Visible‐Light‐Initiated Manganese Catalysis for C−H Alkylation of Heteroarenes: Applications and Mechanistic Studies

A visible‐light‐driven Minisci protocol that employs an inexpensive earth‐abundant metal catalyst, decacarbonyldimanganese Mn₂(CO)₁₀, to generate alkyl radicals from alkyl iodides has been developed. This Minisci protocol is compatible with a wide array of sensitive functional groups, including oxetanes, sugar moieties, azetidines, tert ‐butyl carbamates (Boc‐group), cyclobutanes, and spirocycles. The robustness of this protocol is demonstrated on the late‐stage functionalization of complex nitrogen‐containing drugs. Photophysical and DFT studies indicate a light‐initiated chain reaction mechanism propagated by ^.Mn(CO)₅. The rate‐limiting step is the iodine abstraction from an alkyl iodide by ^.Mn(CO)₅.     

Mn‐Catalyzed Dehydrocyanative Transannulation of Heteroarenes and Propargyl Carbonates through C−H Activation: Beyond the Permanent Directing Effects of Pyridines/Pyrimidines

Pyridines/pyrimidines are common and effective directing groups in C?H activation. However, they are poorly functionalizable heteroarenes. Reported in this work is Mn‐catalyzed dehydrocyanative transannulation between three classes of heteroarenes and propargyl carbonates. The pyridyl/pyrimidyl groups in the heteroarenes initially function as directing groups to enable C?H allenylation; they then undergo intramolecular Diels–Alder/retro‐Diels–Alder reactions with the allene moiety to afford fused carbo/heterocycles. Three key intermediates at different stages of the reaction were isolated.     

Precise potentiometric titration of manganese

Summary A method for the precise automatic potentiometric titration of manganese is described. Manganese ions are titrated with permanganate as a titrant in fluoride medium. The ideal quantity to titrate is about 30 mg of manganese. The endpoint of the reaction is recorded automatically. By adding more than 98% of the titrant by weight and the remaining part by means of an automatic burette the precision of the method could be improved to 0.03%. Systematic deviations are eliminated by calibrating the reagent with well-known reference solutions.

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Genaue potentiometrische Manganbestimmung

Zusammenfassung Mangan wird mit Permanganat in Fluoridmedium titriert. Die optimale Menge für die Titration beträgt etwa 30 mg Mn. Der Endpunkt der Reaktion wird automatisch registriert. Durch Zusatz von mehr als 98% des Titrationsmittels als Einwaage und Vervollständigung der Reaktion mit Hilfe einer automatischen Bürette kann eine Genauigkeit von 0,03% erzielt werden. Systematische Fehler werden durch Eichung mit bekannten Referenzlösungen vermieden.

     

A Stable Manganese Pincer Catalyst for the Selective Dehydrogenation of Methanol

For the first time, structurally defined manganese pincer complexes catalyze the dehydrogenation of aqueous methanol to hydrogen and carbon dioxide, which is a transformation of interest with regard to the implementation of a hydrogen and methanol economy. Excellent long‐term stability was demonstrated for the Mn‐PNPi Pr catalyst, as a turnover of more than 20 000 was reached. In addition to methanol, other important hydrogen carriers were also successfully dehydrogenated.