Titanocenes as Photoredox Catalysts Using Green‐Light Irradiation

Zhang, Zhenhua; Hilche, Tobias; Slak, Daniel; Rietdijk, Niels R.; Oloyede, Ugochinyere N.; Flowers, Robert A.; Gansäuer, Andreas

doi:10.1002/ange.202001508

Cited by 28 publications

(11 citation statements)

References 76 publications

(17 reference statements)

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“…64 65 Moreover, the successful combination of titanium with other transition-metal-catalyzed processes as well as with electrochemical or photoreductive reduction has led to entirely new directions in the field. 7,8,66 Continuing the exploration of low-valent titanium-catalyzed reactions, and even expanding research efforts further towards other early transition metals, will most certainly lead to the discovery of new reactivity and new strategies for organic synthesis.…”

Section: Discussionmentioning

confidence: 99%

“…5 6 More recently, photoreduction through a direct ligand-to-metal charge transfer of a titanocene and the use of a second photoredox catalyst to generate the titanium(III) species have been demonstrated. 7 8 Cp 2 TiCl can be used as a catalyst to generate ketyl-like radicals from carbonyls as well as homo-ketyl radicals from epoxides through homolytic C–O cleavage, for example. 9 10 This reactivity was established in the 1990s in the form of homo-pinacol couplings and homolytic epoxide-opening reactions.…”

Section: Introductionmentioning

confidence: 99%

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Reductive Umpolung and Defunctionalization Reactions through Higher-Order Titanium(III) Catalysis

Streuff¹

2022

Synlett

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The single-electron transfer from an in situ formed titanium(III) catalyst to ketones, imines, nitriles, Michael acceptors, and many other functions has enabled a large number of intra- and intermolecular reductive umpolung reactions. Likewise, it allows the homolytic cleavage of functional groups for selective defunctionalizations. These reactions often take place with the participation of two titanium(III) species, avoiding free-radical pathways and enabling high catalyst control of the reaction selectivity. This account discusses the development of the individual reactions together with the fundamental mechanistic discoveries that led to a better understanding of such titanium(III)-catalyzed processes in general.1 Introduction2 Active Titanium(III) Species and Additives3 Ketone-Nitrile Couplings4 Further Reductive Umpolung Reactions5 Catalytic Homolytic C–CN and C–SO2R Cleavage6 Conclusion

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Reductive Umpolung and Defunctionalization Reactions through Higher-Order Titanium(III) Catalysis

Streuff¹

2022

Synlett

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“…Very recently, Gansauer and Flowers reported the first example of titanocene as an effective photocatalyst for epoxide reduction and radical cyclization. 76 Upon irradiation of green light, the Cp 2 Ti(IV)Cl 2 catalyst undergoes LMCT, which results in an excited species with a sufficiently long solution lifetime to undergo reductive quenching with iPr 2 NEt ( Figure 18 C). The resultant Ti(III) catalyst ( 18 - 11 ) then reductively ring-opens an epoxide, with the nascent alkyl radical abstracting a hydrogen atom from a thiol cocatalyst to complete product formation.…”

Section: Photocatalysismentioning

confidence: 99%

New Redox Strategies in Organic Synthesis by Means of Electrochemistry and Photochemistry

et al. 2020

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As the breadth of radical chemistry grows, new means to promote and regulate single-electron redox activities play increasingly important roles in driving modern synthetic innovation. In this regard, photochemistry and electrochemistry—both considered as niche fields for decades—have seen an explosive renewal of interest in recent years and gradually have become a cornerstone of organic chemistry. In this Outlook article, we examine the current state-of-the-art in the areas of electrochemistry and photochemistry, as well as the nascent area of electrophotochemistry. These techniques employ external stimuli to activate organic molecules and imbue privileged control of reaction progress and selectivity that is challenging to traditional chemical methods. Thus, they provide alternative entries to known and new reactive intermediates and enable distinct synthetic strategies that were previously unimaginable. Of the many hallmarks, electro- and photochemistry are often classified as “green” technologies, promoting organic reactions under mild conditions without the necessity for potent and wasteful oxidants and reductants. This Outlook reviews the most recent growth of these fields with special emphasis on conceptual advances that have given rise to enhanced accessibility to the tools of the modern chemical trade.

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“…In the case of nickel, cobalt, and titanium, the catalytic cycle is feasible with the use of an organic reducing agent. In both cases, the allylation reaction is performed in the presence of a photocatalyst (iridium complex or an organic dye), although recently Gansäuer pointed out [16] that titanium complexes themselves can act as photocatalysts under precise conditions (green light irradiation). The described methodologies are certainly innovative and can be further expanded towards other C–C bond‐forming transformations.…”

Section: Entry[a] Deviation From Standard Conditions Conv [%][B] 3 Amentioning

confidence: 99%

Photoredox Allylation Reactions Mediated by Bismuth in Aqueous Conditions

et al. 2021

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Organometallic allylic reagents are widely used in the construction of C−C bonds by Barbier‐type reactions. In this communication, we have described a photoredox Barbier allylation of aldehydes mediated by bismuth, in absence of other metals as co‐reductants. Mild reaction conditions, tolerance of oxygen, and use of aqueous solvent make this photoredox methodology attractive for green and sustainable synthesis of homoallylic alcohols.

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Titanocenes as Photoredox Catalysts Using Green‐Light Irradiation

Cited by 28 publications

References 76 publications

Reductive Umpolung and Defunctionalization Reactions through Higher-Order Titanium(III) Catalysis

Reductive Umpolung and Defunctionalization Reactions through Higher-Order Titanium(III) Catalysis

New Redox Strategies in Organic Synthesis by Means of Electrochemistry and Photochemistry

Photoredox Allylation Reactions Mediated by Bismuth in Aqueous Conditions

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