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Abstract

The extreme steric bulk of tris(trimethylsilyl)methyl derivatives (1-X) provides interesting structural and dynamic behavior for study. Dynamic NMR studies on 1-SePh and 1-I showed restricted rotation around the C−Si bonds of each trimethylsilyl groups. An extensive multinuclear NMR study of natural abundance and ⁶Li and ¹³C enriched 1-Li revealed three species in THF-containing solvents, a dimer 1T, and two monomers, the contact ion pair 1C, and solvent separated ion pair 1S. Observed barriers for interconversion of 1-Li aggregates were unusually high (ΔG ca. 9 kcal/mol for exchange of 1S and 1C, ΔG₄₁ = 16.4 kcal/mol for exchange of 1T with 1C and 1S), allowing for study of reactivity of each aggregate individually. We can show that 1S is at least 50 times as reactive as 1C and at least 5 × 10¹⁰ times as reactive as 1T toward MeI. The large difference in reactivity allowed further study on the mechanism of the lithium−iodine exchange of 1-I with 1-Li and characterization of the intermediate iodine ate complex 4. Additional calibrations are presented for the sensitive yet chemically inert ¹³C NMR chemical shift thermometer 1-H.

Citing Articles

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This article has been cited by 4 ACS Journal articles (4 most recent appear below).

• 

  Synthesis, Structure, and Solution Behavior of a Phosphine−Borane-Stabilized 1,3-Dicarbanion

  Keith Izod, Corinne Wills, William Clegg, and Ross W. Harrington
  Organometallics2010 29 (21), 4774-4777

  • Synthesis, Structure, and Solution Behavior of a Phosphine−Borane-Stabilized 1,3-Dicarbanion

    Keith Izod, Corinne Wills, William Clegg, and Ross W. Harrington
    Organometallics2010 29 (21), 4774-4777

    The reaction between the phosphine−borane {(Me3Si)CH2}2P(BH3)Ph (2) and 2 equiv of n-BuLi in THF yields the 1,3-dicarbanion complex (THF)2Li{(Me3SiCH)2P(BH3)Ph}Li(THF)3 (3), which crystallizes as an unusual contact ion pair. In solution 3 is subject to ...

    Abstract | Full Text HTML | Hi-Res PDF | PDF w/ Links
• 

  Structure and Dynamics of α-Aryl Amide and Ketone Enolates: THF, PMDTA, TMTAN, HMPA, and Crypt-Solvated Lithium Enolates, and Comparison with Phosphazenium Analogues

  Kristopher J. Kolonko, Ilia A. Guzei, and Hans J. Reich
  The Journal of Organic Chemistry2010 75 (18), 6163-6172

  • Structure and Dynamics of α-Aryl Amide and Ketone Enolates: THF, PMDTA, TMTAN, HMPA, and Crypt-Solvated Lithium Enolates, and Comparison with Phosphazenium Analogues

    Kristopher J. Kolonko, Ilia A. Guzei, and Hans J. Reich
    The Journal of Organic Chemistry2010 75 (18), 6163-6172

    A variety of multinuclear NMR techniques, in combination with X-ray diffraction methods, were used to probe the solution structure of α-aryl lithium enolates of bis(4-fluorobenzyl) ketone (1-H), phenyl 4-fluorobenzyl ketone (2-H), and N,N-dimethyl 4-...

    Abstract | Full Text HTML | Hi-Res PDF | PDF w/ Links
• 

  Solution Structures of Lithium Enolates of Cyclopentanone, Cyclohexanone, Acetophenones, and Benzyl Ketones. Triple Ions and Higher Lithiate Complexes

  Kristopher J. Kolonko, Margaret M. Biddle, Ilia A. Guzei and Hans J. Reich
  Journal of the American Chemical Society2009 131 (32), 11525-11534

  • Solution Structures of Lithium Enolates of Cyclopentanone, Cyclohexanone, Acetophenones, and Benzyl Ketones. Triple Ions and Higher Lithiate Complexes

    Kristopher J. Kolonko, Margaret M. Biddle, Ilia A. Guzei and Hans J. Reich
    Journal of the American Chemical Society2009 131 (32), 11525-11534

    Multinuclear NMR spectroscopic studies at low temperature (−110 to −150 °C) revealed that lithium p-fluorophenolate and the lithium enolates of cyclohexanone, cyclopentanone and 4-fluoroacetophenone have tetrameric structures in THF/Et2O and THF/Et2O−HMPA ...

    Abstract | Full Text HTML | Hi-Res PDF | PDF w/ Links
• 

  Multinuclear NMR Study of the Solution Structure and Reactivity of Tris(trimethylsilyl)methyllithium and its Iodine Ate Complex

  Hans J. Reich, William H. Sikorski, Aaron W. Sanders, Amanda C. Jones and Kristin N. Plessel
  The Journal of Organic Chemistry2009 74 (2), 719-729

  • Multinuclear NMR Study of the Solution Structure and Reactivity of Tris(trimethylsilyl)methyllithium and its Iodine Ate Complex

    Hans J. Reich, William H. Sikorski, Aaron W. Sanders, Amanda C. Jones and Kristin N. Plessel
    The Journal of Organic Chemistry2009 74 (2), 719-729

    The extreme steric bulk of tris(trimethylsilyl)methyl derivatives (1-X) provides interesting structural and dynamic behavior for study. Dynamic NMR studies on 1-SePh and 1-I showed restricted rotation around the C−Si bonds of each trimethylsilyl groups. ...

    Abstract | Full Text HTML | Hi-Res PDF | PDF w/ Links

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