Silver(I) promotes the highly chemoselective N-amidation of tertiary amines under catalytic conditions to form aminimides by nitrene transfer from PhI=NTs. Remarkably, this transformation proceeds in the presence of olefins and other functional groups without formation of the commonly observed aziridines or C-H insertion products. The methodology can be applied to complex natural molecules such as brucine or quinine, where the products derived from N-N formation were exclusively formed. Mechanistic studies have shown that this selective N-amidation reaction proceeds through triplet silver-nitrenes.