Conformational Switching of Multi‐Responsive Ferrocenyl‐Phenol Conjugates

Abstract

Multifunctional conformational switches based on the ferrocenyl‐salicylic acid amide motif with increasing additional complexity at the Fc moiety (R = COOMe, CONHEt, CONHFc; H‐2–H‐4; Fc = ferrocenyl) have been prepared and their preferred secondary structures in solution have been elucidated by NMR and IR spectroscopy in combination with conformational searches based on DFT calculations. Their distinct conformational responses to deprotonation ([2]––[4]–) and oxidation ([H‐2]+·–[H‐4]+·) have been revealed by IR, EPR, and UV/Vis spectroscopy as well as by DFT calculations. Deprotonation inverts all amide units (double amide twist) whereas oxidation selectively flips the terminal amide unit (single amide twist). The combined action of deprotonation and oxidation has also been explored.

Redox-Induced Hydrogen Bond Reorientation Mimicking Electronic Coupling in Mixed-Valent Diruthenium and Macrocyclic Tetraruthenium Complexes

“…The ensuing decrease in electron density then increases the potential required for oxidation of this side and is also held responsible for the slight blue shift of the Ru­(CO) stretch­(es) during the first oxidations of complexes 2-OH and 4-BOH and the third oxidation of 4-BOH . Here, we also note that redox-induced shifts of NH ··· O hydrogen bonds in ferrocene carboxamides or ferrocene-1,1′-diamides to NH ··· F hydrogen bonds of F atoms of the SbF 6 – counterions were observed on previous occasions. ,, …”

“…Nevertheless, there are some rare cases where hydrogen bonding was found to mediate efficient electron transfer between adjacent redox sites. Such systems typically assume the characteristics of electronically moderately coupled mixed-valent systems of Class II with inherently localized valencies, but they still exhibit thermally or light-induced diabatic electron transfer. − Some metallamacrocyclic complexes with redox-active metal nodes or linkers have also been investigated with respect to their capabilities of fostering intramolecular electron transfer in their mixed-valent states, either by through-space or through-bond pathways. Particularly relevant in this context is the beautiful work of Hupp and co-workers, who have constructed several tetranuclear macrocyclic complexes by interconnecting ditopic dirhenium clamps featuring short, dianionic, bis­(bidentate) linkers via redox-active diimine bridging ligands.…”

N-Cobaltocenium Amide as Reactive Nucleophilic Reagent for Donor–Acceptor Bimetallocenes

“…In contrast to Fc-NH 2 derivatives, ,,,,,,, N -substituted Cc + complexes which would constitute more electron-rich Cc + building blocks are rare. In fact, only few reactions toward N -substituted Cc + units are known so far.…”

“…The accessible potential range for the Fc/Fc + redox process spans approximately 1.7 V based on substituent effects . Furthermore, ferrocene can be conjugated to nearly every conceivable building block, including biomolecules, dyes or electrode surfaces for sensing applications. ,− Typically, Fc is introduced in the neutral form, thus acting as an electron-donating unit in photoinduced electron transfer (PET) systems , and in charge transfer (CT) complexes. , …”

Application of the Curtius rearrangement to the synthesis of 1′-aminoferrocene-1-carboxylic acid derivatives

“…[15][16][17][18] It has also been used to access polyferrocenic structures to study electronic communication between the redox-active units [19][20][21][22][23][24][25][26] and in various scaffolds for specific applications. [27][28][29][30][31][32][33][34][35][36] Surprisingly, despite the wide use of Fca, the price of its commercially available N-protected derivatives remains expensive, probably due to the lack of easy and fast syntheses. The first approach was reported by Butler and co-workers in 1998 starting from 1,1'-dibromoferrocene (Scheme 1, A).…”