An ansa-Cobaltocene with a Naphthalene Handle: Synthesis and Spectroscopic and Structural Characterization

The ansa-cobaltocene 1,1′-(naphthalen-1,8-diyl)cobaltocene (2) and the corresponding cation 1,1′-(naphthalen-1,8-diyl)cobaltocenium hexafluoridophosphate (2+) have been synthesized utilizing two different pathways. The solid-state molecular structure of the two complexes was determined by single-crystal X-ray diffraction. The redox properties were characterized by means of cyclic voltammetry. The electronic structure of the neutral, paramagnetic complex 2 has been studied by EPR, variable-temperature (VT) 1H NMR, and UV−vis spectroscopy, as well as DFT calculations. Due to the bent structure of the ansa-cobaltocene 2, the 2-fold degeneracy of the e1g-orbitals of the archetype cobaltocene is broken, which allows recording a well-resolved EPR spectrum at 100 K. The VT 1H NMR measurements in the temperature range −60 to +60 °C confirm 2 as a pure paramagnet. DFT calculations reveal an energy gap between the SOMO and LUMO of about 263 kJ/mol.