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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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See detailMicrowave-Assisted Synthesis of 1,3-Dimesitylimidazolinium Chloride
Hans, Morgan ULg; Delaude, Lionel ULg

in Wipf, Peter (Ed.) Organic Syntheses. Volume 87 (2010)

A procedure for the microwave-assisted synthesis of 1,3-dimesitylimidazolinium chloride on a preparative scale is described starting from simple, commercially available reagents. Prior to a microwave ... [more ▼]

A procedure for the microwave-assisted synthesis of 1,3-dimesitylimidazolinium chloride on a preparative scale is described starting from simple, commercially available reagents. Prior to a microwave-assisted cyclization, it involves the formation of N,N'-dimesitylethane-1,2-diamine dihydrochloride via condensation of glyoxal with two equivalents of mesitylamine, followed by reduction of the intermediate Schiff base with sodium borohydride under acidic conditions. All three steps proceed readily under normal atmosphere. Laboratory grade solvents and reagents taken straight from the bottles do not require any additional purification. The two intermediates and the final product are isolated in high yield and purity by simple filtration and washing and may be used without any further purification for most applications. [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 detailThe Use of Imidazolium-2-dithiocarboxylates in the Formation of Gold(l) Complexes and Gold Nanoparticles
Naeem, Saira; Delaude, Lionel ULg; White, Andrew J. P. et al

in Inorganic Chemistry (2010), 49(4), 1784-1793

The imidazolium-2-dithiocarboxylate ligands IPr.CS2, Mes.CS2, and IDip.CS2 react with [AuCl(PPh3)] to yield [(Ph3P)Au(S2C.IPr))(+), [(Ph3P)Au(S2C.IMes)](+), and [(Ph3P)Au(S2C-IDip)](+), respectively. The ... [more ▼]

The imidazolium-2-dithiocarboxylate ligands IPr.CS2, Mes.CS2, and IDip.CS2 react with [AuCl(PPh3)] to yield [(Ph3P)Au(S2C.IPr))(+), [(Ph3P)Au(S2C.IMes)](+), and [(Ph3P)Au(S2C-IDip)](+), respectively. The compounds [(L)Au(S2C-IMes)](+) are prepared from the reaction of IMes.CS2 with [AuCl(L) (L = PMe3, PCy3, (CNBu)-Bu-t). The carbene-containing precursor [(IDip)AuCl] reacts with IPr.CS2 and IMes.CS2 to afford the complexes [(IDip)Au(S2C.IPr)](+) and [(IDip)Au(S2C.IMes)](+) with two carbene units, one bound to the metal center and the other to the dithiocarboxylate unit. Treatment of the diphosphine-gold complex [(dppm)(AuCl)(2)] with 1 equiv of IMes.CS2 yields [(dppm)Au-2(S2C.IMeS)](2+), while the reaction of [L-2(AuCl)(2)] (L-2 = dppb, dppf) with 2 equiv of IMes.CS2 results in [(L-2){Au(S2C.IMes)}(2)](2+). The homoleptic complexes [Au(S2C.IPr)(2)](2+), [Au(S2C.IMes)(2)](2+), and [Au(S2C.IDiP)(2)](2+) are obtained from the reaction of [AuCl(tht)] with 2 equiv of the appropriate imidazolium-2-dithiocarboxylate ligand. The compounds [(Ph3P)Au(S2C.NHC)](+) (NHC = IMes, IDip) and [(IDip)Au(S2C.NHC)](+) (NHC = IPr, IMes) are characterized crystallographically. The IMes.CS2 ligand is also used to prepare functionalized gold nanoparticles with diameters of 11.5 (+/-1.2) and 2.6 (+/-0.3) nm. [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 detailRecent Advances in Ruthenium Catalysts for Alkene Metathesis
Delaude, Lionel ULg; Demonceau, Albert ULg; Dragutan, Ileana et al

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

Although ruthenium initiators currently available for alkene metathesis are endowed with many beneficial properties, there is still room for improvement and many research groups are actively pursuing the ... [more ▼]

