Skip to comments.Tripling up on boron bonds
Posted on 06/18/2012 1:11:50 AM PDT by neverdem
Carbon and nitrogen are well known for their triple bonds, but making stable compounds with a triple bond between two boron atoms hadnt been achieved despite the computational possibilities. Until now.
Holger Braunschweig of the Institute for Inorganic Chemistry at Julius-Maximilians-Universität in Würzburg, Germany, and colleagues found that reacting a bis(N-heterocyclic carbene) stabilised tetrabromodiborane with either two or four equivalents of sodium naphthalenide, a single electron reducing agent, generates a diborene or diboryne compound, which they isolated and characterised. Their analysis confirms a linear, halogen-free compound with a boron-boron triple bond.1
The formation of triple bonds among the lighter main group elements has always been a problem, with the exception of carbon and nitrogen. When chemists have embedded steric stabilisers in the form of inert groups or simply used heavier elements, the results have been bent molecules.
Aesthetically, boron is an obvious target for efforts to create triple bonded compounds, but chemically it has always been reluctant to play its part, even in attempts to form triple bonds with other elements. A decade ago, chemists succeeded in creating a chilly OCBBCO molecule, which ostensibly contains a B2 unit with a triple bond, but this was possible only at 8K in an argon matrix with a laser to direct proceedings. This is not the most desirable synthetic approach to any molecule, although the success led to much theoretical follow up, which hinted at the possibility of triple bonded boron-boron and other analogous compounds.
The subsequent formation of a diborene compound suggested to Braunschweig and colleagues that if the opportunistic scavenging of hydrogen from the solvent could be avoided then the same reaction for making the diborene might be pushed to create a triple bonded diboryne that is stable at room temperature in the absence of air and water. The team has now succeeded in this quest, exploiting boron-11 nuclear magnetic resonance spectroscopy to show the clear progression from double to triple bond between the pair of boron atoms. Their crystallographic data show a statistically significant contraction of the distance between borons in the double to the triple bonded molecule.
Gregory Robinson of the University of Georgia, US, whose team synthesised the diborene that inspired Braunschweigs group, describes the work as an outstanding result that will have repercussions throughout the main of chemistry. He adds: This amazing result shows, once again, the unique capabilities of the determined synthetic chemist. The fact that the boron-boron triple bond has, at long last, been experimentally realised shows that main group chemistry is alive and well.
References 1. H Braunschweig et al, Science, 2012, 336, 1420 (DOI: 10.1126/science.1221138)
This is great news....the world has long been anticipating the boron-boron triple bond.
Could open the door to some hellacious explosives.
And to some nice rocket fuels.
Caveat: people have been trying to make boron-based rocket fuels for a long time. Stability problems have so far prevented development of a useful borinated fuel.
Google “zip fuel.”
Are boron bonds available on AMEX?
“people have been trying to make boron-based rocket fuels for a long time.”
To non-technical people like me, it’s not intuitively obvious what the advantage of such fuels is over conventional fuels. Cheaper? Lighter? Less explosive? Given your allusion to “hellacious explosives” it would appear the latter is not true. The point being, this article doesn’t really give a clue about what practical implications this development has for the average American.
In nitrogen-based explosives (nitroglycerin, ammonium nitrate, RDX, etc.) it is the ease with which naked nitrogen atoms (freed by the destabilization of their single and double bonds to the molecule of explosive) form triple bonds with each other (and thus release much energy quickly) that enables the explosive to detonate rather than just burn.
Naked boron atoms apparently loathe forming triple bonds, hence the difficulty of achieving this breakthrough.
“Are boron bonds available on AMEX?”
Until this development, they were too speculative and only available on the OTCC Bulletin Board system.
Don’t most boron chemists end up mad as hatters?
You can still load up on tax-free boron bonds and defer a portion of your taxable income from the 2011 tax year. I prefer the more common carbon bonds, but I know a couple of guys who are heavy into hydrogen. One even has extensive holdings in the ionic market. Talk about risky ...!
Braunschweigs team is already investigating the reactivity of the new compound, as well as its potential uses in organic electronic materials. Boron-containing compounds are already used in commercial production of organic light-emitting diodes, for example. I think it might be a useful building block, says Braunschweig. The future will tell us whether this is a good approach.
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