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

Abstract

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 κ3‐SNS mode to give 1 whereas pbcta coordinated via a κ3‐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 κ3‐SNS pincer ligand enhances the activity of the Pd(II) towards proton reduction relative to 1.

Optical and Electrochemical Sensing of Co(II), Ni(II) and Cu(II) in DMSO. Pyridyl Thiazole and (Thio)Amide Pincer Ligands versus Di‐2‐pyridyl Ketone Hydrazones

“…Nevertheless, the shift in the C=N reduction potential was a key diagnostic tool in assessing the coordination of M 2+ to the hydrazone. Unlike the hydrazones, species 2 , 3 , 5 and 6 were more resistant to bond cleavage upon reduction, however the thienyl radicals generated from electrochemical processes may undergo chemical reactions which ultimately impede the reversibility of the process [7a–c] . Similar to the hydrazones, the coordination to M 2+ and resulting shift in the reduction potential of the thioamide is a diagnostic tool in assessing the coordination of 2 , 5 and 6 .…”

“…In addition to the improved electrochemical stability, the redox non‐innocence of these pyridyl based pincers may improve the stability of metal centers in various oxidation states in catalytic transformations. In these studies, [7b,c] it was found that the coordinating atoms of the ligand system influenced the electrocatalytic behavior in the hydrogen evolution reaction (HER). To further understand and develop these ligand systems, quantifying binding (formation) constants, and the relative equilibrium constants amongst these pyridyl thiazoles and thioamides ligand systems can also provide insights about the modifications that can be made to the ligand framework.…”

Effect of chalcogen bonding interactions on molecular structures; theoretical and crystallographic studies on two palladium(ii) acetate complexes

“…[9][10][11][12] Pt(II) and Pd(II) complexes composed of NNS tridentate pincer ligands were found to have significant biological activities. [13][14][15][16][17][18][19] Both metals have similar chemistry but the later has less side effects and better solubility, which led researchers to focus on Pd(II) complexes as antitumor drugs. [13][14][15][16][17][18][19] Palladium complexes [Pd II (HY)Cl] built from H 2 Y(SNN) pincer ligands were previously prepared in our laboratory.…”

“…[13][14][15][16][17][18][19] Both metals have similar chemistry but the later has less side effects and better solubility, which led researchers to focus on Pd(II) complexes as antitumor drugs. [13][14][15][16][17][18][19] Palladium complexes [Pd II (HY)Cl] built from H 2 Y(SNN) pincer ligands were previously prepared in our laboratory. 20 The ligand H 2 Y (Scheme 1, left) was bound in anionic form to Pd(II) to form neutral cis and trans isomers.…”