Proton coupled electron transfer (PCET) plays an important role in many biological systems including bacterial reaction centers, the amino acid radicals present in Photosystem II, and oxidative phosphorylation processes in cellular respiration. Given the size and complexity of biomolecules, understanding how biological systems undergo PCET reactions is challenging. One approach is to develop small scale model complexes that mimic this effect. To this end, we have prepared a series of complexes of the type [Ru(trpy)PPh3)(oximeH2)]2+ where trpy is terpyridine, PPh3 is triphenyl phosphine and the oxime ligands are dimethyl glyoxime, diphenyl glyoxime and difuryl glyoxime (see figure). We have characterized the complexes spectroscopically and electrochemically. The oxime ligand binds to ruthenium through the oxime nitrogen as evidenced from the C=N stretch in the FTIR, and the 31P NMR signal is characteristic of a phosphine ligand. In acetonitrile, the complexes exhibit metal to ligand charge transfer bands between 380 and 450 nm. The bands shift to lower energy on titration with base. In aqueous solution, the Ru(II)/Ru(III) couple shifts to lower potential with increasing pH. The spectral and electrochemical properties of this series of complexes will be elaborated.

Terpyridine ruthenium oxime complexes: Models for proton coupled electron transfer

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