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See detailProbing the Diastereoselectivity of Staudinger Reactions Catalyzed by N-Heterocyclic Carbenes
Hans, Morgan ULg; Wouters, Johan; Demonceau, Albert ULg et al

in Chemistry : A European Journal (2015), 21(30), 10870-10877

The reaction of ethylphenylketene with 1,3-dimesitylimidazol-2-ylidene (IMes) or 1,3-dimesitylimidazolin-2-ylidene (SIMes) afforded the corresponding azolium enolates in high yields. The two zwitterions ... [more ▼]

The reaction of ethylphenylketene with 1,3-dimesitylimidazol-2-ylidene (IMes) or 1,3-dimesitylimidazolin-2-ylidene (SIMes) afforded the corresponding azolium enolates in high yields. The two zwitterions were fully characterized by various analytical techniques. Their thermal stabilities were monitored by thermogravimetric analysis and the molecular structure of SIMes.EtPhC=C=O was determined by means of X-ray crystallography. A mechanism was proposed to account for the trans-diastereoselectivity observed in the [2+2] cycloaddition of ketenes and N-protected imines catalyzed by N-heterocyclic carbenes and an extensive catalytic screening was performed to test its validity. The steric bulk of the NHC catalyst markedly affected the cis/trans ratio of the model β-lactam product. The nature of the solvent used to carry out the Staudinger reaction also significantly influenced its diastereoselectivity. Conversely, the nature of the substituent on the N-sulfonated imine reagent and the reaction temperature were less critical parameters. [less ▲]

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See detailRuthenium–arene catalysts bearing N-heterocyclic carbene ligands for olefin cyclopropanation and metathesis
Méret, M.; Maj, A. M.; Demonceau, Albert ULg et al

in Monatshefte für Chemie = Chemical Monthly (2015), 146(7), 1099-1105

Abstract: Ruthenium–arene complexes bearing N-heterocyclic carbene (NHC) ligands with the generic formula [RuCl2(p-cymene)(NHC)] are efficient catalyst precursors for the cyclopropanation of activated ... [more ▼]

Abstract: Ruthenium–arene complexes bearing N-heterocyclic carbene (NHC) ligands with the generic formula [RuCl2(p-cymene)(NHC)] are efficient catalyst precursors for the cyclopropanation of activated olefins with ethyl diazoacetate, and the cis/trans diastereoselectivity of the reaction markedly depends on the steric bulk of the NHC. The procedure was successfully applied to styrene, α-methylstyrene, and various other styrenic derivatives bearing electron-withdrawing or donating substituents on their aromatic rings. The reaction of unactivated internal or terminal alkenes was more sluggish, and the use of norbornene as a substrate afforded only olefin metathesis. Further investigation of the ring-opening metathesis polymerization of this strained cycloolefin in the presence of trimethylsilyldiazomethane led to high molecular weight polynorbornene whose microstructure was not significantly affected by the choice of the NHC ancillary ligand. [less ▲]

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See detailRuthenium catalysts bearing a benzimidazolylidene ligand for the metathetical ring-closure of tetrasubstituted cycloolefins
Borguet, Yannick; Zaragoza, Guillermo; Demonceau, Albert ULg et al

in Dalton Transactions (2015), 44

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 ... [more ▼]

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. [less ▲]

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See detailAssessment of catalysis by arene-ruthenium complexes
Le Gendre, Pierre; Borguet, Yannick; Nicks, François et al

in European Journal of Inorganic Chemistry (2015)

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See detailA new and efficient one-pot synthesis of 2-hydroxy-1,4-dihydrobenzoxazines via a three-component Petasis reaction
Chouguiat, Louisa; Boulcina, Raouf; Carboni, Bertrand et al

in Tetrahedron Letters (2014), 55

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See detailSynthesis of Castanospermine and Epimers by Metathesis Routes
Dragutan, Ileana; Dragutan, Valerian; Demonceau, Albert ULg et al

in Current Organic Chemistry (2013), 17(22), 2719-2737

This article provides a fairly comprehensive overview on olefin metathesis reactions applied as pivotal steps in the total syntheses of indolizidine alkaloids belonging to the families of castanospermine ... [more ▼]

This article provides a fairly comprehensive overview on olefin metathesis reactions applied as pivotal steps in the total syntheses of indolizidine alkaloids belonging to the families of castanospermine, deoxycastanospermine and diastereomers thereof, natural or non-natural compounds that play multiple roles in biological processes. A well-balanced mixture of topics is proposed, covering most relevant traits of their biological activity, therapeutic applications, and structural similarities to, or differences from, other established iminosugar drugs. While mainly focussing on a critical discussion of the metathesis-based processes (RCM, CM, RRM), their promoters and conditions, their advantages and limitations, also shown is how metathesis has contributed to more efficient and shorter protocols for accessing this important class of antiviral, antitumor, antimetastatic, anti-inflammatory and immunoregulating agents. [less ▲]

