Chemoselective, Practical Synthesis of Cobaltocenium Carboxylic Acid Hexafluorophosphate

Cobaltocenium carboxylic acid (carboxycobaltocenium) hexafluorophosphate, a key compound for other monofunctionalized cobaltocenium salts, has been synthesized in >70% overall yield starting from cobaltocenium hexafluorophosphate by a synthetic sequence involving (i) nucleophilic addition of lithium (trimethylsilyl)­ethynide, (ii) hydride removal by tritylium hexafluorophosphate, and (iii) oxidative cleavage of the alkynyl substituent by potassium permanganate

Chemoselective, Practical Synthesis of Cobaltocenium Carboxylic Acid Hexafluorophosphate

Cobaltocenium carboxylic acid (carboxycobaltocenium) hexafluorophosphate, a key compound for other monofunctionalized cobaltocenium salts, has been synthesized in >70% overall yield starting from cobaltocenium hexafluorophosphate by a synthetic sequence involving (i) nucleophilic addition of lithium (trimethylsilyl)­ethynide, (ii) hydride removal by tritylium hexafluorophosphate, and (iii) oxidative cleavage of the alkynyl substituent by potassium permanganate

Monofunctionalized Cobaltocenium Compounds by Dediazoniation Reactions of Cobaltoceniumdiazonium Bis(hexafluorophosphate)

Monofunctionalized cobaltocenium salts are obtained for the first time from cobaltoceniumdiazonium bis­(hexafluorophosphate) with various nucleophiles via Sandmeyer-type and related reactions. For successful conversions, reaction conditions are quite critical: either standard solution chemistry in nitromethane or solvent-free ball milling proved necessary, depending on the type of reactant. By this synthetic approach valuable synthons such as iodocobaltocenium and azidocobaltocenium salts are accessible that open up new vistas in cobaltocenium chemistry. Spectroscopic characterization by NMR, IR, HRMS, and single-crystal structure analysis as well as the results of electrochemical studies are reported. Derivatives with two reversible reductions show the expected relation of the half-wave potentials with the Hammett substituent parameter σ_p of the respective substituent with a slightly larger slope for the first reduction. The carboxylic acid (reductive deprotonation of the −COOH functionality), the iodo (protodehalogenation), and the azido derivatives undergo irreversible subsequent reactions after primary reduction

Monofunctionalized Cobaltocenium Compounds by Dediazoniation Reactions of Cobaltoceniumdiazonium Bis(hexafluorophosphate)

Monofunctionalized cobaltocenium salts are obtained for the first time from cobaltoceniumdiazonium bis­(hexafluorophosphate) with various nucleophiles via Sandmeyer-type and related reactions. For successful conversions, reaction conditions are quite critical: either standard solution chemistry in nitromethane or solvent-free ball milling proved necessary, depending on the type of reactant. By this synthetic approach valuable synthons such as iodocobaltocenium and azidocobaltocenium salts are accessible that open up new vistas in cobaltocenium chemistry. Spectroscopic characterization by NMR, IR, HRMS, and single-crystal structure analysis as well as the results of electrochemical studies are reported. Derivatives with two reversible reductions show the expected relation of the half-wave potentials with the Hammett substituent parameter σ_p of the respective substituent with a slightly larger slope for the first reduction. The carboxylic acid (reductive deprotonation of the −COOH functionality), the iodo (protodehalogenation), and the azido derivatives undergo irreversible subsequent reactions after primary reduction

Enhanced Kinetic Stability of Pure and Y‑Doped Tetragonal ZrO₂

The kinetic stability of pure and yttrium-doped tetragonal zirconia (ZrO₂) polymorphs prepared via a pathway involving decomposition of pure zirconium and zirconium + yttrium isopropoxide is reported. Following this preparation routine, high surface area, pure, and structurally stable polymorphic modifications of pure and Y-doped tetragonal zirconia are obtained in a fast and reproducible way. Combined analytical high-resolution in situ transmission electron microscopy, high-temperature X-ray diffraction, and chemical and thermogravimetric analyses reveals that the thermal stability of the pure tetragonal ZrO₂ structure is very much dominated by kinetic effects. Tetragonal ZrO₂ crystallizes at 400 °C from an amorphous ZrO₂ precursor state and persists in the further substantial transformation into the thermodynamically more stable monoclinic modification at higher temperatures at fast heating rates. Lower heating rates favor the formation of an increasing amount of monoclinic phase in the product mixture, especially in the temperature region near 600 °C and during/after recooling. If the heat treatment is restricted to 400 °C even under moist conditions, the tetragonal phase is permanently stable, regardless of the heating or cooling rate and, as such, can be used as pure catalyst support. In contrast, the corresponding Y-doped tetragonal ZrO₂ phase retains its structure independent of the heating or cooling rate or reaction environment. Pure tetragonal ZrO₂ can now be obtained in a structurally stable form, allowing its structural, chemical, or catalytic characterization without in-parallel triggering of unwanted phase transformations, at least if the annealing or reaction temperature is restricted to <i>T</i> ≤ 400 °C