This study presents a novel Co(salen)-catalyzed hydrofluorination method for the synthesis of aliphatic fluorides using Et3N·3HF as both the proton and fluoride donor. The process operates via a polar-radical-polar crossover mechanism, overcoming the challenges associated with the low acidity and poor nucleophilicity of HF. The method demonstrates broad substrate scope, including unactivated alkenes and styrenes with varying degrees of substitution and diverse functional groups. The versatility of this approach is further demonstrated by its successful application to 18F-hydrofluorination reactions, enabling the introduction of 18F into potential radiopharmaceuticals. Mechanistic investigations using rotating disk electrode voltammetry and DFT calculations reveal the involvement of both carbocation and CoIV species as intermediates, with the contribution of each pathway depending on the structure of the starting alkene. This study highlights the potential of Co(salen) catalysts in facilitating chemoselective and regioselective hydrofluorination reactions.This study presents a novel Co(salen)-catalyzed hydrofluorination method for the synthesis of aliphatic fluorides using Et3N·3HF as both the proton and fluoride donor. The process operates via a polar-radical-polar crossover mechanism, overcoming the challenges associated with the low acidity and poor nucleophilicity of HF. The method demonstrates broad substrate scope, including unactivated alkenes and styrenes with varying degrees of substitution and diverse functional groups. The versatility of this approach is further demonstrated by its successful application to 18F-hydrofluorination reactions, enabling the introduction of 18F into potential radiopharmaceuticals. Mechanistic investigations using rotating disk electrode voltammetry and DFT calculations reveal the involvement of both carbocation and CoIV species as intermediates, with the contribution of each pathway depending on the structure of the starting alkene. This study highlights the potential of Co(salen) catalysts in facilitating chemoselective and regioselective hydrofluorination reactions.