Two unique new tetradentate ligands have been developed whose transition metal complexes show interesting activity as catalysts for water oxidation. The ligand 2,9-di(pyrid-2'-yl)-1,10-phenanthroline (dpp) is prepared by the Stille coupling of 2,9-dichlorophenanthroline with a 2-pyridylstannane. The Friedländer condensation of 3-bromo-2-aminobenzaldehyde with 2-acetylpyridine followed by a Suzuki coupling leads to 2-(pyrid-2'-yl)-8-(1'',10''-phenanthrolin-2''-yl)-quinoline (ppq). Both ligands may be considered as derivatives of quaterpyridine with ppq presenting the smaller, more square-planar metal binding cavity. The dpp will complex with RuCl3 in the presence of 4-picoline to provide [Ru(dpp)(pic)2]2+. In the presence of Ce(IV) at pH = 1 in aqueous buffer this complex generates O2 with a rate of 43 h-1. On the other hand, when ppq is treated with FeCl3, it forms a complex in which the X-ray structure indicates that two Fe(ppq) subunits are linked as an oxo-bridged dimer. When exposed to Ce(IV) in aqueous solution this system generates oxygen with a TOF = 7920 h-1.

Catalytic water oxidation: From Ru(II) to Fe(III)

251st National Meeting (2016)

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