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See detailN-heterocyclic carbene catalyzed carba-, sulfa-, and phospha-Michael additions with NHC·CO2 adducts as precatalysts
Hans, Morgan ULg; Delaude, Lionel ULg; Rodriguez, Jean et al

in Journal of Organic Chemistry (2014), 79(6), 2758-2764

N-heterocyclic carbene catalyzed Michael additions have been revisited with 1,3-dialkyl- or 1,3-diarylimidazol(in)ium-2-carboxylates, that is, NHC·CO2 adducts, as the source of the free NHC catalysts in ... [more ▼]

N-heterocyclic carbene catalyzed Michael additions have been revisited with 1,3-dialkyl- or 1,3-diarylimidazol(in)ium-2-carboxylates, that is, NHC·CO2 adducts, as the source of the free NHC catalysts in solution. Using these precatalysts, a number of efficient carba-, sulfa-, and phospha-Michael additions were achieved very conveniently, without the need for an external strong base to generate the NHC by deprotonation of an azolium salt. To further expand the scope of the procedure, some NHC-catalyzed sulfa-Michael/aldol organocascades were also investigated. [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 detailSynthesis and catalytic application of palladium imidazol(in)ium-2- dithiocarboxylate complexes
Champion, Martin J. D.; Solanki, Riten; Delaude, Lionel ULg et al

in Dalton Transactions (2012), 41(40), 12386-12394

The palladium(ii) dimer, [Pd(C,N-C 6H 4CH 2NMe 2)Cl] 2 reacts with two equivalents of the NHC·CS 2 zwitterionic ligands [NHC = IPr (1,3- diisopropylimidazol-2-ylidene), ICy (1,3-dicyclohexylimidazol-2 ... [more ▼]

The palladium(ii) dimer, [Pd(C,N-C 6H 4CH 2NMe 2)Cl] 2 reacts with two equivalents of the NHC·CS 2 zwitterionic ligands [NHC = IPr (1,3- diisopropylimidazol-2-ylidene), ICy (1,3-dicyclohexylimidazol-2-ylidene), IMes (1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), IDip (1,3-bis(2,6- diisopropylphenyl)imidazol-2-ylidene), SIMes (1,3-bis(2,4,6-trimethylphenyl) imidazolin-2-ylidene)] in the presence of NH 4PF 6, to yield the cationic products [Pd(C,N-C 6H 4CH 2NMe 2)(S 2C·NHC)] +. In a similar fashion, the compounds [Pd(C,N-bzq)(S 2C·NHC)] + (bzq = benzo[h]quinolinyl, NHC = ICy, IMes, IDip) are obtained from the corresponding dimer [Pd(C,N-bzq)Cl] 2. The bis(phosphine) compounds [Pd(S 2C·NHC)(PPh 3) 2] 2+ (NHC = ICy, IMes, IDip, SIMes) are obtained on treatment of [PdCl 2(PPh 3) 2] with NHC·CS 2 zwitterions in the presence of NH 4PF 6. The reaction of [PdCl 2(dppf)] with IMes·CS 2 and NH 4PF 6 provides the complex [Pd(S 2C·IMes)(dppf)] 2+. The complexes [Pd(S 2C·NHC)(PPh 3) 2](PF 6) 2 (NHC = IMes, IDip) were active pre-catalysts (1 mol% loading) for the conversion of benzo[h]quinoline to 10-methoxybenzo[h]quinoline in the presence of PhI(OAc) 2 and methanol. The intermediacy of [Pd(C,N-bzq)(S 2C·NHC)] + was supported by the high yield of 10-methoxybenzo[h]quinoline using [Pd(C,N-bzq)(S 2C·IDip)] + to promote the same reaction. Small amounts of 2,10-dimethoxybenzo[h]quinoline were also isolated from these reactions. Using [Pd(C,N-bzq)(S 2C·IDip)] + and N-chlorosuccinimide as the oxidant led to the formation of 10-chlorobenzo[h]quinoline in moderate yield from benzo[h]quinoline. The molecular structures of [Pd(S 2C·IMes)(PPh 3) 2](PF 6) 2 and [Pd(S 2C·IMes) (dppf)](PF 6) 2 were determined crystallographically. [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 detailGold(I) complexes bearing mixed-donor ligands derived from N-heterocyclic carbenes
Chia, Eugene Y; Naeem, Saira; Delaude, Lionel ULg et al

in Dalton Transactions (2011), 40(25), 6645-6658

The new 2-phenylthiocarbamoyl-1,3-dimesitylimidazolium inner salt (IMes•CSNPh) reacts with [AuCl(L)] in the presence of NH4PF6 to yield [(L)Au(SCNPh•IMes)]+ (L = PMe3, PPh3, PCy3, CNBut). The carbene ... [more ▼]

