Development of novel dinuclear molybdenum complexes with long-lived excited states for the photochemical N2 activation

开发具有长寿命激发态的新型双核钼配合物，用于光化学 N2 活化

• 批准号: 460752300
• 负责人: Dr. Sascha Ossinger
• 金额: --
• 依托单位: Department of Chemistry
• 依托单位国家: 德国
• 项目类别: WBP Fellowship
• 财政年份: 2021
• 资助国家: 德国
• 起止时间: 2020-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/460752300?language=en
• 关键词: Development; novel; dinuclear; molybdenum; complexes

The overall goal of this proposed project is the rational development of catalysts for the light-driven activation of metal-bound dinitrogen. To this end, the primary goal is the establishment of long-lived MLCT excited states on Mo-N=N-Mo dimers, from which photochemical N2 activation will occur. The growing world population combined with an increase in the demand of food have led to greater importance in the production and use of nitrogenous fertilizers in recent decades. Therefore, industrial ammonia production via the HABER-BOSCH process, which consumes 1 2% of the world’s energy supply, is one of the most important large-scale industrial processes. Besides this, the synthetic nitrogen fixation on well-defined transition metal complexes as a further way to convert N2 to NH3 has developed considerably in the last years. In the field of synthetic nitrogen fixation, only a handful of characterized molecular systems are capable of photochemical or light-driven N2 activation. For some of these molecular compounds the mechanisms of thermal N2 splitting is understood in much detail. Whereas, the operating principles of light-driven N2 activation are still poorly understood. Therefore, if light-driven N2 splitting could ultimately be performed in catalytic fashion, this would have very important socio-economic implications and on a more fundamental level, the development of photoactive excited states on N2-bridged dimers will open up new possibilities in the area of light-driven N2 activation and inorganic photochemistry in general. Recently, CHIRIK and SCHOLES described a Mo-N=N-Mo dimer, and its photophysical properties provided the first direct insight into MLCT states that could be suitable for N2 splitting. This molecular compound exhibits only a very short excited-state lifetime, and therefore, photochemical reactions cannot compete with the rapid nonradiative deactivation of the 3MLCT state. Consequently, this proposed project aims to develop new N2-bridged Mo-N=N-Mo dimers with a coordination environment that combines a more idealized octahedral coordination geometry with a stronger ligand field resulting in long-lived 3MLCT excited states. These new compounds, including a variety of different combinations of equatorial chelate and axial monodentate ligands, will be synthesized and fully characterized. Furthermore, the excited states investigations and the light-driven N2-activation studies of the target complex will be performed using time-resolved UV-Vis and IR spectroscopy. In addition, all investigations in this project will be supported by computational studies. Finally, systems with long-lived enough excited states will be investigated in view of reductive 3MLCT quenching by sacrificial donors, which represents the key step towards the development of a photocatalyst for the light-driven formation of NH3 from N2.

这项拟议项目的总体目标是合理开发用于金属结合氮素光驱动活化的催化剂。为此，主要的目标是在Mo-N=N-Mo二聚体上建立长寿命的MLCT激发态，由此产生光化学N_2活化。近几十年来，世界人口不断增长，加上粮食需求的增加，使得氮肥的生产和使用变得更加重要。因此，消耗世界能源供应12%的哈伯-博世工艺生产工业氨是最重要的大型工业工艺之一。此外，在定义明确的过渡金属络合物上的合成固氮作为进一步将氮气转化为氨气的方法在过去几年中得到了长足的发展。在合成固氮领域，只有少数表征的分子体系能够进行光化学或光驱动的氮气活化。对于这些分子化合物中的一些分子，我们更详细地了解了氮气热裂解的机理。然而，光驱动的氮气活化的工作原理仍然知之甚少。因此，如果光驱动的氮气裂解最终能够以催化的方式进行，这将具有非常重要的社会经济意义，在更基本的水平上，氮桥联二聚体上光活性激发态的发展将在光驱动的氮气活化和一般的无机光化学领域开辟新的可能性。最近，CHIRIK和Scholes描述了一种Mo-N=N-Mo二聚体，它的光物理性质首次提供了对适合于氮气分裂的MLCT态的直接洞察。这种分子化合物只表现出很短的激发态寿命，因此，光化学反应不能与3MLCT态的快速非辐射失活竞争。因此，这个拟议的项目旨在开发新的氮桥联Mo-N=N-Mo二聚体，其配位环境结合了更理想的八面体配位几何结构和更强的配位场，从而产生长寿命的3MLCT激发态。这些新的化合物，包括各种不同的赤道螯合和轴向单齿配体的组合，将被合成并充分表征。此外，还将利用时间分辨的UV-Vis和IR光谱对目标络合物的激发态和光驱动的氮气活化进行研究。此外，该项目的所有研究都将得到计算研究的支持。最后，考虑到牺牲施主对3MLCT的还原猝灭，研究了具有足够长激发态的体系，这是开发光催化剂用于光驱动由氮气生成NH3的关键一步。