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络合物可以以明确的方式在时间和空间上引发所需的反应，这是从工程和合成化学到生物医学研究的科学领域中的众多应用的基础。光诱导的配体释放在过去几年中已经作为一种有效的方法出现，通常通过在过渡金属络合物中充当单齿配体的官能团来实现，该官能团可以被光解掉。在本提案中，这一作用过程将扩展到具有两个非等效或非相同配体的化合物，这些配体可以在电子激发时释放，目的是揭示如何以及在何种程度上可以在这些物质中实现光选择性。从过渡金属络合物的潜在的双模式配体释放机制的识别和表征将追求从合成有机金属和配位化学，方便的模拟技术，和多功能的超快紫外-可见-MIR光谱的先进方法。这些研究将包括具有两个离去基团的各种系统，最初是羰基和亚硝酰基，进一步沿着该项目还包括一个或两个吡啶衍生物。重点是钼和钌配合物，与其他金属中心也设想了深刻的比较。为了解释化合物对双模式配体释放的适用性，将通过在待释放的配体或共配体球上引入正交官能团以间接但预定的方式影响离去基团来合理地调节电子性质。这些修改的影响进行了探讨，在全面的超快光化学研究，这也将揭示的波长依赖性的初期反应的时间分辨的方式。此外，在用于选择性配体释放的先进方法中，不稳定的激发态结构由第一泵浦激光脉冲产生，并且随后由第二泵浦激光脉冲重新激发以用于配体排出。通过这种方式，逐步激发的好处，从带有两个潜在的离去基团的化合物的选择性配体释放的目标阐明作为前瞻性的成就，这些研究将展示新的反应模式，从过渡金属配合物的光诱导配体释放，提供了一个决定性的图片如何光选择性的双模式配体释放可以实现，在哪些系统和条件下。

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.