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[Pd(Fmes) 2 (tmeda)]: A Case of Intermittent CH⋅⋅⋅FC Hydrogen‐Bond Interaction in Solution
Author(s) -
Bartolomé Camino,
Villafañe Fernando,
MartínAlvarez Jose M.,
MartínezIlarduya Jesús M.,
Espinet Pablo
Publication year - 2013
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201203512
Subject(s) - steric effects , chemistry , hydrogen bond , tetramethylethylenediamine , ligand (biochemistry) , crystallography , hydrogen , trifluoromethyl , stereochemistry , medicinal chemistry , molecule , organic chemistry , alkyl , biochemistry , receptor
The X‐ray structure of the title compound [Pd(Fmes) 2 (tmeda)] (Fmes=2,4,6‐tris(trifluoromethyl)phenyl; tmeda= N , N , N′ , N′ ‐tetramethylethylenediamine) shows the existence of uncommon CH⋅⋅⋅FC hydrogen‐bond interactions between methyl groups of the TMEDA ligand and ortho ‐CF 3 groups of the Fmes ligand. The 19 F NMR spectra in CD 2 Cl 2 at very low temperature (157 K) detect restricted rotation for the two ortho ‐CF 3 groups involved in hydrogen bonding, which might suggest that the hydrogen bond is responsible for this hindrance to rotation. However, a theoretical study of the hydrogen‐bond energy shows that it is too weak (about 7 kJ mol −1 ) to account for the rotational barrier observed (Δ H ≠ =26.8 kJ mol −1 ), and it is the steric hindrance associated with the puckering of the TMEDA ligand that should be held responsible for most of the rotational barrier. At higher temperatures the rotation becomes fast, which requires that the hydrogen bond is continuously being split up and restored and exists only intermittently, following the pulse of the conformational changes of TMEDA.