A Di‐Substituted Boron Dication and Its Hydride‐Induced Transformation to an NHC‐Stabilized Borabenzene

Shen, Chao-Tang; Liu, Yi-Hung; Peng, Shie‐Ming; Chiu, Ching‐Wen

doi:10.1002/anie.201308385

Cited by 46 publications

(11 citation statements)

References 83 publications

(20 reference statements)

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“…With the aid of NHCs, Chiu et al were able to stabilize and structurally characterize the dicationic boron species 217 (Scheme ). It was synthesized upon stepwise treatment of [Cp*BCl 2 (IMes)] with AlCl 3 as chloride ion scavenger in chlorobenzene. Compound 217 (C NHC –B bond distance 1.558(4) Å) features a sharp signal at −49 ppm in the 11 B NMR spectra.…”

Section: Nhc Complexes Of Main Group Elementsmentioning

confidence: 99%

NHCs in Main Group Chemistry

et al. 2018

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Since the discovery of the first stable N-heterocyclic carbene (NHC) in the beginning of the 1990s, these divalent carbon species have become a common and available class of compounds, which have found numerous applications in academic and industrial research. Their important role as two-electron donor ligands, especially in transition metal chemistry and catalysis, is difficult to overestimate. In the past decade, there has been tremendous research attention given to the chemistry of low-coordinate main group element compounds. Significant progress has been achieved in stabilization and isolation of such species as Lewis acid/base adducts with highly tunable NHC ligands. This has allowed investigation of numerous novel types of compounds with unique electronic structures and opened new opportunities in the rational design of novel organic catalysts and materials. This Review gives a general overview of this research, basic synthetic approaches, key features of NHC-main group element adducts, and might be useful for the broad research community.

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Section: Nhc Complexes Of Main Group Elementsmentioning

confidence: 99%

NHCs in Main Group Chemistry

et al. 2018

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“…In addition, a terminal borylene complex containing an h 5 -Cp* ligand, namely [(h 5 -Cp*)BFe(CO) 4 ], 22 was described by Cowley. In addition, examples of dicationic [(h 5 -Cp*)B(L)] 2+ species have been reported. 23,24 For group 14 derivatives, the heavier elements form metallocenes(II) [(h 5 -Cp*) 2 E] (E = Si, 25 Ge, 26 Sn, 26 Pb 27 ) and half-naked E(II) cations of the form [(h 5 -Cp*)E] + (E = Si, 28 Ge, 26 Sn, 29 Pb 30 ) (Figure 1B). Interestingly, a carbon dication [C 6 (CH 3 ) 6 ] 2+ , recently reported by Malischewski and Seppelt, 31 could be described as an h 5 -Cp*-bonded carbon dication [(h 5 -Cp*)CCH 3 ] 2+ .…”

Section: Introductionmentioning

confidence: 99%

A Phosphorus Lewis Super Acid: η5-Pentamethylcyclopentadienyl Phosphorus Dication

Zhou

Liu

Cao

et al. 2018

Chem

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“…Thermolysis of boracyclohexadiene boronium ion affords the NHC-stabilized borabenzene . Our group has also demonstrated that structural rearrangement of a hypercoordinated boron dication ([Cp*B-IMes] 2+ , [ 1 ] 2+ ) to a planar neutral borabenzene ( 2 ) could be initiated through the addition of Li[Et 3 BH] (Scheme c) . Similar boron atom insertion to the Cp* ring has been observed only within the coordination sphere of transition metals .…”

Section: Introductionmentioning

confidence: 55%

Mechanistic Studies on the Rearrangement of a Boron Cation: From a nido-Carborane to a Planar Boracycle

et al. 2016

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The reaction mechanism of the [Et3BH]−-induced conversion of a dicationic boron compound ([Cp*B-IMes]2+, [1]2+) to a planar neutral carbene-coordinated borabenzene (2) is investigated experimentally and theoretically. Owing to the steric congestion around the boron center, bulky [Et3BH]− attacks the less encumbered carbon atom of Cp*, leading to a metastable 5-borabicyclo[2.1.1]hex-2-ene borenium cation ([3-CH]+) at low temperature. Upon raising the temperature, the bicyclic-borenium ion undergoes sequential pericyclic reactions, including suprafacial [1,3]-sigmatropic shift, two-electron electrocyclic ring opening, and then [1,2]-hydrogen shift to a planar cyclic borenium ion, [4-CH]+, which can then be deprotonated to yield the neutral aromatic borabenzene. The attack of hydride at the boron center of [1]2+ was excluded through the preparation and isolation of 6-borabicyclo[3.1.0]hexenylium, [3-BH]+, which could not be transformed into [3-CH]+ or [4-CH]+. The borenium ion rearrangement follows first-order kinetics with activation parameters of Δ H ⧧ = 19.6 (±0.31) kcal/mol and Δ S ⧧ = −2.03 (±1.15) cal/mol·K. The observed kinetic isotope effect of 0.87 at 265 K is consistent with the DFT-calculated reaction mechanism, which predicts an overall KIE value of 0.90. These results show that [1]2+ reacts with [Et3BH]− as a carbon-based electrophile and the formation of an electron-deficient borenium center is responsible for the skeletal rearrangement of the nido-cluster.

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A Di‐Substituted Boron Dication and Its Hydride‐Induced Transformation to an NHC‐Stabilized Borabenzene

Cited by 46 publications

References 83 publications

NHCs in Main Group Chemistry

NHCs in Main Group Chemistry

A Phosphorus Lewis Super Acid: η5-Pentamethylcyclopentadienyl Phosphorus Dication

Mechanistic Studies on the Rearrangement of a Boron Cation: From a nido-Carborane to a Planar Boracycle

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