Bio-inspired [NiFe] Hydrogenase Catalysts for H2 production

从长远来看，通过水分解制氢似乎是储存可再生能源的首选解决方案之一。自然界提供了氢化酶形式的有效的H2析出催化剂，所述氢化酶是含有镍和/或铁位点的有机金属酶，其催化性能可与通常使用的用于氢气生产的铂催化剂相媲美。因此，氢化酶为设计基于地球上丰富的金属的新分子催化剂提供了迷人的蓝图，这些催化剂将在电解槽或光电化学电池等技术设备中实施。然而，迄今为止报道的所有异双核NiFe模型系统都没有再现发生在[NiFe]氢化酶活性位点的Ni中心化学，与酶相比，它们的效率仍然很低。通过开发创新的生物启发的H2释放催化剂，我们的主要目标是（i）有助于充分理解[NiFe]氢化酶的催化机制和（ii）开发这种酶的有效模拟物，不仅模拟活性位点的结构和功能，而且模拟其令人印象深刻的反应性。这要求H+/H2反应性和氧化还原事件发生在二硫羟合桥连的杂环NiFe络合物的Ni位点处。我们的初步结果与前所未有的Ni为中心的H+还原催化剂，它准确地模拟多个国家的[NiFe]-氢化酶的表征，代表了一个真实的突破，在这一领域，将是这个项目的基础。具体而言，我们计划重点关注以下几点：（i）与[NiFe]-氢化酶机制相关的活性金属氢化物中间体的分离和表征，（ii）确定关键结构元素以实现Ni中心氢化酶化学的有效催化，（iii）定义在催化循环期间控制电子和质子转移顺序的因素，（iv）质子中继对于催化剂性能的重要性和第二配位层的作用，以及（v）用硒供体原子取代硫对NiFe络合物的氧化还原和电子性质的影响，以及对它们对H2析出和朝向O2的反应性的影响。后者将为[NiFe]和[NiFeSe]氢化酶之间的关键功能差异提供重要的见解。参与这一基础研究项目的法德联合体汇集了合作伙伴，他们联合收割机结合了实现雄心勃勃的多学科目标所需的所有专业知识，即合成配位化学、光谱学和动力学、电化学、催化和量子化学的专业知识。

Hydrogen production through water splitting appears to be among the preferred solutions in the long run for the storage of renewable energy. Nature offers efficient H2 evolution catalysts in the form of hydrogenases, organometallic enzymes containing nickel and/or iron sites whose catalytic performances rival commonly used platinum catalysts for hydrogen production. Hydrogenases thus offer fascinating blueprints for the design of new molecular catalysts based on earth-abundant metals, to be implemented in technological devices such as electrolysers or photo-electrochemical cells. However, all heterodinuclear NiFe model systems reported so far do not reproduce the Ni-centered chemistry that occurs at the active site of [NiFe] hydrogenases, and their efficiency is still very low compared to the enzyme.By means of the development of innovative bio-inspired H2 evolution catalysts, our major objectives are (i) to contribute to the full understanding of the catalytic mechanism of the [NiFe] hydrogenase and (ii) to develop efficient mimics of this enzyme that model not only the structure and function of the active site but also its impressive reactivity. This requires that the H+/H2 reactivity and redox events occur at the Ni site of a dithiolato-bridged heterobimetallic NiFe complex. Our preliminary results with the characterization of an unprecedented Ni-centered H+ reduction catalyst, which accurately models multiple states of the [NiFe]-hydrogenase, represent a real breakthrough in this field and will be the foundation of this project. More specifically, we plan to focus on the following points: (i) isolation and characterization of active metal hydride intermediates relevant to the [NiFe]-hydrogenase mechanism, (ii) determination of the crucial structural elements to achieve efficient catalysis with Ni-centered hydrogenase chemistry, (iii) definition of the factors that control the electron and proton transfer sequence during the catalytic cycle, (iv) importance of a proton relay for the performance of the catalysts and role of the second coordination sphere, and (v) effect of replacing a sulfur by a selenium donor atom on the redox and electronic properties of the NiFe complexes, and on their reactivity for H2 evolution and toward O2. The latter will provide important insight into key functional differences between [NiFe] and [NiFeSe] hydrogenases. The French-German consortium involved in this fundamental research project brings together partners who combine all expertise required to reach the ambitious multidisciplinary goals, namely expertise from synthetic coordination chemistry, spectroscopy and kinetics, electrochemistry, catalysis and quantum chemistry.