Electronic Tuneable Dynamic and Electrochemical Behavior of N‐(Diferrocenylmethylene)anilines

Abstract

N-(Diferrocenylmethylene)anilines Fc 2 C=N-4-C 6 H 4 -R [3a R = CF 3 ; 3b R = Cl; 3c R = H; 3d R = CH 3 ; 3e R = OCH 3 ; Fc = Fe(η 5 -C 5 H 4 )(η 5 -C 5 H 5 )] with different electron-donating or -withdrawing functionalities were synthesized by a Schiff base reaction of substituted anilines H 2 N-4-C 6 H 4 -R (2a-2e) with diferrocenyl ketone (1). Within variable temperature NMR experiments activation enthalpies between 68.1 and 72.3 kJ·mol -1 for an E/Z exchange reaction of the imines were determined. It could be shown that the inversion barrier depends on the nature of the substituent R. Furthermore, electrochemical measurements were performed, demonstrating that the ferrocenyl units are oxidized separately. The electron density at the nitrogen

On the mechanism of imine elimination from Fischer tungsten carbene complexes

“…Because of the non-crossing rule, this path is symmetry forbidden for aromatic carbenes [ 47 , 72 ]. The calculated barrier of the E / Z isomerization Z -3 → E -3 (Δ G ‡ = 52 kJ mol −1 ) is in good agreement with experimental data for other imines with similar steric bulk, e.g., (Fc) 2 C=NAr, leading to the global minimum E -3 of pathways 2a and 2b ( Scheme 3 ) [ 66 – 67 ]. E -2 is the RDI for pathways 2a and 2b.…”

“…The interconversion between these isomers E -2 → Z -2 (Δ G ‡ = 130 kJ mol −1 ) proceeds via a bending vibration of the Cp–C(carbene)–N moiety. This reaction coordinate is fully analogous to the proposed mechanism of the E / Z isomerization of imines [ 66 – 67 ]. During the 1,2-H-shift of E -2 to E -3 , the migrating hydrogen atom interacts with the empty p π -type orbital of the carbene carbon atom (Δ G ‡ = 250 kJ mol −1 ), which is in accordance with the established mechanism of 1,2-migration reactions of carbenes [ 47 – 48 68 – 71 ].…”

Competitive NH···Ru/Fe Hydrogen Bonding in Ferrocenyl Ruthenocenyl Tosyl Hydrazone

“…We envisaged that the dimetallocenyl tosyl hydrazone platform is ideally suited to address the fundamental question of which metal center (Fe/Ru) forms stronger NH···M hydrogen bonds in metallocenes for the following reasons: the hydrogen bond encompasses the stable six-membered-ring conformation and competition of the NH···Cp hydrogen bonding is essentially excluded due to the restricted conformational mobility caused by the CN double bond. Next, we were interested in the E / Z isomer directing abilities as a consequence of the competition of nonclassical NH···M hydrogen bonds in the synthesis of a mixed-metal (Ru/Fe) tosyl hydrazone as a prototype for imine type E / Z R­(R′)­CNR′′ compounds …”

“…Next, we were interested in the E/Z isomer directing abilities as a consequence of the competition of nonclassical NH•••M hydrogen bonds in the synthesis of a mixed-metal (Ru/Fe) tosyl hydrazone as a prototype for imine type E/Z R(R′)C NR′′ compounds. 54 Hence, we prepared the diruthenocenyl tosyl hydrazone 2 and the mixed ferrocenyl ruthenocenyl tosyl hydrazone 3 from the respective ketones 55−60 (Scheme 1) and investigated their structures in solution and in the solid state by NMR and IR spectroscopy as well as by single-crystal XRD. For the heterobimetallic hydrazone 3, E/Z isomers are envisaged, namely 3a (Z) featuring a NH•••Ru IHB and 3b (E) with a NH•••Fe IHB.…”

“…The relative stability of these two isomers will be probed by NMR and IR spectroscopy in combination with density functional theory studies. A conceivable interconversion between the two hydrogen-bonded isomers 3a,b will be attempted by thermal means, as described for ferrocenyl imines, 54 by photochemical means, and by acid assistance similarly to isomerization of purely organic hydrazones lacking XH•••M IHBs. 61…”