Secondary Interaction and n-π Conjugation in Ferrocenylimine Derivatives of Mercury as Probed by Hg–199 NMR

Abstract

The 199Hg NMR spectra of three series of 37 ortho-mercurated ferrocenylimines, (η5–C5H5Fe[ (η5–C5H3) (HgCI)C(R) = NAr](R = H(1), CH3(2), C6H5 (3); Ar = substituted phenyl groups, 1-naphthyl and 2-naphthyl), have been recorded. The 199Hg chemical shifts are regularly disturbed by the substituents in the N-phenyl rings, and excellent linear relationships are found to exist between the 199Hg shifts (δ) and Hammett substituent constants in all three series. The directions of the substituent effect on δ are the same in the three series, i.e. electron-donating substituents cause shifts to lower field, but the sensitivities of hte 199Hg shift toward the substituent effect are different, ascending in the order of 1,2, and 3. These 199Hg NMR features support the intramolecular secondary interaction between the n- electrons of the imino nitrogen atom and the unoccupied 6p orbital of the mercury atom and the n–π conjugation between the nitrogen and the N–phenyl ring.