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See detailSynthesis and application of new N-heterocyclic carbene ruthenium complexes in catalysis: A case study
Delaude, Lionel ULg; Demonceau, Albert ULg; Noels, Alfred ULg

in Current Organic Chemistry (2006), 10(2), 203-215

New imidazolium and imidazolinium salts were synthesized and their ability to act as stable N-heterocyclic carbene (NHC) ligand precursors was investigated in various ruthenium-catalyzed processes. Thus ... [more ▼]

New imidazolium and imidazolinium salts were synthesized and their ability to act as stable N-heterocyclic carbene (NHC) ligand precursors was investigated in various ruthenium-catalyzed processes. Thus, 1,3-diarylimidazol(in)ium chlorides bearing the phenyl, 1-naphthyl, 4-biphenyl, 3,5-dimethylphenyl, 2-tolyl, 2,6-dimethylphenyl, 2,4,6-trimethylphenyl (mesityl), and 2,6-diisopropylphenyl substituents were prepared. They were combined with the [RuCl2(p-cymene)](2) dimer and potassium tert-butoxide or sodium hydride to generate the corresponding ruthenium-arene complexes [RuCl2(p-cymene)(NHC)] in situ. The catalytic activity of all these species was investigated in the photoinduced ring-opening metathesis polymerization (ROMP) of norbornene and cyclooctene. Results from this study showed that the C4-C5 double bond in the imidazole ring of the NHC ligands was not crucial to achieve high catalytic efficiencies. The presence or the absence of alkyl groups on the ortho positions of the phenyl rings had a more pronounced influence. Blocking all the ortho positions was a requisite for obtaining efficient catalysts. Failure to do so probably resulted in the ortho-metallation of the carbene ligand, thereby altering the coordination sphere of the ruthenium active centers. Catalytic screenings were also carried out with the various imidazol(in)ium salts to evaluate their ability at promoting the cyclopropanation of styrene and cyclooctene with ethyl diazoacetate. Under the experimental conditions adopted, the exact nature of the N,N'-diaryl groups had very little influence on the outcome of these reactions. The imidazolium salts were further probed as catalyst modifiers for the Atom Transfer Radical Addition (ATRA) of carbon tetrachloride to styrene. Some species displayed a dual activity and promoted both olefin metathesis and ATRA. [less ▲]

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See detailSynthesis of stilbenoids via the Suzuki-Miyaura reaction catalysed by palladium N-heterocyclic carbene complexes
Tudose, Adriana; Maj, Anna M.; Sauvage, Xavier ULg et al

in Journal of Molecular Catalysis A: Chemical (2006), 257(1-2), 158-166

The Suzuki-Miyaura reaction of aryl halides with trans-2-phenylvinylboronic acid using a series of related in situ generated N-heterocyclic carbene palladium(II) complexes was studied in order to evaluate ... [more ▼]

The Suzuki-Miyaura reaction of aryl halides with trans-2-phenylvinylboronic acid using a series of related in situ generated N-heterocyclic carbene palladium(II) complexes was studied in order to evaluate the effect of ligand structure and electronics on the catalytic activity and to investigate the nature of the catalyst species. The nature of the substituents of the carbene ligand was found to be critical. Specifically, the presence of alkyl groups on the ortho positions of the phenyl substituents was a requisite for obtaining the most efficient catalyst systems. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

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See detailThe step-by-step Robinson annulation of chalcone and ethyl acetoacetate - An advanced undergraduate project in organic synthesis and structural analysis
Delaude, Lionel ULg; Grandjean, Jean ULg; Noels, Alfred ULg

in Journal of Chemical Education (2006), 83(8), 1225-1228

The Robinson annulation is a three-step process involving a Michael addition followed by an internal aldol condensation and a dehydration. Under appropriate experimental conditions, it is possible to stop ... [more ▼]

