Due to the intermittent nature of most renewable energy sources, such as solar and wind, energy storage is increasingly required. Since electricity is difficult to store, hydrogen obtained by electrochemical water splitting has been proposed as an energy carrier. However, the handling and transportation of hydrogen in large quantities is in itself a challenge. We therefore present here a method for hydrogen storage based on a CO₂(HCO₃⁻)/H₂ and formate equilibrium. This amine-free and efficient reversible system (>90 % yield in both directions) is catalyzed by well-defined and commercially available Ru pincer complexes. The formate dehydrogenation was triggered by simple pressure swing without requiring external pH control or the change of either the solvent or the catalyst. Up to six hydrogenation–dehydrogenation cycles were performed and the catalyst performance remained steady with high selectivity (CO free H₂/CO₂ mixture was produced).

Condensed heterocycles such as quinazolines constitute the framework of many promising drugs. The great impact of the dramatic fluorine effect in pharmaceuticals prompted a great surge in the quest for fluorinated drug design resulting in over 20 % fluorine-containing drugs in the market today. Therefore, finding an efficient and cost-effective method for the direct synthesis of fluorine-tagged quinazoline systems is of great significance in the pharmaceutical arena. For the first time, a one-pot sequential condensation–cyclization reaction to form selectively the difluoro/trifluoromethylated tetrahydroquinazolines from simple components difluoro/trifluoroacetaldehyde hemiacetal and aromatic amines is reported. Our recent studies using difluoro/trifluoroacetaldehyde hemiacetal as simple and elegant difluoro/trifluoromethyl synthons and metal triflates such as gallium triflate as safe and stable Lewis acid catalysts led us to this direct synthesis protocol for the expedient and convenient synthesis of fluorinated quinazolines. DFT calculations at PCM/B3LYP/6-31++G** were carried out for evaluating a possible reaction mechanism for this cyclization. According to the DFT calculations, product stereochemistry is thermodynamically driven, favoring the cis isomer as the major product, which is also confirmed experimentally.

With rising levels of CO₂ in our atmosphere, technologies capable of converting CO₂ into useful products have become more valuable. The field of electrochemical CO₂ reduction is reviewed here, with sections on mechanism, formate (formic acid) production, carbon monoxide production, reduction to higher products (methanol, methane, etc.), use of flow cells, high pressure approaches, molecular catalysts, non-aqueous electrolytes, and solid oxide electrolysis cells. These diverse approaches to electrochemical CO₂ reduction are compared and contrasted, emphasizing potential processes that would be feasible for large-scale use. Although the focus is on recent reports, highlights of older reports are also included due to their important contributions to the field, particularly for high-rate electrolysis.

The trifluoromethanide anion is the postulated key intermediate in nucleophilic trifluoromethylation reactions. However, for more than six decades, the trifluoromethanide anion was widely believed to exist only as a short-lived transient species in the condensed phase. It has now been prepared in bulk for the first time in THF solution. The trifluoromethanide anion with the [K(18-crown-6)]⁺ cation was unequivocally characterized by low-temperature ¹⁹F and ¹³C NMR spectroscopy. Its intermediacy in nucleophilic trifluoromethylation reactions was directly evident by its reaction chemistry with various electrophilic substrates. Variable-temperature NMR spectroscopy, along with quantum mechanical calculations, support the persistence of the trifluoromethanide anion.

α-Fluoroalkenoates and 4-fluoro-5-isoxazolidinones are of vast interest due to their potential biological applications. We now demonstrate the syntheses of (E)-α-fluoroalkenoates and 4-fluoro-5-isoxazolidinones by the reactions between nitrones and α-fluoro-α-bromoacetate. By altering N-substituents in nitrones, (E)-α-fluoroalkenoates and 4-fluoro-5-isoxazolidinones can be achieved, respectively, with high chemo- and stereoselectivities. Experimental and computational studies have been conducted to elucidate the reaction mechanisms. Linear free energy relationship studies further revealed that the N-substituent effects are primarily of electronic origin.

