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CC BY 4.0 · SynOpen 2024; 08(03): 153-168
DOI: 10.1055/s-0040-1720126
graphical review

Exploring Porphyrins, Phthalocyanines and Corroles as Photocatalysts for Organic Transformations

Ashmita Jain
,
Iti Gupta∗
I.G. thanks the Council of Scientific & Industrial Research (CSIR), Government of India (Grant No. 01/3132/23/EMR-II) and the Indian Institute of Technology Gandhinagar (IIT Gandhinagar) for financial support. A.J. thanks IIT Gandhinagar for a fellowship.
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Abstract

In recent years, macrocycles have emerged as efficient and sustainable photosensitizers for the catalysis of organic transformations. This graphical review provides a concise overview of photocatalysis and photoredox catalysis utilizing three common macrocycles: porphyrins, phthalocyanines and corroles. They exhibit strong absorption in the visible region and can be easily oxidized or reduced, making them good candidates for photocatalysis.


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Key words

photocatalysis - photoredox catalysis - porphyrins - phthalocyanines - corroles

Biographical Sketches

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Ashmita Jain received her M.Sc. in chemistry from Jamia Millia Islamia, India. In 2021, she began her Ph.D. research at the Indian Institute of Technology Gandhinagar, India with Dr. Iti Gupta. Her research is focused on photocatalytic transformations of organic compounds utilizing macrocycles such as corroles and their metal complexes.

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Iti Gupta obtained her Ph.D. in chemistry from the Indian Institute of Technology Bombay, India. She received a JSPS Fellowship from Japan and undertook postdoctoral research at Kyushu University, where she worked on expanded porphyrins. Subsequently, she joined the Chemistry Faculty at BITS Pilani, K K Birla Goa Campus (2007–2009), before moving to the Indian Institute of Technology Gandhinagar in July 2009, where she is currently an associate professor. She is a member of the Society of Porphyrins & Phthalocyanines, and is also a life-member of the Chemical Research Society of India. Her current research interests are focused on the applications of porphyrins, corroles and metal dipyrrinato complexes in photocatalysis and the photodynamic therapy of cancer.

Photocatalysis offers the advantage of using light as an affordable, sustainable and green source of energy to carry out endergonic reactions.[1] It offers the advantage of milder conditions over those of thermal reactions.[2] As visible light is absorbed by sensitizers but not by most organic compounds, it offers an efficient approach to prevent product degradation and side reactions.[3] In photoredox catalysis, the photocatalyst in its excited state differs from that of the ground state by providing a higher electron affinity and a lower ionization potential, thereby making it a better electron donor as well as an acceptor. Versatile applications of photocatalysts are found in CO2 reduction, H2O splitting, proton-coupled electron transfer, photovoltaics and in the development of photo-electrochemical solar cells.[4]

The formation of carbon–carbon and carbon–heteroatom bonds has been a challenge in organic chemistry, which has been efficiently tackled by photocatalysis.[5] Traditionally, metal complexes (such as Ru and Ir polypyridyl complexes) and organic dyes (such as eosin Y) have been employed extensively as photocatalysts.[6] However, the high cost and toxic nature of metal complexes, as well as the pH-sensitive nature of organic dyes have prompted researchers to explore macrocycles such as porphyrins, phthalocyanines and corroles for photocatalysis.[7] These macrocycles have been examined for the catalysis of cyclopropanations, hydroxylations, aziridinations, epoxidations, sulfoxidations, etc.[8] [9] [10] Typically in photoredox catalysis, under light irradiation, these photocatalysts may undergo oxidation or reduction at different potentials and participate in SET (single-electron transfer) with the substrates. In photooxidation reactions, upon photoexcitation, such catalysts can switch from singlet to triplet excited states via ISC (intersystem crossing), and during this process, they can generate singlet oxygen via the type II pathway. Their ability to participate in SET depends on the reaction conditions, the nature of the substrate and also on the types of meso-substituents (electron-donating or electron-withdrawing) present on the catalyst, which in turn will govern their efficiency.

This graphical review provides an overview of organic transformations photocatalyzed by porphyrins, phthalocyanines and corroles, along with selected substrate scopes, that have been reported over the last five years (2019 to 2023). As photocatalysis by corroles is relatively less explored, all the examples described since 2005 are included. This graphical review describes photooxidations, epoxidations, sulfoxidations, aziridinations and cyanations of aliphatic and/or aromatic compounds by employing these macrocycles. In addition, C–H arylations of heteroarenes and thiocyanations utilizing porphyrins are discussed. Researchers have also explored hydroxylations, cycloadditions, perfluoroalkylations and phosphonylations by employing phthalocyanines as photocatalysts. Examples of brominations mediated by corroles are also provided. However, reactions involving inorganic transformations, polymerization, photodegradation and heterogenous catalysis are excluded.

