Unsymmetrical cyrhetrenyl and ferrocenyl azines derived from 5-nitrofurane: Synthesis, structural characterization and electrochemistry

A new series of unsymmetrical cyrhetrenyl and ferrocenyl azines that were monosubstituted [(η⁵-C₅H₄)-C(R)=N-N=CH(5-NO₂-2-C₄H₂O)]M {with M=Re(CO)₃ and R=H (1a) or R=Me (1b); M=Fe(η⁵-C₅H₅) and R=H (2a) or R=Me (2b)} and disubstituted [Fe{(η⁵-C₅H₄)-C(Me)=N-N=CH(5-NO₂-2-C₄H₂O)}₂] (3a) were prepared by condensation reactions of the corresponding organometallic hydrazone [(η⁵-C₅H₄)-C(R)=N-NH₂)]M with 5-nitro-2-furaldehyde. The ¹H and ¹³C{¹H} NMR spectra indicated that these compounds adopted an (E,E)-configuration about the ^〉C=N - bond and an s-trans conformation about the N1-N2 bond, and this result was confirmed by X-ray crystallographic analyses of 1a and 2b. The opposite electronic effects of the organometallic fragments correlate with the co-planarity of the [(η⁵-C₅H₄)-C(R)=N-N=CH(5-NO₂-2-C₄H₂O)] system, the reduction potential of the nitro group (E_1/2) and the chemical shifts of the iminic carbons.