Diferrocenyl tosyl hydrazone with an ultrastrong NH⋯Fe hydrogen bond as double click switch

Abstract

The ultrastrong and short intramolecular NHFe hydrogen bond in diferrocenyl hydrazone raises the barrier for intramolecular electron transfer in its mixed-valent cation and is only disrupted by double oxidation to .

Solution Conformation and Self‐Assembly of Ferrocenyl(thio)ureas

“…Chelating and monodentate coordination modes of SbF 6 – ions to doubly charged trans ‐ trans diferrocenylurea is also observed in the solid state for 1 [SbF 6 ] 2 (Figure e). As expected, NH ··· Fe hydrogen bonds play no role in ferrocenium cations (Supporting Information) , …”

“…In addition to the intermolecular NH ··· S hydrogen bonds, the diferrocenyl derivative 6 forms an intramolecular nonclassical NH ··· Fe hydrogen bond (Figure c). The six‐membered ring of the hydrogen‐bonding motif is analogous to those in recently reported dimetallocenyl tosyl hydrazones (Mc)Mc′C=N–NHTs (Mc, Mc′ = Fc, ruthenocenyl; Ts = tosyl) , . In the absence of other factors, this nonclassical NH ··· M hydrogen‐bond‐type appears to represent a favorable bonding situation in Mc–A–B–NH structural motifs with sufficiently acidic NH groups and electron‐rich metal centers (Mc = Fc, ruthenocyl).…”

“…A second, less intense band is found in the ν̃ = 3362–3377 cm –1 region in each case; these correspond to associated NH groups. Intramolecular NH ··· Fe hydrogen bonds and formation of dimers of 1 + – 5 + can be neglected for the oxidized monoferrocenylureas, due to the accumulation of a positive charge at the iron atom upon oxidation . Rather, the coordination of hexafluoroantimonate counterions, resulting in strong charge‐assisted NH ··· F hydrogen bonds, is probable.…”

“…The six-membered ring of the hydrogen-bonding motif is analogous to those in recently reported dimetallocenyl tosyl hydrazones (Mc)Mc′C=N-NHTs (Mc, Mc′ = Fc, ruthenocenyl; Ts = tosyl). [67,68] In the absence of other factors, this nonclassical NH···M hydrogen-bond-type appears to represent a favorable bonding situation in Mc-A-B-NH structural motifs with sufficiently acidic NH groups and electron-rich metal centers (Mc = Fc, ruthenocyl). In the aggregate 6 2 in the solid state, this NH···Fe hydrogen bond profits from cooperative NH···S hydrogen bonds ( Figure 1c).…”

“…Intramolecular NH···Fe hydrogen bonds and formation of dimers of 1 + -5 + can be neglected for the oxidized monoferrocenylureas, due to the accumulation of a positive charge at the iron atom upon oxidation. [67] Rather, the coordination of hexafluoroantimonate counterions, resulting in strong charge-assisted NH···F hydrogen bonds, is probable. Similar coordination of counterions has been proposed for the (acetylamino)ferrocenium cation [FcNHC(O)Me] + .…”