Highly Fluorinated (σ-Aryl)-Chelating Titanium(IV) Post-Metallocene: NMR Characterization, Scalar [C-H...F-C] Coupling and Olefin Polymerization Studies

The observation of weak intramolecular C-H···F-C contacts in Group 4 post-metallocene complexes, using NMR spectroscopic and neutron diffraction studies, was recently reported.[1,2] In this work, a new titanium(IV) catalyst supported by a tridentate pyridine-2-phenolate-6-(s-aryl) ligand, featuring a metal center surrounded by multiple CF3 substituents, has been designed and prepared. The nature of intramolecular interactions in the bis(benzyl) complex in solution was probed using multinuclear NMR spectroscopic experiments (including [1H,19F]-HMQC and -HMBC), which reveal scalar coupling across C–H···F–C interactions between methylene hydrogens and the proximal CF3 group on the s-aryl (but not the phenolate) moiety. High activities are observed for ethylene polymerization at different temperatures, which exceed those for the tBu-phenolate congener. Dispersion-corrected DFT calculations for the cationic Ti(IV) propyl model species revealed a weak interaction between a fluorine atom and a b-hydrogen of the n-propyl chain in the energy-minimized structure.