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See detailAssessing the ligand properties of 1,3-dimesitylbenzimidazol-2-ylidene in ruthenium-catalyzed olefin metathesis
Borguet, Yannick ULg; Zaragoza, Guillermo; Demonceau, Albert ULg et al

in Dalton Transactions (2013), 42(20), 7287-7296

The 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 ... [more ▼]

The 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. [less ▲]

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See detailOlefin metathesis as key step in the synthesis of bioactive compounds: Challenges in the total synthesis of (-)-kendomycin
Bicchielli, Dario; Borguet, Yannick ULg; Delaude, Lionel ULg et al

in Current Organic Synthesis (2012), 9(3), 397-405

In this short review article, we highlight the application of the olefin metathesis reaction as a key step in the total synthesis of (-)-kendomycin, a macrocyclic polyketide ansamycin exhibiting ... [more ▼]

In this short review article, we highlight the application of the olefin metathesis reaction as a key step in the total synthesis of (-)-kendomycin, a macrocyclic polyketide ansamycin exhibiting pronounced activity as an endothelin receptor antagonist and antiosteoporotic agent, as well as important antibiotic potency against multiresistant bacteria and remarkable cytotoxicity versus a series of human tumour cell lines. By selecting this example from the recent literature, we hope to illustrate the great synthetic ability of olefin metathesis, while also revealing some problems encountered in the syntheses. © 2012 Bentham Science Publishers. [less ▲]

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See detailAn Unexpected Synthesis of Dihydrophenazines en Route to Benzimidazolium Salts
Borguet, Yannick ULg; Zaragoza, Guillermo; Demonceau, Albert ULg et al

in Advanced Synthesis & Catalysis (2012), 354(7), 1356--1362

The oxidation of various N,N′-diarylbenzene-1,2-diamines bearing bulky aromatic substituents with sodium periodate on wet silica gel afforded a series of five new dihydrophenazines instead of the expected ... [more ▼]

The oxidation of various N,N′-diarylbenzene-1,2-diamines bearing bulky aromatic substituents with sodium periodate on wet silica gel afforded a series of five new dihydrophenazines instead of the expected cyclohexadiene-1,2-diimines. The reaction most likely proceeds via a 1,6-electrocyclic path and provides a convenient access to an important class of nitrogen heterocycles. Subsequent treatment of the mesityl derivative with chloromethyl pivalate and silver triflate led to the corresponding benzimidazolium salt. [less ▲]

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See detailHomobimetallic Ethylene− and Vinylidene−Ruthenium Complexes for ATRP
Borguet, Yannick ULg; Delaude, Lionel ULg; Demonceau, Albert ULg

in Matyjaszewski, Krysztof; Sumerlin, Brent S.; Tsarevsky, Nicolay V. (Eds.) Progress in Controlled Radical Polymerization: Mechanisms and Techniques (2012)

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 ... [more ▼]

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. [less ▲]

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See detailConception et synthèse de nouveaux complexes de ruthénium pour la formation catalytique de liaisons C–C
Borguet, Yannick ULg

Doctoral thesis (2011)

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 ... [more ▼]

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. [less ▲]

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See detailSynthesis and Catalytic Evaluation in Olefin Metathesis of a Second-Generation Homobimetallic Ruthenium-Arene Complex Bearing a Vinylidene Ligand
Borguet, Yannick ULg; Sauvage, Xavier ULg; Zaragoza, Guillermo et al

in Organometallics (2011), 30(10), 2730-2738

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 ... [more ▼]

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. [less ▲]

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See detailRecent Applications of Alkene Metathesis in Fine Chemical Synthesis
Bicchielli, Dario ULg; Borguet, Yannick ULg; Delaude, Lionel ULg et al

in Dragutan, Valerian; Demonceau, Albert; Dragutan, Ileana (Eds.) et al Green Metathesis Chemistry (2010)

During the last decade or so, the emergence of the metathesis reaction in organic synthesis has revolutionised the strategies used for the construction of complex molecular structures. Olefin metathesis ... [more ▼]