The new 2-phenylthiocarbamoyl-1,3-dimesitylimidazolium inner salt (IMes•CSNPh) reacts with [AuCl(L)] in the presence of NH4PF6 to yield [(L)Au(SCNPh•IMes)]+ (L = PMe3, PPh3, PCy3, CNBut). The carbene-containing precursor [(IDip)AuCl] reacts with IMes•CSNPh under the same conditions to afford the complex [(IDip)Au(SCNPh•IMes)] + (IDip = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene). Treatment of the diphosphine complex [(dppm)(AuCl)2] with one equivalent of IMes•CSNPh yields the digold metallacycle, [(dppm)Au 2(SCNPh•IMes)]2+, while reaction of [L 2(AuCl)2] with two equivalents of IMes•CSNPh results in [(L2){Au(SCNPh•IMes)}2]2+ (L2 = dppb, dppf, or dppa; dppb = 1,4-bis(diphenylphosphino)butane, dppf = 1,1'-bis(diphenylphosphino)ferrocene, dppa = 1,4- bis(diphenylphosphino)acetylene). The homoleptic complex [Au(SCNPh•IMes) 2]+ is formed on reaction of [AuCl(tht)] (tht = tetrahydrothiophene) with two equivalents of the imidazolium-2- phenylthiocarbamoyl ligand. This product reacts with AgOTf to yield the mixed metal compound [AuAg(SCNPh•IMes)2]2+. Over time, the unusual trimetallic complex [Au(AgOTf)2(SCNPh•IMes) 2]+ is formed. The sulfur-oxygen mixed-donor ligands IMes•COS and SIMes•COS (SIMes = 1,3-bis(2,4,6-trimethylphenyl) imidazolin-2-ylidene) were used to prepare [(L)Au(SOC•IMes)]+ and [(L)Au(SOC•SIMes)]+ from [(L)AuCl] (L = PPh3, CNtBu). The bimetallic examples [(dppf){Au(SOC•IMes)} 2]2+ and [(dppf){Au(SOC•SIMes)}2] 2+ were synthesized from the reaction of [(dppf)(AuCl)2] with the appropriate ligand. Reaction of [(tht)AuCl] with one equivalent of IMes•COS or SIMes•COS yields [Au(SOC•IMes) 2]+ and [Au(SOC•SIMes)2]+, respectively. The compounds [(Ph3P)Au(SCNPh•IMes)]PF 6, [(Cy3P)Au(SCNPh•IMes)]PF6 and [Au(AgOTf)2(SCNPh•IMes)2]OTf were characterized crystallographically. [less ▲]

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See detailDithiocarboxylate complexes of ruthenium(II) and osmium(II)
Naeem, Saira; Thompson, Amber L; White, Andrew J P et al

in Dalton Transactions (Cambridge, England : 2003) (2011), 40(14), 3737-3747

The ruthenium(II) complexes [Ru(R)(kappa(2)-S2C center dot IPr)(CO)(PPh3)(2)](+) (R = CH=CHBut, CH CHC6H4Me-4, C(C CPh)=CHPh) are formed on reaction of IPr center dot CS2 with [Ru(R)Cl(CO)(BTD)(PPh3)(2 ... [more ▼]

