Syntheses and Crystal Structures of Mono(di-2-pyridylamine)chloro(dimethyl sulfoxide-S)ruthenium(II) Complexes [RuCl2(Hdpa)(dmso-S)2] and [RuCl(Hdpa)(dmso-O)(dmso-S)2](OTf)

The reaction between trans-[RuCl2(dmso-S)4] (dmso = dimethyl sulfoxide) and di-2-pyridylamine (Hdpa) in EtOH–H2O at ca. 273 K afforded trans(Cl),cis(S)-[RuCl2(Hdpa)(dmso-S)2] (1) in moderate to high yield. When dissolved in DMSO, 1 rearranged to the more thermodynamically stable cis(Cl),cis(S)-[RuCl2(Hdpa)(dmso-S)2] (2), along with cis(Cl),trans(X)-[RuCl2(Hdpa)(dmso)2] (X = S- or O-bonded dmso). The reaction of 2 with Ag(OTf) afforded cis(Cl,S),trans(O,S)-[RuCl(Hdpa)(dmso-O)(dmso-S)2](OTf) (3·(OTf)) (OTf− = trifluoromethanesulfonate). X-ray crystal structures of 1, 2, and 3·(OTf) revealed that the conformation of the six-membered chelate ring formed by the Hdpa ligand with the Ru ion varies according to interactions among the co-ligands (dmso and Cl−) and the counter-anion (OTf−). For 3·(OTf), the structural parameters, apart from the dmso-O ligand, were essentially comparable to those of 2, except for the axial Cl− ligand; the remaining axial site is occupied by the O-donor of the dmso ligand instead of the S-donor. The solution structures (in DMSO solution) of 1, 2, and 3·(OTf) are discussed on the basis of their 1H NMR spectra. In 3·(OTf), “flapping” of the Hdpa ligand causes the coordination modes (O- and S-bonded) of the two axial dmso ligands to undergo mutual alternation.