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Stoeckli-Evans, Helen

Nom
Stoeckli-Evans, Helen
Affiliation principale
Email
helen.stoeckli-evans@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/470

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  • Publication
    Accès libre
    Tri- and Tetranuclear Mixed-Metal Clusters Containing Alkyne Ligands : Synthesis and Structure of [Ru3Ir(CO)11(RCCR’)]-, [Ru2Ir(CO)9(RCCR’)]-, and [HRu2Ir(CO)9(RCCR’)]
    (1999)
    Ferrand, Vincent
    ;
    Süss-Fink, Georg 
    ;
    Neels, Antonia
    ;
    Stoeckli-Evans, Helen 
    The tetrahedral cluster anion [Ru3Ir(CO)13]- (1) reacts with internal alkynes RCCR to afford the alkyne derivatives [Ru3Ir(CO)11(RCCR)]- (2: R = R’ = Ph; 3: R = R’ = Et; 4: R = Ph; R’ = Me; 5: R = R’ = Me) which have a butterfly arrangement of the Ru3Ir skeleton in which the alkyne is coordinated in a μ4-η2 fashion. Under CO pressure they undergo fragmentation to give the trinuclear cluster anions [Ru2Ir(CO)9 (RCCR)]- (6: R = R’ = Ph; 7: R = R’ = Et; 8: R’ = Ph; R’ = Me; 9: R = R’ = Me), in which the alkyne ligand is coordinated in a μ3-η2 parallel fashion. Protonation of these trinuclear anions leads to the formation of the corresponding neutral hydrido clusters [HRu2Ir(CO)9 (RCCR)] (10: R = R’ = Ph; 11: R = R’ = Et; 12: R = Ph; R’ = Me; 13: R = R’ = Me). The protonation of the butterfly anions 2 and 3, however, gives rise to the formation of the neutral tetrahedral clusters [HRu3Ir(CO)11(RCCR)] (14: R = R’ = Ph and 15: R = R’ = Et), respectively. The analogous clusters [HRu3Ir(CO)11(PhCCCH3)] (16) and [HRu3Ir(CO)11(CH3CCCH3)] (17) are only accessible from the reaction of the neutral cluster [HRu3Ir(CO)13] with the corresponding alkynes. The complexes 2, 4, 5, 6, 10, 12 and 15 are characterised by X-ray structure analysis.
  • Publication
    Accès libre
    Triruthenium–iridium clusters containing alkyne ligands : synthesis, structure, and catalytic implications of [(µ-H)IrRu3(CO)11(µ3-η2-PhC≡CPh)] and [IrRu3(CO)10(µ4-η2-PhC≡CPh)(µ-η2-PhC=CHPh)]
    (1998)
    Ferrand, Vincent
    ;
    Süss-Fink, Georg 
    ;
    Neels, Antonia
    ;
    Stoeckli-Evans, Helen 
    The mixed-metal cluster [HIrRu3(CO)13] 1 reacts with one equivalent of disubstituted alkynes RC≡CR to give [HIrRu3(CO)11(µ3-η2-RC≡CR)] (R = Ph 2; R = Me 3), with a second equivalent of the alkyne the clusters [IrRu3(CO)10(µ4-η2-RC≡CR)(µ-η2-RC=CHR)] (R = Ph 4; R = Me 5) are obtained. The single-crystal X-ray structure analyses of 2 and 3 show these clusters to have a tetrahedral Ru3Ir framework containing the alkyne ligand coordinated in a parallel fashion over the Ru3 face of the metal skeleton. In contrast, the clusters 4 and 5 consist of a butterfly arrangement of the Ru3Ir framework with the alkyne ligand coordinated to all four metal atoms, giving an overall octahedral Ru3IrC2 skeleton, as demonstrated by the single-crystal structure analysis of 4. Cluster 1 is an excellent catalyst for the hydrogenation of diphenylacetylene to give stilbene (catalytic turnover number 990 within 15 min), clusters 2 and 4 are also catalytically active but seem to represent side-channels of the catalytic cycle.
