[Pd(Fmes)2(tmeda)]: a case of intermittent C-H···F-C hydrogen-bond interaction in solution.
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 CH⋅⋅⋅FC hydrogen-bond interactions between methyl groups of the TMEDA ligand and ortho-CF3 groups of the Fmes ligand. The (19) F NMR spectra in CD2 Cl2 at very low temperature (157 K) detect restricted rotation for the two ortho-CF3 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 (ΔH(≠) =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.
IU CINQUIMA/Química Inorgánica, Universidad de Valladolid, 47071 Valladolid, Spain.
Camino
C
Bartolomé
Fernando
F
Villafañe
Jose M
JM
Martín-Alvarez
Jesús M
JM
Martínez-Ilarduya
Pablo
P
Espinet
D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D012996:Solutions
D056831:Coordination Complexes; D009942:Organometallic Compounds; D012996:Solutions; C582829:palladium(2,4,6-tris(trifluoromethyl)2)-(N,N,N',N'-tetramethylethylenediamine)