Bis(cyclopentadienyl)nickel(II) μ-Thiolato Complexes as Proton Reduction Electrocatalysts

Abstract

Thiolato-bridged cyclopentadienylnickel dimeric complexes have been prepared and found to be efficient and robust proton reduction electrocatalysts using acetic acid as the proton source. From cyclic voltammetry studies, moderate overpotentials of around 0.6 V and i c / i p values from 7.8 to 12.2 have been determined for 20 equiv of acetic acid at a scan rate of 100 mV/s. A turnover number of around 7 has been determined for each of the nickel complexes. The thiolato substituent of the complex does not appear to influence the catalysis significantly. Each of the nickel complexes acts as a robust homogeneous catalyst that could sustain continuous proton reduction for hours. On the basis of the experimental data, an electrochemical− chemical−electrochemical−chemical mechanism describing the catalytic process has been proposed as well.

Nickel(II)–Nickel(II) Azadithiolates: Synthesis, Structural Characterization, and Electrocatalytic H2 Production

“…As shown in Table and Figure , complexes 8 and 9 display one quasi-reversible reduction wave at −1.36 and −1.34 V, one irreversible reduction wave at −1.74 and −1.72 V, and one irreversible oxidation wave at 0.18 and 0.20 V, respectively. Similar to the previously reported cases, ,, the oxidation events of 8 and 9 each are one-electron processes, which was confirmed by bulk electrolysis of a MeCN solution of 8 at 0.18 V (1.01 F mol –1 passed in 1 h) or 9 at 0.20 V (1.08 F mol –1 passed in 1 h). The reduction events displayed by 8 and 9 each are also one-electron processes, since their reduction peak current heights are close to their oxidation peak current heights.…”

“…However, in contrast to this, when 1–20 mM HOAc is sequentially added, the current heights of their original second reduction waves are considerably increased. Apparently, such an observation features an electrocatalytic process for proton reduction to hydrogen. ,, Furthermore, as shown in Figures and , when 1–8 mM HOAc is continuously added, the original second reduction waves are positively shifted by about 40 mV, which is most likely caused by protonation of the central N atoms in their bridged azadithiolato ligands …”

“…The reduction events displayed by 8 and 9 each are also one-electron processes, since their reduction peak current heights are close to their oxidation peak current heights. While the first reduction events of 8 and 9 could be assigned to the CpNi II Ni II (dppv)/CpNi I Ni II (dppv) couple due to the CpNi II moieties in 8 and 9 each bearing a positive charge, the second reduction events of 8 and 9 could be attributed to the CpNi I Ni II (dppv)/CpNi I Ni I (dppv) couple since the second reduction potentials of 8 and 9 are positively shifted relative to those displayed by their precursors 4 (−1.94 V) and 5 (−1.91 V) (see Figure S1) and in turn the oxidation events of 8 and 9 might be ascribed to the CpNi II Ni II (dppv)/CpNi II Ni III (dppv) couple. ,, It should be noted that all of the reduction and oxidation waves of complex 9 are positively shifted by 20 mV relative to those of complex 8 , which is consistent with 4-ClC 6 H 4 group in 9 being an electron-withdrawing group stronger than the C 6 H 5 group in 8 . Additionally, the two reduction processes of 8 and 9 are all diffusion-controlled, since their reduction peak currents versus the square root of the scan rates (25–2000 mV s –1 ) are linearly correlated (see Figures S2 and S3).…”

“…To date, a variety of homodinuclear Ni 2 complexes have been synthesized and some of them have been found to be electrocatalytic H 2 -producing catalysts. − Having prepared the targeted dinuclear complexes 8 – 11 , we chose complexes 8 and 9 as representatives (due to 8 and 9 having the same types of structures as those of 10 and 11 ) to study their electrochemical properties and electrocatalytic H 2 -producing ability. The electrochemical properties of 8 and 9 were determined by cyclic voltammetric (CV) techniques by using n -Bu 4 NPF 6 as the supporting electrolyte in MeCN at a scan rate of 100 mV s –1 .…”

Electrocatalytic property, anticancer activity, and density functional theory calculation of [NiCl(P^N^P)]Cl.EtOH

“…The proposed reaction pathways for reducing two hydrogen ions to generate an dihydrogen molecule involve four steps in the form of either chemical (C) or electrochemical (E) reactions. [71] In another study, Hong et al synthesized high-spin Ni(II) complexes with S 2 N 2 ligands. The proposed electrocatalytic mechanism involves the stepwise reduction of Ni(II) by two electrons to form [LNi 0 ] 0 in acetonitrile.…”