Oligomerization of an ansa-ferrocene with pyrazabole bridge

ansa-Ferrocenes with pyrazabole bridges are chemically robust entities and therefore suitable building blocks for the synthe-sis of rigid-rod polymers that combine redox-active Fe(II) centers and beltene-like n-faces. The specific monomers we developed bear OEt groups at both tetracoordinated boron atoms (for solubility reasons) and ethynyl substituents at the 4-positions of the two pyrazole rings. Polymerization was accomplished by a condensation reaction with 1,4-diiodobenzene using a Sonogashira- Hagihara-type protocol. As a result, oligomers with a number-average molecular weight of Mn = 7.6 kDa and dispersity of = 1.55 were obtained, suggesting an average chain length of about 14 repeating units based on gel permeation chromatog-raphy analysis in THF relative to narrow polystyrene standards. The molecular weight determination was complemented by MALDI-TOF mass spectrometry and (heteronuclear) NMR spectroscopy to verify the intact pyrazabole monomer repeat units and the nature of the end groups. The oligomers were further characterized by UV-vis spectroscopy and cyclic voltammetry, which demonstrated the successful synthesis of a new class of redox-active materials.