Weix Group Reveals New Multimetallic-Catalyzed Biaryl Synthesis
September 25, 2015
The Weix Group recently discovered a new solution to the long-standing challenge of cross-coupling two different aryl electrophiles - a multimetallic cross-Ullman reaction. Graduate student Laura Ackerman, assisted by undergraduate Matt Lovell, developed a method to couple an aryl bromide with an aryl sulfonate ester selectively. The secret is to use a combination of two different metal catalysts, palladium and nickel, along with a simple fluoride salt. Given the abundance of the aryl starting materials and the importance of biaryls in pharmaceuticals and materials, this new reaction could find wide application.
In addition to revealing a new method to make biaryls, preliminary mechanistic analysis of this reaction points to a general approach to persuade two catalysts to work together cooperatively - combine one very reactive catalyst with one very stable catalyst. This hypothesis, inspired by the “persistent radical effect” in radical chemistry, suggests that differences in the reactivity of the resting state of catalysts can be adjusted to favor exchange of ligands to form cross products and disfavor homodimerization.