Ru dimer vs monomer splits CO from formate
Dilute, bright photolysis of Ru(bpy)(CO)2Cl2 gives CO; concentrated or dim light favours a Ru(I) dimer that makes formate.
Source
Unexpected effect of catalyst concentration on photochemical CO<sub>2</sub> reduction by <i>trans</i>(Cl)-Ru(bpy)(CO)<sub>2</sub>Cl<sub>2</sub>: new mechanistic insight into the CO/HCOO<sup>-</sup> selectivity
Study at a glance
- Design
- Other — Photochemical CO2 reduction with [Ru(bpy)3]2+/Ru carbonyl catalysts varying concentration and light
- N
- Molecular photocatalysis concentration-dependence study — no sample N
- Population
- DMA/water photoreduction mixtures with Ru catalysts and BNAH
- Outcome
- TON and CO/formate selectivity as a function of catalyst concentration
Structured fields used in claim comparison tables when every cited study has a complete layer.
What they did
Authors irradiated DMA/water (9:1) with [Ru(bpy)3]2+/BNAH, varied catalyst loading and light intensity, compared the isolated Cl-bridged dimer, and made a 6Mes-bpy analogue that cannot dimerise.
What they found
TON ~300 at 0.10 mM vs ~4000 at 5.0 μM. CO/HCOO– ~2 vs ~7 after 30 min. CO rate peaks at 20–30 μM then falls while formate keeps rising. Low light grows the 700–800 nm polymer and favours formate. The 6Mes complex gives CO only (formate = photosensitizer blank).
The limits
What it doesn't show
The dimer was not detected in situ by UV-vis or ESI-MS during catalysis; how the Ru(I) dimer makes formate remains computationally open; [Ru(bpy)3]2+ itself produces blank CO/formate.
Key terms
- trans(Cl)–Ru(bpy)(CO)2Cl2
- Monomeric Ru(II) catalyst whose one-electron reduced form can dimerise.
- Ru(I)–Ru(I) dimer
- Proposed resting species that reduces CO2 to formate when a second electron is scarce.
- BNAH
- 1-Benzyl-1,4-dihydronicotinamide sacrificial reductant that quenches *Ru(bpy)3 2+.
- 6Mes-bpy
- 6,6′-Dimesityl-2,2′-bipyridine ligand that sterically blocks Ru–Ru bond formation.
- DMA/water
- 9:1 N,N-dimethylacetamide/water solvent chosen to avoid DMF formate contamination.
Flashcards
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Quiz yourself
Formate-selective intermediate proposed:
Common questions
Why does more catalyst make more formate?
PS– is shared among more Ru; Ru+ dimerises instead of taking a second electron.
What does low light do?
Same as high [cat]: fewer PS–, more Ru–Ru, more HCOO–.
How was the dimer hypothesis tested?
Bulky 6Mes-bpy catalyst cannot polymerise and yields CO only.
Does the isolated dimer persist?
0.05 mM [Ru(bpy)(CO)2Cl]2 matches 0.10 mM monomer, implying cleavage during turnover.
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