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See detailSelected Recent Advances in the Synthesis of Bioactive Compounds Using Olefin Metathesis as a Key Step
Dassonneville, Benjamin ULg; Delaude, Lionel ULg; Demonceau, Albert ULg et al

in Current Organic Chemistry (2013), 17(22), 2609-2653

Synthesis of biologically active compounds is of paramount importance to the biomedical sciences for the development of novel therapeutic agents. Such substances often feature various types of unique and ... [more ▼]

Synthesis of biologically active compounds is of paramount importance to the biomedical sciences for the development of novel therapeutic agents. Such substances often feature various types of unique and complex structures, which make them challenging targets for synthetic efforts. Their total synthesis offers the chance to implement the use of newly developed, efficient and highly selective synthetic procedures and/or strategies in a complex environment. In this respect, thanks to the development of increasingly efficient molybdenum and ruthenium catalysts, olefin metathesis is now an integral part of modern synthetic methods. This review article will highlight with selected examples from the recent literature assets and limitations of the olefin metathesis reaction in the synthesis of biologically active compounds. [less ▲]

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See detailEnabling Access to Diverse Bioactive Molecules Through Enyne Metathesis Concepts
Dragutan, Ileana; Dragutan, Valerian; Demonceau, Albert ULg et al

in Current Organic Chemistry (2013), 17(22), 2678-2720

This paper surveys recent advances in valorization of transition-metal-catalyzed enyne metathesis as key events in the total synthesis of naturally occurring compounds of biological and medicinal ... [more ▼]

This paper surveys recent advances in valorization of transition-metal-catalyzed enyne metathesis as key events in the total synthesis of naturally occurring compounds of biological and medicinal importance. Special attention is devoted to methodologies based on dienyne ring-closing metathesis (RCM) applied in tandem and sequential processes, on relay ring-closing metathesis (RRCM), ring-rearrangement metathesis (RRM), enyne cross-metathesis (CM) and enyne skeletal bond reorganization, all proceeding under metalcarbenes (Ru or Mo alkylidenes) or metal-salts (Pd or Pt) catalysis. The high potential of these procedures in constructing versatile scaffolds as essential structural cores of a diversity of bioactive natural products is highlighted. Inventive functionalizations by non-metathesis transformations intervening in the total synthesis of the targeted natural compounds, prior to (Michael addition, Wittig olefination, allylation etc.) or after (Diels-Alder cycloaddion, Heck and Suzuki-Miyaura reactions, Dess-Martin oxidation, dihydroxylation, epoxidation etc.) the pivotal metathesis step have also been included. [less ▲]

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See detailMechanistic Insight into the Staudinger Reaction Catalyzed by N-Heterocyclic Carbenes
Hans, Morgan ULg; Wouters, J.; Demonceau, Albert ULg et al

in Chemistry : A European Journal (2013), 19(19), 9668-9676

Four zwitterions were prepared by treating 1,3-dimesitylimidazolin-2-ylidene (SIMes) or 1,3-dimesitylimidazol-2-ylidene (IMes) with either N-tosyl benzaldimine or diphenylketene. They were isolated in ... [more ▼]

Four zwitterions were prepared by treating 1,3-dimesitylimidazolin-2-ylidene (SIMes) or 1,3-dimesitylimidazol-2-ylidene (IMes) with either N-tosyl benzaldimine or diphenylketene. They were isolated in high yields and characterized by IR and NMR spectroscopy. The molecular structures of three of them were determined by using X-ray crystallography and their thermal stability was monitored by using thermogravimetric analysis. The imidazol(in)ium-2-amides were rather labile white solids that did not show any tendency to tautomerize into the corresponding 1,2,2-triaminoethene derivatives. They displayed a mediocre catalytic activity in the Staudinger reaction of N-tosyl benzaldimine with diphenylketene. In contrast, the imidazol(in)ium-2-enolates were orange-red crystalline materials that remained stable over extended periods of time. Despite their greater stability, these zwitterions turned out to be efficient promoters for the model cycloaddition under scrutiny. As a matter of fact, their catalytic activity matched those recorded with the free carbenes. Altogether, these results provide strong experimental insight into the mechanism of the Staudinger reaction catalyzed by N-heterocyclic carbenes. They also highlight the superior catalytic activity of the imidazole-based carbene IMes compared with its saturated analogue SIMes in the reaction under consideration. [less ▲]

