Aerobic oxidation of amines to imines catalyzed by a ruthenium complex under solvent-free conditions

A novel fluorescent probe of alkyne compounds for putrescine detection based on click reaction

Putrescine is a toxic biogenic amine produced in the process of food spoilage, and a high concentration of biogenic amines in foods will cause health problems such as abnormal blood pressure, headaches and tachycardia asthma/worsening asthma. The detection of putrescine is necessary. However, traditional putrescine detection requires specialized instruments and complex operations. To detect putrescine quickly, sensitively and accurately, we designed and successfully prepared a fluorescent probe (DPY) with active alkynyl groups. DPY takes p-dimethoxybenzene as the raw material, adding a highly active alkyne group. It is stable in experimental pH (∼7) because the UV-vis absorption and fluorescence emission spectra in pH = 3-12 have little change. The fluorescence intensity of DPY decreased only about 1% under the irradiation of 420 nm within 2 h, showing its better photostability. DPY has a high selectivity to putrescine because of the amino-alkyne click reaction without any catalyst in presence of different biogenic amines. The obvious response to putrescine was found in 30 seconds at room temperature. The mechanism between DPY and putrescine was investigated before and after adding putrescine by 1H NMR spectra and the Job plot. The results indicated a typical 1 : 1 stoichiometry between the DPY and DAB. Furthermore, the higher sensitivity of DPY to putrescine was obtained with the detection of limit (LOD) of 3.19 × 10-7 mol L-1, which was better than that of the national standard (2.27 × 10-5 mol L-1). The novel fluorescent probe was successfully applied to beer samples to detect putrescine. The proposed strategy is expected to provide some guidance for the development of some new ways to detect food security.

Sn,P-coordinated Ru cation: a robust catalyst for aerobic oxidations of benzylamine and benzyl alcohol

A stable ionic κ²Sn,P-coordinated Ru complex shows excellent catalytic activity in aerobic oxidations of benzylamine and benzyl alcohol. This complex is stabilized by a stannylene-phosphine peri-substituted naphthalene ligand, which can act as either a reducing agent for a Ru(III) complex or as a κ²Sn,P-chelating ligand for Ru(II) compounds.

1,2-Disubstituted Benzimidazoles by the Iron Catalyzed Cross-Dehydrogenative Coupling of Isomeric o-Phenylenediamine Substrates

Benzimidazoles are common in nature, medicines, and materials. Numerous strategies for preparing 2-arylbenzimidazoles exist. In this work, 1,2-disubstituted benzimidazoles were prepared from various mono- and disubstituted ortho-phenylenediamines (OPD) by iron-catalyzed oxidative coupling. Specifically, O₂ and FeCl₃·6H₂O catalyzed the cross-dehydrogenative coupling and aromatization of diarylmethyl and dialkyl benzimidazole precursors. N,N'-Disubstituted-OPD substrates were significantly more reactive than their N,N-disubstituted isomers, which appears to be relative to their propensity for complexation and charge transfer with Fe³⁺. The reaction also converted N-monosubstituted OPD substrates to 2-substituted benzimidazoles; however, electron-poor substrates produce 1,2-disubstituted benzimidazoles by intermolecular imino-transfer. Kinetic, reagent, and spectroscopic (UV-vis and EPR) studies suggest a mechanism involving metal-substrate complexation, charge transfer, and aerobic turnover, involving high-valent Fe(IV) intermediates. Overall, comparative strategies for the relatively sustainable and efficient synthesis of 1,2-disubstituted benzimidazoles are demonstrated.

Ruthenium-catalyzed deaminative redistribution of primary and secondary amines

A ruthenium–hydride complex, [Ru(H)(Cl)(CO)(PCy₃)₂], was found to be active in the highly selective redistribution of primary and secondary amines bearing an α-hydrogen atom.