An effective non-chromatographic method for the purification of phenanthrolines and related ligands

1,10-Phenanthrolines are widely employed as ligands, but their use on a large scale is constrained by their difficult purification, which usually requires lengthy chromatographic separations. Herein, we describe a purification strategy that takes advantage of the high stability and low solubility of phenanthroline complexes to separate them from the by products of their synthesis. The formation of ZnCl2 complexes was employed, from which the free ligand can be recovered by reaction with aqueous NH3 in a biphasic CH2Cl2/H2O system. The same strategy was also successfully employed to purify related quinolino-guanidine ligands, demonstrating that the procedure is of general applicability.