Since the report of the ruthenium “blue dimer” as a homogeneous water oxidation catalyst (WOC) by Meyer and coworkers in 1982,1 an increasingly wide variety of mononuclear and dinuclear WOC have been studied. Among all of these systems one standout complex, Ru(bda)(pic)2 (bda = 2,2’-bipyridine-6,6’-dicarboxylic acid, pic = 4-picoline) has demonstrated exemplary catalytic activity by chemical and electrochemical oxidation.2 The remarkable activity of Ru(bda)(pic)2 has been attributed largely to electronic and geometric properties of tetradentate-bound bda. The outstanding reactivity imparted by bda motivated us to explore new tetradentate ligands. Phosphonates are versatile ligands, particularly for the design of porous materials. Moreover, in the context of WOC, the affinity of phosphonate groups for metal oxide surfaces has been exploited for electrode functionalization.3 In contrast, using phosphonates as ligands for the catalytic metal(s) in molecular WOC appears to be completely unexplored. We considered that phosphonates are promising for WOC because of unique characteristics that may prove to be advantageous. Phosphonate groups contain three O atoms in tetrahedral geometry. If only one O is coordinated to a metal, there remain one OH and one O, and this HO-P=O unit can be protonated or deprotonated depending on the pH; therefore, unlike metal-bound carboxylates, phosphonate ligands have the advantage of being pH responsive. Here we report the synthesis, catalysis and relevant properties of the first water oxidation complexes deliberately bearing phosphonate groups positioned to serve as metal-bound ligands. References: 1. Gersten, S. W.; Samuels, G. J; Meyer, T. J. J. Am. Chem. Soc., 1982, 104, 4029–4030 2. (a) Duan, L.; Fisher, A.; Xu, Y.; Sun, L., J. Am. Chem. Soc., 2009, 131, 10397. (b) Duan, L.; Bozoglian, F.; Mandal, S.; Stewart, B.; Privalov, T.; Llobet, A.; Sun, L. Nature Chem. 2012, 4, 418. 3. Selected example: Chen, Z.; Concepcion, J. J.; Jurss, J. W.; Meyer, T. J. J. Am. Chem. Soc. 2009, 131, 15580.

Ruthenium complexes bearing metal-coordinated phosphonates for water oxidation

251st National Meeting (2016)

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