Structure and chemistry of N-substituted corroles and their rhodium(I) and zinc(II) metal-ion complexes

In the present work we report on the detailed structural features of the chiral N²¹- and N²²-substituted benzyl and picolyl derivatives of tris(pentafluorophenyl)corrole [H₃(tpfc)]. The main difference between the isomers is that substitution on N²² creates a much more crowded environment, reflected in higher deformation of the corrole ring from planarity and of the meso-aryls from perpendicular orientation. The effects of metal-ion chelation on corrole geometry are demonstrated by structural investigations of the zinc(II) and rhodium(I) complexes of the N²¹- and N²²-alkylated corroles. The major finding is the intramolecular coordination of the pyridine moiety of the picolyl substituent in the case of [Zn¹¹(N²¹-picolyl-tpfc)]. This pyridine is readily attracted to the zinc ion as an axial ligand, thus replacing the external pyridine molecule of the precursor [Zn^II(N²¹-benzyl-tpfc)(py)]. The change is associated with a considerable flattening of the corrole ring in order to allow a more convenient coordination of the zinc ion to all four pyrrole nitrogen atoms (at Zn-N(pyrrole) distances of 1.956 - 1.987 Å for the nonsubstituted sites, and 2.224 - 2.247 Å for the substituted sites). These structural investigations also aid a good understanding of the spectroscopic characteristics of the derivatives.