Syntheses and Characterization of a Pair of Isomers of Heteroleptic Bis(Bidentate) Ruthenium(II) Complexes with Two Different Monodentate Ligands.

Two isomers of heteroleptic bis(bidentate) ruthenium(II) complexes with dimethyl sulfoxide (dmso) and chloride ligands, trans(Cl,Nbpy )- and trans(Cl,NHdpa )-[Ru(bpy)Cl(dmso-S)(Hdpa)]+ (bpy: 2,2'-bipyridine; Hdpa: di-2-pyridylamine), are synthesized. This is the first report on the selective synthesis of a pair of isomers of cis-[Ru(L)(L')XY]n+ (L≠L': bidentate ligands; X≠Y: monodentate ligands). The structures of the ruthenium(II) complexes are clarified by means of X-ray crystallography, and the signals in the 1 H NMR spectra are assigned based on 1 H-1 H COSY spectra. The colors of the two isomers are clearly different in both the solid state and solution: the trans(Cl,Nbpy ) isomer has a deep red color, whereas the trans(Cl,NHdpa ) isomer is yellow. Although both complexes have intense absorption bands at λ≈440-450 nm, only the trans(Cl,Nbpy ) isomer has a shoulder band at λ≈550 nm. DFT calculations indicate that the LUMOs of both isomers are the π* orbitals in the bpy ligand, and that the LUMO level of the trans(Cl,Nbpy ) isomer is lower than that of the trans(Cl,NHdpa ) isomer due to the trans effect of the Cl ligand; thus resulting in the appearance of the shoulder band. The HOMO levels are almost the same in both isomers. The energy levels are experimentally supported by cyclic voltammograms, in which these isomers have different reduction potentials and similar oxidation potentials.

Colorimetric fluoride detection in dimethyl sulfoxide using a heteroleptic ruthenium(ii) complex with amino and amide groups: X-ray crystallographic and spectroscopic analyses.

A bis-heteroleptic ruthenium(ii) complex, [Ru(Hdpa)2(H2pia)]X2 (1·X2; X = Cl, OTf, or F; Hdpa = di-2-pyridylamine; H2pia = 2-pycolinamide; OTf- = CF3SO3 -), was synthesized and spectroscopically and crystallographically characterized. The crystal structures of 1·Cl2·2.5H2O and 1·F2·2EtOH revealed essentially identical geometries for the 12+ dication; however, the dihedral angle between the two pyridyl groups in the Hdpa ligands, which represented the degree of bending of the bent conformation, was affected by hydrogen-bonding interactions between the NH group and counterions. In 1·F2·2EtOH, one of the Hdpa ligands had an unusually smaller dihedral angle (15.8°) than the others (29.9°-35.0°). The two NH groups of each Hdpa ligand and the NH2 group of the H2pia ligand in 12+ acted as receptors for F- anion recognition via hydrogen-bonding interactions in a dimethyl sulfoxide (DMSO) solution, and the reaction showed an unambiguous color change in the visible region. Upon the addition of tetra-n-butylammonium fluoride to the red DMSO solution of 1·(OTf)2·H2O, the solution turned dark brown. 1H NMR analysis and absorption spectroscopy of the reaction between 12+ and the added F- anions revealed that the F- anions did not distinguish between the two amino groups of Hdpa and the amide group of H2pia, although they were in different environments in the DMSO solution. A tris-F-adduct with 12+, 1·F3 -, was formed when sufficient F- anions were present in the solution, despite the presence of four NH protons in 12+. Time-dependent DFT calculations of 12+ and 1·F3 - were consistent with their absorption spectra.

Synthesis and characterization of trans-[Os(en)2py(H)]2+ and related studies.

trans-[Os(en)(2)pyH](Otf)(2), 2, is recovered from an acidic solution of trans-[Os(en)(2)py(H(2))](OTf)(2), 1, which has been subjected to one electron oxidation. The structures of both 1 and 2 have been determined by single crystal X-ray analysis. In cyclic voltammetry, 2 shows a one electron oxidation wave at 0.95 V and a one electron reduction wave at -1.2 V, neither accompanied by a signal for the reverse process. Reduction of 2 by Zn/Hg in methanol solution leads to quantitative formation of [Os(en)(2)(py)H(2))](2+), predominantly in the trans-form. In aqueous solution, species 2 reacts rapidly with N-methylacridium ion, [MAH](+), by hydride transfer. One electron chemical oxidation of 2 to the corresponding Os(IV) is slower than that of 1 to 2 owing to the increase in coordination number when Os(IV) is produced. Treatment of 1, or the cis-form, 1', in DMSO by sodium t-butoxide produces mainly the corresponding isomers of the monohydrides of Os(II), that derived from 1' is deep red in color while the trans-monohydride is colorless. Both react with [MAH](+) to form [MAH](2), and both disappear rapidly in acetone or acetonitrile, presumably by reducing the solvents. Reaction of trans-[Os(NH(3))(4)(H(2))H(2)O](BPh(4))(2), 4, in acetone-d(6) as solvent with either CH(3)CHO or styrene leads to hydrogenation of the substrate. Reactions which compete with trans-[Os(en)(2)(eta(2)-H(2))(CF(3)SO)(3)]CF(3)SO(3) release of substrate from the trans-complex before isomerization to the cis-form, required for hydrogenation to occur, result in the trans-derivative of the added solute. When H(2)C=CH-CH(2)-SCH(3) is the substrate, binding takes place at sulfur. Complete conversion to the cis-substrate isomer is observed, without hydrogenation occurring even though contact between dihydrogen and the double bond is possible.