During the last decade or so, the emergence of the metathesis reaction in organic synthesis has revolutionised the strategies used for the construction of complex molecular structures. Olefin metathesis is indeed particularly suited for the construction of small open-chain molecules and macrocycles using crossmetathesis and ring-closing metathesis, respectively. These reactions serve, inter alia, as key steps in the synthesis of various agrochemicals and pharmaceuticals such as macrocyclic peptides, cyclic sulfonamides, novel macrolides, or insect pheromones. The present chapter is aiming at illustrating the great synthetic potential of metathesis reactions. Shortcomings, such as the control of olefin geometry and the unpredictable effect of substituents on the reacting olefins, will also be addressed. Examples to be presented include epothilones, amphidinolides, spirofungin A, and archazolid. Synthetic approaches involving silicon-tethered ring-closing metathesis, relay ring-closing metathesis, sequential reactions, domino as well as tandem metathesis reactions will also be illustrated. [less ▲]

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See detailMicrowave-Assisted Olefin Metathesis
Nicks, François; Borguet, Yannick ULg; Sauvage, Xavier et al

in Dragutan, Valerian; Demonceau, Albert; Dragutan, Ileana (Eds.) et al Green Metathesis Chemistry (2010)

Since the first reports on the use of microwave irradiation to accelerate organic chemical transformations, a plethora of papers have been published in this field. In most examples, microwave heating has ... [more ▼]

Since the first reports on the use of microwave irradiation to accelerate organic chemical transformations, a plethora of papers have been published in this field. In most examples, microwave heating has been shown to dramatically reduce reaction times, increase product yields, and enhance product purity by reducing unwanted side reactions compared to conventional heating methods. The present contribution aims at illustrating the advantages of this technology in olefin metathesis and, when data are available, at comparing microwave-heated and conventionally heated experiments. [less ▲]

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See detailHomobimetallic Ruthenium-Arene Complexes Bearing Vinylidene Ligands Synthesis, Characterization, and Catalytic Application in Olefin Metathesis
Borguet, Yannick ULg; Sauvage, Xavier ULg; Zaragoza, Guillermo et al

in Organometallics (2010), 29(24), 6675-6686

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 ... [more ▼]

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 fragment [less ▲]

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See detailMono- and Bimetallic Ruthenium—Arene Catalysts for Olefin Metathesis: A Survey
Borguet, Yannick ULg; Sauvage, Xavier; Demonceau, Albert ULg et al

in Dragutan, Valerian; Demonceau, Albert; Dragutan, Ileana (Eds.) et al Green Metathesis Chemistry (2010)

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 ... [more ▼]

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 units [less ▲]

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See detailTandem catalysis of ring-closing metathesis/atom transfer radical reactions with homobimetallic ruthenium-arene complexes
Borguet, Yannick ULg; Sauvage, Xavier ULg; Zaragoza, Guillermo et al

in Beilstein Journal of Organic Chemistry (2010), 6

The tandem catalysis of ring-closing metathesis/atom transfer radical reactions was investigated with the homobimetallic ruthenium-indenylidene complex [(p-cymene)Ru(mu-Cl)(3)RuCl(3-phenyl-1-indenylidene ... [more ▼]

The tandem catalysis of ring-closing metathesis/atom transfer radical reactions was investigated with the homobimetallic ruthenium-indenylidene complex [(p-cymene)Ru(mu-Cl)(3)RuCl(3-phenyl-1-indenylidene)(PCy3)] (1) to generate active species in situ. The two catalytic processes were first carried out independently in a case study before the whole sequence was optimized and applied to the synthesis of several polyhalogenated bicyclic gamma-lactams and lactones from alpha,omega-diene substrates bearing trihaloacetamide or trichloroacetate functionalities. The individual steps were carefully monitored by H-1 and P-31 NMR spectroscopies in order to understand the intimate details of the catalytic cycles. Polyhalogenated substrates and the ethylene released upon metathesis induced the clean transformation of catalyst precursor 1 into the Ru(II)-Ru(III) mixed-valence compound [(p-cymene) Ru(mu-Cl)(3)RuCl2(PCy3)], which was found to be an efficient promoter for atom transfer radical reactions under the adopted experimental conditions. [less ▲]

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See detailATRP of Methacrylates Catalysed by Homo- and Heterobimetallic Ruthenium Complexes
Borguet, Yannick ULg; Sauvage, Xavier; Bicchielli, Dario ULg et al

in Matyjaszewski, Krzysztof (Ed.) Controlled/Living Radical Polymerization: Progress in ATRP (2009)

The catalytic activity of a series of ruthenium-based homo- and heterobimetallic complexes was determined by investigating the atom transfer radical polymerisation of methyl methacrylate. The complexes ... [more ▼]

