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 the effect of pyrazine versus pyridine and sulphur 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.2
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.
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.
A vanadium‐catalysed deoxydehydration (DODH) of neat glycerol has been developed. Cheap and readily available ammonium metavanadate (NH4VO3) affords higher yields of allyl alcohol than the well‐established catalyst methyltrioxorhenium. A study in which deuterium‐labelled glycerol was used was undertaken to further elucidate the dual role of glycerol as both an oxidant and reductant. This study led to the proposal of a metal‐catalysed DODH mechanism for the production of allyl alcohol and a deeper understanding of the formation of the byproducts acrolein and propanal.
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 PhCH OH at 175 °C. Under these conditions, PhCH OH underwent disproportionation to yield benzaldehyde, toluene, and significant amounts of bibenzyl. Isotopic-labelling experiments (using PhCH OD and PhCD 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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.