| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2006: ¥1,700,000 (Direct Cost: ¥1,700,000)
Fiscal Year 2005: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Research Abstract |
Hydride in metal hydride complexes is usually considered to be electronegative and, in turn, difficult to remove in the form of proton. However, the release of hydrogen as the form of proton thermally occurs in some metal hydrides. Metal hydride complexes which contain a removable proton have never been shown to act as photoacids in contrast to organic photoacids, however, we have reported the first example of the excited-state deprotonation of an iridium hydride complex [Cp*Ir(bpy)H]+ (Cp*=η5-C5Me5, bpy=2,2'-bipyridine) under irradiation of visible light (λ<500 nm). The photoinduced deprotonation mechanism was examined by both the fs- and ns-laser flash photolysis. The rate of proton recombination reaction to form metal-hydrogen bond is significantly dependent on the electron-withdrawing or donating substituents of the π-conjugated diimine ligand. Photocatalytic hydrogen evolution was found to proceed in water via the excited-state deprotonation of [Cp*Ir(bpy)H]+ under irradiation of
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visible light. The role of the excited state of [Cp*Ir(bpy)H]+ in the hydrogen evolution reaction has yet to be clarified so far. Irradiation of the visible absorption band of [Cp*Ir(bpy)H]+ (λ>400 nm) results in hydrogen evolution accompanied by the disappearance of the absorption band due to [Cp*Ir(bpy)H]+ in deaerated water at room temperature. The quantum yields (Φ) of the hydrogen evolution reaction were determined from the spectral change under irradiation of monochromatized light of λ = 430 nm. The amount of hydrogen evolved was measured by GC. The Φ value increases with an increase in the concentration of [Cp*Ir(bpy)H]+ to approach a limiting value, indicating the excited state of [Cp*Ir(bpy)H]+ reacts with its ground state. The deprotonation from the iridium hydride occurs upon laser excitation even at λ = 600 nm in the case of a newly synthesized dinuclear metal complex bridged by a 2,2'-bipyrimidine ligand containing a bis(2,2'- bipyridine)ruthenium(II) complex moiety and an organometallic iridium hydride complex moiety. Less
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