Methylation of tetrakis(fod) europate NMR shift reagent by S-methyldibenzothiophenium ion

Thomas K. Green, Lester L. Pesterfield, Bijan Radmard, Johnathan R. Whetstine

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NMR and luminescence spectroscopy were combined to study S-methyldibenzothiophenium ion in the presence of the anionic shift reagent Eu(fod)4-, where fod is 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyloctane-3,5-dione. The NMR resonances of the methyl hydrogens are observed to shift from 3.4 pprn for the fluoroborate salt to 25.4 ppm for the Eu(fod)4- salt at 0.1 M concentration in chloroform-d. The thiophenium ion is observed to methylate Eu(fod)4- anion at 25°C resulting in the formation of Eu(fod)3, CH3fod and dibenzothiophene. The reaction is >95% complete in about 4 h. Evidence for the formation of dibenzothiophene and CH3fod is revealed by 1H NMR spectroscopy. The fod enolate anion is both C-and O-methylated in nearly equal amounts. C-Methylated fod exists almost entirely in the keto form with no evidence of enol formation, consistent with semiempirical AM1 calculations. Additional evidence supporting the methylation of Eu(fod)4- is observed in the luminescence spectrum of the Eu(III) ion. By monitoring changes in the luminescence spectrum as a function of time, the transformation of Eu(fod)4- into Eu(fod)3 is observed. S-Methylbenzothiophenium ion also methylates Eu(fod)4~ but more rapidly than S-methyldibenzothiophenium cation.

Original languageEnglish
Pages (from-to)79-86
Number of pages8
JournalMagnetic Resonance in Chemistry
Issue number2
StatePublished - Feb 1998
Externally publishedYes


  • C NMR
  • H NMR
  • Methylation
  • NMR
  • NMR shift reagents
  • Tetrakis(fod) europate
  • Thiophenium ions


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