Sebastian Schebesta

Friedrich-Schiller-University Jena, Jena, Thuringia, Germany

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Publications (7)13.19 Total impact

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    ABSTRACT: Syntheses and Structures of Bis(4,4′-t-butyl-2,2′-bipyridine) Ruthenium(II) Complexes with functional Derivatives of Tetramethyl-bibenzimidazole[(tbbpy)2RuCl2] reacts with dinitro-tetramethylbibenzimidazole (A) in DMF to form the complex [(tbbpy)2Ru(A)](PF6)2 (1a) (tbbpy: bis(4,4′-t-butyl)-2,2′bipyridine). Exchange of the two PF6− anions by a mixture of tetrafluor-terephthalat/tetrafluor-terephthalic acid results in the formation of 1b in which an extended hydrogen-bonded network is formed. According to the 1H NMR spectra and X-ray analyses of both 1a and 1b, the two nitro groups of the bibenzimidazole ligand are situated at the periphery of the complex in cis position to each other. Reduction of the nitro groups in 1a with SnCl2/HCl results in the corresponding diamino complex 2 which is a useful starting product for further functionalization reactions. Substitution of the two amino groups in 2 by bromide or iodide viaSandmeyer reaction results in the crystalline complexes [(tbbpy)2Ru(C)](PF6)2 and [(tbbpy)2Ru(D)](PF6)2 (C: dibromo-tetrabibenzimidazole, D: diiodo-tetrabibenzimidazole). Furthermore, 2 readily reacts with 4-t-butyl-salicylaldehyde or pyridine-2-carbaldehyde under formation of the corresponding Schiff base RuII complexes 5 and 6. 1H NMR spectra show that the substituents (NH2, Br, I, azomethines) in 2 - 6 are also situated in peripheral positions, cis to each other. The solid state structure of both 2, and 3, determined by X-ray analyses confirm this structure. In addition, the X-ray diffraction analyses of single crystals of the complexes [(tri-t-butyl-terpy)(Cl)Ru(A)] (7) and [(A)PtCl2] (8) display also that the nitro groups in these complexes are in a cis-arrangement.
    Zeitschrift für anorganische Chemie 04/2007; 633(7):961 - 970. DOI:10.1002/zaac.200700007 · 1.16 Impact Factor
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    ABSTRACT: The reaction between [(tbbpy)2Ru(tmbiH2)](PF6)2 (tbbpy = 4,4′-di-tert-butyl-2,2′-bipyridine; tmbiH2 = 5,5′,6,6′-tetramethyl-2,2′-dibenzimidazole) and LiMe/CuI affords the tetranuclear complex 1 containing the dication [{(tbbpy)2Ru(tmbi)}2Cu2]2+. The X-ray structure of 1 shows that the two [(tbbpy)2Ru(tmbi)] units coordinate the two Cu atoms in a twofold monodentate manner. Each copper atom is surrounded by two N-donor atoms of different ruthenium(II) units with N–Cu–N angles of 167.3°. The Cu···Cu separation (2.72 Å) indicates intranuclear contacts. LiMe/[(allyl)PdCl]2 reacts with the starting Ru complex to form 2, which contains the tetranuclear dication [{(tbbpy)2Ru(tmbi)}2{Pd(η3-allyl)}2]2+. Its crystal structure shows that the RuII units act as twofold monodentate ligands as well. Each PdII is in an essentially planar coordination environment containing two nitrogen atoms of two different dibenzimidazolates in the cis position with the η3-bonded allyl group occupying the two remaining positions. In contrast to 1, where the Ru–Cu–Cu–Ru unit forms an essentially planar structure, a strongly bent structure is formed in compound 2. ESI mass spectra of 1 and 2 clearly show that the tetranuclear complexes are present in solution as well. Both complexes are luminescent. In addition, 2 catalyses the Heck coupling at 120 °C in N,N-dimethylacetamide. In contrast to 1 and 2, the homodinuclear complex [(tbbpy)2Ru(tmbi)Ru(tbbpy)2] (3) contains the dibenzimidazolate as a twofold chelating ligand that forms two five-membered chelate rings with the Ru centres. Electrochemical measurements of 2 show two reversible, one-electron oxidation steps, the difference between which (ΔE = 89 mV) is distinctly larger than the pure entropic effect. Furthermore, four reduction steps are observed, the first two of which are fully reversible. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
