Structural, electrochemical and UV/VIS/NIR spectroelectrochemical properties of diastereomerically pure dinuclear ruthenium complexes based on the bridging ligand phenanthroline-5,6-diimine, and a mononuclear by-product witha peripheral isoimidazole group

Mono- and di-nuclear ruthenium(II) complexes derived from the potentially b ridging ligand 5,6-diaminophenanthroline (dap) have been prepared and inves tigated. Reaction of dap (which has one 'bipyridyl-like' and one diamine co -ordination site) with [Ru(bipy)(2)Cl-2] afforded [{Ru(bipy)(2)}(2)(mu-pdi) ](4+), where pdi = phenanthroline-5,6-diimine, in which the diamine site ha s undergone a two-electron oxidation to give a quinone diimine site. The co mplex (as its hexafluorophosphate salt) could be separated chromatographica lly into its two diastereoisomers which were fully characterised independen tly, including the crystal structure of the homochiral diastereoisomer as i ts perchlorate salt. Electrochemical studies revealed six reversible reduct ions, of which the first two were shown by spectroelectrochemical studies t o be centred on the bridging ligand (diimine/diiminosemiquinone and diimino semiquinone/diamide couples), and the rest based on the terminal bipyridyl ligands. Although these six reductions occurred at identical potentials for both diastereoisomers, the separation between the two closely spaced Ru-II -Ru-III couples varied slightly between the diastereoisomers indicating som e sensitivity of delocalisation in the Ru-II-Ru-III mixed-valence state to the optical configuration of the metal centres. The mononuclear complex [Ru (bipy)(2)(dap)](2+), in which the metal is co-ordinated at the bipyridyl si te of dap with the diamine site vacant, easily reacts with acetone to give [Ru(bipy)(2)L](2+) where L is a phenanthroline derivative with a peripheral isoimidazole ring derived from condensation of one equivalent of acetone w ith the o-diamine group. The electrochemical, spectroscopic and luminescenc e properties of [Ru(bipy)(2)L](2+) are only slightly perturbed from those o f [Ru(bipy)(3)](2+).