Cross-coupling reactions: Semiheterogeneous PCN-Cu based metallaphotocatalysis

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Dual Cu/semiconductor photocatalyzed C–H arylation, chalcogenation and C–N cross-coupling reactions. Credit: Science China Press

Recently, photoredox catalysis has emerged as an appealing coupling partner for transition metal catalysis, termed metallaphotocatalysis, to develop new synthetic methodologies as well as improve the efficiency of established transformations. Conversely, most of these dual catalytic platforms have focused on the use of homogeneous photoredox catalysts such as Ru- and Ir-based polypyridyl complexes as well as organic dyes. These compounds’ applications are restricted by their high cost and poor stability, recovery, and reusability.

Aryl-heterocycles are ubiquitous structural motifs in many bioactive natural products and pharmaceuticals. Developing effective and sustainable strategies to produce these high-value compounds is a long-standing goal in synthetic chemistry. The most straightforward approach is the direct C–H functionalization of heterocycles. Do and Daugulis reported copper catalyzed C–H arylation of heterocycle C–H bonds with aryl iodides. However, harsh conditions and high temperatures severely limit their practical application. Ackerman’s group discovered that the arylation reaction could be performed via photoinduced copper catalysis under UV light in the absence of a photocatalyst, where an extra ligand and excess amount of aryl iodides were generally required.

Recently, a research team led by Prof. Chenliang Su’ group from Shenzhen University has successfully developed a semi-heterogeneous photo-Cu-dual-catalytic system for multi-types cross-coupling reactions. This unique catalytic system could enable mild C–H arylation under visible light irradiation with a broad substrate scope. Good to excellent yields were obtained with appreciable site selectivity and functional group tolerance. Notably, this mild process enabled to produce alkaloid natural products, such as balsoxin and texamine in a single step. Impressively, this dual catalytic system could also enable C–S and C–Se forming cross-couplings (chalcogenation) and C–N cross-coupling reactions of aromatic N-heterocycles effectively, demonstrating the versatility of the dual catalytic system. Competitive yields were obtained compared to previously reported photoinduced copper catalysis under UV light. This environment-friendly and cost-effective polymeric semiconductor shows better photocatalytic reactivity than many expensive and unrecyclable homogeneous transition metal complexes. Further, the PCN photocatalyst could remain its reactivity even after six-run experiments. The superior reusability of PCN photocatalyst and its easy scalability further highlight the practical potential of this method.

The research was published in Science Bulletin.


Visible-light-driven arylcarboxylation of styrenes with carbon dioxide and aryl halides


More information:
Zhaofei Zhang et al, Semi-heterogeneous photo-Cu-dual-catalytic cross-coupling reactions using polymeric carbon nitrides, Science Bulletin (2021). DOI: 10.1016/j.scib.2021.08.001

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Science China Press


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Cross-coupling reactions: Semiheterogeneous PCN-Cu based metallaphotocatalysis (2021, October 19)
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