Coordination Chemistry with CF Units as σ Donors: Ag+ of Partially Fluorinated Crown Ethers Direct Metal-Fluorine Interactions

Article abstract of DOI:10.1002/cber.19961291012

The partially fluorinated cryptands FM₂O₄ and BenzoFN₂O₄ which are relatives of the [2.2.1]cryptand, were synthesized in good yields from l,3-bis(bromomethyl)-2-fluorobenzene and diaza-18-crown-6 or benzodiaza-18-crown-6, respectively. These macrobicyclic ligands form very stable complexes with Ag(I) salts, and it was shown that close fluorinesilver interactions occur in solution as well as in the solid state. Numerous experimental evidence for this is available: NMR competition experiments show that Ag⁺ complexes of FN₂O₄ are significantly more stable than those of HN₂O₄ (the two ligands are identical except that one fluorine atom is replaced by one hydrogen atom in HN₂O₄); the ¹J_CF coupling constants of Ag⁺ ·FN₂O₄ and Ag⁺ · BenzoFM₂O₄ are reduced by 10 Hz compared to those of the respective free ligands FN₂O₄ (¹J_CF = 253 Hz) and BenzoFN₂O₄. (¹J_CF = 252 Hz). The X-ray crystal structure of Ag⁺ ·FN₂O₄ reveals short Ag⁺-F distances [271,4(3) pm]; coupling of the ^107,109Ag⁺ and ¹⁹F nuclei is observed in the ¹⁹F-NMR spectra (J = 24 Hz for Ag⁺ · FN₂O₄, J= 25 Hz for Ag⁺ ·BenzoFN₂O₄). The ¹H-NMR spectrum of Ag⁺ ·FN₂O₄ is very complex and exhibits sixteen unique proton resonances, whose evaluation yielded coupling constants and NOEs, which show that the structure in solution is compatible with the results obtained by the X-ray crystal structure determination. VCH Verlagsgesellschaft mbH 1996.