Diruthenium complexes with 5-methyl-7-phenyl-1,8-naphthyridin-2-one as an ambidentate bridging ligand

Abstract

Reaction of [Ru 2Cl(OAc) 4] with mphonp − (Hmphonp=5-met hyl-7-phenyl-1,8-naphthyridin-2-one) in methanol at reflux leads to precipitation of the diruthenium(II,III) complex [Ru 2Cl(mphonp) 2(OAc) 2] ( 1) within 0.5 h. The compound exhibits a polar arrangement of ligands with Ru(1) coordinated by two trans-sited mphonp N1 atoms, Ru(2) by two trans-sited mphonp O2 atoms and the axial chloride ligand. 1 is reduced to the diruthenium(II,III) complex [Ru 2(mphonp) 2] ( 2) on further refluxing (6 h). In contrast to 1, the trans-sited mphonp − ligands now display the N,N′ coordination mode and point in opposite directions. The further reaction of 2 with mphonp − in refluxing methanol (36 h) then leads to substitution of all four acetate ligands and the formation of [Ru 2(mphonp) 4] ( 3a). Steric interactions between adjacent phenyl substituents appear to be responsible for the adoption of the electronically less preferred N,O coordination mode by three of the bridging ligands in the polar water adduct [Ru 2(mphonp) 4(H 2O)] ( 3b). Hmphonp, 1, 2 and 3b were characterised by X-ray structural analysis.