Synthesis, structure and hydrolysis of some [(η5-cyclopentadienyl) (η6-arene) iron(II)][PF6] complexes bearing an imine or a nitrone function in α-position of the arene ligand

Article abstract of DOI:10.1016/S0022-328X(96)06632-6

Condensation between [(η⁵-Cp)(η⁶-fluorene)Fe]⁺] I and various nitrosoarenes R-Ph-NO (R = H, 2-Me, 3-Me, 4-Me, 3-COMe, 4-COMe and 4-NMe₂) were initiated with 5% t-BuOK and led to [(η⁵-Cp)(η⁶-fluorenone-anil)Fe]⁺ complexes Ia-g (57-88%) as syn-anti mixtures (ca. 30:70 respectively). [(η⁵-Cp)(η⁶-diphenylmethane)Fe]⁺ II with nitrosobenzene or nitrosotoluenes gave mixtures of [(η⁵-Cp)(η⁶-benzophenone-N-phenylnitrone)Fe]⁺ IIa-d and [(η⁵-Cp)(η⁶-benzophenone-anil)Fe]⁺ IIa-d complexes (ca. 80:20) with good yields (80-92%). Nitrone complexes IIa,c,d were isolated as pure Z-isomer by fractional recrystallisation (22-35%). 2D-¹H, ¹³C NMR correlation and X-ray analysis were used to identify the new compounds. Owing to the high nitrosobenzene oxidative character, condensation with other [(η⁵-Cp)(η⁶-arene)Fe]⁺ complexes (arene = toluene, ethylbenzene, indane and tetraline) failed. Acidic hydrolysis of these imine and nitrone complexes has been investigated kinetically using polarography. Macroscale hydrolysis yielded [(η⁵-Cp)(η⁶-fluorenone)Fe]⁺ Ii (82%) and [(η⁵-Cp)(η⁶-benzophenone)Fe]⁺ IIi (91%).