  • Publication
    Accès libre
    Application of the Novel Tandem Process Diels-Alder Reaction/Ireland-Claisen Rearrangement to the Synthesis of rac-Juvabione and rac-Epijuvabione
    (2000)
    Soldermann, Nicolas
    ;
    Velker, Joerg
    ;
    Vallat, Olivier
    ;
    Stoeckli-Evans, Helen 
    ;
    Neier, Reinhard 
    The novel tandem process Diels-Alder reaction/Ireland-Claisen rearrangement shows a high diastereoselectivity for the Ireland-Claisen rearrangement starting from the endo-product of the Diels-Alder reaction. Based on this mechanistic knowledge, the novel tandem process could be applied to the synthesis of rac-juvabione.
  • Publication
    Accès libre
    Mono and oligonuclear vanadium complexes as catalysts for alkane oxidation : synthesis, molecular structure, and catalytic potential
    (2004-01-30)
    Süss-Fink, Georg 
    ;
    Gonzalez Cuervo, Laura
    ;
    Therrien, Bruno 
    ;
    Stoeckli-Evans, Helen 
    ;
    Shul’pin, Georgiy B.
    A series of mono- and oligonuclear vanadium(V) and vanadium(IV) complexes containing various chelating N,O-, N3-, and O2-ligands have been prepared. The biphasic reaction of an aqueous solution of ammonium vanadate and a dichloromethane solution of hexamethylphosphoramide (hmpa) and pyrazine-2-carboxylic acid (pcaH) or pyrazine-2,5-dicarboxylic acid (pdcaH2) or pyridine-2,5-dicarboxylic acid (pycaH2) yields yellow crystals of [VO2 (pca)(hmpa)] (1), [(VO2)2(pdca)(hmpa)2] (2), and [VO2(pycaH)(hmpa)] (3), respectively. The single-crystal X-ray structure analyses reveal 1 and 3 to be mononuclear vanadium(V) complexes, in which a VO2 unit coordinates to one nitrogen and one oxygen atom of a pca or pycaH chelating ligand, and 2 to be a dinuclear vanadium(V) complex, in which two VO2 units are coordinated through one nitrogen and one oxygen atom of a pdca bridging ligand; in the three complexes the vanadium atoms also coordinate to the oxygen atom of a hmpa ligand. The reaction of N,N,N′,N′-tetrakis(2-benzimidazolylmethyl)-2-hydroxo-1,3-diaminopropane (hptbH) and VOSO4 in methanol gives the cationic complex [(VO)4(hptb) 2(μ-O)]4+ (4), which can be crystallized as the perchlorate salt. In this tetranuclear complex, two dinuclear vanadium(IV) units are held together by a μ-oxo bridge. The known complex [VOCl2 (tmtacn)] (5) was synthesized from the reaction of 1,4,7-trimethyl-1,4,7-triazacyclononane (tmtacn) and VCl3 in acetonitrile; the reaction of tetrabutylammonium vanadate with pyro-cathecol (catH2) in acetonitrile gives the known anionic complex [V(cat)3]− (6), in which the vanadium(V) center is bonded to three cat chelating ligands through the oxygen atoms, obtained as the tetrabutylammonium salt. All compounds synthesized are highly efficient oxidation catalysts for the reaction of cyclohexane with air and hydrogen peroxide in the presence of four equivalents of pcaH per vanadium, although the catalytic activity of the complexes containing bulky chelating ligands 4 and 5 is somewhat lower in the initial period of the reaction. During this period the active species are formed from the complexes and final turnover numbers are high. The catecholate ligands of complex 6 may reduce from V(V) to V(IV) in the beginning of the process, thus providing very high initial oxidation rates.
  • Publication
    Accès libre
    The mixed-metal carbonyl cluster anion [Ru3Ir(CO)13]– : synthesis, molecular structure, fluxionality, reactivity
    (1997)
    Süss-Fink, Georg 
    ;
    Haak, Susanne
    ;
    Ferrand, Vincent
    ;
    Stoeckli-Evans, Helen 
    The new cluster anion [Ru3Ir(CO)13]–1 was synthesized in high yield from [Ru3(CO)12] and [Ir(CO)4]–. The single-crystal X-ray structure analysis of the bis(triphenylphosphoranylidene)ammonium salt revealed the presence of two isomers, [Ru3Ir(CO)11(µ-CO)2]–1a and Ru3Ir(CO)9(µ-CO)4]–1b in the same crystal. Both 1a and 1b present a tetrahedral Ru3Ir framework, differing only by the number of bridging carbonyl ligands. Variable-temperature 13C NMR spectroscopic studies of 1 revealed the fluxionality of the carbonyl ligands and the interconversion of both isomers in solution. Protonation of 1 gave the neutral cluster [HRu3Ir(CO)13] 2, whereas reaction of 1 with molecular hydrogen yielded the anion [H2Ru3Ir(CO)12]–3. Either hydrogenation of 2 or protonation of 3 gave [H3Ru3Ir(CO)12] 4. The tetrahedral structure of the hydrido derivatives was confirmed by a single-crystal X-ray structure analysis of the bis(triphenylphosphoranylidene)ammonium salt of 3.
