A series of four ferrocenyl ester compounds, 1-methoxycarbonyl- (1), 1,1’-bis(methoxycarbonyl)- (2), 1,1’,3-tris(methoxycarbonyl)- (3) and 1,1’,3,3’-tetrakis(methoxycarbonyl)ferrocene (4), has been studied with respect to their potential use as redox mediators. The impact of the number and position of ester groups present in 1–4 on the electrochemical potential E 1/2 is correlated with the sum of Hammett constants. The 1/1 +–4/4 + redox couples are chemically stable under the conditions of electrolysis as demonstrated by IR and UV–vis spectroelectrochemical methods. The energies of the C=O stretching vibrations of the ester moieties and the energies of the UV–vis absorptions of 1–4 and 1 +–4 + correlate with the number of ester groups. Paramagnetic 1H NMR redox titration experiments give access to the chemical shifts of 1 +–4 + and underline the fast electron self-exchange of the ferrocene/ferrocenium redox couples, required for rapid redox mediation in organic electrosynthesis.
Two mononuclear protic ferrocenyl acyclic diamino carbene gold(I) complexes AuCl[C(NHFc)(NR 2 )] were prepared by nucleophilic attack of diethylamine (R = Et) and diisopropylamine (R = i Pr) at the ferrocenyl substituted isocyanide complex chlorido (isocyanoferrocene)gold(I) AuCl(CNÀ Fc). In the solid state, the multifunctional protic carbene gold(I) complexes display intermolecular aurophilic interactions or intermolecular NH•••Cl hydrogen bonding in addition to intramolecular non-classical NH•••Fe hydrogen bonds. Oxidation of the AuCl[C(NHFc)(NR 2 )] complexes initially takes place at the iron centres giving highly coloured ferrocenium ions, which subsequently likely undergo electron transfer from gold(I) to iron(III) yielding putative EPRactive gold(II) species.
Bis[1]benzothieno[1,4]thiazines (BBTT) are particularly electron-rich S,N-heteropentacenes and their radical cations and dications can be relevant intermediates in charge transport materials. All three regioisomers of N-p-fluorophenyl-BBTT (syn-syn, syn-anti, and anti-anti) were...
The dicobaltocenium ion [Cc 2 NH] 2+ [H−1] 2+ was obtained via nucleophilic substitution of the nitro group of [Cc− NO 2 ] + by amino cobaltocenium [Cc−NH 2 ] + (Cc = Co(η 5 -C 5 H 4 )(η 5 -C 5 H 5 )). [H−1] 2+ is moderately acidic, giving the conjugate base 1 + after deprotonation (pK a = 16.36 in acetonitrile). Single-crystal X-ray diffraction analyses and quantum chemical calculations of the [H−1] 2+ /1 + acid/base pair show only minor geometric changes during the proton transfer. One-electron reduction of [H−1] 2+ at −1.32 V versus ferrocene furnishes [H−1] + , which is a strong hydrogen atom donor with a bond dissociation free energy (BDFE) of the NH group of only 44.6 kcal mol −1 . Hydrogen gas evolves from [H−1] + , generating cation 1 + . One-electron oxidation of 1 + at E p = +0.47 V gives the highly reactive aminyl radical 1 2+ . The BDFE of the NH group of [H−1] 2+ amounts to 85.9 kcal mol −1 . Spin trapping experiments confirm that 1 2+ abstracts a hydrogen atom from the CH 3 CN solvent, regenerating [H−1] 2+ . Consequently, the [H−1] 2+/+ redox couple is competent in the hydrogen evolution reaction and the [H−1] 2+ /1 2+ pair enables hydrogen atom abstraction from CH 3 CN. The [H−1] 2+ /[H−1] + /1 2+ ions exhibit a unique proton, electron, and hydrogen atom transfer reactivity.
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