Synthesis and cytotoxicity of dinuclear complexes containing ruthenium(ii) bipyridyl units linked by a bis(pyridylimine) ligand

Abstract

Enantiopure dinuclear ruthenium polypyridyl complexes of the form [Ru₂(LL)₄L¹](PF₆)₄ (LL = 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen); L¹ = C₂₅H₂₀N₄ a bis(pyridylimine) ligand containing a diphenylmethane spacer) have been synthesized using the chiral building blocks cis-[Ru(bpy)₂(py)₂]²⁺ and cis-[Ru(phen)₂(py)₂]²⁺. These dinuclear ruthenium complexes have been characterised using NMR, mass spectrometry, UV-visible absorbance, circular dichroism and linear dichroism. The compounds exhibit good photo and thermal stability. The extinction coefficient for the bpy complex at 478 nm is ε₄₇₈ = 15 700 mol⁻¹ cm⁻¹ dm³ and for the phen complex is ε₄₇₈ = 24 900 mol⁻¹ cm⁻¹ dm³. Both complexes have their longest wavelength (metal to ligand charge transfer) transition predominantly x/y (short axis)-polarised while the transitions at shorter wavelength are a mixture of x/y and z-polarisations, similar to both the copper helicate and iron triple helicate studied previously. Cytotoxicity studies reveal that the compounds are dramatically less active against cancer cell lines than the recently reported supramolecular cylinders prepared from the same bis(pyridylimine) ligand.