The Robinson annulation is a three-step process involving a Michael addition followed by an internal aldol condensation and a dehydration. Under appropriate experimental conditions, it is possible to stop the reaction after every step and to isolate the three products separately. This feature is particularly attractive in the frame of an organic chemistry course. It allows students to confirm experimentally the validity of the stepwise mechanism and to get a more thorough understanding of the whole process. It also permits them to synthesize a rich set of related molecules that can be compared and characterized through various analytical techniques. Thus, a stoichiometric mixture of chalcone and ethyl acetoacetate was reacted in ethanol. Depending on the quantity of barium hydroxide monohydrate used as catalyst, the reaction time, and the temperature, three different products were obtained. Their full IR, 1H, 13C, COSY, NOESY, and HETCOR NMR spectra are supplied. Examination of the spectroscopic data helps uncover many challenging structural analysis problems. Among them, the diastereoselective formation of chiral centers during the annulation process, the distinction between axial and equatorial substituents on a cyclohexane ring, and the possibility of a keto-enol tautomerism are extensively discussed. [less ▲]

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See detailMicrowave-assisted synthesis of N-heterocyclic carbene precursors
Aidouni, Adila; Demonceau, Albert ULg; Delaude, Lionel ULg

in Synlett (2006), (3), 493-495

A very simple and efficient procedure is reported for the synthesis of 1,3-diarylimidazolinium chlorides by cyclization of N,N'-diarylethylenediamines dihydrochlorides with triethyl ortho-formate under ... [more ▼]

A very simple and efficient procedure is reported for the synthesis of 1,3-diarylimidazolinium chlorides by cyclization of N,N'-diarylethylenediamines dihydrochlorides with triethyl ortho-formate under microwave irradiation. [less ▲]

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See detailImidazol(in)ium-2-carboxylates as N-heterocyclic carbene precursors in ruthenium-arene catalysts for olefin metathesis and cyclopropanation
Tudose, Adriana; Demonceau, Albert ULg; Delaude, Lionel ULg

in Journal of Organometallic Chemistry (2006), 691(24-25), 5356-5365

Five imidazol(in)ium-2-carboxylates bearing cyclohexyl, mesityl, or 2,.6-diisopropylphenyl substituents on their nitrogen atoms were prepared from the corresponding N-heterocyclic carbenes (NHCs) by ... [more ▼]

Five imidazol(in)ium-2-carboxylates bearing cyclohexyl, mesityl, or 2,.6-diisopropylphenyl substituents on their nitrogen atoms were prepared from the corresponding N-heterocyclic carbenes (NHCs) by reaction with carbon dioxide. They were characterized by IR and NMR spectroscopies, and by TGA. Their ability to act as NHC precursors for in situ catalytic applications was probed in ruthenium-promoted olefin metathesis and cyclopropanation reactions. When visible light induced ring-opening metathesis polymerization of cyclooctene or cyclopropanation of styrene with ethyl diazoacetate were carried out at 60 degrees C in the presence of [RuCl2(p-cymene)](2), the NHC (.) CO2 adducts and their NHC (.) HX counterparts (X = Cl, BF4) displayed similar activities. When metathesis polymerizations were performed at room temperature, the carboxylates proved far superior to the corresponding imidazol(in)ium acid salts. They displayed the same level of activity as the preformed RuCl2(p-cymene)(IMes) complex, whereas the combination of NHC (.) HX and KO-t-Bu were almost totally inactive. Results obtained for cyclopropanation reactions at room temperature did not show such a large discrepancy of behavior between the two types of adducts. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

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See detailImidazol(in)ium carboxylates as N-heterocyclic carbene ligand precursors for Suzuki-Miyaura reactions
Tudose, Adriana; Delaude, Lionel ULg; André, Benoît et al

in Tetrahedron Letters (2006), 47(48), 8529-8533

Simple catalysts formed in situ from palladium acetate and a variety of imidazolium and imidazolinium carboxylates and dithiocarboxylates have been screened in the coupling of aryl halides with trans-2 ... [more ▼]

