An amine-N-oxide-ligated palladium complex, in conjunction with a silver cocatalyst, catalyzes imidation of arenes by the reagent N-fluorobenzenesulfonimide. The reaction enables imidation of a variety of arenes at or below room temperature, requires no coordinating directing group on the substrate, and gives synthetically useful yields with only 1 equiv of arene. Mechanistic data implicate an unusual mechanism devoid of commonly invoked organometallic intermediates: oxidation of the Pd catalyst occurs as the turnover-limiting step, while C-H bond functionalization occurs subsequently at a high oxidation state of the catalyst.