Aerobic Oxidative Homo- and Cross-Coupling of Amines Catalyzed by Phenazine Radical Cations.

Phenazine radical cations (PhRCs) were used for the first time as efficient metal-free catalysts for the oxidative homo- and cross-coupling of a variety of different amines. A series of functional PhRCs were prepared, characterized with X-ray diffraction, and their radical character was investigated with DFT calculations. They were tested as catalysts under neat conditions with low oxygen pressure to prepare homo- and cross-coupled aliphatic and aromatic imines in high yields. Although all synthesized phenazines were catalytically active, the highest reaction rates and the best selectivity were achieved using the 5,10-dihydro-5,10-dimethylphenazine radical cation. By means of fluorescence, UV-vis and EPR spectroscopy, a mechanism of the oxidative amine coupling, catalyzed by PhRCs, is proposed.

B(C6F5)3-Catalyzed transfer hydrogenation of esters and organic carbonates towards alcohols with ammonia borane.

Herein, we report an efficient metal-free system for the transfer hydrogenation of esters and carbonates by-passing the otherwise ubiquitous formation of transesterification side-products. The Lewis acid B(C6F5)3 is used as catalyst and ammonia borane as hydrogen donor. This methodology shows broad substrate scope and functional group tolerance in excellent yields at very mild conditions.

Preparation, Characterization and Antimicrobial Properties of Nanosized Silver-Containing Carbon/Silica Composites from Rice Husk Waste.

Rice husk, one of the main side products in the rice production, and its sustainable management represent a challenge in many countries. Herein, we describe the use of this abundant agricultural bio-waste as feedstock for the preparation of silver-containing carbon/silica nano composites with antimicrobial properties. The synthesis was performed using a fast and cheap methodology consisting of wet impregnation followed by pyrolysis, yielding C/SiO2 composite materials doped with varying amounts of silver from 28 to 0.001 wt %. The materials were fully characterized and their antimicrobial activity against ESKAPE pathogens, namely E. faecium, S. aureus, K. pneumoniae, A. baumannii, P. aeruginosa, and E. coli, and the pathogenic yeast C. albicans was investigated. Sensitivities of these strains against the prepared materials were demonstrated, even with exceptional low amounts of 0.015 m% silver. Hence, we report a straightforward method for the synthesis of antimicrobial agents from abundant sources which addresses urgent questions like bio-waste valorization and affordable alternatives to increasingly fewer effective antibiotics.