New molecules may accelerate drug manufacturing

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 nature.

“For more than a century, most catalysts were prepared using chemical compounds called phosphines,” said Guy Bertrand, the lead author of the study and professor of chemistry at the University of California, Riverside. “But in the 1990s, carbenes were found to be useful to make catalysts. The new carbenes we have prepared in the laboratory are such that they protect the metals to which they bind, making the metal catalysts more stable and longer lasting.”

The carbenes synthesized in the recent study has only one nitrogen atom, rather than two as was previously thought a pre-requisite. Using only one atom gives the molecule a far more flexible structure. In effect, the carbenes are bigger at the metallic center of the catalyst, a feature that improves the efficiency of the catalyst.

“The carbene-based catalysts we report can simplify complex chemical preparations. Further, just mild temperatures are needed for the catalyst to be effective. Because of the catalyst’s longevity, you need only a small amount to achieve your final product. All of this can dramatically reduce the cost of manufacturing drugs, given that pharmaceutical companies are increasingly using carbene-supported catalysts for their chemical reactions,” said Vincent Lavallo, an undergraduate researcher in Bertrand’s laboratory and the first author of the paper.