The present application discloses compositions and methods of synthesis and use involving click chemistry reactions for in vivo or in vitro formation of therapeutic and/or diagnostic complexes. Preferably, the diagnostic complex is of use for 18F imaging, while the therapeutic complex is of use for targeted delivery of chemotherapeutic drugs or toxins. More preferably, a chelating moiety or targetable construct may be conjugated to a targeting molecule, such as an antibody or antibody fragment, using a click chemistry reaction involving cyclooctyne, nitrone or azide reactive moieties. In most preferred embodiments, the click chemistry reaction occurs in vivo. In vivo click chemistry is not limited to 18F labeling but can be used for delivering a variety of therapeutic and/or diagnostic agents.