Porphyrin analogues of Tröger's base: large chiral cavities with a bimetallic binding site

2-Amino-5,10,15,20-tetraarylporphyrins react with formaldehyde to give good yields of the corresponding octaaryl derivatives of the Tröger's base analogue in which two porphyrins are covalently Jinked by a diazocine bridge; the X-ray crystal-structure of the bis(tetraphenylporphyrinato)dipalladium(II) derivative 6 reveals a concave chiral cavity with two metal ion binding sites suitable for ditopic interactions with guest molecules.