title: Studies on the atropisomerism of Fe(II) 2,6-bis(N-arylimino)pyridine complexes.
abstract: NMR spectra of free 2,6-bis(N-arylimino)pyridine (PDI) ligands displaying different substituents at the ortho and ortho' positions of the two N-aryl rings indicate that they can exist in syn (meso) and anti (chiral) configurations. These interconvert in solution at room temperature, via rotation of the aryl group. The corresponding paramagnetic FeX(2)(PDI) complexes exhibit the same kind of isomerism, a property that is thought to be important for their activity as alpha-olefin polymerization catalysts. For the first time, this has been detected by (1)H NMR and studied in solution. Although the conformational stability of the diastereoisomeric complexes varies widely (depending on the size of the substituents at the imine and the aromatic rings), a moderate degree of steric hindrance suffices to allow their chemical separation. A simple procedure is developed for the preparation of these complexes in diastereoisomerically pure form. In addition, introduction of a prochiral substituent in the pyridine ring enables positive assignment of the stereoisomers. Isomerization rate measurements of the Fe(II) complexes in solution suggest that isomerization very likely involves the dissociation of the corresponding Fe-N(imino) bond prior to the rotation of N-aryl groups. DFT calculations provide additional support to the conformational assignment as well as the dissociative isomerization mechanism.
authors.affiliation: Instituto de Investigaciones Químicas, CSIC, Universidad de Sevilla, 49, 41092, Sevilla, Spain.
authors.forename: Juan
authors.initials: J
authors.lastname: Cámpora
authors.forename: M Angeles
authors.initials: MA
authors.lastname: Cartes
authors.forename: Antonio
authors.initials: A
authors.lastname: Rodríguez-Delgado
authors.forename: A Marcos
authors.initials: AM
authors.lastname: Naz
authors.forename: Pilar
authors.initials: P
authors.lastname: Palma
authors.forename: Carmen M
authors.initials: CM
authors.lastname: Pérez
authors.forename: Diego
authors.initials: D
authors.lastname: del Rio
mesh_terms: D003198:Computer Simulation; D018360:Crystallography, X-Ray; D005296:Ferrous Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D011725:Pyridines / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D005296:Ferrous Compounds; D008024:Ligands; D011725:Pyridines