C4B2H6 Isomers: Destabilization of the nido‐Carbaborane Structure by Amino Substituents and a Novel Classical Isomer

Herberich, Gerhard E.; Ohst, Holger; Mayer, H.

doi:10.1002/anie.198409691

Cited by 47 publications

(8 citation statements)

References 12 publications

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“…38 Organoboration of tetrakis(alkynyl)stannanes leads to the spiro-cyclic compound 9 in high yield. The reactions of 9 with MeBBr 2 , i-PrBBr 2 , and PhBCl 2 in dichloromethane between −78 and B-C-B compounds 15 and 16 39 could be synthesized from compound 14, and 18 40 from compound 17 (Scheme 5). Formation of a 2,5-diborabicyclo[2.1.1]-hexane 20 and its conversion product tetracarbahexaborane (19), which also have a B-C-B structure, have been reported by Enders et al 40 Synthesis of carbaboron compounds has also been reviewed recently.…”

Section: Formation Of B-c-b Compoundsmentioning

confidence: 99%

Recent developments in bisdiborane chemistry: BCB, BCCB, BCCB and BCCB compounds

Dembitsky

Ali

Srebnik

2003

Applied Organom Chemis

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An overview of the development of new strategies in organic synthesis with a minimum of chemical steps is becoming increasingly necessary for the efficient assembly of complex molecular structures. Therefore, the combination of multiple reactions in a single operation represents a particularly efficient approach. Among these strategies, the synthesis and reactivity of bisdiboranes has never been reviewed although its popularity for the synthesis of complex architectural molecules has been steadily increasing during the last decade. This review is intended to highlight the use of partly geminated boranes (B-C-B), and also bisdiborane reagents (B-C-C-B, B-C C-B, B-C C-B).

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Section: Formation Of B-c-b Compoundsmentioning

confidence: 99%

Recent developments in bisdiborane chemistry: BCB, BCCB, BCCB and BCCB compounds

Dembitsky

Ali

Srebnik

2003

Applied Organom Chemis

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“…Owing to the incomplete valence octet electron configuration of tricoordinate boron centers, neutral boranes can be utilized as optoelectronic materials, molecular sensors, and homogeneous catalysts for small-molecule activation . The avidity of tricoordinate boron centers for electrons also plays an important role in the rearrangement reactions of boranes . As demonstrated in the early studies on the sigmatropic rearrangement of borylated cyclopentadienes, the increase in electron population of the boron 2p orbital through π-donation or base coordination resulted in a significant increase in the activation barrier of the pericyclic reaction .…”

Section: Introductionmentioning

confidence: 99%

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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“…The (HC) 4 (BR) 2 organoborane/carborane system ( A , B ) has attracted considerable interest because the structures observed depend on the substituents (R) which attached to the boron atoms. Apart from the classical 1,4‐diboracyclo‐2,5‐hexadienes A ,1 and non‐classical 2,3,4,5‐tetracarba‐ nido ‐hexaboranes(6) B ,2 the compounds C ,3a D ,3b E 3c in between these two limits have also been reported. Peralkylated 2,3,4,5‐tetracarba‐ nido ‐hexaboranes(6), known since the mid‐1960s, are more stable than the parent compound C 4 B 2 H 6 4 but their reactivities have only recently been studied 5,6…”

Section: Introductionmentioning

confidence: 99%

One‐Pot Synthesis of 1,6‐Diiodo‐2,3,4,5‐tetracarba‐nido‐hexaboranes(6) and Mechanistic Studies on the Reaction System Alkynes/BI₃/NaK_2.8

