Novel ruthenium nitrosyl complexes formed by nitrosating the tris(violurato)- and tris(1,3-dimethylviolurato)-ruthenate(II) anions

The salt Na2[Ru(NO)(NO2)4(OH)] reacts with barbituric acid in water to give Na[Ru(H2va)3](H2va–= bidentate violurate), and with 1,3-dimethylbarbituric acid to give Na[Ru(dmva)3](dmva–= bidentate 1,3-dimethylviolurate). The complexes react with Na[NO2] in acidic aqueous solutions to afford a series of novel diamagnetic nitrosylruthenium complexes of the general type cis-[Ru(L–L)2(NO)X](L–L = bidentate H2va– or dmva–; X–= Cl–, Br–, or unidentate H2va– or dmva–). In water, acetomtrile, or dimethyl sulphoxide. the complexes cis-[Ru(L–;L)3(NO)] release the co-ordinated nitrosyl lirgand owing to the intramolecular transformation: cis-[Ru(L–L)2(NO)(unidentate L–L)]→[Ru(L–L)2(bidentate L–L)]–+[NO]+. On the basis of the i.r. and 1H n.m.r. spectra, the most probable structures of the complexes are given and the high electrophilicity of co-ordinated NO is shown to result from the strong π-backbonding properties of the bidentate violurate ligands.