Synthesis and molecular structure of perhalogenated rhenium-oxo corroles

Abstract

As part of our efforts to develop rhenium-oxo corroles as photosensitizers for oxygen sensing and photodynamic therapy, we investigated the potential <i>β</i>-perhalogenation of five ReO <i>meso</i>-tris(<i>para</i>-X-phenyl)corroles, Re[T<i>p</i>XPC](O) (X = CF₃, H, F, CH₃, and OCH₃), with elemental chlorine and bromine. With Cl₂, <i>β</i>-octachlorinated products Re[Cl₈T<i>p</i>XPC](O) were rapidly obtained for X = CF₃, H, and CH₃, but X = OCH₃ resulted in overchlorination on the <i>meso</i>-aryl groups. Full <i>β</i>-octabromination proved slower relative to Cu and Ir corroles, but the desired Re[Br₈T<i>p</i>XPC](O) products were finally obtained for X = H and F after a week at room temperature. For X = CH₃ and OCH₃, these conditions led to undecabrominated products Re[Br₁₁T<i>p</i>XPC](O). Compared to the <i>β</i>-unsubstituted starting materials, the <i>β</i>-octahalogenated products were found to exhibit sharp ¹H NMR signals at room temperature, indicating that the aryl groups are locked in place by the <i>β</i>-halogens, and substantially redshifted Soret and Q bands. Single-crystal X-ray structures of Re[Cl₈T<i>p</i>CF₃PC](O), Re[Cl₈T<i>p</i>CH₃PC](O), and Re[Br₈T<i>p</i>FPC](O) revealed mild saddling for one Cl₈ structure and the Br₈ structure. These structural variations, however, appear too insignificant to explain the slowness of the <i>β</i>-octabromination protocols, which seems best attributed to the deactivating influence of the high-valent Re center.