Influence of the Metal Ion on the Electrocatalytic Hydrogen Production by a Thiosemicarbazone Palladium Complex

Abstract

We describe the synthesis and characterization of a new mononuclear palladium complex (PdL) based on a thiosemicarbazone ligand. X-ray diffraction data collected on single crystals reveal that the complex is a neutral mononuclear entity with symmetric square-planar geometry around the metal center. The complex exhibits an electrocatalytic behavior for proton reduction in DMF solvent using trifluoroacetic acid (TFA) as a proton source. Gas analysis under controlled electrocatalytic [a] 2265 and the COST Action CM1202 Perspect-H 2 O (Supramolecular photocatalytic water splitting). The authors would like to thank Jennifer Fize and Dr. Vincent Artero for assistance in the electrocatalytic measurements and fruitful discussions.

Recent advances in the mechanisms of the hydrogen evolution reaction by non-innocent sulfur-coordinating metal complexes

“…Recently, the Ni(II) complex of thiosemicarbazone was also studied as a potential electrocatalyst for H 2 formation. 179 Complex 67 undergoes ligand centred reduction at −1.83 V vs. Fc + /Fc and the Ni(II/I) reduction takes place at −2.45 V. The electrocatalytic activity of 67 was examined in acetonitrile and dimethylformamide with acetic acid and TFA as the proton sources. In acetonitrile, 67 was reported to catalyse H 2 evolution at −2.35 V vs. Fc + /Fc when acetic acid ( pK a = 23.5) was introduced, with a TON of 48 over 4 h of CPE and an initial TOF of 4200 s −1 .…”

“…The hydride subsequently reacts with a proton in solution to form H 2 via a low energy (10.5 kcal mol −1 ) transition state and reenter the catalytic cycle. 179 The {bis[4-(p-methoxyphenyl)thiosemicarbazone]}-2,3-butane ligand was further investigated with Pd(II) as the metal centre, forming the square planar diamagnetic complex 69. 179 The coordinated ligand is reduced at −1.02 V vs. Ag/AgCl (−1.4 V vs. Fc + /Fc) and Pd(II/I) reduction is possible at −1.64 V. Note that the free ligand is reduced at −1.6 V vs. Ag/AgCl.…”

“…179 The {bis[4-(p-methoxyphenyl)thiosemicarbazone]}-2,3-butane ligand was further investigated with Pd(II) as the metal centre, forming the square planar diamagnetic complex 69. 179 The coordinated ligand is reduced at −1.02 V vs. Ag/AgCl (−1.4 V vs. Fc + /Fc) and Pd(II/I) reduction is possible at −1.64 V. Note that the free ligand is reduced at −1.6 V vs. Ag/AgCl. Complex 69 achieved proton reduction to form H 2 in DMF using TFA (pK a = 6) as the proton source.…”

Neutral Lipophilic Palladium(II) Complexes and their Applications in Electrocatalytic Hydrogen Production and C‐C Coupling Reactions

“…A faradaic efficiency of 70 % was obtained for proton reduction in dimethylformamide (DMF) at –1.5 V vs. saturated calomel electrode (SCE) at a glassy carbon working electrode. A mononuclear palladium complex based on a thiosemicarbazone ligand has shown electrocatalytic behaviour for proton reduction in DMF in the presence of TFA, however the faradaic efficiency of this compound was only 34 % with a turnover number of 2 after 4 h.…”

Efficient Light-Driven Hydrogen Evolution Using a Thiosemicarbazone-Nickel (II) Complex

“…Due to the effect of non-innocent ligands, (Han et al, 2012, 2013; Rao et al, 2015, 2016; Inoue et al, 2017) such nickel complexes have displayed excellent efficiency as catalyst reaching around 7,500 TON (Han et al, 2013; Rao et al, 2016). Thiosemicarbazone metal complexes are an emerging class of new HER electrocatalysts (Haddad et al, 2016, 2017; Straistari et al, 2017, 2018a,b) that have already been proved to be redox active (Blanchard et al, 2005; Haddad et al, 2017; Straistari et al, 2017) The presence of S-donors as well as N-atoms in thiosemicarbazone allows the protonation of the ligand and serve as proton relays (Campbell, 1975; DuBois, 2014; Coutard et al, 2016). One of the most essential aspect of light-driven proton reduction is the appropriate choice of the light-harvesting unit (i.e., photosensitizer, Ps).…”