ont suscité un intérêt croissant de la part des chimistes. Parmi ces méthodes, la métathèse des oléfines est apparue comme une technique de choix en synthèse organique et en chimie des polymères. Son avènement est en partie dû aux travaux de R.H. Grubbs et de ses collaborateurs qui ont été les premiers, au milieu des années 1990, à rapporter la synthèse et l’activité d’un complexe ruthénium-alkylidène pour la polymérisation du norbornène. Depuis lors, un travail conséquent a été fourni par de nombreuses équipes de recherche de par le monde pour synthétiser des catalyseurs bien définis possédant des propriétés améliorées (telles que l’activité, la stabilité, la solubilité, . . . ). Le recours au complexe de Grubbs de première génération comme source du fragment Ru–carbène dans ces composés s’avère toutefois problématique en termes de propriété intellectuelle et de coût notamment. Il est donc plus que jamais d’actualité de proposer des alternatives aux complexes classiques ruthénium–benzylidène tout en continuant à améliorer l’activité de ceux-ci. Dans cette thèse, nous avons plus particulièrement développé la chimie des dérivés du complexe homobimétallique de ruthénium I, rapporté pour la première fois par Severin en 2005 et très actif pour les réactions d’addition, de cyclisation et de polymérisation par transfert d’atome (ATRA, ATRC et ATRP, respectivement) ; notre premier objectif étant de mettre au point des synthèses rapides et fiables de complexes dérivés, possédant une activité accrue pour la métathèse des oléfines et les réactions radicalaires contrôlées

Homobimetallic Ethylene− and Vinylidene−Ruthenium Complexes for ATRP

The catalytic activity of a series of homobimetallic ruthenium complexes of the type [(p-cymene)Ru(μ-Cl)3RuCl(L)(L′)] [L = C2H4 or a vinylidene ligand (=C=CHR); L′ = PPh3, PCy3, or an N-heterocyclic carbene ligand] was determined by investigating the atom transfer radical polymerisation of methyl methacrylate. The results clearly demonstrate that the ligands strongly affect the ability of the ruthenium complexes to favour the occurrence of a well-behaved ATRP

Assessing the ligand properties of 1,3-dimesitylbenzimidazol-2-ylidene in ruthenium-catalyzed olefin metathesis

peer reviewedThe deprotonation of 1,3-dimesitylbenzimidazolium tetrafluoroborate with a strong base afforded 1,3-dimesitylbenzimidazol-2-ylidene (BMes), which was further reacted in situ with rhodium or ruthenium complexes to afford three new organometallic products. The compounds [RhCl(COD)(BMes)] (COD is 1,5-cyclooctadiene) and cis-[RhCl(CO)2(BMes)] were used to probe the steric and electronic parameters of BMes. Comparison of the percentage of buried volume (%VBur) and of the Tolman electronic parameter (TEP) of BMes with those determined previously for 1,3-dimesitylimidazol-2-ylidene (IMes) and 1,3-dimesitylimidazolin-2-ylidene (SIMes) revealed that the three N-heterocyclic carbenes (NHCs) had very similar profiles. Nonetheless, changes in the hydrocarbon backbone subtly affected the stereoelectronic properties of these ligands. Accordingly, the corresponding [RuCl2(PCy 3)(NHC)(CHPh)] complexes displayed different catalytic behaviors in the ring-closing metathesis (RCM) of α,ω-dienes. In the benchmark cyclization of diethyl 2,2-diallylmalonate, the new [RuCl2(PCy 3)(BMes)(CHPh)] compound (1d) performed slightly better than the Grubbs second-generation catalyst (1a), which was in turn significantly more active than the related [RuCl2(PCy3)(IMes)(CHPh)] initiator (1b). For the formation of a model trisubstituted cycloolefin, complex 1d ranked in-between catalyst precursors 1a and 1b, whereas in the RCM of tetrasubstituted cycloalkenes it lost its catalytic efficiency much more rapidly

Ruthenium catalysts bearing a benzimidazolylidene ligand for the metathetical ring-closure of tetrasubstituted cycloolefins

Deprotonation of 1,3-di(2-tolyl)benzimidazolium tetrafluoroborate with a strong base afforded 1,3-di(2-tolyl)benzimidazol-2-ylidene (BTol), which dimerized progressively into the corresponding dibenzotetraazafulvalene. The complexes [RhCl(COD)(BTol)] (COD is 1,5-cyclooctadiene) and cis-[RhCl(CO)2(BTol)] were synthesized to probe the steric and electronic parameters of BTol. Comparison of the percentage of buried volume (%VBur) and of the Tolman electronic parameter (TEP) of BTol with those determined previously for 1,3-dimesitylbenzimidazol-2-ylidene (BMes) revealed that the two N-heterocyclic carbenes displayed similar electron donicities, yet the 2-tolyl substituents took a slightly greater share of the rhodium coordination sphere than the mesityl groups, due to a more pronounced tilt. The anti,anti conformation adopted by BTol in the molecular structure of [RhCl(COD)(BTol)] ensured nonetheless a remarkably unhindered access to the metal center, as evidenced by steric maps. Second-generation ruthenium-benzylidene and isopropoxybenzylidene complexes featuring the BTol ligand were obtained via phosphine exchange from the first generation Grubbs and Hoveyda-Grubbs catalysts, respectively. The atropisomerism of the 2-tolyl substituents within [RuCl2([double bond, length as m-dash]CHPh)(PCy3)(BTol)] was investigated by using variable temperature NMR spectroscopy, and the molecular structures of all four possible rotamers of [RuCl2([double bond, length as m-dash]CH-o-OiPrC6H4)(BTol)] were determined by X-ray crystallography. Both complexes were highly active at promoting the ring-closing metathesis (RCM) of model [small alpha],[small omega]-dienes. The replacement of BMes with BTol was particularly beneficial to achieve the ring-closure of tetrasubstituted cycloalkenes. More specifically, the stable isopropoxybenzylidene chelate enabled an almost quantitative RCM of two challenging substrates, viz., diethyl 2,2-bis(2-methylallyl)malonate and N,N-bis(2-methylallyl)tosylamide, within a few hours at 60 °C