Simple catalysts formed in situ from palladium acetate and a variety of imidazolium and imidazolinium carboxylates and dithiocarboxylates have been screened in the coupling of aryl halides with trans-2-phenylvinylboronic acid. Imidazol(in)ium carboxylates show an excellent activity, which compares to that displayed by the parent imidazol(in)ium chlorides, whereas imidazol(in)ium dithiocarboxylates are poorly efficient. Interestingly, the base employed exerts a profound influence on the trans/cis stereochemistry of the coupling product. (c) 2006 Elsevier Ltd. All rights reserved. [less ▲]

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See detailControlled radical polymerization of vinyl monomers catalyzed by ruthenium N-heterocyclic carbene complexes
Delfosse, Sébastien; Richel, Aurore ULg; Delaude, Lionel ULg et al

in Matyjaszewski, K. (Ed.) Progress in Controlled/Living Radical Polymerization / ACS Symposium Series 944 (2006)

The relative catalytic activities of a series of ruthenium-based complexes of the general formula [RuCl2(p-cymene)(NHC)], [RuCl2(=CHPh)(PR3)(NHC)] and [RuCl2(=CHPh)(NHC)2] (NHC is a N-heterocyclic carbene ... [more ▼]

The relative catalytic activities of a series of ruthenium-based complexes of the general formula [RuCl2(p-cymene)(NHC)], [RuCl2(=CHPh)(PR3)(NHC)] and [RuCl2(=CHPh)(NHC)2] (NHC is a N-heterocyclic carbene ligand) were determined by investigating the atom transfer radical polymerization (ATRP) of methyl mathacrylate and styrene. The catalytic activity of a variety of related [RuCl(O^N)(=CHR)(NHC)] complexes and their cationic couterparts, [Ru(O^N)(=CHR)(NHC)]+BF4- (R = Ph or OEt, O^N is a Schiff base ligand), is also reported. The results clearly demonstrate that, with both methyl methacrylate and styrene, subtle modifications of the substituents of the NHC ligand lead to dramatic changes in the ability of the resulting ruthenium complexes to favor the occurence of a well-behaved ATRP. [less ▲]

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See detailMétathèse des oléfines et réactions radicalaires catalysées par des complexes ruthénium-carbène N-hétérocycliques
Demonceau, Albert ULg; Delfosse, Sébastien; Richel, Aurore ULg et al

Scientific conference (2005, November)

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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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See detailCatalytic applications of transition metal N-heterocyclic carbene complexes bearing nitrogen-containing substituents
Sauvage, Xavier ULg; Tudose, Adriana; Delfosse, Sébastien et al

Poster (2005)

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See detailCatalytic applications of transition metal N-heterocyclic carbene complexes bearing nitrogen-containing substituents
Sauvage, Xavier ULg; Tudose, Adriana; Delfosse, Sébastien et al

Conference (2005)

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See detailStereoselective synthesis of (E)-hydroxystilbenoids by ruthenium-catalyzed cross-metathesis
Ferre-Filmon, Karine; Delaude, Lionel ULg; Demonceau, Albert ULg et al

in European Journal of Organic Chemistry (2005), (15), 3319-3325

An efficient and highly stereoselective synthetic procedure is reported for the construction of symmetrical and unsymmetrical (E)-polymethoxystilbene and (E)-polyhydroxystilbene derivatives. The strategy ... [more ▼]

An efficient and highly stereoselective synthetic procedure is reported for the construction of symmetrical and unsymmetrical (E)-polymethoxystilbene and (E)-polyhydroxystilbene derivatives. The strategy rests on a cross-metathesis reaction catalyzed by stable, well-defined (alkylidene)ruthenium complexes, in particular the second-generation Grubbs catalyst [RuCl2(=CHPh)(SlMes)(PCY3)1 [SIMes = 1,3-bis(2,4,6-trimethylphenyl)imidazolidin-2-ylidene]. The metathesis of unprotected phenolic styrenes is illustrated by the synthesis of the important phytoalexins (E)-3,4',5-trihydroxystilbene (resveratrol) and (E)-3,3',4,5'-tetrahydroxystilbene (piceatannol). (c) Wiley-VCH Verlag GmbH [less ▲]

