Effects of ligand topology on the properties of dinuclear ruthenium complexes of bis-semiquinone bridging ligands

Abstract

The two ligands H 4L 1 and H 4L 2 were prepared in which two catechol donor groups are linked by vinyl groups to a central phenyl ring which is 1,3-substituted (for H 4L 1) or 1,4-substituted (for H 4L 2). These were used to prepare dinuclear complexes [{Ru( 1Bu 2bipy) 2} 2(μ-L)] 2+ (L = L 1, complex 1: or L 2, complex 2) in which aerial oxidation of the catecholate ligands to the semiquinone state has occurred. In 2 the two unpaired electrons that would be expected for two semiquinones can pair up to give a diamagnetic complex with a quinonoidal bridge, due to the 1,4-substitution pattern of the phenyl spacer: in 1 this cannot occur due to the 1,3 substitution pattern and the complex is a diradical as shown by EPR spectroscopy.