Electrostatic Interactions Accelerating Water Oxidation Catalysis via Intercatalyst O–O Coupling

Abstract

Intercatalyst coupling has been widely applied in the functional mimics for binuclear synergy in natural metal enzymes. Herein, we introduce two facile and effective design strategies, which facilitate the coupling of two catalytic units via electrostatic interactions. The first system is based on a catalyst molecule functionalized with both a positively charged and a negatively charged group in the structure being able to pair with each other in an antiparallel manner arranged by electrostatic interactions. The other system consists of a mixture of two different of catalysts modified with either positively or negatively charged groups to generate intermolecular electrostatic interactions. Applying these designs to Ru­(bda) (H2bda = 2,2′-bipyridine-6,6′-dicarboxylic acid) water-oxidation catalysts improved the catalytic performance by more than an order of magnitude. The intermolecular electrostatic interactions in these two systems were fully identified by 1H NMR, TEM, SAXS, and electrical conductivity experiments. Molecular dynamics simulations further verified that electrostatic interactions contribute to the formation of prereactive dimers, which were found to play a key role in dramatically improving the catalytic performance. The successful strategies demonstrated here can be used in designing other intercatalyst coupling systems for activation and formation of small molecules and organic synthesis.

Hydrophobic Interactions of Ru-bda-Type Catalysts for Promoting Water Oxidation Activity

“…However, considering the complexity of the synthesis of multinuclear structures, non-covalent assembly strategies seem more attractive. Many reported works have emphasized the role of secondary interactions in intercatalyst coupling, as shown in Figure , such as π–π interaction, , electrostatic interaction, off-set interaction, etc. We envisage that those non-covalent interactions between the axial ligands can be expanded to hydrophobic interactions by replacing the substituents of axial ligands.…”

Oriented internal electrostatic fields: an emerging design element in coordination chemistry and catalysis

“…19a-c). 98 The authors found that water oxidation using either a Ru-dba catalyst containing both cationic and anionic charges (Fig. 19a) or a mixture of a Ru-dba catalyst containing two cationic charges with a Ru-dba catalyst containing two anionic charges (Fig.…”

“…and (c) may be used to ease the formation of the pre-reactive dimer complex. 98 for the resulting cupric aqua complexes were measured in both organic and aqueous media, and the complex containing cationic charges in the secondary coordination sphere was found to have slightly stronger O-H bonds than the complex containing anionic charges in the secondary coordination sphere (91-91.5 kcal mol À1 vs. 87-91 kcal mol À1 respectively). Despite the modest increase in the thermodynamic driving force for hydrogen atom abstraction by the Cu III -OH complex containing cationic charges, the kinetics for HAT with this complex were over two orders of magnitude slower than that of the Cu III -OH complex containing anionic charges.…”

Electrosteric Stabilization of End-on Cupric Superoxide Complexes

“…The use of oriented internal electrostatic fields for impacting the binding, 1-3 activation, 1,2,4-8 and reactivity 7,[9][10][11][12][13][14][15][16] of small molecules is a rapidly emerging method for tuning the physical and chemical properties of metal complexes. 17,18 Internal electrostatic fields can be introduced into metal complexes either through incorporation of charged functional groups into ligands or through positioning of outer sphere ions, and they have been shown to be impactful in both ground state and catalytic contexts.…”