Dual-mode ligand release from transition metal complexes: Towards photoselectivity by complementary synthetic and ultrafast UV-VIS-MIR spectroscopic approaches

通过与光的特定相互作用激活过渡金属配合物，可以以明确的方式在时间和空间上引发所需的反应，这是从工程、合成化学到生物医学研究等科学领域众多应用的基础。光诱导配体释放是近年来出现的一种有效的方法，通常是通过在过渡金属配合物中使用一个功能基作为单齿配体来实现的。在目前的建议中，这一过程将扩展到具有两个不相等或不相同的配体的化合物，这些配体可以在电子激发下被释放，目的是揭示如何以及在多大程度上可以在这些物质中完成光选择性。过渡金属配合物的潜在双模配体释放机制的鉴定和表征将通过合成有机金属和配位化学、便利的模拟技术和多功能超快紫外-可见- mir光谱的先进方法来追求。这些研究将包括具有两个离开基团的各种系统，最初是羰基和亚硝基，在项目的进一步发展中还包括一种或两种吡啶衍生物。重点是钼和钌配合物，与其他金属中心也设想了一个深刻的比较。通过在待释放的配体或配体球体上引入正交官能团，以间接而预定的方式影响离去基，合理调整化合物的电子性质，从而判断化合物是否适合双模配体释放。这些修饰的影响将在全面的超快光化学研究中进行探讨，这也将以时间分辨的方式揭示初始反应的波长依赖性。此外，在一种选择性释放配体的先进方法中，由第一个泵浦激光脉冲产生稳定的激发态结构，随后由第二个激光脉冲重新激发以排出配体。通过这种方式，逐步激发的好处，为目标的选择性配体释放的化合物具有两个潜在的离开基团被阐明。作为前瞻性的成果，这些研究将展示过渡金属配合物光诱导配体释放的新反应模式，为如何实现双模配体释放的光选择性、在何种系统和何种条件下实现提供结束语。

The activation of transition metal complexes by a specific interaction with light can spark a desired reaction temporally and spatially in a well-defined way, which is the basis of numerous applications in scientific fields ranging from engineering and synthetic chemistry to biomedical research. Photo-induced ligand release has emerged in the past years as an effective approach, commonly realized by a functional group serving as a monodentate ligand in a transition metal complex from which it can be photolyzed off. In the present proposal, this course of action will be extended to compounds with two non-equivalent or non-identical ligands which can be liberated upon electronic excitation, with the goal to unravel how and to which extent photoselectivity can be accomplished in such substances. Identification and characterization of the underlying dual-mode ligand release mechanisms from transition metal complexes will be pursued by advanced methods from synthetic organometallic and coordination chemistry, expedient simulation techniques, and versatile ultrafast UV-Vis-MIR spectroscopy. The studies will comprise a variety of systems with two leaving groups, initially carbonyl and nitrosyl, further along the project also incorporating one or two pyridine derivatives. The emphasis is on molybdenum and ruthenium complexes, with other metal centers also envisioned for a profound comparison. For deciphering the compounds’ suitability for dual-mode ligand release, the electronic properties will be rationally tuned by introducing orthogonal functional groups either on the ligands to be released or the coligand sphere to influence the leaving groups in an indirect yet predetermined way. The impact of these modifications is explored in comprehensive ultrafast photochemical studies, which will also disclose the wavelength-dependence of the incipient reaction in a time-resolved manner. Moreover, in an advanced approach for selective ligand release, labilized excite-state structures are generated by a first pump laser pulse and subsequently re-excited for ligand expulsion by a second one. In this way, the benefit of step-wise excitation for the goal of selective ligand release from compounds bearing two potential leaving groups is elucidated.As prospective achievement, the studies will demonstrate new reactivity patterns for photo-induced ligand release from transition metal complexes, providing a conclusive picture of how photoselectivity of dual-mode ligand release can be realized, in which systems and under which conditions.