In contrast, the use of nucleophilic group 13 compounds as catalyst for carbon-fluorine bond functionalisation is less common. It might be expected that by increasing the coordination number of a group 13 compound from three to four-coordinate that its Lewis acid behaviour could be tempered and nucleophilic reactivity of the coordinated ligands exposed (Figure ). The switch in electronic behaviour might be expected to expand scope of accessible substrates for catalytic transformations, as Lewis acid catalysts operate primarily on sp 3 C-F bonds, whereas nucleophilic species would be capable of addition to sp 2 C-F bonds. This hypothesis is largely untested.