Simple, Axial Ligand-Mediated Route to Water-Soluble Iridium Corroles

The synthesis and purification of water-soluble porphyrin-type compounds for photodynamic therapy and other medical applications is often a tedious exercise. Here, we have investigated the simple stratagem of adding a water-soluble axial ligand to the standard protocol for iridium insertion into simple meso-triarylcorroles. Early results showed that six-coordinate Ir­[TpXPC]­(dna)2 derivatives, in which TpXPC = tris­(para-X-phenyl)­corrole (X = CF3, CN, H, and OMe) and dna = dinicotinic acid, are highly water-soluble. In the end, however, all axially nitrogen-ligated complexes proved unstable with respect to chromatographic purification and storage. Five-coordinate water-soluble phosphine adducts, fortunately, proved a great improvement. From the point of view of ease of purification and storage, the best products proved to be Ir­[TpXPC]­(L), where X = CF3 and OMe and L = tris­(2-carboxyethyl)­phosphine (tcep) and trisodium tris­(3-sulfonatophenyl)­phosphine (tppts); carefully optimized synthetic protocols are presented for these four compounds.