    Berichte der deutschen chemischen Gesellschaft 06/2006; 2006(12):2385 - 2392. DOI:10.1002/ejic.200501130 · 2.94 Impact Factor
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    ABSTRACT: Complexes of the type (R-bpy)2RuCl2 (R: H, Me, tert-but) were synthesised by microwave-activated reactions of [Ru(cod)Cl2]n with substituted 2,2′-bipyridines in dimethylformamide as the solvent. The complexes were isolated in high yields and high purity from the reaction mixture. Microwave-assisted or thermal reaction of the (R-bpy)2RuCl2 solutions with substituted bibenzimidazoles, 1,10 phenanthroline or bipyrimidine in dmf/water mixtures resulted in the formation of mixed ligand complexes of the type [(R-bpy)2Ru(L–L)]Cl2. The complexes were characterised by NMR spectroscopy and MS. Furthermore, their photochemical and electrochemical properties were investigated and the solid state structure of (4-tert-butyl-bpy)2RuCl2 (3), [(4-tert-butyl-bpy)2Ru(tetramethylbibenzimidazole)](PF6)2 (4), and [(4-tert-butyl-bpy)2Ru(bipyrimidine] (PF6)2 (5) was determined by X-ray diffraction analysis of single crystals.
    Inorganica Chimica Acta 12/2004; 357(15):4496-4503. DOI:10.1016/j.ica.2004.07.007 · 2.05 Impact Factor
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    ABSTRACT: Hydrogen bond association between ruthenium bibenzimidazole and carboxylated polypyridylosmium complexes results in stable supramolecular aggregates. The determined stability constant of logK ≈ 6 ± 0.3 allows efficient energy transfer from the ruthenium to the osmium moiety.
    Berichte der deutschen chemischen Gesellschaft 04/2003; 2003(8). DOI:10.1002/ejic.200390193 · 2.94 Impact Factor
  • Sven Rau · Lars Böttcher · Sebastian Schebesta · Michael Stollenz · Helmar Görls · Dirk Walther ·
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    ABSTRACT: The reaction between [(η6-p-cymene)RuCl2]2 and tetra-p-tolyloxalic amidine (oxam1) results in a coupled cation/anion coordination forming the ion-paired complex [(η6-p-cymene)RuCl(oxam1)Cl] (1a). According to an X-ray single crystal diffraction analysis the Ru moiety is coordinated at the 1,2-diimine part yielding a five-membered chelate ring. Furthermore, the 1,2-diamine group on the opposite side binds to a chloride anion via two N−H groups. Exchange of the chloride anion by trifluoractetate yields [(η6-p-cymene)RuCl(oxam1)CF3CO2] (1c) in which the C=O group is bonded to the diamine part. Similarly, bis(mesityl)bis(pyridylmethyl)oxalic amidine (oxam2) reacts with FeX2 to yield the ion-paired complexes 3a (X: Cl), and 3b (X: Br). X-ray diffraction studies of both compounds reveal that the oxalic amidine ligand acts as a four-dentate chelating ligand. One halide is fixed in the same way as in 1a. The complex 1a reacts with Pd(acac)2 (acac: acetylacetonate) to give the tetranuclear heterobimetallic complex [(η6-p-cymene)RuCl(oxam1)PdCl]2 (2). The related complexes [(tbbpy)2Ru(bbimH2)(OOC−CF3)](PF6) (4), [(tbbpy)2Ru(bbimH2){OOC(CF2)7CF3})][OOC(CF2)7CF3] (5), [{(tbbpy)2Ru(bbimH2)}2(OOC−C6F4−COO)](PF6)2 (6), and [{(tbbpy)2Ru(bbimH2)}2(OOC−C6F4−COO)] (7), (bbimH2: bibenzimidazole; tbbpy: 4,4′-di-tert-butyl-2,2′-bipyridine) also form ion-paired compounds. According to the X-ray diffraction analyses of 4−6 both oxygen atoms of the carboxylate ions are coordinated to the two N−H functions via strong N−H···O bonds. Although 5 contains a dication, the compound is soluble in solvents of low polarity, even in supercritical carbon dioxide. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)
