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Review
. 2023 Apr 6;14(17):4449-4462.
doi: 10.1039/d3sc00388d. eCollection 2023 May 3.

Light-induced homolysis of copper(ii)-complexes - a perspective for photocatalysis

Alexander Reichle  1 , Oliver Reiser  1
Affiliations
Review

Light-induced homolysis of copper(ii)-complexes - a perspective for photocatalysis

Alexander Reichle et al. Chem Sci. .

Abstract

Over the past decade, photocatalysis has developed into a powerful strategy for the selective functionalization of molecules through radical intermediates. Besides the well-established iridium- or ruthenium-based photocatalysts, which ideally fulfill the requirements for a photocatalyst, such as long excited-state lifetimes and photostability, the shift towards earth-abundant metal-based photocatalysts has so far been less explored. The concept of light-induced homolysis (LIH) for generating radicals has recently gained significant interest as a new platform for inducing photoreactions with earth-abundant 3d-metal complexes despite only having excited-state lifetimes in the low nanosecond range or even below. Cu(ii)-complexes play a prominent role in exploiting this concept, which will be discussed by showcasing recent developments in organic synthesis with a view to identifying the future prospects of this growing field.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Fig. 1
Fig. 1. Abundance (atomic fraction) of the chemical elements in the Earth's upper continental crust as a function of atomic number. (Figure adapted from ref. , Creative Commons, public domain.)
Scheme 1
Scheme 1. Traditional photoredox activation and the concept of LIH.
Scheme 2
Scheme 2. The general concept of LIH of Cu(ii)-intermediates.
Scheme 3
Scheme 3. Pioneering work of Kochi in 1962: photolysis of cupric chloride (CuCl2).
Scheme 4
Scheme 4. Cu(ii)-complexes as catalyst precursors: LIH of defined complexes.
Scheme 5
Scheme 5. Vicinal dichlorination of activated and unactivated olefins.
Scheme 6
Scheme 6. Synthesis of α-keto-dichlorination of arylalkynes.
Scheme 7
Scheme 7. Regioselective chlorination of coumarins.
Scheme 8
Scheme 8. α-Chloroketonation of aromatic alkenes.
Scheme 9
Scheme 9. CuCl2-mediated activation of aliphatic feedstock chemicals.
Scheme 10
Scheme 10. Photocatalytic functionalization of amine derivatives.
Scheme 11
Scheme 11. Copper(ii)-photocatalyzed oxo-azidation of styrenes.
Scheme 12
Scheme 12. Enantioselective alkylation of imines.
Scheme 13
Scheme 13. Aerobic oxidative cleavage of cycloalkanones.
Scheme 14
Scheme 14. Cu(ii)-photocatalyzed oxo-alkylation of vinylarenes.
Scheme 15
Scheme 15. Cu(ii)-photocatalyzed oxidative cyclization reaction of aromatic amines.
Scheme 16
Scheme 16. Visible-light-accelerated copper-catalyzed [3 + 2] cycloaddition of N-tosylcyclopropylamines with alkynes/alkenes.
Scheme 17
Scheme 17. Decarboxylative oxygenation of carboxylic acids.
Scheme 18
Scheme 18. Decarboxylative borylation of (hetero)arylcarboxylic acids.
Scheme 19
Scheme 19. Decarboxylative halogenation of (hetero)arylcarboxylic acids.
Scheme 20
Scheme 20. Cu(ii)-photocatalyzed decarboxylative fluorination of benzoic acids.
Scheme 21
Scheme 21. Decarboxylative hydroxylation of benzoic acids.
Scheme 22
Scheme 22. Decarboxylative sulfoximination of benzoic acids.
Scheme 23
Scheme 23. C–H sulfoximination of arenes.
Scheme 24
Scheme 24. Decarboxylative cross-coupling reaction with different nucleophiles.
Scheme 25
Scheme 25. Heteroleptic complexes acting in the Cu(i)* → Cu(0) cycle.
Scheme 26
Scheme 26. Copper-catalyzed [3 + 2] cycloaddition involving a Cu(i)*/Cu(0) cycle.
Scheme 27
Scheme 27. Copper-promoted C(sp3)–H glycosylation involving a Cu(iii)*/Cu(ii) cycle.
Scheme 28
Scheme 28. Prospects: achieving a platform for possible synthetic transformations.
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