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See detailControlled radical polymerization of vinyl monomers catalyzed by ruthenium N-heterocyclic carbene complexes
Demonceau, Albert ULg; Delfosse, Sébastien ULg; Richel, Aurore ULg et al

in Abstracts of Papers - American Chemical Society, National Meeting (2005), 230

As part of our program devoted to the development of new metal-NHC catalyst systems, we have launched a detailed investigation on the catalytic activity of ruthenium-p-cymene complexes bearing NHC ligands ... [more ▼]

As part of our program devoted to the development of new metal-NHC catalyst systems, we have launched a detailed investigation on the catalytic activity of ruthenium-p-cymene complexes bearing NHC ligands for the ring opening metathesis polymerization (ROMP) of cyclic olefins and for the ATRP of vinyl monomers. We report herein on the use for ATRP of [RuCl2(p-cymene)(NHC)] complexes generated in situ by combining the [RuCl2(p-cymene)]2 dimer with an imidazolium salt and a base such as potassium tert-butoxide, cesium carbonate or aluminum isopropoxide. [less ▲]

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See detailCatalytic methods for the synthesis of stilbenes with an emphasis on their phytoalexins
Ferre-Filmon, Karine; Delaude, Lionel ULg; Demonceau, Albert ULg et al

in Coordination Chemistry Reviews (2004), 248(21-24), 2323-2336

This review aims at summarizing the recent significant advances in catalytic methods available for the synthesis of stilbene and functionalized stilbenes with an emphasis on their phytoalexins. Most ... [more ▼]

This review aims at summarizing the recent significant advances in catalytic methods available for the synthesis of stilbene and functionalized stilbenes with an emphasis on their phytoalexins. Most strategies developed so far involve palladium-mediated coupling reactions. Among them, the Heck and Suzuki reactions stand out for their synthetic versatility and efficiency, but the Stille and Negishi reactions have also found useful applications. Palladium also served as a catalyst to convert Z-stilbenes into the corresponding E-isomers. Other transition metal promoted stilbene syntheses include the McMurry coupling of aldehydes and ketones and alkene cross metathesis. Because non transition metal catalyzed syntheses of hydroxystilbenes continue to attract a lot of attention, significant recent developments in this area are also reported. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

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See detailRuthenium-promoted radical processes toward fine chemistry
Delaude, Lionel ULg; Demonceau, Albert ULg; Noels, Alfred ULg

in Dixneuf, Pierre Henri; Bruneau, Christian (Eds.) Ruthenium catalysts and fine chemistry (2004)

A review. Ruthenium holds a prominent position among the many transition metals used in radical chem. The dichlorotris(triphenylphosphine) complex [RuCl2(PPh3)3] was the first active ruthenium-based ... [more ▼]

A review. Ruthenium holds a prominent position among the many transition metals used in radical chem. The dichlorotris(triphenylphosphine) complex [RuCl2(PPh3)3] was the first active ruthenium-based catalyst investigated for atom-transfer radical addn. processes and has found numerous applications in org. synthesis. Other catalytic systems that have been devised since include (1) neutral or cationic Grubbs-type complexes bearing an alkylidene fragment and either phosphine, N-heterocyclic carbene, or Schiff base ligands, (2) half-sandwich ruthenium complexes bearing a cyclopentadienyl, a pentamethylcyclopentadienyl, or an indenyl ligand, and (3) ruthenium complexes bearing anionic carborane-phosphine and dicarbollide ligands. Their activities are discussed and the predictive value of cyclic voltammetry in radical chem. is questioned. A related example of a ruthenium-catalyzed C-H hydroxylation reaction is also reported. [less ▲]

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See detailRuthenium N-heterocyclic carbene complexes: Versatile catalysts precursors for olefin metathesis, olefin cyclopropanation, and radical reactions
Demonceau, Albert ULg; Richel, Aurore ULg; Delfosse, Sébastien et al

Conference (2003, August)

N-heterocyclic carbenes are divalent carbon species, which are commonly used as neutral, two-electron ligands with a negligible p-back-bonding tendency. They behave as phosphine mimics, yet they are ... [more ▼]

