Ein gürtelförmiger, monofacialer Ionophor mit hoher Selektivität für die Komplexierung von Lithiumionen

On the Regio- and Stereoselective Synthesis of Aminocyclitols from Cyclitol Epoxides: The Effect of Li as a Chelating Agent

Experimental and theoretical studies on the influence of Li ions on the regio- and the stereoselectivity of the reaction of cyclitol epoxides with nitrogen nucleophiles have been carried out. Model studies with NaN3 as a nucleophile in the absence of Li ions predict a mixture of C1 and C2 regioadducts. The inclusion of two Li ions as a chelating agent favours the operation of a low populated "all-axial" conformation leading ultimately to the C1 adducts. In all cases, the results can be rationalised by geometric and energetic considerations of the corresponding transition states. Predictions of the theoretical calculations are in good agreement with the experimental results using primary and secondary amines as nucleophiles, and thus confirm the validity of this study.

Self-assembled organometallic [12]metallacrown-3 complexes

The reaction of [(arene)RuCl2]2 (arene = C6H6, cymene, C6H3Et3, or C6Me6) or [Cp*RhCl2]2 with 3-hydroxy-2-pyridone in the presence of Cs2CO3 gives trinuclear metallamacrocyclic complexes. The self-assembly process was shown to be completely diastereoselective, and a racemic mixture of complexes with M(R)M(R)M(R) or MsMsMs (M=Ru, Rh) configuration was obtained. Plausible mononuclear intermediates of the formula [(arene)RuCl(C5H4NO2)] (arene = cymene, C6Me6) have been isolated and characterized. A structurally related trimer was synthesized by using [(cymene)RuCl2]2 and 3-acetamido-2-pyridone instead of 3-hydroxy-2-pyridone. The macrocycles were shown to be highly potent ionophores for Na+ and/or Li+ with negligible affinities for the larger cation K+. The selectivities of the receptors depend on the pi-ligand present: whereas the (C6H6)Ru- and (cymene)Ru complexes bind both Li+ and Na+, the (C6Me6)Ru-, (C6H3Et3)Ru-, and Cp*Rh complexes bind exclusively Li+. For all receptors, the presence of alkali metal ions can be detected electrochemically: the peak potential is shifted by > 300 mV toward anionic potential upon binding. This behavior was utilized to detect Li+ and Na+ colorimetrically. Single crystal X-ray analyses have been carried out on eight complexes, four of which are bound to an alkali metal halide ion pair. Structural parameters, which affect the affinity and selectivity are discussed. A computational study on [[MX][12]crown-3] complexes (M =Li, Na; X=Cl, Br, I) was performed in order to compare relevant bond lengths and angles of the energy-minimized structures with those of the organometallic receptors.