Ru dimer vs monomer splits CO from formate

What unexpected variable changes CO vs formate?

Catalyst concentration of trans(Cl)–Ru(bpy)(CO)2Cl2.

Source: Unexpected effect of catalyst concentration on photochemical CO₂ reduction by <i>trans</i>(Cl)-Ru(bpy)(CO)₂Cl₂: new mechanistic insight into the CO/HCOO^- selectivity · DOI · quote verified

What intermediate is proposed for formate?

A Ru(I)–Ru(I) dimer that forms when a second electron is scarce.

Source: Unexpected effect of catalyst concentration on photochemical CO₂ reduction by <i>trans</i>(Cl)-Ru(bpy)(CO)₂Cl₂: new mechanistic insight into the CO/HCOO^- selectivity · DOI · quote verified

What are typical photocatalytic conditions?

DMA/water 9:1, [Ru(bpy)3]2+ 0.50 mM, BNAH 0.10 M, λ > 400 nm.

Source: Unexpected effect of catalyst concentration on photochemical CO₂ reduction by <i>trans</i>(Cl)-Ru(bpy)(CO)₂Cl₂: new mechanistic insight into the CO/HCOO^- selectivity · DOI · quote verified

How do TONs compare at 0.10 mM vs 5.0 μM?

ca. 300 after 4 h vs ca. 4000 at the dilute loading.

Source: Unexpected effect of catalyst concentration on photochemical CO₂ reduction by <i>trans</i>(Cl)-Ru(bpy)(CO)₂Cl₂: new mechanistic insight into the CO/HCOO^- selectivity · DOI · quote verified

How does the initial CO/HCOO– ratio change with dilution?

About 2 at 0.1 mM vs ca. 7 at 5.0 μM after 30 min.

Source: Unexpected effect of catalyst concentration on photochemical CO₂ reduction by <i>trans</i>(Cl)-Ru(bpy)(CO)₂Cl₂: new mechanistic insight into the CO/HCOO^- selectivity · DOI · quote verified

Where does the CO formation rate peak?

It rises up to 20–30 μM catalyst then falls, while formate keeps increasing.

Source: Unexpected effect of catalyst concentration on photochemical CO₂ reduction by <i>trans</i>(Cl)-Ru(bpy)(CO)₂Cl₂: new mechanistic insight into the CO/HCOO^- selectivity · DOI · quote verified

What UV-vis signature marks the polymer?

Broad 700–800 nm band of [Ru(bpy)(CO)2]n under Ar or low light.

Source: Unexpected effect of catalyst concentration on photochemical CO₂ reduction by <i>trans</i>(Cl)-Ru(bpy)(CO)₂Cl₂: new mechanistic insight into the CO/HCOO^- selectivity · DOI · quote verified

How does light intensity change selectivity?

Lower intensity favours HCOO– because Ru–Ru bonds form more readily.

Source: Unexpected effect of catalyst concentration on photochemical CO₂ reduction by <i>trans</i>(Cl)-Ru(bpy)(CO)₂Cl₂: new mechanistic insight into the CO/HCOO^- selectivity · DOI · quote verified

What does the 6Mes-bpy catalyst prove?

Bulky 6,6′-mesityls block dimerisation and the reaction yields CO selectively.

Source: Unexpected effect of catalyst concentration on photochemical CO₂ reduction by <i>trans</i>(Cl)-Ru(bpy)(CO)₂Cl₂: new mechanistic insight into the CO/HCOO^- selectivity · DOI · quote verified

Does the isolated Cl-bridged dimer stay intact?

0.05 mM dimer matches 0.10 mM monomer time courses, implying Ru–Ru cleavage during turnover.

Source: Unexpected effect of catalyst concentration on photochemical CO₂ reduction by <i>trans</i>(Cl)-Ru(bpy)(CO)₂Cl₂: new mechanistic insight into the CO/HCOO^- selectivity · DOI · quote verified

What reduction potentials allow electron transfer?

Catalyst –1.51 V vs Ag/Ag+; [Ru(bpy)3]2+/+ –1.68 V in DMA/water 9:1.

Source: Unexpected effect of catalyst concentration on photochemical CO₂ reduction by <i>trans</i>(Cl)-Ru(bpy)(CO)₂Cl₂: new mechanistic insight into the CO/HCOO^- selectivity · DOI · quote verified

Where does residual formate come from with 6Mes-bpy?

Independent of [catalyst]; it is the [Ru(bpy)3]2+ blank.

Source: Unexpected effect of catalyst concentration on photochemical CO₂ reduction by <i>trans</i>(Cl)-Ru(bpy)(CO)₂Cl₂: new mechanistic insight into the CO/HCOO^- selectivity · DOI · quote verified