Trifluoroethoxy-Coated Subphthalocyanine affects Trifluoromethylation of Alkenes and Alkynes even under Low-Energy Red-Light Irradiation

Photocatalytic Perfluoroalkylation of Disulfides and Diselenides. Syntheses of Perfluoroalkyl Thio- and Seleno-ethers

The synthesis of alkyl(aryl)-fluoroalkyl sulfanyl [R(Ar)-S-RF] and aryl-fluoroalkyl selenolyl (Ar-Se-RF) ethers through visible-light photocatalysis has been successfully carried out. This process involves disulfides, and diselenides [R(Ar)-X-X-R(Ar), where X = S or Se], and fluoroalkyl iodides (RF-I) in the presence of a base as an additive under photocatalysis. The photocatalyst Eosin Y and green light-emitting diodes are utilized for irradiation of R(Ar)-S-RF and Ar-Se-RF syntheses. Our method integrates low-energy visible-light photocatalysis, commercially available perfluoroalkylating reagents (RF-I), and easily obtainable disulfides and diselenides as starting materials. Mechanistic studies and a detailed synthetic procedure for (Ar)-S-RF on a large scale are presented.

Red-Light-Promoted Radical Cascade Reaction to Access Tetralins and Dialins Enabled by Zinc(II)porphyrin, A Light-Flexible Catalyst

[5,15-Bis(pentafluorophenyl)-10,20-diphenylporphinato]zinc(II) (1), a metalloporphyrin derivative that was recently reported as an efficient photocatalyst driven by blue LEDs by our group, was found to catalyze a red-light-promoted (630 nm LEDs) radical cascade reaction of N-3-arylpropionyloxyphthalimides with radicophiles including electron-deficient alkenes and alkynes, providing access to a range of functionalized tetralin and dialin derivatives. The radical cascade reaction catalyzed by 1 took place via an oxidative quenching cycle in DMSO, where no sacrificial electron donor was required, uncovering a unique solvent effect capable of promoting the porphyrin catalysis.

Red-light-mediated Barton decarboxylation reaction and one-pot wavelength-selective transformations

In organic chemistry, selecting mild conditions for transformations and saving energy are increasingly important for achieving sustainable development goals. Herein, we describe a red-light-mediated Barton decarboxylation using readily available red-light-emitting diodes as the energy source and zinc tetraphenylporphyrin as the catalyst, avoiding explosive or hazardous reagents or external heating. Mechanistic studies suggest that the reaction probably proceeds via Dexter energy transfer between the activated catalyst and the Barton ester. Furthermore, a one-pot wavelength-selective reaction within the visible light range is developed in combination with a blue-light-mediated photoredox reaction, demonstrating the compatibility of two photochemical transformations based on mechanistic differences. This one-pot process expands the limits of the decarboxylative Giese reaction beyond polarity matching.

Applications of red light photoredox catalysis in organic synthesis

Photoredox catalysis has emerged as an efficient and versatile approach for developing novel synthetic methodologies. Particularly, red light photocatalysis has attracted more attention due to its intrinsic advantages of low energy, few health risks, few side reactions, and high penetration depth through various media. Impressive progress has been made in this field. In this review, we outline the applications of different photoredox catalysts in a wide range of red light-mediated reactions including direct red light photoredox catalysis, red light photoredox catalysis through upconversion, and dual red light photoredox catalysis. Due to the similarities between near-infrared (NIR) and red light, an overview of NIR-induced reactions is also presented. Lastly, current evidence showing the advantages of red light and NIR photoredox catalysis is also described.

The forgotten reagent of photoredox catalysis

Visible light powers an ever-expanding suite of reactions to both make and break chemical bonds under otherwise mild conditions. As a reagent in photochemical synthesis, light is obviously critical for reactivity but rarely optimized other than in light/dark controls. This Frontier Article presents an overview of recent research that investigates the unique ways light may be manipulated, and its unusual interactions with homogeneous transition metal and organic photocatalysts.