N-heterocyclic carbenes are divalent carbon species, which are commonly used as neutral, two-electron ligands with a negligible p-back-bonding tendency. They behave as phosphine mimics, yet they are better s-donors and they form stronger bonds to metal centres than most phosphines. Their electronic and steric properties are liable to ample modification simply by varying the substituents on the nitrogen atoms. Therefore, N-heterocyclic carbenes constitute a promising new class of ligands available for catalyst engineering and fine tuning, and a great deal of attention has been paid to them recently. We found that the 18-electron complex RuCl2(p-cymene)(PCy3) was a versatile and efficient promoter for the ring-opening metathesis polymerisation of both strained and low-strain cyclic olefins when activated by a suitable carbene precursor such as trimethylsilyl-diazomethane. RuCl2(p-cymene)(PCy3) was also an excellent catalyst for ATRP (Atom Transfer Radical Polymerisation) of methyl methacrylate and styrene. Here, we present preliminary results obtained in olefin metathesis, olefin cyclopropanation, and radical reactions (ATRP and Kharasch addition) when tricyclohexylphosphine was substituted by an N-heterocyclic ligand. [less ▲]

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See detailDual activity of ruthenium catalysts in controlled radical reactions and olefin metathesis
Delaude, Lionel ULg; Filmon, Karine; Delfosse, Sébastien et al

Conference (2003, May)

The catalytic activity of five ruthenium-arene complexes of the RuCl2(p-cymene)L type was investigated in controlled radical reactions and olefin metathesis. The ligands L were stable Nheterocyclic ... [more ▼]

The catalytic activity of five ruthenium-arene complexes of the RuCl2(p-cymene)L type was investigated in controlled radical reactions and olefin metathesis. The ligands L were stable Nheterocyclic carbenes (NHCs) derived from imidazol-2-ylidene. They differed by the nature of the substituents on the nitrogen atoms (R1) and on the carbon-carbon double bond (R2) of the heterocyclic ring. Thus, R1 was either the mesityl or the cyclohexyl group, and R2 included methyl, hydrogen, or chloro substituents.The complexes were tested as initiators for the Atom Transfer Radical Addition (ATRA) of carbon tetrachloride to methyl methacrylate and styrene, for the Atom Transfer Radical Polymerization (ATRP) of methyl methacrylate and styrene, and for the Ring-Opening Metathesis Polymerization (ROMP) of cyclooctene. Some species displayed a dual activity and promoted both olefin metathesis and ATRP. [less ▲]

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See detailNew ruthenium catalysts bearing N-heterocyclic carbene ligands for ATRP
Sauvage, Xavier ULg; Richel, Aurore ULg; Delfosse, Sébastien et al

Poster (2003, May)

Stable nucleophilic N-heterocyclic carbenes (NHCs) are neutral, two-electron ligands with a negligible p-back-bonding tendency. They behave as phosphine mimics, yet they are better s- donors and they form ... [more ▼]

Stable nucleophilic N-heterocyclic carbenes (NHCs) are neutral, two-electron ligands with a negligible p-back-bonding tendency. They behave as phosphine mimics, yet they are better s- donors and they form stronger bonds to metal centers than most phosphines. Their electronic and steric properties are liable to ample modification simply by varying the substituents on the nitrogen atoms. Therefore, NHCs constitute a promising new class of ligands available for catalyst engineering and fine-tuning. We found that the 18-electron complex RuCl2(p-cymene)(PCy3) was a versatile and efficient promoter for ring-opening metathesis polymerization of both strained and low-strain cyclic olefins when activated by a suitable precursor such as trimethylsilyldiazomethane. This complex was also an excellent catalyst for ATRP (Atom Transfer Radical Polymerization) of MMA and styrene. In this poster, we present preliminary results obtained in olefin metathesis and in radical reactions (ATRP and Kharasch addition) when tricyclohexylphosphine was substituted by an N-heterocylic carbene ligand. [less ▲]

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