The boron–boron triple bond? A thermodynamic and force field based interpretation of the N-heterocyclic carbene (NHC) stabilization procedure

Köppe, Ralf; Schnöckel, Hansgeorg

doi:10.1039/c4sc02997f

Cited by 59 publications

(51 citation statements)

References 56 publications

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“…The interpretation of force and compliance constants seem to have caused troubles in the literature, especially if oversimplified potential functions are used. For example, the existence of a boron–boron triple bond in Holger Braunschweig's diboryne NHCBBNHC was questioned quite recently as a matter of principle . The analysis by Köppe and Schnöckel was based on the calculation of coupling force constants, which showed a strong coupling between the BB and the BC bonds, pointing to a delocalisation of the bonding electrons and by this an equalization of the BB and the BC bond orders.…”

Section: Force Constantsmentioning

confidence: 99%

Ill‐defined chemical concepts: The problem of quantification

Grunenberg

2017

Int J of Quantum Chemistry

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From time to time, ill‐defined concepts leads to never‐ending discussions in the chemical literature. “Is there a quadruple bond in the C2 molecule? What about the boron–boron triple bond? Can we uniquely define concepts like aromaticity or bond order at all?” With this tutorial review I would like to point out that some of the contemporary publications in chemistry are characterized by a confusion of ideas and concepts, and in part ill definitions. And, that exactly those ill‐defined concepts lead to never ending controversies in the literature. Examples of well‐ and ill‐defined concepts in chemistry are discussed.

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Section: Force Constantsmentioning

confidence: 99%

Ill‐defined chemical concepts: The problem of quantification

Grunenberg

2017

Int J of Quantum Chemistry

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“…Thel inear geometry in 1 circumvented arguments over the effects of trans-bending on bond order,a nd fell in line with the idea that the co-residence of boron and carbon in the second row of the periodic table would result in as imilar capacity for strong p bonding. [20] This work concluded that the bond order between the boron atoms in 1 was approximately 1.5;h owever, the methods in that report have not been universally accepted, [21] and as eparate study of the mechanical strength of the bond, based on recorded Raman spectra, indicated no reason to doubt the triple bond assignment as the derived force constant of the B Bb ond falls in line with the trend established by the triple bonds in alkynes and dinitrogen. [19] Recently,areport has surfaced in which the assignment of at riple bond in 1 is questioned through thermodynamic comparison with as tabilized two-atom segment of a-boron, and through the use of calculated vibrational data.…”

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confidence: 92%

Reductive Insertion of Elemental Chalcogens into Boron–Boron Multiple Bonds

et al. 2015

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The syntheses of sulfur- and selenium-bridged cyclic compounds containing boron stabilized by N-heterocyclic carbenes (NHCs) have been achieved by the reductive insertion of elemental chalcogens into boron-boron multiple bonds. The three pairs of bonding electrons between the boron atoms in the triply bonded diboryne enabled six-electron reduction reactions, resulting in the formation of [2.2.1]-bicyclic systems wherein bridgehead boron atoms are spanned by three chalcogen bridges. A similar reaction using a diborene (boron-boron double bond) resulted in the reductive transfer of both pairs of bonding electrons to three sulfur atoms, yielding a NHC-stabilized trisulfidodiborolane. The demonstration of these six- and four-electron reductions lends support to the presence of three and two pairs of bonding electrons between the boron atoms of the diboryne and diborene, respectively, a fact that may be useful in future discussions on bond order.

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“…The latest evidence showed that the L−E bonds for L−B 2 −L are quite strong, suggesting substantial covalent character. 6 However, Frenking argued that dative bonds could also be very strong by the combination of σ donation from L and π-back-bonding from the E 2 fragment in this case. 5b The same bonding arguments would also apply to the recently synthesized heteronuclear PN fragment stabilized by two carbene moieties (A in Figure 1).…”

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confidence: 97%