Base-enhanced catalytic water oxidation by a carboxylate-bipyridine Ru(II) complex

In aqueous solution above pH 2.4 with 4% (vol/vol) CH3CN, the complex [Ru-II(bda)(isoq)(2)] (bda is 2,2'-bipyridine-6,6'-dicarboxylate; isoq is isoquinoline) exists as the open-arm chelate, [Ru-II(CO2-bpy-CO2-)(isoq)(2)(NCCH3)], as shown by H-1 and C-13-NMR, X-ray crystallography, and pH titrations. Rates of water oxidation with the open-arm chelate are remarkably enhanced by added proton acceptor bases, as measured by cyclic voltammetry (CV). In 1.0M PO43-, the calculated half-time for water oxidation is similar to 7 mu s. The key to the rate accelerations with added bases is direct involvement of the buffer base in either atom-proton transfer (APT) or concerted electron-proton transfer (EPT) pathways.