FACILE SYNTHESIS OF MESO-TETRAARYL COFACIAL DIPORPHYRINS

Metalated derivatives of cofacial diporphyrin ligands have been employ ed in the binding and catalytic multielectron redox transformations of small molecules. To date, the syntheses of these interesting molecule s have been extremely cumbersome and low yielding. In addition, their synthetic methodologies have presented no convenient way to modify the electronic and structural properties of the constituent porphyrins. H ere, we report a new method for the synthesis of a family of cofacial diporphyrin ligands in which the two porphyrins are attached via one r igid aromatic linker. The synthesis is considerably shorter-three step s from a suitable dialdehyde bridge-utilizes inexpensive, commercially available reagents, results in markedly increased yields, and allows for convenient variation of the constituent porphyrins. The method inv olves the monoprotection of a dialdehyde using 1,3-propanedithiol. The monoprotected aldehyde is then cocondensed under modified Lindsey con ditions with pyrrole and the aromatic aldehyde of choice. The aldehyde of the resulting species is subsequently deprotected using DDQ and BF 3 . O(Et)(2)-a new method for cleavage of dithiane protecting groups. A second Lindsey condensation results in formation of the cofacial dip orphyrin ligand. Employing this method, we have synthesized a wide var iety of cofacial hetero- and homodiporphyrin ligands, the metalated de rivatives of which are currently under investigation in our laboratori es.