Sawaki Takuya, Ishizuka Tomoya, Namura Nanase, Hong Dachao, Miyanishi Mayuko, Shiota Yoshihito, Kotani Hiroaki, Yoshizawa Kazunari, Jung Jieun, Fukuzumi Shunichi, Kojima Takahiko
Department of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba and CREST (JST), 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8571, Japan.
Dalton Trans. 2020 Dec 21;49(47):17230-17242. doi: 10.1039/d0dt03546g. Epub 2020 Nov 19.
A Ru complex, [Ru(tpphz)(bpy)] (1) (tpphz = tetrapyridophenazine, bpy = 2,2'-bipyridine), whose tpphz ligand has a pyrazine moiety, is converted efficiently to [Ru(tpphz-HH)(bpy)] (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 (MLCT*) of 1 is firstly formed upon photoirradiation and the MLCT* state is reductively quenched with an electron donor to afford [Ru(tpphz˙)(bpy)], 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 H evolution and the hydrogenation of organic substrates. In the reactions, complex 2 is required to be excited to form its MLCT* state to react with a proton and aldehydes. In photocatalytic H 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 H evolving rates. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations on the reaction mechanism of H evolution from the ground and photo-excited states of 2 were performed to have a better understanding of the photocatalytic processes.
一种钌配合物[Ru(tpphz)(bpy)] (1)（tpphz = 四吡啶并菲嗪，bpy = 2,2'-联吡啶），其tpphz配体含有吡嗪部分，在电子供体存在下，对1的水 - 甲醇混合溶剂溶液进行光照射时，能高效转化为具有二氢吡嗪部分的[Ru(tpphz - HH)(bpy)] (2)。在该反应中，光照射时首先形成1的三重态金属到配体电荷转移激发态（MLCT*），MLCT态被电子供体还原猝灭得到[Ru(tpphz˙)(bpy)]，通过纳秒激光闪光光解将其转化为2，未观察到可检测到的还原中间体。在二氢吡嗪部分形成2的N - H键时，观察到逆动力学同位素效应（KIE）为0.63。在惰性气氛下，在质子溶剂中，于电子供体存在下对1的溶液进行白光（380 - 670 nm）照射，导致光催化析氢和有机底物的氢化。在这些反应中，需要激发配合物2以形成其MLCT态，使其与质子和醛反应。在光催化析氢过程中，光激发的2与质子之间形成H - H键参与了速率决定步骤，析氢速率的正常KIE为5.2。对2的基态和光激发态析氢反应机理进行了密度泛函理论（DFT）和含时密度泛函理论（TD - DFT）计算，以更好地理解光催化过程。
