Visible light photocatalysis as a greener approach to photochemical synthesis

Abstract

Light can be considered an ideal reagent for environmentally friendly, 'green' chemical synthesis; unlike many conventional reagents, light is non-toxic, generates no waste, and can be obtained from renewable sources. Nevertheless, the need for high-energy ultraviolet radiation in most organic photochemical processes has limited both the practicality and environmental benefits of photochemical synthesis on industrially relevant scales. This perspective describes recent approaches to the use of metal polypyridyl photocatalysts in synthetic organic transformations. Given the remarkable photophysical properties of these complexes, these new transformations, which use Ru(bpy)(3)(2+) and related photocatalysts, can be conducted using almost any source of visible light, including both store-bought fluorescent light bulbs and ambient sunlight. Transition metal photocatalysis thus represents a promising strategy towards the development of practical, scalable industrial processes with great environmental benefits.

Anthraquinones as Photoredox Catalysts for the Reductive Activation of Aryl Halides

“…[1][2][3][4][5][6][7][8][9] Ru-and Ir-based coordination complexes have received enormous attention because of their excellent visible-light-harvesting properties, modest to extremely high oxidation and reduction potentials, relatively long excited-state lifetimes, and reasonably good chemical and photostabilities under synthetic oxidative and reductive conditions. [2] In addition, considerable efforts have been made to develop metal-free photoredox catalytic methods with organic dyes [8,[10][11][12][13][14] such as eosin Y [10,11] or rhodamine derivatives [13,14] and organic heterogeneous photocatalysts [15] for synthetic transformations.…”

Visible Light Promoted Allylic C–H Oxidation

“…Moreover, the reaction was quenched with 2,2,6,6-tetramethylpiperidyl-1-oxyl (TEMPO) (1.0 mmol) in standard state showing that there may be radical intermediates involved in reaction (Table 2, entry 15). Furthermore, the reaction did not quench in the presence of DABCO (1.0 mmol) ( Table 2, entry 19), which indicates the involvement of triplet oxygen in the reaction. Since, DABCO is a good quencher of singlet oxygen and quenching was not observed, it suggests that singlet oxygen was not involved in the reaction.…”

“…[12,13] The visible light photoredox catalysis has recently received much attention in organic synthesis owing to readily availability, sustainability, non-toxicity and ease of handling of visible light. [14][15][16][17][18][19] Recently, a superior alternative to transition metal photoredox catalysts, especially metal-free organic dyes such as eosin Y, fluorescein, rose bengal, nile red, perylene and rhodamine B have been used as economically and ecologically superior surrogates for Ru(II) and Ir(II) complexes in visible-light promoted organic transformations involving SET [20][21][22][23] (single electron transfer). These organic dyes have got much more attention with the last few years also due to easy handling, eco-friendly and have great potential for applications in visible-light-mediated organic synthesis [24][25][26][27] which fulfils the basic principle of green chemistry.…”

A Non‐Heme Iron Photocatalyst for Light‐Driven Aerobic Oxidation of Methanol

“…Photoredox catalysis has emerged as a versatile method to access highly reactive species in a selective and clean manner 1, 2. The redox‐active photosensitizers available include organic dyes,3 inorganic clusters,4 and transition‐metal complexes, such as [Ru(bpy) 3 ] 2+ and its derivatives,5, 6 whose redox potentials can be fine‐tuned by ligand modification 7, 8, 9.…”