The catalytic activity of a series of ruthenium-based homo- and heterobimetallic complexes was determined by investigating the atom transfer radical polymerisation of methyl methacrylate. The complexes under investigation were [(arene)Ru(µ-Cl)3RuCl(C2H4)-(L)] (L = PCy3 or a N-heterocyclic carbene ligand), [(p-cymene)-Ru(µ-Cl)3RuCl(=C=CHR)(PCy3)] (R = Ph or t-Bu), and [RuCl2-(p-cymene){PCy2(CH2)2(eta5-C5H4)TiX2(eta5-C5H5)}] (X = Cl, F, and OBz). The catalytic activity of a variety of related [(p-cymene)-ClRu(µ-Cl)2Ru(O‚^N)(=CHPh)] complexes (O^N is a Schiff base ligand) is also reported. The results clearly demonstrate that the ligands strongly affect the ability of the resulting ruthenium complexes to favour the occurrence of a well-behaved ATRP. [less ▲]

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See detailMicrowave-Assisted Ruthenium-Catalyzed Reactions
Nicks, Francois ULg; Borguet, Yannick ULg; Delfosse, Sebastien et al

in Australian Journal of Chemistry (2009), 62(3), 184-207

Since the first reports on the use of microwave irradiation to accelerate organic chemical transformations, a plethora of papers has been published in this field. In most examples, microwave heating has ... [more ▼]

Since the first reports on the use of microwave irradiation to accelerate organic chemical transformations, a plethora of papers has been published in this field. In most examples, microwave heating has been shown to dramatically reduce reaction times, increase product yields, and enhance product purity by reducing unwanted side reactions compared with conventional heating methods. The present contribution aims at illustrating the advantages of this technology in homogeneous catalysis by ruthenium complexes and, when data are available, at comparing microwave-heated and conventionally heated experiments. Selected examples refer to olefin metathesis, isomerization reactions, 1,3-dipolar cycloadditions, atom transfer radical reactions, transfer hydrogenation reactions, and H/D exchange reactions. [less ▲]

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See detailHomobimetallic Ruthenium Vinylidene, Allenylidene, and Indenylidene Complexes: Synthesis, Characterization, and Catalytic Studies
Sauvage, Xavier ULg; Borguet, Yannick ULg; Zaragoza, Guillermo et al

in Advanced Synthesis & Catalysis (2009), 351(3), 441-455

Four homobimetallic ruthenium-(p-cymene) complexes bearing a tricyclohexylphosphine ligand and polyunsaturated carbon-rich fragments were obtained via a vinylidene-allenylidene-indenylidene cascade ... [more ▼]

Four homobimetallic ruthenium-(p-cymene) complexes bearing a tricyclohexylphosphine ligand and polyunsaturated carbon-rich fragments were obtained via a vinylidene-allenylidene-indenylidene cascade pathway from the ethylene complex [(p-cymene)Ru(mu-Cl)(3)RuCl(PCy3)(eta(2)-C2H4)] (7a). All the products were isolated and fully characterized by IR and NMR spectroscopies. The molecular structure of the indenylidene complex 11 was determined by X-ray crystallographic analysis. The catalytic activity of the four complexes was probed in various types of olefin metathesis reactions and compared with those of a related homobimetallic ruthenium-benzylidene complex, as well as first, second, and third generation monometallic Grubbs catalysts. In the ring-closing metathesis (RCM) of diethyl diallylmalonate, the homobimetallic ruthenium-indenylidene complex 11. outperformed all the ruthenium-benzylidene complexes under investigation and was only slightly less efficient than its monometallic parent. Cross-metathesis experiments with ethylene showed that deactivation of ruthenium-benzylidene or indenylidene complexes was due to the rapid bimolecular decomposition of methylidene active species into ethylene complex 7a. Vinylidene and allenylidene complexes were far less efficient catalyst precursors for ring-opening metathesis polymerization (ROMP) or RCM and remained inert under an ethylene atmosphere. Their catalytic activity was, however, substantially enhanced upon addition of an acidic co-catalyst that most likely promoted their in situ transformation into indenylidene species. Due to its straightforward synthesis and high metathetical activity, homobimetallic ruthenium-indenylidene complex 11 is a valuable intermediate for the preparation of the Hoveyda-Grubbs catalyst [Cl2Ru(PCy3)(=CH-o-O-i-PrC6H4)] via stoichiometric cross-metathesis with 2-isopropoxystyrene. ne procedure did not require any sacrificial phosphine and the transition metal not incorporated into the final product was easily recovered and recycled at the end of the process. [less ▲]

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See detailATRP of methyl methacrylate and styrene catalysed by homobimetallic ruthenium-vinylidene complexes
Bicchielli, Dario ULg; Borguet, Yannick ULg; Sauvage, Xavier ULg et al

in Polymer Preprints (2008)

