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

π‑Complexes of Tropolone and Its N‑Derivatives: Ambidentate [O,O]/[N,O]/[N,N]-Cycloheptatrienyl Pentamethylcyclopentadienyl Ruthenium Sandwich Complexes

Tropolone and its N-derivatives isopropylaminotropone and diisopropylaminotroponimine react with [Cp*Ru­(CH₃CN)₃]­PF₆ as the source of the electron-rich Cp*Ru⁺ synthon in a simple “capping reaction” to the first cyclopentadienyl/cycloheptatrienyl sandwich complexes containing two vicinal oxo or amino substituents. These heteroleptic, cationic C₅/C₇ π-complexes, [Cp*Ru­(C₇H₅)­O₂H]⁺ (<b>4</b>), [Cp*Ru­(C₇H₅)­O­(NⁱPr)­H]⁺ (<b>5</b>), and [Cp*Ru­(C₇H₅)­(NⁱPr)₂H]⁺ (<b>6</b>), are air-stable 18-electron metallocenes without precedence. In solution, NMR spectroscopy proves the principal π-coordination of the substituted η⁷-cycloheptatrienyl ligands, whereas in the solid state a η⁵-cycloheptatrienyl coordination mode with bent oxo/imino moieties prevails, as shown by X-ray single-crystal structure analyses. Chemically, these compounds are the conjugate Brønsted acids of neutral [O,O]-, [N,O]-, or [N,N]-metalloligands. Reaction with metal acetates or acetylacetonates by <i>in situ</i> deprotonation and complex formation gives access to trimetallic (M = Cu²⁺, <b>10</b>–<b>12</b>) or tetrametallic (M = Fe³⁺, <b>13</b>) complex cations. Their single-crystal structure analyses show square-planar or square-pyramidal (M = Cu²⁺) or octahedral (M = Fe³⁺) coordination motifs with peripheral, η⁵-coordinated Cp*Ru moieties. Electrochemical studies on the trorucenes <b>4</b>–<b>6</b> showed a likely metal-based chemically reversible (<b>4</b>) or irreversible one-electron reduction (<b>5</b>, <b>6</b>) as well as an irreversible one-electron oxidation for the N-substituted compounds <b>5</b> and <b>6</b>. The behavior of the heterotri- and tetrametallic complexes <b>10</b>, <b>11</b>, and <b>13</b> was rationalized by a combination of cyclic and square-wave voltammetry as well as the combination of chronocoulometry and linear-sweep voltammetry and by comparison with the mononuclear copper or iron tropolone and topolonimine precursors <b>14</b>–<b>16</b>. These studies indicate that in <b>10</b> and <b>11</b> the trorucene moieties are reduced first in two coincident or slightly separated one-electron reductions with the Cu²⁺ reduction at very negative potential, whereas in <b>13</b> the central Fe­(III)-tris­(troponolato) moiety is reduced prior to the trorucene appendices. An <i>in vitro</i> anticancer screening in MDA-MB-231 breast adenocarcinoma and HT-29 colon carcinoma cell lines showed enhanced antiproliferative activity for the [O,O]-coordinated iron and copper complexes