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Figure 1 Photocatalytic oxidation of aldehydes by porphyrins[11] [12] [13] [14] [15] [16] [17]
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Figure 2 Photocatalytic epoxidation of styrenes, sulfoxidation of thioanisoles and C–H activation of alkenes by porphyrins[18] [19] [20] [21]
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Figure 3 Photocatalytic oxidation of anthracene, benzyl amine coupling, sulfoxidation of thioanisole and oxygenation of hexamethylbenzene by porphyrins[22] [23] [24] [25]
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Figure 4 Photoredox catalysis and C–H bond amination by porphyrins[26] [27]
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Figure 5 Photocatalytic thiocyanation of diketones and indoles and C–H arylation of heteroarenes by porphyrins[28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40]
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Figure 6 Photocatalytic oxygenation of a furanic compound, amination and aziridination of alkenes by porphyrins[41] [42]
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Figure 7 Photocatalytic hydroxylation of benzene, oxidation of benzylic alcohol and cross-dehydrogenative couplings by phthalocyanines[43] [44] [45] [46] [47]
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Figure 8 Photocatalytic oxidation of nitrophenol, cyanation of amines and cyclization to quinolones by phthalocyanines[48] [49] [50] [51] [52]
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Figure 9 Photocatalytic perfluoroalkylation of aromatics, sulfides and alkenes, cycloaddition and dehalogenation, and oxidation by phthalocyanines[53] [54] [55] [56]
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Figure 10 Photocatalytic chlorotrifluoromethylation of alkenes, oxidation of nitrophenol and phosphonylation of hydrazines by phthalocyanines[57] [58] [59] [60] [61] [62] [63] [64] [65] [66] [67]
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Figure 11 Photocatalytic oxygenation of thioanisole and alkenes, bromination of phenol and toluene, and oxidation of toluene, thioanisole and cyclohexene by corroles[8c] , [68] [69] [70] [71] [72] [73] [74] [75] [76] [77]
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Figure 12 Photocatalytic oxygenation of aromatics, benzylamine coupling and bromination of benzene, phenol and toluene by corroles[78] [79] [80] [81]

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Conflict of Interest

The authors declare no conflict of interest.

Acknowledgment

A.J. is grateful to the Indian Institute of Technology Gandhinagar for infrastructural support.


Corresponding Author

Iti Gupta
Indian Institute of Technology Gandhinagar, Palaj Campus
Gandhinagar, Gujarat-382355
India   

Publication History

Received: 27 March 2024

Accepted after revision: 26 June 2024

Article published online:
13 August 2024

© 2024. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by/4.0/)

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Figure 1 Photocatalytic oxidation of aldehydes by porphyrins[11] [12] [13] [14] [15] [16] [17]
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Figure 2 Photocatalytic epoxidation of styrenes, sulfoxidation of thioanisoles and C–H activation of alkenes by porphyrins[18] [19] [20] [21]
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Figure 3 Photocatalytic oxidation of anthracene, benzyl amine coupling, sulfoxidation of thioanisole and oxygenation of hexamethylbenzene by porphyrins[22] [23] [24] [25]
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Figure 4 Photoredox catalysis and C–H bond amination by porphyrins[26] [27]
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Figure 5 Photocatalytic thiocyanation of diketones and indoles and C–H arylation of heteroarenes by porphyrins[28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40]
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Figure 6 Photocatalytic oxygenation of a furanic compound, amination and aziridination of alkenes by porphyrins[41] [42]
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Figure 7 Photocatalytic hydroxylation of benzene, oxidation of benzylic alcohol and cross-dehydrogenative couplings by phthalocyanines[43] [44] [45] [46] [47]
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Figure 8 Photocatalytic oxidation of nitrophenol, cyanation of amines and cyclization to quinolones by phthalocyanines[48] [49] [50] [51] [52]
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Figure 9 Photocatalytic perfluoroalkylation of aromatics, sulfides and alkenes, cycloaddition and dehalogenation, and oxidation by phthalocyanines[53] [54] [55] [56]
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Figure 10 Photocatalytic chlorotrifluoromethylation of alkenes, oxidation of nitrophenol and phosphonylation of hydrazines by phthalocyanines[57] [58] [59] [60] [61] [62] [63] [64] [65] [66] [67]
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Figure 11 Photocatalytic oxygenation of thioanisole and alkenes, bromination of phenol and toluene, and oxidation of toluene, thioanisole and cyclohexene by corroles[8c] , [68] [69] [70] [71] [72] [73] [74] [75] [76] [77]
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Figure 12 Photocatalytic oxygenation of aromatics, benzylamine coupling and bromination of benzene, phenol and toluene by corroles[78] [79] [80] [81]