Jerome F. McAleer

Towards conformationally dependent redox-responsive molecular switches. New polyferrocene bis benzo crown ether receptors

New polyferrocene bis benzo-15-crown-5 ligands have been prepared and shown to form 1:1 intramolecular sandwich complexes with the potassium cation. Electrochemical investigations reveal that both receptors undergo small anodic perturbations of the respective ferrocene-ferrocenium redox couples in the presence of alkali metal cations.

Redox responsive crown ethers containing a direct link between the ferrocene redox-active centre and benzo crown ether. Crystal structure of a ferrocene benzo-15-crown-5 sodium complex

Abstract The binding of Na+, K+ and Mg2+ to benzo-15-crown-5 and aza-15-crown-5 directly-linked ferrocenes results in shifts of the ferrocene oxidation wave to more positive potentials. The magnitude of these anodic shifts is related to the charge/radius ratio of the cationic guest. The results of an X-ray diffraction study of the structure of a ferrocene benzo-15-crown-5 sodium complex are also reported.

Redox-active lithium-selective ionophores based on new 2,9-bis(ferrocenyl) substituted phenanthroline derivatives

Abstract A variety of new redox-active 2,9-bis(ferrocenyl)-substituted phenanthroline derivatives have been prepared, and the structure of one of them, 2,9-bis(ferrocenyl)ethenyl-1,10-phenanthroline, has been determined by an X-ray diffraction study. Solution 1 H NMR complexation studies suggest the 2,9-bis(ferrocenyl)vinylic- and amine-linked phenanthroline ligands form complexes with the ligand and Li + in 2 : 1 stoichiometric ratio, whereas Schiff-base-containing ionophores produced an equilibrium mixture of 2 : 1 and 1 : 1 complexes. The 2,9-bis(ferrocenyl)amide-linked phenanthroline ligands formed solution lithium complexes of 1 : 1 stoichiometry. Electrochemical investigations reveal that the respective ferrocene-ferricenium redox couples of most of the ligands are shifted to more positive potentials on co-ordination of Li + , but are electrochemically insensitive to Na + or K + guest cations. The above lithium redox-responsive ionophores recognise Li + electrochemically in the presence of equimolar concentrations of Na + and K + .

Lithium redox-responsive ferrocene bis-tertiary amide derivatives

Abstract The addition of Li + to ferrocene bis-tertiary amide derivatives in acetonitrile results in a shift of the ferrocene oxidation wave to more positive potentials and the appearance of a new redox couple associated with a Li + complex.

Metallocene bis(aza-crown ether) ligands and related compounds. Their syntheses, co-ordination chemistry, and electrochemical properties

The syntheses of new ferrocene and ruthenocene bis(aza-crown ethers)(11)–(14) containing amide bond linkages between the metallocene redox centre and aza-15-crown-5 (1,4,7,10-tetraoxa-13-azacyclopentadecane) and aza-18-crown-6 (1,4,7,10,13-pentaoxa-16-azacyclo-octadecane) are described. Variable-temperature 13C 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 to 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 to Li+ while being electrochemically insensitive to Na+ and K+.

A potassium-selective sulfide-linked redox-active ferrocene ionophore that exhibits extraordinary electrochemical recognition behaviour

A new ferrocenyl ionophore L1 selectively complexes, electrochemically recognises and responds to, via an extraordinary cathodic perturbation of the metallocene redox centre, the potassium guest cation in the presence of equimolar amounts of sodium ions.

Redox-responsive crown ethers containing a direct link between the ferrocene redox-active centre and a benzo-crown ether. Crystal structures of a ferrocene benzo-15-crown-5 ligand and of its sodium complex

New redox-active crown ethers, 15-ferrocenyl-2,3,5,6,8,9,11,12-octahydro-1,4,7,10,13-benzopentaoxacyclopentadecine (L1) and N-(4-ferrocenylphenyl)-1,4,7,10-tetraoxa-13-azacyclopentadecane (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 with the same ligands, which were also observed by fast-atom-bombardment mass spectrometry. Single-crystal X-ray structures of L1 and of its sodium complex [NaL1]PF6 have also been determined. Electrochemical investigations reveal that the binding of Na+, K+, and Mg2+ guest cations by L1 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.

Redox-active crown ethers: transmission of cation binding to a redox centre via a conjugated link

The binding of Li+ to aza-15-crown-5-linked ferrocenes results in a shift of the ferrocene oxidation wave to more positive potentials when a conjugated link exists between the azacrown nitrogen atom and the redox centre.

Selective electrochemical recognition of the potassium guest cation in the presence of sodium and magnesium ions by a new ferrocenyl ionophore

The new ferrocenyl ionophore (6) selectively complexes, electrochemically recognises, and responds to the potassium guest cation in the presence of equimolar amounts of sodium and magnesium ions.