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

Cobaltocene [η 5 -C 5 H 4 COOC(CH 3 )CH 2 ] 2 Co ( 1 ) was synthesized from CoCl 2 ·6H 2 O 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. (η 5 -C 5 H 4 COOCH 3 )Co(C 8 H 12 ) ( 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.