After extensive research on living organisms, chemistry is now looking to another vast source of inspiration: outer space. CNRS researchers have already managed to reproduce, on Earth, one of the molecules most commonly observed among the stars. This has led, in turn, to a whole spectrum of new applications.
French scientists working in the US have recently managed to produce on Earth a substance that only exists in outer space.1 Guy Bertrand and his team at the Joint Research Chemistry Laboratory (an international joint unit between CNRS and the University of California, Riverside), specialize in producing molecules that are too “unstable” to survive on our planet for more than a very brief period of time. Their latest achievement is to have synthesized and then isolated a strange material, that until now has only been detected in interstellar space: “cyclopropenylidene carbene.” And this space molecule already has a bright industrial future on Earth.
Nature is such that chemists are not always able to confine all the substances they are capable of producing to test tubes. This is sometimes explained by the extreme “reactivity” of the products that are generated: Certain molecules have an unfortunate tendency to combine with their neighbors as soon as they are formed. Consequently, they disappear very quickly from the test tube, as is the case with “carbenes.” Unlike what happens with better-known organic molecules like methane (CH4), “carbenes” do not have eight electrons surrounding their carbon atoms but six, a deficit which according to the laws of chemistry, leads to very high reactivity.
Cyclopropenylidene (C3H2) is also affected by this rule. On Earth, this carbene–made up of three carbon atoms arranged in a triangle with two hydrogen atoms attached–only survives for a fraction of a second at best before reacting with a surrounding molecule and disappearing. However, in the freezing and rarefied environment of outer space, where intermolecular combinations are rare, it can survive for quite a long time in its normal state. First spotted in 1985, C3H2 is now considered one of the most abundant organic substances found in space to date. Apart from being observed in galaxies, astronomers have also detected it within interstellar molecular clouds.
Bertrand and his colleagues could not ignore such a prominent space dweller and set up their laboratory five years ago to “prepare, under normal conditions, molecules considered unstable.” They have had several “impossible” successes such as the stabilization, four years ago, of a “diradical,” a molecule with a promising future in the preparation of organic magnets.2
To curb the particularly reactive nature of cyclopropenylidene and create a stable version of the molecule, the research team replaced the two atoms of hydrogen by two “amino” groups, in other words compounds containing one atom of nitrogen and two other identical atoms (NR2). But why go to such trouble? “Many molecules that have applications in everyday life are derived from natural substances,” explains Bertrand. “Until now, researchers have been inspired by molecules that exist on our planet. Why not look beyond?” And these efforts have already been rewarded. “Our first results on cyclopropenylidene, partially funded by the chemical firm Rhodia, show that this carbene could be used to activate organometallic catalysts or even act as a catalyst itself.”
Vahé Ter Minassian
1. V. Lavallo, et al., “Cyclopropenylidenes: from interstellar space to an isolated derivative in the laboratory,” Science. 312 (5774): 722-4. 2006.
2. D. Scheschkewitz, “Singlet diradicals: from transition states to crystalline compounds,” Science. 295 (5561): 1880-1. 2002.
Joint Research Chemistry Laboratory, CA, USA.