Polysubstituted ferrocenes as tunable redox mediators

• Sven D. Waniek,
• Jan Klett,
• Christoph Förster and
• Katja Heinze

Beilstein J. Org. Chem. 2018, 14, 1004–1015, doi:10.3762/bjoc.14.86

• 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

• electron ferrocenium cation (FcH+) at a useful electrochemical potential (FcH/FcH+ +630 mV vs NHE; +380 mV vs SCE in CH3CN) [4]. The 0/+ redox couple of ferrocene and its derivatives possesses high electron self-exchange rates kex = 106–107 M−1 s−1, remarkably independent on the electrolyte and solvent [5

• esters 1–4 and 1+–4+ In contrast to typical organic paramagnetic redox mediators, the relaxation properties of proton nuclei of paramagnetic ferrocenium derivatives allow the observation of reasonable sharp resonances [87]. The fast electron self-exchange of the ferrocene/ferrocenium redox couple and

Electron self-exchange activation parameters of diethyl sulfide and tetrahydrothiophene

• Martin Goez and
• Martin Vogtherr

Beilstein J. Org. Chem. 2013, 9, 1448–1454, doi:10.3762/bjoc.9.164

• solvent reorganization. Keywords: CIDNP; electron transfer; free radicals; kinetics; photochemistry; pyrylium salts; self-exchange; sulfides; Introduction Single-electron transfer is probably the simplest chemical process of an organic molecule, because usually no full bonds are broken or formed. For

• this reaction type, the relationship between its thermodynamic driving force and its rate is well understood [1][2]; it only depends on a single parameter for each reagent involved, namely, the activation barrier of its self-exchange, e.g., Observing these key reactions is complicated by the fact that

• radicals A•− and D•+, in other words, labels all four species with their respective polarizations, e.g., D↑ and . As was first recognized by Closs [12], the self-exchange leads to a gradual cancelation of the opposite polarizations in each substrate and its corresponding radical ion, e.g., on a timescale

Electron and hydrogen self-exchange of free radicals of sterically hindered tertiary aliphatic amines investigated by photo-CIDNP

• Martin Goez,
• Isabell Frisch and
• Ingo Sartorius

Beilstein J. Org. Chem. 2013, 9, 437–446, doi:10.3762/bjoc.9.46

• anthraquinone (AQ) and xanthone (XA) or benzophenone (BP) were investigated by time-resolved photo-CIDNP (photochemically induced dynamic nuclear polarization) experiments. By varying the radical-pair concentration, it was ensured that these measurements respond only to self-exchange reactions of the free amine

• reaction occurs through successive radical pairs. With AQ, the polarizations stem from the initially formed radical-ion pairs, and escaping DH•+ then undergoes electron self-exchange with DH. In the reaction sensitized with XA (or BP), the polarizations arise in a secondary pair of neutral radicals that is

• rapidly produced by in-cage proton transfer, and the CIDNP kinetics are due to hydrogen self-exchange between escaping D• and DH. For TIPA, the activation parameters of both self-exchange reactions were determined. Outer-sphere reorganization energies obtained with the Marcus theory gave very good