Corroles as a Platform for Fundamental Transition Metal Chemistry, with Emphasis on Heavy Elements

Hemoglobin, the red color of blood, and chlorophyll, the green color of plants, both consist of ring-shaped organic molecules with a metal atom at the center. In our laboratory, we have prepared artificial versions of these molecules with much larger atoms such as gold, osmium, and rhenium at the center. While these preparations involved some fancy molecular acrobatics, which are of great fundamental interest, the new molecules also proved useful in a variety of contexts. Of particular interest was their interaction with light, which led to long-lived high-energy states of the molecules, so-called excited states. Such molecules are called phosphorescent and good examples are provided by various glow-in-the-dark dyes sometimes used on T-shirts. The new dyes proved useful for cancer chemotherapy in the presence of light, so-called photodynamic therapy, as well as for a new type of solar cells based on phosphorescent dyes. Current efforts are also directed at inserting radioactive atoms such as 99mTc and 64Cu into our molecules to create both new theranostic reagents, i.e., molecules capable of both therapy and diagnostics (imaging).

Three well-defined goals will be pursued, all linked by our interest in fundamental aspects of transition metal electronic structure and reaction mechanisms, as well as our practical expertise in porphyrin/corrole chemistry. 1. A large body of crystallog raphic work in our laboratory has shown that copper corroles are inherently nonplanar and chiral (on electronic grounds), but to date they have only been prepared in racemic form. Both chiral resolution and chiral synthesis will be employed to synthesize copper corroles as pure enantiomers. Once synthesized, the enantiomers will be extensively studied via various chiroptical spectroscopies and also theoretically modeled. 2. The compressed, trianionic core of corroles provides a little studied environment for heavy elements. Recent successes in the synthesis of Ir and Au corroles have encouraged a search for Pt corroles, which are of interest because of their potential for reactivity at the axial sites. According to the literature, such efforts have so fa r been unsuccessful. Very recently, however, the first platinum corroles have been synthesized in our laboratory and the first crystal structure obtained, laying the foundation of a major exploration of structure-property relationships of these complexes. Once such a knowledge base is in place, we will increasingly move our attention to chemical reactivity and catalysis, particularly in relation to C-H and C-F activation. 3. Iridium corroles have been reported in the literature, but the higher-valent sta tes remain little explored. For oxo/imido/nitrido complexes, such states are likely to be highly reactive, being on the "wrong" side of the so-called oxo wall. With undecaarylcorroles and other highly sterically hindered ligands, however, we hope to kinet ically trap such species and study their structures and reactivity. It will be of great interest to compare these complexes/intermediates with more stable, low-coordinate complexes such as Mes3IrO (Mes = mesit