Straightforward Immobilization of Phosphonic Acids and Phosphoric Acid Esters on Mesoporous Silica and Their Application in an Asymmetric Aldol Reaction.

The combined benefits of moisture-stable phosphonic acids and mesoporous silica materials (SBA-15 and MCM-41) as large-surface-area solid supports offer new opportunities for several applications, such as catalysis or drug delivery. We present a comprehensive study of a straightforward synthesis method via direct immobilization of several phosphonic acids and phosphoric acid esters on various mesoporous silicas in a Dean⁻Stark apparatus with toluene as the solvent. Due to the utilization of azeotropic distillation, there was no need to dry phosphonic acids, phosphoric acid esters, solvents, or silicas prior to synthesis.

Hexaarylcyclotriplumbane: a molecule with a homonuclear ring system of lead.

The reaction of lead(II) bromide with RMgBr, R = 2,4,6-Et3C6H2, furnishes black crystals of hexakis(2,4,6-triethylphenyl)cyclotriplumbane (1) as the first molecule with a homonuclear lead ring. 1 adopts a skewed structure with highly stretched Pb-Pb bond lengths of 3.185 A (average), which indicate that the three-membered ring is formed by weak interactions of 3 singlet plumbylene molecules.

Chalcogenatetrasilacyclopentenes: Five-Membered Rings with Endocyclic Si-Si Double Bonds.

The formal [4+1] cycloaddition of the chalcogens S, Se, and Te to the tetrasilabuta-1,3-diene 1 furnishes the molecules 2-4, the first five-membered rings with endocyclic Si-Si double bonds. The new compounds are thermally stable and chemically inert. However, 4 is light-sensitive and decomposes in daylight with deposition of tellurium.