The ruthenium(II) complexes [Ru(R)(kappa(2)-S2C center dot IPr)(CO)(PPh3)(2)](+) (R = CH=CHBut, CH CHC6H4Me-4, C(C CPh)=CHPh) are formed on reaction of IPr center dot CS2 with [Ru(R)Cl(CO)(BTD)(PPh3)(2)] (BTD = 2,1,3-benzothiadiazole) or [Ru(C(C CPh)=CHPh)Cl(CO)(PPh3)(2)] in the presence of ammonium hexafluorophosphate. Similarly, the complexes [Ru(CH=CHC6H4Me-4)(kappa(2)-S2C center dot ICy)(CO)(PPh3)(2)](+) and [Ru(C(C CPh)=CHPh)(kappa(2)-S2C center dot ICy)(CO)(PPh3)(2)](+) are formed in the same manner when ICy center dot CS2 is employed. The ligand IMes center dot CS2 reacts with [Ru(R)Cl(CO)(BTD)(PPh3)(2)] to form the compounds [Ru(R)(kappa(2)-S2C center dot IMes)(CO)(PPh3)(2)](+) (R = CH=CHBut, CH=CHC6H4Me-4, C(C CPh)=CHPh). Two osmium analogues, [Os(CH CHC(6)H4(M)e-4)(kappa(2)-S2C center dot IMes)(CO)(PPh3)(2)](+) and [Os(C(C CPh)=CHPh)(kappa(2)-S2C center dot IMes)(CO)(PPh3)(2)](+) were also prepared. When the more bulky diisopropylphenyl derivative IDip center dot CS2 is used, an unusual product, [Ru(kappa(2)-SC(H)S(CH= CHC6H4Me-4)center dot IDip)Cl(CO)(PPh3)(2)](+), with a migrated vinyl group, is obtained. Over extended reaction times, [Ru(CH=CHC6H4Me-4)Cl(BTD)(CO)(PPh3)(2)] also reacts with IMes center dot CS2 and NH4PF6 to yield the analogous product [Ru{kappa(2)-SC(H)S(CH=CHC6H4Me-4)center dot IMes}Cl(CO)(PPh3)(2)](+) via the intermediate [Ru(CH=CHC6H4Me-4)(kappa(2)-S2C center dot IMes)(CO)(PPh3)(2)](+). Structural studies are reported for [Ru(CH=CHC6H4Me-4)(kappa(2)-S2C center dot IPr)(CO)(PPh3)(2)]PF6 and [Ru(C(C CPh)=CHPh)(kappa(2)-S2C center dot ICy)(CO)(PPh3)(2)]PF6. [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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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 detailMixed Isobutylphobane/N-Heterocyclic Carbene Ruthenium-Indenylidene Complexes: Synthesis and Catalytic Evaluation in Olefin Metathesis Reactions
Sauvage, Xavier ULg; Zaragoza, Guillermo; Demonceau, Albert ULg et al

in Advanced synthesis & catalysis (2010), 352(11-12), 1934-1948

Two new second generation ruthenium(11) dichloride-indenylidene complexes [RuCl2(9-isobutylphosphabicyclo[3.3.1]nonane)(NHC)(3-phenyl-1-indenylide ne)1, where NHC,3-bis(2,4,6-tri-methylphenyl)imidazolin-2 ... [more ▼]

Two new second generation ruthenium(11) dichloride-indenylidene complexes [RuCl2(9-isobutylphosphabicyclo[3.3.1]nonane)(NHC)(3-phenyl-1-indenylide ne)1, where NHC,3-bis(2,4,6-tri-methylphenyl)imidazolin-2-ylidene (SIMes) or its unsaturated imidazol-2-ylidene analogue (1Mes). were isolated in high yields upon heating a tetrahydrofuran (THF) solution of the diphosphane complex [RuCl2(isobutylphobane)2(3-phenyl-1-indenylidene)] with a two-fold excess of the corresponding imidazol(in)ium-2-carboxylate zwitterions. Both products were characterized by H-1, C-13, and P-33 NMR spectroscopy, and the molecular structure of [RuCl2(isobutylphobane)(SIMes)(3-phenyl-1-indenylidene)] was determined by X-ray diffraction analysis. A close inspection of the packing structure revealed the presence of different types of intra- and intermolecular interactions that enhanced the global stability of the crystals, while low temperature NMR experiments showed the existence of two distinct rotational isomers due to the unsymmetrical nature of the phobane ligand The catalytic activity of both compounds was assessed in olefin metathesis using [less ▲]

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