From diacetylferrocene to 1,1′-ferrocenyldiimines: Substituent effects on synthesis, molecular structure, electrochemical behavior and optical absorption property

A series of 1,1′-ferrocenyldiimines [Fe{(η⁵-C₅H₄)-C(Me)N-R}₂ ], where R = n-hexyl 1a, cyclohexyl 1b, phenyl 1c, 4-methoxyphenyl 1d, 3-methoxyphenyl 1e, 4-nitrophenyl 1f, and 3-nitrophenyl 1g, have been synthesized by reactions of ca. 1:2 M ratio of 1,1′-diacetylferrocene and the corresponding amines. While ca. 1:1 M ratio of the starting materials was employed, acetylferrocenylimines [Fe{(η⁵-C₅H₄)-C(CH₃){dou ble bond, long}O}{(η⁵-C₅H₄)-C(CH₃) {double bond, long}N-R}], where R = 4-nitrophenyl 2f, and 3-nitrophenyl 2g, were obtained. Single crystal X-ray structural analysis revealed that the two cyclopentadienyl rings in 1d, 1e, 1g, 2f, and 2g were antiperiplanar staggered, anticlinal eclipsed, anticlinal eclipsed/synclinal eclipsed, synclinal eclipsed, and synclinal eclipsed to each other in solid state, respectively. All synthesized ferrocene derivatives exhibited a reversible one-electron redox process in their cyclic voltammograms, and the values of their redox potentials relied on the R groups. The correlation between the redox potential and the Hammett substituent constant, σ_p was quite well, with a correlation coefficient of 0.98. The UV-vis spectra showed that their optical property was also substituent dependent.