Silanone vs Silicone: When the name is already taken

Scientific nomenclature can be a bit of a funny thing, as we’ve discussed before. When you make something entirely new, it obviously needs a name. Today we’re talking about the strange situation of silanones, where the most obvious name was already taken by something that is not accurately described by the name.

Silicone

Since silicon is right underneath carbon on the periodic table, a lot of early silicon chemistry dealt with trying to make it do the same things that carbon already does. In retrospect, this was an awfully limiting approach, but there is logic to it.  In 1901, Kipping and Saunders were trying to make a silicon version of a ketone (carbon with a double bond to oxygen).

It turns out that silicon doesn’t really like to have a double bond to oxygen when it could have two single bonds to oxygen instead. (On a side note to all science fiction writers, this is why your silicon based life forms need to come from worlds with low oxygen atmosphere and never remove their environmental suits on Earth.) They knew that what they wound up with instead had very different chemistry from the carbon version and was in fact a polymer with a continuous chain. But they decided to stick with the name silicone (silaketone) anyway.

It must be noted that the polymer they wound up with was far more useful than the simple ketone analogue would have been. There are a myriad of uses for an inert, highly flexible polymer. Everything from greases to kitchenware to medical devices. But we wouldn’t have it if no one had tried to make a different structure to see if they could. Basic research matters.  As I’ve mentioned previously, science doesn’t always take predictable paths.

The name silicone wasn’t a big problem so long as everyone accepted that double bonds involving elements below the first row were impossible. Main group chemists are awfully fond of the word impossible though. Specifically, they like to respond to it with “challenge accepted”.

Silanone

There are basically two answers in organic chemistry: Sterics and electronics (sometimes phrased kinetics and thermodynamics). The electronics said that silicon didn’t want to double bond to oxygen. So the solution was to use sterics to make it do it anyway. Various chemists kept sticking bigger and bigger groups on either side of the silicon atom so that it was impossible for two molecules to get close enough together to react. If the silicon atom can’t get two single bonds, one double bond is better than nothing.

While “silicones” had long been formally renamed polysiloxanes, the term silicone was far too enduring as a common name to apply when discussing the possibility of silicon-oxygen double bonds. Can you imagine that conversation? “What are you researching?” “I’m trying to make silicones exist.” “We use silicone grease everyday, how much more existent do they need to be?” Unfortunately, I couldn’t pinpoint who first used silanone as an alternative, but it was definitely much needed in the theoretical discussions.

In 2014, Fillipou finally managed to get the bond that Kipping and Saunders had been trying to make in the first place. He actually combined both kinds of stabilization by using a chromium complex to change the energy at the silicon atom along with the classic “put something so big it has to stay isolate” approach. He showed remarkable restraint in his title, but the highlight note for that issue got to declare “The Century Long Wait is Over”.

Bringing the whole thing full circle, Fillipou was given the Wacker Silicone Award for his isolation of a silanone. The reasoning? It has potential for making novel silicone structures.

The moral of the story is when you’re a silicon chemist, there’s really no escaping silicone.