Chemistry of Boryl Anions

Yamashita, Makoto

doi:10.1002/9781119448877.ch7

Cited by 6 publications

(7 citation statements)

References 74 publications

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“…Borylenes have attracted considerable interest as a result of their intriguing electronic structures and their unusual transition-metal-like reactivity . The pioneering works by the groups of Bertrand, Braunschweig, Bettinger, Kinjo, and Xie et al have revealed the interesting utility of borylenes in the activation and functionalization of small molecules. − Despite these advances, borylene-ligand cooperativity appears to be elusive to the best of our knowledge, probably as a consequence of the paucity of proper ligands.…”

Section: Introductionmentioning

confidence: 99%

Cooperative Bond Activation and Catalytic CO₂ Functionalization with a Geometrically Constrained Bis(silylene)-Stabilized Borylene

et al. 2023

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Metal−ligand cooperativity has emerged as an important strategy to tune the reactivity of transition-metal complexes for the catalysis and activation of small molecules. Studies of main-group compounds, however, are scarce. Here, we report the synthesis, structural characterization, and reactivity of a geometrically constrained bis(silylene)-stabilized borylene. The one-pot reaction of [(SiNSi)Li(OEt 2 )] (SiNSi = 4,5-bis(silylene)-2,7,9,9-tetramethyl-9H-acridin-10-ide) with 1 equiv of [BBr 3 (SMe 2 )] in toluene at room temperature followed by reduction with 2 equiv of potassium graphite (KC 8 ) leads to borylene [(SiNSi)B] (1), isolated as blue crystals in 45% yield. Xray crystallography shows that borylene (1) has a tricoordinate boron center with a distorted T-shaped geometry. Computational studies reveal that the HOMO of 1 represents the lone pair orbital on the boron center and is delocalized over the Si−B−Si unit, while the geometric perturbation significantly increases its energy. Borylene (1) shows single electron transfer reactivity toward tris(pentafluorophenyl)borane (B(C 6 F 5 ) 3 ), forming a frustrated radical pair [(SiNSi)B] •+ [B(C 6 F 5 ) 3 ] •− , which can be trapped by its reaction with PhSSPh, affording an ion pair [(SiNSi)BSPh][PhSB(C 6 F 5 ) 3 ] (3). Remarkably, the cooperation between borylene and silylene allows the facile cleavage of the N−H bond of aniline, the P−P bond in white phosphorus, and the C�O bond in ketones and carbon dioxide, thus representing a new type of main-group element-ligand cooperativity for the activation of small molecules. In addition, 1 is a strikingly effective catalyst for carbon dioxide reduction. Computational studies reveal that the cooperation between borylene and silylene plays a key role in the catalytic chemical bond activation process.

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Section: Introductionmentioning

confidence: 99%

Cooperative Bond Activation and Catalytic CO₂ Functionalization with a Geometrically Constrained Bis(silylene)-Stabilized Borylene

et al. 2023

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“…As boracycles are reduced, the electron-richness at the boron center increases, transforming inherently electrophilic molecules into powerful nucleophiles. ,,,,, Consequently, these types of molecules are often extremely reactive and difficult to isolate. However, isolable radicals and anions can be realized with appropriate ligand design strategies, whereby electronic and steric factors significantly influence the ground state electronic structure.…”

Section: Introductionmentioning

confidence: 99%

Redox- and Charge-State Dependent Trends in 5, 6, and 7-Membered Boron Heterocycles: A Neutral Ligand Coordination Chemistry Approach to Boracyclic Cations, Anions, and Radicals

Hollister,

Wentz,

Gilliard

2024

Acc. Chem. Res.

