Modular and Selective Arylation of Aryl Germanes (C−GeEt3) over C−Bpin,C−SiR3 and Halogens Enabled by Light-Activated Gold Catalysis

Selective C –C couplings are powerful strategies for the rapid and programmable construction of bi- or multiaryls. To this end, the next frontier of synthetic modularity will likely arise from harnessing the coupling space that is orthogonal to the powerful Pd-catalyzed coupling regime. This report details the realization of this concept and presents the fully selective arylation of aryl germanes (which are inert under Pd⁰/Pd^II catalysis) in the presence of the valuable functionalities C−BPin, C−SiMe₃, C−I, C−Br, C−Cl, which in turn offer versatile opportunities for diversification. The protocol makes use of visible light activation combined with gold catalysis, which facilitates the selective coupling of C−Ge with aryl diazonium salts. Contrary to previous light-/gold-catalyzed couplings of Ar–N₂⁺, which were specialized in Ar–N₂⁺ scope, we present conditions to efficiently couple electron-rich, electron-poor, heterocyclic and sterically hindered aryl diazonium salts. Our computational data suggest that while electron-poor Ar–N₂⁺ salts are readily activated by gold under blue-light irradiation, there is a competing dissociative deactivation pathway for excited electron-rich Ar–N₂⁺, which requires an alternative photo-redox approach to enable productive couplings.     

Detection of traces of oxidized and reduced sulfur compounds in small samples by combination of different high-performance liquid chromatography methods

Depending on the sulfur species, picomoles of different inorganic sulfur compounds can be detected and separated by HPLC in one arrangement in a sample volume less than 50 μl. The combination of fluorescence labelling of reduced inorganic sulfur compounds such as sulfide (S²⁻), sulfite(SO₃²⁻ and thiosulfate (S₂O₃²⁻) with monobromobimane followed by an extraction of elemental sulfur (S°) by chloroform treatment enables the detection of all mentioned sulfur compounds as well as sulfate (remaining aqueous phase) in the same sample. While the derivatized sulfur compounds could be detected by their fluorescence emission at 480 nm, elemental sulfur is identified by its UV absorption at 263 nm. Sulfate in the remaining aqueous phase is detected by HPLC with indirect UV detection at 254 nm. Detection ranges for the different sulfur compounds examined are as follows: sulfide (5 μM to 1.5 mM), sulfite (5 μM to 1.0 mM), thiosulfate (1 μM to 1.5 mM), elemental sulfur (2 μM to 32 mM) and sulfate (5 μM to >1 mM).     

Polymer-bound osmium oxide catalysts

Polymer-supported oxidic osmium catalysts based on cross-linked poly(4-vinyl pyridine) were synthesized by various routes and characterized by a number of physical techniques (Raman, IR, XPS, ¹³C and ¹⁵N solid-state NMR spectroscopy). Model compounds of type Os₂O₆L₄ (L = pyridine, 4-iso-propyl pyridine, and 4-tert-butyl pyridine) were obtained under the conditions of the catalyst synthesis. The catalytic systems were successful in the dihydroxylation of alkenes.     

In Process Citation

In a systematic study of the sulphonating properties of SO(3)B complexes, we have paid attention to the thiocyanosulphates KSO(3)SCN and NH(4)SO(3)SCN. We have shown conductimetrically that these salts are dissociated and that the ionic salvation is weak in the chosen solvent-sulpholane-which is strongly aprotic in character. We have determined potentiometrically the equilibrium constant K of the reaction MSO(3)SCN measured angle MSCN + SO(3), by means of the electrochemical couple Ag + SO(3)SCN(-) measured angle AgSCN + SO(3) + e(-). The values foun the ammonium and potassium salts are K = 10(-11.5 +/- 0.45) and 10(-9.7 +/- 0.7) respectively. Thiocyanosulphates appear to be stronger than chlorosulphates as sulphonating agents. Therefore SCN(-) is a weaker base than Cl(-) in sulpholane medium.