Michael G Klimpel

Publications (6)33.08 Total impact

• Article: Stereospecific polymerization of isoprene with molecular and MCM-48-grafted lanthanide(III) tetraalkylaluminates.

  Andreas Fischbach, Michael G Klimpel, Markus Widenmeyer, Eberhardt Herdtweck, Wolfgang Scherer, Reiner Anwander
  Angewandte Chemie International Edition 05/2004; 43(17):2234-9. · 13.45 Impact Factor
• Article: High tetraalkylaluminate fluxionality in half-sandwich complexes of the trivalent rare-earth metals.

  Reiner Anwander, Michael G Klimpel, H Martin Dietrich, Dmitry J Shorokhov, Wolfgang Scherer
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  ABSTRACT: Steric factors govern the formation of half-sandwich complexes (C5Me4R)Ln[N(SiHMe2)2]2 according to acid-base reactions utilising Ln[N(SiHMe2)2)3(thf)2 and substituted cyclopentadienes. Subsequent trimethylaluminium-promoted silylamide elimination produces the first half-sandwich bis(tetramethylaluminate) complexes (C5Me4R)Ln(AlMe4)2.
  Chemical Communications 05/2003; · 6.17 Impact Factor
• Article: DIBAH-mediated amide/hydride transformation in ansa-lanthanidocene(III) complexes.

  Michael G Klimpel, Peter Sirsch, Wolfgang Scherer, Reiner Anwander
  Angewandte Chemie International Edition 03/2003; 42(5):574-7. · 13.45 Impact Factor
• Article: The Lanthanide Ziegler−Natta Model:  Aluminum-Mediated Chain Transfer

  Michael G. Klimpel, Jörg Eppinger, Peter Sirsch, Wolfgang Scherer, Reiner Anwander
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  ABSTRACT: C2-symmetric tetraalkylaluminate complexes rac-[Me2Si(2-Me-C9H5)2]Y(μ-R)2AlR2 and terminal alkyl complexes rac-[Me2Si(2-Me-C9H5)2]YR(THF) (R = Me, Et, iBu) are quantitatively formed via a special silylamide elimination reaction. The “reversibility” of tetraalkylaluminate coordination gives access to the first mixed-alkyl lanthanidocene complexes, which can be discussed as models for polymer chain transfer in organoaluminum-dependent Ziegler−Natta catalysts.
  08/2002;
• Article: Peralkylated Ytterbium(II) Aluminate Complexes YbAl2R8. New Insights into the Nature of Aluminate Coordination

  Michael G. Klimpel, Reiner Anwander, Maxim Tafipolsky, Wolfgang Scherer
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  ABSTRACT: The homoleptic ytterbium(II) tetraalkylaluminate complexes {Yb[AlR4]2}n have been obtained according to a silylamide elimination reaction from Yb[N(SiMe3)2]2(THF)2 and excess AlR3 (R = Me, Et, iBu). While the tetramethylaluminate derivative is a pyrophoric powder which is insoluble in aliphatic and aromatic hydrocarbons, the ethyl and isobutyl congeners are readily soluble in n-hexane. Perethylated polymeric {Yb[AlEt4]2}n is constituted formally of the two molecular fragments [Yb(AlEt4)]+ and [Yb(AlEt4)3]-, forming an intricate three-dimensional network in the solid state. Both fragments are linked by bridging α-carbon atoms and secondary Yb···H−C agostic interactions combining μ,η1, μ,η2, and μ,η3 coordination modes which result in remarkably short Yb···Al (2.809(2) Å) and a large range of Yb···C (2.649(5)−3.364(6) Å) distances. DFT calculations on the molecular fragments [Yb(AlEt4)3]- and [Yb(AlEt4)]+ reproduced the X-ray geometry remarkably well. Moreover, the theoretical investigations on model systems for the aluminate coordination support the highly fluxional nature of the aluminate coordination (ΔE(η2→η3) = −8 kcal/mol), which is also indicated by solution NMR spectroscopy. A topological analysis of the total electron density of the μ,η2-bonded aluminate ligand in the benchmark systems Y(AlR4)3 (R = Me, Et) revealed the presence of two bond critical points between the Y−Cb and Cb−Al bonds (Cb = bridging carbon atom) and thus suggests a hypervalent character of the bridging carbon atom.
  08/2001;
• Article: Fluxional Behavior of Indenyl-Derived Ytterbocene(II) Complexes. The SiHR2 Group as a NMR Spectroscopic Probe

  Michael G. Klimpel, Wolfgang A. Herrmann, Reiner Anwander
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  ABSTRACT: Indenyl-derived ytterbocene(II) complexes [1-(SiHR2)-2-R‘-C9H5]2Yb(L)2 (R = Me, C6H5; R‘ = H, Me; L = donor ligand) have been synthesized via silylamine elimination from Yb[N(SiMe3)2]2(THF)2 and the indene derivatives in hexane at ambient temperature. The “SiH-decorated” silyl substituents assist in the examination of the fluxional behavior of the stereoisomers in solution, the ratio and interconversion of which are affected by the size and ring position of the substituents as well as the type of donor ligand, e.g., THF vs TMEDA.
  10/2000;