Synthesis and reactivity impact from electron-withdrawing substituent on the cyclopentadienyl ligand of cobalt(I)–(III) complexes

Cobaltocene [η5-C5H4COOC(CH3)CH2]2Co (1) was synthesized from CoCl2·6H2O at −30 °C. 1 showed two reversible redox potentials at −0.335 and −1.418 V, respectively. It was found that the electron-withdrawing substituent on the cyclopentadienyl ligand facilitated the formation of cobaltocene quantitatively. (η5-C5H4COOCH3)Co(C8H12) (2) was synthesized from 1 at −50 °C under sodium amalgam and the structure of 2 was determined by single-crystal X-ray diffraction. The change of the electron-withdrawing group from the carboisopropenyloxy to the carbomethoxy group on the cyclopentadienyl ligand is also discussed.