Novel polypyridyl ruthenium(II) complexes containing oxalamidines as ligands

The complexes [Ru(bpy)2(H2TPOA)](PF6)2·4H2O (1); [Ru(Me-bpy)2(H2TPOA)](PF6)2·2H2O (2); [Ru(bpy)2(H2TTOA)](PF6)2·2H2O (3); [Ru(Me-bpy)2(H2TTOA)](PF6)2·2H2O (4) and {[Ru(bpy)2]2(TPOA)}(PF6)2·2H2O (5) (where bpy is 2,2′-bipyridine; Me-bpy is 4,4′-dimethyl-2,2′-bipyridine; H2TPOA is N,N′,N′′,N′′′-tetraphenyloxalamidine; H2TTOA is N,N′,N′′,N′′′-tetratolyloxalamidine) have been synthesised and characterised by 1H NMR, FAB MS, infrared spectroscopy and elemental analysis. The X-ray investigation shows the coordination of the still protonated oxalamidine moiety via the 1,2-diimine unit. The dimeric compound (5) could be separated in its diastereoisomers (5′) and (5′′) by repeated recrystallisation. The diastereomeric forms exhibit different 1H NMR spectra and slightly shifted electronic spectra. Compared with the model compound [Ru(bpy)3]2+, the absorption maxima of (1)–(5) are shifted to lower energies. The mononuclear complexes show Ru(III/II)-couples at about 0.9 V versus SCE, while for the dinuclear complex two well defined metal based redox couples are observed at 0.45 and 0.65 V, indicating substantial interaction between the two metal centres.