199588-27-7Relevant articles and documents
O- and m-(bromotetrafluorophenyl)palladium(II) complexes: Atropisomerism studies by 19F NMR and measurement of through-space F-F coupling constants
Albéniz, Ana C.,Casado, Arturo L.,Espinet, Pablo
, p. 5416 - 5423 (2008/10/08)
Palladium(II) complexes with the asymmetric aryl groups o-C6BrF4 and m-C6BrF4 have been synthesized, namely [Pd2(C6BrF4)2(μ-Cl) 2(tht)2], trans-[Pd(C6BrF4)Cl(tht)2] (tht = tetrahydrothiophene), trans-[Pd(C6BrF4)2L2], and cis-[Pd(C6BrF4)2L2] (L2 = 2tht, COD, Me2-bipy (4,4′-dimethyl-2,2′-bipyridine), OPPy2Ph (Py = 2-pyridyl), 2PMe3, 2CNMe). A mixture of atropisomers (syn-Br,Br and anti-Br,Br) is found for most bis(aryl) complexes, and the ratio of syn:anti atropisomers depends upon the R group, the cis or trans geometry of the complexes, and the ancillary ligand: A ratio close to 1:1 is observed for the cis- and trans-m-C6BrF4 derivatives and for the trans-o-C6BrF4 complexes, but the anti atropisomer is preferred in the cis-o-C6BrF4 derivatives, particularly if the ancillary ligands extend out of the coordination plane. Strong through-space coupling between syn Fortho atoms of mutually cis R groups is observed in the 19F NMR spectra for cis-[Pd(C6BrF4)2L2] complexes. J-values were determined which prove useful to unequivocally identify the atropisomers formed and to detect distortions in the structure of the complexes. Atropisomerization by aryl rotation is observed in several cases at different rates: Faster for m-C6BrF4 than for o-C6BrF4 derivatives, and faster for small-in-plane than for bulk-in-plane ancillary ligands. The fastest rotation occurs in the complexes with CNMe, which do not show atropisomers by 19F NMR at room temperature.
