Complexation between ferrocene-based 2,2′-bipyridineligands and copper(i) cations

Abstract

Copper(I) cations bind to a ferrocene-based ligand bearing two pendant 2,2′-bipyridine groups to form three distinct complexes possessing compositions of 1 ∶ 1, 1 ∶ 2 and 2 ∶ 2 (metal to ligand), respectively. The 2 ∶ 2 complex exists in the form of a double-stranded metallo-helicate but it is unstable in solution with respect to dissociation into the mononuclear species. Stability constants have been determined for each of the complexes using UV-visible spectrophotometric titrations. With this information, together with data derived from competitive complexation studies, electrospray mass spectrometry and electrochemistry, the mechanism by which the metallo-helicate self assembles in solution has been deduced. It is clear that the binuclear complex forms on dimerization of the 1 ∶ 1 complex, for which there is only a small thermodynamic driving force (ΔG⁰ = −3.5 kJ mol⁻¹).