Generation and Oligomerization of N‑Ferrocenyl Ketenimines via Open-Shell Intermediates

In the presence of oxidant (Ag­[SbF6]) and base, N-ferrocenyl thioamide Fc-NHC­(S)­CH3 (H-1; Fc = Fe­(η5-C5H5)­(η5-C5H4)) converts in an unexpected multistep reaction sequence to a novel N,S-heterocyclic ring, which initiates an oligomerization reaction. Key intermediates toward the resulting complicated material are Ag6(1)6 silver clusters of the anionic N,S-chelating ligand 1− and EPR-active piano stool complexes resulting from ring-slipped cyclopentadienyl ligands, as well as electrophilic N-ferrocenyl ketenimine Fc-NCCH2 (2) and its ferrocenium cation 2•+ formed by hydrosulfide elimination. Mechanistic insight is achieved using X-ray diffraction and mass spectrometry, as well as EPR and NMR spectroscopic studies, combined with DFT calculations. In addition to the fundamental mechanistic insight, the results could have implications for smart oligomers/polymers, heterocycle synthesis, and controlled-release materials.