Efficient Hydrogen Evolution Accompanied by Photoacid Generation of Organometallic Hydride Complexes

金属氢化物络合物中的氢化物通常被认为是电负性的，因此很难以质子的形式去除。然而，氢以质子的形式在某些金属氢化物中热释放。与有机光酸相比，含有可移除质子的金属氢化物络合物从未被证明是光酸，然而，我们首次报道了在可见光(η&lt；500 nm)照射下Ir氢化物络合物[Cp*Ir(Bpy)H]+(Cp*=λ5-C5Me5，bpy=2，2‘-联吡啶)的激发态去质子化反应。用飞秒和纳秒激光闪光光解研究了光致去质子化机理。形成金属氢键的质子复合反应速率与π偶联的二亚胺配体的吸电子或给电子取代基密切相关。在…的照射下，[Cp*Ir(Bpy)H]+在水中通过激发态去质子化进行光催化析氢更多的可见光。到目前为止，[Cp*Ir(Bpy)H]+的激发态在析氢反应中的作用尚不清楚。在室温下，[Cp*Ir(Bpy)H]+(λ&gt；400 nm)的可见吸收带被辐照，伴随着除氧水中的[Cp*Ir(Bpy)H]+吸收带的消失。根据Φ=430 nm的单色光照射下的光谱变化，确定了析氢反应的量子产率(λ)。用气相色谱(GC)法测定放氢量。Φ值随着[Cp*Ir(Bpy)H]+浓度的增加而增大，接近一个极限值，表明[Cp*Ir(Bpy)H]+的激发态与其基态发生反应。即使在λ=6 0 0 nm的激光激发下，由含有双(2，2‘-联吡啶)Ru(II)络合物部分和有机金属Ir氢化物部分的2，2’-联嘧啶配体桥联的双核金属络合物在激光激发下也会发生去质子化反应。较少

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 … More 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