ChemCatChem

Amination of Alcohols The cover picture shows the catalytic cycle for the environmentally benign amination of alcohols via the so-called Borrowing Hydrogen methodology. In their Minireview on p. 1853 ff., Beller and co-workers describe the actual developments for the synthesis of amines by amination of alcohols. Notably, compared to other synthetic methodologies for the synthesis of amines, this type of transformation is highly attractive because alcohols are readily available and the only side-product is water.

A new door is open! Conceptually new organocatalytic enantioselective 1,6-addition reactions have recently been uncovered by the groups of Jørgensen, Alexakis, and Stephens. Key to their success was the design of appropriate organocatalyts and Michael acceptors with unique reactivities, which lead to highly regioselective and enantioselective products.

Versatile hydrogen source: A number of intriguing features of benzothiazoline are summarized to highlight its achievement in the reduction of CN bonds. Its inherently versatile skeleton will allow benzothiazoline to become an important complement to the Hantzsch ester and find broad applications in the field of transfer hydrogenation.

Something borrowed, something new: The amination of alcohols is a valuable method for the synthesis of amines and is already used on an industrial scale. This elegant transformation makes use of readily available, in some cases bio-derived alcohols and produces water as the only by-product. In this Minireview, recent developments in the amination of alcohols by means of the so-called borrowing hydrogen methodology are presented.

iPr tips the scales: Simple introduction of an iPr group to the Cp ligand in titanocene alkyne complexes of the type [Cp′₂Ti(η²-Me₃SiC₂SiMe₃)] (Cp′= cyclopentadienyl) gives a highly active catalyst for dimethylamine borane dehydrogenation. In this communication, a detailed study of the scope of this complex and the reaction kinetics is presented.

Take CHAnce on zeolites: A new titanium silicate oxidation catalyst (Ti-CHA) and a bifunctional titanium aluminum silicate catalyst (Ti-Al-CHA) with the chabazite (CHA) topology have been synthesized. The materials have a 3-dimensional channel system with small pore openings that enable shape selective oxidation catalysis. The new Ti-Al-CHA material facilitates a high conversion of methanol to methyl formate with a selectivity of 85 % at 60 °C, using H₂O₂ as the oxidation agent.

The incredible bulk: Although nano-sized Au is required in numerous reactions, π-activated alcohols, such as benzyl alcohol and cinnamyl alcohol, can be catalytically oxidized by unsupported bulk Au, which provides a promising starting point to explore the origin of Au catalysis.

The propargyl way: Various [3]dendralenes can be obtained from propargylic alcohols by means of a straightforward one-pot two-step reaction in the presence of ruthenium complexes, with water as the only side product.

Precipitation–the solution? The recovery of a chiral copper(II) bis(oxazoline) catalyst by charge-transfer complexation and subsequent precipitation allows its efficient reuse in ene and cyclopropanation reactions for up to ten successive catalytic cycles and affords the desired products in high yields and enantioselectivities. The same catalyst batch is also successfully reused in three different asymmetric transformations in an original multireaction procedure.

Glucose oxidase has it all: Under anaerobic conditions, glucose oxidase mediates H₂ evolution, hydrogenation processes, and biocatalytic cascades reducing NO₃⁻. These processes may provide new biotechnological platforms for the generation of fuel products from biomass or for the synthesis of products.

Once, twice, three times a catalyst: Iron oxide nanoparticles (NPs) were functionalized through a silane linker by a chiral imidazolium salt on the surface, a latent N-heterocyclic carbene precursor. This system was utilized in three ways in the enantioselective allylation of 4-nitrobenzaldehyde: as an organocatalyst (1); as a molecular metal complex catalyst (2), when together with [Pd(OAc)₂]; and as a matrix for the formation of Pd NPs and, subsequently, as an active chiral NP catalyst (3). Enantiomeric excesses of up to 74 % were obtained.

A new twist for activity: Adding a second metal M to supported Pd/TiO₂ catalysts modifies the state of Pd and improves the performance in the acetoxylation of toluene to benzyl acetate, but in a different way: The more noble the metal M, the higher the selectivity, but the lower the activity.

Enzyme's sweet tooth: Incorporation of a sugar tag into an enzyme is an interesting methodology to improve its catalytic properties. Candida antarctica lipase (fraction B) modified with tailor-made oligosaccharides on a protein surface in the solid phase exhibits improved activity, selectivity, or regioselectivity values.

Amides ride the ionic liquid cycles: A novel catalytic method to perform amide bond formation from esters and carboxylic acids in ionic liquids is described. Mechanistic studies and the ionic liquid effect are also investigated. Recycling reactions are performed successfully. NMR and electrospray ionization–quadrupole time-of-flight experiments allowed for the proposition of a catalytic cycle to explain the reaction with Brønsted acids, such as SnCl₂ and CdO.

Pure as the driven salt: A straightforward chemoenzymatic synthesis and organocatalytic applications of a new family of enantiopure triazolium salts are demonstrated. The influence of the different structural design vectors is discussed, and a broad range of conversions and some degree of enantiopreference for all catalysts tested is observed.

Inexpensive and environmentally friendly! In this study, the iron-catalyzed oxidation of 1,2-substituted alkynes with hydrogen peroxide is investigated. Two different pathways can be observed: First, the formation of 1,2-diones, and second, the oxidative cleavage of the triple bond to obtain carboxylic acids. The reaction temperature is found to be crucial in determining the path.

The more the merrier: This paper discusses the contributions of significant combinations of elements to the mean values of selectivity and yield in the oxidative coupling of methane (OCM) reaction derived from the statistical analysis of about 1870 past catalytic data sets (see figure). The applied methodology allows the identification of the main prerequisites in catalyst compositions for advanced design of high-performance OCM catalysts. Correlation coefficients, decision trees, and analysis of variance are most useful tools.

Pin that enzyme down: Hierarchical porous silica, synthesized by using sodium silicate, is used as support for immobilization of β-galactosidase by the adsorption pathway. Their loading capacity and enzyme retention are explained in terms of their large mesopores and macropores and the surface silanol groups. Under extreme conditions, the hybrid biocatalyst is more stable than the soluble β-galactosidase.

VWB Verlag für Wissenschaft und Bildung Berlin 2010, (Edition Ostwald, volume 2), 268 pages, € 34, ISBN 978-3-86135-232-7