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
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.
Flashcards
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Quiz yourself
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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