Styrene and Me methacrylate were subjected to atom transfer radical polymn. using a homobimetallic ruthenium-vinylidene complex (p-cymene)RuCl2/(PCy3)(styrylidene)RuCl2 as catalyst and Et 2 ... [more ▼]

Styrene and Me methacrylate were subjected to atom transfer radical polymn. using a homobimetallic ruthenium-vinylidene complex (p-cymene)RuCl2/(PCy3)(styrylidene)RuCl2 as catalyst and Et 2-bromoisobutyrate (EBiB), 1-phenylethyl bromide, or CCl4 as initiators (in toluene). The polymns. proceeded in a controlled fashion and the polydispersities were quite narrow. Using (EBiB), an induction period was obsd. The polymn. of styrene ceased after 80% conversion because of the degrdn. of the complex into inactive species. With both monomers and CCl4 as initiator, the mol. wt. of the polymers was lower than the calcd. value, i.e., the initiation efficiency was >1. [less ▲]

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See detailATRP of methyl methacrylate catalysed by novel homo- and heterobimetallic ruthenium complexes
Borguet, Yannick ULg; Delfosse, Sebastien; Sauvage, Xavier ULg et al

in Polymer Preprints (2008), 49(2), 24-25

The atom transfer radical polymn. of Me methacrylate was studied in the presence of 6 novel homo- and heterobimetallic Ru complexes: (p-cymene)RuCl2/(PCy3)(ethylene)RuCl2, (p-cymene)RuCl2/(1,3-Mes2-4,5-X2 ... [more ▼]

The atom transfer radical polymn. of Me methacrylate was studied in the presence of 6 novel homo- and heterobimetallic Ru complexes: (p-cymene)RuCl2/(PCy3)(ethylene)RuCl2, (p-cymene)RuCl2/(1,3-Mes2-4,5-X2-imidazolin-2-ylidene)(ethylene)RuCl2 (X = H or Cl, Mes = 2,4,6-trimethylphenyl), and (p-cymene)RuCl2/[(2-dicyclohexylphosphinoethyl)cyclopentadienyl](Cp)TiX2 (X = F, Cl, or OBz). Et 2-bromoisobutyrate was used as initiator in all expts. All catalysts showed high efficiency in controlled synthesis of poly(Me methacrylate). Using the ruthenium/titanocene dibenzoate complex, the polymn. stopped after a few hours of reaction, affording nevertheless a polymer with a decent polydispersity. [less ▲]

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See detailSingle-mode microwave-assisted atom transfer radical polymerization catalyzed by [RuCl2(p-cymene)(PCy3)]
Delfosse, Sebastien; Borguet, Yannick ULg; Delaude, Lionel ULg et al

in Macromolecular Rapid Communications (2007), 28(4), 492-503

In the atom transfer radical polymerization (ATRP) of methyl methacrylate in the presence of [RuCl2(p-cymene)(PCy3)] (p-cymene=4-isopropyltoluene, PCy3=tricyclohexylphosphine), a microwave effect is noted ... [more ▼]

In the atom transfer radical polymerization (ATRP) of methyl methacrylate in the presence of [RuCl2(p-cymene)(PCy3)] (p-cymene=4-isopropyltoluene, PCy3=tricyclohexylphosphine), a microwave effect is noted which strikingly depends on both the temperature and the method used (conventional microwave synthesis (CMS, i.e., without simultaneous cooling) or enhanced microwave synthesis (EMS, with simultaneous cooling)). Thus, between 85 and 120 degrees C under CMS conditions, microwave-assisted polymerizations take place in a controlled fashion, and at 120 degrees C the microwave-assisted polymerization is three times faster than the conventionally heated protocol. However, from 130 degrees C, microwave irradiation has a deleterious effect and the polymerizations are no longer controlled. Likewise, using the EMS method in the temperature range of 85-120 degrees C results in uncontrolled processes, as indicated by the unsuccessful resumption of the polymerizations. These failures might be attributed to a significantly high concentration of radical species, which results in enhanced propagation and termination - mostly disproportionation - rates. [less ▲]

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See detailHomobimetallic ruthenium-N-heterocyclic carbene complexes: Synthesis, characterization, and catalytic applications
Sauvage, Xavier ULg; Borguet, Yannick ULg; Noels, Alfred ULg et al

in Advanced Synthesis & Catalysis (2007), 349(1-2), 255-265

Two new homobimetallic ruthenium-arene complexes [(p-cymene)Ru(mu-Cl)(3)RuCl(eta(2)-C2H4)(L)], where L=1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene (3a) or 1,3-bis(2,4,6-trimethylphenyl)-4,5 ... [more ▼]

