Fe L- and K-edge XAS of Low-Spin Ferric Corrole: Bonding and Reactivity Relative to Low-Spin Ferric Porphyrin

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• 作者：Rosalie K. Hocking ; Serena DeBeer George ; Zeev Gross ; F. Ann Walker ; Keith O. Hodgson ; Britt Hedman ; Edward I. Solomon
• 刊名：Inorganic Chemistry
• 出版年：2009
• 出版时间：February 16, 2009
• 年：2009
• 卷：48
• 期：4
• 页码：1678-1688
• 全文大小：427K
• 年卷期：v.48,no.4(February 16, 2009)
• ISSN：1520-510X

文摘

Corrole is a tetrapyrrolic macrocycle that has one carbon atom less than a porphyrin. The ring contraction reduces the symmetry from D_4h to C_2v, changes the electronic structure of the heterocycle, and leads to a smaller central cavity with three protons rather than the two of a porphyrin. The differences between ferric corroles and porphyrins lead to a number of differences in reactivity including increased axial ligand lability and a tendency to form 5-coordinate complexes. The electronic structure origin of these differences has been difficult to study experimentally as the dominant porphyrin/corrole π → π* transitions obscure the electronic transitions of the metal. Recently, we have developed a methodology that allows for the interpretation of the multiplet structure of Fe L-edges in terms of differential orbital covalency (i.e., the differences in mixing of the metal d orbitals with the ligand valence orbitals) using a valence bond configuration interaction model. Herein, we apply this methodology, combined with a ligand field analysis of the Fe K pre-edge to a low-spin ferric corrole, and compare it to a low-spin ferric porphyrin. The experimental results combined with DFT calculations show that the contracted corrole is both a stronger σ donor and a very anisotropic π donor. These differences decrease the bonding interactions with axial ligands and contribute to the increased axial ligand lability and reactivity of ferric corroles relative to ferric porphyrins.