Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Kraków, Poland.
Inorg Chem. 2010 Aug 16;49(16):7362-71. doi: 10.1021/ic100466s.
The structure-reactivity relationships in metalation reactions of porphyrinoids have been studied using experimental and theoretical methods. A series of eight porphyrinoic ligands, derivatives of chlorophylls, was prepared in which both the peripheral groups and the degrees of saturation of the macrocycle were systematically varied. To reveal the solvent and structural factors which control the interactions of these macroligands with metal centers, their interactions with reactive Zn(2+) and inert Pt(2+) ions were investigated using absorption spectroscopy. In parallel, quantum chemical calculations (density functional theory, DFT) were performed for the same set of molecules to examine the influence of structural and electronic factors on the energy of the frontier orbitals, the nucleophilicity/electronegativity of the macrocycle, its hardness, and conformation. These static descriptors of chemical reactivity, relevant to metalation reactions, were verified against the results obtained in the experimental model. The experimentally obtained kinetic data clearly show that the solvent has a crucial role in the activation of the incoming metal center. In terms of chelator structure, the largest effects concern the size of the delocalized pi-electron system and the presence of side groups. Both the DFT calculations and experimental results show the strong influence of the macrocycle rigidity and of the peripheral groups on the chelating ability of porphyrinoids. In particular, the peripheral functionalization of the macrocyclic system seems to drastically reduce its reactivity toward metal ions. The effect of peripheral groups is two-fold: (i) a lower electron density on the core nitrogens, and (ii) increased rigidity of the macrocycle. The outcomes of the theoretical and experimental analyses are discussed also in terms of their relevance to the mechanism of biological metal insertion in the biosynthesis of heme and chlorophyll.
用实验和理论方法研究了卟啉类化合物的金属化反应的结构-反应性关系。合成了一系列八个卟啉啉配体，它们是叶绿素的衍生物，其中大环的外围基团和饱和度都得到了系统的改变。为了揭示控制这些大环配体与金属中心相互作用的溶剂和结构因素，用吸收光谱法研究了它们与反应性 Zn(2+)和惰性 Pt(2+)离子的相互作用。同时，为同一组分子进行了量子化学计算（密度泛函理论，DFT），以研究结构和电子因素对前线轨道能量、大环的亲核性/电负性、其硬度和构象的影响。这些与金属化反应相关的化学反应性静态描述符，与实验模型的结果进行了验证。实验获得的动力学数据清楚地表明，溶剂在激活进入的金属中心方面起着至关重要的作用。就螯合剂结构而言，最大的影响涉及离域π电子系统的大小和侧基的存在。DFT 计算和实验结果都表明，大环的刚性和外围基团对卟啉类化合物的螯合能力有很强的影响。特别是，大环体系的外围官能化似乎大大降低了其对金属离子的反应性。外围基团的影响有两个方面：（i）核心氮上的电子密度降低，以及（ii）大环的刚性增加。理论和实验分析的结果还根据它们与血红素和叶绿素生物合成中金属插入机制的相关性进行了讨论。
