In summary, a series of four-coordinate group 13 fluoride complexes (M = B, Al, Ga) are reported as catalysts for the thiodefluorination and hydrodefluorination of poly-and perfluoroarenes using silanes as terminal reagents. The scope of reactivity in the electrophile is broad, provided the aromatic ring is electron deficient. For thiodefluorination, mechanistic studies support a plausible role for group 13 thiolate intermediates which are capable of C-S bond formation through nucleophilic attack on the aromatic ring. Similarly, for hydrodefluorination, group 13 hydrides are likely key catalytic intermediates. In both cases, catalytic turnover requires metathesis (ligand exchange) between the group 13 complex and silicon reagent; a step that requires breaking of strong group 13 metal-fluoride bonds. While in the case of thiodefluorination RS --to-F -metathesis occurs in the absence of an additive, for hydrodefluorination H --to-F -exchange requires the use of NaBAr F 4 as an additive. Stoichiometric experiments and DFT calculations are consistent with NaBAr F 4 playing a role to activate and weaken the group 13 metal-fluoride bond through a M-F---Na + , facilitating metathesis with silane reagents. This additive effect may have important implications for future catalyst design.