Cobaloxime-based photocatalytic devices for hydrogen production
Cobaloxime-based photocatalytic devices for hydrogen production
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DOI：
10.1002/anie.200702953
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发表时间：
2008-01-01
影响因子：
16.6
通讯作者：
Fontecave, Marc
中科院分区：
文献类型：
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作者：
Fihri, Aziz;Artero, Vincent;Fontecave, Marc
用于制氢的均相光驱动催化系统以及更普遍的高效光活化合成多电子催化剂仍然相对稀少。[1]这类系统[2-4]通常包括1)光敏剂，通常基于Ru三(二亚胺)部分，[5]2)基于金属的催化中心，在某些情况下3)额外的氧化还原介体。然而，它们的效率在周转次数(稳定性)和周转频率方面仍有待提高，这些系统最好依赖廉价的第一排过渡金属催化剂，而不是不可持续的贵金属。我们和其他人最近报道，钴肟是非常有效和廉价的析氢电催化剂。[6-9]因此，我们决定将钴肟与Ru三(二亚胺)部分偶联，以制备Lehn等人以前研究的体系的超分子变体。在这样的分子装置中，通过微调金属中心之间的距离和桥的性质，可以潜在地控制分子内电子从光活化中心到催化中心的转移，并且电荷复合过程受到的限制比分子间系统中的要大。[2，10]在进化氢气的绿藻中发现了这样的有序组装，其中光系统I与氢酶紧密偶联。[11]在本文中，我们描述了一系列新型的能够实现光化学产氢的新型异核Ru-钴肟光催化剂的合成和活性。化合物1-3(方案1)通过用以前报道的[(Bpy)2Ru(L-吡咯)]2+络合物(L-吡啶=(4-吡啶)恶唑-[4，[13]核磁共振谱和电喷雾质谱分析与连接Ru和Co中心的L-吡咯配体一致。循环伏安法进一步支持了这一点：[12]除了以Ru为中心的过程(这些过程在络合到钴中心时不会有明显的改变)外，1-3的循环伏安图显示CoII/COI可逆过程相对于起始钴肟移动了%80 mV到更正的电位，这可能是因为化合物的总的2+电荷。我们用循环伏安法验证了钴肟部分在所有三种异双核配合物中都保持了它们的电催化产氢性能：对应于质子还原的电催化波在±0。在CH3CN[12]中1的溶液中加入更多的对氰基苯胺四氟硼酸盐时，45V与Ag/AgCl的比较(在±0。9 V与
Homogeneous light-driven catalytic systems for hydrogen production and, more generally, efficient photoactivated synthetic multielectron catalysts remain relatively scarce.[1] Such systems [2–4] generally consist of 1) a photosensitizer, often based on the ruthenium tris (diimine) moiety,[5] 2) a metal-based catalytic center, and in some cases 3) an additional redox mediator. However, their efficiency remains to be improved in terms of both turnover numbers (stability) and turnover frequencies, and these systems should preferably rely on inexpensive first-row transition-metal catalysts rather than unsustainable noble metals. We and others recently reported that cobaloximes are very efficient and cheap electrocatalysts for hydrogen evolution.[6–9] We thus decided to couple cobaloximes with ruthenium tris (diimine) moieties in order to make a supramolecular variant of the system previously studied by Lehn et al. for photochemical production of hydrogen.[3] In such a molecular device, the intramolecular electron transfer from the photoactivated center to the catalytic center can potentially be controlled, and the charge-recombination processes limited, to an extent larger than in intermolecular systems, by fine-tuning both the distance between metal centers and the nature of the bridge.[2, 10] Such an organized assembly is found in hydrogen-evolving green algae, where the photosystem I is tightly coupled to hydrogenase enzymes.[11] In this paper we describe the synthesis and activity of a series of novel heterodinuclear ruthenium–cobaloxime photocatalysts able to achieve the photochemical production of hydrogen with the highest turnover numbers so far reported for such devices.Compounds 1–3 (Scheme1) were synthesized in good yields [12] by replacing one axial ligand of cobaloxime moieties with the pyridine residue of the previously reported [(bpy) 2Ru (L-pyr)] 2+ complex (L-pyr=(4-pyridine) oxazolo-[4, 5-f] phenanthroline).[13] NMR measurements and ESI-MS analysis are consistent with the L-pyr ligand connecting the ruthenium and cobalt centers. This was further supported by cyclic voltammetry:[12] in addition to ruthenium-centered processes, which are not significantly modified upon complexation to the cobalt center, cyclic voltammograms of 1–3 show CoII/CoI reversible processes shifted by% 80 mV to more positive potentials relative to the starting cobaloximes, probably because of the overall 2+ charge of the compounds. We checked by cyclic voltammetry that the cobaloxime moieties retain their electrocatalytic properties for hydrogen production in all three heterobinuclear complexes: an electrocatalytic wave corresponding to proton reduction develops at À0. 45 V vs. Ag/AgCl upon addition of increasing amounts of p-cyanoanilinium tetrafluoroborate to a solution of 1 in CH3CN [12](electrocatalytic waves are observed at À0. 9 V vs.