Four monoferrocenyl tritylium derivatives with donor-substituted (OMe, NMe ) aryl rings are reported, along with their spectroscopic and electrochemical properties. All the complexes show a one-electron reduction and a quasi-reversible ferrocene oxidation at a very positive potential. Small quadrupole splittings, ΔE , in Mößbauer spectra agree with highly electron-deficient ferrocenes. Comparison of the experimental half-wave potentials for ferrocene oxidation, E (Fc/Fc ), with those estimated from established correlations of E (Fc/Fc ) with ΔE indicates that the E values of the anisyl-substituted congeners FcOMe and FcMeOMe are affected by Coulombic repulsion between the positive charges at the Fe ion and the neighboring methylium site. Electronic spectra are recorded and interpreted with the aid of quantum chemical calculations. UV/Vis spectroelectrochemical measurements as well as chemical reduction provide insight into the redox-induced color changes upon ferrocene oxidation or upon reduction to the neutral trityl radicals. The neutral radicals reversibly form EPR-silent dimers. This process is studied by temperature-dependent EPR spectroscopy, and thermodynamic data for their dimerization are determined. Experimental and quantum chemical data suggest that the dimers assume classical hexaarylethane structures as opposed to normal or "offset" Jacobson-Nauta-type structures.

The preparation of polymer nanoparticles with a uniform size and shape, beyond spheres, is an unresolved problem. Here we report a living aqueous catalytic polymerization, resulting in particles grown by a single active site and composed of a single ultra high molecular weight polyethylene (UHMWPE) chain. The control on a molecular level ( M w / M n = 1.1–1.2) and at the same time on a particle level (PDI < 0.05) together with the immediate deposition of the growing chain on the growing nanocrystal results in a distinct evolution of the particle morphology over time. These uniform nanocrystals are obtained as concentrated aqueous dispersions of > 10 wt-% ( N ≈ 10 19 particles L −1 ) polymer content. Key to this robust procedure to single chain nanoparticles are long-lived water-stable Ni(II) catalysts that do not undergo any chain transfer. These findings are a relevant step towards polymer materials based on nanoparticle assembly.

We report on seven 4-ferrocenylphenyl-substituted tritylium dyes Fc-C 6 H 4 -C + Ar 2 with either unlinked or interlinked aryl residues Ar, including congeners with six-membered (thio)xanthylium and seven-membered (dihydro)dibenzo[a,d]cycloheptatrienylium motifs. All complexes are intensely colored and show more or less intense absorption bands owing to charge transfer from the 4-ferrocenylphenyl donor to the C + Ar 2 acceptor unit as well as reversible electrochromism upon reduction and oxidation. The spectral profiles and redox potentials depend on whether or not the methylium center is incorporated into a 14-πelectron arene system. T-dependent EPR spectroscopy indicates that their one-electron-reduced neutral radicals dimerize. The ensuing monomer−dimer equilibria were studied by quantitative spincounting methods, which revealed an unexpectedly large extent of 85.0−99.6% of dimerization.

We have prepared and studied extremely electron‐poor, deeply colored dicationic 1,1'‐bis(diarylmethylium)‐substituted ferrocenes [(η5‐C5H4‐CAr2)2Fe]2+ with various aryl substituents as their [B{C6H3(CF3)2‐3,5}4]– salts. Due to the strong acceptor substitution, the redox potential for the ferrocene‐based oxidation of the anisyl‐ or 2‐methylanisyl‐substituted congeners 1b2+ and 1c2+ is close to or even surpasses that of the second oxidation of parent ferrocene, i.e. the Cp2Fe+/2+ couple. The strongly Lewis‐acidic character of these complexes is manifest through strong interactions with donor solvents, which lead to a significant reduction of the intensities of the charge‐transfer bands in their electronic spectra and to solvatochromism. The reduced forms of the complexes tend to dimerize or oligomerize as revealed by EPR spectroscopy. Direduced 1b selectively reacts with molecular oxygen to form a peroxo‐bis(diarylmethyl)[4]ferrocenophane, which was also characterized by X‐ray crystallography.

In this contribution, we revisit the neglected and forgotten cationic, air-stable, 18-valence electron, heteroleptic sandwich complex (cycloheptatrienyl)(cyclopentadienyl)manganese, which was reported independently by Fischer and by Pauson about 50 years ago. Using advanced high-power LED photochemical synthesis, an expedient rapid access to the parent complex and to functionalized derivatives with alkyl, carboxymethyl, bromo, and amino substituents was developed. A thorough study of these “tromancenium” salts by a range of spectroscopic techniques ( 1 H/ 13 C/ 55 Mn-NMR, IR, UV–vis, HRMS, XRD, XPS, EPR), cyclic voltammetry (CV), and quantum chemical calculations (DFT) shows that these manganese sandwich complexes are unique metallocenes with quite different chemical and physical properties in comparison to those of isoelectronic cobaltocenium salts or (cycloheptatrienyl)(cyclopentadienyl) sandwich complexes of the early transition metals. Electrochemically, all tromancenium ions undergo a chemically partially reversible oxidation and a chemically irreversible reduction at half-wave or peak potentials that respond to the substituents at the Cp deck. As exemplarily shown for the parent tromancenium ion, the product generated during the irreversible reduction process reverts at least partially to the starting material upon reoxidation. Quantum-chemical calculations of the parent tromancenium salt indicate that metal–ligand bonding is distinctly weaker for the cycloheptatrienyl ligand in comparison to that of the cyclopentadienyl ligand. Both the HOMO and the LUMO are metal and cycloheptatrienyl-ligand centered, indicating that chemical reactions will occur either metal-based or at the seven-membered ring, but not on the cyclopentadienyl ligand.