Gueret Robin, Castillo Carmen E, Rebarz Mateusz, Thomas Fabrice, Hargrove Aaron-Albert, Pécaut Jacques, Sliwa Michel, Fortage Jérôme, Collomb Marie-Noëlle
Univ. Grenoble Alpes, DCM, F-38000 Grenoble, France; CNRS, DCM, F-38000 Grenoble, France.
Laboratoire de Spectrochimie Infrarouge et Raman, UMR 8516 CNRS-Université Lille 1 Sciences et Technologies, 59655 Villeneuve d'Ascq Cedex, France.
J Photochem Photobiol B. 2015 Nov;152(Pt A):82-94. doi: 10.1016/j.jphotobiol.2015.04.010. Epub 2015 Apr 30.
We recently reported a very efficient homogeneous system for visible-light driven hydrogen production in water based on the cobalt(III) tetraaza-macrocyclic complex Co(CR)Cl2 (1) (CR=2,12-dimethyl-3,7,11,17-tetra-azabicyclo(11.3.1)-heptadeca-1(17),2,11,13,15-pentaene) as a noble metal-free catalyst, with Ru(II)(bpy)3 (Ru) as photosensitizer and ascorbate/ascorbic acid (HA(-)/H2A) as a sacrificial electron donor and buffer (PhysChemChemPhys 2013, 15, 17544). This catalyst presents the particularity to achieve very high turnover numbers (TONs) (up to 1000) at pH 4.0 at a relative high concentration (0.1mM) generating a large amount of hydrogen and having a long term stability. A similar activity was observed for the aquo derivative Co(III)(CR)(H2O)2 (2) due to substitution of chloro ligands by water molecule in water. In this work, the geometry and electronic structures of 2 and its analog Zn(II)(CR)Cl (3) derivative containing the redox innocent Zn(II) metal ion have been investigated by DFT calculations under various oxidation states. We also further studied the photocatalytic activity of this system and evaluated the influence of varying the relative concentration of the different components on the H2-evolving activity. Turnover numbers versus catalyst (TONCat) were found to be dependent on the catalyst concentration with the highest value of 1130 obtained at 0.05 mM. Interestingly, the analogous nickel derivative, [Ni(II)(CR)Cl2] (4), when tested under the same experimental conditions was found to be fully inactive for H2 production. Nanosecond transient absorption spectroscopy measurements have revealed that the first electron-transfer steps of the photocatalytic H2-evolution mechanism with the Ru/cobalt tetraaza/HA(-)/H2A system involve a reductive quenching of the excited state of the photosensitizer by ascorbate (kq=2.5×10(7) M(-1) s(-1)) followed by an electron transfer from the reduced photosensitizer to the catalyst (ket=1.4×10(9) M(-1) s(-1)). The reduced catalyst can then enter into the cycle of hydrogen evolution.
我们最近报道了一种基于钴（III）四氮大环配合物Co(CR)Cl2（1）（CR = 2,12 - 二甲基 - 3,7,11,17 - 四氮双环(11.3.1)-十七碳 - 1(17),2,11,13,15 - 戊烯）作为无贵金属催化剂、Ru(II)(bpy)3（Ru）作为光敏剂以及抗坏血酸盐/抗坏血酸（HA(-)/H2A）作为牺牲电子供体和缓冲剂的非常高效的均相体系，用于可见光驱动的水中产氢（《物理化学化学物理》2013年，15卷，17544页）。这种催化剂具有在pH 4.0、相对高浓度（0.1 mM）下实现非常高的周转数（TONs）（高达1000）的特殊性，能产生大量氢气且具有长期稳定性。由于在水中氯配体被水分子取代，水合衍生物Co(III)(CR)(H2O)2（2）也观察到了类似的活性。在这项工作中，通过DFT计算研究了2及其含有氧化还原惰性Zn(II)金属离子的类似物Zn(II)(CR)Cl（3）衍生物在各种氧化态下的几何结构和电子结构。我们还进一步研究了该体系的光催化活性，并评估了改变不同组分的相对浓度对析氢活性的影响。发现周转数与催化剂（TONCat）取决于催化剂浓度，在0.05 mM时获得的最高值为1130。有趣的是，类似的镍衍生物[Ni(II)(CR)Cl2]（4）在相同实验条件下测试时，发现对产氢完全无活性。纳秒瞬态吸收光谱测量表明，Ru/钴四氮/HA(-)/H2A体系光催化析氢机制的第一步电子转移涉及抗坏血酸盐对光敏剂激发态的还原猝灭（kq = 2.5×10(7) M(-1) s(-1)），随后是电子从还原的光敏剂转移到催化剂（ket = 1.4×10(9) M(-1) s(-1)）。还原后的催化剂然后可以进入析氢循环。