    Berichte der deutschen chemischen Gesellschaft 11/2002; 2002(11):2800 - 2809. DOI:10.1002/1099-0682(200211)2002:11<2800::AID-EJIC2800>3.0.CO;2-E · 2.94 Impact Factor
  • Ulf Kreher · Sebastian Schebesta · Dirk Walther ·
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    ABSTRACT: Monomere Verbindungen des Typs Cp2M (z. B. M = Fe, Co, Ni) lösen sich in flüssigem und superkritischem CO2 („scCO2”), ohne mit dem Solvens zu reagieren. Die polymeren Komplexe Zinkocen oder Manganocen reagieren mit CO2 zu unlöslichen Carboxylaten.Homoleptische Metallcarbonyle und eine Reihe von ligandstabilisierten Metallcarbonylen sind ebenfalls in scCO2 löslich. Fe(CO)5 reagiert in diesem Solvens photochemisch zu Fe2(CO)9 und thermisch zu Fe3(CO)12. Auch das hochreaktive (cdt)Ni(0) (cdt: Cyclododeca-1,5,9-trien) ist in flüssigem CO2 gut löslich, ohne das eine Reaktion mit CO2 beobachtet wird. In scCO2 gelöst, reagiert (cdt)Ni nach kurzer Zeit thermisch unter Nickelabscheidung.CpCo(cod) katalysiert langsam die Cyclo-cooligomerisation von Hex-3-in mit Acetonitril unter Bildung von 2,3,4,5-Tetraethyl-6-methylpyridin. Propargylalkohol reagiert am (cod)2Ni- oder (cdt)Ni-Katalysator mit 90% Selektivität zu Cyclotetrameren, Hex-3-in in und mit CO2 unter selektiver Bildung von Tetraethyl-2-pyron mit dem Katalysatorsystem R3P/(cod)2Ni (R: Me, Et). In situ IR-Messungen zeigen, daß die katalytisch aktiven Spezies durch Bildung von Ni-Carbonylkomplexen desaktiviert werden.Die katalytische Oxidation von cis-Cycloocten zu Cyclooctenepoxid mit t-BuOOH verläuft bei Verwendung des in scCO2 löslichen Titan(IV)-isopropylats mäßig selektiv, in Gegenwart von Mo(CO)6 wird jedoch in guten Ausbeuten und in einer hochselektiven Reaktion das Epoxid gebildet.Organometallics of Transition Metals in Supercritical Carbon Dioxide: Solubilities, Reactions, CatalysisMonomeric compounds of the type Cp2M (p. e. M = Fe, Co, Ni) are soluble in liquid or supercritical CO2 (”scCO2””) without any reaction with the solvent. The polymeric compounds zincocene or manganocene form with CO2 insoluble CO2 insertion products.As well homoleptic metal carbonyls as a number of ligand-stabilized metal carbonyls are also soluble in scCO2. Fe(CO)5 reacts photochemically in this solvent to Fe2(CO)9 and thermically to Fe3(CO)12. The highly reactive (cdt)Ni(0) (cdt: cyclododeca-1,5,9-triene) is soluble in liquid CO2. A reaction with the solvent could not been observed. Solved in scCO2 (cdt)Ni reacts thermically to form Ni after a short time.CpCo(cod) catalyzes slowly the cyclo-cooligomerization of hex-3-yne with acetonitrile to form 2,3,4,5-Tetraethyl-6-methylpyridine. Propargylic alcohol reacts under formation of cyclotetrameres with a selectivity of 90% using (cod)2Ni or (cdt)Ni as catalysts, hex-3-yne in and with carbon dioxide under selective formation of tetraethyl-2-pyrone when the catalyst system R3P/(cod)2Ni (R: Me, Et) is used. In situ IR measurements show that the catalytically active species will be desactivated by formation of nickel carbonyl complexes.The catalytic oxidation of cyclooctene to form cycloocteneoxid with t-BuOOH using Titan(IV)-isopropylate as soluble catalyst proceeds less selectively, however in the presence of Mo(CO)6 the epoxid is formed in good yields and in a highly selective reaction.
    Zeitschrift für anorganische Chemie 02/1999; 624(4):602 - 612. DOI:10.1002/(SICI)1521-3749(199804)624:4<602::AID-ZAAC602>3.0.CO;2-K · 1.16 Impact Factor
  • Sebastian. Schebesta ·
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    ABSTRACT: Jena, Universiẗat, Diss., 2003 (Nicht für den Austausch).