FACILE SYNTHESIS OF MESO-TETRAARYL COFACIAL DIPORPHYRINS

Metalated derivatives of cofacial diporphyrin ligands have been employed in the binding and catalytic multielectron redox transformations of small molecules. To date, the syntheses of these interesting molecules 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. Here, we report a new method for the synthesis of a family of cofacial diporphyrin ligands in which the two porphyrins are attached via one rigid aromatic linker. The synthesis is considerably shorter-three steps 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 involves the monoprotection of a dialdehyde using 1,3-propanedithiol. The monoprotected aldehyde is then cocondensed under modified Lindsey conditions with pyrrole and the aromatic aldehyde of choice. The aldehyde of the resulting species is subsequently deprotected using DDQ and BF3 . O(Et)(2)-a new method for cleavage of dithiane protecting groups. A second Lindsey condensation results in formation of the cofacial diporphyrin ligand. Employing this method, we have synthesized a wide variety of cofacial hetero- and homodiporphyrin ligands, the metalated derivatives of which are currently under investigation in our laboratories.