Generation of a stable supramolecular hydrogen evolving photocatalyst by alteration of the catalytic center

Abstract

A new dyad consisting of a Ru(II) chromophore, a tetrapyridophenazine bridging ligand and a Rh(Cp*)Cl catalytic center, [Ru(tbbpy)2(tpphz)Rh(Cp*)Cl]Cl(PF6)2, acts as durable photocatalyst for hydrogen production from water. Catalytic activity is observed for more than 650 hours. Electrochemical investigations reveal that up to two electrons can be transferred to the catalytic center by a thermodynamically favorable intramolecular process, which has so far not been reported for similar tpphz based supramolecular photocatalysts. Additionally, mercury poisoning tests indicate that the new dyad works as a homogeneous photocatalyst.

Synthesis and Characterization of a Ruthenium(II) Complex for the Development of Supramolecular Photocatalysts Containing Multidentate Coordination Spheres

“…Molecules exhibiting extended π‐conjugation tend to form dimers, a fact that might act detrimental to catalytic activity of the system . As such, tpphz‐based complexes have been reported to form dimers due to π–π stacking , , , . For this reason, the dimerization behaviour of 7 was studied by concentration‐dependent 1 H NMR spectroscopy on the basis of the change of the chemical shift of selected proton signals.…”

Unraveling the Light‐Activated Reaction Mechanism in a Catalytically Competent Key Intermediate of a Multifunctional Molecular Catalyst for Artificial Photosynthesis

“…Finally,t he intermediate was prepared in an electrochemical approach and characterized by UV/Vis,r R-SEC,T A-SEC, and quantum-chemical simulations.T he electrochemical characterization reveals that the first and second reduction in Ru(tpphz)RhCp* is located at the Rh ion:The irreversible reduction at À0.6 Vvs. [5] Ru-(tpphz)RhCp* exhibits similar absorption properties as the structurally related compounds Ru(tpphz)PdCl 2 and Ru-(tpphz)PtX 2 (X = Cl, I). [9] This process can be explained by two possible pathways:Either aone-electron reduction is followed by fast disproportion of the Rh II intermediate, [9b] or potential inversion of the redox potential of the Rh II /Rh I and Rh III /Rh II pairs allows for an ECE (electrochemical reaction, chemical reaction, electrochemical reaction) process at the applied potential.…”

“…[5] UV/Vis-SEC,r R-SEC,a nd electrochemical measurements were performed as described in detail in the Supporting Information. [5] UV/Vis-SEC,r R-SEC,a nd electrochemical measurements were performed as described in detail in the Supporting Information.…”

“…[9] This process can be explained by two possible pathways:Either aone-electron reduction is followed by fast disproportion of the Rh II intermediate, [9b] or potential inversion of the redox potential of the Rh II /Rh I and Rh III /Rh II pairs allows for an ECE (electrochemical reaction, chemical reaction, electrochemical reaction) process at the applied potential. [5,13] Theb and at 440 nm is due to metal-to-ligand charge-transfer (MLCT) transitions from the Ru II center to both the tpphz and the tbbpy ligands ( Figure 2B). [11] In analogy with previous studies,t he reduction at À0.9 Vi sa ssigned to the first reduction of the tpphz ligand ( Figure 2B).…”

Product Selectivity in Homogeneous Artificial Photosynthesis Using [(bpy)Rh(Cp*)X]n+-Based Catalysts

“…An example of these catalysts is depicted in Figure 13, where a photoredox active ruthenium polypyridine chromophore is linked to a [(NN)Rh(Cp*)Cl] catalyst via a tetrapyridophenazine bridging ligand [99]. The molecular catalyst exhibits suitable redox potentials for intramolecular electron transfers [113]. Figure 12 also shows that reduced nicotinamide cofactors are exposed to oxidative decomposition during a photocatalytic process since they are stronger reductants than the commonly used tertiary amines such as triethylamine or triethanolamine [114].…”