Photocatalytic Hydrogen Evolution Using a Ru(II)-Bound Heteroaromatic Ligand as a Reactive Site
Photocatalytic Hydrogen Evolution Using a Ru(II)-Bound Heteroaromatic Ligand as a Reactive Site
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使用 Ru(II) 结合的杂芳族配体作为反应位点的光催化析氢
DOI：
10.1039/d0dt03546g
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发表时间：
2020
影响因子：
4
通讯作者：
Takahiko Kojima
中科院分区：
文献类型：
--
作者：
Takuya Sawaki;Tomoya Ishizuka;Nanase Namura;Dachao Hong;Mayuko Miyanishi;Yoshihito Shiota;Hiroaki Kotani;Kazunari Yoshizawa;Jieun Jung;Shunichi Fukuzumi;Takahiko Kojima
在电子供体存在下，通过对1的水-甲醇混合溶剂溶液进行光照射，将tpphz配体具有吡嗪部分的Ru II络合物[Ru II（tpphz）（bpy）2]2+（1）（tpphz =四吡啶并吩嗪，bpy = 2，2 ′-联吡啶）有效地转化为具有二氢吡嗪部分的[Ru II（tpphz-HH）（bpy）2]2+（2）。在该反应中，1的三重态金属-配体电荷转移激发态（3 MLCT *）首先在光照射下形成，并且3 MLCT * 状态用电子供体还原淬灭以提供[RuII（tpphz stec −）（bpy）2]+，其通过纳秒激光闪光光解转化为2，而没有观察到可检测的还原中间体。2在二氢吡嗪上形成N-H键的逆动力学同位素效应（KIE）为0.63。在惰性气氛下，在电子供体的存在下，1在质子溶剂中的溶液的白光（380-670 nm）照射导致光催化H2析出和有机底物的氢化。在反应中，配合物2需要被激发以形成其3 MLCT * 状态，从而与质子和醛反应。在光催化放氢中，光激发态2和质子之间的H-H键形成参与了速率决定步骤，正常KIE为5.2。采用密度泛函理论（DFT）和含时密度泛函理论（TD-DFT）对2的基态和光激发态放氢反应机理进行了计算，以更好地理解光催化过程.
A RuII complex, [RuII(tpphz)(bpy)2]2+ (1) (tpphz = tetrapyridophenazine, bpy = 2,2′-bipyridine), whose tpphz ligand has a pyrazine moiety, is converted efficiently to [RuII(tpphz-HH)(bpy)2]2+ (2) having a dihydropyrazine moiety upon photoirradiation of a water–methanol mixed solvent solution of 1 in the presence of an electron donor. In this reaction, the triplet metal-to-ligand charge-transfer excited state (3MLCT*) of 1 is firstly formed upon photoirradiation and the 3MLCT* state is reductively quenched with an electron donor to afford [RuII(tpphz˙−)(bpy)2]+, which is converted to 2 without the observation of detectable reduced intermediates by nano-second laser flash photolysis. The inverse kinetic isotope effect (KIE) was observed to be 0.63 in the N–H bond formation of 2 at the dihydropyrazine moiety. White-light (380–670 nm) irradiation of a solution of 1 in a protic solvent, in the presence of an electron donor under an inert atmosphere, led to photocatalytic H2 evolution and the hydrogenation of organic substrates. In the reactions, complex 2 is required to be excited to form its 3MLCT* state to react with a proton and aldehydes. In photocatalytic H2 evolution, the H–H bond formation between photoexcited 2 and a proton is involved in the rate-determining step with normal KIE being 5.2 on H2 evolving rates. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations on the reaction mechanism of H2 evolution from the ground and photo-excited states of 2 were performed to have a better understanding of the photocatalytic processes.