Peter Klüfers

Ludwig-Maximilian-University of Munich, München, Bavaria, Germany

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Publications (173)386.2 Total impact

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    ABSTRACT: Two different structure types were found for a series of mononuclear dinitrosyl complexes of the general formula [RuL2(NO)2X]BF4 (L = monodentate phosphane, X = Cl, Br, I). The {Ru(NO)2}(8)-type target compounds were prepared by the reduction of the respective {RuNO}(6) precursors and subsequent oxidative addition of (NO)BF4. About one half of the new compounds share their molecular structure with the hitherto only representative of this class of dinitrosyls, Pierpont and Eisenberg's [RuCl(NO)2(PPh3)2]PF6·C6H6 (Inorg. Chem., 1972, 11, 1088-1094). The Cs-symmetric cations exhibit both a linear and a bent Ru-N-O fragment, in line with a formal 6 + 2 split of the {Ru(NO)2}(8) electron sum in the sense of a [Ru(II)(NO(+))((1)NO(-))](2+) bonding. The coordination entity's configuration in this subgroup is described by IUPAC's polyhedral symbol SPY-5. Continuous shape measures (CShM) as defined by Alvarez et al. (Coord. Chem. Rev., 2005, 249, 1693-1708) reveal a uniform deviation from the L-M-L angles expected for SPY-5, in a narrower sense, towards a vacant octahedron (vOC-5). DFT calculations confirmed that Enemark and Feltham's analysis (Coord. Chem. Rev., 1974, 13, 339-406) of the electronic situation of the {Ru(NO)2}(8) group remains adequate. The same holds for the second subclass of new compounds the existence of which had been predicted in the same paper by Enemark and Feltham, namely C2v-symmetric, TBPY-5-type cations with two almost equally bonded nitrosyl ligands. In agreement with an 8 + 0 distribution of the relevant electrons, the formal [Ru(0)(NO(+))2](2+) entities are found for L/X couples that donate more electron density on the central metal. Two solid compounds (/, /) were found in both structures including the special case of the P(i)Pr3/Br couple /, which led to crystals that contained both structure types in the same solid. Conversely, four compounds showed a single form in the solid but both forms in dichloromethane solution in terms of the solutions' IR spectra. The irradiation of crystalline with blue laser light resulted in the photoisomerisation of, mainly, the bent (1)NO(-) ligand in terms of low-temperature IR spectroscopy.
    Dalton Transactions 07/2014; · 4.10 Impact Factor
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    ABSTRACT: Crystals of the bis(tert-butyl)silylene (DTBS) derivatives of the tartaric acids were synthesized from D-, L-, rac-, and meso-tartaric acid and DTBS bis(trifluoromethanesulfonate): two polymorphs of Si2tBu4(L-Tart1,2;3,4H–4) (L-1a and L-1b), the mirror image of the denser modification (D-1b) as well as the racemate (2), and the meso analogue Si2tBu4(meso-Tart1,3;2,4H–4) (3). The structures were determined by single-crystal X-ray diffraction. The threo-configured D- and L- (and rac-) tartrates were coordinated by two tBu2Si units forming five-membered chelate rings, whereas the erythro-configured meso-tartrate formed six-membered chelate rings. The new compounds were analyzed by NMR techniques, including 29Si NMR spectroscopy, and single-crystal X-ray crystallography.
    Zeitschrift für anorganische Chemie 01/2014; 640(1). · 1.16 Impact Factor
  • Xaver Kästele, Christine Sturm, Peter Klüfers
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    ABSTRACT: (13)C NMR spectroscopy provides insight into the chemistry of carbohydrate-based ferric preparations. Specifically, it reveals whether oxygen atoms of the carbohydrate are directly bonded to the preparations' ferric centres or whether more distant interactions are present. After having validated the method by investigating the ferric solutions of low-molecular complexes as well as polynuclear ferric samples, it is demonstrated that common constituents of medically used ferric preparations such as sucrose and other glucose-based saccharides do not support ferric carbohydrate chelates. Instead, these carbohydrates reside outside the NMR-spectroscopically 'blinded' region about the ferric centres and experience the so-called Evans effect that can be used to measure the magnetic moment of the solutions. As a result, an easily accessible physicochemical parameter is provided to characterise commercial iron(III) preparations, namely the samples' magnetism in terms of the in-situ-measured spin-normalised effective Bohr magneton number μeff(2)/35. The procedure can, moreover, be combined with a facile NMR-spectroscopic iron assay.