Adsorbents prepared easily by impregnation of fumed silica with polyethylenimine (PEI) are promising candidates for the capture of CO₂ directly from the air. These inexpensive adsorbents have high CO₂ adsorption capacity at ambient temperature and can be regenerated in repeated cycles under mild conditions. Despite the very low CO₂ concentration, they are able to scrub efficiently all CO₂ out of the air in the initial hours of the experiments. The influence of parameters such as PEI loading, adsorption and desorption temperature, particle size, and PEI molecular weight on the adsorption behavior were investigated. The mild regeneration temperatures required could allow the use of waste heat available in many industrial processes as well as solar heat. CO₂ adsorption from the air has a number of applications. Removal of CO₂ from a closed environment, such as a submarine or space vehicles, is essential for life support. The supply of CO₂-free air is also critical for alkaline fuel cells and batteries. Direct air capture of CO₂ could also help mitigate the rising concerns about atmospheric CO₂ concentration and associated climatic changes, while, at the same time, provide the first step for an anthropogenic carbon cycle.

The trifluoromethanide anion is the postulated key intermediate in nucleophilic trifluoromethylation reactions. However, for more than six decades, the trifluoromethanide anion was widely believed to exist only as a short-lived transient species in the condensed phase. It has now been prepared in bulk for the first time in THF solution. The trifluoromethanide anion with the [K(18-crown-6)]⁺ cation was unequivocally characterized by low-temperature ¹⁹F and ¹³C NMR spectroscopy. Its intermediacy in nucleophilic trifluoromethylation reactions was directly evident by its reaction chemistry with various electrophilic substrates. Variable-temperature NMR spectroscopy, along with quantum mechanical calculations, support the persistence of the trifluoromethanide anion.

Tetraflic acid offers ample acidity for various organic reactions that require high acidity. Its gallium(III) salt is an efficient catalyst under mild condtions for synthetic transformations such as the ketonic Strecker reaction for the synthesis of fluorinated α-amino nitriles and condensation–cyclzation reactions using suitable fluoro ketones and 1,2-disubstituted benzenes for the direct preparation of 5-membered or 6-membered fluorinated heterocycles.

The present Minireview covers the formation and the structural characterization of noble metal carbonyl and hydrido carbonyl complexes, with particular emphasis on ruthenium complexes using formic acid as a carbonyl and hydride source. The catalytic activity of these organometallic compounds for the decarboxylation of formic acid, a potential hydrogen storage material, is also reviewed. In addition, the first preparation of [Ru₄(CO)₁₂H₄] from RuCl₃ and formic acid as well as the catalytic activity of [Ru₄(CO)₁₂H₄] for the decomposition of formic acid to hydrogen and carbon dioxide are presented.

Solid hydrogen peroxide complexes based on poly(N-vinylpyrrolidone) and poly(4-vinylpyridine) were prepared and used as solid hydroxylating reagents. These solid hydrogen peroxide equivalents are found to be much safer, convenient and efficient reagent systems for the ipso-hydroxylation of arylboronic acids to the corresponding phenols in high yields at a faster rate. The versatility of the reagents has been further expanded for the one-pot synthesis of halophenols. Density functional theory calculations were carried out on hydrogen peroxide complexes of N-ethylpyrrolidone and 4-ethylpyridine as models to get a better understanding of structure and behavior of hydrogen peroxide complexes of the polymers poly(N-vinylpyrrolidone) and poly(4-vinylpyridine) compared to aqueous hydrogen peroxide.

The missing member of the heteroadamantane series, 1-oxoniaadamantane (4a), was prepared by the ionization of suitable bicyclic precursors under strongly acidic conditions. The ion 4a was characterized by ¹H and ¹³C NMR spectroscopy. The X-ray crystal structure of ion 4a was also obtained with a CB₁₁H₆Cl₆ counter anion. DFT calculations were performed on 1-elementaadamantane cations for comparison. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

The cover picture shows the preparation of 1-oxoniaadamantane by several different pathways under superacidic conditions. The structure of the intriguing bridgehead oxonium ion was characterized by NMR spectroscopy, DFT calculations and X-ray crystallography as a CB₁₁Cl₁₆H₆ counteranion salt. The cation is a missing member of the diamondoid 1-heteroadamantane series. Details are discussed in the Short Communication by G. K. S. Prakash, G. A. Olah et al. on p. 4555 ff.