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 novel concept. Moreover, the existence, importance, and applicability of extremely weak hydrogen bonds such as C−H···F−C remain controversial. We have presented a family of Group 4 post-metallocene catalysts, supported by F-functionalized chelating s-aryl 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 aspects for improving polymerization efficiencies have been established.3 This work was supported by the Research Grants Council of the Hong Kong SAR, China (CityU 100406 and 100409).