Redox-neutral synthesis of π-allylcobalt complexes from alkenes for aldehyde allylation <i>via</i> photoredox catalysis

Zhang, Dandan; Li, Haoyu; Guo, Zhuowen; Chen, Yuqing; Yan, Huaipu; Ye, Zenghui; Zhang, Fengzhi; Lu, Binghui; Hao, Er‐Jun; Shi, Lei

doi:10.1039/d2gc02990a

Cited by 8 publications

(7 citation statements)

References 53 publications

(65 reference statements)

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“…As we have already remarked in the Introduction, the better reducing properties of 2 were the key for the reaction, while 3DPAFIPN or 4CzIPN were not suitable. The cobalt salt, the photocatalyst, Hantzsch’s ester, and irradiation with visible light are all required for a successful reaction.…”

Section: Resultsmentioning

confidence: 99%

“…On the basis of the experiments performed, we can suggest the mechanistic picture depicted in Figure . In recent years, several authors have suggested that the reaction follows a Co(II)–Co(I)–Co(III)–Co(II) cycle. ,,, Co(II) is reduced by 2 in its excited state [E( 2 •+ /* 2 ) = −1.31 vs SCE] to Co(I) { E [Co(II)/Co(I)] = −1.05 V vs SCE} that is reacting with allyl acetate to form a Co(III) allyl intermediate. The Co(III) allyl is then further reduced by a SET event ( 2 or HE •+ ) to Co(II) allyl, the reactive organometallic species that can react with aldehydes by a Zimmerman–Traxler transition state…”

Section: Resultsmentioning

confidence: 99%

“…Because reduced compound 2 •– is a stronger reductant [ E ( 2 / 2 •– ) = −1.74 V vs SCE (vide infra)] compared to the parent species 1 •– [ E ( 1 / 1 •– ) = −1.53 V vs SCE (vide infra)], we examined the performance of 1 and 2 in the challenging allylation reaction of aldehydes mediated by cobalt with allyl acetate . We in fact report that the widely used and commercially available 4CzIPN was giving only traces of the desired homoallylic product . Herein, we report the full and detailed photophysical investigation of the new photocatalyst 2 and its application in the cobalt-mediated allylation reaction (Figure ).…”

Section: Introductionmentioning

confidence: 99%

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Light-Induced Access to Carbazole-1,3-dicarbonitrile: A Thermally Activated Delayed Fluorescent (TADF) Photocatalyst for Cobalt-Mediated Allylations

et al. 2022

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The stability of a photocatalyst under irradiation is important in photoredox applications. In this work, we investigated the stability of a thermally activated delayed fluorescence (TADF) photocatalyst {3DPAFIPN [2,4,-5-fluoroisophthalonitrile]}, recently employed in photoredox-mediated processes, discovering that in the absence of quenchers the chromophore is unstable and is efficiently converted by irradiation with visible light into another species based on the carbazole-1,3-dicarbonitrile moiety. The new species obtained is itself a TADF emitter and finds useful applications in photoredox transformations. At the excited state, it is a strong reductant and was efficiently applied to cobalt-mediated allylation of aldehydes, whereas other TADFs (4CzIPN and 3DPAFIPN) failed to promote efficient photocatalytic cycles.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Light-Induced Access to Carbazole-1,3-dicarbonitrile: A Thermally Activated Delayed Fluorescent (TADF) Photocatalyst for Cobalt-Mediated Allylations

et al. 2022

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“…In 2022/2023, the Shi group reported the formation of a reactive allylcobalt by photoredox catalysis under the framework of a radical-to-polar crossover (Scheme 24 ). 116 117…”

Section: Cobalt Nucleophilic Organometallic Reagentsmentioning

confidence: 99%

“…In 2022/2023, the Shi group reported the formation of a reactive allylcobalt by photoredox catalysis under the framework of a radical-to-polar crossover (Scheme 24). 116,117 They investigated the possibility of using the redox neutral system employed by the Glorius group 23 and Kanai, Mitsunuma, and co-workers 53 based on the formation of the allyl radical by oxidation of a C=C and deprotonation. Since the reduction potential of the cobalt complexes are lower compared to chromium, this limits the selection of suitable photoredox complexes for the reaction.…”

Section: Allylation Reactionsmentioning

confidence: 99%

Developing Organometallic Nucleophilic Reagents Via Photoredox Catalysis

et al. 2023

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The addition of organometallic reagents to the carbonyl group represents a key transformation, both in Academia and industry. Most of these transformations rely in a mechanism in which accessible and reactive halides are transformed into the corresponding nucleophilic organometallic reactive compounds through a redox mechanism, using a metal (Cr, Mg, In, etc.) in low oxidation state, by electron transfer. With the advent of photoredox catalysis, the formation of radicals, through oxidation or reduction of suitable and tailored organic precursors, was merged with transition metal catalysis. By radical to polar crossover (RRPCO), a radical metal is combined with an organic radical to produce, via radical-radical trapping, a polar nucleophilic organometallic reagent. Using dual photoredox catalysis (metallaphotoredox catalysis), a reactive organometallic reagent could be prepared, avoiding the use of metals in low oxidation state. Herein, in addition to the description of the results obtained by our group and others’ contributions at the connection between carbonyl addition and radical-based photochemistry, we provide a core guiding for further synthetic developments. We anticipate that extending the photoredox dual strategy beyond the Barbier’s reactions described here, taming less-activated carbonyls, studying other important electrophiles, will realize important breakthroughs soon.

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Photocatalytic Metal Hydride Hydrogen Atom Transfer Mediated Allene Functionalization by Cobalt and Titanium Dual Catalysis

et al. 2023

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Catalytic metal hydride hydrogen atom transfer (MHAT) reactions have proven to be a powerful method for alkene functionalization. This work reports the discovery of Co‐porphines as highly efficient MHAT catalysts with a loading of only 0.01 mol % for unprecedented chemoselective allene functionalization under photoirradiation. Moreover, the newly developed bimetallic strategy by the combination of photo Co‐MHAT and Ti catalysis enabled the successful carbonyl allylation with a wide range of amino, oxy, thio, aryl, and alkyl‐allenes providing expedient access to valuable β‐functionalized homoallylic alcohols in over 100 examples with exceptional regio‐ and diastereoselectivity. Mechanism studies and DFT calculations supported that selectively transferring hydrogen atoms from cobalt hydride to allenes and generating allyl radicals is the key step in the catalytic cycle.

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Redox-neutral synthesis of π-allylcobalt complexes from alkenes for aldehyde allylation via photoredox catalysis

Abstract: This work reports the first visible-light mediated cobalt-catalyzed aldehyde allylation with simple alkenes to produce homo-allylic alcohols. This novel strategy directly uses easily available unactivated alkenes as allyl sources instead of pre-synthesized allylic halides.

Cited by 8 publications

References 53 publications

Light-Induced Access to Carbazole-1,3-dicarbonitrile: A Thermally Activated Delayed Fluorescent (TADF) Photocatalyst for Cobalt-Mediated Allylations

Light-Induced Access to Carbazole-1,3-dicarbonitrile: A Thermally Activated Delayed Fluorescent (TADF) Photocatalyst for Cobalt-Mediated Allylations

Developing Organometallic Nucleophilic Reagents Via Photoredox Catalysis

Photocatalytic Metal Hydride Hydrogen Atom Transfer Mediated Allene Functionalization by Cobalt and Titanium Dual Catalysis

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