Red Light-Based Dual Photoredox Strategy Resembling the Z-Scheme of Natural Photosynthesis

Photoredox catalysis typically relies on the use of single chromophores, whereas strategies, in which two different light absorbers are combined, are rare. In photosystems I and II of green plants, the two separate chromophores P₆₈₀ and P₇₀₀ both absorb light independently of one another, and then their excitation energy is combined in the so-called Z-scheme, to drive an overall reaction that is thermodynamically very demanding. Here, we adapt this concept to perform photoredox reactions on organic substrates with the combined energy input of two red photons instead of blue or UV light. Specifically, a Cu^I bis(α-diimine) complex in combination with in situ formed 9,10-dicyanoanthracenyl radical anion in the presence of excess diisopropylethylamine catalyzes ca. 50 dehalogenation and detosylation reactions. This dual photoredox approach seems useful because red light is less damaging and has a greater penetration depth than blue or UV radiation. UV-vis transient absorption spectroscopy reveals that the subtle change in solvent from acetonitrile to acetone induces a changeover in the reaction mechanism, involving either a dominant photoinduced electron transfer or a dominant triplet-triplet energy transfer pathway. Our study illustrates the mechanistic complexity in systems operating under multiphotonic excitation conditions, and it provides insights into how the competition between desirable and unwanted reaction steps can become more controllable.

Recent advances in subphthalocyanines and related subporphyrinoids

Subporphyrinoids constitute a class of extremely versatile and attractive compounds. Herein, a comprehensive review of the most recent advances in the fundamentals and applications of these cone-shaped aromatic macrocycles is presented.

Subphthalocyanine capsules: molecular reactors for photoredox transformations of fullerenes

The internal cavity formed by a dimeric subphthalocyanine (SubPc) capsule (SubPc₂Pd₃, 2), ensembled by coordination of pyridyl substituents in the monomeric SubPc 1 to Pd centers, has proved an optimal space for the complexation of C₆₀ fullerene. Taking advantage of the intense absorption of green light of the SubPc component at around 550 nm, we have tested different green-light induced photoredox addition reactions over the double bonds of guest C₆₀. Both addition of amine radicals, generated by reductive quenching of the excited state of 2 by aromatic trimethylsilylamines, and addition of trifluoroethyl radicals, obtained from oxidative quenching of the photosensitizer, have successfully taken place with good yields in the 2:C₆₀ host:guest complex. On the other hand, both the photoredox reactions result in much lower yields when the monomeric pyridyl-SubPc is used as a photocatalyst, demonstrating that encapsulation results in a strong acceleration of the reaction. Importantly, this is the first example of the use of a confined microenvironment to trigger photoredox chemical transformations of fullerenes.

A photoredox cage built by coordination of two pyridyl-subphthalocyanines to Pd centers has proved versatile and efficient to catalyze photoredox addition reactions over encapsulated C₆₀.

Red-light-activatable ruthenium phthalocyanine catalysts

Phthalocyanine ruthenium complexes were identified as red-light activatable catalysts for trifluoromethylation reactions. The red-light mediated chlorotrifluoromethylation of alkenes could proceed without any sacrificial reducing reagents. This reaction exhibited good compatibility with a blue-light-absorbing substrate, while under irradiation with blue light, i.e., under traditional photoreaction conditions, this substrate decomposed completely.

Photophysics of Perylene Diimide Dianions and Their Application in Photoredox Catalysis

The two‐electron reduced forms of perylene diimides (PDIs) are luminescent closed‐shell species whose photochemical properties seem underexplored. Our proof‐of‐concept study demonstrates that straightforward (single) excitation of PDI dianions with green photons provides an excited state that is similarly or more reducing than the much shorter‐lived excited states of PDI radical monoanions, which are typically accessible after biphotonic excitation with blue photons. Thermodynamically demanding photocatalytic reductive dehalogenations and reductive C−O bond cleavage reactions of lignin model compounds have been performed using sodium dithionite acts as a reductant, either in aqueous solution or in biphasic water–acetonitrile mixtures in the presence of a phase transfer reagent. Our work illustrates the concept of multi‐electron reduction of a photocatalyst by a sacrificial reagent prior to irradiation with low‐energy photons as a means of generating very reactive excited states.

