Chemo- and diastereoselective epoxidation of allylic alcohols with a titania–silica aerogel

Asymmetric Heterogeneous Catalysis

Limited natural resources and an increasing demand for enantiomerically pure compounds render catalysis and especially heterogeneous asymmetric catalysis a key technology. The field has rapidly advanced from the initial use of chiral biopolymers, such as silk, as a support for metal catalysts to the modern research areas. Mesoporous supports, noncovalent immobilization, metal-organic catalysts, chiral modifiers: many areas are rapidly evolving. This Review shows that these catalysts have more to them than facile separation or recycling. Better activities and selectivities can be obtained than with the homogeneous catalyst and novel, efficient reaction mechanisms can be employed. Especially fascinating is the outlook for highly ordered metal-organic catalysts that might allow a rational design, synthesis, and the unequivocal structural characterization to give tailor-made catalysts.

Aerogels: II. Applications in catalysis

Sol-gel synthesis, and the resulting materials (xerogels and aerogels) are finding increasing application in the synthesis of catalysts, due to their unique characteristics. The most important features of the sol-gel process are: the ability to achieve homogeneity at the molecular level, the introduction of several species in only one step and the ability to stabilize metastable phases. The supercritical drying process produces aerogels with structural features quite different to conventional materials. Some of these characteristics of aerogels can make them very effective catalysts.