Mono- and Bimetallic Ruthenium—Arene Catalysts for Olefin Metathesis: A Survey

In this chapter, we summarize the main achievements of our group toward the development of easily accessible, highly efficient ruthenium—arene catalyst precursors for olefin metathesis. Major advances in this field are presented chronologically, with an emphasis on catalyst design and mechanistic details. The first part of this survey focuses on monometallic complexes with the general formula RuCl2(p-cymene)(L), where L is a phosphine or N-heterocyclic carbene ancillary ligand. In the second part, we disclose recent developments in the synthesis and catalytic applications of homobimetallic ruthenium—arene complexes of generic formula (p-cymene)Ru(μ-Cl)3RuCl(η2-C2H4)(L) and their derivatives resulting from the substitution of the labile ethylene moiety with vinylidene, allenylidene, or indenylidene unit

Homobimetallic Ruthenium-Arene Complexes Bearing Vinylidene Ligands Synthesis, Characterization, and Catalytic Application in Olefin Metathesis

Five new arylvinylidene complexes with substituents ranging from electron donating to strongly withdrawing (p OMe p Me p Cl p CF3 and m (CF3)(2)) were isolated in high yields by reacting [(p cymene)Ru(mu Cl)(3)RuCl(eta(2) C2H4)(PCy3)] (3) with the corresponding phenylacetylene derivatives The known phenylvinylidene complex [(p cymene)Ru(mu Cl)(3)RuCl(=C=CHPh)(PCy3)] (5) was also obtained from [RuCl2(p cymene)](2) tricyclohexylphosphine and phenylacetylene under microwave irradiation The influence of the remote aryl substituents on structural features was investigated by IR NMR and XRD spectroscopes A very good linear relationship was observed between the chemical shift of the vinylidene alpha carbon atom and the Hammett sigma constants of the aryl group substituents The catalytic activity of the six homobimetallic complexes was probed in various types of olefin metathesis reactions Unsubstituted phenylvinylidene compound 5 served as a lead structure for these experiments Its reaction with norbornene afforded high molecular weight polymers with a broad polydispersity index and mostly trans double bonds Aluminum chloride was a suitable cocatalyst for the ring opening metathesis polymerization of cyclooctene and led to the formation of high molecular weight polyoctenamer with a rather narrow polydispersity index (M-w/M-n = 1 25) and an almost equimolar proportion of cis and trans double bonds No major changes were observed in the polymer yields and microstructures when complexes bearing donor groups on their aryl rings were employed as catalyst precursors On the other hand compounds bearing strongly electron withdrawing substituents were significantly less active Model vinylidene compound 5 and its ruthenium-ethylene parent (3) both required the addition of phenylacetylene to achieve the ring closing metathesis of diethyl 2 2 diallylmalonate Thus the role of this terminal alkyne cocatalyst goes beyond the facile replacement of the eta(2) alkene ligand with a vinylidene fragmen

Synthesis and Catalytic Evaluation in Olefin Metathesis of a Second-Generation Homobimetallic Ruthenium-Arene Complex Bearing a Vinylidene Ligand

The new homobimetallic ruthenium–vinylidene complex [(p-cymene)Ru(μ-Cl)3RuCl(═C═CHPh)(IMes)] (6) was isolated in high yield upon treatment of [(p-cymene)Ru(μ-Cl)3RuCl(η2-C2H4)(IMes)] (5) with a slight excess of phenylacetylene at −50 °C. Although it was very stable under normal atmosphere in the solid state, this product underwent an oxidative cleavage into the corresponding carbonyl compound [(p-cymene)Ru(μ-Cl)3RuCl(CO)(IMes)] (7) when dissolved in oxygen-containing solvents. Second-generation complexes 6 and 7 were characterized by IR and NMR spectroscopies, and their molecular structures were determined by X-ray diffraction analysis. The catalytic activity of complex 6 was probed in various types of olefin metathesis reactions. Compared to its first-generation analogue [(p-cymene)Ru(μ-Cl)3RuCl(═C═CHPh)(PCy3)], the new ruthenium initiator displayed an enhanced activity. It was also much more selective than ruthenium–ethylene complex 5. Aluminum chloride was a valuable cocatalyst for the ROMP of cyclooctene, whereas phenylacetylene was better suited to achieve the fast and quantitative RCM of α,ω-dienes into the corresponding di- or trisubstituted cycloolefins. The role of the terminal alkyne was rationalized by assuming that it would allow an enyne metathesis to take place, thereby transforming saturated vinylidene precursor 6 into a highly active mono- or bimetallic ruthenium–alkylidene species

New Insights into the Quasar Type 1/Type 2 Dichotomy from Correlations between Quasar Host Orientation and Polarization

We investigate correlations between the direction of the optical linear polarization and the orientation of the host galaxy/extended emission for type 1 and type 2 radio-loud and radio-quiet quasars. We have used high resolution Hubble Space Telescope data and a deconvolution process to obtain a good determination of the host galaxy/extended emission (EE) position angle. With these new measurements and a compilation of data from the literature, we find a significant correlation, different for type 1 and type 2 objects, between the linear polarization position angle and the orientation of the EE, suggesting scattering by an extended UV/blue region in both types of objects. Our observations support the extension of the Unification Model to the higher luminosity AGNs like the quasars, assuming a two component scattering model