Reactivity of the Verdoheme Analogues. Opening of the Planar Macrocycle by Amide and Thiolate Nucleophiles To Form Helical Complexes

The 5-oxaporphyrin macrocycle is a modified porphyrin that has an oxygen atom in place of one meso-methine
group. These 5-oxaporphyrins are readily produced from heme degradation by both chemical and biological
processes. Treatment of metal complexes of 5-oxaporphyrins with nucleophiles can lead to reactions either at the
metal or on the ligand. Here we report that the diamagnetic zinc(II) verdoheme analogue [ZnII(OEOP)](O2CCH3)
{OEOP is the monoanion of octaethyl-5-oxaporphyrin} reacts with dimethylamide and with methanethiolate to
form ring-opened products ZnII(OEBNMe2) and ZnII(OEBSMe). The ring-opened products have been subjected
to crystallographic study. In both complexes the helical tetrapyrrole ligand imposes a structure in which the zinc
ion is trapped between planar and tetrahedral coordination. The structures of these two complexes are compared
with that of ZnII(OEBOMe), which has a similar helical shape.