Biferrocene Amino Acid, a Ferrocenylogoue of Ferrocene Amino Acid: Synthesis, Cross-Linking, and Redox Chemistry

Abstract

Access of the novel biferrocene amino acid 7 is provided by two different routes, namely, via desymmetrization of a biferrocene and via palladium-catalyzed cross-coupling of two substituted ferrocenes. The dissymmetric biferrocene 7 is head−head coupled to ureylene-bridged bis(biferrocene) 9 and also head−tail coupled to amide-bridged bis(biferrocene) 14. The monomer 7 and the dimers 9 and 14 are oxidized to mixed-valent cations 7 + , 9 + , 9 2+ , and 14 2+ . The valencies are trapped in the solid state as shown by Mössbauer and EPR spectroscopy and by X-ray diffraction analysis of [7](I 3 ). Paramagnetic NMR shift studies (7 → 7 + ) suggest that the hole is localized at the N-substituted ferrocene unit [BocNH-{III}-{II}-COOMe]+. According to DFT calculations and individual redox potentials, the dications 9 2+ and 14 2+ are best described as [MeOOC-{II}-{III}-NHCONH-{III}-{II}-COOMe]2+ and [BocNH-{III}-{II}-CONH-{III}-{II}-COOMe]2+ valence isomers, respectively. The interaction between neighboring ferrocene/ferrocenium sites in the mixed-valent systems is determined by Hush analyses of the NIR intervalence bands. The extent depends on the bridge type (direct link, amide, ureylene) and the zero-point difference of the individual redox-active units.

Polysubstituted ferrocenes as tunable redox mediators

“…Analogous to the IR-SEC experiments, the esters 1 – 4 were also probed by UV–vis-SEC investigations. The UV–vis spectra of 1 – 4 recorded in dichloromethane show the ferrocene ligand field absorption band at λ max = 444, 449, 455 and 457 nm, which is typically around λ max ≈ 440–490 nm [ 66 , 70 , 79 – 80 ] ( Fig. 5 ).…”

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

“…Paramagnetic 1 H NMR spectroscopy was used to identify the localization of the ferrocenium site in 2 + . [11][12][13][14][15] Upon titration of 2 with substoichiometric amounts of iodine only resonances of protons H 13 , H 14 and H 15 (Scheme 1, ESI †) are affected suggesting spin density at the non-hydrogen bonded iron site. This is fully confirmed by DFT calculations on 2 + showing spin density at the non-hydrogen bonded iron site (FeÁ Á ÁN distance 3.54 Å; FeÁ Á ÁH distance 2.66 Å; Fig.…”

Redox-Dependent Conformational Switching of Diphenylacetylenes

“…Having shown that putative switch 3 undergoes reversible oxidation, we attempted to use the [36,49]. They report that, while partial oxidation causes the Fc signals to broaden and shift downfield, other resonances belonging to protons further from the FcA group remain sharp.…”