The syntheses of new redox-active crown ethers 8a, 8b, 9a, and 9b containing cis-and trans-conjugated olefinic linkages between the ferrocene redox center and respectively benzo-15-crown-5 and /V-phenylaza-15-crown-5 are described. The sodium cation forms 1:1 stoichiometric complexes with the trans ferrocenyl ionophores 8b and 9b, whereas potassium produces 1:2 intermolecular sandwich complexes with the same ligands, which were also observed by fast atom bombardment mass spectrometry. Electrochemical investigations reveal the binding of Na+, K+, and Mg2+ guest cations at the respective crown ether coordinating sites results in shifts of the ferrocene oxidation wave to more positive potentials if a conjugated -electron system links the heteroatoms of the ionophore to the redox center. The magnitude and type (one or two waves) of the anodic shift are related to the charge:radius ratio of the cationic guest, Mg2+ producing the largest value and K+ the smallest.
The syntheses of n e w ferrocene and ruthenocene bis(aza-crown ethers) (1 1 )-( 14) containing amide bond linkages between the metallocene redox centre and aza-I 5-crown-5 (1,4,7,1 O-tetraoxa-13-azacyclopentadecane) and aza-I 8-crown-6 (1,4,7,10,13-pentaoxa-I 6-azacyclo-octadecane) are described. Variable-temperature I3C n.m.r. studies on these compounds reveal a common intramolecular dynamic process involving rotation about the N-CO bond whose energy barrier to rotation is cation (Na' or Li') dependent. The sodium cation forms 1 : 2 stoicheiometric complexes with the ferrocene bis(aza-crown ethers), whereas potassium produces a 1 : 1 intramolecular sandwich complex with the former and a 1 : 2 complex with the latter. Electrochemical investigations reveal that binding of Na' and K + guest cations at the respective aza-crown ether co-ordinating sites results in shifts of the ferrocene oxidation wave t o more positive potentials. Lithium produces analogous electrochemical effects with these two compounds, however 13C n.m.r. results suggest this cation exclusively co-ordinates to the respective amide carbonyl oxygen donor atoms. This rationalisation is supported by 'model' ferrocene bis(tertiary amide) derivatives which exhibit redox-responsive behaviour t o Li' while being electrochemically insensitive to Na' and K'.
benzopentaoxacyclopentadecine (L') and N-(4-ferrocenylphenyl) -lr4,7,10-tetraoxa-13azacyclopentadecane ( L2), containing a direct link between the ferrocene redox centre and respectively benzo-15-crown-5 and N-phenylaza-15-crown-5, have been prepared. The sodium cation forms 1 1 stoicheiometric complexes with both ionophores whereas the larger potassium cation produces 1 : 2 intermolecular sandwich complexes w i t h the same ligands, which were also observed b y fast-atom-bombardment mass spectrometry. Single-crystal X-ray structures of L1 and of its sodium complex [NaL'] PF, have also been determined. Electrochemical investigations reveal that the binding of Na', K', and Mg2+ guest cations by L' and L2 results in shifts of the respective ferrocene-ferrocenium redox couple to more positive potentials. The magnitude of these one-wave anodic shifts is related to the charge: radius ratio of the cationic guest species.
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