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. 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 (Organometallics 2013, DOI: 10.1021/om401016k). The team prepared the reagents from diethylzinc and I(CF₂)_nI (n = 3, 4, or 6). 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 (shown). These compounds could serve as skeletons for medicinal or materials applications. The Lehigh team has filed a provisional patent on the method.