    European journal of pharmaceutics and biopharmaceutics: official journal of Arbeitsgemeinschaft fur Pharmazeutische Verfahrenstechnik e.V 12/2013; · 3.15 Impact Factor
  • Angewandte Chemie 05/2013; 125(19).
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    ABSTRACT: They can't do it alone: The Jahn-Teller instability found in the iron(II) species is missing in the homologous bis(perfluoropinacolato) cobalt(II) complex. Thus the stable conformation of the cobalt center is closer to tetrahedral than square planar, as shown by a DFT approach, and also in an isolatable salt.
    Angewandte Chemie International Edition 04/2013; · 11.34 Impact Factor
  • Martin Steinborn, Mihael Suhanji, Peter Klüfers
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    ABSTRACT: Sugar phosphates provide metal-binding sites both at their sugar core and at their phosphate group(s). Mixed sugar-core-phosphate chelation has been considered as a typical bonding mode within the physiological pH range for the central metabolite d-fructose 1,6-bisphosphate. The ReVO(tmen) metal fragment was used to enrich this coordination type. The formation of the [ReO(tmen)(Fruf2,3H-21,6P2H2-κ3O2,3,P1)]- monoanion was determined by NMR spectroscopy and mass spectrometry. The model compound rac-glycerol 1-phosphate yielded similar results in terms of NMR spectroscopy. Crystal-structure analyses of [ReO(tmen)(rac-Glyc2,3H-21PH-κ3O2,3,P)]·2H2O and [ReO(phen)(rac-Glyc2,3H-21PH-κ3O2,3,P)]·MeOH confirmed the coordination pattern.
    Dalton Transactions 02/2013; · 4.10 Impact Factor
  • Sandra Albrecht, Peter Klüfers
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    ABSTRACT: Fehling's solution is an aqueous alkaline solution (pH ca. 13) of D-, L-, or rac-tartrato-cuprates(II) and both excess tartrate and hydroxide. The isolation of crystalline solids succeeded for rac-tartrate-containing samples. Crystal structure analyses revealed the formulas K8[Cu10(rac-tartH-1)4(rac-tartH-2)4(H2O)4]·18H2O (1), Li4[Cu2(rac-tartH-2-κ2O1,O2:κ2O3,O4)2]·11.75H2O (2), and Na6[Cu(rac-tartH-2-κ2O2,O3)2]·14H2O (3). The cupric central atom is in a square-planar tetracoordination in the bis(diolato) chelate in 3, and in square-pyramidal 4+1 coordination in the mixed carboxylato-alkoxido chelates 1 and 2. In terms of stoichiometry, 3 is closest to typical Fehling recipes.
    Zeitschrift für anorganische Chemie 02/2013; 639(2). · 1.16 Impact Factor
  • Sarah Illi, Johanna Schulten, Peter Klüfers
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    ABSTRACT: Sialic acid represents a group of thirty derivates of neuraminic acid with various substituents at the amino residue and the alcoholic hydroxy groups. We analysed the behaviour of the tetracoordinated metal ions palladium(II) and silicon(IV) against the most important derivative N-acetylneuraminic acid (NANA). The molecular structures were assigned by a combined 1H, 13C and 29Si NMR-spectroscopic approach. Despite the presence of many different functional groups, the coordination chemistry of NANA with PdII follows established rules. Coordination via the N-acetyl-group – sterically impossible with PdII – was realised with SiIV.
    Zeitschrift für anorganische Chemie 01/2013; 639(1). · 1.16 Impact Factor
  • Thorsten Allscher, Peter Klüfers
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    ABSTRACT: Alditols ("sugar alcohols", "glycitols") form palladium(II) complexes in neutral aqueous solution if they can provide the threitol partial structure. This requirement excludes erythritol, ribitol, and allitol when applied to the common tetritols, pentitols, and hexitols. The remaining alditols are able to arrange their threo-tetraol-O(4) pattern to an almost planar rhomb, to which four Pd(II) N(2) (N(2) =bidentate nitrogen ligand) centres bind in a butterfly-shaped Pd(4) motif. Bridging is the exclusive bonding mode of the four alkoxido donors. In contrast to the butterfly complexes, all alditols are able to form a species at a pH intermediate between neutrality and the stronger alkaline conditions of non-bridging diolato-palladium(II) binding, namely, the μ-triolato bonding mode. A Pd(2) (μ-triolato) unit shows the middle O atom of a propanetriolato fragment as a bridging ligator, with the lateral O atoms binding in the terminal mode.