Direct Near Infrared Light-Activatable Phthalocyanine Catalysts

The high penetration of near-infrared (NIR) light makes it effective for use in selective reactions under light-shielded conditions, such as in sealed reactors and deep tissues. Herein, we report the development of phthalocyanine catalysts directly activated by NIR light to transform small organic molecules. The desired photocatalytic properties were achieved in the phthalocyanines by introducing the appropriate peripheral substituents and central metal. These phthalocyanine photocatalysts promote cross-dehydrogenative-coupling (CDC) under irradiation with 810 nm NIR light. The choice of solvent is important, and a mixture of a reaction-accelerating (pyridine) and -decelerating (methanol) solvents was particularly effective. Moreover, we demonstrate photoreactions under visible-light-shielded conditions through the transmission of NIR light. A combined experimental and computational mechanistic analysis revealed that this NIR reaction does not involve a photoredox-type mechanism with electron transfer, but instead a singlet-oxygen-mediated mechanism with energy transfer.

The dark side of photocatalysis: near-infrared photoredox catalysis for organic synthesis

Near-Infrared photoredox catalysis is now consider as the next evolution of this field.

Deoxyfluorination of acyl fluorides to trifluoromethyl compounds by FLUOLEAD®/Olah's reagent under solvent-free conditions

A new protocol enabling the formation of trifluoromethyl compounds from acyl fluorides has been developed. The combination of FLUOLEAD® and Olah's reagent in solvent-free conditions at 70 °C initiated the significant deoxyfluorination of the acyl fluorides and resulted in the corresponding trifluoromethyl products with high yields (up to 99%). This strategy showed a great tolerance for various acyl fluorides containing aryloyl, (heteroaryl)oyl, or aliphatic acyl moieties, providing good to excellent yields of the trifluoromethyl products. Synthetic drug-like molecules were also transformed into the corresponding trifluoromethyl compounds under the same reaction conditions. A reaction mechanism is proposed.

Helical Carbenium Ion-Based Organic Photoredox Catalyst: A Versatile and Sustainable Option in Red-Light-Induced Reactions

The development of a sustainable catalytic system for red-light-induced photocatalysis is presented. The catalytic system consists of a helical carbenium ion-based organic photoredox catalyst (PC) that is capable of using low-energy red light (λmax = 640 nm) for both photooxidations and photoreductions. Its successful applications in the aerobic oxidative hydroxylation of arylboronic acids and in the oxidation of benzylic C(sp3)–H bonds (reductive quenching), as well as in dual transition-metal/organocatalyzed C–H arylations and intermolecular atom-transfer radical additions (oxidative quenching) provide further support for its role as a versatile and efficient organic PC.

1 Introduction

2 Red-Light-Induced Photocatalysis

3 Properties of N,N′-Dipropyl-1,13-dimethoxyquinacridinium Tetrafluoroborate

4 Two Proposed Representative Catalytic Cycles of [ n Pr-DMQA+][BF4 –]

5 Applications of [ n Pr-DMQA+][BF4 –] in Red-Light-Induced Photocatalysis

6 Conclusion

Modular synthesis of α-aryl β-perfluoroalkyl ketones via N-heterocyclic carbene catalysis

A new strategy of assembling alkene, aldehyde and perfluoroalkyl reagents under the catalysis of an N-heterocyclic carbene afforded valuable α-aryl β-perfluoroalkyl ketones.

