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，并且反过来难以以质子的形式除去。然而，氢以质子的形式热释放发生在某些金属氧化物中。与有机光酸相比，含有可去除质子的金属氢化物络合物从未被证明作为光酸，然而，我们已经报道了铱氢化物络合物[Cp*Ir（bpy）H]+（Cp*=η5-C5 Me 5，bpy= 2，2 '-bipyridine）在可见光（λ<500 nm）照射下的激发态去质子化的第一个例子。通过飞秒和纳秒激光闪光光解研究了光诱导去质子化机制。质子重组反应形成金属-氢键的速率与π共轭二亚胺配体上的吸电子或供电子取代基密切相关。在紫外光照射下，[Cp*Ir（bpy）H]+的激发态去质子化是光催化析氢的主要途径。 ...更多信息 可见光[Cp*Ir（bpy）H]+的激发态在析氢反应中的作用至今尚未明确。[Cp*Ir（bpy）H]+的可见吸收带（λ>400 nm）的照射导致氢析出，伴随着室温下脱气水中[Cp*Ir（bpy）H]+的吸收带的消失。在波长为430 nm的单色光照射下，由光谱变化确定了析氢反应的量子产率（Φ）。通过GC测量放出的氢的量。Φ值随[Cp*Ir（bpy）H]+浓度的增加而增加，并接近一个极限值，表明[Cp*Ir（bpy）H]+的激发态与其基态发生了反应.在新合成的双核金属配合物的情况下，即使在λ = 600 nm处，也会在激光激发下发生氢化铱的去质子化，所述双核金属配合物由含有双（2，2 '-联吡啶）钌（II）配合物部分和有机金属氢化铱配合物部分的2，2'-联嘧啶配体桥接。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