While photosubstitution reactions in metal complexes are usually thought of as dissociative processes poorly dependent on the environment, they are, in fact, very sensitive to solvent effects. Therefore, it is crucial to explicitly consider solvent molecules in theoretical models of these reactions. Here, we experimentally and computationally investigated the selectivity of the photosubstitution of diimine chelates in a series of sterically strained ruthenium(II) polypyridyl complexes in water and acetonitrile. The complexes differ essentially by the rigidity of the chelates, which strongly influenced the observed selectivity of the photosubstitution. As the ratio between the different photoproducts was also influenced by the solvent, we developed a full density functional theory modeling of the reaction mechanism that included explicit solvent molecules. Three reaction pathways leading to photodissociation were identified on the triplet hypersurface, each characterized by either one or two energy barriers. Photodissociation in water was promoted by a proton transfer in the triplet state, which was facilitated by the dissociated pyridine ring acting as a pendent base. We show that the temperature variation of the photosubstitution quantum yield is an excellent tool to compare theory with experiments. An unusual phenomenon was observed for one of the compounds in acetonitrile, for which an increase in temperature led to a surprising decrease in the photosubstitution reaction rate. We interpret this experimental observation based on complete mapping of the triplet hypersurface of this complex, revealing thermal deactivation to the singlet ground state through intersystem crossing.

中文翻译：

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配体刚性控制应变钌聚吡啶配合物光取代反应的选择性和效率

虽然金属配合物中的光取代反应通常被认为是不太依赖环境的解离过程，但事实上，它们对溶剂效应非常敏感。因此，在这些反应的理论模型中明确考虑溶剂分子至关重要。在这里，我们通过实验和计算研究了水和乙腈中一系列空间应变钌(II)聚吡啶配合物中二亚胺螯合物光取代的选择性。这些配合物的本质区别在于螯合物的刚性，这强烈影响了观察到的光取代的选择性。由于不同光产物之间的比例也受到溶剂的影响，我们开发了反应机理的全密度泛函理论模型，其中包括显式溶剂分子。在三重态超表面上确定了导致光解离的三种反应途径，每种反应途径都以一个或两个能垒为特征。三线态的质子转移促进了水中的光解离，而解离的吡啶环作为悬垂碱基促进了质子转移。我们证明，光取​​代量子产率的温度变化是比较理论与实验的绝佳工具。在乙腈中观察到一种不寻常的现象，温度升高导致光取代反应速率惊人地降低。