SNS versus SNN Pincer Ligands: Electrochemical Studies and Their Palladium(II) Complexes as Electro‐Catalyst for Proton Reduction

Electrochemical measurements on pincer ligands bis‐ N ‐(2,5‐dimethoxyphenyl)pyridine‐2,6‐dicarbothioamide ( pdcta ) and 6‐(4,7‐dimethoxy‐2‐benzothiazolyl)‐ N ‐(2,5‐dimethoxyphenyl)‐2‐pyridinecarbothioamide ( pbcta ) in N,N ‐dimethylformamide (DMF) and dimethylsulfoxide (DMSO) on a glassy carbon working electrode revealed sulfur centred electrochemical processes. Spectroscopic, elemental and electrochemical analyses indicated that pdcta coordinated to Pd(II) via a κ 3 ‐SNS mode to give 1 whereas pbcta coordinated via a κ 3 ‐SNN mode to give 2 . Electrochemical measurements in DMF indicated that the reduction of Pd(II)→Pd(0) proceeded in a concerted manner in the 2 , whereas reduction was resolved into the Pd(II)→Pd(I)→Pd(0) in the case of 1 . In the presence of p ‐toluenesulfonic acid, both palladium complexes displayed electro‐catalytic proton reduction in DMF, with associated overpotentials calculated to be 97 mV and 156 mV for 1 and 2 , respectively. The data suggests that the κ 3 ‐SNS pincer ligand enhances the activity of the Pd(II) towards proton reduction relative to 1 .