The present invention concerns compounds and methods of labeling peptides or other molecules with 18 F or 19 F or any other suitable radionuclide of use, for example, in PET or NMR in vivo imaging. A targeting molecule such as a protein or a peptide is linked to a substituted metallocene complex which is reacted with the 18 F or 19 F shortly before performing the PET or NMR in vivo imaging on the patient. The labeled molecule is then used for targeting a cell, tissue, organ or pathogen to be imaged or detected.