Single Site Isomeric Ru WOCs with Electron Withdrawing Groups: Synthesis, Electrochemical Characterization and Reactivity

Abstract

<p> The synthetic intermediate <i>cis(out),cis</i>-[Ru(Cl)2(HL)(DMSO)2], <b>1</b> (DMSO = dimethyl sulfoxide), and four new mononuclear ruthenium complexes with general formula <i>out/in</i>-[Ru(HL)(trpy)(X)]<i>m</i>+ (trpy = 4-<i>tert</i>-butylpyridine; X = Cl&ndash;, <i>m</i> = 1, <b>2a</b>+ and <b>2b</b>+; X = H2O, <i>m</i> = 2, <b>3a</b>2+ and <b>3b</b>2+) based on the ligand 1<i>H</i>-pyrazole-3-carboxylic acid, 5-(2-pyridinil)-, ethyl ester (HL), are synthesized and characterized by analytical, spectroscopic, and electrochemical methods. A linkage isomerism is observed for a DMSO moiety of <b>1</b>, and relevant thermodynamics and kinetics values are obtained through electrochemical experiments and compared to literature. Different synthetic routes are developed to obtain isomeric <b>2a</b>+ and <b>2b</b>+, with different relative yields. Water oxidation activity of<b>3a</b>2+ and <b>3b</b>2+ is analyzed by means of electrochemical methods, through foot of the wave analysis, yielding <i>k</i>obs values of 1.00 and 2.23 s&ndash;1, respectively. Chemically driven water oxidation activity is tested using [(NH4)2Ce(NO3)6] as sacrificial electron acceptor, and turnover number (TON) and turnover frequency (TOF) values of TON = 10.8 and TOFi = 58.2 &times; 10&ndash;3 s&ndash;1 for <b>3a</b>2+and TON = 4.2 and TOFi = 15.4 &times; 10&ndash;3 s&ndash;1 for <b>3b</b>2+ are obtained.</p>