Design, synthesis, and characterization of new iron-complexed azo dyes

As part of a continuing study pertaining to the use of Fe as a substitute for metals such as Cr and Co in the design and synthesis of metal-complexed azo and formazan dyes, the synthesis of dye ligands containing ortho-trifluoroacetamido or mesylamido groups in the diazo components was undertaken. It was anticipated that these groups would mimic the acidity and metallizing properties of an ortho-OH group, thus producing new Fe-complexed dyes. The target ligands were synthesized in 4–5 steps and 80–91% yields from commercially available intermediates. 1H NMR was used to confirm the structures of the target dye ligands. The resultant azo and formazan systems readily formed 1:2 Fe-complexes when an ortho-NHSO2Me group was employed, while preparation of Fe-complexes from dye ligands having an ortho-NHCOCF3 group proved difficult, with mixtures of unmetallized dye, Fe-complex, and Fe hydroxide obtained despite variations in reaction conditions. Results of DFT calculations suggest that electron density at the N-22 atom was significantly diminished by the electron-withdrawing power of the CF3 moiety, inhibiting complex formation.