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.