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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 detailOlefin metathesis as key step in the synthesis of bioactive compounds: Challenges in the total synthesis of irioteolides
Demonceau, Albert ULg; Dragutan, I.; Dragutan, V. et al

in Current Organic Synthesis (2012), 9

Iriomoteolides are novel macrolides possessing either a unique 15-membered or a 20-membered macrocycle, and displaying exceedingly potent cytotoxicity with IC50 values of up to 2 ng/mL. Thus far, over a ... [more ▼]

Iriomoteolides are novel macrolides possessing either a unique 15-membered or a 20-membered macrocycle, and displaying exceedingly potent cytotoxicity with IC50 values of up to 2 ng/mL. Thus far, over a period of about four years, ten research groups worldwide have published their synthetic efforts resulting in four total syntheses of iriomoteolides and a few diastereomers thereof, and a number of fragment and macrocyclic core syntheses. Interestingly, three total syntheses involved ring-closing metathesis as the key step for the construction of the macrocycle, whereas the synthesis of three fragments was accomplished using a cross-metathesis reaction. Herein we highlight assets and limitations of the olefin metathesis reaction in the synthesis of the title compounds. [less ▲]

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See detailRetracing the evolution of monometallic ruthenium-arene catalysts for C-C bond formation
Delaude, Lionel ULg; Demonceau, Albert ULg

in Dalton Transactions (2012), 41(31), 9257-9268

Preformed or in situ generated monometallic ruthenium-arene complexes with the generic formula RuX2(arene)(L) (L = phosphine or N-heterocyclic carbene) are versatile and efficient catalyst precursors for ... [more ▼]

Preformed or in situ generated monometallic ruthenium-arene complexes with the generic formula RuX2(arene)(L) (L = phosphine or N-heterocyclic carbene) are versatile and efficient catalyst precursors for olefin metathesis and atom transfer radical reactions. Their synthesis is usually accomplished using simple and straightforward experimental procedures starting from the [RuCl2(p-cymene)]2 dimer. This article retraces their evolution over the past 20 years and highlights similarities and differences with the parallel development of well-defined RuX2(CHR)(L1)(L2) ruthenium-alkylidene catalysts. [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 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 detailSynthesis and organocatalytic applications of imidazol(in)ium-2- thiocarboxylates
Hans, Morgan ULg; Wouters, Johan; Demonceau, Albert ULg et al

in European Journal of Organic Chemistry (2011), (35), 7083-7091

Five imidazol(in)ium-2-thiocarboxylates bearing cyclohexyl, mesityl, or 2,6-diisopropylphenyl substituents on their nitrogen atoms were prepared from the corresponding imidazol(in)ium chlorides or ... [more ▼]

Five imidazol(in)ium-2-thiocarboxylates bearing cyclohexyl, mesityl, or 2,6-diisopropylphenyl substituents on their nitrogen atoms were prepared from the corresponding imidazol(in)ium chlorides or tetrafluoroborates in a one-pot, two-step procedure involving the in situ generation of free N-heterocyclic carbenes (NHCs) with a strong base followed by trapping with carbonyl sulfide. The resulting NHC•COS zwitterions were isolated in high yields and characterized by IR and NMR spectroscopy. The molecular structure of SIMes•COS was determined by X-ray diffraction analysis. Experimental data and DFT calculations indicated that the negative charge on the thiocarboxylate anion is preferentially delocalized on the sulfur atom. Thermogravimetric analysis showed that the NHC•COS zwitterions undergo thermolysis at temperatures ranging between 110 and 180 °C in the solid state. They are also rather labile in solution. Unlike the related NHC•CS2 betaines, which are highly stable, crystalline materials, they displayed the same type of behavior as the analogous carboxylate adducts, which readily lose their CO2 moiety upon heating or dissolution. Thus, imidazol(in)ium-2-thiocarboxylates acted as convenient NHC precursors in two model organocatalytic transformations. Of the five thiocarboxylates examined, ICy•COS was the most efficient at promoting the acylation of benzyl alcohol with vinyl acetate, whereas SIMes•COS afforded the highest activity in benzoin condensation. [less ▲]

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See detailSynthesis and Catalytic Evaluation of Ruthenium-Arene Complexes Bearing Imidazol(in)ium-2-thiocarboxylate Ligands
Hans, Morgan ULg; Willem, Quentin ULg; Wouters, Johan et al

in Organometallics (2011), 30(22), 6133-6142

Five new complexes with the generic formula [RuCl(2)(p-cymene)(SOC.NHC)] (2-6) were isolated in high yields by reacting the [RuCl(2)(p-cymene)](2) dimer with a range of imidazol(in)ium-2-thiocarboxylate ... [more ▼]

