Photoredox catalyst

When suitable independent reactions for the reduction and oxidation of water are available, it still would not be simple to combine them to a cyclic process with Eq. (1) as net reaction. Accordingly, it is desired to perform reduction and oxidation by an interconvertible redox pair based on the same metal complex. This backgroimd motivated our recent study with osmocene (OsCp2, Cp =C5Hs ) as photoredox catalyst 12). 

Photocatalytic Polymers. The electrochemical experiments cited above were chosen from a vast body of recent polymer coated electrode work. Likewise the field of polymer supported photoredox catalysts is also broad and has a more extended history. Possibly a common linkage between electrochemical and photochemical catalyses, assisted by polymers, can be traced to oxidation of ascorbic acid (AH2). In 1966 Davidov (20a) found that light exposed, polyacrylonitrile (PAN) containing solutions of AH2 consumed oxygen in a measurably different manner than similar solutions without AH2. (Simple photoabsorption of 02 also occurs). 

N-Heterocyclic carbenes (NHCs) have been well known for their unique reactivity to cleave the acyl C—H bond of aldehydes. In 2012, DiRocco and Rovis reported elegant asymmetric a-acylation reactions of tertiary amines 17 with various aldehydes 16 by employing a combination of an NHC catalyst and photoredox catalyst. Since the Breslow intermediate or NHC itself is sensitive to oxidative conditions, a judicious choice of oxidant and photoredox catalyst is crucial. After careful evaluation of the reaction conditions, Ru(bpy)3Cl2 was proved to be the optimal photoredox catalyst and m-dinitrobenzene (m-DNB) as the co-oxidant under irradiation with blue light. The aminoinda-nol-derived NHC C2 (generated in situ from the corresponding triazolium salt using NaH) exhibited the best asymmetric induction. An array of the desired products 18 was obtained in up to 94% yield and 92% ee (Scheme 2.7). 

In 2011, Rueping and eo orkers realized asymmetric CDC reactions between THIQs and aeetone by utilizing a dual catal3 ic system eontaining photoredox catalyst Ru(bpy)3(PFg)2 and L-proline under the irradiation of 5 W fluorescent bulb. The interplay between the photoredox catalytie eyele and the effective addition of ketones to the photocatalytically generated iminium... 

A versatile, simple and inexpensive method has been recently proposed for the synthesis of sequence-controlled multiblock copolymers by one-pot polymerisation at ambient temperature. Aciylic block copolymerisation under UV irradiation 360 nm) was obtained in the absence of conventional photoredox catalysts and dye-sensitizers, by means of low concentrations of CuBra in synergy with MCe-Tren [MCe-Tren Tren = tris(2-aminoethyl)amine]. The potential of the method was demonstrated by alternating four different aciylate monomers in various combinations within the polymer composition. Quantitative conversion and narrow dispersity were achieved. " The procedure is versatile, as demonstrated by polymerisation of a number of (meth)aciylate monomers, including poly(ethylene glycol) methyl ether aciylate (PEGA480), te/t-butyl aciylate, methyl methaciylate, and styrene. Moreover, hydrojyl- and vic-diol-functional initiators are tolerated, forming a,co-heterofunctional poly(aciylates). Notably, temporal control is... 

Rueping reported a combined photoredox- and palladium-catalyzed system that allows for the synthesis of 3-acylindole 101 under mild conditions starting from aniline lOO.This procedure obviates the need for large amounts of an external oxidant mechanistic studies showed the oxidation was achieved by either (1) the photoredox catalyst (in the absence of oxygen) or (2) an in situ formed superoxide anion (in the presence of oxygen and pho-toredox catalyst). This allows for the synthesis of oxidant-sensitive substrates and an improved scope (14AG(I)13264). 

Ru(bpy)3] + as a photoredox catalyst providing an electron-deficient alkyl radical from the starting a-bromo carbonyl compound was used, along with an... 

Recently, Ferroud et al. [154] found another dye sensitizer. Rose Bengal, highly effective as a visible light photoredox catalyst in the direct enantioselective a-alkylation of aldehydes with stabilized dimethyl 2-bromomalonate (132) (Scheme 8.40). The reaction proceeded smoothly under visible light irradiation at room temperature and with short reaction times when co-catalyst (LiCl) was used, providing a-alkylated aldehydes in high yields (up to quantitative yield) with high enantioselectivity (up to 85% ee). 

The complex, Ir[(dF(CF3)ppy)2(dtbbpy)]PF6 acted as a good photoredox catalyst for atom transfer radical addition of haloalkanes to alkenes. ... 

Bianchini G, Scarso A, La Sorella G, Strukul G. Switching the adivity of a photoredox catalyst through reversible encapsulation and release. Chem Commun 2012 48 12082-4. 

In 2014, Chen and co-workers reported an alternative method based on the oxidative alkynylation of trifluoroboronate salts using a photoredox catalyst. 

Type of reaction C-N and N-S bond formation Reaction conditions N,iV-Dimethyl formamide, room temperature Synthetic strategy Visible-light-driven aerobic oxidative cyclization Catalyst Eosin Y (1) as a photoredox catalyst... 

Photoaddition. Ir(ppy)3 (ppy = 2-phenylpyridine) was used as a photoredox catalyst in the oxyatylation, aminoarylation, and o [Pg.68]

This topic is detailed in the chapter Visible-light-induced Redox Reactions by Ruthenium Photoredox Catalyst by Akita and Koike. 

Visible-Light-Induced Redox Reactions by Ruthenium Photoredox Catalyst... 

The redox potentials of the catalytic species can be modified by ligands and changing central metal. In particular, relevant cyclometalated Ir catalysts such as /ac-Ir(ppy)3 (ppy 2-phenylpyridine) have been often used as alternative photoredox catalysts. 

Before 2008, a limited number of works about photoredox catalysis by [Ru(bpy)3] had been reported in the field of synthetic organic chemistry [4—17]. After publication of the undermentioned seminal works during 2008-2010, however, a great number of reports on redox reactions by photoredox catalysis have appeared [18-29]. In this section, we will concisely review redox reactions by photoredox catalysts around 2008. 

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