Strongly reducing Ir photoredox on aryl chlorides
Ir(ppy)2(NacNac) photocatalysts with BIH hydrodehalogenate unactivated aryl bromides, chlorides, fluorides, and alkyl bromides, including with green light.
Source
Photoredox catalysis on unactivated substrates with strongly reducing iridium photosensitizers
Study at a glance
- Design
- Animal / in-vitro — Ir(ppy)2(NacNac) photoredox hydrodehalogenation with BIH under blue or green LEDs
- N
- Substrate-scope reactions plus Stern–Volmer and quantum-yield measurements
- Population
- Unactivated aryl bromides, chlorides, fluorides, and alkyl bromides
- Outcome
- Strongly reducing iridium photosensitizers hydrodehalogenate unactivated substrates, including under green light
Structured fields used in claim comparison tables when every cited study has a complete layer.
Inspect source passages
Strongly reducing Ir photoredox on aryl chlorides
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
Excited-state potentials are −2.6 V and −2.4 V vs Fc+/Fc for Ir1 and Ir2
Their formal Ir IV /Ir III redox couples occur below the ferrocene couple, which in combination with their triplet excited-state energies ( E T1 ) leads to the prediction that Ir1 and Ir2 are much stronger excited-state reductants than fac -Ir(ppy) 3 and [Ir(ppy) 2 (dtbbpy)] + , with E (Ir IV /*Ir III ) = −2.6 V and −2.4 V for Ir1 and Ir2 , respectively.
Quantum yield is 4.7% for S2 to P2 and 1.4% for S7 to P7
The measured quantum yields are 4.7% for the conversion of S2 to P2 , and 1.4% for the conversion of S7 to P7 .
What they did
They used two β-diketiminate iridium complexes (Ir1, Ir2) plus 1,3-dimethyl-2-phenylbenzimidazoline (BIH) under blue or green LEDs. Scope included hydrodebromination, hydrodechlorination, alkyl bromides, radical cyclization, and ether C–O cleavage. Quantum yields and Stern–Volmer quenching rates were measured.
What they found
Excited-state potentials are −2.6 V (Ir1) and −2.4 V (Ir2) vs Fc+/Fc, ~300–500 mV more reducing than fac-Ir(ppy)3. With 1 mol% Ir and BIH, aryl bromides work in 24 h; aryl chlorides give quantitative yields with Ir1/blue light. Quantum yields are 4.7% (S2) and 1.4% (S7). Light/dark cycling shows catalysis needs light.
The limits
What it doesn't show
Quantum yields <100% do not fully exclude short radical chains. Many reactions were set up in a glovebox; ambient stability of stock solutions is limited. Isolated-yield tables for every substrate are not all in the main text.
Key terms
- Photoredox catalysis
- A photosensitizer absorbs visible light and does single-electron transfer to start an organic reaction.
- β-Diketiminate (NacNac)
- Anionic N,N-chelate that raises the Ir HOMO, making the excited complex a stronger reductant.
- BIH
- 1,3-Dimethyl-2-phenylbenzimidazoline, a sacrificial electron and hydrogen-atom donor (Eox = −0.07 V vs Fc).
- Hydrodehalogenation
- Replacement of C–X (Br, Cl, F) with C–H after reductive cleavage to a radical.
- Oxidative quenching
- Excited Ir* donates an electron to the substrate (or mediator), becoming Ir(IV) before BIH regenerates Ir(III).
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Quiz yourself
The excited-state reduction potential of Ir1 versus Fc+/Fc is
Common questions
Why are these Ir complexes stronger photoreductants?
NacNac destabilizes the HOMO so E(IrIV/*IrIII) reaches −2.6 / −2.4 V vs Fc, ~0.3–0.5 V beyond fac-Ir(ppy)3.
What sacrificial reagent replaced TMEDA?
BIH, allowing 1 mol% catalyst and 24 h instead of 2.5 mol% / 48 h.
Can they reduce aryl chlorides with visible light?
Yes—four substrates, quantitative with Ir1 and blue LEDs; Ir2/green is slightly lower.
Is a long radical chain operating?
Φ = 4.7% and 1.4% and dark periods stop conversion, so chains are not dominant.
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