Probing [C–H···F–C] and related contacts as models of weak attractive ligand–polymer interactions

What are ‘weak attractive ligand–polymer interactions’? In metal-catalyzed olefin polymerization reactions, the study of non-covalent interactions between a non-passive ancillary ligand and the growing polymer chain is a new concept. Moreover, the existence, importance, and applicability of extremely weak hydrogen bonds such as C−H···F−C remain controversial. We have described a family of Group 4 post-metallocene catalysts, supported by F-functionalized tridentate ligands with fluorine groups adjacent to the active site, as models of weak attractive ligand–polymer interactions. For the first time, the elusive C-H···F-C interaction was manifested as NMR-discernible 1H-19F coupling in solution and characterized by a neutron diffraction study.1 These observations may have important implications for polyolefin catalyst design, since they corroborate the practical feasibility of the ortho-F···H(b) ligand–polymer contacts proposed for the living Group 4 fluorinated phenoxyimine catalysts.2 In recent developments, catalysts exhibiting new types of intramolecular non-covalent interactions have been realized, and unexpected design features for improving polymerization activities have been established. [This work was supported by the Research Grants Council of the Hong Kong SAR, China (CityU 100406).]