Although ruthenium initiators currently available for alkene metathesis are endowed with many beneficial properties, there is still room for improvement and many research groups are actively pursuing the quest for the next generation of alkene metathesis catalysts. The present contribution aims at providing a critical survey of some of the most significant achievements accomplished toward this goal during the last few years. New ligands and complexes designed to achieve the appropriate balance between electronic and steric properties of the ruthenium active centres are depicted, and their stability, activity, and chemoselectivity are briefly discussed. [less ▲]

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See detailRuthenium—Arene Complexes Derived from NHC∙CO2 and NHC∙CS2 Zwitterionic Adducts and Their Use in Olefin Metathesis
Delaude, Lionel ULg; Demonceau, Albert ULg

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

A range of imidazol(in)ium-2-carboxylates and -dithiocarboxylates bearing alkyl or aryl groups on their nitrogen atoms were prepared by reacting the corresponding N-heterocyclic carbenes (NHCs) with ... [more ▼]

A range of imidazol(in)ium-2-carboxylates and -dithiocarboxylates bearing alkyl or aryl groups on their nitrogen atoms were prepared by reacting the corresponding N-heterocyclic carbenes (NHCs) with either carbon dioxide or carbon disulfide. All the zwitterionic products were characterized by various analytical techniques, including thermogravimetric analysis (TGA). Their ability to act as NHC ligand precursors for in situ catalytic applications was investigated in the ruthenium-promoted ring-opening metathesis polymerization (ROMP) of cyclo-octene. Upon exposure to the [RuCl2(p-cymene)]2 dimer, the NHC CO2 adducts readily dissociated to generate [RuCl2(p-cymene)(NHC)] complexes that were highly active catalyst precursors for olefin metathesis. Conversely, the NHC CS2 betaines retained their zwitterionic nature and led to new cationic complexes of the [RuCl(p-cymene)(NHC CS2)]+PF6 − type that were devoid of any significant catalytic activity in the reaction under consideration [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 detailNon-innocent Behaviour of Dithiocarboxylate Ligands Based on N-Heterocyclic Carbenes
Naeem, Saira; Thompson, Amber L.; Delaude, Lionel ULg et al

in Chemistry : A European Journal (2010), 16(36), 10971-10974

The ruthenium(II) complex [Ru(CH=CHC6H4Me-4)(κ2-S2C•NHC)(CO)(PPh3)2]+ is formed on reaction of NHC•CS2 (NHC = ICy, IMes) with [Ru(CH=CHC6H4Me-4)Cl(CO)(BTD)(PPh3)2] in the presence of NH4PF6, whereas the ... [more ▼]

The ruthenium(II) complex [Ru(CH=CHC6H4Me-4)(κ2-S2C•NHC)(CO)(PPh3)2]+ is formed on reaction of NHC•CS2 (NHC = ICy, IMes) with [Ru(CH=CHC6H4Me-4)Cl(CO)(BTD)(PPh3)2] in the presence of NH4PF6, whereas the analogous reaction with the more bulky IDip•CS2 leads to the remarkable product, [Ru{κ2-SC(H)S(CH=CHC6H4Me-4)•IDip}Cl(CO)(PPh3)2]+. [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 detailExploring new achievements in olefin metathesis catalysts. Part 2 - Compelling innovations in ruthenium complexes
Dragutan, Ileana; Dragutan, Valerian; Delaude, Lionel ULg et al

in Chimica Oggi = Chemistry Today (2009), 27(3), 13-16

This part of the survey introduces recent developments on de novo designed types of ruthenium complexes used as promoters in olefin metathesis reactions. Encompassing diversity-oriented initiators not ... [more ▼]

This part of the survey introduces recent developments on de novo designed types of ruthenium complexes used as promoters in olefin metathesis reactions. Encompassing diversity-oriented initiators not illustrated in Part 1, in this second part of the review emphasis is placed on the leading role played by distinct ligands in an exquisite control of metathesis reactions. [less ▲]

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See detailExploring New Achievements in olefin metathesis catalysts. Part 1 - Highlights on N-heterocyclic carbene ruthenium complexes
Dragutan, Valerian; Dragutan, Ileana; Delaude, Lionel ULg et al

in Chimica Oggi = Chemistry Today (2009), 27(3), 9-12

Most important advances in ruthenium catalysts for olefin metathesis achieved during the last 4 years are briefly reviewed. The first part of the survey focuses on new catalytic precursors endowed with ... [more ▼]

