Synthesis, protonation and Cu2+ co-ordination studies on a new family of thiophenophane receptors†

Abstract

The synthesis of the new thiophenophanes 2,5,8,11-tetraaza[12](2,5)thiophenophane (L¹), 2,6,9,13-tetraaza[14](2,5)thiophenophane (L²) and 2,5,8,11,14-pentaaza[15](2,5)thiophenophane (L³) is described. The stepwise protonation constants of the macrocycles are determined by pH-metric titration and their protonation patterns are analysed by means of ¹H and ¹³C NMR spectroscopy. L¹ and L² present first protonation on the thenylic nitrogens while L³ protonates first on the central nitrogens of the polyamine bridge. Molecular orbital calculations are used to locate the atomic orbitals contributing to the HOMO of the free amines. The interaction with Cu²⁺ shows for L¹ and L³ formation of binuclear complexes which readily hydrolyse to give very stable species. Electrochemical studies show for all three Cu²⁺–receptor systems an important stabilisation of the Cu⁺ oxidation state towards its disproportionation into Cu²⁺ and Cu⁰ oxidation states.