Perfluoroalkane photodefluorination via mercury photosensitization: experimental and theoretical aspects
Mercury photosensitization in the presence of NH3 leads to partial defluorination and functionalization of a variety of perfluoroalkanes to give perfluoroalkyl imines, amines and nitriles. Poly(tetrafluoroethylene) (PTFE) can be surface-functionalized to give a robust hydrophilic surface by this method. Theoretical studies with DFT-B3LYP geometries and PCI-80 energies suggest the [Hg*(NH3)2] excited state complex may be involved as a key reactive intermediate. These studies show that while pure F-atom abstraction by the H atom is very slow, the highly reducing exciplex can give a net F-atom abstraction by a concerted electron transfer/fluoride ion back-transfer pathway, which has a very much lower activation barrier. Subsequent formation of perfluoroalkene is thought to be followed by nucleophilic attack by ammonia, which initiates an ammonia addition/HF elimination sequence leading to the final products.