Eu(II) cryptate photocatalyzes bibenzyl coupling
A visible-absorbing Eu(II) azacryptate, assembled in situ from EuCl3, ligand and Zn0, reductively couples benzyl chloride to 1,2-diphenylethane with an excited-state potential near −3 V.
Source
First use of a divalent lanthanide for visible-light-promoted photoredox catalysis
Study at a glance
- Design
- Animal / in-vitro — In situ Eu(II) azacryptate photoredox coupling of benzyl chloride under blue light
- N
- Stoichiometric and 0.5–5 mol% catalytic loadings with photophysical replicates
- Population
- Visible-light reductive coupling in methanol, including wet EuCl3·6H2O conditions
- Outcome
- Eu(II) photoredox gives bibenzyl in 60–85% yield with an excited-state potential near −3 V vs Ag/AgCl
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Inspect source passages
Eu(II) cryptate photocatalyzes bibenzyl coupling
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
Stoichiometric irradiation gave 85±2% 1,2-diphenylethane within 30 minutes.
We observed the formation of 1,2-diphenylethane (85 ± 2%) and toluene (4.7 ± 0.4%) within 30 minutes ().
At 5, 1, and 0.5% catalyst, bibenzyl yields were 71±5%, 70±5%, and 60±3%.
Yields of 1,2-diphenylethane of 71 ± 5% (∼14 turnovers), 70 ± 5% (∼70 turnovers), and 60 ± 3% (∼120 turnovers), respectively, were observed.
What they did
Authors encapsulated Eu(II) in octaazacryptand 1, measured absorption/emission, lifetime, quantum yield and electrochemistry, then ran blue-light couplings of benzyl chloride with sacrificial Zn0, including wet EuCl3·6H2O conditions.
What they found
Stoichiometric irradiation gave 85±2% bibenzyl in 30 min. Catalytic loadings of 5/1/0.5 mol% gave 71/70/60% bibenzyl (~14–120 turnovers). Excited-state E* ≈ −3.0 V vs Ag/AgCl; τ = 0.98 μs; Φ = 37% in MeOH. The system tolerates some water.
The limits
What it doesn't show
Scope on unactivated aryl bromides is proposed, not demonstrated; E1/2 was measured in DMF not methanol.
Key terms
- Eu(II) photoredox
- Visible 5d–4f excitation of divalent europium used to transfer electrons.
- Azacryptand 1
- Octaazacryptand that shifts Eu(II) absorption into the visible.
- Sacrificial Zn0
- Reductant that returns Eu(III) to Eu(II) for catalysis.
- Excited-state potential
- Estimated −3.0 V vs Ag/AgCl from E1/2 and emission energy.
- Bibenzyl
- 1,2-Diphenylethane, the C–C coupled product from PhCH2Cl.
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The C–C product from PhCH2Cl is:
Common questions
What C–C product is formed?
1,2-Diphenylethane from benzyl chloride.
What regenerates Eu(II)?
Zn0.
Approximate E*?
−3.0 V vs Ag/AgCl.
Can it start from Eu(III)?
Yes—in situ from EuCl3, 1 and Zn0.
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