Modified [(IPr)Pd(R‐acac)Cl] Complexes: Influence of the acac Substitution on the Catalytic Activity in Aryl Amination

The synthesis of a series of [(IPr)Pd(R‐acac)Cl] precatalysts (acac=acetylacetonato; IPr=1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene), where the acac ligand on palladium has been systematically modified through terminal substitution, is reported. The following substituted acac ligands are employed in this study: dibenzoylmethanato (dbm), benzoylacetonato (bac), tetramethylheptanedionato (tmhd), and hexafluoroacetylacetonato (hfac). Full spectroscopic characterization of the new complexes is provided along with X‐ray studies for three of these. Investigation of their catalytic activity in cross‐coupling is also presented through a comparative study in an aryl amination reaction. The catalytic results show a strong correlation between the increased steric bulk of the acac substituents and an increased activation rate of the precatalyst, going from the acac to the tmhd ligand. This observation, along with the inertness of the hfac compound, seems to support our previous proposal for the activation mechanism of these complexes under cross‐coupling conditions.     

TEOS–colloidal silica–PDMS‐OH hybrid formulation used for stone consolidation

The consolidation of materials concept, which consists of introducing a chemical substance (consolidant) into degraded stone, has been applied to architectural conservation. Silicon compounds such as tetraethoxysilane (TEOS) are frequently used as a base for commercial consolidant formulations due to their ability to form a siloxane polymer such as SiO₂. However, the silica xerogels deposited into the stone show poor performance and the gels obtained are non‐porous and tend to crack during the drying stage. In order to avoid the fractures and to improve gel properties, we propose the synthesis of a hybrid consolidant based on TEOS and fillers such as colloidal silica (200 nm in diameter) and hydroxy‐terminated polydimethylsiloxane (PDMS‐OH). Both additives enhance gel properties such as porosity and elasticity, leading to the formation of non‐fractured and permeable gels. Characterization of the hybrid xerogel was carried out by nitrogen adsorption and ²⁹Si MAS‐NMR. The properties of the hybrid xerogels were compared with those prepared from a formulation based on TEOS (T‐ME) with a composition similar to a commercial product. In order to evaluate the effectiveness of the hybrid consolidant, it was applied to tuff‐stone of historical monuments in the city of Guanajuato, Mexico. The tuff‐stone was also treated with the formulation T‐ME. Both treatments were studied by determining the percentage of consolidant deposited, evaluating changes in porosity and hardness of the treated stone. The applicability of the hybrid consolidant for the decayed tuff‐stone is under study. Copyright © 2010 John Wiley & Sons, Ltd.     

Ronchigram simulations for free-form concave reflective surfaces

A new algorithm to simulate ronchigrams and bironchigrams for free-form reflective concave surfaces is reported. In order to know the surface saggita and its partial derivatives at any point within mirror domain a bicubic spline interpolation is done over a finite set of points where the free surface is defined. To simulate the ronchigram irradiances we used ruling with cosinusoidal transmittance instead of Ronchi ruling. Several examples of bironchigrams are shown for spherical surface affected by local and/or radial errors; and surfaces used in ophthalmic progressive lenses.     

Structured Frames by Weil Entourages

In the framework of pointfree topology, we discuss the rôle of Weil entourages in the study of structures such as uniformities, quasi-uniformities, nearnesses, quasi-nearnesses, proximities and infinitesimal relations.     

An alternating direction scheme on a nonuniform mesh for reaction-diffusion parabolic problems

In this paper we develop a numerical method for two-dimensionaltime-dependent reaction-diffusion problems. This method, whichcan immediately be generalized to higher dimensions, is shownto be uniformly convergent with respect to the diffusion problems.This method, which can immediately be generalized to higherdimensions, is shown to be uniformly convergent with respectto the diffusion parameter.     

Finite groups whose same degree characters are Galois conjugate

We classify the finite groups which satisfy the condition that any two nonprincipal complex irreducible characters of the same degree are Galois conjugate.