A fundamental aim in the field of catalysis is the development of new modes of small molecule activation. One approach toward the catalytic activation of organic molecules that has received much attention recently is visible light photoredox catalysis. In a general sense, this approach relies on the ability of metal complexes and organic dyes to engage in single-electron-transfer (SET) processes with organic substrates upon photoexcitation with visible light.

Many of the most commonly employed visible light photocatalysts are polypyridyl complexes of ruthenium and iridium, and are typified by the complex tris(2,2′-bipyridine) ruthenium(II), or Ru(bpy)32+ (Figure 1). These complexes absorb light in the visible region of the electromagnetic spectrum to give stable, long-lived photoexcited states.1,2 The lifetime of the excited species is sufficiently long (1100 ns for Ru(bpy)32+) that it may engage in bimolecular electron-transfer reactions in competition with deactivation pathways.3 Although these species are poor single-electron oxidants and reductants in the ground state, excitation of an electron affords excited states that are very potent single-electron-transfer reagents. Importantly, the conversion of these bench stable, benign catalysts to redox-active species upon irradiation with simple household lightbulbs represents a remarkably chemoselective trigger to induce unique and valuable catalytic processes.






Open in a separate window


Figure 1


Ruthenium polypyridyl complexes: versatile visible light photocatalysts.

/pdf/visible-light-photoredox-catalysis-with-transition-metal-5d1oxrsczo.pdf

Visible Light Photoredox Catalysis with Transition Metal Complexes: Applications in Organic Synthesis

The use of visible light sensitization as a means to initiate organic reactions is attractive due to the lack of visible light absorbance by organic compounds, reducing side reactions often associated with photochemical reactions conducted with high energy UV light. This tutorial review provides a historical overview of visible light photoredox catalysis in organic synthesis along with recent examples which underscore its vast potential to initiate organic transformations.

Visible light photoredox catalysis: applications in organic synthesis

In the last few years, visible-light initiated organic transformations have attracted increasing attention. The development of visible-light-promoted photocatalytic reactions, which enable rapid and efficient synthesis of fine chemicals, is highly desirable from the viewpoint of cost, safety, availability, and environmental friendliness. In this Minireview, recent advances made in this fast developing area of research are discussed.

Visible-light photoredox catalysis.

Visible-light photocatalysis has evolved over the last decade into a widely used method in organic synthesis. Photocatalytic variants have been reported for many important transformations, such as cross-coupling reactions, α-amino functionalizations, cycloadditions, ATRA reactions, or fluorinations. To help chemists select photocatalytic methods for their synthesis, we compare in this Review classical and photocatalytic procedures for selected classes of reactions and highlight their advantages and limitations. In many cases, the photocatalytic reactions proceed under milder reaction conditions, typically at room temperature, and stoichiometric reagents are replaced by simple oxidants or reductants, such as air, oxygen, or amines. Does visible-light photocatalysis make a difference in organic synthesis? The prospect of shuttling electrons back and forth to substrates and intermediates or to selectively transfer energy through a visible-light-absorbing photocatalyst holds the promise to improve current procedures in radical chemistry and to open up new avenues by accessing reactive species hitherto unknown, especially by merging photocatalysis with organo- or metal catalysis.

Visible-Light Photocatalysis: Does It Make a Difference in Organic Synthesis?

Isolation and synthesis of biologically active carbazole alkaloids

Reagents, containing a P-H bond, such as dimethyl phosphite, diethyl phosphite, hypophosphorous acid and various salts of hypophosphorous acid are effective radical reducing agents for organic amides, thionoesters, and isocyanides affording high yields of the corresponding hydrocarbons. Reduction of tertiary phenyl selenides and tertiary nitro compounds are not efficient under these conditions. Oleamination of 1,2-diols is also accomplished via the corresponding thiocarbonyl derivatives using hypophosphorous acid and triethylamine in the presence of a suitable «sacrificial olefin» in moderate to good yields

The invention of radical reactions. Part 32. Radical deoxygenations, dehalogenations, and deaminations with dialkyl phosphites and hypophosphorous acid as hydrogen sources

Hypophosphorous acid and its salts: New reagents for radical chain deoxygenation, dehalogenation and deamination

Improved methods for the radical deoxygenation of secondary alcohols

An improved radical chain procedure for the deoxygenation of secondary and primary alcohols using diphenylsilane as hydrogen atom donor and triethylborane-air as initiator

Joseph Cs. Jaszberenyi

Papers

The invention of radical reactions. Part 32. Radical deoxygenations, dehalogenations, and deaminations with dialkyl phosphites and hypophosphorous acid as hydrogen sources

Hypophosphorous acid and its salts: New reagents for radical chain deoxygenation, dehalogenation and deamination

Improved methods for the radical deoxygenation of secondary alcohols

An improved radical chain procedure for the deoxygenation of secondary and primary alcohols using diphenylsilane as hydrogen atom donor and triethylborane-air as initiator

On the mechanism of deoxygenation of secondary alcohols by tin hydride reduction of methyl xanthates and other thiocarbonyl derivatives