    Chemistry - A European Journal 07/2012; 18(34):10571-84. · 5.93 Impact Factor
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    David Hess, Peter Klüfers
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    ABSTRACT: The title compound, C(6)H(12)O(5), is the α-pyran-ose form of the reducing aldose 2-de-oxy-d-arabino-hexose. The six-membered pyran-ose ring adopts a (4)C(1) conformation, with the anomeric hy-droxy group in axial and the other substituents in equatorial positions. In the crystal, each of the four hy-droxy groups acts as an inter-molecular hydrogen-bond donor function, resulting in a three-dimensional hydrogen-bonded network.
    Acta Crystallographica Section E Structure Reports Online 10/2011; 67(Pt 10):o2615. · 0.35 Impact Factor
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    D. Hess, P. Klüfers
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    ABSTRACT: The title compound, C6H12O5, is the α-pyran­ose form of the reducing aldose 2-de­oxy-d-arabino-hexose. The six-membered pyran­ose ring adopts a 4C1 conformation, with the anomeric hy­droxy group in axial and the other substituents in equatorial positions. In the crystal, each of the four hy­droxy groups acts as an inter­molecular hydrogen-bond donor function, resulting in a three-dimensional hydrogen-bonded network.
    Acta Crystallographica Section E Structure Reports Online 09/2011; 67(10). · 0.35 Impact Factor
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    David Hess, Peter Klüfers
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    ABSTRACT: Phenylboronic acid esters are formed by the three common 2-deoxy aldoses: 2-deoxy-d-erythro-pentose ('2-deoxy-d-ribose'), 2-deoxy-d-lyxo-hexose ('2-deoxy-d-galactose'), and 2-deoxy-d-arabino-hexose ('2-deoxy-d-glucose'). The major species that was formed from equimolar quantities of boronic acid and the aldose, was the 3,4-monoester of the pentopyranose in a skew-boat conformation, and the 4,6-monoester in the case of the two hexopyranoses. A double molar quantity of boronic acid led, for both 2-deoxy-hexoses, to the diester of the open-chain aldehydo isomer as the major product: the 3,5:4,6-diester for the lyxo-configured deoxy-hexose, and the 3,4:5,6-diester of the arabino-configured isomer. Minor products of all reactions were identified by a combined NMR/DFT methodology.
    Carbohydrate research 07/2011; 346(13):1752-9. · 2.03 Impact Factor
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    Johanna Schulten, Peter Klüfers
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    ABSTRACT: Excess di(tert-butyl)silylene (DTBS) bis(trifluoromethanesulfonate) formed bis-DTBS derivatives with the four aldopentoses (arabinose, lyxose, ribose and xylose). The structure of the bis-chelates was affected by the bulk of the DTBS groups and the requirement of flat silacycles in the case of five-membered chelate rings. These restrictions resulted in unusual cyclic bis-chelates for ribofuranose (κO(1,5),κO(2,3) bis-chelate) and lyxopyranose (κO(1,4),κO(2,3) bis-chelate of a twisted boat conformation). Most importantly, all aldopentoses formed bis-chelates of their open-chain aldehydo isomers. The bis-chelates of aldehydo-arabinose and -xylose were κO(2,3),κO(4,5)-bonded and thus exhibited five-membered chelate rings. The bis-chelates of aldehydo-lyxose and -ribose were κO(2,4),κO(3,5)-bonded and resembled six-membered chelate rings. For lyxose, the aldehydo bis-chelate was isolated as a solid. The molecular structures were assigned by a combined (1)H, (13)C, and (29)Si NMR spectroscopic approach, which was supported by X-ray analyses on crystals of the bis-DTBS chelates of κO(1,2),κO(3,5)-bonded rac-xylofuranose, κO(1,5),κO(2,3)-bonded d-ribofuranose, and κO(2,4),κO(3,5)-bonded aldehydo-d-lyxose.
    Carbohydrate research 07/2011; 346(13):1767-75. · 2.03 Impact Factor
  • Angewandte Chemie 05/2011; 123(21).
  • Gerhard Kettenbach, Peter Klüfers, Peter Mayer
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    ABSTRACT: Crystals of metal complexes of deprotonated open-chain oligosaccharides which may serve as models for the action of coordinating cellulose solvents on the polysaccharide molecule, are generally harder to obtain in a quality suitable for X-ray analysis than in the case of monosaccharides. Four preliminary crystal structure analyses are presented which settle the significance of intramolecular hydrogen bonds towards the metal ligating acceptors. The metal binding sites of sucrose include both 1,2- and 1,3-diolato complex formation, whereas α,α-trehalose has been found in the 1,2-diolato coordination mode.
