Incorporation of non-planar chelating ligands in the coordination sphere of ruthenium(II) complexes: Unusual S-thioether N-pyridyl chelation mode of di-2-pyridyl sulfide (dps) to Ru(N,N-dps)2 core: NMR studies of sterically induced internal dynamics

The unexpected products of the reaction of Ru(N,N-dps)2Cl2 with L [L=di-2-pyridyl sulfide (dps) and 2-(6-methylpyridyl) 2-pyridyl sulfide (mdps) are [Ru(dps)2(N,S-L)][PF6]2, where L is acting in an N,S-bidentate chelate mode as shown in the crystal structure of [Ru(N,N-dps)2(N,S-dps)][PF6]2·H2O (1). The Ru atom exhibits a distorted octahedral geometry involving five N atoms and an S atom. The four-membered chelate ring and the coordinated pyridine ring of the NS-ligand are coplanar, whereas the pendant pyridine is rotated by 113.9(2)°. In addition to the pendant ring, the N,S-coordination produces a sulfur chiral centre. The variable-temperature 1H and 13C NMR spectra show the fluxionality of the complexes. In acetone at all temperatures the spectra are consistent with the presence of intramolecular processes, whereas in acetonitrile above 300 K dissociation occurs and [Ru(N,N-dps)2(solvent)2]2+ and free ligand are present. In order to understand this dynamic behaviour, a synthetic methodology to obtain other octahedral [Ru(N,N-diimmine)2(N,S-L′)][PF6]2 and [Ru(dps)2(N,S-T)][PF6] complexes has been developed (N,N-diimmine=dps, dipyrimidin-2-yl sulfide (dprs), 2,2′-bipyridine (bipy); N,S-L′=phenyl pyridyl sulfide (phpys); N,S-T=2-mercaptopyridinate and 2-mercaptopyrimidinate). [Ru(dps)2(phpys)][PF6]2 and [Ru(dprs)2(phpys)][PF6]2 are fluxional species suitable for DNMR studies because of the presence of the anisochronous ortho (and meta) protons on the phenyl group. In acetone, restricted rotation of the uncoordinated ring is observed below 240 K and ΔH‡, ΔS‡ and ΔG‡ calculated. Above this latter temperature a more extensive internal rearrangement occurs, and the latter process may involve inversion at the sulfur chiral centre.