A library of 50 copper-based complexes derived from bisphosphines and diamines was prepared and evaluated in three mechanistically distinct photocatalytic reactions. In all cases, a copper-based catalyst was identified to afford high yields, where new heteroleptic complexes derived from the bisphosphine BINAP displayed high efficiency across all reaction types. Importantly, the evaluation of the library of copper complexes revealed that even when photophysical data is available, it is not always possible to predict which catalyst structure will be efficient or inefficient in a given process, emphasizing the advantages for catalyst structures with high modularity and structural variability.
A bifunctional
copper-based photocatalyst has been prepared that
employs a pyrazole-pyridine ligand incorporating a sulfonamide moiety
that functions as an intramolecular hydrogen-bond donor for a photochemical
PCET process. In typical reductive PCET processes, the photocatalyst
and H-bond donor must have an appropriate redox potential and pK
a, respectively, to promote the PCET. When working
in concert in a bifunctional catalyst such as Cu(pypzs)(BINAP)BF4, the pK
a of the H-bond donor
can have an acidity that is orders of magnitude less and still efficiently
promote the PCET process. A reductive pinacol-type coupling can be
performed using a base-metal derived photocatalyst to afford valuable
diols (24 examples, 46–99% yield), from readily available aldehydes
and ketones.
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