The impact of secondary coordination sphere engineering on water oxidation reactivity catalysed by molecular ruthenium complexes: a next-generation approach to develop advanced catalysts

Abstract

Water oxidation is the bottleneck to producing hydrogen from the water-splitting reaction. The development of efficient water oxidation catalysts (WOCs) is of paramount interest in recent years. Ru-based WOCs have...

Ruthenium Complexes of Rigid, Dianionic, Tetradentate N‐Donor Ligands and their Potential as Catalysts for Water Oxidation

“…A first‐order behaviour with respect to the catalyst indicates a mononuclear mechanism, likely operating via WNA for O−O bond formation. It may be speculated that the non‐coordinating N‐atom of the in ‐positioned imidazo[4,5‐ b ]pyridine moiety in 2 may H‐bond to incoming water and thus assist a WNA mechanism at a high‐valent Ru=O intermediate [52,53] …”

“…It may be speculated that the non-coordinating N-atom of the in-positioned imidazo [4,5-b]pyridine moiety in 2 may H-bond to incoming water and thus assist a WNA mechanism at a high-valent Ru=O intermediate. [52,53] To gain information about the complex species present in solution after catalysis, solutions of 2 in a 1 : 1 mixture of 0.10 M triflic acid (pH 1.0) and TFE (viz., conditions as above) were treated with 30 equiv. CAN, and ESI(+) mass spectra were then recorded.…”

Tuning primary and secondary coordination spheres of ruthenium complexes for the homogeneous water oxidation reaction: a perspective from catalytic activity and overpotential

“…The development of an effective secondary coordination environment has recently been introduced to Ru-based WOCs. [37][38][39]53,67 Several strategies have been used, as shown in Fig. 1.…”

“…37 Although ligands in the primary coordination sphere directly influence the steric and electronic properties of the metal center, the secondary coordination sphere also needs to be assessed during catalyst engineering. 36,38,39 For instance, literature studies have demonstrated that smallmolecule catalysis, such as the reduction of CO 2 , O 2 , H + , and oxidation of NH 3 and H 2 O, could benefit rationally by finetuning the secondary coordination sphere of the corresponding catalysts. [40][41][42][43][44][45][46] The manipulation of the secondary coordination sphere of Ru-based WOCs has primarily been achieved via non-covalent interactions, such as hydrogen bonding, π-π stacking, hydrophobic/hydrophilic effects, steric hindrance, and electronic influence.…”

“…[40][41][42][43][44][45][46] The manipulation of the secondary coordination sphere of Ru-based WOCs has primarily been achieved via non-covalent interactions, such as hydrogen bonding, π-π stacking, hydrophobic/hydrophilic effects, steric hindrance, and electronic influence. 38,39 Although various approaches have been employed to control the primary and secondary coordination spheres of Ru catalysts toward the WOR, 47 there is minimal information on the cross-comparison of these studies from the kinetic and thermodynamic points of view. Perhaps the main reason is that these studies were conducted under different conditions, and a uniform standard to assess the performance of these Ru-based WOCs is lacking.…”