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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.
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What is claimed as a first in photoredox catalysis?
Catalytic C–C bond formation with a europium complex and visible light.
Source: First use of a divalent lanthanide for visible-light-promoted photoredox catalysis · DOI · quote verified
What ligand makes Eu(II) absorb visible light?
Azacryptand 1 (octaazabicyclo cryptand) encapsulating Eu(II).
Source: First use of a divalent lanthanide for visible-light-promoted photoredox catalysis · DOI · quote verified
What stoichiometric product distribution appears in 30 min of blue light?
85±2% 1,2-diphenylethane and 4.7±0.4% toluene.
Source: First use of a divalent lanthanide for visible-light-promoted photoredox catalysis · DOI · quote verified
What catalytic yields/TON were seen at 5, 1 and 0.5 mol%?
71±5% (~14 TON), 70±5% (~70), 60±3% (~120).
Source: First use of a divalent lanthanide for visible-light-promoted photoredox catalysis · DOI · quote verified
What sacrificial reductant closes the cycle?
Zn0, which reduces Eu(III) back to Eu(II) in situ.
Source: First use of a divalent lanthanide for visible-light-promoted photoredox catalysis · DOI · quote verified
Excited-state lifetime and quantum yield in methanol?
0.98±0.03 μs and 37%.
Source: First use of a divalent lanthanide for visible-light-promoted photoredox catalysis · DOI · quote verified
What ground-state E1/2 was measured?
A reversible Eu(II/III) couple at −0.90 V vs Ag/AgCl.
Source: First use of a divalent lanthanide for visible-light-promoted photoredox catalysis · DOI · quote verified
What excited-state potential was estimated?
−3.0 V vs Ag/AgCl from E1/2 and 580 nm emission.
Source: First use of a divalent lanthanide for visible-light-promoted photoredox catalysis · DOI · quote verified
Does the catalyst tolerate water?
Yes—10 mol% with EuCl3·6H2O in a wet glovebox gave 80±3% bibenzyl.
Source: First use of a divalent lanthanide for visible-light-promoted photoredox catalysis · DOI · quote verified
What light source drove the stoichiometric reaction?
Blue light (~7.6 W, λem = 460 nm).
Source: First use of a divalent lanthanide for visible-light-promoted photoredox catalysis · DOI · quote verified
What happens at 0.005% catalyst loading?
Only toluene is observed, not bibenzyl.
Source: First use of a divalent lanthanide for visible-light-promoted photoredox catalysis · DOI · quote verified