Carbene work could give cheaper drugs

Chemists at the University of California, Riverside have synthesised a new class of carbenes - molecules that have unusual carbon atoms - that is expected to have wide applications in the pharmaceutical industry, ultimately resulting in a reduction in the price of drugs.

Called cyclic alkyl amino carbenes or CAACs, the molecules attach themselves to metals, such as palladium, to form highly efficient catalysts that allow chemical transformations otherwise considered impossible.

The carbenes modulate the properties of the metals to which they are bound and can facilitate and speed up reactions involving their use.

A carbene is a molecule that has a carbon atom with six electrons instead of the usual eight. Because of the electron deficiency, carbenes are highly reactive and usually unstable.

In their paper, the UCR chemists discuss a set of chemical reactions involving the use of catalysts other than those that are CAAC based. The authors note that these catalysts need strong heating to be effective. They add that the CAAC-based catalysts, on the other hand, can be used not only at room temperature but also in smaller amounts than is necessary for the other catalysts.

Because nitrogen atoms stabilise a carbene when they are adjacent to it, chemists believed until now that two nitrogen atoms were necessary in a carbene to make efficient catalysts. But having two nitrogen atoms also imposes structural limitations at the centre of the carbene.

The carbenes synthesised by the UCR chemists have only one nitrogen atom, which lends the molecule a far more flexible structure. In effect, the carbenes are bigger at the metallic centre of the catalyst, a feature that improves the efficiency of the catalyst.