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

该项目的总体目标是合理开发光驱动活化金属结合二氮的催化剂。为此，主要目标是在Mo-N=N-Mo二聚体上建立长寿命的MLCT激发态，由此将发生光化学N2活化。近几十年来，随着世界人口的增长以及对粮食需求的增加，氮肥的生产和使用变得更加重要。因此，通过哈伯-博世工艺的工业氨生产是最重要的大规模工业过程之一，其消耗世界能源供应的12%。除此之外，在定义明确的过渡金属络合物上的合成固氮作为将N2转化为NH3的另一种方式在过去几年中得到了相当大的发展。在合成固氮领域，只有少数表征的分子系统能够进行光化学或光驱动的N2活化。对于这些分子化合物中的一些，热N2裂解的机制被更详细地理解。然而，光驱动N2激活的工作原理仍然知之甚少。因此，如果光驱动的N2分裂最终可以以催化方式进行，这将具有非常重要的社会经济意义，并且在更基本的水平上，N2桥接二聚体上的光活性激发态的发展将在光驱动的N2活化和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，它的电子物理性质提供了第一个直接洞察MLCT状态，可以适合N2分裂。这种分子化合物仅表现出非常短的激发态寿命，因此，光化学反应不能与3 MLCT状态的快速非辐射失活竞争。因此，该项目旨在开发新的N2桥连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体场，从而产生长寿命的3 MLCT激发态。这些新的化合物，包括赤道螯合物和轴向单齿配体的各种不同组合，将被合成和充分表征。此外，激发态的调查和光驱动的N2-活化的目标复合物的研究将使用时间分辨的紫外-可见光谱和红外光谱进行。此外，本项目的所有调查都将得到计算研究的支持。最后，系统具有足够长的寿命的激发态将被调查鉴于还原3 MLCT淬灭的牺牲供体，这是朝着光催化剂的发展的关键一步光驱动形成NH3从N2。

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.