A facile gold(I)-catalysed intramolecular alkyne hydroarylation approach to methyl 5-amino-2H-1-benzopyran-8-carboxylate derivatives

A high yielding and selective method for producing methyl 5-amino-2H-1-benzopyran-8-carboxylate derivatives via gold(I)-catalysed intramolecular alkyne hydroarylation has been developed.     

Ruthenium complexes of phosphine-aminophosphine ligands

Ruthenium complexes of phosphinoferrocenylaminophosphine ligands (BoPhoz™ ligands) have been prepared by combining the ligands with tris(triphenylphosphine)ruthenium dichloride and precipitating the complexes. The optimal species exhibit high enantioselectivities for the asymmetric hydrogenation of functionalized ketones, particularly β-ketoesters.     

A practical synthesis of 2,3-dihydro-2-benzofurancarboxylic acid: A general route to 2,3-dihydrobenzofurans

A practical synthesis of 2,3-dihydro-2-benzofurancarboxylic acid is reported in five steps and approximately 40% overall yield. The methodology offers a useful new route to 2-substituted-2,3-dihydrobenzofurans.     

Comparison of the apparent masses and cross-axis apparent masses of seated humans exposed to single- and dual-axis whole-body vibration

Humans are exposed to whole-body vibration in many types of environment. In almost all cases, the vibration to which the human is exposed comprises multi-axis vibration, such that vibration occurs in all directions simultaneously. Despite the complex nature of vibration to which humans are exposed in the workplace, almost all laboratory studies investigating the biomechanical response of the person have been completed using single-axis simulators. This paper presents a study whereby 15 male subjects were exposed to single-axis whole-body vibration in the x-, y- and z-directions and dual-axis vibration in the xy-, xz-, and yz-directions using a 6 degree-of-freedom vibration simulator. All vibration magnitudes were 0.4 ms⁻² rms in each axis. Acceleration and force was measured in the x-, y-, and z-direction during all trials. Subjects sat in two postures (‘back-on’ and ‘back-off’) on a flat rigid seat. Apparent masses measured using single-axis and dual-axis vibration stimuli showed comparable results; similarly, cross-axis apparent masses (i.e. the ratio of the force in one direction to the acceleration in another direction) were almost identical for the single- and dual-axis vibration stimuli. All results were in agreement with data previously published using single-axis vibration. In most cases, the peaks in the apparent mass and the cross-axis apparent mass occurred at a slightly lower frequency for the dual-axis vibration than for the single-axis vibration. It is hypothesised that this change is due to a nonlinear effect, analogous to that which occurs with increasing vibration magnitude for single-axis vibration.     

Supported platinum-tin catalysts: The identification by tin-119 Mössbauer spectroscopy of the unusual oxidation of tin during pretreatment under reducing conditions

Titania-supported platinum-tin hydrocarbon dehydrogenation catalysts formed by initial treatment in air contain Sn⁴⁺ which is reduced by low temperature treatment in hydrogen to Sn²⁺. Subsequent exposure to the reducing atmosphere at moderate temperatures results in the reoxidation of some of the Sn²⁺ species. Continued treatment at elevated temperatures gives rise to the formation of a platinum-tin alloy. The unusual behaviour of titania-supported platinum-tin described in this work resembles results previously recorded from other titania-supported bimetallic catalysts containing iron and Group VIII precious metals.     

An iron-57 Mössbauer spectroscopic study of titania-supported iron- and iron-iridium catalysts

⁵⁷Fe Mössbauer spectroscopy shows that titania-supported iron is reduced by treatment in hydrogen at significantly lower temperatures than corresponding silica- and alumina-supported catalysts. The metallic iron formed under hydrogen at 600°C is partially converted to carbide by treatment in carbon monoxide and hydrogen. In contrast to its alumina- and silica-supported counterparts, the remainder of the titania-supported iron is unchanged by this gaseous mixture. The⁵⁷Fe Mössbauer spectra and EXAFS show that iron and iridium in the titania-supported iron-iridium catalysts are reduced in hydrogen at even lower temperatures and, after treatment at 600°C, are predominantly present as the iron-iridium alloy. The treatment of these reduced catalysts in carbon monoxide and hydrogen is shown by Mössbauer spectroscopy and EXAFS to induce the segregation of iron from the iron-iridium alloy and its conversion to iron oxide.     

Quantification of substituent and ligand size by the use of solid angles

A new, generalized, method for measuring the steric size of ligands and substituents has been developed. The method is based on the solid angle concept, the solid angle being generated by the pairwise addition of spheres (atoms). The problem of overlapping spheres (atoms) has been solved analytically and the algorithm provided permits evaluation of the steric space occupied by any combination of spheres (atoms). A range of solid angles for commonly encountered ligands and substituents has been determined and compared to literature values for linear cone angles. © John Wiley & Sons, Inc.