Homocoupling and Heterocoupling of Grignard Perfluorobenzene Reagents via Aryne Intermediates: A DFT Study.

Perfluorobenzenes are reactive species with the lowest magnesium metalation barriers among all hexahalobenzenes. This fact makes them good candidates for the study of heterocoupling reactions of the Grignard type. In this work, we investigated a number of pathways for both heterocoupling and homocoupling reactions and estimated the solvated energy barrier heights. According to the results of our density functional theory (DFT)-based computations, the heterocoupling reaction (C6F5)MgF + C6F6 is a single-step process. We have also studied the (C6F5)MgF + (C6F5)MgF homocoupling reaction with an aryne intermediate. In this particular reaction, a carbon-carbon bond is formed between two nucleophilic carbon centers in a chemically predictable way. The final product, (C12F9)Mg2F3, retains even stronger nucleophilic activity than that of the starting (C6F5)MgF reagent. A very surprising result of our calculations is that this homocoupling of two nucleophilic centers is spontaneous in THF solvent.