Hydrodefluorination (HDF) is a type of organic reaction in which in a substrate of a carbonâÂÂfluorine bond is replaced by a carbonâÂÂhydrogen bond. The topic is of some interest to scientific research. In one general strategy for the synthesis of fluorinated compounds with a specific substitution pattern, the substrate is a cheaply available perfluorinated hydrocarbon. An example is the conversion of hexafluorobenzene (C<sub>6</sub>F<sub>6</sub>) to pentafluorobenzene (C<sub>6</sub>F<sub>5</sub>H) by certain zirconocene hydrido complexes. In this type of reaction the thermodynamic driving force is the formation of a metal-fluorine bond that can offset the cleavage of the very stable C-F bond. Other substrates that have been investigated are fluorinated alkenes. Another reaction type is oxidative addition of a metal into a C-F bond followed by a reductive elimination step in presence of a hydrogen source. For example, perfluorinated pyridine reacts with bis(cyclooctadiene)nickel(0) and triethylphosphine to the oxidative addition product and then with HCl to the ortho-hydrodefluorinated product. In reductive hydrodefluorination the fluorocarbon is reduced in a series of single electron transfer steps through the radical anion, the radical and the anion with ultimate loss of a fluorine anion. An example is the conversion of pentafluorobenzoic acid to 3,4,5-tetrafluorobenzoic acid in a reaction of zinc dust in aqueous ammonia.
Specific systems that have been reported for fluoroalkyl group HDF are triethylsilane / carborane acid, and NiCl<sub>2</sub>(PCy<sub>3</sub>)<sub>2</sub> / (LiAl(O-t-Bu)<sub>3</sub>H)