Intramolecular 'CH···π(Metal Chelate Ring) Interactions' as Structural Evidence for Metalloaromaticity in Bis(pyridine‐2,6‐diimine)Ru II Complexes

The synthesis and structural characterization of two novel RuII complexes (1 and 2) with tridentate pyridine-2,6-diimine ligands are described. In both compounds, ortho-CH bonds from the phenyl or phenyl-like rings produce unexpected CH···π interactions with ruthenium-α,α'-diimine chelate rings. This insight is thought to provide new structural evidence for the metalloaromaticity of the chelate rings in the ruthenium complexes studied. The molecular geometry of complex 1 is remarkably similar to S4 symmetrical geometry, which is also a consequence of the four CH···π(chelate ring) interactions working cooperatively. In contrast, there are only two pairs of these interactions working in complex 2 because of the steric effects and electronic influences caused by the methyl-group substitutions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)