et al. 2004

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Attempts to prepare the tetracarba‐nido‐octaborane(8) derivative (EtC)4(BI)4 (4) by treatment of 3‐hexyne with BI3 (2 equiv.) and NaK2.8 led to 2,3,4,5‐tetraethyl‐1,6‐diiodo‐2,3,4,5‐tetracarba‐nido‐hexaborane(6) (2a) as the predominant product with trace quantities of 4 as well as 2,3‐diethyl‐1,4,5,6,7‐pentaiodo‐2,3‐dicarba‐closo‐heptaborane(7) (5). Starting at −78 °C, reactions of 3‐hexyne, 2‐butyne or diphenylacetylene, respectively, with BI3 (1 equiv.) and NaK2.8 afforded the corresponding 1,6‐diiodo‐2,3,4,5‐tetracarba‐nido‐hexaboranes(6) 2a−c as the single carborane products. In the cases of 3‐hexyne and diphenylacetylene, the formation of hexaorganylbenzene derivatives was also detected. To confirm the formation of 4 and 5, the independent dehalogenation of cis‐3,4‐bis(diiodoboryl)‐3‐hexene (3) with NaK2.8 has been studied, which indeed affords 4 and 5, with the former being the predominant product. A mechanism for the formation of 2a has been proposed, which involves iodoboration of the alkyne to give the borylalkene 1a. This is followed by deiodination, presumably yielding the iodoborirene derivative 7, which easily dimerizes to form the 1,4‐diboracyclo‐2,5‐hexadiene derivative 8. Subsequent rearrangement leads to the final C4B2‐nido‐carborane 2a. To determine the stereochemistry of 1a, its pyridine adduct 9 (and the isomer 9′) and catechol derivative 10 (and the isomer 10′), and the diisopropylamino derivative 11 have also been prepared. The new compounds have been characterized by MS and NMR spectroscopy, and the structures of 2a, 3, 9 and 9′ were confirmed by single‐crystal X‐ray analyses. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

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C₄B₂H₆ Isomers: Destabilization of the nido‐Carbaborane Structure by Amino Substituents and a Novel Classical Isomer

Abstract: 3] a) 0. J. Scherer, H. Sitzmann, G. Wolmershauser, J. Organomet. Chem. 268 (1984) C9; b) 1 is also formed in the reaction of Cp(CO)3MoX (X=Cl, Br) with (Me3Si),P, (Me3Si)zPH, and Me3SiPHz, H. Schhfer, Universitat Karlsruhe, private communication.

Cited by 47 publications

References 12 publications

Recent developments in bisdiborane chemistry: BCB, BCCB, BCCB and BCCB compounds

Recent developments in bisdiborane chemistry: BCB, BCCB, BCCB and BCCB compounds

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

One‐Pot Synthesis of 1,6‐Diiodo‐2,3,4,5‐tetracarba‐nido‐hexaboranes(6) and Mechanistic Studies on the Reaction System Alkynes/BI₃/NaK_2.8

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C4B2H6 Isomers: Destabilization of the nido‐Carbaborane Structure by Amino Substituents and a Novel Classical Isomer

Abstract: 3] a) 0. J. Scherer, H. Sitzmann, G. Wolmershauser, J. Organomet. Chem. 268 (1984) C9; b) 1 is also formed in the reaction of Cp(CO)3MoX (X=Cl, Br) with (Me3Si),P, (Me3Si)zPH, and Me3SiPHz, H. Schhfer, Universitat Karlsruhe, private communication.

Cited by 47 publications

References 12 publications

Recent developments in bisdiborane chemistry: BCB, BCCB, BCCB and BCCB compounds

Recent developments in bisdiborane chemistry: BCB, BCCB, BCCB and BCCB compounds

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

One‐Pot Synthesis of 1,6‐Diiodo‐2,3,4,5‐tetracarba‐nido‐hexaboranes(6) and Mechanistic Studies on the Reaction System Alkynes/BI3/NaK2.8

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Product

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About

C₄B₂H₆ Isomers: Destabilization of the nido‐Carbaborane Structure by Amino Substituents and a Novel Classical Isomer

One‐Pot Synthesis of 1,6‐Diiodo‐2,3,4,5‐tetracarba‐nido‐hexaboranes(6) and Mechanistic Studies on the Reaction System Alkynes/BI₃/NaK_2.8