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Methylation of tetrakis(fod) europate NMR shift reagent by S ‐methyldibenzothiophenium ion
Author(s) -
Green Thomas K.,
Pesterfield Lester L.,
Radmard Bijan,
Whetstine Johnathan R.
Publication year - 1998
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/(sici)1097-458x(199802)36:2<79::aid-omr203>3.0.co;2-5
Subject(s) - chemistry , reagent , luminescence , ion , chloroform , nuclear magnetic resonance spectroscopy , spectroscopy , proton nmr , dibenzothiophene , europium , medicinal chemistry , photochemistry , stereochemistry , catalysis , organic chemistry , physics , optoelectronics , quantum mechanics
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 ppm 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 , CH 3 fod and dibenzothiophene. The reaction is >95% complete in about 4 h. Evidence for the formation of dibenzothiophene and CH 3 fod is revealed by 1 H 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 semi‐empirical 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. © 1998 John Wiley and Sons, Ltd.