OK, now I’m confused. I can’t help but have doubts about this sentence: “Despite their high nitrogen content, the geminal triazides are easy to handle, even when preparative-scale syntheses are performed.” It’s from a new paper in Ang. Chem., and that just might take these things right out of the “Things I Won’t Work With” category. So consider this a marginal entry in the series. I have no “Things That Really Aren’t So Bad” category, unfortunately. But I still wondered if these people were pulling my leg. “Easy to handle” compared to what? Cocaine-soaked cobras?
But the authors (from the Kirsch group at the Bergische Universität Wuppertal), mean what they say. And they won my admiration quickly, starting their paper by saying “Over the last decade, the field of organic azides has witnessed a tremendous “boom” (a joke that works just as well in German as it does in English). I also like their summary of previous polyazide literature:
Besides the compounds described herein, only a limited number of polyazidated molecules have been reported with carbon atoms having a similarly high degree of azide substitution. For example, Banert et al. generated the highly explosive tetraazidomethane C(N3)4 in 2007. Hassner et al. described triazidomethane HC(N3)3, the handling of which is also not straightforward. Moreover, several polyazides from higher homologues of Group 14 elements are known, some of which are highly explosive. . .
I’ve covered some of those very compounds before, and yeah, “not straightforward” is one way to describe their handling. Although looked at from another angle, they’re very straightforward indeed: if you make them, they will blow you up.
So anyone who knows anything about azide chemistry would take a look at the current compounds, dive under the desk, and wait for the kaboom. Mystifyingly, it does not come. You can tell that the authors were puzzled, too – I’m sure that they arrived at the proposed structure somewhat reluctantly, because surely these compounds (well, what’s left of them) should be accelerating through the newly created skylight by now, right?
It took some analytical work to figure them out, since (as the manuscript points out) there’s not too much comparison data out there. I remember the triazidomethane paper having an NMR spectrum, but I always suspected that they ran it in somebody else’s magnet down the hall without telling them. But in this case, 15N labeling studies indicated the triazide, and reaction with cyclooctyne to give the (very odd looking) tris-triazole derivative nailed it down for sure. The chemistry to make them seems pretty robust, but looking at the reaction scheme, I still can’t shake the sensation, seeing stoichiometric IBX being used to make a geminal triazide, that I’m looking at crater bait. But the products are stable in solution up to 60C, and small amounts could be rota-vapped down without explosion.
The authors advise appropriate caution, of course – these things have to blow up under some sort of provocation, and they’ll be bad news when they do. I would not advise scraping them out of a sintered glass funnel with a metal spatula. But the Supplementary Information file describes the prep of two grams of one of these things, which is a convincing demonstration of confidence. If you tried that with any of the previously known organic polyazides, you’d want to get your affairs in order first, hand out earplugs as a courtesy to the crowd, and probably get the cameras running so your descendants can make money off the YouTube ad revenues. No, that’s really remarkable stability.
So are these things I won’t work with, or not? I’m still not too enthusiastic about trying any of these myself – I most particularly would not have wanted to be the person who made the two-gram batch. (I wonder if they’re figured out the structure before the guy did that or not? I hope that’s a joke). But under duress, forced to synthesize polyazides at gunpoint, that these are certainly the ones I’d pick. “Most stable triazide” isn’t a very reassuring endorsement, but you have to take what you can get.