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Metrics & MoreArticle Recommendations CONSPECTUS: Boron heterocycles represent an important subset of heteroatom-incorporated rings, attracting attention from organic, inorganic, and materials chemists. The empty p z orbital at the boron center makes them stand out as quintessential Lewis acidic molecules, also serving as a means to modulate electronic structure and photophysical properties in a facile manner. As boracycles are ripe for extensive functionalization, they are used in catalysis, chemical biology, materials science, and continue to be explored as chemical synthons for conjugated materials and reagents.Neutral boron(III)-incorporated polycyclic molecules are some of the most studied types of boracycles, and understanding their redox transformations is important for applications relying on electron transfer and charge transport. While relevant redox species can often be electrochemically observed, it remains challenging to isolate and characterize boracycles where the boron center and/or polycyclic skeleton have been chemically reduced. We describe our recent work isolating 5-, 6-, and 7-membered boracyclic radicals, anions, and cations, focusing on stabilization strategies, ligand-mediated bonding situations, and reactivity. We present a versatile neutral ligand coordination chemistry approach that permits the transformation of boracycles from potent electrophiles to powerful nucleophilic heterocycles that facilitate diverse electron transfer and bond activation chemistry. Although there are a wide range of suitable stabilizing ligands, we have employed both diamino-N-heterocyclic carbenes (NHCs) and cyclic(alkyl)(amino) carbenes (CAACs), which led to boracycles with tunable electronic structures and aromaticity trends. We highlight successful isolation of borafluorene radicals and demonstrate their reversible redox behavior, undergoing oxidation to the cation or reduction to the anion. The borafluorene anion is a chemical synthon that has been used to prepare boryl main-group and transition-metal bonds, luminescent oxabora-spirocycles, borafluorenate-crown ethers, and CO-releasing molecules via carbon dioxide activation. We expanded to 6-membered boracycles and characterized neutral bis(NHC-supported 9-boraphenanthrene)s and the corresponding bis(CAAC-stabilized 9-boraphenanthrene) biradical. We detail the interconvertible multiredox states of boraphenalene, where the boraphenalenyl radical, anion, and cation mimic the charge-states of the all-hydrocarbon analogue. Reactivity studies of the boraphenalenyl anion displayed unusual nucleophilic reactivity at multiple sites on the periphery of the boraphenalenyl tricyclic scaffold. Reduced borepins, 7-membered boron containing heterocycles, have also been isolated. We used a stepwise one-pot synthesis combining the halo-borepin precursor, CAAC, and KC 8 to afford the monomeric borepin radicals and anions. The π-system was extended to contain two borepin rings fused in a pentacyclic scaffold, which permitted isolation of diborepin biradicals and a diborep...

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“…2 These anions have shown diverse reactivity in small molecule activation, been used as strong Sigma donor ligands in both transition metal and main group chemistry, and also allowed access to many new boron-containing compounds that would have been inaccessible through traditional routes via electrophilic boron. 3…”

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confidence: 99%

“…Boryl anions are formally boron( i ) compounds bearing a lone pair of electrons at boron 1–3 and can behave as boron-centred nucleophiles. To access this signature nucleophilic reactivity, the boryl anion lone pair must be minimally covalently stabilised by the cation, typically necessitating s-block cations.…”

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confidence: 99%

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Intramolecular C–N bond activation by a transient boryl anion

Nahon,

Nelmes,

Brothers

et al. 2023

Chem. Commun.

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Chemistry of Boryl Anions

Cited by 6 publications

References 74 publications

Cooperative Bond Activation and Catalytic CO₂ Functionalization with a Geometrically Constrained Bis(silylene)-Stabilized Borylene

Cooperative Bond Activation and Catalytic CO₂ Functionalization with a Geometrically Constrained Bis(silylene)-Stabilized Borylene

Redox- and Charge-State Dependent Trends in 5, 6, and 7-Membered Boron Heterocycles: A Neutral Ligand Coordination Chemistry Approach to Boracyclic Cations, Anions, and Radicals

Intramolecular C–N bond activation by a transient boryl anion

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Chemistry of Boryl Anions

Cited by 6 publications

References 74 publications

Cooperative Bond Activation and Catalytic CO2 Functionalization with a Geometrically Constrained Bis(silylene)-Stabilized Borylene

Cooperative Bond Activation and Catalytic CO2 Functionalization with a Geometrically Constrained Bis(silylene)-Stabilized Borylene

Redox- and Charge-State Dependent Trends in 5, 6, and 7-Membered Boron Heterocycles: A Neutral Ligand Coordination Chemistry Approach to Boracyclic Cations, Anions, and Radicals

Intramolecular C–N bond activation by a transient boryl anion

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Cooperative Bond Activation and Catalytic CO₂ Functionalization with a Geometrically Constrained Bis(silylene)-Stabilized Borylene

Cooperative Bond Activation and Catalytic CO₂ Functionalization with a Geometrically Constrained Bis(silylene)-Stabilized Borylene