Two new homobimetallic ruthenium-arene complexes [(p-cymene)Ru(mu-Cl)(3)RuCl(eta(2)-C2H4)(L)], where L=1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene (3a) or 1,3-bis(2,4,6-trimethylphenyl)-4,5-dichloroimidazolin-2-ylidene (3b), were isolated in high yields upon heating a toluene solution of [RuCl2 (p-cymene)](2) with 1 equivalent of carbene ligand under an ethylene atmosphere. They were characterized by NMR and TGA. Their catalytic activity was investigated in the atom transfer radical polymerization of vinyl monomers. In the polymerization of methyl methacrylate, complex 3a displayed faster reaction rates than 3b and the related phosphine-based complex 2a (L=tricyclohexylphosphine), although control was more effective with the latter catalyst. When n-butyl acrylate or styrene served as monomer, a major shift of reactivity was observed between complex 2a that promoted controlled radical polymerization, and complexes 3a or 3b that favored metathetical coupling. Further homocoupling experiments with various styrene derivatives confirmed the outstanding aptitude of complex 3a (and to a lesser extent of 3b) to catalyze olefin metathesis reactions. Contrary to monometallic ruthenium-arene complexes of the [RuCl2(p-cymene)(L)] type, the new homobimetallic species did not require the addition of a diazo compound or visible light illumination to initiate the ring-opening metathesis of norbornene or cyclooctene. When alpha,omega-dienes were exposed to 3a or 3b, a mixture of cycloisomerization and ring-closing metathesis products was obtained in a non-selective way. Addition of a terminal alkyne co-catalyst enhanced the metathetical activity while completely repressing the cycloisomerization process. Thus, quantitative conversions of diethyl 2,2-diallylmalonate and N,N-diallyltosylamide were achieved within 2 h at room temperature using 2 mol % of catalyst precursor 3 a and 6 mol % of phenylacetylene. [less ▲]

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See detailMicrowave-enhanced ruthenium-catalysed atom transfer radical additions
Borguet, Yannick ULg; Richel, Aurore ULg; Delfosse, Sbastien et al

in Tetrahedron Letters (2007), 48(36), 6334-6338

The first monomode microwave-assisted atom transfer radical additions (ATRA) of carbon tetrachloride to various olefins were successfully performed, affording the adducts with almost quantitative yields ... [more ▼]

The first monomode microwave-assisted atom transfer radical additions (ATRA) of carbon tetrachloride to various olefins were successfully performed, affording the adducts with almost quantitative yields in less than 10 min at 160 'C. (c) 2007 Elsevier Ltd. All rights reserved. [less ▲]

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See detailControlled radical polymerisation of vinyl monomers catalysed by ruthenium N-heterocyclic carbene complexes
Delfosse, Sebastien; Richel, Aurore ULg; Borguet, Yannick ULg et al

in Matyjaszewski, Krzysztof (Ed.) Controlled/living radical polymerization. From synthesis to materials (2005)

N-heterocyclic carbene (NHC)-modified ruthenium catalysts of type [RuCl2(p-cymene)(NHC)] (NHC = substituted 2,3-dihydro-1H-imidazol-2-ylidenes: 1,3-Mes2-4,5-Me2, 1,3-Mes2-4,5-H2, 1,3-Mes2-4,5-Cl2, 1,3-Cy2 ... [more ▼]

N-heterocyclic carbene (NHC)-modified ruthenium catalysts of type [RuCl2(p-cymene)(NHC)] (NHC = substituted 2,3-dihydro-1H-imidazol-2-ylidenes: 1,3-Mes2-4,5-Me2, 1,3-Mes2-4,5-H2, 1,3-Mes2-4,5-Cl2, 1,3-Cy2-4,5-Me2, and 1,3-Cy2-4,5-H2; Mes = mesityl, Cy = cyclohexyl) were prepd. beforehand or in situ by combining the [RuCl2(p-cymene)] dimer with the imidazolium salt in presence of a base (e.g., t-BuOK, Cs2CO3, or Al(OiPr)3). The catalysts were then used in homogeneous atom transfer radical polymns. of Me methacrylate and styrene. The polymn. outcome was studied in dependence of catalyst (substitution pattern) and base. [less ▲]

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