There are plenty of chemical reagents and reactions that go in and out of fashion over the years, and even entire elements. For the last couple of years, it’s been gold – ten years ago, gold-catalyzed reactions were a backwater, and now they’re all over the literature. (Catalysts are the way to go; reactions that need excess gold to run are unlikely to catch on). Hardly an issue of Organic Letters goes by these days without some gold-catalyzed cyclization in it. But there are some elements that have never been in fashion, and odds are that they’re never going to be.
Tellurium comes to mind. It does some interesting reactions, and if it wasn’t rather poisonous and if its compounds didn’t stink beyond the ability of anyone to stand them, I’m sure that we would have discovered even more. But it is and they do, and there’s no way to stop either one, so no one’s going to make the effort any time soon. It’s the stench that really seals the deal, actually. Poisonous we work with all the time, but you don’t come across stuff that smells like organotelluriums very often, or so I hear. I’ve never had the pleasure myself.
And as for lab fashions, it’s also safe to say the day of the heavy metals is past. Mercury has a long, long pedigree in both organic and inorganic chemistry – back to the alchemists, actually. Everyone figured that there must be something special and/or magical about a metal that’s liquid at room temperature. They were right, in a way. Mercury does a lot of interesting reactions which are still taught in sophomore organic classes and are still run once in a while. I’ve done a few organomercurations myself, but most of them were years ago in grad school. I’ve only reached for the mercuric chloride once or twice in the last twenty years. That’s doubtless because I’m in the drug industry, but I think that the general use of the element has been trending down because of waste disposal issues. Lead, for its part, never had as much use in the art as mercury, and will probably never get the chance.
It’s not just the heavy metals, either. Beryllium is probably one of the most underused elements in the whole periodic table, as far as organic chemistry is concerned. Considering its spot up near the light end of the periodic table, where all its neighbors are on every lab shelf, you’d think that there’d at least be something you could do with the stuff. But I can’t think of a single reaction I’ve ever seen that uses it. The element’s peculiar toxicity (which mostly seems to be a problem by inhalation) helps keep it out of the spotlight: no organic chemist has ever found a need for it that outweighs its disadvantages, and not many are motivated to try.
None of these are going to be the next hot thing. But what is? Gold’s turn in the organic chemistry spotlight will end at some point – for all I know, things are already slowing down. If I had to guess, I’d pick another candidate from the precious-metal crowd, and I’ll nominate iridium. There are plenty of iridium-based catalysts, but none of them are the absolute first thing a chemist reaches for. It wouldn’t surprise me a bit if the element turned out to have a number of tricks in it that haven’t been discovered yet. They should at least be worth some JACS and Org Lett papers, that’s for sure. . .