Spying on the boron–boron triple bond using spin–spin coupling measured from ¹¹B solid-state NMR spectroscopy

Abstract

Boron–boron J coupling constants provide new insight into the nature of the boron–boron triple bond.

Reductive Insertion of Elemental Chalcogens into Boron–Boron Multiple Bonds

“…[18] Thecompound displayed avery short BBbond, was linear across its central C-B-B-C core,and orbital analysis indicated an alkyne-like assembly of one s and two p bonds. [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. [11] If the p bonds in an alkyne give it abond order of three,the same should be true for 1.A very recent NMR spectroscopy study of the scalar 11 B-11 B coupling between the boron atoms in 1 closely links the electronic structure of the BBb ond to the CCb onds of alkynes.…”

Formation and Reactivity of Electron‐Precise B−B Single and Multiple Bonds

“…Further experimental data were also obtained, reaching as imilar conclusion:as ubsequent Raman spectroscopic study on compound 61 a found the B-B stretching frequencytofit well into the trend already established for C Ca nd N Nt riple bonds. [88] Our group subsequently explored the effects of modifying the carbene ligand in diborynes.O ft he plethora of carbenes now accessible, [89] the cyclic (alkyl)(amino)carbenes (cAAC) pioneered by Bertrand and co-workers are particularly noteworthy owing to their considerably stronger p-acceptor strength compared to NHCs. [88] Our group subsequently explored the effects of modifying the carbene ligand in diborynes.O ft he plethora of carbenes now accessible, [89] the cyclic (alkyl)(amino)carbenes (cAAC) pioneered by Bertrand and co-workers are particularly noteworthy owing to their considerably stronger p-acceptor strength compared to NHCs.…”

New Experimental Insight into the Nature of Metal−Metal Bonds in Digallium Compounds: J Coupling between Quadrupolar Nuclei

“…This behavior suggests non‐classical bonding character (non‐traditional multiple bonds) in these systems. The influence of the bond order on the J coupling constants can be assessed using direct comparisons with experimental data for different spin pairs such as 13 C− 13 C or 11 B− 11 B in systems where the nature of the bonding is well‐established and accepted . We have converted the experimental J coupling constants to reduced coupling constants ( K ), which removes the dependence of the values on nuclide‐specific magnetogyric ratios, thereby providing a more suitable parameter for the comparison of differences or similarities in electronic structure between different spin pairs.…”

“…The nature of multiple bonding between elements is a topic of great fundamental and practical interest . For example, a series of recent papers has provided experimental evidence and a theoretical understanding of the nature of the boron≡boron triple bond . The excitement around this work is somewhat reminiscent of that generated by the first report by Robinson in 1997 of a gallyne, purported to contain a gallium≡gallium triple bond.…”