Theoretical and experimental correlations between solution phase and gas phase photoredox-reactivity of molecular vanadium oxide clusters

分子金属氧化物阴离子，即所谓的聚氧乙烯酸盐（POM）是一种多用途的光氧化还原催化剂，用于重要的有机转化，包括醇氧化，环氧化和CH-活化。虽然POM光反应性是经验上建立良好的，有一个根本缺乏了解的机制，控制激发态的POM光催化剂的电子结构，光激发后的电荷分离模式和结构和化学催化剂改性对整体光反应性的影响。此外，光化学的关键过程，如底物-催化剂预缔合和催化剂/溶剂相互作用没有得到很好的理解。因此，知识驱动的新的基于POM的光氧化还原过程的开发远非微不足道。本项目将解决这些挑战，并旨在提供控制多钒酸盐（POVs）的光氧化还原活性的结构和电子特征的基本理解。POVs是理想的POM光氧化还原催化剂模型，因为它们联合收割机了对有机底物（焦点：醇作为模型生物原料）的公认的光氧化活性与可预测的（光）化学可调性和可见光吸收。为了了解控制光氧化步骤的溶液和气相过程，所选衬底和POV之间的模型反应将检查衬底催化剂预聚集，光氧化和产物选择性在溶液和气相中。将使用溶液相光氧化分析（Streb组）进行实验研究，并使用泵-探测碎裂作用光谱法（即高分辨率电喷雾电离质谱法与飞秒激光光谱法相结合（Riehn组））进行气相模型研究。将使用高水平的定制密度泛函理论计算（Jacob组）对底物-催化剂相互作用、光激发时的电荷分布和再定位以及光氧化反应机制进行理论研究。该项目将通过以下方面取得重大进展：（i）提供可调的可见光活性光氧化催化剂;（ii）提供对这些催化剂的光氧化还原机制的实验和理论理解;（iii）展示它们将模型底物选择性转化为增值产品的性能。对于优先计划SPP 2102，该项目增加了对一类重要的分子光催化剂的访问，以及时间分辨实验和理论专业知识的独特组合，以研究溶液和气相中的复杂光反应。在可能的第二个供资阶段，该项目将研究高活性多元醇催化剂的理论预测、其合成开发及其在生物多元醇底物（如乙二醇）光氧化为羰基化合物或羧酸等增值产品中的用途。

Molecular metal oxide anions, so-called polyoxometalates (POMs) are versatile photoredox catalysts for important organic transformations including alcohol oxidations, epoxidations and C H-activations. Although POM photoreactivity is empirically well established, there is a fundamental lack of understanding of the mechanisms, which control the electronic structure of the POM photocatalyst in the excited state, the mode of charge separation upon photoexcitation and the effects of structural and chemical catalyst modification on the overall photoreactivity. Further, photochemical key processes such as substrate-catalyst pre-association and catalyst / solvent-interactions are not well understood. Knowledge-driven development of new POM-based photoredox-processes is therefore far from trivial.This project will address these challenges and aim at providing fundamental understanding of the structural and electronic features which control the photoredox-activity of polyoxovanadates (POVs). POVs are ideal POM photoredox catalyst models as they combine well-established photooxidative activity towards organic substrates (focus: alcohols as model bio-feedstock) with predictable (photo-)chemical tunability and visible light absorption. To understand the solution- and gas-phase processes which control the photooxidation steps, model reactions between selected substrates and POVs will examine substrate-catalyst pre-aggregation, photooxidation and product selectivity in solution and in the gas phase. The experimental studies will be performed using solution-phase photooxidation analyses (Streb group) as well as model studies in the gas phase using pump-probe fragmentation action spectroscopy, i.e. high-resolution electrospray ionization mass spectrometry coupled with femtosecond laser spectroscopy (Riehn group). Theoretical investigations of substrate-catalyst interactions, charge-distribution and relocalization upon photoexcitation as well as photooxidation reaction mechanisms will be performed using high-level, customized density functional theory calculations (Jacob group). The project will provide significant progress by (i) delivering tuneable visible light-active POV photooxidation catalysts; (ii) providing experimental and theoretical understanding of the photoredox-mechanism of these catalysts and (iii) demonstrate their performance for the selective conversion of model substrates into value-added products. For the priority program SPP2102, the project adds access to an important class of molecular photocatalysts as well as a unique combination of time-resolved experimental and theoretical expertise to investigate complex photoreactions in solution and the gas phase. In a potential 2nd funding phase, the project would study the theoretical prediction of high activity POV catalysts, their synthetic development and their use for the photooxidation of biogenic polyol substrates (e.g. glycols) to value-added products as carbonyls or carboxylic acids.