Five new complexes with the generic formula [RuCl(2)(p-cymene)(SOC.NHC)] (2-6) were isolated in high yields by reacting the [RuCl(2)(p-cymene)](2) dimer with a range of imidazol(in)ium-2-thiocarboxylate zwitterions bearing cyclohexyl, 2,4,6-trimethylphenyl (mesityl), or 2,6-diisopropylphenyl groups on their nitrogen atoms in CH(2)Cl(2) at -20 degrees C. All the products were fully characterized by IR and NMR spectroscopy, and the molecular structures of [RuCl(2)(p-cymene)(SOC.IMes)] (3) and [RuCl(2)(p-cymene)(SOC.SIMes)] (5) were determined by X-ray diffraction analysis. Coordination of the NHC.COS ligands took place via the sulfur atom. A remarkable shielding of the methine proton on the p-cymene isopropyl group was observed by (1)H NMR spectroscopy for complexes 3-6. It is most likely caused by the aromatic ring current of a neighboring mesityl or 2,6-diisopropylphenyl substituent. The catalytic activity of compounds 2-6 was probed in the ring-opening metathesis polymerization (ROMP) of cyclooctene, in the atom transfer radical polymerization (ATRP) of methyl methacrylate, and in the synthesis of enol esters from 1-hexyne and 4-acetoxybenzoic acid. In all these reactions, the [RuCl(2)(p-cymene)(SOC.NHC)] complexes displayed performances slightly inferior to those exhibited by [RuCl(2)(p-cymene)(NHC)] species that result from the reaction of [RuCl(2)(p-cymene)](2) with NHC.CO(2) inner salts. However, they were significantly better catalyst precursors than the much more robust chelates of the [RuCl(p-cymene)(S(2)C.NHC)PF(6) type obtained by coordination of NHC.CS(2) betaines to the ruthenium dimer. These results suggest that the Ru-(SOC.NHC) motif undergoes a dethiocarboxylation under the experimental conditions adopted for the catalytic tests and leads to the same elusive Ru-NHC active species as the preformed [RuCl(2)(p-cymene)-(NHC)] family of complexes. [less ▲]

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See detailChapter 7 NHC-Iron, Ruthenium and Osmium Complexes in Catalysis
Delaude, Lionel ULg; Demonceau, Albert ULg

in Diez-Gonzalez, Silvia (Ed.) N-Heterocyclic Carbenes (2011)

In this Chapter, the catalytic applications of organometallic species -either pre-formed or generated in situ- based on Group 8 transition metals and N-heterocyclic carbene (NHC) ligands are surveyed ... [more ▼]

In this Chapter, the catalytic applications of organometallic species -either pre-formed or generated in situ- based on Group 8 transition metals and N-heterocyclic carbene (NHC) ligands are surveyed. Thus far, only a few reports on the use of NHC-Fe complexes in organic catalysis are available, although significant work has been reported in the related field of biocatalysis. Contrastingly, the chemistry of NHC-Ru complexes has reached an unprecedented level of maturity, thanks to the relentless research efforts thrown into the development of olefin metathesis catalysts. Other carbon skeletal transformations based on NHC-Ru promoters include cyclopropanation, allylation, or cycloisomerisation reactions. Lastly, with only two reports to date concerning olefin metathesis and transfer hydrogenation, NHC-Os-based catalysis can hardly be considered anything else than a curiosity. [less ▲]

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See detailMetathesis access to monocyclic iminocyclitol-based therapeutic agents
Dragutan, Ileana; Dragutan, Valerian; Mitan, Carmen et al

in Beilstein Journal Of Organic Chemistry (2011), 7

By focusing on recent developments on natural and non-natural azasugars (iminocyclitols), this review bolsters the case for the role of olefin metathesis reactions (RCM, CM) as key transformations in the ... [more ▼]

By focusing on recent developments on natural and non-natural azasugars (iminocyclitols), this review bolsters the case for the role of olefin metathesis reactions (RCM, CM) as key transformations in the multistep syntheses of pyrrolidine-, piperidine-and azepane-based iminocyclitols, as important therapeutic agents against a range of common diseases and as tools for studying metabolic disorders. Considerable improvements brought about by introduction of one or more metathesis steps are outlined, with emphasis on the exquisite steric control and atom-economical outcome of the overall process. The comparative performance of several established metathesis catalysts is also highlighted. [less ▲]

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