Cp*^–‐Ruthenium–Nickel‐Based H₂‐Evolving Electrocatalysts as Bio‐inspired Models of NiFe Hydrogenases

Abstract

Three dinuclear nickel–ruthenium complexes [Ni(xbsms)RuCp*(L)](PF6) [H2xbsms = 1,2‐bis(4‐mercapto‐3,3‐dimethyl‐2‐thiabutyl)benzene; Cp* = pentamethylcyclopentadienyl; L = CH3CN, CO and O2] are reported that act as bio‐inspired mimics of NiFe hydrogenases. Because of an increased electron density at the metal centres in comparison with the previously described [Ni(xbsms)RuCp(L)](PF6) (Cp = cyclopentadienyl) analogues, these compounds catalyze the evolution of hydrogen from Et3NH+ in DMF with an overpotential reduced by around 50 mV, thereby corroborating a previously established structure–function relationship [Eur. J. Inorg. Chem. 2007, 18, 2613–2626; Chem. Eur. J. 2009, 15, 9350–9364]. In addition, the steric protection provided by the bulky Cp*– ligand results in an increased catalytic rate and stability upon cycling.

Syntheses, characterizations and properties of [Mo2O2S2]-based oxothiomolybdenum wheels incorporating bisphosphonate ligands

“…The protonation of the bridging bisphosphonate ligands followed by the partial degradation of Mo 8 S 8 (Ale) 4 and consequently the partial degradation of the deposit onto the surface of the electrode, could explain this phenomenon. Finally, the overpotential was estimated from the half-wave potential of the electrocatalytic process for highest concentrations of TFA in CH 3 CN (between −1.3 V and −1.2 V vs. Ag/AgCl) and was found to be of ∼0.8 V for H 2 evolution, 37 a value which compares well with those observed for NiFe-based or NiRu-based bio-inspired catalysts ranging between ∼0.6 to 1 V. 41,42 Similar studies were performed on the oxo analogous compound Mo 8 O 8 (Ale) 4 . As observed for Mo 8 S 8 (Ale) 4 , in acetonitrile free from TFA, the compound appears electrochemically silent in the 0 to −1.95 V vs. Ag/AgCl range.…”

Active-Site Models for the Nickel–Iron Hydrogenases: Effects of Ligands on Reactivity and Catalytic Properties

“…Most active site models for the NiFe-hydrogenases use Ni centers bound to diaminodithiolate (S 2 N 2 ) ligands. 4,6,15,30 Such tetradentate ligands probably constrain Ni to a square-planar geometry, 29 although square-pyramidal or trans-octahedral NiS 2 N 2 centers have been observed for Ni-Ru system where the fifth and sixth site are occupied by hydride and aquo ligands. 16 In the Ni-diphosphine catalysts, the coordination sphere at Ni is proposed to alternate between square-pyramidal (with a bridging hydride), tetrahedral, and, possibly, square planar geometries (Figure 11).…”

“…One family of catalysts is based on Ru derivatives of NiN 2 S 2 and NiS 4 metalloligands (N 2 S 2 = diaminodithiolates and S 4 = dithioetherdithiolates). 15,16 Even oligomeric nickel dithiolates have been shown the catalyze proton reduction. 18 In other Ni-Fe complexes, catalysis was not observed when the Fe center is high spin.…”

Wasserspaltung mit Cobalt

“…[57][58][59][60][61] Darüber hinaus wurden einige koordinativ gesättigte Verbindungen wie die oktaedrisch koordinierten Hexaminkomplexe 24-27 (Abbildung 6), [62] darunter auch Sepulchrat-Derivate, [62,63] und die Trisdioxim-Clathrochelate 28 und 29 (Abbildung 7) [64] beschrieben. Als letzte Klasse wären noch Organometallverbindungen mit Cyclopentadienyl- (30)(31)(32)(33) [63,65,66] oder Diphosphanliganden (34) [67,68] [72] Somit erhält man ein Maß für den Energieaufwand, der betrieben werden muss, damit die Reaktion mit einer signifikanten Geschwindigkeit ablaufen kann. [72][73][74] Der zweite charakteristische Parameter eines Katalysators ist seine Umsatzfrequenz ("turnover frequency", TOF).…”