Neutron and X-ray diffraction and spectroscopic investigations of intramolecular [C-H⋯F-C] contacts in post-metallocene polyolefin catalysts: Modeling weak attractive polymer-ligand interactions

Abstract

A family of Group 4 post-metallocene catalysts, supported by fluorine-functionalized tridentate ligands with the fluorine substituent in the locality of the metal center, is described. For the first time, the contentious C-H⋯F-C interaction has been characterized by a neutron diffraction study, which has allowed the position of the hydrogen atoms to be accurately determined. The nature of the weak intramolecular C-H⋯F-C contacts in these complexes in solution and the solid state was probed by using multinuclear NMR spectroscopy in tandem with neutron and X-ray crystallography. Evidence is presented to demonstrate that the spectroscopic C-H⋯F-C coupling occurs "through-space" rather than "through-bond" or by M⋯F coordination. The titanium catalysts exhibit excellent activities and high co-monomer incorporation in olefin polymerization. The observed intramolecular C-H⋯F-C interactions are important with regards to potential applications in polyolefin catalysis because they substantiate the proposed ortho-F⋯H(β) ligand-(polymer chain) contacts derived from DFT calculations for the remarkable fluorinated phenoxyimine Group 4 catalysts. Compared with agostic and co-catalyst⋯metal contacts, weak attractive noncovalent interactions between a polymer chain and a judiciously designed "active" ligand is a new concept in polyolefin catalysis. © 2006 Wiley-VCH Verlag GmbH & Co. KGaA.