an object of the present invention is to provide a novel substance that has a high reactivity as a fluorinating agent , is effectively used in various fluorination reactions , and is safely handled even in air . as the solution for achieving this object , the present invention provides a complex obtained by reacting bromine trifluoride with at least one metal halide selected from the group consisting of halogenated metals and halogenated hydrogen metals in a nonpolar solvent . this complex serves as a fluorinating agent that provides excellent fluorination performance and that is stable in air .