C^sub 1^-symmetrical cis-bis(di-2-pyridylamine)chloro(dimethyl sulfoxide-S)ruthenium(II) complex: Synthesis, crystal structure, and anion recognition using the NH groups in the chelating ligands

The C1-symmetrical cis-bis(Hdpa)Ru(II) complex, cis-[RuCl(Hdpa)2(dmso-S)]X (1·X; X = Cl or OTf, Hdpa = di-2-pyridylamine, dmso = dimethyl sulfoxide, OTf− = CF3SO3−), was synthesized and spectroscopically and crystallographically characterized. The crystal structures of 1·Cl and 1·(OTf) revealed that the Hdpa(N(4),N(6)) ligand was more planar with a near ideal bite angle compared with the Hdpa(N(1),N(3)) ligand. The two NH groups in 1+ were distinguishable in solution, and both NH groups could act as receptors for DMSO molecules or for Cl− and F− anion recognition via hydrogen bonding interactions. Among them, the reaction of 1+ with F− was noteworthy because of the obvious color change in the visible region. For 1·(OTf) in DMSO with TBAF, 1H NMR revealed that the F− adduct reaction with Hdpa ligands selectively and successively occurred in two steps. The NH group of the Hdpa(C,D) ligand, which was with a dmso-S ligand at the cis position of the two pyridine rings of itself and corresponds to the planar Hdpa(N(4),N(6)) ligand in the crystal structure, initially interacted with a F− anion to form [RuCl(F-Hdpa)(Hdpa)(dmso)] (mono-F-adduct-1). Then, the NH group of the remaining Hdpa(A,B) ligand also interacted with a F− anion to form [RuCl(F-Hdpa)2(dmso)]− (di-F-adduct-1). When excessive Li(OTf) was added to the mono- or di-F-adduct-1 solution, the solution turned yellow, suggesting that the adducted F− anion was removed by the Li+ ion to form 1+ and LiF.