  • Publication
    Accès libre
    Three-dimensional bimetallic octacyanidometalates [MIV{(μ-CN)4MnII (H2O)2}2•4H2O]n (M = Nb, Mo, W): Synthesis, single-crystal X-ray diffraction and magnetism
    (2008)
    Herrera, Juan Manuel
    ;
    Franz, Patrick
    ;
    Podgajny, Robert
    ;
    Pilkington, Melanie
    ;
    Biner, Margret
    ;
    Decurtins, Silvio
    ;
    Stoeckli-Evans, Helen 
    ;
    Neels, Antonia
    ;
    Garde, Raquel
    ;
    Dromzée, Yves
    ;
    Julve, Miguel
    ;
    Sieclucka, Barbara
    ;
    Hashimoto, Kazuhito
    ;
    Okhoshi, Shin-ichi
    ;
    Verdaguer, Michel
    Nous présentons la synthèse et les propriétés structurales et magnétiques de trois nouveaux composés tridimensionnels isostructuraux, synthétisés à partir des précurseurs octacyanométallates [MIV (CN)8]−4: [MIV{(μ-CN) 4MnII (H2O)2}2•4H2O]n [MIV = NbIV (1), MoIV (2), WIV (3)]. Pour le composé 1, les propriétés magnétiques montrent l'existence d'une phase ferrimagnétique en dessous de 50 K. Par contre, les propriétés magnétiques de 2 et 3 correspondent à celles de deux ions MnII magnétiquement isolés. La seule différence électronique dans les deux types des composés est la présence de deux électrons appariés dans les ions MoIV (2) et WIV (3) (configuration électronique d2, S = 0) ce qui rend impossible une interaction d'échange avec le spin des ions MnII voisins (configuration électronique d5, S = 5/2) et d'un électron célibataire dans l'ion NbIV (1) (d1, S = 1/2) qui donne naissance à des interactions d'échange antiferromagnétiques NbIV–MnII et à l'apparition d'un ordre magnétique tridimensionnel sous la température de Curie. Ces trois composés montrent comment un électron célibataire, stratégiquement situé, peut changer de façon dramatique les propriétés magnétiques des composés par ailleurs isostructuraux., We report the synthesis, the single-crystal X-ray crystallographic structures and the magnetic properties of three new isostructural cyanido-bridged networks: [MIV{(μ-CN) 4MnII (H2O)2}2•4H2O]n [MIV = NbIV (1), MoIV (2), WIV (3)]. For compound 1, the magnetic properties reveal a ferrimagnetic phase below 50 K. In contrast, compounds 2 and 3 show a paramagnetic behaviour with no magnetic ordering down to 2 K. The only electronic difference between the two kinds of compounds is the presence of two paired electrons on MoIV (2) and WIV (3) (d2 electronic configuration, S = 0) with no possible exchange interactions with MnII ions (d5 electronic configuration, S = 5/2) and one unpaired electron on NbIV (1) (d1, S = 1/2) which allows NbIV–MnII antiferromagnetic exchange interactions and the onset of a three-dimensional magnetic ordering under Curie temperature. These three compounds demonstrate how one unpaired electron, well located, can dramatically change the magnetic behaviour of isostructural octacyanido-based three-dimensional networks.
  • Publication
    Accès libre
    Oxidation of alkanes with m-chloroperbenzoic acid catalyzed by iron(III) chloride and a polydentate amine
    (2004)
    Shul’pin, Georgiy B.
    ;
    Stoeckli-Evans, Helen 
    ;
    Mandelli, Dalmo
    ;
    Kozlov, Yuriy N.
