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Novel heterodinuclear IrIII–MII complexes (M = Co, Ni, or Cu) with two adjacent reaction sites were synthesized by using 3,5-bis­(2-pyridyl)-pyrazole (Hbpp) as a structure-directing ligand and employed as catalysts for H2 evolution through formic acid dehydrogenation in water. A cooperative effect of the hetero-metal centers was observed in the H2 evolution in comparison with the corresponding mononuclear IrIII and MII complexes as the components of the IrIII–MII complexes. The H2 evolution rate for the IrIII–MII complexes was at most 350-fold higher than that of the mononuclear IrIII complex. The catalytic activity increased in the following order: IrIII–CuII complex < IrIII–CoII complex < IrIII–NiII complex . The IrIII–H intermediates of the IrIII–MII complexes were successfully detected by ultraviolet–visible, 1H nuclear magnetic resonance, and ESI-TOF-MS spectra. The catalytic enhancement of H2 evolution by the IrIII–MII complexes indicates that the IrIII–H species formed in the IrIII moiety act as reactive species and the MII moieties act as acceleration sites by the electronic effect from the MII center to the IrIII center through the bridging bpp– ligand. The IrIII–MII complexes may also activate H2O at the 3d MII centers as a proton source to facilitate H2 evolution. In addition, the affinity of formate for the IrIII–MII complexes was investigated on the basis of Michaelis–Menten plots; the IrIII–CoII and IrIII–NiII complexes exhibited affinities that were relatively higher than that of the IrIII–CuII complex. The catalytic mechanism of H2 evolution by the IrIII–MII complexes was revealed on the basis of spectroscopic detection of reaction intermediates, kinetic analysis, and isotope labeling experiments.

Tris-, tetrakis-, and pentakisazo dyes have been prepared by the oxidation of 4-(arylazo)arylamines. Iodobenzene diacetate was the preferred oxidant for preparation of 4,4'-bis(arylazo)azobenzenes and 4,4'bis(arylazo)-2,2',3,3',5,5',6,6'-octa¯uoroazobenzenes, whereas silver(II) oxide proved a satisfactory oxidant for synthesis of 4,4'-(arylazo)(methyl-substituted)azobenzenes. Unsymmetrical tris-and tetrakisazo dyes were also obtained by cross oxidation. The absorption bands of these azo dyes were observed in the range of 381±472 nm in liquid crystals. The solubility of the trisazo dyes in hexane was the highest, followed by the tetrakis-and pentakisazo dyes. The unsymmetrical derivative having methyl groups in the central p-phenylene moieties was most soluble among the trisazo dyes. The order parameters (S) of the tris-, tetrakis-, and pentakisazo derivatives were in the range 0.66±0.81, suf®ciently high for the practical application of these dyes in liquid crystal displays.

We have designed and synthesized a hetero-dinuclear Ru II −Co II complex with a dinucleating ligand inspired by hetero-dinuclear active sites of metalloenzymes. A synergistic effect between the adjacent Ru II and Co II sites has been confirmed in catalytic olefin hydrogenation by the complex, exhibiting a much higher turnover number than those of mononuclear Ru II or Co II complexes as the components. A Ru II -hydrido species was detected by 1 H NMR and electrospray ionization (ESI)time-of-flight (TOF)-MS measurements as an intermediate to react with olefins, and Co II -bound methanol was suggested to act as a proton source.

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