Tailoring Valence Tautomerism by Using Redox Potentials: Studies on Ferrocene‐Based Triarylmethylium Dyes with Electron‐Poor Fluorenylium and Thioxanthylium Acceptors

Abstract

dimerization occurs on the timescale of cyclic voltammetry; this allowed us to determine the kinetics and equilibrium constant for this process by digital simulation. Mößbauer spectroscopy indicated that 1 a + and 1 b + retain VT even in the solid state. UV/Vis/NIR spectroelectrochemistry revealed the poly-electrochromic behaviour of these complexes by establishing the distinctly different electronic absorption profiles of the corresponding oxidized and reduced forms.

Electrochemical and Spectroscopic Studies on Triarylamine‐Polychlorotriphenylmethyl Dyads with Particularly Strong Triarylamine Donors

“…[6,16] Other work has described valence tautomerism in conceptually related ferrocene-diarylmethylium dyads with intrinsic half-wave potential differences as large as 500 mV, albeit in these cases subsequent dimerization of the ferrocenium-trityl isomers, which provides an additional driving force, is entangled with the valence tautomeric equilibria. [31] We therefore mused that TAA-PTM * dyads might also be capable of exhibiting valence tautomerism, if particularly strong TAA donors are used. By screening the literature we identified the planar 2,2':6',2'':6'',6-trioxytriphenylamine (TOTA) [32][33][34] and bis(4-dimethylaminophenyl)(phenyl) amine as particular promising candidates (see Figure 2).…”

Linker permethylation as a means to foster valence tautomerism and thwart dimerization in ferrocenyl-triarylmethylium cations

“…The resulting carbinol FcDurSXanth CF3 -OH was then converted into the target donoracceptor dyad with the action of Brookhart's acid, 20 according to an established protocol. 18,19,21 at the duryl linker as a consequence of hindered rotation around the aryl-Cp and aryl-aryl bonds. These resonances sharpen to different degrees on warming.…”

“…[16][17][18] At odds with Veciana′s systems, the individual valence tautomers (VTs) here differ with respect to the number of unpaired spins, none for the Fc-TAM + ground state isomer, two for the higher energy ferrocenium-triarylmethyl form Fc •+ -TAM • . As established by quantitative spin counting methods, the content of the diradical VT amounts to 6.3(±1.4)% for the ferrocene-9-phenylthioxanthy-lium dyad FcPhSXanth CF3+ (Scheme 1, R = H), 19 rendering it a promising magnetochemical switch. Unfortunately, Fc •+ -TAM • diradicals engage in monomer-dimer equilibria with formation of a covalent C-C bond between the methyl carbon atoms.…”

“…The resulting carbinol FcDurSXanth CF3 -OH was then converted into the target donoracceptor dyad with the action of Brookhart's acid, 20 according to an established protocol. 18,19,21 1 H NMR resonances of the complex cation FcDurSXanth CF3+ are suspiciously broad, while those of the BAr F24− anions remain sharp (Fig. S5 of the ESI †).…”

“…These values are typical for neutral ferrocene species. 16,19,28,29 EPR studies on single crystals nevertheless provided a weak EPR signal at g = 2.0047, which can be assigned to an organic spin centred at the (duryl)(thioxanthyl)methyl entity (see Fig. S13 of the ESI †).…”