    ;
    Tesouro Vallina, Ana
    ;
    Woitiski, Camile B.
    ;
    Jimenez, Ricardo S.
    ;
    Carvalho, Wagner A.
    Tetradentate amine N,N′-bis(2-pyridylmethylene)-1,4-diaminodiphenyl ether (compound 1) dramatically accelerates the oxidation of alkanes with MCPBA in acetonitrile catalyzed by FeCl3, whereas N,N′-bis(2-pyrrolidinmethylene)-1,4-diaminodiphenyl ether (2) does not affect the reaction. The selectivity of the reaction in the presence of 1 is noticeably higher than that in its absence. On the basis of the kinetic study and selectivity parameters a mechanism has been proposed which includes the formation of a complex between a molecule of MCPBA and coordinated to ligand 1 iron ion. This complex decomposes to produce a Fe(II) derivative which is further oxidized by MCPBA to generate a (1•Fe=O)4+ species reacting with both alkane and acetonitrile. Finally, alkyl hydroperoxide is formed which partially decomposes to produce more stable corresponding alcohol and ketone (aldehyde).
  • Publication
    Accès libre
    4,4-Bis(1H-pyrrol-2-yl)pentanol
    (2010)
    Journot, Guillaume 
    ;
    Neier, Reinhard 
    ;
    Stoeckli-Evans, Helen 
    The title achiral compound, C13H18N2O, crystallized in the chiral monoclinic space group P21. The pyrrole rings are inclined to one another by 62.30 (11)°, and the propanol chain is in an extended conformation. In the crystal, the two pyrrole NH groups are involved in intermolecular N-H ··· O hydrogen bonds, leading to the formation of a helical arrangement propagating along the b axis. An interesting feature of the crystal structure is the absence of any conventional hydrogen bonds involving the hydroxy H atom. There is, however, a weak intermolecular O-H ··· π interaction involving one of the pyrrole rings.
  • Publication
    Accès libre
    Water-Soluble Arene Ruthenium Complexes Containing a trans-1,2-Diaminocyclohexane Ligand as Enantioselective Transfer Hydrogenation Catalysts in Aqueous Solution
    (2005)
    Canivet, Jérôme
    ;
    Labat, Gael
    ;
    Stoeckli-Evans, Helen 
    ;
    Süss-Fink, Georg 
    The cationic chloro complexes [(arene)Ru(H2N∩NH2)Cl]+ (1: arene = C6H6; 2: arene = p-MeC6H4iPr; 3: arene = C6Me6) have been synthesised from the corresponding arene ruthenium dichloride dimers and enantiopure (R,R or S,S) trans-1,2-diaminocyclohexane (H2N∩NH2) and isolated as the chloride salts. The compounds are all water-soluble and, in the case of the hexamethylbenzene derivative 3, the aqua complex formed upon hydrolysis [(C6Me6)Ru(H2N∩NH2)OH2]2+ (4) could be isolated as the tetrafluoroborate salt. The molecular structures of 3 and 4 have been determined by single-crystal X-ray diffraction analyses of [(C6Me6)Ru(H2N∩NH2)Cl]Cl and [(C6Me6)Ru(H2N∩NH2)OH2][BF4]2. Treatment of [Ru2 (arene) 2Cl4] with the monotosylated trans-1,2-diaminocyclohexane derivative (TsHN∩NH2) does not yield the expected cationic complexes, analogous to 1-3 but the neutral deprotonated complexes [(arene)Ru(TsN∩NH2)Cl] (5: arene = C6H6; 6: arene = p-MeC6H4iPr; 7: arene = C6Me6; 8: arene = C6H5COOMe). Hydrolysis of the chloro complex 7 in aqueous solution gave, upon precipitation of silver chloride, the corresponding monocationic aqua complex [(C6Me6)Ru(TsHN∩NH2)(OH2)]+ (9) which was isolated and characterised as its tetrafluoroborate salt. The enantiopure complexes 1-9 have been employed as catalysts for the transfer hydrogenation of acetophenone in aqueous solution using sodium formate and water as a hydrogen source. The best results were obtained (60 °C) with 7, giving a catalytic turnover frequency of 43 h-1 and an enantiomeric excess of 93 %.