Porphyrins Like Boron After All

The central core and the macrocycle skeleton of porphyrins both offer room for boron, and a gap in the chemistry of nonmetal-containing porphyrins has now been filled. In one case a four-membered B₂O₂ ring coordinates to a porphyrin cavity that has been distorted to a rectangle ( A ), and in the other case four boron atoms are located in the meso positions of a tetrathiaporphyrinogen ( B ).