DIRUTHENIUM COMPLEXES WITH 5-METHYL-7-PHENYL-1,8-NAPHTHYRIDIN-2-ONE AS AN AMBIDENTATE BRIDGING LIGAND

Reaction of [Ru2Cl(OAc)(4)] with mphonp(-) (Hmphonp = 5-methyl-7-pheny l-1,8-naphthyridin-2-one) in methanol at reflux leads to precipitation of the diruthenium(II,III) complex [Ru2Cl(mphonp)(2)(OAc)(2)] (1) wit hin 0.5 h. The compound exhibits a polar arrangement of ligands with R u(1) coordinated by two trans-sited mphonp N1 atoms, Ru(2) by two tran s-sited mphonp O2 atoms and the axial chloride ligand. 1 is reduced to the diruthenium(II,II) complex [Ru-2(mphonp)(2)(OAc)(2)] (2) on furth er refluxing (6 h). In contrast to 1, the trans-sited mphonp(-) ligand s now display the N,N' coordination mode and point in opposite directi ons. The further reaction of 2 with mphonp(-) in refluxing methanol (3 6 h) then leads to substitution of all four acetate ligands and the fo rmation of [Ru-2(mphonp)(4)] (3a). Steric interactions between adjacen t phenyl substituents appear to be responsible for the adoption of the electronically less preferred N,O coordination mode by three of the b ridging ligands in the polar water adduct [Ru-2(mphonp)(4)(H2O)] (3b). Hmphonp, 1, 2 and 3b were characterised by X-ray structural analysis.