The role of photocatalysts in radical chains in homolytic aromatic substitution, radical addition to olefins, and nucleophilic radical substitution mechanisms

Initiation, propagation and chain termination steps in oxidative and reductive quenching cycles for the photoinitiated perfluoroalkylation reaction of an olefin.

Radical fluoroalkylation reactions of (hetero)arenes and sulfides under red light photocatalysis

Fluoroalkylation reactions of (hetero)aromatics have been accomplished through the low-power illumination from red LEDs (λmax = 635 nm) of commercially available perfluoroalkyl iodides RF-I and phthalocyanine zinc salt as photocatalyst in MeCN : DMF solvent mixture. This methodology has been extended to the perfluorobutylation of sulfides. As far as we are concerned, this is the first report on a perfluoroalkylation reaction of (hetero)aromatics and sulfides under red-light photocatalysis.

Synthesis of fluoroalkylated alkynes via visible-light photocatalysis

Fluoroalkylated alkynes, which are versatile building blocks for the synthesis of various biologically active organofluorine compounds, were synthesized from easily available alkynyl halides and fluoroalkyl halides by visible-light photocatalysis.

Trifluoroethoxy-Coated Subphthalocyanines Attract Small Arenes in Their π-Concave Cavity

X-ray crystallographic analyses of a series of trifluoroethoxy-substituted subphthalocyanines disclosed that a molecule of toluene is clasped at the center of the molecular concave cavity. Twelve trifluoroethoxy substituents, which flexibly surround the toluene molecule to hold it on the 14 π-electron-conjugated surface of the subphthalocyanines, can also catch a molecule of benzene. In contrast, a nonsubstituted subphthalocyanine does not show the same phenomena, and two subphthalocyanine units are required to maintain a small aromatic compound in their concave cavity. DFT calculations of the complexes were conducted to better understand the arene clathrates. Trifluoroethoxy-substituted subphthalocyanines can be used to prepare arene clathrates as a result of their concave space. This is a unique approach to obtaining X-ray crystal structures of small noncrystalline aromatic compounds.

Light-mediated iodoperfluoroalkylation of alkenes/alkynes catalyzed by chloride ions: role of halogen bonding

A catalytic amount of chloride ions greatly facilitates the UVA-mediated iodoperfluoroalkylation of alkenes and alkynes.

Oximinotrifluoromethylation of unactivated alkenes under ambient conditions

An oximinotrifluoromethylation of unactivated alkenes was developed via trifluoromethyl radical-induced intramolecular remote oximino migration under mild reaction conditions.

Trifluoroethoxy-Coated Phthalocyanine Catalyzes Perfluoroalkylation of Alkenes under Visible-Light Irradiation

We disclose herein the perfluoroalkylation of alkenes catalyzed by trifluoroethoxy-coated zinc phthalocyanine under irradiation of visible light. Perfluoroalkyl iodides were nicely incorporated into unsaturated substrates, including alkyne, to provide perfluoroalkyl and iodide adducts in moderate to good yields. Trifluoromethylation is also possible by trifluoromethyl iodide under the same reaction conditions. The mechanistic study is discussed.

Trifluoroethoxy-Coated Subphthalocyanine affects Trifluoromethylation of Alkenes and Alkynes even under Low-Energy Red-Light Irradiation

Photoredox chemical reactions induced by visible light have undergone a renaissance in recent years. Polypyridyl dyes such as Ir(ppy)3 and Ru(bpy)3 are key catalysts in this event, and blue- or white-light irradiation is required for the chemical transformations. However, it remains a challenge to achieve reactions under the lower energy of red light. We disclose, herein, that trifluoroethoxy-coated subphthalocyanine realizes the red-light-driven trifluoromethylation of alkenes and alkynes with trifluoromethyl iodide in good-to-high yields. Perfluoroalkylations were also achieved under red light. The reaction mechanism is discussed with the support of UV/Vis spectroscopy and cyclic voltammetry of trifluoroethoxy-coated subphthalocyanine. Light irradiation/dark study also supports the proposed mechanism.