The first report on specific binding mode of diethylmalonate acting as a bridging ligand between ruthenium (II) ions stabilized by intramolecular hydrogen bonds

Abstract

Typically 2,2-diethylmalonate (dem) acts as a chelating ligand and binds to the metal in a η 2 (dem-O, O′) mode. However, when cis,fac-[RuCl 2(TMSO-S) 4] is treated with K 2(dem), it prefers to bind in an unusual bridging mode (μ-dem-O, O′) with the ruthenium (II) cation containing coordinated water, forming a strong hydrogen bond with the non-coordinated oxygen atoms of the 2,2-diethylmalonate ligand. The reaction products of cis, fac-[RuCl 2(TMSO-S) 4] ( 1) and cis, fac-[RuCl 2(DMSO-S) 3(DMSO-O)] ( 2) with dem are the dinuclear species with two bridging dem units, fac-[Ru(TMSO-S) 3(H 2O)(μ 2-dem-O, O′)] 2 ( 3) and fac-[Ru(DMSO-S) 3(H 2O)(μ 2-dem-O, O′)] 2 ( 4), respectively. The complex 3 was characterized by X-ray crystallography in which water ligands occupy anti positions with respect to each other. The NMR and X-ray study support each other with respect to dinuclear structure of 3 and 4, indicating that the dinuclear structure observed in the solid state is preserved in solution as well. The mononuclear anionic complex with chelating dem unit, K{ fac-[RuCl(η 2-dem-O, O′)(TMSO-S) 3} ( 5), was also isolated from the reaction of 1 and K 2(dem) demonstrating that 5 is an intermediate in the formation of 3.