Stibasilene Sb═Si and its lighter homologues: a comparative study.

The multiply bonded derivatives of the heavier main group elements are among the most challenging targets for synthetic pursuits. Those of them featuring a double bond between the silicon and group 15 element are represented mostly by the silaimines -N═Si< and phosphasilenes -P═Si< with a very few examples of arsasilenes -As═Si<. In this contribution, we report on the synthesis and structural elucidation of the first stable stibasilene and novel phosphasilene and arsasilene derivatives, featuring an identical substitution pattern. A systematic comparison within the series phosphasilene-arsasilene-stibasilene is made on the basis of their experimental and computational studies.

Toward a silicon version of metathesis: from Schrock-type titanium silylidenes to silatitanacyclobutenes.

Olefin metathesis is one of the most important industrial processes for the production of alkenes. In contrast, silicon versions of metathesis are unknown given the lack of available silylene transition-metal complexes suitable for [2 + 2] cycloaddition with unsaturated substrates. Here, we report the synthesis of 18-electron titanium silylene complexes featuring different Lewis base ligands and classified on the basis of structural, computational, and reactivity studies as Schrock-type silylene complexes. Because of the presence of loosely bound Lewis base ligands, such silylene complexes readily undergo reaction with simple unsaturated hydrocarbons, such as alkynes, forming the corresponding [2 + 2] cycloaddition products.

Impact of compression pressure on tablet appearance.

The color of model tablets deepened and tablet gloss increased with increase in compression pressure regardless of colorant type. The possible reasons for these phenomena were examined. These observations could not be explained either by polymorphic transition of the colorant or by condensation of the colorant during compression. Instead, a change in surface roughness was assumed to be the most likely reason. The increase in compression pressure made the tablet surface smoother. With the increase in the surface smoothness, diffuse reflection decreased while specular reflection increased, indicating the opposite relation between diffuse and specular reflection as a function of surface roughness. A decrease in diffuse reflection results in a deepening of color. In contrast, an increase in specular reflection causes an increase in glossiness. Thus, the surface roughness seemed to govern gloss and color. The compression pressure seems to be one of the most important factors to control tablet appearance.