Photoinduced de(thio)carboxylation dynamics monitored by time-resolved mid-IR-to-near-UV spectroscopies. From transition metals to main-group elements

3d-过渡金属（TM）配合物的光化学对于自然界和技术中的各种过程具有重要意义。在过去，这个项目致力于阐明光化学过程中诱导的配体到金属的电荷转移激发这种物种使用超快非线性激光光谱。在第一个资助期内的主要发现是：（I）当连接到TM时，双齿双金属配体变得容易受到异裂CC键的断裂，导致形成中性CO2，其迅速离开配体球和碳酸根阴离子（CO2 ^2 ─），其作为氧化还原活性配体保持与金属中心结合。(II)这种光反应性模式建立了进入TM-CO2-络合物化学的入口。(III)对于高自旋体系，发现了初级产物草酸铁络合物，其特征在于异常弯曲的O-末端结合的CO2●─自由基阴离子配体，其铁磁耦合到Fe（II）中心。(IV)对于一个低自旋的monoacetamato-iron（III）模型复合物，主要产品的特点是经典的侧结合模式的CO2。(V)前期研究结果表明，CO2的结合模式可以通过自旋来控制，因此可以通过精心设计TM的配体球来控制。受其与CO2活化主题的相关性和生物碳固定的启发，延续项目现在打算将其研究扩展到（1）主族元素配合物的光诱导脱羧，特别是Al和Si的硅酸盐。为了了解更多关于所得开壳配体的性质及其与配位中心的相互作用，该项目还将扩展其研究，以研究与连接到TM和主族元素的复杂双官能羧酸配体相关的光化学。因此，本文着重于（2）TM的高级二羧酸盐和氨基羧酸盐的光诱导脱羧作用和（3）硫代二羧酸盐的光诱导脱（硫代）羧作用，所有这些都与TM和主族元素相连。初步的量子化学计算表明，CO2损失的S-配位的硫代草酸盐可以产生一个终端硫代配体。因此，该项目可能会开辟一条优雅的路线，以后期-TM-硫化物-一类配位化合物，其分离是非常罕见的。所有这三条研究线将再次使用超快非线性激光光谱学在中红外，可见光和近紫外光谱区域进行处理。

The photochemistry of 3d-transition metal (TM) oxalates is of significant importance for a variety of processes in nature and technology. In the past, this project was dedicated to elucidating the photochemical processes induced upon ligand-to-metal charge-transfer excitation of such species using ultrafast non-linear laser spectroscopy. The major findings during the first funding period are: (I) When attached to a TM, the bidentate oxalato ligand becomes susceptible to heterolytic CC-bond cleavage leading to the formation of a neutral CO2 that departs promptly from the ligand sphere and a carbonite anion (CO2^2─) that remains bound to the metal center as a redox-active ligand. (II) This photoreactivity pattern establishes an entry into the chemistry of TM-CO2-complexes. (III) For the high-spin system, ferrioxalate, a primary product complex was discovered, which features an exceptional bent, O-end-on-bound CO2●─ radical anion ligand that is ferromagentically coupled to an Fe(II)-center. (IV) For a low-spin monooxalato-iron(III) model complex, the primary product features the classical side-on binding mode of CO2. (V) The results obtained in previous project strongly suggest that the CO2-binding mode can be controlled by the spin and hence, by a careful design of the TM’s ligand sphere.Driven by its relevance for the topic of CO2-activation and inspired by biological carbon fixation, the continuation project now intends to expand ist research toward (1) the photo-induced decarboxylation of coordination compounds of main-group elements, specifically of Al and Si oxalates. To learn more about the nature of the resultant open-shell ligands and their interaction with the coordinating center, the project shall also expand ist research towards the photochemistry associated with intricate bifunctional carboxylate ligands attached to TMs and main-group elements. An emphasis is therefore laid here on (2) the photo-induced decarboxylation of higher dicarboxylates and amino carboxylates of TMs and on (3) the photo-induced de(thio)carboxylation of the thiooxalates, all of which attached to TMs and main-groups elements. Preliminary quantum-chemical calculations suggest that the CO2-loss of an S-coordinated thiooxalate can generate a terminal sulfido ligand. This project may thus open up an elegant route to late-TM-sulfides – a class of coordination compounds whose isolation is exceedingly rare. All three lines of research shall be tackled again using ultrafast non-linear laser spectroscopy in the mid-infrared, the visible, and the near ultraviolet spectral regions.