Synthesis and molecular structure of perhalogenated rhenium-oxo corroles.

As part of our efforts to develop rhenium-oxo corroles as photosensitizers for oxygen sensing and photodynamic therapy, we investigated the potential β-perhalogenation of five ReO meso-tris(para-X-phenyl)corroles, Re[TpXPC](O) (X = CF ₃ , H, F, CH ₃ , and OCH ₃ ), with elemental chlorine and bromine. With Cl ₂ , β-octachlorinated products Re[Cl ₈ TpXPC](O) were rapidly obtained for X = CF ₃ , H, and CH ₃ , but X = OCH ₃ resulted in overchlorination on the meso-aryl groups. Full β-octabromination proved slower relative to Cu and Ir corroles, but the desired Re[Br ₈ TpXPC](O) products were finally obtained for X = H and F after a week at room temperature. For X = CH ₃ and OCH ₃ , these conditions led to undecabrominated products Re[Br ₁₁ TpXPC](O). Compared to the β-unsubstituted starting materials, the β-octahalogenated products were found to exhibit sharp ¹ H NMR signals at room temperature, indicating that the aryl groups are locked in place by the β-halogens, and substantially redshifted Soret and Q bands. Single-crystal X-ray structures of Re[Cl ₈ TpCF ₃ PC](O), Re[Cl ₈ TpCH ₃ PC](O), and Re[Br ₈ TpFPC](O) revealed mild saddling for one Cl ₈ structure and the Br ₈ structure. These structural variations, however, appear too insignificant to explain the slowness of the β-octabromination protocols, which seems best attributed to the deactivating influence of the high-valent Re center.