Electrochemical response of a Ru(II) benzothiazolyl-2-pyridinecarbothioamide pincer towards carbon dioxide and transfer hydrogenation of aryl ketones in air

A ruthenium(II) complex of 6-(4,7-dimethoxy-2-benzothiazolyl)-N-(2,5-dimethoxyphenyl)-2-pyridinecarbothioamide (pbcta), of the formula [Ru(pbcta)Cl2(dmf)] (1, where DMF = dimethyl formamide) was prepared from RuCl3•xH2O and pbcta in DMF at reflux under argon atmosphere. The identity of 1 was confirmed from its elemental analysis, ESI MS, and a series of spectroscopic measurements. Voltammetric measurements on 1 in DMF and DFT studies on the structure optimized in the gas phase revealed predominantly ligand based electron transfer processes under argon. In the presence of a proton source, proton coupled electron transfer to the ligand occurs. Under a carbon dioxide atmosphere, voltammetric studies revealed that 1 is inactive for CO2 reduction, and the redox responses observed in the presence of the proton source and/or CO2 are ligand based leading to reactions with the coordinated pbcta. Transfer hydrogenation (TH) of aryl ketones was efficiently carried out in 2-propanol using 1 at reflux. TH of the aryl ketone substrates proceeded in air with almost quantitative conversions at 0.2–1.0 mol% catalyst.