Most important advances in ruthenium catalysts for olefin metathesis achieved during the last 4 years are briefly reviewed. The first part of the survey focuses on new catalytic precursors endowed with inventive N-heterocyclic carbene ligands which have proved highly proficient in a diversity of applications based on metathesis reactions. Part two extends the progress in other types of Ru initiators. [less ▲]

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See detailRuthenium-arene complexes bearing imidazol(in)ium-2-dithiocarboxylate ligands: Evaluation of their catalytic activity in the synthesis of enol esters
Willem, Quentin ULg; Nicks, Francois ULg; Sauvage, Xavier et al

in Journal of Organometallic Chemistry (2009), 694(25), 4049-4055

The catalytic activity of four ruthenium imidazol(in)ium-2-dithiocarboxylates was evaluated for the synthesis of vinyl esters through addition of 4-acetoxybenzoic acid to 1-hexyne, and compared to those ... [more ▼]

The catalytic activity of four ruthenium imidazol(in)ium-2-dithiocarboxylates was evaluated for the synthesis of vinyl esters through addition of 4-acetoxybenzoic acid to 1-hexyne, and compared to those of the parent ruthenium-N-heterocyclic carbene complexes and [RuCl2(p-cymene)(PPh3)] (a standard catalyst). It turned out that ruthenium imidazol(in)ium-2-dithiocarboxylates were poorly active and selective. Quantitative yields, indeed, were obtained only after extended reaction times. However, the catalytic activity could be improved significantly under microwave heating or conventional heating in a sealed tube at 160 degrees C, driving the reaction to completion in less than 4 h of reaction. [less ▲]

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See detailPolymerization of ortho-Substituted Phenylacetylenes with Well-Defined Ruthenium-Alkylidene Catalysts and Related Metathesis Initiators
Katsumata, T.; Shiotsuki, M.; Sanda, F. et al

in Macromolecular Chemistry And Physics (2009), 210(22), 1891-1902

The polymerization of (2-isopropoxyphenyl)acetylene was investigated using a wide range of well-defined ruthenium-alkylidene complexes and related olefin metathesis initiators. In view of its superior ... [more ▼]

The polymerization of (2-isopropoxyphenyl)acetylene was investigated using a wide range of well-defined ruthenium-alkylidene complexes and related olefin metathesis initiators. In view of its superior activity, the second generation Hoveyda-Grubbs catalyst was singled out for further studies. Only phenylacetylenes ortho-substituted with alkoxy, ester, fluoro, and silyl groups afforded polymers with moderate molecular weights. They were characterized by various analytical techniques, and their properties were pared with those of samples prepared using Rh and W initiators. The Ru-based polymers possessed high trans contents and took a helical conformation with predominantly one-handed screw sense when chiral side-chains were present. [less ▲]

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See detailAssessing the Potential of Zwitterionic NHC•CS2 Adducts for Probing the Stereoelectronic Parameters of N-Heterocyclic Carbenes
Delaude, Lionel ULg; Demonceau, Albert ULg; Wouters, Johan

in European Journal Of Inorganic Chemistry (2009), (13), 1882-1891

Five imidazol(in)ium-2-dithiocarboxylates 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-dithiocarboxylates 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 disulfide. They were characterized by IR, UV/Vis, and NMR spectroscopy, and by thermogravimetric analysis. Their molecular structures were determined by X-ray diffraction. For the sake of comparison, tricyclohexylphosphonium dithiocarboxylate was also examined. The data acquired were scrutinized to evaluate their usefulness for assessing the steric and electronic properties of NHC ligands. Because of their outstanding ability to crystallize, the five NHC center dot CS2 betaines were found to be highly suitable for probing the steric influence of nitrogen atom substituents on imidazolylidene-based ligand precursors via XRD analysis, while the corresponding NHC center dot CO2 adducts were deemed more appropriate for evaluating the sigma-donating properties of carbene ligands. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [less ▲]

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