Slow photogenerated Rh–H prefers aldehydes

Proflavine plus a Cp*Rh mediator makes dilute Rh(III)–H that reduces aldehydes while ketones wait, unlike fast formate hydride transfer.

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What reductant is generated photochemically?

The same Rh(III)–H used in formate chemistry, but kept dilute so aldehydes outrun ketones.

What solvent and catalyst loading were chosen?

DMF/H2O 1:1 (v/v) with 10 mol% PF and 10 mol% Rh cat, 455 nm.

Does a flow reactor hurt selectivity?

No—it speeds the reaction 5× while selectivity is retained.

What are PFH+ photophysics?

Absorbs at 443 nm, Φfl = 0.39, λem = 508 nm; pKa(N-10) = 9.5; dimer KD = 500 M–1.

Who reduces 3PFH+*?

TEOA (E0 = +0.76 V vs SCE) vs 3PFH+* at +1.44 V vs SCE, giving PFH· then PF·–.

How is Rh(III)–H identified in the mixture?

612 nm shoulder matching authentic formate-generated hydride; air reoxidises it.

Can H2 itself reduce the carbonyls here?

No—H2 atmosphere without TEOA gives no alcohol; protonation of Rh–H is irreversible.

What is the product quantum yield?

Φ = (0.14 ± 0.05)% at 455 nm (Pabs = 9.3 mW).

What pump–probe peaks appear?

3PFH+* at 550/610/670 nm (~2 μs aerated); PF·– at ~530 nm (~8 μs with TEOA, ~3 μs with Rh).

Does oxygen kill all reactivity?

No—undegassed runs still give ~30% via an oxygen-tolerant photoionization path.

What happens after one-electron reduction of Rh(III)?

Unstable Rh(II) disproportionates (kdisp = 3.7×10^8 M–1 s–1) to Rh(I), which is protonated to Rh(III)–H.

What PF photoproducts form without Rh?

Leuco PF (340 nm, anaerobic, from PF·–) and diacridine (424 nm, oxygen-insensitive, from PF·+).