Derivation from heterogeneous catalysts

One problem associated with the peroxotungstate-catalyzed epoxidation system described above is the separation of the catalyst after the completed reaction. To overcome this obstacle, efforts to prepare heterogeneous tungstate catalysts have been conducted. De Vos and coworkers employed W catalysts derived from sodium tungstate and layered double hydroxides (LDH - coprecipitated MgCU, AICI3, and NaOH) for the epoxidation of simple olefins and allyl alcohols with... 

IV. Heterogeneous Polymerization Catalysts Derived from Transition... 

The first reaction yields a mixture of all deuterobenzenes, the second one, the deuteration reaction, a mixture of deuterocyclohexanes, mainly C6H6D6 up to C6Di2. The rates of these reactions can be measured with fair accuracy, and additional information can be derived from the isotopic distributions of the reaction products. Schrage and Burwell 36) already demonstrated the usefulness of exchange reactions for studying the heterogeneity of catalyst surfaces. 

Before 1968, attempts to perform enantioselective hydrogenations had either used a chiral auxiliary attached to the substrate [1] or a heterogeneous catalyst that was on a chiral support, usually derived from Nature [2]. Since the disclosure of chiral phosphine ligands to bring about enantioselective induction in a hydrogenation, many systems have been developed, as evidenced in this book. The evolution of these transition-metal catalysts has been discussed in a number of reviews [3-12]. 

Bis(oxazoline)-copper complexes supported on clays were investigated as heterogeneous catalysts in the cyclopropanation reaction (37, 38). Optimal results were obtained from chloride-derived complexes in nitroethane as reaction medium. Laponite clay was found to provide higher selectivities than montmorillonite or bentonite. In every case, the heterogeneous reaction afforded increased amounts of the cis cyclopropane relative to the homogeneous reaction. 

---