Aryl Insertion vs Aryl–Aryl Coupling in C,C-Chelated Organoborates: The “Missing Link” of Tetraarylborate Photochemistry

Radtke, Julian; Mellerup, Soren K.; Bolte, Michael; Lerner, Hans‐Wolfram; Wang, Suning

doi:10.1021/acs.orglett.8b01534

Cited by 32 publications

(36 citation statements)

References 40 publications

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“…With irradiation, the characteristic vinyl species 2S‐a + 2S‐a′ ( 2R‐a + 2R‐a′ ) were observed, which is similar to those identified previously for the non‐chiral B(bza)Mes 2 and B(2‐Ph‐azo)Mes 2 (azo=azolyl) analogues . Although the dark‐colored isomers 2S + 2S′ ( 2R + 2R′ ) were not observed in the NMR spectra owing to their known low thermal stability and rapid conversion to 2S‐a + 2S‐a′ ( 2R‐a + 2R‐a′ ) at ambient temperature, based on the previously established mechanism for photoisomerization of B(bza)Mes 2 , it is the initial photoisomerization product involving a C−C bond formation between Mes 1 and the phenyl ring, following a classic di‐π‐methane rearrangement mechanism . Thus, the photoconversion of 1S / 1S′ is proposed to follow the sequence shown in Figure .…”

Section: Resultssupporting

confidence: 82%

Structural Dynamics and Stereoselectivity of Chiral Benzylideneamine N,C‐Chelate Borane Photo–Thermal Isomerization

Novoseltseva

Wang

et al. 2020

Chemistry A European J

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New chiral N,C‐chelate organoboron compounds based on benzylideneamines (bza) with the general formula of B(bza‐R)Mes2 (R=H or Me; Mes=mesityl) are reported. A chiral substituent group R‐ or S‐CH(CH3)Ph (Ph=phenyl) was introduced to the imine center, which imposed a previously unobserved pseudo‐ or axial‐chirality on the BMes2, creating distinct diastereomers. NMR spectroscopic studies established that the diastereomers undergo slow exchange in solution at ambient temperature. The chiral N,C‐chelate B(bza‐R)Mes2 molecules undergo photoisomerization in the same manner as their non‐chiral analogues, generating chiral BN‐cyclooctatriene (BN‐COT) derivatives. Most significantly, by tracking the photoisomerization with circular dichroism (CD) and 1H NMR spectra along with time‐dependent density functional theory (TD‐DFT) computational studies, the photoisomerization was established to proceed in a highly stereoselective manner, that is, one diastereomer converts exclusively to the corresponding diastereomer product in the photoreaction.

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Section: Resultssupporting

confidence: 82%

Structural Dynamics and Stereoselectivity of Chiral Benzylideneamine N,C‐Chelate Borane Photo–Thermal Isomerization

Novoseltseva

Wang

et al. 2020

Chemistry A European J

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“…Finally, an easy access to 2-pyridine-substituted TAPPs prompted us to use them for the synthesis of N , C -chelated boron compounds ( Scheme 5 ). In the past decade, 2-phenylpyridine-derived four-coordinate organoboron chelates have been extensively studied, mostly by the group of Wang, and found to show interesting properties, including photochromic reactivity, 33 two-photon absorption, 34 strong emission, high photostability, 35 etc. Following the well-established protocol, we treated compound 25 with BuLi, and the resulting lithiated intermediate was reacted with dimesitylboron fluoride, which yielded compound 54 ( Scheme 5 ).…”

