Synthesis of New Porphyrins with Peripheral Conjugated Chelates and Their Use for the Preparation of Porphyrin Dimers Linked by Metal Ions

This article describes the preparation of several new porphyrins bearing chelating peripheral groups fully conjugated
with the macrocyclic π-system. Treatment of a 2-nitro-meso-tetraarylporphyrin with phosphite gave a cyclic enamine,
whose formylation gave an enaminoaldehyde. The thio analogue was obtained on treatment with Lawesson's
reagent. The same reagent was also used to obtain the isomeric thioenaminoketone chelates. A enaminoketone
ligand was prepared from a porphyrinic pyrrolone. All these ligands, as internal nickel complexes, could be metalated
with palladium to yield porphyrinic dimers. The dimers obtained from enaminoketones and thioketones show a
trans geometry, while in the enaminoaldehyde and -thioaldehyde series the cis isomer is thermodynamically favored.
The bathochromic shifts of the electronic spectra of the aldehyde-derived dimers illustrate the strong electronic
effect of peripheral metalation and dimerization. However, in the case of the pyrrolone-derived ligand, opposite
effects were observed, due to partial reconstitution of the porphyrin chromophore on complexation. As with the
dimers derived from enaminoketones, the dimers derived from the new ligands show typical splitting (up to 190
mV) of the electrochemical waves confirming large porphyrin−porphyrin interactions.