ACS Meeting News: Teaching Zinc A New Trick

Metallacyclobutanes hold a special place in synthetic chemistry as intermediates in the olefin metathesis reactions that have revolutionized the way chemists make small molecules and polymers. At the American Chemical Society meeting in Dallas this week, David A. Vicic of Lehigh University reported that his group has taken a step toward using this approach to make new types of fluorinated small molecules and polymers. The key, he suggested, is using metallacyclic zinc reagents bearing fluoroalkyl groups.

Current routes to fluorinated metallacycles use tetrafluoroethylene gas, which works well for adding C₂F₄ and C₄F₈ units via radical addition reactions. But the gas is hard to handle and leaves a significant environmental footprint. Vicic and his team developed an alternative metathesis route using metallacyclic dizinc reagents that incorporate C₃F₆ and longer fluoroalkyl units into molecules without directly using tetrafluoroethylene. He described the strategy, which was published in Organometallics last year, in the Division of Inorganic Chemistry (2013, DOI: 10.1021/om401016k).

Alkylzinc reagents are often used in metathesis cross-coupling and polymerization reactions to shuttle alkyl groups from a starting material to a substrate molecule. The Lehigh team prepared its reagents from diethylzinc and I(CF₂)_nI (n = 3, 4, or 6), which form unprecedented dizinc metallacyclic intermediates. The fluoroalkyl units can be transferred via a copper-mediated process to aryl iodides to form bicyclic fluorinated organometallic ring systems or ring systems with perfluoroalkyl linkers. These compounds can serve as skeletons for medicinal or materials applications.

Chemistry professor Michael G. Organ of the University of York, in Toronto, who helped elucidate the mechanism of zinc-mediated coupling reactions, called the study “good work.” He said the development is not an unexpected finding, but it could complement other coupling reactions now available to prepare fluorinated materials.

The Lehigh team has filed a provisional patent on the method. Vicic thinks the approach will be particularly useful for small laboratories that are not equipped for generating and handling tetrafluoroethylene.