    Macromolecular Symposia 03/2011; 120(1):291 - 301.
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    ABSTRACT: Taking into account the coordination chemistry of divalent palladium and nickel, two new cellulose solvents have been developed. Pd-en is an aqueous solution of the ethylenediamine palladium complex [(en)Pd(OH)2]. Low molecular diols are deprotonated twice in Pd-en and form a five membered chelate ring with the transition metal. Cellulose dissolves in Pd-en to give a yellow solution, which allows light scattering analysis. NMR investigation of the solutions are simplified due to the diamagnetism of palladium(II) complexes. — The analysis of solution equilibria is essential in the development of complexing polysaccharide solvents. This feature is demonstrated by means of the new cellulose solvent Ni-tren, which is an aqueous solution containing tris(2-aminoethyl)amine, nickel salt and hydroxide in a molar ratio of ≥1:1:2. The difference in the cellulose solving mechanism between Ni-tren and the long known solvents ‘nioxen’ and ‘nioxam’ developed by Jayme in the 1950ths is outlined. The question, wether or not the dissolution of cellulose in a complexing solvent is a derivatization, is discussed.
    Macromolecular Symposia 03/2011; 99(1):113 - 126.
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    Angewandte Chemie International Edition 03/2011; 50(21):4974-8. · 11.34 Impact Factor
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    Thorsten Allscher, Yvonne Arendt, Peter Klüfers
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    ABSTRACT: Four methyl d-pentopyranosides (β-Ara, α-Lyx, β-Rib, β-Xyl), as well as Me-β-l-Ara, some of them residing in a well-defined conformation in the solution state (Ara, Xyl) and some showing pronounced chair inversion in solution (Lyx, Rib), form bidentate chelates of the general formula [Pd(chxn)(LH₋₂)-κO,O'] and [Pd(tmen)(LH₋₂)-κO,O'], chxn=(R,R)-cyclohexane-1,2-diamine, tmen=N,N,N',N'-ethane-1,2-diamine and L=glycoside, with Pd(II)N₂-type metal probes. The dynamic behaviour of the free glycosides is maintained in their chelates, the only case where the metal is bonded by a cis-vicinal diol function. Thus, one fluctuating chelate was detected with the lyxopyranoside in the κO(2,3) binding mode, and two fluctuating chelates were found for the ribopyranoside (κO(2,3) and κO(3,4)). No fluctuating chelate was found for the arabinopyranoside (the free arabinopyranoside being non-fluctuating as well), or for the xylopyranoside (no cis-vicinal diol function). In addition, syn-diaxial chelation (κO(2,4)) was observed for the ribopyranoside and the xylopyranoside. The spectroscopic results were supplemented by X-ray analyses.
    Carbohydrate research 11/2010; 345(16):2381-9. · 2.03 Impact Factor
  • Thorsten Allscher, Peter Klüfers
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    ABSTRACT: In methyl beta-D-fructopyranoside, C(7)H(14)O(6), the thermodynamically most stable methyl glycoside of the ketose D-fructose, the pyranose ring is close to being an ideal (2)C(5) chair. The compound forms bilayers involving a complex hydrogen-bonding pattern of five independent hydrogen bonds. Graph-set analysis was applied to distinguish the hydrogen-bond patterns at unary and higher level graph sets.
    Acta Crystallographica Section C Crystal Structure Communications 07/2010; 66(Pt 7):o321-3. · 0.78 Impact Factor
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    ABSTRACT: Co(III)(tacn) and Ga(III)(tacn) fragments (tacn = 1,4,7-triazacyclononane) are suitable metal probes for the detection of the tridentate chelating sites of a glycose. Three moles of hydroxide per mole of cobalt or gallium support triple deprotonation of the chelating triol functions at a glycose's backbone. The individual chelating sites are detected using 1D and 2D NMR techniques. The metal-binding sites always include the hydroxy function at the anomeric carbon atom. Chelators are derived from both the pyranose and the furanose isomers while forming five- and six-membered chelate rings by the use of cis,cis-1,2,3-triol functions. The assignment of less frequently occurring ligand isomers are supported by a DFT approach. Crystal-structure analysis on Na(4)[Cr(beta-d-Manf1,2,3H(-3))(2)]NO(3).8.5H(2)O (Man = mannose) additionally upholds the NMR assignments.
    Dalton Transactions 06/2010; 39(23):5535-43. · 4.10 Impact Factor