The nature and importance of C-H···F-C interactions is a topical yet controversial issue, and the development of spectroscopic methods to probe such contacts is therefore warranted. A series of Group 4 bis(benzyl) complexes supported by (σ-aryl)-2-phenolate-6-pyridyl [O,C,N-R(1)] ligands bearing a fluorinated R(1) group (CF(3) or F) in the vicinity of the metal has been prepared. The X-ray crystal structure of the CF(3)-substituted Hf derivative features intramolecular C-H···F-C and Hf···F-C contacts. All complexes have been characterized by multinuclear NMR spectroscopy. The (1)H and (13)C NMR spectra of [M(O,C,N-CF(3))(CH(2)Ph)(2)] derivatives display coupling (assigned to (1h)J(HF) and (2h)J(CF) for Ti; (3)J(HF) and (2)J(CF) (through M···F) for Hf and Zr) between the benzyl CH(2) and CF(3) moieties. [(1)H,(19)F]-HMBC NMR experiments have been performed for the M-[O,C,N-R(1)] complexes and their [O,N,C] counterparts, revealing significant scalar coupling across the C-H···F-C interactions for Ti-[O,C,N] and [O,N,C] species.

The observation of weak intramolecular C−H•••F−C interactions in group 4 (σ-aryl)-chelating complexes using NMR spectroscopic and neutron diffraction studies was recently reported. In this work, a new titanium(IV) catalyst precursor supported by a tridentate pyridine-2-phenolate-6-(σ-aryl) ligand, featuring a metal center surrounded by multiple CF 3 substituents, has been synthesized. The nature of intramolecular interactions in the bis(benzyl) complex in solution was probed using multinuclear NMR spectroscopic experiments (including [ 1 H, 19 F]-HMQC and -HMBC), which reveal scalar coupling across C−H•••F−C interactions between methylene hydrogens and the proximal CF 3 group on the σ-aryl (but not the phenolate) moiety. High activities are observed for ethylene polymerization at different temperatures, which exceed those for the t Bu-phenolate congener.

A new series of group 4 bis(benzyl) complexes supported by (σ-aryl)-2-phenolate-6-pyridyl [O,C,N] ligands have been prepared, and all derivatives have been characterized by multinuclear NMR spectroscopy. In the (1)H NMR spectrum of the Ti derivative where [N] = (ortho-F)-substituted isoquinolinyl, one of the two CH2 resonances is observed as a doublet of doublets (collapsing to a normal d upon (19)F-decoupling), whereas the [(1)H,(19)F]-HMQC correlation spectrum reveals a strong crosspeak for this dd resonance only, thus indicating the presence of intramolecular C-HF-C interactions. [(1)H,(19)F]-HMBC experiments have been performed which reveal a significant scalar component for this coupling and confirm that the interactions are genuine. The contrasting NMR spectral patterns for the (ortho-F)-pyridyl Hf analogue, which exhibits two sets of non-identical doublet of doublets for the methylene resonances, have been rationalized. The activities of the isoquinolinyl-based Ti-[O,C,N] catalysts for ethylene polymerization are superior to those of pyridyl-based congeners.

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Correction for ‘Synthesis and spectroscopic characterization of group 4 post-metallocenes bearing (σ-aryl)-2-phenolate-6-pyridyl and -isoquinolinyl auxiliaries’ by Jerry C. Y. Lo et al., Dalton Trans., 2015, 44, 15905–15913.