Green Chem. 18 (2016) 9, 2675-2681, http://dx.doi.org/10.1039/C5GC02777B ; Cent. Quim. Estrut., Univ. Lisboa, P-1049 Lisboa, Port.; Eng.) -G. Mueller 38-044

Ionic liquids have been recognised as interesting solvents applicable in efficient lignocellulosic biomass valorisation, especially in biomass fractionation into individual polymeric components or direct hydrolysis of some biomass fractions. Considering the chemical character of ionic liquids, two different approaches paved the way for the fractionation of biomass. The first strategy integrated a pre-treatment, hydrolysis and conversion of biomass through the employment of hydrogen-bond acidic 1-ethyl-3-methyimidazolim hydrogen sulphate ionic liquid. The second strategy relied on the use of a three-step fractionation process with hydrogen-bond basic 1-ethyl-3-methylimidazolium acetate to produce high purity cellulose, hemicellulose and lignin fractions. The proposed approaches were scrutinised for wheat straw and eucalyptus residues. These different biomasses enabled an understanding that enzymatic hydrolysis yields are dependent on the crystallinity of the pre-treated biomass. The use of acetate based ionic liquid allowed crystalline cellulose I to change to cellulose II and consequently enhanced the glucan to glucose yield to 93.1 ± 4.1 mol% and 82.9 ± 1.2 mol% for wheat straw and eucalyptus, respectively. However, for hydrogen sulphate ionic liquid, the same enzymatic hydrolysis yields were 61.6 ± 0.2 mol% for wheat straw and only 7.9 ± 0.3 mol% for eucalyptus residues. These results demonstrate the importance of both ionic liquid character and biomass type for efficient biomass processing.

The first methodology for the direct reductive deoxygenation of ketones catalyzed by high‐valent oxo‐rhenium complexes by using a silane as reducing agent is described. The systems PhSiH3/[ReOCl3(SMe2)(OPPh3)] (2 mmol/5 mol %) and PhSiH3/[ReOCl3(PPh3)2] (2 mmol/5 mol %) proved to be efficient for the deoxygenation of aryl ketones, producing selectively the corresponding alkane, or a mixture of alkane and alkene derivatives with the alkane as the major product.

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This work reports the catalytic activity of a large variety of oxo‐rhenium(V) complexes (1 mol‐%) containing the ligands 2‐(2‐hydroxy‐5‐methylphenyl)benzotriazole (Hhmpbta), 2‐(2‐hydroxyphenyl)benzothiazole (Hhpbt), 2‐(2‐hydroxyphenyl)benzoxazole (Hhpbo), and 2‐(2‐hydroxyphenyl)‐1H‐benzimidazole (Hhpbi) in the deoxygenation of sulfoxides with silanes or boranes as the reducing agents. In general, all of the complexes are excellent catalysts, although the PhSiH3/[ReOBr2(hmpbta)(PPh3)] and pinacolborane/[ReOBr2(hmpbta)(PPh3)] systems are the most efficient for the reduction of aromatic and aliphatic sulfoxides and tolerate different functional groups.

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