[(η6-C6H6)RuII(L)(Cl/N3/CN/CH3CN)]+/2+ complexes of non-planar pyrazolylmethylpyridine ligands: Formation of helices due to C–H⋯X (X = Cl, N) interaction

Structural analysis of a previously reported half-sandwich complex having three-legged “piano-stool” geometry [(η6-C6H6)RuII(L1)Cl][PF6] (1) (L1 = 2-(pyrazol-1-ylmethyl)pyridine) is described. Treatment of 1 with (i) Ag(CF3SO3) in CH3CN and (ii) NaN3 in CH3OH, and (iii) the reaction between [(η6-C6H6)Ru(L2)Cl]-[PF6] (2) (previously reported) and NaCN in C2H5OH led to the isolation of [(η6-C6H6)Ru(L1)(CH3CN)][PF6]2 (3), [(η6-C6H6)Ru(L1)(N3)][PF6] (4), and [(η6-C6H6)Ru(L2)(CN)][PF6] (5), respectively (L2 = 2-(3,5-dimethyl-pyrazol-1-ylmethyl)pyridine). The complex [(η6-C6H6)Ru(L4)Cl][PF6] (6) with a new ligand (L4 = 2-[3-(4-fluorophenyl)pyrazol-1-ylmethyl]pyridine) has also been synthesized. The structures of 3–6 have been elucidated (1H NMR spectra; CD3CN). The molecular structures of 1, 4, and 6·C6H5CH3 have been determined. Notably, the crystal-packing in these structures is governed by C–H⋯X (X = Cl, N) interactions, generating helical architectures.

Systematic comparative studies (X-ray and 1H NMR) have been made on “piano-stool” complexes of RuII with non-planar pyrazolylmethylpyridine ligands. Analysis of crystal-packing diagrams reveals predominance of helix formation.Figure optionsDownload as PowerPoint slide