Section: Resultsmentioning

confidence: 99%

Method for the Large-Scale Synthesis of Multifunctional 1,4-Dihydro-pyrrolo[3,2-b]pyrroles

et al. 2020

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A thorough investigation has enabled the optimization of the synthesis of 1,4-dihydro-pyrrolo[3,2- b ]pyrroles. Although salts of such metals as vanadium, niobium, cerium, and manganese were found to facilitate the formation of 1,4-dihydro-pyrrolo[3,2- b ]pyrroles from amines, aldehydes, and diacetyl, we confirmed that iron salts are the most efficient catalysts. The conditions identified (first step: toluene/AcOH = 1:1, 1 h, 50 °C; second step: toluene/AcOH = 1:1, Fe(ClO 4 ) 3 ·H 2 O, 16 h, 50 °C) resulted in the formation of tetraarylpyrrolo[3,2- b ]pyrroles in a 6–69% yield. For the first time, very electron-rich substituents (4-Me 2 NC 6 H 4 , 3-(OH)C 6 H 4 , pyrrol-2-yl) originating from aldehydes and sterically hindered substituents (2-ClC 6 H 4 , 2-BrC 6 H 4 , 2-CNC 6 H 4 , 2-(CO 2 Me)C 6 H 4 , 2-(TMS-C≡C)C 6 H 4 ) present on anilines can be appended to the pyrrolo[3,2- b ]pyrrole core. It is now also possible to prepare 1,4-dihydropyrrolo[3,2- b ]pyrroles bearing an ordered arrangement of N -substituents and C -substituents ranging from coumarin, quinoline, phthalimide to truxene. These advances in scope enable independent regulations of many desired photophysical properties, including the Stokes shift value and emission color ranging from violet-blue through deep blue, green, yellow to red. Simultaneously, the optimized conditions have finally allowed the synthesis of these extremely promising heterocycles in amounts of more than 10 g per run without a concomitant decrease in yield or product contamination. Empowered with better functional group compatibility, novel derivatization strategies were developed.

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“…[51] This report sparked a heated debate about the true nature of the "solution reagent", [52] and continues to inspire research today. [53] Braunschweig's isolable tetraphenylborolyl-NHC complex K [14] (Scheme 8) has been acclaimed as a base-stabilized boryl anion and actually behaves like a π nucleophile toward MeI, affording an NHC-coordinated 1-methyl-2,3,4,5-tetraphenylborole. [54,55] With the 9H-9-borafluorene dianion [15] 2-, our group developed a related borole-anion system, which contains a "hydride ligand" in place of the NHC ligand (Scheme 8; cf.…”

Section: Eurjicmentioning

confidence: 99%

Anionic Organoboranes: Delicate Flowers Worth Caring for

2020

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Subvalent boron compounds contain boron atoms with oxidation numbers lower than +III. Over the last decades, the development of isolable derivatives has relied heavily on the use of specially designed ligands capable of stabilizing the electron‐rich boron centers electronically or through steric protection. Herein, we are exclusively reviewing anionic organo(hydro)boranes largely devoid of stabilizing ligands or heteroatom substituents. The restriction to these subvalent species is intended to minimize the risk of ligand artifacts being included when carving out the characteristic properties of the respective boron centers, such as nucleophilic or carbenoid behavior. The scope of this review encompasses triorganoborane radical monoanions ([·BR3]–) along with closed‐shell dianions ([:BR3]2–), boryl anions ([:BR2]–), as well as B–B single‐bonded diborane(6) dianions ([R3B–BR3]2–) and diborane(5) monoanions ([R2B–BR3]–), and finally B=B double‐bonded diborane(4) dianions ([R2B=BR2]2–). We are showing how these species are related to each other and comment on their bonding situations from an experimentalist's perspective.

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Aryl Insertion vs Aryl–Aryl Coupling in C,C-Chelated Organoborates: The “Missing Link” of Tetraarylborate Photochemistry

Cited by 32 publications

References 40 publications

Structural Dynamics and Stereoselectivity of Chiral Benzylideneamine N,C‐Chelate Borane Photo–Thermal Isomerization

Structural Dynamics and Stereoselectivity of Chiral Benzylideneamine N,C‐Chelate Borane Photo–Thermal Isomerization

Method for the Large-Scale Synthesis of Multifunctional 1,4-Dihydro-pyrrolo[3,2-b]pyrroles

Anionic Organoboranes: Delicate Flowers Worth Caring for

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