Elementary Steps in Gold Photocatalysis

尽管取得了很大的进展，但涉及双核金(I)配合物或单核金(III)配合物的光催化的许多关键步骤仍然知之甚少。因此，对基元反应和关键中间体的详细了解对于从概念上设计新的合成路线至关重要。因此，双核金络合物与碘取代的炔烃反应中是否会形成游离的“炔基自由基”仍然是一个很大的疑问。因此，一个中心问题涉及到这种“炔基”衍生产物和其他活性物种的来源。在这方面，金-炔基物种的形成是可行的。因此，需要阐明确切的机理步骤。金催化的电子转移机理已经被提出用于双核金络合物和金(III)络合物。在不吸收蓝色发光二极管的光的双核配合物的情况下，为了形成金基聚集体，需要碱，从而可以避免使用高能UVA光。这种中间体的性质仍需澄清。为此，需要一种实验/计算相结合的方法。实验机理研究包括原位光谱、化学计量控制实验、荧光猝灭实验和关键中间体的分离。在这方面，可以通过在理论方法指导下对底物或金属络合物进行修饰来实现关键中间体的分离。由于双核金络合物的光催化行为的理论描述与其实验应用相比很少见，我们将首先开发一个全面的计算协议。这不仅使研究这类反应机理的能量学成为可能，而且也使激发态性质的计算成为可能。这将被用来识别光活性中间体，并彻底评估双核Au光催化中随后的催化步骤。这种对催化循环的审查的关键特征将是预测可疑中间体的光谱特征以进行实验验证，以及计算该机制的能量分布。此外，该方案将有助于系统地从理论上阐明双核金光催化中SET和ENT机理的差异。

Despite great progress, many key steps in photocatalysis involving dinuclear gold(I) complexes or mononuclear gold(III) complexes remain poorly understood. A detailed understanding of elementary reactions and key intermediates is therefore crucial to conceptually design new synthetic routes. As such, the formation of free “alkynyl radicals” in the reaction of dinuclear gold complexes with iodo-substituted alkynes remains highly doubtable. Therefore, a central question involves the origin of such “alkynyl radical”-derived products and other present reactive species. In this regard the formation of gold-alkynyl species could be feasible. Thus, the exact mechanistic steps need to be elucidated.Gold-catalyzed electron transfer mechanisms were already proposed for dinuclear gold complexes as well as gold(III) complexes. In case of the dinuclear complex which does not absorb the light of blue LEDs, a base is necessary in order to form a gold-base aggregate so that the use of highly energetic UVA light can be avoided. The nature of this intermediate still needs to be clarified. For this, a combined experimental/computational approach is required. Experimental mechanistic studies consist of in situ spectroscopy, stoichiometric control experiments, fluorescence quenching experiments and isolation of key intermediates. In this regard, isolation of key intermediates could be achieved by modification of the substrates or metal complex guided by a theoretical approach. With a theoretical description of the photocatalytic behavior of dinuclear gold complexes being rare in comparison to their experimental application, a comprehensive computational protocol will first be developed. This not only enables the investigation of the energetics of such reaction mechanisms but also the calculation of excited state properties. This will be employed for the identification of photoactive intermediates and for the thorough evaluation of the subsequent catalytic steps within dinuclear Au-photocatalysis. Key features within this examination of the catalytic cycle will be the prediction of spectroscopic signatures of suspected intermediates for experimental verification as well as the computation of the energetic profile of the mechanism. Furthermore the protocol will be instrumental for the systematic theoretical elucidation of differences between SET and EnT mechanisms in dinuclear gold photocatalysis.