Carbon Dioxide-Mediated Desalination.

Conventional desalination membrane technologies, although offer portable drinking water, are still energy-intensive processes. This paper proposes a potentially new approach for performing water desalination and purification by utilizing the reversible interaction of carbon dioxide (CO2) with nucleophilic amines─reminiscent of the Solvay process. Based on our model studies with small molecules, CO2-responsive amphiphilic insoluble diamines were prepared, characterized, and applied in the formation of soda and ammonium chloride upon exposure to ambient CO2 (1 atm), thus removing chloride ions from model and real seawater. This ion-exchange process and separation of chloride from the aqueous phase are spontaneous in the presence of CO2 without the need for external energy sources. We demonstrate a flow system to envisage energy-efficient CO2-mediated desalination and simultaneous carbon capture and sequestration.

CO2 -Enabled Cyanohydrin Synthesis and Facile Iterative Homologation Reactions*.

Thermodynamic and kinetic control of a chemical process is the key to access desired products and states. Changes are made when a desired product is not accessible; one may manipulate the reaction with additional reagents, catalysts and/or protecting groups. Here we report the use of carbon dioxide to accelerate cyanohydrin synthesis under neutral conditions with an insoluble cyanide source (KCN) without generating toxic HCN. Under inert atmosphere, the reaction is essentially not operative due to the unfavored equilibrium. The utility of CO2 -mediated selective cyanohydrin synthesis was further showcased by broadening Kiliani-Fischer synthesis under neutral conditions. This protocol offers an easy access to a variety of polyols, cyanohydrins, linear alkylnitriles, by simply starting from alkyl- and arylaldehydes, KCN and an atmospheric pressure of CO2 .

New Motifs in Deoxydehydration: Beyond the Realms of Rhenium.

The deoxydehydration (DODH) reaction remains one of the most efficient methods of reducing the oxygen content of biomass while keeping important functionality in place. This reaction is traditionally catalysed by high-valent oxo-rhenium species. Recent research into heterogeneous rhenium-based catalysts for DODH demonstrates their ability to rival and in some cases surpass their homogeneous counterparts. Furthermore, catalysts based on the metals molybdenum and vanadium show great potential as inexpensive alternatives to rhenium catalysts. In this Minireview, we detail the recent developments within the field of DODH with particular emphasis on discoveries outside the realms of rhenium.

Mechanistic Investigation of Molybdate-Catalysed Transfer Hydrodeoxygenation.

The molybdate-catalysed transfer hydrodeoxygenation (HDO) of benzyl alcohol to toluene driven by oxidation of the solvent isopropyl alcohol to acetone has been investigated by using a combination of experimental and computational methods. A Hammett study that compared the relative rates for the transfer HDO of five para-substituted benzylic alcohols was carried out. Density-functional theory (DFT) calculations suggest a transition state with significant loss of aromaticity contributes to the lack of linearity observed in the Hammett study. The transfer HDO could also be carried out in neat PhCH2 OH at 175 °C. Under these conditions, PhCH2 OH underwent disproportionation to yield benzaldehyde, toluene, and significant amounts of bibenzyl. Isotopic-labelling experiments (using PhCH2 OD and PhCD2 OH) showed that incorporation of deuterium into the resultant toluene originated from the α position of benzyl alcohol, which is in line with the mechanism suggested by the DFT study.

Divergent reactivity of platinum(ii) and palladium(ii) methylperoxo complexes and the formation of an unusual hemi-aminal complex.

The 6,6''-diaminoterpyridine palladium(ii) methylperoxo complex eliminates methyl hydroperoxide and reacts with acetone to form a novel hemi-aminal palladium complex, whereas the analogous platinum(ii) complex generates formaldehyde and a platinum(ii) hydroxo complex.

Oxygen insertion into metal carbon bonds: formation of methylperoxo Pd(II) and Pt(II) complexes via photogenerated dinuclear intermediates.

Platinum(II) and palladium(II) complexes [M(CH3)(L)]SbF6 with substituted terpyridine ligands L undergo light-driven oxygen insertion reactions into metal methyl bonds resulting in methylperoxo complexes [M(OOCH3)(L)]SbF6. The oxygen insertion reactions occur readily for complexes with methyl ligands that are activated due to steric interaction with substituents (NH2, NHMe or CH3) at the 6,6″-positions on the terpyridine ligand. All complexes exhibit attractive intermolecular π···π or M···M interactions in the solid state and in solution, which lead to excited triplet dinuclear M-M complexes upon irradiation. A mechanism is proposed whereby a dinuclear intermediate is generated upon irradiation that has a weakened M-C bond in the excited state, resulting in the observed oxygen insertion reactions.

Towards robust alkane oxidation catalysts: electronic variations in non-heme iron(ii) complexes and their effect in catalytic alkane oxidation.

A series of non-heme iron(ii) bis(triflate) complexes containing linear and tripodal tetradentate ligands has been prepared. Electron withdrawing and electron donating substituents in the para position of the pyridine ligands as well as the effect of pyrazine versus pyridine and sulfur or oxygen donors instead of nitrogen donors have been investigated. The electronic effects induced by these substituents influence the strength of the ligand field. UV-vis spectroscopy and magnetic susceptibility studies have been used to quantify these effects and VT (1)H and (19)F NMR spectroscopy as well as X-ray diffraction have been used to elucidate structural and geometrical aspects of these complexes. The catalytic properties of the iron(ii) complexes as catalysts for the oxidation of cyclohexane with hydrogen peroxide have been evaluated. In the strongly oxidising environment required to oxidise alkanes, catalyst stability determines the overall catalytic efficiency of a given catalyst, which can be related to the ligand field strength and the basicity of the ligand and its propensity to undergo oxidation.