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

Abstract

AbstractThe partially fluorinated cryptandsFN2O4andBenzoFN2O4, which are relatives of the [2.2.1]cryptand, were synthesized in good yields from 1,3‐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 ofFN2O4are significantly more stable than those ofHN2O4(the two ligands are identical except that one fluorine atom is replaced by one hydrogen atom inHN2O4); the1JCFcoupling constants of Ag+·FN2O4and Ag+·BenzoFN2O4are reduced by 10 Hz compared to those of the respective free ligandsFN2O4(1JCF=253 Hz) andBenzoFN2O4. (1JCF=252 Hz). The X‐ray crystal structure of Ag+·FN2O4revelas short Ag+–F distances [271.4(3) pm]; coupling of the107,109Ag+and19F nuclei is observed in the19F‐NMR spectra (J=24 Hz for Ag+·FN2O4,J=25 Hz for Ag+·BenzoFN2O4). The1H‐NMR spectrum of Ag+·FN2O4is 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.