The synthesis of efficient molecular water oxidation catalysts (WOCs) and their stable anchoring on suitable electron acceptor supports are crucial, yet challenging, steps for the development of artificial photosynthesis schemes. Here, a highly active diruthenium complex based on the bis­(bipyridyl)­pyrazolate (bbp–) ligand scaffold is anchored on electronically conducting multiwall carbon nanotubes (MWCNTs) using a pyrene group attached to either the pyrazolate backbone (2) or to multiple axial ligand positions (1). High-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) show the presence of >75% sp2 hybridization of the MWCNTs and an increase of spectral weight of π–π* transitions upon immobilization of the pyrene-modified ligand or diruthenium complex, supporting pyrene anchoring via π–π interactions. Upon electrochemical oxidation the pyrene groups confined to the MWCNT-modified electrodes are rapidly converted to redox-active surface-bound quinone species. The water oxidation performance of the hybrid systems is studied by cyclic voltammetry and rotating ring disk electrode (RRDE) experiments under acidic aqueous condition (triflic acid, pH 1). Whereas the complex anchored at the backbone position shows higher initial catalytic activity, the complex anchored via four axial ligand positions features a higher stability. X-ray photoemission (XPS) data before and after electrochemical measurements reveal that the chemical structure of the immobilized complex remains intact under catalytic conditions. The results suggest that anchoring of Ru2 complexes by differently located pyrene groups on MWCNTs offers good performance for electron transfer, however, a single pyrene group at the pyrazolate backbone does not provide sufficiently strong surface attachment. The distinct experimental results for MWCNT hybrids with anchored 1 and 2 are further discussed in terms of the preferred attachment position at the pyrazolate-based Ru2 scaffold and the orientation of the catalyst’s active site with respect to the supporting surface.

Herein, we report on the homogeneous and heterogeneous H+/CO2-reduction forming syngas with a binuclear Re complex having a proton rely.

Two mononuclear ruthenium(II) complexes based on dianionic {N4} ligands and with axial pyridines have been prepared and characterized crystallographically (1) or by 2D NMR spectroscopy using residual dipolar couplings (2). The {N4} ligands provide a constrained equatorial coordination with one large N−Ru−N angle, and additional non‐coordinating N atoms in case of 2. Their redox properties have been investigated (spectro)electrochemically, and their potential to serve as water oxidation catalysts has been probed using cerium ammonium nitrate (CAN) at pH 1.0. Complex 1 undergoes rapid degradation, likely via ligand oxidation, whereas 2 is more rugged and exhibits 80 % efficiency in the CeIV‐driven water oxidation, with a high initial turnover frequency (TOFi) of 3.07×10−2 s−1 (at 100 equiv. CAN). The initial rate of O2 evolution exhibits 1st order dependence on catalyst concentration, suggesting a water nucleophilic attack mechanism. Repeated addition of CAN and control experiments show that high ionic strength conditions (both NO3− and CeIII) significantly decrease the TOF.

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