Scalar Coupling Across [C-H⋯F-C] Interactions in (σ-Aryl)-Chelating Post-Metallocenes

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 ¹H and ¹³C NMR spectra of [M(O,C,N-CF ₃)(CH ₂Ph) ₂] derivatives display coupling (assigned to ^1hJ _HF and ^2hJ _CF for Ti; ³J _HF and ²J _CF (through M⋯F) for Hf and Zr) between the benzyl CH ₂ and CF ₃ moieties. [ ¹H, ¹⁹F]-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. Genuinely attractive! The titled complexes have been characterized by multinuclear NMR (including [ ¹H, ¹⁹F]-HMBC) experiments, which for the first time confirm that the observed ¹H- ¹⁹F coupling occurs with chemical connectivity across C-H⋯F-C interactions for Ti complexes (see scheme); differences in coupling patterns for Zr and Hf congeners are also rationalized. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.