Synthesis of a Family of Highly Substituted Porphyrin Thioethers via Nitro Displacement in 2,3,7,8,12,13,17,18-Octaethyl-5,10,15,20-tetranitroporphyrin

A series of highly substituted porphyrin
thioethers was synthesized from 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetranitroporphyrin
(H2OETNP). The reactions proceeded via a SNAr
mechanism with a broad range of aromatic thiols in the presence of
a base. This is a rapid way to prepare a large variety of meso-substituted
porphyrins from only one precursor. Single crystal X-ray analysis
revealed that these new porphyrin thioethers are highly distorted,
exhibiting conformational properties that are distinctive of both
meso-sulfur substitution and steric overcrowding in general. Additionally,
denitration of H2OETNP under basic conditions was investigated,
yielding products of stepwise desubstitution. This allowed a comparative
X-ray crystallographic study to delineate the successive structural
effects of an increasing degree of nitro substitution in the complete
series of nitro-substituted octaethylporphyrins.